Improved electrode geometry for electrooptic frequency translation in a channel waveguide

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 light guide under the central strip. Elimination of a cyclic modulation of field amplitude, characterizing the results of a previous study 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 counter-rotating field component are thus removed. It is shown that with a residual modal birefringence equivalent to
\lambda/20
-differential phase retardation, the device here described can achieve 98 percent translation into the single first-order sideband with less than 0.5 percent combined spurious carrier and second-order upper sideband.