Design and fabrication of long-period fibre gratings and wavelength-selective couplers for wavelength-division multiplexing networks

D.Ing.Optical fibre-based devices (e.g. fibre gratings) play an important role in the optical com- munications and sensing industry. One type of fibre grating, the long-period grating (LPG), is becoming more and more popular as a simple and versatile component for a multitude of applications in optical engineering. The sensitivity of LPGs to various external perturbations and their ability to manipulate selectively light propagating in optical fibres make them well- suited to creating fibre-based devices. LPGs can be used in various applications, for example as gain equalisers for erbium-doped fibre amplifiers, as channel routers in optical add-drop multiplexers and as sensors. LPGs are typically fabricated by exposing photosensitive optical fibre to ultraviolet light. However, a variety of other techniques can be used to fabricate LPGs, including exposure to carbon dioxide (CO2) laser light. Over the years, it has become evident that CO2 laser- induced LPGs exhibit unique properties and features that can be harnessed to develop devices for important applications. It is necessary to understand the physical properties and optical characteristics of CO2 laser-induced LPGs to harness, manipulate and enhance their features. Research has been conducted on the development of an automated fabrication system that produces axially symmetric LPGs in single-mode fibre with a CO2 laser. A detailed study was undertaken on the design of uniform and non-uniform LPGs for wavelength-division multiplexing networks, as well as the characterisation of the CO2 laser beam propagating in the LPG fabrication system. These LPGs have been designed, using either analysis or syn- thesis techniques. The polarisation-dependent loss of the LPGs has also been investigated. Wavelength-selective couplers (WSCs) have been constructed using CO2 laser-induced LPGs and it was shown that these couplers were e®ective but not efficient in routing power to the output port of the tapping fibre. The physical properties, optical transmission characteris- tics, applications and other related issues of CO2 laser-induced LPGs have been investigated and satisfactory experimental results have been obtained. Areas for potential future research concerning CO2 laser-induced LPGs have been identified and discussed