川月 喜弘

© 2019 Optical Society of America. We have succeeded in forming a polarization grating whose polarization diffraction properties are extremely independent of the incident angle by using polymer liquid crystal exhibiting biaxial optical anisotropy. It is considered that the extension of the optical path length and the decrease in the effective amplitude of optical anisotropy due to oblique incidences are offset by the biaxial optical anisotropy and, as a result, the retardation is compensated. The properties of this developed device have been experimentally demonstrated and theoretically explained.

© 2019 Optical Society of America. A scheme is presented for an optical vortex (OV) generator comprising a uniaxially aligned azo-dye-doped liquid crystal (ADDLC) and a space-variant polarization projection (SVPP) system. The SVPP system consisting of an electro-optic modulator and a micro-electromechanical system projects a time-averaged SVP field equal to a vector beam onto the ADDLC and fabricates a three-dimensional twisted anisotropic structure, which has spatial phase modulation properties from plane to helical shape. The generation of OVs with odd- and even-numbered topological charge is experimentally demonstrated. As a flexible and broadband spatial light modulator, the proposed scheme should be applicable to the research and development of OV applications.

© 2019 Author(s). A crossed-fork-shaped polarization grating (crossed-FPG) is presented for use in vector beam division demultiplexing. The crossed-FPG was fabricated in a thin photocrosslinkable liquid crystal polymer film by recording multiple polarization holograms between optical vortices and Gaussian beams that have opposite circular polarizations to each other. The recorded holograms work individually to act as FPG with a polarization-dependent topological charge conversion property that corresponds to a recorded pair of vortices. The feasibility of mode demultiplexing was demonstrated experimentally. The proposed crossed-FPG should be used as a mode demultiplexer for optical communications based on vector beam division multiplexing.

© 2019 Optical Society of America A quaternary liquid crystal (LC) grating simultaneously performs dynamic control of diffraction angle, polarization, and wavelength-separation properties as shown in the following: (1) Diffraction orders in which light waves are diffracted can be selected by applying a voltage, (2) the efficiency of each diffraction order can be controlled depending on a wavelength of an incident beam, and (3) a pair of counter-rotated circular polarizations or linear polarizations with an orthogonal relationship are diffracted simultaneously, and this property can be controlled by applying a voltage. These diffraction properties and LC alignment structures are proposed based on theoretical analyses using Jones calculus, and their properties are now demonstrated experimentally. The quaternary LC grating can be used as an advanced optical element for industrial applications such as tunable polarization beam splitters and dynamic switching of propagation directions of light depending on wavelength.

© 2019 Optical Society of America The diffraction properties of liquid crystal (LC) cells fabricated by photoalignment substrates with different periodic optical anisotropic distributions are demonstrated. The twist angle distribution structure inside the LC cells formed by the grating period difference between photoalignment substrates is called “beat structure.” In addition to diffraction corresponding to the grating periods of photoalignment substrates, beat structure itself also functions as a diffraction grating. The diffraction properties can be controlled by varying the retardation. The fabrication method and diffraction properties of the LC cells with beat structure are explained by both experiment and theoretical analysis. © 2019 Optical Society of America

© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim In this study, mechanochromic luminescence was induced in a complex of mechano-inactive compounds. Dye/acid complexes containing the same π-conjugated backbones were prepared. While the luminophore showed blue and red shifts in photoluminescence spectra when combined with different acids by grinding, it exhibited slight mechanoresponsiveness itself. Also, compounds with similar molecular backbones to the dye/acid complex were synthesized to clarify the color change mechanism. The compounds showed both blue and red shifts in photoluminescence and diffuse reflectance spectra upon grinding, indicating that mechanochromic luminescence in the hydrogen-bonded complex is like its monomeric analogue and that aggregation structure plays an important role in mechanoresponsive behavior rather than the π-conjugated structure. It was shown that a color change can be mechanically induced by imitating the solid-state aggregation structure of other mechanoresponsive compounds without synthetic modification.

