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In the previous study, we evaluated the effectiveness of an orthogonal polarizer array to suppress the inter-pixel cross talk with respect to the page data recording in holographic memory (Nobukawa et al. in Opt Express 25:22425, 2017). The reconstruction quality was improved by the use of the orthogonal polarizer array applied for the signal beam, based on the reduction of inter-pixel cross talk. In the present study, we also employed a similar polarizer array for the detection of a reconstructed image. Simultaneously, some phase shift masks and various apertures restricting the recording spot were also applied for the holographic recording. As a result, we found that the areal density and reconstruction quality were improved significantly based on the suppression of inter-pixel cross talk and reduction of recording spot size. These findings can be used for the realization of practical high-density holographic memory.

In this paper, we evaluate a novel flaw-detection technique for metallic surfaces based on the use of phase-type blazed gratings. Transparent blazed gratings were prepared by the soft nanoi...

A random phase mask is often used for Fourier transform holography to improve its recording and reconstruction characteristics. However, a conventional random phase pattern has the disadvantage of expanding the recording spot, which is caused by the high-resolution phase modulation. Previously, we proposed a random phase pattern that makes the recording spot narrower than the conventional one with maintaining a moderate reconstruction quality. In the present study, we apply the proposed random phase pattern to computer-generated binary holograms and evaluate both the hologram distribution and reconstruction quality in terms of practical holographic memory systems. The results confirm the effectiveness of the random phase in the reconstruction for an elementary data pattern.

New technologies for adaptive optics are becoming increasingly important for miniature devices such as cell-phone cameras. In particular, motion-free autofocusing and optical image stabilization require sophisticated approaches for alternative lens architectures, materials, and processing to replace multiple solid elements. We discuss a new method, to the best of our knowledge, that provides image stabilization via an annular piezoelectric ceramic that uses ultrasound to drive a liquid crystal layer sandwiched between two circular glass substrates. The piezoelectric ceramic is divided into four quadrants that are independently driven with sinusoidal voltages at the resonant frequency of the lens. The technique is based on ultrasound vibrations with a suitable driving scheme. The lens configuration was modeled via finite-element analysis. Various combinations of the four-channel ultrasound transducer can be used to define the focal point of the liquid crystal lens. Clear optical images could be obtained with the lens. By using two-dimensional fast Fourier transforms, the focal point position was defined and shifted in the radial direction.

In this paper, we propose a ring-type grating in which grating vectors formed by periodic molecular alignments are superimposed radially. Depending on incident polarization states, the anisotropic gratings generate polarization dependencies for the ring-like first order diffraction. To determine the polarization states of incident light for both single and multi-wavelengths, we attempted to extract the optical intensity distribution on the ring-like diffraction from each single-shot diffraction image. In addition, a system that enables the detection of spatial modulation of optical birefringence is proposed. Finally, we concluded that the optical intensity distribution on the circumference of the ring-like diffraction has sufficient potential to be available.

Fresnel lens has a distinct wavelength dispersion for the focal lengths. This characteristic allows to apply Fresnel lens to a wavelength dispersion element for spectrometers. We have simulated the focusing characteristics of an advanced Fresnel lens which has a feature of eccentric modification to realizing a compact spectrometer.

A method to estimate orientation direction of liquid crystal molecules three-dimensionally under ultrasound excitation was proposed and the relationship between the ultrasound vibration and the molecular orientation was discussed. Our group have reported a technique to control orientation direction of liquid crystal molecules using ultrasound vibration which could be applied to an optical variable-focus liquid crystal lens. The lens consisted of a liquid crystal layer sandwiched by two glass circular discs and a piezoelectric ring. Ultrasound vibration induces change in the refractive index of the lens, enabling the variable-focus function. The three-dimensional orientation direction of the liquid crystal molecules in the lens was predicted from the transmitted light distributions under the crossed Nicol conditions. The liquid crystal molecules were inclined from vertical alignment by the ultrasound vibration, and larger ultrasound vibration gave larger inclination of the molecules. There was a strong correlation between the distributions of ultrasound vibration and the liquid crystal molecular orientation; the molecular orientation was changed remarkably between the antinodal and nodal parts of the ultrasound flexural vibration on the glass plate and the molecules aligned towards the antinode.

