Development of wideband optical amplifiers and associated technology

Abstract

This thesis presents a comprehensive investigation into the development and optimization of wideband ytterbium-doped fibre amplifiers (YDFAs) for next-generation optical communication systems operating in the 1 µm spectral region. The research encompasses a systematic exploration of various technologies and configurations, from gain-flattening filters to advanced multi-stage amplifier designs.

The research first examines gain flattening filters and long period fibre gratings as flexible, low-loss solutions for flattening amplifier gain. Dielectric thin-film filters and programmable waveshapers are also evaluated for their precision and flexibility, offering a range of approaches to address gain flattening in optical amplifiers. Further analysis and design of multi-stage EDFAs (Erbium-doped fibre amplifiers) show how optimized GFFs (gain flattening filters) improve gain flatness with minimal noise figure degradation. Despite bandwidth extension challenges, the findings suggest multi-stage configurations and filter optimization as effective strategies for enhancing amplifier performance, providing crucial insights that informed subsequent work on YDFAs.

The core of the thesis presents groundbreaking advancements in YDFA technology. Single-stage and dual-stage configurations were extensively simulated and experimentally validated, culminating in the demonstration of a dual-stage YDFA with a 50 nm gain bandwidth (1025-1075 nm). This bandwidth, equivalent to 13.7 THz, significantly surpasses that of conventional C-band EDFAs. Further optimization led to the development of cladding-pumped YDFAs for long-wavelength operation, showcasing superior gain stability and power conversion efficiency. A hybrid core + cladding pump scheme demonstrated particular promise, achieving broader bandwidth and lower noise figures. The research culminated in the creation of an ultra-wideband YDFA combining two amplifiers operating in different windows (1025-1072 nm and 1075-1110 nm). This innovative parallel configuration achieved a remarkable bandwidth of 21.9 THz, nearly five times that of a C-band EDFA. Simulations also explored potential extensions to both shorter and longer wavelengths, indicating promising avenues for future development. The thesis concludes by outlining key areas for future research.

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Identifiers

ORCID for Xin Huang: orcid.org/0000-0001-8105-3611

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

ORCID for Yongmin Jung: orcid.org/0000-0002-9054-4372

ORCID for Lin Xu: orcid.org/0000-0002-4074-3883

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