This PDF file contains the front matter associated with SPIE Proceedings Volume 11303, including the Title Page, Copyright information, Table of Contents, Author and Conference lists

By controlling the deposition time of indium–tin–oxide (ITO) film, a high resistance of ultra-thin ITO (UTITO) layer can be realized. The UTITO layer is then deposited at the interface between the dielectric and LC layers in the hole-patterned liquid crystal (LC) lens. The UTITO application spreads the fringing field into the aperture hole center of LC lens and thus assists the LC reorientation therein. That considerably decreases the addressing voltage and switching-on time of LC lens. The UTITO LC lens also provides a wide tunable focus function, and preserves the lens quality and imaging performance as the conventional hole-patterned LC lens.

Liquid crystal based lenses with variable focal length are of broad interest due to their wide area of applications ranging from techniques to medicine. We present the modeling approaches and results for a couple of tunable liquid crystal based lenses, namely: curved electrode lens, lens with hole patterned electrode and high resistivity layer, lens based on modulated anchoring and contact lens. We also discuss the current challenges associated with the modeling of LC lenses and possible ways to overcome them.

Accurate optical modeling for design and optimization of liquid crystal on silicon spatial light modulators (LCoS SLMs) is important for phase-related applications. Traditional matrix method cannot accurately predict the optical performance when the LC distribution is complex, therefore the rigorous finite element method (FEM) is preferred. However, the optical modeling of LCoS is a multidimensional problem, which is difficult to simulate with FEM. Here, we present the development of an improved FEM by combining the scattering matrix method with the domain decomposition method to reduce the computational burden for optical simulation of LCoS. Furthermore, a 2D simulation example with phase grating displayed on LCoS is presented and compared with experiment.

We have demonstrated a Liquid crystal (LC) analog phase modulator based on the flexoelectric-optic effect that can achieve full 2π phase modulation with sub-millisecond switching speed. The LC mixture in the device consists of the bimesogen CBC7CB with chiral dopant R5011 that can exhibit ±𝜋/4 rotation of the optic axis for an electric field of ±4.2Vμm^(-1). This is then converted to a ±π phase modulation with the aid of a chiral reflector and a quarter waveplate. The residual amplitude modulation is found to be very low, and we show how these elements can be combined to form a integrated device.

Hyperbolic metamaterials are uniaxial birefringent materials with the eigenvalues of the tensorial permittivity opposite in sign. In this work, we were interested in homogeneous hyperbolic metamaterials with optical axis spatially varying in a defect manner, and observing how such structure in uences the extraordinarily polarized light wave. More broadly, this work is an attempt towards realising liquid crystal-like performing metamaterials.

We have developed reverse- and normal-mode thermoresponsive polymer network liquid crystals (PNLCs) that are applicable to switchable windows and other devices. Our nonuniform photoirradiation is an easy technique to produce meso- (submicron- to micron-) scale phase separation of orientation-ordered liquid crystals (LCs) with (an)isotropicpolymerized reactive mesogens (RMs) and achieve various thermoresponsive light attenuators. The PNLCs were fabricated in a simple self-assembling process through photopolymerization induced phase separation (PPIPS) by nonuniform irradiation. The size of phase-separation domains and the orientation order of LC molecules in the domains are intrinsic factors to produce high transparence at low temperatures and intense light scattering at high temperatures. Their factors are controlled by size of laser speckle patterns projected on the samples during PPIPS in nonuniform irradiations. Optical polarization property of the transmittance spectrum is also controlled by speckle patterns projected on the sample in the nonuniform irradiation. Different microscopic structures of PNLCs were formed depending on the size of speckle patterns but not simply in proportion to the size. The results suggest that the dynamics of domain formation through PPIPS is connected to the competition between intrinsic nature of phase separation and extrinsic influence by nonuniform light intensity in the irradiated area.

This Conference Presentation, Bio-inspired photo-actuation based on cholesteric liquid-crystal elastomers with photosensitive derivatives was recorded at Photonics West 2020 held in San Francisco, California, United States.

