Application of Phase Modulation to Digital Data Recording By Means of Superposed Diffraction Gratings

Abstract

Optical phase modulation has been applied to a system for digital data recording based on the photography of a multiplicity of superposed interference fields. When piezoelectrically driven mirrors or electro-optic crystals are placed suitably in the interfering beams and sinusoidally excited to the proper amplitude, the corresponding fringe pattern exposure is effectively spoiled. Since the effect arises from variations in optical path or refractive index, tolerances on optical quality are relatively modest. Extinction ratios in excess of 100:1 are readily obtained.