# US 11,079,269 B2 · Method and apparatus for optical sensing > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,079,269 B2 - Document ID: US11079269B2 - Status: Granted - Kind: B2 - Application number: 16/508,522 - Filed: 2019-07-11 - Published: 2019-10-31 - Granted: 2021-08-03 - Earliest claimed: 2009-05-27 - Assignees: Silixa Ltd. - Applicants: Silixa Ltd. - Inventors: Mahmoud Farhadiroushan; Tom Richard Parker; Sergey Shatalin - Web page: https://patentgrep.com/patent/US11079269B2 ## CPC - G01H 9/004: {using fibre optic sensors (light guides per se G02B6/00, acousto-optical devices specially adapted for gating or modulating in optical wave guides G02F1/125)} - E21B 47/002: by visual inspection - E21B 47/107: using acoustic means - G01D 5/35303: {using a reference fibre, e.g. interferometric devices} - G01D 5/35306: {using an interferometer arrangement} - G01D 5/35325: {using interferometer with two arms in reflection, e.g. Mickelson interferometer} - G01D 5/35335: {Aspects of emitters or receivers used by an interferometer in an optical fibre sensor arrangement (using multiple sensor devices using multiplexing techniques G01D5/35383)} - G01D 5/35358: {using backscattering to detect the measured quantity} - G01D 5/35364: {using inelastic backscattering to detect the measured quantity, e.g. using Brillouin or Raman backscattering} - G01D 5/35377: {Means for amplifying or modifying the measured quantity} - G01D 5/35383: {using multiple sensor devices using multiplexing techniques} - G01F 1/66: by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters - G01F 1/661: using light - G01F 1/662: {Constructional details} - G01F 1/666: {by detecting noise and sounds generated by the flowing fluid} - G01F 1/667: Arrangements of transducers for ultrasonic flowmeters; Circuits for operating ultrasonic flowmeters - G01M 3/24: using infrasonic, sonic or ultrasonic vibrations - G01M 5/0058: {of elongated objects, e.g. pipes, masts, towers or railways} - G01M 5/0066: {by exciting or detecting vibration or acceleration (vibration testing of structures G01M7/00)} - G01M 5/0091: {by using electromagnetic excitation or detection} - G01M 11/085: {the optical fiber being on or near the surface of the DUT} - G01M 11/331: {by using interferometer} - G01V 1/226: {Optoseismic systems} - G01V 1/40: specially adapted for well-logging - E21B 47/0025: {generating an image of the borehole wall using down-hole measurements, e.g. acoustic or electric} - G01H: MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES - E21B: EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS - G01D: MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR - G01F: MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME - G01M: TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR - G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02) ## Abstract 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. ## Claims ### Claim 1 An apparatus for monitoring seepage along a dam or a dyke, the apparatus comprising: an optical fiber distributed acoustic sensing system, the optical fiber distributed acoustic sensing system comprising an optical sensing fiber deployed in use along the dam or dyke and arranged to receive an input optical signal and propagate the received optical signal along its length; and an acoustic source located in use within a body of fluid contained by the dam or dyke, or within the dam or dyke itself; wherein the optical fiber distributed acoustic sensing system is arranged in use to process light backscattered and/or reflected from along the optical sensing fiber as the optical signal travels therealong, the light being backscattered and/or reflected in dependence on acoustic signals incident along the length of the optical sensing fiber, the backscattered and/or reflected light being processed to determine a relative optical phase modulation along at least one section of the optical sensing fiber to thereby measure a strength of an acoustic signal generated by the acoustic source, and to determine areas of seepage in the dam or dyke based thereon; wherein the optical fiber distributed acoustic sensing system is arranged in use to detect a louder acoustic signal in areas of seepage, wherein areas of seepage provide low acoustic impedance paths for acoustic wave transmission. ### Claim 2 (depends on 1) An apparatus according to claim 1, wherein the optical fiber distributed acoustic sensing system includes an interferometer arranged to receive backscattered light from along the optical sensing fiber, the interferometer comprising at least two optical paths with a path length difference therebetween, the backscattered light interfering in the interferometer to produce interference components, the DAS system further comprising plural photodetectors to measure the interference components, and a processor arranged to determine optical phase angle data therefrom. ### Claim 3 (depends on 2) An apparatus of claim 2, wherein the interferometer further comprises an optical coupler arranged to introduce a relative phase shift between the interference components. ### Claim 4 (depends on 2) An apparatus of claim 2, wherein the interferometer further comprises an optical amplifier arranged to amplify the received backscattered light to produce an amplified light signal. ### Claim 5 (depends on 4) An apparatus of claim 4, wherein the interferometer further comprises an optical filter to filter out the out of band Amplified Spontaneous Emission (ASE) noise generated by the optical