Generation of topological defect that has a particular type (topological charge) and specific shape (radial, spiral, or circular) on a designed position is a crucial step in producing q plates and defect-mediated self-assembled micro structures. Shaping and positioning of topological defects can be achieved by applying delicately designed electric field on nematic liquid crystal (NLC). The guidelines for the electrode design are provided in this paper. The following are the three frequently asked questions: 1) What kinds of defects can exist in NLC? Points, lines, or walls? 2) How to generate a defect with a particular topological charge by setting proper boundary condition? 3) How to control the orientation of liquid crystal to have a defect with desired vorticity? The three questions can be answered by the three theories in physics: 1) Symmetry breaking in ordered material, 2) Euler characteristic and vectors in closed confinement, and 3) Minimization of free energy of NLC in electric field. Topological defects in spherical and toroidal confinements were generated in NLC cell and examined under polarized microscope. Radial and circular hedgehog defects were successfully created by fishbone- and coil-shaped patterned electrodes, respectively. By applying the three physical theories in NLC cell design, topological defects were successfully arranged in square and hexagonal arrays. They are large, stable, and re-configurable, and the applications in optics are demonstrated.

Photo-alignment materials are widely used for liquid crystal displays (LCDs) due to dustless and easy to realize fine patternings. In 2009, the Sharp UV²A (Ultra violet induced multi-domain Vertical Alignment) technology was applied to LCDs for the first time in the world. In order to commercialize ultra-high definition displays such as 8K in UV²A display, there are two challenges in photo-vertical alignment materials. The first is lowering pre-tilt angle for improvement of panel transmittance, and the second is application of low temperature cure process with NMP-less alignment materials for wide color gamut. While The transmittance of 8K displays is much lower than full-high definition or 4K because the ratio of disclination region (dark line) and black matrix increases as the pixel size decreases, the low pre-tilt angle property enables to narrow dark line width. The low temperature cure process with NMP-less alignment material may realize to apply high performance color filter (CF) materials (e.g.: dye-based CFs). In this paper, we developed novel low pre-tilt angle material (New-AL) with excellent propeties of alternating current image sticking and a wide range of pretilt angle between 84 degrees and 90 degrees by polarized ultra-violet exposure dose. Furthermore, not only New-AL can be applied to low temperature cure process even at 120 °C, but also New-AL is prospective NMP-less material which enables to apply dye-based CFs due to better solubility than the conventional materials.

A liquid crystal (LC) phase grating devices have been studied actively because of their outstanding features, such as the high diffraction efficiency, large diffraction angle, no diffraction at the initial state, and the simple fabrication process. It can be used to control the haze value owing to its high diffraction efficiency. Although it can be operated with low power, power consumption needs to be further reduced because it requires power to maintain the diffraction. To reduce the power consumption in a phase grating device, bistable operation, which consumes power only while it is being switched between the states, is necessary. In this paper, we will introduce bistable LC phase grating devices which can provide a translucent state with a high haze value thanks to its strong diffraction. Moreover, it can be operated with very low power as the transparent [translucent] state is maintained even after the applied vertical [in-plane] electric field is removed. We believe that these devices can be one of the new candidates for power-saving smart window or window display applications.

We discuss the electric field tuning of ferroelectric liquid crystal microlasers. The microlasers were made of 90:10 wt % mixture of CE3 and CE14 ferroelectric liquid crystals (FLCs), which was doped with ~0.1% Pyrromethene 580 fluorescent dye. The ferroelectric Sm C* phase was observed between 42°C and 74°C. The droplets were embedded into the CYTOP CTX-809A, a polymer with low electric conductivity and high viscosity. Within the temperature range 42-60°C the droplets obtained good homeotropic structure with the perpendicular anchoring of the molecules to the surface of the droplets. When the droplets were illuminated with a 532 nm pulsed laser light, Whispering Gallery Mode lasing was observed. The application of a low frequency electric field induced a red-shift of the WGM resonance peaks. The shift was reversible and had a quadratic dependency on the electric field. The observed tuning range was 4.5 nm for 2 V/μm applied electric field. The observed behaviour is explained by the soliton-like deformation of the helical ferroelectric Sm C* structure in an external electric field.

