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This PDF file contains the front matter associated with SPIE Proceedings Volume 4185, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.
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Intelligent Transport Systems(ITS) are under active development in many countries as a construction program of social infrastructures, in which many kinds of sensor technologies are being used or studied. This paper categorizes the sensing needs for some typical service applications, and introduces four examples utilizing optical sensing technologies.
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Three phase volume fraction measurement is demostrated in three-phase flows using an optical fiber probe placed into the flow. Fluorescence from oil and reflectance signal from gas are detected from the same probe end.
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A thermally insensitive pressure measurement up to 300 degree C was demonstrated utilizing fiber Bragg gratings written onto a side-hole single mode fiber. The resulting temperature sensitivity is about 300 times lower than normal FBGs.
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Results of an evaluation of a single crystalline sapphire fiber with a Cr3- doped (ruby) tip for thermometric use up to 1500°C are reported. The study shows that the single crystal probe is able to operate continuously at temperatures up to 1400°C. and can reliably cover a wide temperature measurement range from -50°C to 1400°C.
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An optical sensor system for an aerospace application that demonstrates a multi-measurement capability from a single, generic processing module is presented. The principle is applied to two diverse sensing tasks: proximity and hydraulic pressure measurements.
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A novel torsion sensor is made of a corrugated long period fiber grating whose shift of peak resonant wavelength is directly sensitive to the applied torsional angle per length.
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Distributed strain measurement along an optical fiber is performed by a correlated-based continuous wave technique using Brillouin scattering. We demonstrate the spatial resolution of 1cm, which is quite difficult to be achieved by conventional techniques using a pulsed lightwave.
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A technique to measure Brillouin gain spectrum distribution along an optical fiber with cm spatial resolution is developed. This technique employs frequency-modulated pump and probe lightwaves, which are generated by a direct-frequency-modulation of a laser diode. The frequency difference of about 11GHz between the pump and prove are generated by two ways. The former is a precise way, and the latter is a simple way. The Brilloum gain spectrum is measured at the position of the fiber where the pump-probe correlation is high. The position to be measured is chosen through the frequency of the direct frequency modulation. While the conventional pulse-based technique suffers the spatial resolution limit of several meters imposed by the acoustic damping time, our correlation-based one circumvents it. A spatial-resolution of about 6.5 cm has been demonstrated with this technique. Moreover, a noise compensation technique is also presented.
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We present distributed forward propagation sensor system that utilizes specially designed multimode fiber. The proposed system allows for direct detection of the optical signals that provide information on position and amplitude of microbend disturbances located down the sensing fiber.
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Updated results using an improved 40km Sagnac detection system are presented. Real-time simultaneous positioning of multiple disturbances has now been realized. The new system has a higher output ASE source, improved WDM's and enhanced signal processing.
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We propose and demonstrate a novel quasi-distributed fiber laser stress sensor. A stress position is located by the FSR shift induced by mode coupling in an intracavity PMF. Resolution of 54cm in the 150m-range could be realized with the mode-locking technique.
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Distribution of Brillouin shift frequencies along optical fibers are measured by a newly developed Brillouin loop amplification scheme. The frequency shift measurement for a 40-km test fiber has been successfully carried out.
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A variable spatial aperture, high resolution distributed strain sensor is reported based on coherent Raleigh backscattering in optical fiber.
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This paper reviews some of the optical imaging methods developed by the Applied Optics Laboratory of the Rover Group for structural and fluid analysis. The techniques discussed provide measurements of several parameters, specifically: deformation, vibration, surface form, and fluid flow velocity. Illustrative examples are presented for each technique.
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Blue Road Research installed fiber optic grating sensors on the Horsetail Falls bridge in 1998 to monitor static strain in support of health monitoring of the bridge. In November 1999 Blue Road Research utilized high speed, high sensitivity fiber grating demodulation systems on this bridge to monitor the weight arid speed of traffic. Sensitivity levels used were sufficiently high that joggers could be detected easily as well as people walking on the bridge. This paper provides an overview of these recent tests that show both health monitoring and traffic monitoring functions can be performed on a bridge using the same set of fiber grating strain sensors.
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We report on results from a field test involving pavement embedded fiber Bragg grating pressure transducers. Data from the test is compared to theoretically predicted stress distribution in soil as obtained from the Boussinesq equation.
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Optical Line monitoring of PONs by a tunable OTDR is demonstrated by the reference reflector method and the wavelength routing method. Branched individual path can be analyzed by the measurement at the central office as the active fiber monitoring. The prospective of the practical use has been offered by the field trial on ATM-PON.
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We demonstrate a modular semi-autonomous system for permanent ship hull structural health monitoring based on fiber Bragg gratings, Fabry-Perot interrogation, and a distributed software system for acquisition, real-time signal processing and visualization.
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Operational costs during launch preparation, mission and maintenance of spacecraft do not only rely on technical and logistical improvements of subsystems or components but to an even greater extent on the implementation of a Health Monitoring System.
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Bragg gratings have been widely utilized in both sensing and telecommunications applications. This paper will review recent developments in tunable grating technology that permits reliable, ultra high precision tuning capability. The application of this to wavelength management in next generation optical networks will also be discussed.
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The novel properties possible in microstructured optical fibres present new alternatives for a range of sensing applications. We review applications such as gas sensing, ultra-broadband sources, new source wavelengths, rotational sensing and bend sensing.
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We present a fault locator developed for diagnosing an optical fiber transmission line. This locator works under the principle of phase—modulating optical coherence domain refiectometry, and as a precisely tunable light source it takes a fiber loop including an EDFA and a frequency shifter. By optimizing the characteristics of this light source, spatial resolution of 10cm is demonstrated.
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Optical fibres operating by the photonic bandgap effect offers an alternative approach to evanescent field waveguides for opticai sensing applications. In addition to this, these photonic crystal fibres provide completely new waveguiding properties, which include different macro-bending loss performance compared to standard optical fibres. A first estimation of these new properties is demonstrated for air-guiding fibre designs by combining accurate vectorial mode analysis and an adaptation of more traditional macro-bending loss theory.
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Optical fiber sensors have been embedded in structural elements for over fifteen years in order to obtain information regarding the internal stress, strain, or temperature states of the structures. However, the degree to which the mechanical reliability and data stream integrity are maintained will strongly depend on the type of sensor being used, the measurement application, and the structural integration method.
In this paper we present a fiber optic sensor that demonstrates higher sensitivity than the typical fiber Bragg grating sensor, and it is capable of monitoring the state of its own health. The sensor design uses an induced phase discontinuity in the fiber Bragg grating to create a narrow pass-band within the reflection spectrum of the grating. The position of this narrow window within the Bragg spectrum is used to monitor the sensor's health.
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By using fiber Bragg grating sensors for temperature measurement in high-voltage transformers a new technique for the enhancement of the sensing element's sensitivity is developed and two low cost detector units for the measurement of the Bragg wavelength are presented.
