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The influence of the annealing conditions on the thermally stimulated photoinduced molecular reorientation of a photoinactive liquid crystalline polymethacrylate with phenyl aldehyde and benzoic acid side groups (P1) doped with 4-methoxyaniline, which forms photoalignable 4-methoxy-N-benzylideneaniline (MNBA) side groups in situ, was investigated. Light exposure and subsequent thermal stimulation under a N2 atmosphere realized sufficient cooperative molecular reorientation (D > 0.7), but the simultaneous thermal hydrolysis of the MNBA groups under humid air lowered the molecular reorientation performance. By contrast, subsequent thermal hydrolysis of MNBA after molecular reorientation introduced different aromatic amines into the reoriented P1 film, which regulated the birefringence and photofunctionality of the oriented film.

The incident angle dependence of the diffraction properties of orthogonal-circular polarization gratings (OCPGs) fabricated using a polymer liquid crystal exhibiting biaxial anisotropy have been investigated. It was found that a specific biaxial anisotropy reduces the incident angle dependence of optically thin OCPGs against the wavelength of an incident light.

We have studied current induced magnetization switching in W/CoFeB/MgO based three terminal magnetic tunnel junctions. The switching driven by spin—orbit torque (SOT) is evaluated in the so-called type-Y structure, in which the magnetic easy-axis of the CoFeB layer lies in the film plane and is orthogonal to the current flow. The effective spin Hall angle estimated from the bias field dependence of critical current (Ic) is ~ 0.07. The field and current dependence of the switching probability are studied. The field and DC current induced switching can be described using a model based on thermally assisted magnetization switching. In contrast, the 50 ns long pulse current dependence of the switching probability shows significant deviation from the model, even if contribution from the field-like torque is included. The deviation is particularly evident when the threshold switching current is larger. These results show that conventional thermally assisted magnetization switching model cannot be used to describe SOT induced switching using short current pulses.

A polarized laser beam steering system using multiply cascaded rotating polarization gratings (PGs) is presented. The rotating PGs steer incident circularly polarized beams with high optical throughput because the theoretical limitation of the PG diffraction efficiency is 100%. The system also offers more rapid rotation when compared with wedge prism pairs because of the weight of the PGs. The beam steering performance was analyzed theoretically for schemes using two and four rotating PGs. The system’s feasibility was demonstrated experimentally by projecting Lissajous and raster patterns using PGs fabricated from photocrosslinkable polymer liquid crystal films via a photo-alignment technique. The steered beam’s diffraction efficiency and ellipticity were maintained at 83 ∼ 89 % and 96 ∼ 99 % , respectively, during PG rotation. This beam steering system will be applicable to light detection and ranging, optical imaging, and laser displays.

To augment the magnetoresistance (MR) ratio of n-type non-degenerate Si-based lateral spin valves (Si-LSVs), we modify the doping profile in the Si layer and introduce a larger local strain into the Si channel by changing a capping insulator. The highest MR ratio of 1.4% is achieved in the Si-LSVs through these improvements, with significant roles played by a reduction in the resistance-area product of the ferromagnetic contacts and an enhancement of the momentum relaxation time in the Si channel., 14 pages, 4 figures

In recent years, vector beam (VB)-based optical multiplexing communication is attracting attention to increase the information transfer capacity, and hence several types of VB demultiplexers fabricated by using liquid crystals have been reported. In this presentation, we propose a crossed-fork-shaped polarization grating (CFPG) as a new VB demultiplexer. The CFPG was fabricated by recording multiple polarization holograms onto the photocrosslinkable polymer liquid crystal. Recorded each polarization hologram works individually to act as a VB detector, which converts specific VB into a Gaussian beam with diffraction. The CFPG has the potential to miniaturize the demultiplexer because several VB detection functions can be integrated. VB detection between radial and azimuthal polarizations also demonstrated by using a pair of quarter-wave PG and normal-FPG.

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.

