Showing papers on "Fiber optic sensor published in 2006"

Fiber Bragg grating sensors for structural health monitoring of Tsing Ma bridge : Background and experimental observation

Abstract: The rapid expansion of the optical fiber telecommunication industry due to the explosion of the Internet has substantially driven down the cost of optical components, making fiber optic sensors more economically viable. In addition, the rapid development of fiber-optic sensors, particularly the fiber Bragg grating (FBG) sensors offers many advantages and capability that could not be achieved otherwise. In the past few years, fiber Bragg grating sensors have attracted a lot of interest and they are being used in numerous applications. This paper describes the FBG sensors developed for structural health monitoring, and were installed on Hong Kong's landmark Tsing Ma bridge (TMB), which is the world longest (1377 m) suspension bridge that carried both railway and regular road traffic. Forty FBG sensors divided into three arrays were installed on the hanger cable, rocker bearing and truss girders of the TMB. The objectives of the study are to investigate the feasibility of using the developed FBG sensors for structural health monitoring, via monitoring the strain of different parts of the TMB under both the railway and highway loads as well as comparing the FBG sensors' performance with the conventional structural health monitoring system - Wind and Structural Health Monitoring System (WASHMS) that has been operating at TMB since the bridge's commissioning in May 1997. The experimental observations in this project show that the results using FBG sensors were in excellent agreement with those acquired by WASHMS.

Fiber optic position and shape sensing device and method relating thereto

Abstract: The present invention is directed toward a fiber optic position and shape sensing device and the method of use. The device comprises an optical fiber means. The optical fiber means comprises either at least two single core optical fibers or a multicore optical fiber having at least two fiber cores. In either case, the fiber cores are spaced apart such that mode coupling between the fiber cores is minimized. An array of fiber Bragg gratings are disposed within each fiber core and a frequency domain reflectometer is positioned in an operable relationship to the optical fiber means. In use, the device is affixed to an object. Strain on the optical fiber is measured and the strain measurements correlated to local bend measurements. Local bend measurements are integrated to determine position and/or shape of the object.

All-fiber multimode-interference-based refractometer sensor: proposal and design

Abstract: A novel all-fiber refractometer sensor is proposed, which is based on multimode interference in the multimode fiber core section sandwiched between two single-mode fibers. A wide-angle beam propagation method in the cylindrical coordinate is employed as the modeling tool for simulation and design of the proposed refractometer sensor. The design for a refractometer is presented that shows that the refractometer would have an estimated resolution of 5.4 x 10(-5) for refractive indices from 1.33 to 1.45 and of 3.3 x 10(-5) for refractive indices from 1.38 to 1.45 through the choice of an appropriate length of the multimode fiber core section.

Fiber-optic temperature sensor based on interference of selective higher-order modes

Abstract: A fiber-optic temperature sensor based on the interference of selective higher-order modes in circular optical fibers is described. The authors demonstrate that by coupling the LP01 mode in a standard single-mode fiber to the LP0m modes in a multimode fiber, and utilizing the interference of the higher-order modes, a fiber-optic temperature sensor which has an extremely simple structure and is suitable for high-temperature measurements can be constructed. The sensing principle, temperature measurement experiments, and results are presented.

Distributed strain measurement with millimeter-order spatial resolution based on Brillouin optical correlation domain analysis

Abstract: Distributed strain sensing with millimeter-order spatial resolution is demonstrated in optical fibers based on Brillouin optical correlation domain analysis. A novel beat lock-in detection scheme is introduced to suppress background noises coming from the reflection of Brillouin pump waves. The Brillouin frequency shifts of 3 mm fiber sections are successfully measured with a theoretical spatial resolution of 1.6 mm.

Microstructured-core optical fibre for evanescent sensing applications.

Abstract: The development of microstructured fibres offers the prospect of improved fibre sensing for low refractive index materials such as liquids and gases. A number of approaches are possible. Here we present a new approach to evanescent field sensing, in which both core and cladding are microstructured. The fibre was fabricated and tested, and simulations and experimental results are shown in the visible region to demonstrate the utility of this approach for sensing.

Highly sensitive long-period fiber-grating strain sensor with low temperature sensitivity.

Abstract: A long-period fiber-grating sensor with a high strain sensitivity of −7.6 pm/μe and a low temperature sensitivity of 3.91 pm/°C is fabricated by use of focused CO2 laser beam to carve periodic grooves on a large- mode-area photonic crystal fiber. Such a strain sensor can effectively reduce the cross-sensitivity between strain and temperature, and the temperature-induced strain error obtained is only 0.5 μe/°C without using temperature compensation.

