Bragg Wavelength Shift Research Articles

Simulating a Temperature, Stress And Strain FBG Sensor for Troposphere Layer

In this study, a simulation and design for a temperature (T) sensor are investigated by using the fiber Bragg gratings (FBG). The study investigated and characterized the FBG regarding maximum reflectivity, bandwidth, and the influence of applied strain on the shift in Bragg wavelength (λB). This is via measuring sensitivity of wavelength shift under strain in an optical sensing system. The response of FBG sensors was also investigated and optimized. Uniform FBG spectra and theoretical comparisons were conducted considering the influence of several selected external strain/stress (S) values: 101.325, 89.874, 79.495, 70.108, 61.640, 54.019, 47.181, 41.060, 35.599, 30.742, 26.436. The Optisystem 16 software is analyzing these two types of effects. The measured parameters, such as sensitivity, were determined by using a white light source. The light source operating wavelength was 1550 nm. This is to design the sensor especially for troposphere that have high sensitivity (1279.7472 pm/oC. The sensitivity obtained exhibited varying values between 1279.7472 and 1239.7551 for strain. The peak sensitivity observed is associated with 550 nm of wavelength. Result for measured sensitivity against S by the FBG sensor was 15.5087 pm/oC with sensor length 20 mm. While it was found equals 15.5131 pm/oC with sensor length 10 mm. T sensing is simulated for selected values (15, 8.5, 2, -4.5, -11, -17.5, -24, -30.5, -37, -43.5, -50 oC). Resulted sensitivity was found to fluctuate fitting sine, Long Normal, and Boltzmann functions, indicating large sensitivity for the simulated sensor responses.

Temperature-insensitive and cost-effective distributed NP-Doped optical fiber sensors

This paper presents the development of a cost-effective distributed optical fiber sensor for temperature-insensitive assessment of mechanical disturbances along an optical fiber cable. The proposed sensor system uses a nanoparticle (NP)-doped optical fiber with enhanced Rayleigh backscattering to provide higher sensitivity and spatial resolution using the transmission and reflection analysis (TRA) approach, where the transmitted and backscattered optical powers are analyzed as a function of the mechanical disturbance. In addition, Fiber Bragg Gratings (FBGs) are used as wavelength filters to provide the wavelength division multiplexing of the proposed device, which enable the use of 3 different NP-doped optical fiber sections for simultaneous detection of multiple curvature conditions in a cost-effective distributed sensing approach. The sensor characterization tests are performed by means of applying curvature angles from 360° to 1080° at different positions along NP-doped fibers (namely 25 mm, 100 mm and 175 mm) at 4 different temperatures of 25 °C, 30 °C, 40 °C and 50 °C. The results indicate the feasibility of the proposed approach, where the temperature variations lead only to a wavelength shift of the Bragg wavelength, whereas the mechanical disturbances (the curvatures) lead only to variations in the transmitted and reflected optical powers. Thus, by analyzing the transmitted and reflected optical powers in conjunction with the Bragg wavelength shift, it is possible to estimate both the mechanical disturbance amplitude (i.e., curvature angle) and the position along each NP-doped optical fiber section. Results indicate a relative error of around 3 % and 4 % for the mechanical disturbance location and absolute value, respectively. Moreover, the temperature cross-sensitivity in this case is below 2 % considering both amplitude and location of the mechanical disturbance. The proposed approach can be applied in structural health monitoring of different types of structures by integrating the fibers in the structures themselves with the possibility of measuring the strain distribution along the fibers (instead of in different points along the fiber) using a lower cost hardware when compared with similar distributed optical fiber sensing approaches.