We report a terahertz (THz) metamaterial consisting of a metal mesh layer with nematic liquid crystals (LCs). The metal mesh has subwavelength apertures that function as a bandpass filter in the THz spectral range. The LCs are embedded and aligned homogeneously in the apertures. The electromagnetic characteristics were calculated with a finite-difference time-domain method. The metamaterial converts the polarization of the THz wave during transmission and the thickness of the LC layer can be reduced by two orders of magnitude relative to the homogeneously aligned LC without the meta-structures. This increases the response speed to applied external fields. We also fabricated the metamaterial using a dielectric substrate with a metal mesh layer, a nematic LC, and a dielectric substrate with a polymeric alignment layer and investigated its polarization conversion using THz time-domain spectroscopy. The experimental results demonstrated that metal mesh structures with LCs are useful for active THz polarization converters.

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.

The incident angle dependences of the diffraction properties of orthogonal-circular polarization gratings (OCPGs) fabricated using a polymer liquid crystal exhibiting biaxial anisotropy have been investigated. The investigations were conducted with the plane orthogonal to the surface of the OCPGs as the plane of incidence. It was found that a specific biaxial anisotropy reduces the incident angle dependence of optically thin OCPGs against the wavelength of the incident light, and is less effective on thick OCPGs. In addition, a method also has been proposed to determine the biaxial anisotropic shape that most reduces the incident angle dependence in thin OCPGs.

Liquid crystalline polymers (LCPs) comprised of N-benzylideneaniline (NBA) side groups with different alkylene spacer length (n = 2, 6, and 10) are synthesized and their photoinduced reorientation ...

In this work, a polarization grating in Raman-Nath regime was fabricated by using a photoreactive polymer liquid crystal exhibiting biaxial optical anisotropy. And from the measured characteristics, it has been demonstrated that the flat incident angle dependences on diffraction efficiency and polarization ellipticity are obtained by introducing biaxial optical anisotropy.

A crossed-fork shaped polarization grating (Crossed-FPG) was developed as a mode demultiplexer for vector beam division multiplexing communication. The Crossed-FPG was fabricated by recording several polarization holograms between optical vortex and Gaussian beam with opposite-handed circular polarizations. Mode detection of vector beams was experimentally demonstrated.

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.

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.

An aerial display scheme consisting of an orthogonal circular polarization grating (OCPG), a waveplate, a retroreflector array (RRA), and a right-angle prism (RAP) was developed. Because of the OCPG’s functionality, retroreflected light from the RRA is transmitted through the RAP boundary surface by avoiding the total reflection condition. The proposed system can potentially increase optical throughput to 100% by designing the boundary surface incidence angle to be Brewster’s angle. The scheme’s feasibility was demonstrated experimentally using an OCPG and waveplate that were fabricated from polymer liquid crystal with optical anisotropy using a photoalignment technique. The scheme should be used as a type of aerial display that is compatible with polarization-diffractive elements called Pancharatnam–Berry phase elements.

We present a simple yet versatile and practical polarization camera for imaging full Stokes parameters. The developed system consists of one anisotropic diffraction grating plate and two electro-switchable retarders and obtains in nearly real-time full Stokes images of the light scattered from the objects. The monochromatic S3 image is obtained by physically separating the right and left circularly polarized components with the aid of the anisotropic grating, and S1 and S2 images are obtained by fast electro-switching the retardation of each retarder. The simple polarization imaging system has possible applications in various types of imaging systems and especially should be incorporated into optical microscopes as well as imaging cameras in future work.

We report herein our investigation of planar terahertz (THz) metamaterials with metallic fish-scale structure. The fish-scale metamaterials with different slant angles were designed based on finite-difference time-domain simulations and fabricated on a dielectric substrate by using a laser-beam drawing system. Theoretical simulations indicate that the eigenpolarization states of the slant fish-scale metamaterials are corotating elliptical polarizations with orthogonal azimuth angles (i.e., the slant fish-scale metamaterials possess planar chirality in the THz spectral range). We measured the transmission spectra and polarization-conversion property of the fabricated metamaterials by using THz time-domain spectroscopy with a wire-grid polarizer. The results were consistent with the theoretical simulations. The experimental and calculation data clarify that both the azimuth angle and elliptical angle of the polarized THz wave transmitted through the planar metamaterial can be controlled by the slant angle of the fish-scale pattern. This study demonstrates the potential of the fish-scale metamaterials for polarization converters in the THz spectral range.

