This PDF file contains the front matter associated with SPIE Proceedings Volume 6796, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

In a step towards the development of improved long-term prognostic indicators for patients with end-stage renal disease, we utilized absorption spectroscopy to determine the baseline status of whole blood in a cohort of 5 clinically-stable hemodialysis patients. The optical absorption spectrum of pre-dialysis and post-dialysis blood samples in the 400-1700nm wavelength range was measured for the cohort over a four-week period. Absorption spectra were consistent over time, with a maximum coefficient of variation (CV) of absorption under 2% (650-1650nm) for any given patient over the four-week period (pre and post-dialysis). Spectra varied by a greater amount across patients, with a maximum CV of 5% in any given week. Analysis of variance indicated a broad spectral range (650-1400nm) where within-patient spectral variation was significantly less than between-patient variation (p<0.001), providing the potential for development of stable baseline blood status indicators. The spectra were investigated using principal component analysis (PCA) including a further set of whole blood absorption spectra obtained from 4 peritoneal dialysis patients. PCA revealed the fingerprint-like nature of the blood spectrum, an overall similarity of the spectrum within each treatment mode (hemodialysis or peritoneal dialysis), and a distinct spectral difference between the treatment modes.

Ferrofluid mirrors have the potential to be an inexpensive adaptive optical element which can be used to improve images of structures at the rear of the eye. Their low cost could allow adaptive optics technology to find widespread use in clinical settings. As discussed elsewhere1, their stroke and speed are suitable for correcting the aberrations of the human eye. We present work on the static and dynamic responses of these mirrors using a Hartmann-Shack wavefront reconstruction technique. The displacement of the mirror versus the current in the magnetic field actuators has been measured, as well as actuator influence functions (including non-linearities). In addition, the real-time dynamics of the mirror have been characterized.

In this paper we investigate anisoplanatism effect in human eye. We measured off-axis aberrations of eyes of several subjects and also performed measurements of corneal and internal optics aberrations. Using the results of the experiments we estimated anisoplanatism effect in human eye and developed human eye models reproducing on-axis and off-axis eye aberrations and their distribution between optical elements of the eye.

We present an optical metrology system for measuring the outer shape of small animals in 3D using a stereo camera pair. This system will be integrated into a non-contact small animal diffuse optical tomography (DOT) scanner we are currently developing. The key feature of our approach is to use the same laser beam as that for the tomographic measurements, thus considerably reducing system complexity. Moreover, the 3D data are acquired simultaneously with the DOT measurements. Precise measurements (< 1 mm) are achieved via a novel axis (rotational and translational) optical calibration technique allowing the acquisition of full 3D models. Our approach allows to measure, rather than indirectly infer, the exact position where laser light is injected into the animal, in contrast to other approaches. This is extremely useful information for the tomographic reconstruction algorithm. 3D measurements of a reference shape and of a small animal are presented, showing the precision and effectiveness of our system.

Recent advances in the design and fabrication of avalanche photodiodes (APDs) and quenching circuits for timecorrelated single photon counting (TCSPC) have made available detectors with timing resolutions comparable to microchannel plate photomultiplier tubes (MCP-PMTs). The latter, were until recently the best TCSPC detectors in terms of temporal resolution (≤30ps). Comparable resolutions can now be obtained with TCSPC APDs at a much lower cost. It should also be possible to manufacture APDs with standard electronics fabrication processes in a near future. This will contribute to further decrease their price and ease their integration in complex multi-channel detection systems, as required in diuse optical imaging (DOI) and tomography (DOT). We present, to our knowledge for the first time, results which demonstrate that, despite their small sensitive area, TCSPC APDs can be used in time-domain (TD) DOT and more generally in TD DOI. With appropriate optical design of the detection channel, our experiments show that it is possible to obtain comparable measurements with APDs as with PMTs.

Currents eorts in tissue engineering (TE) are directed towards growing 3D volumes of tissues. In response to TE needs, we are developing a non-invasive technique based on fluorescence diuse optical tomography (FDOT) to image in 3D, via fluorescence labelling, the formation of micro-blood vessels in tissue cultures grown on biodegradable scaolds in bioreactor conditions. In the present work, we use a non-contact FDOT setup developed for small animal imaging for our measurements. We present experimental results showing the feasability to localize a fluorophore-filled 500μm capillary immersed in a scattering medium contained in a cylindrically-shaped glass tube. These conditions are representative of experiments to be carried on real tissue cultures. Time-resolved scattering-fluorescence measurements are made via Time-Correlated Single Photon Counting (TCSPC) and we use numerical constant fraction discrimination (NCFD) to obtain primary localization information from our time-resolved data.

Orientation anisotropies in structural properties relevant to the use of cellulosic polymers as membranes for lab-on-chips were investigated for cellulose acetate (CA) and regenerated cellulose (RC) films deposited as slab waveguides. Anisotropy was probed with mode and polarization state selected guided wave Raman spectroscopy. CA exhibits partial chain orientation in the plane of the film, and this orientation is independent of sample substrate and film preparation conditions. RC films also show in-plane anisotropy, where the hexose sugar rings lie roughly in the plane of the film. Explanations are given of the role of artifacts in interpreting waveguide Raman spectra, including anomalous contributions to Raman spectra that arise from deviations from right angle scattering geometry, mode-dependent contributions to longitudinal electric field components and TE↔TM mode conversion. We explore diffusion profiles of small molecules in cellulosic films by adaptations of an inverse-Wentzel-Kramers-Brillouin (iWKB) recursive, noninteger virtual mode index algorithm. Perturbations in the refractive index distribution, n(z), are recovered from the measured relative propagation constants, neffective,m, of the planar waveguide. The refractive index distribution then yields the diffusion profile.

In this paper, we propose a novel lab-on-a-chip with an integrated spectrometer that uses a single, sensitive off-chip photomultiplier tube (PMT) for detection and the motion of fluorescent cells or other analytes in a microchannel to generate a signal that is equivalent to a time-dependent scan of the spectrum. The excitation light from off-chip lasers is carried to the channel by integrated waveguides and integrated lenses capture and focus the fluorescence into an optical waveguide that carries the fluorescent to the chip edge and into the fiber-coupled PMT. All elements can be fabricated in a single transparent layer of SU-8 or another polymer using standard microfabrication methods.

It is demonstrated how cells that respond to different wavelengths of excitation laser light in a lab-on-a-chip device may be uniquely identified using only a single sensitive photodetector. The technique used is to apply modulation to the excitation lasers and test for the modulation in the emitted optical signals. A simple sliding-window Fourier transform algorithm is applied to the streaming data to eliminate all but the modulation frequency of interest. The method is demonstrated in principle by detecting and identifying two different types of fluorescent polystyrene beads in a pressure-driven flow in a microchannel

This paper describes the development of multi-level lab-on-a-chip devices that use integrated optics to reduce the size and cost of portable dual-function analysis systems. Silicon/polymer and all-polymer devices were fabricated that have separate optics and fluidics layers that are bonded together. The optical layer has hollow v-groove waveguides in anisotropically etched silicon or in polymethylmethacrylate (PMMA) that is replicated from the silicon in a two-step replication procedure using polyvinyl alcohol (PVA) as an intermediate negative replica. Light from hollow v-groove waveguides in the optical layer is coupled to the fluidic layer by reflection from metallized reflective planes. The fluidic layer is constructed of polydimethylsiloxane (PDMS) in a two-step positive replication procedure from a micromachined glass master. A thin intermediate PMMA layer with reflective metal strips seals both the hollow optical waveguides and the PDMS microchannels.

Raman spectroscopy has demonstrated to be an effective tool in the detection and classification of pathogenic microorganisms. The technique is, however, limited by the inherently low cross-section of the Raman scattering process. Among the many enhanced Raman processes, surface enhanced Raman scattering (SERS) technique provides the highest sensitivity and can be easily adapted in the bio-sensing applications such as DNA hybridization and protein binding events. In this study, we report the targeted detection of the pathogenic bacteria, Staphylococcus aureus, with novel single domain antibody (sdAb) conjugated SERS nanoprobes. A sdAb specific to protein A of S. aureus cells was conjugated to silver nanoparticles (Ag-NP). Bacteria recognition was achieved through specific binding of the sdAb (conjugated to SERS nanoprobe) to protein A. Binding rendered the nanoparticle-labeled S. aureus cells SERS active. As a result, S. aureus cells could be detected rapidly and with excellent sensitivity by monitoring the SERS vibrational signatures. This work demonstrates that the SERS imaging technique offers excellent sensitivity with a detection limit of a single bacterium.

We have recently demonstrated coherent anti-Stokes Raman scattering (CARS) microscopy and multiplex CARS spectroscopy of lipid-rich structures based on a single femtosecond Ti:sapphire laser. A nonlinear photonic crystal fiber (PCF) with two closely lying zero dispersion wavelengths is used to generate the Stokes pulse. Further optimization in terms of higher spectral resolution in the CARS spectra can be achieved by adding a second PCF to the pump arm to produce a spectrally compressed picosecond pulse. Theoretical predictions from modeling the propagation of the negatively chirped pump pulse in the PCF, are compared with experimental results. The effect of pulse duration, peak power and the length of the PCF in determining the bandwidth of the spectrally compressed pump pulse are considered. It is shown that for higher average output power and constant pulse duration, it is desirable to use shorter length of the PCF for attaining transform limited spectral width of the pump pulse.

Holographic interferometric metrology is an established technique for technical non-destructive testing. In connection with microscopy, digital holography provides contact-less and marker-free quantitative phase contrast imaging. The reconstruction of digitally captured holograms is performed numerically. Thus, multi-focus imaging of different object planes is achieved from a single captured hologram. In combination with (subsequent) numerical autofocus adjustment, this feature opens up applications for microscopic time-lapse investigations by avoidance of mechanical focus-maintenance. Results obtained from digital holographic investigations of toxin induced reactions of adherent cancer cells demonstrate applications prospects of digital holographic microscopy in quantitative life cell imaging. Furthermore, data obtained by cell spreading process analysis, the cell response to osmotic changes and the observation of shape variations of human erythrocytes supplies new information in marker-free life cell imaging.

We present an instantaneous complex conjugate resolved swept-source optical coherence tomography (SS-OCT) using a 3x3 optical fiber coupler. A dual-channel balanced (dual-balanced) detection with phase shifted signals was formed by a Mach-Zehnder interferometer (MZI) with a 3x3 and one or more 2x2 optical fiber couplers. Non-complementary phase components of the complex interferometric signals from the dual-balanced detector were converted to quadrature components by a simple trigonometric formula. A-scans with resolved complex conjugate artifact were obtained by inverse Fourier transformation. This approach provides a two times increase in the effective depth of image. Two configurations of the quadrature interferometers based on Mach-Zehnder interferometer (MZI) topology are investigated. The first configuration with one 3x3 and three 2x2 optical fiber couplers is arranged for DC signal removal, and the second configuration with one 3x3 and one 2x2 optical fiber couplers is organised for optical power optimisation. We focus on the comparison of the measured sensitivity and complex conjugate artifact suppression between the two configurations of the quadrature MZI SS-OCT system. The suppression of complex conjugate artifact of >25 dB for the second configuration, i.e. 3x3 SS-OCT with one 2x2 fiber couplers, was obtained, which is 6 dB higher than that for the first configuration, i.e. 3x3 SS-OCT with three 2x2 coupler. The reason for the performance of the second configuration over the first one is the optimisation of the optical power handling. In the second configuration, the DC components of the complex interferometric signal caused by unequal optical power level have been removed by the balanced detection and DC noise subtraction.

Dispersive objects result in a loss of resolution in time-domain optical coherence tomography (TD-OCT). A typical technique to compensate for this effect is to introduce dispersive material in the reference arm. This method however is not very effective, as the dispersion effect of the object is depth dependent. We implement a dispersion compensation algorithm in the Wigner domain for TD-OCT. This shift-variant numerical compensation approach is more efficient than the previously reported shift-invariant methods which required a deconvolution operation for every depth.

Broadband sources (BBSs) are commonly used in a wide range of applications in optical communication systems and biophotonics. They are particularly useful tools for Optical Coherence Tomography (OCT), which is a biomedical imaging technique that uses low-coherence light sources. In order to obtain high image quality, we have developed a novel, spectrally-flat S+C+L band source with > 120 nm bandwidth and more than 4 mW output power based on two cascaded semiconductor optical amplifiers (SOA) mixed with an Erbium-doped fiber (EDF) amplifier. Bandwidth and output power improvements are achieved by modifying the former configuration and mixing the EDF with the first SOA before amplification in the second SOA. This configuration results in bandwidth and output power enhancements of up to 146 nm and 8 mW, respectively. The source was then tested in an OCT system. It gives a 10 &mgr;m FWHM, low sidelobe OCT autocorrelation trace. Images and OCT autocorrelation traces were compared for the two aforementioned (which two; you mentioned one?) configurations. Images of miscellaneous samples made with the BBS show an image aspect and sharpness that is comparable with more expensive sources such as Ti:Sapphire lasers.

