Evanescent Wave Fiber Optic Sensor Research Articles

Humidity sensing by tailoring light absorption of SiO2/bromophenol blue (BPB) thin film on optical fiber

The fabrication of an evanescent wave fiber optic humidity sensor based on bromophenol blue (BPB) doped SiO2 thin film was demonstrated, modulating in light intensity. The sensing film was coated on a fiber core via a single-step dip coating method, followed by sol-gel processing of the precursor. A good exponential relationship was established between output light intensity and relative humidity. The sensor exhibited a high sensitivity and fast response and recovery, as well as low hysteresis, good stability and repeatability. Adsorption of ambient water triggered a ring-opening reaction of BPB, which enhanced light absorption of the sensing film significantly and affected the transmission of the evanescent wave.

Sensitivity Enhancement in U-Shaped Evanescent Wave Fiber Sensor

In this paper, sensitivity enhancement in U-shaped evanescent wave fiber optic sensor has been reported. The overall effect of surface roughness, material deformation and probe geometry on the sensitivity of U-shaped fiber optic evanescent wave fiber optic sensor has been investigated. The experimental results of the developed sensors demonstrate that rough surfaced fiber probe has ~7% enhancement in sensitivity as compared with smooth fiber probes.

Recent Progress in Functional-Nucleic-Acid-Based Fluorescent Fiber-Optic Evanescent Wave Biosensors.

Biosensors capable of onsite and continuous detection of environmental and food pollutants and biomarkers are highly desired, but only a few sensing platforms meet the "2-SAR" requirements (sensitivity, specificity, affordability, automation, rapidity, and reusability). A fiber optic evanescent wave (FOEW) sensor is an attractive type of portable device that has the advantages of high sensitivity, low cost, good reusability, and long-term stability. By utilizing functional nucleic acids (FNAs) such as aptamers, DNAzymes, and rational designed nucleic acid probes as specific recognition ligands, the FOEW sensor has been demonstrated to be a general sensing platform for the onsite and continuous detection of various targets ranging from small molecules and heavy metal ions to proteins, nucleic acids, and pathogens. In this review, we cover the progress of the fluorescent FNA-based FOEW biosensor since its first report in 1995. We focus on the chemical modification of the optical fiber and the sensing mechanisms for the five above-mentioned types of targets. The challenges and prospects on the isolation of high-quality aptamers, reagent-free detection, long-term stability under application conditions, and high throughput are also included in this review to highlight the future trends for the development of FOEW biosensors capable of onsite and continuous detection.

Fiber Optic Monitoring of Composite Lithium Iron Phosphate Cathodes in Pouch Cell Batteries

Developing techniques for real-time monitoring of the complex and dynamic environment in lithium-ion batteries is crucial for optimal use of the cells and to develop the next generation of batteries. In this work, we demonstrate the use of fiber optic evanescent wave (FOEW) sensors for monitoring lithium iron phosphate (LFP) composite cathodes in pouch cells. The fiber optic sensors were placed on top of the LFP electrodes, and the pouch cells were found to cycle well with significantly improved electrochemical performance compared to fully embedded fibers in Swagelok cells. Galvanostatic, voltammetric, and pulsed current techniques demonstrated that the optical response correlated well with the capacity, and a clear difference in sensor response was seen when the sensors were placed at the surface of composite electrodes compared to fibers embedded in the cathode. The optical response from LFP at different rates was also investigated, but no apparent influence on intensity output was found even though polarization was observed in the voltage profiles at higher currents. It was also demonstrated that the electrolyte itself functioned as a fiber cladding and that the salt concentration in the electrolyte did not influence the optical signal. In addition, given the short penetration depth of the evanescent waves, the sensor response is most likely dominated by the surface conditions of electrode particles near the sensing region. These findings provide further insight into the application and performance of FOEW sensors integrated into batteries, as well as the possibility of developing low-cost fiber optic sensors for battery monitoring under working conditions.

Nanoscale Affinity Double Layer Overcomes the Poor Antimatrix Interference Capability of Aptamers.

