A well system includes a fiber-optic cable that can be positioned downhole along a wellbore. The well system further includes a plurality of opto-electrical interfaces to communicatively couple to the fiber-optic cable to monitor temperature and strain along the fiber-optic cable. Additionally, the well system includes a processing device and a memory device that includes instructions executable by the processing device to cause the processing device to perform operations. The operations include receiving data representing frequency or phase shift measurements from the opto-electrical interfaces using at least two frequency or phase shift measurement techniques. Further, the operations include generating a temperature shift output and a strain change output using an inversion comprising sensitivity ratios and the data representing the frequency or phase shift measurements from the plurality of opto-electrical interfaces.

Systems and methods are provided for enabling improved sensitivity in low-gain regimes. Embodiments of the present disclosure use polarization pulling to separate a signal of interest (e.g., amplified probe light) from the background probe light. This enables a dramatic increase in probe power and thereby increases the signal-to-noise ratio of the measurement. Embodiments of the present disclosure provide a vector subtraction technique to compensate for undesirable interference effects resulting from the finite extinction of standard polarization components (i.e. polarizing beam splitters) and polarization fluctuations. Embodiments of the present disclosure enable Brillouin sensing with improved accuracy in low-gain regimes and is particularly relevant for high-spatial resolution sensing applications.

To uniquely determine a Brillouin frequency shift (BFS) even if a relation between phase and intensity of an intensity signal corresponding to a phase difference between the two optical paths in an interferometer varies. An optical fiber sensor includes a reference section average value calculation unit 180 configured to acquire average intensity in a reference section, a phase control unit 142 configured to control a delay unit in such a manner that a phase difference between two optical paths is swept from 0 to 2π, a Brillouin scattering coefficient elimination unit 176 configured to eliminate a Brillouin scattering coefficient from an interference signal by using an intensity signal, a phase/amplitude calculation unit 184 configured to acquire an initial phase φ.sub.offset and amplitude of the interference signal by using a relation between average intensity I.sub.ave and the phase obtained through the phase sweep from 0 to 2π, a normalization unit 179 configured to use the amplitude of the interference signal to normalize the interference signal from which the Brillouin scattering coefficient is eliminated, and a BFS computation unit 188 configured to compute a BFS by using the normalized interference signal.

To uniquely determine a Brillouin frequency shift (BFS) even if a relation between phase and intensity of an intensity signal corresponding to a phase difference between the two optical paths in an interferometer varies. An optical fiber sensor includes a reference section average value calculation unit 180 configured to acquire average intensity in a reference section, a phase control unit 142 configured to control a delay unit in such a manner that a phase difference between two optical paths is swept from 0 to 2π, a Brillouin scattering coefficient elimination unit 176 configured to eliminate a Brillouin scattering coefficient from an interference signal by using an intensity signal, a phase/amplitude calculation unit 184 configured to acquire an initial phase φ.sub.offset and amplitude of the interference signal by using a relation between average intensity I.sub.ave and the phase obtained through the phase sweep from 0 to 2π, a normalization unit 179 configured to use the amplitude of the interference signal to normalize the interference signal from which the Brillouin scattering coefficient is eliminated, and a BFS computation unit 188 configured to compute a BFS by using the normalized interference signal.

A distributed optical fibre sensor is discussed which is arranged to detect acoustic vibration and at least a first of two or more other measurands, which could be for example two or more of changes in temperature, changes in static pressure, and changes in static strain. At least first and second optical waveguides are arranged to have optical path length response characteristics to at least one of the other measurands which are different from each other, and an analyser is arranged to determine at least said first other measurand using differences between the interference signals from each of the optical waveguides.

The disclosure concerns a device (101) for distributed sensing comprising: a pump generator (1) for generating an optical pump signal, a pump splitter (2) configured to split the pump signal in a number N of channels (3), each channel comprising an optical fiber (31) or a connector (32) arranged for connecting an optical fiber, a controller configured to control the pump splitter, an optical receiver (4) for receiving a backscattered signal from the optical fiber or from the connector of each channel. The pump splitter comprises a gating system comprising a gate (21) for each channel among the N channels. Each gate is associated to a given channel and has an open state allowing the pump signal to go from the pump generator to the optical fiber or the connector of the associated channel, and a closed state for which the pump signal cannot go from the pump generator to the optical fiber or the connector of the associated channel.

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 is to provide a backscattered light amplification device, an optical pulse test apparatus, a backscattered light amplification method, and an optical pulse test method for amplifying a desired propagation mode of Rayleigh backscattered light with a desired gain by stimulated Brillouin scattering in a fiber under test having the plurality of propagation modes. The backscattered light amplification device according to the present invention is configured to control individually power, incident timing, and pulse width of a pump pulse for each propagation mode when the pump pulse is incident in a plurality of propagation modes after the probe pulse is input to the fiber under test in any propagation mode.

Methods of measuring an anomaly, any induced change in physical parameters such as strain, temperature, and so forth, in an optical fiber. One method may include launching a plurality of probe pulses from a probe source; recording a Brillouin scattering spectrum from a plurality of reflection signals generated in the optical fiber, responsive to the plurality of probe pulses; determining a relative motion between the optical fiber and the anomaly during the recording the Brillouin back-scattering spectrum; and dynamically adjusting the Brillouin back-scattering spectrum according to the relative motion, or performing an adjustment of the Brillouin back-scattering spectrum after acquisition of the Brillouin back-scattering spectrum.

According to examples, an optical fiber-based sensing membrane may include at least one optical fiber, and a substrate. The at least one optical fiber may be integrated in the substrate. The substrate may include a thickness and a material property that are specified to ascertain, via the at least one optical fiber and for a device that is contiguously engaged with a surface of the substrate, includes the substrate embedded in the device, or includes the surface of the substrate at a predetermined distance from the device, a thermal and/or a mechanical property associated with the device, or a radiation level associated with a device environment.