Nominally undoped BaTiO₃ crystals, processed in atmospheres of various oxygen partial pressure at 900 degree(s)C and 1000 degree(s)C, respectively, were fabricated and systematically investigated. The photorefractive properties are sequentially controlled by the factor from dark decay, deep/shallow trap, deep/shallow trap with hole/electron competition to dark conductivity, as the oxygen partial pressure is reduced. The trend is similar for both of the processing temperature, however, the compensation point is shifted about three of oxygen partial pressure. This can be attributed to a higher oxygen vacancy concentration st higher processing temperature.

The design latitude for photonic engineering in amorphous silicon-based materials is great because of the very high solubility limits for impurities in the amorphous phase and the large change in refractive index that accompanies impurity infusion. Our recent experimental work found both the classical dynamic light induced refractive index changes and a rich set of light induced changes in the optical constants of amorphous silicon materials not found in classical systems. Included in the changes unique to amorphous silicon are slow light induced structure changes triggered by an above gap illumination induced defect's effect on the relaxation of surrounding structure. There are also very fast refractive index changes associated with above gap illumination which our recent work reports are not be associated with heating nor is it directly related to the slow change. Additionally, it has long been known that amorphous silicon has a strong electro-absorption response near the band edge. The fast changes and the electro- absorption are explained in terms of a simple tetrahedral bonded silicon model in which the electron coherence length is limited and the optical transitions are indirect. This model provides a framework for the development of a photo- active integrated photonic technology based on amorphous silicon.

The times of information input and access during the processes of a hologram recording and reconstruction basically depend on the amount of information stored in a medium. This dependence is different for different media. Besides dependence on each other, these values depend on the medium characteristics such as sensitivity dynamic range (DR) and medium indices defining the hologram diffraction efficiency (DE). Amount of the stored information, access and input times - important parameters for holographic memory devices (HMD) -- are of different importance for different problems solving. Usually the total information amount and data access rate are of the biggest importance. In this case it is necessary to provide wide DR of a medium, multiplexing possibility, and recording of phase holograms which have bigger DE. For large amount of information fast input it is necessary to provide high holographic sensitivity. Its threshold value is defined by the value reciprocal to input energy enough to produce DE providing the information unit reconstruction. For DE providing transmission of N information units the energy must be increased in more than N times. Such recording media as lithium niobate and some photopolymers have the characteristics which allow to provide very high information capacity, acceptable access rate but insufficient holographic sensitivity which allows to input large data amount only at expense of parallelism. The medium characteristics variations allow to provide the optimal relationship of the parameters.

Effect of doping on the UV optical absorption in silica sol gel glasses is studied through investigating the variation of structure and photochemical transformation of oxygen deficient centers. Optical absorption spectra of silica and lithium, aluminum germano-silica sol gel glasses reveal a change in the structure with changing the concentration of complements, specifically transformation of oxygen deficient centers and formation of new centers. Photosensitive response in germano-silicate glasses is enhanced by lithium ions, which act efficiently as charge compensators. Improvement on the change of refractive index is shown in samples containing lithium.

The volume holographic gratings in polymer materials are promising candidates for spectrally selective optical elements, dense data storage, optical communication, and spectral selective imaging. Recently new application of volume reflection-type grating for fast all-optical temporal/spatial light modulators was suggested. Spatial modulation of diffracted red beam by green laser was demonstrated. We also suggest and analyze theoretical model for material with diffusional amplification for different modes of recording: (1) Fast recording with following annealing; (2) Slow recording (real-time grating).

To enhance the recorded space-charge field and to suppress the scattering noise in the recording of photorefractive nonvolatile holograms in LiNbO₃:Fe:Mn crystals, we propose and investigate a cyclic recording scheme by the repeat of a recording interval with the red pattern and the ultraviolet light and a followed post-exposure interval with ultraviolet light. The ultraviolet light used for the post- exposure not only excites more electrons into the shallower (Fe) centers to lead to faster and stronger recording for the next recording cycle, but also acts as an additional incoherent illumination to erase the initially developed scattering noise gratings. Furthermore, we have observed the self-enhancement and the self-depletion phenomena originated from the beam-coupling effect in the holographic recording. It shows that the highest diffraction efficiency available from the self-enhancement during both the recording and fixing phases may be twice as large as the lowest one from the self-depletion, and it is necessary to consider the arrangement of self-enhancement in the practical applications. As a result, such a self-enhanced accumulative recording has a great benefit for the increase of diffraction efficiency and the suppression of scatter noise, no additional equipment being needed. The detailed experimental results and corresponding theoretical analysis are given.

