This PDF file contains the front matter associated with SPIE Proceedings Volume 6593, including the Title Page, Copyright information, Table of Contents, Introduction, Conference Committee listing, and Plenary Papers.

Recent progress in the understanding of the transmission properties of optical microfibers and their applications in photonics are reviewed. An optical microfiber (MF) is usually fabricated from a standard telecom optical fiber by drawing and has a diameter of ~ 1 micron. The interest in photonic devices fabricated of MFs is basically caused by two advantages of MFs compared to lithographically-fabricated waveguides: significantly smaller losses for a given index contrast and the potential ability of micro-assemblage in 3D. Eventually, these properties could make possible the creation of MF devices, which are significantly more compact than those fabricated lithographically. Furthermore, some MF-based devices possess functionalities, which are not possible or much harder to achieve by other means. The first part of this paper discusses methods of fabrication and transmission properties of MFs. The effects of microdeformations (in particular, the frozen-in microdeformations) and the adiabatically slow deformations of an MF are considered. The recently developed theory of adiabatic MF tapers is presented and applied to the investigation of transmission loss and evanescent field structure of MF tapers. The second part of the paper considers applications of MFs in photonics. Generally, MF devices and circuits can be created by the macro- and micromanipulation (bending, looping, coiling, twisting, crossing, etc.) of uniform and tapered MFs. The most straightforward application of an MF is using a regular MF taper as a sensor of an ambient medium. More advanced applications of MFs include MF loop resonators and MF circuits assembled by wrapping an MF around a cylindrical rod. It is believed that further exploration of MF properties and possible applications will give rise to the invention and practical realization of innovative MF photonic devices with unique functionalities.

The application of transversal strain on an optical fiber leads to an asymmetry of the fiber section that locally induces fiber birefringence. In this paper, we show that it is possible to use FBG as a probe to obtain the amount of this induced birefringence. We describe two techniques able to get the birefringence value. They are both based on differential group delay (DGD) measurement. The first technique makes use of the comparison between the measurement and the simulation of the wavelength dependency of grating DGD. Considering that all grating parameters are known, we adjust the birefringence value to obtain the best fit between experiment and simulation. For the second technique, we first demonstrate that the wavelength dependencies of chromatic dispersion (CD) and DGD parameters differ in their amplitude by a quantity proportional to the birefringence. We exploit this relationship to get the birefringence value by separately measuring the DGD and CD spectral evolutions. The birefringence value is adjusted to obtain the best fit between the two measurements. These two techniques are discussed and experimental results are finally reported.

We report on a new type of optical switch based on submicron structures and present the results obtained on the first nanophotonics based optical switch. First, we present results obtained on passive components that are required in an optical switch or switching matrix: straight waveguides, bend waveguides and Y junctions. Measured propagation loss are lower than 1dB/mm for waveguides wider than 1&mgr;m. Excess bending loss is 1dB for curvature radius as small as 30&mgr;m. Loss due to branching angle in a Y junction is 2dB for angle as wide as 20°. Optical switch design is based on two dissymmetric DOS like active junctions; theoretical crosstalk is 28dB, 14dB for each junction. We present the technological process to realize this active component. Finally, we report on the first characterization of a single Y junction a crosstalk of 11dB.

Light can be slowed down to ultraslow speeds v ia electromagnetically induced transparency in atomic Bose-Einstein condensates. This is thought to be useful for storage of quantum information for weak probe pulses. We investigate the effects of inhomogeneous density profile of the condensate on propagation of such ultraslow pulses. We find that spatial density of an atomic condensate leads to a graded refractive index profile, for an off-resonant probe pulse when condensate parameters are suitably chosen. Within the window of negligible absorption, conditions for degenerate multiple waveguide modes are determined. Both analytical and numerical studies are presented to reveal the effects of experimentally controllable parameters, such as temperature and interatomic interaction strength on the number of modes. Group velocity dispersion and modal dispersion are discussed. The effect of waveguide dispersion, in addition to usual material dispersion, on ultraslow pulses is pointed out.

We present two complementary interferometric techniques for measuring the complete spatio-temporal intensity and phase, E(x,y,z,t), of ultrashort pulses. The first technique, called SEA TADPOLE, allows for the first time the complete measurement of pulses near a focus, while the second technique, called STRIPED FISH, allows the complete measurement of mostly collimated pulses, but on a single-shot basis.

The use of optical techniques is increasing the possibilities and success of medical praxis in certain cases, either in tissue characterization or treatment. Photodynamic therapy (PDT) or low intensity laser treatment (LILT) are two examples of the latter. Another very interesting implementation is thermotherapy, which consists of controlling temperature increase in a pathological biological tissue. With this method it is possible to provoke an improvement on specific diseases, but a previous analysis of treatment is needed in order for the patient not to suffer any collateral damage, an essential point due to security margins in medical procedures. In this work, a predictive analysis of thermal distribution in a biological tissue irradiated by an optical source is presented. Optical propagation is based on a RTT (Radiation Transport Theory) model solved via a numerical Monte Carlo method, in a multi-layered tissue. Data obtained are included in a bio-heat equation that models heat transference, taking into account conduction, convection, radiation, blood perfusion and vaporization depending on the specific problem. Spatial-temporal differential bio-heat equation is solved via a numerical finite difference approach. Experimental temperature distributions on animal tissue irradiated by laser radiation are shown. From thermal distribution in tissue, thermal damage is studied, based on an Arrhenius analysis, as a way of predicting harmful effects. The complete model can be used for concrete treatment proposals, as a way of predicting treatment effects and consequently decide which optical source parameters are appropriate for the specific disease, mainly wavelength and optical power, with reasonable security margins in the process.

Current-pumped picosecond-range laser diodes with a peak power significantly exceeding that achievable from gainswitched lasers are of major interest for a large variety of commercial applications. A group of phenomena have been explored in which the peak transient gain is efficiently controlled by a fast reduction in the pumping current. Common to all these phenomena is the fact that the peak powers of the emitted picosecond optical pulses (15-100 ps) exceed that obtainable from gain-switched laser diodes by at least an order of magnitude, although the physical reasons for the high gain and the design principles of the semiconductor structures are different. The main problem in the realization of these picosecond modes in low-cost practical systems is the high sensitivity of the operation regime to structural and circuit parameters. A related problem is the questionable reproducibility of the fabrication processes used so far. Proper development of reliable high-power picosecond transmitters will require the use of more advanced fabrication methods and further study of the effect of structural parameters on the properties of the picosecond lasing mode. In this paper we report on a record value for the power density of the picosecond lasing (50W / 30ps) obtained from a laser diode chip of width 20 &mgr;m and give a qualitative interpretation of the operating mode. Use of the MOCVD process for diode fabrication should allow reproducible technology for picosecond laser diodes to be developed.

Recently, since the size of component becomes smaller, then the welding of thin metal sheet has been required. Besides, the flexibility of process is important according to the accessibility especially for small components. Fraunhofer Institute for Laser Technology had developed the SHADOW^® welding technology, in which the high speed joining with small distortion is possible using pulsed Nd:YAG laser. The possibility of high speed and high quality welding had been reported by using single-mode fiber laser. The combination of micro beam and high speed laser scanning has the advantages for thin metal sheet welding. Therefore, the characteristics of micro-welding for thin metal sheet were investigated by high speed laser scanning, in which the welding was carried out by high speed scanner system with single-mode fiber laser and pulsed Nd:YAG laser. The proper welding region was narrow by the laser beam with a large focus diameter of 160 μm without pulse control, while a small focus diameter of 22 μm can control the welding state widely. A small focus diameter can perform the excellent welding seam from the extreme beginning without pulse control. The penetration depth can be controlled by the energy density with a small focus diameter of 22 μm at the energy densities less than 1 J/mm². Besides, the unique periodic structure appeared at the high velocity of beam scanning with a small focus diameter. Moreover, the overlap welding of 25 μm thickness sheet can be performed regardless of small gap distance between two sheets by the laser beam with a small focus diameter of 22 μm.