As in conventional time-domain optical coherence tomography (OCT), speckle is inherent to any Optical Fourier Domain Imaging (OFDI) of biological tissue. OFDI is also known as swept-source OCT (SS-OCT). The axial speckle size is mainly determined by the OCT resolution length and the transverse speckle size by the focusing optics illuminating the sample. There is also a contribution from the sample related to the number of scatterers contained within the probed volume. In the OFDI data processing, there is some liberty in selecting the range of wavelengths used and this allows variation in the OCT resolution length. Consequently the probed volume can be varied. By performing measurements on an optical phantom with a controlled density of discrete scatterers and by changing the probed volume with different range of wavelengths in the OFDI data processing, there is an obvious change in the axial speckle size, but we show that there is also a less obvious variation in the transverse speckle size. This work contributes to a better understanding of speckle in OCT.

In this paper, design and Finite Element analysis of a new tactile optical sensor for the measurement of contact-pressure and tissue compliance in endovascular surgeries are presented. Using Micro-Electro-Mechanical-Systems (MEMS) technology, this sensor can be fabricated and integrated with the medical tools for endovascular surgeries such as Catheter tool. The designed sensor is capable of detecting the magnitude of the applied forces, the pressure distribution on contact objects, and also estimating the compliance of the contact tissue. The designed sensor is made of three layers, the upper layer is fabricated from monocrystalline silicon to form silicon membranes, the middle layer which is the supporting element is fabricated from both silicon and silicone rubber as a soft material and the lower layer is a supporting Plexiglas substrate to connect the designed sensor to the optical fibers. Simulation results show that for the given contact forces, the magnitude and the distribution of contacting tissues pressure along with tissue compliance can be determined. This sensor as proposed is a good candidate for batch micromachining, which is yet another commercial advantage for this design. Because of its less expensive cost, the surgeon can use it as a disposal part of the endovascular tools, requiring no re-sterilization and reducing the cost of surgery.

Photo-acoustic (PA) imaging has been developped for different purposes but recent years has seen the technique gain interest with applications to small animal imaging. As a technique it is sensitive to endogenous optical contrast present in tissues and, contrary to diffuse optical imaging, it promises to bring high resolution imaging for in vivo studies at mid-range depths (3mm-10mm). However, a typical acquisition for the reconstruction of one slice in PA tomography can take up to approximatively 30 minutes which is clearly prohibitive for 3D imaging. This paper suggests a new reconstruction strategy using the compressive sampling formalism which states that a small number of linear projection of a compressible image contains enough information for reconstruction. This new scheme allows perfect reconstruction of numerical phantoms with only a fraction of the measurements normally needed with classical methods such as the pseudo-inverse.

Objective: Pc 4, a phthalocyanine photosensitizer in Phase I photodynamic therapy (PDT) trials, requires laser activation near 672 nm. For effective PDT, photosensitizer must be present in the target tissues. OPS uses elastic scattering spectroscopy to measure Pc 4 optical absorption non-invasively, and that absorbance can be converted to concentration using Pc 4 standard curves in 1% Intralipid®. In this study, we used OPS to evaluate Pc 4 optical absorption with time in subcutaneous tumor (with or without laser activation) and in contralateral skin. Tumor response was also evaluated after Pc 4-PDT. Conclusions: Both Pc 4 and hemoglobin optical absorption could be monitored by OPS. The decrease of Pc 4 absorption after PDT and the appearance of d-hbg indicated that alterations occurred in the tumor following Pc 4-PDT. The increase in d-hbg suggests that oxygen was not replaced completely, possibly due to circulation damage in tumor.

The optical absorption, fluorescence and phosphorescence of the novel styryl dyes developed for the fluorescent detection of DNA were investigated. The energy structures of dye molecules as well as spectral manifestations of the dyes aggregate formation and interaction with DNA were studied. The dramatic increase (up to 1000 times) of the fluorescence intensity of dyes in the presence of DNA was observed. The photostability and phototoxic influence on the DNA of several styryl dyes were studied by analyzing absorption, fluorescence and phosphorescence spectra of these dyes and dye-DNA systems. Changes of the optical density value of dye-DNA solutions caused by the visible light irradiation were fixed in the wavelength regions of the DNA absorption and of the dye absorption. Fluorescence emission of dye-DNA complexes upon two-photon excitation (TPE) at wavelength 1064 nm with the 20 ns pulsed YAG: Nd3+ laser and at 840 nm with the 90 fs pulsed Ti:sapphire laser was registered. The values of two-photon absorption cross-sections of dye-DNA complexes were evaluated.

Cell scattering produces a speckle pattern, while imaging produces a contrast pattern. This family of fluctuation signals can be studied by analysis techniques such as correlation and fractal dimension. Human breast cell (normal and cancerous) samples were investigated using laser speckle and imaging microscopy. Image data from tetraploid human cell motion and quorum sensing biofilm growth were studied as well, and we found that the signal fluctuations could be interpreted as gene expression fluctuations occurring during inter-cell communication. We have mapped nucleotide sequences as images and studied the fluctuation. We showed that the fractal dimension and correlation can be used for the description of bio-information from the DNA (nanometer) scale to the tissue (millimeter) level. Fluctuations of the HAR1 nucleotide sequence and IRF-6 single-mutation cases in the van der Woude syndrome were discussed. Sub-cell structures such as the 40S ribosome, GroEL, and lysozyme, were shown to carry texture fractal dimension information in their images consistent with their biological states. Clinical applications to X-ray mammography and Parkinson disease MRI data were discussed.

Two-photon (2-γ) photodynamic therapy (PDT) as opposed to "standard" one-photon (1-γ) PDT with Visudyne has recently been suggested as a targeted treatment alternative for wet-form age-related macular degeneration (AMD) and other neovascular diseases. AMD is a major cause of severe vision loss in the older population. It occurs due to growth of new leaky blood vessels (neovasculature) from the choriocapillaris, which results in destruction of photoreceptors in the fovea and loss of central vision. Damage outside the diseased region is always a concern, due to photosensitizer accumulation and its 1-γ excitation. Highly targeted 2-γ excitation, due to its non-linear intensity dependence, intrinsically avoids out-of-focus damage to healthy tissues and so could be valuable for wet-AMD. We have previously developed a quantitative approach for comparing the 2-γ efficacy of photosensitizers in vitro. In this study, we report further the development of ex vivo and in vivo techniques. A mouse mesenteric vessel has been investigated as the ex vivo model of neovasculature. For the in vivo studies, we have explored a mouse dorsal skin-fold window chamber model. Two-photon PDT is delivered using tightly focused ~300 fs laser pulses from a Ti:sapphire laser operating at 850 nm with 90 MHz pulse repetition rate. Confocal microscopy coupled to the laser was used to visualize the vessel's/cell's response before, during and after the treatment. We are able to demonstrate quantitative biological techniques to evaluate efficacy of 2-γ PDT photosensitizers in vivo.

Optical coherence tomography (OCT) is a well known microscopy technique used to observe micrometer structures in biological samples. Here we propose new experimental OCT setups using one Michelson interferometer and a CCD camera. Unlike the standard time domain OCT setup, our approach allows for high resolution imaging of a sample without any mechanical motion of the mirrors or the sample. The OCT signal is directly obtained at the CCD camera and does not require Fourier transformations or any mathematical operation as in Fourier domain OCT. The speed of data acquisition is not limited by any mechanical displacement or calculations but only by the camera throughput.

Quantum dots (QDs) are nanostructures that are highly attractive to optical biosensing. We have developed a nucleic acid biosensing strategy based on the use of quantum dots as energy donors in FRET. One of the challenges in such an approach is avoiding the non-specific adsorption of oligonucleotides. In this report, we describe our efforts to develop poly(ethylene glycol) (PEG)-based hydrophilic surface chemistry and hexanethiol based hydrophobic surface chemistry to alleviate non-specific adsorption. With respect to the former, it was found that the PEG surface chemistry strongly quenched the band-edge luminescence of CdSe/ZnS QDs and yielded significant band-gap luminescence. Furthermore, the PEG chemistry proved ineffective in preventing adsorption. With respect to hexanethiol capped CdSe/ZnS QDs, it was found that good QD luminescence was retained in organic solvent but was quenched in aqueous solution. The use of hydrophobic hexanethiol QDs in aqueous solution required the immobilization of QDs. To achieve this, we used thiol modified biotin and avidin coated fused silica optical fibers. Despite the quenching of the QDs, minimal adsorption was observed suggesting the methodology has good potential. In addition, we describe the development of a one-pot method for both the synthesis and capping of silicon QDs. Our approach also allows versatile post-synthetic modification of the silicon QD capping to produce a variety of functional groups. Silicon QDs are of interest in biosensing due to their biocompatibility and much lower toxicity compared to II-VI semiconductors.

The results of the design, synthesis and investigations of the compounds (possessing predicted unidirect excitations conductivity) containing several &pgr;-electron systems (including nucleotides - the short DNA-fragments) are reported. The predicted processes of unidirect triplet excitations transfer in all investigated compounds were proved. The nature of electronic excitations traps in the compounds investigated is discussed. For the molecular systems composed from the DNA-fragments spectral investigations show the adenosine-thymidine-sequences are such traps in these compounds as well as the DNA [1]. The energy levels lowering existence from chromophore to chromophore along the molecular system gives the ground to predict not only unidirect neutral excitation transfer but unidirect charge carrier current. Really the "diode" I(U) characteristic for metal-organic system of gold islands connected by &pgr;-electron-containing molecules was observed. This gives the possibility to propose these compounds to be used for nanoelectronic devices design. Computer simulations of electronic excitations passing through the oligomer functional macromolecule taking into account reverse exciton currents show such type macromolecules are perspective for applying in nanophotonics.

The charge variable range hopping mechanism is used to study the charge conduction in biomaterials such as DNA. We have considered that the charge particles are localized in bases of DNA nucleotides and nucleosides. The H-bonds and pi-pi bonds between the bases couple the two strands together and this structure is ideal for electron transfer due to hopping mechanism. The electron orbital belonging to the bases overlap quite well with each other along the long axis of the DNA. A DNA helix with random base couple sequence can be viewed as one dimensional disordered system. The charge carriers are localization in bases due the disorder in the system and the localization is enhanced by strong thermal fluctuations (i.e. phonons) in these structures. The interaction between localized carriers and phonons create polarons which are responsible for charge conduction in DNA due to the variable range hopping mechanism. Numerical simulations are performed for different type of DNA structures such as ribbons and films. A good agreement between our simulations and experiment is found.

In previous work, we have introduced a numerical constant fraction discrimination (NCFD) technique for processing time-resolved optical signals. It allows to extract, in a stable manner, the arrival time of early photons emitted by a fluorescent inclusion embedded in a scattering medium. We showed experimentally that these arrival times correlate quasi-linearly with inclusion depth. We now exploit this arrival time vs depth relationship for inferring the inclusion position by way of a time of flight algorithm. The algorithm uses the relative arrival times measured at several detector positions around the scattering medium with respect to a reference detector position. The latter is chosen as that detector position for which the arrival time is shortest. Our approach provides accurate inclusion localization, showing the potential of direct time-of-flight fluorescence diffuse optical tomography.

Mode-locked regimes of Yb-doped fiber laser with the photonic bandgap fiber (PBF) used for dispersion compensation in the laser cavity are studied using numerical modeling. The impact of the PBF's third-order dispersion on the dynamic instabilities of mode-locked regimes is elucidated. It is demonstrated that the instabilities leading to multi-period pulsing results from destabilization of resonant sidebands associated with dispersive waves. Novel type of stretched-pulse multi-period pulsing regime with symmetry-breaking features is identified. It is demonstrated that third-order dispersion suppresses the multi-period instabilities in the stretched-pulse regime. From the analysis of the spectral sidebands, we conclude that the suppression mechanism relies on resonant coupling of the phase-velocity matched and group-velocity matched dispersive waves with the main pulse spectrum.

A high power and widely tunable all-fiber Raman laser using a linear cavity configuration is demonstrated for the first time. The Raman fiber laser has been tuned from 1075 to 1135nm and delivers up to 5.0W of Stokes output power for 6.5W of launched pump power. Efficiencies ranging from 76.1 to 93.1% have been demonstrated.

