Nina I. Pletneva

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.

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.

Reversible recording medium of the photoconductor-liquid-crystal type with a rectifying stibnite-germanium-glass semiconductor junction

This paper discusses optically controlled structures with a modulating liquid-crystal layer and an Sb2S3 photoconductor with a sublayer made from germanium glass of composition As17.6S26.4Ge17.5Se38.5 (IKS24). It is shown that the response rate of the indicated structure is greater by a factor of 4 than that of the Sb2S3-liquid-crystal control structure with no sublayer. With reversible writing of thin holograms, a recording regime with a nonsymmetrical line profile is implemented that makes it possible to obtain a diffraction efficiency of 41.5% on the structures with a sublayer.

New elements and schemes for holographic correction in mid-IR

We discuss several schemes and methods, providing the possibility to extend the method of dynamic holographic correction of distortions by means of optically addressed liquid crystal spatial light modulators (OA LC SLMs) to IR spectral range. These are first of all the schemes with TV (computer) relay of interferogram to modulator and double-wavelength dynamic holography schemes. We consider also the performance of the first OA LC SLMs, specially developed for correction in 2.5-4 μm spectral range, providing diffraction efficiency of ~10% in traditional scheme and about 75% in the case of grating with asymmetric profile.

Response rate of optically controlled space-time light modulators based on a bismuth-silicate-nematic-liquid-crystal structure

This paper presents an experimental study of the possibility of enhancing the response rate of a photoconductor-nematic-liquid-crystal structure. The contribution introduced by the inertia of the individual layers is analyzed for various structures and under various conditions. It is proven that, when the read-out is done with radiation from the mid-IR region, it is impossible in principle to achieve response rates higher than several hertz. This applies to all space-time light modulators of the given type, since the response rate depends not on the properties of the semiconductor but on the thickness of the liquid-crystal layer, which in turn is entirely determined by the wavelength of the readout radiation.

Optically addressed spatial light modulators based on the photoconductor: liquid crystal structures for real-time optical applications

Main characteristics of the Optically Addressed Spatial Light Modulators based on the chalcogenide glass photoconductor--nematic liquid crystal and the a-Si:H-- ferroelectric liquid crystal structures, advantages of both types of the devices and possible applications are discussed.

Optically addressed spatial light modulators for coherent optical data processing applications

Main characteristics of the Optically Addressed SLMs based on the chalcogenide glass photoconductor--nematic liquid crystal and the a-Si:H--ferroelectric liquid crystal structures, advantages of both types of the SLMs and possible applications are discussed.

Laser-Damage Resistance of the Liquid Crystal Modulators

Abstract Experimental results have been given on laser-damage resistance of the liquid crystal modulator with longitudinal operating electrical field. It was shown that laser-damage resistance of the modulator is limited by the ITO transparent electrodes and equals 2.5 − 2.9 J/cm2 at 1.06 nm, τ = 15 ns. To improve this parameter we proposed an liquid crystal structure controlled by a transverse electric field in which the ITO electrodes are removed out of the zone intense laser radiation. The main characteristics of this mode liquid crystal modulator are discussed.

Liquid Crystal Modulators with improved laser damage resistance

Experimental results have been given on laser-damage resistance of the liquid crystal modulator with longitudinal operating electrical field. It was shown that laser-damage resistance of the modulator is limited by the ITO transparent electrodes and equals 2.5 - 2.9 J/cm2 at 1.06 nm, (tau) equals 15 ns. To improve this parameter we proposed an liquid crystal structure controlled by a transverse electric field in which the ITO electrodes are removed out of the zone intense laser radiation. The main characteristics of this mode liquid crystal modulator are discussed.