Collinear^TM Holography, proposed and demonstrated by OPTWARE Corporation, can produce a small, practical holographic versatile disc (HVD^TM) drive system more easily than conventional 2-axis holography. With Collinear^TM technologies' unique configuration the optical pickup can be designed as small as DVDs, and can be placed on one side of the recording media. As servo technology is being introduced to control the objective lens to be maintained precisely to the disc in the recording and the reconstructing process, a vibration isolator is no longer necessary. Experimental and theoretical studies suggest that the holographic material is very effective in increasing the recording density of the system. A high density data recording of Collinear^TM Holography by reducing optical noise is also demonstrated.

We describe the diffraction properties of organic nanoparticle-dispersed photopolymers in which hyperbranched polymers (HBPs) act as transporting organic nanoparticles that increase the refractive-index contrast of a hologram. We prepared HBPs by the living radical vinyl polymerization of inimers under ultraviolet-light illumination. Such synthesized HBPs are easy to disperse into monomers without any aggregation, so that samples with good optical quality are available. We investigate the role of HBPs in the recording process for two different types of photopolymers capable of radical polymerization and cationic ring-opening polymerization. We also evaluate the effect of HBP dispersion on recording sensitivities and polymerization shrinkage.

The nonlocal polymerization driven diffusion model is used to describe holographic grating formation in acrylamidebased photopolymer. The free radical chain polymerization process results in polymer being generated nonlocal both in space and time to the point of chain initiation. A Gaussian spatial material response function and an exponential temporal material response function are used to account for these effects. In this paper we firstly examine the nature of the temporal evolution of grating formation for short recording periods. It is shown that in this case, temporal effects become most notable and the inclusion of the nonlocal temporal response function is shown to be necessary to accurately describe the process. In particular, brief post exposure selfamplification of the refractive index modulation is noted. This is attributed to continued chain growth for a brief period after exposure. Following this a slight decay in the grating amplitude also occurs. This we believe is due to the continued diffusion of monomer after exposure. Since the sinusoidal recording pattern generates a monomer concentration gradient during the recording process monomer diffusion occurs both during and after exposure. The evolution of the refractive index modulation is determined by the respective refractive index values of the recording material components. From independent measurements it is noted that the refractive index value of the monomer is slightly less than that of the background material. Therefore as monomer diffuses back into the dark regions, a reduction in overall refractive index modulation occurs. Volume changes occurring within the material also affect the nature of grating evolution. To model these effects we employ a free volume concept. Due to the fact that the covalent single carbon bond in the polymer is up to 50% shorter than the van der Waals bond in the liquid monomer state, free volume is created when monomer is converted to polymer. For each bond conversion we assume a hole is generated which then collapses at some characteristic rate constant. Incorporating each of these effects into our model, the model is then solved using a Finite-Difference Time- Domain method (FDTD). The Lorentz-Lorenz relation is used to determine the overall evolution refractive index modulation and the corresponding diffraction efficiency of the resulting grating is calculated using Rigorous Coupled Wave Analysis (RCWA). Fits are then carried out to experimental data for 1 second exposures. Good quality fits are achieved and material parameters extracted. Monomer diffusion rates are determined to be of the order of D ~ 10^-10 cm^2/s and the time constant of the nonlocal material temporal response function being of the order of τ_n ~ 10^-2s. Material shrinkage occurring over these recording periods is also determined.

Photopolymerizable hybrid sol-gel are extremely interesting for optical and photonic applications. They combine the properties of glasses with the possibility of photopatterning the layer at the micrometer scale. The presented results concern the generation of volume gratings created by transmission and reflection using an interferences pattern at 514 nm. In transmission, the diffraction efficiencies were going from 30 % to 95 % (ratio of the diffracted intensity to the diffracted plus transmitted intensities) for a thickness ranging respectively from 40 μm to 100 μm and a spatial frequency of 1000 lines/mm. It corresponded to a refractive index modulation estimated between 4 and 5 x 10^-3according to Kogelnik's theory. Reflection gratings with fringe spacing of 0.17 or 0.39 μm were recorded in the material. In normal incidence light beams were highly diffused, whatever the wavelength in the visible range. On the contrary, in oblique incidence, light beams were transmitted through the device without being diffused. This unusual behavior is not yet explained. Applications for information storage can be expected in view of the experimental results, the ease of use and the versatility of this hybrid material.

We inscribed long-period gratings in a hydrogenated SMF-28 fiber by high-intensity femtosecond near-UV pulses via a three-photon absorption mechanism. Due to energy deposition in the fiber cladding, such gratings are similar to those fabricated by C0₂ laser induced heating, mechanical pressure or electric arc. We found that these gratings exhibit significant polarization properties.

