Method and apparatus for converting phase-modulated light to amplitude-modulated light and communication method and apparatus employing the same

摘要

A light modulator for generating a beam of amplitude-modulated light including a source of polarized light, at least one and preferably two liquid crystal cells having a thin layer of nematic liquid crystals of positive dielectric anisotropy through which the polarized light is directed to produce a beam of light having a phase shift corresponding to a modulating electrical signal which is applied to each of the liquid crystal cells. The liquid crystal cells in addition have a continuing electrical bias applied across the layers in order to achieve the rapid response times necessary to achieve phase modulation of the polarized light. The resulting phase-modulated light is converted in a linear polarizer to amplitude-modulated light corresponding to the modulating electrical signal. The amplitude-modulated light is detected in a suitable light detector which generates an electrical signal corresponding to the modulating electrical signal. The linear polarizer may be oriented with either the transmitter or the receiver. A communication system involving a transmitting modulator and a receiving demodulator transmits communication through light either as phase-modulated light or as amplitude-modulated light.