Shogo Ura

Parallel two-step phase-shifting digital holography

We propose a parallel two-step phase-shifting digital holography technique capable of instantaneous measurement of three-dimensional objects, with a view toward measurement of dynamically moving objects. The technique is based on phase-shifting interferometry. The proposed technique carries out the two-step phase-shifting method at one time and can be optically implemented by using a phase-shifting array device located in the reference beam. The array device has a periodic two-step phase distribution, and its configuration is simplified compared with that required for three-step and four-step parallel phase-shifting digital holographies. Therefore the optical system of the proposed technique is more suitable for the realization of a parallel phase-shifting digital holography system. We conduct both a numerical simulation and a preliminary experiment in the proposed technique. The results of the simulation and the experiment agree well with those of sequential phase-shifting digital holography, and results are superior to those obtained by conventional digital holography using the Fresnel transform alone. Thus the effectiveness of the proposed technique is verified.

An integrated-optic disk pickup device

A monolithic-integrated optical-disk pickup device capable of detecting readout and focus/tracking error signals is proposed, designed, and fabricated. The integrated-optic disk pickup device (IODPU) is constructed by integrating a focusing grating coupler, a grating beam splitter, and photodiodes in a film waveguide on a Si substrate. The function of detecting readout and error signals is demonstrated by butt-coupling a laser diode to the fabricated IODPU.

ESR and Transport Studies in Electrochemically Doped Polythiophene Film

Electron spin resonance (ESR), electrical conductivity and thermoelectric power are studied in electrochemically prepared and doped polythiophene films. The ESR spin density increases by two orders of magnitude up to dopant concentration of ca. 3 mol%, then decreases, while the conductivity increases drastically by more than ten orders of magnitude until this doping level, followed by a rather mild increase. The ESR linewidth decreases sharply from 9 G to 0.4 G upon slight doping with shape change from Gaussian to Lorenzian. The contribution of Pauli-paramagnetism to the spin succeptibility and the positive thermoelectric power of ca. 20 µV/K which depends linearly on the temperature are observed at heavily doped region. These results are discussed in terms of shallow and deep polarons, and formation of bipolaron up to intermediate doping levels and the hole conduction at the metallic regime.

High-speed phase imaging by parallel phase-shifting digital holography.

Parallel phase-shifting digital holography can obtain three-dimensional information of a dynamically moving object with high accuracy by using space-division multiplexing of multiple holograms required for phase-shifting interferometry. We demonstrated high-speed parallel phase-shifting digital holography and obtained images of the phase variation of air caused by a compressed gas flow sprayed from a nozzle. In particular, we found the interesting phenomenon of periodic phase distributions. Reconstructed images were obtained at frame rates of 20,000 and 180,000 frames per second.

Experimental demonstration of parallel two-step phase-shifting digital holography

Parallel two-step phase-shifting digital holography is a technique for single-shot implementation of phase-shifting interferometry and requires only the intensity distribution of the reference wave and spatial two phase-shifted holograms. We constructed a system of parallel two-step phase-shifting digital holography and experimentally demonstrated the technique, for the first time. The system uses an originally fabricated image sensor having an array of 2 × 1 micro polarizers. Each micro polarizer was attached on pixel by pixel. In the experiment, the unwanted images, the zero-order diffraction wave and the conjugate image, are removed from the reconstructed image of objects by the system, while the images superimpose on the image of objects reconstructed by Fresnel transform alone. Also the capability of single-shot and three-dimensional imaging is demonstrated by the system.

Parallel phase-shifting digital holographic microscopy

We propose parallel phase-shifting digital holographic microscopy (PPSDHM) which has the ability of three-dimensional (3-D) motion measurement using space-division multiplexing technique. By the PPSDHM, instantaneous information of both the 3-D structure and the phase distributions of specimens can be simultaneously acquired with a single-shot exposure. We constructed a parallel phase-shifting digital holographic microscope consisting of an optical interferometer and an image sensor on which micro polarizers are attached pixel by pixel. The validity of the PPSDHM was experimentally verified by demonstrating the single-shot 3-D imaging and phase-imaging ability of the constructed microscope.

Cavity-resonator-integrated guided-mode resonance filter for aperture miniaturization.

A guided-mode resonance filter integrated in a waveguide cavity resonator constructed by two distributed Bragg reflectors is designed and fabricated for miniaturization of aperture size. Reflection efficiency of >90% and wavelength selectivity of 0.4 nm are predicted in the designed SiO(2)-based filter with 50-μm aperture by a numerical calculation using the finite-difference time-domain method. A maximum reflectance of 67% with 0.5-nm bandwidth is experimentally demonstrated by the fabricated device at around 850-nm wavelength.

Optical and Electrical Properties of Electrochemically Doped n- and p-Type Polythiophenes

Absorption spectra have been measured on polythiophene films subjected to electrochemical Bu4N+ doping. The spectra show essentially the same evolution as those for BF-4 doping, i.e., peaks at 0.6~0.7 eV and 1.5~1.8 eV appear upon doping in addition to the band-to-band absorption peak at 2.6 eV. Propagation velocities of electrochemical doping of Bu4N+ and BF-4 along polythiophene films were estimated to be on the order of 10-3 cm/sec.

Improvement of color reproduction in color digital holography by using spectral estimation technique

We propose a color digital holography by using spectral estimation technique to improve the color reproduction of objects. In conventional color digital holography, there is insufficient spectral information in holograms, and the color of the reconstructed images depend on only reflectances at three discrete wavelengths used in the recording of holograms. Therefore the color-composite image of the three reconstructed images is not accurate in color reproduction. However, in our proposed method, the spectral estimation technique was applied, which has been reported in multispectral imaging. According to the spectral estimation technique, the continuous spectrum of object can be estimated and the color reproduction is improved. The effectiveness of the proposed method was confirmed by a numerical simulation and an experiment, and, in the results, the average color differences are decreased from 35.81 to 7.88 and from 43.60 to 25.28, respectively.

Parallel phase-shifting color digital holography using two phase shifts

We propose parallel phase-shifting color digital holography using two phase shifts. This technique enables the instantaneous acquisition of three-dimensional information of a moving color object. The interference fringe image that contains six holograms with two phase shifts for three wavelengths is recorded by a single shot exposure. Decreasing the degree of space-division multiplexing of these holograms makes it possible to suppress the degradation of the image quality owing to the aliasing caused by the multiplexing. Numerical simulation and preliminary experiments demonstrate the validity of the proposed technique; the reconstructed images of the proposed technique are clearer than those of the previously reported single-shot phase-shifting color digital holography that uses four phase steps.