Showing papers on "Fiber optic sensor published in 1999"

Fabrication of long-period fiber gratings by focused irradiation of infrared femtosecond laser pulses

Abstract: We have fabricated long-period fiber gratings by use of a novel technique using focused irradiation of infrared femtosecond laser pulses. We investigate the thermal stability of the fabricated fiber gratings. The values of the loss peak wavelength and the transmittance of the fiber gratings after heat treatment below 500°C are the same as initial values before heat treatment. The fiber gratings that were fabricated by this technique have a high resistance to thermal decay. We propose that this technique mill be useful for fabrication of fiber gratings with a superior aging characteristic.

Optical Fiber Sensor Technology

Abstract: List of contributors. Preface. 1. Overview of fiber sensor developments D.A. Jackson. 2. Foundations of optical fiber technology V. Handerek. 3. Sources for optical fiber sensors K.T.V. Grattan. 4. Optical detectors and receivers J.D.C. Jones. 5. Multimode optical fiber sensors G.R. Jones, R.E. Jones, R. Jones. 6. Multimode optical fiber chemical sensors J.O.W. Norris. 7. Single mode optical fiber sensors V. Handerek. 8. Optical fiber modulation techniques for single mode fiber sensors R.P. Tatam. 9. Fiber optic white-light interferometric sensors B.T. Meggitt. 10. Nonlinear effects in optical fibers A.J. Rogers. 11. Distributed fiber optic sensors A.H. Hartog. 12. Schemes for referencing of intensity-modulated optical sensor systems G. Murtaza, J.M. Senior. 13A. Hybrid optical fiber sensors R.C. Spooncer, G.S. Philp. 13B. Optical fiber current measurement A.J. Rogers. 13C. Fiber optic techniques for temperature measurement K.T.V. Grattan. 14. Advanced external fiber optic sensors D.A. Jackson. Index.

Pd-coated elastooptic fiber optic Bragg grating sensors for multiplexed hydrogen sensing

Abstract: We report a new type of optical hydrogen sensor with a fiber optic Bragg grating (FBG) coated with palladium thin film. The sensing mechanism in this device is based on mechanical stress that is induced in the palladium coating when it absorbs hydrogen. The stress in the palladium coating stretches and shifts the Bragg wavelength of the FBG. Using FBGs with different wavelengths many such hydrogen sensors can be multiplexed on a single optical fiber. Here multiplexing two sensors is demonstrated. Moreover, hydrogen and thermal sensitivities of the sensors were calculated using a simple elastic model. Additionally, to quantify the amount of stress in the palladium film as a function of hydrogen concentration, a novel and very sensitive method was devised and used to detect deflections in a Pd-coated cantilever using an evanescent microwave probe. This stress was in the range of 5.26–8.59×10−7 Pa for H2 concentrations of 0.5–1.4% at room temperature, which is about three times larger than that found in the bulk palladium for the same range of H2 concentrations.

Spontaneous Raman scattering in optical fibers with modulated probe light for distributed temperature Raman remote sensing

Abstract: Long-length fiber-optic remote Raman sensors are used for distributed temperature measurements. Toward this aim, we apply optical-fiber frequency-domain reflectometry. The Raman intensity generated in single- and multimode optical fibers is theoretically investigated for sinusoidally intensity-modulated probe light. Thus, a proper sensor element and wavelength for fiber-optic Raman sensing is determined. Further, the temperature error for long sensor fibers is theoretically analyzed.

Highly sensitive hydrogen sensors using palladium coated fiber optics with exposed cores and evanescent field interactions

Abstract: A novel fiber optic hydrogen sensor which is constructed by depositing palladium over an exposed core region of a multimode fiber is reported. The sensing mechanism is based on evanescent field interaction with the palladium coating. Since the length, thickness, and composition of the palladium patch can be controlled independently of each other, it is possible to increase the speed of our sensor at lower temperatures while maintaining its sensitivity. In micromirror sensors such an optimization is not possible due to a restriction imposed on their active area of interaction by the fiber optic cross-section. Micromirror fiber optic sensors, studied in the past, take advantage of the reflection/absorption of a palladium film deposited at the end of a fiber resulting in one sensor per fiber optic strand. On the other hand, many evanescent field-based sensors can be deposited over a single fiber optic strand. Using a 100 A thick palladium with 1.5 cm interaction length, we could detect hydrogen in the 0.2–0.6% range with corresponding response times of 30–20 s at room temperature. At −10°C, these response times increased by a factor of only 2.