Luminous textiles have the potential to satisfy a need for thin and flexible light diffusers for treatment of intraoral cancerous tissue. Plastic optical fibers (POF) with diameters of 250 microns and smaller are used to make the textiles luminous. Usually light is supplied to the optical fiber at both ends. On the textile surface light emission occurs in a woven structure via damaged straight POFs, whereas the embroidered structure radiates the light out of macroscopically bent POFs. We compared the optical properties of these two types of textile diffusers using red light laser for the embroidery and light emitting diode (LED) for the woven structure as light sources, and found efficiencies for the luminous areas of the two samples of 19 % (woven) and 32 % (embroidery), respectively. It was shown that the efficiency can be greatly improved using an aluminium backing. Additional scattering layers lower the fluence rate by around 30 %. To analyse the homogeneity we took a photo of the illuminated surface using a 3CCD camera and found, for both textiles, a slightly skewed distribution of the dark and bright pixels. The interquartile range of brightness distribution of the embroidery is more than double as the woven structure.

Multi-beam laser interference lithography (MB-LIL) is a rapid and cost-effective maskless optical lithography technique to parallelly pattern periodic or quasi- periodic micro/nano-structured material over large areas more than square centimetres. An interference pattern between two or more coherent laser beams is set up and recorded in a recording material of substrate. This interference pattern consists of a periodic series of geometries representing intensity minima and maxima. The patterns that can be formed depend on the number and configuration of laser beams. This review introduces the development and application of MB-LIL system for fabrication of micro/nano-structured material. At first, it surveys various types of MB-LIL methods by classifying different beam configurations. Then the paper shows some application results for fabrication 2D/3D micro/nano structure arrays by means of interference patterns with multi-exposed or directly ablation technique. The patterend micro/nano-structure arrays include crossed diffraction grating array in photoresist, 3D pattern in polymetric photonic crystals, and magnetic nanoarrays in thin film. Finally, an innovative four-beam LIL system is introduced, which is being developed within the EC-granted project DELILA.

Nanoscale periodic and quasiperiodic relieves on fused quartz are of interest for the creation of a variety of optical and electronic devices such as phase masks, one- and two-dimensional stamps for nanoimprint and wide-band antireflection structures. The authors of this paper have developed a method of interference lithography to pattern nanoscale relief on quartz with a high-power pulsed XeCl laser with high-quality output radiation at wavelength 308nm. One of the advantages of the proposed technique is the significantly smaller influence of mechanical oscillations in an optical setup on the results of nanoscale modification. The relief on quartz was formed with the use of a complete cycle of lithography. As the mask, a two-layer structure of a copper film of 50nm in thickness and a photoresist of 400nm in thickness were employed. The mask pattern was formed by exposure of a photoresist by two radiation beams of a XeCl laser with energy density ~ 30mJ/cm², aqueous-alkali development of a photoresist, and copper etching by the ion beam (Ar⁺). Quartz was etched by the method of ion-beam reactive etching in a flow of CF₄ - O₂(20%) gas mixture, with etching rate 30nm/min.

This paper presents a theoretical analysis of formation of 4-beam laser interference patterns for nanolithography. Parameters of 4-beam interference patterns including the pattern amplitude, period, orientation and uniformity were discussed. Analytical expressions were obtained for the spatial distribution of radiation of the interfering beams as a function of their amplitudes, phases, angles of incidence on the sample, and polarization planes with computer simulation and experimental results.

Transmission of light and other electromagnetic waves through apertures smaller than the wavelength are now well known to yield field intensity enhancements due to morphological resonances of the aperture or, if these are periodically arranged, as a consequence of Rayleigh or other Wood anomalies. In this communication we study the effect of this transmission on the photonic force induced by light on a particle in front of a hole practiced in a metallic slab. Several shapes, constitution and sizes of particles are analyzed. A correlation of the strength of the force with the transmittivity is found, although it can be either attractive or repulsive depending on the wavelength and the corresponding hole resonance. Also, we study the effect of coupling of both the hole and the particle Mie resonances.

The recent developments of optically confined structures and nanocomposite materials activated by rare earth ions have opened new possibilities in the field of both basic and applied physics, in a large area covering Information Communication Technologies, Health and Biology, Structural Engineering, and Environment Monitoring Systems. As far as optical telecommunications are concerned, Er³⁺-activated glasses have become one of the key materials because of their relevance for the development of optical amplifiers. The short-term goal is to develop appropriate material systems and devices to exploit at the best the luminescence properties of Erbium. Er³⁺-activated confined structures at different scales thus offer interesting solutions. The last decade has seen a remarkable increase in the experimental efforts to control and enhance emission properties of emitters by tailoring the dielectric surrounding of the source. The aim of this paper is to give a review concerning the advances in glass-based photonic systems, where light confinement or the presence of nanostructured hosts for the rare-earth induces an enhancement and a control of the optical and/or spectroscopic properties.

Stimulated emission and light amplification have been observed in Ho³⁺-doped transparent oxyfluoride glasses and glass-ceramics. A pump and probe experiment has been designed to show this result. A doubled-frequency Nd-YAG pulsed laser oscillating at 532nm was used as the pump source to strongly populate the Ho^{3+ 5}S₂:⁵F₄ level. Low power laser radiation at 750nm was used as the probe beam to stimulate the Ho^{3+ 5}S₂:⁵F₄ → ⁵I₇ electronic transition at the same wavelength. The high power pump pulses provide population inversion between the Ho^{3+ 5}S₂:⁵F₄ and ⁵I₇ electronic levels and a net positive gain in the 750nm signal is observed both in the precursor glass and in the glass-ceramic. The highest optical gain was obtained for the glass-ceramic sample and corresponds to about 3.7cm^-1 (~16dB/cm). The dynamics of the gain is also investigated.

The use of broadband efficient sensitizers for Er³⁺ ions relaxes the expensive conditions needed for the pump source and raises the performances of the optical amplifier. Within this context Si nanoclusters (Si-nc) in silica matrices have revealed as optimum sensitizers and open the route towards electrically pumped optical amplifiers. In this work we present insertion losses and pump/probe measurements, which have been carried out on rib-loaded waveguides containing Er³⁺ ions coupled to Si-nc. These samples have been prepared by a multi-wafers reactive magnetron cosputtering of a pure silica target topped with Er₂O₃ pellets. Our objective with this research is to characterize, understand and optimize the main factors that are preventing net optical gain in these samples, i.e. low excitable erbium fraction through the nanoclusters. Evidences of signal enhancement and partial inversion of the Er³⁺ ions excited via Si-nc will be presented and discussed.

