Suppression of stimulated Brillouin scattering in high power fibre lasers and amplifiers

Abstract

Fibre sources in high power devices have significant advantages over conventional gas and solid state lasers. However, for applications that require the so-called singlefrequency sources with narrow linewidths, the output power is low mainly because of the problem of the stimulated Brillouin scattering (SBS).

A model that accounts for the SBS in dual-clad fibre lasers and amplifiers is presented. This was carried out in order to study the key parameters that affect the Brillouin threshold. Furthermore, the model was extended to account for the effect that the fibre axial temperature distribution has on the SBS threshold. Numerical solutions of the coupled differential equations for the evolution of the different beams showed a good agreement between the simulated data and reported experimental results. In addition, the model was used to study the relation of the core radius, the fibre length, and the fibre background loss on the SBS threshold. It was demonstrated that an adequate fibre structure design and a proper thermal management of the fibre amplifier lead to the suppression of SBS.

Rare-earth doped fibre preforms with different compositions and geometries were fabricated by Modified Chemical Vapour Deposition technique in order to characterise the effect of doping and fibre structure on the Brillouin frequency and linewidth. Measurements using a microwave detection system for coherent detection of the anti-Stokes spontaneous Brillouin backscatter were performed on these fibres. The results showed that the actual Brillouin gain, linewidth and frequency shift widely differ from the values for pure fused silica fibres. It was confirmed that the fibre structure and composition play a big role in the Brillouin linewidth and Brillouin frequency shift of the fibre

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Identifiers

ORCID for Jayanta Sahu: orcid.org/0000-0003-3560-6152

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