Etched Fiber Bragg Grating Research Articles

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.

L-cysteine modified gold nanoparticles for copper (II) ion detection using etched Fiber Bragg Grating sensor

L-cysteine modified gold nanoparticles for copper (II) ion detection using etched Fiber Bragg Grating sensor

Au coated etched FBG SPR sensor for the detection of ethanol in aqueous solution

Over the past few years, there has been a growing need for reliable ethanol sensors in the pharmaceutical and food industries. These industries require constant monitoring to ensure that the acceptable ethanol levels are maintained. This study reports a new fiber optic sensor that uses etched single mode fiber Bragg grating (FBG) coated with the thin layer of 45 nm gold to produce Surface Plasmon Resonance (SPR). A thin layer of 45 nm gold improves the sensitivity of sensor by improving the evanescent wave around the fiber, resulting in better interaction with the analyte. The sensing performance of developed structure was examined by analyzing the change in wavelength shift observed by varying ethanol concentration in aqueous solution from 0 to 100 %. The performance of developed sensor in terms of sensitivity is 20 pm/RIU. Which is expected to play an important role in food and pharmaceutical industries to protect human health from detrimental affects due to high concentration of ethanol.

A Silver Nanoparticle Modified Etched Fiber Bragg Grating Sensor for Arsenic Detection

A Silver Nanoparticle Modified Etched Fiber Bragg Grating Sensor for Arsenic Detection

High-Sensitivity Seawater Salinity Sensing With Cladding Etched Fiber Bragg Grating Technology

Seawater salinity is an essential parameter to show the basic hydrological information of the ocean. Cladding etched fiber Bragg grating (CE-FBG) technology has potential in seawater salinity sensing because of its high sensitivity to surrounding refractive index. Here, we fabricated the different CE-FBG salinity sensing elements by using hydrofluoric (HF) acid based wet chemical etching. We encapsulated a CE-FBG and a bare FBG (B-FBG) into a salinity sensor to realize simultaneous measurement of seawater salinity and temperature. Various sensing characteristics of the CE-FBG, including salinity and temperature sensitivity, response time, hysteresis, repeatability, and long-term stability were investigated systematically. The salinity and temperature measurements of the CE-FBG sensor were highly consistent with those of the electronic salinometer, which indicates that fiber optic salinity sensor provides a new means for salinity measurement. Together, our results demonstrate the great potential of the CE-FBG salinity sensor for high sensitivity, long-term, and quasi-distributed seawater salinity monitoring.

High sensitivity detection of different pH ranges with rGO-nanocomposite coated eFBG sensor.

In the proposed work, a highly sensitive reduced graphene oxide (rGO) coated etched fiber Bragg grating (eFBG) pH sensor is developed and characterized. To create the sensing probe, a nanocomposite layer of rGO is coated over the unclad area of the eFBG. The analysis of rGO material has been done using different characterization tools such as UV-VIS-NIR spectroscopy, x-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM). Experiments are performed using pH samples ranging from pH 2 to pH 12 to validate the operational sensing range of the proposed sensor. The effectiveness of the proposed sensor is evaluated with various pH values by monitoring the shift in the resonance peak of the sensor's reflection spectrum in a real-time interrogation system. The sensor performs well in both low and high pH ranges, with a maximum sensitivity of 0.232nm/pH at pH 12. Due to a shift in the rGO's optical band-gap at both low and high pH values in the samples, the sensor can detect minimal changes in concentration. In the reflected spectrum, the Bragg wavelength (λ B) shifts as a result of the change in the refractive index. The λ B is observed to change as the pH of the aqueous solution is changed experimentally. Its performance is shown to be minimally affected by the ambient temperature (in the range of 19-21∘ C). The sensor also has the capacity for remote sensing, a quick response time, a small size, a low cost, a miniaturized probe, and the ability to reuse the probe.

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.