The very narrow bandwidth laser system, which is generated by diode-pumped solid-state laser emitting at 1064nm wavelength with a fiber Bragg grating external cavity, has up to 20nm spectral line width and up to 40dB side mode suppression ratio. Due to the resolution limitation of measurement equipment the real spectral line width could be smaller than 20nm.

The doped fiber external cavity semiconductor laser (DFECL) has been reported with a simple structure, high power, narrow linewidth, and stable wavelength. The DFECL is mostly suitable to be an optical carrier generator for external modulation or microwave optical generation. Because of mode locking, the DFECL, with saturable absorber in its external cavity, has the possibility to be direct modulated at its multiples of cavity resonant frequency. The useful modulation frequency of the laser can be increased significantly. In this paper, we present experimental results about the transmission response of direct modulation of an ultra-long DFECL, and the modulated microwave signal transmission at the frequency of the 22^nd. multiple of the cavity resonant frequency. Modulated narrow bandwidth microwave signals at 2.4GHz were transmitted by this DFECL. The received RF spectrum has no obvious distortion for a 10MHz narrow band microwave signal and, all the resonant and harmonic frequencies in the 0~2.5GHz region are 50 dB lower than the transmitted wave. The results show that narrowband modulated microwave can be transmitted at high frequency by the long DFECL; even through the cavity round-trip frequency is very low. We conclude that this ultra-long doped fiber external cavity semiconductor laser can be used for narrowband wireless communication with direct modulation.

We report FM laser operation in a tunable single-frequency SOA-based fiber ring laser. Phase modulation is applied by means of either an intracavity phase modulator or a direct modulation of the SOA bias current. FM laser operation permits the effective laser linewidth to be adjusted from SLM to over 5 GHz, while controlling the spectral lineshape. A tunable laser having an adjustable linewidth and Gaussian lineshape is an ideal source for telecom optical test and measurement applications.

We present an alternative method to fabricate multi-wavelength distributed-feedback fiber lasers made of superstructured chirped fiber Bragg gratings in a single writing laser scan with a custom period-profiled phase mask and a tailored amplitude apodization profile produced by phase mask dithering. This method simplifies the fabrication process and increases the yield of samples having the right number of laser lines and a small frequency error with respect to a reference grid.

We are in the process of developing a hollow core fiber that contains a 2 nm to 3 nm thick AlAu alloy film near the core region, see Fig. 1. The fiber has a Photonic Crystal cladding that reflects the light back into the core region.

A simple technique to obtain a tunable laser using an erbium doped fiber in a ring cavity is proposed and demonstrated. The design does not include intra cavity filters to achieve tunable action; instead, it relies on the influence of intra cavity loss on the lasing wavelength. The dependence of tunability on factors such as the doping concentration of the fiber, reflectivity of the coupler, length of the doped fiber and pump power is discussed comprehensively using an analytical model and demonstrated experimentally. The effect of pump power on the lasing wavelength as seen in the experiment, which is not a direct consequence of the analytical model of fiber lasers, is discussed qualitatively. The key to enhance tunability is to increase the inversion levels in the fiber, which is possible with the use of shorter lengths of fiber with higher dopant concentration and larger pump powers, with maximum reflection into the cavity.

Stability and linewidth (FWHM & 20-dB) measurements of a tuneable, high power, narrow linewidth multiwavelength Hybrid Cavity Semiconductor Fibre Ring Laser (HC-SFRL) are presented. The laser incorporates a SOA, a polarization controller (PC), and a tuneable optical filter. The ring cavity itself is composed of Single Mode Fibre (SMF) and a 1-m long Polarization Maintaining Fibre (PMF). The laser is capable of single, dual and triple lasing wavelengths with ultra-narrow wavelength spacing (less than 30 pm) with good stability for periods over 2 hours.

Short fiber lasers are increasingly studied due to their applications in communications and sensing¹. These lasers require high concentrations of Erbium (Er) and Ytterbium (Yb) that are not compatible with the presence of Germanium (Ge) in the fiber core². In stark contrast with more conventional fabrication methods, ultrafast lasers now allow for grating inscription within fibers having no Ge doping³. Normally for short gratings the reflected signal dispersion is small and relatively harmless to the operation of long cavities. As cavity length decreases however the signal will tend to travel more and more within the gratings, interacting with them proportionately more often. Hence a thorough understanding of the grating dispersion characteristics becomes even more important. As a result of their physical differences, the characteristics of ultrafast gratings can vary substantially from those produced using more conventional fabrication methods, and it is unknown whether these factors in combination with a high dopant concentration will significantly affect the dispersion properties of such gratings. In this study, Bragg gratings made with infrared (IR) femtosecond radiation and a first order phase mask were inscribed in fibers heavily doped with Er and Yb as well as a pure silica core fiber. Subsequent measurements of the power spectra, group delay and group delay ripple (GDR) are reported herein.

The fabrication of a very short fiber laser made in heavily doped (0.23 wt% Er³⁺, 2.5 wt% Yb³⁺) Erbium-Ytterbium silica fiber is presented. The laser cavity is built by inscribing two identical Bragg gratings 8 mm apart as cavity mirrors using ultrafast femtosecond radiation from an infrared regenerative amplifier and the phase mask method. The fiber Bragg gratings have a 6.4 mm Gaussian distribution of the refractive index modulation and a 99.9% reflectivity. The evaluation of the broadband loss induced during the ultrafast laser exposure resulted in < 0.1 dB at the resonant wavelength. The fiber laser efficiency and the influence of thermal effects of the pump dissipation on the grating Brass resonance is also presented. Major advantages of ultrafast IR laser inscription of Bragg gratings for fiber lasers cavities will also be discussed.

We estimate the effective photo-elastic constants peculiar to a two- and three-phonon scattering of light in Bragg regime in optical modulators based on tellurium dioxide crystalline structures. A triplet or quartet of modes appears within the interaction between the incident light beam and the acoustic wave under action of a square-law nonlinearity in similar structures. The analysis and numerical simulations are formulated in terms of the eigen-vectors for light modes in anisotropic medium and take into account the effect of optical activity in TeO₂. This analysis is devoted to estimating and comparing the effective photo-elastic constants inherent in normal and anomalous regimes of acousto-optical interaction in tellurium dioxide and oriented to performing the optical modulators. The obtained experimental data on a two- and three-phonon light scattering are discussed in connection with practical estimations.

One of the most promising devices for high speed optical signal processing is the Nonlinear Directional Coupler (NLDC). In this paper an asymmetric nonlinear directional coupler controlled by an external laser beam focused on the surface of the coupler has been analyzed. The analysis is based on couple-mode theory using rigorous perturbation technique and enables one to obtain asymptotically correct coupled-mode equations. The effects of various parameters such as plasma density, waveguide width, laser beam frequency and laser spot position on the coupling of power have been investigated and presented.

We demonstrate an ultra-wide optical frequency comb generation method by dispersion compensation of an amplified recirculating optical loop with successive phase modulation. At the reference wavelength of 1553 nm, up to 230 comb lines within a 40 dB envelope are generated with 10 GHz spacing.

In this paper, noise characteristics of second-harmonic generation (SHG) in periodically poled lithium niobate (PPLN) using the quasi-phase-matching (QPM) technique are studied experimentally. In the experiment, a 0.78-&mgr;m second-harmonic (SH) wave was generated when a 1.55-&mgr;m fundamental wave passed through a PPLN crystal (bulk or annealed proton-exchanged waveguide). The fundamental and SH waves were then separated through a beam splitter and sent to two photodetectors, respectively. The time-domain and frequency-domain characteristics of the fundamental and SH waves were analyzed. By using the pump-probe method, the noise characteristics were studied further when 532-nm irradiation light co-propagated with the 1.55-&mgr;m fundamental light in the PPLN crystals. It is found that for the bulk and waveguides of PPLN crystals, the SH wave has a higher relative noise level than the corresponding fundamental wave. For the same fundamental wave, the SH wave has lower noise in a bulk crystal than in a waveguide, and in MgO-doped PPLN than in undoped PPLN. In addition, the photorefractive effect incurred by the irradiation light can influence the SHG noise.

Quasi-phase-matched (QPM) wavelength conversions based on the second-order nonlinear interaction, such as second-harmonic generation (SHG), difference-frequency generation (DFG) and sum-frequency generation (SFG), in periodically poled lithium niobate (PPLN)) have attracted much attention due to their excellent conversion properties such as broad bandwidth, high efficiency, and low noise. To achieve an efficient conversion, high-power pump light is always desired. However, PPLN crystals (either bulk or waveguide) are somehow vulnerable to high-power irradiating light, especially at a short wavelength due to the photorefractive effect (PRE), known as a refractive index change induced by an intense light illumination. The PRE may deteriorate device performance significantly. To suppress the PRE, PPLN crystals usually have to be operated at high temperatures (over one hundred degrees Celsius) or to be specially doped. Despite the significant impacts of the PRE on device performance, to date, there is limited information in the literature on the PRE mechanism in QPM PPLN. In this work, we adopt the pump-probe method and characterize the PRE in undoped and 5-mol% MgO-doped PPLN crystals. Especially, we compare the PRE in bulk and annealed proton-exchanged (APE) waveguides of PPLN. A broadband light source at 1.55 &mgr;m was used as the probe, and narrowband light at two wavelengths of 0.5 and 1.1 &mgr;m was alternatively taken as the pump. The period of crystals were selected to meet the QPM condition of SHG. It is shown that the decay property and temperature dependence of PRE, the wavelength and amplitude changes of the SHG tuning curve are distinct for the undoped and MgO-doped PPLN, as well as for the bulk and waveguide, which implies a few competing interactions in the crystals, such as the PRE, thermal-optic, photogalvanic and two-photon absorption effect, etc.

The present work is devoted to simulation of photonic and magnetophotonic bandgap structures/crystals intended for various applications, particularly in the telecommunications in the GHz, THz to optical frequency bands (as waveguides, beam-guides, filters etc). The results of experimental and theoretical study of several types of 1 D photonic crystals are discussed. Structures under study are presented by periodical multilayered systems formed with: 1st type--ferrite/quartz and 2nd type--quartz/teflon/thin-film-bismuth and ruby/teflon/thin-film-copper. Theoretical predictions are fulfilled for a wide frequency band. The experimental verification of these the modeling results was performed in the EHF band (20-40 GHz). The possibility to control the shape of frequency stop-band zones has been modeled by using magnetically sensitive thin films forming the periodical structure of the 2nd type. It was demonstrated that the shape of the stop bands of the given magnetophotonic structure can be changed effectively by applying a magnetic field not exceeding 100 Oe. Various promising applications of these structures such as tunable extra high frequency and optical passive devices are discussed.

Previous work has demonstrated that the thermal stability of Fiber Bragg gratings can be influenced by pre- or postirradiation of the grating with uniform (non-modulated) light, thereby changing the grating contrast (or modulation index). We present new experimental results about the thermal stability of gratings where the contrast is determined by the fiber-phase mask distance during the irradiation with excimer laser light. Due to the low spatial coherence of the excimer laser light, the fringe contrast behind the mask drops from near 100% to less than 10% over 1 mm.

We report the realization of a Bragg grating optical filter at telecommunication wavelengths in silicon-on-insulator (SOI) through the use of ion implantation induced refractive index modulation. Silicon self-irradiation damage accumulation results in an increase of the refractive index to a saturated value, upon amorphization, of approximately 3.75. This makes it an interesting candidate for passive gratings as the silicon retains a planar surface, making it ideal for further processing. Monte Carlo simulations and coupled mode theory demonstrate the viability of the approach. Planar implanted SOI waveguides showed extinction ratios of -5 dB for TE and -2 dB for TM. An annealing study suggests complete amorphization was not achieved and future results should be improved dramatically.

The performance of silica-on-silicon planar waveguide devices is highly dependent on the properties of the layers comprising their structure. In this work we have investigated in some detail the properties of doped-silica layers formed by plasma enhanced chemical vapour deposition (PECVD). Parameters such as the refractive index, optical loss, stress and reflow characteristics of borophosphosilicate glass (BPSG) layers have been studied as a function of composition and processing conditions. Using the information gained, we have fabricated arrayed waveguide grating (AWG) demultiplexers and Bragg grating wavelength filter devices. Through careful adjustment of the properties of the top BPSG cladding layers, the performance of these devices, which are highly wavelength and polarization sensitive, can be easily controlled. Correlation of wavelength dependence, optical loss, and polarization dependence of different device designs, with the properties of the top BPSG cladding layer has allowed optimization of these devices and provides invaluable materials and process knowledge for the future use of silica-based layers in these and other photonic device applications.

