Fiber Grating Sensor Research Articles

Molybdenum sulfide/citric acid composite membrane-coated long period fiber grating sensor for measuring trace hydrogen sulfide gas

A molybdenum sulfide/citric acid composite membrane-coated long period fiber grating (LPFG) sensor was demonstrated and applied to detect the trace hydrogen sulfide gas. The sensor was fabricated by growing molybdenum sulfide/citric acid composite film on the surface of optical fiber grating by using the sol-gel and dip-coating techniques. The sensor measures the hydrogen sulfide concentration by monitoring the molecular adsorption-induced resonant wavelength shift of LPFG in near infrared (∼1555 nm) region. Experimental results show that with the increasing concentration of hydrogen sulfide, the transmission spectrum appears blue shift with time response of 89 s. In addition, a high sensitivity of 10.52 pm/ppm and a good linear relationship are achieved within a measurement range from 0 to 70 ppm. Furthermore, there is an excellent selectivity for H2S, which has also been confirmed by the surface adsorption energy results of molybdenum sulfide with five common gases in the air (H2S, N2, CO2, O2 and Ar) based on the density functional theory calculations. The proposed sensor has an excellent detection limit of hydrogen sulfide which is as low as 0.5 ppm. This sensor has the advantages of simple structure, easy manufacture, high sensitivity and low cost, and can be used in hydrogen sulfide gas sensing places such as factories, sewers, and so on.

Application of Fe-C coated LPFG sensor for early stage corrosion monitoring of steel bar in RC structures

Fe-C coated long period fiber grating (LPFG) sensor was employed to monitor the corrosion-induced mass loss of steel bar in 3.5 wt% NaCl solution and steel bar in mortar cylinder. A two-stage process of the change in resonant wavelength as a function of the corrosion-induced mass loss of steel bar was observed. The LPFG sensor can effectively monitor steel bar corrosion loss in 3.5 wt% NaCl solution for 14 h with a sensitivity of 0.124 mg/nm change of the resonant wavelength, and in mortar cylinder for 14 days with a sensitivity of 0.405 mg/nm change of the resonant wavelength, respectively.

Fiber sphere-embedded long-period fiber grating for curvature measurement with high sensitivity

A fiber sphere-embedded long-period fiber grating (LPFG) sensor has been proposed and fabricated for curvature measurement with high sensitivity. Compared with the normal LPFG, the embedded fiber sphere excites cladding modes and two dips of the output spectrum have been observed. The curvature measurement can be realized by monitoring the shift of the two dips. Experimental results show that the highest curvature sensitivity is up to −104.642 nm/m − 1 with the curvature ranging from 0 to 0.71 m − 1. The temperature response of the sensor has also been studied and a quadratic linear relationship between the dip shift and the temperature has been observed. The highest temperature sensitivity is 0.36 nm / ° C with the temperature range between 20°C and 90°C.

Detection of mercury (II) ions in water by polyelectrolyte–gold nanoparticles coated long period fiber grating sensor

This paper presents mercury (II) ions detection based on long period fiber grating (LPFG) sensor written on a single mode optical fiber by electrical arc induced technique that is suitable to be used for long term monitoring purpose. In the work, the LPFG was coated with both polyelectrolyte (PE) layers to enhance its sensitivity as well as a layer of gold nanoparticles (AuNP) for reaction to the mercury (II) ions. Experiments were conducted using double-pass configurations with mercury (II) ions concentrations varied between 0.5 ppm to 10 ppm. The results showed that the resonance wavelength of the PE–AuNP coated LPFG notch shifted to the longer wavelength, with a total shift of 1.34 nm and transmission power increment of 1.74 dBm over a period of 5 h. The results were then compared with uncoated as well as PE-only coated LPFGs, where no significant changes in resonance wavelength and transmission power were observed for these LPFGs. A novel PE–AuNP coated LPFG sensor that is suitable to be used for in-situ, long term and remote monitoring has been successfully demonstrated and tested for the detection of mercury (II) ions in water.