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FBG sensors were embedded in CFRP cross-ply laminates. Experimental results and theoretical calculation showed that the monitoring of reflection spectrum form had a potential for real-time detection of transverse cracks in the composite laminates.
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An alarm system based on a thulium-doped fiber loops, using the fluorescence decay technique in the frequency domain, has proved operational with a demonstrated minimum differential temperature of 125°C within 10cm along a 1.2m fiber length.
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The application of a novel tunable mirror to the stabilisation of a distributed-feedback fibre laser (DFB-FL) sensor is described. Theory of operation is outlined and the implementation of the stability control system is demonstrated.
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The fluorescence emission of single-crystal ruby fibres has been investigated as a function of both temperature and strain. A very weak strain dependence is exhibited while a stronger temperature dependence is found.
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We report on the first results of a fiber optic acceleration sensor which consists of two partially spectral overlapping Bragg gratings. The motion of an inertial mass shifts the Bragg reflections of the gratings in different spectral directions and thus modulates the overall amount of reflected light.
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A self-referenced fibre optic intensity sensor supported by a multiple beam SagnaC Configuration is investigated. Sensor linearity and sensitivity are analysed. Theoretical and experimental results are Compared, being Considered the sensor design and its optimisation.
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The attenuation bands of the transmission spectrum of a long period grating subjected to bending are observed to split into two. The split attenuation bands' wavelength separation increases significantly with increasing bend curvature. This effect is exploited to allow the measurement of bending in structures.
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By using a Mach-Zehnder-Interferometer for acousto-optic measurement of Partial Discharges in insulating oil an on-line monitoring system is developed, which offers the possibility of recognition and location of defects in transformers.
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The results of an experimental and theoretical analysis of the noise and signal-to-noise levels associated with the interferometric detection of fiber Bragg grating (FBC) reflected light are presented.
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We propose a temperature fiber sensor based on CdSe-nanocrystal-doped phosphate glass. This glass demonstrates a reversible temperature-induced absorption edge shift at temperatures less than annealing temperature ofthe glass (<370°C). A sensor, tested in the temperature range of—20 to +120°C, is shown to exhibit a linear response to temperature variations.
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Low-temperature sensing by a fiber Bragg grating fixed on Teflon substrates was studied. The temperature sensitivity at 77 K was 33 pm/K, which is 1.5 times higher than that of the sensor using a poly(methyl methacrylate) substrate.
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A method for measuring sensitivity of Bragg gratings to external parameters for different spatial and polarization modes is presented, along with the results of sensitivity measurements to temperature and elongation for LP01x, LP01y, LP11x, LP11y modes. The difference in responses according to the type of mode shows the possibility of simultaneous temperature and elongation measurement using two-mode Bragg gratings.
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A novel fiber grating-type angle displacement sensor based on the torsion beam is reported for the first time. The Bragg wavelength shift is linear to the angle displacement and is no-chirped between -45° and +45° . The angle displacement sensitivity is 11.547 degree/nm.
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We describe a fiberoptic sensor that uses a frequency modulated laser to simultaneously measure both the position and velocity of a reflecting target. We also discuss the effects ofresidual amplitude modulation and multiple reflections.
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We propose a sub-carrier phase detection scheme for interrogation of a chirped Bragg grating sensor. Amplitude modulation of the light source and phase detection of the light reflected from the grating is used in the sensor.
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A simple sensor for measuring the air density in the atmospheric pressure has been developed using a usual optical fiber cable and a radioactive alpha-ray sour. The air density wuld be measured with an accuracy of ±4x10-6g/cm3 in the range from 1.07 X 10-3g/cm3 to 1.309 X10-3 g/cm3. Coupling the two air density sensors has also developed the absolute humidity sensor.
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We have designed a compact multi-component force sensor using an elastic transducing body and eight multiplexed fibre Bragg gratings. We discuss its design and calibration issues.
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Measurements of the velocity of stress waves with a Mach-Zehnder interferometer yielded estimates of the moisture content of concrete. Values ranged from 3433 .4 m.s-1 to 5131 .3 m.s-1 for dry and wet specimens respectively.
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We have proposed and demonstrated a high-resolution interrogation system for fiber Bragg grating strain sensor with prominent temperature stability using long period grating pair and EDF inserted between the two gratings.
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The temperature insensitive fiber-optic bending sensor with high resolution and high sensitivity based on a pair of long period fiber gratings will be discussed. Dependence of the resonant wavelength shift and change of peak depth on the curvature change was investigated experimentally.
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A fiber optic hydrophone array with four sensor elements ofthe air-backed mandrel type has been manufactured and tested. Frequency response, crosstalk, noise and directional response have been measured in an acoustic tank.
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To develop a health monitoring system for satellite, FBG sensor was applied to a composite panel with heat-pipe. Temperature and strain in the panel were successfully measured during thermallvacuum test in a vacuum thermal chamber.
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Velocity vector sensing by using fiber-optic low coherent interferometer is proposed and demonstrated. The velocity vector component is measured directly from a peak position of correlation signal between two backscattering lights from flow.
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A new type of 2x2 fused taper 16 channel wavelength division multiplexer with 20 nm spacing from 1310 to 1610nm was fabricated for application in a multi-channel strain and temperature sensor. The spectral response of each channel under strain and temperature variation was experimentally analyzed. The strain sensitivity in the range of 400-2000με and the temperature sensitivity in 20-100°C were measured. The optical power response to the strain was also measured.
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A fiber optic surface sensor is described in which depolarization of light by a rough surface is measured. Polarization maintaining single mode fibers are used for the illumination and observation of the reflected light. An optimization of the measurement configuration aimed in restriction of the observation to the first Fresnel zone has been performed.
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We demonstrate a novel application for DFB fibre laser temperature sensors, i.e. characterization of the pump induced temperature distribution along another DFB fibre laser, with high temperature and spatial resolution. This provides valuable information for improving DFB fibre laser performance.
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This new sensor works in reflection mode with a thermochromic material never used in fiber optic sensors at the end of the fiber. It works under water, is easy to build and at low cost.
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Based on the intensity-modulation method, we constructed an ultrasonic vibration sensor using a fiber Bragg gratitg. The sensor can measure linearly amplitude of mechanical vibration in nm resolution without having influence on the vibrator.
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The temperature characteristics and strain effects in a thulium/holmium co-doped optical fibre sensor are investigated for application to optical fibre thermometer schemes. Results show a high temperature sensitivity between 200°C and 700°C and a strain sensitivity similar to other doped fibres.
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Fiber Bragg grating-based sensor systems utilizing different wavelength shift detection schemes have been reported with various ranges of performance characteristics. This work considers sensor count requirements and strain resolution requirements through studies involving two damage scenarios. Such sensitivity studies result in limiting requirements for system deployment in structural applications.
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The performance of a time-division-multiplexed fiber Bragg grating sensor array which uses a tunable laser source and a first derivative technique has been investigated. It is found that the wavelength detection accuracy is affected by the extinction ratio of the optical pulse modalator.
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A setup using wavelength tuning of a pulsed DFB laser to get reflectivity profiles of each FBG element in a low reflectivity FBG array has been tested. For crosscheck purpose, the array under test was rechecked in reversed connection, and the corresponding profiles over wavelength variation showed good agreement.
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The paper presents a method that can be used to measure metal corrosions based on the evanescent field of a fiber, and a pair of fiber Bragg gratings between the transducer is utilized for multiplexing. The technique is based on the ratio of the reflecting intensities from the reference and the sensing fiber Bragg gratings. The ratio has been found to be independent of optical intensity variations.
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Angle Division Multiplexing (ADM) has recently been proposed for fibre-based parallel short distance interconnects. Here, practical issues are discussed such as robustness against environmental stress, alignment requirements for micro-integration and the interconnection of 8 workstations as a demonstration.
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A novel optical fiber multiplexer using a single GRIN-rod lens and a planar microlens array is proposed and demonstrated. The advantages ofthe multiplexer are simple construction and a large number of multiplexing channels.
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A method for tracking interferometer drift is presented, enabling the development of a system for interrogating fiber Bragg gratings both for very low-frequency measurements and for applications requiring sampling rates into the kilohertz range.
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This paper describes a novel, patented wavelength- and time-division multiplexing sensor system based on a tunable laser source with an additional optical modulator geared for intenogating a large number of low-reflective Bragg grating sensors with high accuracy.
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The paper presents experimental construction of a liquid-crystalline Bragg filter. The filter is designed as a lowcost WDM decoupler but can also function as demultiplexer in polarisation-coded transmission or may be used as a variable, electrically controllable bandpass filter. Theoretical basis, principle of operation and results of experimental examination of the device are given.
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A differential demodulation technique capable of accommodating dynamic, high strain and high rate events is presented. The sensor system, based on a single fiber Bragg grating and a pulse modulated white light source, demodulates the first derivative of the strain signal. From model simulation, noise-limited resolution and dynamic range have been determined as functions of tunable system parameters.
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Visibility of a core region in a high temperature gas cooled reactor is poor. Realization of optical diagnostics there will improve safety and maintenancibility. Applicability optical fibers for diagnostics there was studied in the study.
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This paper reports on the first realisation of embedding fiber Bragg grating temperature sensors inside the stator bars of a large air cooled power generator. Furthermore first measurements of the conductor temperature inside the bushings have been carried out during a generator prototype test run.
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To enhance the applicability of optical fiber image guides to high radiation fields, an automatic color correction system has been developed against radiation induced effects. Its feasibility has been shown through irradiation tests.
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A measurement system based on a sophisticated time-of-flight technique and a single mode optical fibre with internal reflectors has been developed for measuring integral strain inside a composite structure. The strain and spatial resolutions are 0.1 mm and 5 m respectively and the measurement time 1 s. The measurement system is widely tested with different types of composite structures.
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The surface temperature of window glass during a fire has been measured. When subjected to radiant heat, a discrepancy in temperature measurement of about 25°C between thermocouples and a bare optical fibre sensor has been observed.
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The resolution performance of a new fiberoptic probe is analysed using its MTF and its resolution limit that are evaluated both with a simple theoretical model and with experimental data obtained with a laboratory prototype.
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An optical fibre SPR sensor has been developed for the detection of hydrogen leakages. This sensor uses a selective injection of a monochromatic light and a thin palladium layer as transducer. Detectable concentrations of hydrogen in nitrogen have been found within the range [0,8%, 100%] with response times varying between 300 to 3 seconds at room temperature.
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To avoid induction noise, a novel principle for the electrocardiography is proposed The measured potential is transmitted as the digital light pulses via IrDA protocol. microcomputer (DSP) is utilized for the filtering, A/D and D/A conversions.
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Phenol red was retained in cellulose acetate loaded with plasticiser. The resultant polymer enabled optical determination of physiological pH . Continuous pH measurements were achieved in whole blood with a flow cell and customised fibre optic probe.
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A harmful gas optical fiber sensor is presented for the detection of dichioromethane. The sensor element is a fiber grating built up with the Electronic Self Assembly Process. No cross-sensitivity with the temperature was observed.
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The evanescent wave optical fibre probe for Cu2+ ions detection was elaborated. As an optical transducer a porphrine (H2TMePvP) was used. The detection limit of the probe as evaluated to be 5x10-5 mol/1 (3ppm).
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New fiber-optic carbon dioxide sensors utilizing a sensitive film containing an indicator dye on a polymer clad optical fiber (PCF) are demonstrated. The sensitive film is a SiO2 gel film including an indicator dye of thymol blue or phenolphthalein, which is dip-coated by a sol-gel method. The attenuation of this sensor changes at the wavelength range of 500 to 700nm detecting CO2 gas.
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An optical fibre sensor system is presented utilising Optical Time Domain Retlectometry and Artificial Neural Networks pattern recognition techniques to recognise the degree of sensor fouling associated with lime-scale build up in hard water systems.
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The sensor involves application of a chemical agent on an unclad portion of a multimode optical fiber which produces brown stains due to the presence of H2S gas resulting in anenuation of the light signal propagating in the fiber. The paper discusses the salient technical features and experimental details of the sensor.
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A multi-point gas sensor network based on a frequency-modulated continuous wave technique and wavelength modulation spectroscopy has been demonstrated for the detection of acetylene gas. A minimum detectable concentration of 6.75ppmrn is obtained with a three-sensor system. The crosstalk between the sensors is estimated about -22 dB.
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Evanescent field interaction in side-polished fibre Bragg gratings (FBG) provides a sensor for measuring refractive indices of liquid analytes and thin films with spectral read-out. The specific advantages of FBG sensors - networking capability, independence of variable signal transmission losses - give the potential to a higher diversity and accuracy of opto-chemical measurements than the measurement of transmission intensities through evanescent field sensitive fibre structures.
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The degree of salinity of water is measured by determining its refractive index with a fiber-optics sensor. The physical principle of the device is the attenuation of the optical power guided by the fibre by the resonant coupling with surface plasmons of a metal layer deposited on the polished cladding of the fibre. The linearity and accuracy of the sensor make it suitable for in situ measurements.
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Different probe-heads, designed at IROE for reflectance measurements on works of art, were compared with each other for highlighting the differences on the obtained spectra when applied on such diverse surfaces like paintings and textiles.
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A strain modulated fibre laser is compared with a DFB laser and an extended cavity laser by studying absorption lines in CO2 at 1578.665 nm and 1572.992 nm in second harmonic spectroscopy.
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Refractive index sensors based on resonant excitation of surface plasma modes in metal-coated tapered fibers can be fabricated to be polarization independent and with 30 db dynamic range. The devices can be operated as wavelength-output sensors.
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Neural network analysis of absorption spectroscopy is used to quantitatively analyze pollutant concentration in aqueous solutions. With proper training, sub ppm resolution was attained. An optical fiber instrumentation is presented, for cost-effective and in-situ measurements.
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We present the design of a fibre optic system for both intra-cavity and ring down absorption measurements in trace gas detection. The system is constructed from standard fibre optic components with a micro-optic gas cell.
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Gastrointestinal neoplasm is a pathology that receives particular attention owing to its high and increasing incidence. In western industrialized countries, the estimated incidence rate of gastrointestinal malignant cancers is second only to lung cancer.
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A Quasi-distributed pH sensing system was developed to utilise information derived from evanescently excited fluorescence signals originating from sensor sites fabricated on an optical fibre. The sensor sites comprise a fluorophore immobilised covalently within a hydrogel matrix.
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A new flow-cell for test of fiber optic chemical sensors was designed and tested. The head was made of plexiglass and consisted of the main body and sensor compartments, in which optomembranes and optical fibers were mounted. The performances of the head were determined with pH sensors working in different pH ranges.
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A pH sensor has been fabricated using a tapered single-mode optical fiber coated with cellulose and direct dyes. A range from 3 to 7.4 and from 8 to 1 1 (pH) was achieved without using UV light.
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The interferometer with illumination of a halogen lamp is characterized, in which the resulting coherence length is only 1.6μm at the center wavelength of 657nm. This sort of ultra-low coherence interferometer is used for simultaneous measurement of refractive index and thickness of sputtered film even when the film thickness is 2μm or less. The measurement is made by a novel coherence-gate reflectance method, to our knowledge, which has an advantage that the measurement time is only 15sec with an error of only 0.3%. Both the refractive index and thickness distributions of SiO2 sputtered film are also presented.
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Polarization effects in liquid crystal-core optical fibers have been investigated and the initial experimental results of the liquid crystal fiber in the polarimetric configuration subjected to the influence of hydrostatic pressure and temperature are presented.
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We present an apparatus for accurate balancing of optical path difference in all-fiber optical interferometers. Interferometers with various arm lengths (1-30m) and initial optical path difference up to 1cm have been successfully balanced within 5μm.
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Digital processing is used to linearly reproduce dynamic phase signals in fiber interferometers passively demodulated using a 3x3 coupler. The phase is retrieved as a weighted sum of the three received signals. High resolution down to the 1 μrad level is achieved.
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A shearography system, that measures two displacement derivative components, using polarisation switching is described. This is achieved using wavelength tuning and highly birefringent optical fibre. Interferometer pathlength imbalance with wavelength tuning provides the phase-stepping.
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An in-line fibre optic reference beam laser anemometer, which utilises a fibre Bragg grating to provide a variable power reference beam is presented. Laser diode injection current modulation provides frequency shifting allowing directional discrimination.
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An interrogation scheme for a passive 3 x 3 Sagnac interferometer is described which exhibits reciprocity and corrects to first order for small departures from ideal coupler splitting ratios.
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Interferometric fiber-optic sensing is used for monitoring the vibrations inside a medium-power transformer. Disturbances are present in the measurement, mainly associated to mechanical transduction to the accessing path cords and to the interrogation scheme. Mechanical vibrations other than of interest are characterized and an optoelectronic and processing scheme is proposed to avoid them.
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An Innovative methodology for compensating systematic errors introduced at every internal reflection of laser beam in bulk-glass optical current sensors is presented. A comparison between numerical simulations and experimental results has been made.
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An integrated multi-layer waveguide has been realised in order to be empioyed for the detection of low humidity concentration. Using such a waveguide we measured the phase changes induced by diffusion of water vapour into the structure as well as the absolute sign of the fringe movement. It offers a promising possibility to fabricate a compact, disposable and low cost optical-sensing device.
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In this paper, we present a novel method for calibration of the current induced optical frequency shift in LDs. The spatial synchronous phase measurement technique is developed for phase shift measurement. Two OPDs in the unbalanced Michelson mterferometer are independently introduced in order to calibrate the current tuning rate.
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A novel idea of laser Doppler velocimetry application for testing rotation elements is presented. The presented system uses stable interferometric measurement of Doppler effect by new modified one-reflection fiber-optic Fabry-Perot interferometer.
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We report on a fiber optic voltage sensor with optically controlled sensitivity. The sensor operates at two widely separated wavelengths (633 nm and 976 nm). one of which is a control signal (976 nm). We have demonstrated experinientally the variation of the sensor's sensitivity from 0.0 1 % to 0 per I Vnns for control power changes in the range of 0 ÷ 7 μW.
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By using two flint glass fibers as the sensing element for an optical current sensor disturbance effects caused by linear birefringence of beamsplitters are prevented. The excellent behaviour of the arrangement is confirmed by experimental investigations on currents with different waveforms.
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The influence of photoconductivity upon operation of a Bi12TiO20—based optical voltage sensor is reported. We have demonstrated, that the presence of photoconductivity defines non-uniform sensitivity of the sensor in the cross section of an infrared light beam. The sensitivity of the sensor is shown to depend on the intensity of light as a consequence of photoconductivity of a crystal. An agreement between our theoretical model and experimental results has been demonstrated.
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We propose a simple, passive signal-processing scheme for stabilizing the Faraday effect current sensor that relies on the use of a twisted fiber or a spun highly birefringent fiber as the sensing element. Experimental results are presented to demonstrate the effectiveness of the scheme.
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The combination of a double-pass superfluorescent fibre source with a wavelength-selective reflector fabricated using the thin film deposition technology enables us to design a broadband light source with fairly good performances (output power < 20 mW, bandwidth of 30 nm, coherence length of 81 μm) and at low cost.
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We describe a multimode fiber optic gyroscope. To compensate the distortions introduced along the propagation through the multimode fiber, a double phase conjugate mirror (DPCM) is inserted in the middle of the loop.
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A novel technique has been demonstrated for making chirped fiber Bragg gratings (CFBG), which was used as the means for in situ absolute center wavelength shifting and reflection bandwidth broadening of a CFBG.
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There are numerous types of fiber optic sensors and sensor systems that rely on the use of detector arrays to determine sensor output from returned optical signals. Spectrally modulating sensors such as those based on Bragg gratings and Fabry-Perot sensors based on white light interferometry are but two examples. One problem with such systems is often the resolution of the detector array. In this paper, a new technique is presented in which the signal from one or more sensors can be demodulated with high resolution. In the technique, the conventional detection system utilizing a linear detector array is replaced by a rotated 2-D array such as a CCD. This results in a much higher sampling resolution than is obtained via linear sampling due to the "folding" of the detector array elements relative to the linearly varying parameter filter directly in front of the array. A theoretical description of the technique is given and potential application areas are discussed.
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Photosensitive materials, i.e., a photochromic dye and a silver halide, were used for fabricating optical fiber devices. Variable transmiUaixe was demonstmted with a photochmmic liquid-core fiber. A periodic photodarkening pattern was induced in an infrared silver halide fiber.
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This paper reports and provides an explanation for the growth behavior of long-period gratings in H2-loaded fiber immediately after 193nm UV inscription. Growth of grating resonance peak by as much as 14 dB was measured. Impact of temperature and grating strength, immediately after UV inscription, on the growth behavior are also discussed.
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The thermal stability of fibre Bragg gratings written in hydrogen-loaded standard telecommunication fibres can be significantly enhanced by pre-irradiating the fibre with UV beam before writing gratings. Our experimental result shows that these gratings maintained more than 60% of their initial index modulation after 10 hours at 605°C.
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We have demonstrated an effective new method of realising optical bend sensing based on the measurement of bending-curvature encoded resonance mode splitting of long-period fibre grating, showing enhanced sensitivity compared with wavelength shift detection method.
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The use of rigorous numerical methods shows that the widely used coupled mode theory is inadequate for the characterisation of semiconductor Bragg grating devices. Simulated results for various types of grating devices are presented.
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An interrogation device capable of monitoring 50 optical fibres each with 14 FBGs was designed based on an imaging spectrograph combined with a C-mount CMOS camera. The wavelength range is 780 nm —850 nm with dispersion 0.14 nm/pixel.
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A novel optical fibre fluid velocity sensor is described that is based on a specially manufactured optical fibre fused tapered coupler, folded to produce a probe geometry. The splitting ratio of this miniature transducer is sensitive to bending and can be easily and cheaply measured using an LED source and simple opto-electronics. The packaging of the transducer has been optimised to produce a sensor for fluid velocity measurements. A description of the fabrication process and the results obtained during initial airflow measurements in a wind tunnel are presented.
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The influence of dopant concentration and temperature on the fluorescence lifetime of the 3P0 state, in Pr3+: ZBLAN was studied. The study found that the lifetime increases with temperature at low concentrations, but decreases with temperature at high concentrations.
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We describe an extension of the active homodyne feedback technique in order to produce stabilised, π/2 radian phase steps in a full-field interferometer used to project interference fringes onto a test-object and hence to measure its shape. The phase stability and accuracy of each step was measured to be 17 milliradians in a 50 Hzbandwidth.
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In this paper, a novel fiber optic system for measuring the dynamic forces in textiles is presented. The approach is demonstrated on a real-time characterization of a parachute during inflation using two different techniques.
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A self-referencing fiber-optic sensor has been demonstrated for macro-bending detection immune to temperature and strain perturbations using an assembly of a hollow-core splice and fiber Bragg gratings, which can detect the macro-bending curvature over hundreds of centimeters.
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Bragg gratings were used to measure strain around holes in carbon fibre laminates in bolted joints due to their small size. These laminates were representatives of conventional structural mechanical joints. Different configurations were tested and results are reported. Bragg gratings are suitable where conventional strain gauges cannot be placed without degradation of host.
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Both piezoelectric and fiber-optic hydrophones are sensitive to acceleration. The acceleration can be a major noise source in rough environment. The pressure to acceleration responsivity ratio is therefore a figure of merit for a hydrophone.
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The performance of the ordinary FBG sensor strain measurement system, which uses Fabry-Perot filter for scanning wavelength, has limitation for application because of hysteresis characteristics of PZT element in the filter, slow scan rate of the filter and the high cost of system.
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An all fiber technique for interrogation of interferometric low-finesse Fabry-Pérot cavities is presented. It is based on the modulation of the spectral transfer function of a wavelength division multiplexer. Results are given when both serrodyne and sinusoidal modulation formats are considered.
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We describe the measurements of curvature made using Bragg gratings written in separate cores of a multicore optical fibre. The gratings act as independent, but isothermal, strain gauges. Thus the difference in Bragg wavelength between the gratings provides a measurement of local curvature.
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We have demonstrated a technique for full spectral characterization of potentially embedded FBG that will enable multiaxial strain measurements in the presence of strain gradients.
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An all fiber interrogation technique for Bragg sensors is presented. It is based on generation of an electric carrier by modulating the coupling length of a wavelength division multiplexer. Results are given when both serrodyne and sinusoidal modulation formats are considered.
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In this paper, a new approach for the fiber optic sensor system in high speed weigh-in motion (WIM) is proposed. Multiple Bragg gratings with same wavelengths and same bandwidths are used in the system. Fabry-Perot filter for the signal process, which cannot be used in the high speed measurement because of the limitation in fast operation of PZT, is excluded. Among the multiple gratings in the WIM system, the gratings under the load act as sensors and the rest of the gratings are filters in the signal process. The proposed fiber optic WIM system is tested by several actual experiments with trucks
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Performance of Bragg grating based strain and temperature sensors were studied. Using a thermal stripping method we achieved sensor gratings with high mechanical stability. Results on long term stability and temperature sensitivity are also reported.
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An opto-electronic processing system is described for quasi-simultaneous interrogation of 64 fibre Bragg grating dynamic strain sensors. Dynamic strain resolutions of 35n?/?Hz with a signal bandwidth <20Khz has been achieved.
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A fibre-optic system capable of measuring deformations, impacts and modes of vibration of a composite panel is presented. Wavelength-division signal de-multiplexing allows for the simultaneous interrogation of 8 distributed strain sensors.
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A Raman Distributed Temperature Sensor (RDTS) has been installed at the experimental fast reactor JOYO with two correction techniques. The measurement errors showed a saturation tendency and the feasibility of the correction techniques was demonstrated. With these correction techniques, RDTS can be operated in nuclear plants for more than 35 years.
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We propose and experimentally demonstrate a novel sensor array based on a Sagnac interferometer having a stable π/2 phase bias without the use of a 3x3 coupler. Signal processing is drastically simplified and polarization induced signal fading is eliminated by using a broadband source and a depolarizer.
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We report here an implementation of high-spatial resolution distributed sensors employing compact-gratingarray structure, offering advantages of free designing dynamic range and simple interrogation by utilising established wavelength-division-multiplexing technique.
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A distributed optical fibre detection system has been developed for damage detection in composite structures. Low coherence interferometry was used to identify damage locations due to coupling of power between the two orthogonal polarisation modes in an embedded fibre.
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A fibre-based optical preamplifier system has been used to improve the signal-to-noise capabilities of a Brillouin-based fibre-optic distributed temperature sensor. A 17dB optical signal-to-noise improvement in a 23km sensor is demonstrated.
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This system is an OTDR based system, using optical fiber sensor which has most suitable structure and characteristic for monitoring the growth of a fissure in a rock.
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The first feasibility for simultaneous independent distributed pressure and temperature measurement in a single optical fibre is shown here using Bnllouin scattering. Pressure coefficients are measured for various fibres and optimised system performances are evaluated.
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We report on the performance of coherence addressed quasi-distributed sensor system for narrow band absorbers using the frequency-modulated continuous wave (FMCW) method, including signal to noise analysis.
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A new distributed sensing technique using spontaneous Brillouin backscatter has been demonstrated. For the first time ever, direct 11GHz heterodyne detection allows measurements of both Stokes and anti-Stokes signals. Results have been obtained for a sensing fibre length of over 10km with a spatial resolution of 20m.
