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Sensors 2013, 13(9), 11260-11270; doi:10.3390/s130911260

A Refractive Index Sensor Based on the Resonant Coupling to Cladding Modes in a Fiber Loop

2,* , 2
1 Departamento de Física Aplicada, Instituto de Ciencia de los Materiales, Universidad de Valencia, Burjassot 46100, Spain 2 Grupo de Sensores Ópticos y Microdispositivos, Centro de Investigaciones en Óptica A.C., Loma del Bosque 115, col. Lomas del Campestre, Leon, Guanajuato 37150, Mexico 3 Departamento de Óptica, Universidad de Valencia, Burjassot 46100, Spain
* Author to whom correspondence should be addressed.
Received: 23 July 2013 / Revised: 2 August 2013 / Accepted: 16 August 2013 / Published: 23 August 2013
(This article belongs to the Special Issue Optomechatronics)
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We report an easy-to-build, compact, and low-cost optical fiber refractive index sensor. It consists of a single fiber loop whose transmission spectra exhibit a series of notches produced by the resonant coupling between the fundamental mode and the cladding modes in a uniformly bent fiber. The wavelength of the notches, distributed in a wavelength span from 1,400 to 1,700 nm, can be tuned by adjusting the diameter of the fiber loop and are sensitive to refractive index changes of the external medium. Sensitivities of 170 and 800 nm per refractive index unit for water solutions and for the refractive index interval 1.40–1.442, respectively, are demonstrated. We estimate a long range resolution of 3 × 10−4 and a short range resolution of 2 × 10−5 for water solutions.
Keywords: mode coupling; optical fiber devices; refractive index sensor mode coupling; optical fiber devices; refractive index sensor
This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Reyes, M.; Monzón-Hernández, D.; Martínez-Ríos, A.; Silvestre, E.; Díez, A.; Cruz, J.L.; Andrés, M.V. A Refractive Index Sensor Based on the Resonant Coupling to Cladding Modes in a Fiber Loop. Sensors 2013, 13, 11260-11270.

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