Optical multiple-input-multiple-output (MIMO) demultiplexers

An optical multi-input-multi-output (MIMO) receiver, comprising:

• an input port configured to receive input light;
• means for performing adaptive 2×2 optical MIMO polarization demultiplexing on the input light using 3-stage optical phase-shifting to output a first optical signal and a second optical signal, the means comprising
• a first optical phase shifter controlled to apply a first relative phase shift that varies in a discontinuous manner,
• a second optical phase shifter controlled to apply a second relative phase shift that varies in a continuous manner, and
• a third optical phase shifter controlled to apply a third relative phase shift that varies in a continuous manner;
• and
• at least one photodetector configured to detect the first optical signal and the second optical signal.

A method of performing 2×2 optical multi-input-multi-output (MIMO) demultiplexing, the method comprising:

• receiving light through a pair of MIMO inputs into a first pair of optical transmission paths;
• controlling a first optical phase shifter to apply a first relative phase shift between the first pair of optical transmission paths, the first relative phase shift varying in a discontinuous manner;
• combining the first pair of optical transmission paths with a first 2×2 optical coupler to output a second pair of optical transmission paths;
• controlling a second optical phase shifter to apply a second relative phase shift between the second pair of optical transmission paths, the second relative phase shift varying in a continuous manner;
• combining the second pair of optical transmission paths with a second 2×2 optical coupler to output a third pair of optical transmission paths;
• controlling a third optical phase shifter to apply a third relative phase shift between the third pair of optical transmission paths, the third relative phase shift varying in a continuous manner;
• combining the third pair of optical transmission paths with a third 2×2 optical coupler to output a fourth pair of optical transmission paths;
• and
• outputting the fourth pair of optical transmission paths through a pair of MIMO outputs, which are output from the third 2×2 optical coupler, as a pair of demultiplexed output light signals.