Abstract: A method and apparatus for reducing crosstalk between sensors in an inline Fabry-Perot (FP) sensor array. The inline FP sensor array comprises a plurality of fiber Bragg gratings arranged periodically along an optical fiber. The sensors are formed between each of the Bragg gratings. A light source provides multiplexed pulses as interrogation pulses for the array. The light pulses are applied to one end of the sensor array and a light detector detects reflected pulses. The detected pulses comprise a composite of reflections from all the Bragg gratings along the fiber. The apparatus processes the detected signals using an inverse scattering algorithm to detect an accurate phase response from each of the Bragg sensors while reducing crosstalk from other Bragg sensors within the array. One form of inverse scattering algorithm is a layer-peeling algorithm.

Abstract: A method and apparatus for producing depolarized light that is useful in forming interrogation signals for an optical sensor array and demodulator having reduced polarization-induced fading and phase noise. The depolarized light is produced by splitting a light beam, delaying a first orthogonal component of the light beam with respect to a second orthogonal component of the light beam using a predefined delay, while maintaining the polarization of the first orthogonal component and the polarization of the second orthogonal component. The delayed light beams are combined to produce a depolarized light beam by selecting a predefined delay that causes an interference signal having a delay equal to the predefined delay to be suppressed during a demodulation process.

Abstract: A method and apparatus that uses specific source modulation and detectors to detect a response that carries information about a system response matrix associated with each sensor in a interferometric sensor array and extracting a sensor response in a manner that eliminates polarization-induced signal fading and that is insensitive to lead fiber birefringence fluctuations.

Abstract: An optical wavelength readout system for application in optical sensing systems is disclosed. The system includes a Master unit including a wavelength swept optical source for launching light into a string of optical sensors, and a detection and processing unit for detecting and processing the light emitted by the source. The system also includes a Slave unit including a light coupling device for coupling light from the light source into the string of sensors and for coupling light reflected from the string of sensors to a detection and processing unit arranged to detect and process the reflected light. The Master unit includes a wavelength reference unit adapted to make a reference signal available to other parts of the sensing system. The reference signal represents a generally exact relation between the wavelength of the light emitted from the source and time.

Abstract: A downhole sub for instrumentation, such as a fiber optic sensor. The sub is configured to be connected to a string of pipe, such as a string of tubing. The sub first comprises an essentially concentric tubular body. The tubular body has an inner diameter that generally conforms to the inner diameter of the tubing string. A recess is formed within the wall of the tubular body. Next, the sub comprises a gauge housing that is received within the recess of the tubular body. The gauge housing includes a plate portion that is exposed to fluids within the production tubing. The gauge housing further includes a side bore that receives a sensor. One or more gauge housing ports are pre-fabricated into the gauge housing to provide fluid communication between the inner bore of the production tubing and the side bore of the gauge housing. The entire sub is preferably self-contained without any elastomers or metal-to-metal seals.

Abstract: A fiber optic sensor system comprises at least one measuring sensor 1 providing an optical output dependent upon one or more parameters to be measured, e.g. temperature, and at least one reference sensor 2 providing a reference output for comparison with the measuring sensor output. The reference sensor is provided in a birefringent fiber. The system includes a detecting means 13,14 whereby a reference beat signal f2 is derived by measuring the optical frequency splitting between frequency components in different polarization planes of the reference sensor output. A further beat signal f3 is generated between the measuring and reference sensor outputs, such beat signals being used to derive a measurement of one or more parameters.

Abstract: Method and assembly for sustained elimination or reduction of polarization induced signal fading in optical interferometer networks comprising at least two optical paths from an input port to an output port, the transmission delays of the paths differing by ?, an interrogation arrangement interrogating the optical phase differences between the paths, containing at least one optical source launching optical power into a port, a detector arrangement converting the optical power from an output port into electrical detector signals, and a control and signal processing unit capable of processing detector signals to determine the phase difference. The method comprising the steps of: altering the input polarization state produced by the source with a modulation frequency that is comparable to or higher than 1/(4?) receiving the optical signals at the detector arrangement providing a detector signal; processing the detector signal determining the phase difference between the optical signals.

Abstract: An optical waveguide Bragg grating fabrication apparatus (1) comprises a light source (2) providing ultra-violet (UV) light and optical means (4,5A-B,6A-B,7A-B,9) for adapting the light beam to form an interference pattern in a photosensitive optical waveguide (8). The interference pattern has a spatial intensity modulation along the length of the optical waveguide and thus providing an optical grating in the waveguide in the form of a refractive index modulation. The optical means comprises a movable non-uniform diffractive mask (4) for dividing the optical beam in at least two beams (12A-B) and optical elements for collecting two or more of the light beams to interfere on the optical waveguide. The optical means comprises position control means for controlling the position of at least one mirror or lens. Corresponding methods and the use of a super-periodic diffractive mask in such fabrication are described.

Abstract: A method for measurements of the orthogonally polarized minimum and maximum Bragg wavelengths of one of several birefringent fiber Bragg grate FBG sensors, and alternatively a method for eliminating errors in FBG sensor measurements caused by undesired grating birefringence, using an FBG wavelength interrogation apparatus, where the light from a polarized wavelength swept narrowband source (1) is passed through an electrically controllable polarization controller (2), operated in either a scanning mode or a tracking mode to find the two orthogonally polarized reflection spectra of the birefringent FBGs (6) with corresponding minimum and maximum Bragg wavelength &ggr;nx and &ggr;nx, where a low-birefringent reference FBG with known wavelength (5) and a low-birefringent fixed Fabry-Perod interferometer (8), generating frequency equidistant peaks are used in combination to provide accurate and readable wavelength measurements.

