Subwavelength-grating-based compact and broadband TE-pass polarizer for slot waveguides on a SOI platform

Abstract

We have numerically proposed a compact, broadband, and high-extinction-ratio (ER) TE-pass polarizer for vertical slot waveguides using a subwavelength grating slot (SWGS) waveguide on a silicon-on-insulator (SOI) platform. By carefully tailoring the equivalent material index, the TE fundamental mode (i.e., TE0) is supported in the SWGS waveguide, while the TM fundamental mode (i.e., TM0) is suppressed under the cutoff condition. Consequently, the input TE0 mode can pass through with negligible loss, whereas the injected TM0 mode will leak from the SWGS waveguide completely, realizing an efficient TE-pass polarizer. The proposed device only needs a single etching step, substantially reducing the fabrication difficulty compared with the previous counterparts. Moreover, thanks to the used SWGS configuration, such a device also exhibits a remarkable broadband property. From the results, the proposed polarizer with a total length of ∼56 μm has a high ER of 40.5 dB and an insertion loss (IL) of 0.42 dB at 1.55 μm, and its bandwidth is as large as ∼210 nm with ER>36 dB and IL<1 dB. In addition, fabrication tolerances to the key structural parameters are analyzed, and field evolution through the suggested polarizer is also presented.