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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 Poincare beam.

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.

To fabricate two-dimensional anisotropic diffractive optical elements, the polarization drawing method using polarization-sensitive liquid-crystal polymers and a galvano scanner offers a flexible approach. This method produces an arbitrary anisotropic distribution in the polymer films by controlling the polarization state of an ultraviolet laser beam during scanning. The fabrication of two patterned anisotropic diffractive elements, which cannot be fabricated using conventional methods of polarization holography, demonstrates its efficacy. In addition, we also fabricate a liquid-crystal Fresnel lens using this method. Our approach has the potential to produce highly functionalized diffractive optical elements having complex anisotropic spatial distributions.

Polarization gratings (PGs) were fabricated by the recording of vector holograms between two orthogonally polarized vector vortex beams (VVBs). The polarization and diffraction properties of the resulting PGs were analyzed theoretically. The feasibility of the process was demonstrated experimentally using a photo-crosslinkable liquid crystal polymer film as the polarization-sensitive material. The fabricated PGs can convert homogeneously polarized laser beams into VVBs, vector beams, optical vortices, and ring-shaped optical lattices by controlling the incident beam’s state of polarization. The PGs that are presented will be applicable to optical communications and optical manipulation processes as vortex generators and converters.

Tunable wavelength-selective diffraction with polarization conversion is realized by the design of a liquid crystal (LC) grating containing a twisted nematic alignment structure that is fabricated by an efficient one-step photoalignment method. The diffraction efficiency strongly depends on the wavelength of the incident beam, and this property can be controlled by adjusting the birefringence of the nematic LC using a thermal control. These properties are well described by a theoretical analysis based on the Jones calculus and are experimentally demonstrated using 488, 532, and 633 nm wavelength incident polarized laser beams. The resultant LC grating has potential applications as diffractive optical elements that can simultaneously control the parameters of light such as amplitude, wavelength, and polarization.

We characterized the photoalignment anchoring energy of photocrosslinkable liquid crystalline polymers (PLCPs) doped in a liquid crystal (LC). PLCP-doped LC cells with homogeneous alignment were fabricated using rubbed polyimide (PI) films. The PLCP-doped LC cells were exposed to a linearly polarized ultraviolet laser beam, and were then annealed. As a result, the PLCP-doped LCs were realigned owing to the axis-selective photocrosslink reaction. We investigated the relationship between the surface anchoring strength of the rubbed PI films and the realignment direction. The result suggested that the photoalignment anchoring strength of the PLCP in the LC is higher than 4 × 102 J/m3 at the maximum. The photoalignment realized substantial realignment in the LC cell with the surface anchoring strength of 10−4 J/m2.

A holographic liquid crystal polarization grating with a Fabry-Perot structure was developed. Because of its resonant structure, the device offers high levels of control of the diffraction properties of incident-polarized light beams, depending on the resonance conditions. The diffracted light beams are emitted in both the reflection and transmission directions, and the device thus works as a multibranch polarization grating with double optical paths, unlike a conventional polarization grating. These device features were experimentally demonstrated and were also explained theoretically.

Three-dimensional anisotropic structures were fabricated by a recording axisymmetrically polarized beam in azobenzene (azo)-dye doped liquid crystal polymer composites. Polarization and wavefront modulation properties of fabricated anisotropic structures are investigated by experimentally and theoretically analyzing the diffraction properties. Photo-induced anisotropic structures would be utilized to generate singular light waves, such as optical and polarization vortices.

Three-dimensional (3D) vector holograms have been formed in twisted-nematic (TN) azo-dye-doped polymer liquid crystal (LC) composites whose director is gradually rotated around the thickness direction in the initial state. Polarization states of diffracted beams were rotated in accordance with the twist angle, and the diffraction efficiency depended markedly on the incident angle. We confirmed that the 3D director distributions corresponded to the polarization modulation caused not only by light interference and the propagation in the LCs but also by the initial orientation of the LCs. In order to explain the observed properties a theoretical model of the periodic reorientation distribution in TN LCs was presented. The Jones matrix method is used to describe the interference of two polarized light beams in the anisotropic media. Then the finite-difference time-domain method was applied to analyze the diffraction properties of the 3D vector holograms recorded in the model medium.

Vector grating liquid crystal (LC) cells, with periodically intermixed 0° planar and 90° twisted nematic alignments and director distributions rotated in the grating vector, were fabricated using a one-step polarization holographic exposure. A nonorthogonal elliptically polarized interference UV beam was irradiated to the empty glass cell, which had the inner walls coated with a photocrosslinkable polymer liquid crystal film. The dependence of the diffraction properties on the birefringence of the nematic LC (E7) in the resultant vector grating LC cell was determined through experimental and theoretical analysis. The polarization azimuth and ellipticity of the diffracted beams were varied using the temperature of the nematic LC.

