High-Performance Polarizing Beam Splitters Based on Cascaded Bent Directional Couplers

A fabrication-tolerant high-performance polarizing beam splitter (PBS) is proposed and demonstrated with silicon-on-insulator nanowire waveguides. This PBS is realized with cascaded bent direction couplers, which is designed to make the phase-matching condition satisfied for the transverse-magnetic (TM) polarization mode. There is significant phase-mismatch for the transverse-electric (TE) polarization mode. As a result, TM-polarization mode is cross coupled efficiently to the cross port, while TE-polarization mode outputs from the through port with a low loss. The present PBS has a footprint of as small as $\sim 4\times 15\,\,\mu \text{m}^{2}$ . The extinction ratio at the center wavelength is 32.6 and 36.8 dB for TE and TM polarizations, respectively. The bandwidth for achieving a >25-dB extinction ratio is ~32nm, and the excess loss is <0.9 dB for both polarizations. The fabrication tolerance is as large as ±50 nm for the waveguide core width.