Ultra-compact SOI-based higher-order mode pass wavelength demultiplexer

We propose an ultra-compact mode filtering wavelength demultiplexer design with a footprint of 3µm×3µm. Our device can route input TE 1 mode signals at 1310 nm and 1550 nm to different output ports while simultaneously blocking fundamental transverse electric (TE 0 ) mode input. Our device is designed based on the topology optimization algorithm, which results in an ultra-compact footprint combining wavelength routing and mode filtering functions for the first time, to the best of our knowledge. Our final optimized devices demonstrated insertion losses of 1.26 dB and 1.47 dB for the C- and O-band output ports, respectively, with inter-port crosstalk as low as −21.25dB and −30.99dB. The extinction ratios between TE 1 mode and TE 0 mode are 24.02 dB and 30.12 dB at the 1310 nm and 1550 nm output ports. The combination of small footprint, broad transmission bandwidth, TE 1 to TE 0 mode selectively filtering, and C- and O-band TE 1 mode demultiplexing functions make this a uniquely versatile device that can play an important role in future high density mode-wavelength multiplexing systems.