Showing papers on "Fiber optic sensor published in 2000"
1,603 citations
TL;DR: This work presents an overview of progress and developments in the field of fiber optic sensor technology, highlighting the major issues underpinning recent research and illustrating a number of important applications and key areas of effective Fiber optic sensor development.
Abstract: This work presents an overview of progress and developments in the field of fiber optic sensor technology, highlighting the major issues underpinning recent research and illustrating a number of important applications and key areas of effective fiber optic sensor development.
823 citations
TL;DR: An optical fiber humidity sensor (OFHS) was fabricated using a hydrophilic gel (agarose) deposited on the thinner zone of a biconically tapered single-mode optical fiber as discussed by the authors.
Abstract: An optical fiber humidity sensor (OFHS) has been fabricated using a hydrophilic gel (agarose) deposited on the thinner zone of a biconically tapered single-mode optical fiber. A variation of up to 6.5 dB of the transmitted optical power was obtained with relative humidity (RH) changes between 30% and 80%. Furthermore, the sensor shows an invariant behavior with time. This inexpensive material showed a good reproducibility with low hysteresis and its use with tapered optical fiber makes it useful for industrial and environmental applications.
263 citations
TL;DR: It is shown that single-element arrays permit the detection of low-level nitroaromatic compound vapors because of sensor-to-sensor reproducibility and signal averaging.
Abstract: In this paper, we report on the preparation of novel cross-reactive optical microsensors for high-speed detection of low-level explosives and explosives-like vapors. Porous silica microspheres with an incorporated environmentally sensitive fluorescent dye are employed in high-density sensor arrays to monitor fluorescence changes during nitroaromatic compound (NAC) vapor exposure. The porous silica-based sensor materials have good adsorption characteristics, high surface areas, and surface functionality to help maximize analyte-dye interactions. These interactions occur immediately upon vapor exposure, i.e., in less than 200 ms and are monitored with a high-speed charge-coupled device camera to produce characteristic and reproducible vapor response profiles for individual sensors within an array. Employing thousands of identical microsensors permits sensor responses to be combined, which significantly reduces sensor noise and enhances detection limits. Normalized response profiles for 1,3-dinitrobenzene (1,3-DNB) are independent of analyte concentration, analyte exposure time, or sensor age for an array of one sensor type. Explosives-like NACs such as 2,4-dinitrotoluene and DNB are detected at low part-per-billion levels in seconds. Sensor-analyte profiles of some sensor types are more sensitive to low-level NAC vapor even when in a higher organic vapor background. We show that single-element arrays permit the detection of low-level nitroaromatic compound vapors because of sensor-to-sensor reproducibility and signal averaging.
194 citations
TL;DR: In this paper, a new optical fiber hydrogen sensor has been developed, which utilizes the absorption change of the evanescent field in the clad region to measure the spatial distribution along the fiber line, unlike the traditional hydrogen sensors that measure the concentration of a certain spatial point.
Abstract: A new optical-fiber hydrogen sensor has been developed. The sensor utilizes the absorption change of the evanescent field in the clad region. The platinum- or palladium-supported tungsten oxide was used as sensing media. Two different approaches were adopted for the fiber fabrication. One used Pd/WO3 containing silicone resin as the clad. The other utilized the sol–gel process to form a thin Pd/WO3 clad. In the presence of hydrogen, strong evanescent-wave absorption was observed as a result of the formation of tungsten bronze. The sensor sensitively and immediately responded to hydrogen. It was found that the characteristics of the sensor were easily controlled by the amount of catalysts. The sensor developed in this study has potential to measure the spatial distribution along the fiber line, unlike the traditional hydrogen sensors that measure the concentration of a certain spatial point.
187 citations
TL;DR: In this article, an effective method of realizing optical bend sensing based on the measurement of bending-curvature encoded resonance mode splitting of long-period fiber grating was proposed.
Abstract: We report an effective new method of realizing optical bend sensing based on the measurement of bending-curvature encoded resonance mode splitting of long-period fiber grating. The bending induced mode splitting exhibits a near-linear response and the bending sensitivity achieved by this method is nearly four times higher than the previously reported wavelength shift detection method. The evolution of the transmission loss under bending appears dependent on the initial mode coupling strength.