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We monitored the debonding of bare and coated fibers surface adhered with epoxy resin as a function of the longitudinal load during pullout experiments. The measurement method is based on distributed sensing along optical fiber Bragg gratings.
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A rugged and non mechanically moving interrogator for distributed FBG sensors using an arrayed waveguide grating is proposed and its operating features are investigated both theoretically and experimentally. A high sensitivity of ±3.8pm as well as a very good linearity over 0.7nm shift is demonstrated.
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The influence of the spectral characteristics of the pulsed light source of OTDRs on the interrogation of fiber Bragg grating-based sensors is analyzed in this paper. An extensive analysis with several kinds of light sources and FBGs have identified the optimum combination of them that maximize the sensitivity and linearity of the measurement.
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A fiber-optic stress-location sensor is proposed by synthesis of rectangular-shaped optical coherence function. By shifting the edge of the coherence function with judgement which side the stress is appeared, its location is determined with spatial-resolution of the full-range/2n by the n times judgement.
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We demonstrate a high spatial resolution single-ended spontaneous Brillouin-based distributed temperature sensor for a 500m length of single-mode silica fibre. Using a short pulsewidth laser source at 1 .5μm, measurements down to a spatial resolution of 20cm and temperature resolution of 4.4°C were achieved.
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This paper suggests a transform relation in Brillouin Optical Time Domain Analyzer (BOTDA). By computerized signal processing using the relationship, the spatial resolution of BOTDA can be improved to sub millimeter order theoretically, compares to about 1m of present art of view.
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Monitoring and control of RTM process is essential to minimise trial and errors and optimise cycle productions. Hence a research programme was established to study different systems to control the process. In this paper, several experiments are described in which an on-line system based on fibre Bragg sensors was implemented.
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This paper describes a new application of Bragg grating sensors. A high resolution sensor carrier and a fast interrogation unit were used in field tests for measuring blast vibrations and damages caused by these vibrations.
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Optical dosimetry system will have several advantages over present traditional dosimetry system. The paper will focus on results of radiation tests on fiber Bragg gratings, which will be used as a temperature monitor.
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In order to increase the power transport capacity and reliability of electrical infrastructure, the practical application of three integrated optical sensors for the distributed measurement of temperature, mechanical stress and moisture will be discussed.
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The structure and operation principle of the infrared (3.39 μm) laser methanometer have been presented. Fluoride glass optical cables are used in the instrument. Methane detection characteristics of the 3.39 μm absorption line as compared to those at 1.67μm and 1.33μm in the overtone range have been discussed. The dual wavelength (3.39/0.63μm) laser/fibre-optic methane measuring system for measuring emission from extended methane generators has been presented and the related phenomena, such as mutual extinction and refraction of both versions of equipment, in particular to coal mining and environmental monitoring have been discussed.
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Hydration temperature and bonding strain between concrete and steel rebar during the hardening process are characterized by using fiber Bragg grating sensors. A novel technique for accessing structural damages such as crack locations and corresponding depths is also demonstrated.
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We demonstrate a novel method for equalising the spectra of erbium doped superfluorescent fibre sources in the double-pass forward configuration. The equalising technique uses novel single-mode fibre to planar waveguide filters in a double-pass forward superfluorescent source to smooth the output spectrum. The insertion loss of the filter device used in this paper is <0.9dB but insertion losses of 0.2dB are typical. The unfiattened double-pass forward superfluorescent source with 108.5mW pump power has an output power of <30mW, 44.2% of the quantum efficiency and a 3dB linewidth of 5.43nm. The equalised DPF SFS with 108.5mW pump power has an output <30mW, 44.85% of the quantum efficiency, a 3dB linewidth of 31.26mn with a small ~0.936dB ripple. The overall gain flattened spectral density is increased from 468.6μW/nm to 887.8?W/um in the lSSOnm region.
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A novel method for simultaneous measurements of the differential effective index and the thermo-optic coefficient ofafiber is presented. The method is based on the interference in a long-period fiber grating pair.
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Polymeric optical films were deposited by CF4+H2 plasma process. The polymeric films contain Fluorine increasing gradually with depth. As Fluorine reduces polymer refractive index it is concluded that the films refractive index is also varying gradually.
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In this paper, we present a novel long period grating fabrication technique that can control the higher harmonics resonant peaks. By using piano-convex microlens array with different thickness, the higher harmonic peaks in LPGs can be selectively enhanced or suppressed.
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A static Michelson interferometer and optical spectral analysis have been used to perform optical coherence-domain reflectometry (OCDR). Direct compensation for non-Gaussian source spectrum and dispersion are shown. Reflections indistinguishable using an EDFA source and conventional scanning OCDR are clearly distinguished with this method.
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A novel study and modelling of curved long period fiber gratings is described. Different spectral characteristics evaluated are according with previous published experimental data.
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Initial attempts to photo-induce refractive mdcx changes in bulk poly methyl methacrylate (PMMA) and in PMMA based plastic optical fibres (POF) using UV light are described. Optimum changes have been achieved at 216 nm, causing path length changes of 10π, corresponding to possible refractive index modulation of between 5 and 14 % over thicknesses up to 100 μm. The effects of refractive index changes on the far field modal distribution of tapered PMMA plastic optical fibres are described.
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We propose a theoretical expression of the Brillouin gain linewidth ΔVB evolution with temperature.
Combined with a more precise model of the Stockes power analytic expression, this should enable to decouple the effects of strain and temperature in BOTDA sensors.
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This work presents a novel fiber optic rotation rate sensor based on the characteristics of an OEO with feedback loop tuned by Sagnac interferometer. Experimental results, which agree with theoretical predictions, show high sensitivity.
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Polarization mode dispersion in optical fibers has recently become a critical issue in high bit-rates communication systems. The paper describes this effect and its relevance to some classes of fiber-optic sensors and lasers.
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A novel method to achieve both large dynamic range and high resolution for static strain measurement is proposed and demonstrated. This method is based on the combination of two in fibre Bragg gratings (FBG) and an all-fibre Fabry-Perot interferometric sensor (FFPI) formed by the two FBGs. The FFPI is used to obtain high-resolution strain measurement via phase detection of the interferometric signal whilst the wavelength-shift of the two FBGs forming the FFPI is used for determination of the fringe number of the interferometric signal.
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We demonstrate a novel optical tomography along the geometrical thickness, reflecting a real cross-sectional structure of an object. This unique tomography is formed by combination of the conventional optical coherence tomography (OCT) and a confocal tomography that is demonstrated for the first time, to our knowledge. The imaging principle and optics are presented as well as imaging examples.
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We have demonstrated that Beny's topological phase is readily observable if a helical fibre coil is included in a loop mirror. This configuration has the potential to be used in linear or torsional strain measurement.
