ANALYSIS OF ELECTROOPTIC FREQUENCY TRANSLATION IN A CHANNEL WAVEGUIDE.

In bulk electrooptic crystals having trigonal symmetry, an electric field rotating in the (001) plane induces a birefringence in that plane whose axes rotate in the opposite sense. With a half-wave field strength, a right-circularly polarized beam propagating along the optic axis is completely transformed to left-circular polarization and shifted by the rotation frequency of the field. The author has analyzed this interaction in a channel-waveguide configuration where TE/TM modal birefringence is present. Using coupled-mode theory in a base representation of circularly-polarized eigenstates, it is found that additional sidebands are generated at frequencies shifted both up and down by various harmonics of the drive frequency. However, with modal differential phase delay less than lambda/20, about 98% coupling into the single first-order sideband can result. To implement the rotating electric field in a planar geometry, an electrode configuration is adopted consisting of three coplanar collinear metal strips driven in phase quadrature, with the light guide under the central strip. The resulting inhomogeneous field is shown to exacerbate somewhat the spurious frequency couplings. How these may be minimized by proper choice of system parameters is shown.