Silicon-based hybrid demultiplexer for wavelength- and mode-division multiplexing

A silicon-based hybrid demultiplexer for wavelength-division multiplexing (WDM) and mode-division multiplexing (MDM) is proposed and demonstrated by integrating an M-channel-mode demultiplexer and N-channel WDM filters based on microring resonators (MRRs) with box-like responses. For the mode demultiplexer, the 2k-th output port is connected with the (2k+1)-th output port through the bus waveguide for the k-th MRR array, so that each MRR-based optical filter works bi-directionally and provides two drop ports. As an example, a 32-channel hybrid MDM-WDM demultiplexer is realized by integrating a 4-channel mode demultiplexer based on dual-core adiabatic tapers and two bi-directional MRR-based WDM filters with eight wavelength-channels. For the fabricated hybrid demultiplexer, the excess loss is 0.5-5 dB, the intermode cross talk is -16.5 to -23.5  dB, and the cross talks between the adjacent and nonadjacent wavelength channels are about -25  dB and -35  dB, respectively.