We present continuing theoretical and experimental investigations into the characterisation of fibre taper coupled microspherical lasers. We investigate the spectral emissions of these micro resonators as a function of the wavelength and power of the pump radiation. We also consider various means of efficiently coupling radiation into and out of these devices. We are particularly interested in studying emissions about 1.55 μm with the aim of exploiting potential telecommunications applications of these devices. We study microspheres with diameters in the range 40-150 μm. Pump light about 980 nm or 1480 nm is coupled into the microsphere through evanescent wave coupling between microsphere and optical fibre. The resulting spatial and spectral distribution of radiation within the spheres is described by whispering gallery modes. Half and full-taper optical fibres are used to both couple the pump light into the sphere and to out couple the resulting infra red lasing. The physics of whispering gallery modes and the challenges of coupling to such modes is discussed. Experimental techniques and results will be presented and future directions indicated.

Light sources, focusing elements and detectors working at wavelengths from 5nm to 40nm, so called EUV, are of increasing interest for the semiconductor industry, especially for lithography. A metrology has been developed to characterize modified nested Wolter grazing incidence optics which act as the condenser optic. It consists of a monochromatic EUV source and a MCP detector. The EUV source is designed to emit radiation at a wavelength of 13.5nm into a solid angle of up to 1.8sr, which is realized by a silicon-zirconium target used in transmission. Detector and EUV source have been calibrated. In particular, the angular dependences of the source radiation and the detector efficiency have been investigated. The calibrated metrology could be used for measuring the imaging properties of modified nested Wolter optics revealing the point-spread function (psf), the focal length and the effective collecting area. In this paper we will report on experimental setup in the X-ray test facility "PUMA," developing the EUV source, multi-channel plate detector properties, and the results of testing a modified EUV optics.

A theoretical and experimental analysis of group velocity reduction in periodic super-structured Bragg gratings is presented. Experimental demonstration of group velocity reduction of sub-nanosecond pulses at the 1.5 μm wavelength of optical communications is reported using either a 20-cm-long Moire and a periodically-spaced πphase shift fiber gratings. Time delays up to approximately 690 ps for 250-ps-duration optical pulses have been achieved leading to the realization of an optical buffer.

Laser polarization control is revisited at the light of the possibilities offered by resonant gratings associated with the multilayer mirror of the laser. As compared with classical Brewster elements, resonant grating mirrors have a richer functionality in that they can achieve transverse mode control. Furthermore, they are fully planar monolithic elements which can be fabricated by batch technologies and lead to the utmost miniaturization of the laser module. A number of designs and experimental demonstrations are presented.

Performance of diffractive optics is determined by high-quality design and a suitable fabrication process that can actually realize the design. Engineers who are tasked with developing or implementing a diffractive optic solution into a product need to take into consideration the risks of using grayscale versus binary fabrication processes. In many cases, grayscale design doesn't always provide the best solution or cost benefit during product development. This fabrication dilemma arises when the engineer has to select a source for design and/or fabrication. Engineers come face to face with reality in view of the fact that diffractive optic suppliers tend to provide their services on a "best effort basis". This can be very disheartening to an engineer who is trying to implement diffractive optics. This paper will compare and contrast the design and performance of a 1 to 24 beam, two dimensional; beam splitter fabricated using a fifty (50) phase level grayscale and a five (5) phase level binary fabrication methods. Optical modeling data will be presented showing both designs and the performance expected prior to fabrication. An overview of the optical testing methods used will be discussed including the specific test equipment and metrology techniques used to verify actual optical performance and fabricated dimensional stability of each optical element. Presentation of the two versions of the splitter will include data on fabrication dimensional errors, split beam-to-beam uniformity, split beam-to-beam spatial size uniformity and splitter efficiency as compared to the original intended design performance and models. This is a continuation of work from 2005, Laser Beam Shaping VI.

In this work we present the analysis of polarization diffractive elements, and its experimental realization with a twisted nematic liquid-crystal spatial light modulator. We analyze different spatially variant polarization diffractive elements by an extension of the scalar Fourier optics theory to a vectorial theory based on the Jones matrix formalism. Both the intensity and the local state of polarization distributions in the Fraunhoffer approximation are analyzed. We also present the extension of this formalism to study a polarization / diffractive element with rotational symmetry and we consider a binary polarization pupil filter for an optical system. We describe both the transversal plane and the axial polarization behavior. We show how the response of the optical system can be easily changed from apodizing to superresolving behavior, through the orientation of an analyzer placed behind the pupil. Finally we present the experimental realization of these polarization diffractive elements with a twisted nematic liquid crystal spatial light modulator (TN-SLM). We discuss the required polarization configuration of the display and experimentally demonstrate the polarization / diffraction properties of binary polarization diffractive elements. Experimental realization of the proposed binary polarization pupil filter is also demonstrated by placing the liquid crystal spatial light modulator at the exit pupil of an optical system.

The amplitude and phase modulations provided by a liquid-crystal spatial light modulator (LCSLM) depend strongly on the wavelength used for illumination. This is the main reason why usually LCSLMs are only applied with monochromatic illumination. However, there are a number of potential applications where it would be very interesting to combine the programmability provided by LCSLMs and the use of non- monochromatic illumination. In this work we focus on two such applications. On one hand, we use an axial apodizing filter to compensate the longitudinal secondary axial color (LSAC) effects of a commercial refractive optical system on the polychromatic point-spread function (PSF). The configuration of the LCSLM has been optimized to obtain the amplitude-mostly regime in polychromatic light. On the other hand, we show a programmable diffractive lens which is able to provide equal focal length for several wavelengths simultaneously. To achieve this achromatization it is necessary that the LCD operates in the phase-only regime simultaneously for the different wavelengths. Both experimental and numerical results will be provided in this work showing the feasibility of the two applications, and thus the use of LCSLMs under non-monochromatic illumination.