We investigate control of the photoinduced orientation of photoalignable polymeric films from polymethacrylate with 4-oxybenzaldehyde side groups (1) and monomeric 4-methoxyanilline (2) composites, where both 1 and 2 have no photoreactivity. Annealing the 1/2 composite film with various 1/2 ratio generates N-benzylideneaniline (NBA) side groups, which exhibit photoreactivity and photoinduced molecular reorientation when irradiated with linearly polarized (LP) 365 nm light. Adjusting the 1/2 mixture ratio controls the amount of NBA side group's formation, as well as the photoinduced orientation performance of the film. Analyses of the three-dimensional refractive indices reveal biaxial photoinduced reorientation for a 1/2 film saturated with NBA side groups (∼96%), while in-plane motion plays a major role for 1/2 films containing unreacted 4-oxybenzaldehyde side groups. Furthermore, a post-annealing procedure after exposure greatly amplifies the in-plane reorientation structure for film consisting of more than 75% NBA side groups, which exhibits LC characteristics.

Polarization holographic gratings were formed in liquid crystal (LC) cells fabricated from a mixture of low molecular weight nematic LC and a photoreactive liquid crystalline polymer (PLCP) with 4-(4-methoxycinnamoyloxy)biphenyl side groups. The diffraction properties of the gratings were analyzed using theoretical models which were determined based on the polarization patterns of the polarization holography. The results demonstrated that vector gratings comprised of periodic orientation distributions of the LC molecule were induced in the cells based on the axis-selective photoreaction of the PLCP. The vector gratings were erased by applying a sufficiently high voltage to the cells and then were reformed with no hysteresis after the voltage was removed. This phenomenon suggested that the PLCP molecules were stabilized based on the axis-selective photocrosslink reaction and that the LC molecules were aligned by the photocrosslinked PLCP. This LC composite with axis-selective photoreactivity is useful for various optical applications, because of their stability, transparency, and response to applied voltage.

Enhancement of optical transmittance of polymer-dispersed liquid crystal (PDLC) cells was investigated by introducing a modification into the substrates. Surface treatment by rubbing was performed on both network-type and droplet-type PDLCs to investigate the effect on the optical transmittance of the cells. Differences in the transmittance of the PDLC in the polymer matrix were observed by introducing rubbing effect on network-type PDLC but not on droplet-type PDLC. These phenomena might be used to distinguish the application field of both types of PDLC cells by enhancing optical transmittance and scattering properties.

The photoinduced reorientation behaviors of liquid crystalline (co)polymethacrylates (LCPs) comprised of N -benzylideneaniline (NBA) and 4-cyanobiphenyl or 4-methoxybiphenyl side groups are compared using linearly polarized (LP) 313 nm and LP 365 nm light. LCP films realize effective cooperative reorientation based on trans-cis-trans photoisomerization of the NBA moieties using LP 365 nm light and stabilization of the orientation structure due to copolymerization. In contrast, photochemical hydrolysis lowers the reorientation efficiency of LCP films when using 313 nm light. Changing the polarization direction of the LP 365 nm light controls the reorientation direction of the LCP films for several cycles, but the in-plane orientation order gradually decreases. Finally, LP 365 nm exposure and subsequent solvent annealing using a photo-cross-linked film achieve a repeatable write-erase-write of the orientation structure of the copolymer film.

To fabricate fine metal structure, we proposed and demonstrated a method by using interference pattern of copropagating optical vortices and lift-off process. This method can fabricate more fine structure compared with the conventional laser drawing method using Gaussian beam even if the low numerical aperture condition.

