Photonic-crystal demultiplexer with improved crosstalk by second-order cavity filtering

In this paper, we implement on a silicon-on-insulator (SoI) platform a photonic-crystal demultiplexer that operates on the principle of mini-stopbands of broader waveguides. Previous InP-based membrane versions showed modest crosstalk at 10 nm spacing. Here, we implement a second cavity in the form of a second parallel waveguide almost identical to the core one. Simulations employing three-modes coupled-mode theory and finite-difference time-domain help optimizing the coupling. The experimental realization with deep ultraviolet exposure and grating couplers is the first of this demux strategy on SoI. It successfully shows crosstalk in the 15-20 dB range on a very small footprint