We present our simulation model on the time evolution of the hexagon pattern formation in KNbO₃. The result has been compared with the previous work concerning the steady state ring analysis. By starting with different amplitude of the scattered waves, we are able to obtain some preliminary results relative to the hexagon pattern.

Ferromagnetic resonance (FMR) absorptions from six fine particle-samples of barium ferrite were studied over a temperature range of -195 degree(s)C to 500 degree(s)C. It was found that the shape of the FMR absorption signal is affected by the particle shape and crystalline anisotropy of each sample. From this analysis, the first magnetic anisotropy constant K₁ was estimated approximately as a function of temperature. The estimation suggested that the value of K₁ was sensitive to the condition of preparation of fine powders. In addition the photosensitivity of the LiNbO₃:BaFe doped crystal was enhanced, suggesting the importance of Barium Ferrite powder as a potential candidate with NOL materials.

We have studied the characteristic of the angular multiplexing with spherical reference wave in volume holographic storage. Through the theoretical analysis and the corresponding experimental observation, the angular sensitivity is almost independent of the distances between the point source and the hologram. Accordingly, an all- optical angular sensing system have been proposed and demonstrated.

Contradirectional two-beam coupling was achieved using a single laser beam incident on fibers grown from congruent iron doped lithium niobate using the laser heated pedestal growth technique. To our knowledge, this is the first time that a grating has been written in a fiber using a single laser beam and its Fresnel reflection in a 180 degree(s) contradirectional two-beam coupling geometry. Beam-coupling efficiencies were compared as a function of beam spot size for fibers and bulk crystals. At small spot sizes, the fibers outperformed the bulk crystals by reducing the diffraction effect.

The process of two-beam holographic coupling in optically anisotropic media is analyzed. We consider holographic media possessing birefringence, optically, and spatial modulation of these effects. In this paper energy transfer between two beams interfering in an electro-optic is analyzed as a function of the grating period of the recording hologram. The theory for two-beam coupling in Bi₁₂SiO₂₀ (BSO) with an external electric field and a moving grating is developed. We report high coefficients in a wide range of low spatial frequencies. Exponential gain coefficients of (Gamma) equals 7 cm^-1 have been reached for high intensity beams ratio and moving gratings. These results have been compared with GaAs crystals.

Two-step excitation processes have been used for hologram storage in photorefractive crystals. Then the interference pattern can be formed with red or near-IR light and nondestructive readout of information is possible. Often shallow levels are involved in the holographic recording process in photorefractive crystals. The shallow levels can be populated by illumination with visible or UV pulses forming states with relatively long life times, thus sensitizing the crystals for holographic recording with IR pulses. In LiNbO₃ and LiTaO₃ the most important shallow levels have been identified. They result from Nb_Li⁵⁺ and Ta_Li⁵⁺ antisite defects (Nb⁵⁺ or Ta⁵⁺ on Li⁺ site). The crystals can also be pre-illuminated with visible light of a cw argon laser or of a Xenon lamp and holograms can be recorded with red light of a laser diode. The sensitization process is possible for other photorefractive crystals, too. The holograms can be read nondestructively with IR light and can be erased with green light.

Laser-diode phase-conjugate interferometer with two self- pumped (cat) phase-conjugate mirrors instead of two ordinary mirrors is constructed for distance measurement over extended ranges. The measurement is based on frequency- modulated continuous-wave techniques. A wide-tunable laser diode (LD) with an external cavity is used to generate the chirping signal. The interferometer is immune to spatially nonuniform phase distortion, but can only detect the spatially uniform phase change introduced by the displacement of one cat mirror. The distance can be measured by detecting the beat frequency with an rf spectrum analyzer. The linear regression of the beat frequency as a function of the distance has been ascertained. The system has been characterized over a measurement range from 0.09 mm to 15.75 mm within 2.49 nm of 0.08 nm in wavelength diversities.

