Optical Fibre Sensor Set‐Up Elements

This chapter is devoted to describe the necessary elements to build an optical fibre based sensing application system. A fibre‐optic sensing system is composed of a light source, a signal input optical fibre, a signal output optical fibre, and a detector (optionally the system may include other components such as an optical modulator and a demodulator). All radiation sources capable of generating light radiation are called light sources, including natural and artificial light sources. According to the phase characteristics of light waves in time and space, light sources are generally divided into coherent light sources and non‐coherent light sources. The interaction between light and matter is the physical basis of the light source. Light‐emitting diodes are solid‐state PN junction devices, and their electroluminescent mechanisms mainly include PN junction luminescence and heterojunction injection luminescence. Their work is based on spontaneous emission, and they belong to incoherent light sources.