Abstract: A contact gauge utilizable for determining contact pressure conditions between two bodies at their interface including a thin plastic sheet capable of memorizing an induced birefringence and a thin, load transmitting member attached to the sheet for inducing the birefringence therein. A method of employing the contact gauge for determining the contact pressure conditions between the two bodies also forms a part of the present invention.

Abstract: An optical device for monitoring pressure is described. The device is capable of monitoring pressure in relatively hostile high temperature, high pressure environments through the use of a pressure-sensitive means having an all-glass housing. The subject optical device relies on the photoelastic effect produced when a material is subjected to a uniaxial stress to produce birefringent banding. In the subject device, polychromatic light is modified to produce a signal having wavelength-dependent intensity variations to allow the pressure-sensitive device to monitor pressure over a relatively wide range.

Abstract: A system for remote measurement of structural forces includes a plurality of microbend transducers mounted along the length of the structure for microbending an optical fiber in response to structural forces, such as stress acting upon an oil or gas pipeline or the like. An optical time domain reflectometer (OTDR) has a light source for launching a pulsed optical signal for passage through the fiber and a photodetector for sensing as a function of time the intensity of backscattered light reflected back through the fiber, wherein this sensed time function is correlated directly with discrete longitudinal positions along the length of the fiber and the structure. When one or more of the microbend transducers is activated to induce a microbend in the fiber in response to localized forces acting upon the structure, a portion of the backscattered light is lost at the microbend. This attenuation in backscattered light intensity is sensed quantitatively and positionally identified by the photodetector.

Abstract: An optical sensor has a gain medium situated at a first location and defines one end of a resonating optical cavity. An optical fiber couples electromagnetic radiation to a predetermined point at a second location where it is directed toward a reflective surface. The physical condition to be sensed causes the reflective surface to move with respect to the end of the optical fiber. This movement essentially changes the length of the cavity in which the electromagnetic energy is resonating causing a corresponding change in the axial mode difference frequency within the cavity. A small portion of electromagnetic energy is coupled out of the cavity at the first location to a photodetector. Finally, the photodetector creates an electrical signal which varies as the change in the axial mode difference frequency, thus indicating the change in the physical condition.

Abstract: In a strain sensing system in which a strained grating is illuminated with a pair of beams chosen from three possible beams to sense strain in two dimensions, an arrangement is disclosed of two beam splitters, as least one plane mirror, and three tilted mirrors, all fixed to a support plate and which can supply the three required illuminating beams.

Abstract: Photoelastic sensing means, and more particularly photoelastic sensing means capable of providing high sensitivity for measuring pressure, force, displacement, acceleration or inertial force, proximity, temperature and other measurands. The photoelastic sensing means comprises a thin photoelastic member of transparent material having closely spaced top and bottom outer surfaces with peripheral edges and an edge surface extending between the peripheral edges of the other surfaces. Light flux is provided to the edge surface of the member at a first region for transmission by the member along a path to a second region at the edge surface where it is received and detected. The spacing between the top and bottom outer surfaces of the member is relatively small compared to the length of the path of the light flux in the member. The member is supported to produce bending stresses in the member in a direction transverse to the path of the light flux in the member with the application of force to the member.

Abstract: A system for remote measurement of structural forces includes a plurality of microbend transducers mounted along the length of the structure for microbending an optical fiber in response to structural forces, such as stress acting upon an oil or gas pipeline or the like. An optical time domain reflectometer (OTDR) has a light source for launching a pulsed optical signal for passage through the fiber and a photodetector for sensing as a function of time the intensity of backscattered light reflected back through the fiber, wherein this sensed time function is correlated directly with discrete longitudinal positions along the length of the fiber and the structure. When one or more of the microband transducers is activated to induce a microbend in the fiber in response to localized forces acting upon the structure, a portion of the backscattered light is lost at the microbend. This attenuation in backscattered light intensity is sensed quantitatively and positionally identified by the photodetector.

Abstract: A transducer for the measurement of minute displacements incorporates a fiber optic coupler having a coupling efficiency which varies in relation to the relative position of coupler elements. The transducer may also be used indirectly as an accurate sensor of physical parameters, such as temperature and pressure, through the use of a secondary transducer which provides a displacement proportional to such physical parameter. The outputs from the fiber optic coupler may be compared to provide a measure of the coupling efficiency, and may be monitored by a display which provides a direct measurement of displacement or a secondary physical parameter.

Abstract: An optical measuring apparatus for measuring force or pressure, having at least one light source, at least one optical fiber for passing light from and to a sensor, and one detector system. The sensor includes a material having pressure- and force-dependent photo luminescence properties, the signal received in the detector system being dependent on the pressure or the force applied to the sensor.

Abstract: Arranged in succession on a common optical axis is a laser, a modulator for shifting the frequency of light produced by the laser, an optical system for forming two light beams, a system of markers formed on the surface of a specimen being tested and a recorder of an interference pattern resulting from the interference of light scattered by the markers.

Abstract: A system for remote measurement of structural forces includes a plurality of microbend transducers mounted along the length of the structure for microbending an optical fiber in response to structural forces, such as stress acting upon an oil or gas pipeline or the like. An optical time domain reflectometer (OTDR) has a light source for launching a pulsed optical signal for passage through the fiber and a photodetector for sensing as a function of time the intensity of backscattered light reflected back through the fiber, wherein this sensed time function is correlated directly with discrete longitudinal positions along the length of the fiber and the structure. When one or more of the microbend transducers is activated to induce a microbend in the fiber in response to localized forces acting upon the structure, a portion of the backscattered light is lost at the microbend. This attenuation in backscattered light intensity is sensed quantitatively and positionally identified by the photodetector.

Abstract: This invention relates to a lightweight and compact optical sensor that provides an indication of a deformation (e.g. fatigue, vibration, flex, torsion, bending, slippage) occurring at a monitored area. The sensor includes at least one light transmitting optical fiber and an optical detector that is responsive to the optical characteristics (e.g. amplitude, phase, polarization angle) of a supply of light signals being transmitted through the fiber. In the event that deformation occurs at the monitored region, the optical fiber undergoes a displacement which thereby causes a corresponding change in the optical characteristics of the light signals supplied to the detector. The optical characteristics of the light signals supplied to the detector relative to those of the light signals supplied to the optical fiber provide an accurate indication of the physical parameter.

Abstract: A self-contained, unitary device for collecting and interpreting data reflecting the effect of a force acting on a structure includes a housing adapted to be attached at spaced points to the surface of the structure, an optical sensor within the housing for detecting the relative orientation of spaced surface coordinate vectors of the structure, circuitry within the housing for converting signals from the optical sensor to a form usable by signal-processing electronics also located within the housing. The output of this structural information detector embodies useful information which directly indicates the effect of the force acting on the structure.

Abstract: A deformograph comprises a sensitive element shaped as a tube of an optically sensitive material and fixed in a borehole by cementing the gap between said tube and walls of the borehole. One end of the tube is tapered off and provided with a specular coating, while the other end thereof has a specular coating with transparent sections. There are also provided a polarized light source furnishing a light signal transmitted through the material of the tube, and a sensing unit designed to pick off from the sensitive element a useful light signal indicative of the changing condition of the earth's crust in a given area.

Abstract: Disclosed is an apparatus for measuring surface stress of glass coating and transparent plastic product, which comprises means for projecting the coherent light on the surface of the object to be measured, an output prism having a refractive index greater than that of said surface, mounted proximal to the light incident point on said surface in such a manner that one face thereof is in optically close contact with said surface, a telescope to measure the critical angle at the interface of said surface and said output prism in respect of the projected light from said output prism, and a polarizer located on the optical path of said projected light. The apparatus facilitates easily a direct and non-destructive measurement of the surface stress without any complex calculation.

Abstract: An apparatus for pressure measurement employs fiber optics to transport a broadband beam light to and from a remote electrically passive sensing head. In the sensing head, a linearly polarized beam is phase shifted in a birefringent plate, then passed through a photoelastic pressure sensor and a polarization analyzer. The wavelength for which the output light has an intensity minimum is a measure of the applied pressure.

Abstract: An optical fiber having at least two cores positioned in a common cladding can be fabricated to be responsive to strain or hydrostatic pressure but not to temperature through the selection of materials, spacing and shape of the cores and cladding in the fiber. Accordingly, the cross-talk between adjacent cores in the optical waveguide can be optimized to respond to a change in hydrostatic pressure or in unidirectional strain along the length of the fiber. The strain or pressure change, can be determined by measuring the relative intensity of light emerging from the different cores of the fiber. A larger unambiguous range for strain or hydrostatic pressure changes can be provided by a multi-core optical fiber embodiment.

Abstract: A fiber optical measuring device for measuring physical magnitudes comprises a transducer having a body constituting an optical modulator. The optical properties of the modulator are dependent on the mechanical forces acting on the modulator. The optical property utilized is the pressure dependency of at least one light-absorption edge of the absorption spectrum of the modulator material. Optical fibers are used for leading light into the modulator and for leading out light that has passed through the modulator.

Abstract: In a device for determining the influence of physical parameters on the lth of a path, an elastically stretchable optical fiber is guided with minimal pretensioning along the path which is subjected to length changes. The optical fiber is mounted at least sectionally on supports subjected to positional changes with changes in the length of the path. A transit-time measuring device is also provided as part of the measuring device together with the optical fiber. The transit-time measuring device includes a light-pulse repeater forming a closed signal path with the optical fiber. The repeater generates signal pulses circulating in the signal path with the periodicity of the signal circulation time of the signal path. From an electronically measured total travel time through the closed signal path and a total number of which signal pulses the electrical display signal can then be derived to determine the length and change in length of the path being measured.

