In recent years the prospect of engineering an integrated photonic technology based on amorphous silicon-based has focused efforts on providing a unified understanding of the optical properties of this material. From a optical properties prospective the science of amorphous silicon is most transparent from a nano-crystalline material framework. Of particular interest for photonic engineering is the tunable range of the refractive index in amorphous silicon, the fast and slow light induced changes in epsilon 1 and 2, the means by which to deposit films of sufficient thickness and smoothness for the photonic application and the relationships among deposition conditions, material properties, and in particular the optical parameters. The present work reviews some of the previous work and examines the experimental and theoretical basis for the fast light induced refractive index change with the hope of providing the insight needed for device engineering. This work suggests several novel designs for light amorphous silicon based light valves and other devices.

The feasibility of using the combined advantage of ion implantation and laser ablation to form a waveguide has been investigated in SiC implanted with Oxygen 2 MeV wiht concentration of 2-3 × 10¹⁷ ions/cm² and Au²⁺ 2 MeV with concentration of 1x10¹⁶ ions/cm². Then a 2-micron Ge thin film was deposited on the surface with pulsed laser ablation to form a multilayer waveguide. It is shown that the waveguide acts as a laser wavelength differentiator under thermal stress achieving high selcitivy of wavelength in 9.6 micron using CO₂ laser. Electron paramagnetic results ffor this material will be presented as well to show the possible sites of doped and implanted ions.

We have studied holographic grating recordings in Fe-doped photorefractive crystals LiNbO₃ (LN), in doped As-S-Se chalcogenide glassy semiconductors (CGS), and in CGS based photothermoplastic structures (PTPS). Transmission gratings in a-cut crystals of LN were efficient enough to demonstrate the effect of optical channeling. Volume gratings recorded in LN crystals may be used as a parallel array of the planar waveguides. For CGS, slanted grating geometry was tested, with the goal being the creation of asymmetric blazed gratings. Asymmetry of non-Bragg diffraction orders was observed. For the first time, reflection volume grating were recorded in 2μm thick CGS by green solid-state laser. We have also tested the possibility of single beam contact recording in LN, using CGS with recorded grating as beam-splitter attached to the surface of LN.

We simulate exact spatio-temporal evolutions of self-organization in KNbO₃ using a reflection grating based phenomenological model, and a rigorous model including the time evolution of photovoltaic voltage. The initial phase difference of scattering waves is critical to hexagon formation. Finally, we compare the stability range for those two models.

The detailed performance of two-center holographic recording is theoretically studied. We present here a systematic method for global optimization of two-center holographic recording, and apply the method to lithium niobate crystals doped with iron and manganese (LiNbO₃:Fe:Mn). Both the dynamic range (M/#) and sensitivity (S) are considered, and the optimum design parameters for LiNbO₃:Fe:Mn crystals are predicted. To perform optimization, we use both an analytic approach and a complete numerical approach. The light absorption in the crystal is also considered. We show that the optimum design parameters for maximizing the M/# are different from those for maximizing S.

We present an RC-model approach for understanding and analysis of holographic storage in photorefractive materials. In this model the resistor, capacitor and the current source are completely defined based on material parameters and light intensities. The model has good accuracy for the practical applications. It can also be used to understand and improve the properties of photorefractive materials for holographic recording. One interesting application of the model is the qualitative analysis of two-center recording. We also discuss this application in detail.

Three effects of photochromism, bleaching and no-sensitization were found by us in lithium niobate (LN) with deep and shallow dopants. And two recording schemes were correspondingly proposed to record nonvolatile photorefractive holograms, in the first scheme two coherent red beams simultaneous with a UV light are used for recording and one red beam then for fixing, in the another two coherent red beams is used for recording and one red beam together with a UV light then for fixing. This paper presents a uniform theoretic analysis. The two-center band-transport equations together with the wave coupling equations are used and the optimal conditions for processing and material prescriptions are found. Particularly, the lithium niobate crystals doped with Fe:Mn, Ce:Mn, Fe:Cu and Ce:Cu are discussed in detail, which include the dopant concentrations, the oxidation/reduction states, the intensities of UV-sensitizing light and two red recording beams. The supporting experimental results are outlined, too. Both theoretic and experimental results verify that the LN:Ce:Cu has the best performance among the four kinds of doped crystals.

