Abstract

Using methods that are applicable to any crystal class, the form of the third-rank bulk photovoltaic tensor for LiNbO₃ is found to be composed of a symmetric part (similar to the piezoelectric tensor) and an antisymmetric part. In LiNbCO₃ the antisymmetric part contains two positive elements and two negative elements, all of the same magnitude, and these are shown to lead to polarization conversion in bulk crystals and in waveguides. The polarization conversion¹ is examined in terms of the propagation direction, the initial polarization direction, the electro-optic effect, and the nonlinear interaction. For propagation perpendicular to the optic axis, a space-oscillating photocurrent is produced, forming an index grating in the direction of propagation. The nonlinear coupled-wave equations that result from this grating show a unidirectional conversion to an extraordinarily polarizated output wave.²,³ For propagation parallel to the optic axis, a uniform photocurrent is produced, which can couple orthogonal polarizations by a rotation of the index ellipsoid. Experimental results for bulk LiNbO₃ and Ti:LiNbO₃ waveguides are presented.

© 1990 Optical Society of America