Inverse design of ultra-compact wavelength mode hybrid demultiplexing photonic devices based on adjoint optimization

Abstract As optical networks advance toward higher data rates and greater integration densities, silicon-based photonic platforms face increasing constraints in transmission capacity. To address these limitations, we present an ultra-compact mode demultiplexer specifically designed for on-chip hybrid multiplexing systems that combine multi-wavelength and multi-mode techniques. Implemented on a silicon-on-insulator platform with a footprint of 6.2 × 6.2 μm 2 , the device is designed using an adjoint-based inverse design method. It efficiently separates multiple wavelengths and modes while preserving mode order. At operating wavelengths of 1310 nm and 1550 nm, the single-input configuration exhibits insertion loss (IL) and crosstalk (CT) below 0.19 dB and −24.83 dB per channel, respectively. The dual-input configuration extends the bandwidth to 100 nm without significantly increasing IL or CT. The proposed photonic integrated device demonstrates strong potential for deployment in multiplexed optical communication networks.