Optimization Efficiency of Monte Carlo Simulation Tool for Evanescent Wave Spectroscopy Fiber-Optic Probe

In a previous work, we described the simulation tool (FOPS 3D) (Khankin et al., 2001) which can simulate the full three-dimensional geometrical structure of a fiber and the propagation of a light beam sent through it. In this paper we are focusing on three major points: the first concerns the improvements made with respect to the simulation tool and the second, optimizations implemented with respect to the calculations' efficiency. Finally, the major research improvement from our previous works is the simulation results of the optimal absorbance value, as a function of bending angle for a given uncladded part diameter, that are presented; it is suggested that fiber-bending may improve the efficiency of recording the relevant measurements. This is the third iteration of the FOPS development process (Mann et al., 2009) which was significantly optimized by decreasing memory usage and increasing CPU utilization. 1. Introduction The evanescent wave spectroscopy technique, generally used in the IR range, is useful for inspecting materials and examining their properties, as well as for establishing biomedical diagnoses [1]. The diagnosis technique is based on a phenomenon called Attenuated Total Reflection (ATR) [2], in which incident rays are completely reflected within the medium, leaving evanescent waves on the interface between the medium and the adjacent sample. As the number of reflections occurring in the sensing fiber increases, a greater number of evanescent waves are created. Consequently, use of this spectroscopic method requires detailed planning, since fiber wave spectroscopy intensifies as fiber absorbance increases. Two primary methods can be used, the first involves tapering the untapped part of the fiber and the second, bending the fiber about its untapped part. These two actions make it more difficult for the light beam to propagate, causing more hits in the untapped part and thus creating additional evanescent waves, which in turn increase the absorption intensity. The first method was investigated experimentally by [3] and by [1]; these papers provided correlations between the absorbance and the thickness of the untapped fiber section, [1] the optimal width of the untapped part. In our previous work [4], we computed and investigated the relation between the diameter of the uncladded part and the resultant absorption value, using an in-house Monte Carlo simulation tool. In this work, we investigate an additional method of determining the optimal bending angle of a fiber with a constant width. In a previous work, the Monte Carlo simulation