This PDF file contains the front matter associated with SPIE Proceedings Volume 12442, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Liquid Crystal (LC) devices for Terahertz (THz) phase shifters have a thick cell gap, which inevitably results in a very slow response, particularly when they rely on the passive relaxation of LCs. To vastly improve the response characteristics of LCs for use in THz phase shifters, we virtually demonstrate a novel type of LC switching in which all processes are governed by an electric field between in-plane and out-of-plane tristable states, resulting in hexadirectional switching with three orthogonal orientation states and thereby attaining a broader range of phase shifts. This type of LC switching is achieved using a pair of substrates that mirror each other, each of which has two pairs of orthogonally arranged finger-shaped electrodes for in-plane switching. Further, the two substrates each have one grating-shaped electrode, thus forming a pair of electrodes for out-of-plane switching. Each hexadirectional switching process between the tristable states is driven by an electric field, thus maintaining a rapid response by avoiding long relaxation times.

Driven by the need for new low-cost data communication technologies, liquid crystals are used not only by the display industry but also by companies in the satellite and telecommunications area. Recent developments in liquid crystal mixtures for tunable microwave components have led to material classes with substantially increased performance. High performance materials provide a high tunability with low associated dielectric losses meeting requirements of commercial applications. This presentation gives an overview about the state-of-the-art in liquid crystal materials for microwave applications, future development targets as well as emerging fields of applications.

We use few-cycle THz pulses to perform time-domain spectroscopy measurements of 8CB Liquid Crystal (LC). The measured absorption spectra for uniformly AC-aligned samples clearly indicate activity in the THz region: a set of strong bands above 4 THz followed by a broad plateau below are observed. DFT gas-phase calculations have been performed to assign the vibrational bands and to support the understanding of the observed features.

For next-generation mobile communications, the application of millimeter wave bands is being explored for high-speed and large-capacity communications. However, coverage holes occur because millimeter waves are found to be blocked by objects. To overcome this problem of coverage holes, we have developed a reconfigurable liquid crystal metasurface reflector by applying thin film transistor liquid crystal display technology. The developed reconfigurable liquid crystal metasurface reflector was designed to operate at 28 GHz, and the measurement findings confirmed that the reflection phase control range was 260° and exhibited equivalent reflection characteristics for both vertical and horizontal polarization. Furthermore, the reflection direction control function was confirmed by varying the reflection direction between 0° and 60° with several phase distributions.

In this work we install liquid crystal lasers into an optical setup as the light sources for generating holographic images. The replayed images of the liquid crystal laser beam modulated by a Spatial Light Modulator (SLM) are captured by a monochrome camera to analyze the image performances, including contrast-to-noise ratio and speckle contrast. Two alternative lasers, a gas He-Ne laser and a solid-state laser, are also installed in the optical path to show their replayed images from the SLM. The generated holographic images using these lasers as light sources are compared to demonstrate the potential of liquid crystals for holographic imaging applications.

We theoretically model two-dimensional waveguides with different surface perturbations and examine the effects of these perturbations on the transmission of light with wavelengths in visible and IR parts of the spectrum. Surface perturbations are modelled as sine, square and triangular waves with different amplitudes and periods, and as volumetric fractal-voronoi noise with different amplitudes and at different length scales. We use refractive indices which are characteristic for soft matter and solid-state photonics, in order to examine the effects of surface perturbations in different well-known systems. The effects of surface perturbations greatly depend on the wavelength and polarization of the incident light.

This study developed a Liquid Crystal (LC) device that incorporated lasers for machining with output power of the order of kW. The use of sapphire as a substrate along with an appropriate cooling system facilitated the LCs in enabling the control of the phase and polarization of high-power laser light, which is not possible in case of conventional LCs. The exposure of LCs to high-power laser light results in heat accumulation, which causes the destruction of the LC cells. As photochemical damage has a lower occurrence probability at longer wavelengths, the promotion of heat radiation is an important strategy for the application of LCs to near infrared laser beams. The phase control of laser beams up to 6 kW was achieved using the proposed LC substrate as a cooling plate and optimizing the cooling system. Moreover, we compensated for the variation in the properties of the LC with temperature via adjustments to the drive voltage of the LC.

A strategy of efficient laser emission with resonant feedback based on a microemulsion comprising of a Blue-Phase Liquid Crystal (BPLC), laser dye and block copolymer is presented here. BPLCs are produced and confined in microspheres with a microfluidic apparatus. These spatially assembled dye doped BPLC microdroplets are used to generate laser light. The topologically directed assemblies of BPLC microspheres with specific shape and symmetry are essential for reducing threshold and increasing Q-factor of laser emission. These results provide new avenues for a wide range of photonic applications.

