Abstract:
Background U-band fiber lasers are of significant value for applications in communications, sensing, and scientific research.
Purpose This paper employs a 1.55 μm fiber laser as the pump source and demonstrates a U-band 1.65 μm Raman fiber laser based on commercially available single-mode silica fiber. The effects of the Raman fiber length and the reflectivity of the output coupling fiber Bragg grating (OC-FBG) on the power conversion efficiency of the Raman laser were systematically investigated.
Methods The optimal Raman fiber length was determined to be 2.1 km in experiment. Then, with the optimal Raman fiber length, experiments were conducted by varying the reflectivity of the OC-FBG to analyze its influence on the output power and spectral broadening of Stokes light. By combining the measured forward and backward Stokes powers with the collected forward and backward spectra, the optimal OC-FBG reflectivity under the current experimental conditions was determined.
Results The results indicated that as the Raman laser power increased, the broadening of the Stokes spectral linewidth reduced the effective reflectivity of the fiber Bragg grating, leading to backward power leakage, which became the main factor limiting the forward output power.
Conclusions By selecting an OC-FBG with a low reflectivity of 15.7% and using a 2.1 km silica fiber as the Raman gain medium, a 1648.8 nm Raman laser output with a power of 10.1 W and a 3 dB bandwidth of 2.5 nm was achieved, corresponding to an optical-to-optical conversion efficiency of 65.2%.
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