Optical phase conjugation based on a ferroelectric semiconductor

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Photorefractive nonlinear wave mixing at the telecommunication wavelength 1.55 μm has been intensely investigated, because it enables us potentially to demonstrate beam combination, beam cleanup, and optical phase conjugation in combination with fiber optics. Photorefraction at this wavelength regime has been investigated mostly in semiconductors such as CdTe : V, since conventional ferroelectric materials, i.e., Rh doped BaTiO_3 has property of very poor photorefractive sensitivity at this wavelength. However, the CdTe : V requires an additional large alternating current (AC) electric field (.4 kV/cm) and 1.3 μm stimulating illumination to achieve an efficient photorefractive two wave mixing gain.In this work, we investigate 1.55 μm photorefractive phase conjugation in a ferroelectric semiconductor material, tin thiohypodiphosphate (Sn_2P_2S_6, SPS), showing a relatively narrow band gap (～2.3 eV), a high charge mobility, as well as a large dielectric constant.