Abstract
The simultaneous measurement of transverse load and temperature using two long-period fiber gratings multiplexed in the wavelength domain is presented experimentally. For this, a mechanically induced long-period fiber grating (MI-LPFG) and a long-period fiber grating inscribed by a continuous-wave CO2 laser (CO2 LPFG) are connected in cascade. First, the transverse load and the temperature measurements were individually performed by the multiplexed long-period fiber gratings configuration. The MI-LPFG is subject to a transverse load variation from 0–2000 g with steps of 500 g, whereas the CO2 LPFG is unloaded and they are kept at room temperature. Similarly, the CO2 LPFG is subject to a temperature variation from 30 to 110 °C by increments of 20 °C, while the MI-LPFG with a constant transverse load of 2000 g is kept at room temperature. Subsequently, the simultaneous measurement of the transverse load and the temperature is performed by the multiplexed long-period fiber grating following the steps outlined above. According to the experimental results, the transverse load and temperature measurement present high repeatability for the individual and simultaneous process. Moreover, the multiplexed LPFGs exhibit low cladding-mode crosstalk of transverse load and temperature. The coarse wavelength-division multiplexing (CWDM) of long-period fiber gratings is an attractive alternative technique in optical fiber distributed sensing applications.
Highlights
Long-period fiber gratings (LPFGs) are versatile components widely studied with relevant applications in telecommunications, fiber-optic lasers, and sensing systems [1,2,3].Concerning sensing applications, LPFGs offer high sensitivity to external perturbations of the surrounding medium, immunity to electromagnetic fields, passive measurements, fast response, low insertion loss, small backscattering, compactness, and remote monitoring
We have used an mechanically induced long-period fiber grating (MI-LPFG) with a CO2 LPFG connected in cascade to measure the transverse load and the temperature, respectively
The experimental results show that the transverse load and temperature measurements show low cladding-mode crosstalk between the multiplexed LPFGs
Summary
Long-period fiber gratings (LPFGs) are versatile components widely studied with relevant applications in telecommunications, fiber-optic lasers, and sensing systems [1,2,3]. Two different approaches have been reported for the optical fiber distributed sensing applications with wavelength-division multiplexing of LPFGs. The first method uses two similar concatenated LPFGs to conform a Mach–Zehnder interferometer [15]. The second method entails implementing two or more different LPFGs in series in such form that their reference rejection bands do not overlap and operate independently [19,20,21,22] These schemes require simple demodulation techniques, the wavelength-division multiplexing of LPFGs is delimited because LPFGs usually generate multiple rejection bands. Mechanically induced long-period fiber gratings (MI-LPFGs) with a primary rejection band have recently been reported using laminated plates [23] Such MI-LPFGs with a principal rejection band facilitate the use of the CWDM technique for LPFG sensors in cascade.
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