Interlayer Polarization Beam Splitter Based on Asymmetrical Si Wire Directional Coupler

Abstract

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- $\text {nm}\times 220$ -nm first-layer waveguide and a 340- $\text {nm} \times 200$ -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 $C$ -band. The device is robust in terms of alignment error between the two waveguides.