Polarization sensitivity of a silica waveguide thermooptic phase shifter for planar lightwave circuits

A thermooptic (TO) phase shifter, which consists of a thin-film heater loaded on a silica-based single-mode waveguide on a Si substrate, was found to exhibit a sli1h,t polarization dependence of about 3.1% between the TE and TM modes. This dependence, which is caused by anisotropic stress concentration due to local heating, was successfully reduced by forming stress-releasing grooves on either side of the heater.>