This PDF file contains the front matter associated with SPIE Proceedings Volume 11472, including the Title Page, Copyright information, and Table of Contents.

Liquid crystal materials containing flexible molecular dimers and chiral dopants form a peculiar type of a cholesteric with an oblique helicoidal structure (ChOH), in which the director is titled with respect to the helicoidal axis rather than orthogonal to it, as in regular cholecterics. The heliconical ChOH state occurs in presence of an electric or magnetic field. Tilted configuration of the director and absence of density modulation makes ChOH a unique material for various electro-optical applications. The presentation discusses electrically tunable selective reflection by ChOH and how it can be used to get an insight into the elastic properties of these materials such as bend modulus. The work is supported by NSF grant ECCS-190610.

Electrochromic devices have found widespread use in automotive, aerospace, and architectural implementations. Electrical control of the absorption of metallic or polymeric materials can result in transmission swings of more than 50%. This talk will detail our recent research of liquid crystalline compositions in which the selective reflection can be tuned, broadened, and switched. This distinctive electro-optic control is enabled by polymer stabilization of the cholesteric liquid crystal phase. Through control of the materials chemistry and polymerization conditions, we will report findings in which we uniquely demonstrate dynamic control of two separate reflective bands in a single element.

In this lecture we describe the interaction between a laser beam and the helical structure of the heliconical cholesteric phase. We show that strong optical reorientation is possible in this case differently from planar cholesterics where the observation orientational optical nonlinearities are prevented by the helical structure. The key factor allowing the efficient coupling between the optical field and the liquid crystal director is the bend distortion of the heliconical phase, that can be easily modulated by the light beam. We discuss here and present the most recent results related to light induced pitch tuning and optical modulation of light polarization in heliconical cholesterics.

Previous work has reported that polymer stabilized cholesteric liquid crystals (PSCLCs) have shown dynamic photonic properties with the application of direct current (DC) field, including bandwidth broadening, switchable scattering, red tuning and blue tuning. Recently, we have prepared holographic polymer stabilized cholesteric liquid crystals reflection gratings (H-PSCLCs). High order diffraction peaks, such as the second or/and third order diffraction peaks, are observed from the H-PSCLC samples written with a 363.8 nm Argon laser. The higher order reflection bands are caused by the deformed helical structure of the polymer stabilizing network formed under reflection grating conditions. The spectral position of the second-order reflection band is simply adjusted by chiral dopant concentrations in the CLC mixture. The selective main and higher order reflection notches can be red-tuned and broadened by the application of DC fields.

Thermo-plasmonics deals with the generation of nanoscale heating produced by light activated plasmonic nanoparticles (NPs) such as gold and silver NPs. The combination of smart-responsive materials (e.g. thermotropic liquid crystals and thermo-responsive hydrogels) and highly photo-thermal efficient plasmonic (gold) NPs has been used for the realization of light assisted, reconfigurable, thermo-plasmonic driven Bragg mirrors, diffraction gratings, waveplates and smart windows.

We investigate a vortex triplet induced by the combination of an electric and magnetic field onto a homeotropic nematic liquid crystal cell. The electric and magnetic fields are generated by two parallel electrodes and a magnetic ring, respectively. The vortex triplet remains stable and trapped at the center of the magnetic ring. Based on forcing the Ginzburg-Landau equation, valid close to the re-orientational transition, allow us to establish the origin of the vortex triplet. Numerical simulations show a quite fair agreement with theoretical findings and experimental observations.

Inorganic nanoparticles (NPs) can be added to liquid crystals (LCs) to form LC nanocomposites. These nanocomposites can impart the electro-optical properties of the NPs to the LCs while the LCs can control the spatial distribution and properties of the particles. The surface coatings of these NPs can be designed to prevent uncontrolled aggregation. Mesogenic ligands often provide the best stabilization but require custom synthesis. We are exploring polymer ligands as an alternative, as they offer synthetic simplicity as well as chemical and molecular weight tunability. In particular, we are varying the polymer chain flexibility since more rigid chains can better couple to the nematic order whereas flexible polymers should strongly phase separate.

Photovoltaic light modulators integrate liquid crystals and solar cells and offer an exciting prospect for autonomous, smart displays and visors. Illumination produces a photovoltage that modifies the liquid crystal alignment and light transmission. However, determining their properties, for example, the voltage dropped across the liquid crystal, different pretilts or anchoring energies, inherent to asymmetric cell designs, poses significant challenges. We have successfully applied to such photovoltaic modulators a new measurement methodology based on wide-area cross-polarized intensity measurements, coupled to an Ericksen-Leslie model. We have implemented it in a versatile optical analyzer, driven by a Matlab graphical user interface.

