Efficient mode converters and filters using asymmetrical directional couplers with subwavelength gratings

Mode-division multiplexing (MDM) is a promising solution to improve data transmission capacity for future optical interconnect networks. Mode converters and mode filters play a key role in on-chip MDM systems. Here, we propose and experimentally demonstrate a device, enabling mode conversion and filtering simultaneously, which is composed of asymmetrical directional couplers with subwavelength gratings, in a small footprint of 14.7 mu m x 1.42 mu m. The device can realize optical mode conversion between the first -order transverse electric (TE) mode and the fundamental TE mode, and can also filter the fundamental TE mode effi-ciently. The conversion efficiency is over 95%, with a broad 1 dB bandwidth over 80 nm and a high mode extinction ratio of >29 dB. As a mode filter, strong mode elimination of >30 dB is achieved.(c) 2022 Optica Publishing Group