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

We propose an ultra-compact mode filtering wavelength demultiplexer design with a footprint of 3µ×3µ. Our device can route input mode signals at 1310 nm and 1550 nm to different output ports while simultaneously blocking fundamental transverse electric ( ) 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 -21.25 and -30.99 . The extinction ratios between mode and 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, to mode selectively filtering, and C- and O-band mode demultiplexing functions make this a uniquely versatile device that can play an important role in future high density mode-wavelength multiplexing systems.