Inverse-Designed Low-Crosstalk CWDM (De)Multiplexer Assisted by Photonic Crystals

Compact and integrated wavelength demultiplexers are key components of photonic integrated circuits for on-chip communications. The inverse design method has shown excellent performance in achieving compact footprint, but is still hindered by large channel spacing and small channel numbers for wavelength demultiplexer. Here we propose and experimentally demonstrate a compact and low-crosstalk coarse wavelength division demultiplexer. The proposed device is composed of an inverse-designed meta-structure with the wavelength splitting function and cascaded photonic crystal filters with the crosstalk reduction function. The wavelength demultiplexer has six-channels with a 20-nm spacing in the C-band and a compact total footprint of 27 × 12 μm². The experimental results show that the measured peak insertion loss is 6 dB and the crosstalk is below −20 dB for all output channels. The simulation results also indicate that the device has a good fabrication tolerance. This will significantly improve the integration density for on-chip wavelength division multiplexing systems.