Ultra-compact mode (de) multiplexer based on subwavelength asymmetric Y-junction

We propose and experimentally demonstrate a novel multimode ultra-compact mode (de)multiplexer for highly integrated on-chip mode-division multiplexing systems. This device is composed of a wide divergence angle asymmetric Y-junction based on subwavelength structure and optimized using an inverse design method. The proposed device occupied a footprint of only 2.4 × 3 µm . The measured insertion loss and crosstalk were less than 1dB and -24 dB from 1530 nm to 1590 nm for both TE mode and TE mode, respectively. Likewise, a three mode multiplexer is also designed and fabricated with a compact footprint of 3.6 × 4.8 µm . Furthermore, our scheme could also be expanded to include more modes.