Phase-modulated light detection

Abstract

Abstract A beam of coherent monochromatic light from a laser interacts with an acoustic wave signal in a Debye-Sears interaction cell, thereby to phase modulate the beam with the acoustic wave signal and with intelligence information carried thereby. At a fixed distance along the beam path from the interaction cell the modulation of the light beam shall have been converted from phase to amplitude modulation and a slit positioned at such location admits both the undiffracted and the first-order diffracted components of the modulated beam to a detector where the beam is demodulated and the intelligence recovered. Increased efficiency is obtained by using a series of slits, rather than a single slit, disposed across the light beam at the aforesaid particular location. Where Bragg angle diffraction is achieved in an interaction cell, as distinguished from Debye-Sears diffraction, the emerging light beam exhibits both amplitude and phase modulation. If the system employs two acoustic wave signals interacting with a single light beam in the cell, with the pair of acoustic wave signals having the proper angular relation, the output of the interaction cell may be demodulated as to its phase modulation content by the same technique employed in demodulating the output of the Debye-Sears diffraction cell. This increases the efficiency of the system over what is otherwise obtained if demodulation is confined to the initial amplitude modulation of the modulated light beam.

Inventors

• 👤 Adrianus Korpel

Bibliographic Details