We report on optical properties and prospect applications on rare-earth doped oxyfluoride precursor glass and ensuing nano-glass-ceramics. We find out the spectral optical gain of the nano-glass-ceramics and show that its flatness and breadth are advantageous as compared to contemporary used erbium doped optical amplifiers. We present the possibility of flat gain cross-section erbium doped waveguide amplifiers as short 'chip', all-optical, devices capable of dense wavelength division multiplexing, including the potential for direct writing of these devices inside bulk glasses for three-dimensional photonic integration. We carried out a comparative study of the up-conversion luminescence in Er³⁺-doped and Yb³⁺-Er³⁺-Tm³⁺ co-doped samples, which indicates that these materials can be used as green/red tuneable up-conversion phosphors and white light simulation respectively. Observed changes in the spectra of the up-conversion luminescence provide a tool for tuning the colour opening the way for producing 3-dimensional optical recording.

We present the spectroscopic study of the mechanisms of excitation transfer between rare earth ions excited by energy transfer from SnO₂ nanocrystals in silica. Bulk samples of pure and Er-doped silica with SnO₂ nanoparticles were prepared by a sol gel technique and further thermal sintering process. Transmission electron microscopy (TEM) reveals the formation of spherical nanoclusters with a size distribution strongly determined by erbium doping. Small angle neutron scattering (SANS) experiments confirm and detail the TEM data evidencing the existence of a interphase region at the cluster boundaries where a SnOlike phase compensates the structural mismatch between the crystalline lattice in SnO₂ nanoparticles and the amorphous silica network. The analysis of the SANS patterns show what kind of modification of the interphase morphology of SnO₂ nanoparticles in silica brings to the passivation of interfacial defects. Surface states, which may preclude the exploitation of UV excitonic emission, are reduced after doping by rare earth ions. We demonstrate, by means of transmission-electron-microscopy and small-angle-neutron-scattering data, that a smooth interphase with a non negligible thickness takes the place of the fractal and discontinuous boundary observed in undoped material. The time resolved photoluminescence spectra of erbium in the infrared region show the spectral profile ascribable to ions in a ordered environment. Moreover, the absence of the broad contribution of the radiative decay of erbium ions dispersed in the silica amorphous matrix indicates that the excitation transfer follows paths enveloped in the interphase region. The spectroscopic analysis allows us to conclude that the excitation is transferred from ion to ion within a quasi-crystalline region where each site is surrounded by a different distribution of PL quenching sites which are responsible for the multi-exponential decay kinetics.

Metal nanoparticles are lately emerging materials to improve the optical performances of photonic device. This is ascribable to the high cross-section of the metal nanoparticle leading to high energy transfer and consequent luminescent emission from rare earth dopants. In this work we study Ag nanoparticles embedded in a sodalime network. Silver dispersions with different concentrations in the host network were obtained through ion-exchange treatments at temperatures below T_g. Optical properties were investigated through absorption and emission photoluminescence spectra. X-ray Photoelectron Spectroscopy was used to investigate the chemical state as well as size-dependent electronic confinement effects. The changes of the photoelectron core-line binding energies, the change of Auger and valence band line-shapes put forward that there is a clear correlation between the experimental parameters used to make the samples and the extent of quantum confinement. Data from photoelectron spectroscopy well correlate with those from optical measurements. Physico-chemical characterization of optical materials by XPS demonstrated to be of great importance to improve the quality of photonic devices.

A structurally consistent, high aspect ratio nanopores template, featuring 110 nm diameter, 110 nm deep pores have been fabricated and used as a shadow mask to evaporate multilayer nano OLED cylinders based on Iridium organic-metal complex emitters on ITO/glass. We have characterised the nanostructures using atomic force microscope (AFM) and scanning electron microscope (SEM) images. The emissive properties and electrical characteristics of the nano-device are presented. Luminescence efficiency and power efficiency have been studied and compared with conventional large area device.

The study and development of Structural Health Monitoring (SHM) systems for aerospace applications is one of the best challenges for the research in the field of fiber optic (FO) sensors. The harsh environments in which these aerospace structures have to work are the major limit for the employment of standard fiber optic sensors for the thermo-mechanical monitoring processes. Thermal loads which act on these structures do not allow using standard fiber optic sensors used for classic avionics application. In fact, many aerospace structures can be exposed to temperatures up to 1000°C, higher than the operation temperature of the standard fiber optic sensors. In this paper a new fiber optic system for structural analysis of ultra high temperature ceramic (UHTC) materials is proposed. A tunable laser source is used to easily measure the spectral response of different fiber optic sensors. Moreover the employment of an in-fiber optical circulator and TLC 1x4 optical switch, allows to perform a multi-sensor interrogation, to analyse many physical parameters, such as: temperature, strain, pressure, etc.. In particular the monitoring system has been used to test high temperature resistant Fiber Bragg Grating sensors. The first tests at high temperature, up to 600°C, have shown a good response in terms of: sensitivity, resolution, repeatability and dynamic range of the measurement. At last, the flexibility of the electro-optical system developed for the interrogation of the fiber optic sensors, allows the extension of the instruments to mechanical stress analysis, using custom fiber optic strain sensors currently under development.

In this paper, we present hydrogen sensors based on uniform fiber Bragg gratings and long period fiber gratings covered by a catalytic sensitive layer made of a ceramic doped with noble metal. In presence of hydrogen in air, the sensitive layer has the unique property of being the siege of an exothermic reaction. Hence, for increasing hydrogen concentrations, this chemical reaction leads to an increase of temperature around the fiber gratings, which consequently shifts the resonance wavelength. The sensing mechanism is thus based on the monitoring of the resonance wavelength shift. For both kinds of gratings, the sensor response is linear and without hysteresis between increasing and decreasing hydrogen concentrations. It is also selective and extremely fast. Different experiments obtained on uniform fiber Bragg gratings of different physical lengths and on long period fiber gratings are reported in this paper.

Optical devices have the potential for large scale integration and can be successfully used in mission critical environments; in particular optical probes interacting with electric fields can be used in several electromagnetic compatibility (EMC) and industrial, scientifical and medical (ISM) applications. We describe an electro-optical device based on a LiNbO₃ Mach-Zehnder integrated interferometer which has, with respect to standard metallic probes, a very reduced coupling effect on the electromagnetic field to be measured. The probe is mainly made by non conductive materials, making such device suitable for experimental measurement of electromagnetic fields in near field region (or Fresnel's one) of transmitting antennas or in their reactive zone. Here no simple theory is available in order to evaluate the fields and mutual coupling between antennas and standard probes strongly affect the measurements: the optical probe avoids the coupling of the fields with metallic structures and the loss of antenna calibration which typically yield measurement errors. The probe has been tested in the ELF and VHF bands as shown in the Figures below. The device characterization is discussed and its performance is optimised by an electro-optical device mathematic model.

In this paper, an integrated all-optical high precision (well below 0.01 ^0C ) temperature sensor based on ring resonators implemented by GaAs and InP is proposed. Analytical relations illustrating the effect of temperature on the intensity transfer function and group delay are proposed. The index of refraction and length of the ring are changed due to applied temperature. Based on the derived relations the effects of temperature on the output quantities are illustrated. The output intensity and group delay can be used as suitable quantities for measuring of the applied temperature. In this analysis matrix formulation of the light propagation through networks including ring resonator is used. The obtained analytical relations are evaluated and simulated numerically. Based on our proposed method, it is shown that the proposed technique supports ultra-high precision measurement. Our calculation and simulations show that based on the proposed structure so sensitive sensor can be implemented easily using GaAs and InP as suitable material for manufacturing of ring resonators.

