Electrooptic coupling between TE and TM modes in anisotropic slabs

In an electrooptic crystal TE and TM modes can be coupled by application of a modulation voltage. Two types of modulators using anisotropic crystals are discussed. In the first type a voltage that is constant along the direction of wave propagation couples a guided mode to a radiation mode of the orthogonal polarization so that the radiation loss of the guided mode can be controlled by the applied voltage. The modulator of the second type uses voltage-controlled coupling between guided TE and TM modes. The computation of the coupling coefficients is outlined and numerical examples are plotted for LiNbO3and LiTaO3crystals.