Guide wire assembly

Abstract: Systems and methods for guiding the advancement of a guide wire through body tissue are described. In one embodiment, the guide wire has a first end, a second end, or guide wire head, a bore (34) extending through the first ends, the second ends, and includes an interferometric guidance system (22). The interferometric guidance system (22) includes a low coherent illumination source (46), an optical beam splitter (40), a first optic fiber (42), a second optic fiber (44), and a photo-detector (52). Each optic fiber includes a first end, a second end, and is wrapped around a piezoelectric transducer (48, 50). The second optic fiber (44) has a fixed reflector on the second end. The photo-detector (52) is configured to determine interference between a first reflected light beam propagating through the first optic fiber (42), and a second reflected light beam propagating through the second optic fiber (44).

Long-period fiber gratings based on periodic microbends.

Abstract: We demonstrate a new type of high-performance long-period fiber grating based on arc-induced periodic microbends. The fabrication method is simple and does not require special fibers. Flexibility in controlling the filter parameters makes it possible to produce arbitrary filter profiles by use of a simple apodization technique, which is difficult to do with conventional long-period gratings.

Single-mode optical fiber surface plasmon resonance sensor

Abstract: A fiber optic surface plasmon resonance (SPR) sensor utilizing the resonant interaction between a guided mode of a single-mode optical fiber and a surface plasma wave supported by a thin metal film is described. Theoretical analysis of the SPR sensing structure based on the equivalent planar waveguide approach and the mode expansion and propagation method is presented. A detailed analysis of the effect of the major parameters of the SPR sensing structure on the sensor performance is carried out. Experimental results obtained with fabricated laboratory prototypes of the SPR sensing device for measurement of the refractive index of analyte are reported. It has been demonstrated that the fiber optic SPR sensing device may be used as a spectral as well as an amplitude sensor.

Fiber Bragg Grating Temperature Sensor with Controllable Sensitivity

Abstract: We demonstrate a fiber Bragg grating (FBG) sensor with controllable sensitivity by connecting two metal strips that have different temperature-expansion coefficients. By changing the lengths of the metal strips we successfully controlled and improved the temperature sensitivity to 3.3 times of that of bare FBG.

A fiber optic sensor for transverse strain measurement

Abstract: A fiber optic sensor capable of measuring two independent components of transverse strain is described. The sensor consists of a single Bragg grating written into high-birefringent, polarization-maintaining optical fiber. When light from a broadband source is used to illuminate the sensor, the spectra of light reflected from the Bragg grating contain two peaks corresponding to the two orthogonal polarization modes of the fiber. Two independent components of transverse strain in the core of the fiber can be computed from the changes in wavelength of the two peaks if axial strain and temperature changes in the fiber are zero or known. Experiments were performed to determine the response of the sensor by loading an uncoated sensor in diametral compression over a range of fiber orientations relative to the loading. The results of these experiments were used with a finite element model to determine a calibration matrix relating the transverse strain in the sensor to the wavelength shifts of the Bragg peaks. The performance of the sensor was then verified by measuring the transverse strains produced by loading the fiber in a V-groove fixture.

Bragg grating pressure sensor

Abstract: A fiber grating pressure sensor includes an optical sensing element (20, 600) which includes an optical fiber (10) having a Bragg grating (12) impressed therein which is encased within and fused to at least a portion of a glass capillary tube (20) and/or a large diameter waveguide grating (600) having a core and a wide cladding and which has an outer transverse dimension of at least 0.3 mm. Light (14) is incident on the grating (12) and light (16) is reflected from the grating (12) at a reflection wavelength μ1. The sensing element (20, 600) may be used by itself as a sensor or located within a housing (48, 60, 90, 270, 300). When external pressure P increases, the grating (12) is compressed and the reflection wavelength μ1 changes.

Optical fiber/waveguide illumination system

Abstract: A fiber optic illumination system includes a light source, a waveguide, and an optical fiber. One or more lamps and/or solid-state devices may be employed as the light source. The waveguide includes a straight collecting segment, a tapered condensing segment, and a straight homogenizing segment, may be fabricated from fused silica as a single monolithic component, conveys light from the light source to the optical fiber by transmission and/or internal reflection, and may be provided with UV and/or IR blocking filter coating(s). The optical fiber may be colorless or fluorescent optical fiber. Light transmitted by the optical fiber may be delivered to any one or more of a variety of light output devices, including diffusive flat panels, diffusive rods or wands, fluorescent light emitting converters, projectors, spectrum generators, and so on.

Non-intrusive fiber optic pressure sensor for measuring unsteady pressures within a pipe

Abstract: Non-intrusive pressure sensors (14-18) for measuring unsteady pressures within a pipe (12) include an optical fiber (10) wrapped in coils (20-24) around the circumference of the pipe (12). The length or change in the length of the coils (20-24) is indicative of the unsteady pressure in the pipe. Bragg gratings (310-324) impressed in the fiber (10) may be used having reflection wavelength μ that relate to the unsteady pressure in the pipe. One or more of sensors (14-18) may be axially distributed along the fiber (10) using wavelength division multiplexing and/or time division multiplexing.

Fiber laser hydrophone array

Abstract: In recent years growing interest has surrounded the development of fiber laser sensors (FLS). This is due to their ultra high sensitivity to temperature and strain as well as their ability to be multiplexed along a single fiber using WDM techniques. It is their extreme sensitivity that has led to them being considered as acoustic pressure sensors rather than standard fiber Bragg gratings. The work presented here describes the development of an array of FLS configured as hydrophones. We discuss the design of the single mode fiber laser used throughout our system; comparing examples based upon distributed Bragg reflectors (DBR) and distributed feedback (DFB). In addition we discuss both the theoretical and experimental acoustic sensitivity enhancements obtained by the application of an elasto-plastic coating to the FLS. The array configuration is described, as is the heterodyne interrogation scheme using an unbalanced Mach-Zehnder interferometer with WDM channel selection. Results from the measurement of the minimal detectable acoustic signal of a bare fiber laser are shown to be -69 dB re.Pa/(root)Hz at 1 kHz when using a 200 m path imbalanced readout interferometer. Further gains in the sensitivity due to the application of various coatings are reported, as is a full characterization of an array of fiber laser hydrophones. Finally we discuss the future research of the FLS, and the areas in which the technology is particularly applicable.

Simultaneous measurement of strain and temperature by use of a single-fiber Bragg grating and an erbium-doped fiber amplifier

Abstract: We propose and demonstrate a novel sensor by using a single-fiber Bragg grating that can simultaneously measure strain and temperature with the aid of an erbium-doped fiber amplifier. By using a linear variation in the amplified spontaneous emission power of the erbium-doped fiber amplifier with temperature, we determine the temperature. By subtracting the temperature effect from the fiber Bragg grating Bragg wavelength shift, we determine the strain. Experiments show rms deviations of 18.2 µe and 0.7 °C for strain and temperature, respectively.

Tuning Dynamic Range and Sensitivity of White-Light, Multimode, Fiber-Optic Surface Plasmon Resonance Sensors

Abstract: This paper presents the advantages of modifying the geometry of the sensing tip of a white-light, multimode optical fiber SPR sensor to optimize the dynamic range and sensitivity. By selectively beveling the distal end of the fiber probe, the wavelength of resonance can be red-shifted by more than 100 nm and blue-shifted by more than 30 nm. This increases the flexibility of a white-light SPR sensor by increasing the dynamic range of accessible RIs and by shifting the resonance to the most sensitive regions of the detector. Sensitivity, measured in wavelength shift per RI change, can be increased by a factor of 4. Also, multiple-wavelength regions of SPR activity can simultaneously be observed on the same probe, thus increasing the information content of a SPR spectrum.

Power density of the evanescent field in the vicinity of a tapered fiber

Abstract: The power density in the vicinity of a tapered fiber is calculated, with the vectorial model of step-index circular waveguides. For the fundamental HE11 mode carrying a power of 1 Watt, we show that it is possible to obtain theoretical densities in the range of 108 W/cm2 at the fiber surface. The promising use of such intense evanescent fields as “atomic mirrors” is considered, and the feasibility of these guides is investigated.

Tunable fiber optic parametric oscillator

Abstract: A tunable fiber optic parametric oscillator includes a nonlinear optical loop mirror or fiber Sagnac interferometer NFSI with a dispersion shifted fiber portion. The oscillator is synchronously pumped to amplify a signal wave, while reflecting the depleted pump pulse back towards the pump. The amplified signal wave and simultaneously generated idler waves are directed to a spectral filter. The spectral filter may be a diffraction grating, a Faraday mirror or other optical filter that is tunable to change the signal wavelength that is reflected back to the NFSI. The fiber optic parametric oscillator is tunable over substantially the entire gain bandwidth and is insensitive to the polarization of the pump pulses. The fiber optic parametric oscillator may be used as a tunable source of short pulses for high speed optical communication systems. The fiber optic parametric oscillator may also be used for synchronization and clock recovery.

Connector for coupling an optical fiber tissue localization device to a light source

Abstract: A quick-connect coupling couples an optical fiber tissue localization device to a light source to cause the forward tip of the device to illuminate. The coupling can be quickly, easily, and reliably mounted to the fiber under operating room conditions. The coupling physically isolates the optical fiber from the light source while optically coupling the fiber to the light source, thereby preventing contamination of the light source by a contaminated optical fiber. The coupling is inexpensive to manufacture, such that the coupling is disposable after a single-patient use.

Fiber optic network using space and wavelength multiplexed data channel arrays

Abstract: A network for multi-bit word parallel communication between optoelectronic chips on a two dimensional array of optical input and output channels carried on a single dimension of optical fibers. Each bit of a word is carried on a different wavelength and the multiple wavelengths carrying a word are wavelength multiplexed onto a single optical fiber. Multiple fibers can be joined into a one dimensional array of fibers. A transceiver for transmitting and receiving along the optical data channels comprises an array of modulators powered by individual wavelength light beams, either from individual monochromatic light sources and a light beam from a single broadband light source made to pass through a diffraction grating. The modulators are positioned so that each modulator reflects a different wavelength light beam, thereby providing multiple optical channels. Alternatively, multiple wavelengths are generated from CMOS integrated light sources. These multiple optical channels are then collimated and guided into one single mode fiber or multiple multimode fibers at its transmitting end. At the receiving end a diffraction grating is used to separate the distinct data channels by their individual wavelengths. The multiple wavelengths are then caused to fall on an array of optical detectors spaced according to the individual wavelengths to be detected. By constructing a one dimensional array of these fibers, a two dimensional array of optical data channels is realized. The size of the array is determined by the number of fibers and the number of distinct wavelengths combined in each fiber.

Transverse load sensing by use of pi-phase-shifted fiber Bragg gratings

Abstract: The birefringence of a pi -phase-shifted fiber Bragg grating can be determined with high accuracy by measurement of the polarization-induced spectral splitting of its narrow central transmission window. The use of this feature for sensing of a load applied in the direction transverse to the optical fiber is demonstrated. A distributed force resolution of 1.4x10(-3) N/mm was obtained, which corresponds to a difference in the principal strains of the fiber core of 0.5mu? . We also show that the transverse load response of the sensor is insensitive to temperature.

Methods and apparatus for filtering an optical fiber

Abstract: Filtering of optical fibers and other related devices. High-energy methods for depositing thin films directly onto the ends of optical fibers can be used to produce high-quality, high-performance filters in quantity at a reasonable cost. These high-quality filters provide the high performance needed for many demanding applications and often eliminate the need for filters applied to wafers or expanded-beam filtering techniques. Having high-quality filters applied directly to optical fiber and faces permits production of high-performance, micro-sized devices that incorporate optical filters. Devices in which these filters may be used include spectroscopic applications including those using fiber optic probes, wavelength division multiplexing, telecommunications, general fiber optic sensor usage, photonic computing, photonic amplifiers, pump blocking and a variety of laser devices.

