Showing papers on "Fiber optic sensor published in 1984"

Fiber-optic sensors for biomedical applications

Abstract: In this article the development of fiber-optic sensors for biomedical applications is reviewed. Light-carrying fibers are potentially useful in oximetry, dye dilution measurements, laser-Doppler velocimetry, and fluorometry; as physical sensors of temperature, pressure, and radiation; and as chemical sensors of pH, partial pressure of blood gases, and glucose. Emphasis is placed on the principles and ideas used in the various devices rather than on detailed descriptions or critical discussions.

An overview of fiber-optic gyroscopes

Abstract: The principles of operation of fiber-optic gyroscopes are reviewed. Performance-limiting phenomena are discussed along with methods to reduce their effect on the rotation-rate signal. Current technology and performance of state-of-the-art systems are presented. Finally, a direction of future research and possible applications are indicated.

Fiber Optic Communications

Abstract: Preface. 1. Fiber Optic Communications Systems. 2. Optics Review. 3. Lightwave Fundamentals. 4. Integrated Optic Waveguides. 5. Optic Fiber Waveguides. 6. Optical Sources and Amplifiers. 7. Light Detectors. 8. Couplers and Connectors. 9. Distribution Networks and Fiber Components. 10. Modulation. 11. Noise and Detection. 12. System Design. Bibliography. Answers. Index.

Optical fiber hydrogen sensor

Abstract: A new type of hydrogen sensor is reported in which an optical fiber is used as the sensing element. The fiber is coated with palladium which expands on exposure to hydrogen. This changes the effective optical path length of the fiber, which is detected by interferometric techniques. Preliminary experiments have demonstrated the effect and suggest a high sensitivity and a wide dynamic range for this kind of sensor. The experimental results are compared to calculated optical path length changes. Application of this kind of sensor to the detection of other chemicals appears feasible.

Optical communications system using raman repeaters and components therefor

Abstract: An optical fiber communication system for transmitting information-bearing optical signals over an optical fiber transmission line includes a signal generator coupled to the transmission line for introducing information-bearing optical signals thereonto, preferably as wavelength modulated signals, and one or more optical amplifiers for periodically, collectively amplifying the transmitted signals to overcome the effects of attenuation. Wavelength modulation is achieved by altering the resonant characteristics of an optical resonator, optically coupled to a gain medium so as to provide an output that varies between a first and second wavelength. The optical amplification is achieved by injecting, preferably via lateral optical fiber couplings, pumping beams into the optical fiber so as to effect an increase in the amplitude of the information-bearing signals by stimulated Raman scattering.

Analytical method for calculation of stresses and material birefringence in polarization-maintaining optical fiber

Abstract: An analytical method is presented for the calculation of 1 thermal stress and the material birefringence in polarization-maintaining 1 optical fiber. The method is based on the thermoelastic displacement c potential in which the principle of superposition applies. The method is applicable to any fiber structure. Its application to fibers with isolated stress-producing regions and a variety of core shapes is demonstrated. The optimum fiber parameters required to achieve maximum material birefringence for fibers with circular or bow-tie shaped stress regions are given. It is also shown that the thermal stresses tend to make the bow-tie fiber more crack-resistant than the fiber with circular stress lobes.

High power laser energy delivery system

Abstract: A low-divergence 1.06 micrometer wavelength beam from a total-internal-reflection, face-pumped laser (TIR-FPL) is focused onto the end of a quartz optical fiber to a spot having a size smaller than the fiber diameter and with a beam cone angle less than twice the numerical aperture of the fiber. The fiber transmits the energy to emerge at the other end where it is collimated and focused onto material to be processed. A laser average output power level greater than 400 watts can be transmitted through an optical fiber having a diameter less than 600 micrometers.

Remote spectroscopic sensing of chemical adsorption using a single multimode optical fiber.

