Comprehensive Modeling of Multimode Fiber Sensors for Refractive Index Measurement and Experimental Validation

Abstract

We propose and develop a comprehensive model for estimating the refractive index (RI) response over three potential sensing zones in a multimode fiber. The model has been developed based on a combined ray optics, Gaussian beam, and wave optics analysis coupled to the consideration of the injected interrogating lightwave characteristics and validated experimentally through the realization of three sensors with different lengths of stripped cladding sections as the sensing region. The experimental results highly corroborate and validate the simulation output from the model for the three RI sensing zones. The sensors can be employed over a very wide dynamic RI range from 1.316 to over 1.608 at a wavelength of 1550 nm, with the best resolution of 2.2447 × 10−5 RI unit (RIU) obtained in Zone II for a 1-cm sensor length.

Refractive Index Sensing through Surface Plasmon Resonance in Light-Diffusing Fibers

“…This behavior is consistent with a ray-optic description of light transmission through a multimode fiber [16]: as long as the external medium's RI is lower than the cladding index (about 1.38 in our case), the power guided in the fiber is only affected by evanescent wave absorption (EWA), which is negligible in our case due to the short sensing region. Vice versa, when the RI of the external medium is situated between the cladding RI and the core RI, the variation in the transmitted power is mostly due to the reduction of the number of propagation modes satisfying the total internal reflection (TIR) condition at the boundary between the fiber core and the external medium (see Figure 1b).…”

Optical fiber methane sensor using refractometry

“…A polymer variant of SAN [12,14,16] with an RI value of 1.5496 RIU at a wavelength of 1052 nm, is used as the polymeric host. To synthesize the sensing film, a carefully-proportioned quantity of the 1,1,2,2,-tetrachloroethane solvent is used to dissolve both cryptophane-A and SAN, as reported in [17]. 10 mg of cryptophane-A in powder form is first dissolved in 2 ml of 1,1,2,2,-tetrachloroethane after which 100 mg of SAN powder are then added.…”

“…The MMF evanescent wave sensor based on intensity modulation, on the other hand, while relatively simple and cost-effective to realize, has been reported to potentially offer very good resolution and sensitivity [13,15]. In our previous work [16,17], three operating RI regimes were identified and modeled in MMFbased refractometric sensor. This paper will thus describe development effort on intensity-based MMF sensor for methane gas detection through functionalized polymeric thin films encapsulating cryptophane-A supramolecular traps.…”

Critical-Angle Differential Refractometry of Lossy Media: A Theoretical Study and Practical Design Issues

“…Refractive index sensors are intensely investigated for numerous biomedical [1][2][3], chemical [4,5] and industrial [6,7] applications. An indicative yet far from exhaustive list of sensing mechanisms relies on plasmonic [8][9][10][11], photonic crystal [12][13][14][15], micro-cavity [16][17][18][19], optical fiber [20][21][22][23] and wave-guide [24][25][26][27] configurations. Associated with Fresnel reflectance properties at planar interfaces, differential refractometry offers an alternative path to sensing refractive index changes, by exploitation of interference [28], deflection [29] or (more relevant to the present work) critical-angle [30][31][32][33][34][35] effects.…”