A novel ultrasensitive integrated nanomechanical optical sensor is proposed and analyzed. The photonic device consists of a silicon nitride disk resonator formed by a horizontal slot-waveguide acting as a circular cantilever. The device sensitivity results from the product of the sensitivities of the slot-waveguide and the disk resonator. A deflection sensitivity of 11.5 nm^-1 is predicted, representing an enhancement of 4 orders of magnitude as compared to state-of-the-art microcantilever sensors.

Optical fiber sensor have shown a great potential to become chemical sensors and have appropriate properties as long term stability, immune to electromagnetic radiation and multiplexing capability. In this work we present a way of measure the hydrogen present with just optic fiber as sensing device. The hydrogen enters the fiber following a diffusion behaviour. This hydrogen generates absorption peaks at several frequencies. We study that frequencies and determine witch ones are appropriate to use for a hydrogen sensor. We use the data collected to do a model of the fiber and simulate and validate that model with the experiments. We conclude the analysis with the advantages of that kind of sensor in a nuclear waste repository.

Liquid crystals are a growing technology bringing solutions for a number of applications in high performance displays featuring video-rate, color and high resolution images, and in prototypes of photonic devices. Electrooptic response of antiferroelectric liquid crystals (AFLC) might be superior to nematic liquid crystals that are been customarily employed nowadays. AFLC show reduced time response being promising candidates for portable multimedia devices, optical routing applications, among others. In this work, temperature and frequency dependence of impedance measurements, in passive devices of commercial antiferroelectric liquid crystals, has been studied. Measurements of the temperature dependence of optical transmission have been obtained. 1Hz triangular waveforms with different amplitude have been applied to the devices to carry out such characterization. Simultaneous measurements of optical transmission and electrical impedance have been performed. Specific addressing schemes have been tested in order to obtain the optimum electrooptical performance. Display blanking takes place when a saturation pulse is applied. Results achieved show that increasing temperature shifts the dynamic range of the analogue grayscale towards lower voltages. Impedance analysis of these devices upon switching has been performed as well. Temperature and frequency dependence of the impedance measurements have been characterized. Negative phase responses show there is a combined capacitive and resistive behavior. As the frequency increases the capacitive effect grows. Magnitude shows a linear decrease on a log-log frequency scale. As temperature increases, phase profile becomes slight more complex. New capacitive effects are suggested in a model of the electric response of AFLC cells at low frequencies.

We report on the employ of several kinds of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) dispersions as hole injection layer to increase the stability and the charge injection in organic light emitting diodes (OLEDs). The PEDOT:PSS dispersions are different for PEDOT:PSS ratios and their properties were characterized by contact angle measurement, UV-Vis-IR transmittance and I-V characteristics. Multi layer ITO-PEDOT:PSS-PF6-Alq₃- Al OLEDs have been manufactured and the electrical and optical properties have been extensively investigated and discussed in function of PEDOT:PSS ratio. We have found that a major quantity of PEDOT induces a decrement of ITO hole barrier and so an increment of OLED current and luminance. Performed transport analysis have pointed out that PEDOT:PSS carrier density N_D has a notable role in electrical transport at high bias.

The effects induced by different electrical contacts, both for the anode and for the cathode, have been analyzed in Organic Light Emitting Diodes (OLEDs). The properties of anode electrode, Indium Tin Oxide (ITO), have been varied through different surface treatments allowing roughness control, carbon impurity removal, spikes decrement. These induce changes of ITO surface chemical-physical characteristics as roughness, surface energy and surface polarity. OLEDs manufactured employing treated ITO have showed an improvement of 25 times in luminance. Thermionic injection model has been used to estimate decrement in effective hole barrier at ITO-organic layer. It is shown that this effect is correlated to ITO surface energy. The second step of process optimization has concerned the cathode electrode investigation. In order to perform this task, Al, Ca/Al, Ag, Mg/Ag have been used to realize different ITO/PEDOT:PSS/PF6/Alq₃/Metal OLEDs. Measurements of electrical and optical behaviour have been performed. A thermionic injection model, with and without Schottky barrier decrement, has been used to calculate the change of the cathode electrical barrier.

We review the studies conducted in our group concerning electromagnetic properties of metamaterials and photonic crystals with negative effective index of refraction. In particular, we demonstate the true left handed behavior of a 2D composite metamaterial, by analyzing the electric and magnetic response of the material components systematically. The negative refraction, subwavelength focusing, and flat lens phenomena using left handed metamaterials and photonic crystals are also presented.

Complex micro- and nano-structured materials for photonic applications are designed and fabricated using top technologies. A completely different approach to engineering systems at the sub-micron-scale consists in recognizing the nanostructures and morphologies that nature has optimized during life's history on earth. In fact, biological organisms could exhibit ordered geometries and complex photonic structures which often overcome the products of the best available fabrication technologies. An example is given by diatoms. They are microalgae with a peculiar cell wall made of amorphous hydrated silica valves, reciprocally interconnected in a structure called the frustule. Valve surfaces exhibit specie-specific patterns of regular arrays of chambers, called areolae, developed into the frustule depth. Areolae range in diameter from few hundreds of nanometers up to few microns, and can be circular, polygonal or elongate. The formation of these patterns can be modeled by self-organised phase separation. Despite of the high level of knowledge on the genesis and morphology of diatom frustules, their functions are not completely understood. In this work, we show that the silica skeletons of marine diatoms, characterized by a photonic crystal-like structure, have surprising optical properties, being capable of filtering and focalizing light, as well as exhibiting optical sensing capabilities.

A 1D photonic crystal slab based on preferential etching of commercially available silicon-on-insulator wafers is presented. Compared to dry etching, anisotropic wet etching is more tolerant to errors as it is self-stopping on crystallographic {111} planes and it produces a more precise geometry with symmetries and homothetic properties, with surface roughness close to 1 nm. The resulting grooves are infiltrated by low viscosity liquid crystal having large positive optical anisotropy. The use of slanted grooves provides advantages: first of all the complete filling of slanted grooves is simplified when compared to vertical walls structures. Furthermore alignment is significantly facilitated. Indeed the liquid crystal molecules tend to align with their long axis along the submicron grooves. Therefore by forcing reorientation out of a rest position, the liquid crystal presents a choice of refractive indices to the propagating optical field. The liquid crystal behavior is simulated by a finite element method, and coupled to a finite difference time domain method. We investigate different photonic crystal configurations. Large tunability of bandgap edge for TE polarization is demonstrated when switching the liquid crystal with an applied voltage. We have also studied the use of the same device geometry as a very compact microfluidic refractometric sensor.

We propose the fusion of the superprism effect and of the second harmonic generation: small variations of the fundamental field parameters cause large variations in the direction of the second harmonic emission. Phase matching conditions with very different propagation directions for the fundamental and the second harmonic fields are achieved inside 2D PCs. These results are obtained by the use of a multiple scattering method extended to the second harmonic generation problem. This nonlinear effect could possibly be applied for the design of new directional compact sources or of sensor devices.

Light passing through a photonic crystal can undergo a negative or a positive refraction. The two refraction states can be functions of the contrast index, the incident angle and the slab thickness. By suitably using these properties it is possible to realize very simple and very efficient optical components to route the light. As example we present two devices: a passive device acting as a polarizing beam splitter and a tunable switch. In the first device TM polarization is refracted in positive direction whereas TE component is negatively refracted, in the second device the light is positively refracted at room temperature and negatively refracted varying the local temperature of the device.

