Numerical Simulation Method for a Liquid-Crystal Aberration Compensation Device

In this study, we report the improved response time of a thick nematic liquid crystal (LC) device by using an electrospun nanofiber (NF). We investigated the influence of NF characteristics including polymer material, NF volume ratio, and diameter, on the electrical characteristic of the NF/LC composite. A conventional LC device and a polymer-stabilized liquid crystal (PSLC) device were fabricated to compare their electrical characteristics with those of the NF/LC composite. The rise time, decay time, and threshold voltage of these LC devices are determined by measuring the dielectric permittivity. In comparison with the conventional LC device, the decay time of the NF/LC device is significantly improved. Compared with the PSLC device with the same thickness, the NF/LC device shows a lower threshold voltage while exhibiting the same decay time. Finally, we demonstrated the markedly improved response time of a THz phase shifter by using an NF/LC composite.

Liquid crystal (LC) devices are described, which modulate the orientation of incoming linearly polarized light. The reorientation is due to the twisted nematic effect and is therefore achromatic. In contrast to practically all other LC devices, the elements described here use alignment layers with modulated orientations [1]. Two new classes of LC devices will be considered. First, LC devices with macroscopic modulations leading to polarization converter devices will be examined. They are capable of generating linearly polarized light with axial symmetry, the beam propagation axis representing the symmetry axis [2]. When such polarization converters are illuminated with circularly polarized light they behave as achromatic spiral phaseplates [3] of integer order.

We have developed a novel transmissive nematic liquid crystal device which is capable of compensating spherical wavefront aberration that occurs during the operation of optical pickup systems. In order to increase the storage capacity, next generation optical data storage systems beyond CD and DVD will use according to the Blu-Ray specification (BD) blue laser light and an objective lens with high numerical aperture (N.A.) of 0.85. However, such high N.A. systems have an inherent higher sensitivity on aberrations. For example spherical aberration is inversely proportional to the wavelength and grows with the fourth power of N.A. of the objective lens. In an optical pickup system there are two sources for spherical aberration: The first one is the variation of the substrate thickness due to manufacturing tolerances under mass production conditions. The second one concerns disks with multiple data-layers, which cause spherical aberration when layers are switched, as the objective lens can only be optimized for a single layer thickness. We report a method for effective compensation of spherical aberration by utilizing a novel liquid crystal device, which generates a parabolic wavefront profile. This particular shape makes the device highly tolerant against lateral movement. A sophisticated electrode design allows us to reduce the number of driving electrodes down to two by using the method of conductive ladder mashing. Further evaluation in a blue-DVD test drive has been carried out with good results. By placing the device into an optical pick-up we were able to readout a dual-layer ROM disk with a total capacity of 50 gigabytes (GB). A data-to-clock jitter of 6.9% for the 80 μm and of 8.0% for the 100 μm cover layer could be realized.

Light wave propagation in liquid crystal displays by the 2-D finite-difference time-domain method

Photo-embossing has been developed as a convenient and economical method for creating complex surface relief structures in polymer films. The pursuit for large aspect ratios of the photo-embossed structures has never stopped. Here, we demonstrate a simple strategy to obtain improved aspect ratios by adding a quick solvent developing step into the photo-embossing process. A good solvent for the monomer is used to remove unreacted monomers from the unexposed region, resulting in deepened valleys of the surface reliefs. In a polymer film as thin as 2.5 µm, the height of the surface reliefs can be increased by a factor of three to around 1.0 µm. This strategy is also shown to be compatible with other methods used to improve the aspect ratios of the photo-embossed structures. Lastly, we employ these surface relief structures in the fabrication of liquid crystal (LC) devices and investigate their performances for visible light regulation.

Variation in extremely-weak photon counts with changing gate time was investigated using a Mach–Zehnder interferometer and a liquid crystal (LC) device. The number of photon counts per unit time of measurement was miniaturized, and changes in the discrete counts were observed by changing the gate time. In addition, changing the voltage applied to the LC device confirmed that the average photon count in the extremely weak light state can be treated statistically and changes according to the Poisson distribution. This indicates that the photons flew independently. This phenomenon is considered a promising simple variable photon light source for Boson sampling.

