Ultracompact dual-mode waveguide crossing based on subwavelength multimode-interference couplers

We propose and experimentally demonstrate a novel ultracompact dual-mode waveguide crossing based on subwavelength multimode-interference couplers for a densely integrated on-chip mode-division multiplexing system.By engineering the lateral-cladding material index and manipulating phase profiles of light at the nanoscale using an improved inverse design method, a subwavelength structure could theoretically realize the identical beat length for both TEand TE1, which can reduce the scale of the device greatly. The fabricated device occupied a footprint of only 4.8 μm× 4.8 μm. The measured insertion losses and crosstalks were less than 0.6 d B and-24 d B from 1530 nm to 1590 nm for both TE0 and TE1 modes, respectively. Furthermore, our scheme could also be expandedto design waveguide crossings that support more modes.