Low-loss ultracompact transverse-magnetic-pass polarizer with a silicon subwavelength grating waveguide

TLDR

An ultracompact, low‑loss silicon TM‑pass polarizer is proposed and experimentally demonstrated using a subwavelength‑grating waveguide. The subwavelength‑grating waveguide supports a Bloch mode for TM polarization, enabling low‑loss transmission, while acting as a Bragg reflector for TE polarization. The fabricated 9 µm polarizer achieved a 27 dB extinction ratio and 0.5 dB loss at 1550 nm, with a 60 nm bandwidth for 20 dB extinction, and increasing the period to N = 40 raised the extinction to 40 dB.

Abstract

An ultracompact and low-loss TM-pass polarizer on silicon is proposed and demonstrated experimentally with a subwavelength-grating (SWG) waveguide. The SWG waveguide is designed to support Bloch mode for TM polarization so that the incident TM-polarized light goes through the SWG waveguide with very low excess loss. On the other hand, for TE polarization, the SWG waveguide works as a Bragg reflector, and consequently the incident TE-polarized light is reflected. For a fabricated ∼9 μm long polarizer (with the period number N=20), the measured extinction ratio is ∼27 dB and the excess loss is ∼0.5 dB at the central wavelength 1550 nm. The bandwidth to achieve an extinction ratio of 20 dB is about 60 nm (from 1520 to 1580 nm). When increasing the period number to N=40, the measured extinction ratio is up to 40 dB (which is not as high as the expected theoretical value 65 dB due to the limit of the measurement system).