Detection of chromium using polymer coated etched FBG

A chemo-mechanical-optical sensing technique is presented in this paper to detect carcinogenic Chromium Cr(VI) metal ion utilizing etched FBG (Fiber Bragg Grating) coated with stimulus responsive hydrogel. The Hydrogel is formed with blends of p(AMPSNa-co-APTMACl) which are greatly responsive to Cr (chromium) ions and exhibit a volume variation whenever dipped in the Cr solution. When the sensor head is exposed to different hexavalent Chromium (VI) ion concentration solutions, it exhibits a peak shifts because of the induced mechanical strain through the gel swelling. Chromium (VI) ion concentration is correlated with the peak shift. The sensor’s sensitivity is observed to be 15.1 pm/ppb which is 10 times the sensitivity of an unetched gel coated FBG sensor. The Cr (VI) ions trace amount is as low as 10 ppb will be sensed through technique. The proposed sensor has exhibited better repeatability, selectivity and sensitivity and the significant features of the proposed sensor are less weight, adoptability and compact size to monitor remotely.

Tailoring surface structure and diameter of etched fiber Bragg grating for high strain sensing

Sensitivity and mechanical properties are the key factors that affect the performance of strain-sensitive etched fiber Bragg grating (EFBG) sensors. Typically, EFBG sensors are fabricated via solvent etching. The manipulation of etching temperature and hydrofluoric acid (HF) concentration during the solvent etching process is particularly crucial to control the surface and mechanical properties of the sensors. In this study, the effects of these two etching conditions on the surface and mechanical properties of the etched fiber surface were investigated. It is found that higher etching temperature and higher HF concentration can cause rougher fiber surface with lower Young’s modulus, fracture stress and strain. EFBG produced at 20 °C temperature and 30% HF concentration exhibits smooth surface and high mechanical properties. Under these optimized etching conditions, the sensitivity of EFBGs was improved by reducing the fiber diameter. The results show that EFBGs with smaller diameters demonstrate higher strain sensing performance due to lower fiber stiffness. EFBG with a diameter of 15 μm has Young modulus of 7.21 GPa and achieves the highest strain sensitivity of 52.74 pm/με. To conclude, EFBG with excellent strain sensing performance can be obtained by tailoring the surface structures and fiber’s diameter during the etching process.

Doped silica sol layer coatings on evanescent field fiber Bragg gratings for optical detection of nitroaromate based explosives

Evanescent field etched fiber Bragg gratings (eFBG) were prepared with doped and non-doped nanoporous silica sol coatings for optical detection of the nitroaromatic explosives 2,4-dinitrotoluene (DNT), 1,3-dinitrobenzene (DNB) and trinitrotoluene (TNT). We used 3-aminopropyltrimethoxysilane (APTMS) and tetrabutylammonium hydroxide based receptors (TBAH, C16H37NO) as dopants in order to increase the specific identification of the nitroaromates. In nitroaromatic trace gas atmosphere the induced wavelength shift of the Bragg reflection signal was highest for the sensor with TBAH-doped silica sol receptor coating. Within the first two minutes during exposure the change of the signal intensity, reflecting the adsorption dynamics of the nitroaromatic explosives, was most significant and characteristically depending on the type of receptor dopant used. The cross sensitivities of the sensor with TBAH-doped silica sol receptor coating with four common solvents like acetone, ethanol, 2-propanol and tetrahydrofuran (THF) in comparison to the sensitivity of the tested explosives was more than six orders of magnitude (106) lower than that of solvents, indicating a very high selectivity of the sensor. By applying a simplified diffusion model correlated to a series of measurements with different distances to the target we estimated the limit of detection for a sensor coated with TBAH doped silica sol with 35.8 ± 0.9 ppb for DNB and 140.2 ± 1.8 ppb for DNT in air at room temperature. Using a more etched FBG (but mechanically less robust) sensor we were able to detect TNT as well at concentrations about 5 ppb at room temperature in air. A major result of our investigations was to demonstrate, that the nanoporous silica sol host matrix is suited for fast adapting with low technological effort the affinity of the receptor coating for silica-based evanescent field sensors. For future applications a set of sensors of silica-sol coatings with different dopants in combination with pattern recognition of the sensor signals could be used for clear identification of explosives.

