A 1.3 mu m directional coupler polarization splitter by ion exchange

A glass waveguide polarization splitter for operation in the 1.3 mu m wavelength region is reported. The device, which has a symmetric directional coupler configuration, exploits the stress-induced birefringence in K/sup +/-Na/sup +/, ion-exchanged waveguides, giving rise to an adequate difference in the coupling lengths for the two polarizations. Starting from the measured potassium concentration (refractive index) profile of the structure and utilizing a combination of the multilayer stack theory and the effective-index method, the normal mode propagation constants and mode field profiles are calculated to determine the polarization splitting length and the extinction ratio, and the results are compared with the experimental data. It is shown that in a given coupler, the splitting occurs at several wavelengths in the 1.0-1.45 mu m range. A 25 mm-long coupler, fabricated by thermal diffusion of K/sup +/ ions in BK7 glass, exhibits an extinction ratio of 18.2 dB at 1.32 mu m, in excellent agreement with the simulation results.>