Characteristics of the Fiber Laser Sensor System Based on Etched-Bragg Grating Sensing Probe for Determination of the Low Nitrate Concentration in Water

Abstract

The necessity of environmental protection has stimulated the development of many kinds of methods allowing the determination of different pollutants in the natural environment, including methods for determining nitrate in source water. In this paper, the characteristics of an etched fiber Bragg grating (e-FBG) sensing probe—which integrated in fiber laser structure—are studied by numerical simulation and experiment. The proposed sensor is demonstrated for determination of the low nitrate concentration in a water environment. Experimental results show that this sensor could determine nitrate in water samples at a low concentration range of 0–80 ppm with good repeatability, rapid response, and average sensitivity of 3.5 × 10−3 nm/ppm with the detection limit of 3 ppm. The e-FBG sensing probe integrated in fiber laser demonstrates many advantages, such as a high resolution for wavelength shift identification, high optical signal-to-noise ratio (OSNR of 40 dB), narrow bandwidth of 0.02 nm that enhanced accuracy and precision of wavelength peak measurement, and capability for optical remote sensing. The obtained results suggested that the proposed e-FBG sensor has a large potential for the determination of low nitrate concentrations in water in outdoor field work.

A Novel Technique for Designing High Power Semiconductor Optical Amplifier (SOA)-Based Tunable Fiber Compound-Ring Lasers Using Low Power Optical Components

“…The power fluctuations during the stability measurement can be minimized by properly packaging the proposed fiber compound-ring laser system. The obtained OSNR spectrum is in the range that is comparable to the OSNR levels for fiber lasers used in remote sensing [69,70], fiber sensors that utilize wavelength-peak measurement method [62] and optical communication systems [71].…”

“…Moreover, its wide range wavelength tunability can benefit several applications in fiber sensors [61][62][63][64][65] and wavelength division multiplexer (WDM) optical communications [66] as well as biomedical imaging systems [67] working in the third near infrared biological window [68].…”

Wavelength Shift Measurement Method Without Use of Spectrometer: The New Way for Environment Photonic Sensors

“…In experiment of the ring-cavity fiber laser combined with two FBGs, we used the re-FBG as the same characteristics as used in [14] (the Bragg wavelength at room temperature was in the range of 1530 ÷ 1550 nm and a reflectivity was 75 -90%; the full-width-half-maximum (FWHM) bandwidth of 0.15÷0.30 nm and FBG length of 15 mm). But the e-FBG fabricated by wet chemical etching only half part of fiber cladding of the FBG region in hydrofluoric acid (HF) solution for creating D-form of FBG-fiber to increase the interaction of the propagating optical field in the FBG with the surrounding medium, which is different form in comparison with e-FBG presented in previous works [14,17]. In the e-FBG and fiber ring laser combined configuration, the reflected light from e-FBG can be used to analyze the interaction between the evanescent wave and the surrounding medium by measuring wavelength shift of lasing emission.…”

Optical temperature sensing on flexible polymer foils

“…A surface grating, shown in (b), is a physical modulation of the core size resulting in a modulation of the effective refractive index N eff . Although such modulations were also shown in silica fibers by the direct etching of the fiber core [43,44], they are mainly the fabrication technique of choice in planar waveguides.…”

“…The result is a surface grating, sketched in Figure 1.2 (b), and a modulation of the effective refractive index of the fiber. Several research groups fabricated sensors by this technique [43,44]. However, chemical etching of the core makes it directly exposed to the environment as the process additionally requires a local removal of the cladding layer from the fiber.…”