As a potential means of measuring birefringence distribution, we analyzed the interference fringes based on three circularly polarized beams: a right-handed signal beam, a left-handed reference beam, and a right-handed reference beam. All beams were crossed at the same angle on the interfering plane, creating a two-dimensional interference fringe with three grating vectors. We proposed that by analyzing the interference fringes, we can measure the anisotropic phase shift in the signal beam. The obtained features of the anisotropic phase shift can be extended to the measurement of two-dimensional birefringence distributions without rotational manipulations of the objectives or polarizers. The fringes were generated by monolithic gratings, which can generate three-beam interfering fields precisely and easily. Finally, we confirmed the feasibility of a birefringence measurement system without any rotational manipulations of optics.

Nematic liquid crystal is widely used in optical devices such as liquid crystal displays. The optical characteristics of liquid crystal devices (ex, birefringence) can be controlled by applying an electric field because the liquid crystal molecules have electric dipoles. Although indium tin oxide (ITO) is generally employed as the transparent electrode material, ITO needs the rare metal indium and has problems of low electric conductivity and transparency. Our group has proposed a novel control technique of liquid crystal molecular orientation using ultrasound vibration without using ITO [1]. In this report, an optical variable-focus liquid crystal lens using ultrasound was discussed.

Submicron-size of colloidal spheres itself and their self-assembled structures are useful basis for obtaining various functional structures. Up to now, we have succeeded to fabricate several unique structures that are expected to be applied to various components of a specific optical device, or the substrate for material- and/or bio-science research purpose. Facile fabrication procedures and obtained structures for an inverse opal structure, a binary colloidal structure, an alternating photonic crystal and glass structure, and an anisotropic hemispherical structure are introduced. Their optical functions are also described.

A first-order beam diffracted by periodic arrays of GMR structures consisting of Pt/Co free layers having perpendicular magnetization without a top electrode is investigated. Linear and two-dimensional arrays of various shapes having sizes of 10–50 μm and periods of 20–100 μm embedded in SiO 2 are fabricated. The angles of the plane of polarization for first or (1,0) diffraction spots at a wavelength of 633 nm are measured to be approximately 0.5° for all samples. The polarization angles for one- and two-dimensional arrays of magnetic patterns are studied theoretically by assuming that the structures have sinusoidal magnetic distributions. They are found to depend on the Kerr rotation angle of the Pt/Co multilayer and on the difference in reflectance between the Pt/Co and SiO 2 , but they are independent of the periodicities, sizes, and shapes of the patterns. On the other hand, the diffraction efficiencies due to the magneto-optical effect depend on the reflectance and Kerr rotation angles of the magnetic materials. The diffraction efficiency of the component arising from the magneto-optical effect is discussed.

Random phase masks are important technical elements for realizing holographic memory systems that enable high density recording. However, the broadly distributed Fourier spectrum often presents a problem because wide recording spots result in reduced total storage capacity for a recording medium. In the present study, we propose modified random phase masks with phase modulation elements exhibiting Gaussian profiles to suppress the spread of the recording spot and keep it in a narrow area, based on the reduction of the high-frequency components in a random phase pattern. We confirm the effectiveness of the proposed random phase mask using simulations of a computer-generated binary hologram. However, issues still remain in terms of the fabrication of random phase masks with Gaussian profiles. Therefore, we evaluate the feasibility of fabricating the proposed random phase mask using molecular diffusion under photopolymerization. The results confirm the feasibility of this approach over a relatively wide area for actual fabrication.