Volume holography has been widely investigated for information storage and other applications. An increase in the number of multiplexed holograms leads to dynamic range loss when they are optically recorded. Computer generated holograms can achieve better performance if constructed voxel-by-voxel or as a multilayer structure. Advancements in 3D printing enabled the fabrication of multilayered diffractive elements in the micro-scale. To obtain an accurate design, we deploy the Learning Tomography (LT) method, which is an optimization algorithm for computationally imaging 3D distribution of the refractive index. Here, instead of imaging an object, we define a 3D structure that achieves a desired functionality.

Cellulose Nanocrystals are readily produced from many plant and bacterial sources and have been studied extensively for low cost self-assembled optical elements. Nanocrystals are known to form a chiral nematic phase, which allows for production of films with chiral character. I will discuss recent advances in understanding how to control the chirality of cellulose nanocrystal solutions. The Debye length of a nanocrystal solution is typically around 4nm for pH between 1.5 and 10 and abruptly drops to around 1 nm for pH lower or higher than this range. With a Debye Length of 1nm, the solution can only form nematic phase, which is more useful for production of waveplates and other birefringent optics. Additionally I will discuss the behavior of cellulose solutions with amorphous material remaining in solution which form discotic- like systems.

A wavefront calculation based on Zernike polynomials is applied to an optically addressed liquid crystal modulator for ultrafast laser machining.

Nematic liquid crystals of achiral molecules or racemic mixtures of chiral ones form flat films and show uniform textures between circular polarizers when suspended in sub-millimeter size grids and submersed under water. Recently it was shown that on addition of chiral dopants to the liquid crystal, the films exhibit optical textures with concentric ring patterns with radial variation of the birefringence color, while the films become biconvex. The curved shape together with degenerate planar anchoring leads to a radial variation of the optical axis along the plane of the film, providing a Pancharatnam-Berry type phase lens that dominates the imaging. Here we describe preliminary results of nematic liquid crystal microlenses formed by the addition of chiral nanoparticles. It is found that the helical twisting power of the nanoparticles, the key factor to form the lens, is an order of magnitude greater than that of the strongest molecular chiral dopants. From the observations we present here, we were able to estimate the shape and the geometric focal length of the lens and demonstrated its performance as an optical device. The use of chiral nanoparticles to make microlenses may allow tuning by light that the nanoparticles absorb or, for magnetic NPs, by magnetic fields. Further, the measurement of focal length at known NP concentration offers a new method to measure the helical twisting power of chiral nanoparticles.

This paper describes a robust liquid crystal alignment layer that can be applied to the interior surfaces of a preformed cavity. In this paper, we describe a method of infusing a dye into a microcavity to produce an effective photodefinable alignment layer. Additionally, we demonstrate that after the application of a diffused RM layer, the alignment of the liquid crystal can be rendered insensitive to subsequent light exposure. In this work we make clear the effect of the RM is not stabilizing the azodye layer, but becomes the stable alignment layer. This is demonstrated by using the process described above with the additional step of realigning of the azodye layer to be perpendicular to the surface through photo-bleaching; and showing the alignment of the LC is unaffected by this process. This versatile alignment layer method, offers significant promise for new photonics applications.

In recent years, vector beam (VB)-based optical multiplexing communication is attracting attention to increase the information transfer capacity, and hence several types of VB demultiplexers fabricated by using liquid crystals have been reported. In this presentation, we propose a crossed-fork-shaped polarization grating (CFPG) as a new VB demultiplexer. The CFPG was fabricated by recording multiple polarization holograms onto the photocrosslinkable polymer liquid crystal. Recorded each polarization hologram works individually to act as a VB detector, which converts specific VB into a Gaussian beam with diffraction. The CFPG has the potential to miniaturize the demultiplexer because several VB detection functions can be integrated. VB detection between radial and azimuthal polarizations also demonstrated by using a pair of quarter-wave PG and normal-FPG.

