Inverse design of multi-band and wideband waveguide crossings.

Photonic integrated circuits for wideband and multi-band optical communications will need waveguide crossings that operate at all the wavelengths required by the system. In this Letter, we use the modified gradient decedent method to optimize the dual-wavelength band (DWB) crossings on both single- and double-level platforms. On the single-level platform, the simulation results show insertion losses (ILs) less than 0.07 and 0.11 dB for a crossing working at a DWB of 1.5-1.6 and 1.95-2.05 µm. ILs are less than 0.1 and 0.2 dB for a crossing operating in the DWB of 1.5-1.6 and 2.2-2.3 µm. On the double-layer platform, the simulated results show IL less than 0.08 dB across the wavelength range of 1.25-2.25 µm. We experimentally demonstrate the DWB crossing operating at 1.5-1.6 and 2.2-2.3 µm to have IL less than 0.3 and 0.4 dB and crosstalk of -28 and -26dB in the two bands, respectively.