Home – Home – Jornals – Avtometriya 2025 number 1

The role of the cross-phase modulation between the pump and generation waves in a fiber laser with randomly distributed feedback due to weak Rayleigh backscattering, operating in the ultra-narrow regime, which is observed just above the threshold, is discussed. The spectrum in this case consists of narrow (less than 1 MHz) modes with a typical lifetime of 1 ms. It was demonstrated earlier that both external noises (thermal or acoustic) and the nonlinear process of four-wave interaction between the generation modes can be responsible for the mode decomposition process. In present study, a model of the nonlinear interaction of the pump wave with an ultra-narrow generation mode is constructed, and it is shown that the cross-phase modulation between them can lead to the destruction of the mode if the walk-off is sufficiently slow. It means that the narrow-band generation depends on the fiber dispersion, because the latter determines the corresponding walk-off length. A comparison with experiments confirms this conclusion: in lasers based on fibers with low dispersion, narrow-band generation is not observed, while it does exist in cases with high dispersion coefficients.