Abstract: A transducer utilizes a laser source, photoelastic waveguides, two optical beam paths and detectors for processing optical energy from the laser through a stress transfer medium and thereby detects stress forces present on the transducer. This allows forces such as pressure, strain, voltage, or current to be detected and converted from one form to another for measurement of the force and response thereto. Input forces are detected as optical frequency shifts and converted to electrical signal outputs for indicating circuitry. In an integrated optic format, the transducer package volume is small, allowing ready use in guidance or navigation systems. Light generated by the laser travels along two paths, is optically stressed by the force transfer member and is either combined or compared with a reference signal to obtain the stress intelligence.

Abstract: A sensor is provided for sensing or detecting the presence of an environmental field condition such as acceleration, temperature change, magnetic or acoustic fields. The field is sensed by interference between two mutually orthogonal polarized eigenmodes in a single monomode optical fiber which may be disposed either linearly or wound on a mandrel made of compliant material for sensing an acoustic field, or made of magnetostrictive material for sensing a magnetic field. Polarized light propagated through the optical fiber is detected at its outlet independent of environmentally induced low frequency variations whereby the sensor may be maintained at quadrature and maximum sensitivity.

Abstract: The invention relates to an inerferometer based on the exploitation of an optical fibre through which both the phase signal which is of interest for the measurements concerned and a reference signal are simultaneously forwarded in order that in the differential measurement the noise introduced by the optical fibre for both thermal and mechanical reasons is ruled out.

Abstract: An apparatus for sensing the acoustic energy responsive deformation of a workpiece surface by optical means, that is without physical contact with the workpiece surface, comprises the use of a laser light beam illuminating the workpiece surface portion along which the acoustic energy responsive deformation is manifest. The laser light incident upon the workpiece surface is reflected at the workpiece surface and, modulated responsive to the surface deflection, is transmitted to an optical phase interferometer and to a photoelectric means associated therewith. The output from the photoelectric means is transmitted to an evaluation unit. The improvement shown in this invention concerns means for maintaining the reflected light intensity at a predetermined level by comparing the reflected light intensity with a preset level and feeding a control signal to a light control means controlling the laser light intensity incident upon the workpiece surface.

Abstract: An apparatus for maintaining the adjustment of coincidence and relative phase relationship of light beams in an optical interferometer comprises the passing of a measuring light beam and of a control beam through substantially the same paths of the interferometer. Any change in optical alignment of interferometer components from a set condition is manifest as a change of the electrical signal produced by photoelectric sensing means which receive the control beam. The change of the electrical signal is processed by an electrical circuit and fed to one or more positioning means supporting an optical component of the interferometer for causing a repositioning of such component to thereby restore the set condition. In a typical embodiment, the component is a reflective surface mounted on a set of piezoelectric positioning means.

Abstract: A light beam is transmitted by a fiber optical cable to a light modulation device such as a vibrating filament, bar or plate. This device or oscillator modulates the light intensity with a frequency which is dependent upon the physical parameter to be measured. Oscillations are sustained by a striking device. The modulated light beam is transmitted by a fiber optical cable from the measurement location to an evaluation location where the frequency of the modulated light beam is measured. The measured frequency is a function of the physical parameter.

Abstract: An optical system for frequency-modulation heterodyne detection of an acoustic pressure wave signal. An optical beam is directed into a Bragg cell outside of the fluid medium in which acoustic signals are to be detected. The Bragg cell modulates the incident beam such that two beams of different frequency exit the cell. The two beams are directed into an input optical fiber and the resultant combined beam is transmitted over a desired distance to a fiber optic transducer disposed in the fluid medium. The transducer includes two coiled optical fibers, a reference fiber and a signal fiber, each of which has a different sensitivity to incident acoustic pressure wave signals. The transmitted beam is directed from the input optical fiber through a power divider which splits the beam into two equal parts, one part passing through the reference fiber, the other part passing through the signal fiber. A filter in the signal fiber transmits only a fraction of the light at one of the two frequencies.

Abstract: When sensing the presence of ultrasonic energy in a workpiece portion by illuminating such portion with light from a single-mode frequency stabilized laser, the reflected light, frequency modulated by the Doppler effect due to the ultrasonic energy induced deflection of the workpiece portion, is passed through a gas filled light filter. The frequency modulated light is amplitude modulated by the filter by selecting the frequency of the laser to cause a point of operation which is located along a steep slope portion of the absorption curve characteristic of the filter. To increase the steepness of the slope portion of the filter, the present invention discloses the use of laser light to saturate the filter in a part region.