We studied the polarization state in an apertureless scanning near-field microscopy (a-SNOM) operating in reflection mode by using three-dimensional Finite-difference Time-domain (FDTD) method. As a result, the electric field around tip apex in the near-field region enhanced four times stronger than the incident light for ppolarization when the tip-sample separation was 10 nm. We find that the p- and s-polarization state is maintained for the scattered light when the probe is perpendicular to the sample. When the probe is not perpendicular to the sample, the polarization state of scattered light will rotate an angle that equals to the inclination angle of probe with p-polarization illumination. On the other hand, the polarization state will not rotate with s-polarization illumination.

In this work, we report on a dichroic reflection phenomenon in the specular direction. The reflective medium is an Au-coated anisotropic hemispherical structure (AuAHeS), composed of a polymer material, which is fabricated via a replication process based on a polystyrene (PS) spherical particle array monolayer. Structural anisotropy is provided artificially by stretching the silicone rubber mold used in the replication process. Depending on the anisotropy of the resulting structure, the absorbance spectra are significantly altered for incident light that is polarized either parallel or perpendicular to the stretching direction. Based on the optical characteristics of the structures observed in the present study, the generation of unique devices for optical, photonic, and bio-photonic applications is expected to be possible.

Anisotropic diffractive gratings formed by birefringent molecular alignment are fabricated by a holographic technique using a photo-cross-linkable liquid crystalline copolymer (PLCCP). Depending on the exposure energy used for holographic recording, bright or dark regions of the interference fringe can be chosen for the molecular-aligned region, analogous to positive- and negative-type photoresist processing in photolithography. In conjunction with simultaneously generated surface relief gratings, the anisotropic refractive index modulation inherent in the PLCCP film exhibits different diffraction properties depending on the incident beam polarization. The anisotropic refractive index grating profiles are quantitatively presented for two cases determined by the exposure energy, based on the Fourier analysis of diffractive optics. The selection of different grating formations selected by varying only the exposure energy could provide a strategy for the fabrication of functionalized diffractive optical elements.

A new asymmetric polarization holography was conducted to form a blazed surface relief (SR) structure in a polymethacrylate film comprised of 4-methoxyazobenzene side groups using asymmetrically controlled polarized 325 nm He–Cd laser beams. Asymmetrical molecular migration, which generated the blazed SR structure, was achieved by adjusting the influence of both the intensity and polarization distributions of the two beams on molecular migration.

Nematic liquid crystal is widely used in optical devices such as liquid crystal displays and controlled by electric fields through the liquid crystal layer. Our group has proposed a control technique of liquid crystal molecular orientation using ultrasound vibration without indium tin oxide electrodes [1]. In this study, using ultrasound and nematic liquid crystal, we realized a variable focus liquid crystal lens. The liquid crystal lens has no transparent electrodes and consists of a simple structure; a nematic liquid crystal layer with a thickness of 50 μm is formed between two circular grass plates. An annular PZT ultrasonic transducer was bonded on the glass plate. By exciting the transducer at the resonance frequencies (28 kHz), the flexural vibration modes were generated. The acoustic radiation force from the vibration changed the molecular orientation of the liquid crystals, which induced the distribution of the execution refractive indices. The liquid crystal layer then worked as a lens. The focal...

Surface relief (SR) gratings with a molecularly oriented structure and pure polarization hologram were fabricated on a photo-cross-linkable liquid crystalline copolymer using a 325-nm laser with various two-beam polarization modes. For intensity holography, the polarization information from the two beams simultaneously provided the molecular motion and molecular reorientation; the SR height reached up to 186 nm and the concave area revealed a molecular reorientation when the exposing beams were linearly polarized. In contrast, SR formation was negligible for polarization holography when molecular reorientation due to the polarization modulation was observed. The resulting polarization gratings changed the polarization properties of the diffraction beams, and their diffraction efficiency was reached 24%, which agreed with theoretical expectations.

