Turbulent broadening of optical spectra in ultralong Raman fiber lasers

We study the properties of radiation generated in ultralong fiber lasers and find an interesting link between these optical systems and the theory of weak wave turbulence. Experimental observations strongly suggest that turbulentlike weak interactions between the multitude of laser cavity modes are responsible for practical characteristics of ultralong fiber lasers such as spectra of the output radiation.

Figure 1

Schematics of the ultralong Raman fiber laser.

Figure 2

(Color online) (a) Total intracavity power at $1455\mathrm{nm}$ as a function of the total pump power at $1365\mathrm{nm}$: Experimental points and numerical simulation (solid curves). (b) $1455\mathrm{nm}$ spectrum measured at point $C2$; Stokes power=0.6, 265, and $714\mathrm{mW}$ for $L=6.6\mathrm{km}$.

Figure 3

(Color online) $1455\mathrm{nm}$ spectral widths at $3\mathrm{dB}$ (a) as a function of $1455\mathrm{nm}$ power for different fiber cavity lengths $L=6.6$, 22, 42, and $84\mathrm{km}$. The dashed lines represent the fit by function $y=A{x}^{1∕2}$. (b) Typical temporal behavior of $1455\mathrm{nm}$ intensity, $L=22\mathrm{km}$, and $I\sim 100\mathrm{mW}$.

Figure 4

(Color online) (a) Experimental values for spectral width of the RF peaks [5] as a function of the total intracavity power at $1455\mathrm{nm}$ for cavity lengths of 6.6, 22, 44, and $84\mathrm{km}$ and corresponding mode spacing values marked by dots $\left(22\mathrm{km}\right)$, dash dots $\left(44\mathrm{km}\right)$, and dashes $\left(84\mathrm{km}\right)$; $15.5\mathrm{kHz}$ spacing at $6.6\mathrm{km}$ lies beyond the graph. (b) Maximum power with resolved mode structure as a function of the cavity length; solid lines are (a) linear fit and (b) $A∕x$ fit.