Abstract: Methods and apparatus are disclosed for detecting a rate of change of temperature in the environment around a sensing optical fibre at a position along the fibre, in which a time varying coherent Rayleigh backscatter interference signal is detected using probe light backscattered within the sensing fibre from the position. A spectral density profile is calculated which represents frequency components in time variations of the interference signal. One or more properties of a feature of the spectral density profile are then used to determine the rate of change of temperature. The feature may be, for example, a decline in the spectral density profile with increasing frequency, or a peak in the spectral density profile.

Abstract: The disclosure relates to distributed optical fiber sensors arranged to detect coherent Rayleigh backscatter from a sensing optical fiber disposed in an environment, and to determine an infrasonic signal in the backscatter, or to determine a change in the environment within an infrasonic frequency range from the backscatter.

Abstract: The disclosure relates to a distributed optical fibre sensor having an optical switch arranged to selectively and simultaneously couple each of a plurality of interrogators to each of a plurality of sensing optical fibres.

Abstract: The disclosure relates to distributed optical fibre sensors arranged to detect coherent Rayleigh backscatter from a sensing optical fibre disposed in an environment, and to determine an infrasonic signal in the backscatter, or to determine a change in the environment within an infrasonic frequency range from the backscatter.

Abstract: 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.

Abstract: Distributed optical fibre sensor measures vibration, as a concurrent function of position along each of a plurality of sensing optical fibres, from properties of probe light backscattered within the sensing optical fibres. The sensor includes a light-pulse-generating probe light source, a detector, an optical switch. The sensor is arranged to control the optical switch such that all of the sensing optical fibres can be used concurrently to detect acoustic vibration, and an analyser is arranged to determine vibration, as a concurrent function of position along each of the sensing optical fibres, from the detected backscattered probe light.

Abstract: 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.

Abstract: There is described a distributed optical fiber sensor for detecting one or more physical parameters indicative of an environmental influence on a sensor optical fiber, as a function of position along the sensor fiber. 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.

Abstract: There is described a distributed optical fiber sensor for detecting one or more physical parameters indicative of an environmental influence on a sensor optical fiber, as a function of position along the sensor fiber. 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.

Abstract: There is described a distributed optical fiber sensor for detecting one or more physical parameters indicative of an environmental influence on a sensor optical fiber, as a function of position along the sensor fiber. 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.

Abstract: There is disclosed a distributed optical fiber sensor arranged to deliver probe light pulses of different wavelengths into corresponding different sensing optical fibers, and to determine one or more parameters as functions of position along each of the sensing fibers from detected backscattered light of each corresponding wavelength. In another arrangement, the different wavelengths are directed in different corresponding directions around a loop of sensing optical fiber.

Abstract: There is disclosed a distributed optical fiber sensor arranged to deliver probe light pulses of different wavelengths into corresponding different sensing optical fibers, and to determine one or more parameters as functions of position along each of the sensing fibers from detected backscattered light of each corresponding wavelength. In another arrangement, the different wavelengths are directed in different corresponding directions around a loop of sensing optical fiber.

Abstract: A fiber optic sensing method and apparatus for determining location and direction information of disturbances occurring in the environment of a sensor optical fiber are provided. The method comprises launching optical pulses into at least one polarisation eigenmode of a polarisation maintaining fiber as the sensor optical fiber, detecting temporal speckle patterns of light backscattered from the at least one polarisation eigenmode of the fiber, comparing the temporal speckle patterns to determine the location and direction information of a disturbance in the environment of the sensor optical fiber. The location information may be a distance along the fiber, and the direction information may be a direction radially from the axis of the fiber. The apparatus or instrument may be used to detect disturbance over long distances such as pipes, pipelines, or wells. Other applications include detecting intruders entering a controlled area.

Abstract: There are disclosed methods and apparatus for monitoring fluid flow along a conduit such as a well bore or a pipeline. A sensor optical fiber is disposed along the conduit, and an optical interrogator is used to launch probe light pulses into the fiber and to determine optical properties of probe light backscattered within the fiber, the properties being indicative of vibration as a function along the fiber. An analyzer is used to detect one or more vibration features moving along the conduit and to determine a measure of fluid flow based on the detected movement.

Abstract: There is disclosed a distributed optical fiber sensing system in which the sensor fiber comprises at least first and second waveguides used for separate sensing operations. The sensor fiber may be, for example, a double clad fiber having a monomode core and a multimode inner cladding.

Abstract: An optical fiber cable for distributed fiber sensing of fluid pressure is disclosed. There are also disclosed a method and an apparatus for distributed fiber sensing of fluid pressure using the optical fiber cable. The optical fiber cable is adapted for distributed pressure sensing, and comprises: one or more optical fibers (120); and a buffer (130) surrounding the one or more optical fibers and adapted to deform asymmetrically under isotropic pressure (P) such that the fiber experiences asymmetric strain changing the birefringence of the one or more optical fibers. The optical fibers incorporated in the cable may be conventional single mode optical fibers. The optical fiber cable may be used to determine a pressure distribution along the length of the cable. The cable, apparatus or method may be used to detect pressures over long distances such as in pipes, pipelines, or wells.

Abstract: There is disclosed a distributed optical fibre sensor arranged to deliver probe light pulses of different wavelengths into corresponding different sensing optical fibres, and to determine one or more parameters as functions of position along each of the sensing fibres from detected backscattered light of each corresponding wavelength. In another arrangement, the different wavelengths are directed in different corresponding directions around a loop of sensing optical fibre.

Abstract: 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.

Abstract: There is disclosed a distributed optical fiber sensing system in which the sensor fiber comprises at least first and second waveguides used for separate sensing operations. The sensor fiber may be, for example, a double clad fiber having a monomode core and a multimode inner cladding.

Abstract: There are disclosed methods and apparatus for monitoring fluid flow along a conduit such as a well bore or a pipeline. A sensor optical fibre is disposed along the conduit, and an optical interrogator is used to launch probe light pulses into the fibre and to determine optical properties of probe light backscattered within the fibre, the properties being indicative of vibration as a function along the fibre. An analyser is used to detect one or more vibration features moving along the conduit and to determine a measure of fluid flow based on the detected movement.