Waveguide holograms in optical computations

Conclusion The circuitry for optical computers is at present far from advanced, a reflection of the lack of well developed elements. Our investigations were aimed at demonstrating the capabilities of waveguide holography as a universal basis for the development of computer-structure elements, but the applications considered here do not exhaust all the possibilities of waveguide holography, since they touch upon (mainly) only one of the types of waveguide holograms.Translated from Preprint No. 46 of the Lebedev Physics Institute, Academy of Sciences of the USSR, Moscow, 1989.     

离子交换LiNbO_3:Fe平面光波导中两波混合的研究

本文利用耦合波理论分析推导了单模平面光波导中两波混合的耦合波方程和弱相干光放大率的表示式.并且,在LiNbO_3:Fe单模平面光波导中进行了两波混合的实验研究,得到了与理论分析相符合的结果.     

Symmetry dependence of holograms for optical trapping

No iterative algorithm is necessary to calculate holograms for most holographic optical trapping patterns. Instead, holograms may be produced by a simple extension of the prisms-and-lenses method. This formulaic approach yields the same diffraction efficiency as iterative algorithms for any asymmetric or symmetric but nonperiodic pattern of points while requiring less calculation time. A slight spatial disordering of periodic patterns significantly reduces intensity variations between the different traps without extra calculation costs. Eliminating laborious hologram calculations should greatly facilitate interactive holographic trapping.     

计算全息图在光学变换中的应用

本文讨论如何利用计算全息图作为全息透镜以实现圆环到直线,直线到点以及圆环到点等光学变换,采用液晶电视空间光调制品准实时地产生计算全息图。     

Coherent optical image deblurring using computer generated holograms

The low space-bandwidth product of simple computer generated filters is increased by holographic techniques to form holographic filters which may be combined with coherent optical processing to restore blurred photographs.     

Dynamic holograms and phase conjugation in multilevel resonant media

The generation of dynamic holograms and four-wave phase conjugation in resonant media has been investigated under conditions of interaction between radiation and excited singlet and triplet states. Two mechanisms of optical control of resonant media non-linearities using independent pump-up to increase the diffraction efficiency of dynamic holograms have been considered. The peculiarities of non-linear recording of holograms, and a variant of quadratic recording, have been investigated. The dependence of the efficiency of diffraction by dynamic holograms on the intensity of interacting waves and the spectroscopic characteristics of the medium has been analysed.     

Synthesis of multifrequency optical holograms of rotating objects

A two-channel system for synthesizing two-dimensional complex multifrequency optical holograms of rotating objects was developed. In the object irradiation (longitudinal) direction, a hologram is synthesized due to multifrequency laser radiation, and in the transverse direction, the synthesis is provided by object rotation. The object image is reconstructed in the plane coinciding with the plane of its rotation. The resolution of the synthesized hologram in the longitudinal direction is determined by the frequency bandwidth of the laser radiation, and in the transverse direction, the resolution is determined by the initial laser-radiation frequency and the angle of object rotation during the time of hologram synthesis. Using a digital simulation, the degree of isoplanarity of the multifrequency system for synthesizing holograms of rotating objects and its noise immunity under conditions of phase noises were analyzed.     

Transformation of optical vortices by polarization dynamic holograms

Results of theoretical and experimental studies of regularities in the transformation of the topological and polarization structures of optical vortices by polarization dynamic holograms formed by pulse Gaussian and singular light beams in dye solutions are presented.     

Voltage reduction for photorefractive two-wave mixing in InP:Fe by optical gap control

We report a method to increase the photorefractive two-wave mixing gain coefficient in semiconductors by using additional incident laser radiation. Two auxiliary beams are used to optimize the spatial distribution of an applied electrical field via modulation of the photoconductivity of the sample. By applying a voltage of 3.5 kV on a 4.3 mm thick InP:Fe crystal we obtain a two-wave mixing gain of 9 cm^–1. This is about 50% larger than that obtained without auxiliary beams.     

Nonlinear optical and optical limiting properties of individual single-walled carbon nanotubes

A large number of individual single-walled carbon nanotubes (SWNTs) were obtained by dilution of nanotube dispersions in N-methyl-2-pyrrolidone (NMP). Up to 70% individual SWNTs are contained in the NMP dispersions with concentrations of less than 4.0×10^-3 mg/mL. The nonlinear optical and optical limiting properties of SWNT dispersions were studied by using the Z-scan technique at 532 nm. As the concentration of SWNTs is increased, the nonlinear extinction (NLE) and optical limiting effects improve significantly, while the limiting thresholds decrease gradually. The individual SWNTs show similar NLE effect to zinc phthalocyanine nanoparticles, while also exhibiting larger NLE coefficients than Mo₆S_4.5I_4.5 nanowires.     

