In present paper correlations between different parts of spectrum of a fiber laser with randomly distributed feedback (RDFL) were experimentally measured directly. Implemented statistical analysis demonstrate weak cross-correlations between different lines in generation spectrum. These correlations were vizualized by plotting 2-D probability density functions. Linear correlation coefficient (Pearson coefficient) was calculated for each pair of spectrum lines.
In the present paper we experimentally demonstrate a generation in a short Raman fiber laser having 10 000 different
longitudinal modes only. We design the laser using 12 meters of commercially available fiber. Contrary to the recently
demonstrated single longitudinal mode DFB Raman laser and short DBR Raman laser, in the laser under study the
number of modes is high enough for efficient nonlinear interactions. Experimentally measured time dynamics reveals the
presence of mode correlations in the radiation: the measured extreme events lasts for more than 10 round-trips.
In the present paper we numerically study instrumental impact on statistical properties of quasi-CW Raman fiber laser
using a simple model of multimode laser radiation. Effects, that have the most influence, are limited electrical bandwidth
of measurement equipment and noise. To check this influence, we developed a simple model of the multimode quasi-
CW generation with exponential statistics (i.e. uncorrelated modes). We found that the area near zero intensity in
probability density function (PDF) is strongly affected by both factors, for example both lead to formation of a negative
wing of intensity distribution. But far wing slope of PDF is not affected by noise and, for moderate mismatch between
optical and electrical bandwidth, is only slightly affected by bandwidth limitation. The generation spectrum often
becomes broader at higher power in experiments, so the spectral/electrical bandwidth mismatch factor increases over the
power that can lead to artificial dependence of the PDF slope over the power. It was also found that both effects
influence the ACF background level: noise impact decreases it, while limited bandwidth leads to its increase.
We present the numerical study of the statistical properties of the partially coherent quasi-CW high-Q cavity
Raman fiber laser. The statistical properties are different for the radiation generated at the spectrum center or
spectral wings. It is found that rare extreme events are generated at the far spectral wings at one pass only. The
mechanism of the extreme events generation is a turbulent-like four-wave mixing of numerous longitudinal
generation modes. The similar mechanism of extreme waves appearance during the laser generation could be
important in other types of fiber lasers.