Improved 8-channel silicon mode demultiplexer with grating polarizers.

An improved 8-channel silicon mode demultiplexer is realized with TE-type and TM-type grating polarizers at the output ends, and these gratings serve as fiber-chip couplers simultaneously. The present 8-channel silicon mode demultiplexer includes a three-waveguide PBS (for separating the TE0 and TM0 modes) and six cascaded ADCs (for demultiplexing the high-order modes of both polarizations). The grating polarizers with high extinction ratios are used to filter out the polarization crosstalk in the 8-channel hybrid multiplexer efficiently and the measured crosstalk for all the mode-channels of the improved 8-channel mode multiplexer is reduced greatly to ~-20dB in a ~100nm bandwidth.