Phase mask assisted fabrication of Bragg gratings in Ge-doped SMF-28 fiber with an ultrafast 800nm IR laser was first demonstrated in 2003. The wide variety of materials accessible to ultrafast laser modification allows for the fabricating of components that were not previously realizable with UV laser photosensitivity. Ultrafast fabricated gratings themselves have proven to have a number of common properties with UV induced gratings, and some unique elements. This paper will introduce phase mask assisted ultrafast infrared induced grating fabrication and some of their unique properties.

Optical coherence tomography (OCT) is an emerging technology for high-resolution cross-sectional imaging of 3D structures. Not only could OCT extract the internal features of an object, but it could acquire the 3D profile of an object as well. Hence it has huge potentials for industrial applications. Owing to non-scanning along the X-Y axis, full-field OCT could be the simplest and most economic imaging system, especially for applications where the speed is critical. For an OCT system, the performance and cost basically depends on the light source being used. The broader the source bandwidth, the finer of the depth resolution that could be reached; the more power of the source, the better signal-to-noise ratio and the deeper of penetration the system achieves. A typical SLD (Superluminescent Diode) light source has a bandwidth of 15 nm and 10 mW optical power at a price around $6,000. However, a Halogen bulb having 50W power and 200nm bandwidth only costs less than $10. The design and implementation of a large-area, full-field OCT system using Halogen white-light source is described in the paper. The experimental results obtained from 3D shaping and multiple-layer tomographies are also presented.

Fiber lasers in MOPA configuration are a very flexible tool for micromachining applications since they allow to independently adjust the pulse parameters such as pulse duration, repetition rates and pulse energy while maintaining a constant beam quality. The developed fiber laser provides an average power of 11 W and maximum pulse energy of 0.5 mJ for a wide range of pulse parameters at diffraction limited beam quality. Its pulse duration and repetition rate are continuously adjustable from 10 ns to cw and from 10kHz to 1MHz respectively. Ablation experiments were carried out on stainless steel, nickel and silicon with the goal of optimizing removal rates or surface finish using nanosecond pulses of different parameters. Maximum removal rates are achieved on all three materials using relatively similar pulse parameters. For silicon, pulse duration of 320ns at 100kHz and 45mJ resulted in optimum removal. In single shot experiments on silicon a significant influence of the pulse duration was found with a distinct optimum for removal rate and surface finish. The optimum intensity at the work piece is in the range of 35MW/cm² to 70MW/cm². Lower values are below the ablation threshold, while the plasma shielding effect limits considerable increases in removal rates for intensities exceeding 70MW/cm ².

Much of the current activity in optical coherence tomography aims at increasing the image resolution. Nowadays, two kinds of OCT techniques are available. The first approach is the Time-Domain OCT (TD-OCT) which usually relies on a moving part into the reference arm to probe the sample in depth. The second approach is the Fourier-Domain OCT (FD-OCT) in which the signal is acquired as a function of the wavelength and the depth profile of the sample is obtained by Fourier transform. Theoretically, in both techniques, the resolution is limited by the central wavelength of the source and by its full width at half maximum. Nevertheless, it is shown in this paper that this resolution may be improved by using deconvolution technique based on Wiener filtering and Autoregressive Spectrum Extrapolation (ASE). In our experiment, thanks to deconvolution an improvement of a factor up to 4 is obtained in TD-OCT and about 2 in FD-OCT. As an illustration, the approach is applied to TD and FD-OCT measurements of the profile of a carbon-epoxy composite to evaluate the performance in determining the thickness of the upper layer within a resolution better than that provided by the conventional processing of the OCT envelope.

Fiber optical Sagnac interferometer is applied for absolute calibration of ultrasonic pulsed source. Method of topological phase is used for the maintenance of &pgr;/2 phase bias of the counterpropagating waves. Non-disturbing absolute measurement of the ultrasonic displacement with sensitivity of 10^-1 Å within 100 kHz ÷ 30 MHz band is demonstrated which is comparable with more complicated and expensive analogs.

Fiber Bragg gratings inscribed in sapphire fiber (SFBG) using IR femtosecond radiation and the phase mask method are potential sensors for very high temperature applications (⪆ 1200 °C) where silica based fiber sensors cannot operate due to the low silica glass transition temperature. Sapphire fiber is stable up to 2000 °C and the induced grating structures are stable above 1500 °C. The main difficulty of using the femtosecond IR laser induced sapphire fiber grating sensors is related to the probing of the sensor. Since the sapphire fiber is an air-clad rod, propagating probe light is highly multimode for the commercially available fiber diameters of between 60 and 200 μm. The interrogation of the Bragg grating sensor has to be made either in a multimode regime or an attempt to propagate a single mode signal in the multimode sapphire fiber is required. A study of the probing signal coupling to the SFBG and its influence on the spectral response of the sapphire grating is presented. High-order retro-reflective FBGs were fabricated in crystalline sapphire fibers with diameters in the 60 to 200 μm range. The sapphire Bragg gratings was probed with signals from a tuneable laser launched through a single-mode fiber into the input port of multimode fiber couplers made from 60 and 105 μm core diameter fiber. In the single mode regime, the excitation of the sapphire fiber was made with fiber collimators and fiber tapers.

In this paper, we present results of Bragg grating inscription in optical waveguide glasses other than those based on fused silica, using the femtosecond infrared (IR) laser inscription of Bragg gratings method that is based on the mechanism of multiphoton ionization and plasma absorption. This mechanism allows for the inscription of Bragg grating structures not only in the fused-silica glasses without Ge-doping but also in other glasses such as fluoride, phosphate, chalcogenide and borosilicate which are important optical substrates for applications as mid IR fiber lasers and sensing. The writing method, spectral characteristics, polarization properties and thermal stability of the Bragg gratings are discussed.

A di-block copolymer composed of poly(ethylene oxide) and poly(azobenzene methacrylate) in the ratio of 45:55 has been synthesized. Thin films of about 400-700nm thickness have been prepared from solutions in trichloromethane by gravity settling. ATR-leaky mode spectroscopy has been used for the determination of the optical anisotropy. Homogeneous exposure caused a significant change in this anisotropy. Holographic gratings have been recorded in these films. The in-situ measurements of the diffraction efficiency exhibit a relative maximum after a recording time of about 30 min, followed by a relative minimum before increasing again to high values of up to 40%. Especially for circular polarization high efficiencies were obtained. Depositing this film on a foil of polyethylene the grating constant of a recorded grating could be tuned by the application of mechanical stress in a testing machine.

Dark diffusion transient in a blue-green sensitized holographic photopolymer was investigated based on a previously published theoretical model of monomer diffusion. Diffusion time constant of monomers was obtained by fitting the experimental data to the theoretical model. According to the results of diffusion time constant, experiments were designed and conducted to investigate the evolution of grating efficiency with non-continuous holographic exposure. The experimental result indicated that the saturated diffraction efficiency of a non-continuously exposed grating is about 1.25 times of that of continuously exposed one under the same recording condition.

We have investigated the nonlinear switching mechanism in nanostructures doped in photonic crystals. The nonlinear phenomenon studied in this paper is the two-photon absorption process. A probe laser field is applied between the ground state and the next excited state of the nanoparticles to measure the two-photon absorption spectrum. A coupling field is applied between the two excited states of nanoparticles to control the two-photon process. It is found that when the decay resonance energy lies away from the photonic band edge the inhibition of two-photon absorption is observed. However, when the probe field is not resonance, the inhibition of two photons absorption is not observed. An interesting result is observed when the decay resonance energy lies near the band edge. It is found that the inhibition of the two-photon absorption disappears. It means that the phenomenon of two-photon absorption can be switched on and off by tuning the resonance energy within the lower band of the crystal. This mechanism can be used to make a new type of photonic switching devices using photonic crystals.

ZnTe:V thin cermet films (containing 0 to 10wt% V in ZnTe matrix) were prepared onto glass substrate by e-beam evaporation in vacuum at ~10^-6 torr. The deposition rate of the films was at about 2.05 nms^-1. The effects of various deposition conditions on the electrical and optical properties of the cermet films have been studied in detail. The structure analysis of the film was performed by X-ray diffraction technique and it was found that the films are amorphous in nature. The optical properties of both the as-deposited and annealed films were studied in the wavelength range 300<&lgr;<2500 nm, respectively. The special feature of transmittance spectra is that as the doping vanadium is increased to a concentration of 2.5wt% V, the transmittance value is increased in the entire visible & infra-red up to &lgr;=1600 nm and beyond that concentration value, the transmittance is decreased. Similar behavior has also been observed in annealed films. For both types of cermet sample, the values of Urbach tail, optical band gap, refractive index and dielectric constants were evaluated for different compositions and thicknesses, respectively. Evaluation of these parameters may help in view of their technological applications in selective surface as well as in optoelectronic devices.

Photoresponsive nanocomposite organically modified silica films were prepared by solution sol-gel processing of organo-silicon alkoxide compounds. Waveguiding at 488 and 514.5 nm proceeded with simultaneous self-inscription and self-focusing. Light Induced self inscribed (LISI) waveguides were revealed by wet etching. Under certain conditions, self-inscription exhibited optical beating or became chaotic, and filamentation was observed. Composite waveguides of nanoplasmonic particles and rare earth doped nanoparticles were written by LISI.

We present a systematic analysis of three dimensionally ordered photonic crystals made of dyed-polystyrene spheres fabricated using the newly reported inward growing self assembling method. The SEM and AFM images show good ordering of the spheres with (111) plane parallel to the substrate. The photonic stop band is tuned by varying the angle of incidence of light and made to coincide with the emission wavelength of the dyes. The multiple Bragg diffraction effects observed at high angles of incidence are interpreted. The high reflectance values obtained along with the observation of the higher order bands, and the photonic stop band splitting at high angles of incidence show the superior quality of the photonic crystals fabricated using these dyed polystyrene spheres in less than three hours.

In this work, the effect of photoinitiator concentration and light intensity on conversion of trifunctional acrylate monomers is studied. Polymerization reaction and diffusion of acrylate monomers is examined using Real Time Infrared (RTIR) spectroscopy, differential scanning calorimetry and a holographic technique. An optimal initiator concentration that provides maximized diffraction efficiency is observed.

Generally, it is very difficult to prepare zinc aluminosilicate glasses because of its high melting temperature. In this work, transparent rare earth Eu³⁺-doped ZnO-Al₂O₃-SiO₂ glass-ceramics were obtained by sintering the corresponding precursor gels, which were prepared by using tetraethylorthosilicate and inorganic salts as raw materials and by a sol-gel method. X-ray diffraction, infrared spectrometer and fluorescence spectrometer were used to characterize the as-prepared materials. The luminescence properties of Eu³⁺ in zinc aluminosilicate glass-ceramics were mainly studied. Results showed that ZnAl₂O₄ nanocrystals were precipitated from ZnO-Al₂O₃-SiO₂ system and dispersed in the SiO₂-based glass when the heat-treatment temperature was up to 900^oC. A strong emission peak at 614 nm was observed and the peak is assigned to ⁵D_o→⁷F₂ transition of Eu³⁺ ions. The luminescence mechanism of Eu ³⁺ doped ZnO-Al₂O₃-SiO₂ glass-ceramics was analyzed and discussed.

Properties of RE³⁺(Nd³⁺, Er³⁺) dopped lithium niobate(LN) nanocrystals prepared by sol-gel technique are investigated in this paper. The as-obtained LN nanocrystals are the only crystalline phase according to the X-ray powder diffraction (XRD) and transmission electron microscope (TEM) results. The absorption and emission spectra were measured in the visible and near infrared regions, and compared with that of melt-grown LN crystals. The excitation wavelength was 514 nm and 355 nm for Er³⁺ and Nd³⁺ dopped LN nanocrystal samples, respectively. A (⁴ I_11/2- ⁴I_15/2) and a ( ⁴F_3/2- ⁴I_11/2 ) near infrared lasing transition was measured at 1035 nm and 1077 nm in Er₃₊ and Nd³⁺ dopped LN nanocrystal samples, respectively. The results show red shifts in emission spectra in Er³⁺ dopped LN nanocrystal samples, and blue shifts in emission spectra in Nd³⁺ doped LN nanocrystal will be also discussed in the paper.

In this article, thermo-reversible compounds have been applied as a transducer in a fiber-optic temperature sensor and the dependence of the reflected optical power on the temperature has been investigated. The reflected optical power indicated a monotonous change in the temperature range of observation, corresponding to an 1.4 dB increase in the optical power when the temperature increased from 20 to 125°C. The temperature dependence of the optical properties was found to be reversible, which indicates that the temperature transducer is reversible as well.

