What the study found
The study found that the inner cladding in a high-power ytterbium-doped double-clad fiber amplifier changes the optical and thermal mode structures. This affects the overlap between the fundamental mode, LP01, and higher-order modes, and changes the effective strength of stimulated thermal Rayleigh scattering, or STRS.
Why the authors say this matters
The authors conclude that their formulation provides a quantitative and physically consistent tool for analyzing thermo-optic dynamics in Yb-double-clad fiber amplifiers. They say it supports the design of next-generation high-power fiber lasers with improved modal stability.
What the researchers tested
The researchers developed a coupled optical-thermal model for a continuous-wave forward-pumped fiber amplifier pumped at 976 nm and emitting at 1064 nm, with an optimal length of 12 m. The model explicitly treats the three radial regions of a double-clad fiber and uses the weakly guiding approximation in the core together with the semi-weakly guiding approximation at the cladding interfaces.
What worked and what didn't
The model computed modal fields, including higher-order modes that penetrate into the inner cladding, and evaluated the transverse eigenvalues U01 and Umn relevant to TMI. It also included gain saturation and thermal eigenmodes in the multi-layer geometry when calculating the STRS coupling coefficient. The results showed that the inner cladding alters optical-thermal overlap and the effective STRS strength, which directly affects the predicted TMI threshold.
What to keep in mind
The abstract does not describe experimental validation, so the summary here is based on a modeling study. It also does not provide numerical threshold values or a direct comparison with alternative models in the available text.
Key points
- The inner cladding changes both optical and thermal mode structures in the amplifier.
- Those changes alter the overlap between LP01 and higher-order modes.
- The effective strength of stimulated thermal Rayleigh scattering is modified by the inner cladding.
- The predicted transverse mode instability threshold is affected by the modeled structure.
- The study uses a three-layer optical-thermal model for a 976 nm-pumped, 1064 nm-emitting fiber amplifier.
Disclosure
- Research title:
- Inner cladding changes transverse mode instability predictions
- Authors:
- Elbis Santos Cardoso, Ricardo Elgul Samad, Cláudio C. Motta
- Institutions:
- National Nuclear Energy Commission, Universidade Federal de São Paulo, Universidade Federal de São Paulo
- Publication date:
- 2026-03-05
- DOI:
- 10.3390/mi17030326
- OpenAlex record:
- View
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