181 citations
TL;DR: In this paper, light is coupled from the guided mode along one tapered optical fiber into the whispering gallery modes around the circumference of another by tracking, at different points along it, the wavelengths at which these modes exist.
Abstract: Light is coupled from the guided mode along one tapered optical fiber into the whispering gallery modes around the circumference of another. Small diameter variations in the second fiber are measured by tracking, at different points along it, the wavelengths at which these modes exist. The measurement does not require any optical alignment, and its resolution can be 1 part in 10 000 or better.
151 citations
Patent•
01 Sep 2000
TL;DR: In this paper, the authors proposed a system for underground acoustic signals from an acoustic source, which includes a plurality of laser sources, each emitting light at different frequencies, and a number of optical sensors, receiving and altering the light in response to acoustic waves.
Abstract: A system for sensing subterranean acoustic waves emitted from an acoustic source includes a plurality of laser sources, each emitting light at different frequencies; a plurality of subterranean optical sensors, receiving and altering the light in response to acoustic waves; at least one optical detector, receiving the altered light and outputting an electrical signal; and electronics, receiving the electrical signal and converting it into seismic data format. Light from the optical sources is modulated at a plurality of modulation frequencies. The electronics can demodulate the signal by mixing the signal with periodic waveforms having frequencies corresponding to one and two times the modulation frequencies. The modulation frequencies are selected such that at least one of the second harmonic frequencies associated with the modulation frequencies is interleaved in a non-interfering manner within the corresponding set of first harmonic frequencies, and preferably such that at least one of the first harmonic frequencies is interleaved in a non-interfering manner within the corresponding set of modulation frequencies. The hydrophone for sensing the acoustic signals is able to operate at pressures and temperatures of at least 5,000 psi and 130° C., respectively. The hydrophone may be housed in a cable having a diameter less than about 1.5 inches. The hydrophone's sensor preferably includes a reference mandrel, two sensing mandrels, and a telemetry cam, which are aligned in a coaxial, end-to-end configuration to reduce the profile of the hydrophone. The mandrels have hemispherically-shaped endcaps and are joined by flexible interlinks having grooves for receiving optical fiber.
137 citations
03 May 2000
TL;DR: In this paper, a bioprobe is proposed for biomedical sensing applications using a resonant dielectric waveguide grating structure fabricated on an optical fiber endface to probe reactions occurring in a sensing layer deposited on its surface.
Abstract: A new fiber optic sensor integrating dielectric diffraction gratings and thin films on optical fiber endfaces is prosed for biomedical sensing applications. This device utilizes a resonant dielectric waveguide grating structure fabricated on an optical fiber endface to probe reactions occurring in a sensing layer deposited on its surface. The operation of this sensor is based upon a fundamental resonance effect that occurs in waveguide gratings. An incident broad- spectrum signal is guided within an optical fiber and is filtered to reflect or transmit a desired spectral band by the diffractive thin film structure on its endface. Slight changes in one or more parameters of the waveguide grating, such as refractive index or thickness, can result in a responsive shift of the reflected or transmitted spectral peak that can be detected with spectroscopic instruments. This new sensor concept combines improved sensitivity and accuracy with attractive features found separately in currently available fiber optic sensors, such as large dynamic range, small sensing proximity, real time operation, and remote sensing. Diffractive elements of this type consisting of a photoresist grating on a Si3N4 waveguide have been fabricated on multimode optical fiber endfaces with 100 micrometers cores. Preliminary experimental tests using a tunable Ti:sapphire laser indicate notches of 18 percent in the transmission spectrum of the fiber endface guided-mode resonance devices. A theoretical analysis of the device performance capabilities is presented and applied to evaluate the feasibility and potential advantages of this bioprobe.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
134 citations
TL;DR: A low-loss, long-range, single-ended distributed optical fiber sensor to measure both temperature and strain simultaneously and unambiguously and both strain and temperature measurements can be independently resolved is demonstrated.
Abstract: We demonstrate a low-loss, long-range, single-ended distributed optical fiber sensor to measure both temperature and strain simultaneously and unambiguously By using the Landau-Placzek ratio and cascaded Mach-Zehnder interferometric filters, we measure both the intensity and the frequency changes in the Brillouin backscattered signal Strain and temperature measurements can then be independently resolved A temperature resolution of 4°C, a strain resolution of 290 µepsilon, and a spatial resolution of 10m have been achieved for a sensing length of 15 km
129 citations
TL;DR: In this paper, a 3D skew ray modeling has been developed to consistently explain the experimental phenomena for an intrinsic SPR multimode optical fiber sensor, and the effects of the polarization direction of the incident light at certain conditions have been clarified.
Abstract: A 3D skew ray modeling has been developed to consistently explain the experimental phenomena for an intrinsic SPR multimode optical fiber sensor. The effects of the polarization direction of the incident light at certain conditions have been clarified. This simulation is needed to accurately detect the variations of the refractive index of the bulk medium and of the thickness of the thin surface layer. More complete knowledge about light energy transmission by the skew ray in the multimode step-index fiber is obtained by this investigation.
TL;DR: Long-period gratings written in commercially available boron-codoped fibers operating at wavelengths of <1.1mum are shown to exhibit high temperature and bending sensitivities, and each resonant attenuation band of such LPG's was observed to split in two to allow for simultaneous measurement ofTemperature and bending in smart-structure applications.
Abstract: Long-period gratings (LPG’s) written in commercially available boron-codoped fibers operating at wavelengths of <1.1 µm are shown to exhibit high temperature and bending sensitivities. Each resonant attenuation band of such LPG’s was observed to split in two when the LPG’s were bent. The split attenuation bands’ separation increased significantly with increasing bend curvature, and the central wavelengths of the split bands provided a measure of temperature. We exploit this effect to allow for simultaneous measurement of temperature and bending in smart-structure applications. The demonstrated novel sensor system is simple and low cost.
TL;DR: In this article, a fiber grating tap was used as a feedback element to control the in-fiber polarimeter and demonstrated the stable, broadband (>70 nm) operation of the fiber polarimeter.
Abstract: We fabricate highly blazed, polarization-sensitive fiber grating taps and show how these may be used in combination with a UV-induced fiber waveplate to form a compact, in-fiber polarimeter. We show how the polarimeter may be employed as a feedback element to control polarization and use the feedback loop to demonstrate the stable, broadband (>70 nm) operation of the fiber polarimeter.
01 Jan 2000
TL;DR: In this article, a bioprobe is proposed for biomedical sensing applications using a resonant dielectric waveguide grating structure fabricated on an optical fiber endface to probe reactions occurring in a sensing layer deposited on its surface.
Abstract: A new fiber optic sensor integrating dielectric diffraction gratings and thin films on optical fiber endfaces is prosed for biomedical sensing applications. This device utilizes a resonant dielectric waveguide grating structure fabricated on an optical fiber endface to probe reactions occurring in a sensing layer deposited on its surface. The operation of this sensor is based upon a fundamental resonance effect that occurs in waveguide gratings. An incident broad- spectrum signal is guided within an optical fiber and is filtered to reflect or transmit a desired spectral band by the diffractive thin film structure on its endface. Slight changes in one or more parameters of the waveguide grating, such as refractive index or thickness, can result in a responsive shift of the reflected or transmitted spectral peak that can be detected with spectroscopic instruments. This new sensor concept combines improved sensitivity and accuracy with attractive features found separately in currently available fiber optic sensors, such as large dynamic range, small sensing proximity, real time operation, and remote sensing. Diffractive elements of this type consisting of a photoresist grating on a Si3N4 waveguide have been fabricated on multimode optical fiber endfaces with 100 micrometers cores. Preliminary experimental tests using a tunable Ti:sapphire laser indicate notches of 18 percent in the transmission spectrum of the fiber endface guided-mode resonance devices. A theoretical analysis of the device performance capabilities is presented and applied to evaluate the feasibility and potential advantages of this bioprobe.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
Journal Article•
TL;DR: In this paper, the use of fiber optic sensors for downhole monitoring in the oil and gas industry is discussed, and several types of transducers have been developed, each of which can be addressed along a single (common) optical fiber in the well and read-out using a common surface instrumentation system.
Abstract: This paper reviews the use of fiber optic sensors for downhole monitoring in the oil and gas industry. Due to their multiplexing capabilities and versatility, the use of Bragg grating sensors appears to be particularly suited for this application. Several types of transducer have been developed, each of which can be addressed along a single (common) optical fiber in the well and read-out using a common surface instrumentation system. key words: Bragg gratings, ber optic sensors, pressure sensors,
TL;DR: A simple and highly sensitive phase-demodulation technique is proposed and its use for a fiber Bragg grating strain sensor is experimentally demonstrated, and strain sensing at as much as a 30-kHz sampling rate was obtained.
