This PDF file contains the front matter associated with SPIE Proceedings Volume 11807, including the Title Page, Copyright information, and Table of Contents

Particle-type solutions are generic behaviors in out-of-equilibrium systems. These localized states are characterized by a discrete set of parameters such as position, width, and height. Even these solutions can have topological charges, localized vortices, which enriches the solutions and strengthens their respective stability. These solutions are characterized by exhibiting vorticity surrounded by a homogeneous state without vorticity. Frustrated chiral liquid crystals are a natural habitat for localized vortices, cholesteric bubbles. Here we study the emergence of chiral bubbles in the winding/unwinding transition of a chiral liquid crystal cell with homeotropic anchoring. Experimentally, we show that this winding/unwinding transition is subcritical in nature when one modifies the temperature, which also generates the emergence of spherulites through the contraction of cholesteric labyrinthine patterns. Theoretically, based on an amplitude equation inferred by symmetry arguments, we reveal the emergence of chiral bubbles from a cholesteric labyrinthine patterns.

In this presentation, we propose a scheme for a polarized beam steering system using multiply-cascaded rotating PGs with biaxial anisotropy. Our scheme can steer the polarized beam along both a Lissajous orbit and raster orbit, depending on the synchronization of the rotation frequencies of the PGs. Also, the use of more than two PGs allows us to control the center position of the Lissajous orbit. In addition, by using biaxial anisotropy, the diffraction efficiency and the ellipticity of the steered beam remain almost unchanged during PG rotation. Our beam steering system will apply to LiDAR and laser display.

Thin film holographic liquid crystal gratings are of great interest due to their controllable photonic properties. Holographic polymer dispersed liquid crystal (H-PDLC) with a polymer concentration of 40-90% is an example of a system where nonuniform irradiation is used to template alternating polymer-rich and polymer-poor regions with a periodicity related to the illumination wavelength. Here, we present a tunable holographic polymer stabilized liquid crystal (H-PSLC) reflection grating using a relatively small amount of polymer (6-20 wt%). Switching behavior from transparent to reflective state will be discussed by heating or applying an AC field. Heating above the isotropic temperature of the polymer-poor regions leads to the refractive index mismatch between the ordered LC polymer-rich regions and the disordered isotropic polymer-poor. Alternatively, the application of an AC field can be used as an Ohmic heat source to induce the thermal color change.

We present a dye-free alignment patterning technique, based on a scanning wave photopolymerization (SWaP) concept, that achieves a spatial light–triggered mass flow to direct molecular order using scanning light to propagate the wavefront. This enables one to generate macroscopic, arbitrary 2D alignment patterns in a wide variety of optically transparent polymer films from various polymerizable mesogens with sufficiently high birefringence (>0.1) merely by single-step photopolymerization.

Label-free qualitative and quantitative protein assays were established with a single-substrate biosensing platform based on cholesteric liquid crystal (CLC) films with different ratios of the thickness d to the helical pitch P. By adjusting the amount of chiral dopant incorporated in CLC, the d/P ratio or the center wavelength of Bragg’s reflection band can be fine-tuned to achieve signal amplification or to improve detection sensitivity. The single-substrate platform eliminates the need for LC cell assembly, which requires a pair of glass substrates, and can be conveniently integrated with the format of most clinical assays performed on a single solid surface.

Liquid crystals (LCs) are known to have a facile response under external electric and optical fields, which in the past have led to various technological applications such as LC displays or self-focusing flat lenses. In this contribution, we describe how chirality can increase the overall nonlinear optical response of frustrated liquid crystal samples based on the formalism of Green functions. We describe how such an effect can be leveraged to generate low-power spatial optical solitons in diverse sample geometries, and also suggest possible applications that could be derived from this theoretical and numerical work.

An electrically tunable achromatic polarization rotator has been developed based on the hybrid splay-twist (HST) liquid crystal. The proposed polarization rotator is advantageous over the conventional ones owing to the thin thickness (sub-100μm), continuous angular rotation, and achromatic operation across the entire visible spectrum. The tuning range of the polarization rotator is up to 90° via a simple electric field application; meanwhile, the degree of linear polarization (DOLP) remains. The rotation angle can be expanded to 180° by a tandem-cell geometry. The work will offer possibilities in the design of various optical systems and spatially polarization multiplexing elements.

