The sonorous beat of optical waves in a Michelson interferometer

Overview & Synopsis

This paper describes time-dependent phase modulation experiments using an optical Michelson interferometer. Changes in the path length of the interferometer arms induce phase shifts in time and, thanks to a loudspeaker, make the interferometric signal audible. We produce time-fluctuating refractive indices and mechanical motions of one reflecting mirror. A sinusoidal motion is applied, thus creating a phase modulation of the wave in one of the interferometer arms. Sidebands of the laser frequency appear, which interfere with the other interferometer wave. Our hearing sense is quite developed, and we use it to analyze the non-linear character by the acoustic timbre. Finally, we transfer information by phase modulation. Our setup benefits the visually impaired community as temporal phase changes can be analyzed by the auditory sense, but this unconventional use of an optical interferometer is also attractive to a general audience.