Using adaptive temporal pulse shaping of the driving 800 nm laser pulses, we demonstrate for the first time the complete control over the XUV spectrum of high-order harmonics, generated in a gas-filled hollow fiber. We achieve both the enhancement and the suppression of single or several selected harmonic orders. These arbitrarily shaped soft-x-ray spectra will allow for important modifications of the resulting harmonic pulses in the temporal domain. Experiments are in progress to determine the time structure of the shaped harmonics using a cross-correlation technique. This constitutes first steps towards direct attosecond pulse shaping in the soft-x-ray domain. Moreover, we show that harmonic generation in a hollow-core fiber can be enhanced by coupling into a single fiber mode using a feedback-controlled adaptive two-dimensional spatial light modulator. Temporal and spatial tailoring of harmonics opens the way towards optimal control in the soft-x-ray domain.

In the proposed work, the well-known FDTD method is considerably updated. A new approach taken to the formulation of radiation conditions allows a considerable enhancement of the modeling accuracy to be achieved, compared with the widely used TF/SF technique.

A sinusoidally weakly undulated continuous thin gold film embedded between a polymer substrate and a thin cover of the same polymer, the metal film thickness, the period and the wavelength being such that a normally incident wave excites the long range plasmon mode of the metal film, is shown to exhibit strong resonant transmission for the local TM polarization and strong reflection of the TE polarization. Such structure represents a very simple, average performance polarization beam splitter for white light processing.

In this paper, we describe multiplexing format conversion by supercontinuum generation based lightwave management. The bi-lateral conversion and reconversion of multiplexing format of OTDM-to-WDM-to-OTDM and OCDM-to-WDM-to-OCDM are experimentally demonstrated at 40 Gbit/s (4 x 10 Gbit/s). The experimental scheme is based upon lightwave management both in the time domain and frequency domain. A potential of ultra-high-speed operation, as well as the large scalability, distinguishes the demonstrated lightwave management schemes from the conventional methods in the electronic domain.

We employ a 128-pixel liquid-crystal spatial light modulator to generate variable pulse sequences from a titanium-sapphire femtosecond laser amplifier system centered at 800 nm. By applying phase modulations based on triangular-shaped spectral phase patterns, pulse sequences can be generated whose overall spectrum is still conserved but whose subpulses differ in their spectral composition. We further use nonlinear crystals to analyze the shape of these pulses after frequency conversion. Our experiments show that it is possible to transfer these pulse sequences into the ultraviolet at central wavelengths of 400 nm and 267 nm without losing the ability to spectrally distinguish between the femtosecond subpulses. This is affirmed by measurements using cross-correlation and XFROG (cross-correlation frequency resolved optical gating) techniques with an unmodulated laser pulse. Simulations of the experiments are performed for comparison. We also discuss promising applications in spectroscopy or information encoding.

Employing a grayscale technology for the realization of complex diffractive optical structures does not guarantee superior performance. Even slight variations in etch depth, structure radient or surface geometry can be disastrous to the performance of the element once fabricated. Grayscale structures, such as blazed structures are specifically complicated because the fabrication process must take into account and maintain consistency of materials, photo resist, lithography, and etch process from batch to batch. Engineers who look to implement grayscale diffractive technology need to be conscious of these latent errors and how they emerge during the fabrication process. This paper will present a case study on a beam shaper design which was fabricated in three different batches per year (2001, 2004 and 2005) over a 5 year period. Each batch utilized a grayscale mask (manufactured in 2000, used in 2001) and its established process recipe to fabricate the optical elements from each of these batches. Specific data will be presented covering optical design and modeling data and its comparison to data of actual testing of the elements. An overview will be presented covering the optical testing and metrology techniques used to verify the optical performance and dimensional stability of grayscale structures forming the optical element. In conclusion, a synopsis of potential solutions for verification of process stability and repeatability prior to committing to final fabrication will be offered to engineers seeking to use grayscale technology.

The complex transverse waveguide geometries of integrated photonic devices warrant the application of intricate Numerical Methods when modelling these types of Planar Lightwave Circuits (PLC). To aggravate the problem, difficulties also arise when dealing with back-reflections at interfaces, counter-propagating signals and other associated losses. Routines such as the Finite Element Method (FEM) and Finite Difference Method (FDM) are utilised in simulating the propagation of light through the core waveguide structures of these PLCs. In this paper a novel FEM reliant upon device cross-sectional symmetry is proposed, developed and discussed in regards to its advantages in precision over other procedures. Upon completion of this analysis, the propagation constant and effective refractive indices are known and extensions may be employed to accurately model propagation through the device and outline any reflections or losses that may ensue. A clear and concise review of some of the foremost available schemes is also presented here. These techniques, such as the Bidirectional Eigenmode Propagation Method (BEP) and the Beam Propagation Method (BPM) will be discussed and an effective and precise 3-dimensional model is presented. Due to the myriad of available techniques and algorithms, a comparative study is drawn, listing the advantages and failures of the major methods while suggesting improvements to their application. Necessary considerations such as simulation time and the trade-off between computer memory requirements and accuracy of the solution are also acknowledged.

