Compact Polarization Beam Splitter Using an Asymmetrical Mach–Zehnder Interferometer Based on Silicon-on-Insulator Waveguides

A compact polarization beam splitter based on an asymmetrical Mach-Zehnder interferometer (MZI) on a sub-micron silicon-on-insulator platform is demonstrated experimentally. The present MZI polarization beam splitter (PBS) is fabricated with a double-etching process and the deeply-etched region includes the MZI arms and the multimode- interference (MMI) couplers. In this way, the birefringence of the MZI arms and the power splitting ratio of the MMI coupler become insensitive to the etching depth, which makes the fabrication easier. The 2×2 MMI couplers are optimized to be polarization-insensitive and have a balanced ratio (50:50) for both polarizations. The measured extinction ratio of the fabricated MZI PBS is higher than 10 dB in the wavelength range from 1.54 to 1.58 μm.