Recently the fundamentals of photonic crystal physics have experienced a revival due to investigations on new structures possessing properties such as selfwaveguiding and negative refraction. In this communication we present a theory that gives account of observed total internal reflection beam shifts on the surface of a selfwaveguiding crystal and compare its analogy and differences with the classical Goos-Hanchen shift. We also investigate the phenomenon of surface wave resonance excitation in slabs of these arrays as well as those capable of producing images through negative refraction when cut in a slab shape. A discussion is made of the dispersion relation of these surface waves on comparison with those of both metals and left handed materials, and its consequences for obtaining superfocusing.

Individual, unsupported scales of two male butterflies with dorsal blue and ventral green color were compared by microscpectrometric measurements, optical and electronic microscopy. All the scales are colored by photonic band gap type materials built of chitin (n = 1.58) and air. The different scales are characterized by different degrees of order from fully ordered single crystalline blue scales of the Cyanophrys remus butterfly through polycrystalline green scales on the ventral side of the same butterfly, to the most disordered dorsal blue scales of the Albulina metallica, where only the distance of the first neighbors is constant. The different scale nanoarchitectures and their properties are compared.

In the past few years, self assembly colloidal structures based on opals have received large attention because they offer a cost-effective way of designing ultra-compact and efficient all-optical devices. In this study, we present various approaches to design waveguides and cavities in three-dimensional opal-based photonic crystals. Three practical designs with size suitable to telecommunication technologies at 1.55 μm are presented. First, we show that the creation of a hexagonal superlattice of defects in a direct monolayer of spheres yields the opening of a photonic band gap below the light line so that the inclusion of a linear defect in this structure enables the creation of a theoretically lossless waveguide. We also propose the design of a waveguide in a 2D-3D heterostructure, where a graphite lattice of rods is sandwiched between two inverse opal claddings. This structure enables single-mode waveguiding with a maximal bandwidth of 129 nm. Finally, we give the design of a linear cavity, whose quality factor is increased by a factor of 5 when surrounded by an inverse opal.

In this work, we have compared the optical characteristic of two different photonic dielectric multilayers based on the porous silicon technology. We designed and realized two models devices: a Bragg mirror and the S₆ Thue-Morse sequence. Both the structures have the same thickness, the same porosity, and even the same number of the layers but differently spatially ordered. We demonstrate that the two arrangements of the layers influence not only the optical features of these interferometric devices but also their sensitivity when used as optical sensors. We have measured the change of the reflectivity spectra of the devices on exposure to several organic compounds. The experimental results demonstrated that the Thue-Morse aperiodic structure is more sensitive than the Bragg device due to a higher filling capability.

This paper intends to show that the optical interconnection can be a substitute of the electrical serial interface in mobile application. We designed the optical interconnection interface circuits on the evaluation boards which typically correspond to the mobile phone and transferred the data through the optical waveguide module. There are 4 pairs of VCSEL (Vertical Cavity Surface Emitting Laser) and PD (Photo Diode) arrays in the waveguide module and they are used to send the strobe and the data signal in dual-simplex (i.e. Two Directions with Unidirectional Lanes) configuration. We have demonstrated a successful data transmission of moving picture and real-time camera module images to the main-LCD (Liquid Crystal Display) repeatedly and the still pictures to the sub-LCD at the maximum speed of 400Mbps.

In this paper, an adaptive Orthogonal Frequency Division Multiplexing (OFDM) system is proposed for multiuser communications over indoor wireless optical channels. The designed system uses multi-user least-squares (LS) detection techniques applied to SDMA-OFDM schemes, in conjunction with angle diversity reception. The system, which does not present an excessive complexity, supports high bit rates for multiple users, beyond one hundred megabits per second. It also mitigates the channel fluctuations induced when either the space distribution or the number of emitters and receivers varies. The performance of the new proposed scheme is compared with an adaptive single-user system described in previous works. The obtained results show a significant improvement with respect to previous adaptive single-user one, since the new scheme allows adaptively managing the system throughput on a multi-user environment.

In this paper, the dispersive properties of the optical ring resonator (RR) with an internal Sagnac (SG) loop filter are studied for chromatic dispersion managing in digital transmission systems over amplified single-mode fiber (SMF) spans in DWDM backbone networks. Design issues for the architecture as regards quadratic dispersion and magnitude distortion are provided. The RR+SG compound filter provides frequency tunability of the dispersion peaks by adjusting a coupling coefficient of an optical coupler, with no need for using integrated thermo-optic nor current-injection based phase shifters. The configuration can be employed as an additional structure for a general RR-based design and synthesis architecture, allowing bandwidth increase of dispersion compensators. The performance of a compound filter consisting of a two RR in series stage and a RR+SG filter has been simulated over a 200 km amplified SMF span model, obtaining a power penalty enhancement >3 dB for a 5 Gb/s NRZ transmission with a bit error rate (BER) of 10^-9. Comparative simulations with regards to a dispersion compensating fiber span show that the compound filter is a much more compact and effective solution for existing multi-channel SMF backbone links operating at high bit rates.

In this paper, different optical configurations, simple and compound, based on ring resonators and using liquid crystals as the tuning or controlling block, are reported. Specific attention is given to their application as tunable filters and wavelength switches, in this last case as part of complex matrix fabrics for all optical switching. Simulations of integrated optics ring resonators are developed using FullWave by R-Soft. In the compound configurations that use serial micro ring resonators it is implemented a 3 port reconfigurable demultiplexer in a compact cross-grid configuration. Theoretical 10 nm tuning is reported on SOI substrate with nematic liquid crystals. Optimization of the critical coupling condition by changing the evanescent coupling length is also reported. Theoretical analysis is presented to identify and emphasize the design parameters of each configuration as regards its application of interest. The reported structures can be developed in integrated optic technologies; all designs corresponds to state of the art integrated optics technology. A revision of photonics circuits with equivalent components already developed is reported.

In optical applications including hybrid and integrated cases, there are some inherent phenomena such as dispersion, loss and many others that must be critically removed for performance improvement. Among these dispersion is important for light propagation and speed of transmission. Optical pulse broadening and chirping are main disadvantages of dispersion in pulse propagation. Dispersion cancellation in these applications is crucial. Dispersion compensators are widely used which are realized with different methods. In this paper a novel dispersion compensator and management system based on electromagnetically induced transparency (EIT) is introduced. For realization of EIT phenomenon in this paper four level atoms or quantum dots is used. In this analysis uniform distribution of these atoms is assumed. With application of control fields the absorption and the index of refraction are controlled. So, with intensity of a control light the dispersion factor is manipulated. For implementation of this idea ring resonator is considered. With application of control signal the group delay, phase difference and dispersion are controlled. Easy integration of the proposed technique is an important advantage of this method. Also, intensity of the control signal is main parameter for dispersion tuning. The proposed technique is all-optical dispersion management system. Our calculations show delay time and dispersion value well over nsec and 20 ps/km.nm respectively.

In this paper, we demonstrate a compact and integrated optical spectrum analyzer (OSA) based on ring resonator. In this proposal thermo-optic, electro-optic, acousto-optic and nonlinear optic can be used as control signal to sweep and scan the frequencies of the input signal. The applied control signal changes the index of refraction of ring resonator and therefore the resonance frequency is changed and the output intensity in the reflected port is changed proportional to the input signal contents. Also, the proposed idea can easily be integrated on optical chip. The presented design idea is simple for realization using optical integrated circuits, has high accuracy (less than 4 pm) and compact. This new OSA is suitable for the wavelength-division-multiplexing performance monitoring that requires high speed and high wavelength measurement as well as other related applications.

