ABSTRACT
The operation and limitations of distributed optical fibre sensors are dictated by the design and materials used to manufacture optical fibres, how light propagates in them and how photonic systems are assembled from basic optical components. An optical fibre is an elongated structure-usually round in cross-section – that guides light. Graded-index multimode fibres were developed to overcome the pulse-broadening of step-index fibres; they are designed so that the transit times are as far as possible the same for all modes. The bandwidth of an optical fibre is a measure of its information-carrying capacity; it is inversely proportional to the spreading that pulses suffer when propagating along the fibre. Optical amplifiers are used to boost probe signals prior to launching them into the sensing fibres and sometimes also to preamplify the signals returning from the sensor prior to their reaching the detector.