A simple method is presented for measuring boththe real and imaginary parts of low resistivity semiconductors. The method depends on making two reflection measurements from a bulk sample of material. One measurement is made at normal incidence and the other at an arbitrary angle of incidence greater than zero, but less than 90°. Only a simple reflectometer is required. The method offers an alterantive to traditional, and more complex Brewster angle measurements or ellipsometry.

The comparative performance analysis for single-dimensional and two-dimensional acousto-optic deflectors is presented. A new generalizing parameter equal to the product between the number of resolvable spots and acousto-optic diffraction efficiency is proposed. The possibility to use self-collimating modes in crystals for two-dimensional deflectors is discussed. A new geometry for a two-dimensional deflector with coinciding acoustic beams is proposed. This geometry is based on the deviation of energy transmission direction from the wave normal. The experimental test results for the TeO₂ two-dimensional deflector with coinciding acoustic beams are presented. The test results are in good agreement with estimations.

An innovative compact holographic memory system will be presented. This system utilizes a new electro-optic (E-O) beam steering technology to achieve high-speed, high-density holographic data storage.

Advanced device structures are proposed for high-performance polymeric light emitting diodes based on the ferroelectric, pyroelectric, and piezoelectric properties of the very thin crystalline Langmuir-Blodgett films of P(VDF-TrFE). This ferroelectric incorporated polymeric light emitting diode structure has a capability to lower the barrier height for efficient carrier injection and modulate the balance of the carriers for enhanced quantum efficiency. The barrier height can be reduced up to 1 eV while the tunneling barrier width can be modulated up to 8&percent;. This can be achievable only using the crystalline thin films of P(VDF-TrFE).

Laser diodes have been applied to a phase-measuring interferometer with conventional mirrors and a phase-conjugate interferometer with cat mirrors through the wavelength tunability of laser diodes by controlling their currents. Features of the combination of phase shifting and heterodyning by laser-diode modulation in the interferometer with cat mirrors are reviewed. The wavelength is scanned by the laser injection current and is stepwise or rampwise changed to introduce a time-varying phase difference between the two beams of an interferometer with unbalanced optical path lengths. Cancellation of phase distortions in the interferometer can be performed with wide measurement range. Experimental results are shown.

We present a general survey on phase conjugators including self-pumped phase conjugator (SPPC) and mutually pumped phase conjugator (MPPC) in photorefractive BaTiO₃ crystal along with some recent results on two high-performance phase conjugators using pentagon-shaped BaTiO₃ crystal. We also describe two unconventional conjugators with highly ordinary polarized and purely ordinary polarized incident beams. Finally, an application of phase conjugators in one- and two-way 2-D image transfer in optical interconnection is presented.

The photorefractive effect is a phenomenon in which the local index of refraction is changed by the spatial variation of the light intensity. Although the phrase 'photorefractive effect' has been traditionally used for such effects in electro-optic materials, new materials, including photopolymers and photosensitive glasses, have been developd in recent years and are playing increasingly important roles in optical fiber communication systems. Photopolymers in combination with liquid crystals are ideal materials for wavelength selective tunable devices. The improved optical quality and large dynamic range of photopolymers make them promising materials for holographic recording. Holographic gratings recorded in photopolymers can be employed as distributed Bragg reflectors. The large birefringence of liquid crystals can be used to tune the index of refraction to cover a large wavelength range. In addition, birefringence of liquid crystals can be used to tune the index of refraction to cover a large wavelength range. In addition, the combination of photopolymer and liquid crystal also leads to a new material known as holographic polymer dispersed liquid crystal (H-PDLC) which provides a medium for switchable holograms. Photonic devices made of these materials can be easily incorporated into an optical fiber system because of the low index of refraction of polymers and liquid crystals, and their relatively easy processing techniques. Besides photopolymers, photosensitive glasses are also promising for applications in fiber optic systems. Fiber Bragg gratings (FBGs) have been used as bandpass filters and dispersion compensators. In this paper, we describe the applications of photopolymers, H-PDLCs, and FBGs in fiber optic devices. Specifically, we will describe our recent works on photonic devices such as filters, switches, and dispersion compensators for WDM systems.