© 2018 Elsevier B.V. We report the propagation properties of polarized terahertz (THz) waves in a liquid crystal (LC) cell with subwavelength metallic gratings to produce transmissive THz elements with electrical tunability. One-dimensional metallic gratings, which can be used both as transparent electrodes and linear polarizers in the THz regime, were fabricated on the quartz glass substrates of the LC cell. The substrates with and without the metallic grating showed almost identical transmission spectra for a linearly polarized THz wave whose electric field was parallel to the grating vector. We fabricated a 90∘-twisted nematic LC cell using the two substrates with the metallic grating and examined its transmission spectra in the THz regime. During these measurements, we applied a voltage to the LC via the metallic gratings. We calculated in detail the transmission spectra and its voltage dependence based on the effective medium theory for subwavelength structures, the continuum theory of twisted nematic LCs, and the optical constants of the LC in the THz regime. The observed spectra agreed well with theoretical simulations. These results demonstrate that LC cells with subwavelength metallic gratings are useful as active THz elements in applications such as attenuators and polarization rotators.

Copyright © 2019 American Chemical Society. The photoinduced reorientation of the side-chain mesogens in nematic liquid crystalline (LC) polymer thin films triggered by the axis-selective photo-Fries rearrangements of side-chain phenyl benzoate moieties is studied to understand the regulation of the anisotropic nanostructures supported by LC polymers. The influence of the substrate surface in anchoring the side-chain mesogens near the interfaces is examined by comparing the reorientation of 30- and 120-nm-thick films. Irradiation with linearly polarized ultraviolet (UV) light and subsequent annealing causes the side-chain mesogen reorientation to align perpendicular to the electric field of the incident UV light. The inplane order in the 30-nm-thick films is lower than that in the 120-nm ones. On the other hand, the annealing period required for mesogen alignment is independent of the film thickness. It is suggested that the substrate surfaces anchor the LC mesogens to fix their orientation, rather than slowing down the reorientational motion. In addition, it is demonstrated that small LC molecules miscible with the nematic LC polymer enhance photoinduced reorientation through cooperative molecular interaction with the side-chain mesogens, remarkably accelerating the orientation and improving the inplane order of the unidirectionally aligned mesogens.

© 2019 SPST. Homogeneously aligned liquid crystal (LC) cell was fabricated using nematic LCs (NLCs) doped with a polymerizable monomer comprising of photocrosslinkable mesogenic side groups, combined with the linearly polarized UV light exposure at elevated temperature. We have clarified that the photosensitive layer forms on the substrates via the thermal polymerization, followed by generating the NLC photoalignment based on the axis-selective photocrosslinking. The LC characteristics of the photosensitive side groups of the polymerizable material play an important role in the defect-free alignment for the NLCs.

© 2019 Optical Society of America. The nonlinear propagation characteristics of a radially polarized (RP) beam in uniaxially aligned dye-doped liquid crystal (DDLC) are investigated in experiments and theory. The photothermal effect produces changes in the refractive index of the nonlinear polarization-sensitive medium, in both ordinary and extraordinary directions. The changes promote a self-modulation of the polarization pattern in the incident RP beam as it propagates through the DDLC. The experimental results are explained from theory by modeling the change in the refractive index of the medium. Our results may be applied to spatial polarization modulation, by which an axially symmetric polarized beam is converted into another structured light, such as the full Poincaré beam.

計算機ホログラムによる回折素子形成では,等方的位相差のデジタルパターンを計算し,それを媒体に記録することにより光学素子を形成する.ここに光学異方性を含めた光学素子の設計が可能であれば,偏光制御可能な複合光学素子が実現できる可能性がある.上記実現の為,本研究では光架橋性高分子液晶を用いて光学異方性がデジタルに記録された光学異方性回折素子を形成しその特性を評価した.

高度に光配向する水素結合性高分子液晶材料を用いて偏光ホログラム手法により複数の機能を組み合わせた偏光回折素子を形成し、これによって偏光検出が行えることを実証した。作成された複合偏光回折格子は入射偏光に依存する回折光分布を形成し、その分布を同定することで偏光状態を決定できた。

New oligothiophene derivatives were synthesized and their carrier mobilities were investigated by TOF technique. Further, molecular orientation of oligothiophenes on photoalignment film was evaluated.

We present a simple yet efficient method to automatically fabricate the twisted nematic structure by one-step exposure on an empty glass cell coated with photocrosslinkable polymer liquid crystal (PCLC) films. The resultant photoalignment directions of two substrates can be orthogonal to each other by controlling the difference between the exposure energy for upper and lower PCLC films and the twisted nematic (TN) structure can be automatically fabricated. The vector grating liquid crystalline cell with TN structure was also fabricated by means of a developed method, and the diffraction properties were well explained by the theoretical calculation on the basis of Jones calculus.