Tuneable All-Fiber/sup /spl reg// delay-line interferometer for DPSK demodulation

An All-Fiber/sup /spl reg// tunable Mach-Zehnder delay line interferometer was developed for differential phase shift keying (DPSK) demodulation. Low loss and high isolation are maintained in a compact package by annealing the fibers at high temperature to relieve bending stresses. Reliability data is presented.