Abstract

Performing of quasi-phase-matching devices using Periodic Poled Lithium Niobate (PPLN) has been limited because of the difficulty in fabricating nonlinear gratings over a substantial interaction length and thickness. These limitations and difficulties in making fine PPLN structures are strongly related to the material parameters of PPLN such as the high switching field (> 21 kV/mm) induced domain-broadening effects [1]. Consideration has also been made to the large internal field ( 2.5-5.0 kV/mm) that causes axial anisotropy in the poling process [2]. Therefore one must resort to sophisticated techniques such as backswitching that utilizes the nucleation and pinning process at various poling stages to realize fine structures [3]. It is suggested that high switching and large internal fields of congruent crystals are directly correlated with Li non stoichiometric crystals, thus good control of stoichiometry can reduce the switching field by a factor of 5, and the internal fields <0.1 kV/mm, which tend to disappear. In this way stoichiometric LN crystals have potential as better materials for PPLN, since they show almost one order of magnitude lower switching field for 180° ferroelectric domain reversal than does congruent LN crystals. However patterned electric field poling process on stoichiometric LN crystals has been recently studied and found difficult to grow.

© 2001 EPS