Optimized Strain Long-Period Fiber Grating (LPFG) Sensors Operating at the Dispersion Turning Point

This work was supported in part by the Spanish Ministry of Economy and Competitiveness (TEC2016-78047-R – AEI/FEDER, UE), in part by the Government of Navarra PI044 NANOSEN, and in part by the Pinar del Rio University.

Long-period fiber grating: a specific design for biosensing applications.

In this paper, a detailed investigation on the modeling of long-period fiber grating (LPFG) sensors is discussed with the aim of providing a more realistic solution for their use in biosensing. Add-layer sensitivity, i.e., sensitivity of the sensor to an additional layer adhered onto the fiber surface, is quantified and a clear and complete analysis about the influence of the average thickness of the deposited biological sensing layers, as well as the change in refractive index of these layers, on the resonant wavelength of the cladding modes of an LPFG is provided. Add-layer sensitivity of LPFG sensors close to mode transition (MT) and also at turn-around point (TAP) are taken into account. Adsorbed layer thicknesses, as estimated from measured wavelength shifts of the LPFG, are found to have a good match with the values obtained through other measurement techniques.

Investigation of Detecting Ultrasound Using a Long Period Grating

A long period fiber grating (LPFG) sensor, useful for the detection of ultrasound is proposed and experimentally demonstrated. Some preliminary results are got that (indicate (the capability of the LPG sensor to successfully monitor ultrasound. The resonance wavelength of LPG is linearly related to the amplitude of the ultrasonic wave, and the frequency and duration of the ultrasonic wave hardly change the resonance wavelength. Experimental results showed that LPFG sensors could be applied to determine the corresponding parameters of ultrasonic field (by demodulating the shift of the resonant band of the LPFG.

Quantification of chloride and iron in sugar factory effluent using long period fiber grating chemical sensor

Abstract This paper is an effort to introduce application of Long period fiber grating (LPG) sensors in perpetual monitoring of industrial waste water effluent. A change in ambient refractive index (RI) of an LPG causes a shift in its resonant wavelength. This RI sensitivity of LPG has been used to design a simple and highly sensitive chemical sensor to determine the concentration of Chloride (Cl) and Iron (Fe) ions present in the treated waste water effluent of sugar factories. The concentrations of Cl and Fe ions in the effluent sample determined by our sensor are 97.85 ppm and 0.274 ppm respectively. The results are in good agreement with that of two standard techniques used for the purpose, thus proving the reliability of the LPG sensor. Limit of detection of Cl and Fe ions are found to be as low as 0.038 ppm and 0.007 ppm per pm shift in wavelength respectively, reflecting enormous potential of the sensor in detection of trace elements in waste water with accuracy. Sensitivity of the sensor for Fe ions being about 5 times greater than that for Cl ions, suggests a higher sensitivity of sensor in lower range of concentration in ppm. Miniaturization, cost-effectiveness and ability of online measurement are the most important features of LPG chemical sensors that give them an edge over existing techniques for the purpose.

Simulation of novel intensity modulated cascaded coated LPFG sensor based on PMTP

This paper presents a novel intensity modulated cascaded long-period fiber grating (CLPFG) sensor which is cascaded by two same coated long-period fiber gratings (LPFGs) operating at the phase-matching turning point (PMTP). The sensor combines the high sensitivity of LPFG operating at PMTP and the narrow bandwidth of interference attenuation band of CLPFG, so a higher response to small change of the surrounding refractive index (SRI) can be obtained by intensity modulation. Based on the coupled-mode theory, the grating parameters of the PMTP of a middle odd order cladding mode of a single LPFG are calculated. Then this two same LPFGs are cascaded into a CLPFG, and the optical transmission spectrum of the CLPFG is calculated by transfer matrix method. A resonant wavelength of a special interference attenuation band whose intensity has the highest response to SRI, is selected form CLPFG’s spectrum, and setting the resonant wavelength as the operating wavelength of the sensor. Furthermore, the simulation results show that the resolution of SRI of this CLPFG is available to 1.97 × 10−9 by optimizing the film optical parameters, which is about three orders of magnitude higher than coated dual-peak LPFG and cascaded LPFG sensors. It is noteworthy that the sensor is also sensitive to the refractive index of coat, so that the sensor is expected to be applied to detections of gas, PH value, humidity and so on, in the future.

