Dense wavelength division multiplexing at 2 μm for future optical communications

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Kavanagh, Niamh
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University College Cork
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The internet is ubiquitous in our lives today, enabling instantaneous access to information, increased international collaboration, and even real-time remote surgery. It has changed how we socialise and how we see the world. From 2017 to 2022, global internet traffic is forecasted to triple, creating severe pressure on optical communication systems. Delivering the capacity required to support this traffic presents significant challenges in terms of system design, device performance, and optical fibre capabilities. Novel solutions are needed now, if we are to meet the demands of the near future. While solutions to increase system capacity and bandwidth efficiency of optical communication systems at 1.55 µm is widely discussed in the literature, shifting transmission to the 2 µm wavelength window could open possibilities to new discoveries in optical components, improved bandwidth efficiency, innovative optical fibres, and other applications transcending beyond optical communications. This thesis explores opening the 2 µm transmission window for optical communications. The focus of this work investigates the feasibility of implementing dense wavelength division multiplexing (DWDM) systems at 2 µm, with key enabling technologies developed recently. Strained III-V materials can produce foundry-compatible 2 µm lasers and detectors. Hollow-core photonic band gap fibres (HC-PBGFs) can guide 2 µm light through air, offering potentially lower losses, reduced latency and higher power-handling capabilities (in comparison to standard silica fibre). Also, thulium doped fibre amplifiers (TDFAs) could offer bandwidth of up to ~30 THz in the 2 µm waveband (~double that of EDFAs at 1.55 µm). Contributions of this thesis include the demonstration of a 2 µm DWDM system with channel spacing of 100 GHz and system capacity above 100 Gbit/s, for the first time in this new transmission window. Further increasing the capacity of 2 µm DWDM systems requires improving the spectral efficiency, which can be accomplished by reducing the spacing between channels. While 50 GHz channel spacing is shown to be achievable with current technologies in the transmitter, insufficient filtering can be a barrier for implementation in the receiver. With this in mind, novel filtering technologies are required and optical injection locking (OIL) is investigated as a possible filtering solution. The first study of OIL using two slotted Fabry-Perot lasers at 2 µm is demonstrated, achieving a stable OIL bandwidth of ~7 GHz and OIL-induced single mode operation over a 15 GHz range.
Physics , Photonics , Optics , Optical communications , Fibre optics , Communication systems , Fabry Perot Lasers , 2000nm , Wavelength division multiplexing , Dense wavelength division multiplexing , Optical injection locking , Slotted Fabry Perot lasers
Kavanagh, N. 2019. Dense wavelength division multiplexing at 2 μm for future optical communications. PhD Thesis, University College Cork.