Sensitivity Of Fiber Bragg Grating Research Articles

SENSITIVITY MEASUREMENT OF FIBRE BRAGG GRATING SENSOR

A practical pass-through type fibre Bragg grating (FBG) temperature sensor system have been designed, developed, simulated, and experimentally investigated. The performance of FBG was evaluated in harsh environments exposed under direct sunlight, rain, and wind. The sensor system designed directly focused with convex and hand lens. The temperature of FBG’s sensor head been measured. The broadband laser source was launched into the system using tunable laser source (TLS) and both transmission and reflection spectra of FBG sensor were measured by optical spectrum analyzer (OSA). Results shows that the Bragg wavelength shift, increased proportionally with the temperature changes. The sensitivity of FBG were recorded at 0.0100 and 0.0132 nm °C-1 for the systems where convex and hand lens applied to the FBG’s sensor head respectively, while the sensitivity of 0.0118 nm °C-1 measured for the system without any focusing element applied.

Improvement in temperature sensitivity of FBG by coating of different materials

This paper presents the simulation results of coated Fiber Bragg Grating (FBG) as temperature sensor. As we know that bare FBG cannot be used as temperature sensor because they are made of silica and the thermal expansion coefficient of silica is very less. Hence bare FBG is less sensitive to temperature variation. To enhance the temperature sensitivity of the FBG sensor different types of materials are coated on FBGs whose thermal expansion coefficients are greater than that of silica. In this simulation Lead, Indium, Copper, Aluminium, and PMMA are coated on FBG and the simulation results are compared with the previous experimental work for the temperature range 50K – 300K. PMMA coated FBG sensor showed best sensitivity value among above coating materials.

Improved design of slow light interferometer and its application in FBG displacement sensor

An optical fiber Mach–Zehnder interferometer (MZI) based on slow light in polymer-infiltrated PCW (PI-PCW) was proposed to enhance the demodulation sensitivity of fiber Bragg grating (FBG) displacement sensor. By optimizing the structure of PI-PCW, slow light with high group index of 110 was realized, which is advantageous to develop high-sensitive MZI. And thanks to electro-optic effect of the infiltrated polymer, the working wavelength of flat band slow light, as well as the demodulation range of MZI, could be flexibility changed and enlarged by tuning external driving voltage. At last, differential and orthogonal method was used to demodulate the interference spectrum of MZI with high stability and good linearity. The FBG was pasted on an Omega-like beam, thus the displacement variation of the free end of the Omega-like beam could be measured by monitoring the output phase of MZI. Finally, the proposed displacement sensor demonstrated a high sensitivity of 1.035rad/mm with good linearity and wide measurement range of 55.6mm.

Enhanced sensitivity of fiber Bragg grating hydrogen sensor using flexible substrate

A novel method was proposed to enhance sensitivity of fiber Bragg grating (FBG) hydrogen sensor in this paper. As sensing element, Pd/Ni composite film was deposited on side-face of etched fiber Bragg grating and surface of polypropylene substrate. The atomic ratio of Pd and Ni in hydrogen sensitive film was controlled at 91:9. The sensitivity of FBG hydrogen sensor is significantly improved due to the much lower Young's modulus of polypropylene substrate. FBG hydrogen sensor has 146pm wavelength shift towards 4% hydrogen, and the sensor shows linear response and good repeatability during hydrogen concentration test. FBG hydrogen sensor has good stability even after six months, which demonstrates its great potential in hydrogen leakage monitoring.

