Broadband polarization-insensitive Mach-Zehnder interferometer for quantum manipulation based on thick silicon...

Polarization-insensitive photonic devices are essential for mitigating the adverse effects of random polarization evolution during photon transmission and implementing robust quantum manipulation of light. In this work, we design and demonstrate a polarization-insensitive Mach-Zehnder interferometer (MZI) on a nitride platform with the thickness of 650 nm. We design the device by adopting a particle-swarm-optimized multimode interferometer with tailored edge shapes and sub-wavelength grating structures, combined with a segmented width-varied waveguide design in the interferometer arms to compensate for their intrinsic material birefringences. The experimental results of the fabricated MZI maintain a single-photon interference visibility about 98.7% even under active polarization scrambling, while a polarization-dependent loss < 0.3 dB over a 147 nm 1 dB bandwidth has been achieved. These properties make it a promising component for integrated quantum photonic systems such as quantum key distribution.