Analytical and Experimental Investigation of a Silicon Photonic Two-Stage Mach–Zehnder Delay Interferometer-Type Polarization Beam Splitter

We report the analytical and experimental results of a silicon photonic polarization beam splitter (PBS) consisting of two-stage Mach-Zehnder delay interferometers (MZDIs). The delay length of each MZDI was designed to achieve constructive and destructive interferences for the TE and TM modes simultaneously. First, we have fabricated and estimated a single-stage MZDI-type PBS. Owing to the difference of the in-phase or out-of-phase conditions between TE and TM modes in case of the designed delay length of the MZDI, the center wavelengths of the transmissivity for both the constructive and destructive interference are different for the TE and TM modes. Thus, the polarization extinction ratio (PER) was as small as 5 dB within the C-band. To improve the PER, a two-stage MZDI structure was introduced. In addition, the length of the multimode interferometer type optical splitter was determined to have an optimal splitting ratio of 50:50 for the TM mode for the shortest wavelength within the operating wavelength range. The center wavelength of the MZDIs was shifted to achieve the widest possible bandwidth with a large PER. We have fabricated the silicon photonic PBS to achieve a PER larger than 15 dB. The measurements showed good agreement with the simulations.