Electrically tunable microlens arrays based on polarization-independent optical phase of nano liquid crystal droplets dispersed in polymer matrix

LC-based lightfield camera prototype for rapidly creating target images optimized by finely adjusting several key coefficients and a LC-guided refocusing-rendering

A lightfield camera prototype is constructed by directly coupling a liquid-crystal (LC) microlens array with an arrayed photosensitive sensor for performing a LC-guided refocusing-rendering imaging attached by computing disparity map and extracting featured contours of targets. The proposed camera prototype presents a capability of efficiently selecting the imaging clarity value of the electronic targets interested. Two coefficients of the calibration coefficient k and the rendering coefficient C are defined for quantitively adjusting LC-guided refocusing-rendering operations about the images acquired. A parameter Dp is also introduced for exactly expressing the local disparity of the electronic patterns selected. A parallel computing architecture based on common GPU through the OpenCL platform is adopted for improving the real-time performance of the imaging algorithms proposed, which can effectively be used to extract the pixel-leveled disparity and the featured target contours. In the proposed lightfield imaging strategy, the focusing plane can be easily selected and/or further adjusted by loading and/or varying the signal voltage applied over the LC microlenses for realizing a rapid or even intelligent autofocusing. The research lays a solid foundation for continuously developing or upgrading current lightfield imaging approaches.

Polarization-Dependent Gratings Based on Polymer-Dispersed Liquid Crystal Cells with In-Plane Switching Electrodes

A diffraction grating of polymer-dispersed liquid crystal (PDLC) with polarization-selective characteristics is investigated. Electrically controllable gratings are produced using In-Plane Switching (IPS) electrodes. Indium tin oxide (ITO) electrodes with a stripe pattern are used to generate a horizontal electric field parallel to the substrate on a single glass substrate. It is known from the experimental results that the number of diffraction orders can be controlled by applied voltage. Except for the zeroth order, the consistently highest intensity can be obtained for every other order of diffraction, and the polarization direction of the diffraction is perpendicular to the direction of the electrode stripes. The polarization direction of the zeroth order diffraction is parallel to the direction of the electrode stripes. Therefore, it can be used as a filter for light polarization.

Organic Solvent Sensors Using Polymer-Dispersed Liquid Crystal Films with a Pillar Pattern

An organic solvent sensor of polymer-dispersed liquid crystals (PDLCs) film is fabricated by a combination of tri-functional monomers and LCs. When the patterned PDLC film comes into contact with the organic solvent, the organic solvent will penetrate into the film to induce the orientation of the liquid crystals, which will change from an ordered to a disordered state, which causes the PDLC film to scatter incident light. The experiment used acetone and ethanol as the organic solvents of interest. The results show that the patterned PDLC film has a stronger response to acetone than to ethanol. Based on the difference in the intensity of light scattering and the response time of the patterned PDLC film to different organic solvents, the results can be used to identify and recognize different types of organic solvents.

Recent Advances in The Polymer Dispersed Liquid Crystal Composite and Its Applications

Polymer dispersed liquid crystals (PDLCs) have kindled a spark of interest because of their unique characteristic of electrically controlled switching. However, some issues including high operating voltage, low contrast ratio and poor mechanical properties are hindering their practical applications. To overcome these drawbacks, some measures were taken such as molecular structure optimization of the monomers and liquid crystals, modification of PDLC and doping of nanoparticles and dyes. This review aims at detailing the recent advances in the process, preparations and applications of PDLCs over the past six years.

Helical pitch-dependent electro-optics of optically high transparent nano-phase separated liquid crystals

Feeble light leakage in a dark state of conventional optically isotropic liquid crystal (OILC) device has a strong impact on the contrast ratio of a liquid crystal (LC) device. In order to overcome such intrinsic problem, we proposed an OILC in which the LC directors inside droplets are twisted by introducing chirality. The light leakage is effectively suppressed by matching the refractive indices between LC and polymer matrix; consequently, we achieved a high contrast ratio, 1:1401. Interestingly, the on-state transmittance is enhanced by ~49% compared to conventional OILC. The response time was also improved and the hysteresis was suppressed to be negligible. The improved electro-optic performances of the proposed OILC device would give diverse applications in upcoming flexible display and various photonic devices.

Photo-Polymerization in Chiral Dopant Liquid Crystal Cells via Holographic Exposure to Fabricate Polarization-Independent Phase Modulator with Fast Optical Response

Small liquid crystal domains with random director distributions were obtained to show novel optical isotropy using a holographic exposure processes to treat chiral dopant liquid crystal cells in the isotropic phase (i.e., polymer-stabilized isotropic liquid crystal cells). The cells used to fabricate phase modulators showed unique performances, including low light scattering, polarization-independence, and fast optical response. Furthermore, an extra fluoro-surfactant dopant in cells showed that the phase modulators retained their performance but with considerable reduction of operating voltages, from 180 Vrms to 100 Vrms.

Fast response and transparent optically isotropic liquid crystal diffraction grating

We have demonstrated an electrically tunable less polarization sensitive and fast response nanostructured polymer dispersed liquid crystal (nano-PDLC) diffraction grating. Fabricated nano-PDLC is optically transparent in visible wavelength regime. The optical isotropic nature was increased by minimizing the liquid crystal droplet size below visible wavelength thereby eliminated scattering. Diffraction properties of in-plane switching (IPS) and fringe-field switching (FFS) cells were measured and compared with one another up to four orders. We have obtained a pore-type polymer network constructed by highly interlinked polymer beads at which the response time is improved by strong interaction of liquid crystal molecules with polymer beads at interface. The diffraction pattern obtained by transparent nano-PDLC film has several interesting properties such as less polarization dependence and fast response. This device can be used as transparent tunable diffractor along with other photonic application.

Origins of Kerr phase and orientational phase in polymer-dispersed liquid crystals

Polymer-dispersed liquid crystals (PDLCs) modulate the amplitude and optical phase of light. The optical phase modulation of PDLC can be dissected into two parts: Kerr phase and orientational phase according to the electro-optical (EO) response. We investigated the origins of the Kerr and orientational phases in PDLCs and their connection with the two-step EO response. The Kerr phase is attributed to LC orientation in the center of LC droplets. The orientational phase results from orientation of LC molecules near LC-polymer interfaces. Both phases can be adjusted by varying the droplet size. The two-step EO response in small droplets (<333 nm) is related to the Kerr and orientational phases, and possibly to rotation of point defects. A modified PDLC model considering the Kerr and orientational phases is proposed. Our findings suggest the possibility of versatile photonic devices using pure optical phase modulation.