Liquid crystal holographic configurations for optically reconfigurable gate arrays

An optically reconfigurable gate array (ORGA) system, which consists of an ORGA very large scale integration (VLSI), an easily rewritable liquid crystal holographic memory recording four configuration contexts, and a laser array, is proposed. Circuits on a gate array of the ORGA-VLSI can be programmed rapidly by exploiting large parallel connections between a holographic memory and a gate array VLSI; that programming can be executed even as it is being programmed. Consequently, the gate array can be switched from a certain circuit to another circuit instantaneously. We present a demonstration of the ORGA system and experimental results.     

Characterization of optically switchable holographic polymer-dispersed liquid crystal transmission gratings

This study characterizes the all-optical switching effect in holographic polymer-dispersed liquid crystal transmission gratings. The light-induced switching behaviors of these structures are due to the doped azobenzene-derived LC (azo-LC), which changes the refractive index of phase-separated LC within the polymer composite. This study also optimizes the polymer-dispersed liquid crystal formulation containing 15 wt.% azo-LC and 35 wt.% nematic LC to achieve a grating performance with a tunable diffraction efficiency of 78% and a fast switching-on time (0.5 s) with a relatively small light stimulus of 9 mW/cm².     

Dynamic optically reconfigurable gate array very large-scale integration with partial reconfiguration capability

We present a proposal of a partial reconfiguration architecture for optically reconfigurable gate arrays and present an 11,424 gate dynamic optically reconfigurable gate array VLSI chip that was fabricated on a 96.04 mm(2) chip using an 0.35 μm three-metal complementary metal oxide semiconductor process technology. The fabricated VLSI chip achieved a 2.21 μs partial reconfiguration.     

Optical reconfiguration by anisotropic diffraction in holographic polymer-dispersed liquid crystal memory

Holographic polymer dispersed liquid crystal (HPDLC) memory is fabricated by a photoinduced phase separation comprised of polymer and liquid crystal (LC) phases using laser light interference exposures. The anisotropic diffraction induced by the alignment of LC in the periodic structure of the HPDLC memory is applied to reconstruct the configuration contexts for the optically reconfigurable gate arrays. Optical reconfiguration for various circuits under parallel programmability is implemented by switching the polarization state of incident light on the HPDLC memory using a spatial light modulator.     

Chirped switchable reflection grating in holographic polymer-dispersed liquid crystal for spectral flattening in free-space optical communication systems

We report the design and fabrication of a chirped switchable reflective grating (CSRG) recorded in a holographic polymer-dispersed liquid-crystal material. This CSRG is a spatial wavelength-selective flattener in a free-space dynamic gain equalizer for use in wavelength-division multiplexing (WDM) networks. Prelimenary experimental results show that this device permits the management of the spectral power of a WDM stream with an attenuation range of 6 dB. The polarization-dependent loss introduced by the CSRG is shown to be less than 0.1 dB.     

Holographic grating formation in PVB doped polymer dispersed liquid crystal based on PUA

Different contents of poly(vinyl butyral) (PVB) have been incorporated into the conventional holographic polymer dispersed liquid crystal (HPDLC) composition based on liquid crystal mixture and polyurethane acrylate (PUA) with a particular composition. As the PVB content is increased, the hardness, elastic modulus and thermal stability of polymer matrix are improved because of the entanglement by PVB, which has a relatively high molecular weight compared with PUA oligomer. Diffraction efficiency is enhanced with the addition of PVB except for HPDLC film with 10 wt.% PVB owing to augmentation of the phase separation between polymer and LC, caused by the increase of elasticity of the polymer matrix. However, the increase in viscosity on adding PVB produces a slow saturation time and coalescence of the LC droplet, showing a lower diffraction efficiency at the PVB content of 10 wt.% than at 0 wt.%.     

