Fotech Solutions Limited

National Research Development Corporation

British Technology Group Limited

University of Surrey

Fotech Group Limited

Alan John Rogers

Sotiris Emil Kanellopoulos

Sergey Vladimir Shatalin

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.

Distributed fibre optic sensing for event detection

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 (); and a buffer () 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.

Optical fibre cable for distributed fibre sensing

A pressure sensing apparatus has a light source for transmitting pulses of light along a monomode optical fiber. The polarization of light backscattered from the light pulses in the optical fiber is detected by a polarization processing unit (PPU) and a photo detector. The optical fiber is adapted to deform asymmetrically under the influence of applied external isotropic pressure, e.g. from a fluid. The deformation causes the birefringence of the optical fiber to change proportionally to the applied pressure. The change in birefringence can be determined from the detected polarization of the backscattered light, allowing detection of pressure distribution in the fluid. Importantly, the construction of the optical fiber is such that the birefringence beat length of the optical fiber at the wavelength of light propagated by the fiber remains more than twice the spatial length of the light pulses transmitted along the optical fiber. Applications of the invention include detection of fluid flow; location of an interface between two fluids of different density; and tsunami detection.

Method and apparatus for detecting pressure distribution in fluids

An optical time domain reflectometry apparatus has a laser and light modulator for producing coherent light pulses, each having two sections of higher intensity separated by a gap of lower or substantially zero intensity. As the light pulses propagate along the optical fibre, light is continuously Rayleigh backscattered by inhomogeneities of the optical fibre. A photodetector generates backscatter signals representing the intensity of light Rayleigh backscattered in the optical fibre as each light pulse travels along the optical fibre. The PC uses these backscatter signals to derive a difference signal representing a change dI in intensity between signals generated from two successive pulses. The PC then calculates the Root Mean Square (RMS) of the difference signal averaged over the interval between the two sections of the light pulses. Next, the PC averages the backscatter signal generated from the first of the pulses over the same interval and normalises the RMS difference signal using the averaged signal to obtain a compensated difference signal that depends only on differences in the rate of change of phase of light of the light pulses as they travelled along the waveguide. This is repeated at different wavelengths to allow the compensated difference signal to be adjusted to represent the magnitude of the differences.

Detecting a disturbance in the propagation of light in an optical waveguide

A method of and apparatus for determining the spatial distribution of polarisation properties of an optical fiber (). Pulses () of light are transmitted along the optical fiber () and the polarisation state of light backscattered from portions e and elements R of the optical fiber () detected. A spatial distribution of linear retardance &#x3b4;, orientation of linear retardance axes q and circular retardance axes can be accurately determined. This has application in the analysis of Polarisation Mode Dispension (PMD) in telecommunications as well as, inter alia, strain, stress, temperature and electric current and voltage measurement using optical fibers.

Optical fibre backscatter polarimetry

Method and apparatus for measurements dependent on the faraday effect

Simultaneous time-variable and position-variable control of the polarization properties from any position along the length of an optical fibre, is effected by launching an acoustic disturbance into the fibre, thereby locally modifying the birefringence of the fibre. A current measurement device incorporating a monomode optical fiber 1 may be made insensitive to vibration by launching an acoustic wave from one end of the fiber. This wave 7 consists of two linearly polarized shear waves orthogonal in direction, and in phase quadrature is of such an amplitude and frequency as to provide a circular birefringence very much greater than the vibrationally-induced linear birefringence.

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Bookham, United Kingdom

Alan John Rogers