Optical coupling of GaAs photodetectors integrated with lithium niobate waveguides

The optical coupling of GaAs photodetectors integrated with LiNbO/sub 3/ waveguides using epitaxial liftoff is measured and compared to calculations based on a complex index model. The measured coupling is found to be comparable to that obtained in epitaxial semiconductor waveguide detectors, but it is lower than expected. Low coupling efficiency is attributed to the presence of a low index barrier layer, not present in semiconductor-based structures, at the GaAs-LiNbO/sub 3/ interface. A simple method of restoring the coupling to its original value without the need to eliminate the barrier layer is proposed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>