GB1022323A - Improvements in or relating to light modulating apparatus - Google Patents

Abstract

1,022,323. Light modulation. STANDARD TELEPHONES & CABLES Ltd. June 14, 1963 [June 15, 1962], No. 23126/62. Heading H4F. Light-modulating apparatus comprises a microwave resonator 6, an optical resonator in the form of an interferometer made up of a pair of partial optical reflectors 1, 2 and an electro-optical element 4 within the microwave resonator and in the path of the optical wave within the optical resonator. The optical resonator is " tuned " so that it passes approximately 50% of the incident monochromatic light 3. The electro-optical element responds to the electric field in the microwave resonator to produce a variation in its refractive index with a consequent change in the tuning of the optical resonator and the transmitted light. The electro-optical element comprises a crystal of potassium dihydrogen phosphate in the form of a right circular cylinder with the physical axis coinciding with the Z-axis of the crystal. A polarizing filter 10 in the incident light beam is rotated so that the light is polarized to match one of the principal refractive indices of the element. The end faces of the element are bloomed to reduce optical reflection. Cooling of the optical element may be effected by thermal contact with the end faces of the resonator and/or by blowing air through the resonator. Light source 9 may be an optical Maser. A multi-channel modulating system is described with reference to Fig. 6 (not shown), where a beam of monochromatic light is split by a cylindrical lens structure into a plurality of partial beams which pass through separate modulators operating at different microwave different optical frequencies and are then recombined to form a single beam.