All-fiber phase controlled delay interferometer and method of making the same

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, the couplers being concatenated in series to form a two-branch interferometer, and having a splitting ratio close to 50% over the wavelength operating range of the device;
• b) the two branches between the couplers being of unequal length and being 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;
• d) a fiber heater for heating at least one of the branches between the couplers so as to obtain an phase control of the interferometer;
• and
• e) a substrate to which the couplers are bonded with hard bond points and to which the branches are bonded with soft bond points.

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, the couplers being concatenated in series to form a two-branch interferometer, and having a splitting ratio close to 50% over the wavelength operating range of the device;
• b) the two branches between the couplers being of unequal length and being 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;
• d) a fiber heater for heating at least one of the branches between the couplers so as to obtain an phase control of the interferometer;
• and
• e) two output fibers where the length difference therebetween produces a time-of-flight difference between the signals travelling therein smaller than 2% of the interferometer device delay.