Fully logical NOT operation of self-aligned liquid crystal optical control devices with two-slit Young’s interference experiment

In this paper, we propose a novel approach for realising a nematic liquid crystal 128 × 128 elements cylindrical lens array. This liquid crystal-cylindrical lens array is realised with an element clear aperture of 200 μm × 60 μm. In addition, its electro-optical feature is tuneable via the change of external electric field frequency. Based on the equivalent circuit theory proposed, the electro-optical features of the proposed liquid crystal-cylindrical lens array are analysed from the electric perspective. Experiments have been conducted to confirm the validity of the proposed algorithm. According to the experimental result, the liquid crystal device is able to focus collimated light in the range of 20–600 μm when the frequency of the applied voltage ranges from 100 Hz to 100 KHz. Thus, the effect of frequency-driving focusing is similar to that of applied voltage-driving focusing, which suggests a new way for liquid crystal device driving. Besides, power consumption of liquid crystal devices can also be reduced with the proposed method.

In this paper we propose a new approach to fiber optic voltage sensors via voltage-controlled Liquid Crystals (LC), which would allow direct measurement of up to 400 kV/m electric fields at multiple points. In addition, the electro-optical behavior of deformed helix ferroelectric (DHF) liquid crystal in reflective mode is described and tested. The electrically controlled reflectance has been measured at sub-kilohertz driving voltage frequency for different polarizations of the incident light. Full Text: PDF References Y.V. Izdebskaya, V.G. Shvedov, A.S. Desyatnikov, W. Krolikowski and Y.S. Kivshar, "Soliton bending and routing induced by interaction with curved surfaces in nematic liquid crystals", Opt. Lett. 35, 1692-1694 (2010). CrossRef Z. Ge, S. Gauza, M. Jiao, H. Xianyu and S.T. Wu, "Electro-optics of polymer-stabilized blue phase liquid crystal displays", Appl. Phys. Lett. 94, 101104 (2009). CrossRef Z. Brodzeli, F. Ladouceur, L. Silvestri, A. Michie, V. Chigrinov, G. Q. Guo, E. P. Pozhidaev and A. D. Kiselev, "Liquid crystal-based hydrophone arrays", APOS (2012). CrossRef T. Tanigawa, Y. Sakakibara, S. Fang, T. Sekikawa and M. Yamashita, "Spatial light modulator of 648 pixels with liquid crystal transparent from ultraviolet to near-infrared and its chirp compensation application", Opt. Lett. 34, 1696-1698 (2009). CrossRef K. H. Yang and T. C. Chieu, "Transport Properties of Ions in Ferroelectric Liquid Crystal Cells", Jpn. J. Appl. Phys. 28, 2240-2246 (1989) CrossRef I.C. Khoo and S.T. Wu, "Optics and Nonlinear Optics of Liquid Crystals", World Scientific, Singapore (1993). V.G. Chigrinov, "Liquid Crystal Devices: Physics and Applications", Artech House, Boston: London, (1999). A.D. Kiselev, E.P. Pozhidaev, V.G. Chigrinov and H.S. Kwok, "Polarization-gratings approach to deformed-helix ferroelectric liquid crystals with subwavelength pitch", Phys. Rev. E 83, 31703 (2011). CrossRef N. A. Clark and S. T. Lagerwall, "Submicrosecond bistable electro-optic switching in liquid crystals", Appl. Phys. Lett. 36, 899-901 (1980). CrossRef L.A. Beresnev, V.G. Chigrinov, D.I. Dergachev, E.P. Pozhidaev, J. Funfshilling and M. Schadt, "Deformed helix ferroelectric liquid crystal display: A new electrooptic mode in ferroelectric chiral smectic C liquid crystals", Liq. Cryst. 5, 1171-1177 (1989). CrossRef Z. Brodzeli, H.K. Bal, V.G. Chigrinov, A. Murauski, and F. Ladouceur, "Electrical energy harvesting device for current/voltage fibre-based sensors", Optical Fibre Technology (ACOFT), 2010 35th Australian Conference on Fibre Technology, 1-2, (2010). DirectLink X. Zhao, F. Boussaid, A. Bermak and V.G. Chigrinov, "High-resolution thin ?guest-host? micropolarizer arrays for visible imaging polarimetry", Opt. Exp. 19, 5565-5573 (2011). CrossRef X.H. Li, A. Murauski, A. Muravsky, P.Z. Xu, H.L. Cheung, and V. Chigrinov, "Grayscale Generation and Stabilization in Ferroelectric Liquid Crystal Display," J. Display Technol. 3, 273-279 (2007). CrossRef E.P. Pozhidaev, S. Torgova, M. Minchenko, C. Yednak, A. Strigazzi and E. Miraldi, "Phase modulation and ellipticity of the light transmitted through a smectic C* layer with short helix pitch", Liq. Cryst. 37, 1067-1081, (2010). CrossRef E.P. Pozhidaev and V.G. Chigrinov, "Bistable and multistable states in ferroelectric liquid crystals", Crystallography Reports. 51, 1030-1040 (2006). CrossRef Q. Guo, F. Fan, T. Du, and V.G. Chigrinov, "Electrooptic Response of FLC: Effect of Alignment Materials", SID'11 Conference, P-144, Los Angeles, USA, May, (2011). CrossRef G. Hegde, P. Xu, E.P. Pozhidaev, V.G. Chigrinov, and H.S. Kwok, "Electrically controlled birefringence colours in deformed helix ferroelectric liquid crystals", Liq. Cryst. 35, 1137-1144 (2008). CrossRef

