Silicon Multimode Waveguide Crossing Based on Anisotropic Subwavelength Gratings

Abstract Multimode waveguide crossings (MWCs) are becoming more and more important as one of the key elements for on‐chip optical routing and cross‐connection. However, it is still very challenging to achieve scalable MWCs with compact footprints, low excess losses (ELs), and low intermode cross‐talks (CTs). This work demonstrates an unprecedented silicon MWC with high performances by using the anisotropy of one‐/two‐dimensional (1D/2D) subwavelength grating (SWG) structures. For the proposed silicon MWC, the 2D‐SWG crossing region at the center has a higher refractive index than the 1D‐SWG regions at both sides for the guided‐modes of TE polarization, due to the anisotropy of the 1D/2D SWGs. As a result, the crossing region can be equivalent to a straight waveguide, and the launched TE modes can transmit through the crossing region with negligible ELs and low intermode CTs. Such an MWC can be scaled very flexibly and easily according to the new principle. The fabricated three‐mode MWC with a footprint of 14.8 × 14.8 µm 2 shows ELs of <0.26 dB and intermode CTs of <−20 dB in the wavelength range of 1525–1605 nm.