This paper will report recent developments in electro-optic polymer optical fibers. We discuss mainly the experimental work done by the Photonics and Optical Communications Group in the University of New South Wales. The relevant issues regarding material processing, design and fabrication of electric-optic polymer fibers and devices will be addressed. In particular, electro-optical polymer fibers that incorporating various electro-optic organic materials, including the well-known disperse red 1, the synthetically attached DR1 side chain monomers, optical liquid crystals, etc., have been fabricated and investigated.

We have demonstrated efficient amplification of 830 nm and 1.06 micrometers light in a ring resonator using Rh:BaTiO₃. The power oscillating inside the ring exceeded the pump power by up to a factor of 2.3 at 1.06 micrometers . We have also showed that such an efficiently working photorefractive cavity is also sensitive to nanometer changes in its cavity length. We have also observed simultaneous, bi-directional and counterpropagating oscillations in a resonator pumped by a single 647 nm pump beam. The intensity of one oscillation beam was up to two orders of magnitude higher than the intensity of the other oscillation beam.

Photorefractive phase conjugators are well known working with extraordinarily polarized light waves with respect to the crystal forming the conjugator. We demonstrate here experimentally a photorefractive phase conjugator, which works with an incident light beam predominantly polarized in ordinary state. The conjugate waves are, however, extraordinarily polarized. Good quality conjugate waves were still observed even when the intensity ratio f the o- component to the e-component in the incident beam is more than one thousand.

We present a new concept for an imaging X-ray sensor based on X-ray-induced hologram erasure. A transmission hologram is recorded by two plane waves in a photorefractive lithium niobate crystal. This hologram acts as a sensor plate that is positioned towards the X-ray radiation like a conventional X-ray film. Spatially modulated X-ray illumination produces a spatially modulated conductivity that erases the hologram. By these means, a hologram with spatially modulated diffraction efficiency is obtained. Reading of the hologram with a plane wave of visible light then yields in the diffracted beam a replica of the original X-ray light pattern. First experimental data are presented. High spatial resolution, limited in principle just by the wavelength of the probe light, together with a time integrating behavior are the main advantages of such a detector.

We developed new production method for thin (0.3 - 1.0 micron) crystalline film (TCF) coating. Method comprises three steps: first, deposition of solvent based liquid crystalline ink on the surface in thin (10 micron) layer, second, orientation of the liquid by laminar shear flow in desirable direction, drying/crystallization of the laser into submicron thin solid crystalline layer. Final solid crystalline layer can be chemically modified. TCF has properties that defined by properties of molecular materials that are used for liquid crystalline ink. Liquid crystalline ink is ordered media with highly none-linear dependence of viscosity upon shear stress. Application of stress produces orientation of liquid crystal and high viscosity preserves order in drying process. hear flow direction determines the direction of crystallographic axes in crystal thin film. Film has monoclinic symmetry with relatively high defect concentration. Flat molecules of aromatic organic dyes are packed in layered crystalline structure with flat plane oriented perpendicular to the surface of the substrate. In present paper we describe properties of TCF with anisotropy of absorption and birefringence. TCF is highly optically anisotropic film with refraction coefficient difference between ordinary and extraordinary directions up to (Delta) n equals 0.8 in the visible spectrum and (Delta) n equals 0.3 at 1550 nm. Dichroic dyes with narrow band absorption in different areas of UV, visible and IR spectra allow to produce polarizers and retarders with new color band design flexibility.

We present experimental results on the recording and retrieving multiplexed near-field holograms using near-field scanning optical microscopy (NSOM) and a conventional rectangular-parallelpiped or cubic photorefractive crystal. We use the fiber tip of NSOM both as an object and as a probe for scanning (reading) the images. The recording distance between the tapered tip of NSOM and the crystal (i.e. between the object and the recording medium) is a crucial factor determining the size of the stored spot and the angular selectivity since it is dependent on that distance whether the near-field components of the object wave can reach the crystal or not. Experiments on angular multiplexing show that the angular selectivity was about 0.01 degree and the retrieved spot size was smaller than the Rayleigh limit when the recording distance is about 10 nm. In addition, experiments show that near-fields originated from sub-diffraction-limit -size objects could be stored in a photorefractive crystal at 2 mm apart from the crystal surface resulting in the retrieval of sub-diffraction-limit- size spots which means that our scheme can provide a way of multilayer (stack-wise) near-field storage and, thus, contribute to the significant enhancement of the storage capacity of the near-field optical memory.