The field of Silicon Photonics has gained a significant amount of momentum in recent years. Announcements of high speed modulators and cost-efficient light sources in the Silicon-on-insulator material system have helped to make Silicon Photonics a viable contender as a low-cost active photonic platform. As a pioneer in the field, the University of Surrey continues to investigate the prospects of silicon photonics. Herein we present a summary of our work on several key areas such as ion implanted grating devices, high-speed modulators, switches and ring resonators. We conclude with a discussion on an advanced fabrication technique, proton beam writing.

Electrophotonic integrated circuits (EPICs), or alternatively, optoelectronic integrated circuit (OEICs) are the natural evolution of the microelectronic integrated circuit (IC) with the added benefit of photonic capabilities. Traditionally, the microelectronics IC industry has been based on group IV silicon, whereas the microphotonics industry on group III-V semiconductors. However, silicon based photonic microdevices have been making strands in "siliconizing" photonics. Silicon microspheres with their high quality factor whispering gallery modes (WGMs), are ideal candidates for wavelength division multiplexing (WDM) in the standard near-infrared telecommunications bands. In our experiments, we are using silicon microspheres with a refractive index of 3.48 and a radius of 500 micrometers. The optical resonances of the silicon microspheres provide the necessary narrow linewidths, that are needed for high resolution WDM applications. Potential WDM applications include filters, modulators, switches, detectors, and possibly light sources.

This work describes the infiltration of a polymeric solution into porous Si structures towards the fabrication of tunable photonic crystals (PC) and microcavities for photonics applications. The tunability is achieved by infiltrating the porous silicon based PCs by active organic materials, such as an emissive and nonlinear polymer called 2-methoxy-5-(2- ethylhexyloxy)-p-phenylenevinylene (namely MEH-PPV). This preliminary work shows the infiltration of this polymeric solution into PC based on macroporous Si structure as well as in microcavities based on multiple layers of microporous Si. The solidification of the polymer was obtained by the evaporation of the solvent. Various techniques of infiltration were studied to obtain an optimized filling of the pores. The infiltration was then characterized using photoluminescence measurements. Finally, we will report on the study of third harmonic generation (THG) in samples of porous silicon microcavity infiltrated with MEHPPV. The k-domain THG spectroscopy was applied and an increase of the THG intensity up to an order of magnitude was achieved for the filled microcavity.

This paper describes the realization of high quality-factor (Q-factor) and high transmission photonic crystal micro-cavity and extended cavity structures embedded in photonic wire waveguides. Q-factor of as much as 16600 have been achieved in micro-cavities with transmission of more than 80%. We have also fabricated an 8 μm long extended cavity with a measured Q-factor of 5100 with normalised transmission of around 67%. Three-dimensional (3D) Finite Difference Time Domain (FDTD) computation has been used to simulate the devices. Comparison of the simulation and measured result shows reasonably good agreement.

Silicon is the most diffused material for microelectronic industry and, in recent times, it is becoming more and more widespread in integrated optic and optoelectronic fields. We present the thermo-electro-optical analysis of an integrated waveguide-vanishing-based optical modulator based on free-carrier dispersion effect, realizable on standard SOI wafer. The optical behavior is based on the vanishing of the lateral confinement in the rib region, and consequent cut-off of the propagating mode. Results show that an optical modulation depth close to 100% can be reached with a bandwidth of about 154 MHz. Smart electrical driving, that is an injection overdrive of a few volts for a very short time, allows to reach total ON-OFF switching time of about 860 ps. For that bias scheme the fall transient is then limiting the whole dynamic and the resulting bit rate in a pure digital modulation scheme is about 1.2 Gb/s.

The action of molecular interaction between a fluid and an adsorbent results in adsorption and wetting phenomena. However, the adsorbent is also submitted to the action of the molecular forces. In order to provide a large adsorption capacity, adsorbents with a large specific surface area are preferable. For this reason, for the study of adsorption phenomena, porous silicon is a material of great interest. Wetting phenomena in porous silicon layers are experimentally investigated by Raman scattering. The experimental results prove a reversible blue-shift of Raman spectra of wetted porous silicon layers with isopropanol or ethanol with respect to unperturbed layers. We ascribe the shift to a compressive stress due to the increased lattice mismatch between the porous silicon layer and the bulk silicon substrate in wetting conditions. The use of two liquids having quite similar density and surface tension resulted, as expected, in quite comparable blue shift of the peak. This effect may be conveniently used in sensing applications of liquids on porous silicon layers.

The role of the aging in the photoluminescence (PL) of stain etched porous silicon (PS) layers and its behaviour at different temperatures have been studied. The photoluminescence has been measured at different temperatures showing the influence of the phonons in the intensity of the emissions and the lifetimes. Two contributions to the photoluminescence spectra have been found: one due to quantum confinement effects and the other one due to the presence of non-bridging oxygen hole centre defects. There is no evidence of energetic shifts on the maximum at different temperatures.

There is a limited variety of pore shapes that can be attained by electrochemical etching itself. We show that these limitations can be overcome and new pore geometries can be realized by additional post-etching treatment of macroporous silicon. Repeated oxidation and subsequent oxide-removal steps are used to correct the initially faceted pore cross-section and to obtain cylindrical pores. We demonstrate that the anisotropy of oxidation process is just opposite to the anisotropy exhibited by the electrochemical etching and accounts for the observed evolution of pore shape from a rounded square towards circular one. On the other hand, alkaline post-etching treatment is used to fabricate pores with square cross-section. Careful choice of concentration, alcohol additives and temperature of alkaline solution allows for certain crystallographic directions to be preferentially etched. In this way, pores with square, eight-sided (octagonal) or rotated square shapes can be attained. When applied on 2D macropore arrays with modulated pores, such post-etching treatment enables the realization of truly 3D structures with very complex geometries.

Using quantum channels to transmit classical information has been proven to be advantageous in several scenarios. These channels have been assumed to be memoryless, meaning that consecutive transmissions of information are uncorrelated. However, as shown experimentally, such correlations do exist, and thereby retain memory of previous information. This memory complicates the protection of entangled-information transmission from decoherence. We have recently addressed these fundamental questions by developing a generalized master equation for multipartite entangled systems coupled to finite-temperature baths and subject to arbitrary external perturbations whose role is to provide dynamical protection from decay and decoherence. Here we explore and extend the foregoing strategy to quantum optical communication schemes wherein polarization-entangled photons traverse a bit-flip channel with temporal and spatial memory, such that the two channels experience cross-decoherence. We introduce a novel approach to the protection of the entangled information from decoherence in such schemes. It is based on selectively modulating the photon polarizations in each channel. We show that by applying selective modulation, one can independently control the symmetry and spatial memory attributes of the channel. We then explore the effects of these attributes on the channel capacity. Remarkably, we show that there is a nontrivial interplay between the effects of asymmetry and memory on the channel capacity.

