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Optical interferometry experiment in the time-frequency domain

We have developed an optical heterodyning experiment for the undergraduate physics laboratory curriculum that permits observation of optical beat phenomena associated with the interference of two light beams with slightly different frequencies. For optical beat frequencies below 10 Hz the interference of the light beams is observed on a viewing screen as a slowly drifting Michelson interference fringe pattern.
For beat frequencies greater than 10 Hz the drift of the interference fringes is too rapid to be observed visually; however, if a photodetector is placed so as to detect light from within the rapidly drifting fringe pattern, the time variation of the detected light signal can be amplified and fed to a loudspeaker, allowing an individual student or a lecture audience to hear the beating of the two light beams. Since commercial amateur radio transceivers are used to control the frequencies of the two interfering light beams, the transceivers can be modulated with a voice signal to generate single sideband modulated light beams that can be demodulated using standard optical homodyne detection techniques. This simple optical communications system demonstrates clearly how transmitter and receiver design principles at radio frequencies can be transferred to optical frequencies for the implementation of modem lightwave communication systems.