Photo-voltaic light modulators consist of a liquid crystal layer integrated with an organic photovoltaic structure. Addressing them with light produces an internal voltage that changes the liquid crystal orientation and the optical transmission properties of the device. They offer an exciting prospect for autonomous, light controlled smart displays and visors. Herein we report the development of self-activated light modulators, whose transmittance drops with increasing light intensity without applying an external power supply. This could be achieved by introducing a tandem photovoltaic structure that allows to produce larger voltages. Crossed polarized intensity measurements on devices based on different liquid crystals and photovoltaic layers are presented to clarify the physical mechanisms underlying self-activation.

Nanostructured surfaces with engineered electromagnetic response, so called metasurfaces, are a very active topic of research in the nanophotonics community, stemming from their ability to manipulate the light wavefront at will with unparalleled resolution. Currently, one of the main limitations of this kind of devices is their static character, i.e., the fact that their functionality (e.g. focusing light, steering light, etc.) becomes fixed upon fabrication. To circumvent this issue, significant efforts are being made to achieve dynamic control of these devices by different means, one of the most promising being interfacing them with liquid crystals. In this talk, we will present our recent results in this direction, towards achieving dynamic control over each individual nanoantenna of the metasurface, as to realize the next generation of Spatial Light Modulators with sub-wavelength resolution, with broad applications in areas such as near-eye and holographic displays or LIDAR.

We report on orientational, optical nonlinearity of nematic liquid crystals (NLCs), observed when integrated with THz metallic metamaterial (MM) resonators. Our findings show that the bulk NLCs orientation breaks down close to the MM-NLC interface. The THz MMs exhibit extreme electric field ‘hotspots’, when on resonance, that strongly alter the NLCs local orientation. We model numerically the distribution of the refractive index of NLCs molecules close to the MM interface which demonstrates that the resonantly induced electric fields of the MMs are able to drive the birefringence of the NLC device. We experimentally verified our theoretical predictions with THz-Time Domain Spectroscopy (THz-TDS) in the 0.1-1.4 THz range and showed that, even a relatively thin layer of NLCs (20μm) integrated with MMs, can manipulate long wavelengths (such as 300 μm), beyond the limitations imposed by the NLC anisotropy.

Advancements in 3D printing, specifically by 2-photon polymerization, enabled the fabrication of high resolution novel optical elements for various applications by engineering the topography of the structures. Recently, the ability to obtain a varying refractive index distribution by 2-photon polymerization also started to gain momentum to design and produce gradient-index (GRIN) micro-optics. Here, we demonstrate micro-scale volume holograms by 2-photon polymerization by tuning the exposure point by point in the 3D volume to obtain the necessary refractive index distribution. 3D printed micro-scale GRIN volume holograms lay an opportunity to open a complimentary dimension in various systems thanks to in-situ fabrication advantage, which can provide complex interconnections and beam shaping in micro-scale.

We have investigated the new types of the continuous isotropic(I)-nematic(N) phase transition originated from the shape transformation of micelles from sphere to rod in extremely dilute concentration region(3~9wt%). In this paper, we measure the response time of the flow birefringence dependent on the AC flow field and discuss the origin and dynamics of the flow induced birefringence. The flow birefringence is 3-order slower than the relaxation time of the order parameter fluctuation in the isotropic phase near I-N transition point.

In the chiral-liquid-crystal (LC*) phase, calamitic molecules are aligned helically; hence, the refractive indices of the materials are altered periodically along the helical axis. The LC* materials have unique optical properties, such as selective reflection, that arise from the periodic structure of the refractive index. Here, we report a simple method for preparing monodispersed microparticles of LC* polymers. Optimizing polymerization conditions, monodispersed LC* polymer microparticles were obtained. In these particles, we could three-dimensionally control the helical-axis orientation of molecules. Based on the helical alignment, each single particle selectively reflected visible light. Because of the monodispersity, the microparticles showed no photonic cross-communication; namely, a clear reflection color without any optical degradation was observed, suggesting that LC* materials have potential for optical application in holographic coatings and omni-directional lasing.

Interfaces between two phases may exhibit enthralling shapes. Optically driven phase transitions are a benchmark that enables spatial control in the order parameter. Dye-doped liquid crystals allow purely optically induced phase transitions. Here we show the temporal evolution of finger-like structures at the nematic-isotropic interface in a photoisomerization experiment in a liquid crystal mixture between E7 and methyl-red dye in twisted planar cells both in the turn-on and turn-o of light scenarios. From the nematic to isotropic liquid transition, triggered by turning on the light, the emergence, growth, and retraction of finger-like structures are observed and characterized. In contrast, the isotropic-to-nematic phase transition when the light turns off transient foam-like and labyrinthine textures are observed. A reduced model based on dopant concentration and the liquid crystal order parameter reproduces all the observed phenomena.

This presentation video was recorded for the SPIE Optics + Photonics 2021 symposium.

This presentation reveals the re-writability property of azobenzene liquid crystal photoalignment. Stable in thermal fluctuations, one can change existing photoalignment by exposing it to polarized light in the visible regime. One can use this unique property by patterning photoalignment through the liquid crystal bulk in that the sample’s front and back have differing director orientations. Photoalignment using linear polarized light as well as complex polarizations will be covered. No surface alignment on sample substrates is necessary because the azobenzene is mixed with the liquid crystal in-situ in sample preparation.

Computational methods based on Density Functional Theory (DFT) are valuable for making pre-synthesis predictions of specific molecular structural elements in liquid crystals materials that will result in enhanced performance for terahertz (THz) region applications. Our previous DFT modeling efforts demonstrated that a two-fold improvement in THz-region birefringence (Δn) over existing materials is possible by utilizing design elements that favor high π electron delocalization, low molar mass, and electromagnetic asymmetry. In this work, we apply these design principles to examine the potential of mesogens with extended polarizable electron-rich structures, such as fused-ring nematics and discotics, as high-performance materials for THz-region applications.

Spatial beam shaping can be achieved using wavefront modulators to increase ultrafast laser processing efficiency. These modulators can display a pre-calculated phase mask on the beam path in order to shape the laser intensity distribution following a user defined target in the processing plane or volume. Due to the non-perfect optical response of wavefront modulators, the experimental distribution may differ from the target. We investigate the use of electrically addressed and optically addressed liquid crystal spatial light modulators with ultrafast laser pulses. Applications in parallelized surface and bulk processing are achieved with both modulators showing the advantages and drawbacks of these technologies. In particular, we focus on the limitations of these devices in terms of spatial and phase delay resolution, showing the consequences on the shaped beam distribution. Calculation strategies to overcome these limitations are discussed.

It has been just over 20 years from the first disclosure of a thin and transparent film that would allow controlling propagation of light, an unpolarized and broadband light, with 100% efficiency. First it was an idea seemingly at odds with conventional optics. Then came demonstrations of the thinnest planar optics - “prisms”, lenses, beam shapers, arrays and vortices, switchable or not, - in sizes currently 8” and larger. Novel film architectures extended spectral and angular bandwidths of planar optics to unprecedented scales, changing the ways optics is made and opening avenues to long cherished dreams of adaptation, tunability, multifunctionality, and cost. History is in the making and will be presented first hand with an outline of the marvels in functionality and capabilities waiting for optics behind the horizon.

Pancharatnam Phase Devices (PPDs) are an exciting new area for optical component development. Single layer active devices that provide optical beam steering over a range of several degrees will be discussed. The devices considered here use a comb electrode structure to provide an in-plane electric field to control the optical axis orientation of the liquid crystal director to have the desired spiral pattern of a PPD device. Two basic concepts will be discussed: one that used the in-plane fields to “pin” the only the ends of the spiral pattern; and another that uses sub elements to defines the desired director orientation at several locations in the spiral. The concepts, design details, and modeling results are shown.

This presentation video was recorded for the SPIE Optics + Photonics 2021 symposium.

