Efficient 3D silicon mode (de)multiplexer based on a sidewall-aligned vertical coupler.

An efficient three-dimensional (3D) quasi- and quasi- mode (de)multiplexer [(De)MUX] is proposed and optimized based on a dual-waveguide 3D-coupler, in which the sidewalls of a bottom silicon waveguide and an upper poly-silicon waveguide are aligned vertically. The full-vectorial finite element method and 3D full-vectorial finite difference time domain method are utilized to study the performances of the proposed 3D mode (De)MUX. The results indicate that the proposed mode (De)MUX can achieve a compact coupling length of 6.88 µm, a mode crosstalk of -30.04, an insertion loss of 0.02 dB, and an ultra-broad 1 dB bandwidth of 300 nm. The proposed 3D mode (De)MUX based on a sidewall-aligned vertical coupler has the potential to extend the functionality and to increase the integration of the mode division multiplexing (MDM) systems.