Bismuth-doped optical fibre fabrication and laser development

Abstract

The incorporation of bismuth (Bi) as a dopant in silica fibre has demonstrated great potential for the development of fibre lasers and amplifiers. Silica fibres doped with Bi, in combination with aluminium (Al), phosphorus (P), and germanium (Ge), can provide amplification covering different spectral bands in the wavelength range of 1.1-1.5 µm and 1.62-1.75 µm, which are typically inaccessible to rare-earth (RE) doped silica fibres.
This thesis presents a detailed study of Bi-doped fibres (BDFs) in phosphosilicate and aluminosilicate host, fabricated using the modified chemical vapour deposition (MCVD)-solution doping technique. The study investigates the impact of various fabrication conditions on the performance of Bi-doped phosphosilicate fibres (BPSFs) and Bi-doped aluminosilicate fibres (BASFs). The conditions include soot deposition temperature, solution composition, collapsing of preforms in O2/He atmospheres, and fibre drawing speed. The optical properties of the BDFs were characterised through measurements of absorption and unsaturable loss. The results of this characterisation and the subsequent laser experiments were used as feedback for the optimisation of the fabrication process. Spectroscopic studies of BASFs were also conducted, including measurements of fluorescence spectrum, lifetime, absorption and emission cross-section, and unique anti-stoke emission in the visible wavelength region.
Additionally, Bi-doped fibre lasers (BDFLs) were developed to assess the performance of the fibres. A BDFL based on a 200m BPSF was demonstrated to operate at 1340nm with 172mW output power and 38% slope efficiency. Afterwards, the laser was continuously tuned in the spectra range of 1305-1375nm by employing different tuning elements, such as an optical filter and a tunable fibre Bragg grating. However, the development of BDFLs in the 1.1µm band based on BASFs faces challenges due to high unsaturable loss in the fibre, resulting in poor laser output performance. Thus, further optimisation of the fabrication process is crucial to increase the efficiency of BASFs.
Overall, this work provides important insights into the fabrication and optimisation of Bi-doped silica fibres for use in fibre lasers and amplifiers.

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Identifiers

ORCID for Siyi Wang: orcid.org/0000-0002-1374-1196

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

ORCID for David Richardson: orcid.org/0000-0002-7751-1058

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