Abstract: A remote chemical sensor using a single optical fiber has been developed for collecting evanescently excited spectral signals from liquid samples. The sensor is particularly useful for the study of species adsorbed from solution onto the sensor surface. Fluorescence spectra were taken from dye solutions and dye-labeled proteins to demonstrate the evanescent operation of the probe. Raman data from benzene were collected to indicate its sensitivity in the bulk mode.

Fiber optical modulator and data multiplexer

Abstract: A data gathering system comprising a single optical fiber having one or more modulators formed thereon, means for launching into the fiber an interrogating light pulse which propagates in a first direction, means for generating at each modulator an optical return signal which propagates in the fiber in a second direction opposite the first direction and which has an intensity which is variable in response to variations in an external signal incident at the modulator, and means for detecting and processing each such return signal. The return signal comprises a portion of the interrogating light pulse which is coupled into the fiber in the second direction via evanescent coupling. The return signal from each modulator (or array of modulators) is identified via time division multiplexing. A signal processing means may be coupled to the fiber for generating a unique return signal from each of one or more modulator arrays, each array comprising a selected subset of the modulators. In a preferred embodiment, each modulator comprises a looped section of the fiber having a coupling region in which the distance between adjacent fiber segments is variable in response to variations in an external signal incident thereon. In another embodiment, each modulator comprises a short fiber segment positioned adjacent to the main fiber and separated therefrom by a distance variable in response to pressure changes incident on the modulator.

Polarizer requirements for fiber gyroscopes with high-birefringence fiber and broad-band sources

Abstract: Polarizer requirements for fiber-optic gyroscopes with high-birefringence fiber and broad-band sources are investigated theoretically by employing a model with a single coupling center between polarization modes. The phase bias offset due to a finite polarizer extinction ratio is greatly reduced by incoherent effects, and may be further reduced by using a depolarized source or by appropriate orientation of the polarizer transmission axis. Some experimental data is presented which supports the theoretical model.

Distributed Sensing Using Stimulated Raman Interaction In A Monomode Optical Fibre

Abstract: A distributed optical-fibre stress sensor with a measurement path length of 25m and a spatial resolution of lm is described. The sensor, the first of its kind, uses the stimulated Raman interaction between counterpropagating pump and Stokes waves.

Passive sampling interferometric sensor arrays

Abstract: This invention provides a sensor array using a plurality of fiber optic sensors connected between transmit fibers and receive fibers The laser transmitter supplies pulses to the transmit fiber and fiber optic couplers couple the pulses from the transmit fiber into the fiber optic sensors The pulses from the laser transmitter may be frequency chirped or frequency stepped to provide passive sampling of interferometric sensors in addition to intensity sensors, or otherwise frequency modulated Each sensor is configured to respond to changes in a predetermined physical parameter by altering the shape of the pulse input thereto Fiber optic couplers couple the sensor output signals into the receive fiber for input to a receiver, which converts the optical signals into electrical signals for input to a processer A timing reference correlates the sensor output pulses with the sensors

Fiber optic interferometer transducer

Abstract: A sensor or transducer having a dual path optical fiber, such as a single mode, two polarization state, waveguide fiber, utilizes the relative change in propagation constant of the paths to sense and transduce an applied force to an interference variation and ultimately an electrical signal. In this arrangement, in-phase light is introduced to both polarized states or paths in the fiber and transmitted therealong past a stress area of birefringement inducing force and ultimately combined, thereby producing in the combined beam a variation in interference which is related to the applied force. Specific structures are provided for converting isotropic forces such as pressure and temperature to anisotropic forces on the fiber to thereby produce birefringement and to also magnify the latter effect.

Progress in monomode optical-fiber interconnection devices

Abstract: We review recent progress in coupling devices for monomode fiber systems, with an eye towards practical performance limits in the near future. Emphasis is placed on key subjects such as laser-to-fiber coupling and packaging, connectors, and splicing. In addition, we also discuss planar lenses which are being developed for various applications.

Fiber optic structure and method for making.

Abstract: A fiber optic structure comprising an optical fiber having a body of material deposited upon the exterior surface such that the body of material is sufficiently strong and rigid to permit processing of the fiber for various fiber optics applications. The process for forming the fiber optic structure involves the electroplating of a body of material upon the exterior surface of the optical fiber which is to be processed. A built-up body on fiber allows coupling structures to be created. The built-up body enables the fiber to be used as liquid level sensors and other types of mode strippers.

Wavelength-division-multiplexed receiver array for vertical seismic profiling

Abstract: An optical telemetric system for use in a borehole consists of a bidirectional optical fiber to which are coupled a plurality of acousto-optical seismic sensors. The sensors consist of an optical cavity that becomes resonant at certain wavelengths depending upon parameters of cavity length and index of refraction. Those parameters are capable of being modified on the basis of static and dynamic pressure differences within the borehole. A swept-wavelength laser chirp pulse is launched into the bidirectional optical fiber. The static pressure at each sensor establishes a resonant wavelength that serves as a carrier signal. Dynamic pressure changes due to seismic waves, modulate the carrier signal. The modulated carrier signals from each sensor are reradiated through the bidirectional optical fiber in a wavelength-division multiplexed format. The multiplexed signals are received by and demultiplexed by a suitable signal receiving apparatus.

Method of aligning a polarization-preserving optical fiber with a semiconductor laser for attachment of the fiber to the laser

Abstract: A method of aligning the polarization-preserving axis of a receiving end of a polarization-preserving optical fiber with the linearly-polarized output of a semiconductor laser in which the fiber optic end is placed substantially adjacent the laser rather than being separated from the laser by a polarizing optical system.

Nuclear and pressure sensitive line/perimeter detection system

Abstract: A system for simultaneously detecting nuclear radiation and pressure combines light signals from a radiation sensitive scintillating optical fiber with light signals from a pressure sensitive optical fiber. The scintillating fiber is coupled to a light transmitting optical fiber for long distance light transmission to a detector unit such as a photomultiplier tube. The concurrent detection of radiation and pressure of radiation and pressure is used to trigger an alarm signal.

Switching fiber optic amplifier

Abstract: A fiber optic amplifier utilizes a crystal fiber of laser material to bidirectionally amplify light signals This amplifier permits the application of both pumping illumination and the signal to be amplified to the end of the crystal fiber to avoid the disadvantages inherent in side pumping this fiber End pumping is accomplished by taking advantage of the slow spontaneous fluorescence of the laser crystal to sequentially apply the pumping illumination and then the signal to be amplified to the crystal This sequential application of signals is made possible through the use of a switchable coupler which allows light to be selectively coupled from either of a pair of input optical fibers to a single output optical fiber which is coupled to the crystal fiber The pumping illumination is initially supplied to the crystal fiber to invert the ions within the crystal Once these ions are inverted, the coupler is switched to permit the application of the signal to be amplified to the crystal, and the application of pumping illumination is temporarily discontinued The signal to be amplified propagates through the crystal to stimulate emission of coherent light from the laser material resulting in amplification of the signal When this amplification process is complete, pumping illumination is again applied through the switch to the crystal fiber

All-fiber gyroscope with polarization-holding fiber

Abstract: An all-fiber gyroscope is reported that is constructed entirely of polarization-holding fiber. The random-drift coefficient was 5 x 10(-3) deg/ radicalh. Gyro bias drift is shown to be stable over periods of hundreds of hours. Device construction details and some thermal dependence of components are given.

Design and performance of tuned fiber coil isolators

Abstract: Optical isolators using coiled single-mode fibers with controlled birefringence have been thoroughly analyzed and tested experimentally. Isolation ratios as high as 44.5 dB with insertion losses (excluding coupling and polarizer losses) of 0.3 to 0.4 dB have been obtained at 633 nm. Analysis indicates that these devices will have >20-dB isolation over a spectral range of 2.5 nm or a temperature range of 36°C.