광섬유 브래그 격자의 방사선 민감도에 대한 수소로딩의 영향

본 논문은 광섬유 브래그 격자의 방사선 민감도에 대한 수소로딩 공정의 영향에 대해서 연구하였다. 게르마늄이 함유된 광섬유에 수소로딩 기간을 달리하여 광섬유 브래그 격자를 제작하였다. 광섬유 브래그 격자는 총 18 kGy 감마선에 조사하여 방사선에 의한 브래그 파장의 변화를 측정하였고, 방사선 조사 후에는 반치대역폭과 온도 감도 계수의 변화를 평가하였다. 수소로딩 조건에 따라서 방사선에 의한 브래그 파장의 변화는 약 2 배 이상의 차이를 보였다. This paper investigates the influence of hydrogen loading process on the radiation sensitivity of fiber Bragg gratings (FBG). We made the FBG inscribed in the same commercial Ge-doped fiber with different hydrogen loading periods. We measured the Bragg wavelength shift (BWS) of the FBG exposed to gamma-radiation up to a dose of 18 kGy, and evaluated the change of full width at half maximum (FWHM) and the FBG temperature sensitivity coefficient after irradiation. Varying hydrogen loading parameter led to BWS differences up to nearly a factor of two.

Magnetic field sensor based on fiber Bragg grating with a spiral microgroove ablated by femtosecond laser

A novel magnetic field sensor based on Terfenol-D coated fiber Bragg grating with spiral microstructure was proposed and demonstrated. Through a specially-designed holder, the spiral microstructure was ablated into the fiber Bragg grating (FBG) cladding by femtosecond laser. Due to the spiral microstructure, the sensitivity of FBG coated with magnetostrictive film was enhanced greatly. When the spiral pitch is 50 μm and microgroove depth is 13.5 μm, the sensitivity of the magnetic field sensor is roughly 5 times higher than that of non-microstructured standard FBG. The response to magnetic field is reversible, and could be applicable for magnetic field detection.

Intrinsic Temperature Sensitivity of Fiber Bragg Gratings in PMMA-Based Optical Fibers

Thermal response of fiber Bragg gratings (FBGs) in polymethyl methacrylate-based optical fibers doped with trans-4-stilbenemethanol is studied at 0% relative humidity (RH) from -20°C to 60°C. The Bragg wavelength is found to negatively shift upon heating in a nonlinear manner. The higher the temperature, the larger the magnitude of wavelength shift is. The absolute value of calculated temperature sensitivity also increased with temperature. The sensitivity at room temperature is about -1 pm/°C, which is one order of magnitude lower than that measured at constant RH for polymer FBGs and that of silica FBGs. Such low temperature sensitivity challenges the common notion of high temperature sensitivity of polymer FBGs. In addition, it is found that the dependence of Bragg wavelength of the polymer FBGs on RH is nonlinear. Below 30% RH, the Bragg wavelength shift upon RH increase is minimal compared to that above 30% RH.

Simultaneous measurement of refractive index and temperature using dual-period grapefruit microstructured fiber grating

By cascading the long period fiber grating (LPFG) and fiber Bragg grating (FBG) in grapefruit microstructured fiber, a novel dual-period fiber grating sensor is proposed. The refractive index and temperature are measured simultaneously by using the different sensitivity of FBG and LPFG. The relationship between dual-period fiber grating transmission spectrum and refractive index, resonant wavelengths and temperature are analyzed theoretically, respectively. The simulation results show that the accuracy of the sensor in measuring refractive index and temperature is estimated to be 2319.6nm/RIU in a range from 1.33 to 1.36 and 0.017nm/°C from 0°C to 100°C, respectively. Thus, the sensor has high refractive index sensitivity, and can provide the theoretical foundation for the optical fiber biosensor.

Influence of the Fiber Coating Type on the Strain Response of Proton-Irradiated Fiber Bragg Gratings

We report on the effect of the fiber coating on the radiation sensitivity of Fiber Bragg Gratings (FBG). For the first time this type of study has been carried out using a 13.5 MeV proton beam up to a fluence of $3.3 \times 10^{15}$ protons/cm $^{2}$ (total absorbed dose of 15 MGy). We observed a clear dependence of the radiation sensitivity on the coating, in particular, we have investigated the irradiation induced changes on the strain sensitivity; FBG strain coefficient remains stable for all the fiber within a 5%. This result demonstrates the suitability of FBGs as structural health and deformation monitors in the very hostile environment of the new generation of high-intensity particle physics proton colliders.

