Abstract: A method of making an all-fiber Mach-Zehnder interferometer comprising at least two optical fibers comprises the steps of bringing the fibers in a reciprocal contact relationship for a contact section thereof; fusing together and tapering the fibers in at least a first portion of said contact section; forming at least two optical couplers between the fibers in a second and a third portions of said contact section, located at opposite sides of said first portion.