Abstract
We present a portable and low-cost system for interrogation of long-period fiber gratings (LPFGs) costing around a 30th of the price of a typical setup using an optical spectrum analyzer and a broadband light source. The unit is capable of performing real-time monitoring or as a stand-alone data-logger. The proposed technique uses three thermally modulated fiber-coupled laser diodes, sweeping a few nanometers around their central wavelength. The light signal is then modulated by the LPFG and its intensity is acquired by a single photo-detector. Through curve-fitting algorithms the sensor transmission spectrum is reconstructed. Testing and validation were accomplished by inducing variations in the spectral features of an LPFG through changes either in external air temperature from 22 to 425 °C or in refractive index (RI) of the surrounding medium from 1.3000 to 1.4240. A dynamic resolution between 3.5 and 1.9 °C was achieved, in temperatures from 125 to 325 °C. In RI measurements, maximum wavelength and optical power deviations of 2.75 nm and 2.86 dB, respectively, were obtained in the range from 1530 to 1570 nm. The worse RI resolution obtained was . The interrogation platform was then applied in the detection of iron corrosion, expressing wavelength peak values within 1.12 nm from the real value in the region between 1530 and 1570 nm.
Highlights
Optical fiber sensors are resistant to most common chemicals, lightweight, inherently small, and capable of withstanding high temperatures, and possess immunity to electromagnetic interference.These characteristics together with their flexible geometry make them promising solutions for corrosion detection in remote and hard-to-reach areas, including sea-based metallic infrastructures [1].Sensors based on long-period fiber gratings (LPFGs) have been used in the determination of several chemical and physical parameters in multiple harsh environments [2,3,4]
The fabrication of LPFGs is done by applying a periodic modulation on the core refractive index (RI), which can be accomplished using phase masks or point-by-point markings, with femtosecond lasers, CO2 lasers, or induced electric-arc discharges in the fiber [6,7]
Band through optical power variations at their wavelengths, which achieved high correlation with changes in multi-parameter sensing [17]. In this manuscript we present a new and affordable interrogation unit (IU) as a complete embedded solution for in-field operation, lowering the costs to around a 30th of the price of a typical setup with an optical spectrum analyzers (OSAs) and broadband light sources (BBLS)
Summary
Optical fiber sensors are resistant to most common chemicals, lightweight, inherently small, and capable of withstanding high temperatures, and possess immunity to electromagnetic interference.These characteristics together with their flexible geometry make them promising solutions for corrosion detection in remote and hard-to-reach areas, including sea-based metallic infrastructures [1].Sensors based on long-period fiber gratings (LPFGs) have been used in the determination of several chemical and physical parameters in multiple harsh environments [2,3,4]. Optical fiber sensors are resistant to most common chemicals, lightweight, inherently small, and capable of withstanding high temperatures, and possess immunity to electromagnetic interference. These characteristics together with their flexible geometry make them promising solutions for corrosion detection in remote and hard-to-reach areas, including sea-based metallic infrastructures [1]. Sensors based on long-period fiber gratings (LPFGs) have been used in the determination of several chemical and physical parameters in multiple harsh environments [2,3,4] This type of sensors makes use of light coupling between the fundamental core mode with co-propagating cladding modes. The spectral position of their attenuation bands depends on the RI of the surrounding medium [8]
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