Abstract: A pressure sensitive optical fiber is enclosed within a pressure chamber. A mass is positioned so as to vary the pressure in the pressure chamber in response to a seismic signal. Variations in the chamber pressure are directly detected by the pressure sensitive fiber.

Abstract: An apparatus for interferometric sensing comprises a first broadband switched optical source, a first matched interferometer, a plurality of first sensing interferometers, and a detector. The first matched interferometer contains a first phase modulator. The optical path length difference in each of the first sensing interferometers is approximately equal to the optical path length difference in the first matched interferometer Each of the first sensing interferometers returns an optical interference signal to the detector at a substantially different wavelength The first broadband switched optical source is switched so as to emit optical radiation at wavelengths corresponding to each of the first sensing interferometers at different times.

Abstract: A structure for incorporating fiber optic acoustic sensor in a seismic array includes means for supporting the sensor in a spiral around a central strength member in a manner to isolate shear waves from the sensor. In another aspect, an axially oriented sensor in a seismic array comprises a pressure sensitive optical fiber wound in a spiral around the axis, the fiber having a plurality of optical Bragg gratings and a plurality of channels. The preferred structure may include four tubes spiraling around the strength member. One of the tubes encloses an optical fiber sensor which is maintained in an extended orientation by fluid flow through the tube. Another of the tubes serves as a return path for fluid through the sensor tube. The other tubes enclose high speed and low speed data conductors, respectively. The sensor fiber may also be wound in a spiral around a compliant core in a manner to satisfy Poisson's Ratio such that strain on the compliant core does not alter the tension of the sensor fiber.

Abstract: An interferometric sensor includes a broadband optical source, a depolarizer for depolarizing optical radiation emitted by the broadband optical source, a matched interferometer, a sensing interferometer, and a detector. The matched interferometer contains a phase modulator. The sensor is configured so that the optical path length difference in the sensing interferometer is approximately equal to the optical path length difference in the matched interferometer.

Abstract: Apparatus for the remote measurement of physical parameters, the apparatus comprises a sensor (1) for sensing one or more physical parameters, an interrogator (2) for interrogating the sensor (1) and making a measurement, a cable (3) for extending between the sensor (1) and the interrogator (2), a conduit (4) for extending to a measurement location (5) and which is of such a cross-sectional size that it is able to accept the cable (3) and the sensor (1), and a cable installer (6) for installing the sensor (1) and the cable (3) through the conduit (4) and for placing the sensor (1) at the measurement location (5), the cable installer (6) being such that it includes a device (7) for propelling a fluid along the conduit (4), and the conduit (4) being such that it contains a lead-in section (8) for providing sufficient fluid drag on the cable (3) as it enters the conduit (4) from the cable installer (6) to ensure that the sensor (1) is able to be transported through the conduit (4).

Abstract: Apparatus for multiplexing fiber-optic sensing interferometers, which apparatus comprises at least one optical source, a plurality of matched interferometers connected to the optical source and each containing a phase modulator having a unique identifying characteristic, a network of fiber-optic sensing interferometers each containing a path-length difference, at least one detector, and interconnections provided between the matched interferometers, the network of fiber-optic sensing interferometers and the detector, the path length difference in each fiber-optic sensing interferometer being approximately matched to a path length difference in its associated matched interferometer, and the interconnection means between the matched interferometers, the network of fiber-optic sensing interferometers and the detector being such that there is no more than one signal on the detector having the same unique identifying characteristic associated with one of the phase modulators.

Abstract: An optical fibre sensor element (1) comprising an optical fibre (2), a protective coating on the optical fibre, and shape constraining means (3) which causes the optical fibre (2) to follow a path which extends in a generally longitudinal direction and which is such that the coated optical fibre (3) is not perfectly straight and it is impossible to draw an imaginary straight line in any direction which remains inside the coated optical fibre (3) along the entire length of the optical fibre sensor element (1).

Abstract: The invention is an apparatus for measuring pressure, which comprises a pressure communicating device (3) for location at a point (4) at which pressure is to be measured, a primary tube (1) containing a fluid for linking the pressure communicating device (3) to a control point (9) where the pressure information is required, a sealing device for sealing the primary tube (1) so as to form a closed system when the pressure communicating device (3) is closed, a pressure control device (6) for changing the pressure of the fluid within the primary tube (1), a volume measuring device (8) for measuring changes in the volume of the fluid within the primary tube (1) as the pressure of the fluid is varied, a pressure measuring device (7) for measuring the pressure of the fluid at some point within the fluid, and device remote from the control point (9), and a transmitter device for transmitting pressure information from the pressure measuring device to the control point (9).