An SSD (Smectic Single Domain) liquid crystal panel was investigated of its in-plane retardation switching behavior. Focused factor in terms of retardation switching behavior was azimuthal anchoring strength of an SSD panel. The empirical approach clarified that as long as azimuthal anchoring at the surface of the panel was strong enough to keep initial liquid crystal molecular alignment forming as a “quasi-Smectic A” like uniform molecular stacking, its retardation switching was completely in-plane only. A thicker panel gap of an SSD panel having not strong enough azimuthal anchoring strength throughout the panel gap provides some local twisted molecular stacking, resulting in mixing some limited out-of-plane retardation switching. These dynamic retardation switching measurements have been with relatively simple optical measurement set-ups. Using a crossed Nicols optical setting whose incident light to sample panels is linearly polarized light, light throughput behavior was observed. With using additional pair of quarter wave plates whose incident light is circularly polarized light, in-plane only retardation dynamics was measured. Although quantitative lift-up angle which causes out-of-plane retardation switching still requires further detail investigation, this series of research has clarified surface azimuthal anchoring significance on in-plane only retardation switching behavior, and such relatively simple optical measurement provides an overall molecular stacking configuration at an SSD-LC panel. The quantitative lift-up angle during the switching at an SSD-LC panel is even possible with precision light throughput amount measurement. This approach would possibly provide some local molecular twisted stacking detail at an SSD liquid crystal panel.

The use of terahertz waves for imaging has been studied intensively from the scientific, medical, and industrial viewpoints. Phase information is important for terahertz imaging and thus several kinds of phase detection methods for terahertz waves have been reported. Phase imaging using continuous wave terahertz interferometry has the advantage of having a high signal-to-noise ratio. Phase-shifting interferometry by using a liquid crystal (LC) phase shifter is a possible candidate for terahertz phase imaging. Accordingly, it has several advantages, such as a simple experimental setup and a low drive voltage. In our previous research, we confirmed that hydrogen-bonded LCs do not exhibit dichroism at 2.5 THz. Furthermore, hydrogen-bonded LCs exhibit higher birefringence in the terahertz range than in the visible range. Recently, we studied phase-shifting interferometry by using a hydrogen-bonded LC device. Since the hydrogen-bonded LC do not exhibit dichroism at 2.5 THz, the birefringence of the sample could be successfully obtained. To improve repeatability of this measurement, it is important to monitor the operational state of the LC phase shifter while making phase measurements. To simultaneously measure the phase of the sample and the degree of the phase shift of an LC device, we introduced a beam splitter and an additional detector into the phase-shifting interferometry technique. We report an improved measurement method for phase-shifting interferometry by using the LC phase shifter.

For broadband, mobile satellite communications applications such as autonomous driving, a high gain, scanning antenna is required. The satellite communications industry, however, is dominated by dish antennas mounted on motorized gimbals for these use cases. These solutions are too large, heavy, and power-consuming to offer solutions for consumer applications. We have addressed these issues by commercializing a novel, electronically scanned antenna technology, which is achieved using diffractive metasurfaces and high-birefringence radio frequency liquid crystals. This technology is positioned for mass production by leveraging the manufacturing capabilities of the LC display industry.

Laser-based displays suffer from speckle noise due to the random inference patterns of scattered coherent light from rough surfaces. Commonly utilized solution, such as moving diffusers, creates time-varying speckle patterns that were averaged on the observer’s retina or the image sensor. This solution requires the use of motorized parts and can be bulky with the potential risk of mechanical failure. We present a liquid crystal device that reduces speckle noise by over 90%. It is electrically driven, compact, and with no motorized parts. The randomized, time-varying domains with mismatched refractive indices of the liquid crystals produce varying speckle patterns. A near zero speckle contrast is achieved.

The challenges associated with developing a flexible defect-mode liquid crystal (LC) laser are addressed in this paper. To begin with, we discuss the process for creating a well-aligned photopolymerized film of chiral nematic LC using various surface alignment layers such as polyvinyl alcohol, sulphonic azo-dye and rubbed polyimide. A single mode flexible defect-mode laser is demonstrated with an excitation threshold fluence of 60μJ/cm2/pulse. In accordance with previous studies, results from simulations based on the 4×4 Berreman model show that the wavelength and the number of laser modes are determined by the thickness of the defect layer. The proposed flexible laser can be used to form lasers that can be integrated into conformable platforms and that can be used to control the beam direction without the need for additional optical components.

This Conference Presentation, Electrically-tunable holographic polymer stabilized liquid-crystal reflection gratings was recorded at Photonics West 2020 held at San Francisco, California, United States.

