A Novel Phase-Locking-Free Phase Sensitive Amplifier-Based Regenerator

We propose a scheme for phase regeneration of optical binary phase-shift keying (BPSK) data signals based on phase sensitive amplification without active phase locking. A delay interferometer is used to convert a BPSK signal impaired by noise to an amplitude modulated signal followed by cross-phase modulation in a highly nonlinear fiber (HNLF), which transfers the data modulation from the amplitude modulated signal to the phase of a locally generated carrier. By placing the HNLF in a loop, a stable phase relation is maintained relative to a set of counter propagating locally generated phase-locked pumps. As a result, active phase stabilization is avoided. A proof-of-principle experiment is carried out with a dual-pump degenerate phase sensitive amplifier, demonstrating regeneration for a 10-Gb/s non-return-to-zero differential BPSK data signal degraded by a sinusoidal phase-noise tone. Receiver sensitivity improvements of 3.5 dB are achieved at a bit error rate of 10^-9. In addition, numerical simulations are performed comparing the idealized regenerator performance in the presence of sinusoidal phase modulation as well as Gaussian phase noise.