One of the challenges in see-through AR headsets is rendering outdoor scenes when there is high ambient brightness. This is because in such conditions the luminance of real objects becomes comparable to or higher than the maximum luminance of the virtual object, severely impacting the virtual image contrast. One solution to this is to use LC-based ambient dimming cells to modulate background brightness. However, conventional glass LC cells add unwanted weight and volume to headsets and cannot be biaxially curved. This talk will explain how a breakthrough liquid crystal optics technology built on ultra-thin, light bioplastic films instead of glass uniquely enables active matrix pixelated ambient dimming on biaxially curved surfaces.

In our Augmented Reality (AR) project, we are investigating the use of a retinal projection display based on the association of pixelated holograms and a dense distribution of waveguides. We study the use of gratings impregnated with liquid crystal to actively extract light from waveguides. We explore two extraction strategies: tuning the refractive index contrast between the grating teeth and grooves to erase the grating diffraction effect and changing the index of the waveguide cladding to tune the evanescence of the guided mode. Firstly, we present and discuss the measurements of the diffraction efficiency of nano-imprint gratings impregnated with liquid crystal and refractive liquid index. Secondly, we discuss the results of integrated switchable extraction grating of the second strategy.

Leaning angle dependence of incident light beam throughput measurement effectively revealed in-plane only retardation switching characteristics of an SSD liquid crystal panel. In addition to in-plane only retardation switching, some influence of the initial molecular stacking configuration on retardation switching characteristics were clarified. Observed asymmetric light throughput change by leaning angle either clockwise, or counter-clockwise direction is attributed to surface pre-tilt influence of the SSD liquid crystal molecules.

We developed a liquid-crystal spatial light modulator having a 30 mm active area and a multilayered dielectric mirror for industrial infrared lasers to establish an innovative manufacturing and fabrication technique in the smart-manufacturing post-pandemic era. The reconstruction of computer-generated holograms was achieved to demonstrate the concept of this device in the IR region. The incident phase performance characteristics of this device under high-power laser irradiation were obtained using a 1030 nm ultrashort pulse laser. The work presented here will accelerate the use of liquid-crystal SLMs in high-precision laser processing of the process-resistant materials and high-throughput processing for additive manufacturing.

Self-assembled periodic micro-nanostructures triggered by responses to external influences often occur in anisotropic self-assembled supramolecular soft-matter systems (such as liquid crystal (LC) systems). However, these structures are often not easily to control or even change, e.g., orderliness of the structures. A pre-built 1D periodic microgroove structure on the planar cholesteric LC cell is used to study whether it can effectively improve the large-area order of the electro-induced 2D deformation structure. Experimental results show that the 2D microgrid structure caused by the Helfrich deformation of the CLC can be effectively controlled to be ordered macroscopically by the pre-built 1D periodic microgroove structure. Furthermore, the uniformity of the microgrid size is also improved. The findings enhance the potential applicability of the well-known Helfrich deformation phenomenon and provide an example for further control of periodic micro-nanostructures in self-assembled supramolecular systems.

Switchable optical elements incorporating polymer structure and a liquid crystal material offer devices with a voltage controlled spatially varying phase difference at low cost. The polymer structure may be fabricated using established replication techniques and suitable liquid crystal materials are readily available. The voltage controlled effective refractive indices in the liquid crystal regions allow the path length difference between polymer regions and LC regions to be modulated facilitating voltage switchable diffractive devices. This approach has been used to make switchable diffraction gratings and these have been demonstrated in a reconfigurable optical system. Using multiple devices and enabling the diffraction effect of each in turn offers the possibility of reconfiguration of optical systems. In this demonstration two cascaded switchable diffraction gratings with periods of 100µm and 30µm respectively have been used to provide wavelength range selection reconfiguration for a photodiode array detector. The optical reconfiguration switched between first order diffraction from the 100µm grating and first order diffraction from the 30µm grating. This allows a given wavelength range to be covered with a lower resolution array detector optically switching between different wavelength ranges. This might allow the use of more compact detectors or detectors with larger pixels. The grating periods are set at the time of fabrication but may be designed to cover the wavelength ranges required of the particular application.

In this study, the bent dimers were added in the azobenzene chiral doped cholesteric liquid crystals. The photoisomerization of azo-chiral material can induce a change in pitch and eventually lead to the occurrence of Helfrich deformation. Experimental results show that the photoinduced microgrid structure can be significantly stabilized by adding bent dimers and simultaneously applying a low voltage below the threshold of electric-induced Helfrich deformation. Furthermore, the spacing of the resulting meshed microgrids can be tuned by dimer concentration or applied voltage, revealing its potential for multiparameter controllable optical diffraction devices.

Recently found ferroelectric nematic (N_F) liquid crystals are unique polar states with highly fluidic nature, which may realize many unconventional/unprecedented applications. Here in this study, we doped N_F with an infrared laser dye so that it equips laser gain. Since NF is a non-centrosymmetric state and thus inherently activated for even-order nonlinear optics, this makes it possible to upconvert infrared photons into ultra-violet, via the simultaneous coherent processes of lasing and frequency doubling.