Experiments on optical fiber interferometers and laser modes

Three experiments on optical fiber interferometers, suitable for a teaching laboratory, are described. The guiding characteristics of single mode optical fibers enable simple interferometry experiments with large path differences to be carried out easily. These experiments show that the fringe visibility exhibits a periodic dependence on the path difference when using a multilongitudinal mode HeNe laser. A simple model can be used to explain this dependence in terms of the mode spectrum of the laser.