High Sensitivity CH4 and CO2 Gas Sensor Using Fiber Bragg Grating Coated with Single Layer Graphene

This article outlines the development of a Fiber Bragg Grating (FBG) intended for use as a sensor for CH4 and CO2 gases. Following fabrication, the FBG was effectively treated with a layer of Graphene Material through a modified RF Sputtering process. This coating procedure involved introducing argon gas into the chamber and subjecting the FBG, securely held by two vacuum stages, to a temperature range of 27°C to 600°C by adjusting the power supplied to the cathode and anode, ranging from 0 to 125 Watts. Subsequently, the FBG was employed as a key sensing element within an experimental setup aimed at measuring gas concentrations within a confined space. The assessment involved analyzing the reflected signal of the FBG using an Optical Interrogator System, which demonstrated a shift in the Bragg wavelength of the reflected signal corresponding to varying gas concentrations. This study indicates promising outcomes for the Graphene-coated FBG as a gas sensor. The sensor’s sensitivity was evaluated based on the Bragg wavelength shift resulting from gas presence within the chamber. The Graphene-coated FBG exhibited sensitivities of 3.3 ppm for CH4 and 3.7 ppm for CO2, surpassing those reported in prior research efforts.

Enhancing data sparsity in spectral signals using wavelet decomposition for improved compression and storage efficiency

Wavelet decomposition (WD) is integrated into the Compressive Sensing (CS) model to enhance data sparsity. This approach aims to ensure efficiency and quality in the received data after compression and reconstruction processes. The proposed WD-CS model is developed for reflected spectra signals from Fiber Bragg Gratings-based extensometers, which were subjected to induced deflections simulating the underground soil movement. WD decomposes the input signal before compressive measurement, followed by transferring and storing the compressed data in the cloud. The spectral data were reconstructed using Orthogonal Matching Pursuit (OMP) followed by wavelet reconstruction. The impact of wavelet decomposition on the quality of compression and reconstruction is assessed and compared against that of the standard CS model. The findings indicate that the WD-CS model can improve data sparsity by a factor of three and compressibility by a factor of ten without degenerating the reconstructed data quality. The error in the Bragg wavelength shift of the reconstructed spectra is minimal extracted using Pseudo-high Resolution Interrogation (PHRI) method. The proposed WD-CS model is useful in improving data compression for FBG spectra as well as storage efficiency, which make it potentially applicable in FBG-based sensor networks for long-term structural health monitoring applications.

Non-invasive FBG-based contact lens for continuous intraocular pressure monitoring

The intraocular pressure (IOP), or pressure inside the eye, is one of the key indicator for glaucoma diagnosis and treatment. The present work shows the design and fabrication of a non-invasive Fiber Bragg Grating (FBG) based contact lens for continuous IOP monitoring. By employing wet etching to reduce the FBG diameter, FBG based contact lens sensitivity and mechanical flexibility are enhanced. The contact lens is made of an optical fiber with a small core diameter that has an inscribed FBG of length 3 mm and is etched for a length of 40 mm to facilitate coiling the eFBG during fabrication. The soft contact lens was fabricated using flexible thin film technology with a transparent and flexible etched Fiber Bragg Grating (eFBG) integrated within flexible polydimethylsiloxane (PDMS) for sensing corneal deformations brought about by IOP variations. Experimental studies on the bionic eyeball model show that the Bragg wavelength shift is highly linear (r2 = 0.9694), with a very good sensitivity of 49.243 pm/mmHg in the IOP pressure range of 0 to 50 mmHg. Due to its ease of fabricating, simplicity of design, and ability to continuously measure pressure with good repeatability and stability, the proposed sensor thus offers a potential solution for IOP monitoring.

Fiber-Optic Bragg Grating Sensor for Photothermally Examinating Moisture of Meat

The illegal water injection into meat not only breaks the market equity, but also deteriorates the meat quality and produces harmful substances. In this work, we proposed a fiber Bragg grating (FBG) sensor that enabled fast, quantitative, and in-situ detection of the moisture content of water-injected meat. The FBG was written in the erbium-ytterbium (Er/Yb) co-doped fiber, which could perform the self-photothermal effect by injecting the near infrared laser into the fiber. As the heated fiber sensor probe was inserted into the meat sample, the temperature decreased due to the heat dissipation mediated by moisture. The intracore Bragg grating could monitor the temperature loss by recording the Bragg wavelength shift, which reflected the water content quantitatively. The results revealed that the sensor could complete the detection within 15 s. The sensor’s sensitivity to detect changes in the pork water content was theoretically calculated to be 0.090847%. The proposed sensor is expected to provide a novel approach for examination of the meat moisture.