16 - Electrooptical Properties of Polymer–Liquid Crystal Mixtures

The first part of this tutorial text discussed many of the standard approaches to image stabilization, focusing on optical correction for optical systems. Image-stabilization technology continues to grow and expand and new devices are constantly evolving. Two devices of particular interest are liquid crystal (LC) spatial light modulators and orthogonal transfer CCDs. These devices are being introduced into systems and provide novel, compact means for image stabilization. Microelectro-mechanical systems (MEMS) are now available for motion and vibration detection and can be used to provide mechanical sensing and compensation in optical systems. The idea of using LC as corrective elements dates back to the early 1980s. However, at that time LC technology was not developed enough to produce usable devices. Things started to change dramatically in the early 1990s, thanks especially to display-technology research and investments. Now, LC devices are available for use in laboratory setups and first telescope demonstrations.

Molecular orientation states in the liquid crystal (LC) cell can easily be deformed and change their properties by applying low driving voltage with low power consumption. Those features are also attractive for the various functional devices in the wider frequency regions such as a millimeter wave (MMW), although only the optics applications are well investigated as the display application is put the head of them. Waveguide systems are well known as an excellent way to make a low loss transmission circuit in the ultrahigh frequency region such as microwaves and MMWs, and then the LC devices utilizing the waveguide have been proposed so far. However, the planar waveguide has gathered many attractions for the wider functionality by integration. We adopt here a coplanar waveguide (CPW) substrate to prepare the planar type of LC MMW devices combined with an ITO glass substrate. Since the ITO film acts as a floating electrode to simplify the electrode structure, LC molecules can be driven by applying the voltage only to the CPW substrate. Unfortunately, since the ITO electrode close to the CPW decreases the transmission of the MMW, the molecular orientation effects related with the electrode structure are very important to minimize the electrode area. We prepare the transparent LC cell which has exactly the same electrode structure with the CPW LC cell, and observe the molecular orientation states in detail by using a polarization microscope. It becomes clear that only the narrow area above the signal electrode of the CPW affects strongly to the phase change of the MMW propagation in the CPW type LC cell.

The bulk and surface properties of liquid crystals are very important for the performance of liquid crystal displays and devices. The bulk properties of thermotropic liquid crystals depend strongly on the molecular structure and on the molecular interactions. The liquid crystal surface properties, which is of vital importance for the alignment of the liquid crystals and thus for the appearance and operation of these devices, depends, in addition, on the solid surface-liquid crystal interactions. Both liquid crystal physical properties can effectively be controlled by external factors that result in changes of the molecular structure and, hence, of the molecular properties. Here, we report on the reversible changes of bulk and surface liquid crystal properties caused by the photoisomerisation process that takes place in the organic photochromic materials. The photocontrol of these physical properties could be utilized in liquid crystal devices such as all-optical switches, light modulators and optical memories.

Vertically aligned carbon nanotube (VA-CNT) arrays were grown on several chromium (Cr)-coated glass substrates using a plasma-enhanced chemical vapor deposition system. The CNTs were 2μm long and had a site density of 2×10^{9}cm^{-2} on the substrates. Two VA-CNT slides on Cr glass substrates were put together to design a homeotropic electro-optic liquid crystal (LC) device. A negative dielectric anisotropic LC was used in the device. The π-π stacking interaction between the LC and the VA-CNTs allows the LC material to align homeotropically in the cell. When an external electric field was applied using the transparent conducting Cr layers, the LC achieves a planar orientation above a threshold field. These results successfully demonstrate the optical, electro-optical operations, and the field-induced dynamic response of a homeotropic LC device employing the VA-CNT arrays as the homeotropic-alignment agent. This study significantly advances the range and understanding of nanostructured surfaces that provide vertical alignment of LCs.

We propose an optical manipulation system for simultaneously trapping and controlling the positions of microscopic multiple particles by using a liquid crystal (LC) optical device and a condenser lens. The positions of the multiple particles trapped at the bright region of the linear interference fringe patterns can easily be shifted along the fringe patterns by controlling the applied voltage to the LC optical device.