Apparatus and methods for fast quantitative measurement of perturbation of optical fields transmitted, reflected and/or scattered along a length of an optical fiber 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 fiber while achieving fine spatial resolution. Advantages of this technique include 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.

Systems and methods for distributed acoustic sensing based on coherent Rayleigh scattering are disclosed herein. A system comprises a pulse generator, an interferometer, a photo detector assembly, and an information handling system. The interferometer comprises a first and second optical switch each comprising a plurality of ports. The information handling system activates one port on each of the first and second optical switches so as to vary the optical path length of the interferometer. A method comprises splitting backscattered light from an optical pulse into a first portion and a second portion, activating one port of a first optical switch and one port of a second optical switch, sending the first portion into a first arm of an interferometer, sending the second portion into a second arm of the interferometer, combining the first and second portions to form an interferometric signal, and receiving the interferometric signal at a photodetector assembly.

Certain aspects of the present disclosure generally relate to an optical reference element having a wavelength spectrum comprising a plurality of wavelength functions having wavelength peaks spaced over a range of wavelengths, wherein adjacent wavelength functions are due to two orthogonal birefringence axes in the optical reference element. Aspects of the present disclosure may eliminate the drift issues associated with residual polarization and polarization dependent loss (PDL) with respect to grating-based sensor and reference element measurements.

A system for sensing phase changes in a medium includes a bidirectional interferometer having a reference arm and a sensing arm, two inputs at each of the two ends of the interferometer, and a circulator disposed between each input and the interferometer. Sources provide squeezed state pulses at an input at each end of the interferometer. Spaced-apart partial reflectors are disposed along the arms. There are detectors associated with each input. The circulators pass the squeezed state pulses into the interferometer and route reflections of the pulses to the detectors. Classical pulses may provided at the other input at each end of the interferometer.

The invention relates to a method for digitally processing a signal from an optoelectronic distributed measuring device based on Brillouin scattering, said device comprising a continuous light source (1), a coupler (2), an acousto-optic modulator (3), an optical fiber (5) to be tested so that it emits in return a signal by spontaneous Brillouin backscattering at a frequency F equal to pBz, where Bz is the Brillouin frequency to be measured at every point z of said optical fiber (5), a local oscillator (16) emitting another light signal intended to be mixed with said return signal emitted by Brillouin backscattering by said optical fiber (5) to be tested, a detection module (9) able to detect said Brillouin shift frequency Bz at every point z of said optical fiber and a processing module for linking this Brillouin shift frequency Bz at every point z of said optical fiber to a temperature value and a strain value. According to the invention, the local oscillator (16) comprises a reference optical fiber (18) having a Brillouin frequency identical or close to that of the optical fiber (5) to be tested, said reference optical fiber (18) emitting a signal by spontaneous Brillouin backscattering, in response to said continuous light signal emitted in said second arm by said light source (1), said Brillouin backscattering signal being emitted at a frequency .sub.OL=0.sub.BRef, where .sub.BRef is the Brillouin frequency of the reference fiber without strain and at a reference temperature.

Certain aspects of the present disclosure generally relate to an optical reference element having a wavelength spectrum comprising a plurality of wavelength functions having wavelength peaks spaced over a range of wavelengths, wherein adjacent wavelength functions are due to two orthogonal birefringence axes in the optical reference element. Aspects of the present disclosure may eliminate the drift issues associated with residual polarization and polarization dependent loss (PDL) with respect to grating-based sensor and reference element measurements.

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.

The present invention is the optical fiber sensor, that laser pulses from a laser source are separated into a reference path and a measurement path by the second optical coupler via the first optical coupler, the first FRM is provided at an end of the reference path, the second FRM is provided at an end of the measurement path, and the reference reflected light of the first FRM and the measurement reflected light of the second FRM are interfered at the second optical coupler and are converted into three phases. The first phase pulses are transmitted to the optical synthesis section via the first optical coupler, second phase pulses are transmitted to the optical synthesis section via the first delay section, and third phase pulses are transmitted to the optical synthesis section via the second delay section. The time division pulse train is outputted from the optical synthesis section.

The invention relates to a method for digitally processing a signal from an optoelectronic distributed measuring device based on Brillouin scattering, said device comprising a continuous light source (1), a coupler (2), an acousto-optic modulator (3), an optical fiber (5) to be tested so that it emits in return a signal by spontaneous Brillouin backscattering at a frequency F equal to pBz, where Bz is the Brillouin frequency to be measured at every point z of said optical fiber (5), a local oscillator (16) emitting another light signal intended to be mixed with said return signal emitted by Brillouin backscattering by said optical fiber (5) to be tested, a detection module (9) able to detect said Brillouin shift frequency Bz at every point z of said optical fiber and a processing module for linking this Brillouin shift frequency Bz at every point z of said optical fiber to a temperature value and a strain value. According to the invention, the local oscillator (16) comprises a reference optical fiber (18) having a Brillouin frequency identical or close to that of the optical fiber (5) to be tested, said reference optical fiber (18) emitting a signal by spontaneous Brillouin backscattering, in response to said continuous light signal emitted in said second arm by said light source (1), said Brillouin backscattering signal being emitted at a frequency .sub.OL=0.sub.BRef, where .sub.BRef is the Brillouin frequency of the reference fiber without strain and at a reference temperature.

An optical sensor and a deformation detection system in which the optical sensor is used. The optical sensor includes an optical fiber, an elongated hollow housing having an interior portion, and a material disposed on an inner surface of the housing that produces a persistent change in an optical signal transmission property of the optical fiber when the optical fiber contacts the material. The optical fiber elastically extends between opposing ends of the housing such that a bending deformation of the housing beyond a threshold radius of curvature causes a contact to occur between the material and the optical fiber. The contact results in persistent change in the optical signal transmission property of the optical fiber, which can be detected to determine whether deformation of the device occurred beyond a predetermined threshold value. The deformation detection system can use one or more of the optical sensors attached to the device.