Thermal Effects on Optical Properties of Bismuth Active Centres in Bismuth/Erbium Co-Doped Optical Fibres

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Abstract
The bismuth/erbium co-doped optical fibres (BEDFs) have attracted much attention due to their ultra-broadband luminescence in the near-infrared (NIR) region with great potential for optical amplifiers and fibre lasers in the telecommunication system. To gain the fundamental understanding of bismuth active centres (BACs) and know the nature of their NIR luminescence in BEDF, a number of studies that focus on the fabrication process, spectral properties, and post-treatment effects have been conducted. These studies revealed that the BACs in BEDFs could be sensitive to the post-draw processes/conditions, such as laser irradiation, ionizing irradiation, H2 loading and thermal treatment. Based on the reported work, the understandings of both the nature of BACs and their responses to various post-draw processes are still quite limited. My PhD research has been aimed at better understanding the thermal effects on BACs in BEDFs and studies several special cases of thermal treatments/processes that show significant effects on the optical characteristics of BACs. In this thesis, I report: The thermal activation effect on BAC-Si in BEDF. The evolution of BAC-Si luminescence is systematically investigated with different thermal treatment conditions (temperature, dwell time and cooling rate). By optimizing these dynamics parameters, the luminescence of BAC-Si at 1405 nm could be enhanced to ~2.5 times. The thermal activation effect on BAC-P in BEDF. In this work, the significant increase of BAC-P related absorption and luminescence is observed after the thermal treatment. The thermal activation of BAC-P is studied in terms of treatment temperature and dwell time. The maximum enhancement of BAC-P luminescence at 1290 nm (~4.3 times) is achieved by optimizing the dynamics parameters. Thermal effect on photobleaching of BAC-Al in BEDF. The effect of temperature on photobleaching of BAC-Al is comprehensively investigated from room temperature up to 350°C under the irradiation of 980 nm laser. No visible bleaching of BAC-Al is observed at room temperature, but significant bleaching appears at higher temperatures above 150°C. Such thermal aggravation of photobleaching effect needs to be considered in the design and application of BEDF-based devices at different temperatures. The thermal bleaching effect on BAC-Al in BEDF. The variation of luminescence spectra is inquired into when the BEDF is thermally treated with different treatment conditions. The higher temperature and longer dwell time can lead to more severe thermal bleaching of BAC-Al. To the best of our knowledge, this is the first observation of thermal bleaching of BAC-Al in BEDF, which provides a better understanding of thermal effects on BACs. The thermal bleaching effect on BAC-Si in BEDF. For the first time, the thermal bleaching of BAC-Si peak luminescence is characterized by the stretched exponential function. Besides, the temperature dependence of bleaching ratio and bleaching rate are analysed. Based on the results, the possible mechanism of thermal bleaching of BAC-Si is discussed. The dynamic study on the thermal bleaching process provides a deeper understanding of the variation rule, which helps to reveal its mechanism. The findings/discoveries from this thesis work allow us to better understand the fundamental structure of BACs and the thermal-induced effects on their luminescence characteristics in BEDF. Especially, the thermal activation effect, thermally aggravated photobleaching effect and thermal bleaching effect on various BACs are studied, providing more comprehensive cognition of thermal properties of BACs. With further knowledge of the BACs, it helps to develop an effective way to control the BACs with better optical performance in BEDF for practical applications.
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Author(s)
Zhang, Bowen
Supervisor(s)
Peng, Gang-Ding
Canning, John
Wang, Chang
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Publication Year
2021
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty