Showing papers on "Fiber optic sensor published in 1979"

Single-mode optical waveguides.

Abstract: An efficient and powerful technique has been developed to treat the problem of wave propagation along arbitrarily shaped single-mode dielectric waveguides with inhomogeneous index variations in the cross-sectional plane. This technique is based on a modified finite-element method. Illustrative examples were given for the following guides: (a) the triangular fiber guide; (b) the elliptical fiber guide; (c) the single material fiber guide; (d) the rectangular fiber guide; (e) the embossed integrated optics guide; (f) the diffused channel guide; (g) the optical stripline guide.

Polarization stabilization on single‐mode fiber

Abstract: The state of polarization at the output end of a long nominally circular single‐mode optical fiber is stabilized by an active control system. It contains a polarimeter and two electromagnetic fiber squeezers which introduce variable amounts of stress birefringence directly into the fiber, compensating for the effects of changing intrinsic fiber birefringence.

Fiber-ring interferometer: polarization analysis.

Abstract: In a rotation-sensing fiber-optical Sagnac interferometer, temperature fluctuations and mechanical vibrations affect the birefringence of the fiber and may cause phase shifts like those resulting from rotation. Insertion of polarizing elements, acting at both ends of the fiber, yields a stable phase.

Optical fiber acoustic sensor utilizing mode-mode interference.

Abstract: A method for detecting sound using a single step-index multimode fiber is presented. The detected signal results from differences in acoustically induced phase shifts between two different waveguide modes propagating in the fiber. The relative sensitivity of this technique compared with a two-path interferometer was experimentally determined and agreed with that calculated using the fiber parameters. Because the sensitivity of this approach is proportional to the difference in propagation constants for modes in the fiber, it is approximately 10−3 less sensitive than the single-mode interferometer arrangement.

Phase-nulling fiber-optic laser gyro

Abstract: A fiber-optic gyro is described that employs closed-loop phase compensation. Preliminary experimental results are reported of the sensing of rotation rates down to 0.5 degrees /sec for a 135-mm-radius, 100-m-length fiber coil.

Theory of cw Raman oscillation in optical fibers

Abstract: A theory for Raman fiber laser oscillators is presented. The Stokes output and the residual pump power are shown to be calculable from a knowledge of the input pump power and the fiber characteristics. The evolution of the pump and the Stokes waves along the fiber are also obtained. The threshold pump power and the oscillation condition are considered. Pump depletion is incorporated in the analysis and is shown to be the dominant saturation effect present in a Raman fiber laser.

Fiber optic acoustic sensors with composite structure: an analysis.

Abstract: Fiber optic acoustic sensors with composite structures are analyzed and shown to offer greatly increased acoustic sensitivity. The composite structure consists of an optical fiber coated with or embedded in an elastic material of lower elastic modulus. Sensitivity increases of 10–100 times are indicated. Important advantages of this technique in practical acoustic sensors are also described.

Method and apparatus for a Fabry-Perot multiple beam fringe sensor

Abstract: A method and the resulting apparatus for implementing a unique multiple beam fringe sensor that is adapted to be interfaced with a low cost, compact fiber optic transmission system in order to provide an accurate digital representation of a physical parameter (e.g. temperature) of a remote sample. The sensor is fabricated so as to include a Fabry-Perot gap formed between the ends of two mated optical fibers. By examining the optical characteristics of light that is transmitted through the Fabry-Perot sensor gap, an indication of gap width can be ascertained. Accordingly, a change in Fabry-Perot sensor gap width is related to a change in the particular physical parameter to be measured.

Fiber optic hydrophone: improved strain configuration and environmental noise protection.

Abstract: It is shown that the pressure sensitivity of a fiber-optic hydrophone is strongly dependent on the fiber’s strain configuration Longitudinal strain is found to be much more effective than uniform strain, and consequently modifications to the sensor’s design are proposed Environmental noise sources such as ocean motion and mechanical vibrations are then discussed, and a new double-cavity configuration, which is unaffected by those perturbations, is presented A tunable-cavity detection method is finally proposed, and it is shown how this method can overcome problems related to drift of the point of operation, laser intensity fluctuations, and nonlinearity for high dynamic ranges

Wavelength selective optical coupler

Abstract: An optical coupler for a fiber optic communication system, which couples one band of wavelengths out of the fiber while allowing others to be carried further. This allows wavelength division multiplexing of different signals within a single fiber. The preferred embodiment of the invention is comprised of a waveguide having aperiodic corrugations in one wall and a Fabry-Perot type resonator enclosing the waveguide around the corrugations with its axis transverse thereto.

Intrusion sensor using optic fiber

Abstract: A transparent continuous optical fiber is embedded in a transparent panel made of glass or plastic, with the two ends of the fiber accessible from outside the panel for coupling to a visible or invisible light source and detector respectively. By nearly matching the refractive indices of the panel and the fiber, and using good-quality material for the fiber so that it does not scatter significant amounts of the light passing through it, the fiber can be made virtually invisible although it establishes a complete light circuit. Cutting or breaking through the panel at a point intersecting the fiber interrupts the light circuit and triggers an alarm.