This paper presents a theoretical and experimental investigation of the self-focusing of a single infrared laser beam in the photorefractive semi-conductor InP : Fe for applications in the telecommunications wavelengths as reconfigurable optical switching. The temporal response of two-wave-mixing in photorefractive InP:Fe under a dc electric field at different temperatures has been studied showing that the temperature as well as the intensity can be used to tune the photorefractive response time. In that way, we analyze both experimentally and theoretically the space-charge field build-up with respect to time and space and provide strong hints on the short time self-focusing of an infrared laser beam in InP:Fe with time response in the range of the microseconds.

Structured light beams have useful attributes to different scientific, industrial and technological applications. Of particular interest are light distributions containing well-defined dark regions. Such distributions are usually called - dark beams, black beams, "doughnut" mode and light bottles and have widely known applications in optical metrology and atom physics. The conventional way to generate these distributions is by various diffractive optical elements and also by special laser cavity design. In this paper we present a simple method, which is based on the Bragg selectivity of volume gratings. Initial experimental results show promising potentials of such approach.

Introduction of diffractive optical elements (DOEs) opened the possibility to control field distribution in the cross-section of laser beam. In fact, by use of DOE one can focus the laser beam into predicted areas as well as form the beam with pre- given behavior propagation through waveguide medium. Diffractive optical element is the plate made from optical material (substrate) with diffractive micro-relief realized on the one or both sides of the plate. Note, that the diffractive micro- relief can be realized directly on the waveguide surface as well. Some applications need the focusing of the output waveguiding beam into predicted area. Generally, one can use diffractive micro-relief on the output end face of the waveguide in the case of excitement of selected waveguide mode. Other applications need selected waveguide mode excitement for fiber sensor sensitivity improvement. In the present paper it is suggested to use micro-relief on the input waveguide cross-section for effective excitement of selected mode. The strategy of the search of Gaussian mode with intensity distribution closed to the illuminating beam intensity distribution is suggested to be used. Corresponding numerical procedure is described. Computer simulation results as well as first experimental results are presented.

A European consortium has been working since September 2004 on all video-based technical aspects of three-dimensional television. The group has structured its technical activities under five technical committees focusing on capturing 3D live scenes, converting the captured scenes to an abstract 3D representations, transmitting the 3D visual information, displaying the 3D video, and processing of signals for the conversion of the abstract 3D video to signals needed to drive the display. The display of 3D video signals by holographic means is highly desirable. Synthesis of high-resolution computer generated holograms with high spatial frequency content, using fast algorithms, is crucial. Fresnel approximation with its fast implementations, fast superposition of zone-lens terms, look-up tables using pre-computed holoprimitives are reported in the literature. Phase-retrieval methods are also under investigation. Successful solutions to this problem will benefit from proper utilization and adaptation of signal processing tools like waveletes, fresnelets, chirplets, and atomic decompositions and various optimization algorithms like matching pursuit or simulated annealing.

The performance of four passive optical network topologies in implementing multi-user quantum key distribution is compared, using 3 protocols proposed by quantum cryptography (B92, EPR, SSP). The networks considered are the passive-star network, the optical-ring network based on the Sagnac interferometer, the wavelength-routed network, and the wavelength-addressed bus network . An analysis of the quantum bit-error rate and sifted key rate for each of these topologies is used to determine their suitability for providing quantum key distribution-service to networks of various sizes. The efficiency of the three considered protocols is also determinated.

We propose a task-specific digital holographic capture system for three-dimensional scenes, which can reduce the amount of data sent from the camera system to the receiver, and can effectively reconstruct partially occluded objects. The system requires knowledge of the object of interest, but it does not require a priori knowledge of either the occlusion, or the distance the object is from the camera. Subwindows of the camera-plane Fresnel field are digitally propagated to reveal different perspectives of the scene, and these are combined to overcome the unknown foreground occlusions. We demonstrate that careful combination of reconstructions from subwindows can reveal features not apparent in a reconstruction from the whole hologram. We provide results using optically captured digital holograms of real-world objects, and simulated occlusions.

It has been shown that complex paraxial optical systems, consisting of various lens and distances of free space propagation, can be described using the Linear Canonical Transform (LCT). Indeed it can be shown that many well know optical transforms such as the Optical Fourier Transform (OFT), Optical Fractional Fourier Transform (OFRT), the effect of a lens or Chirp Modulation Transform (CMT) are all subsets of the more general LCT. Using the ABCD Collins matrix formula it is possible to represent these integral transforms in a simpler form, which facilitates system analysis and design. Speckle Photography (SP) in combination with an optical LCT can be used to measure surface motion of an optically rough body. It has previously been shown that Optical FRT's (OFRT) can be used in speckle based metrology systems to vary the range and sensitivity of a metrology system and also to determine both, the magnitude and direction, of tilting (rotation) and translation motion simultaneously, provided that the motion is captured in two separate OFRT domains. In this paper we extend the OFRT analysis to more general LCT systems and demonstrate how simultaneous tilt and translation measurements can be discerned from the speckle images captured prior to, and after motion. A spherical wavefront can be conveniently described using the Collin's matrix notation. By changing the wavefront of the illuminating light we show that we effectively change the domain of the LCT system without changing the bulk elements in the optical system. Thus the complete motion (in-plane translation and small surface tilting) of a rigid body can be determined using one optical LCT system and illuminating fields of varying curvature.