Photorefractive polymer is a promising material for optical data storage and another photonic applications. In this paper, we review our recent development of erasable 3D bit optical data storage, the formation of micro-cavities and micro-fabrication of waveguide structures in photorefractive polymers.

Bleaching effect, i. e., the absorption of a crystal to the visible lights is decreased after the crystal is illuminated by ultraviolet light, has been observed in congruent LiNbO₃:Fe:Cu crystals. Based on this bleaching effect, two three-step recording schemes are proposed to record nonvolatile photorefractive holograms in LiNbO₃:Fe:Cu, which use two red laser beams and an ultraviolet illumination selectively for the writing of charge grating in the shallow Fe centers, the developing of charge grating in the deep Cu centers by transferring the Fe grating, and the fixing of only the Cu grating for unerasable read-out. Experimental results show that the technique including recording phase by two interfering red beams and fixing phase by both UV light and a coherent red beam is optimal. The theoretical verification and optimal concentration are also simulated. As a conclusion, a comparison on the lithium niobate crystals of the same double doping system of Fe:Mn, Ce:Mn, Ce:Cu and Fe:Cu for nonvolatile holographic storage is outlined.

Photosensitivity has been observed and Bragg gratings have been created in various polymer optical fibres in recent years. Nevertheless the mechanisms of Bragg grating formation in polymer optical fibres are yet to be fully investigated and understood. We carried out experimental investigations on the dynamic growth of Bragg grating under various exposure conditions. For the first time, we observed clearly a threshold behaviour in the grating creation process. The threshold distinguishes two types of fibre gratings that have quite differently properties and performance.

We demonstrate an optical setup being capable of transferring a two-dimensional picture in either way from one plane to another. The transferring takes place only when the receiving port sends a requesting signal. This setup consists of a LiNbO₃ crystal for the purpose of four-wave mixing, and a BaTiO₃ crystal for the purpose of producing self pumped phase conjugate wave. The characteristic of this setup is that it does not require any change in the experimental arrangement when the transferring direction of the picture is reversed. Finally, this setup can perform not only static but also dynamic image transferring.

We propose a phase-coded multiplexing method that employs the rotation of a crossed cylindrical-collimating lens system to encode the reference beam of each multiplexed hologram for volume hologram storage. This phase coding scheme is compared with that based on random phase-coded multiplexing. Our experimental results demonstrate that the method can simplify the procedures of recording and reading in hologram storage.

The advantages of phase-encoded computer-generated-hologram (CGH) are high diffraction efficiency and the ability to reconstruct images on-axis. These advantages are very fundamental and important for many applications. The implementation of phase-encoded CGH by using electrical-addressable liquid crystal television (LCTV) with pure phase-modulation provides the ability for programmable optical interconnections, optical neural systems, optical switches etc. In this paper we adopt the iterative Fourier transform algorithm to design a pure phase CGH. We also report the modulation characteristics of LCTV and its application for displaying the phase-encoded CGH. Criterions for evaluating the quality of output images are proposed.

Optical information processing techniques offer many advantages for data security applications. Optics offers many degrees of freedom like phase, spatial frequency, and polarization to encode data more securely. Being inherently two-dimensional, optical systems can process and relay two-dimensional information in parallel resulting in higher throughput rate compared to the electronic systems. The above advantages offered by optical information processing systems, coupled with advancements in enabling technologies like photorefractive crystals, spatial light modulators, charge coupled device cameras, and smart pixel technology have led to an increasing use of optoelectronic data processing techniques for security applications. Holographic memories that use photorefractive materials are attractive due to their high-density storage capacity, high-speed access to data, and rewritability. Thus photorefractive materials can be used for secured data storage and retrieval. Encrypted memory can be used in a secure communication network using ultrashort pulses. Encryption of amplitude and phase images, and storage of the subsequent encrypted image in photorefractive material has been achieved by various researchers. The present paper reviews various optical encryption techniques developed by us, based on photorefractive crystals. These techniques include double random encoding, fractional Fourier plane encoding, and fully phase encoding.