Paper presents results of own development in the field of organic recording media for working (WERM) and archives (WORM) optical memory. Recording media for working optical memory have been prepared with the use of original thermally irreversible photochromic compounds from diarylethenes and fulgimides as well as polycarbonate as a polymer binder. Using these recording media, refractive and fluorescent methods for nondestructive readout of optical information have been elaborated. Aiming at making recording media for archives optical memory organic compounds (chalcone, diarylethene) which formed fluorescent products during irreversible photochemical reaction under laser irradiation were used. Based on developed photochromic materials samples of three-layer photochromic recording media have been prepared and tested with positive results on the developed optical device. This device includes Nd - laser and provides generation of several harmonics of laser irradiation.

This paper is dedicated to the investigation of stoichiometric defect semiconductors, allowing extremely high vacancy concentrations of 10²¹ cm^-3, determining their unusual physical properties. The material studied, Hg₃In₂Te₆, is of high interest for creation of efficient photonic structures: self-calibrating photodiodes, high-speed photodiodes, multi-element photodiodes with improved sensitivity, as well as optical filters for the spectral ranges of 2-28μm. Measurements of photoconductivity confirmed high sensitivity of this material in wide spectral ranges (λ=0.35-1.85 μm), including the areas of sensitivity for CdS, CdSe, GaAs, Si and Ge. In comparison with the latter, Hg₃In₂Te₆ is characterized with the lowest melting temperature (983K) that allows reduction of energy consumption during the synthesis process. The experimental results prove high photoconductive quantum yield for Hg₃In₂Te₆ at hν = 0.74 - 3.5 eV. For the sake of comparison, we are also presenting the investigation results concerning CdIn₂Te₄ crystals. In general, defect semiconductors are ideal for creation of surface-barrier structures and hetero-junctions because of low surface state concentration and atmospheric oxygen absorption rate.

This paper presents the investigation results for the technology to obtain the films of SnO₂, ITO, and CdO by magnetron sputtering in the pure argon and oxygen-argon mixture, as well as the physical characteristics of the films. For the deposition we have used the substrates made from the quartz glass, sital and silicon. Pure metallic tin, indium and cadmium were used as targets together with the synthesized powder oxides. The authors determined the optimal technological regimes allowing to obtain reproducible high-quality thin films of tin, indium and cadmium oxides with the following electrical and optical parameters: SnO₂ - specific resistivity ρ = 1.5 - 6.0•10^-4 Ω•cm, optical transmission T = 90 - 95% in transparency region; ITO - ρ = 4.0 - 6.0•10^-4 Ω•cm, T = 90 - 95%; CdO - ρ = 2.0 - 3.0•10^-4 Ω•cm, T = 80 - 90%.

We monitored the distributed strain during the pipeline buckling process using distributed Brillouin sensor, which allows us to predict the buckling or crack location according to the sequence and location of the deformation for the first time using the broadening factor of Brillouin spectrum width. Two pipelines were designed and instrumented with polymer and carbon/polyimide coated fibers, and then the pipelines were subjected to internal pressure, axial tensile force and bending moment. We show that 1) the localized buckling occurred at the top, median and bottom of the pipeline, where the maximum broaden factors were obtained; 2) the deformation sequence can be measured using the nonlinearity of the broadening factor, 3) a high strength carbon/polyimide-coated fiber can detect higher stress accurately than standard telecom fibers. Our results strengthen the distributed Brillouin fiber sensor position as a nervous system to identify the potential problem in early stage for structural health monitoring.

A new Surface Plasmon Resonance (SPR) sensor design is proposed and fabricated based on an optical fiber with a photo-written Tilted Fiber Bragg Grating (TFBG) and a thin gold deposited layer. The TFBG allows the transfer of light from the core mode into a multitude of cladding modes, each wavelength corresponding to a different incidence angle. The most pronounced SPR effect was obtained for a gold thickness of 20 nm, however every tested thickness showed SPR at a certain level. To characterize the uniformity of gold films, the coated fiber were imaged using Atomic Force Microscopy (AFM) and showed a high level of graininess, as expected from such thin layers. Scanning Electron Microscope (SEM) images were used to characterize the quality of the gold coating before and after experiments. Despite the high non-uniformity and graininess of gold coating, the angular spread of SPR is as narrow as expected from theory. The sensitivity obtained reaches 454 nm per refractive index unit.

We present results of Bragg gratings inscription in several crystalline optical weveguiding structures. Using infrared femtosecond radiation and the phase mask method, Bragg gratings were inscribed in multimode crystalline sapphire fiber, RPE lithium niobate waveguides and large area core multimode YAG fibers. It was shown that Bragg grating structures could be created in all these crystalline substrates with comparable IR- intensities. The spectral characteristics and the thermal stability of these Bragg gratings is also presented.

This paper investigates an evanescent field refractive index sensor based on a planar waveguide silicon-on-insulator (SOI) unbalanced Mach-Zehnder interferometer structure. The key element used for enhancing the sensitivity of the device is a waveguide structure that contains perforations through its core guiding layer. Three-dimensional numerical solution of the wave equation was used to determine optimal device dimensions and model device behavior. Devices were then fabricated in 3.4 μm thick SOI material and optically characterized. It was found that the perforations in the waveguide increased its sensitivity to refractive index changes in the cladding by a factor of two. The sensitivity of the device, which contained a 100 μm long sensing region, was estimated to be 2.2 nm shift in the interferometer output spectrum per unit refractive index change of the cladding. It is expected that further optimization of the perforated waveguide structure will result in a significant increase in sensitivity.

An intensity interrogation system for a long-period-grating (LPG) -based fiber sensor using a linear combination of two Gaussian functions as the curve fitting function is proposed and demonstrated. The selected resonant dip of the LPG transmission spectrum can be reconstructed with the curve fitting function based on the measured intensities at different wavelengths. Thus, the center wavelength and the minimum transmission value of the resonant dip can be interrogated simultaneously. The center wavelength is obtained by calculating the first-order derivative of the fitting function, which is 1562.74 nm compared to 1562.3 nm directly measured using an optical spectrum analyzer (OSA). The minimum transmission value is obtained directly from the fitting curve, which is -35.6 dBm is compared to -34.2 dBm directly measured from an OSA. An arrayed waveguide grating (AWG) is supposed to be adopted for the intensity measurement. However, the experiment is carried out using a tunable optical filter to approve the concept due to the unavailability of a suitable AWG at the time of experiment.

In this paper, the hybrid modes are used to analyze the cladding mode resonances of TFBGs and compared with those using the linear polarization modes. As the TFBG spectrum span is larger than 30nm, the material dispersion effect can not be ignored and must be considered for accurately analyzing the cladding mode resonance peaks. Both analysis and experimental results will be presented, and they are well matched. By accurately analyzing the higher order cladding mode resonances with double or triple peaks, the tracking of higher order cladding mode resonances is facilitated, and these modes have the largest differential strain and index sensitivities relative to the core modes.

In this paper, the wavelength dependent Polarization Dependent Loss (PDL) characteristics of fiber Bragg gratings (FBG) are discussed. The PDL in FBG is measured by applying the polarization scanning method and the Mueller matrix method. The experiment results indicate that the wavelength dependent PDL in uniform FBG has the potential to realize temperature sensing measurement.

Emission of individual single-walled carbon nanotubes (SWNTs) in aqueous suspension with single-stranded DNA (ss-DNA) wrapped around the tube with and without glucose oxidase (GOX) has been studied in the spectral range (9-13)•10³ cm^-1. GOX was added into the aqueous suspension of SWNTs with wrapped ss-DNA, which was prepared before using ultrasonication/ultracentrifugation treatment. AFM images of the nanotube with the adsorbed enzyme show that GOX retains its native globular structure. Computer simulation of SWNT:DNA:GOX bionanohybrid formation in water demonstrates effective coupling of the enzyme with DNA wrapped around the nanotube. GOX adding was not accompanied by a change of Raman spectrum of nanotubes. However, in the spectrum of nanotubes emission a small spectral blue shift was observed after GOX immobilization. Small glucose injections (1 mM in portion) into the prepared aqueous suspension lead to the quenching of the intensity of nanotube luminescence due to the appearance of H₂O₂ in the solution as a result of glucose oxidizing. The DNA interlayer between the GOX and nanotube keeps the enzyme activity which usually decreases when the enzyme is bound directly to the nanotube.

In our previous work, a highly sensitive waveguide Bragg grating (WBG) sensor for measuring small changes in the refractive index of a surrounding liquid was developed [1]. We proposed a technique for creating a temperature insensitive refractometer that utilizes core and cladding modes in an open-top ridge waveguide architecture in order to discriminate between Bragg wavelength changes in temperature and refractive index [2]. In this work, a technique for creating a temperature insensitive refractometer that utilizes TE and TM modes in an open-top ridge waveguide design is presented. By using the TE mode resonance as a temperature reference, the relative shift of the TM mode can be monitored in order to measure the refractive index of liquids under test. Specifically, the device fabricated here produces a relative resonance shift of 1 pm for every 1×10^-4 of measured index change, with a temperature sensitivity less than 0.2 pm/°C.

The advent of microfluidics has provided a tremendous boost to the field of health care for the development of practical in-situ medical diagnoses and Point-of-Care (POC) testing methods. Optical microfluidics offers a lot of scope for carrying out successful biodetections through different target detection techniques such as optical absorption, fluorescence, etc. Two main issues in carrying out successful biodetection on microfluidic platform are the problem of biomolecule immobilization onto the surface of the microfluidic channel and efficient mixing of the bio-fluids necessary to achieve proper bio-interaction. In most cases, the biodetection involves two or more biological specimens, such as enzyme-substrate, antigen-antibody, protein-protein etc., and therefore, it is necessary to discover a solution which addresses to the needs of both immobilization and multi-molecular interactions. In this work, a novel technique of flow controlled molecular sorting is presented, wherein, by appropriate design of the microfluidic channel and by careful control of fluid flow in the system, optimal interaction of the specimens can be achieved through biomolecular sorting, thereby overcoming the problem of bio-immobilization onto the surface of the microfluidic channel. Herein, Finite Element Modeling (FEM) of flow behavior within the microfluidic channel has been carried out for different channel geometries, which is essential for the appropriate choice of microfluidic system for the present application. The technique of implementing the immobilization-free multi molecular bio-interactions in the proposed microfluidic system is explained and the feasibility of carrying out optical microfluidics based biodetection is demonstrated.

This paper presents fluid modeling and simulation of microchambers within microfluidic chip for immunoassay based biosensing applications. A microfluidic biosensor chip for fluorescence based immunoassay detection of biological elements should include suitably designed chambers with rinsing channels. Microfluidic chambers are necessary in holding and immobilizing enzymes onto the microfluidic surface. They function as center of interest for enzyme interactions and optical detection. It is also necessary to incorporate cleaning function into the micro-chambers to instigate reusability. The shape and size of the chamber is a crucial factor for sensitivity of the integrated biosensor as the optical detection unit would be placed at the top of the chamber. In the present work, combinations of chambers and channels with various geometries and sizes are simulated for rinsing flows. Chambers are analyzed for rinsing behavior under certain pressure drops between the inlet and outlet channels. Average velocity and flow contours are plotted and compared at different cross-sections within the chambers. Simulations are performed using FEM software, FEMLAB (Comsol, Inc., Burlington, MA). Optimized chambers are selected based on optimal rinsing, negligible slow zones without reverse flows, relatively simple geometry and low pressure drops.

A compact, lightweight Earth horizon sensor has been designed based on uncooled infrared microbolometer array technology developed at INO. The design has been optimized for use on small satellites in Low Earth Orbits. The sensor may be used either as an attitude sensor or as an atmospheric limb detector. Various configurations may be implemented for both spinning and 3-axis stabilized satellites. The core of the sensor is the microbolometer focal plane array equipped with 256 x 1 VO_x thermistor pixels with a pitch of 52 μm. The optics consists of a single Zinc Selenide lens with a focal length of 39.7 mm. The system's F-number is 3.8 and the detector limited Noise Equivalent Temperature Difference is estimated to be 0.75 K at 300 K for the 14 - 16 μm wavelength range. A single-sensor configuration will have a mass of less than 300g, a volume of 125 cm³ and a power consumption of 600 mW, making it well-suited for small satellite missions.

Ring interferometer for ultrasonic sensing with homodyne amplification of interference signal is proposed and experimentally investigated. Owing to an inherent mechanism of suppression of laser phase noise, the proposed interferometer is significantly less critical to the path imbalance between signal and reference waves than classical interferometers with homodyne amplification (Michelson and Mach-Zander). Experiment shows that actual performance of fiber optic homodyne ring interferometer is seriously corrupted by the backscattering interference noise. Backscattering noise-free, non-ring topology of time-delay homodyne interferometer with laser phase noise rejection is discussed.

