Spectral characteristics of a Raman fiber laser with temperature-tunable FBGs

摘要

In a two-stage phosphosilicate Raman fiber laser (1.26/1.53μm) pumped by Yb-fiber laser (1.08μm), a temperature tuning of FBGs forming Raman cavities has been performed by means of thermoelectric modules baaed on Peltier elements. Output power and spectral profiles at 1.26μm and 1.53μm have been monitored during such T~0-tuning in the range of +-25 C corresponding to the FBG wavelength shift of +-0.2 nm. The most pronounced effect is that the observed spectral profile at 1.26μm corresponding to the first-stage highly-reflective cavity consists of two splitting components, which become strongly asymmetric while independent T~0-tuning of cavity FBGs. A simple model considering spectral broadening with increasing pump power and T~0-induced shift between central wavelengths of the FBGs has been developed. The model takes into account wavelength-dependent Raman gain saturation and qualitatively describes the observed effects of the splitting and asymmetry with T~0-tuning. It is also demonstrated, that the studied spectral broadening and shift lead to the effective "bleaching" of the highly-reflective cavity, so estimated integral transmission may increase by order of magnitude from minimum transmission ～ 1%, corresponding to central FBG wavelength.