In the present presentation, we report the experimentally and theoretically investigated spatial wavefront conversion properties of an optical vortex (OV) generation system including azo-dye doped liquid crystal (ADDLC) polymer composite and vector beam illuminator, focusing on the abilities of flexibility and achromaticity. Threedimensional anisotropic structure was induced by recording vector beam in ADDLC and it can convert a polarized Gaussian beam into polarized OVs whose topological charge is depending on the structure of anisotropy. The photo-induced anisotropic structure can be re-initialized by turning it off and changing the illuminating polarization pattern of vector beam. Numerical simulations and experimental results showed that our anisotropic structure can generate OV with broadband spectrum.

Liquid crystal grating with three-dimensionally modulated anisotropic structure is fabricated by one-step exposure of an empty glass cell whose inner walls are coated with photocrosslinkable polymer liquid crystals to four-beam polarization interference UV beams. The diffraction properties were probed with a 633 nm wavelength laser and a 532 nm wavelength laser which were the coaxial incident. The novel properties, which diffraction directions are threedimensionally different depending on the wavelengths, are realized by the resultant liquid crystal grating. Furthermore, the resultant liquid crystal grating can be also applied to an advanced polarizing beam splitter which opposite circular polarization and linear polarizations are diffracted simultaneously. These diffraction properties were well-explained by Jones calculus. The resultant liquid crystal grating has the plural of the functions of optical elements such as wave plates, polarization beam splitter, dichroic beam splitter, Wollaston/Rochon prism, and tunable wavelength filter. Therefore, the resultant liquid crystal grating can contribute to miniaturization, sophistication, and cost reduction of optical systems using for, such as optical measurement, communication, and information processing.

Polarization is one of the important parameters of the light wave. Diffractive elements, which can control the polarization, have been attracted as high-performance light control device. We have implemented various studies on the formation method and the diffraction characteristics of the anisotropic diffractive element using a photoreactive material. Photocross linkable polymer liquid crystal (PCLC) is an attractive material that can induce anisotropy along the polarization direction of linearly polarized ultraviolet light (LPUV). Also, owing to its relatively large anchoring strength, PCLC have been used as an alignment film of low-molar-mass liquid crystal (LC). Galvanometer scanners (GS) can freely control the exposure position of the laser beam by adjusting the two mirrors, it is possible to form a highly functionalized optical element by drawing the arbitrary exposure lines to the photo-reactive material with temporally changing the polarization state of the laser beam. In this study, we report the polarization drawing method based on GS for the fabrication of anisotropic diffractive optical elements. First, the two types anisotropic diffractive optical elements were fabricated on the PCLC films. To investigate the diffraction properties of fabricated anisotropic diffractive optical elements, we used a polarized He-Ne laser beam as probe and observed diffracted lights. Diffracted beam was twodimensionally emitted depending on the formed anisotropic optical distribution. Then we fabricated LC cell, which works as polarization dependent anisotropic Fresnel lens. The experimental investigations show that it has functions of light condensing and polarization control. From these results, high-performance light control device can be fabricated by the polarization drawing method.

A polarization-independent terahertz (THz) phase shifter was proposed using a liquid crystal (LC) grating with subwavelength periodic alignment. The LC grating was constructed with one-dimensional periodic planar alignment and was designed based on the effective medium theory. The phase of the transmitted wave was theoretically independent of the polarization state and the phase was shifted by transition from a periodic planar alignment to a homeotropic alignment. The LC grating was fabricated using a nematic LC and photoalignment layers. The easy axes of the photoalignment layers were periodically regulated using a grating photomask with a subwavelength pitch. There was minimal dependence of the obtained phase shift on the polarization state, and the results were in agreement with the theoretical calculations.

Display Omitted We evaluate molecular orientation of photoreactive liquid crystalline polymer P6CAM.Thermal nanoimprinting and graphoepitaxy were used to align P6CAM.P6CAM was reoriented parallel to the line in both processes.Thermal nanoimprinting strongly induced P6CAM orientation compared to graphoepitaxy. Molecular orientation in photoreactive liquid crystals (LCs) can be induced by linearly polarized ultraviolet light and heat. Thermal nanoimprinting has similarities to graphoepitaxy, including using patterned substrates and heating. Diffraction efficiencies were measured to compare the molecular orientation of the photoreactive LC polymer P6CAM induced by thermal nanoimprinting, with that induced by graphoepitaxy. P6CAM was reoriented by graphoepitaxy, but the degree of orientation was much smaller than that induced by thermal nanoimprinting.