Poor antimatrix interference capability of aptamers is one of the major obstacles preventing their wide applications for real-sample detections. Here, we devise a multiple-function interface, denoted as a nanoscale affinity double layer (NADL), to overcome this bottleneck via in situ simultaneous target enrichment, purification, and detection. The NADL consists of an upper aptamer layer for target purification and sensing and a lower nanoscale solid-phase microextraction (SPME) layer for sample enrichment. The targets flowing through the NADL-functionalized surface are instantly million-fold enriched and purified by the sequential extraction of aptamer and SPME. The formation of the aptamer-target complex is greatly enhanced, enabling ultrasensitive detection of targets with minimized interference from the matrix. Taking the fiber-optic evanescent wave sensor as an example, we demonstrated the feasibility and generality of the NADL. The unprecedented detection of limits of 800, 4.8, 40, and 0.14 fM were, respectively, achieved for three representative small-molecule targets with distinct hydrophobicity (kanamycin A, sulfadimethoxine, and di-(2-ethylhexyl) phthalate) and protein target (human serum albumin), corresponding to 2500 to 3 × 108-fold improvement compared to the sensors without the NADL. Our sensors also showed exceptionally high target specificity (>1000) and tunable dynamic ranges simply by manipulating the SPME layer. With these features comes the ability to directly detect targets in diluted environmental, food, and biological samples at concentrations all well below the tolerance limits.

Fibre Optic Sensor for Characterisation of Lithium-Ion Batteries.

The interaction between a fibre optic evanescent wave sensor and the positive electrode material, lithium iron phosphate, in a battery cell is presented. The optical–electrochemical combination was investigated in a reflection‐based and a transmission‐based configuration, both leading to comparable results. Both constant current cycling and cyclic voltammetry were employed to link the optical response to the charge and discharge of the battery cells, and the results demonstrated that the optical signal changed consistently with lithium ion insertion and extraction. More precisely, cyclic voltammetry showed that the intensity increased when iron was oxidised during charge and then decreased as iron was reduced during discharge. Cyclic voltammetry also revealed that the optical signal remained unchanged when essentially no oxidation or reduction of the electrode material took place. This shows that optical fibre sensors may be used as a way of monitoring state of charge and electrode properties under dynamic conditions.

Graphite lithiation and capacity fade monitoring of lithium ion batteries using optical fibers

Abstract Increasing the efficiency and safety of battery management systems may require internal monitoring of lithium ion batteries. In this work, we present an analysis of the interaction between fiber-optic evanescent wave sensors (FOEWS) and graphite particles within a lithium ion battery over multiple cycles. Through slow charging and long rest periods, the FOEWS signal has shown sensitivity to lithium concentration at the surface of graphite particles by demonstrating a response to the slow diffusion of lithium ions within graphite particles during rest periods (i.e. relaxation of the electrode). The slope of the FOEWS signal during a full charge is found to exhibit three distinct peaks that occur within lithiated graphite's stage transitions zones IV, III and II. Deviation from the observed three peak trend correlates with significant battery capacity fade and thus indicate the sensors ability to detect capacity fade in real-time. During experiments, significant deviations in the slope during charging occurred at about ~5% SOC and minor disturbances to the slope were observed at ~80% SOC, which supports limiting the depth of charge and discharge to avoid accelerated capacity fade. These results deepen our understanding of the FOEWS's interaction with lithium ion batteries and supports the development of algorithms that optimize the control and monitoring of graphite lithiation with the aim of achieving safer operation as well as maximizing capacity and battery life.

Hybrid U-Shaped-Microbend SMF Evanescent Wave Sensor for River Water Quality Assessment: A Preliminary Study

A hybrid U-shaped-microbend fiber optic evanescent wave sensor was developed by combining two types of bending structures on the optical communication single mode optical fiber (SMF28). To study the effect optical microbending on the output power, corrugated plates consisted of cylindrical structured surface with various distance between the glass rods of 6 cm, 12 cm and 18 cm were constructed. The macrobending effect was introduced by bending the SMF into two shapes, namely U-shaped and Sshaped. The bare SMF with various bending designs were immersed into numerous water sources from Sg. Simin, Sg. Batang Benar and Sg. Klang. The output demonstrated that Sg. Simin was the most polluted river, followed by Sg. Klang and Sg. Batang Benar using U-shaped microbend SMF with distance between glass rod of 6cm and 1310 nm laser source. This result showed an excellent agreement with water quality index (WQI) data released by the Department of Environment (DOE), Malaysia. Maximum optical output power was obtained by using Sg. Simin’s water sample due to better light absorption from the evanescent waves by the pollutant particles, that avoided light leakage in comparison with less polluted water sources. The optimum sensing performance was successfully resulted by using U-shaped SMF due to its durability and uniform evanescent waves radiated from the cladding. In conclusion, the hybrid U-shaped-microbend SMF sensor based on evanescent waves propagation portrays an excellent potential to detect water pollution by monitoring the presence of pollutants around the fiber.