Abstract: A Bragg Grating optical waveguide laser source comprising at least one Bragg grating in a rare earth doped waveguide and an optical pump source coupled to said doped waveguide, said Bragg gratings having at least two different peak reflection wavelengths and at least one of said Bragg gratings comprising a phase-shift and a phase-shift actuator being coupled to the phase-shift for controlled application of changes in the phase-shift thus activating or deactivating the corresponding Bragg grating waveguide laser.

Abstract: Fibre optic apparatus for accurate and repeatable measurements of light comprising one or more wavelength ranges, and system employing the apparatus. The apparatus according to the invention comprises: a directional coupler adapted to lead the light into an optical fibre, said optical fibre containing at least one analysis filter for each wavelength range, said analysis filters consisting of at least one fibre-optical Bragg-grating (FBG) which reflects incident light with a chosen wavelength back through said directional coupler and onto a detector having an associated signal processing unit, a modulator device for pulsing the incident light with a chosen pulse width, and an optical fibre delay line in front of each analysis filter, with a length adapted to provide for a sufficient time delay larger than the pulse width, so that the pulses reflected from each analysis filter at different wavelengths can be separated in time and thereby be demodulated in the signal processing unit.

Abstract: Method and system for obtaining scale factor calibration of a fiber optic sensor head (3, 6) comprising a conversion unit (3) with a conversion element (14) made from a material being subject to changes in its shape or physical dimensions under the influence of magnetic or electric fields, e.g. a magnetostrictive, electrostrictive, or piezoelectric material, and an optical fiber (4) being attached to the conversion element (14), the conversion element (14) thus straining the optical fiber causing a phase and/or intensity modulation of the optical signal in the fiber when subject to the fields. The method is characterized in that a chosen electrical energy is applied to the sensor head (3, 6) resulting in a change in the optical signal being received by the optical interrogation device, and calculating a calibration signal, e.g. a calibration scale factor, based on the applied electrical energy and the measured change in the optical signal.

Abstract: A combination of an optical fiber, a device for fastening the optical fiber to at least one Bragg grating including a generally cylindrical sleeve through which the fiber passes, and a bond between the fiber and the sleeve at one end thereof. The end of the sleeve to which the fiber is bonded permits expansion of the bond radially with respect to the optical fiber.

Abstract: A device is provided for measuring a bending load in mechanical constructions, which device enables measurement over a broad range of stresses with high precision and which simultaneously compensates for deviations caused by temperature fluctuations.

Abstract: Signal cable for transmission of optical signals, especially in oil and gas wells, includes at least one elongated optical fiber, and an elongated, generally tubular container within which the optical fiber is disposed, the container having an inner wall and an outer wall, a space being defined between the optical fiber and the inner wall. At least one of the inner wall and the outer wall has a thin continuous surface coating of gold or a gold alloy.

Abstract: A device (100) for measurement of pressure in fluids is disclosed that includes a cylindrical housing (101) having a pressure port (103), an inner cavity (102) and an opening (102b). A closed pipe (131) is situated in the cavity (102) and closes the opening (102b) in the housing (101) and establishes a cavity (134) between the pipe (131) and the inner wall of the housing (101). A connection element (133) is situated in the pipe (131), so that one end of the element (133) is connected to the free end of the pipe (131) for transfer of axial length change of the pipe (131), whereas the connected element (133) is arranged for establishing a cavity (132) between the connection element (133) and the pipe (131). An optical fiber (171) is laid in a slot (171) in the external surface of the housing (101), and includes a Bragg grating (150) fixed between the housing (101) and the connection organ (133) by fastening points (151, 152).

Abstract: A tension sensor including an optical fibre having a Bragg grating is disclosed, the sensor including a housing and a support member shorter that the housing coaxially disposed therein and connected to the housing at one end. The fiber runs along the longitudinal axis of the housing and is connected to one end of the housing and to at least one location on the support member. A second Bragg grating may be provided within the support member to allow for additional measurements for temperature compensation purposes.

Abstract: A device for accurate and repeatable measurements of optical wavelengths, including an interrogation broadband light source (1) and a tuneable optical filter (2). A first part of the light is, in either order, transmitted through the filter (2) and reflected from, or transmitted through, at least one fibre Bragg grating (5) with known Bragg wavelength, providing an absolute wavelength reference, and directed to a first detector (7). A second part of the light is, in either order, transmitted through the filter and transmitted through, or reflected from a Fabry-Perot filter (8) with fixed and known free spectral range, creating a comb spectrum sampling the interrogation source spectrum to provide an accurate frequency/wavelength scale.

Abstract: An optical end-pumped fiber laser doped with one or more rare-earths and with distributed feedback (DFB) via a fiber Bragg-grating, which is oscillating on two orthogonally polarized wavelengths. The distance between the wavelengths may be tuned by changing the birefringence of the fiber. The laser may be applied as a polarimetric sensor in which an asymmetrical force changes the wavelength separation, or as a tunable two-wavelength source. A particular preferred field of application is for measuring the pressure in pipes, to determine the flow.