Optical phase fluctuations thermally induced in a single-mode optical fiber

The use of a fiber-optic Mach-Zehnder interferometer to measure differences in temperature or pressure between two single-mode fiber arms is described. Temperature or pressure changes are observed as a motion of an optical interference fringe pattern. Values are calculated for the pressure and temperature dependence of the fringe motion. Pressure and temperature measurements are made with the interferometer, and the experimental values for sensitivity are in good agreement with those calculated.