Passive Fiber Optic Evanescent Wave Sensor for the Measurement of Refractive Index at Various Temperatures Using a Tunable Light Source

The study of refractive index of liquids over a range of 10oC to 60oC shows very interesting results to design and develop a highly sensitive passive fiber optic sensor based on a U-shaped glass probe. The depth of penetration of light that escaping from the core of the fiber into the cladding plays a crucial role in the development of a highly sensitive fiber optic evanescent wave sensor. The depth of penetration of an optical fiber striped off its cladding is directly related to the wavelength of the light, the index of refraction of the surrounding medium, the angle of incidence of light, the bending radius and thickness of the U-shaped probe. In the design of the sensor a U-shaped glass probe is used to replace the core of the fiber in the region of sensing, the diameter of which is same as that of the cores of a pair of insensitive fibers which in-turn connected to a tunable light source and an optical detector. The sensor is highly reliable, robust and easy to configure using multimode PCS fibers and the source operating at the wavelengths of 630nm, 660nm, 820nm and 850nm.

Fiber optic evanescent wave absorption-based sensors: A detailed review of advancements in the last decade (2007–18)

The review article presents the advancements occurred in the area of fiber optic evanescent wave (FOEW) sensors in the past decade (2007–2018). The fundamental working principle of FOEW sensor is discussed in detail followed by the rigorous discussion on the different geometries of FOEW sensor probes such as straight, tapered, U-shaped, and d-shaped etc. The importance of infrared (IR) glasses and two-dimensional (2D) materials in the development of FOEW sensors is discussed. The developments in the theoretical modeling strategies have been discussed. The review is concluded with a mention of future scope in the area of FOEW sensors.

Enhancement in performance of an evanescent wave fiber optic sensor in the near-infrared region by graphene’s chemical potential

An intensity interrogation-based fiber optic evanescent wave sensor with graphene monolayer is simulated and analyzed in the near-infrared spectral region. Chalcogenide glasses are considered as fiber’s core and clad materials. Dispersion relations of normal and malignant human liver tissues are considered for analysis. The effect of graphene’s chemical potential (μ) on sensor’s performance is examined, which is evaluated in terms of sensitivity and resolution. The analysis of simulation results indicates that if μ is set around 0.45 eV at 1550-nm light wavelength (λ), the sensitivity achieved is nearly 47 mW/RIU (real index) and 280 mW/RIU (imaginary index), and the resolution achieved is of the order of 10−9 RIU (real index) and 10-10 RIU (imaginary index). Even further improvement in the sensing performance can be achieved around μ = 0.6 eV. The analysis shows that it is preferable to use p-polarized light as it provides significantly better values of sensitivity and resolution than s-polarized light. In addition to smaller photodamage and reduced Rayleigh scattering (due to being operated in NIR), the proposed fiber optic sensor probe has the capability to provide considerably superior resolution than existing fiber optic sensors based on different techniques.

Fiber Optic Sensor’s Performance Enhancement by Tuning NIR Wavelength, Polarization, and 2D Material

Fiber optic evanescent wave sensor consisting of chalcogenide core, silica clad, and 2D material (graphene and MoS2) monolayer is simulated and analyzed in near infrared (NIR) aiming at highly sensitive and reliable detection of malignancies in human liver tissues. Dispersion relations of normal and malignant human liver tissues are considered. The sensor’s performance is examined in terms of sensitivity and resolution. The analysis indicates that using MoS2 as 2D material provides enhanced (nearly two-fold) performance compared with graphene. At 1200-nm wavelength, the sensitivity achieved is nearly 93.7 mW/RIU (real index) and 548.30 mW/RIU (imaginary index) whereas resolution achievable is of the order of 10−9 RIU (real index) and 10−10 RIU (imaginary index). Longer NIR wavelength should be used and p-polarization provides significantly better performance compared with s-polarization. With lesser photodamage and reduced Rayleigh scattering (due to being operated in NIR), the proposed sensor probe also has the ability to deliver considerably finer resolution than the current lot of fiber optic sensors based on different techniques. The limitations of the proposed sensor model are also discussed.