We consider a double random phase encoding Encryption/Decryption system in which the image encryption/decryption process is performed numerically. In this paper we look at the effect of quantisation in the decryption process due to the discrete values which a spatial light modulator can display. We look at the characterisation of a transmissive spatial light modulator and we present results from simulations of the system.

The improved reconstruction quality that phase-shifting interferometry digital holography offers compared to conventional digital holography comes with an extra computation cost, increased recording complexity and additional data storage demands. The compression techniques that have been proposed to date aim at compressing the complex wavefront at the plane of the recording camera. We propose data compression at an earlier stage of the phase-shifting procedure that may lead to enhanced compression rates. More specifically we propose the compression of the interference patterns which are input to the phase-shifting algorithm. These interferograms are gray scale images making possible the use of standard image compression techniques for their compression. We investigate the use of baseline JPEG, JPEG-2000 and Set Partitioning in Hierarchical Trees for their compression. In order to verify the use of the proposed methods we apply them to real holographic data and compare their performance with other coding techniques that have been proposed in the literature. The study reveals that the proposed methods not only outperforms existing techniques in terms of compression performance but also they offer additional advantages including increased flexibility into the choice of the compression parameters as well as increased compatibility.

We propose a novel optical holographic encrypted data storage scheme based on phase encoding multiplexed scheme. In the proposed data storage scheme, patterns of encrypted images are stored holographically in a photorefractive LiNbO₃:Fe crystal by using lenticular lens array (LLA) sheet phase-encoded multiplexing. Experimental results show that rotating a LLA placed as a phase modulator in the path of the reference beam provides a simple yet effective method of increasing the holographic storage capabilities of the crystal. Combining this rotational multiplexing with two-axis tilting multiplexing offers not only further data storage capabilities but also data encryption possibilities.

Micro-optical elements and related technologies are becoming increasingly important in a number of areas. There are many different methods of fabricating these micro-optical elements. One such technique to produce microlenses is the UV-curable resin method. This method involves the application of droplets of UV-curable resin to a substrate, which can then be cured using UV light. The quality of the lenses produced using this method can vary due to a number of experimental difficulties. These include the fact that the UV resin shrinks as it is cured. This shrinkage effect is a difficult problem, as it is a property of the UV material and the substrate. The ability to pre-shape the liquid droplet may enable the manufacturer to compensate for this shrinkage. In this paper we propose a method to generate a controlled perturbation of the liquid profile and hence the optical properties of the final lens. We describe our method of inducing variations in the droplet profile using an applied electric field. This method enables the fabrication of aspheric lenses. The analysis of this fabrication method requires the development of an accurate lens profile measurement system. A number of techniques can be used to examine the resulting lens elements including mechanical techniques such as Dektak profilometry and optical techniques such as interferometric techniques including laser profiler and white light profiler. In this paper we give the details of the modified Mach-Zehnder interferometric measurement system used, discuss the optical properties of the lens and show a demonstration of the perturbation of the lens profile.

A peristrophic multiplexing method is used to store various diffraction gratings at the same spot in the material. This material is formed of acrylamide photopolymers which are considered interesting materials for recording holographic memories. They have high diffraction efficiency (ratio between diffracted and incident beams), high energetic sensitivity and optical quality, and developing processes are not necessary. In this work, the photopolymer is composed of acrylamide (AA) as the polymerizable monomer, triethanolamine (TEA) as radical generator, N,N′methylene-bis-acrylamide (BMA) as crosslinker, yellowish eosin (YE) as sensitizer and a binder of polyvinyl alcohol (PVA). The layers of material obtained are approximately 1 mm thick. Using holographic recording schedules, the exposure energy each hologram should receive in order to achieve uniform diffraction efficiency is optimized. The purpose of these recording schedules is to enable full advantage to be taken of the whole dynamic range of the material and to share it between the individual holograms. The Scheduled Exposure Method (SEM) and the Incremental Exposure Method (IEM) are the two multiplexing schedules used to determine the recording times. Having determined these times, the results obtained with both methods are compared to ascertain which method enables the greatest number of holograms to be recorded with the highest, most uniform diffraction efficiencies.

