Ultracompact TM-Pass Silicon Nanophotonic Waveguide Polarizer and Design

An ultracompact transverse magnetic (TM)-pass polarizer based on silicon nanophotonic waveguides is proposed, which contains two tapered waveguides sandwiching a narrow waveguide section only supporting TM-mode propagation. A full-vectorial eigenmode solver is employed to determine the appropriate cross section of the silicon nanophotonic waveguide. The device is first designed in a 2-D approximate model using a wide-angle beam propagation method, and numerical verification is carried out afterward using a parallel full-vectorial 3-D finite-difference time-domain simulation. Both approaches indicate that the finite thickness of the buried Si0₂ layer and the reflection at the substrate play important roles on the extinction ratio of the device. A designed numerical example shows an extinction ratio of ∼26 dB for the waveguide polarizer with a length of ∼10 µm, while the insertion loss for the TM mode is negligible.