Graphene based chalcogenide fiber-optic evanescent wave sensor for detection of hemoglobin in human blood

Abstract Fiber optic evanescent wave sensor with graphene as an absorption-enhancing layer to measure hemoglobin concentration in human blood is proposed. Previous modal functions and experimental results describing the variation of optical constants of human blood with different hemoglobin concentrations in the near-infrared spectral region are considered for sensor design simulation. The sensor’s performance is closely analyzed in terms of its absorption coefficient, sensitivity, and detection limit. It is found that the proposed sensor should be operated at longer light wavelength to get more enhanced sensitivity and smaller detection limit. At 1000 nm wavelength, a detection limit of 18 μg/dL and sensitivity of 6.71 × 10−4 per g/dL is achievable with the proposed sensor. The sensitivity is found to be better for larger hemoglobin concentrations. The results are correlated with the evanescent wave penetration depth.

Development of Embedded Fiber-Optic Evanescent Wave Sensors for Optical Characterization of Graphite Anodes in Lithium-Ion Batteries.

The development, fabrication, and embedment of fiber-optic evanescent wave sensors (FOEWSs) to monitor the state of charge (SOC) and the state of health (SOH) of lithium-ion batteries (LIBs) are presented. Etching of FOEWSs is performed using a solution of 40 wt % ammonium fluoride (NH4F) and 49 wt % hydrofluoric acid (HF) (6:1), which is found to be superior to an etching solution containing just 49 wt % HF. FOEWSs were characterized using glycerol and found to have the highest sensitivity in a lithium-ion battery when they lose 92% of their transmittance in the presence of glycerol on their sensing region. The physical effect that the FOEWS has on the graphite anode is also investigated and is found to be much more significant in Swagelok cells compared to that in in-house-fabricated pouch cells, mainly due to pressure variation. The FOEWS was found to be most sensitive to the changes in the LIB when it was completely embedded using a slurry of graphite anode material within a pouch cell. The optimized fabrication process of the embedded FOEWS demonstrates the potential of using such sensors commercially for real-time monitoring of the SOC and SOH of LIBs while in operation.

Three-layer-structure polymer optical fiber with a rough inter-layer surface as a highly sensitive evanescent wave sensor

We present a high-sensitivity and high-accuracy D-shaped polymer fiber-optic evanescent wave (FOEW) sensor with a three-layer structure (i.e., bottom, inter-, and surface layers) and a rough inter-layer surface in the sensing region. The surface layer is made of dilute Canada balsam in xylene, and the longitudinal section is coated with light-absorbing (LA) film. To obtain the maximum sensitivity and accuracy, the morphologies of the inter-layer and surface layer are determined. The effects of coating thickness and the refractive index of the surface layer and LA film on the performance of FOEW sensors are investigated both theoretically and experimentally. The sensitivity, accuracy and repeatability of the sensors are evaluated using glucose solutions; the response of the sensors, which are self-assembled from the polycation (tris[2-(4-phenyldiazenyl) phenylaminoethoxy] cyclotriveratrylene (TPC) plus poly dimethyl diallyl ammonium chloride (PDDAC)) and polyanion (TPC plus polyacrylic acid (PAA)), to Hg(II) in aqueous solutions is examined. The results highlighted the high sensitivity of the FOEW sensor with a three-layer structure and appropriate roughness of the inter-layer surface, which showed a 6.5-fold improvement in the detection of the target Hg(II) ions compared to the conventional FOEW sensor with a core-cladding structure, and the novel sensor was validated with a lower limit of detection of 0.1mgL−1.

Low-cost wavelength-selective evanescent fiber optic temperature and refractive index sensor

We report here a low-cost evanescent field wave fiber optic temperature sensor. The amount of rays guided along the fiber probe is the result of the absorption of evanescent waves produced at the core-cladding interface. We systematically investigate the wavelength dependence of this sensor during the measurement of the temperature. The degree of variation with respect to the temperature is also determined by alteration of measuring liquid. We observe an enhanced responsivity of the fiber sensor towards a higher wavelength side. The sensor set-up offers simultaneous detection of refractive indices when correlated with temperature variation. All the results reported here bear a good repeatability.

