Abstract: A fiber-optic sensor array (100) comprises a line array of fiber-optic sensor packages (AX, BX, CX, DX, AY, BY, CY, DY, AZ, BZ, CZ, DZ) each having a package input/output (i/o) fiber and each being arranged to output a finite output pulse series of optical output pulses via the package i/o fiber in response to input thereto of one or more interrogating optical pulses. The array further comprises a fiber-optic bus (104,106, 108, 110) extending along the length of the line array, each package i/o fiber being optically coupled to the fiber-optic bus at a respective positions along the line array. The array allows interrogation at a higher frequency than is the case for a serial array of the same number of fiber-optic sensing packages.

Abstract: A method of sensing using a phase based transducer in which a transducer response is provided at multiple different levels of sensitivity. The different levels of sensitivity are used to produce an output which does not overscale across a wide range of signal levels. This is particularly useful for use in conjunction with multiplexed arrays of fiber optic sensors for seismic surveying. Methods of sensor calibration and noise reduction are also described.

Abstract: A fiber-optic sensor package (10) comprises a serial array of fiber-optic sensing coils (14, 16, 18, 20, 22) each of which is comprised in a respective fiber-optic sensor. Four (14, 16, 18, 22) of the coils are housed in a protective casing (24). One of the coils (22) is comprised in a fiber-optic electromagnetic field sensor. The other coils are comprised in respective fiber-optic geophones and/or hydrophones. A single package of the invention allows detection of both seismic and electromagnetic signals. An array of packages of the invention provides detection of both seismic and electromagnetic signal at a series of positions over a long distance or wide area, thus avoiding the need for two conventional arrays. A packages of the invention, and an array of such packages, require little or no electrical power input.

Abstract: A sensor arrangement for monitoring a oil reservoir comprises a sensor array (1) comprising a plurality of sensor units (5) located over an area to be monitored; an interrogator unit (30) comprising a transmitter (402) for transmitting optical signals and receiver for obtaining data on the reservoir from the sensor units, a demodulator (418) for demodulating the received signals, and a recorder (420) for recording the demodulated signals. The arrangement includes an uplink optical cable (408) for transmitting the signals to the sensor array and a downlink optical cable (410) for transmitting signals from the array to the receiver. At least one of the optical cables has an optical amplifier (412, 414). The arrangement enables the interrogator to be remote from the array, for example 150 km or more, obviating the need for significant power to be supplied at the array.

Abstract: Demodulation apparatus for demodulating phase-modulated signals comprises a quadrature signal generator (QSG) for generating in-phase (I) and quadrature-phase (Q) signals in response to an unmodulated input signal. The QSG provides fast frequency tracking of the input signal and excludes any high-frequency content the input signal.

Abstract: A method of sensing using a phase based transducer in which a transducer response is provided at multiple different levels of sensitivity. The different levels of sensitivity are used to produce an output which does not overscale across a wide range of signal levels. This is particularly useful for use in conjunction with multiplexed arrays of fibre optic sensors for seismic surveying. Methods of sensor calibration and noise reduction are also described.

Abstract: Demodulation apparatus for demodulating phase-modulated signals comprises a quadrature signal generator (QSG) for generating in-phase (I) and quadrature-phase (Q) signals in response to an unmodulated input signal. The QSG provides fast frequency tracking of the input signal and excludes any high-frequency content the input signal.

Abstract: A fibre-optic sensor package (10) comprises a serial array of fibre-optic sensing coils (14, 16, 18, 20, 22) each of which is comprised in a respective fibre-optic sensor. Four (14, 16, 18, 22) of the coils are housed in a protective casing (24). One of the coils (22) is comprised in a fibre-optic electromagnetic field sensor. The other coils are comprised in respective fibre-optic geophones and/or hydrophones. A single package of the invention allows detection of both seismic and electromagnetic signals. An array of packages of the invention provides detection of both seismic and electromagnetic signal at a series of positions over a long distance or wide area, thus avoiding the need for two conventional arrays. A packages of the invention, and an array of such packages, require little or no electrical power input.

Abstract: A fibre-optic sensor array (100) comprises a line array of fibre-optic sensor packages (AX, BX, CX, DX, AY, BY, CY, DY, AZ, BZ, CZ, DZ) each having a package input/output (i/o) fibre and each being arranged to output a finite output pulse series of optical output pulses via the package i/o fibre in response to input thereto of one or more interrogating optical pulses. The array further comprises a fibre-optic bus (104,106, 108, 110) extending along the length of the line array, each package i/o fibre being optically coupled to the fibre-optic bus at a respective positions along the line array. The array allows interrogation at a higher frequency than is the case for a serial array of the same number of fibre-optic sensing packages.

Abstract: An optical sensor assembly comprising a plurality of optical fibre sensor coils optically coupled by optical fibre; and an elongate support element, on which said plurality of optical fibre sensor coils and optically coupling optical fibre are mounted is disclosed. The support element has an elastic limit such that when said support element is bent from the elongate axis, the optical fibre fracture limit is reached before the elastic limit is reached. An array of these optical sensor assemblies, the mandrel on which the sensing coils are mounted and their method of manufacture are also disclosed.

Abstract: A fibre-optic package comprises at least two fibre optic devices or components (102, 104, 106, 118, 120, 122, 124) coupled together by fused-fibre coupling. The package typically comprises two or more fibre optic accelerometers, and may be of reduced size compared to fibre-optics packages of the prior art, due to the reduced length of optical fibre required to connect the devices or components.

Abstract: A vibration sensing device, package and system and a method of manufacturing a vibration sensing device are disclosed. The vibration sensing device comprises a body whose geometry is such that it exhibits flextensional properties.

Abstract: An optical sensor assembly including a coupler and an optical fibre coil. The coupler is attached to the central member of the cable at a position where outer layers of the cable been removed. A first terminal of the coupler is connected to an optical fibre traveling along the cable in a fibre conduit external to the central strength member. A second terminal of the coupler is connected to a first end of the coil and a third terminal of the coupler is connected to an optical fibre a mirrored end. The coil is supported about a tubular mandrel, which mandrel fits over the cable. The other end of the coil is attached to the fibre in the cable. The mandrel is located about the cable at a position covering the coupler and the part of the cable where the outer layers are removed.

Abstract: A vibration sensing device, an acceleration sensing system and a method of manufacturing a vibration sensing device wherein the vibration sensing device comprises a flexible disk that is mounted symmetrically about a radial plane and has a mass located on the disk substantially symmetrical about this radial plane which exerts a force that is greater towards the edge than it is towards the centre of the disk. The vibration sensing device is sensitive to on-axis signals and insensitive to cross axis signals.

Abstract: The present invention provides an attitude sensing device and method for determining an attitude of a reference axis of a package containing a fiber optic sensor sensor. The attitude sensing device comprises an electro-mechanical attitude sensor for generating an electrical signal indicative of the attitude sensor, and converter logic for converting the electrical signal into a stimulus signal. A local power source is preferably provided for the electro-mechanical attitude sensor in the converter logic. The stimulus signal is such that the fiber optical sensor is responsive to the stimulus signal to cause a variation in at least one predetermined property of an optical signal transmitted through the fiber optic sensor, the attitude of the reference axis being determinable from the variation of the predetermined property.