Low-Polarization-Dependent Silica Waveguide Monolithically Integrated on SOI Photonic Platform

We developed a low-polarization-dependent silica- based waveguide, which can be monolithically integrated with a silicon (Si) waveguide device on a silicon-on-insulator (SOI) substrate. For the monolithic integration, silica-based materials must be deposited at low temperature in order not to damage Si waveguide devices. Due to this low-temperature fabrication method, however, the silica films exhibit high residual stress, resulting in high material birefringence. In order to compensate for this birefringence, we introduce a multi-layer core structure. First, we design the structure taking the monolithic integration with the Si waveguide devices into account. Then, the designed waveguides and arrayed-waveguide gratings (AWGs) are fabricated using low-temperature fabrication processes. Next, we experimentally confirm that the waveguide exhibits low waveguide birefringence. In addition, we monolithically integrate the AWG and Si waveguide devices.