We demonstrate a new tool called optical spectrogram scope (OSS) for visualization of a spectrogram or a scalogram of optical ultrafast phenomenon. The optical spectrogram scope is constructed on the basis of the time-to-two-dimensional- space conversion technique which is capable of expanding a set of time-varying frequency distributions into a two- dimensional spatial plane.

In photorefractive polymers, higher order diffraction and energy exchange are analyzed in two wave coupling configuration. The dependence of the second-order diffraction on the two-wave intensity ratio was simulated and investigated experimentally. The maximum value second- order intensity increases with increasing applied voltage, however for energy exchange of photorefractive polymer, beam ratio for the maximum second-order intensity shift from equal beam intensity. Using this programmable edge enhancement can be obtained by changing the voltage and incident beam intensity ratio.

Direction [110] in the TeO₂ crystal has unique acoustic and acousto-optic properties. This direction is widely used in many applications. But a slow shear acoustic wave traveling in this direction looks very unpromising for multichannel acousto-optic cells because of its low channel- to-channel isolation under reasonable channel package density. This low isolation is due to the abnormally high physical spread of this slow shear wave traveling in the [110] direction, and the therefore high value of the acoustic anisotropy coefficient b equals 26. During recent investigations, a direction exhibiting self-collimation with the coefficient b approximately equals 0.3 was found. This direction lies in the optical plane under the angle of 29 degree(s) with respect to the [110] axis. But the acousto-optic figure of merit M₂ appears smaller for this direction. A number of directions in the TeO₂ crystal's optical plane combining acceptable values of the acousto-optic figure of merit M₂ and channel-to-channel insulation under high channel package density have been experimentally and theoretically studied. Discussed and analyzed are the features of these directions when they are used in multichannel acousto-optic cells with the wideband anisotropic diffraction.

A new method, using genetic algorithms, for constructing a redundant unipolar interconnection weight matrix of the Interpattern Association model is presented. The global searching features of the genetic algorithms are adopted to help us avoiding too complicate procedures to complete a link search of using exhaustive search method. The upper bond and the lower bond of the searching links are adapted from the results of the maximum mode and the minimum mode of the RIPA model respectively. Computer simulation results show that the proposed genetic algorithms method not only has the features of accurate of constructing the IWM, but also has better network performance.

Optical interconnections based on random phase encoding using a ground glass in a volume hologram have been presented. In the system, a crystal plays the role of interconnector, which translates Chinese words into English words. The stimulation results and experimental results of the translation system are demonstrated.

In this paper, based on the volume holographic storage in a photorefractive crystal, a new rotation-, shift-invariant pattern recognition system, with the wavelet transform, has been set up. Parameters of rotated input pattern are first estimated and normalized. Rotation-, shift-invariant pattern recognition is then achieved by correlating the normalized input pattern with the undistorted reference, using the system. Simulation result and experiments demonstrate the effectiveness of this approach.

A new method, based on fuzzy membership function, for constructing the interconnection weight matrix of the InterPattern Association model is presented. Applying fuzzy uncertain processing to construct the interconnection weight matrix of the IPA model, the advantages of increasing the dynamic range and automatic threshold are obtained, which can greatly improve the network performances. The proposed concept can also be very suitable applied to those Hebbian type associative memories. A Matlab program was developed for simulation. The simulation results show that the proposed fuzzy-based IPA model is better than the original IPA model.

A broadband (1530 to 1565 nm) waveguide polarizer is fabricated by utilizing the growth birefringence organic crystal at control temperature and hybrid with an organophosphazene contained sol-gel SiO₂-PMMA IPN polymers. The polarizer consists of the fiber optic waveguide supporting different polarizer mode, which is design with optic active film in the middle of the passive component waveguide. It has a fiber-in-line structure and requires no high temperature process like poling. The measured polarization extinction ratio is about 12 dB at the wavelengths from 1520 to 1570 nm, and the estimated insertion loss is less 3 dB.

