Directional Coupling Measurements And Calculations In Ti:LiNbO 3 Channel Waveguides

Measurements are described at 0.83 µm and 1.3 µm to investigate the directional coupling between two identical, single mode, Ti :diffused channel waveguides for the ordinary (TE) and extraordinary (TM) polarizations in Z-cut, X-propagating LiNb03. The coupling parameters for each polarization are a function of the waveguide fabrication parameters and hence of the waveguide mode dispersion. Also the coupling characteristics for the TE and TM modes vary somewhat differently with changes in mode dispersion. Hence, for different waveguide fabrication conditions, the TE and TM mode coupling coefficients may be equal at one coupler gap or may be unequal for all gaps or, most significantly, may be equal for all gaps. Experimentally determined coupling variables are compared with theoretical ones, calculated using channel mode dispersion parameters and diffusion parameters determined from mode measurements on planar waveguides. Experimental/theoretical agreement is generally good and the calculations correctly predict the effect on the coupling characteristics of changes in waveguide fabrication parameters.