Any paraxial optical system which can be implemented using only thin lenses and propagation through free space or through sections of graded index (GRIN) media, belongs to the class of systems known as Quadratic Phase Systems (QPS). Given some input optical wave field, the output of any QPS can be described using the linear canonical transform (LCT), a unitary, additive, three-parameter class of linear integral transform first discovered in the 1970s. The terminology used in relation to the LCT is not at all consistent across the literature, and it is frequently called by other names, such as Quadratic-phase Integral and Generalized Fresnel Transform. In this paper, we examine a new, more flexible numerical implementation of the FLCT. This algorithm is similar to the Sande-Tukey FFT algorithm, and is of general radix. We demonstrate the savings possible in terms of required samples with the flexibility inherent in a general radix algorithm.

The characterization of the behavior of photopolymers is an important fact in order to control the holographic memories based on photopolymers. In recent years many 2-dimensional models have been proposed for the analysis of photopolymers. These models suppose that the photopolymer layer is homogeneous in depth and good agreement between theoretical simulations and experimental results has been obtained for layers thinner than 200 μm. The attenuation of the light inside the material by Beer's law is an important factor when higher thickness are considered. In this work we use a Finite-Difference method to solve the 3 dimensional problem. Now diffusion in depth direction and the attenuation of the light inside the material by Beer's law are also considered, the influence of the diffusivity of material in the attenuation of the refractive index profile in depth is analyzed.

We propose a new optical intersatellite communications system with a phase conjugate mirror (PCM) in formation flying (FF). In conventional optical intersatellite communications, high-accurate target acquisition and tracking are required for both the transmitter and the receiver. In our system with a PCM, when a control beam from the receiver is captured by a PCM in the transmitter, the signal beam from the transmitter introduced back to the receiver as its phase-conjugate replica. Thus, it is not necessary for the transmitter to target the receiver. Another advantage of using a PCM is that we can utilize spatial filtering. Background noise by sunlight with the laser wavelength can also be efficiently suppressed by a spatial phase modulation/demodulation and filtering processes using phase compensation by the PCM, which leads to the improvement of the signal-to-noise ratio (SNR) and hence provides high data transmission rates in the system. In order to efficiently filter out the background noise, a large beam propagation angle is required in spatial filtering. We spatially modulate the background noise by the diffuser and reduce the beam diameter by the expansion/downscale optical system as a method to enlarge the beam propagation angle. In this paper, we show that our system can separate the noise from the signal by using the expansion/downscale optical system even under spatial phase modulation. In the analysis, the SNR is 32.6[dB] at scale=8.0×10⁴, when a spatial phase modulation by the diffuser is θ=1.5×10^-5[rad].

We investigate the application of Independent Component Analysis to the reduction of speckle in reconstructions from digital holograms. Independent Component Analysis computes a linear transformation of a multidimensional distribution that minimizes the statistical dependence between components. It can be seen as an extension of Principal Component Analysis where the transformed bases do not need to be orthonormal. We attempt speckle reduction across multiple hologram reconstructions. A number of situations are investigated, including recording two holograms over the interval of a day, changing the illumination between two holograms and adding a diffuser in the path of the object beam between subsequent hologram captures. This ensured significant speckle differences between the observations. Results are provided using simulated and optical data.

We demonstrate highly-efficient generation of green-blue light using 20-fs femtosecond laser pulses propagating in short highly-nonlinear photonic crystal fibres. Three 5-mm-long fibres with different zero dispersion wavelengths were pumped by Ti:Sapphire pulses centred around 800-nm, and the relevant spectral characteristics of the generated radiation were studied as a function of pulse energy and chirp. In addition to the non-solitonic green-blue light, a well-defined infrared peak was simultaneously observed that follows the same power and wavelength dependence found on the green-blue peak. This work shows that short photonic crystal fibres can be used as an efficient source of ultrashort blue-green pulses (and possibly near-IR pulses) since linear dispersion (and consequent temporal broadening) and absorption of fused silica are minimized when using short fibres.

Compression is essential for efficient storage and transmission of three-dimensional (3D) digital holograms. The inherent speckle content in holographic data causes lossless compression techniques, such as Huffman and Burrows-Wheeler (BW), to perform poorly. Therefore, the combination of lossy quantisation followed by lossless compression is essential for effective compression of digital holograms. Our complex-valued digital holograms of 3D real-world objects were captured using phase-shift interferometry (PSI). Quantisation reduces the number of different real and imaginary values required to describe each hologram. Traditional data compression techniques can then be applied to the hologram to actually reduce its size. Since our data has a nonuniform distribution, the uniform quantisation technique does not perform optimally. We require nonuniform quantisation, since in a histogram representation our data is denser around the origin (low amplitudes), thus requiring more cluster centres, and sparser away from the origin (high amplitudes). By nonuniformly positioning the cluster centres to match the fact that there is a higher probability that the pixel will have a low amplitude value, the cluster centres can be used more efficiently. Nonuniform quantisation results in cluster centres that are adapted to the exact statistics of the input data. We analyse a number of iterative (k-means clustering, Kohonen competitive neural network, SOM, and annealed Hopfield neural network), and non-iterative (companding, histogram, and optimal) nonuniform quantisation techniques. We discuss the strengths and weaknesses of each technique and highlight important factors that must be considered when choosing between iterative and non-iterative nonuniform quantisation. We measure the degradation due to lossy quantisation in the reconstruction domain, using the normalised rms (NRMS) metric.

