Theoretical models of optical fibre intensity modulated pressure and displacement sensors

In recent years, optical fibres have been widely applied to various applications in communication and sensor systems. Optical fibre sensors have the advantage over electrical transducers in their high sensitivity and immunity from any electromagnetic interference effects. The main work concentrates on the theoretical application of optical fibre sensors in pressure and displacement sensing. The computer modelling of these two systems is achieved via the use of the mathematica software package. In the pressure sensing system, optical fibre is cut and rejoined in housings which allow for the application of forces near the jointed sections. Models are generated to describe these configurations using geometrical optics. The calculation of the coupling efficiency and sensitivity of the system are then investigated for various fibre geometries. In the displacement sensor system, models are developed to describe the coupling between launch fibre, reflective surface and receive fibre in which the system geometries and fibre type are variable. Again the coupling efficiency and sensitivity are measured for various geometrical configurations. Initially, the two fibres are positioned parallel to each other with the reflective surface being set normal to the fibre arrangement. Subsequently, the receive fibre is tilted with respect to the transmitting fibre and finally both the fibres are tilted equally with respect to each other. The main aim of the work is to provide models to facilitate the design of sensor systems with prescribed sensitivities and geometrical limits.