A device useful as a receiver including a waveguide interface to an antenna guiding a radio frequency (RF) signal to an RF waveguide cavity coupling the RF signal to a crystal resonator. The crystal resonator comprises a nonlinear material generating an optical output in response to a nonlinear interaction between the RF signal and an optical pump in the resonator. An optical port coupled to the crystal resonator for outputting the optical output from which the RF signal received on the antenna can be determined.