a phase-change metasurface waveguide mode converter comprising a plurality of phase-change antennas comprising a phase-change material and protruding from a surface, wherein each phase-change antenna of the plurality of phase-change antennas is configured to scatter an optical waveguide mode and cause a phase shift of light travelling through an optical waveguide optically coupled thereto, and wherein the plurality of phase-change antennas defines a longitudinal axis, and wherein widths of the plurality of phase-change antennas change along the longitudinal axis;

an optical waveguide optically coupled to the plurality of phase-change antennas;

an input light source configured to emit signal light into a first end of a first portion of the optical waveguide;

a variable optical attenuator disposed between the input light source and the first end of the first portion; and

a signal photodetector configured to receive the signal light from a second end of the first portion of the optical waveguide and generate a modulated signal based upon the received signal light,

wherein the optical waveguide supports a first transverse optical mode and a second transverse optical mode, and wherein a wavevector difference between the first transverse optical mode and the second transverse optical mode is equal to a wavevector produced by the plurality of phase-change antennas in a crystalline phase.