Yasuhiro Awatsuji

Parallel quasi-phase-shifting digital holography

We propose parallel quasi-phase-shifting digital holography as a technique capable of noiseless instantaneous measurement of three-dimensional objects. The technique implements four kinds of phase shifting at a time using a phase shifting array device located in the reference beam. The device is an array of 2×2 phase retarders. We conduct both numerical simulation and preliminary experiment, and the results agree well with those of the conventional phase shifting method. Also, the results are superior to those using a Fresnel transform alone, which is another digital holography method that can achieve instantaneous measurement.

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.

Parallel three-step phase-shifting digital holography

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

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.

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.

Parallel phase-shifting digital holography with adaptive function using phase-mode spatial light modulator

Parallel phase-shifting digital holography using a phase-mode spatial light modulator (SLM) is proposed. The phase-mode SLM implements spatial distribution of phase retardation required in the parallel phase-shifting digital holography. This SLM can also compensate dynamically the phase distortion caused by optical elements such as beam splitters, lenses, and air fluctuation. Experimental demonstration using a static object is presented.

Aperture Miniaturization of Guided-Mode Resonance Filter by Cavity Resonator Integration

A small-aperture wavelength filter consisting of a guided-mode resonance grating and a cavity resonator integrated in a SiO2-based waveguide was designed. The operation principle was experimentally confirmed at around 1540-nm wavelength for the first time.