In this work we investigate the dynamics of a spatial soliton pulse under the presence of a linear Periodic Wave (PW), which dynamically induces a photonic lattice. We consider that propagation phenomena are governed by the well-known non-linear Schrodinger equation (NLSE), while Kerr-type non-linearity is in effect. Interaction phenomena are analyzed by forming a non-linear coupled differential equation system of the evolution of the soliton-beam parameters, which are the pulse amplitude, the transverse velocity, the mean position and the phase. The dynamical system governing the evolution of soliton parameters is derived by utilizing a quasi-particle approach based on the perturbed inverse scattering method. Direct numerical simulations of the NLS equation are shown to be in good agreement with the solution of the dynamical system, for a wide range of the parameters. The results show that efficient photon management, in terms of soliton control and beam steering, can occur for appropriate choices of the characteristics of the periodic lattice, which are the amplitude, the period, the pulse duration, the relative position with respect to the soliton beam in the transverse dimension and the initial transverse velocity.

We investigate the possibility of signal waveguiding, through the formation of spatial solitons in slab cells containing a nematic liquid crystal, biased externally by a quasi-static electric field. The model equations assume a non-local response on the coupling between the optical beam and the elastic properties of the molecules. A semi-analytical approach is achieved via the variational method. Comparison with numerical results from the full model equations is shown and the selection of suitable initial profiles, as far as stability is concerned, is investigated.

Holographic data storage systems, utilising photopolymer material as the recording medium, have recently been presented. Because of their relatively low cost and ease of use, due to their self-processing nature, photopolymers provide many potential advantages as the holographic recording material and data storage medium of choice. Photopolymers show promise, for example, for Write-Once Read-Many (WORM) storage systems. The photopolymer recording medium used in this study is an Acrylamide/Polyvinylalcohol (A/PVA) based dry layer. An important material characteristic, which determines the performance of any photopolymer medium, is the spatial frequency response of that material. Previously, applying our Non-local Photo-Polymerisation Driven Diffusion Model, (NPDD), we have discussed the effects on material behaviour of the length of the polymer chains and the rates of diffusion within the material. These parameters have been shown to be critically important in determining the response of the material. If the average length of the Polyacrylamide (photopolymerised Acrylamide monomer, PA), chains is shortened, an increase in the diffusion coefficient of these molecules might be observed. According to the NPDD shorter PA chains should then result in an increase in the materials spatial frequency response, and ultimately in an increase in holographic data storage capacity. In this paper we report on several experiments carried out (a) to determine the diffusion constant of the PA and (b) to also determine the diffusion constants of both water and Propanol in our material layers.

In recent years there has been an increasing interest in holography and its applications. One such application is data storage. Optimising the holographic recording materials is therefore of critical importance in the capacity and clarity of the information stored. Photopolymer materials are practical materials for use as holographic recording media, as they are inexpensive and self-processing. Understanding the photochemical mechanisms present during recording in these materials is crucial in enabling further developments. Obtaining critical material parameters allows improvements of the performance of these materials, such as its spatial frequency response or its environmental stability. This also allows a better understanding of the photochemical processes that occur during the formation of the holographic grating. Our current work, which is presented in this paper deals with two of the processes that occur during holographic grating formation. The first of these is the photochemistry involved in the absorption of the light by the photosensitive dye. We monitor the power of the transmitted beams, which are used for recording the gratings. The second process we concentrate on is the inhibition effect present during grating growth. It has been noted in the literature that there is a slight delay at the start of grating growth. The reason for this delay is due to an inhibition process, which is present to some extent in all photopolymer recordings. The work presented here explains why it occurs. A theoretical model is developed to predict the behaviour of the temporal evolution of the grating. This model has been improved to account for the absorption effects of the material due to the photosensitive dye and the inhibition period, which results in a reduction in the rate of polymerisation.

Compared with conventional optical systems, diffractive optical elements are more suitable to transform laser diode beams because they can form more complex wavefronts and better fulfill requirements of miniaturization. However, high numerical aperture needed to collimate the fast axis of edge-emitting laser diodes demands extremely high spatial frequency elements when single DOE is used. That involves complicated design methods based on rigorous diffraction theory and fabricating technology with sub-wavelength resolution and nanometer accuracy. To overcome these difficulties we propose a transmission DOE consisting of elliptical and cylindrical zone plates fabricated onto opposite sides of a substrate. The main advantage of such a solution lies in fact that each of the zone plates has smaller spatial frequency and can be made even as 8-phase-level element with theoretically 95% diffraction efficiency using available microlithographic technology. In result, monolithic collimating system that allows to compensate astigmatism and to convert an elliptical laser diode light beam to circular one can be achieved with NA higher than 0.5 and efficiency over 80%.

We derive analytical expressions containing a hypergeometric function to describe the Fresnel and Fraunhofer diffraction of a plane wave of circular and ring-like cross-section by a spiral phase plate (SPP) of an arbitrary integer order. Experimental diffraction patterns generated by an SPP fabricated in resist through direct e-beam writing are in good agreement with the theoretical intensity distribution. We discuss experiments on manipulation of a group of microspheres in light beams with angular harmonics generated by diffractive optical elements.

