Broadband and low-cross talk mode multiplexer based on subwavelength-assisted phase matching

Integrated mode multiplexers are key components in photonic networks and are crucial to achieving higher data density. Asymmetric directional couplers represent one of the most common multiplexing architectures, owing to their low losses and scalability, but further bandwidth enhancements are sought after. In this Letter, we demonstrate a multiplexer/demultiplexer link based on asymmetric directional couplers assisted by subwavelength grating metamaterials. Through subwavelength-assisted phase matching, low losses and cross talk are achieved on a small form factor over a broad bandwidth. Experimental measurements show insertion losses under 0.8 dB and cross talk under -19.8 dB in a 170 nm bandwidth (1500 nm to 1670 nm) for a full multiplexer/demultiplexer link.