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7 March 2014 Use of a hybrid ray-thin film interference model for the optimization of a FTIR FOEWS
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Certain designs for frustrated total internal reflection fiber optic evanescent wave sensors (FTIR FOEWS) include the partial removal of cladding along a finite length of the fiber optic that acts as the sensing region. This paper presents a model for a FTIR FOEWS that has a thin, partial cladding in the sensing region. Since the thickness of the cladding in the sensing region is in the 1 μm range, while the propagating light is on the order of 850 nm, commonly used ray optic modeling techniques fail to properly simulate the thin film interference effects. In this study, a modification to the usual ray model is performed by including thin film optic analysis at the thin film sensing interface. The resulting hybrid ray/thin film model maintains the efficiency of previously reported models, but also adds the ability to fully model the partial cladding of the sensing region. The intensity and angular distributions of light from a Lambertian LED source onto the fiber input face is also derived to discuss the effects of launching conditions on the sensor performance. Investigation of a variety of meridional propagation ray distributions into the fiber are performed by varying the distance and angle of the point source to the fiber input face. Optimal cladding thicknesses, LED distance and tilt angle are studied and used to draw conclusions about FTIR FOEWS performance based on launching conditions.
© (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
J. R. Godin and P. Nieva "Use of a hybrid ray-thin film interference model for the optimization of a FTIR FOEWS", Proc. SPIE 8980, Physics and Simulation of Optoelectronic Devices XXII, 898008 (7 March 2014);


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