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