OPTICAL FIBRE SENSORS

摘要

A perturbation (P), such as pressure or vibration, is employed to periodically deform an optical fibre (1) supporting two modes, or two polarisations of one mode, of optical power launched into the fibre by, for example, urging it against an undulating support (2). The period of the undulations is chosen to match the beat length between the two modes, or polarisations, at a predetermined optical frequency. When the fibre (1) is thus deformed coupling between the modes, or polarisations, is achieved; the extent of coupling being a measure of the perturbation causing the deformation. A distributed sensor comprising a number of such sensors is also described; the optical fibre comprising both the sensing elements and the means interconnecting them. Since the beat length varies with optical frequency, the different sensing elements of such a distributed sensor may be resolved by using correspondingly different optical frequencies.