We present sub-millisecond response time of liquid crystal light valves (LCLV), optically addressable spatial light modulators with a continuous photosensitive layer used to drive the orientation of a nematic LC layer. By using a LCLV with a Bi12SiO20 crystal as a photoconductor, we show that the voltage working point can be set close to the saturation of the optical response, providing a reduced molecular excursion and, correspondingly, a faster response time. With a small refractive index change but still detectable diffractive efficiency, the LCLV responds in a large frequency band. Phase gratings are observed at ~ kHz modulations. Applications include dynamic holography, biomedical imaging, turbulence correction and/or simulation, lidar applications.

Heating, ventilation, and air conditioning of buildings account for about 15% of the global energy consumption, but about 20% of this building-related energy is lost because of inefficient windows. Greenhouse emissions associated with producing and using this energy contribute substantially to climate change. Is there a solution to this challenging problem? Starting from the physical principles associated with energy loss through windows, I will describe our development of visibly transparent, infrared-reflecting, thermally super-insulating materials that may replace or retrofit the inefficient windowpanes of residential and commercial buildings. I will discuss how production of such unusual transparent porous materials is enabled by mesoscale templating of orderly porous structures using lyotropic surfactant-based liquid crystals. I will discuss how these metamaterials can boos energy efficiency of windows and buildings in general.

Liquid crystalline materials have been shown to be an excellent host matrix enabling the easy observation of bacteria movements. In some cases, even the high sensitivity of such matrix was used to control materials’ properties by bacteria. Motivated by the key role played by bacteria in the health and food industries, our group is working on the development of dynamic micro control techniques by using photosensitivity of azobenzene or DSCG molecules. We think that the capability to control their movement may be useful for many applications, and, in the present work, we explore the possibility of such active control of the movement of flagellated bacteria (a bacterium that can swim thanks to the rotation of its helix). We demonstrate that we can dynamically change the swimming direction of bacteria by incorporating them into a liquid crystal where the phase transition is locally controlled by UV illumination. We shall also mention briefly about other types of control (magnetic, isomeriz)

Cholesteric liquid crystals (CLCs) form self-assembled helical structures of rodlike molecules. From its periodic helical structure, the CLC exhibits a structural color by selectively reflecting circularly polarized light of the same handedness as the helix. Here, without external stimuli of electric fields, temperature, and light, we show tuning of spectral position, width, viewing angle, and diffusivity of its reflection color in a CLC by employing amorphous and nanostructured perfluoropolymer (called CYTOP) films as alignment layers. This CLC combined with perfluoropolymer films provides new possibilities in various photonic applications such as active components of photonic sensors, reflective displays, and tunable lasers.

We aim to realize a novel nanotechnology-based biosensor specifically utilized to detect harmful bacteria in potable water. The nano-inspired device makes use of a chemically functionalized gold nanorods array (for the selective selection of specific pathogens) layered with a photo-responsive nematic liquid crystal (NLC) film for real-time and high sensitivity detection. The first experimental results are presented and discussed.

Under an applied electric field, BPLC lattice undergoes with complex reconfiguration dynamics and exhibit meta-stability and new crystal symmetries. Detailed theoretical considerations and experimental results with such Repetitively Applied Field (RAF)Technique for transforming BPLC crystalline lattice structures from cubic to final stable configuration with orthorhombic or tetragonal symmetry will be presented.

Colloidal liquid crystals offer a route to change physical properties and create micro and nano structures. Optical methods only characterise relatively simple colloidal systems. More complex systems require powerful data analytic methods. We present a new approach using Topological Data Analysis to reveal the structural and morphological features in a nematic liquid crystal doped with gold nanoparticles confined in a thin capillary, including the changes occurring during phase transitions. Our topological framework allows us to identify distinct temperature-induced macroscopic states, obtain a geometric representation of the time-dependent topological states and identify several configurations with different degrees of symmetry and order.

Using the potential of liquid crystal, we developed highly aligned organic semiconductor thin film. Especially, upon considering soft crystals as an intermediate state between liquid crystals (LCs) and crystals, we aim to “crystallize” LC while ensuring the flexibility and mobility of the LC and create a soft crystal that combines precise orientation order of molecules in angstrom scale and molecular arrangement order of meter scale by self-organization.