A new photo-cross-linkable liquid crystalline polymer (PLCP) comprised 4-methoxycinnamoyloxy groups connected with a bistolane side group was synthesized to investigate thermally enhanced photoinduced molecular reorientation of a thin film with linearly polarized (LP) 365 nm light exposure. Due to the axis-selective photoreaction of the cinnamate groups followed by the thermally induced self-organization, large molecular reorientation parallel to the polarization of LPUV light ( S > 0.6) and large birefringence at the non-resonance region (Δ n = 0.34 at 632.8 nm) were obtained. The obtained Δ n value is the largest among transparent PLCPs in the visible region. The influence of the degree of photoreaction and the annealing temperature on the thermally enhanced molecular reorientation behavior was explored in detail. Finally, for an application of thin optical devices using the PLCP films, pure polarization holographic gratings with large birefringence, which showed periodic molecularly oriented structure, were fabricated using a 325 nm He–Cd laser in various polarization modes and characterized their optical properties.

A variable-focus lens using a combination of liquid crystals and ultrasound is discussed. The lens uses a technique based on ultrasound vibration to control the molecular orientation of the liquid crystal. The lens structure is simple, with no mechanical moving parts and no transparent electrodes, which is helpful for device downsizing; the structure consists of a liquid crystal layer sandwiched between two glass substrates with a piezoelectric ring. The tens-of-kHz ultrasonic resonance flexural vibration used to excite the lens generates an acoustic radiation force on the liquid crystal layer to induce changes in the molecular orientation of the liquid crystal. The orientations of the liquid crystal molecules and the optical characteristics of the lens were investigated under ultrasound excitation. Clear optical images were observed through the lens, and the focal point could be controlled using the input voltage to the piezoelectric ring to give the lens its variable-focus action.

Effects of recording wavelength on the recently proposed (Sasaki, 2008) three-dimensional vector holograms, in which the optical anisotropy is three-dimensionally modulated, are presented experimentally and theoretically. The polarization states of the interference light are three-dimensionally modulated due to both the polarization interference and optical anisotropy in the recording medium. These spatial distributions of the polarization states and the resulting diffraction properties in the three-dimensional vector holograms are strongly dependent on the recording wavelength. Theoretical consideration based on the finite-difference time-domain (FDTD) method reveals the mechanism of the optical characteristics of the three-dimensional vector holograms recorded by various kinds of light sources with different wavelengths.

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 present the results from some experimental and theoretical studies aimed at revealing the mechanism leading to the diffraction properties of two-dimensional cross polarization gratings in photocrosslinkable polymer liquid crystals. Although the polarization gratings are overwritten at the same place, each polarization grating works independently in our material system. The above-mentioned characteristic of our cross polarization gratings originates in the grating formation mechanism in the photocrosslinkable polymer liquid crystals, in which the molecules in the solid-state polymeric materials are not reoriented during exposure and reorientation is generated during the annealing process after multiple exposure.

We have presented the results of some experimental studies aimed at quantifying the anisotropic holographic recordings in photoreactive polymer liquid crystals. In addition to the surface-relief gratings, index modulation gratings also appear during the holographic recording process, and the resulting dual gratings with strong anisotropy were characterized using the diffraction theory. The index modulation gratings showed strong optical anisotropy although the gratings were recorded by means of intensity holographic technique with only circularly polarized light. The experimental results including the induced birefringence were explained on the basis of the molecular migration.

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.

One-dimensional multiplexed anisotropic gratings were fabricated in photoreactive polymer liquid crystals (PPLCs), and the diffraction properties were characterized. Based on the holographic technique, the overwriting process is combined with the highly-stable and –controllable molecular alignment of the PPLCs. As a result, 1st- and 2nd-order diffraction intensities variable gratings dependent on the polarization direction of probe beam were obtained without significant changing their total diffraction intensity. The multiplexed gratings can be used as polarization-selective diffractive optical elements.

Optical image reconstruction, a type of intensity amplification of a two-dimensional optical image, was demonstrated using photorefractive polymer-dissolved liquid crystals. Image amplification originated in nonlocal gratings generated in a photorefractive mesogenic composite consisting of a low-molar-mass nematic mixture, a functionalized copolymer, and sensitizing dye. This process was well-explained using Fourier optics and two-beam coupling theory for photorefractive effects.

