Characterization of an optical fiber bundle sensor

An optical fiber sensor made of a central emitting fiber and two concentric crowns of receiving fibers is presented. This sensor is mainly used to measure high solid volume concentrations in suspension. The aim of this article is to accurately characterize the geometrical properties of this sensor comparing experimental data and simulation. Experimentally, the sensor is used as a displacement sensor with a metallic mirror as a target. This geometrical problem is simulated by a Monte Carlo method, which takes into account: (1) The experimental determination of the angular distribution of light intensity for the emitting fiber; (2) The finite size of fibers by means of a numerical integration procedure; and (3) The multiple reflections of light on the fiber sections with an explicit use of Fresnel’s factors. By fitting the experimental data with the results of the simulation, we can determine the geometrical properties of the probe and photon efficiency (voltage output versus number of launched photons) of the device. Finally, we discuss the use of this sensor as a displacement sensor. In this case a simple electronic device is given to gain a single valued response of the probe when the distance between the target and the sensor is varied. In this framework, the nature of the scattering target is also discussed.