Abstract: A simple and highly sensitive phase-demodulation technique is proposed, and its use for a fiber Bragg grating strain sensor is experimentally demonstrated. Sampling a phase-modulated Mach–Zehnder output with controlled time delay produced two quadrature data streams that have relative quadrature phase difference (90°). The Bragg wavelength-dependent phase information is extracted by application of digital arctangent function and phase unwrapping to the quadrature signals. By use of this technique with a reference grating, strain sensing at as much as a 30-kHz sampling rate was obtained with strain resolution of 3.5 microstrains and 6 nanostrains/ Hzin quasi-static and dynamic strain measurements, respectively.
Book•
01 Jan 2000
TL;DR: In this article, Hartog and Othonos discuss the relationship between nonlinear optical fiber and distributed fiber optic sensors and their application in the field of optical fiber chemical sensors.
Abstract: List of Contributors. Preface. 1. Multimode Optical Fiber Sensors G.R. Jones, et al. 2. Bragg Gratings in Optical Fibers: Fundamentals and Applications A. Othonos. 3. Nonlinear Optics and Optical Fibers A.J. Rogers. 4. Distributed Fiber Optic Sensors: Principles and Applications A. Hartog. 5. Referencing Schemes for Intensity Modulated Optical Fiber Systems G. Murtaza, J.M. Senior. 6. Optical Fiber Chemical Sensors: Fundamentals and Applications J.O. Norris. Index.
TL;DR: A long-period grating whose resonance varies in strength but remains fixed in wavelength with either temperature or strain is demonstrated, which requires no spectrometer or other frequency-selective components and can operate in real time.
Abstract: We demonstrate a long-period grating whose resonance varies in strength but remains fixed in wavelength with either temperature or strain. Using this fiber-grating sensor, we resolved a change of 1 muepsilon of strain or 0.04 degrees C in temperature. Such sensors require no spectrometer or other frequency-selective components and can operate in real time.
TL;DR: A new approach to measuring displacement and temperature simultaneously by use of a specially designed isosceles triangular cantilevered beam as a strain agent is demonstrated.
Abstract: A new approach to measuring displacement and temperature simultaneously by use of a specially designed isosceles triangular cantilevered beam as a strain agent is demonstrated. A fiber Bragg grating epoxied onto the beam surface is experimentally demonstrated to have a temperature sensitivity of ~0.113 nm/ degrees C below 60 degrees C and a displacement sensitivity of 9.24x10(-2) nm/mm .
Patent•
13 Apr 2000
TL;DR: In this article, the authors proposed an interferometric sensor that permits the simultaneous measurement of a change in more than one environmental condition, which consists of an optical fiber and a plurality of sensing regions positioned in an operable relationship to the optical fiber.
Abstract: The present invention is directed toward an interferometric sensor that permits the simultaneous measurement of a change in more than one environmental condition. The interferometric sensor comprises an optical fiber and a plurality of sensing regions positioned in an operable relationship to the optical fiber. Each sensing region has partially reflective boundaries and produces an interferometric signal.
Journal Article•
TL;DR: In this paper, a bending-to-linear displacement converter and a liquid adhesion sensor using a 9-5-9 structure with a low insertion loss and a cladding interactive 9-3-9 was demonstrated.
Abstract: distributed sensings on temperature and strain have been extensively investigated based on Raman [1] and Brillouin [2] scattering methods, respectively. During the course of our developments on a new sensor which can work as one of sensing elements for multi-point detection using a Rayleighscattering based OTDR through an optical fiber network, a hetero-core fiber optic sensor was exploratively examined [3], [4] in which a hetero-core structure is implemented in a single mode, low-transmission-loss fiber line at the wave length of 1.3 μm by fusion splicing. In a series of experiments, two types of the sensor are typically found in depending on a small difference in the core diameters of 3 and 5 μm for the inserted hetero-core portion which are referred to as 9-3-9 and 9-5-9 types, respectively. It was interestingly found that their bending loss characteristics was distinctively different. In this paper, the explorative applications of the two types of hetero-core sensors are successfully demonstrated as a bending-to-linear displacement converter and a liquid adhesion sensor using a 9-5-9 structure with a low insertion loss and a cladding interactive 9-3-9 structure with a high sensitivity, respectively. Relatively large distortion in the order of several millimeters in length can be reproducibly monitored by means of an OTDR combined with 9-5-9 bending loss change on a curvature radius of about several tens of millimeters given in this experiment. On the other hand, experiments with the use of 9-3-9 type have shown an outstanding feature as a viable new technology in detecting liquid adhesion around the curved hetero-core portion. Because of possible building-up of cladding modes in the 93-9 type sensor, the loss mechanisms for such modes would be closely interactive to boundary conditions in the close vicinity of cladding surface. A conceivable model for the cladding mode interaction has been also discussed in terms of mode transition and possible recoupled power to a 9-μm transmission fiber which follows the hetero-core portion.