In this paper, we investigate the latest advancements in real time pattern recognition using the joint transform correlator (JTC) architectures and algorithms. We propose two class associative correlation filters to detect a class of objects consisting of dissimilar patterns. For enhanced performance, both phase and amplitude information is incorporated in the class detection filters. To suppress undesired crosscorrelation between selected objects a new algorithm is introduced. In addition fringe-adjusted joint transform correlation is utilized to enhance the correlation performance, thus ensuring strong and equal correlation peak for each element of the selected class. The feasibility of the proposed technique has been tested by computer simulation.

We present experimental results showing the feasibility of parallel recording and reading of near-field holograms and also of fast data access time using a Si nanometric aperture array. We uses a Si(100) wafer and its anisotropic wet etching for the fabrication of nanometric aperture array. Then, this fabricated aperture array is applied to the storage and reading of binary near-field holograms using the near-field components generated at the aperture as object waves. A brief analysis on the amount of these evanescent components has been presented using the modified Bethe and Bouwkamp's formulation. Two near-field holograms are recorded in parallel and retrieved sequentially successfully with the array in contact with the surface of the photorefractive crystal, which shows the feasibility of parallel recording and reading of near-field holograms. The data access speed (reading speed) can be improved by more than 100 times compared with the case in which a fiber tip of the NSOM records and reads the near-field hologram.

We describe various optical techniques for processing and detection of femtosecond laser pulses. Photorefractive and cascaded second order nonlinear wave mixing are used for space-to-time conversion, transforming space domain information into ultrafast temporal waveforms. An inverse operation that transforms a femtosecond pulse sequence into a quasi-stationary spatial image is performed with spectral domain three wave-mixing. We also demonstrate single-shot phase sensitive femtosecond pulse detection with two-photon absorption in a conventional silicon detector array. This approach allows efficient detection of wide-bandwidth ultrafast signals in the wavelength range of 1-2 μm.

We have observed the conversion of CW laser Ar-ion beam power into pulsating multi-channel outputs: optical, electric and piezoelectric with simultaneous dynamic pattern formation. Frequencies of multi-channel pulsations have characteristic sigmoidal dependence (with threshold) on laser intensity. We have also demonstrated the possibility of synchronization of two optical pulsators, through regulated optical coupling in a photorefractive LiNbO₃ crystal. Spatial distribution of scattered light is selforganized in different patterns (hexagonal and cross-type)

We have observed regenerative optical and electrical pulsations in Fe-doped photogalvanic/photorefractive crystals LiNbO₃ (LN). Rise time of the emitted electromagnetic pulses was 2 ns and amplitude of up to 10V for Continuous Wave (CW) laser power 50-200 mW. Optical pulsators, predicted by our theoretical approach were realized in LiNbO₃:Fe crystals using Ar-ion laser, of wavelength 514 and 457 nm, and power P= 50-200 mW, with frequencies of pulsation ranging from sec to msec. The arrays of the Optical Photogalvanic Pulsators (OPP) may be constructed as a testing field for a novel parallel processing logic based on the pulsed-couple neural networks (PCNN). We have also tested the synchronous nature of the optical, electrical and piezoelectric signals.

Random optical field i.e. speckle pattern of light, has been extensively investigated for various applications. Recently, it becomes generally known that the random optical field is appropriate for reference beam of holographic recording with spatial multiplexing. There are several methods to implement random optical field. Ground glass, multimode fiber, random binary mask etc., are used to implement random optical field. However these conventional methods can give only arbitrary randomness to light but cannot allow specific randomness. In this paper, we propose a design method of diffractive optical element for generating random optical field with specifically designed randomness that is applicable to hologram multiplexing system.

In this paper, a series of PMMA-containing sol-gel hybrid films has been prepared and used with the DAST single crystal grown to form a sandwiched NLO material. The prepared NLO material was used to fabricate an optical polarizer device. The optical polarization properties of the NLO material were measured between 1520 nm and 1560 nm, the DWDM transmission window. The result shows that the optical polarizer has good polarization property and can be used as a variable optical attenuator in the window of the DWDM transmission system.