Abstract: Measurement of small oscillatory movements of an irregular surface involves the production of a speckle pattern therefrom by coherent light illumination, and the arrangement of a photodetector for direct response to such pattern, variations in photodetector output component at the frequency of the surface movement representing that movement. Another, stationary, illuminated irregular surface can be involved to produce a speckle interference pattern for response of the photodectector thereto and, in the case where the two surfaces are closely adjacent, a single beam can be used to illuminate the first and other surfaces predominantly and by stray light, respectively. This common beam illumination can be used in prior speckle interferometry. The first surface can be an eardrum oscillated by a sound wave, suitably of swept frequency or impulse form, with detection of the photodetector variations respectively being in synchronous manner or by Fourier analysis, respectively.

Abstract: Methods and apparatus are disclosed for studying motion of an object or element, to determine not only quantities of motion but also direction of motion. A laser beam or the like is circularly polarized and directed to two or more retroreflectors and then to a detector. Beams of different frequencies are established and determination of relative direction of motion of the retroreflectors is made from the increase or decrease of frequency of beats of one beam against the other. In one embodiment, left and right circularly polarized light is reflected, and one of the beams is frequency-shifted. The light, being circularly polarized, is insensitive to rotational orientation of the test object, while maintaining directional and motion information.

Abstract: The presence of a signal is sensed by a signal transducer around which an optical fibre is wrapped so that the length of the fibre is modulated by any signal present. A laser supplies coherent light to one end of the fibre and a homodyne detector is provided at the other end. Discontinuities at both ends of the fibre cause multiple reflections which produce differential phase modulations of the signal. The detected signal contains a large number of frequency components and the peak frequency is related to the amplitude of the original signal. The peak frequency is indicated by a suitable filter arrangement.

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.

Abstract: A method for measuring the velocity of earth surface motion utilizing coherent light energy which comprises steps of generating and directing a coherent light beam toward a selected earth surface position, reflecting said beam from a stationary reflector located at the earth surface position, and simultaneously reflecting said beam from a reflector at said earth surface position which moves with earth surface motion; and, detecting the reflected beam, including both the reflection path components, to derive an instantaneous difference frequency that is proportional to the velocity of the earth surface motion.

Abstract: An interferometer which is compensated for the effects of low frequency vibrations in the measuring arm. The resultant changes in optical path length are detected and control signals are applied to an electro-optical device adapted to change the phase of the light in the reference arm of the interferometer relative to that in the measuring arm of the interferometer so as to compensate for the changes of optical path length in the measuring arm of the interferometer.

Abstract: This invention relates to an interferometric laser method and apparatus for sensing the acoustic wave responsive deformation of a workpiece surface. A laser provides a coherent beam of light which after reflection at the workpiece surface is split into a first measuring beam portion and a second reference beam portion, the latter portion being delayed by being transmitted over a long delay path. The optical length of the delay path is dimensioned to be a multiple integer of the optical length of the resonator of the laser.

Abstract: An optical homodyne microscope is disclosed which detects phase modulation of the optical radiation that is reflected from an object under study which is in a state of periodic motion. The dimensions of the object may be smaller than the optical wavelength with this technique. By analyzing the resultant phase modulation spectrum, information concerning the shape of the object can be obtained.

Abstract: Ultrasonic waves present on the surface of a workpiece are received contact-free by an optical sensing arrangement which includes a frequency stabilized single mode laser which illuminates the vibrating surface portion. Reflected light from the illuminated portion, which light is frequency modulated by the Doppler effect of the ultrasonic wave, is collected by a lens and applied to a narrow band absorption light filter. The frequency of the laser and the filter are selected to cause the center frequency of the light to fall at a point along the steepest slope of the filter absorption curve. The change in light frequency causes a corresponding change in light intensity passing through the light filter and the filtered light, now amplitude modulated, is provided to photoelectric means. A feedback circuit maintains the frequency of the laser constant.

Abstract: A portable apparatus for measuring ultrasonic signal waves using interference between a reference reflected laser beam and one reflected from a gold-coated plastic film exposed to the sonic signal and located at the interface between liquids of different viscosity but which have substantially equal acoustic impedances. The liquids may respectively comprise water and fluorocarbon liquid.

Abstract: An optical detector of remote vibration, comprising a system for obtaining a Doppler signal by mixing reference light with laser light reflected from a vibrating object. The Doppler signal is rectified and the successively highest value of it are stored. The laser light is scanned over the object and the values of scanning waveforms at the time of storage of a maximum return signal are stored, the stored values being read out to control the direction of the laser light so as to locate the region giving maximum return.

Abstract: A detector of remote movement in which light from a laser is directed at a target and, on reflection from the target, is mixed with reference light from the laser to produce a Doppler signal denoting the movement of the target. The beam of light from the laser is directed through an optical system which brings the light to a focus and thereafter projects the light from the focus at the target. The optical system includes a lens which is mounted in a ferromagnetic carrier which can be vibrated in two orthogonal directions each normal to the axis of the light beam and the axis of the lens. Coils disposed to produce these orthogonal movements are energized in quadrature so as to produce conical scanning of the beam of light on the target.