Analysis of dichroic dye-doped polymer-dispersed liquid crystal materials for display devices

Dichroic polymer-dispersed liquid crystals (DPDLCs) based on nematic liquid crystal materials with azo dye were investigated in detail for the application of display devices. Polarizing optical microscopy, differential scanning calorimeter and electro-optic experiments all have shown that the DPDLC containing low concentration of dyes modifies the basic properties of these materials like optical transmission, threshold voltage, contrast ratio and absorbance factor. A minimum amount of dye needs to be added to the liquid crystal with the polymer matrix for its effective phase separation and to minimize the transmittance in the OFF state and therefore gives rise to an overall improvement in contrast ratio of the devices. Molecular orientation and dynamics in droplet sizes are readily controlled in these DPDLC materials. These findings imply that the value of the threshold electric field E_th is approximately 8 V/μm for pure polymer-dispersed liquid crystal (without dye) where the threshold electric field E_th values are approximately 4.0 V/μm, 2.0 V/μm, 1.7 V/μm 1.0 V/μm, for 0.0625%, 0.125%, 0.25% and 0.5% with azo dye in DPDLCs, respectively. From the results we can also infer that the maximum contrast is approximately 2.55 times the minimum contrast observed in the experiment for DPDLCs. The results show that the DPDLC with proscribed dye concentration will be possibly suitable and promising functional electronic materials for green technology flexible liquid crystal display.     

A liquid crystal phase grating for instrumentation applications

Abstract

A liquid crystal phase grating, suitable for instrumentation applications has been developed that utilizes refractive index matching to enable it to be switched from a diffracting to a non-diffracting state by application of an electric field. The effect of the non-uniform molecular alignment during switching is considered and compared with measured data for such a device. The observed switching potentially offers a device in which the mark/space ratio may be varied with the applied electric field.     

Linear size gradient single layers of polymer-dispersed liquid crystal micrometer-sized droplets for diffractive optics

An experimental study of coherent light diffraction by wedge-formed single layers composed of liquid crystal (LC) micro-sized droplets dispersed in a transparent solid polymer matrix is reported. The micrometer-sized polymer-dispersed liquid crystal (PDLC) material contains prolate-ellipsoid-like LC droplets with a linear-gradient size distribution along the wedge slope. The droplet diameter in the films reaches several tens of micrometers, defined by the wedge. Such a droplet organization in a two-dimensional layer provides both spatial and electrical control of the coherent light diffraction by the LC/polymer interface.     

Formation of anisotropic diffraction gratings in a polymer-dispersed liquid crystal by polarization modulation using a spatial light modulator

Anisotropic diffraction gratings based on a holographic polymer-dispersed liquid crystal (HPDLC) are realized by interferometric exposure using a spatial light modulator (SLM). The SLM is used in the HPDLC grating formation for anisotropic holographic recordings of two-dimensional polarization states for an incident light beam. The diffraction efficiency for P-polarization and the distinctive ratio of diffraction efficiency in P-polarization to that in S-polarization increases with the signal level applied to the SLM. The resulting volume gratings exhibit diffraction efficiency of more than 60% and a distinctive ratio of diffraction over 100. The microscopic origin of the anisotropic property is investigated by an optical polarizing microscope. The novel characteristics of the anisotropic diffraction properties of HPDLC are applied to an image reconstruction technique.     

利用FPGA实现红外焦平面阵列实时非均匀性校正

实时非均匀性校正是红外成像的一项关键技术。根据红外焦平面阵列探测元光谱响应的特点和基于参照源的两点温标非均匀性校正理论，提出一种利用FPGA硬件实现红外焦平面阵列实时非均匀性两点校正的新方法。该方法动态范围大、处理速度快，适用于红外成像系统实时图像处理场合。仿真和实验结果证明是可行的。     

Parametric optimization of narrow bandstop optical filters using the self-suspended subwavelength grating for TE polarization

Instead of a conventional fixed multilayer grating, a self-suspended subwavelength grating (SSG) which consists of a single grating layer and possesses tunable functions, is investigated by the rigorous coupled-wave method in detail. Through optimizing various parameters including the incident wavelength, the grating period, the grating thickness and the grating filling factor, we demonstrate that the silicon dioxide (SiO₂) SSG owns a narrow reflectance linewidth in the case of TE polarization. For the SiO₂ SSG, the reflectance peak splits into two branches when the incident light deviates from normal incidence. In addition, the reflectance property of the SiO₂ SSG with unoptimized parameters is also presented for comparison, which exhibits a much larger reflectance linewidth. It is expected that the SiO₂ SSG should be used as narrow bandstop optical filters for TE polarization in micro optics systems.     