The structural characteristics of carbon nanotube (CNT) make them new interesting aligning layers for liquid crystals (LCs). These highly elongated nanoparticles have surface on which LC strongly anchor and with the use of CNTs sheets, continuous films of aligned CNTs can be easily obtained. Despite the fact that CNT sheets are inhomogenous layers since the linear networks of nanotubes cover partially the plane with gaps, of different distance, in the perpendicular direction and that their degree of orientational order can vary locally, with values well below 1, nematic LCs are oriented by the CNTs along their direction of alignment. The alignment of the LC can be clearly affected by the chosen geometry, as studied with symmetric and asymmetric boundary conditions. Certain alignment could be recognized even with only one aligning surface but two are needed for better and more uniform alignment. The orientational order of CNTs was measured by the anisotropic absorption and found being dependent on the processing steps that decrease its value. Higher value of orientational order of the CNTs seem to be relevant for improving the LC alignment even in the case of use of inorganic coatings of CNTs. With simple assemblies, using two substrates or a single one coated even with one CNT sheet, novel LC applications can be realized such as carbon nanotube-based flexible LCDs or pressure sensors.

An oblique helicoidal cholesteric ChOH represents a unique optical material with a pitch that can be tuned by an electric or magnetic field in a broad range from sub micrometers to micrometers. In this work, we demonstrate that the oblique helicoidal cholesteric doped with azoxybenzene molecules and stabilized by an electric field could also be tuned by light irradiation. At a fixed voltage, UV irradiation causes a redshift of the reflection peak by more than 200 nm. The demonstrated effect has the potential for applications such as smart windows, sensors, tunable lasers, and filters.

Electrochromic devices have found widespread use in automotive, aerospace, and architectural implementations. 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. Enabled by recent advancements in the preparation of liquid crystalline elastomers, we also detail the thermal and electrical adjustment of reflection in fully solid optical elements.

Molecular alignment control in polymer films is key to the development of high-performance materials with optical, electronic and thermal functions. Among molecular alignment techniques, a photoalignment method offers the fine and remote control of two-dimensional molecular alignment by the irradiation with linearly polarized light. We have recently proposed a novel photoalignment method based on the molecular diffusion caused by the polymer concentration gradient, termed scanning wave photopolymerization. In this study, we report specific polymerization behavior occurring during the process of the scanning wave photopolymerization. We investigate the effect of molecular diffusion on the photopolymerization behavior by measuring molecular weight of the polymers obtained under various photopolymerization conditions.

Macroscopic and precise alignment control of functional molecules represented by liquid crystals (LCs) and polymers is the key to generating a new function and enhancing their performances. Among various alignment techniques, a photoalignment method offers the greatest potential to finely control molecular alignment because of the capability of micro- to nano-patterning with remote processes. Recently, we have proposed a novel photoalignment method based on a new concept of scanning wave photopolymerization (SWaP). This method utilizes molecular diffusion triggered by the localized photopolymerization, enabling to generate an arbitrary alignment patterns merely by single-step photo-irradiation. In this study, we fabricated liquid-crystalline polymer networks directed by SWaP.

Over the past decades, flexible electronics such as flexible liquid crystal devices composed of polymer film substrates have been dramatically growing. Understanding bending behavior of polymer films is the key to designing flexible electronic devices with high mechanical durability. Although various bending analysis methods have been proposed, they are still limited to macroscopic and qualitative analyses. Recently, we have newly proposed a method for analyzing the surface bending strain in flexible materials, termed surface labeled grating method. This method enables us to quantitatively evaluate the surface bending strain by monitoring the diffraction angle of a He-Ne laser beam that passes through a grating label attached on a sample. In this study, we measure the surface bending strain in polyethylene terephthalate films and reveal that tension and compression occurs in their outer and inner surfaces, respectively.

Liquid crystals (LCs) have been utilized for the innovative optical devices because the molecular reorientation triggers a change in their optical properties. Among them, oligothiophene-doped LCs can induce the molecular reorientation by irradiation with a laser beam, which is useful for all-optical devices. However, the photoinduced reorientational behavior was observed only by irradiation with a high-intensity laser beam. In this study, we investigated the effect of incident light properties on photoresponsive behavior of oligothiophene-doped LCs by irradiation with a collimated laser beam from the perspective of improvement of the photoresponsive sensitivity of the molecular reorientation. As a result, the irradiation of oligothiophene-doped LCs with a collimated laser beam enhanced the sensitivity of the molecular reorientation.

