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

Abstract

Interferometry (the use of interference phenomena) provides ampleopportunities for measurements in various areas of physics, particularlyin optics. In an interferometer, light from a single source is splitinto two beams that travel along different paths. The beams arerecombined to produce an interference pattern that can be used to detectchanges in the optical path length in one of the two arms. Here wereport about the use of a fiber optic version of the Mach-Zehnderinterferometer in measurements of the index of refraction of water andair.The open air version of the Mach-Zehnder interferometer employs two beamsplitters and two highly reflective mirrors. This open air version isdifficult to align and sensitive to environmental disturbance. In ourfiber optic version we have replaced one beamsplitter and two mirrors bya bidirectional coupler supplied with single mode fibers. Thisreplacement greatly simplified the operation of the interferometer. Astable interference pattern could quite easily be obtained. Thesimplified operation allowed the introduction of the instrument in ourBS program. This year two students performed highly accuratemeasurements on the index of refraction of various fluids (water, air)for their graduate project. Recently the instrument has been introducedin the regular laboratory classes.