Apparatus for sensing intrusion into a predefined perimeter comprises means for producing a coherent pulsed light, which is injected into an optical sensing fiber having a first predetermined length and positioned along the predefined perimeter. A backscattered light in response to receiving the coherent light pulses is produced and coupled into an optical receiving fiber. The backscattered light is detected by a photodetector and a signal indicative of the backscattered light is produced. An intrusion is detectable from the produced signal as indicated by a change in the backscattered light. To increase the sensitivity of the apparatus, a reference fiber and an interferometer may also be employed.

Apparatus and method for fiber optic intrusion sensing

There is described a distributed optical fibre sensor for detecting one or more physical parameters indicative of an environmental influence on a sensor optical fibre, as a function of position along the sensor fibre. The sensor uses probe light pulses of different wavelengths. At least some of the probe light pulses may also be of different pulse lengths. The relative phase bias between interferometric signals in backscattered probe light of different wavelength pulses may also be controlled.

Distributed Optical Fibre Sensor

A multi-layered liner for lining a pipeline which has an external jacket, an interior liner, a woven intermediate layer between the external jacket and the interior liner. At least one optical fiber is in the woven intermediate liner for purposes of monitoring stress or for communication, and a capacitance leak detection circuit is also in the multi-layered liner for the purpose of detecting leaks in the multi-layered liner. Also included is the method of monitoring a pipeline for stress or leakage by use of a stress detector connected to an optic fiber in a multi-layered liner installed in the pipeline and a leak detector connected to a capacitance circuit in a multi-layered liner installed in a pipeline.

Pipe liner and monitoring system

Methods, apparatus and articles for systems comprising optical fibers, in particular for feeding an optical signal into an optical fiber through the buffer thereof and for withdrawing an optical signal from an optical fiber through the buffer thereof. Preferably this is achieved with the aid of an optical coupling means which contacts and conforms to the surface of the buffer at a bent portion of the fiber. The coupling means can for example be a resiliently deformable material such as a polysiloxane. In a preferred aspect, the invention provides an apparatus and method for axially aligning, and preferably joining, the ends of optical fibers. The apparatus comprises means for holding two fibers so that the fiber ends are approximately abutting and axially aligned, adjacent means for passing an optical signal into one of the fibers through the buffer thereof, and adjacent means for withdrawing that signal from the other fiber through the buffer thereof. At least one of the holding means is movable to maximize the withdrawn optical signal and thus to align the fibers. The invention also includes novel splices which can be made in this way and novel splicing aids for use in the method.

Methods and apparatus for optical fiber systems

A fiber optic acoustic emission (FOAE) sensor particularly suitable for vibration sensing in a hostile environment has a pair of optical fibers each having an end face. In one embodiment, a hollow tube or core having opposite open ends receives the end faces of the optical fibers. Means are provided for fixing the optical fibers in the hollow core with the end faces facing each other and spaced by a distance from each other in the core. A signal processing unit is connected to the optical fibers for supplying light to, and for receiving light from, the optical fibers and for measuring variations in optical phase which result in changes in the light intensity due to vibrations of the hollow core. The hollow core is fixed in a resonant cylinder, and the resonant cylinder is fixed in a housing to complete the sensor. Other embodiments dispense with the need for the hollow tube or core and employ means for fixing the optical fibers within a precision hole, advantageously produced by electrical discharge machining (EDM) or similar processes, provided in the resonant cylinder. A system employing these embodiments of the FOAE sensor is also disclosed.

Fiber optic acoustic emission sensor

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. Specific preferred constructions for microbend transducers and system arrangements particularly adapted for detecting structural strain in an oil or gas pipeline are disclosed.

Michael K. Barnoski

Papers

Microbending of optical fibers for remote force measurement