The present invention provides novel apparatus and methods for fast quantitative measurement of perturbation of optical fields transmitted, reflected and/or scattered along a length of an optical fibre. The present invention can be used for point sensors as well as distributed sensors or the combination of both. In particular this technique can be applied to distributed sensors while extending dramatically the speed and sensitivity to allow the detection of acoustic perturbations anywhere along a length of an optical fibre while achieving fine spatial resolution. The present invention offers unique advantages in a broad range of acoustic sensing and imaging applications. Typical uses are for monitoring oil and gas wells such as for distributed flow metering and/or imaging, seismic imaging, monitoring long cables and pipelines, imaging within large vessel as well as for security applications.

The present invention provides novel apparatus and methods for fast quantitative measurement of perturbation of optical fields transmitted, reflected and/or scattered along a length of an optical fibre. The present invention can be used for point sensors as well as distributed sensors or the combination of both. In particular this technique can be applied to distributed sensors while extending dramatically the speed and sensitivity to allow the detection of acoustic perturbations anywhere along a length of an optical fibre while achieving fine spatial resolution. The present invention offers unique advantages in a broad range of acoustic sensing and imaging applications. Typical uses are for monitoring oil and gas wells such as for distributed flow metering and/or imaging, seismic imaging, monitoring long cables and pipelines, imaging within large vessel as well as for security applications.

An optical fiber includes multiple optical cores configured in the fiber including a set of primary cores and an auxiliary core. An interferometric measurement system uses measurements from the multiple primary cores to predict a response from the auxiliary core. The predicted auxiliary core response is compared with the actual auxiliary core response to determine if they differ by more than a predetermined amount, in which case the measurements from the multiple primary cores may be deemed unreliable.

Optical polarization control devices that include two pairs of squeezing plates oriented in mutually perpendicular directions are described. Compressive forces exerted by the two pairs of plates onto an optical fiber can be configured for low polarization mode dispersion. Various methods and systems in which the polarization control devices can be employed are also described.

An optical fiber includes multiple optical cores configured in the fiber including a set of primary cores and an auxiliary core. An interferometric measurement system uses measurements from the multiple primary cores to predict a response from the auxiliary core. The predicted auxiliary core response is compared with the actual auxiliary core response to determine if they differ by more than a predetermined amount, in which case the measurements from the multiple primary cores may be deemed unreliable.

A cable comprising: a plurality of optical fiber cores; and one or more optical fiber core wires including one or more of the optical fiber cores. Further, at least one of the optical fiber core wire is fixed at a plurality of positions in a longitudinal direction of the cable so as to achieve substantially no displacement in a cable radial direction, at least a pair of the optical fiber core wires are fixed in a plane perpendicular to the longitudinal direction of the cable so as to achieve substantially no displacement relative to each other, and sensing of a strain profile in the longitudinal direction of at least the pair of the optical fiber core wires leads to achievement of sensing of a shape of the cable in the longitudinal direction.

Systems and methods for sensing changes in an optical sensing fibre, principally for detecting changes in strain. A plurality of optical probe pulses at different optical frequencies (f.sub.1, f.sub.2, . . . f.sub.n) spaced by f are transmitted into the sensing fibre. Light backscattered from the optical sensing fibre may be mixed with delayed backscatter frequency shifted by f+f.sub.m where f.sub.m is a heterodyne frequency. The backscattered or mixed light may be detected to determine changes in the sensing fibre. f may be chosen to optimise performance.

A monitoring humidity measurement system includes: a humidity measurement optical fiber including a first optical fiber and a humidity detection layer provided so as to annularly cover the first optical fiber; a reference optical fiber including a second optical fiber; a plurality of optical communication cables; and a signal processing device configured to, with a laser beam entering into the first and second optical fibers, calculate and obtain Brillouin frequency shift and Rayleigh frequency shift of backscatter light from the first and second optical fibers based on the entering laser beam, and store predetermined constants, wherein reference data and target data are measured from the Rayleigh frequency shift and an initial humidity value calculated from the Brillouin frequency shift, and the value of humidity at the present time is calculated on the basis of Rayleigh frequency shift per unit humidity calculated from a difference between the above two data.

The rolling bearing provides a first ring, a second ring and at least one row of rolling elements arranged therebetween. Each of the first and second rings include an inner bore having an outer surface and at least one raceway for the row of rolling elements formed on one of the inner bore and outer surface. The first ring provides at least one part ring delimiting the raceway, and at least one sleeve secured to the part ring and delimiting at least partly the other of the inner bore and outer surface of the first ring. The rolling bearing further provides at least one optical fiber sensor mounted inside at least one circumferential groove formed on the first ring and passing through at least one optical fiber sensor passage opening into the circumferential groove.

An in-situ, non-destructive sensor device, system and method are provided to detect or assess fouling at a very early stage of development. They can be used to detect or assess fouling on a surface of an aquatic system. They can be used to obtain a depth profile of the fouling. Data concerning the depth profile can be extracted and used to assess the fouling on the surface. In one or more aspects, the method can include providing an optical tomography spectrometer; optically positioning the optical tomography spectrometer in association with a surface of an area to be assessed for fouling in an aqueous system; irradiating the surface; acquiring, from irradiating the surface, a plurality of signals as a function of a distance from the surface at different times; extracting data from the signals as a function of the distance to obtain a depth profile of the surface at the different times; and determining a change in the depth profile between the different times to assess fouling on the surface.