POLARIZATION-INDEPENDENT SILICA-ON-SILICON MACH-ZEHNDER INTERFEROMETERS

The birefringence induced by compressive strain in silica waveguides o n silicon substrates is compensated with a silicon nitride patch place d below the core. We demonstrate Mach-Zehnder interferometers with pol arization-independent spectral response, including a compensated Mach- Zehnder interferometer suitable for stabilization of multiple laser so urces in a dense wavelength division multiplexed fiber optic communica tion network. Furthermore, we show how silicon nitride can also be use d to compensate polarization dependent losses. Polarization independen ce achieved with a silicon nitride patch is applicable to a wide varie ty of other devices such as arrayed waveguide grating multiplexers and Bragg reflectors.