Abstract: A method and apparatus for generating and transmitting high energy optical pulses are described. Distributed temperature sensors usually use Raman scattering in optical fibers as the means to determine the temperature. Here, light from a laser source is sent down a fiber and the small amount of light that is scattered back towards the source is analysed. As the fiber length increases, the resolutions of the temperature and loss measurements become poorer. This is because losses in an optical fiber attenuate the signal. An obvious solution to this problem is to launch more light into the fiber to compensate for the losses but stimulated Raman scattering limits how much light may be launched. The present invention solves this problem by using a pulse conversion method to maximize the resultant pulse energy while the power is kept below SRS threshold.

Abstract: Splicing optical fibers from cables running along an infrastructure involves passing the cables into a housing (80) having space to contain a fiber splice (100) and contain an additional length of slack fiber extending around a bend of at least 180 degrees, or a number of coils, in a substantially annular plane. After splicing, the fiber splice and slack fiber are placed in the housing, which is sealed to resist pressures of at least 200 psi, and the assembly is fixed to the infrastructure. The space in the housing can enable the housing to be used for protecting U-bends or to provide some slack fiber within the housing. This can enable faster onsite splicing operations or allow for rework without needing to relocate and strip more cable, to save costs. The housing can be suitable for fitting in the annular space between production tube and casing for use in sensing down boreholes.

Abstract: Remote sensing in an environment having temperatures greater than 300° C., using an optical fiber having a core (10), a cladding (20), and a metallic protective coating (30) on the cladding to protect a surface of the cladding, the cladding having a diameter greater than 150 ?m, and a thickness of at least 50 ?m. The larger diameter cladding means stress from the metallic protective layer can be reduced, giving lower optical loss and better hydrogen protection. A metal conduit (330) encapsulates the sensing fiber, and a pump evacuates the conduit to reduce hydrogen seepage. Ceramic splice protectors are used. OTDR is used to determine differential loss at different locations along the fiber. A reflective element at the far-end of the fiber eases calibration.

Abstract: Software (140) for processing measurements from a distributed sensing system (100) receives the measurements, and generates a graphical representation of the measurements indicating their location or time sequence, and a representation of locations of physical features along the path (50), or times of external events, the representations being scaled and associated to provide a visual correlation between the locations of the measurements and locations of the physical features, or between times of measurements and times of external events. The enhanced visual correlation can lead to cost savings if more rapid interpretation of large volumes of measurements can give warning of changes such as subsidence of structures, or of ingress of water into oil wells, for example in time for remedial action to be taken.

Abstract: A rod having an embedded optical fiber has a stiff composite outer layer (10) to make the rod self straightening to enable it to be pushed into a pipe or borehole from a spool. This can help enable a reduction of friction between rod and conduit and can enable longer reach. A barrier layer is provided to separate the fiber from the composite layer. The rod can be retrieved after use. The rod can be narrow enough to enable normal flow along the pipe or borehole, and can be injected and retrieved even when the pipe or borehole is pressurized. The fiber can be used for remote sensing of conditions along the conduit. Other tools can be inserted by the rod during the intervention.

Abstract: A rod having an embedded optical fibre has a stiff composite outer layer (10) to make the rod self straightening to enable it to be pushed into a pipe or borehole from a spool. This can help enable a reduction of friction between rod and conduit and can enable longer reach. A barrier layer is provided to separate the fibre from the composite layer. The rod can be retrieved after use. The rod can be narrow enough to enable normal flow along the pipe or borehole, and can be injected and retrieved even when the pipe or borehole is pressurised. The fibre can be used for remote sensing of conditions along the conduit. Other tools can be inserted by the rod during the intervention.

Abstract: Remote sensing in an environment having temperatures greater than 300° C., using an optical fiber having a core (10), a cladding (20), and a metallic protective coating (30) on the cladding to protect a surface of the cladding, the cladding having a diameter greater than 150 ?m, and a thickness of at least 50 ?m. The larger diameter cladding means stress from the metallic protective layer can be reduced, giving lower optical loss and better hydrogen protection. A metal conduit (330) encapsulates the sensing fiber, and a pump evacuates the conduit to reduce hydrogen seepage. Ceramic splice protectors are used. OTDR is used to determine differential loss at different locations along the fiber. A reflective element at the far-end of the fiber eases calibration.

Abstract: An optical sensing system uses light scattered from a sensing fibre to sense conditions along the fibre, and has a receiver with a frequency to amplitude converter to obtain a frequency of a Brillouin component of the received scattered light, to deduce the conditions. This converter can avoid time consuming scanning of frequencies to obtain the Brillouin frequency spectrum, and avoids the heavy processing load of deducing a peak or average frequency from the spectrum. The converter can be implemented in the optical domain using a grating or interferometer, or in the electrical domain using a diplexer or electrical interferometer. It can generate complementary signals, having opposite signs, a ratio of these signals representing the frequency. This can avoid sensitivity to amplitude changes in the received scattered signals and provide common mode rejection of noise.

Abstract: An optical sensing system uses light scattered from a sensing fibre to sense conditions along the fibre, and has a receiver with a frequency to amplitude converter to obtain a frequency of a Brillouin component of the received scattered light, to deduce the conditions. This converter can avoid time consuming scanning of frequencies to obtain the Brillouin frequency spectrum, and avoids the heavy processing load of deducing a peak or average frequency from the spectrum. The converter can be implemented in the optical domain using a grating or interferometer, or in the electrical domain using a diplexer or electrical interferometer. It can generate complementary signals, having opposite signs, a ratio of these signals representing the frequency. This can avoid sensitivity to amplitude changes in the received scattered signals and provide common mode rejection of noise.

Abstract: A method for measuring the wavelength of light, particularly short pulses of light, with improved accuracy comprises passing the light down a backscatter medium such as an optical fiber and detecting and measuring the wavelength of the backscattered light which will have a pulse length of potentially far greater length than that of the initial pulse. The use of interferometers in conjunction with a reference light of known wavelength enables very accurate measurements to be made.

Abstract: A method and apparatus for measuring the temperature and strain within a structure consists in having optical fibres incorporated in the structure, passing pulses of light down the fibre and detecting the backscattered light.

Abstract: A system for measuring the strain in a structure in which the temperature at the location the strain is measured is also measured in which an optic fiber is incorporated in the structure which has an interferometer positioned at the point or points where the strain is to be measured. A pulse of light is sent down the fiber and the backscattered light is split to separate the Raman Scattered Spectrum light. The interferometer is used to measure the strain and the Raman Scattered Spectrum light is used to measure temperature and loss.