Coherent few mode demultiplexer realized as a 2D grating coupler array in silicon

We demonstrate an on-chip coherent mode scrambling demultiplexer for polarization multiplexed few mode signals. The device has been fabricated in the standard silicon-on-insulator platform. The mode demultiplexer consists of an array of 2D grating couplers for dual polarization few mode fiber-to-chip coupling and optical hybrids realized by 4x4 MMIs. The array of perfect vertical 2D grating couplers allows us an efficient fiber-to-chip coupling with experimental peak coupling efficiencies of -5.2 dB and -9.0 dB at 1570 nm tbr LP01 and LP11 modes, respectively, while simulated coupling efficiencies at 1550 nm are -3.6 dB and -3.3 dB for LP01 and LP11, respectively. We successfully pertbrmed a back-to-back three LP modes division multiplexing transmission experiment with single polarization 32 Gbaud QPSK signals using the fabricated mode demultiplexer relying on offline MIMO DSP techniques. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement