Interlayer Polarization Beam Splitter Based on Asymmetrical Si Wire Directional Coupler

We proposed and designed a compact Si interlayer polarization beam splitter (PBS) that is based on a crystalline Si and hydrogenated amorphous Si (a-Si:H) vertical asymmetrical directional coupler toward 3-D Si photonics integrated circuits. The changeable thickness of the upper a-Si:H waveguide enables the realization of the TM-mode-coupled PBS with simple-structured parallel Si wire waveguides. The device with a 260-nm x 220-nm first-layer waveguide and a 340-nm x 200-nm second-layer waveguide operates in a broadband width of 77 nm, with a crosstalk of less than -20 dB and an insertion loss of <0.3 dB in the C-band. The device is robust in terms of alignment error between the two waveguides.