Bismuth-doped Fibre Amplifiers for Multi-band Optical Networks

Abstract

Fibre-optic networks are the backbone of the global communications infrastructure that made possible modern Internet, providing a multitude of online services and a digital economy. The development of novel approaches for further increasing capacity of optical communication systems is in the focus of research around the world due to the constantly growing data traffic and the corresponding bandwidth demand. Arguably, the most practical technique is multi-band transmission which utilises a huge spectral bandwidth of the existing fibre base that has not previously been used. Unlike spatial division multiplexing, multi-band transmission does not require a new fibre deployment. However, it involves a significant upgrade of current networks with novel amplifiers in the O-, E-, S-, and U- optical bands that are yet to be developed and optimised. In this thesis, E- and S-band bismuth-doped fibre amplifiers (BDFAs) are demonstrated. The following record characteristics of BDFAs are achieved: 40 dB gain, 4.5 dB noise figure, and 38% power conversion efficiency. In total, three BDFAs have been developed, characterised and optimised using pump laser diodes at different wavelengths. Two modelling techniques of BDFAs are proposed: one based on conventional rate equations, and another one based on a neural network "black box" approach. Both of these methods are analysed and their challenges are discussed. A big part of the thesis is devoted to data transmission demonstrations supported by developed BDFAs in E- and S-bands. The experiments include both IM/DD and coherent signal transmissions through various lengths of single mode fibre including record E-band transmission through 160 km of single mode fibre. In addition, a multi-band transmission experiment in E-, S-, C-, and L-band is performed with an in-line amplifier based on combined bismuth-doped fibre and discrete Raman amplification. The total signal bandwidth is 195 nm and the total number of transmitted channels is 143. The obtained results pave the way towards commercial implementation of multi-band transmission enabled by BDFAs in E- and S- optical communication bands.