Inverse-designed low-loss and wideband polarization-insensitive silicon waveguide crossing

Waveguide crossings are an essential component for constructing complex and functional on-chip photonic networks. Polarization-insensitive waveguide crossings are desired because photonic networks usually involve light with different polarizations. Here, we propose a polarization-insensitive waveguide crossing on a 250-nm silicon-on-insulator platform by using an inverse design method. In simulation, the designed waveguide crossing can maintain insertion loss below 0.18 (0.25) dB in the wavelength range of 1440-1640 nm for the TE₀ (TM₀) mode and achieve minimal insertion loss as small as 0.08 (0.07) dB at the wavelength of 1550 nm. The cross talk maintains below -32  dB and -35  dB for the TE₀ and TM₀ modes, respectively. Experimentally, the fabricated waveguide crossing achieves measured insertion loss less than 0.20 (0.25) dB for the TE₀ (TM₀) mode with minimal insertion loss as small as 0.1 dB. The measured cross talk is below -28  dB and -31  dB for the TE₀ and TM₀ modes, respectively. Therefore, our proposed waveguide crossing can be widely applied in photonic integrated circuits to construct photonic systems with the capabilities of polarization control and mode (de)multiplexing.