Aleksander N. Chaika

Phase OA LC SLMs for record of thin dynamic holographic correctors with diffraction efficiency over 50

It was found out, that in optically addressed liquid crystal spatial light modulator with the nematic liquid crystal and photoconductor, comprised by p-i-n diode on the base of amorphous hydrogenated silicon, it is possible to record the dynamic diffraction gratings with diffraction efficiency over 50%. The gratings were recorded with the use of S- effect. Possible reasons of the discovered effect are considered in the paper.

Optically Addressed Spatial Light Modulator with Highly Sensitive Layer of Amorphous Hydrogenated Silicon Carbide

Abstract The photoaddressed spatial light modulator (PLSM) with thin hydrogenated amorphous silicon carbide photoreceptor α-Si1−XCx:H and nematic liquid crystal has been fabricated. The films were prepared by rf plasma decomposition of SiH4 and CH4 gas mixture. They have a high dark resistivity and photosensitivity as a hydrogenated amorphous silicon, but a more transmittance in visible spectrum. The maximum of diffraction efficiency for PLSM was achieved for the write light intensity 40 μW/cm2, a resolution on the one half of maximum of diffraction efficiency was 54 mm−1. The optical response of PLSM was observed in the frequency region from 1 Hz to 100 Hz.

Pixelated liquid-crystal light valve for neural network application

The liquid-crystal light valve (LCLV) is a useful component for performing integration, thresholding, and gain functions in optical neural networks. Integration of the neural activation channels is implemented by pixelation of the LCLV, with use of a structured metallic layer between the photoconductor and the liquid-crystal layer. Measurements are presented for this type of valve, examples of which were prepared for two specific neural network implementations. The valve fabrication and measurement were carried out at the State Optical Institute, St. Petersburg, Russia, and the modeling and system applications were investigated at the Institute of Microtechnology, Neuchâtel, Switzerland.

Spatial light modulators based on chalcogenide glass photoconductor - liquid crystal structure operating in pulse regime

Main characteristics of the SLMs based on the chalcogenide glass photoconductor--liquid crystal structure under different operating conditions and SLM applications as input and real-time holographic devices in the JTC and as integrating/threshold elements in optical neural networks are discussed.

Novel liquid crystal spatial light modulators for adaptive optics and image processing

We have developed laboratory prototypes of nematic and ferroelectric liquid crystal optically addressed spatial light modulators with photosensitive layers based on ZnSe, alpha-SiH, pin alpha-SiH, alpha-SiCH, and pin alpha-SiCH. The SLM performance characteristics measured using standard projection and holographic techniques are presented. The advantages and shortcoming of different SLM design versions are analyzed for the use in the wavefront correction and dynamic hologram recording systems. The examples are given for specific implementation of the SLMs in these systems.

Nonlinear regime of the reversible recording of holograms on photoconductor-liquid-crystal structures with high sensitivity to He-Ne laser radiation

A comparative study of two types of optically controlled structures with a modulating liquid-crystal layer and antimonite (Sb2S3) or arsenic selenide (As40Se60) as the photoconductor has been carried out. It is shown that diffraction efficiency up to 42% was able to be obtained in the reversible thin-hologram recording regime, while the use of a photoconductor layer whose maximum spectral sensitivity is close to the radiation wavelength of a He-Ne laser provided sensitivity of 0.75 µW/cm2 at a recording wavelength of lambda=633nm. The structures considered here are characterized by the presence of a decreasing section of the modulation response, with a falloff of the diffraction efficiency to 0.05 epsilonmax (for an Sb2S3 photoconductor layer) and 0.01 epsilonmax (for an As40Se60 photoconductor layer), because of which they can be used in holographic correlation systems for implementing nonlinear information-processing algorithms.

OA LC SLM with high-net optical efficiency for holographic correction of distortions

The reflective type optically addressed spatial light modulators (OASLMs) with an amorphous hydrogenated carbon (a- C:H) light-blocking layer (LBL) sandwiched between an intrinsic hydrogenated silicon carbide (a-Si:C:H) photoconductor and broad-band and narrow-band dielectric mirrors have been developed. FLC was used as a light modulating medium. The DHF effect in an FLC with tilt angle (Theta) equals 39 degrees and SS (Clark-Lagerwall) effect with angle 22,5 degree(s) were employed. The study showed that a flexible design of the OASLMs are possible. As a result of optimal design of the reflective type OASLMs with the dielectric mirrors of two types, the following performance characteristics have been obtained. Diffraction efficiency (DE) was about 30%, net diffraction efficiency (NE) was about 20% (spatial frequency equal 30 lp/mm and frame refreshment rate equal 200 Hz). This net diffraction efficiency practically does not depend on the direction of the reading- out light polarization for the OASLMs operating on the DHF mode.

Orientation dependencies of diffraction efficiency of the dynamic holographic corrector recorded in optically addressed spatial light modulator with the ferroelectric liquid crystal

The results are reported of theoretical and experimental studies of the dependence of diffraction efficiency of hologram-corrector upon an orientation of a diffraction grating vector and of the polarization of the reading-out radiation with respect to the normal to the smectic layers. The gratings recorded using DHF-effect and Clark-Lagerwall effect were studied. The conditions were determined when the dependence of diffraction efficiency vs. radiation polarization is weak. It was found out that in the hologram- corrector, using the polymer photoconductor, the diffraction efficiency is significantly dependent of the vector of grating orientation, while for the hologram-correctors using a-Si:C:H photoconductor this dependence is practically absent.

Development of the optically addressed spatial light modulators for dynamic holography applications using deformed-helix ferroelectric liquid crystals

The basic characteristics of the optically addressed spatial light modulators are presented based on ferroelectric liquid crystal (FLC) as a light modulating media and amorphous hydrogenated silicon carbide a-SiC:H and dye-doped polyimide films as photoconducting layers. The parameters of the constituent parts are described, among them: photoconductivity of photosensitive layers, data about newly developed light blocking layers, characteristics of the FLC materials, utilizing the deformed helix ferroelectric effect. The dynamics of the response in hundreds Hz region, the diffraction efficiency of 20% at spatial resolution better than 501 p/mm, and sensitivity in range of microWatt/cm2 are obtained.

Reversible recording of interference gratings with a diffraction efficiency above 50% in an amorphous hydrogenized silicon-nematic liquid crystal structure

The properties of a space-time light modulator comprising an a-Si:H based p-i-n diode and a nematic liquid crystal layer were studied using a holographic technique. Under certain conditions, an asymmetry of the diffraction efficiency in the +1 and −1 diffraction orders was observed. The maximum diffraction efficiency in one of these orders may reach up to 52%, which is a record value for devices of this type.