Method and apparatus for use in measuring frequency difference between light signals

Abstract

The frequency separation between two light signals, one having a first and the other having a second frequency, is determined by first forming three light beams, each including both frequencies; directing the three beams through an interferometer in which they traverse three optical paths having three different known optical path lengths; determining the interferometric phases for each of the three optical paths at both frequencies; and determining the difference between the first and second frequencies from the interferometric phases and known optical path lengths. The light signals may be light from two lasers operating at different frequencies. The optical path lengths can be predetermined by calibration using two light sources of know frequencies. An apparatus for carrying out this method is also disclosed.

Dependencies are inferred from the claim text.