High-Precision Magnetic Field Sensor Based on Fiber Bragg Grating and Dual-Loop Optoelectronic Oscillator

A novel fiber-optic magnetic field sensor with high interrogation speed and resolution by using an etched fiber Bragg grating (FBG) in conjunction with a dual-loop optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. A commercial FBG is firstly dipped into mixed hydrofluoric acid solution to remove the cladding layer and then is embedded with the magnetic fluid (MF) as a sensing element. The central wavelength reflected from the FBG is related to the overall time delay of the dual-loop OEO, which determines the oscillating frequency of the OEO. Therefore, the magnetic field can be estimated by measuring the oscillating frequency shift of OEO. The experimental results show that the oscillating frequency linearly increases with the increment of the magnetic field, achieving the sensitivity of 16.3 Hz/Oe with a R-square of 0.991 in the range of 5 mT–10 mT. In addition, the maximum error is within ±0.05 mT in the range of 7 mT–8 mT, which offers potentials in many fields where the high-precision magnetic field measurement is required.

A New Type of Etched Fiber Grating Hydrophone

We propose a new type of fiber hydrophone composed of an etched fiber Bragg grating and a special packaging structure for detecting acoustic waves in the low-frequency band under water. The operating mechanism is based on the mechanical vibration of the fiber Bragg grating from the induced vibrating stress of acoustic pressure. The induced pressure of acoustic waves pushes the silicone rubber thin film, causing its vibration and then stretching the fiber Bragg grating, thus resulting in the grating wavelength shift which is overlapped with a tunable laser. The variation in the overlapped light intensity is transferred to an electrical signal by using a photodetector. From the experimental results, we can determine that the smaller the fiber diameter, the higher the sensitivity and frequency response. In order to confirm that this FBG hydrophone has the ability to work in high-frequency acoustic waves, this fiber grating hydrophone and a standard piezoelectric hydrophone are experimentally compared to in the same test conditions in the frequency range from 4 to 10 kHz. According to the experimental results, the fiber grating hydrophone has better responsivity than that of the conventional hydrophone. Due to the unique sensing structure design, this wide-band fiber hydrophone can be useful in long-term continuous monitoring of acoustic waves.

Selective detection of lead in water using etched fiber Bragg grating sensor

In this work, we demonstrate a maleic acid (MA) functionalized gold nanoparticle (AuNP) coated, clad etched-fiber Bragg grating (e-FBG) sensor, capable of detecting lead metal ion (Pb2+) in water. The self-assembled carboxylic group in MA-AuNP shows an assertive coordination behavior towards Pb2+ for selective detection through a Bragg wavelength shift. The limit of detection (LOD) is found to be 10 femtomolar (fM, 0.0000002 ppb) with a dynamic range up to 100 nanomolar (nM, 20.72 ppb), which is within the acceptable limit stipulated by the World Health Organization (WHO) for safe drinking water (10 ppb). The sensor's recovery concentration is > 90% for spiked real water samples. A good reproducibility (standard error < 10 pm) and specificity along with portability, small footprint and real time response make e-FBG sensor an ideal optical probe for drinking water.

Etched fiber Bragg grating probe using a regular CNC machine and a 3D printer

Etched fiber Bragg gratings (EFBGs) have been widely employed for refractive index (RI) measurements that can be used to monitor sugar consumption during the fermentation of alcoholic beverages. EFBGs are obtained by removing the cladding of a fiber Bragg grating, which is traditionally performed by a chemical attack with hydrogen fluoride, an extremely hazardous corrosive substance that causes severe wounds and even death. To overcome such drawbacks, this technical note presents a simple, practical, and low cost method for the diameter reduction of single mode optical fibers by mechanical polishing, employing a small scale computer numerical control device and an ad hoc 3D-printed rod. The sensor probe obtained was tested using sucrose aqueous solutions with RIs between 1.333 and 1.394, measured in an Abbe refractometer. The results show a linear shift of the Bragg wavelength with respect to RI with a correlation of 0.928.

