Abstract

In the process of parametric downconversion in a nonlinear crystal, incident photons split up into two lower frequency photons that emerge in different directions. Because the downconverted photons appear simultaneously, an optical communication channel based on transmission and simultaneous detection of these photon pairs should be able to achieve great discrimination against background. Indeed, it should be able to operate even in conditions in which the light signal would otherwise be lost in the noise. Such a communication channel requires relatively few photons per second and could be almost interception proof. The feasibility of the idea has been explored experimentally, and the results involving photoelectric coincidence counting measurements are presented.

© 1985 Optical Society of America