Technologies in the 2 µm waveband

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Russell, Eoin
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University College Cork
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Over the last couple of decades, photonic technologies have become an integral part of many fields of scientific research and industry. Some of these applications include, but are not limited to, optical communications, metrology and optical sensing. As the field of photonics continues to mature and develop, the diversity of its applications also expands. One of the keys to maintaining this growth is the development of technologies that enable the operation of photonic devices at different wavelengths. The near-infrared waveband has been extensively studied due to its applications in the telecommunications industry, mostly around the 1550 nm wavelength. When looking further along the IR waveband the 2 μm wavelength region is of particular interest due to its potential applications in the fields of optical communications, silicon photonics and optical sensing. In this thesis, we develop two technologies for enabling applications and research in the 2 μm waveband. The first achievement was the realisation of a semiconductor laser based frequency comb source at 2 μm. Optical combs are becoming ubiquitous in research applications, from spectroscopy to carrier generation for coherent optical communications. Beyond laboratory application, optical combs have seen little implementation due to their cost, size and complexity. In this thesis, we develop a compact and robust comb source for the 2 μm waveband using recently developed InP based semiconductor laser sources and the gain switching modulation method. In addition to this, the first demonstration of a dual frequency comb was shown at this wavelength. This allowed for the analysis of these combs using low speed photodetectors at near real-time acquisition rates. The optical frequency combs developed could be key components in enabling optical sensing and metrology applications in the 2 μm wavelength region. The second achievement of this thesis was the development of fibre amplifiers for the 2 μm waveband using the rare-earth element Thulium (Tm3+). Due to the relative immaturity of technologies at this wavelength, managing component losses and maintaining optical power is essential. Thulium doped fibre amplifiers (TDFAs) offer a broad amplification bandwidth ranging from 1650 nm-2150 nm. These amplifiers can be pumped using a variety of wavelengths, each having their benefits and weaknesses which are explored in this thesis. Through variation in pump wavelength and doped fibre length, amplifiers were developed which were optimised for wavelengths around 2 μm while utilising low pump power.
Photonics , 2 µm , Laser , Optical frequency combs , Dual frequency combs , 2 µm waveband , Optical spectroscopy , Gain switching , Laser pulse generation , Thulium doped fiber amplifier , Fiber amplifier , Multi-quantum well laser
Russell, E. 2021. Technologies in the 2 µm waveband. PhD Thesis, University College Cork.