Tunable liquid crystal microlens array using hole patterned electrode structure with ultrathin glass slab

A configuration of hole patterned electrode liquid crystal microlens array with an ultrathin glass slab was fabricated. To reduce the fringing electric field effect and avoid the occurrence of disclination lines, an ultrathin glass slab was introduced between the patterned electrode and liquid crystal layer. The glass slab thickness played an important role in effecting the optical performance of the liquid crystal microlens array. An optimum thickness of 30 μm was selected employing numerical simulation method. Using this method, we demonstrated a microlens array that greatly improved the phase profile and focus power. The dynamic focal range of the liquid crystal microlens array may extend from <1.2 mm to >8 mm and the minimum diameter of the focus spot could be as small as 15 μm.     

Holographic femtosecond laser processing using optimal-rotation-angle method with compensation of spatial frequency response of liquid crystal spatial light modulator

Holographic femtosecond laser processing performs high-speed parallel processing using a computer-generated hologram (CGH) displayed on a liquid crystal spatial light modulator. A critical issue is to precisely control the intensities of the diffraction peaks of the CGH. We propose a method of compensating for the spatial frequency response in the design of CGH using the optimal-rotation-angle method. By applying the proposed method, the uniformity of the diffraction peaks was improved. We demonstrate holographic femtosecond laser processing with two-dimensional and three-dimensional parallelism.     

Three-dimensional-two-dimensional mixed display system using integral imaging with an active pinhole array on a liquid crystal panel

A display system that simultaneously displays two-dimensional (2D) and three-dimensional (3D) images using a pinhole array on a liquid crystal (LC) panel is proposed. Using the transparent structure of the LC panel, the system can generate or eliminate pinholes electrically and can display a 3D image in a selectable specific area of the display panel, while 2D images are displayed on the rest of the screen. An analysis showing the advantages and limitations of the proposed system is provided. Finally, the proposed principle is proven by experimental results.     

Study of the dynamic characteristics of polymer-dispersed liquid crystal compositions: Prospects for optoelectronic applications of fullerene complexes with phthalocyanine nanocrystals

The switching and modulation characteristics of fullerene-containing polymer-dispersed liquid crystal structures involving fullerene complexes with magnesium phthalocyanine nanocrystals are studied for the first time. It is established that these systems are characterized by small switching times of the electrooptical response to pulsed drive voltage under the conditions of cw He-Ne laser irradiation. It is suggested that effective charge carrier production in the structures doped with pure phthalocyanine leads to frustration of a homogeneous orientation of the liquid crystal mesophase, which is restored upon adding C₆₀and/or C₇₀ fullerenes. A possible reorientation mechanism is considered and it is shown that fullerene-containing polymer-dispersed liquid crystal systems with distributed orientation related to the presence of fullerene complexes with magnesium phthalocyanine can be used for the effective switching of electrooptical response and have good prospects for application in the systems of optical data processing and in display technologies.     

Modeling of the diffraction efficiency and polarization sensitivity for a liquid crystal 2D spatial light modulator for reconfigurable beam steering

A nematic liquid crystal spatial light modulator used as a phase-modulating device and operating in the reflective mode is analyzed using three-dimensional modeling. Two configurations, which differ in their electrode placement relative to a fixed quarter-wave plate, are considered across a range of steering directions, with the grating conformal and in some cases oblique to the pixel grid. For each steering direction the sensitivity of the diffraction orders to the polarization state of the incident wavefront is studied. Optimal alignment of the liquid crystal is suggested to reduce this sensitivity.     

液晶光学相控阵的改进型口径拓展方法及远场特性分析

天线通光口径是液晶光学相控阵的重要技术指标,本文在多子阵并行驱动和两级器件级联方法(PAPA)的基础上,提出改进型的i-PAPA方法,通过对COM电极进行分区域驱动,在单个相控阵天线上实现大口径相控光束控制,具备单器件工作、插损低等优点。通过数值仿真分析,结果表明：相控阵天线后的近场相位分布连续;当指向角度在0°到+6°范围内,远场衍射效率和指向角度的数值关系呈现平滑单调下降,衍射效率均大于48%;当指向角度在0°到+3°范围内,衍射效率均大于80%。     

Optical sensors for electric substations: a voltage presencedetector using a liquid crystal cell

A new fiber optic voltage presence detector is presented, based on the detection of the excitation state of a liquid crystal cell by means of an optical technique. The sensor was designed to work in electric metal-clad medium-voltage (MV) switchboards with SF₆ insulation where EM immunity and insulation requirements make fiber optic sensing the most suitable choice. The small size of the probe, its high reliability, and its low cost make it especially suited for these compact structures. Working principle and design details are reported