A fiber optic version of the Mach-Zehnder interferometer for use in the undergraduate physics laboratory

Abstract

In an interferometer, light from a single source is split into two beams which travel along different paths after which they are recombined. The resulting interference pattern can be used to detect changes in the optical path length in one ofthe two arms. A change of a physical parameter causing the optical path length in one arm to change by one wavelength can easily be detected. Using a source in the visible region results in a high sensitivity. Interferometers can be used for the measurement of the index of refraction of a gas by gradually allowing the gas to flow in an evacuated tube, placed in one of the arms of the interferometer. The Michelson, Rayleigh and Mach-Zehnder interferometers are examples of refractometers. Open-air interferometers have the general disadvantage that they are extremely sensitive to environmental disturbances (fluctuations in temperature and pressure).
We have constructed a fiber optic version ofthe Mach-Zehnder interferometer by replacing the open-air arms by single mode fibers. The introduction of fibers greatly reduces the sensitivity for environmental disturbances. It also simplifies the operation of the Mach-Zehnder interferometer to such an extent that it can be introduced in undergraduate lab courses. The geometry of our system with the recombination still taking place in the open, allows for use as a refractometer while the system can also be used as a sensitive pressure and temperature sensor.