We report a room temperature operating InAs quantum-dot infrared photodetector grown on InP substrate. The self-assembled InAs quantum dots and the device structure were grown by low-pressure metalorganic chemical vapor depositon. The detectivity was 2.8 x 10¹¹ cmHz^1/2/W at 120 K and a bias of -5 V with a peak detection wavelength around 4.1 &mgr;m and a quantum efficiency of 35 %. Due to the low dark current and high responsivity, a clear photoresponse has been observed at room temperature, which gives a detectivity of 6.7 x 10⁷ cmHz^1/2/W. A 320 x 256 middle wavelength infrared focal plane array operating at temperatures up to 200 K was also fabricated based on this kind of a device. The focal plane array had 34 mA/W responsivity, 1.1 % conversion efficiency, and noise equivalent temperature difference of 344 mK at 120 K operating temperature.

Laser-based free-space communications have been developed to serve specific roles in "last mile" high-speed data networks due to their high security, low cost, portability, and high bandwidth. Conventional free-space systems based on near infrared optical devices suffer from reliability problems due to atmospheric scattering losses and scintillation effects, such as those encountered with storms, dust, and fog. Mid-infrared wavelengths are less affected by atmospheric effects and can significantly enhance link uptime and range. This paper will discuss some of the recent advances in high-power, high temperature, high reliability mid-infrared Quantum Cascade Lasers and their potential application in highly reliable free space communication links.

A recently reported theory of gain recovery in semiconductor optical amplifiers (SOAs) is extended to develop approximate expressions for the gain compression and recovery time in terms of probe wavelength, unsaturated gain and device length. These results indicate (1) that the gain recovery time should be approximately inversely proportional to the transmission gain spectrum, and (2) that the wavelength dependence of the gain compression caused by the pump pulse will be dominated by the spectrum of the SOA gain at the probe wavelength. These predictions are tested against pump-probe measurements of gain compression and recovery in a series of four semiconductor optical amplifiers of different lengths but otherwise identical structures. A continuous wave probe beam from a tunable laser is used to measure the wavelength dependence of gain compression and recovery times. Spectral features are used to verify the correlations between these quantities and their dependence on device length.

A short review of self-reference techniques for remote fiber-optic intensity sensors and possible integration in multiplexing sensor networks is reported. Special focus is given to developments on radio-frequency (RF) source modulation techniques in interferometric configurations operating under incoherent regime. Experimental results on ring resonator (RR) configurations in transmission and reflection modes are included. Sensitivity, optimum insertion losses and robustness to intensity error fluctuations are reported. Sensors are interrogated at two sub carrier frequencies having a high rejection of interference from laser source intensity fluctuations and loss in the fiber lead. Dependence on source coherence is also analysed. Scalable self-referencing sensor networks with low insertion losses implemented in Coarse Wavelength Division Multiplexing (CWDM) technology are reported. The possibility of remote self-referenced measurements using a full-duplex fiber down-lead tenths of kilometers long with no need for optical amplification is also described. Fiber Bragg gratings (FBG) are used in the reflection configuration, thus increasing the sensitivity of the optical transducers. Low-cost off-the-shelf devices in CWDM and DWDM technology can be used to implement and scale the network. Applications to specific photonic sensors are also envisaged and these techniques can be used in networks of microfiber loop resonators, being the microfiber loop the sensing element itself.

We investigate, both theoretically and experimentally, how the use of an all-Optical Decision Element (ODE) in front of a conventional receiver improves, in Return-to-Zero (RZ) systems, the receiver performance when the signal bandwidth exceeds the bandwidth of the available opto-electronic components. A theoretical analysis of the ODE behavior shows the field of applicability of the investigated solution. The experimental evaluation of the performance improvement in an RZ system is realized using an ODE based on two cascaded Nonlinear Optical Loop Mirrors. Benefits in terms of Bit Error Rate for different signal bandwidths and for different received Optical Signal-to-Noise Ratio (OSNR) are presented. Substantial agreement of the experimental results with the theoretical analysis is obtained. The impact of the ODE in the presence of relevant thermal noise at the receiver is also considered. The ODE can extend the use of common band-limited receivers to wide-bandwidth signals, and can be an alternative solution to the development of wide-band receivers.

We report experimental measurements of Optical Bistability (OB) and nonlinear switching in a 1550 nm-Vertical-Cavity Semiconductor Optical Amplifier (VCSOA) operated in reflection and biased below and above its threshold current. Two different types of OB and nonlinear switching, anticlockwise and clockwise, have been observed in both the optical power and wavelength domain. The influence of important parameters including the bias current, the initial wavelength detuning and the optical input power has also been studied. The existence of diverse forms of OB and nonlinear switching in a VCSOA operated in reflection opens the door for the development of inverting and non-inverting logic gates, using, respectively, the anticlockwise or the clockwise nonlinear switching transitions appearing in the VCSOA under external optical injection.

We report on a novel organic/inorganic hybrid waveguide approach, which is composed of a cladding of extremely low refractive index oxidized porous silicon formed on a bulk silicon substrate and of it, a polymeric (polymethylmethacrylate) core doped with a visible laser dye (Nile-Blue) was deposited by spin coating. The waveguiding properties of the structures have been characterised by means of the m-line technique, demonstrating that the use of oxidized porous silicon as a cladding can considerably improve the mode confinement factor of single-mode waveguides. The low refractive index achievable in the cladding (n=1.16) allows forming waveguides with a low index polymer cores. Variable stripe length (VSL) measurements have been also performed in order to characterise the amplification properties of the waveguides. We demonstrate a clear transition from losses to gain at 694nm with a pump threshold of 28mJ/cm². Values of net optical gain up to 104dB/cm have been measured at this wavelength.

We present continuous-wave laser operation at room temperature at 1.55 μm by optically pumping a photonic crystal structure containing an InGaAs/InP quantum well active layer. The active layer is integrated onto a Silicon chip by means of Au/In bonding technology. This metallic layer provides the reduction of heating by thermal dissipation into the substrate, and increases the quality-factor by reducing the radiative losses.

Photonics logic devices are currently finding applications in most of the fields where optical signals are employed. These areas range from optical communications to optical computing, covering as well as other applications in photonics sensing and metrology. Most of the proposed configurations with photonics logic devices are based on semiconductor laser structures with "on/off" behaviors, operating in an optical amplifier configuration. They are able to offer non-linear gain or bistable operation, being these properties the basis for their applications in these fields. Moreover, their large number of potential affecting parameters onto their behavior offers the possibility to choose the best solution for each case.

We present a novel dual-operation InGaN/GaN based quantum optoelectronic device (QOD) that operates as a quantum electroabsorption modulator in reverse bias and as a light emitter in forward bias in the spectral range of near-ultraviolet (UV). Here we report the design, epitaxial growth, fabrication, and characterization of such QODs that incorporate ~2-3 nm thick InGaN/GaN quantum structures for operation between 380 nm and 400 nm. In reverse bias, our QODs show an optical absorption coefficient change of ~14000 cm^-1 with a reverse bias of 9 V (corresponding to ~40 cm^-1 absorption coefficient change for 1 V/&mgr;m field swing) at 385 nm, reported for the first time for InGaN/GaN quantum structures in the near-UV range. In forward bias, though, our QODs exhibit optical electroluminescence spectrum centered around 383 nm with a full width at half maximum of 20 nm and photoluminescence spectrum centered around 370 nm with a full width at half maximum of 12 nm. This dual operation makes such quantum optoelectronic devices find a wide range of optoelectronics applications both as an electroabsorption modulator and a light emitting diode (LED).

