Patent ID: 7126695

Claim:
A heterodyne interferometer comprising: an acoustic-optical modulator (AOM) for receiving an optical source signal and an electrical radio frequency (RF) signal, superimposing the RF signal on the source signal, and thereafter outputting a zero order, un-modulated optical beam and a higher order, modulated optical beam, wherein one of the zero order and higher order beams comprises a target beam and the other beam comprises a local oscillator beam; a telescope for receiving the target beam, and thereafter directing the target beam through a beam propagation medium to a target such that at least a portion of the target beam reflects off of the target; a beam splitter for receiving the local oscillator beam and the reflected beam from the target, wherein the beam splitter is also for coherently combining the local oscillator beam and the reflected beam to produce a fringe pattern; a detector for detecting the fringe pattern to thereby generate an electrical beat signal to permit the beat signal to be subsequently demodulated based upon the RF signal to thereby determine an electrical signal proportional to a phase difference between the reflected beam and the local oscillator beam, wherein the phase difference represent an optical path difference between the beam splitter and the target; a half-wave plate for receiving the target beam from the AOM and rotating the plane of polarization of the target beam; a polarizing beam splitter for receiving the target beam from the half-wave plate, and thereafter dividing the target beam into a horizontally-polarized target beam and a vertically-polarized target beam; and a quarter-wave plate for receiving the vertically-polarized target beam, circularly-polarizing the target beam, and thereafter passing the circularly-polarized target beam to the telescope, wherein the circularly-polarized target beam becomes circularly-polarized in an opposite direction when the target beam reflects off the target, wherein the quarter-wave plate is also for receiving the reflected beam and rotating the plane of polarization of the reflected beam ninety degrees compared to the polarization of the beam passed to the telescope, and wherein the polarizing beam splitter receives the reflected beam from the quarter-wave plate and thereafter reflect the reflected beam to the beam splitter as a non-polarized reflected beam.