Fiber Optic Chemical Sensor Research Articles

Graphene oxide coated U-bent plastic optical fiber based chemical sensor for organic solvents

This study describes the development of a refractive index (RI) based fiber optic chemical sensor using a U-bent plastic optical fiber (BPOF) probe made of 0.5 mm polymethylmethacrylate (PMMA) core and optimum bend diameter of 1.4 mm coated with graphene oxide (GO) film. GO film on BPOF sensor surface significantly enhance the RI sensitivity of the sensor as well as its chemical resistance due to improved refractive index contrast and (PMMA) surface passivation by GO respectively. GO was chemisorbed to hexamethylenediamine (HMDA) functionalized BPOF probe surface by identifying the optimum GO concentration (100 μg/ml) and incubation time (24 h). An enhanced RI sensitivity of 9.42 ± 0.37 (ΔA845nm/ΔRIU) was achieved using GO coating of thickness 3.3 μm, which is 3.6 times higher than that of the bare BPOF probe. The RI sensitivities in presence of organic solvents including methanol, ethanol and isopropyl alcohol are found to be 12.75 ± 1.19, 9.97 ± 0.66 and 13.93 ± 0.92 (ΔA845nm/ΔRIU) respectively. GO film over BPOF was stable even after incubation of the probes in the alcohols over 12 h. In addition, GO-BPOF probes were able to tolerate acetone environment for a prolonged duration of 30 min as opposed to 10 min in case of the bare probes due to improved chemical resistance. Hence, the GO-BPOF could potentially be utilized as a sensitive RI sensor not only for aqueous solutions but also for reactive organic solvents such as alcohols and acetone which are known to damage the PMMA surface.

Exploring the Use of Native Spider Silk as an Optical Fiber for Chemical Sensing

A spider uses up to seven different types of silk, all having specific functions, as building material, weapon, and sensory organ to detect the presence of preys on its web. Recently, scientists have put under the limelight the extraordinary properties of this ancient material. Indeed, native silk, directly extracted from spiders, is a tough, biodegradable, and biocompatible thread used mainly for tissue engineering and textile applications. Blessed with outstanding optical properties, this protein strand can also be used as a bioresorbable optical fiber and is, moreover, intrinsically sensitive to chemical compounds. In this communication, the waveguiding properties of native dragline silk are assessed and a pioneering proof-of-concept experiment using pristine spider silk as an optical fiber to measure humidity content is demonstrated. The feasibility of using silk-based optical fiber chemical sensors is also discussed.

Phase Change Chalcogenide Materials for Optical Data Storage

Objective: To understand the structural and characteristic properties of phase change materials which are predominant for development of existing as well as future technologies. Crystallization kinetics and unlikeness between the amorphous and crystalline phases are the two main characterizations of phase change materials. Methods: This review demonstrates the different crystallization techniques in details. For re-writable DVD, the crystallization rate should be large enough to enable a high data rate at inflated temperature. Findings: Se-Te based chalcogenide alloys are frequently used in optical memory devices. But due to some drawbacks of these alloys, we have made an attempt to enhance their properties by addition of third element. Activation energy of crystallization (using Kissinger model) and rate of crystallization for ternary glassy alloys have been listed. It has been found that Ge is the favorable dopant for data storage applications because it has low activation energy of crystallization and high rate of crystallization. Applications: The chalcogenide fibers are used in fiber optic chemical sensor systems for remote detection and identification as well as detecting chemicals in mixtures. Keywords: Chalcogenide Glasses, Crystallization Techniques, Kissinger Model, Phase Change Materials, Rate of Crystallization

Spider silk thread as a fiber optic chemical sensor

Monitoring the properties of light transmitted through a thread of spider silk enables detection of trace amounts of chemical compounds.

Colorimetric fiber optic probe for measurement of chemical parameters in surface water

In this paper a novel fiber optic chemical sensor is proposed with possibility of measuring several chemical parameters using simple structured and low-cost colorimetric probe with high precision. Proposed sensor is based on user oriented and intuitive HSV color model. Concentrations of the orthophosphate, nitrite, sulfate, hexavalent chromium (Cr (VI)) and total chlorine obtained with laboratory analysis were compared with concentrations obtained with proposed sensor in order to demonstrate the effectiveness of the sensor. Relative differences in determined concentrations ranged from 2.31% for sulfate to 6.20% for total chlorine. Implemented sensor with its advantages such as low cost, simple use, reliability and small size, could be used for monitoring of water quality. Sensor is applicable for laboratory work, under controlled conditions, and could be used as a replacement for standard laboratory equipment as an effective, precise, repeatable and low-cost solution.