Induced Birefringence by Drop Cast in EFBG Ammonia Sensors

In this paper, an induced birefringence was observed on an ammonia sensor based on an etched fiber Bragg grating (EFBG) coated with an organic film. The film was prepared with a solution of the perylene derivative, along with the copolymer PCDTBT in chlorobenzene. The EFBG was coated by drop cast technique, and a split in the reflection band, characteristic of birefringence, was observed after deposition. The response of the two observed peaks as a function of time was modeled by a pair of exponentials that could represent two processes: adsorption followed by diffusion of the gas molecules in the microstructured film. Such phenomena alter the boundary conditions of the optical fiber propagating mode, which allows an indirect ammonia detection by monitoring the EFBG wavelength shift of the reflected peaks. The sensor was experimentally tested in a concentration range from 3 ppm to 41,700 ppm, and the calibrations curves were determined in a range from 27 ppm to 6960 ppm. The two observed peaks showed different sensitivities, which presents an intrinsic potential for multiparameter measurements. The split in the reflection band was hypothesized to be birefringence induced by the formation of an asymmetric film. This hypothesis was numerically evaluated and compared with the experimental results.

Performance of Etched Silica FBG for Simultaneous Strain Temperature Measurement

In this paper, we have proposed an etched silica Fiber Bragg Gratings (FBGs) based interrogation technique using an optical spectrum analyser (OSA). The efficiency of the proposed system has extensively been investigated for measuring the temperature and strain simultaneously with higher sensitivity and accuracy covering a larger measurement range. A Single mode-Multi mode-Single mode fiber (SMS) which acts as a bandpass filter is employed in the circuitry for an efficient and fast interrogation technique. We recorded a remarkable enhancement in sensitivity of 20.30 pm/°C and 2.89 pm/μɛ over the temperature and strain range of 25–225 °C and 50–2050 μɛ, respectively. These data were recorded with the strain resolution of ±10 μɛ whereas the resolution for the temperature is ±0.50 °C. The experimental results show the capability of the sensor for measuring the strain and temperature simultaneously with higher intrinsic sensitivity and resolution. The performance of the proposed sensor has been compared with various reported techniques.

Enhanced Optical Sensitivity of Polyvinyl Alcohol–Reduced Graphene Oxide Electrospun Nanofiber Coated Etched Fiber Bragg Grating Sensor for Detection of Myoglobin a Cardiac Biomarker

Etched fiber Bragg grating (eFBG) sensors have shown to be highly sensitive with the capability of giving accurate real‐time response to a variety of measurands such as pressure, gas, biomolecules, to name a few. These sensors have not shown their mettle as competitive products mainly due to nonreproducibility in results and inefficiency in upscaling for large‐scale production; the main reason being nonuniform and complicated coating procedures. Herein, the enhancement in refractive index (RI) sensitivity (≈4 times) obtained with electrospinning of polyvinyl alcohol–reduced graphene oxide (PVA–rGO) nanofibers onto eFBG sensor using a customized target and a unique sandwich arrangement is demonstrated. The enhancement in RI sensitivity has led to a lower detection limit and increased sensitivity and linear range for a case study using myoglobin (Mb), an early‐stage cardiac biomarker with high reproducible results (standard error ≤±2.3%). rGO embedded PVA nanofiber electrospun onto an eFBG sensor (PVA–rGO sensor) is the first of its kind and has significant importance in developing cost‐effective, label‐free, multianalyte, portable, real‐time, point‐of‐care (POC) kits at ambient conditions.