Single-mode fiber-optical polarization rotator.

Abstract: A birefringent single-mode optical fiber is twisted mechanically in alternating sense on successive half-wave fiber sections. This arrangement, applicable in-line to a fiber, permits continuous adjustment of the state of polarization at the fiber output.

Fiber optic intruder alarm system

Abstract: An intruder alarm for protecting the perimeter of an area utilizes a multimode optic fiber as the deformable sensing element, wherein a length of multimode optic fiber is buried in the ground of an area or perimeter to be protected. As coherent light from a laser is directed through a length of optic fiber, the output light pattern therefrom is speckled. When a deformation of the fiber occurs, even a small amount, the speckle pattern changes and is detected electronically indicating that a disturbance has taken place.

Fiber optical measurement apparatus

Abstract: The invention relates to an optical measuring device for measuring physical magnitudes such as position, speed, acceleration, force, pressure, elongation, temperature, etc., comprising at least one optical fiber for conducting light between an electronic unit and a transducer forming an optical modulator which is directly or indirectly influenced by the quantity being measured and, in dependence thereon, modulates the light emitted to the transducer. The transducer contains at least one optical filter having spectrally varying absorbing and/or transmitting and/or reflecting characteristics within the spectra of the emitted light. The light filter generates one or more stabilizing signals for the fiber optic and optoelectronics, and possibly one or more measurement signals within one or more wavelength ranges.

Optical resonator single-mode fiber hydrophone

Abstract: A hydrophone remotely senses impinging acoustic energy. Light output from a laser is split and launched into a single-mode fiber which transmits it to an optical resonator at its end. The resonator is made up of a fixed fiber end having a dielectric coating and a movable mirror which is displaced in response to an incident acoustic signal. The acoustic signal displaces the mirror so that mirror movement modulates the intensity of the reflected beam which is transmitted back through the single-mode fiber and received at a detector. The frequency and magnitude of the reflected beam yield acoustic signal information.

Fiber-optic acoustic sensors with increased sensitivity by use of composite structures

Abstract: Fiber-optic acoustic sensors having sensitivity nearly 2 orders of magnitude greater than that of sensors using bare fiber are reported. These new devices utilize a composite structure wherein the fiber is embedded in a material of lower elastic modulus that serves to increase the stress, and hence the optical phase shift, in the fiber for a given pressure.

Fiber optics security system

Abstract: Closed loop fiber optic link means, transferring energy from a radiant source to a receiver, includes serially connected fiber optic links and detectors. Energy cessation causes alarm. Detectors include: (1) A pair of optical transducers oriented whereby light, air transmitted, is received with insignificant loss. In water, light received is so insignificant that energy to the receiver ceases. The first transducer provides a light beam within a constant index of refraction medium to the second transducer spaced and oriented to ordinarily receive the light beam. When light passes through media having different refraction indices at non-normal angles, light is refracted whereby receiver energy ceases. The transducers are oriented in a straight inclined path. (2) Optical fiber, stable to approximately 135° F., which melts above approximately 155° F., provides fire detection. (3) A bimetallic element attached to one of axially aligned optical fiber holders, when heated, mis-align the fibers. A snap action bimetal device displaces at a specific temperature. (4) A connector holds optical fiber and condensing lens for narrow light beam emergence. A second connector, holding the end of a second fiber in proximity to a second lens focus, is axially aligned with the first so that the second fiber transmits light. Opaque objects therebetween interrupt the beam causing energy cessation. (5) Opening of an entrance device having optical fibers coupled in axial alignment to opposite sides thereof causes the fibers to mis-align, causing energy interruption. The radiant energy source and receiver are in proximity to each other.

Fiber optical temperature measurement devices

Abstract: The invention relates to a fiber optical temperature measuring device of the pyrometer type, comprising a transducer section and an electronic section, which are mutually interconnected by at least one optical fiber. The electronic section includes at least one light source and the light therefrom is arranged to be emitted via the optical fiber to the transducer, and in the transducer at least part of the light is reflected back into the fiber and is conducted through the optical fiber together with an output measuring signal from the transducer to one or more detectors included in the electronic section.

Temperature sensing arrangement and method

Abstract: An arrangement for sensing temperature changes at an object, specifically within a transformer or the like, is disclosed herein. In one embodiment, this arrangement utilizes as one of its main components a sensor including a solid glass medium which changes in optical density with changes in temperature, a single optical fiber for directing a beam of light into the glass media, a single optical fiber for collecting the light transmitted through the medium, and an optical means for imaging the transmitted light to the collecting fiber. In addition, in this embodiment, the light is caused to pass through the glass medium such that the amount of light reaching the collecting fiber is linearly dependent upon the temperature at the medium with respect to temperatures within a wide range.

