Inverse design of a binary waveguide crossing by the particle swarm optimization algorithm

This paper describes the inverse design of the particle swarm optimization algorithm combined with the three-dimensional finite-difference time-domain simulation to design a waveguide crossing that resembles a binary code. The device consists of 15 × 15 air holes in a 220-nm silicon slab on a 3-μm-thick SiO2 substrate with one input port and three output waveguide ports. The designed device has a small footprint of 4μm2 and a short simulation time of 1.7 h. In the wavelength range of 1.5–1.6μm, the device has insertion loss IL<0.85 dB and crosstalk XT<−14.5 dB. This device tolerates air hole-position disordering of ηp=23%, and hole-radius disordering of ηr=35%, so it is appropriate to use in the complementary metal–oxide–semiconductor fabrication process. The paper also proposes integrated interconnections that contain 2 × 2 waveguide crossings and have IL<2.9 dB and XT<−13 dB, and 3 × 3 waveguide crossings that have IL<5 and XT<−12.5 dB.