Nonvolatile holograms were recorded by using a long wavelength of 633 nm (He-Ne laser) for recording and a short wavelength of 458 nm (Argon ion laser) for sensitizing in double doped LiNbO₃:Cu:Ce crystals. The sensitizing light increases the recording sensitivity by a - bexp(-I_s/c) and saturation behavior will appear with high enough intensity of sensitizing light. The recording light increases the slope of (eta) ^1/2 as a function of time during the initial stages of hologram formation by sublinear I_r^x (x < 1) and thus the recording light decreases the recording sensitivity. The dependence of saturation diffraction efficiency on the intensities of the recording and sensitizing light shows that there is a maximum dynamic range of the recording process.

An optically fixed photorefractive correlator is presented, where two-center nonvolatile holographic recording proposed by Buse et al is employed to write and fix the matched filer in doubly doped LiNbO₃ crystals. This correlator shows good correlation characteristics and insensitivity to recording beam during readout. It can be used in those requiring stability not requiring modified for a long time, and refreshed optically when new information need be registered.

We suggest a way of photorefractive recording of sub- wavelength size optical information using the refractive index change induced by the single beam from the tapered fiber tip of the near-field scanning optical microscopy (NSOM). Data are recorded by the pure (without any change in the topography of the surface) refractive index change induced near the surface of photorefractive crystal by the light intensity distribution from the subwavelength-size fiber tip in NSOM. The size of index variation can be smaller than the size of wavelength since the distance between the tapered tip of NSOM and the crystal is about 10 nm. This can modify the transmission and collection characteristics of the light from the NSOM through the photorefractive crystal. Therefore, the characteristics of the reading beam depend on whether we previously exposed (recorded) the light from the tapered fiber tip or not and thus, the change in transmission or collection characteristics can be regarded as the on/off (binary) data.

Holographic multi-channel demultiplexer for the wavelength division multiplexing optical transmission system has been experimentally demonstrated by using photorefractive lithium niobate crystals doped with iron. As a proof of our scheme, we have designed the 8-channel demultiplexer with a channel spacing of 0.8 nm, and some preliminary experimental results are presented and discussed.

Mutually pumped phase conjugator with +c-face incident geometry is first demonstrated in a photorefractive pentagon-shaped 0 degree(s)-cut BaTiO₃ crystal. Designed choosing the geometry such as the orientation between two mutual incoherent beams and the crystal's c-axis a novel configuration can be formed in the crystal when the mutually pumped phase conjugation established. This configuration provides more efficient interaction, which offer with fast response and high stability, and even high resolution. Two very stable and rather fast phase-conjugate signals with 22% reflectivity can be generated in 0.3 s. Two images with fine structure as high as 8.8 micrometers can be resolved.

Photorefractive CdTe:V crystals are investigated in comparison with undoped CdTe and with As and Cl codoped samples by spectral response of steady-state photoconductivity at various temperatures, mainly in the near infrared region. The deep levels have been characterized. The two charge levels of vanadium, V²⁺ and V³⁺, have been identified and their roles in the photorefractivity properties determined.

The Born approximation with paraxial assumption has often been utilized for a volume hologram analysis, which is a simple and useful method but has limits in the consideration of incident-wave depletion and multiple diffractions of both longitudinal and angular directions. In recent years, the random-phase code multiplexing has received considerable attention because it gives a sharp selectivity compared to other methods, such as angular multiplexing, wavelength multiplexing, etc. In this case, the image of the reference beam is randomly patterned that its spatial frequency bandwidth is widely spread. As the grain size of the random pattern decreases, its spatial frequency of the reference beam becomes more spread. As a result, the paraxial approximation may be insufficient with this case. In addition, the effect of multiple diffractions between different angular spectra can also be magnified because the structures of multiplexed volume holograms are more complicated than others. Here we analyze the volume holographic gratings based on the coupled-mode theory in discrete Fourier domain without assuming the paraxial approximation, in which the continuous spatial spectra of lights are discretized by discrete Fourier transform and the couplings among them are simultaneously considered into account. We propose two methodologies for the coupled-mode analysis of volume hologram: one is by discretization approach and the other by a first-order approximation. These approaches can be extended to any kind of volume hologram analysis, such as for the Fourier or Fresnel plane hologram that includes lenses or not. The selectivity and crosstalk of random-phase-multiplexed volume holograms are discussed by the two methods.

