Mode multiplexer/demultiplexer using metamaterials for optical fiber communications

An apparatus, comprising:

• a plurality of input optical fibers, each configured to propagate one of a plurality of input optical signals in a corresponding input spatial mode;
• an output optical fiber configured to propagate an output optical signal in a selected output spatial mode;
• and
• an optical multiplexer coupled between the plurality of input optical fibers and the output optical fiber, the optical multiplexer comprising:
• a substrate that is optically transmissive;
• a first reflector in contact with a first side of the substrate, the first reflector including at least one input aperture configured to accept the input optical signal from the plurality of input optical fibers and at least one output aperture configured to output the output optical signal to the output optical fiber;
• and
• a multi-stage metamaterial in contact with a second side of the substrate opposite the first side,
• the multi-stage metamaterial including a plurality of structures protruding from the substrate, the plurality of structures arranged in a pattern configured to impart a spatially dependent phase delay to the plurality of input optical signals, the spatially dependent phase delay based on the corresponding input spatial mode and the output spatial mode.