The erbium-doped fibre amplifier (EDFA) has seen rapid development and is now established as a key component in future optical networks. The authors modify and optimise the amplifier characteristics for a given application. They discuss the performance of a composite EDFA with an integral isolator. It is shown that this configuration exhibits high gains and quantum-limited noise figure (NF) at relatively low pump powers. A novel configuration of an optical limiting amplifier is presented which exhibits a input-signal dynamic range in excess of 30 dB. An optical equalising amplifier is demonstrated which is based on an erbium-doped twin-core fibre. This fibre geometry shows wavelength-dependent spatial (longitudinal) hole burning, thus, increasing the effective inhomogeneous broadening in the amplifier and provides enhanced output-signal equalisation in a multichannel system. Finally, the potential of the EDFA as a compact source of high-peak power and high-energy pulses, for medical and military applications, is also explored.
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