Gain constant of two-wave mixing in periodically poled photorefractive crystal waveguide

A photorefractive crystal waveguide with its c-axis periodically reversed along the waveguide axis is studied to realize enhanced two-wave mixing. The gain constant of two-wave mixing in the periodically poled photorefractive waveguide is theoretically derived in terms of mode-coupling analysis. It is found that, in BaTiO₃ periodically poled waveguides, the net two-wave mixing gain constant is increased by 1.5 to 5 times over that of conventional waveguides without periodical poling because the largest electrooptic coefficient r₄₂ can be effectively used by appropriately setting the angle between the c- and z-axes. Several types of test BaTiO₃ periodically poled waveguides are successfully fabricated by using the electrical poling technique. Typical lateral dimensions of the waveguides are O.5 to 1 mm, and the lengths are several millimetres. The measured two-wave mixing gain constants of the fabricated waveguides are well predicted by the theory