Study Of The Spectral Properties Of The High Power Fiber Lasers

Spectral property is one of the basic properties of fiber lasers.With the increasing of the output power,the fiber nonlinearity has a significant effect on the high power laser system.On one hand,the spectral property is the direct characterization of the fiber nonlinearity and the damage effect;on the other hand,the spectral property of the fiber laser will affect the stability of the system and the relative devices.On the base of above reasons,we study the spectral property of the high power fiber laser theoretically and experimentally in this paper.At first,this paper reviews the developments on spectral theories of fiber lasers,and introduces the typical spectral models for Yb-doped fiber lasers,Raman fiber lasers and Yb-doped fiber amplifier respectively with the corresponding application ranges and drawbacks.The spectral models for the typical multi-longitudinal mode oscillator and the super-fluorescent source are proposed through the calculations of the rate equations and nonlinear propagation equations,together with the influence of the structural parameters.It reveals that the linewidth of the multi-longitudinal mode oscillator increases linearly with the bandwidth of the high-reflective fiber brag grating(FBG),pump power and the length of the cavity,while the influence of the bandwidth of the output FBG can be omitted.For the super-fluorescent source,the central wavelength of the output spectrum will shift to longer wavelength with the increase of the length of the active fiber.The spectral model for the high power fiber amplifiers is proposed by describing the seed properties and the amplification process.Numerical simulation of the output spectra has been carried out to study the impacts of various factors on the high power fiber amplifiers.Corresponding experiments have been performed based on two different seeds,and the predictions of the theory are in excellent quantitative agreement with the experimental results.Finally,the approximate formula for the linewidth scale factor is given.The dynamics equations for fiber lasers with the stimulated Raman scattering effect are proposed,together with the study on the influence of the seed and spectral filtering on the Raman threshold of the high power fiber amplifier.It reveals that the temporal properties of the seed greatly affect the Raman threshold of the system.