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25 January 2008 Horizontal resolution enhanced hologram to increase horizontal viewing angle
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We propose a new technique to increase the horizontal viewing angle of a hologram. The narrow viewing angle is one of the main problems of the conventional holography. The proposed technique enables to increase the viewing angle without decreasing the pixel pitch of a SLM. Multiple point light sources arranged on a slant line illuminate a SLM through a condenser lens. A 4f imaging system is used to image the SLM onto the screen. On the Fourier plane of the 4f imaging system, multiple Fourier-transformed images appear on a slant line. A horizontal slit is used to extract a horizontal rectangular area on the Fourier plane. With this method, the width of the Fourier-transformed image becomes K times longer and the height becomes 1/K times shorter, when the number of light sources is K and the light sources and the slit are prepared appropriately. Thus the horizontal resolution on the screen becomes K times larger, and the vertical resolution becomes 1/K times smaller. Consequently, the horizontal viewing angle of a hologram displayed on the screen increases ~K times. We experimentally verified the proposed method. The LCOS with the pixel pitch of 9.5 μm and the resolution of 4,096×2,160 was used as a SLM. The light emitted from a laser diode having the wavelength of 0.635 μm was enlarged to illuminate four micro lenses to generate four point light sources (K = 4). We found that the horizontal viewing angle was enlarged to ~15°. The three-dimensional images could be observed by both eyes.
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Yuki Hayashi and Yasuhiro Takaki "Horizontal resolution enhanced hologram to increase horizontal viewing angle", Proc. SPIE 6912, Practical Holography XXII: Materials and Applications, 69120I (25 January 2008);

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