TL;DR: A new type of optical fiber hydrophone is constructed with a fiber Bragg grating based on the intensity modulation of laser light in an FBG under the influence of sound pressure, which can measure amplitude and phase of an acoustic field in real time and operates in a wide range of acoustic frequency.
TL;DR: In this paper, an online sensor was developed to determine the fouling properties of aqueous process fluids using a plastic optical fiber with its cladding removed over a sensitized length.
Abstract: The development of an online sensor to determine the fouling properties of aqueous process fluids is described. A plastic optical fiber with its cladding removed over a sensitized length measures the growth of biofilms in a closed loop water process system by evanescent field attenuation and intensity modulation. The sensor detects material build-up at the core-cladding interface by means of refractive index modulation. A theoretical model is developed showing that an increase in cladding refractive index reduces the intensity of light propagating in the fiber and attenuates the high order modes. The modulation mechanism of the sensor is demonstrated using a CCD camera and frame grabber to record the far field modal distribution of the fiber, when the outer modes are excited. The intensity distribution changes spatially in response to the biofilm deposit on the sensor, indicating evanescent field attenuation.
TL;DR: This work achieves reconfigurable optical header recognition and penalty-free routing of a 2.5 Gb/s packet stream with a 1.6-ns guard time using cross-gain compression in a semiconductor optical amplifier for time-to-wavelength mapping and two fiber Bragg grating arrays for tunable correlation decoding.
Abstract: We achieve reconfigurable optical header recognition and penalty-free routing of a 2.5 Gb/s packet stream with a 1.6-ns guard time. Our method uses cross-gain compression in a semiconductor optical amplifier for time-to-wavelength mapping, and two fiber Bragg grating arrays for tunable correlation decoding. This technique may be of value in future high-speed optical packet-switching nodes.
TL;DR: In this article, an experimental verification of the response of an embedded optical fiber Bragg grating (OFBG) to applied nonhomogeneous strain fields is presented, and the results are compared with analytical calculations, based on the piecewise-uniform period assumption for chirped gratings.
TL;DR: In this paper, the authors presented a novel work on developing fiber optic micro-sensors and integrating them into soldiers' uniforms, which can be used to sense various battlefield hazards in re...
Abstract: This paper presents novel work on developing fiber optic micro-sensors and integrating them into soldiers’ uniforms. These fiber optic sensors can be used to sense various battlefield hazards in re...
TL;DR: In this paper, a novel optical fiber sensor was developed for the detection of cracks and the subsequent monitoring of their openings, where no apriori knowledge of crack location is required, and a small number of fibers can be employed to detect and monitor a large number of cracks.
TL;DR: In this paper, a study of internal strain measurement by fiber Bragg grating sensors (FBGSs) embedded inside textile composites is presented, where the effects of transverse strain and temperature on the measurement results are discussed.
TL;DR: The BOD of river waters was estimated by using the optical fiber biosensor, and good correlation between the sensor and BOD5 test was obtained, and the range of determination was 1-10 mg l(-1) BOD.
TL;DR: In this article, a frequency multiplexing method for low finesse fiber Fabry-Perot sensors using a white light source and a CCD based monochromator was proposed.
Abstract: We report a novel frequency multiplexing method for addressing low finesse fiber Fabry–Perot sensors using a white light source and a CCD based monochromator. The absolute optical path length imbalance of the sensors can be determined using this method. The concept was demonstrated with three fiber Fabry–Perot interferometers for strain and displacement measurements. The accuracy is better than 0.01 μm and the maximum range is approximately 1 mm.