Improved electrode geometry for frequency translation in a buried channel guide

Abstract

The technique of optical frequency translation by a rotating electric field in a trigonal electrooptic crystal has been adapted to a buried channel waveguide structure. To implement the field rotation under the constraints of a planar geometry, an electrode configuration was adopted consisting of three coplanar, collinear metal strips driven in phase quadrature, with the lightguide under the central strip. Elimination of a cyclic modulation of field amplitude, characterizing the results of a previous study1 by the author, was achieved by appropriately widening the outer electrodes relative to the central one and by choosing a suitable channel depth. Spurious sidebands previously generated by an effective counterrotating field component are thus removed. It is shown that with a residual modal birefringence equivalent to λ/20 differential phase retardation, the device here described can achieve 98% translation into the single first-order upper sideband with <0.5% combined spurious carrier and second-order upper sideband.