Abstract: A method and apparatus of measurement of angular deformation of a body, and in particular, a method and apparatus of load or force sensing are disclosed. Chief applications are found in electronic weighing and related devices. Deformation of a body in the form of angular deflection, or a deformation that can be transformed into angular deflection by mechanical or other means, changes the angle between the polarization axes of a pair of light polarizers, thus changing the intensity of light that is transmitted through the pair of polarizers. A photodetector converts the transmitted light into an electric signal. This signal contains information regarding the amount of deformation of the body and may be used in its analog form to operate a voltmeter to give a visual readout, or converted into a digital form for activating a visual digital display, or for inputing into a digital data processing device. A specially designed feedback-stabilized light source produces an output whose D.C.

Abstract: A method for optically determining the ratio of Poisson's ratio to modulus of elasticity for optically isotropic and optically anisotropic transparent materials and then for determining the stress-optical constants for such materials. A collimated monochromatic light beam is directed at the tip of a crack in a loaded thin plate specimen of the material and the diameters of the resulting transmitted and reflected caustics are measured at points equidistant from the specimen. The light beam also is directed to an uncracked region in a loaded thin plate specimen of the material and the number of displaced fringe reflected on a screen are counted for a predetermined change in loading. The ratio of Poisson's ratio to modulus of elasticity and the stress-optical constants are determined from the thickness of the specimen, the displaced fringe count, the wavelength of the light beam and the ratio of the caustic diameters.

Abstract: This invention is directed to a laser-fiber optic interferometric strain gauge. This is a strain gauge that can be read out by means of fiber optics, which has no power other than optical at the strain gauge. Laser light is directed into two single mode fibers, which fibers are attached to a supporting member the strain of which is to be measured. The ends of the fibers are brought into close proximity and the light coming out of the two fibers interferes. When the supporting member is strained the fringes move giving a measure of the strain.

Abstract: An automatic two wavelength photoelasticimeter comprising, in succession, a light source for emitting light having at least two wavelengths, .lambda..sub.1 and .lambda..sub.2 ; a polarizer rotating at constant speed, an orientable quarter-wave plate of orientation .beta. with respect to a reference axis; a model to be analyzed exhibiting double-refraction and having a fast axis which forms an angle .theta. with respect to the reference axis and which provides a phase shift .phi. (which parameters .theta. and .phi. are to be measured) and three photodetectors 5, 6, and 7 preceded by analyzers 10, 11 and 12 respectively. The photodetectors 6 and 7 are preceded by filters 8 and 9 of wavelengths .lambda..sub.1 and .lambda..sub.2 respectively. The difference between the phases of the signals of the frequency 2.omega.

Abstract: An apparatus is disclosed for measuring strain in a solid object, wherein the apparatus is arranged to use the deflection of a light guiding structure as a strain responsive element for determining the amount of applied stress to be measured. The apparatus typically comprises a curved light guiding structure including a medium of given refractive index surrounded by a medium of lower refractive index than that of the medium of given refractive index; means for injecting light into the structure and means for analyzing the change in the propagation characteristics of the light emerging from the structure; and, means for attaching and maintaining the light guiding structure to the solid object in such a way that stresses acting upon the object are translated into changes of the curved form of the structure, creating changes in the propagation of the injected light whereby the strain in the object can be determined.

Abstract: To obtain a photographic record of an object surface having superimposed interference fringes arrayed as a function of the deformation which results in the object from an applied stress, which may be mechanical, thermal, or the like, the object is first illuminated with coherent light. The illuminated surface is then photographed with a camera having an optical wedge disposed over half of its lens to record two slightly displaced overlapping images of the object on the camera film. The object is then stressed by changing the ambient temperature or pressure or other mechanical loading, and the undeveloped film is exposed to a second set of overlapping images. The developed photograph contains a set of equal amplitude fringes representing the interference pattern between the two fringe sets generated by the two exposures and arrayed as a function of the strain in the object as a result of the stress.

Abstract: There is disclosed a photoelastic strain gauge which displays visual patterns representative of the strain in the workpiece to which the gauge is bonded. The gauge comprises two sheets of reflective material and a body of photoelastic material therebetween. A reflector in the body directs polarized light in such a way as to be reverberated between the reflective sheets and then discharged to produce the visual patterns. Because the light is reverberated, the visual patterns are amplified or enlarged.

Abstract: A pair of mandrels crossing at a right angle are moved into the center of an O-ring and then spread apart to stretch the O-ring around the mandrels to secure it and to form it into a twisted path. The mandrels are rotated to drive the O-ring through the twisted path so that the angular orientation of any given cross section of the O-ring changes as it advances around the path. An optical measurement apparatus senses cross section diameter of the O-ring at several locations. A support for one of the mandrels accommodates a load cell to measure the force developed by stretching the O-ring to provide a measure of O-ring elasticity.

Abstract: A method for optically determining the stress-optical constants of optically isotropic and anisotropic materials. A collimated beam of monochromatic light is directed at the tip of a crack in a thin plate specimen under plane-stress from a direction substantially perpendicular to the surface of the specimen and to the direction of the stress. Reflected and transmitted stress-optical constants are determined from a ratio of the diameters of transmitted and reflected caustics from the specimen and the known Poisson's ratio and modulus of elasticity for the specimen.