Various embodiments of sensors are described that exhibit several spectral features that together offer coverage of a wavelength range corresponding to the desired strain dynamic range (or temperature range) of a system. The spectral features arise from a Fabry-Perot interferometer formed by two overlapping chirped FBGs, the free-spectral range (FSR) of which varies with wavelength. The spectral features may be differentiated due to a combination of spacing and slope of the overlapped, chirped gratings.

Embodiments of the invention provide an improved optical fiber distributed acoustic sensor system that makes use of an optical fiber having reflector portions distributed along its length in at least a first portion. In particular, in order to increase the spatial resolution of the sensor system to the maximum, the reflector portions are positioned along the fiber separated by a distance that is equivalent to twice the distance an optical pulse travels along the fiber in a single sampling period of the data acquisition opto-electronics within the sensor system. As such, no oversampling of the reflections of the optical pulses from the reflector portions is undertaken, which means that it is important that the sampling points for data acquisition in the sensor system are aligned with the reflections that arrive at the sensor system from along the sensing fiber. In order to ensure such alignment, adaptive delay componentry may be used to adaptively align the reflected optical signals (or their electrical analogues) with the sampling points. Alternatively, control over the sampling points can also be undertaken to re-synchronise the sampling points with the returning reflections. In addition, in order to allow higher speed sampling to be undertaken, reflection equalisation componentry may also be used to reduce the dynamic range of the returning reflections.

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.

Example embodiments include an optical assembly for an optical interrogation system having a single core or a multicore sensing fiber, a measurement fiber to couple light into the sensing fiber, and a reference fiber arranged with the measurement fiber as part of an optical interferometer. A beam splitter combines light from the sensing fiber and with light from the reference fiber. A polarization beam splitting prism separates the combined light into first polarized light and second polarized light that is orthogonal to the first polarized light. The optical assembly can substantially reduce the size, complexity, or cost associated with the traditional optical components in an optical interrogation system that it replaces. Other example optical assemblies are described. Embodiments describe optical interrogation systems using the example optical assemblies.

A sensor device including a deflectable membrane made of a 2D nanomaterial, a first optical waveguide for guiding light, disposed adjacent to the membrane and extending along the surface of the membrane at least in a first section, as well as a measuring device for measuring, within the first section the influence of the membrane on an evanescent wave range of the light guided along the first optical waveguide. The influence of the membrane on the light guided in the optical waveguide, in particular on the evanescent wave range of the light, can be measured interferometrically by detecting phasing differences or phase shifts. This allows for a force-free readout of the membrane deflection. By using very thin 2D nanomaterials, the membrane can also react to very quick changes in force.

A fiber-optic sensors for measuring deformation, intended to operate in a harsh environment is provided. The sensor comprises a Fabry-Perot-cavity-based optical measurement head, a linking optical fiber and an expansion reserve case, the case comprising a segment of the linking optical fiber. The inside thickness of the case is comprised between one and several millimeters, the case being flat and of shape referred to as bicorne shape, the shape comprising a convex central portion and two concave symmetric ends, the optical fiber forming, inside the bicorne, one and only one arch, the segment of the optical fiber being, in addition, tangent to the internal surfaces of the reserve case, whatever the temperature conditions.

A manhole position identification method of the present invention includes: measuring, from an end of an optical fiber, a temporal variation in scattering light from the optical fiber when an impact blow is applied to a cover of a manhole located on a path of the optical fiber, so as to obtain temporal variations in a scattering light intensity distribution in a longitudinal direction of the optical fiber; determining an occurrence of vibration due to the impact blow based on the temporal variations at positions in the scattering light intensity distribution, so as to identify an impact blow position on the optical fiber; and associating the impact blow position on the optical fiber with a map position of the manhole whose cover has received the impact blow, so as to identify a position of the manhole expressed in terms of optical fiber length from the end.

Multi-spectral feature sensing techniques and sensor and related digital signal processing circuitry and methods. A method of operating a digital signal processing circuitry includes acquiring optical frequency domain reflectometry (OFDR) data from an interferometer operably coupled to a tunable laser and a sensing fiber, separating sensor signals corresponding to sensors of the sensing fiber from the OFDR data, and inferring a relative shift of a separated sensor signal. A digital signal processing circuitry includes a front end circuitry and a back end circuitry. The front end circuitry is configured to isolate sensor responses from an input signal including OFDR data. The back end circuitry is configured to determine a phase shift corresponding to each isolated sensor response.

Example embodiments include an optical interrogation system with a sensing fiber having a single core, the single core having multiple light propagating modes. Interferometric apparatus probes the single core multimode sensing fiber over a range of predetermined wavelengths and detects measurement interferometric data associated with the multiple light propagating modes of the single core for each predetermined wavelength in the range. Data processing circuitry processes the measurement interferometric data associated with the multiple light propagating modes of the single core to determine one or more shape-sensing parameters of the sensing fiber from which the shape of the fiber in three dimensions can be determined.

A fiber includes M primary cores and N redundant cores, where M an integer is greater than two and N is an integer greater than one. Interferometric circuitry detects interferometric pattern data associated with the M primary cores and the N redundant cores when the optical fiber is placed into a sensing position. Data processing circuitry calculates a primary core fiber bend value for the M primary cores and a redundant core fiber bend value for the N redundant cores based on a predetermined geometry of the M primary cores and the N redundant cores in the fiber and detected interferometric pattern data associated with the M primary cores and the N redundant cores. The primary core fiber bend value and the redundant core fiber bend value are compared in a comparison. The detected data for the M primary cores is determined reliable or unreliable based on the comparison. A signal is generated in response to an unreliable determination.