Abstract

Proton-exchange is a low temperature process (140°C to 300°C) involving a chemical reaction between lithium niobate and acid in which lithium ions exchange with protons⁽¹⁾. The resulting waveguides have a step-like refractive index profile with Δn_e= 0.125 (λ= 0.6328μm)⁽²⁾. There are a number of problems associated with proton-exchanged waveguides, namely relaxation of effective mode indices⁽³⁾, d.c. drift effects⁽⁴⁾, high propagation losses⁽⁵⁾ and a substantially reduced electro-optic effect⁽⁶⁾. Although methods have been developed to avoid, for example, the relaxation of effective mode indices⁽⁷⁾, devices are still limited in their performance due to the reduced electro-optic effect and high propagation losses. For the first time, we report the possibility of fabricating waveguides with propagation losses reduced to 1/10 of the losses of 'as-exchanged' waveguides and an r₃₃ value approximately 2/3 of the bulk value.

© 1988 Optical Society of America