Characterization of Long-period Grating Refractive Index Sensors and Their Applications

Abstract

The influence of grating length and bend radius of long-period gratings (LPGs) on refractive index sensing was examined. Sensitivity to refractive indexes smaller than that of silica could be enhanced by bending LPGs. Bent LPGs lost sensitivity to refractive indexes higher than that of silica, whereas a 20-mm-long LPG arranged in a straight line had considerable sensitivity. These experimental results demonstrated that the sensitivity characteristics of LPGs to refractive index could be controlled by grating length and bend radius.

Resin Directional Flow and Degree of Cure Sensing Using Chirped Optical Fiber Long Period Gratings

“…When the RI of the external surroundings is lower than that of the fibre cladding, total internal reflection (TIR) is the dominant effect responsible for guiding the coupled cladding mode [40]. When an LPG is covered by a material whose RI is lower than that of the fibre cladding, the effective refractive index of the cladding increases, causing a blue wavelength shift of the resonance band and a reduction in the depth of the band [41]. When the resin flow began at the lower period end of the CCLPG, the lower-wavelength side of the resonance band decreased in The data points were fitted with a 7 th order polynomial to generate a function relating the wavelength shift to the surrounding RI.…”

An Optical Fiber Sensor and Its Application in UAVs for Current Measurements

“…Thus, from Equation (1) the resonance phase matching condition can be easily determined as [30]: ${\lambda }_m=false(n_{co}-n_{cl}^{m}false)\Lambda$ where λ m is the resonance wavelength of the m th-order cladding mode, and n co and $n_{cl}^m$ are the effective refractive indices of the fundamental core mode and the m th-order cladding mode, respectively. Changes in the temperature, strain, refractive index of the external medium surrounding the LPFG sensor can alter the grating period as well as the differential refractive index of the core and cladding modes and thus, lead to variations in the resonance condition due to the rejection wavelengths ( λ m ) dependence to external parameters variations [31,32,33]. Therefore, it is possible to extract the environmental information from the analysis of the shifts occurring at the λ m parameter.…”

Enhanced refractive index sensor using a combination of a long period fiber grating and a small core singlemode fiber structure

“…The techniques used to implement fiber based RI sensing include a fiber Bragg grating (FBG) [1], long period fiber grating (LPG) [2,3], surface plasmon resonance [4], tapered fiber [5] and a singlemodemultimode-singlemode (SMS) fiber structure [6,7]. Among these techniques, an SMS fiber structure based optical sensor has the advantages of low cost and ease of fabrication and 4 Author to whom any correspondence should be addressed.…”