Undergraduate experiments in optics employing a fiber optic version of the Mach-Zehnder interferometer

Abstract

Interferometry (the use of interference phenomena) provides ample opportunities for measurements in various areas of physics, particularly in optics. In an interferometer, light from a single source is split into two beams that travel along different paths. The beams are recombined to produce an interference pattern that can be used to detect changes in the optical path length in one of the two arms. Here we report about the use of a fiber optic version of the Mach- Zehnder interferometer in measurements of the index of refraction of water and air. The open air version of the Mach-Zehnder interferometer employs two beam splitters and two highly reflective mirrors. This open air version is difficult to align and sensitive to environmental disturbance. In our fiber optic version we have replaced one beamsplitter and two mirrors by a bidirectional coupler supplied with single mode fibers. This replacement greatly simplified the operation of the interferometer. A stable interference pattern could quite easily be obtained. The simplified operation allowed the introduction of the instrument in our BS program. This year two students performed highly accurate measurements on the index of refraction of various fluids (water, air) for their graduate project. Recently the instrument has been introduced in the regular laboratory classes.