We report a photosensitive composite structure consisting of chalcogenide glassy semiconductors and copolymeric thermoplastic materials. Our researches were aimed to find out new approaches of using photothermoplastic materials. (PTPM) as two-layered media for holographic and optical data recording. This approach was based on creating the modified PTPM structures with enhanced characteristics as well as on performing the new processes of recording onto PTPM. Some modifications in the recording procedure and equipment setup were carried out. It is established that PTPM systems based on donor-acceptor layers have a photosensitivity of 10^-3 to 10^-4 J/cm². The introduction into them an additive of photochromic dye increases the photosensitivity of donor-acceptor systems by 2 - 3 times. The essential growth in photosensitivity is observed in the blue-to-green range of spectrum. A method of photothermoplastic recording of holograms on a PTPM with a photosensitive layer of chalcogenide glassy semiconductors is proposed. Storing the whole data file of holograms followed by their development does the recording of optical information.

The combination of the genetic engineering and chemical additive has been used in an attempt to obtain much longer M-state lifetime of bacteriorhodopsin-PVA film. Different compositions of D96N-mutant bacteriorhodopsin-PVA film with the diaza-15-crown-5 (1,4,10-trioxa-7,13- diazacyclopentadecane) additive were prepared and their spectral and kinetic transformation were investigated by absorbance spectroscopy. As the molecular ratio of BR_D96N/diaza-15-crown-5 ranging from 1:50 - 1:150, the decay of the M-state was slowed down gradually. The fitting of the M-state decay kinetics curves needs a three-exponential- function to get sufficiently small residuals. At the highest additive concentration, the photochromism time of BR_D96N film could last as long as one and a half hours. This provides a benefit to the BR_D96N as a candidate material for optical applications under ambient conditions.

We report image formation via single and two-photon photoinduced fluorescence changes in a polymeric medium with two-photon fluorescence readout of multiplayer structures. Photoinduced acid generation in the presence of a two-photon fluorescent dye possessing strongly basic functional groups (7-benzothiazolyl-9,9-didecyl-2,2-(N,N- diphenylamino)fluorene underwent protonation upon exposure with UV or near-IR (740 nm fs pulses). Solution studies demonstrate formation of monoprotonated and diprotonated species upon irradiation, each resulting in distinctly different absorption and fluorescence properties. The fluorescence of the original, neutral, fluorophore is quenched upon monoprotonation with a concomitant increase in fluorescence at longer wavelengths due to the monoprotonated form. Hence, two channel two-photon fluorescence imaging provides 'positive' or 'negative' image readout capability. Results of solution and solid polymer thin films experiments are presented.

We demonstrate 10 plane wave holograms angularly multiplexed at one frequency channel in spectral hole burning medium. We show that the M/# is still a valid system metric and the measured M/# in one frequency channel is about 0.01.

We review recent progress made towards commercializable read-write, fast-access holographic data storage. This includes a recent demonstration of high areal density holographic storage, systems architectures for extending this high density to high capacity using phase-conjugate readout, and recent experimental progress along these lines. Other topics include using signal processing to relieve alignment and distortion constraints, optical elements for improving beam uniformity, and most importantly, requirements and prospects for improved photorefractive materials for two-color, gated nonvolatile holographic storage.

Holographic data storage offers the potential for simultaneous search of an entire database by performing multiple optical correlations between stored data pages and a search argument. This content-addressable retrieval produces one analog correlation score for each stored volume hologram. We have previously developed fuzzy encoding techniques for this fast parallel search, and holographically searched a small database with high fidelity. We recently showed that such systems can be configured to produce true inner-products, and proposed an architecture in which massively-parallel searches could be implemented. However, the speed advantage over conventional electronic search provided by parallelism brings with it the possibility of erroneous search results, since these analog correlation scores are subject to various noise sources. We show that the fidelity of such an optical search depends not only on the usual holographic storage signal-to-noise factors (such as readout power, diffraction efficiency, and readout speed), but also on the particular database query being made. In effect, the presence of non-matching database records with nearly the same correlation score as the targeted matching records reduces the speed advantage of the parallel search. Thus for any given fidelity target, the performance improvement offered by a content-addressable holographic storage can vary from query to query even within the same database.

