Abstract
The pattern-independent phase noise accumulation in a chain of all-optical
clock recovery devices (CRDs) based on two-section gain-coupled distributed
feedback (TS-DFB) laser operating in the coherent mode is studied experimentally
and theoretically. A simple theoretical model, where the CRD output phase
noise is equal to the sum of the phase noise introduced by the CRD and the
CRD input phase noise filtered by the phase noise transfer function, has been
proposed for the CRD equivalent phase noise model. The accumulation of pattern-independent
phase noise is investigated experimentally and theoretically for different
cut-off frequencies of the phase noise transfer function of the TS-DFB laser
and two different optical signal to noise ratios. It is shown that, due to
the phase noise added by the CRD, phase noise accumulates in the passband
of the phase noise transfer function, with the phase noise transfer function
well approximated by a first-order lowpass filter. Excellent qualitative agreement
between the experimental results and the theoretical model is observed. Also,
it is concluded that the phase noise accumulation model for CRD, where the
recovered clock is locked to the optical power of the incoming clock signal,
presented by other authors holds in a qualitative point of view for the TS-DFB
laser operating in the coherent mode. Since the root-mean-square (rms) of
the timing jitter is proportional to the square root of the integrated power
spectral density of the phase noise, the results show that a smaller cut-off
frequency of the phase noise transfer function does not lead to a smaller
rms value of the pattern-independent timing jitter along the chain of all-optical
CRDs based on TS-DFB laser. It is shown that the minimum rms of the pattern-independent
timing jitter along the CRD chain results from a compromise between the cut-off
frequency of the phase noise transfer function and the phase noise introduced
by the TS-DFB laser.
© 2008 IEEE
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