Fiber Bragg Grating Based Technique for Sensing Current

In this article, investigative study for measuring electric current using temperature sensitivity of fiber Bragg grating (FBG) is discussed. An FBG is kept inside a nichrome coil, which was pre-calibrated with respect to current and temperature by applying known value of current and measuring corresponding temperature. Two types of setups were used for the experiment: with and without housing. We found that the results were quite consistent and stable with the housing setup. The proposed current sensor has shown good response, repeatability, and very low hysteresis.

Method for Enhancing and Controlling Temperature Sensitivity of Fiber Bragg Grating Sensor Based on Two Bimetallic Strips

This paper presents a novel structure based on bimetallic strips for enhancing temperature sensitivity of fiber Bragg grating (FBG) sensors. Two different types of sensor heads have been designed for this implementation. The first sensor head consists of an FBG that is fixed between ceramic block on one side and a bimetallic strip made up of aluminum and copper on the other. The second sensor head consists of an FBG that is fixed between two bimetallic strips. Theoretical and experimental studies carried out on these proposed sensor heads resulted in an increase in temperature sensitivity of about six times greater than that of bare FBG sensor. Further, the proposed sensors have shown good linearity and stability.

Experimental investigation of pre-irradiation effect on radiation sensitivity of temperature sensing fiber Bragg gratings

The effect of pre-irradiation on radiation sensitivity of fiber Bragg gratings (FBGs) is verified experimentally. FBGs are fabricated in photosensitive optical fibers and single mode fibers with Ge-concentration in a range from 3 mol% to 23.37 mol% in the core. In experiments, the FBGs are subjected to twice γ-radiation exposures to a Co60 source at a dose-rate of 0.1 Gy/s up to a total dose of 50 kGy. Pre-irradiation treatment can reduce the temperature sensitivity variation of FBGs by 18.12%–35.91%, as well as Bragg wavelength shift (BWS) by 8%–27.08%. Our research demonstrates that pre-irradiation treatment is a feasible method to improve the radiation tolerance of FBGs.

Dual functional performance of fiber Bragg gratings coated with metals using flash evaporation technique

Metallic and other type of coatings on fiber Bragg grating (FBG) sensors alter their sensitivity with thermal and mechanical stress while protecting the fragile optical fiber in harsh sensing surroundings. The behavior of the coated materials is unique in their response to thermal and mechanical stress depending on the thickness and the mode of coating. The thermal stress during the coating affects the temperature sensitivity of FBG sensors. We have explored the thermal response of FBGs coated with Al and Pb to an average thickness of 80nm using flash evaporation technique where the FBG sensor is mounted in a region at room temperature in an evacuated chamber having a pressure of 10−6Torr which will minimize any thermal stress during the coating process. The coating thickness is chosen in the nanometer region with the aim to study thermal behavior of nanocoatings and their effect on FBG sensitivity. The sensitivity of FBGs is evaluated from the wavelengths recorded using an optical sensing interrogator sm 130 (Micron Optics) from room temperature to 300°C both during heating and cooling. It is observed that the sensitivity of the metal coated fibers is better than the reference FBG with no coating for the entire range of temperature. For a coating thickness of 80nm, Al coated FBG is more sensitive than the one coated with Pb up to 170°C and it reverses at higher temperatures. This point is identified as a reversible phase transition in Pb monolayers as the 2-dimensional aspects of the metal layers are dominant in the nanocoatings of Pb. On cooling, the phase transition reverses and the FBGs return to the original state and for repeated cycles of heating and cooling the same pattern is observed. Thus the FBG functions as a sensor of the phase transitions of the coatings also.

The temperature sensitivity of fiber bragg gratings embedded in an Al 6061 matrix by ultrasonic welding

The low temperatures and low pressure employed in ultrasonic welding make it suitable for embedding optical fiber gratings (fiber Bragg gratings (FBGs)) in the fabrication of 3D smart composites. However, FBG sensors embedded in metal matrices are easily damaged and broken. A method is therefore presented for the metallization of FBG by the combination of electroless nickel plating and electro nickel plating, followed by embedding the coated FBG in an aluminum alloy 6061 matrix in order to fabricate smart metal structures. Experimental results show that nickel plating can protect the FBG and provide benefits in the fabrication of aluminum alloy smart structures using ultrasonic welding. The temperature-sensing properties of smart metal structures fabricated in this way are analyzed, and the results show that the temperature sensitivity has been improved twofold. Also, the temperature sensing shows good linearity, and the temperature cross-sensitivity has been effectively controlled; the temperature resolution has also been improved, making the measurements more accurate.