Periodically tapered long-period fiber gratings (TLPFGs) were manufactured with Corning SMF-28 and Blazephotonics ESM-12-01 optical fibers and developed into fiber-optic pressure sensors. Their pressure sensitivity and temperature effect were measured. Compared with pressure sensors using fiber Bragg gratings (FBGs), the pressure sensor equipped with a TLPFG made from photonic ESM-12-01 crystal fiber displayed superior properties both in pressure sensitivity and temperature effect.

Traditional biometric technologies used for security and person identification essentially deal with fingerprints, hand geometry and face images. However, because all these technologies use external features of human body, they can be easily fooled and tampered with by distorting, modifying or counterfeiting these features. Nowadays, internal biometrics which detects the internal ID features of an object is becoming increasingly important. Being capable of exploring under-skin structure, optical coherence tomography (OCT) system can be used as a powerful tool for internal biometrics. We have applied fiber-optic and full-field OCT systems to detect the multiple-layer 2D images and 3D profile of the fingerprints, which eventually result in a higher discrimination than the traditional 2D recognition methods. More importantly, the OCT based fingerprint recognition has the ability to easily distinguish artificial fingerprint dummies by analyzing the extracted layered surfaces. Experiments show that our OCT systems successfully detected the dummy, which was made of plasticene and was used to bypass the commercially available fingerprint scanning system with a false accept rate (FAR) of 100%.

Improvised Explosive Devices (IEDs) are a major threat to Canadian and allies troups involved in peacekeeping and minor conflict operations and despite their relative low technology they represent a major challenge in terms of detection and countermeasures. In order to provide tools to detect these threats, Defence Research & Development Canada - Valcartier initiated a research project to the feasibility of using terahertz (THz) radiations to detect and identify the presence of commonly used explosives and concealed weapons in a standoff method. This paper presents the initial results of the first year of the project and the future directions. A compact THz time domain spectroscopy was developed to build a THz signature table of commonly used explosives.

The Advanced Linked Extended Reconnaissance & Targeting (ALERT) Technology Demonstration (TD) project is addressing key operational needs of the future Canadian Army's Surveillance and Reconnaissance forces by fusing multi-sensor and tactical data, developing automated processes, and integrating beyond line-of-sight sensing. We discuss concepts for displaying and fusing multi-sensor and tactical data within an Enhanced Operator Control Station (EOCS). The sensor data can originate from the Coyote's own visible-band and IR cameras, laser rangefinder, and ground-surveillance radar, as well as beyond line-of-sight systems such as a mini-UAV and unattended ground sensors. The authors address technical issues associated with the use of fully digital IR and day video cameras and discuss video-rate image processing developed to assist the operator to recognize poorly visible targets. Automatic target detection and recognition algorithms processing both IR and visible-band images have been investigated to draw the operator's attention to possible targets. The machine generated information display requirements are presented with the human factors engineering aspects of the user interface in this complex environment, with a view to establishing user trust in the automation. The paper concludes with a summary of achievements to date and steps to project completion.

The proliferation of laser-assisted weapons on the battlefield has prompted the development of laser warning receivers (LWR) to protect the platforms. Such devices are required to identify, locate and characterize the laser threats so that responsive countermeasures (CM) can be effectively deployed. The laser-assisted weapons can be divided in three main categories namely the laser rangefinders (LRF), the laser target designator (LTD) and the laser beam riders (LBR). The two first types are based on low-divergence high peak-power laser sources whereas the LBRs use a variable divergence low-power source. The problem for a LWR to detect these lasers comes from the huge dynamic range (9 decades) necessary to both detect the lasers on-axis and off-axis up to a few degrees. Moreover, in the case of the LBR, the detection threshold has to be set extremely low to cope with the very low irradiance it generates at the LWR. Normally a separate detection channel is necessary for the LBR and the angular resolution very limited. This paper describes the laser threats and the phenomenology involved in the detection process. The work done at DRDC Valcartier in the domain of laser sensors and LWRs is presented together with a series of results obtained in the field. Finally, the CM aspect and the integration of the LWR into a more complete protection suite are discussed.

In this presentation we will present a new passive alignment method used to obtain highly efficient optical fibre coupling from VCSELs (vertical-cavity surface-emitting lasers). This method is compatible with low-cost, high-yield volume production of compact transceivers for applications in rugged environments. Coupling efficiencies larger than 94% have been obtained using this visually-aided passive alignment method for the coupling between a rounded-tip, 50μm core graded-index fibre and an 850nm VCSEL having an emission area diameter of approximately 25&mgr;m. Our alignment procedure was used to make compact, high-speed (2Gbps) transceivers that can work from -50 to 105^oC. They have shown to be able to resist to mechanical shocks of more than 200g. They have also shown to maintain a constant coupling efficiency while being submitted to 35Grms random vibration tests around 200Hz.

This paper presents results of three research and development efforts on the subject of avalanche photodiodes with InGaAs absorbers and InAlAs multiplication layers. The first portion of the paper presents results on 256x256 arrays of InAlAs-InGaAs APDs. These spanned more than 1.5 cm x 1.5 cm, had breakdown voltage variation of less than 2.5 volts and a dark current range between 1.5 and 3.5 nA at a gain of 10. The second portion of the paper presents single photon detection results of a receiver with a 50 micron aperture avalanche photodiode biased into sub-Geiger mode and a Maxim MAX3658 transimpedance amplifier. At temperatures of 200K and average avalanche gains approaching 1000 single photon detection efficiencies greater than 5% were observed with dark count rates of less than 500 kHz. At 175 K detection rates were as high as 14%. Finally, in the third portion of this paper, performance results of a novel impact ionization engineered InGaAs-InAlAs based avalanche photodiode are presented showing excess noise values lower than any previously published InGaAs based avalanche photodiode.

Based on the principle of the Integrated Optical Spectrometer (IOSPEC), a waveguide-based, longwave infrared (LWIR) dispersive spectrometer with multiple input slits for Hadamard spectroscopy was designed and built intended for passive standoff chemical agent detection in 8 to 12μm spectral range. This prototype unit equips with a three-inch input telescope providing a field-of-view of 1.2 degrees, a 16-microslit array (each slit 60 μm by 1.8 mm) module for Hadamard binary coding, a 2-mm core ZnS/ZnSe/ZnS slab waveguide with a 2 by 2 mm² optical input and micro-machined integrated optical output condensor, a Si micro-machined blazing grating, a customized 128-pixel LWIR mercury-cadmium-telluride (MCT) LN2 cooled detector array, proprietary signal processing technique, software and electronics. According to the current configuration, it was estimated that the total system weight to be ~4 kg, spectral resolution <4cm^-1 and Noise Equivalent Spectral Radiance (NESR) <10^-8 Wcm^-2 sr^-1cm^-1 in 8 to 12 μm. System design and preliminary test results of some components will be presented. Upon the arrival of the MCT detector array, the prototype unit will be further tested and its performance validated in fall of 2007.

In this paper, mid-IR light generation based on difference frequency generation (DFG) in a single piece of PPLN is proposed and studied. In the studies, a Yb doped fiber laser at 1.092 μm and a tunable laser around 1.55 μm were used. The output mid-IR laser with the wavelength tunable around 3.7 μm was generated. Since compact Yb doped fiber lasers at 1.092 μm and tunable semiconductor laser diodes around 1.55 μm are available on the market, the proposed mid-IR laser is potentially portable. Our simulations show that tunable mid-IR light as broad as 800 nm can be obtained from a single PPLN chip simply by tuning temperature (from 30 ^oC to 500 ^oC) and signal wavelength (from 1.48 μm to 1.62 μm).

In this paper, we propose and demonstrate a novel approach to optically generating chirped microwave pulse with tunable chirp rate based on spectral shaping and nonlinear wavelength-to-time conversion using a tunable nonlinearly chirped fiber Bragg grating (NL-CFBG). In our approach, the optical power spectrum of a ultrashort pulse from a femtosecond pulsed laser (FSPL) is shaped by a two-tap Sagnac loop filter (SLF) that has a sinusoidal spectral response. The spectrum shaped pulse is then reflected by an appropriately designed NL-CFBG to perform the nonlinear wavelength-to-time mapping. The microwave pulse with a tunable chirp rate is then generated at the output of a high-speed photodector (PD). The NL-CFBG used in the system is produced from a regular linearly chirped fiber Bragg grating (LCFBG) using a new technique based on strain-gradient beam tuning. A simple mathematical model to describe the chirped pulse generation is developed. A proof-of-principle experiment based on the proposed method is carried out.

A novel approach to implementing a tunable optical microwave bandpass filter with positive and negative coefficients based on an optical phase modulator and chirped fiber Bragg gratings is proposed and experimentally demonstrated. The positive and negative coefficients are generated through optical phase-modulation to intensity-modulation (PM-IM) conversion using linearly chirped fiber Bragg gratings (LCFBGs) with opposite dispersions. By changing the wavelength of the optical carrier within the chirp range of the LCFBGs, the tunability of the filter response is realized. A two-tap tunable microwave bandpass filter is experimentally demonstrated.

An all-optical bandpass microwave filter that is implemented using an optical phase modulator and equivalent-chirped superstructured fiber Bragg gratings (SFBGs) to generate negative coefficients is presented in this paper. It is well known that SFBGs, also called sampled FBGs, contain many Fourier orders in their spectrum. By appropriately chirping the period of the sampling function of the SFBG, it is possible to achieve an equivalent chirp in the +1 and the -1 orders. This method allows the fabrication of FBGs with different equivalent chirp rates by using a single uniform phase mask. While other methods to create chirped FBGs require multiple phase masks or variable tension on the optical fiber during the FBG writing process, the use of SFBGs eases the requirements for the fabrication of specific phase and amplitude responses. This is achieved by tailoring the sampling function of the SFBG instead of the Bragg period of the phase mask. In this paper, a two-tap all-optical bandpass microwave filter is demonstrated by using an equivalent-chirped SFBG. The negative coefficients of the filter are realized by exploiting the characteristics of the phase-modulation-to-intensity-modulation (PM-IM) conversion in the CFBG.

An optical switch based on micro electro mechanical systems (MEMS) technology has been analyzed and designed. In the proposed switch the collimating lenses as commonly used in MEMS switches have been eliminated thus making the switch smaller in size. The switch characteristics based on theoretical analysis and experimental results have been compared.

We consider physical principles of realizing the Bragg regimes for a two- and three-phonon light scattering in both optically and acoustically anisotropic tellurium dioxide crystal under specially elaborated conditions. The exact analytical models for describing these regimes are briefly discussed. The performed analysis demonstrates the principal possibilities of realizing 100% efficiency of light modulation in these regimes, and computer simulations illustrate the obtained results. The applications lie in the fields of exploiting large aperture spatial modulators of light. The main attention was paid to estimating the frequency bandwidths as well as the frequency resolution of such modulators.

The spectrum of resonance frequencies in so called stand-alone resonators, built with coupled ring or disk resonators is analytically and numerically investigated. These composite resonators which constitute the core of numerous photonic circuits used in channel dropping filters, dispersion compensators, laser mirrors, etc., determine the width of their passband and their free spectral range (FSR). The spectral characteristics of the resonances are determined by the dimensions of the resonators and the strength of coupling between them. Novel relationships between these parameters are described that ensure invariance of the splitting ratios and as a consequence maintain the passband characteristics of the associated devices. Waveguide attenuation is found to have no effect on the spectral characteristics of the composite resonators.

This paper presents two different devices for tuning fiber Bragg gratings. The first one is called the beam bending technique while the other is based on purely axial compression. We demonstrate that with a proper choice of the embedding material, the composite beam bending method constitutes an effective and reliable approach for tuning fiber Braggs gratings. We present a long-term stable device with a dynamic range of 80 nm which exhibits insertion losses smaller than 0.28 dB and small variations of the full width at half maximum. In order to reduce the amount of insertion losses, we also demonstrate a new tuning device for fiber Bragg gratings with a wavelength tuning range in excess of 65 nm. A purely axial tuning technique using a highly deformable polymer molded in cylinder shape is used to embed a fiber Bragg grating and to achieve a wavelength tuning range from 1551.7 to 1485.5 nm without insertion losses.