Scanning wave photopolymerization of liquid crystal monomers enables arbitrary molecular alignment patterning due to molecular diffusion induced shear stress by spatially selective polymer production. However, the molecular alignment process has not been explored because of the difficulty of measuring such non-equilibrium state. In this study, we investigated molecular alignment behavior by directly observing scanning wave photopolymerization process with a polarized micrograph equipped with a dynamic light processor. Optical anisotropy was generated along with light scanning to trigger photopolymerization, indicating that molecules are aligned parallel to the light scanning direction.

Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TDDFT) are powerful tools for modeling the physical and optical properties of liquid crystals (LC’s). These computational methods have been shown to be equally effective for predicting the polarizability anisotropy and birefringence (Δε) of LC’s in the terahertz (THz) regime. This work describes a series of nematic and chiral nematic LC’s designed using molecular structural elements (e.g., perfluorination) expected to enhance performance in THz regime applications. TDDFT calculations employing Gaussian 09 with B3LYP, along with the Vuks equation, were used to predict the magnitude of Δε in the THz region for these materials as a function of terminal group perfluorination.

Laser beams which carry spin and orbital angular momentum are desired in many applications. They are usually created by manipulating the laser output or by inserting optical components in the laser cavity. Due to their high susceptibility to external fields and birefringent nature, control over the emitted light could be achieved by inserting liquid crystals into the laser cavity. In this work we numerically study lasing in selected nematic liquid crystal director profiles. We use custom written FDFD code to calculate emergent electromagnetic eigenmodes, and show how they are affected by the nematic director field. Control over lasing is of a particular interest with the aim to path the way towards the creation of general arbitrary shaped laser beams.

Out of equilibrium systems under the influence of enough energy injection exhibit complex spa- tiotemporal behaviors. Based on a liquid crystal light valve experiment with translational optical feedback, we observe propagation, spatiotemporal intermittency, and defect turbulence of striped waves. A prototype model of pattern formation with translational coupling shows the same phe- nomenology. Close to the spatial instability, a local amplitude equation is derived. This amplitude equation allows us to reveal the origin and bifurcation diagram of the observed complex spatiotem- poral dynamics. Experimental observations have a quite fair agreement with theoretical findings.

Smart window is the films/glasses having the incredible feature of controlling heat, privacy, and getting their transmission properties changed from opaque to translucent to transparent under the influence of voltage. The flow of light and heat between indoor and outdoor is controllable, providing human life more convenient and comfortable. Smart window technique such as Polymer dispersed liquid crystal (PDLC), Electrochromic glass (EC) and Suspended particle devices (SPD) accounted for 90% of the market. However, these techniques can be only operated at a single function. In order to achieve true energy conservation and versatility, it is highly desirable but challenging to design a single device capable of simultaneously modifying haze and tint as well as exhibiting multi-stability. In this presentation, I will talk about the recent technology and development of multi-functional LC smart windows.

We shall describe our on-going work on the study of the impact of light scattering by liquid crystals on the image quality. We shall start by the analyses of the case of a uniform nematic film. Then, a particular attention will be paid to the case of using electrically tunable liquid crystal lenses for mobile cameras. As a result, we shall show that we can quantify this impact and deploy various deconvolution techniques to reduce the impact of scattering. This, in turn, will eliminate one of the key drawbacks when using liquid crystals for adaptive imaging.

The fronts are waves that connect two equilibria. The liquid crystals are no stranger to these phenomena. Front dynamics also was observed in other physical contexts, such as walls separating magnetic domains, fluidized granular states, chemical reactions, solidification, and combustion processes, and population dynamics, to mention a few. We find these phenomena in differents interface dynamics, as part of a robust phenomenon this ranging from chemistry and biology to physics. The propagation and dynamics of fronts depend on the nature of the states that are being connected. The invasion of a state into another is characterized usually by front propagation into unstable states. In the present work, we investigate the anisotropic front propagation close to phase transition SmA-N*. The bifurcation diagram shows a subcritical behavior, and the front speed is according to the mathematical model. A spatiotemporal diagram shows an evolution of the front with preferential direction.”

We have investigated the azimuthal orientation behavior of blue phase (BPI) lattice reoriented from the electrically unwound homeotropic state, and it was found that the azimuthal angle changes to align the [001] axis parallel to the easy axis on a unidirectionally orienting surface upon an electric filed treatment. By combining this effect with the Pancharatnam-Berry effect, we designed and demonstrated various holographic optical elements (HOEs) such as deflector, lens, and hologram by appropriately designing the distribution of lattice orientations. In contrast to cholesteric liquid crystals that show diminished circular polarization selectivity upon largely oblique incidence, we demonstrate that the BP-based HOEs maintain the circular polarization selectivity even for oblique light incidence, owing to the three-dimensional helical structure of the BP.

