Compact and broadband silicon TE-pass polarizer based on tapered directional coupler

Abstract

We demonstrate a novel TE-pass polarizer, to the best of our knowledge, on a silicon-on-insulator (SOI) platform. The device's working principle is based on the phase-matched coupling of the unwanted TM0 mode in an input waveguide to the TM1 mode in a tapered directional coupler (DC), which is then guided through a low-loss bend (180-degree) and scattered in a terminator section with low back reflections. However, the input TE0 mode is routed through the tapered section uncoupled with negligible loss. An S-bend is added before the output for filtering any residual TM0 mode present in the input waveguide. Tapering the DC helps maintain phase matching for broadband operation and increases the tolerance toward fabrication errors. The measurement shows low insertion loss (IL < 0.44 dB), high extinction ratio (ER > 15 dB), and wide bandwidth (BW = 80 nm). The overall device length is only 13 µm. A high performing TE-pass polarizer (IL < 0.89, ER > 30, and BW = 100 nm) is also demonstrated by cascading two proposed polarizers.