In the last few years Programmable Micro Diffraction Gratings (PMDG) have shown the possibility to be applied in many areas, spanning from imaging, to telecommunication, to spectroscopy. These devices were mainly based on Micro-Electro-Mechanical Systems (MEMS) techniques and realized by moveable mirrors and pop-up structures. Although this approach have held a central stage in Micro-Opto-Electro-Mechanical-Systems (MOEMS), they made the realized devices delicate and not useful for some critical environments. In this work we discuss the possibility to fabricate a fully integrated electrically driven PMDG device where, to avoid the presence of moving parts, the electro-optical properties of a suitable substrate material are used. The theoretical approach and the design procedure of a miniaturized PMDG apparatus useful as a generator of synthetic spectra are illustrated and discussed in details.

Measurement precision is often required in the process of material parameter extraction. This fact is applicable to terahertz time-domain spectroscopy (THz-TDS), which is able to determine the optical/dielectric constants of material in the T-ray regime. Essentially, an ultrafast-pulsed THz-TDS system is composed of several mechanical, optical, and electronic parts, each of which is limited in precision. In operation, the uncertainties of these parts, along with the uncertainties introduced during the parameter extraction process, contribute to the overall uncertainty appearing at the output, i.e. the uncertainty in the extracted optical constants. This paper analyzes the sources of uncertainty and models error propagation through the process.

Polymer Optical Fibers (POF) can be and are used in various fields of applications. Two of the main fields are the automotive and the home entertainment sector. In these sectors, POF can be applied in optical transmission systems. The requirements of bandwidth are increasing very fast in these sectors and therefore there must be solutions for these demands. One solution is wavelength division multiplexing (WDM). This means there is more than one wavelength that can carry information over the POF. The different signals that are transmitted over the fiber must be separated to regain all information. These separators are called Demultiplexers. There are several systems available on the market, which are all afflicted with certain disadvantages. All these solutions have one main disadvantage; they are all too expensive for mass market applications. The goal of this study is to develop a cost-effective demultiplexing solution for WDM transmission over POF. The main idea is to separate the chromatic light in its monochromatic components with the help of a dispersive unit. This unit and the other assemblies, which are needed to adjust the optical path, should be manufactured in injection molding technique. This manufacturing technique is a very simple way to produce a Demultiplexer for POF.

All optical devices based on nonlinear effects that use low-level power pumping acquire a great importance in optical communications systems and photonic processing. These optical devices can be implemented by means of different structures and materials. For instance, Fabry-Perot vertical microcavities, whispering gallery based microcavities or hybrid system of photonic crystal microcavities can improve their performance and so make possible a real implementation. In this research work we review the properties of optical media with three-level systems in which electromagnetically induced transparency has been induced. We analyse the effect of including such kind of material in an optical microcavity of the order of wavelenghts. Transmission properties like as the quality factor, the peak of transmission, the power of the coupling field in these microcavities with very small volume and very high non-linear Kerr coefficients will be analysed. Their application for developing new all-optical photonic devices for the next generation of all-optical networks, optical packets switching networks, and quantum information processing will be presented.

In this paper, a methodology for the analysis of a resonant cavity enhanced (RCE) photodetector, based on internal photoemission effect and working at 1.55 &mgr;m, is reported. In order to quantify the performance of photodetector, quantum efficiency including the image force effect, bandwidth and dark current as a function of bias voltage are calculated. We propose a comparison among three different Schottky barrier Silicon photodetectors, having as metal layers gold, silver or copper respectively. We obtain that the highest efficiency (0.2%) but also the highest dark current is obtained with metal having the lowest barrier, while for all devices, values of order of 100GHz and 100MHz were obtained, respectively, for the carrier-transit time limited 3-dB bandwidth and bandwidth-efficiency.

Among insulating materials containing point defects, Lithium Fluoride, LiF, is a radiation sensitive material well known in dosimetry and as active medium in optically pumped optolectronic devices. Primary and aggregate electronic defects, known as colour centres (CCs), can be efficiently produced in LiF by low-penetrating radiation. A novel imaging detector for soft X-ray microscopy, based on photoluminescence from laser active CCs, is currently under development. The continuous shrinking dimensions of photonic devices has prompted us to use thin LiF films, directly grown by thermal evaporation on different substrates, as recording media in Extreme Ultra-Violet contact-lithography experiments for the fabrication of permanent, regular, light-emitting microstructures, produced with high spatial resolution on large areas in short exposure times. The experiments were performed by using geometrical masks in an excimer-pumped laser-plasma source and the samples analyzed by confocal laser scanning microscopy. Strong visible photoluminescence at room temperature was measured from very thin surface layers. A preliminary comparison between the optical response of CCs in thin LiF films grown on glass and silicon substrates with respect to LiF crystals was performed. The polycrystalline LiF films show a higher sensitivity, which is discussed taking into account light confinement effect in the investigated planar structures.

New single photon avalanche detectors (SPAD), are presented. Device performances, as photo-detection efficiency, timing and dark counts, extracted in several experimental conditions and here reported, make them suitable in many applications. The integration possibility, in order to achieve a new concept of solid state photomultiplier, has been also successfully investigated within the 5x5 arrays manufacture.

We report on experiments where a single quantum dot is strongly coupled to a high-Q mode of a micropillar cavity. Photon correlation measurements confirm that the observed avoided crossing originates from strong coupling of a single quantum dot to the cavity mode. Cross-correlations between the cavity mode and the spectrally detuned quantum dot enabled us to assign the unexpected strong cavity emission to a coupling with the single quantum dot. The coupled quantum dot-microcavity system displays an Purcell factor of 61 and represents a single-photon source with an efficiency of 97%.

We present a detailed study of the photonic modes in microtube cavity of ~ 7-8 μm outer diameter that can act as micron-scale optical cylindrical resonator. We demonstrate a new route to the fabrication of individual microtubes with the maximum length of 200 &mgr;m, using a vacuum assisted wetting and filtration through a microchannel glass matrix. The microtubes were studied using micro-photoluminescence spectroscopy and luminescence lifetime imaging confocal microscopy. In the emission spectra of the microresonators we find periodic very narrow peaks corresponding to the whispering gallery modes of two orthogonal polarizations with quality factors upto 3200 at room temperature. In order to identify the peaks in the observed mode structure, we have adopted the boundary-value solution to the problem of scattering of electromagnetic waves by a dielectric micro-cylinder. A strong enhancement in photoluminescence decay rates at high excitation power suggest the occurrence of amplified spontaneous emission from a single microtube. The evanescent field in these photonic structures extends a couple of micrometers into the surroundings providing the possibility for efficient coupling to an external photonic device.

The operating characteristics of a novel optical near-field generator are described in detail. The generator was fabricated by forming a random metal-dielectric film composed of silver paste and spherical fused silica on the facet of a laser diode. The relationship between the current injected to the laser diode and the intensity of the optical near field is similar to that between the injected current and optical output power emitted from the opposite facet having no metal-dielectric film, although the magnitude of the optical intensity is very different. The threshold current and kink-points in the current-optical intensity relation show no difference in the both relationships. Lasing spectra observed in propagating light scattered from the optical near field corresponds to those of light emitted from the opposite facet. The direct current (DC) characteristics of the optical near field are similar to those of the propagating light emitted from the laser diode, and the linear relationship is maintained between DC characteristics of the optical near field and of the propagating light. The modulation characteristics of the optical near-field coincide with those of laser diodes because the intensity of the optical near field linearly responds to the magnitude of the injected current of the laser diode. These results confirm that the optical near-field generator is a practical optical source and will be important for future photonic devices such as OEICs.