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This paper proposed a board-mounted ultrasonic variable-focus liquid crystal (LC) lens. The lens controls the focus using the acoustic radiation force generated by the resonant flexural vibration mode. The LC lens was fixed to an aluminum substrate with a hole whose aperture corresponded to the inner diameter of the transducer. The part of the LC lens attached to the substrates functioned as a fixed condition, and the flexural vibration mode was successfully generated. The fixed lens exhibited a gradual focal change with current, confirming that fixing the condition affected the rate of focal change.

The orientation angles of liquid crystal (LC) molecules were measured during ultrasound vibrations. Light transmitted through a fabricated LC lens was analyzed via the crossed Nicol condition and a crystal rotation method. The LC orientation angle was estimated with a theoretical model, and its distribution in the lens was determined. There was a strong correlation between the molecular angles and ultrasonic vibrational distributions, indicating that the angle was changed by the acoustic radiation force. The maximum tilt angle was 12° for a 50 V peak-to-peak input.

The effect of the liquid crystal (LC) layer thickness on the optical characteristics of an ultrasound LC lens was explored. Three LC lenses with differing LC layer thicknesses (100, 200, and 300 μm) were fabricated, and the optical focal lengths were measured by an optical microscope with a varying driving voltage. For the lens with a 200 μm thick LC layer, a larger change in the focal length was observed for a smaller driving voltage compared with that of the other two lenses, indicating that the LC layer thickness is appropriate for a variable-focus lens.

Light wave propagation in thick polarization gratings has been studied using the finite-difference time-domain (FDTD) method. The diffraction properties of the polarization Bragg gratings were strongly dependent on both the polarization state and incident angle of the probe beam. These characteristics were well explained by the FDTD calculation and the subsequent Fourier transformation. The FDTD calculation also revealed the light electric field near and/or in the polarization Bragg gratings.

We have developed holographic gratings that enable the asymmetric polarization conversion between ±1-order diffraction beams. The holographic gratings are formed by polarization holography in a poly[(methyl methacrylate)-co-(disperse yellow 7 methacrylate)] film and show both anisotropic phase and surface modulations. For an azobenzene-containing polymer film, molecular reorientation and migration are strongly dependent on the polarization state of the writing beams and can be spatially modulated. Theoretical investigation by the Jones matrix method including both modulations has shown that the polarization ellipticity of ±1-order diffraction changes as a function of relief depth. Experimental results in accordance with theoretical predictions show that the polarization gratings diffract linearly and circularly polarized beams simultaneously.

We have extensively studied the electric field of the light propagating in and/or near polarization holograms by the finite-difference time-domain (FDTD) method. Polarization holograms were fabricated using photoreactive polymer liquid crystals and showed peculiar polarization conversion. This experimental observation is well-explained by the FDTD calculation. The FDTD calculation revealed the connection between the near and far field of the light transmitted through the polarization hologram.

We have investigated two-dimensional anisotropic gratings in photocrosslinkable polymer liquid crystals irradiated with three mutually coherent beams. Both birefringence and surface topological modulation were induced by reorientation and migration of mesogenic molecules. Atomic force microscopy reveals a close-packed hexagonal array of gratings formed according to the interference pattern of the three beams. Diffraction properties including efficiency and optical anisotropy were well explained by the theory based on Jones calculus.

Highly efficient polarization holographic gratings in photoreactive polymer liquid crystal films with azobenzene side groups have been prepared using two orthogonal linearly polarized beams with an off-resonant wavelength and subsequent annealing. The higher order diffracted beams were clearly observed in the diffraction patterns and the diffraction properties including higher order diffraction were well-explained by the diffraction theory.

Surface relief (SR) formation in polymethacrylate films with azobenzene side groups was investigated via a holographic method using 325 nm He–Cd laser, which generated stable cis isomers. Because the azobenzene molecules underwent both photoinduced reorientation and photoisomerization according to the polarization and intensity distribution of the interference beams, formation of the SR structure depended on both the exposure energy and polarization distribution. For intensity holography, both the photogenerated cis isomer distribution and polarization direction of the exposed beams played important roles in SR formation, which accompanied the molecularly reoriented SR structure. For polarization holography, a small SR structure accompanied the periodical molecular orientation in the initial stage of polarization holography due to uniform distribution of cis isomer. However, a SR structure larger than that generated by intensity holography was produced in the photostationary state.

Molecularly oriented surface relief (SR) structures in photo-crosslinkable liquid crystalline copolymer films were fabricated using a 325 nm He–Cd laser with p–p and s–s polarized intensity holographic beams. The SR height increased as the exposure energy increased. In contrast, the molecular orientation structure depended on the exposure dose. For all doses, molecular migration from the lower exposure region to the higher one was due to the difference in the crosslinking density. The SR height reached up to 280 nm for a film that was initially 1.0 µm thick. The diffraction efficiency depended on the fabricated SR grating, while the difference in the molecular reorientation area and the direction of the SR gratings explained the diffraction properties.