Electro-optic (EO) beam steering offers several important advantages over traditional mechanical steering approaches for applications such as laser communication, LiDAR and autonomous vehicles. These advantages include a lower cost, faster steering rates, and a random access beam pointing capability. While progress towards replacing mechanical steering approaches has been promising, challenges remain to achieve large aperture sizes with tunable steering directions. In this paper, we propose a unique liquid crystal based Pancharatnam Phase Device (PPD) for beam steering. The PPD has the advantageous property of allowing a continuous and unbounded optical phase delay across an aperture without requiring any phase resets, thereby maximizing steering efficiency. Our PPD architecture employs a linear array of phase control elements (PCEs) to locally orient the liquid crystal director into a cycloidal pattern for beam steering. The PCEs are comprised of a fringe field switching (FFS) electrode structure to create an in-plane electric field with low-operating voltages and a fast liquid crystal response time of around several milliseconds. Detailed modeling of the proposed design will be presented which demonstrates the design concept.

Nanophotonic all-optical devices have been enthusiastically studied to overcome the speed bottleneck of electrical devices. Recently, chalcogenide phase change material Ge2Sb2Te5 (GST) based active metasurfaces have emerged as a novel platform as complement of all-optical device. GST has two phase, so called amorphous and crystalline phases that can be changed within nanosecond scale by applying external thermal stimuli. Hence, various ultrafast 2-level switchable GST based meta-devices have been proposed and demonstrated. However, since only two switching levels are provided, there are limitations in applying to various photonic fields. In this paper, we expand its switching functionality to three-level through designing two different sizes of GST nanorod that exhibits different heat generation density in case of top-hat shape light illumination. Thanks to this thermo-optical phenomenon, we can obtain partial phase changed state, so called intermediate state once the appropriate intensity of control light is illuminated. Harnessing intermediate state, we propose novel cryptography platform that can provide high security level encryption while providing ultrafast communication speed.

Herein, a new type of smart glass fabricated by using a thermoswtichable salt hydrate with a microheater is reported. The supersaturated sodium hydrate solution is clear and transparent at the liquid, however, it turns solid and opaque state after mechanical impact. The nanomaterial-based transparent micro heater is suitable for flexible applications and it consumes low electrical energy due to its high electrical conductivity and high-efficiency of electrothermal effect. Considering the solubility of the sodium acetate in water and chemical properties such as water of crystallization, a phase transition from the liquid state to solid occurs in few seconds with rapid crystal growth of sodium acetate trihydrate. Therefore, it quickly blocks an intense sunlight and provides privacy protection. In reverse, the phase transition from the solid-state to the liquid is simply controllable within a few minutes by the microheater. Finally, we demonstrate a practical application of mechano-thermo-chromic (MTC) device by constructing a system, which operates by an external environment condition such as intense UV light.

We demonstrated a novel nanoparticle (NP) self-assembly method in a liquid crystal (LC) medium by exploiting two physical phenomena: (i) surface affinity contrast of isotropic pockets in nematic phase for ITO and self-assembled monolayer (SAM), and (ii) NP solubility contrast in isotropic and nematic phase. In the former phenomenon, the higher molecular roughness of ITO surface than SAM surface induced the higher surface affinity of isotropic pockets on the ITO surface. Hence, the isotropic pockets were anchored on the ITO islands of the patterned ITO substrate, while the nematic medium remained on the other area in which SAM was created. In the latter phenomenon, the uni-directional alignment in the bulk LC of nematic phase was mismatched with the one on the NP interface while the isotropic phase did not show any mismatch between the LC alignment in bulk and at the NP interface. The alignment mismatch in nematic phase resulted in the poorer NP solubility than it in isotropic phase. Hence, this large NP solubility contrast in two phases resulted in the NPs were confined to the isotropic pockets and dragged by the phase-boundary. By combining the two phenomena, we successfully fabricated the self-assembled NP cluster array on the ITO islands of the patterned ITO substrate. Since no electric or magnetic field is used in this method, it is applicable to a wide variety of NPs including ferroelectric, ferromagnetic etc. This method can potentially be utilized for fabrication of photonic crystals.

We synthesized 4-[7(4’-Cyanobiphenyl-4-yl)hexyloxy]bezoic acid (CBO7OBA) utilized as liquid crystal (LC) dopant. The CBO7OBA molecules form dimers with hydrogen bonding between molecules. We enhanced significantly the flexoelectric anisotropy of nematic LC mixture only with the small amount of doping of CBO7OBA. The flexoelectric anisotropy of mixtures of T04 (JNC) and ZSM50089 (JNC) doped with CBO7OBA molecules was enhanced 1.42 and 2.67 times compared with pure nematic LC, respectively.Moreover, we investigate the dependence of flexoelectric current on the bending effect of the virtual device. The flexoelectric current improved by about 2.9 times compared with pure LC due to the increase of the dipole moment and the bent-core structure of the dimer.