PROBLEM TO BE SOLVED: To provide a technique for ensuring the extinction ratio of light modulation using photoelectric crystal substrates.;SOLUTION: Photoelectric crystal substrates 31 and 32 are provided. Light is passed through the photoelectric crystal substrate 31 and then through the photoelectric crystal substrate 32. By means of diffraction grating formed according to an applied voltage, each of the photoelectric crystal substrates 31 and 32 causes diffraction of light passed through. Since the respective polarization axes P1 and P2 of the substrates 31 and 32 are inclined at this time, the respective directions in which changes in refractive index increase differ from each other. That is, the respective directions in which the diffraction gratings of the substrates 31 and 32 exhibit anisotropy are different. Such a configuration makes it possible to perform an operation in which the polarization components of light that have not been modulated by the diffraction grating of the photoelectric crystal substrate 31 are modulated by the diffraction grating of the photoelectric crystal substrate 32. As a result, the rate at which light to be modulated is passed through without being modulated is restricted, thus the extinction ratio of light modulation can be ensured.;COPYRIGHT: (C)2014,JPO&INPIT
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