Formula for temperature distribution in multi-layer optical fibres for high-power fibre lasers

Article history: Received 10 Sep. 2021 Received in revised form 22 Oct. 2021 Accepted 23 Oct. 2021 Available online 12 Nov. 2021 High power fibre lasers need to be cooled efficiently to avoid their thermal damage. Temperature distribution in fibre should be estimated during the fibre laser design process. The steady-state heat equation in a cylindrical geometry is solved to derive a practical formula for temperature radial distribution in multi-layered optical fibres with arbitrary number of the layers. The heat source is located in one or more cylindrical domains. The validity of the analytical formula is tested by comparison with static heat transfer simulations of typical application examples including octagonal double clad fibre, air-clad fibre, fibre with nonuniform, microstructured core. The accuracy sufficient for practical use is reported even for cases with not exactly cylindrical domains.