Monte Carlo Simulation Tool of Evanescent Waves Spectroscopy Fiber – Optic Probe for Medical Applications (FOPS 3D)

Abstract

Fiber-optics evanescent wave spectroscopy has become a common technique for IR absorbance spectroscopy. Evanescent waves are formed when waves travelling in a medium undergo total internal reflection, which is the basis for the attenuated total reflectance (ATR) sampling technique [1,2]. Evanescent waves decrease exponentially as they propagates further away into the sample. Optical fibers which are transparent in the mid – IR are used as the ATR elements. The more reflections which cause the evanescent fields, the more efficient will be the measurement. Hence the curvature of the fiber and the radius of the uncladded part of the fiber, which brought in contact with the sample, play an important role in the efficiency of the measurement. In this work, we describe a simulation tool (FOPS 3D) which can simulate full three dimensional geometrical structure of the fiber and the propagation of the light beam through the fiber. The simulation tool has been developed as a two iteration process of three steps each: alpha, beta, and release. The first iteration was a C# module (NMCRC-FEWS) [3] serving as an independent confirmation tool. After a “Software Test Plan”, “Description”, and “Report”, the program moved (second iteration) to Java platform (FOPS 3D) and passed all the testing phases (requirements, design, program installation and regression testing). In addition, the FOPS 3D program favorably passed a black-box testing phase process of validation and verification. This application tool has the facility to freely bend the fiber, what gives the possibility to create any possible curvature folded fiber. Folding the fiber increases the number of beam hits in the uncladded part by slowing down the beam’s propagation. A second feature of the tool is the possibility to change the radius of the uncladded part individually, specifically decreasing the radius relative to the fiber’s radius, which increases the number of beam hits in the uncladded section. In addition, the fiber can be deformed and clay modeled, what gives the possibility to create different alternative geometrical shapes and inspecting their efficiency as ATR elements [2,3,4].