The rapid acceptance of fibre optics technology in commercial systems applications has brought forward an increased need for guided wave optical components (passive and active) which permit coupling, multiplexing and demultiplexing, switching and distributing of light signals propagating in optical waveguides. Optical components such as light sources fibre couplers, splices, connectors, directional couplers, multiplexers, switches and modulators are essential elements for transmission and sensing systems. Splices and connectors between fibres are important because splice losses remain a factor of primary importance in existing and future fibre optics network design. In the search for simplicity, all-fibre components associated with optical functions have recently received considerable attention, mainly because of the strong potential benefits such components may play in the field of light wave technology, including optical fibre communications, opto-electronic signal processing and optical fibre sensing. Devices constructed from optical fibres may have advantages such as low insertion loss due to circular symmetry.