With the rapidly increasing bandwidth requirements of optical communication networks, compact and low-cost large-scale optical switches become necessary. Silicon photonics is a promising technology due to its small footprint, cost competitiveness, and high bandwidth density. In this paper, we demonstrate a 12×12 silicon wavelength routing switch employing cascaded arrayed waveguide gratings (AWGs) connected by a silicon waveguide interconnection network on a single chip. We optimize the connecting strategy of the crossing structure to reduce the switch’s footprint. We develop an algorithm based on minimum standard deviation to minimize the port-to-port insertion loss (IL) fluctuation of the switch globally. The simulated port-to-port IL fluctuation decreases by about 3 dB compared with that of the conventional one. The average measured port-to-port IL is 13.03 dB, with a standard deviation of 0.78 dB and a fluctuation of 2.39 dB. The device can be used for wide applications in core networks and data centers.

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 TE0 and 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 dB and 24 dB from 1530 nm to 1590 nm for both TE0 and TE1 modes, respectively. Furthermore, our scheme could also be expanded to design waveguide crossings that support more modes.