Abstract

Photoinduced polarization conversion is a form of optical damage in LiNbO₃ waveguide devices.¹ In an attempt to better understand this phenomenon, we have studied the effect in bulk LiNbO₃:Fe. In this work, we have observed nearly complete ordinary-to-extraordinary polarization conversion in LiNbO₃:Fe for input ordinary beam diameters greater than ~200 μm and no polarization conversion for beam diameters less than ~60 μm. The extraordinary light was scattered into a wide angular distribution in a plane perpendicular to the optic axis of the crystal.² For small beam diameters, there is no scattered light, and no energy is lost from the ordinary beam. However, as the beam diameter is increased, there is steady-state energy transfer out of the ordinary beam into two broad extraordinary peaks. Using the photovoltaic model,^3,4 we have derived coupled equations that describe the polarization conversion process as a function of scattering angle and beam diameter. This model correctly describes the distribution of the scattered extraordinary light and predicts the beam diameter threshold behavior of the polarization conversion.

© 1991 Optical Society of America