Broadband, Fabrication-Tolerant Polarization Beam Splitters Based on a Tapered Directional Coupler

We propose and demonstrate a polarization beam splitter (PBS) based on a tapered directional coupler (DC). The tapered DC structure has the advantage of being insensitive to variations of the coupling length and the local coupling coefficient, and thus can significantly increase the bandwidth and polarization extinction ratio (ER). The fabricated PBS with one waveguide width tapered from 0.55 to 0.41 μm and another tapered reversely in a length of 29 μm shows a polarization ER above 16 dB and an insertion loss less than 0.4 dB over a wavelength range of 100 nm. The fabrication tolerance of the proposed PBS is also analyzed to be ±50 nm, ensuring the compatibility with the standard 180-nm complementary metal- oxide-semiconductor process.