A set of applications of interest for semiconductor lasers constitutes their use under irradiation conditions in nuclear power plants, radiation processing facilities, high energy physics accelerators, nuclear waste management sites, or even space crafts. One such an example is the task related to remote handling and control in fusion installations (i.e. ITER - the International Thermonuclear Experimental Reactor). The paper reports our results on the irradiation effects on different semiconductor laser structures, emitting at 850 nm, 1310, 1550 nm, as they were subjected either to gamma-ray (total dose of 1.5 MGy) or neutron irradiation (total fluence of 10¹³ n/ cm² ), in the frame of the European Union's Fusion Program. The electrical, optical and optoelectronics characteristics (the optical power vs. the driving current of the semiconductor laser; the embedded photodiode current vs. the emitted optical power; the direct voltage vs. the driving current, the external quantum efficiency, the serial resistance, the photodiode responsivity) were monitored under these conditions. All the investigated devices were commercially available products. The irradiations were done at room temperature, and the measurements were carried off-line.

We present a theoretic approach to the characterization of low-power bright ultrashort optical pulses with an internal frequency modulation simultaneously in both time and frequency domains. This approach exploits the Wigner time-frequency distribution, which can be determined and developed for these bright optical pulses by using a novel interferometric technique under our proposal. At first, the analysis and computer simulations are applied to studying the capability of Wigner distribution to characterize solitary pulses in practically important case of the sech-pulses. Then, the simplest two-beam scanning Michelson interferometer is selected for shaping the field-strength auto-correlation function of low-power picosecond pulse trains. We are proposing the key features of a new interferometric experimental technique for accurate and reliable measurements of the train-average width as well as the value and sign of the frequency chirp of pulses in high-repetition-rate trains. This technique is founded on an ingenious algorithm for the advanced metrology, assumes using a specially designed supplementary semiconductor cell, and suggests carrying out a pair of additional measures with exploiting this semiconductor cell. The procedure makes it possible to construct the Wigner distribution and to describe the time-frequency parameters of low-power bright picosecond optical pulses.

In optical ring networks, the impact of residual fiber dispersion on the cascadability limit of the optical add-drop systems due to in-band crosstalk is investigated. An experimentally verified re-circulating non-zero dispersion shifted fiber (NZ-DSF) loop model is used to emulate the cascade effect of multiple add-drop nodes. The nodes are implemented based on Wavelength Selective Switches (WSSs) at varying node degrees to support different network configurations. It is shown that 16 node metro rings can be constructed cost effectively using NZ-DSF, at link distances of 75 km, for fiber dispersions as high as 4.6 and 1.2 ps/nm-km at bit rates of 2.5 and 10 Gb/s, respectively, at a 1dB of crosstalk induced penalty. A modular architecture extending to large degree ROADM for mesh networks is also proposed and scalability in terms of crosstalk is reported.

In emerging agile all-optical networks, where time division multiplexing (TDM) in the optical domain is implemented on top of wavelength-division multiplexing (WDM) to improve the network utilization and to support dynamic bandwidth demands, a control mechanism is required to handle the setup and tear down of fast flexible all-optical connections. In this paper, we propose two control protocols for WDM-TDM all-optical ring networks based on whether or not global network information is available. For the global information based protocol, we choose a periodic state-updating mechanism to confine the control message overhead within a reasonable range. For the local information based protocol, we select a backward reservation scheme for dynamic routing, wavelength and timeslot assignment (DRWTA) algorithms to prevent bandwidth overbooking. By conducting extensive numerical simulations, we investigate the impact of imprecise information on the blocking probability of the DRWTA algorithms for the two protocols. Our simulation results show that the local information based protocol outperforms the global information based protocol for metro all-optical networks where propagation delay is small compared to the service time of requests.

We give an analytical expression to evaluate the optical eye diagram due to polarization-mode dispersion (PMD), polarization-dependent loss (PDL), and chromatic dispersion (CD) for a system of highly mode coupled fiber with lumped section at any given optical pulse sequence. We found that with considering PDL and the polarization direction correlation between PMD and PDL, a system with highly mode coupled fiber and lumped section can have either higher or lower Q-factor than a highly mode coupled system with same root mean square PDL/PMD values. Also we noticed that a system of two highly mode coupled fibers connected together is not equivalent to a system of highly mode coupled fiber when fluctuation is considered.

The simulation models for a typical PON layout are developed and three major PON technologies are considered. The models support the analysis of various important characteristic parameters, namely: 1) link budget for acceptable losses from splices, attenuation and splitters, 2) link performance characterization based on data (BER, SNR) or video signal quality, and 3) linear and nonlinear fiber effects such as dispersion, PMD, self- and crossmodulation, FWM, etc. Analysis outcomes may be used to optimize the performance of the applied system design including fiber maximum length and type, the need to change some of the optical components (e.g. couplers, splitters, etc.) and digital links bit rate (e.g. 1.2 Gb/s or 2.4 Gb/s) according to the required BER. The simulation models developed enable us with these detailed analyses of PON technologies without the need to build prototypes.

We exploit the unique properties of the silicon-on-insulator material platform to demonstrate a new series of planar waveguide evanescent field sensors for biological / chemical sensing. These sensors, combined with state-of-the-art surface functionalization chemistries, offer a sensitive, label-free means for the specific detection of biomolecules, without the need for fluorescent tags employed in conventional fluorescence-based biochips. The use of silicon photonic wire waveguide technology allows sensors with extremely small footprint and small radius of curvature to be fabricated, facilitating the development of densely packed sensor arrays for multi-parameter analysis, particularly attractive for drug discovery, pathogen detection, genomics and disease diagnostics. We show that high index contrast silicon photonic wire waveguides not only provide the above stated advantages but also offer increased sensitivity over that of evanescent field sensors constructed on other common waveguide material platforms. This results from the unique properties of the optical modes of silicon photonic wire waveguides, which exhibit very large surface electric field magnitude and strong localization near the waveguide surface. We discuss the design and fabrication of silicon-on-insulator-based Mach-Zehnder interferometer sensors and experimentally demonstrate their performance to detect bulk solution refractive index change and to monitor the specific adsorption of streptavidin to biotinylated waveguides.

This paper describes a monolithically integrated 1x2 SOA-based switch in InGaAsP/InP. It can be fabricated in one epitaxial growth step, has a footprint of only 4.2mm x 0.35mm, operates on sub-ns time scales and is meant to be integrated with other passive and active waveguide devices on the same InP substrate. The design process optimized the device dimensions using a modified finite-element modal-overlap method. This method provides significant computational savings compared to full beam-propagation method (BPM) simulations. The device uses a single-mode vertical integration technique for a monolithic integration of active and passive waveguide components. To compensate for the polarization sensitivity, tensile-strained quantum well active regions are used. To switch a signal to an output waveguide, the SOA in that waveguide is forward-biased while the SOA in the other output waveguide is reverse-biased to provide a large attenuation (>30dB), resulting in minimal crosstalk. This switch has an estimated insertion loss of 4dB, with a polarization dependent loss of < 1dB.

Semiconductor quantum dot nanocrystals (QDs) have unique optical properties such as size tunable photoluminescence (PL) wavelength and a chemically functionalized sufrace. Our CdSe/ZnS quantum dot nanocrystals have been made water-soluble by encapsulation in a micelle of positively charged amphiphilic copolymers. Layer-by-layer deposition of these QDs was done on sub-micrometer silica beads as well as magnetic and polymeric micro-sized beads. The negative surface charge of these various beads allowed successive stacking of cationic polyethylnimine, anionic polyacrylic acid sodium salt and the cationic encapsulated QDs. Multiple QD layers can be added by repeating the stacking process. The PL spectral of green QDs is moduoated by whispering galley mode resonances when the QDs arecoating a singe 3 μm bead. Depending on the quality factor of this microsphere, it can also be possible to detect perturbations caused by sufficient adsorption of biomolecules or even living microorganisms on a bead's surface by observing spectral shifts of the resonances. If different colorsof QDs are used to coat smaller beads where the modes are not spectrally resolved, an optical coating system can be devised base on the relative emission intensity for each color. The uniformity of a bead ensemble coded with 2 QD colors has been invesetigated, revealing a ~20% relataive standard deviation for various intensity levels. Better control of photobleaching through QD passivation reduced this number to ~8%, which would allow us to differentiate up to 2.6x10¹⁰ optical codes on our setup. Labelling large amount of molecules in solution, e.g. DNA sequences, then becomes possible with an appropriate biofunctionalization of bead surfaces.

In this paper, the statistical distributions of polarization mode dispersion (PMD) for a pulse and pulse broadening due to PMD for short pulses are examined by simulations using the waveplate model with strong mode coupling. It is found that, like the case of differential group delay (DGD) for a single frequency, the distribution of PMD for a pulse is still Maxwellian with a smaller mean value than the mean DGD for one specific frequency. The statistical distribution of pulse broadening with various pulse widths and PMD values were simulated. The distribution of pulse broadening due to PMD for short pulses fits the modified Rayleigh dis tribution with lower probability of pulse broadening than that for long pulses in the small pulse broadening region.

In this paper we demonstrate the ability of offset sideband modulation (OSBM) to alleviate problems pertaining to the electrical crosstalk between upstream and downstream signals in a transceiver used in the optical network unit of a FTTx system. The OSBM signal consists of an optical carrier and an offset modulated sideband that are created using arbitrary optical waveform generation. The performance of OSBM is investigated in the context of an inline transceiver, which is a very simple, next generation, FTTx transceiver. The downstream OSBM bit rate was 2.5 Gbit/s and the upstream OOK bit rate was 1.25 Gbit/s. A power penalty of only 0.2 dB with respect to an interference free system was observed with an optical signal to interference ratio (OSIR) as small as -8 dB (the interfering signal power is 8 dB larger than the signal power). This was the minimum OSIR available with the experimental setup, and it is expected that lower OSIRs can be tolerated.

The key process steps in the fabrication of a thermally-tuned silicon-on-insulator (SOI) based phase modulator are detailed. By altering the waveguide temperature, the thermo-optic effect is used to vary the modulator's output. Additionally, various experimental approaches are used to determine the operating characteristics of the resulting device. This includes a swept wave system (SWS) suitable for testing the performance of the phase modulator. Analyses will yield such measurements as insertion loss, polarization dependent loss (PDL), peak wavelength, and ripple period.

A two-fold oversampling adaptive maximum likelihood sequence estimation (MLSE) receiver based on Viterbi algorithm has been implemented for 10 Gb/s fiber optical communication systems, taking into account the amplified spontaneous emission noise, uncompensated chromatic dispersion, and nonlinearity due to square-law detection. We use the Volterra theory to model the channel nonlinearity, and Recursive Least Square (RLS) algorithm to update the channel characteristics. We estimate the error probability of the adaptive MLSE receiver for return-to-zero (RZ) on-off-keying (OOK) modulation format using standard Monte-Carlo simulation. Our results show that, when propagated along standard single-mode fibre for a bit-error-ratio (BER) of 10^-3, the dispersion tolerance for two-fold oversampling adaptive MLSE receiver is 1.7 times of that for optimum threshold receiver employing no electronic dispersion compensation (EDC) for RZ-OOK signal with 60 % duty cycle. We have also compared the effects of two-fold oversampling and synchronous sampling for the adaptive MLSE receiver, and our results show that the error probability of MLSE receiver can be reduced by an order of magnitude for the same system parameters when the two-fold oversampling is used.

Optical buffers are central elements in all-optical switched networks to avoid packet contention and loss. With actual traveling buffers, the delay time is discrete and predetermined by the length of the optical fiber delay line (FDL). Traveling buffers are bulky, since a large number of delay lines are required to handle multiple traffics. In this paper, we designed a variable optical delay line based on a re-circulating loop that is controlled by all-optical signal processing technology. We showed that a FDL based on fiber Bragg gratings (FBG) in combination with a single optical wavelength converter can realize variable delays. A simulator was developed to evaluate the performance and limitations of the proposed architecture.

A study of the capability of the Bragg grating writing method using infrared radiation and a phase mask to inscribe Bragg gratings structures in channel waveguides was performed using as a physical model D-shaped silica fibers. Experiments made with different radiation intensities and focusing arrangements produced surface structure damage of the waveguide during Bragg grating inscription in the D-fiber core. An evaluation of the surface damage intensity threshold and the exposure conditions required to avoid it is presented.

We present a numerical framework for the simulation of lasers in the time domain. The algorithm is based on the finite-difference time-domain method, which has been extended to include material gain by using auxiliary differential equations for a frequency dependent conductivity. The algorithm is applied to the simulation of micro-disk lasers based on an erbium doped SiO₂ material system in order to obtain a CMOS compatible fabrication process. Lasing behavior and lasing threshold is studied in two and three dimensions for single and multi-disk systems.