Fiberoptic temperature/pressure sensor system

Abstract: A fiberoptic sensing system comprising a light source, a sensor responsive to external stimulus, an optical fiber connected to the light source and the sensor, a detector arranged to receive light from the optical fiber, and output electronics electrically connected to the detector. The sensor includes a reflective surface arranged so as to reflect light from the optical fiber. This reflective surface is movable relative to the optical fiber. The light source comprises a light-emitting diode and a reference diode electrically connected to the source of electrical energy and to the light-emitting diode. A beamsplitter is disposed about the light source, the optical fiber, and the photodetector. The detector includes a transimpedance amplifier and a RMS to DC converter. The output electronics includes a gain control and a offset control. The sensor may be either a temperature sensor or a pressure sensor.

Optical fiber mode scrambler

Abstract: The present invention relates to a mode scrambling arrangement for a multimode or graded-index optical fiber and, more particularly, to an optical fiber mode scrambler achieved by forming a deformation as, for example, a groove or notch on one side of the multimode or graded-index optical fiber orthogonal to the longitudinal axis thereof. The groove or notch can be produced by any suitable etching or machining process to extend through the cladding layer and at least very slightly into the outer surface of the core of the multimode or graded-index optical fiber. The depth of the groove or notch into the core can be controlled by monitoring the mode pattern in the multimode fiber during the etching or machining process to provide maximum mode scrambling with minimal loss.

Fiber-optic microbend sensors: sensitivity as a function of distortion wavelength

Abstract: The attenuation of optical power in multimode fibers with parabolic-index profiles has been analyzed as a function of the distortion wavelength in microbend sensors with sharp ridges. In agreement with the theory, measurements show that attenuation peaks of almost equal strength originate from the fundamental and the odd higher harmonics in the distortion spectrum.

Electronically switched fiber optic directional coupler

Abstract: This invention relates to an electrically switchable fiber optic directional coupler. Two oppositely oriented blocks of an interaction material are placed adjacent the fibers in an evanescent field coupler. Application of an electromagnetic field to the interaction material increases the refractive index of one fiber and decreases the refractive index of the other. The change in refractive indices of the blocks of the interaction material increases the propagation constant of one fiber and decreases that of the other fiber. The coupling of optical signals between the fibers may be varied between zero and l00% by controlling the applied field to change the propagation constants between values that provide complete cross coupling of light from one fiber into the other and straight through propagation provides an electrically controllable switching action.

Fiber gyroscope with phase-modulated single-sideband detection.

Abstract: Phase-modulated single-sideband detection is applied to a fiber gyroscope. The Sagnac phase is linearly transposed into the phase of an electrical low-frequency signal by using an integrated-optic phase modulator, which is driven by a proper modulating waveform. This detection scheme can provide a high dynamic range. The principle and first experimental results are reported.

Surface roughness studies with DALLAS-detector array for laser light angular scattering

Abstract: An instrument has been developed to study surface roughness by measuring the angular distributions of scattered light. In our instrument, a beam from a He-Ne laser illuminates the surface at an angle of incidence which may be varied. The scattered li,.ght'distribution is detected by an array of 87 fiber optic sensors positioned in a semicircular yoke which can be rotated about its axis so that the scattered radiation may be sampled over an entire hemisphere. The output from the detector array is digitized, stored, and analyzed in a laboratory computer. The initial experiments have concentrated 'on measurements of stainless steel surfaces which are highly two-dimensional and which yield scattering distributions that are localized in the plane of incidence. The results are analyzed by comparing the angular scattering data with theoretical angular scattering distributions computed from digitized roughness profiles measured by a stylus instrument. The theoretical distributions are calculated by substituting the roughness profiles into the operand of an integral equation for electromagnetic scattering developed by Beckmann and Spizzichino. This approach directly tests the accuracy of the basic optical theory.