Michelson Interferometer

The fiber-optic Michelson interferometer is the most popular interferometer configuration in OCT laboratories. In such a configuration, the light from the source is routed through a single-mode fiber. The light enters a fiber-optic coupler (beam-splitter) where the light is split equally into a reference and sample arm. The light propagated through a the reference arm is directed towards a reference mirror. The other half of the light passes through the a sample arm fiber and beam-delivery instrument and on to the sample. Reflected light from the sample re-enters the distal end of the same fiber. As the light returns to the coupler, it combines with the reference arm light and returns to a photodetector. Two photodetectors are often used rather than one to cancel the effects of the noise generated from the optical source. Free-space interferometers, although not as common, are a viable alternative to using fiber-optics and possess distinct advantages. The wide array of mirrors and prisms currently available allow the development of interferometers without fibers. A major advantage of free-space interferometers is their ability to control and change the polarization of light; fibers, when bent, cause polarization changes in light due to silica fibers' birefringent nature. Thus, a free-space interferometer eliminates polarization mismatches (due to propagation from sample/reference mirror to detector) between the sample and reference arms.