Abstract: New sensing and diagnostic methods are implemented with multimode fiber Bragg gratings (MMFBG) and methods for sensor addressing and multiplexing are described. Real time structural strain and vibration monitoring using optical time domain reflectometry (OTDR) is discussed. The first all-mode, wave optics calculations of the reflectivity of Bragg gratings in highly multimode optical fibers are presented, including the effects of individual mode power changes due to microbending transducer loss upstream from the grating. Two categories of multimode fiber gratings are possible, independent mode and mode coupling, and the fabrication differences between these types of gratings are described. The reflectivity properties of independent mode multimode fiber gratings are examined and compared to single mode fiber gratings.

Abstract: A sensor configuration increases the usefulness of Fiber Optic Displacement Sensors by mounting them on an elastomer substrate. The sensor configuration can also be used for most other sensors. The elastomer substrate is used to pre-mount the sensors, making field installation easier, increasing the range of the sensors, allowing strain sensors to measure compression and elongation, and providing a mechanism whereby the sensors can be protected from failure due to excess strain. The sensing range of the sensor is increased by employing an elastomer substrate to which only a portion provides mounting for the fiber, thereby significantly enhancing the dynamic range of the sensor.

Abstract: An assembly which allows use of Fiber Optic Displacement Sensors in a high-temperature environment. The package described is protected against harsh environments. Provisions are taken to allow averaging strains over distances of at least 1/2 to 4 feet, and to allow installation in cramped spaces. A rod is attached to an underlying surface at one point and guided to move in a selected direction of measurement. The distance between a selected movable location on the rod and a point fixed on the surface, is measured using a bent optical fiber having light loss characteristics dependent on that distance. The fiber is gold coated and the holders, guides and other hardware are enclosed in heat shielding trays in which a plurality of sensors are positioned at selected locations along a steam pipe, boiler, vessel or other surface.

Abstract: A fiber-optic rotation sensor particularly adapted to be placed adjacent a drill head to measure the orientation of a drill string with respect to the axis of rotation of the earth during or after drilling for minerals such as oil and gas. The analog sensor is based on a Sagnac interferometer and uses light beams counterrotating in one or more oblong circular shaped coils of optical fiber in which dual phase modulators are used to generate an AC signal to enable detection of a rotation rate output. The sensor also includes means to mechanically or electrically flip to sensitive axis of the rotation sensor to null out bias drift. If one coil is used, the flipping is in 90.degree. segments. When two coils at 90.degree. to each other are used, they are flipped 180.degree..

Abstract: There is provided by this invention a fiber optic transducer for accelerometers and gyroscopes that utilize microbending of an optical fiber between two suspended points by vibrating the optical fiber with electro-static deflection to induce modulation of a light signal to sense acceleration, tension, etc. The amplitude modulation of the light signal induced by the bending lost in the vibrating fiber is demodulated with respect to reference signals to derive an output proportional to acceleration, tension, or other environmental factors.

Abstract: A fiber-optic rotation sensor particularly adapted to be placed adjacent a drill head to measure the orientation of a drill string with respect to the axis of rotation of the earth during or after drilling for minerals such as oil and gas. The analog sensor is based on a Sagnac interferometer and uses light beams counterrotating in one or more oblong circular shaped coils of optical fiber in which dual phase modulators are used to generate an AC signal to enable detection of a rotation rate output. The sensor also includes means to mechanically or electrically flip the sensitive axis of the rotation sensor to null out bias drift. If one coil is used, the flipping is in 90.degree. segments. When two coils at 90.degree. to each other are used, they are flipped 180.degree..