Numerical Analysis of Waveguide Coupling Between Photonic Crystal Fiber and Single-Mode Fiber

A new evanescent-field-based coupler that achieves high coupling efficiency between a single-mode fiber (SMF) and a photonic crystal fiber (PCF) is proposed. The coupling equations are presented and a numerical solution is obtained in this letter. Optimization of the refractive index, the effective radius of PCF, and the coupling length can enhance the coupling efficiency. It is shown that a maximum coupling ratio of 93% can be achieved for a coupling length of 1.72 mm for commercially available SMFs and PCFs. The proposed PCF-SMF fiber coupler opens a path for the development of unique modalities for fiber-optic chemical sensors where the light ingress and egress paths can be via SMF, but the light interaction with analytes of interest occurs in the PCF where enhanced evanescent interactions can be obtained at the multiple air holes.

Fiber-Optic Chemical Sensors and Fiber-Optic Bio-Sensors.

This review summarizes principles and current stage of development of fiber-optic chemical sensors (FOCS) and biosensors (FOBS). Fiber optic sensor (FOS) systems use the ability of optical fibers (OF) to guide the light in the spectral range from ultraviolet (UV) (180 nm) up to middle infrared (IR) (10 µm) and modulation of guided light by the parameters of the surrounding environment of the OF core. The introduction of OF in the sensor systems has brought advantages such as measurement in flammable and explosive environments, immunity to electrical noises, miniaturization, geometrical flexibility, measurement of small sample volumes, remote sensing in inaccessible sites or harsh environments and multi-sensing. The review comprises briefly the theory of OF elaborated for sensors, techniques of fabrications and analytical results reached with fiber-optic chemical and biological sensors.

Intensity Modulated Fiber Optic ChemicalSensor â Molar Volumes, Refractive Indices,Electronic Polarization, Molar Refractions ofBinary Liquids

Refractive indices and densities of binary mixtures like ethanol with benzene and methanol with benzene have been measured at room temperature (303K). From the values of the measured Refractive indices and densities, molar refractions (R), molar volumes (V), and electronic polarization (e) of the mixed solvents were calculated. Intensity modulated fibre optic chemical sensor probes are designed and used to sense the binary mixtures at different concentrations or mole fractions

A long period grating-based chemical sensor insensitive to the influence of interfering parameters

An optical fibre chemical sensor that is insensitive to interfering parameters including temperature and surrounding refractive index is described. The sensor is based upon a Mach-Zehnder interferometer formed by a pair of identical cascaded long period gratings (LPGs), with the entire device coated with a mesoporous coating of silica nanoparticles. A functional material is infused only into the coating over the section of optical fibre separating the LPGs. The transmission spectrum of the device consists of a channeled spectrum arising from interference of the core and cladding modes within the envelope of the LPG resonance band. Parameters such as temperature, strain and surrounding refractive perturb the entire device, causing the phase of the channeled spectrum and the central wavelength of the envelope shift at the same rate. Exposure of the device to the analyte of interest perturbs only the optical characteristics of the section of fibre into which the functional material was infused, thus influencing only the phase of the channeled spectrum. Measurement of the phase of the channeled spectrum relative to the central wavelength of the envelope allows the monitoring of the concentration of the analyte with no interference from other parameters.

Monitoring the cementitious materials subjected to sulfate attack with optical fiber excitation Raman spectroscopy

Formation of ettringite and gypsum from sulfate attack together with carbonation and chloride ingress have been considered as the most serious deterioration mechanisms of concrete structures. Although electrical resistance sensors and fiber optic chemical sensors could be used to monitor the latter two mechanisms on site, currently there is no system for monitoring the deterioration mechanisms of sulfate attack. In this paper, a preliminary study was carried out to investigate the feasibility of monitoring sulfate attack with optical fiber excitation Raman spectroscopy through characterizing the ettringite and gypsum formed in deteriorated cementitious materials under an optical fiber excitation + objective collection configuration. Bench-mounted Raman spectroscopy analysis was also conducted to validate the spectrum obtained from the fiber-objective configuration. The results showed that the expected Raman bands of ettringite and gypsum in the sulfate-attacked cement paste can be clearly identified by the optical fiber excitation Raman spectrometer and are in good agreement with those identified from bench-mounted Raman spectrometer. Therefore, based on these preliminary results, it is considered that there is a good potential for developing an optical fiber-based Raman system to monitor the deterioration mechanisms of concrete subjected to sulfate attack in the future.