Long Period Fiber Grating for Biosensing: An Improved Design Methodology to Enhance Add-Layer Sensitivity

We present our theoretical study on the design of long period fiber grating (LPFG) sensor where its add-layer sensitivity is enhanced. Add-layer sensitivity quantifies the sensitivity of the sensor to the changes taking place within few tens of nanometers around the receptor molecules. Two different methodologies: the use of dual overlay layer and tailoring of the intermodal separation between two cladding modes have been used to enhance the add-layer sensisstivity. Using coupled mode analysis, we compute several examples to carry out a detailed comparative analysis between the results obtained, focusing on the cladding mode near mode transition.

High temperature-sensitivity sensor based on long period fiber grating inscribed with femtosecond laser transversal-scanning method

We propose a high temperature-sensitive long period fiber grating (LPFG) sensor fabricated by using the femtosecond laser transversal-scanning method. The femtosecond pulses scan over the whole fiber core and some part of the cladding region; the modified regions are more extended. It is found that the LPFG-I fabricated by the transversal-scanning method shows higher temperature sensitivity and better temperature uniformity than that of LPFG-II written by the femtosecond laser point-by-point method. The LPFG-I with a temperature sensitivity of 75.96 pm/°C in the range of 25°C–400°C is measured. Moreover, in the range from 400°C to 800°C, a higher temperature sensitivity of 148.64 pm/°C and good linearity of 0.99 are achieved, while the temperature sensitivity of LPFG-II is only 95.55 pm/°C. LPFG-I exhibits better temperature characteristics, which, to the best of our knowledge, has the highest sensitivity in silica fiber temperature sensors.

Fiber sensor network with multipoint sensing using double-pass hybrid LPFG-FBG sensor configuration

This is a study on double-pass intensity-based hybrid Long Period Fiber Grating (LPFG)and Fiber Bragg Grating (FBG) sensor configuration where a fiber sensor network was constructed with multiple sensing capability. The sensing principle is based on interrogation of intensity changes of the reflected signal from an FBG caused by the LPFG spectral response to the surrounding perturbations. The sensor network developed was tested in monitoring diesel adulteration of up to a distance of 8km. Kerosene concentration from 0% to 50% was added as adulterant into diesel. The sensitivity of the double-pass hybrid LPFG-FBG sensor over multiple points was>0.21dB/% (for adulteration range of 0–30%) and >0.45dB/% from 30% to 50% adulteration. It is found that the sensitivity can drop up to 35% when the fiber length increased from 0km to 8km (for the case of adulteration of 0–30%). With the multiple sensing capabilities, normalized FBG's reflected power can be demodulated at the same time for comparison of sensitivity performance across various fiber sensors.

A Fe-C coated long-period fiber grating sensor for corrosion-induced mass loss measurement.

This Letter reports a Fe-C coated long period fiber gratings sensor with a grating period of 387±0.1 μm for corrosion monitoring of low carbon steel in a 3.5 wt. % NaCl solution. An LPFG sensor was first deposited with a 0.8 μm thick layer of silver (Ag) and then electroplated with a 20 μm thick Fe-C coating. The chemical composition of the Fe-C coating was designed to include the main elements of low carbon steel. The resonant wavelength of the coated sensor was correlated with the mass loss of steel over time. Test results indicated a corrosion sensitivity of 0.0423 nm per 1% mass loss up to 80% Fe-C mass loss and 0.576 nm per 1% mass loss between 80% and 95% Fe-C mass loss. The corrosion sensitivity of such a Fe-C coated LPFG sensor was a trade-off for the service life of the sensor, both depending on thicknesses of the inner silver layer and the outer Fe-C coating.