We present a simple yet efficient, competitive, and practical fabrication method, called “polarizer rotation exposure”, for preparing vector gratings with a large area and a high diffraction efficiency. The polarization states of ultraviolet light were modulated by rotating the polarizer, and the resultant ultraviolet light was line-focused onto hydrogen-bonded liquid crystalline polymer films set on a linear stage. Mesogenic molecules in the polymer films were reoriented according to the light electric vectors, and vector gratings in which the optical anisotropy is periodically modulated were fabricated by the polarizer rotation exposure method.

Molecular orientation in a photo-crosslinkable liquid crystalline polymer (PLCP) film was explored by a thermal nanoinprinting technique using a SiO2/Si mold with a line-and-space (L&S) pattern. A molecular oriented structure was confirmed by polarization optical microscopy and diffraction efficiency measurements, at which the reoriented direction was parallel to the mold lines. We demonstrated thermal nanoimprinting on prealigned PLCP films by linearly polarized UV (LPUV) and evaluated the optical characteristics of imprinted PLCP films. As a result, the prealigned PLCP films were reoriented by thermal nanoimprinting.

We achieved facile surface relief (SR) formation with symmetrical and asymmetrical structure in photoreactive polymer/benzophenone (BP) monomer composite films by holographic exposure to 325-nm He–Cd laser beams. Under holographic exposure, photo-excited BP molecules induced photo-crosslinking of the composite film, incorporating BP molecules into the polymer and generating molecular motion, resulting in SR formation. The height of the SR depended on the polymer/BP ratio, and reached 550 nm. Furthermore, slantwise exposure resulted in asymmetrical SR formation. The resultant SR gratings were transparent to visible light and thermally stable up to 95 °C.

The diffraction properties of polarization holographic gratings fabricated using the orthogonally elliptical polarized light have been systematically investigated on the basis of the Jones calculus. The theoretical prediction based on the Jones calculus was experimentally confirmed to be valid by fabricating the polarization holographic gratings in azobenzene-containing amorphous polymer films. The ellipticity of the diffraction beam was well-controlled by varying the ellipticities of the writing beams. The diffraction properties were well explained by the Jones calculus.

We present the results of our experimental studies aimed at quantifying holographic recordings in photoreactive monomer/polymer composites. In addition to surface-relief gratings, index modulation gratings also appear during holographic recording, and the resulting dual gratings are characterized using the diffraction theory. The experimental results including the effects of the annealing temperature on the grating characteristics are explained on the basis of molecular migration.

Various types of two-dimensional crossed polarization gratings have been prepared in a photocrosslinkable polymer liquid crystal substituted with a 4-methoxycinnamoyloxybiphenyl side group by the use of orthogonally polarized ultraviolet interference light and subsequent annealing. The phase grating is almost invisible after irradiating the ultraviolet interference light without annealing and is thermally enhanced during the subsequent annealing. The two-dimensional crossed polarization gratings can generate two-dimensional diffraction patterns with various types of polarization states. The experimental results are in good agreement with the theoretical expectations on the basis of the Jones calculus.

We produced polarization gratings in photocrosslinkable polymer liquid crystal using a two-step ultraviolet exposure method, which causes the molecular reorientation to be modulated periodically in the orthogonal direction corresponding to the direction of linearly polarized ultraviolet light. A theoretical description of the fabricated polarization gratings is given by Jones matrix calculations. The calculated diffraction efficiency using a rectangular function to represent the shape of the grating profile differed from the experimental results in higher-order diffraction. We then applied a trapezoidal function to the same calculation. The difference between the experimental results and the calculated results was explained by considering the effect of scattering on the measured values. Furthermore, from using the trapezoidal function, the area of the molecular alignment transition was estimated to be approximately 3 µm.

The thermally enhanced photoinduced reorientation behavior of liquid crystalline (LC) polymethacrylate films comprising 4-methoxyazobenzene side groups with different spacer lengths between the azobenzene group and the polymer backbone was investigated based on axis-selective Z-to-E photoisomerization using linearly polarized (LP) 633 nm light and thermal amplification of the photoinduced anisotropy. A high-order in-plane reorientation parallel to the polarization (E) of LP 633 nm light was accomplished regardless of the spacer length. We found that the initial orientation of the mesogenic groups played an important role in the reorientation, and clarified the reorientation mechanism by polarization absorption spectroscopy.

In this paper, we describe the thermally enhanced photoinduced reorientation behavior of copolymer liquid crystals, which comprise a methacrylate with 4-(4-methoxycinnamoyloxy)biphenyl (MCB) side groups and N-phenylmaleimide (PM), by irradiating with linearly polarized ultraviolet (LPUV) light and subsequent annealing. Adjusting the exposure energy controls the reorientation direction both perpendicular and parallel to the polarization of LPUV light. The generated birefringence is greater than 0.19 for both directions. A polarization grating with molecular orientation periodically modulated in orthogonal directions is fabricated using a grating photomask. The changes in the polarization of diffracted beams are similar to those of a polarization grating fabricated by a holographic technique.