Nonlinearity-Assisted All-Optical Clock Recovery for Phase Modulated Lightwave Systems

We report all-optical clock recovery from 10 GBaud NRZ shaped lightwave signals in QPSK and 16QAM formats through injection mode-locking of an Erbium-doped fiber laser. Since these optical NRZ phase modulated coherent signals lack in the strength of the clock-tones, a pre-processing stage for the enhancement of these clock-tones based on a nonlinear semiconductor optical amplifier (SOA) is employed. Optical clock recovery is demonstrated experimentally for both modulation formats, along with wavelength tunability of the scheme over the entire C-band. Resilience of the clock recovery process to input OSNR conditions is also demonstrated. The RMS timing jitter of the recovered clock is measured to be \leq 2 ps. We also report the performance analysis of the scheme for coherent modulation formats with respect to the dispersion-induced degradation in practical links through simulations and experiments.