Tunable microwave-frequency light modulator

A tunable microwave-frequency light modulator is described which consists of a rectangular-cross-section coaxial cavity containing two electro-optic crystals. The crystals are ammonium dihydrogen phosphate, the orientation being arranged so that the retardation due to each is added. Modulation has been observed over the frequency range 1.2¿4.8 GHz. The modulation depth was 10% with 3.5 W and a Q-factor of 420, both measured at 4 GHz. An optical communication link has been set up using the modulator and a microwave travelling-wave phototube.