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.

We have demonstrated spatial frequency selective reconstruction (SFSR) of two-dimensional optical images by using functionalized mesogenic composites possessing real-time holographic capability. The two-dimensional optical image was Fourier transformed by a lens and part of the spatial frequency was brought into interference with the reference beam in the Raman-Nath regime. The SFSR images were observed in the self-diffraction patterns and we calculated the expected reconstructed images which were in good agreement with the observed images.

Highly stable polarization gratings have been prepared in photocrosslinkable polymer liquid-crystal films by the use of two orthogonally polarized He–Cd laser beams and subsequent annealing. The resulting pure polarization gratings exhibiting thermal stability up to 150 °C diffract the beam and convert the polarization state at the same time according to the theoretical expectation.

The orientational photorefractive properties of the liquid crystal/polymer composites with different morphology are studied experimentally. The composites consist of the similar chemical components, but one shows phase-separated structure (polymer dispersed liquid crystal) and another one, miscible structure (polymer-dissolved liquid crystal composite). Particular attention is given to the observation and qualitative and/or quantitative modeling of the resolution, dependence of the applied dc field, dynamics of grating generation, and photocurrents, which is strongly dependent on the morphology of the composites.

We present a new fabrication method, called ‘two-step ultraviolet exposure’, to prepare anisotropic gratings in photocrosslinkable polymer liquid crystal films. Using the controllability of the reorientation direction of mesogenic molecules, anisotropic phase gratings, in which the mesogenic molecules were periodically modulated in orthogonal directions, were prepared by the use of one grating photomask. The resultant gratings diffract the light and convert the polarization states at the same time, and have applications as diffraction optical devices.

Nematic liquid crystals used in optical devices such as liquid crystal displays are controlled by the electric fields. Although indium tin oxide (ITO) is generally employed as the transparent electrode material to apply the electric field, it includes the rare metal indium and needs complicated processes such as sputtering deposition method. Our group has been investigating control techniques of molecular orientation of liquid crystals using ultrasound. In this study, we have applied these techniques to optical variable-focus lenses and the optical characteristics were examined. The ultrasonic liquid crystal cell has a simple structure with no transparent electrodes; it consists of has an annular ultrasound PZT transducer (inner diameter: 30 mm; thickness: 2 mm) and a liquid crystal cell in which a nematic liquid crystal layer (thickness: 25 μm) was formed between two glass substrates (thickness: 0.7 mm) and orientational films. The concentric flexural vibration modes could be generated on the cell at the...

We propose a technique to control the orientation of nematic liquid crystals using ultrasound and investigate the optical characteristics of the oriented samples. An ultrasonic liquid crystal cell with a thickness of 5–25 μm and two ultrasonic lead zirconate titanate transducers was fabricated. By exciting the ultrasonic transducers, the flexural vibration modes were generated on the cell. An acoustic radiation force to the liquid crystal layer was generated, changing the molecular orientation and thus the light transmission. By modulating the ultrasonic driving frequency and voltage, the spatial distribution of the molecular orientation of the liquid crystals could be controlled. The distribution of the transmitted light intensity depends on the thickness of the liquid crystal layer because the acoustic field in the liquid crystal layer is changed by the orientational film.

