ALL-FIBER 3-PATH MACH-ZEHNDER INTERFEROMETER

We report the realization of a three-path Mach-Zehnde-r interferometer using single-mode fibers and two integrated 3 x 3 fiber couplers. We observed enhanced phase sensitivity, as compared with two-path interfe rometers, with a visibility of the interference pattern of more than 9 7%. This interferometer has an analog in two-photon interferometry, an d we believe it to be the first nontrivial example of N x N multiport interferometers. (C) 1996 Optical Society of America