All-optical DQPSK signal regeneration using 2R amplitude regenerators

An all-optical regeneration scheme for DQPSK signals is proposed and analyzed. In the regenerator, an incoming DQPSK signal is demodulated to two parallel OOK signals by one-symbol delay interferometers. After the amplitude noise is removed by 2R (reamplifying and reshaping) regenerators and the power levels are suitably amplified, the OOK signals modulate the phase of clocked probe pulses in the subsequent all-optical phase modulators by which the noise-reduced (D)QPSK signal is generated. The alteration of phase data encoded on the pulses in the regeneration process can be undone by suitable encoding or decoding. Numerical simulation for short-pulse RZ-DQPSK signals at 160 Gbit/s (80 Gsymbol/s) shows that reduction in both phase and amplitude noise can be obtained by the regeneration scheme where fiber-based 2R amplitude regenerators and phase modulators using self- and cross-phase modulation, respectively, are employed.