Polarization gratings, in which optical anisotropy is periodically modulated, are very attractive from the point of view of their interesting optical properties, including polarization selectivity of the diffraction efficiency and polarization conversion in the diffraction process (Nikolova et al., 1984). These properties make polarization gratings useful for numerous optical applications related to polarization discrimination (Davis et al., 2001; Asatryan et al., 2004), control (Nikolova et al., 1997; Hasman et al., 2002), and measurement (Gori, 1999; Provenzano et al., 2006). Polarization gratings can be fabricated by holographic exposure with polarized interference light in photoanisotropic media such as azobenzene-containing polymer (azopolymer) films (Todorov et al., 1984; Ebralidze et al., 1992; Huang and Wagner, 1993; Samui, 2008). Since azobenzene molecules reorient in accordance with polarization of light resulting from trans-cis-trans photoisomerization reactions, periodic structures are formed as spatial distribution of the molecular orientation by holographic recording using vectrial light (i.e., by vector holography). In addition, surface relief gratings are obtained by holographic recording in azopolymers (Rochon et al., 1995; Kim et al., 1995; Ramanujam et al., 1996; Naydenova et al., 1998; Labarthet et al., 1998, 1999). Nikolova et al. have investigated the diffraction properties of various types of vector holograms recorded in side-chain azobenzene polyesters (Nikolova et al., 1996). Birabassov and Galstian have analyzed the relationship of polarization states between holographic recording and reconstruction beams with the use of azopolymers (Birabassov et al., 2001). It has been also demonstrated that vector holograms realize recording and reconstruction of polarized optical images (Ono et al., 2009a, 2009b). In a previous paper, we presented three-dimensional (3D) vector holography, which is a novel concept for holographic recording using vectrial light (Sasaki et al., 2008). Common vector holograms are recorded in initially isotropic media such as amorphous azopolymers. In contrast, 3D vector holograms are recoded in initially anisotropic media. Since the propagation velocity of light in anisotropic media varies in accordance with the polarization state, standing waves with a multidimensionally varying state of polarization were obtained in the region of overlap. We recorded anisotropic gratings in a liquid crystalline medium by

This paper demonstrates formation of surface relief (SR) gratings and crossed SR gratings with molecularly oriented structure using photo-cross-linkable liquid crystalline copolymer films by means of holographic exposure of 325 nm He- Cd laser beams combined with linearly polarized (LP) UV light. For the intensity holography using He-Cd laser, SR gratings were formed after annealing the exposed films, where the molecular migration from the lower to the higherexposed region occurred. The reorientational part and SR height were dependent on degree of the photoreaction. When the exposure doses were low, molecular reorientation at the convex region was generated. In contrast, higher exposing doses resulted in the molecular reorientation at the concave area. The resulting gratings showed polarization sensitivity for diffraction efficiencies of the probe light beam according to the molecularly reorientation direction. Furthermore, multi-holographic exposure yielded crossed SR gratings with reoriented structure according the polarization direction of He-Cd laser beams, which exhibited multi-functional diffractions. Furthermore, when combining the multi-holographic exposure and the unidirectional LPUV light exposure, crossed SR grating with multi-directionally oriented film structure was generated., where the whole area was reoriented.

The diffraction properties of thick vector holograms were analyzed with the use of a simple coupled-wave theory. Two eigenpolarizations in the holograms were determined based on the dielectric perturbation, and diffraction efficiencies for the polarizations were calculated by applying the Kogelnik method. The results were compared with those simulated by the finite-difference time-domain method. As a result, it was demonstrated that the diffraction efficiencies calculated by the two methods are in good agreement for any incident polarization when the modulation depth of the anisotropic phase retardation is substantially smaller than the mean retardation. In addition, we confirmed that coupled-wave analysis provides reasonable accuracy for relatively large modulation in the case of Bragg incidence with eigenpolarization.

We theoretically investigate optical birefringence originating from subwavelength structures in intrinsic birefringent media. Assuming alternating layers of isotropic and anisotropic materials, the propagation of optical waves is simulated on the basis of the finite difference time domain method. Optical polarization changes throughout the structure reveal the birefringence of the layered structure as a whole. In addition, the birefringence is also analyzed on the basis of effective medium theory. The results indicate that the optical birefringence of the structure as a whole can be modified by the magnitude and direction of the intrinsic birefringence of the anisotropic layers. This theoretical prediction will be useful for micro- and nanofabrication in optical devices.

