An evanescent-coupling plastic optical fibre refractometer and absorptionmeter based on surface light scattering

Development of stripped-cladding optical fiber sensors for continuous monitoring

“…In order to encompass cases in which an effective absorption occurs as the light travels within the waveguide, simulations with a core refractive index lower than that of the measured fluid (which acts as the optical fiber cladding) are also considered. This case, in which n measured fluid > n core allows for refractive index determination, as recently reported by Ribeiro et al [20].…”

“…Differences in refractive index have been determined by measuring scattering losses that do depend on the measured fluid refractive index [20]. For cases in which the refractive index of the core is smaller than that of the cladding, total internal reflection does not occur.…”

“…Consequently, the light intensity at the detector end of the fiber is attenuated by multiple refractive losses. As such, external reflection constitutes an effective absorption of the transmitted light through the fiber [16,20]. When n core > n measured fluid , light is transmitted through the fiber mainly via reflection at smaller angles.…”

“…In other reports the transducers measure refractive index changes indicating chemical reaction extents [15][16][17][18]. Optical sensing of an environment's corrosiveness, the relative capacity of an environment to affect a metallic corrosion optical transducer, has been reported by Abderrahmane et al [18] and Jaffrezic-Renault's group [19,20]. This paper describes relationships between light propagation within stripped waveguides and the real refractive index of "measured" fluids, with the aim of developing an automated self-referencing mechanism.…”

“…The complex refractive index, m, is then solely represented by its real term, n. When the material deposited in the fiber possesses a non-zero absorptive index, k, light rays are partially reflected at the core/fluid interface and light absorption takes place. This is the case in corrosion optical sensors [18][19][20]. In order to encompass cases in which an effective absorption occurs as the light travels within the waveguide, simulations with a core refractive index lower than that of the measured fluid (which acts as the optical fiber cladding) are also considered.…”