Holographic binary grating liquid crystal (LC) cells, in which the optical anisotropy was rectangularly modulated even as the grating was fabricated using holographic exposure, were fabricated by one-step polarization holographic exposure of an empty glass cell, the interior of which was coated with a photocrosslinkable polymer LC (PCLC). The present study is of great significance in that three types of holographic binary grating LC cells containing twisted alignments can be fabricated by simultaneous exposure of two PCLC substrates to the UV interference beams, which are sinusoidally modulated. The polarization conversion properties of the diffracted beams are explained well by theoretical analysis based on Jones calculus.

We present a universal polarization terahertz (THz) phase controller using a randomly aligned liquid crystal (LC) cell with graphene electrodes. The LC cell was fabricated using a nematic LC and two quartz substrates that were coated with a monolayer of graphene as the transparent electrode. The LC in the cell was prepared without any alignment treatments and was randomly aligned. The size of the random domains and the width of the disclination lines in the LC layer were several tens of microns. These textures disappeared when an alternating voltage was applied to the LC through the graphene layers. Using a THz time domain spectroscopic technique, we investigated the complex transmittance of the LC cell. The LC cell was highly transparent in the THz frequency range, and there was little change in the transmittance with the applied voltage. This indicated that the scattering loss originating in the randomly aligned LC molecules was small for the THz waves. We also demonstrated that the THz phase shift could be controlled by the applied voltage. The amplitude of the phase shift was explained by the ordinary and extraordinary refractive indices of the LC. These LC cells with graphene electrodes can be used to realize universal polarization THz phase controllers because of the random alignment.

We have substantiated a simple yet efficient, competitive, and practical method to automatically fabricate liquid crystalline grating cells with homogeneous or twisted nematic (TN) structures by one-step ultraviolet holographic exposure on an empty glass cell coated with a photocrosslinkable polymer liquid crystal with 4-(4-methoxycinnamoyloxy)biphenyl side group (P6CB) films. The polarization diffraction properties in the resultant liquid crystalline grating cells have also been investigated extensively by varying the grating pitch. The theoretical considerations on the basis of elastic continuum theory revealed that accumulation of elastic free-energy density due to the TN structure affected the diffraction properties, although the strong anchoring of our photoalignment material contributed effectively to form the expected spatial distribution of liquid crystalline directors in the grating cells.

Vector gratings combined with form birefringence in subwavelength-periodic structures were experimentally fabricated by imprinting on polarization-sensitive liquid crystalline polymers and subsequent polarization holographic recordings. Polarization-sensitive optical diffractions were well controlled and the diffraction properties were dependent on the combination of periodic birefringence due to the reorientation of the mesogenic director and form birefringence originating in subwavelength-periodic structures. Finite-difference time-domain was an effective tool for characterizing the optical properties of the polarization holographic gratings with subwavelength-periodic structures.

A subwavelength-period grating made in an intrinsic anisotropic medium was experimentally fabricated by means of imprinting and subsequent photoinduced molecular alignment of photocrosslinkable polymer liquid crystals (PCLC). Optical properties including the total birefringence and optic axis were theoretically and experimentally investigated by varying the crossing angle between the grating vector and the polarization azimuth of linearly polarized ultraviolet light for the photoalignment of PCLC. The total birefringence and optic axis were well-controlled by both form birefringence due to the subwavelength-period grating structure and intrinsic birefringence induced by photoalignment of PCLC. The finite-difference time-domain (FDTD) method was an effective tool for characterizing the optical properties of a subwavelength-period grating made in an intrinsic anisotropic medium.

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.

We investigated theoretically the interference of two counterpropagating polarized light beams in optically anisotropic media whose optical axis is in the film plane and is gradually rotated around the thickness direction. Results indicated that pure polarization modulation without intensity variation is obtained in the inhomogeneous media when the total angle of the rotation is much smaller than the total retardation. Reflective anisotropic gratings recorded by the polarization modulation were formulated as the perturbation of the dielectric tensor, and diffraction properties were studied using coupled-wave analysis (CWA) and a numerical method. By assuming that the period of the intrinsic distribution is substantially larger than that of the induced one, we demonstrated that CWA estimates the diffraction efficiency and the polarization state of the diffracted light with high accuracy.

The diffraction properties of reflective anisotropic gratings, which can be recorded in photoanisotropic media with uniaxial birefringence by three-dimensional vector holography, were characterized through the use of coupled-wave analysis (CWA). By investigating the perturbation of the dielectric tensor, we demonstrated that the gratings with sinusoidal distribution of the azimuthal angle of the optic axis diffract polarized light in which the ordinary and extraordinary components are converted for incident light. The polarization conversion was consistent with that calculated by a numerical method. In addition, it was shown that CWA enables highly accurate calculation of the diffraction efficiency with wavelength dispersion when the amplitude of the azimuthal angle is small.