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 ∼1.6 times smaller than that of the conventional structure.