Highly birefringent side-hole fiber Bragg grating for high-temperature pressure sensing.

We demonstrate a novel, to the best of our knowledge, high-temperature pressure sensor based on a highly birefringent fiber Bragg grating (Hi-Bi FBG) fabricated in a dual side-hole fiber (DSHF). The Hi-Bi FBG is generated by a femtosecond laser directly written sawtooth structure in the DSHF cladding along the fiber core through the slow axis (i.e., the direction perpendicular to the dual-hole axis). The sawtooth structure serves as an in-fiber stressor and also generates Bragg resonance due to its periodicity. The DSHF was etched by hydrofluoric acid to increase its pressure sensitivity, and the diameter of two air holes was enlarged from 38.2 to 49.6 µm. A Hi-Bi FBG with a birefringence of up to 1.8 × 10-3 was successfully created in the etched DSHF. Two distinct reflection peaks could be observed by using a commercial FBG interrogator. Moreover, pressure measurement from 0 to 3 MPa at a high temperature of 700°C was conducted by monitoring the birefringence-induced peak splits and achieved a high-pressure sensitivity of -21.2 pm/MPa. The discrimination of the temperature and pressure could be realized by simultaneously measuring the Bragg wavelength shifts and peak splits. Furthermore, a wavelength-division-multiplexed (WDM) Hi-Bi FBG array was also constructed in the DSHF and was used for quasi-distributed high-pressure sensing up to 3 MPa. As such, the proposed femtosecond laser-inscribed Hi-Bi FBG is a promising tool for high-temperature pressure sensing in harsh environments, such as aerospace vehicles, nuclear reactors, and petrochemical industries.

A high-resolution 3D radiochromic hydrogel photonic crystal dosimeter for clinical radiotherapy.

The precise, rapid and direct visualization of 3D topographical dose in the target tissue that is crucial for effective radiation therapy remains a challenge. Herein, by combining hydrogel photonic crystals with film stacking or 3D printing, a 3D radiochromic dosimeter with a dose sensitivity of up to 10 nm Gy-1, a spatial resolution <50 μm, and the ability to detect complex 3D topographical dose distribution was proposed for clinical radiation dose verification. The sensitivity and response range of the dosimeter by radiation-induced polymer cross-linking and consequent Bragg wavelength shift can be tuned via the solid content and extent of acrylate modification. The combination of rapid readout, low dose response, high spatial resolution, and great pre-irradiation and post-irradiation stability highlights the translational potential of this technology for topographical dose mapping in clinical radiotherapy applications.

Investigation of the effects of grating length, Bragg wavelength and wavelength shift on temperature sensitivity in fiber Bragg grating-based sensing systems

Investigation of the effects of grating length, Bragg wavelength and wavelength shift on temperature sensitivity in fiber Bragg grating-based sensing systems

The Study on the Spectral Analysis of Fiber Bragg Grating (FBG) as a Strain Sensor

Abstract: By adjusting the grating length and refractive index change, parameters of the Fibre Bragg grating which are the effective refractive index, Bragg wavelength, grating period, and strain-optic constant are provided and discussed, along with the characterization of the grating, including strain, Bragg wavelength shift, spectral response, and bandwidth. The coupled mode equations form the basis for data analysis and acquisition. This research uses a high-level computer language, such as GNU Octave software, to simulate FBG spectral responses.

Long-term creep monitoring of composite wing leading edge using embedded fiber Bragg grating

The creep behavior of composite wing leading edges resulting from nonequilibrium residual stresses and material viscoelasticity needs to be evaluated comprehensively as it significantly affects assembly. In this study, long-term creep monitoring of a composite wing leading edge used in an actual airplane for 710 h is conducted using embedded fiber Bragg grating arrays and a creep extraction algorithm. The spectra and Bragg wavelength shifts of two embedded arrays, which involve temperature, thermal expansion, and creep, are recorded and analyzed. The creep curve of the composite wing leading edge is reconstructed and further predicted using the creep extraction algorithm based on multiparameter decoupling and the Burgers model. This study elucidates the enlargement of the opening size in the composite wing leading edge by measuring the tensile strain above the neutral axis. The predicted creep time serves as a valuable reference for determining the appropriate assembly timing.

