Integrated-Optical Mode Converter/Frequency Shifter in Ti:LiTaO3

Abstract

A guided-wave frequency shifter is of current interest for use in interferometric sensors such as the phase-nulling fiber-optic gyroscope. It possesses distinct advantages over bulk acousto-optic Bragg frequency Shifters for use in guided-wave systems. These advantages include: high conversion efficiency, high optical carrier suppression, and low insertion loss. Heismann and Ulrich1,2 have reported a col linear electro-optic, Bragg-type frequency shifter in a single mode LiNbO3 stripe waveguide. The device operates by having a TE input mode with angular frequency ω Bragg scatter from a collinear electro-optically induced traveling wave with angular frequency Ω into a TM output mode having angular frequency ω+Ω or ω-Ω. Eknoyan, et al.,3 have extended this concept by fabricating a similar device in LiTaO3 which achieved an order of magnitude increase in optical bandwidth. However, due to fringing fields, that device did not operate efficiently as a frequency shifter.