Abstract: An optical cable structure is discussed that enables a distributed optical fiber sensor to detect acoustic vibration and other measurands, which could be, for example, changes in temperature, changes in static pressure, and changes in static strain. The optical cable structure includes first and second optical fibers disposed within a thin walled, elliptical, gel filled, loose tube helically wound within a cable wall of the optical cable structure. The optical cable structure further includes an additional optical fiber bonded to a strength member using a tight encapsulant. Because the additional optical fiber is fixed to the strength member and disposed with its axis parallel to the strength member, the additional optical fiber experiences the full axial strain on the optical cable structure, unlike the first and second optical fibers contained within the helically wound loose tube, thereby providing a contrast to the strain response coefficients of the first and second optical fibers.

Abstract: A distributed optical fibre sensor is discussed which is arranged to detect acoustic vibration and at least a first of two or more other measurands, which could be for example two or more of changes in temperature, changes in static pressure, and changes in static strain. At least first and second optical waveguides are arranged to have optical path length response characteristics to at least one of the other measurands which are different from each other, and an analyser is arranged to determine at least said first other measurand using differences between the interference signals from each of the optical waveguides.

Abstract: A distributed optical fibre sensor is described which is arranged to measure one or more parameters as functions of position along a sensing optical fibre that extends along a path through an environment. The sensor includes a first probe light source arranged to generate pulses of first probe light in one or more first wavelength bands, a second probe light source arranged to generate pulses of second probe light in one or more second wavelength bands separate from said first wavelength bands, a wavelength division multiplexer arranged to launch the first probe light pulses and the second probe light pulses into the sensing optical fibre for backscatter within the sensing optical fibre, and a receiver arranged to receive and separately detect both Raman shifted components of the backscattered probe light, and coherent Rayleigh backscattered components of the second probe light.

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: A distributed optical fibre sensor is discussed which is arranged to detect acoustic vibration and at least a first of two or more other measurands, which could be for example two or more of changes in temperature, changes in static pressure, and changes in static strain. At least first and second optical waveguides are arranged to have optical path length response characteristics to at least one of the other measurands which are different from each other, and an analyser is arranged to determine at least said first other measurand using differences between the interference signals from each of the optical waveguides.

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

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

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: 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 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 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.