Digital fiber optic sensor system

Abstract: A digital fiber optic sensor system utilizing a conventional n-track encoder system, but wherein the number of fiber optic paths to and from the sensor is reduced to one or two by utilizing the delay properties of optical fibers. These properties make it possible to divide a single short-duration optical pulse among several optical fibers of differing lengths to produce, at the far ends of the fibers, a like number of short-duration optical pulses essentially identical in shape and amplitude but spaced in time. Each of these fibers can be used to illuminate a different track of a multi-track optical encoder such that the tracks become sequentially interrogated by the time-spaced pulses. When the time-spaced responses are recombined, they form a serial binary word. In effect, a form of time-division multiplexing is achieved with the use of a minimum number of optical fiber elements.

Method and means for improved optical temperature sensor

Abstract: An improved optical fiber temperature sensor includes at least one optical fiber light conductor including an optical fiber core, cladding material around the core, and a jacket surrounding the core and cladding material. The core exhibits an evanescent field which extends through the cladding material into the jacket in a first selected range of optical wavelengths. Light attenuation in the conductor below a first temperature range is less than light attenuation above the temperature range. By applying light to the conductor at a frequency with the selected optical wavelength range and detecting the light passed through the conductor, an approximate temperature within the temperature range can be sensed. A more accurate temperature can be sensed by using either two optical fiber light conductors having different optical properties or by using two light frequencies with a single conductor which responds differently to the two frequencies.

Optical loss measurement in graded-index fiber using a dummy fiber.

Abstract: The utility of an auxiliary fiber, called a dummy fiber, is investigated for optical fiber loss measurements. The dummy fiber is spliced and used to excite the test fiber. Excess loss caused by undesirable modes is found to be reduced to less than 0.05 dB by using a 500-m dummy fiber and choosing the test fiber cut length to be 2 m for reference. Loss linearity to the fiber length is examined on 6-km spliced fibers, and satisfactory agreement is obtained between the total loss and the sum of the individual fiber and splice losses.

Acoustic vibration sensor and sensing system

Abstract: A novel acoustic vibration sensor and novel acoustic vibration sensing system are described having principal application to hydrophones and operating upon the optical heterodyning principle. The sensor employs a pair of single mode fibers, optically coupled by a path whose length is varied by the acoustic vibrations, and including a partially reflecting discontinuity at the sensitive end of each fiber. Optical signals of one frequency are supplied to one fiber, and of another frequency to the other fiber. Optical signals of the same difference frequency emerge from the "dry end" of each fiber. When these two emergent signals are photodetected, and the phase or frequency difference is obtained, the acoustic vibration is sensed. The process effectively cancels out noise pickup in the single mode fibers and in other parts of the system, such as laser noise and oscillator instabilities.

Optical fiber slip ring

Abstract: A system for the coupling of signals from a movable member, such as a tankupola, to a fixed member, such as a tank hull, includes a rotatable drum carrying an optic fiber slip ring (an optical wave guide which may be a rigid fiber optic bundle or a rigid plastic resin optic ring). Electronic-photo transducers, such as photodiodes or light emitting diodes, are embedded in the optic fiber slip ring and their light pulses are transmitted across a gap to an optic fiber block also containing electronic-photo transducers.

Fiber optic hydrophone sensitivity for different sensor configurations

Abstract: Defence Research Establishment Atlantic, P.O. Box 1012, Dartmouth, Nova Scotia. Received 14 July 1979. 0003-6935/79/223720-03$00.50/0. © 1979 Optical Society of America. Fiber optic sensors show promise as highly sensitive, broadband hydrophones. It has been shown that the pres­ sure sensitivity of an optical fiber is strongly dependent on the strain configuration induced in the fiber by the acoustic pressure. In this Letter, strain configurations are derived for various sensor designs, and their hydrophone sensitivities are calculated. It is shown that the sensitivity can be increased by 2 orders of magnitude over that of a simple fiber coil of given length. When a stress configuration with orthogonal components T1, T2, and T3 exists in an isotropic elastic solid, and shear stresses are negligible, the resulting strain components are given by

Fiber and Integrated Optical Devices for Signal Processing

Abstract: The design and performance of some signal processing devices using fiber and integrated optics are discussed. Analog-todigital (A/D) conversion, logic, and computation are among the signal processing functions which can be performed using integrated optical devices. Optical fibers can be used for signal delay and storage and for implementing transversal filters and delay-matched filters. Some other interesting possibilities make use of both fiber delay line and integrated optical elements. These include variable-length delay lines and programmable transversal filters.

Fiber optic waveguides for time-of-flight optical spectrometry

Abstract: Transit time and pulse broadening within an 1100-m optical fiber have been studied with single photon time-correlation techniques at a number of wavelengths. The results confirm that a fiber optic waveguide can be used as the dispersing element in a time-of-flight optical spectrometer. 4 figures.