Advanced erbium-doped fibre devices
Erbium-doped fibre devices, such as lasers and amplifiers, are important components in optical communication systems at 1.5µm. In this thesis four advanced erbium-doped fibre devices to help meet the needs of future systems are described. The first device, an optical limiting amplifier, provides a constant output power for a wide range of input powers. This functionality is required in long-haul amplified links and networks to protect against signal power fade. The other three devices are constructed from erbium-doped twincore fibre which exhibits inhomogeneous saturation characteristics at room temperature, conventional erbium-doped fibre only exhibits this property at cryogenic temperatures. The twincore fibre is demonstrated to particularly suit multi-channel amplification and generation and is used to construct a multiple wavelength laser and channel equalising amplifier. Both of these devices are needed for future wavelength division multiplexing (WDM) systems and are difficult to construct from conventional erbium-doped fibre because of its homogeneous saturation characteristics. Finally, a tracking bandpass filter is constructed from a single piece of unpumped twincore fibre. The filter automatically tunes to the wavelength of the optical signal and has potential for guiding solitons in ultralong communication links.