Fiber amplifiers and pumping sources for fiber amplifiers

Abstract: An optical amplifier system includes a fiber amplifier doped with rare earth dopant provided in its fiber core. A plurality of fiber lasers have their light outputs optically coupled together for launching into the fiber amplifier for optically pumping the amplifier. Each of the fiber lasers have a rare earth dopant provided in its fiber core for stimulated lasing emission with the rare earth dopant of the fiber amplifier being different from the rear earth dopant of the fiber lasers. A reflector may be provided in each of the coupling fibers for reflecting a portion of the respective light outputs back into the fiber lasers to control their wavelength of operation, the wavelength of operation of the reflectors chosen to be within a high absorption region of the absorption band of the fiber amplifier. Where the pump source is a semiconductor laser source, the source may include a flared gain section to increase the output intensity of the light output of the source.

Polarimetric distributed feedback fiber laser sensor for simultaneous strain and temperature measurements.

Abstract: We report the application of a dual polarization distributed feedback (DFB) fiber laser as a strain and temperature sensor. By measurement of the absolute wavelength of one polarization as well as the polarization beat frequency, strain and temperature were determined simultaneously. The sensor has an accuracy of +3 microepsilon and +/-0.04 degrees C. Self-heating of the DFB fiber laser as a function of pump power was measured with this sensor.

High total dose radiation effects on temperature sensing fiber Bragg gratings

Abstract: Fiber Bragg gratings (FBGs) written in a 10 mol.% Ge-doped core silica fiber using a phase mask were exposed to /spl gamma/-radiation. The transmission and reflection spectra were recorded during irradiation up to doses in excess of 1 MGy. There was no detectable change of the Bragg peak amplitude and the grating temperature sensitivity. The radiation-induced shift of the Bragg wavelength saturated at a dose of 0.1 MGy at a level less than 25 pm, which could still be decreased by optimization of the grating parameters. Our results confirm that FBGs are good candidates for sensing applications in radiation environments.

Design and realization of long-period grating devices in conventional and high birefringence fibers and their novel applications as fiber-optic load sensors

Abstract: We report the design and fabrication of long-period fiber gratings with single and cascaded structures in conventional and high birefringence (hi-bi) fibers using amplitude mask and point-by-point writing techniques. We also report a novel application of long-period gratings produced in nonhigh-birefringence fiber as fiber-optic load sensors exhibiting very high transverse strain sensitivity. Sensitivity some 800 times greater than previously reported fiber Bragg grating (FBG) sensors has been achieved.

Optical fiber and optical transmission system including the same

Abstract: The present invention relates to an optical fiber which enables favorable optical communications in 1.3-μm and 1.55-μm wavelength bands, and an optical transmission system including the same. The optical fiber according to the present invention has only one zero-dispersion wavelength within a wavelength range of 1.20 μm to 1.60 μm, the zero-dispersion wavelength existing within a wavelength range of 1.37 μm to 1.50 μm, and has a positive dispersion slope at the zero-dispersion wavelength, thereby enabling favorable optical communications utilizing each signal light in the 1.3-μm and 1.55-μm wavelength bands sandwiching the zero-dispersion wavelength.

Measurement of the degree of salinity of water with a fiber-optic sensor

Abstract: A fiber-optic sensor based on surface-plasmon resonance for the determination of the refractive index is used for measuring the degree of salinity of water. The transducing element consists of a multilayer structure deposited on a side-polished monomode optical fiber. Measuring the attenuation of the power transmitted by the fiber shows that a linear relation with the refractive index of the outer medium of the structure is obtained. The system is characterized by use of a varying refractive index obtained with a mixture of water and ethylene glycol. Experimental results show that the sensor can be used as a salinity-degree measurement device with environmental applications.

Fiber optic sensor for long-term analyte measurements in fluids

Abstract: A fiber optic sensor is disclosed in which an analyte permeable membrane encloses an interrogation region at the distal fiber end. A reservoir member is provided for continuous replenishment of the interrogation region with dye over the lifetime of the sensor. The reservoir member may comprise a permeable polymer material. The sensor may be configured as a specific ion sensor for analyzing dissolved analytes such as gases, cations, and anions. One embodiment comprises a CO2 sensor which has a reversible working dynamic detection range between 200 and 1000 ppm pCO2 and a sensitivity +/- 1 ppm. Methods for remote sensing are also disclosed using electro-optic and data acquisition modules coupled to a conventional satellite transmission system.