Patent ID: 7480423

Claim:
An all-fiber phase controlled delay interferometer device configured for use in an optical Differential Phase Shift Keying (DPSK) demodulation system, which comprises: a) two optical fiber couplers, each having two input and two output ports, which couplers are concatenated in series to form a two-branch interferometer, and have a splitting ratio close to 50% over the wavelength operating range of the device; b) the two branches between the couplers are of unequal length and are shaped to a predetermined shape adapted to provide one bit of delay between the branches when pulses at the input of the interferometer are split into two halves, whereby one half pulse is delayed by one bit so as to interfere in the output coupler with the next bit half pulse coming from the second-branch; c) means of forming an interferometric structure that has minimal birefringence to insure that the optical delay experience by the two half pulses be the same, irrespective of their state of polarization; and d) a fiber heater for heating at least one of the branches between the couplers so as to obtain phase control of the interferometer.