Free-standing veils of parallel carbon nanotube (CNTs) wires can be easily integrated in devices as transparent and conductive layers and they are particularly interesting for liquid crystals since they can act also as aligning layers. We have realized cells for liquid crystals using aligned carbon nanotube wires in sheets drawn from spinnable forests and obtained light modulation by switching the LC. The 5CB and E7 nematic liquid crystal align planarly and the unidirectional alignment direction is determined by the CNT orientation within the sheets and by applying the voltage directly to the CNTs we obtained the electro-optic switching with the LC. The CNT sheets prove to be efficient multifunctional layers for new LC displays, perfectly compatible with flexible substrates due to their mechanical characteristics as it will be described here.

We present the results from recent studies of field-induced reconfiguration of defect network in Blue phase liquid crystals leading to the formation of new stable lattice structures from their natural self-assembled cubic form [Nat. Materials https://www.nature.com/articles/s41563-019-0512-3]. The dynamical evolution of the defect network and reorientation provide new insights into the underlying mechanisms and roles played by various factors, especially the form of applied field for efficient lattice transformation. Recent studies with optical field derived from CW or short-pulsed lasers further demonstrate the possibility of direct reconfiguration/reorientation of the bulk crystals.

Cholesteric liquid crystals (CLCs) with periodical helical structures of nematic molecules are chiral photonic crystals that exhibit photonic band gaps for circularly polarized lights with same handedness as CLC helices. We investigated optical characteristics of CLCs on nanoimprinted CYTOP films. Here, nanoimprinted CYTOP films are used as alignment layers to control orientations of cholesteric helices because of its strongly hydrophobic surface with low polarity and low polarizability. The CLCs on the nanoimprinted films showed not specular but diffusive reflections at the specific spectral region. This nanostructured CYTOP film can provide new possibility to engineer optical characteristics of the CLCs.

As previously reported, direct current (DC) electric field can be used to control the photonic properties of polymer-stabilized cholesteric liquid crystals (PSCLCs) with negative dielectric anisotropy, such as the position and bandwidth modulation of the selective reflection notch. This dynamic EO response of PSCLCs is explained by the field-induced deformation of the polymer stabilized networks mediated by ionic charges trapped in the polymer networks. In this poster, we report the effect of cell thickness on electro-optic response for relatively thin PSCLC samples (≤5 μm). Increasing the DC field strength shifts the reflection notch to longer wavelength (red shifting tuning) and eventually disappears at high DC fields. The tuning range is dependent on the cell thickness. The reversible transition from reflective to clear state is due to an electrically driven chirp in the pitch across the small cell gap.

We investigate topological states of matter in a system with injection and dissipation of energy. In an experiment involving a liquid crystal cell under the influence of a low frequency oscillatory electric field, we observe a transition from no vortex state to a state in which vortices persist. Depending on the period and the type of the forcing, the vortices self-organize forming square lattices, glassy states, and disordered vortex structures. Our results show that the matter maintained out of equilibrium by means of the temporal modulation of parameters can exhibit exotic states at room temperature.

Thin lenses have potentially much lower weight and volume than traditional refractive lenses, and therefore enable compelling solutions in augmented-/virtual-/mixed-reality (AR/VR/MR) headsets. The geometric-phase lens (GPL), formed either with liquid crystals (LCs) or metasurfaces, is emerging as a leading technology because of its ability to implement arbitrary aspherical phase profiles and its potential for low loss and minimal ghosting. However, a strong chromatic dispersion is inherent to each singlet. One prior method to overcome this employs a stack of multiple achromatic GPLs acting on all colors simultaneously with color filters and other waveplates to achieve an apochromatic lens system. Another concept in the prior art is to use multiple color-selective GPLs (CS-GPLs) wherein each diffracts only a single color while transmitting the others. In this work, we report on a family of color-selective GPLs with highly chromatic efficiency spectra, made using multi-twist LC coatings. In both theory and experiment, we show the diffraction efficiency of red, green, and blue lenses is high (< 91%) while the complementary colors of each coating are almost fully transmitted undiffracted. The CS-GPLs is a promising optical element to provide a new route to mitigate the chromatic abberation in the AR/VR/MR lens system.