Polarization insensitive thermally tunable add/drop multiplexer using cascaded Mach-Zehnder coupler

In this paper, a thermally tunable add/drop multiplexer based on a Y symmetric cascaded Mach-Zehnder (CMZ) coupler is found to be polarization dependent due to the stress anisotropy caused by local heating to achieve thermooptic phase change. A thermooptic delay line structure with a stress releasing groove is proposed for reduction of the polarization dependence of a Y symmetric delay line coupler of high index contrast waveguides. It is seen that thermally tunable transmission characteristics of a Y symmetric CMZ device based on the proposed structure is almost polarization independent. It is also found that the reduction of the heating power in the proposed structure is similar to 1.6 times smaller than that of the conventional structure.