Real-time monitoring of urea slow release through fiber Bragg grating sensors

This research aimed at using fiber Bragg grating (FBG) sensors for monitoring the slow release of urea. Urea granules were coated with ethyl cellulose for controlled-nitrogen release. The FBGs were fabricated using a 10 mm single-mode glass fiber optic, and silver nanoparticle coating was deposited on the partially removed cladding of the FBG using the electroless technique. The silver-coated FBGs at three operating wavelengths (FBG1: 1534 nm, FBG2: 1559 nm, and FBG3: 1565 nm) were used to monitor the slow release of urea in water and soil. The Bragg wavelength shift of FBG 1, 2, and 3 to the controlled-release rate in water was 0.028, 0.12, and 0.20 nm, respectively. In soil, the coated fertilizer responded to the FBG 1, 2, and 3 showing wavelength shifts of 0.028, 0.10, and 0.12 nm, respectively. This study demonstrates the potential of FBG sensors in agricultural applications.

Temperature compensated magnetic field sensor based on magnetic fluid infiltrated cascaded structure of micro-tapered long-period fiber grating and fiber Bragg grating

Magnetic fluid (MF) infiltrated fiber-optic interference structures can be used to realize miniature magnetic field sensor for various applications needing sensitive magnetic field measurement, however, these sensors are typically also sensitive to temperature variations. To solve the problem of temperature cross sensitivity, an MF-infiltrated micro-tapered long-period fiber grating (MT-LPFG) and a femtosecond laser inscribed fiber Bragg grating (fsFBG) cascaded sensing structure is proposed and demonstrated. The MT-LPFG is fabricated by a fused tapering method under the illumination of a CO2 laser and is inserted into a glass capillary infiltrated with MF for magnetic field measurement, and the fsFBG is cascaded to the MT-LPFG for temperature measurement. Through the simultaneous monitoring of the resonant wavelength shift of the MT-LPFG and the Bragg wavelength shift of the fsFBG, temperature and magnetic field strength can be simultaneously extracted through a sensitivity coefficient matrix. As a result, the influence of the temperature on the MF-infiltrated MT-LPFG can be effectively compensated. Experimental results show that a magnetic field strength sensitivity of 21.86 pm/Oe can be achieved in a magnetic field strength range of 10-80 Oe and a temperature range of 30-60℃.

Investigation of Hybrid Remote Fiber Optic Sensing Solutions for Railway Applications

Fiber optic sensing (FOS) has become a well-known technology in response to the rising demands of the railway transportation field despite the abundance of electronic sensing systems in the market. FOS application boasts an all-in-one solution that is both efficient and versatile. In order to enhance the understanding of the capabilities of FOS, this paper presents a hybrid fiber optic sensing system with an improved sensing ability to facilitate transportation applications for primary or secondary security interfaces. The hybrid sensing scheme incorporates two different sensing systems designed for long-distance applications. The first system employs a coding technique for the transmitted pulses, which provide information on train location through cross-correlation with the reflected pulses from fiber Bragg grating (FBG) sensors located along the railway. The proposed system can accurately predict the train’s location up to a precision of one cm. The second system examines the wavelength drift of the reflected signal from the FBG sensor affected by the train using a tunable optical filter and photodetector. It determines essential parameters such as the train’s location, speed, and direction by measuring the Bragg wavelength shift and its direction. The effect of the train movement and speed on the applied strain on the FBG sensor is calculated in this work and applied to the simulation to determine the train’s location, speed, and direction. A calibration table facilitates the correlation between the train speed and the shift in the FBG center wavelength, which helps ensure accurate results. The hybrid fiber optic sensing system is designed to facilitate railway transportation applications’ sustainability and security.

