Parametric noise amplification inherent in the coherence of fundamental optical soliton sequence propagating in fiber

When a highly coherent fundamental soliton sequence propagates an optical fiber, in-band amplified spontaneous emission noise is parametrically amplified, and signal-to-noise ratio is degraded thereby. We show experimental evidence that the parametric noise amplification phenomenon is inherent in the coherence of pulse sequence. The characteristics of the phenomenon obtained in normalized space is completely scalable to arbitrary physical space. Numerical studies reveal that the parametric gain of the noise increases with the propagation length and/or the duty ratio of the sequence. It is also found that for a large duty ratio, the feature of the gain depends on the relative phase difference between neighboring pulses in the sequence and that out-of-phase sequence can suppress the total gain.