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We report an interferometric scheme for comprehensive characterisation of the dispersion of birefringence in high birefringence fibres over a broad wavelength range, based on a single OPD scan. The approach is shown to support dispersion-insensitive measurements in a multiplexed serial array.
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We report a novel interferometnc wavelength shift detection scheme with enhanced resolving power by incorporating a fiber chirped Bragg grating reflector in a short coherence length interferometric receiver and achieved a wavelength resolution of 0.6x10-15 m/√Hz.
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Fiberoptic Evanescent Wave Infrared Spectroscopy facilitates measurements on samples in situ and in real time. This will be used for the analysis of chemical processes, for monitoring of pollutants in water or in soil and for diagnosis of diseases
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A fibre optic Bragg grating sensor measures strain on the chest of patients as a method to detect the frequency spectrum of the respiration process. The apparatus can be used to trigger electric ventilation pulses.
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Goat anti-human IgG (antibody) was immobilized on the surface of the LPG and detection of specific antibody-antigen binding was investigated. Binding specificity was confirmed using human interleukin-2 and bovine serum albumin as controls. Antigen detection in a heterogeneous protein mixture and in crude cell lysate from Escherichia coli was also confirmed.
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Novel plastic fiber optic sensors, which is based on the refractive index change in the novolac polymer cladding layer on the norbornene polymer core, have been developed to detect vapor phase methanol and ethanol.
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A new fiber optic sensor based on Bragg reflection influenced by a surface plasmon is presented. This arrangement allows for self-referencing due to its highly polarization-resolved response.
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We investigate the changes in transmission spectra of Long Period Gratings and Slanted FBGs versus the refractive index of the surrounding medium. The metrological characteristics of Slanted FBGs and an analytical method enabling their potential use in accurate refractometry are discussed.
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We demonstrate a single-lead fiber optic magnetic field sensor system based on ferrimagnetic iron garnet crystals. This system automatically compensates for magnetic domain fluctuations in the transducer. Noise floors of 1.1 nT/Hz1/2 at 1 kHz are demonstrated without ferrite flux concentrators. Use of a single distal ferrite flux concentrator improves the sensitivity and noise floor by 17 dB with a frequency response of ~180 MHz; this represents a 3x improvement in gain-bandwidth product over previous reports. Using a pair of flux concentrators yields a 29 dB improvement and a noise floor of 35 pT/Hz1/2 at 1 kHz.
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We present a robust, temperature and vibration insensitive fiber-optic current sensor. The sensor has been integrated into a high-voltage circuit breaker. One year field experience has been gained in two substations of the Italian railways.
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A new unusual type of YIG/ ring-core optical fiber current transducer characterized by the transverse configuration of light beam to current-induced magnetic field is developed and shown to have an ever-reported highest sensitivity of ~0.2/A in modulation rate as well as very good isolation from surrounding currents.
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Performance and stability of a field fibre optics interferometric current sensor are presented, showing ±0.5% a accuracy over a broad temperature range and an excellent insensitivity to the sensing fibre positioning.
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We have measured the influence of the electro-optic (EO) Kerr effect on the response of a spun highbirefringence (hi-bi) fiber current sensor in a simulated Gas Insulated System (GIS) environment. We show that the EO Kerr effect distorts the response of the sensor, and that the second-harmonic signal has a small dependence on the input polarizer angle. We also, have theoretically modeled a polarimetric current sensor using spun hi-bi fiber and compared the models to our experimental results. With the models we predict the response of a fiber current sensor in a 550 kV GIS application.
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Drift due to Faraday effect in twin-depo-I-FOG is simulated by the general formula, and is also experimented, considering bend-induced-linear-birefringence and intrinsic/extrinsic random birefringence. A way to reduce the drift is also discussed.
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We demonstrate a two-stage, polarized, RIN-reduced fiber source which delivers 200 mW at 1.5 microns with 24.4 nm bandwidth. A long period grating reduces the temperature dependence ofthe centroid wavelength to < 0.2 picometers/°C.
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Optical fiber sensor-array technologies provide a means for creating a new generation of diagnostic instruments. Microarrays approach detection with a level of diversity ranging from positionally registered specific sensors to randomly ordered addressable arrays for a multitude of analytical applications.
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We present a low-complexity optical ranging system intended for distance ranging to moving biological tissue. The optical ranging technique used is short tuning range, optical FMCW interferometry, in a Fabry-Perot configuration, with a common-path downlead. We demonstrate ranging to a bovine muscle tissue sample over a 250 mm range with an average resolution of 0.55 mm.
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The sensor is based on the colorimetric interaction of cobalt chloride. Gelatin and hydroxyethylcellulose film claddings have been investigated for humidity range 30% to 96% rh. These immobilising agents have big influence on sensor characteristics
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The development of a contact and a non-contact sensor to measure low turbidity of potable water using fluorescent optical fibres over the range 0 to 1 FTU is presented. The contact sensor had a sensitivity of 3.3 nW I unit FTU and an accuracy of ± 0.1 to 0. 15 FTU. The non-contact version of the sensor had a sensitivity of 1.17 nW/ unit FTU.
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An integrated optical surface plasmon resonance sensor combined with electrochemical control is used to monitor the underpotential deposition of a copper monolayer onto a gold film from 1 mM Cu2+ in 0.1 M perchioric acid.
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We present a distributed fibre optic sensor that incorporates hydrocarbon-swellable polymers to produce a microbend loss. Detection of hydrocarbon fuels at multiple locations along a 2km sensor length is readily achievable using standard OTDR techniques.
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The significant advantages of optical fiber sensor systems for spacecraft applications have been established through demonstration projects on both prototype exemplars and flight articles. These include distributed strain sensing using embedded and surface-mounted fiber Bragg grating arrays and ultrahigh sensitivity strain and temperature sensing with fiber cavity etalon sensors. These projects will be discussed with emphasis on sensor performance, reliability, and survivability during composite fabrication, including egress of the fiber lead from the part.
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The effects of strain upon the fluorescence intensity ratio and fluorescence lifetime temperature sensing techniques is compared for a number of rare-earth-doped optical fibers, for application to the simultaneous measurement of temperature and strain.
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We report a novel optical-load sensor using long period fibre grating based on the measurement of the transverse strain induced birefringence. Transverse strain sensitivity some 400 times higher than that previously reported for fibre Bragg gratings has been achieved.
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We report high sensitivity fiber Bragg grating temperature sensors. Temperature sensitivity of 175 pm/°C and a resolution of 0.002°C rms is reported. A shear-lag strain transfer model is utilized to optimize the sensor's thermal responsivity.
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For the first time the RF beat frequencies between two longitudinal modes and two polarisation modes of a birefringent Moiré DFB fibre laser are employed to measure strain and temperature simultaneously. The sensor accuracy was ±25 με and ±0.7°C.
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The frequency response of a free Bragg grating to an acoustic field is compared to a grating attached to a compliant mandrel. The results demonstrate the unsuitability of a free grating for hydrophone applications.
