Optimal design of a fluorescence oxygen sensing probe based on multimode optical fibers

In this paper, a theoretical model of a multimode optical fiber based fluorescence sensor was proposed and established with the aims to optimize specific physical parameters of the sensor including the refractive index of the fluorescent matrix, external diameter and the length of sensing fiber probe which were calculated using the beam propagation method. The plane wave at wavelengths of 395 or 505 nm was used as the excitation light source. The excitation light power in the coating layer was calculated to obtain more excitation fluorescence. The change of fluorescence intensity with structural differences of the parameters was analyzed. The theoretical results showed that for a pure silica fiber using a matrix of higher refractive index (>1.458) material was effective in improving fluorescence performance. The optimized external diameter of the sensing fiber probe was found to be >206 μm with a 200 µm fiber core diameter when the refractive index of the sensing layer is 1.49. Increasing the thickness of the sensing layer increased the level of fluorescence excitation. The fluorescence intensity excited by 395 nm light is stronger than that of light at 505 nm.