How can you significantly improve the performance of fibers for high power fiber lasers by modifying the glass composition of the fibers?

T.W. Hawkins and coauthors address this question in this Journal of the Optical Society of America B paper. Despite the alternative way to adapt the waveguide structure, the authors concentrate on the origin of Brillouin scattering and of the thermo-optic effect in the light-matter interaction. Considering high power lasers, large mode area fibers are commonly used, but they suffer from instabilities of transverse modal distribution while being operated in effectively single mode operation. At high powers, quantum defect heating is one of the reasons for this mode coupling. On the other hand, Brillouin scattering depends on a variety of material properties.

Starting from a careful analysis of the dependencies, the authors develop two different fiber designs: one is a heavily doped fiber, reducing the thermo-optic effect and the Brillouin gain by 3 and 6 dB respectively. Their second design is closer to standard laser fibers and was demonstrated in a setup with more than 1 kW output power and 70% efficiency.

Experts in the field of glass materials for laser fibers as well as researchers with a basic knowledge of fiber technology and fiber lasers will benefit from this paper.

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