We report on polymer liquid crystals with periodically oriented mesogenic side chains and demonstrate that the resulting two-dimensional polarization gratings multiplex-diffract the laser beam and convert the polarization state at the same time. Two-dimensional diffraction patterns with various kinds of polarization states can be successfully generated by designing a combination of one-dimensional polarization gratings. This study is a considerable advance towards the realization of highly functionalized passive optical devices that can control both the beam propagation direction and the polarization state.

Photoinduced birefringence in the film made of our azobenzene copolymer was demonstrated using blue excitation laser beams and observed by a red probe laser beam. The birefringence values was obtained by polarimeter. The polarization state of the probe beam was changed by the photoinduced birefringent film when the polarization state is not agreed with the polarization state of the excitation laser beam. Then, a polarization component orthogonal to the polarization state of the incident probe beam was observed. Using the principle, an image pattern was recorded in the film using one-beam.

Highly efficient and functionalized polarization gratings have been recorded in azobenzene-containing mesogenic composites with twisted nematic cell configurations. The polarization gratings formed in azobenzene-containing mesogenic composites show a high diffraction efficiency of more than 45% and convert the polarization state of light at the same time. The polarization direction of the diffracted laser beams can be controlled by the twisted angle of the nematic cell. These characteristics of the polarization gratings are well explained by means of Jones calculus.

We have demonstrated the two types of applications in the field of the optical information processing by using the photorefractive mesogenic composite consisting of a mixture of three components including a functionalized copolymer, a low-molar-mass liquid crystal, and sensitizing dye. One of the applications is to amplify the two-dimensional optical image by means of the Fourier transform geometry with the two-beam coupling optical system. The other is to enhance the edge of the optical image using Fourier transform holographic geometry. We calculated the expected images on the basis of the Fourier transform optics and the photorefractive properties of the mesogenic composite, and obtained good agreement with the observed images and the theoretical expectation.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Optical anisotropy was induced in azobenzene copolymer film using linearly or elliptically polarized laser beams. The Jones matrix of the anisotropic film was calculated from the change in polarization of the probe light. Two eigenpolarization states were obtained from the matrix. These two eigenstates are useful as a polarization basis for a polarization-tunable component.

For Fourier transform holography, an effective random phase distribution with randomly displaced phase segments is proposed for obtaining a smooth finite optical intensity distribution in the Fourier transform plane. Since unitary phase segments are randomly distributed in-plane, the blanks give various spatial frequency components to an image, and thus smooth the spectrum. Moreover, by randomly changing the phase segment size, spike generation from the unitary phase segment size in the spectrum can be reduced significantly. As a result, a smooth spectrum including sidebands can be formed at a relatively narrow extent. The proposed phase distribution sustains the primary functions of a random phase mask for holographic-data recording and reconstruction. Therefore, this distribution is expected to find applications in high-density holographic memory systems, replacing conventional random phase mask patterns.

We have developed a magneto-optical spatial light modulator (MOSLM) using giant magneto-resistance (GMR) structures for realizing a holographic three-dimensional (3D) display. For practical applications, reconstructed image of hologram consisting of GMR structures should be investigated in order to study the feasibility of the MOSLM. In this study, we fabricated a hologram with GMR based fringe-pattern and demonstrated a reconstructed image. A fringe-pattern convolving a crossshaped image was calculated by a conventional binary computer generated hologram (CGH) technique. The CGH-pattern has 2,048 × 2,048 with 5 μm pixel pitch. The GMR stack consists of a Tb-Fe-Co/CoFe pinned layer, a Ag spacer, a Gd-Fe free layer for light modulation, and a Ru capping layer, was deposited by dc-magnetron sputtering. The GMR hologram was formed using photo-lithography and Krion milling processes, followed by the deposition of a Tb-Fe-Co reference layer with large coercivity and the same Kerr-rotation angle compared to the free layer, and a lift-off process. The reconstructed image of the ON-state was clearly observed and successfully distinguished from the OFF-state by switching the magnetization direction of the free-layer with an external magnetic field. These results indicate the possibility of realizing a holographic 3D display by the MOSLM using the GMR structures.

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.