An optical system for writing and reading of microscopic holographic gratings in a photopolymer layer is presented. The reflection gratings created by a highly focused laser beam can be used to replace the pit-land structure in a disk-based optical storage system. The modulation range of such three-dimensional microgratings is clearly localized to the focal region of a focused write beam. Holographic recording allows for using various multiplexing methods. To achieve storage densities higher than currently available, we propose a combination of wavelength multiplexing and multilayer storage. The fist steps in the system development as well as microholographic recording in Aprilis CROP photopolymers are reported.

To achieve very high data rates in 3-D multilayer optical data storage systems, a novel approach is investigated to read out in parallel multiple tracks at different layers simultaneously. Data bits at different layers are arranged as titled data pages inside the disk. A uniform optical beam sheet is generated to illuminate the desired data page from the top of the disk, and a depth transfer imaging system is used to collect the fluorescence of the written bits within the data page to a detector array. The performance of the illumination optics has been experimentally evaluated and optimized by aberration compensation and equalization of irradiance distribution on the entire data page. Other important factors including reflection loss, sensitivity to disk quality, and servo requirements of disk wobbling are analyzed.

There are a variety of factors that can limit the set of allowable code words that are useable on an optical memory block. In this paper, we will primarily consider inter- symbol interference (ISI) and the noise margins required to represent an individual bit. Fo example, code words must maintain a specific topological separation of '1' bits so that ISI does not raise the intensity of neighboring '0's' above a pre-set threshold. Typically this is accomplished by a static encoding that uses a pre-selected set of code words based on these properties of the storage media and the optical system. Alternatively, our approach provides for a dynamic analysis of all data currently stored in the region surrounding a particular block and defines the allowable code words uniquely for each block. We assume the existence of a 'smart' read head that is capable of analyzing a page of data and calculating the allowable codes in real-time based on the actual data in the surrounding region. We use point-spread function based mathematical model for optical readout system to evaluate and carry out data encoding. Our experiments show 81% spatial utilization while recent publications present only 45% utilization.

We report ultraslow group velocities of light in a solid. Light speeds as slow as 45 m/s were observed, corresponding to a group delay of 66 microsecond(s) in a 3-mm thick, optically dense crystal of Pr doped Y₂SiO₅. Reduction of the group velocity is accomplished by using a sharp spectral feature in absorption and dispersion that is produced by resonance Raman excitation of a ground-state spin coherence. Potential applications of slow and stopped light for the highly efficient storage and recall of optical data are discussed.

Raman excited spin coherences were experimentally observed in nitrogen-vacancy (N-V) diamond color centers via nondegenerate four-wave mixing (NDFWM) and electromagnetically induced transparency (EIT). The maximal EIT-induced absorption suppression was found to be 17%, which corresponds to 70% of what is possible given the four possible geometric orientations of the N-V center in diamond. The properties of these coherences are discussed in the context of potential applications to solid-state quantum computing and high-temperature spectral hole burning memories.

In this paper we report optical hole-burning in nano- particles of MgS doped with Eu. Nano-particles have been produced by quench condensing the laser-ablated vapors from a solid target. Particle size has been controlled by the pressure of the ambient gas in the chamber. Our experiments produced particles as small as 20 nano-meters in size. Optical data shows typical fluorescence enhancement associated with the confined geometries. Results have been presented on optical properties, the hole-burning characteristics, and the broadening of holes at elevated temperatures.

Large-scale integration of compact photonic devices may be the key technology for the future information age. If optical-waveguide structures with small radius of curvatures are integrated inside a small glass tip along with active devices, a paradigm of microphotonics inside glass may become possible. We will review the fabrication techniques for the waveguides and photonic-band structures inside glass with the ultrashort laser pulses and present our recent results of fabrication experiments. The experimental studies include fabrication of birefringent waveguides, formation of small vacancies called voids, and drilling of a narrow but long hole from the rear side of a glass. We will show the birefringence properties of waveguides that are induced by the lienarly-polarized ultrashort laser pulses of approximately 100 fs duration. Birefringence of the waveguides depends on the polarization states of the fabrication beam. The experimental studies on the stabilities of a void during the fabrication process are also presented. We will show that the voids move during the fabrication process although the beam and sample are fixed. It will be shown that the void moves from pulse to pulse toward the upstream direction along the optical axis. We can currently drill a long hole of more than 200 microns with a diameter of several microns. We also present the results of numerical analysis of optical propagation through photonic structures that are based on the array of voids.