Changes in coherence during the process of supercontinuum generation in a dispersion-shifted fiber (DSF), a dispersion-flattened fiber (DFF) and a dispersion-decreasing fiber (DDF) have been investigated in detail for the first time. It is shown that both time and frequency coherence are greatly degraded in DSF and DFF. This is due to the four wave mixing effect caused by self-phase modulation and group velocity dispersion in the presence of amplified spontaneous emission. Such a light pulse may be unsuitable for long-distance, high-speed transmission because it contains timing jitter and amplitude fluctuations. On the other hand, DDF can maintain its coherence as the spectral broadening occurs coherently through adiabatic N = 1 soliton compression. This fiber is useful for ultra-high-speed communication.
- Four wave mixing