Compact and broadband mode multiplexer and demultiplexer based on asymmetric plasmonic-dielectric coupling

A compact and broadband mode (de)multiplexer utilizing the asymmetrical directional coupling between a hybrid plasmonic waveguide and a silicon nanowire waveguide is proposed. The coupling length is 13.6 μm, which is the shortest in TE0 and TE1 mode multiplexers reported, to the best of our knowledge. It shows a high mode conversion efficiency of 99.2% with excess loss of only 0.35 dB at 1550 nm. The mode multiplexing circuit exhibits a low crosstalk of less than -17  dB over a large bandwidth of 100 nm.