Design and realization of a femtosecond-laser-inscribed fiber Bragg grating for accurate measurement of liquid level and liquid density

An exceptionally sensitive liquid level and density sensor system using Femtosecond-Laser-Inscribed Fiber Bragg Gratings is designed and demonstrated utilizing the basic Archimedes’ Law of Buoyancy. The sensor works based on principles of Archimedes’ law of buoyancy and basic strain sensitivity of Fiber Bragg Grating (FBG). A cylindrical mass of 22.5 cm long is suspended from one end of the FBG and whereas the other end of the fiber is fixed. The mass is partially immersed into the liquid under consideration to measure the liquid level as well as liquid density. Following Archimedes’ law of buoyancy, the relative weight of the suspended mass gets reduced and the corresponding shift in Bragg wavelength is measured using an interrogator connected at the fixed end of the sensor lead fiber. The relative weight of the immersed mass also depends on the liquid density. Therefore, a change in liquid density also is reflected by the shift in Bragg wavelength. The system can be calibrated to measure the accurate liquid level and liquid density. A liquid (water) level measurement sensitivity of 5.47 to 5.60 pm/mm is achieved using the system under three times of consecutive experiments which is very close to the simulated value (5.9 pm/mm). A density measurement sensitivity of ∼ 0.71 nm/(gm/cm3) is calculated in this system and experimentally achieved sensitivity is ∼ 0.7 nm/(gm/cm3). The LOD (limit of detection) was also found to be 1.008 gm/cc for the density measurement and the average error during the measurement was 0.0021 nm/(gm/cm3).It is also shown that the density measurement sensitivity is highly dependent on the amount of immersed portion of the suspended mass and more amount of immersed mass is desirable for better sensitivity.

Theoretical investigation of the impact of apodized fiber Bragg grating and machine learning approaches in quasi-distributed sensing

An apodized fiber Bragg grating (FBG) is designed to investigate the impacts of side lobe elimination in quasi-distributed sensing for the estimation of measurands (like temperature and strain) to assess the condition of civil structures, such as bridges. The adjacent FBG spectrums may overlap with each other because of the impacts of temperature and strain due to the presence of a high range of side lobes in a quasi-distributed sensing network. Therefore, elimination of side lobes is necessary, by introducing a method of apodization. The sensitivity of the designed apodized FBG is estimated by analyzing the variations in the Bragg wavelength due to the impacts of temperature and strain. The changes in Bragg wavelength due to the measurands can affect the grating period and the grating index of the FBG. The period of the grating and the grating index of the FBG are simultaneously varied by temperature and strain. To measure the physical parameters effectively, it is essential to distinguish whether the changes in the Bragg wavelength are owing to the impacts of temperature or to the impacts of strain. The effect of cross-sensitivity between the temperature and the strain is a key problem in any FBG-based sensing application as both the measurands can affect the Bragg wavelength. In this work, machine learning methods (the support vector machine, K-nearest neighbors, logistic regression, naïve Bayes, decision tree, and ensemble models) are introduced to differentiate between the effects of temperature and strain on a single Bragg wavelength shift measurement. An artificial neural network is used for the predictive analysis of physical parameters, to identify any measurements of potential concern. It has been noted that the performance of the proposed ensemble model is higher compared to other models for the classification of temperature and strain.

Shock accelerometer based on fiber Bragg grating sensor with a novel 3D printed structure for medium frequency measurement applications and high acceleration range

This study aims to develop a shock accelerometer that can measure signals from two directions in one-dimensional space for medium frequency measurement applications and high acceleration range. A fiber Bragg grating (FBG) sensor is attached to a structure fabricated using Fused Deposition Modeling technology (FDM) to achieve this. The finite element method is utilized to observe the sensor’s operating mechanism and harmonic response, as well as to demonstrate the accelerometer’s customizability. The sensor’s design enables it to detect acceleration resulting from shock motion on both sides (+X and –X direction) of the Hopkinson bar system. When the elastic structure deforms, the wavelength inside the FBGs’ core changes. During the test with different random accelerations, FBG1 showed a total Bragg wavelength shift of 6.403 nm within the 450 g to 1800 g range, while FBG2 showed a total shift of 2.033 nm within the 330 g to 1200 g range. According to the findings of the linearity analysis conducted on the proposed sensor, the linear values of the data obtained from FBG1 were over 96%, while those from FBG2 were close to 94%. In addition, the sensor’s harmonic response was examined, and it was recommended that the sensor be operated within a frequency range of 20 to 600 Hz, with the resonant frequency being 660 Hz. The sensor’s amplitude anti-interference is also considered negligible when the horizontal noise signal relative to the working axis signal is less than 3% in both directions. These findings suggest that the proposed accelerometer has great potential for various applications. Furthermore, the proposed FBG accelerometer sensor utilizes 3D printing technology, which offers several advantages, including rapid fabrication time, reduced production costs, and high customizability.