The control of the surface topology is important to utilize their high functionality for a wide variety of applications such as optics and mechanics. Several methods of controlling the surface topology have been proposed; in particular, the light irradiation can precisely control the surface topology in a non-contacting manner. However, conventional methods using the light irradiation need complicated processes with specific photoresponsive molecules. Recently, we revealed that patterned photopolymerization, based on a novel method of molecular alignment, induced surface relief structures on a film; yet, the relationship between the surface structures and molecular alignment has not been clarified. In this study, we made the detailed investigation of surface structures and molecular alignment of the film induced by patterned photopolymerization.

The control of molecular alignment patterns in liquid crystals is key to developing high-performance optical devices. In particular, two-dimensionally designed patterns have attracted much attention due to their potential application to novel optical devices such as a high efficiency polarization grating and a vortex converter. However, there remain challenges in obtaining molecular alignment patterns by a simple method. We have recently proposed a novel method for controlling the alignment of liquid crystals termed scanning wave photopolymerization (SWaP). In this method, a mass flow triggered by spatiotemporal photopolymerization causes shear stresses to anisotropic molecules, resulting in the generation of alignment patterns finely guided by the scanned light. In this study, we present the direct fabrication of polymer films with cycloidal molecular alignment patterns by SWaP.

Inorganic materials such as nanotubes and nanorods have attracted much attention due to their anisotropic properties. Although controlling the alignment of inorganic materials is able to enhance their functionality, macroscopic alignment over a large area remains a challenge. We have recently proposed a simple method for inducing unidirectional alignment of ZnO nanorods on a rubbed polyimide layer. In this method, ZnO nanorods grafted with liquid-crystalline (LC) polymers are aligned by cooperative interaction between the LC moieties in the grafted polymers and surrounding LC host molecules. In this study, we investigated the unidirectional alignment of surface-modified ZnO nanorods in nematic LCs in a micrometer-thick cells. Alignment of LC polymer-grafted ZnO nanorods along nematic LC host molecules has been revealed by polarized optical micrography and ultraviolet-visible absorption spectroscopy.

To develop flexible devices that have mechanical durability, understanding the bending behavior of soft material components is quite important. However, measuring bending strain in soft materials has been limited to their surface due to experimental constraints. In addition to the surface strain analysis, internal strain analysis will further clarify the bending behavior of soft materials. In this study, we quantified internal strain in bending polydimethylsiloxane (PDMS) films, which are a common soft material, through the selective reflection of a cholesteric liquid crystal elastomer (CLCE). The strain analysis with the CLCE revealed that internal strains depend on the position of the bending PDMS films. This internal strain quantification of soft materials leads to the development of flexible devices with high mechanical durability.

Cholesteric liquid crystals have attracted the scientific community's attention in the last decades due to the impressive textures displayed in various experiments. In particular, when varying the temperature of a cholesteric liquid crystal sample with homeotropic anchoring, complex textures arise, which resemble labyrinthine patterns built on the connections of the so-called cholesteric fingers. Near the winding/unwinding transition, we proposed a minimal phenomenological model that accounts for the first-order type transition and the symmetries in the system. At this transition, localized cholesteric fingers suffer a tip-splitting instability and the merging of pointed tips. We discuss the emergence of cholesteric labyrinths using experimental, analytical, and numerical techniques.

In this study, a dual-mode smart window is proposed based on a liquid crystal cell characterized by its intrinsic response to solar-thermal radiation (passive control) and applied AC voltage (active control). The cell is made of a chiral nematic confined between two conducting glass substrates and the selective reflection is designed to occur in the near-infrared region. With the temperature-dependent electrohydrodynamic effect that generates varying extent of dynamic scattering, the AC voltage-regulated temperature-vs.-transmittance relation holds great promise for the adaption of the demonstrated device for human inhabitants living in various climate zones.