Ultra-Small and Fabrication-Tolerant Silicon Polarization Beam Splitter Using Sharp Bent Directional Coupler

An ultra-small polarization beam splitter on silicon-on-insulator platform is proposed and demonstrated experimentally employing a sharp bent directional coupler. The coupling length of our device is only 0.764 μm. High-efficient selective coupling can be achieved benefiting from the inner bend chosen as Through port and ultra-small bend (radii are about 3 μm) used in Through and Cross waveguides. The measured excess loss is less than 1 dB and extinction ratio is 15-20 dB for TM polarization, meanwhile, the measured excess loss is less than 2 dB and extinction ratio is 15-16 dB for TE polarization in a wavelength range from 1540 nm to 1580 nm. The fabrication tolerance to variation of waveguide width is also demonstrated. When the waveguide widths of the Through and Cross waveguides vary from -24 nm to +12 nm, the measured excess losses remain lower than 2 dB and the extinction ratios are higher than 10 dB for both polarizations. The footprint of the fabricated device is just 1.5 μm × 1.3 μm.