Multi-chip module and method

A multi-chip module, comprising:

• a carrier;
• a multimode optical waveguide formed on the carrier, in the carrier, or on and in the carrier;
• a first chip and a second chip disposed on the carrier and coupled to the multimode optical waveguide;
• wherein the first chip is configured to transmit a plurality of light beams into the multimode optical waveguide;
• wherein the multimode optical waveguide is configured to generate a plurality of mixed light beams having at least partial superposition of the plurality of light beams;
• wherein the second chip is configured to receive the plurality of mixed light beams from the multimode optical waveguide;
• and
• where the second chip is configured to:
• store a representation of the received plurality of mixed light beams as a transmission signature and/or as a cryptographic key in a memory associated with the second chip, and/or
• compare the representation of the received plurality of mixed light beams with a target representation stored in the memory associated with the second chip.