Optical fibre long period grating with a nanoporous coating formed from silica nanoparticles for ammonia sensing in water

A fibre optic long period grating (LPG) with an nano-assembled mesoporous coating of alternate layers of poly(diallyldimethylammonium chloride) (PDDA) and SiO2 nanospheres was used for the development of a highly sensitive fibre-optic chemical sensor. Sensor fabrication involves a 2-stage process: firstly, the deposition of the base mesoporous thin film (PDDA/SiO2) over an LPG written in the optical fibre using a layer-by layer technique, followed by the infusion of a functional material into the porous film. The refractive index of the base mesoporous coating, determined at a wavelength of 633nm using ellipsometry, was found to be 1.2. The infusion of the functional material into the coating resulted in a significant change in the RI of the coating, producing a dramatic change in the transmission spectrum of the LPG. The sensing mechanism exploited is based upon chemically induced desorption of the functional material from the mesoporous coating. The sensing of ammonia in aqueous solution was chosen as an example to demonstrate the sensing principle of the LPG sensor. The operation of the sensor was characterized using two functional materials, tetrakis-(4-sulfophenyl)porphine (TSPP) and polyacrylic acid (PAA). The device showed high sensitivity to ammonia with a response time less than 100s and a limit of detection of 140ppb when the TSPP infused (PDDA/SiO2) film was employed as a sensitive element.

In Situ Trace Analysis of Oil in Water with Mid-Infrared Fiberoptic Chemical Sensors

The determination of trace amounts of oil in water facilitates the forensic analysis on the presence and origin of oil in the aqueous environment. To this end, the present study focuses on direct sensing schemes for quantifying trace amounts of oil in water using mid-infrared (MIR) evanescent field absorption spectroscopy via fiberoptic chemical sensors. MIR transparent silver halide fibers were utilized as optical transducer for interrogating oil-in-water emulsions via the evanescent field emanating from the waveguide surface, and penetrating the surrounding aqueous environment by a couple of micrometers. Unmodified fibers and fibers surface-modified with grafted epoxidized polybutadiene layers enabled the direct detection of crude oil in a deionized water matrix at the ppm level to ppb concentration level, respectively. Thus, direct chemical sensing of crude oil IR signatures without any sample preparation as low as 46 ppb was achieved with a response time of a few seconds.

Intrinsic Fluorescence-Based Optical Fiber Sensor for Cocaine Using a Molecularly Imprinted Polymer as the Recognition Element

A fiber-optic chemical sensor for the detection of cocaine has been developed, based on a molecularly imprinted polymer (MIP) containing a fluorescein moiety as the signalling group. The fluorescent MIP was formed and covalently attached to the distal end of an optical fiber. The sensor exhibited an increase in fluorescence intensity in response to cocaine in the concentration range of 0 - 500 μM in aqueous acetonitrile mixtures with good reproducibility over one month. Selectivity for cocaine over others drugs has also been demonstrated.

Design of multiplexed fiber optic chemical sensing system using clad-removable optical fibers

To prevent possible threats to public safety and economic loss from chemical leakage accidents, novel chemical sensing techniques for regular monitoring and leakage detection have been developed for various fields. We propose a fiber optic liquid chemical sensor (FOCS) system using specialty optical fibers and an optical time domain reflectometer (OTDR), and is based on the leaky wave mode sensing principle. OTDR enables simple multiplexing where individual sensor nodes along the fiber length could be interrogated by a common OTDR. The sensor node in the optical fiber is prepared by removing the desired length of a protective layer using mechanical stripping and chemical etching techniques. A novel laser stripping technique with superior capability to fabricate quasi-distributed dense sensor nodes is devised as well. The FOCS system is further analyzed to characterize the sensor response behavior in relation to the sensor node length and possible environmental and chemical temperature effect. Under the condition satisfying the leaky wave mode principle and within the minimum acceptable refractive index (RI) range by the system, this FOCS system could monitor numerous liquid chemicals with variable refractive indices and has been tested with positive results. In addition, the system shows the possibility for multi-point detection and is further expanded into a hybrid technique capable of estimating the refractive index range of the detected chemical.

Polypyrrole thin film fiber optic chemical sensor for detection of VOCs

A fiber optic reflectance sensor (FORS) using Polypyrrole (PPy) conducting polymer to detect volatile organic compounds (VOCs) is demonstrated. The conventional interfacial polymerization method is used to synthesize a sensitive polypyrrole membrane, which shows relatively low roughness and high reflectivity. In general the changes in electrical properties of conductive polymers are explored in sensing applications, however their optical properties have been less explored. In the present study, we evaluate the optical properties of PPy and transfer on the end face of polymer optical fiber (POF) for the detection of VOCs. The change in the reflected optical signal from PPy upon interaction with the VOCs is systematically evaluated. The fabricated PPy FORS shows the excellent sensitivity to the VOCs under test with the detection limit up to 1 ppm.

