Acoustically Scanned Delay For White-Light Interferometry

In white-light interferometry, two unbalanced interferometers are coupled in tandem. Typically, two Michelson interferometers are used. The optical pathlength difference between the two arms in each interferometer is large compared to the source coherence length. The measurand acts on one arm of the sensing interferometer, determining its optical pathlength. The length of one arm of the second interferometer, which is called the reference or receiving interferometer, is scanned, and a visibility maximum is observed when the pathlength mismatch is the same for the two interferometers [1]. The technique is closely related to a multiplexing technique called coherence multiplexing, in which fiber-optic Mach-Zehnder interferometers [2,3] or polarimeters [4] are often used.