We propose a method of multiple grating formation in a photorefractive crystal by using a single diffractive mask. The diffractive mask is composed of several spatial frequency components so that the propagating optical wave produces three-dimensional interference patterns in the crystal. We note that it is a system of amplitude and phase gratings having various spatial frequency spectrum. The recorded pattern then can control the flow of another optical wave (signal wave) with different wavelength. This is an integrated version of the conventional hologram multiplexing technique in time domain. The recording and signal wavevectors are determined to satisfy the phase matching condition through the recorded pattern (i.e. Bragg grating). Because this recording method excludes complex time scheduling and mechanical movement of the conventional multiplexing, it provides stability and compactness in the recording procedure for mass production and can make optical devices possessing multiple Bragg gratings.

Optical wavelength shifting is studied using ferroelectric single crystal electrooptic fibers subjected to electric field of microwave frequencies. Sr_1-xBa_xNb₂O₆ single crystals grown by the laser heated pedestal growth technique were tested and compared. The design and verification of the photon acceleration process and the exploration of the materials properties corresponding to growth, orientation and doping condition are presented.

Semi-insulating CdTe:V has been revealed very interesting for photorefractive applications in the near IR region, at room temperature. Addition of Zn, in amounts of some percents, improve highly the photorefractive properties of this material and its mechanical quality. We have studied Cd_1-xZn_xTe:V for x = 0.01, 0.04, 0.07 and 0.10 in comparison with CdTe:V, i.e. for x = 0. Photorefractive CdZnTe:V crystals are investigated by thermal and optical spectroscopies, by spectral response of steady-state photoconductivity at various temperatures, mainly in the near infrared region. The deep levels have been characterized. The role of zinc and those of the two charge levels of vanadium, V²⁺and V³⁺, in the photorefractivity properties have been determined.

The paper considers research and development of arrays of computer-generated multiple-focus phase microholograms for providing given light patterns in the near field zone. Peculiarities of such arrays are discussed. The main result of the talk is the fabrication of the microhologram array providing the given complex image in the focal plane. The size of array was 1.54 mm × 1.54 mm.

Using barium titanate as the photorefractive material, we show self-pumped phase conjugation, beam coupling, higher non-Bragg order generation yielding forward phase conjugate, and image correlation using higher order diffraction. It is shown that 2K gratings are primarily responsible for higher order diffraction.

We have been studying the refractive index changes and vacancies that are induced in silica glass by the irradiation of ultrashort laser pulses. By scanning the laser beam in the glass we can form 3-D shape of waveguides, arrays of tiny vacancies, called voids, and long holes with microscopic diameters. In this paper, we report on the asymmetry of the waveguide formed by linearly polarized ultrashort pulses. The formation of the photo-induced waveguide is normally accompanied by the filamentation, the self-trapping of laser beam due to nonlinear optical effects. The asymmetric cross-section of the waveguide structures explains properly the illusory birefringence of photo-induced waveguides observed earlier. The cross-sectional forms of the waveguides were observed by polishing and etching the cross-psections. We also report the possibility of forming asymmetric shapes of voids. The asymmetry of voids results from the beam profile. We controlled the profile by inserting apertures before the focusing lens. The asymmetry leads to the polarization dependence of diffraction from the array of voids. We also report on the formation of Bragg grating in glass. The Bragg gratings were formed in soda-lime glass. We succeeded in forming a series of three Bragg gratings. The formation of grating inside glass was confirmed by diffraction experiments and chemical etching of polished cross-sections.

Optical fibers have been widely used for transmitting temporal signal. However, the transmission of spatial signal has not been fully exploited. Although multimode fiber has a large space-bandwidth product, transmitting spatial signals by using a fiber is rather difficult. When a laser beam is lached into a multimode fiber, the exit light field produces a complicated speckle pattern caused by the modal phasing of the fiber. It is difficult to recover the transmitted informati from the speckle field. However, the fiber speckle field can be used to fiber sensing with a hologrpahic method. In other words, if a hologram is made with the speckle fiber field, the information of the fiber status can be recovered. Thus by reading the hologram by the same speckle field, the reference beam can be reconstructed, which represents the detection of the speckle field. In other words, instead of exploiting the temporal content, the spatial content from a multimode fiber can be exploited for sensing. Our analyses and experimentations have shown that the fiber specklegram sensor (FSS) is highly senstiive to perturbation, and it is less vulnerable to the environment factors. Applications of the FSS to temperature, transversal displacement, and dynamic sensing are also included.