Fiber-optic chemical and biochemical probes based on localized surface plasmon resonance

Abstract: A novel reflection-based localized surface plasmon resonance fiber-optic probe for chemical and biochemical sensing is reported. The sensor is based on intensity measurement of the internal reflected light at a fixed wavelength from an optical fiber where the extinction cross-section of self-assembled gold nanoparticles on the unclad portion of the optical fiber changes with different refractive index of the environment near the gold surface. The reflection-based localized surface plasmon resonance fiber-optic probe has been shown to be capable of direct sensing of the “spectroscopically silent” Ni2+ ion and label-free detection of streptavidin and staphylococcal enterotoxin B at the picomolar level.

First experimental demonstration of self-synchronous phase locking of an optical array

Abstract: A novel, highly accurate, all electronic technique for phase locking arrays of optical fibers is demonstrated. We report the first demonstration of the only electronic phase locking technique that doesn’t require a reference beam. The measured phase error is λ/20. Excellent phase locking has been demonstrated for fiber amplifier arrays.

All-fused-silica miniature optical fiber tip pressure sensor

Abstract: An all-fused-silica pressure sensor fabricated directly onto a fiber tip of 125 μm diameter is described. Simple fabrication steps include only cleaving and fusion splicing. Because no chemical processes are involved, the fabrication is easy, safe, and cost effective. Issues in sensor design and loss analysis are discussed. The sensor has been tested for static pressure response, showing a sensitivity of 2.2 nm/psi, a resolution of 0.01 psi (68.9 Pa), a hysteresis of 0.025%, and capability of operation at temperatures up to 600°C. This miniature sensor may be suitable for medical diagnostics, environmental monitoring, and other industrial applications.

High Resolution Distributed Strain or Temperature Measurements in Single-and Multi-mode Fiber Using Swept-Wavelength Interferometry

Abstract: We describe use of swept-wavelength interferometry for distributed fiber-optic strain and temperature sensing in single mode and gradient index multimode fiber. The method is used to measure strain in a four-strand multimode cable under twist.

Long-term measurement of optical frequencies using a simple, robust and low-noise fiber based frequency comb

Abstract: We have developed a fiber-based frequency comb system consisting of a simple mode-locked fiber laser and a backward pumping amplifier combined with a highly nonlinear fiber with a short zerodispersion wavelength. As a result, the signal to noise ratio of the obtained carrier-envelope-offset frequency beat is larger than 45 dB at a bandwidth of 100 kHz. Furthermore, we have succeeded in measuring the optical frequencies of a 1542-nm acetylene-stabilized laser and a 532-nm iodinestabilized Nd:YAG laser continuously for more than one week using the fiber-based comb system. The long-term measurement revealed that the frequency stability of the iodine-stabilized laser was 5.7 x 10(-15) with 100 000 s averaging.

Biconical Fiber Taper Sensors

Abstract: We present several simple sensitive fiber-optics-based sensors that utilize a biconical fiber taper. A displacement sensor with 100-nm accuracy, a temperature monitor with sensitivity DeltaT~1degC, and a refractive-index sensor capable of measuring Deltan~1.42times10-5 are demonstrated using tapers made from a standard single-mode fiber

Volatile Organic Compound Optical Fiber Sensors: A Review

Abstract: Volatile organic compound (VOC) detection is a topic of growing interest with applications in diverse fields, ranging from environmental uses to the food or chemical industries. Optical fiber VOC sensors offering new and interesting properties which overcame some of the inconveniences found on traditional gas sensors appeared over two decades ago. Thanks to its minimum invasive nature and the advantages that optical fiber offers such as light weight, passive nature, low attenuation and the possibility of multiplexing, among others, these sensors are a real alternative to electronic ones in electrically noisy environments where electronic sensors cannot operate correctly. In the present work, a classification of these devices has been made according to the sensing mechanism and taking also into account the sensing materials or the different methods of fabrication. In addition, some solutions already implemented for the detection of VOCs using optical fiber sensors will be described with detail.

Sensor properties and surface characterization of the metal-deposited SPR optical fiber sensors with Au, Ag, Cu, and Al

Abstract: Metal-deposited optical fiber sensors with Cu and Al with a film thickness of 45 nm based on surface plasmon resonance (SPR) were fabricated for the first time. The response curves and the properties of these sensors were investigated with a comparison of those of the sensors with Au and Ag. The reflection properties of thin films of Au, Ag, Cu, and Al due to the SPR phenomenon were also measured and considered. The metal-deposited SPR optical fiber sensors with Au, Ag, and Cu have high sensitivities and good responses. Though the sensor with Al shows a lower sensitivity, it has a wider response range in the refractivity. The response curve of the sensor with Au calculated from SPR theoretical equations agreed well with that obtained by the experiment. However, the response curves of the sensors with Ag, Cu, and Al have the effects of the surface oxide layers. The surface characterization of these metal films by X-ray photoelectron spectroscopy (XPS) showed the presence of oxide layers on the films of Ag, Cu, and Al. A very thin (about 0.3 nm) oxide layer is present on Ag, while thick (about 2 nm) oxide layers are present on Cu and Al.

Powered fiber cable

Abstract: An optical fiber for information transmission contains a glass tube core wrapped in a sheath of conductive material attachable to a power source such as a battery or generator to transmit power via the conductive sheath of the fiber. Methods to transmit power via an optical fiber, together with fiber optic networks are described.

Q-switching of an all-fiber laser by acousto-optic modulation of a fiber Bragg grating

Abstract: We report active Q-switching of an all-fiber laser using a Bragg grating based acousto-optic modulator. Q-switching is performed by modulating a fiber Bragg grating with an extensional acoustic wave. The acoustic wave modulates periodically the effective index profile of the FBG and changes its reflection features. This allows controlling the Q-factor of the cavity. Using 1 m of 300 ppm erbium-doped fiber and a maximum pump power of 180 mW, Q-switch pulses of 10 W of peak power and 82 ns wide were generated. The pulse repetition rate of the laser can be continuously varied from few Hz up to 62.5 kHz.

High-resolution refractive index sensing by means of a multiple-peak surface plasmon resonance optical fiber sensor

Abstract: When a thin metal layer is deposited on a single-mode tapered optical fiber the layer takes a semi-cylindrical shape The fundamental fiber mode can excite the different hybrid surface plasmon modes supported by the semi-cylindrical metallic shell As a consequence, the transmission spectrum of the device exhibits multiple resonance peaks with either TE- or TM-polarized light The positions of those peaks are remarkably shifted when the refractive index of the medium adjacent to the metal layer changes Experimentally, we have found that by monitoring the first three resonance peaks a refractive index resolution of about 7 × 10 −7 can be achieved Our devices can be used for high-resolution biosensing

Low-cost optical fiber refractive-index sensor based on core diameter mismatch

Abstract: A simple, compact, and low-cost optical fiber refractive-index (RI) sensor is reported. It consists of a multimode fiber in which a short section of standard single-mode fiber (SMF) is inserted. Owing to the core diameter mismatch, the cladding of the SMF guides light. This makes the device sensitive to the external RI. The maximum resolution of the sensor is about 7times10-5. The fabrication of the sensor only requires cleaving and fusion splicing; moreover, the device can operate at different wavelengths, which makes it attractive for diverse applications

Stable single-mode operation of a narrow-linewidth, linearly polarized, erbium-fiber ring laser using a saturable absorber

Abstract: This paper describes the design and operation of a stable narrow-linewidth linearly polarized fiber ring laser using a polarization-maintaining (PM) erbium-doped fiber as a saturable absorber. The effect of the PM fiber on suppressing mode hopping is experimentally demonstrated and optimum conditions for single-mode operation are identified. Laser output power is /spl sim/ 4.7 mW at 1535 nm for a pump power of 94 mW, the polarization extinction ratio is 24.8 dB, the SNR is larger than 45 dB, the relative intensity noise is below -104 dB/Hz at frequencies above 150 kHz, and the linewidth is less than 1.5 kHz. Potential applications of the fiber laser for interferometric or spectroscopic fiber sensors are briefly discussed.

A distributed optical fiber sensor for temperature detection in power cables

Abstract: The power transfer capacity of an underground power cable is limited by high-temperature regions that occur along the cable. It is very difficult to determine and control these ‘hot spots’. Optimum use and temperature profile control of power cables before and during load transmission can be achieved with real-time processing of temperature data. There are various methods developed for this purpose such as conventional point temperature measurement method, where a large number of sensors and connectors are required, and methods based on mathematical models which can only approach real values by approximation. In this study, temperature detection in an XLPE insulated 154 kV power cable is performed using a distributed sensing method where the optical fiber itself behaves as a sensor. Therefore, there is no need for the devices of conventional method. Moreover, contrary to methods based on mathematical models, where it is difficult to predict environmental variations, this method considers the variations with a temperature resolution of ±1 °C. Distributed temperature sensing (DTS) method, detection system configuration and required system parameters are explained in the paper. Experimental results obtained for 126 and 412 m cables show a temperature resolution of ±1 °C and a spatial resolution of 1.22 m. Simulations for a 10 km cable are also given. Results show that DTS is a reliable method for both short and long range cable systems.

