Abstract

TE/TM polarization splitters are important devices in optical communication systems. Fabrication of such devices requires birefringent waveguides. As a result, Ti:LiNbO₃ is used in real situations in spite of the associated complex waveguide fabrication technology and the inherent fiber incompatibility. Glass waveguides are attractive for economic reasons and for fiber compatibility. In this work, we report a glass waveguide polarization splitter for operation in the 1.3 μm wavelength region. The device, which has a symmetric directional coupler configuration, exploits the rather large stress-induced birefringence in K⁺–Na⁺ 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, we calculate the normal mode propagation constants and mode-field profiles to determine the polarization splitting length and the extinction ratio and, for the first time to our knowledge, compare the results with the experimental data. It is shown that in a given coupler the splitting occurs at several wavelengths in the 1.0–1.45 μm range. A 22.5 mm long coupler, fabricated by thermal diffusion of K⁺ ions in BK7 glass, exhibits an extinction ration of 18.2 dB, in excellent agreement with the simulation results.

© 1992 Optical Society of America