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.

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.

Nonlinear light propagation in a dye-doped liquid crystal (LC) was investigated experimentally. A laser beam with wavelength far from the absorption peak of the material was coupled into an LC cell with homogeneous alignment, and the propagation in the cell was observed. When the polarization azimuth of the incident light was orthogonal to the orientation direction of the LC, soliton-like propagation was obtained for milliwatts of light power in spite of the low absorption. We clarified that the observed nonlinearity is due principally to the photothermal effect enhanced by the dye.

The formation of polarization holographic gratings with both optical anisotropy and surface relief (SR) deformation was studied for polymethylmethacrylate with azobenzene side groups. Temporal contributions of isotropic and anisotropic phase gratings were simultaneously determined by observing transitional intensity and polarization states of the diffraction beams and characterizing by means of Jones calculus. To clarify the mechanism of SR deformation, cross sections of SR were characterized based on the optical gradient force model; experimental observations were in good agreement with the theoretical expectation. We clarified that the anisotropic phase change originating in the reorientation of the azobenzene side groups was induced immediately at the beginning of the holographic recording, while the response time of the isotropic phase change originating in the molecular migration due to the optical gradient force was relatively slow.

This article presents effects of photocrosslinking on photorefractive properties in polymer-liquid crystal composites doped with fullerene (C60) as a photoconductive agent. The efficiency of the photorefraction was improved by crosslinking the polymer network and reached near to the theoretical limit for the thin phase grating. The carrier conduction in the composite films was investigated and the high-performance photorefractivity of the photocrosslinked mesogenic composite was explained by low dark current and high photocurrent. The firm crosslinked polymer network in the polymer-liquid crystal composite has also employed for the stable photorefractive diffraction at elevated temperature and under a static dc field applied the mesogenic composite film.

We investigated the photorefractive performance of the polymer dissolved liquid crystalline composite (PDLCC), in which liquid crystalline polymer and low-molar-mass liquid crystal are miscible without phase separation, doped with three kinds of fullerene derivatives with different length of alkyl groups. The photorefractive performance was improved for the photorefractive PDLCC doped with fullerene derivatives with long length of alkyl groups. The photorefractive grating formation originates in the cooperative reorientation of the liquid crystalline director and the space charge field was estimated using the elastic continuum theory and the field for the PDLCC doped with the functionalized fullerene with longer alkyl side groups was larger than that for the PDLCC doped with conventional fullerene C60.

The blazed vector grating possessing antisymmetric distributions of the birefringence were fabricated by exposing the line-focused linearly polarized ultraviolet light on the photosensitive polymer liquid crystals. The polarization states of the diffraction beams can be highly and widely controlled by designing the blazed structures, and the diffraction properties were well-explained by Jones calculus.

In this paper, we designed and analyzed an efficient taper structure to couple light into and out of photonic crystal waveguides (PhCWs) fabricated by Si-ion implantation and electron beam lithography. The coupling structure employs the gentle refractive-index distribution produced in the SiO2layer by Si-ion implantation. A taper structure is designed for effective coupling of transverse electric (TE) polarized light (λ = 1.55 μm) into a submicron size PhCW consisting of triangular lattice of air holes (lattice constant,a= 0.666 μm, radius of air holes,r= 0.232 μm, waveguide width, W1 ~ 0.7 μm). The influence of the taper length on the transmission characteristics is investigated. Efficiency in excess of 95% is demonstrated using the finite-difference time-domain and beam propagation methods. This is important for their practical applications in photonic integrated circuits.