High-sensitivity four-layer polymer fiber-optic evanescent wave sensor

We present a novel four-layer structure consisting of bottom, second, third, and surface layers in the sensing region, for a D-shaped step-index fiber-optic evanescent wave (FOEW) sensor. To reduce the background noise, the surface of the longitudinal section in the D-shaped region is coated with a light-absorbing film. We check the morphologies of the second and surface layers, examine the refractive indices (RIs) of the third and surface layers, and analyze the composition of the surface layer. We also investigate the effects of the thicknesses and RIs of the third and surface layers and the LA film on the light transmission and sensitivity of the FOEW sensors. The results highlight the very good sensitivity of the proposed FOEW sensor with a four-layer structure, which reached −0.077 (μg/l)−1 in the detection of the target antibody; the sensitivity of the novel FOEW sensor was 7.60 and 1.52 times better than that of a conventional sensor with a core–cladding structure and an FOEW sensor with a three-layer structure doped with GeO2. The applications of this high-sensitivity FOEW sensor can be extended to biodefense, disease diagnosis, and biomedical and biochemical analysis.

A high-sensitivity fiber-optic evanescent wave sensor with a three-layer structure composed of Canada balsam doped with GeO2

In this paper, we present a high-sensitivity polymer fiber-optic evanescent wave (FOEW) sensor with a three-layer structure that includes bottom, inter-, and surface layers in the sensing region. The bottom layer and inter-layer are POFs composed of standard cladding and the core of the plastic optical fiber, and the surface layer is made of dilute Canada balsam in xylene doped with GeO2. We examine the morphology of the doped GeO2, the refractive index and composition of the surface layer and the surface luminous properties of the sensing region. We investigate the effects of the content and morphology of the GeO2 particles on the sensitivity of the FOEW sensors by using glucose solutions. In addition, we examine the response of sensors incubated with staphylococcal protein A plus mouse IgG isotype to goat anti-mouse IgG solutions. Results indicate very good sensitivity of the three-layer FOEW sensor, which showed a 3.91-fold improvement in the detection of the target antibody relative to a conventional sensor with a core-cladding structure, and the novel sensor showed a lower limit of detection of 0.2ng/l and a response time around 320s. The application of this high-sensitivity FOEW sensor can be extended to biodefense, disease diagnosis, biomedical and biochemical analysis.

Temperature-independent polymer optical fiber evanescent wave sensor.

Although the numerous advantages of polymer optical fibers have been exploited in the fields of sensors and telecommunications, such fibers still experience a critical problem: the temperature dependency. Therefore, we explored the temperature-independent operation of a polymer fiber-optic evanescent wave sensor immersed in distilled water. We investigated variations in the surface morphology, deformation trajectory, refractive index, and weight of the fiber-sensing region with varying water temperature. We also examined the spectral transmission and transmitted light intensity of fibers subjected to a heating-cooling treatment. We observed that the light-transmission modes and sensitivity of the sensor were affected by changes in the surface morphology, diameter, and refractive index of the sensing region caused by changes in temperature. The transmitted light intensity of the sensor was maintained at a constant level after five cycles of the heating-cooling treatment, after which the fibers exhibited a smooth surface, low refractive index, and large fiber diameter. Consequently, we utilized the heating-cooling-treated fiber to realize a temperature-independent, U-shaped polymer fiber-optic evanescent wave sensor. The temperature independence was evaluated using glucose solutions in the range of 10 to 70 °C. The fabricated sensor showed significant temperature independence and high degree of consistency in measuring solutions.

A molecularly imprinted polymer-based evanescent wave fiber optic sensor for the detection of basic red 9 dye

A cheap and robust method for the detection and quantification of textile dyes is the use of biomimetic sensors with optical transduction, employing a molecularly imprinted polymer (MIP) as the recognition element. This paper presents the optimization of a MIP for the dye, basic red 9 (BR9) and the immobilization of these polymers on a disposable 4-cm long polystyrene optical waveguide for the development of an evanescent wave fiber optic sensor aimed at the determination and quantification of this dye in different matrices and industrial effluents. MIPs were synthesized using 2-acrylamido-2-methyl-1-propanesulfonic acid and ethylene glycol dimethacrylate, as functional monomer and cross-linker, respectively. The polymer was then immobilized on the waveguide by dip-coating the fiber in the polymer suspension. The sensing element was interrogated with a fiber-coupled spectrophotometer. BR9 could be detected in the low μM range, thus making it a promising device for determining this compound in textile effluents.