Design of Humidity Sensors Based on Tapered Optical Fibers

Abstract: In this paper, the response of a tapered optical fiber humidity sensor is optimized, attending to the thickness of the sensitive coating, the dimensions of the taper, the light source, and the utilization of sensitive materials with different refractive indexes. The main novelty of this study is that the thickness of the sensitive layer is on the order of magnitude of the light wavelength used to excite the sensor. It is shown here that an estimation of the sensor sensitivity can be deducted from the transmitted optical power curve obtained during the layer-by-layer construction process. Theoretical and experimental results are presented

Optical fiber long-period grating humidity sensor with poly(ethylene oxide)/cobalt chloride coating

Abstract: A long-period fiber grating (LPFG) humidity sensor is reported utilizing poly(ethylene oxide)/cobalt chloride (PEO/CoCl2) as a hybrid hygrosensitive cladding coating. A thin overlay of the material is deposited on the LPFG and with exposure to different ambient humidity levels, its spectral properties are modified. The material parameters associated with the sensing mechanism may include those of refractive index, absorption, and morphological alterations of the overlaid material. Relative humidity variations in the range from 50% to 95% have been detected with a resolution better than 0.2%. The response time constant of the fiber sensor is of the order of a few hundred milliseconds.

Low temperature monitoring system for subsurface barriers

Abstract: The invention provides a system for monitoring temperature of a subsurface low temperature zone, that includes a plurality of freeze wells (114) configured to form the low temperature zone; at least one monitor well; one or more lasers; a fiber optic cable (146) coupled to at least one laser (142), and an analyzer (144) coupled to the fiber optic cable. A portion of the fiber optic cable is positioned in at least one monitor well. At least one laser is configured to inject light pulses into at least one end of the fiber optic cable. The analyzer is configured to receive return signals from the light pulses. The invention also provides methods for monitoring temperature of a subsurface low temperature zone.

High-temperature fiber-tip pressure sensor

Abstract: This paper presents a miniature fiber-optic high-temperature pressure sensor fabricated on the tip of a singlemode (SM) fiber by means of fusion splicing, cleaving, and wet chemical etching. A new approach was developed to simplify the fabrication and greatly improve the sensitivity. The sensor is made entirely of fused silica, whose high-temperature sensing capability is explored in detail for the first time. Two sensors were tested up to 611/spl deg/C and 710/spl deg/C, respectively, showing excellent repeatability better than 0.62% and 1.4%. The maximum operating temperature is limited by the mechanical creep of the fused silica diaphragm.

Highly efficient Brillouin slow and fast light using As(2)Se(3) chalcogenide fiber.

Abstract: We demonstrate the generation of slow and fast light based on stimulated Brillouin scattering in As2Se3 chalcogenide fiber with the best efficiency ever reported. The Brillouin gain of 43 dB is achieved with only 60-mW pump power in a 5-m single-mode chalcogenide fiber, which leads to the optical time delay of 37 ns with a 50-ns Gaussian pulse.

Optical inclinometer based on a single long-period fiber grating combined with a fused taper.

Abstract: A new concept to measure rotation angles based on a fiber-optic modal Mach-Zehnder interferometer is demonstrated by using a nonadiabatic taper cascaded with a long-period fiber grating. Information about the magnitude of the rotation angle can be obtained from the measurement of the interference pattern visibility, and under certain conditions it is also possible to obtain the sign of the rotation angle from the induced phase variation in the fiber interferometer.

Nearly transparent SBS slow light in an optical fiber.

Abstract: Slow-light delay via stimulated Brillouin scattering (SBS) in optical fibers is usually achieved with delay-dependent amplification that degrades system performance. To address this problem, we propose a SBS slow-light method that makes use of two widely separated anti-Stokes absorption resonances, and achieve nearly transparent slow light in an optical fiber. We demonstrate the method in a highly nonlinear optical fiber, and achieve a slow-light bandwidth of ~150 MHz and a relative of delay of ~0.3 for ~9-ns pulses with a signal attenuation of ~4.8 dB.