We fabricated a vector diffraction grating using a chiral nematic liquid crystal (LC) and a holographically regulated photoalignment film. Periodic defects were observed in the grating LC cell, and the defect position was affected by the temperature of the cell. To characterize the defect position, the director distribution in the cell was estimated on the basis of the elastic continuum theory of chiral nematic LCs. The result clarified that the defect position depended on the helical pitch of the chiral nematic LC. We also investigated diffraction properties of the grating LC cell. The diffraction efficiency and polarization conversion property could be controlled by the temperature. The experimental results were well explained theoretically by considering the temperature dependence of the optical anisotropy and helical pitch of the chiral nematic LC.

We investigated the photoalignment properties of a liquid crystalline composite. The composite consisted of a low molecular weight nematic liquid crystal (LC) and a photoreactive liquid crystalline polymer containing 4-(4-methoxycinnamoyloxy)biphenyl side groups. Homogeneously aligned LC composite cells were fabricated using rubbed substrates and were then exposed to a linearly polarized (LP) ultraviolet (UV) laser beam. The alignment states of the LC composites were characterized using a LP visible laser beam. The LC composite in the cell was realigned by LP UV exposure and subsequent annealing. The direction of the realignment could be controlled by the polarization direction of the LP UV beam. The relationship between the realignment direction and the rubbing strength of the substrates was also investigated. A large realignment was induced in the LC composite cell when the azimuthal anchoring strength of the rubbed substrates was relatively weak.

Light propagation in an optical waveguide fabricated by employing a dye-doped liquid crystal (DDLC) was observed. The propagation of a light signal in the waveguide was varied by irradiation with a control light whose wavelength was in the absorption band of the DDLC. By considering the photothermal effect of the DDLC, which enables the change of the refractive index due to temperature variation based on the absorption of light, we qualitatively explained the observed light propagation and demonstrated manipulation of the propagation.

Proton beam writing (PBW) has attracted much attention recently as a next-generation micro-fabrication technology. It is a direct-drawing technique and does not need any masks to transfer micro-patterns to sample surfaces. In addition, the refractive index of a poly (methyl methacrylate) (PMMA) can be increased by proton-beam irradiation. In this study, we fabricated the first 1.5-μm-band single-mode, straight-line waveguides and Y-junction waveguides consisting of PMMA layers using the PBW technique.

A novel linked thermoelectric system (LTES), fabricated by a simple structural modification of a conventional thermoelectric system (CTES) with the use of conductive metal rods, is characterized experimentally. The LTES generates higher power to the external load in comparison with the CTES, and the power increases with increasing length of the metal rods when the low temperature side of the system is set in the air at room temperature. In addition, measurements of Seebeck voltages of both the systems indicate that the Seebeck coefficient of thermoelectric materials in the LTES is about 1.2 times higher than that in the CTES.

We propose an optically tunable terahertz (THz) polarization converter based on use of a dye-doped nematic liquid crystal (LC). The dye-doped LC exhibits a photothermally-induced nematic-isotropic phase transition under irradiation by a laser beam with a wavelength that lies within the absorption band of the dye. We investigate the transmission spectra and the polarization-conversion properties of the dye-doped LC cell with twisted alignment using THz time-domain spectroscopy. The polarization state of a THz wave transmitted through the proposed dye-doped LC cell can be controlled using the laser beam irradiation based on the photothermal effect. The experimental results also demonstrate that optical control of this dye-doped LC cell offers an advantage in terms of response speed when compared with voltage-based control of LC cells via their electrodes. The dye-doped LC proposed in this study presents the possibility that a variety of LC-based THz elements with optical tunability may be realized.

We demonstrate the evidence of electrical spin injection into silicon (Si) using the Fe/MgO tunnel barrier by the following two methods: 1) non-local (NL) four-terminal magnetoresistance (MR) scheme with their respective corresponding ferromagnetic (FM) electrode and 2) Hanle-type spin precession scheme. These results are compatible and in agreement with each other. The spin injection signals in the non-local scheme were observed up to 150 K, and the spin diffusion length (?N) was estimated to be 2.8 ?m at 8 K. The experimental data completely matches every detail of the Hanle measurements equation, and spin lifetime (?) was estimated to be 9.44 ns at 8 K. We will be able to discuss the physical properties of a pure spin current in silicon by this compelling data.