Effect of Grating Fabrication on Radiation Sensitivity of Fiber Bragg Gratings in Gamma Radiation Field

The influence of grating fabrication on radiation sensitivity of the FBGs has been investigated experimentally. The FBGs were fabricated in different process and GeO2 concentrations. Pre-irradiation and H2-loading were applied to change the radiation sensitivity of the FBGs. The FBGs were fabricated in photosensitive fiber and coupling single mode fiber with a GeO2 concentration in a range from 0.33 to 23 mol%. The lowest Bragg wavelength shift (13 pm) was obtained by a grating written in photosensitive fiber PSF-GeB-125, with pre-irradiation and without H2-loading for a total dose of about 50 kGy.

Enhanced temperature sensitivity of fiber Bragg grating temperature sensor using thermal expansion of copper tube

AbstractThe temperature sensitivity of fiber Bragg grating (FBG) temperature sensor is enhanced when using a copper tube to jacket of the FBG.Both sides of the FBG are glued with epoxy to cylindrical ferrules tubes that in turn is inserted and glued to a cylindrical copper tube. As the high thermal expansion coefficient of the cylindrical copper tube pulls both sides of the FBG, the temperature sensitivity is improved 3.3‐fold when compared to that of a bare FBG. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26032

Vibration shape testing of space sheet structure

The space sheet for a solar array structure is large in dimension, and flexible to induce complex distortion. It is difficult to measure the distortion. A large-scale flexible test prototype system is built for sheet structure vibration monitoring based on the vibration information of the solar array in space. The system provides an intelligent test method for flexible space structure with embedded sensors and non-visualization reinstruction. Multiple fiber Bragg grating (FBG) sensors are packaged and embedded into the structure with spatial division multiplexing (SDM) and wavelength division multiplexing (WDM). The sensor interrogator distinguishes wavelength shifts that can be turned into curvature of the curve. The structure shape is reconstructed based on the curvature information and the arc-length, and then displayed. The experiment shows that the system has a high FBG sensitivity. The reconstruction algorithm is fast with high precision. The system has great potential for use in health monitoring of the space sheet structure.

Influence of Manufacturing Parameters and Temperature on the Radiation Sensitivity of Fiber Bragg Gratings

For the first time the radiation sensitivity of Bragg gratings was investigated as a function of hydrogen loading pressure before and fiber tension during grating inscription, of the recoating procedure, and of the grating temperature. At -50°C the radiation-induced Bragg wavelength shift was about two times higher than at room temperature. This should be considered when selecting Bragg gratings e.g., for certain space applications.

Effect of the Fiber Coating on the Radiation Sensitivity of Type I FBGs

We have studied the influence of the fiber coating on the radiation sensitivity of fiber Bragg gratings (FBGs). These FBGs are draw tower gratings written before applying the coating in a fiber with a photosensitive 18-mol.% GeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -doped core. Using a Co <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sup> source we irradiated polyimide, acrylate, and ormocer coated gratings as well as mechanically stripped ormocer coated FBGs up to a 40-kGy dose. This total dose level corresponds to a near-earth space radiation environment mission. We show that the coating type must be taken into account for correctly interpreting ionizing radiation effects on FBGs.

Influence of Fiber Composition and Grating Fabrication on the Radiation Sensitivity of Fiber Bragg Gratings

The radiation-induced Bragg wavelength shift (BWS) was measured with type I gratings made of 12 fibers with very different composition, i.e. of fibers with an extremely different radiation-induced attenuation. With two of the fibers fabrication parameters like laser intensity, hydrogen loading, and annealing conditions after grating inscription were varied. With another fiber type I and type II gratings were made by a completely different process. With gratings made under identical conditions of the twelve fibers the radiation-induced BWS only varied by about a factor of three. Varying the fabrication parameters led to BWS differences up to nearly a factor of ten.