Integration of Bragg gratings in aerosol-jetted polymer optical waveguides for strain monitoring capabilities.

We demonstrate and discuss the integration of Bragg gratings in aerosol-jetted polymer optical waveguides, produced in the optical assembly and connection technology for component-integrated bus systems (OPTAVER) process. By using a femtosecond laser and adaptive beam shaping, an elliptical focal voxel generates different types of single pulse modification by nonlinear absorption in the waveguide material, which are arranged periodically to form Bragg gratings. Integration of a single grating structure or, alternatively, an array of Bragg grating structures in the multimode waveguide yields a pronounced reflection signal with typical multimodal properties, i.e., a number of reflection peaks with non-Gaussian shapes. However, the main wavelength of reflection, located around 1555 nm, is evaluable by means of an appropriate smoothing algorithm. When loaded by mechanical bending, a pronounced Bragg wavelength shift of this reflected peak up to 160 pm is detected. This demonstrates that the additively manufactured waveguides can be used not only for signal transmission but also as a sensor.

Fabrication and testing of FBG sensor-based one-dimensional shock accelerometer attached to novel 3D printed structure

This study presents an FBG-based one-dimensional shock accelerometer fabricated by Fused Deposition Modelling (FDM) technology. The bare fiber Bragg grating (FBG) sensor is fixed to the 3D-printed elastomer structure. The dimension of the sensor was simulated by the finite element method to explore the customizability of the acceleration sensor. The deformation in the elastic material structure leads to a change in the wavelength of the FBG sensor, and it is observed that the total Bragg wavelength shift over the acceleration range was recorded as 2.53 nm, corresponding to an acceleration sensitivity of 1.16 pm/g with a randomly generated acceleration between 655 g and 2635 g (1 g = 9.81 m/s2). A linear analysis showed that the linear values of the data obtained in the experiments reached above 96%. A comparison of the accelerometer signal obtained from the piezoelectric accelerometer data with the FBG accelerometer shows an excellent match in pulse amplitudes with pulse durations of only about 100 μs each time the acceleration occurs and the proposed sensor operating frequency is from 200 to 3000 Hz. The proposed FBG acceleration sensor is based on 3D printing technology, so it also inherits the outstanding advantages of this technology such as fast manufacturing time, saving production costs, and especially the ability to easily customize based on the size change of the structure, weight of mass block or the printed material.

Smoke Detection Using rGO-Coated eFBG Sensor for Early Warning of Coal Fire in Mines

This experimental work demonstrates the process of smoke detection in coal mines using reduced graphene oxide (rGO) coated on etched fiber Bragg grating (eFBG)-based sensors. The lab experiments were conducted using the test fire of combustible coals collected from the different geographic regions of coal mines in Jharkhand and West Bengal in India. The experimental results showed that the coal samples higher in carbon elements interacted with rGO on fiber more strongly. Obtained results show that the increment in the shift of reflected Bragg wavelength with respect to air was observed by exposing the sensor head to the smoke particles inside the smoke chamber. The percent enhancement in the Bragg wavelength shifts are found to be 18.82%, 30%, and 34.74% in Ramnagar, Jharia, and Bokaro, and the sensitivity has been achieved by bare eFBG is ~104.32 pm/sample and by the rGO-coated eFBG sensor is ~134.33 pm/sample. Other parameters like gross calorific values (GCVs) of different coals are also measured using proximate analysis and also directly through a bomb calorimeter. The reported sensor can be installed in coal mines for early fire warning detection.