Cladding-pumped neodymium and ytterbium doped fibre lasers

Abstract

This thesis details my work on both high-power neodymium-doped fibre lasers (at around 1.1 µm and around 0.9 µm) and ytterbium-doped fibre lasers (at 980 nm). The main subjects were the study of efficient three-level compact continuous-wave fibre lasers and their power scaling.Ytterbium-doped fibre lasers (YDFLs) with emission at 980 nm were also investigated. I, in collaboration, obtained the highest reported output power from any compact single-mode 980 nm laser to this point. For this, speciality fibres, with special core and inner-cladding designs, were developed, notably the jacketed-air-clad (JAC) fibre, with properties that are not attainable in conventional double-clad fibres. The JAC structure allows for a small pump waveguide (inner cladding) with a high NA. This is an essential advantage for lasers operating on a transition to the ground state, such as Yb. There are many considerations involved with making practical, reliable, and usable 980 nm fibre devices. The integration of all required functions into a single fibre device with a small, high-NA, inner cladding is a challenge that required a large research effort to solve. A thorough and careful design and characterisation effort led to the milestone achievement of an all-fibre pigtailed fibre laser at 980 nm, which later on was used in practice as a pump source for an 8-channel DFB fibre laser transmitter array. In addition, a 980 nm Q-switched fibre laser is realised in a cladding-pumped configuration for the first time.Furthermore, a fibre laser cladding-pumped by a high brightness intra-cavity beam-combined diode was demonstrated. Here, a multi-stripe, multi-mode diode was set-up for intra-cavity beam combination and used for cladding-pumping of fibre lasers with a small inner cladding. This high-brightness pumping scheme with a multi-emitter diode appears very attractive for power scaling of three-level fibre lasers.

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ORCID for Johan Nilsson: orcid.org/0000-0003-1691-7959

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