Axial force analysis using half-etched FBG sensor

Half etched fiber Bragg grating (HEFBG) is designed and studied by spectral properties under applied axial force. To design the HEFBG, a half-length of a given FBG is thinned down to 12μm diameter through the chemical corrosion with hydrofluoric acid. Under an applied axial force, the Bragg wavelengths due to etched and unetched parts of the HEFBG encounter different peak shifts and sensitivity. The peak-to-peak differences due to various axial forces are determined by analysing the spectral responses captured by an optical spectrum analyser (OSA). Theoretically and experimentally, it is observed that the peak-to-peak differences are a linear function of applied force. Using HEFBG as sensor probe, axial force sensitivity of 1.96 nm/N and resolution of 0.010 N are achieved over the range of applied force 0.20 N −2.50 N.

Highly sensitive and Rapid detection of mercury in water using functionalized etched fiber Bragg grating sensors

• CNC bolaamphiphile functionalized eFBG sensor for selective and rapid detection of mercury (Hg). • Thiol-Hg 2+ coordination interaction between CNC and Hg 2+ determined by both UV absorbance and Bragg wavelength shifts. • Low LOD (< WHO standard), linear dynamic range and good repeatability using low sample volumes and minimal instruments. • Promising results with real water sample prove. • eFBG sensor to be used as on-site, real time Hg 2+ probe. An effective optical method has been proposed using cysteine conjugated naphthalene diimide (CNC) bolaamphiphile functionalised etched Fiber Bragg grating (eFBG) sensor for selective and rapid detection of mercury (Hg 2+ ) in drinking water. The sensor responds with a Bragg wavelength shift (Δλ B ) to the thiol-Hg 2+ coordination interaction between CNC and Hg 2+ . The thiol-Hg 2+ interaction was initially studied by UV absorbance studies (bulk solutions) of CNC with increased concentrations of Hg 2+ (600 nM to 3 μM). The study displayed a linear relationship with the limit of detection (LOD) of 100 nM, which is below the world health organisation (WHO) standards for drinking water (22 nM). To enhance the LOD, the CNC was coated onto the eFBG sensor using two coating protocols (dip and spin coating) followed by Hg 2+ detection. The dip (spin) coated sensor displayed a dynamic-range from 1 pM to 1 μM (1 pM to 10 nM) and LOD of 1 pM. The sensor's repeatability (maximum error of 13.2 picometers) and specificity in the presence of other interfering metals like Pb 2+ , Cu 2+ , Na 2+ and Cd 2+ has been determined. The sensor can be developed into a highly sensitive, selective, portable, real-time, on-site Hg 2+ optical probe for drinking water.

A Study on MoS₂ Nanolayer Coated Etched Fiber Bragg Grating Strain Sensor

In this paper, we report on the comprehensive study on Molybdenum disulfide (MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) nanolayer coated etched Fiber Bragg Grating (eFBG) strain sensor. MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanolayer is coated using Physical Vapor Deposition (PVD) of Molybdenum (Mo) on eFBGs followed by sulfurization of the same in an inert atmosphere at 450° C. Such coating technique provides a direct control over the coating thickness of MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , thereby enabling a study based on the effect of nanolayer coating thickness on the intrinsic strain sensitivity as well as the power of the back reflected Bragg wavelength of eFBG in the 0.78eV spectral region. High uniformity of MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanolayer coating ensures consistent, repeatable and highly linear FBG strain sensors with a correlation coefficient of 0.988 in the range of 0 to 2500 με. A maximum intrinsic strain sensitivity of ~6.65 pm/με with a resolution of ~150 nε have been achieved with optimized MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> coated eFBG sensors. This kind of consistent, highly sensitive and linear strain sensors when incorporated with proper packaging schemes can be particularly useful for applications demanding high sensitivity of FBG sensors such detection of seismic vibrations, underwater acoustic signals, low amplitude accelerations, etc.