We present simulations of averaged intensity of light behind apodized phase masks. Two types of apodization profile were assumed: Gaussian and tanh. In reality, because of limitations of electron-beam exposure system used for phase mask fabrication, we simulated phase masks with eight values of step height. For comparison, the averaged intensity distributions behind ideal phase masks with variable intensity were also calculated. Simulations and description of intensity distribution perturbations due to phase jumps in real apodized phase masks were performed.

The paper presents abilities of the Light Sword Optical Element (LSOE) for imaging with extended depth of focus. The LSOE belongs to the class of optical elements focusing incident light into a segment of the optical axis. The elements of this kind can be used as correctors of some defects of human eye accommodation, especially in a case of presbyopia. The paper illustrates imaging properties of the LSOE. In particular, the point spread functions of the LSOE are analysed numerically. Imaging properties of the LSOE are compared with properties of optical elements being potentially useful for presbyopia correction as axicons, bifocal lens and trifocal lens. The experimental results illustrating usefulness of the LSOE in a case of presbyopia are given.

Top hat diffraction efficiency in an all-dielectric SiO₂/HfO₂ grating femtosecond pulse compression grating is demonstrated with a close to 100% flat top over more than 20 nm around 800 nm wavelength. New perspectives are open for high average power femtosecond laser machining.

We investigated the problem of complex scalar monochromatic light field synthesis with a deflectable mirror array device (DMAD). First, an analysis of the diffraction field produced by the device upon certain configurations is given assuming Fresnel diffraction. Specifically, we derived expressions for the diffraction field given the parameters of the illumination wave and the tilt angles of the mirrors. The results of the analysis are used in later stages of the work to compute the samples of light fields produced by mirrors at certain points in space. Second, the light field synthesis problem is formulated as a linear constrained optimization problem assuming that mirrors of the DMAD can be tilted among a finite number of different tilt angles. The formulation is initially developed in the analog domain. Transformation to digital domain is carried out assuming that desired fields are originating from spatially bounded objects. In particular, we arrived at a Dp = b type of problem with some constraints on p, where D and b are known, and p will be solved for and will determine the configuration of the device. This final form is directly amenable to digital processing. Finally, we adapt and apply matching pursuit and simulated annealing algorithms to this digital problem. Simulations are carried out to illustrate the results. Simulated annealing performs successful synthesis when supplied with good initial conditions. However, we should come up with systematic approaches for providing good initial conditions to the algorithm. We do not have an appropriate strategy currently. Our results also suggest that simulated annealing achieves better results than MP. However, if only a part of the mirrors can be used, and the rest can be turned off, the performance of MP is acceptable and it turns out to be stable for different types of fields.

In the work we suppose a mathematical model of 3-dimensional grating spatial profile formation in photopolymer material with light induced optical absorption at polymerization-diffusion processes of holographic recording of transmitted chirped grating. The model is based on kinetics equations of photopolymerisation and diffusion for the zero and the first spatial harmonics of refraction index grating. We have obtained analytical solution of the kinetics equations describing the process of grating profiles transformation during the recording process. The main point of the numerical calculation presented in the paper was examination the possibilities to compensate the non uniformity of the chirped gratings profiles with the help of amplitude profiles of recording beams.

The propagation of an extremely short (one cycle) pulse of an electromagnetic field in a medium with two equilibrium states is considered theoretically. The analysis is based on the set of Maxwell equations and the Landau-Khalatnikov equation, in which the approximations of the slowly varying envelopes are not used. The solutions of this set that describe the steady-state propagation of a solitary polarization wave and electromagnetic pulse are found. In the approximation of unidirectional wave, a numerical simulation of the solitary waves propagation and interaction is performed in terms of the model considered. The switching phenomena in thin ferroelectric films were considered in framework of the numerical simulation.

High speed cameras use the interesting performances of CMOS imagers which offer advantages in on-chip functionalities, system power reduction, cost and miniaturization. The FAst MOS Imager (FAMOSI) project consists in reproducing the streak camera functionality with a CMOS imager. In this paper, we present a new imager called FAMOSI 2 which implements an electronic shutter and analog accumulation capabilities inside the pixel. With this kind of pixel and the new architecture for controlling the integration, FAMOSI 2 can work in repetitive mode for low light power and in single shot mode for higher light power. This repetitive mode utilizes an analog accumulation to improve the sensitivity of the system with a standard N_well/P_sub photodiode. The prototype has been fabricated in the AMS 0.35 μm CMOS process. The chip is composed of 64 columns per 64 rows of pixels. The pixels have a size of 20 μm per 20 μm and a fill factor of 47 %. Characterizations under static and uniform illumination in single shot mode have been done in order to evaluate the performances of the detector. The main noises levels have been evaluated and the experiments show that a conversion gain of 4.8 μV/e^- is obtained with a dynamic range of 1.2 V. Moreover, the charge transfer characterization in single shot mode has been realized. It permits to know which potential must be apply to the charge spill transistor to obtain the whole dynamic of the output with a maximal transfer gain, what is primordial to optimize the analog accumulation.