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We present a powerful method of measuring the strain experienced by fibre during processing. Two specific illustrations are given (a) fibre cleaving and (b) the gluing of a fibre into a ferrule.
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Long period gratings have been made in non-photosensitive optical fibres by maskless irradiation of the fibre core with a focussed beam of high energy protons. The irradiated fibres exhibit a strongly wavelength dependent transmission.
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A new type of mode converter using a tapered hollow silica optical fiber is proposed and experimentally demonstrated. Three segments of single mode, hollow, and multimode fibers were concatenated serially to convert the fundamental mode to a ring shape mode. The proposed scheme could be applied to convert the fundamental LP01 mode to TEN, TM and LP02 modes. Evolution of mode filed along the taper and the insertion loss were measured.
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A low loss all-fiber polarization beam splitter/combiner (AF-PBS/C) is proposed. Achieved insertion losses of slow and fast axis were as low as 0.1 dB and 0.3 dB, respectively. Crosstalk was less than -25dB. High reliability was also confirmed.
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Sensing techniques employing UV-inscribed fibre Bragg gratings and long period fibre gratings continue to make significant advances. A number of recently established concepts are described offering improved sensor performance, multiplex capacity, and simplicity, and results from new application areas presented.
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We present a new sensor configuration based on the intrinsic bend sensitivity of Bragg gratings written in D-type fibres. This sensor can be embedded in any layer of a composite material to evaluate curvature in a way independent of axial strain or temperature. It can also be used to measure other parameters such as acceleration, angle or acoustic pressure.
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A new technique using post-processed fibre Bragg gratings to inscribe stop-band fibre transmission filters with single narrow transmission bands and enhanced sensitivity in the measurement of temperature and strain is reported.
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An FBG-based inclinometer is presented. The opto-mechanical principle is based on a differential method, allowing the temperature, pressure influences and mechanical hysteresis to be compensated for. Metrological qualifications performed in laboratory as well as data gained from a civil engineering field trial are presented.
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A long period grating-based bend sensor featuring direct bend sensitivity along with linear, bipolar curvature response is demonstrated. The sensor can be aligned for optimum sensitivity using the slight intrinsic curvature of the eccentric core fiber.
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We have used the electrostatic self-assembly process to grow nanostructured thin films, molecular layer-by- molecular layer, on the ends of silica optical fibers. Such films form optical cavities that allow measurement of temperature by Fizeau interferometiy.
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We report measurements of the strain and temperature coefficients of optical fibre Bragg gratings with ~1pm wavelength resolution using Fourier transform spectroscopy and Hubert transform signal processing.
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All evidence indicates that new physics, and answers to some of the most profound scientific questions ofour time, lie at energies around 1 TeV. To look for this new physics, the next research instrument in Europe's particle physics armory is the Large Hadron Collider (LHC). This challenging machine will use the most advanced superconducting magnet and accelerator technologies ever employed. LHC experiments are being designed to look for theoretically predicted phenomena.
One or the main challenges in this new machine resides in the design and production of the superconducting dipoles used to steer the particles around the 27 km underground tunnel. These so-called cryodipoles are composed of an external vacuum tube and an insert, appropriately named the cold mass, that contains the particle tubes, the superconducting coil and will be cooled using superfluid Helium to 1.9 K. The particle beam must be placed inside the magnetic field with a sub-millimeter accuracy, this requires in turn that the relative displacements between the vacuum tube and the cold-mass must be monitored with accuracy.
Due to the extreme condition environmental conditions (the displacement measurement must be made in vacuum and between two points with a temperature difference of more than 200°C) no adequate existing monitoring system was found for this application. It was therefore decided to develop an optical sensor suitable for this application.
This contribution describes the development of this novel sensor and the first measurements performed on the LHC cryodipoles.
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We discuss theoretical and experimental in-water acoustic sensitivity measurements from a coated DFB fibre laser sensor. A noise level of -60dB re.Pa/√Hz @ 1kHz, with an acoustic responsivity reaching -10dB re.Rad/Pa was obtained with this sensor.
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This paper will give an update on the current breakthrough of optical sensing systems within the oil and gas industry, with emphasis on FBG technology for in-well multi-point measurements.
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An optical sensor suitable for detecting the main faults which can occur during the laser welding process is described. Process-generated light is collected using an optical fibre and welding errors are detected by analysis of the temporal and chromatic characteristics of this light.
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A system of three fiber optical field probes based on the Pockels effect and a new matrix transformation algorithm is demonstrated to measure voltage in a 3 phase power switch yard with a high accuracy and voltage errors of less than 1%.
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Bragg gratings have been embedded in pultruded carbon fibre composite rods and subjected to cyclic tension tests covering more than one million cycles. Measurements on the performance show almost no built-in strain, excellent stability and no failures.
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An intelligent monitoring procedure has been applied to fibre optic sensors (FOS) field data collected from an innovative structural system—The Taylor Bridge—in Headingley, Manitoba, Canada. The results show that FOS offer unique benefits for effective structural health monitoring of smart structures.
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SOFO is a structural monitoring system using fiber optic deformation sensors. It is able to measure deformations between two points in a structure, which can be from 20 cm up to 10 meters (or more) apart with a resolution of two microns (2/1000 mm) even over years of measurements. The system is composed of optical deformation sensors adapted to direct concrete embedding or surface mounting, the cable network, the reading unit and the data acquisition and analysis software. The system is particularly adapted to precise short and long-term deformation monitoring of large structures.
An array of more than 60 sensors has been installed on the pier of San Giorgio Levante in the Genoa harbor. These sensors allow the measurement of the pier displacements during the dredging works, ship docking and in the long term. The sensors measure the curvature changes in the horizontal and vertical planes and allow a localization of settlements with a spatial resolution of 10 m over a total length of 400 m. The sensors can be measured automatically and remotely. This paper presents the sensor installation and the results from the first monitoring period..
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A system for producing and demultiplexing large numbers of fiber Bragg grating sensors is described. Three thousand gratings were multiplexed in four optical fibers and demonstrated on a large test article. Preliminary results of a strain sensing system in unaltered fiber using OFDR measurements of the Rayleigh scatter is also described.
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A fiber optic demodulation system capable of multiplexing large scale Bragg grating arrays at high samplingfrequencies has been developed A strain resolution ofup to 5,ie and a sample rate up to 1.9kHz has been demonstrated.
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We investigate the performance of a large-scale array of interferometric sensors using time and dense wavelength division multiplexing. By consideration of the noise sources in the system and the bandwidths available for the signals to occupy we have calculated the signal resolution and dynamic range expected from a single sensor. A discussion on the potential applications for these arrays is also given.
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Fundamental limitations on the laser acoustic sensitivity were investigated over the range 200Hz to 20 kHz. Several laser sensors were wavelength division multiplexed along a length of fibre.
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A fiber optic system for two-dimensional array sensor is presented. Temporal and spatial sampling of distributed fields such as sound and stress is demonstrated by matrix-style access to the element sensors with switching of the light sources.
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