Fiber-optic chemical sensor of amine-type compounds

A scheme of a fiber chemical sensor of amine-type compounds has been implemented. The sensor includes a film nanostructure deposited on the end face of an optical fiber 600 μm in diameter. The film consists of luminescent silica nanoparticles modified by functional pyrylocyanine dye, silver nanoparticles, and a photonic crystal opal film. An additional coating of the sensor film from above by a porous selective mirror, such as a photonic crystal, and introduction of silver nanoparticles 5–7 nm in diameter into it make it possible to increase the sensor sensitivity by an order of magnitude.

Fiber optic chemical sensor using fiber coupler probe based on intensity modulation for alcohol detection

AbstractA simple intensity modulation based displacement sensor using fiber optic coupler probe is proposed and demonstrated for sensing the concentration of alcohol solution. The intensity of light reduces almost linearly with the displacement and the sensitivity of the curve is dependent on the concentration of the alcohol solution. For a concentration change of methanol from 0 to 35 % in distilled water, the sensitivity is observed to be increased linearly with the concentration due to the reduction of the refractive index of the solution. The highest sensitivity is obtained at around 0.00002mV/(%). The stability, high sensitivity and simplicity of the sensor make it suitable for chemical, pharmaceutical, biomedical and process control sensing applications. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26124

Fiber-optic sensor for butylamine

Fiber-optic chemical sensor for butylamine was realized. The sensor includes a thin layer nanostructure on the end of optical fiber with a diameter of 600 μm. It consists of luminescent silica nanoparticles modified with pyrylocyanine dye, silver nanoparticles and photonic-crystal film. The sensitivity of the sensor is increased tenfold due to an additional covering of the film with photonic crystal as a porous mirror and the injection of silver nanoparticles with a diameter of 5–7 nm.

Fiber-optic sensor applications in civil and geotechnical engineering

Different types of fiber-optic sensors based on glass or polymeric fibers are used to evaluate material behavior or to monitor the integrity and long-term stability of load-bearing structure components. Fiber-optic sensors have been established as a new and innovative measurement technology in very different fields, such as material science, civil engineering, light-weight structures, geotechnical areas as well as chemical and high-voltage substations. Very often, mechanical quantities such as deformation, strain or vibration are requested. However, measurement of chemical quantities in materials and structure components, such as pH value in steel reinforced concrete members also provides information about the integrity of concrete structures. A special fiber-optic chemical sensor for monitoring the alkaline state (pH value) of the cementitious matrix in steel-reinforced concrete structures with the purpose of early detection of corrosion-initiating factors is described. The paper presents the use of several fiber-optic sensor technologies in engineering. One example concerns the use of highly resolving concrete-embeddable fiber Fabry-Perot acoustic emission (AE) sensors for the assessment of the bearing behaviour of large concrete piles in existing foundations or during and after its installation. Another example concerns fiber Bragg grating (FBG) sensors attached to anchor steels (micro piles) to measure the strain distribution in loaded soil anchors. Polymer optical fibers (POF) can be — because of their high elasticity and high ultimate strain — well integrated into textiles to monitor their deformation behaviour. Such “intelligent” textiles are capable of monitoring displacement of soil or slopes, critical mechanical deformation in geotechnical structures (dikes, dams, and embankments) as well as in masonry structures during and after earthquakes.

Preliminary Development and Evaluation of Fiber-Optic Chemical Sensors

Conventional methods of measuring carbonation and chloride ingress exist, but they are either inaccurate, expensive, or involve destructive testing. In seeking new solutions to this problem, the potential to use novel fiber-optic chemical sensors developed specifically for this application and designed to monitor chemical changes in cementitious materials, in situ and nondestructively, was explored in this study. Three types of fiber-optic sensors were thus constructed, tested, and evaluated, viz a temperature sensor, a pH sensor, and chloride sensors. The temperature sensor was based on the fluorescence decay of temperature-dependent materials, whereas the pH and chloride sensors were based on sol-gel technology, with pH and chloride sensitive indicators impregnated in the sol-gels. All the sensors were tested in situ, and subsequently, the temperature and the pH sensors were embedded in mortar and tested. It was found that both the temperature sensor and the pH sensor could function correctly for over 18 months after placement, but there was an issue with alignment of the sensor each time it was reconnected to the hardware. However, the laboratory tests showed that the chloride sensor was not reversible, and therefore further refinement was considered to be necessary before it could be used in situ in environments where the chloride content was known, from other measurements, to decrease. Research is ongoing to refine the sensor performance and expands the in situ testing program. The sensors themselves are inexpensive to fabricate, but the sensing hardware used in this work is costly because of its high versatility.