Polarization-independent DPSK demodulation using a birefringent fiber loop

A robust polarization-independent technique for demodulating optical differential phase-shift-keying (DPSK) signals using a birefringent-fiber-loop (BFL) is proposed and demonstrated. The BFL has a differential group delay between its fast and slow optical axes, providing interference which allows the phase modulation to be converted to intensity modulation and then directly detected by a photodiode. Error-free bit-error-rate measurements and clear demodulated eyes were observed. The temperature stability of the scheme improves with the bit rate of the DPSK signal.