Silicon subwavelength modal Bragg grating filters with narrow bandwidth and high optical rejection.

Waveguide Bragg grating filters with narrow bandwidths and high optical rejections are key functions for several advanced silicon photonics circuits. Here, we propose and demonstrate a new, to the best of our knowledge, Bragg grating geometry that provides a narrowband and high rejection response. It combines the advantages of subwavelength and modal engineering. As a proof-of-concept demonstration, we implement the proposed Bragg filters in 220-nm-thick Si technology with a single etch step. We experimentally show flexible control of the filter selectivity, with measured null-to-null bandwidths below 2 nm, and strength of 60 dB rejection with a null-to-null bandwidth of 1.8 nm.