Biomedical subjects

Hisao Kikuta

Publications and source records attributed to Hisao Kikuta.

8 recordsLinked to original sources

PubMed2006

Reduced wavelength-dependent quarter-wave plate fabricated by a multilayered subwavelength structure.

We developed a novel fabrication method of a reduced wavelength-dependent quarter-wave plate (QWP) based on form birefringence of a multilayered subwavelength structure. The multilayered structure was constructed by depositing a high-refractive-index thin film on a subwavelength-structured substrate with a low refractive index. The surface structure of the substrate was shallow enough to be formed by a mass replication technology. A high-refractive-index subwavelength grating was formed on ridges of the substrate by sputtering Zn2SnO4 (refractive index of 2.03 at a wavelength of 633 nm). Moreover, since the grooves of the high-refractive-index grating were very deep and narrow, the dispersion of form birefringence suppressed the dependency of phase retardance on the wavelength of light in a limited spectral region. The phase retardance of the fabricated QWP was 89 degrees at a 633 nm wavelength and 79 degrees at a 785 nm wavelength.

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PubMed2006

Method for calibrating system parameters of a multidirectional interferometers system.

A multidirectional interferometer system has been proposed and developed to measure the position and orientation of a positioning stage. In this method the system parameters, such as positions of the corner-cube reflectors and directions of the rays in the interferometers, must be determined beforehand. However, it is difficult to find ways to determine the system parameters for each different system with necessary accuracy. This paper proposes a systematic method for calibrating the system parameters when the number of the interferometers is larger than the degrees of freedom of the stage. The method is verified for a two-dimensional stage by both simulation and experiment.

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PubMed2006

Estimation method for the light extraction efficiency of light-emitting elements with a rigorous grating diffraction theory.

The light extraction efficiency of a light-emitting element with microstructured surface is analyzed with a rigorous grating diffraction theory. The grating theory reveals an improvement of extraction efficiency due to diffraction of light by the surface microstructure. The simulation results show that the improvement of extraction efficiency is due mainly to the reflected diffraction rather than to the transmitted diffraction. A part of total-internal-reflection light is diffracted into directions at less than the critical angle. Extraction efficiency is improved by multiple reflection and diffraction of light in a high-refractive-index layer. We propose a simple design method for an efficient surface microstructure from the viewpoint of reflected diffraction.

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PubMed2005

Numerical study on an asymmetric guided-mode resonant grating with a Kerr medium for optical switching.

Optical switching effects of a guided-mode resonant grating (GMRG) with a Kerr medium have been simulated with the nonlinear finite differential time domain (FDTD) method. An asymmetric waveguide grating with a large second spatial harmonic component has been proposed for the optical switch. Resonant reflection occurs at both of the band-edge wavelengths. These wavelengths are used for the pump light and the probe light. The enhanced electric field of the pump light changes the resonant wavelength for the probe light as a result of the Kerr effect. We designed the GMRG with resonant wavelengths of 1489.6 and 1630 nm, which were used for the pump light and the probe light, respectively. When the grating material has a third-order susceptibility chi(3) of 8.5 x 10(-10) esu, the transmittance of the probe light changes from 0 to 80% by increasing the intensity of the pump light from 0 to 60 kW/mm2.

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PubMed2005

Dynamic guided-mode resonant grating filter with quadratic electro-optic effect.

We propose a novel and simple concept of dynamic switching of guided-mode resonant grating filters with quadratic electro-optic effect within a waveguide layer modulated by external fields due to comb-shaped electrodes that also behave as a grating. As the device has subwavelength structure, the performance must be analyzed electromagnetically. We describe numerical simulation with the finite-difference time-domain method specially modified so that it can treat inhomogeneous anisotropic media such as lead lanthanum zirconate titanate.

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PubMed2004

Optimization of diffraction grating profiles in fabrication by electron-beam lithography.

We propose a new design method for periodic diffraction gratings to be fabricated with direct-writing electron-beam lithography. When the grating has a small period, the proximity effect of electron scattering restricts the grating profile after developing. Our design method optimizes the electron-dose profile and grating profile simultaneously to obtain the desired diffraction efficiency under the restriction of the proximity effect. The optimization is made with rigorous electromagnetic grating analysis and the resist development simulator. When we designed the diffraction grating with a period of 1.0 microm to obtain the highest efficiency of the first-order diffracted light of a 633-nm wavelength, the calculated grating profile was really different from the profile optimized only with rigorous electromagnetic grating analysis. Moreover, the diffraction grating of the electron-beam resist was fabricated according to the simulation result. The estimated diffraction efficiency was 82%, and the measured efficiency was 70%.

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PubMed2003

Measurement by multidirectional interferometers of the position and orientation of a positioning stage.

A multidirectional interferometer system is developed to determine the position and orientation of a stage moved in a two-dimensional (2-D) space. In this system four corner-cube prisms are mounted on the moving stage, and four laser beams are incident on the corner cubes in different directions. Moving distances in the observed directions are measured by laser interferometers. The position and orientation of the stage are calculated from the moving distances of the corner cubes. Some experiments are done on the 2-D moving stage with four interferometers, and measurement errors are estimated from redundant data. The estimated accuracy is higher than 0.2 microm for translation and 0.3 x 10(-3) deg for rotation for a measurement range of 0.5 mm and 0.5 deg.

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PubMed2002

Guided-mode resonant grating filter with an antireflection structured surface.

We describe a new structure of guided-mode resonant grating (GMRG) filters with low sideband reflectance. This GMRG filter consists of a high-index thin film on an antireflective structured surface called "moth-eye structure." Since the high-index film undulates along the surface structure, the film acts as a modulated optical waveguide. An incident light wave satisfying a resonant condition is reflected by the GMRG filter, and nonresonant light waves pass through the filter. This GMRG filter is valid for reducing reflection of nonresonant light waves in a wide spectral range. The resonant reflection of this new filter was investigated by numerical calculation based on an electromagnetic grating analysis. In the case of a triangular antireflective surface structure whose thickness is 2x greater than its period, the sideband reflectance for nonresonant light waves was lower than 0.5% for TM-polarized light in a wide range of wavelengths.

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