Sandwich-double exposure holograms for optical differentiation of displacement patterns

A simple and compact method of optical differentiation of displacement patterns is proposed. It utilizes sandwich-double exposure holograms. Some typical experimental results are presented.     

Dynamics of optical self-amplification of holograms in photopolymeric materials

The proposed theoretical model describes the dynamic optical self-amplification of holograms in amorphous photopolymeric materials with photopolymerization and diffusion. Analytic solutions of the cross-coupled writing and diffraction equations are obtained. Computer-modeling results are used to analyze kinetic aspects of hologram optical amplification, the transformation of the amplitude-phase field of the holographic gratings in space and time, and the evolution of the spectrum-angular sensitivity of the amplification process. Tomsk State Academy of Control Systems and Radioelectronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 81–91, January, 1997.     

Use of Fresnel synthetic holograms in an optical processor

We describe a synthetic Fresnel hologram matrix inserted in a high energy physics oriented optical processor. The purpose of the device is to detect alignment of points in real time.     

Design and fabrication of computer-generated holograms for testing optical freeform surfaces

Freeform optical surfaces (FOSs) will be the best elements in the design of compact optical systems in the future. However, it is extremely difficult to measure freeform surface with sufficient accuracy, which impedes the development of the freeform surface. The design and fabrication of computer-generated hologram (CGH) , which has been successfully applied to the tests for aspheric surfaces, cannot be directly adopted to test FOSs due to their non-rotational asymmetry. A novel ray tracing planning method combined with successively optimizing even and odd power coefficients of phase polynomials in turn is proposed, which can successfully design a non-rotational asymmetry CGH for the tests of FOSs with an F-θ lens. A new eight-step fabrication process is also presented aiming to solve the problem that the linewidth on the same circle of the CGH for testing freeform surface is not uniform. This problem cannot be solved in the original procedure of CGH fabrication. The test results of the step profiler show that the CGH fabricated in the new procedure meets the requirements.     

物理参数对光限幅效应的影响

为了对抗日益严重的激光武器威胁，需要了解激光防护材料的光学性能。该文根据非线性吸收模型，推导出光限幅阈值表达式。并以表达式为理论依据，利用配位聚合物［Cd(L4)(SO4)(H2O)2］n在波长532nm、脉冲宽度为40ps的条件下所获得的实验数据，分析研究非线性吸收参数、线性透过率和有效激发态吸收截面等物理参数对光限幅效应的影响。以此为基础，研究了激光防护材料的非线性光学特性和光限幅特性，为制备光限幅材料提供了理论和实验依据。     

Dynamic holograms recording in fullerene-containing solid-state matrices: Porous glass slides and PMMA films

Fullerene-containing solid-state matrices were studied theoretically and experimentally as the active material for all-optical switching devices. Dynamics hologram recording and spectral analysis were used to study temporal stability and efficiency of nonlinear response of the media. Porous glass and polymethylmethacrylate hosts were utilized as C₆₀-containing matrices. Experiments were carried out using nano- and picosecond laser radiation with wavelength 532 nm.     

Achromatic reconstruction of femtosecond holograms in the planar optical waveguide

Holograms were recorded by 30 fs laser pulses in 20 microm film of dichromated gelatin on the polished quartz substrate and reconstructed in the waveguide mode. The geometric-optical regime of waveguide hologram reconstruction was obtained: the direction of the reconstructed beam was observed to be independent on the reconstructing wavelength within the hologram spectral selectivity band. We discuss the possibility of producing achromatic waveguide optical elements containing only a few periods.     

Imaging of rotating objects by means of synthesized optical holograms

A scheme is presented for producing optical holograms of rotating objects by illuminating the object by a single-frequency coherent laser beam. Along one axis, the synthesis takes place due to rotation of the object; along the other axis, the hologram is synthesized by the coherent radiation field generated by a long linear optical antenna. Numerical simulation shows that reliable discrimination of object images from the accompanying background is possible, for point objects, using a single hologram recorded at one angular position and, for extended flat objects or thin cylinder-like objects, using holograms recorded at two or three angular positions. If the holograms are synthesized in the presence of normally distributed random phase noise, the quality of the reconstructed images of rotating objects remains sufficiently high for root-mean-square noise amplitudes exceeding π/2 and reaching the limiting value 2π/3.