Electro-Optic Coefficient Enhancement in Poled LiNbO3 Waveguides

Lithium niobate crystals (LN) show a significant electro-optic (EO) response which contributes to the fabrication of low-voltage operation, high speed integrated optical modulators routinely used in optical telecommunication and integrated optics [1]. A UV laser direct writing method for the fabrication of optical channel waveguides has been proposed and characterized recently [2–4]. Here we report on the enhancement of the electro-optic response of these UV laser-written LN waveguides as a result of a post-poling process. More specifically we have observed a 26% increase of the r33 coefficient compared to the bulk in LN waveguides, fabricated by direct UV writing, that have been subjected to poling inhibition [5]. Poling inhibition produces inverted ferroelectric domains which are only a few microns deep. These domains are formed exactly in the same place as the UV written tracks which are responsible for the waveguide formation, and they overlap significantly with the propagating waveguide mode as is illustrated schematically in Fig. 1. Due to the polarization-selective transmission in the UV-written waveguides only the r33 coefficient could be investigated.