Design of a Microwave-Frequency Light Modulator

A device is described which intensity modulates a light beam at modulating frequencies in the microwave region. A high-Q re-entrant capacity-loaded coaxial-line resonator employing a properly oriented slab of uniaxial crystal of the dihydrogen phosphate variety as its dielectric medium is coupled to a microwave-frequency generator tuned to the fundamental cavity mode. A light path is provided through the resonator so that a beam of plane polarized light can pass through the crystal into a suitably oriented analyzer. The intensity of the light beam emerging from the latter varies at the same rate as the cavity frequency.