端面反射引起的光纤光栅传感阵列的串扰分析

端面反射引起的光纤光栅传感阵列的串扰分析

The Design of Bending Long Period of Photonic Crystal Fiber Grating Sensors

The bending photonic crystal fiber grating sensor is an important role in underwater monitoring and fire alarm systems. It is studied that the resonant wavelength expression of bending long period photonic crystal fiber gratings is deduced, it is designed that a bending long period photonic crystal fiber grating sensor system, it is calculated in theory that between the bending long period photonic crystal fiber gratings sensor resonance wavelength and the grating period and the bending strain. The result is shown by calculating and analysing in theory, the grating curvature is increased by the increase of the bending strain of the grating, and the resonance wavelength of the grating sensor is drifted, the drift amount is increased, one in this grating, the drifted amount of the resonant wavelength is 0.014 nm.

Double-pass configuration to enhance the sensitivity of a polyelectrolyte-coated arc-induced long-period fiber grating

In this paper, we introduce a simple and effective method to improve the transmission power respond of a polyelectrolyte (PE)-coated arc-induced long-period fiber grating (LPFG) sensor toward external perturbation. Experiments using single-pass and double-pass configurations were conducted to measure sucrose concentrations of between 0 and 80 wt%. The results showed that the transmission power sensitivity of the PE-coated LPFG sensor in the double-pass configuration was almost double compared to the single-pass configuration.

Investigation on high temperature characteristics of FBG sensors

In some extremely severe environments, such as aero engine and oil well, the pure fiber sensor cannot meet the requirement of the high temperature. In this paper, temperature model of the fiber gratings sensor and the heat deterioration theory under high temperature are studied, the experiment tested the 2 relationships: (1) between the reflectance of the fiber gratings and the temperature; (2) between the wavelength of fiber gratings and the high temperature. The result showed, the reflectance of fiber gratings with germanium-doped was decreased gradually when the temperature was increased. When the temperature reached to 850°C, the fiber grating was failed. Under the 850°C, the degree of linearity fitting between the central reflective wavelength of fiber gratings and the increasing temperature became worse, while the temperature sensitivity decreased with temperature increasing. The average temperature sensitivity of gilded germanium-doped fiber grating sensor was 0.0156nm/°C and has been improved greatly compared with the pure fiber grating.

An architecture for measuring joint angles using a long period fiber grating-based sensor.

The implementation of signal filters in a real-time form requires a tradeoff between computation resources and the system performance. Therefore, taking advantage of low lag response and the reduced consumption of resources, in this article, the Recursive Least Square (RLS) algorithm is used to filter a signal acquired from a fiber-optics-based sensor. In particular, a Long-Period Fiber Grating (LPFG) sensor is used to measure the bending movement of a finger. After that, the Gaussian Mixture Model (GMM) technique allows us to classify the corresponding finger position along the motion range. For these measures to help in the development of an autonomous robotic hand, the proposed technique can be straightforwardly implemented on real time platforms such as Field Programmable Gate Array (FPGA) or Digital Signal Processors (DSP). Different angle measurements of the finger's motion are carried out by the prototype and a detailed analysis of the system performance is presented.

Method to sensitize an arc‐induced LPFG‐based sensor using double‐pass configuration

ABSTRACTThe sensitivity of the arc‐induced long period fiber grating (LPFG) sensor was improved utilizing the double‐pass configuration. The sensitivity in terms of transmission attenuation of the resonance wavelength for the double‐pass LPFG configuration was better compared to the single‐pass configuration when it was used to monitor the avidin–biotin interaction over a period of 60 min. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2766–2769, 2014

Spectral characteristics of a two-section multilayer long-period fiber grating sensor

A novel long period fiber grating (LPFG) sensor structure is proposed in this paper. It is constituted by coating an over-layer partially on the fiber grating. Then the LPFG has a two-section multilayer transversely distributed refractive index structure. Using coupling mode theory and transfer matrix method, the influences of refractive index, thickness and length of the coating layer on the spectral characteristics of the new type LPFG were analyzed. The simulation results show that the resonant band is split due to the particularity of the LPFG structure, and the wavelength splitting is strongly dependent on the parameters of the coating layer. This LPFG designing may solve the cross sensitive problem and then realize synchronous measurement of temperature, strain and other physical quantities.