We investigated the dispersion compensation by means of self phase modulation induced by the nonlinear Kerr effect in photonic crystal fibers (PCF). Accurate calculations of both chromatic dispersion and nonlinear coefficient in small core PCF were performed using a vector finite element method. Besides, ultrashort pulse propagation in PCF was simulated using the generalized nonlinear Schrodinger equation. Conditions necessary for the formation of soliton during propagation of a femtosecond pulse were investigated. To compensate the broadening caused by dispersion, we thoroughly examined the pulse propagation in the anomalous dispersion regime at the wavelength λ=810nm. The study showed that by carefully selecting laser and PCF parameters, the pulse broadening and frequency chirping, due to group velocity dispersion of the PCF, can be compensated by using the Kerr nonlinearity of the medium.

We report on an object-oriented based simulation of a passively modelocked fiber laser containing a long period fiber grating. Object oriented concepts, such as polymorphism, encapsulation, operator overload and delegation can be used effciently to implement extendable and reusable C++ code for scientific computing. It was found that decreasing the level of encapsulation reduces the computational time. The numerical model is based on the normalized complex Ginzburg-Landau equation and the nonlinear coupled mode equations of the grating. The modelocked pulse energy was found to exhibit a wide range of nonlinear dynamics. To accurately capture these dynamics highly robust and numerically stable variations of the split step Fourier method were implemented.

A novel approach of a first order optimization technique applicable to design process of photonic sensing devices and waveguide geometries is presented. The application of the optical field sensitivity mapping technique enables first order optimization of geometrical parameters with the final goal of enhancing the overall device sensitivity. The technique is simple, requiring only two simulations of optical field propagation and the extraction of a sensitivity map. The method is demonstrated in a design optimization process of a realistic multi mode interference sensing device. As a result, optimization of the MMI active section length, sensing region width, and the output location was accomplished. A comparison between the optimized device and two other ones of different length showed a 10 dB higher dynamic range of the output power ratio characteristic and better linearity, demonstrating enhanced sensitivity of the final device.

We discuss a novel FDTD-based technique for estimating accurate sensitivities of the desired response. Our technique utilizes the central adjoint variable method (CAVM) for estimating the response sensitivities. This approach features accuracy comparable to that of the central finite difference (CFD) approximation at the response level. Using only two simulations, of the original and the adjoint photonic structures, the sensitivities with respect to all the designable parameters are obtained regardless of their number. Our approach uses the same update equations of the conventional FDTD for the adjoint problem, which simplifies the implementation. A self-adjoint approach based on CAVM (SA-CAVM) is also proposed to extract the sensitivities of the power reflectivity. Using this self-adjoint approach, only the original simulations are needed to evaluate the objective function and its sensitivities as well. Our approach can also supply wideband sensitivities. The additional cost in this case is mainly that of performing the discrete Fourier transform (DFT) which is negligible compared to the FDTD simulation cost. Our SA-CAVM approach is also utilized to minimize the power reflectivity of deeply etched waveguide terminators, and double layer antireflection coatings on laser diode (LD) facets which can be used as an optical amplifier. The accuracy of our approaches is illustrated by comparing the results with the second order accurate CFD. Our results show a very good agreement between the CAVM-based sensitivities and those obtained using the expensive central finite difference approximation.

The simulation method known as eigenmode expansion proves to be a versatile approach for modeling microphotonic devices. Originally the tool was developed for high-contrast linear designs. However, it was also extended towards nonlinear effects, such as the Kerr nonlinearity and second-harmonic generation. Here we address recent numerical and theoretical results, obtained or supported by the eigenmode method. In the linear regime, we study high quality cavities, originating from multimode interference through the multipole cancelation mechanism. For the nonlinear regime we present a photonic crystal switching device based on a symmetry breaking instability.

A wide range of software now exists for the design and simulation of integrated optoelectronic components, especially for finding modes and describing propagation. The sophistication and high performance specifications of many devices mean that techniques must typically not only provide accurate vector results, or at least a reliable error estimate, but also be able to deal with multi-physics, multi-scale problems, intricate materials properties and arbitrary geometries. The design process also demands consideration of process variation and system optimisation issues. Time domain numerical techniques such as FDTD and TLM have come to the forefront in recent years, driven by their flexibility, adaptability and compatibility with parallel computing techniques. Nevertheless much present day simulation and design work involves approximations and an automated all-in-one design tool suitable for every purpose is still far from being realised. In this invited paper we will review features of integrated optics design applications, point out some of the features of emerging technologies that mitigate against the general applicability of present-day software tools, and show how substantial benefit can still to be gained from developing bespoke novel algorithms or exploiting an appreciation of the physical mechanisms underpinning the behaviour of particular components and systems.

The phase velocity in photonic crystals is analyzed with the aid of a finite-difference time-domain simulation. The results of the simulation is used to display an animation of the phase evolution of an electromagnetic wave propagating through a photonic crystal slab. The phase velocity is indicated by the direction of motion of the phase inside the photonic crystal. This motion is found to be in the direction of propagation even though the eective refractive index under the operating conditions is negative. This can be explained by the location of the dominant values of the Fourier coeffcient function in the k-space representation of fields in the photonic crystal.

We demonstrate experimentally and by simulations the use of subwavelength grating patterns on the facets of planar waveguides as a means of modifying facet reflectivity over a wide range of values, from antireflective to highly reflective. An antireflective structure can be obtained from a gradient index effect with triangular gratings. Square gratings can be used to obtain either antireflective or highly reflective facets by an interference effect. Finite difference time domain simulations and calculations based on effective medium theory show that reflectivities well below 1% can be achieved with triangular gratings. Experimentally, facet reflectivities as low as 2.0% and 2.4% for the fundamental TE and TM waveguide modes, respectively, are demonstrated for light of 1.55 μm wavelength in silicon-on-insulator ridge waveguides. The experimental results are in good agreement with both effective medium theory and finite difference time domain simulations. The polarization dependence of the effects is also discussed in detail.

The efficiency of organic light emitting diodes is known to be optically limited by different light trapping effects within the device structure. Several approaches have been suggested to enhance the transfer of radiation generated within the device into free space radiation. These approaches include nanoscale wave optical effects to optimize the stratified active media or to diffract guided modes travelling within the active system, as well as refractive or scattering elements to derange total internal reflection within the substrate. This paper deals with substrate emitting devices, where nano- or microscale structures enforce a 'recycling' of light that originally would have been trapped within the system. An approach enabling for a combined treatment of ray-optical and thin-film-optimization is introduced and applied to the optimization of an example system. The results indicate an improved system design due to that complex optimization

A photonic crystal can behave like a medium with a negative effective refractive index within certain frequency ranges. As a result, under these conditions, a photonic crystal slab acts as a Veselago lens, which produces images via inverse propagation. To have low reflection the effective index is usually designed to be −1. However, this implies that the lens is half as thick as the distance between the object and its image. We investigate the possibility of varying the refractive index along the propagation direction from −1 at the interfaces to an effective index with a smaller magnitude in the bulk of the medium in order to shorten the Veselago lens while keeping the reflections from the interfaces low. The hole radius in the photonic crystal is varied over the photonic crystal to produce a varying effective refractive index. We present finite-difference time-domain simulations of a Veselago lens with a varying index, demonstrating that Veselago lenses can be shortened in this way.

We report on recent progress in simulations, physical layout, fabrication and hybridization of planar grating-based transceivers for passive optical networks (PONs). Until recently, PON transceivers have been manufactured using bulk micro-optical components. Today, advancements in modeling and simulation techniques has made it possible to design complex elements in the same silica-on silicon PLC platform and create an alternative platform for manufacturing of bi-directional transceivers. In our chips we simulated an integrated chip that monolithically combined planar reflective gratings and cascaded Mach-Zehnder interferometers. We used a combination of the finite element method and beam propagation method to model cascaded interferometers with enhanced coupling coefficients. Our simulations show that low-diffraction order planar reflective gratings, designed for small incidence and reflection angles, possess the required dispersion strength to meet the PON specifications. Subsequently, we created structures for passive alignment and hybridized photodetectors and lasers. We believe that advancements in simulation of planar lightwave circuits with embedded planar reflective gratings will result in displacement of the thin-film filters (TFFs) technology in many applications that require a high degree of monolithic and hybrid integration.

An in-line diplexer optical transceiver chip based on an integrated DFB laser and photodiode has been demonstrated and analyzed. The transceiver transmits at 1310nm for upstream signal and receives at 1490nm for downstream signal. For the in-line integrated device, crosstalk between the transmitting and receiving channels become a key issue of system performance. Such crosstalk includes optical-optical, electrical-electrical, and electrical-optical crosstalk. The optical-optical crosstalk is caused by the limited optical isolation between the DFB laser and the photodiode. The electrical-electrical crosstalk is the result of electrical interference between transmitter driver and receiver amplifier. In the in-line transceiver design, the 1490nm downstream signal goes through the DFB laser cavity. When the laser is modulated, the 1490nm signal will experience modulation through the gain and refractive index change in the cavity. This electrical-optical crosstalk has been confirmed by numerical simulation and experimental measurement. The results show that the electrical-optical crosstalk power is proportional to the received 1490nm power and dependent on modulation depth of the DFB laser. A bit error rate model is also presented to describe the impact of the modulation crosstalk from the system performance point of view.

Design and simulations of a Fourier-transform planar waveguide spectrometer are presented in the context of space-born observations of water in the near infrared spectral region. Spatial heterodyning of an optical signal is realized by using arrayed waveguide structures which produce spectrally dependent interference fringes. The light spectrum is calculated using discrete spatial Fourier transformation of the fringes. The arrayed waveguides form a multi-aperture input which markedly increases the optical throughput (étendue) of the device compared to single-aperture spectrometers.

Current optical networks mainly serve very high data rates and long distances while short reach communication and low data rates is dominated by electrical interconnects. In this work, we examine and evaluate optical backplane technology based on substrate guided interconnects.

In this paper, we propose a numerical tool for the synthesis of DS-OCDMA Encoders/Decoders based on Fiber Bragg Gratings. The techniques of synthesizing FBG are described. In particular, we point out the layer peeling method as inverse scattering approach and a genetic algorithm approach to design DS-OCDMA Encoders/Decoders. Finally, we compare the results of the two synthesizing methods.

Cladding-reduced fibers with elliptical cores can be used in the fabrication of fiber-optic sensors. Here we analyze the power transmission ratio in cladding reduced D-shaped optical fibers for the purpose of determining the cladding thickness, in a non-destructive manner, when the fibers have been etched to reduce their cladding thicknesses to allow interaction of the optical evanescent field with an external medium having a refractive index greater than the mode effective index of the fiber. Parameters needed to determine the cladding thickness are determined empirically using the measured power transmission ratio of a few calibration fibers. We show that one can estimate the cladding thickness by fitting the measured transmission ratio curves for the fiber of interest to the curves generated for the calibration fibers.

We propose a new waveguide resonator device with a mirror cavity and a multimode interference (MMI) coupler. We present simulation results for the silicon wire MMI coupler with suppressed reflections and its use as a coupling element in the resonator cavity, built on the silicon-on-insulator waveguide platform. Tapering structures used in the reflection suppression were optimized, and the wavelength dependency of a conventional MMI was compared to that of the MMI with reflection suppression. Two-mirror MMI coupled resonator was studied using finite difference time domain simulation by both pulse and continuous wave excitation. The optimal resonator has a very small footprint of 3 μm × 29.7 μm, with a quality factor of 774.

We present a new class of two-dimensional (in x and t) theoretically invariant optical wave packets characterized by a spatiotemporal Bessel function (STB beams). This particular field distribution induces a balance between the diffraction and the dispersion of the pulse. The solution describing the propagation of the STB beam is independent of the propagation distance, but the infinite dimensions of this beam make it impossible to generate. We can limit the dimensions of this beam by the use of a Gaussian envelope, resulting in a spatiotemporal Bessel-Gauss beam (STBG beam), that we can generate experimentally. We present an experimental setup used to generate STBG beams and an experimental autocorrelation trace which is in good agreement with that of theoretical STBG beams.

The results of variation of the high-order harmonic distribution generating from the manganese plasma plume are presented. Harmonic plateau was extended from the 31st order, at the intensities below the barrier suppression intensity for singly charged Mn ions, to the 101st one (λ = 7.9 nm), at higher intensities, highest ever observed in plasma HHG studies. The second plateau appearance for the harmonics exceeding 31st order was observed in this case, while the low-order harmonic plateau was decreased or completely disappeared, with only plasma lines dominating for the wavelength region above 27.6 nm. Origin of the harmonics appearing at the second plateau was attributed to the interaction of intense laser field with doubly charged manganese ions.