amplifier from the amplified light signal. ### Claim 6 (depends on 1) An apparatus according to claim 1, wherein the optical fiber distributed acoustic sensing system includes an interferometer arranged to receive reflected light from along the optical sensing fiber, the interferometer comprising at least two optical paths with a path length difference therebetween, the reflected light interfering in the interferometer to produce interference components, the DAS system further comprising plural photodetectors to measure the interference components, and a processor arranged to determine optical phase angle data therefrom. ### Claim 7 (depends on 6) An apparatus of claim 6, wherein the interferometer further comprises an optical coupler arranged to introduce a relative phase shift between the interference components. ### Claim 8 (depends on 6) An apparatus of claim 6, wherein the interferometer further comprises an optical amplifier arranged to amplify the received reflected light to produce an amplified light signal. ### Claim 9 (depends on 8) An apparatus of claim 8, wherein the interferometer further comprises an optical filter to filter out the out of band Amplified Spontaneous Emission (ASE) noise generated by the optical amplifier from the amplified light signal. ### Claim 10 (depends on 6) An apparatus of claim 6, wherein the interferometer is further arranged to receive backscattered light from along the optical sensing fiber. ### Claim 11 (depends on 1) An apparatus according to claim 1, wherein the optical fiber distributed acoustic sensing system comprises an optical source configured to output a pulsed optical signal. ### Claim 12 (depends on 1) An apparatus according to claim 1, wherein the optical sensing fiber is arranged in use to receive a pulsed optical signal, the pulsed optical signal being constrained by the optical sensing fiber such that it propagates therealong in a first direction, the pulsed optical signal being backscattered and/or reflected along the length of the optical sensing fiber, the backscattered and/or reflected light being constrained by the optical sensing fiber such that it propagates therealong in a second direction opposite the first direction, wherein acoustic perturbations generated by the acoustic signal of the acoustic source incident along the length of the optical sensing fiber cause the optical sensing fiber to expand and contract such that the backscattered and/or reflected light is modulated. ### Claim 13 (depends on 12) An apparatus according to claim 12, wherein the optical fiber distributed acoustic sensing system comprises a means for receiving the backscattered and/or reflected light from along the length of the optical sensing fiber. ### Claim 14 (depends on 13) An apparatus according to claim 13, wherein the means for receiving comprises optical componentry. ### Claim 15 (depends on 13) An apparatus according to claim 13, wherein the optical fiber distributed acoustic sensing system comprises a means for processing the received backscattered and/or reflected light to measure the phase, frequency and amplitude data of the received backscattered and/or reflected light to provide quantitative measurements of the acoustic perturbations incident along the length of the fiber to thereby measure a strength of the acoustic signal generated by the acoustic source, wherein the processing comprises measuring the backscattered and/or reflected light received from each contiguous section of optical sensing fiber along its length based on the time taken for the pulsed optical signal to propagate along the length of the optical fiber in the first direction, and the time taken for the backscattered and/or reflected light to propagate back in the second direction, to thereby map the received backscattered and/or reflected light to a respective section of optical fiber. ### Claim 16 (depends on 15) An apparatus according to claim 15, wherein the means for processing comprises a plurality of photodetectors and a processor. ### Claim 17 A method of monitoring seepage along a dam or dyke using an optical fiber distributed acoustic sensing system, the method comprising: measuring, using the optical fiber distributed acoustic sensing system, an acoustic signal generated by an acoustic source located within the body of fluid contained by the dam or dyke, or within the dam or dyke itself, wherein the optical fiber distributed acoustic sensing system: transmits an optical signal into an optical sensing fiber deployed along the dam or dyke, the optical signal being backscattered and/or reflected in dependence on acoustic signals incident along the length of the optical sensing fiber; and processes the backscattered and/or reflected light to determine a relative optical phase modulation along at least one section of the optical sensing fiber to thereby measure a strength of the acoustic signal generated by the acoustic source; and determining areas of seepage in the dam or dyke based on the measured acoustic signal, wherein the optical fiber distributed acoustic sensing system detects a louder acoustic signal in areas of seepage, wherein areas of seepage provide low acoustic impedance paths for acoustic wave transmission. ### Claim 18 (depends on 17) A method according to claim 17, wherein the method further comprises: transmitting a pulsed optical signal into the optical sensing fiber, the pulsed optical signal being constrained by the optical sensing fiber such that it propagates therealong in a first direction, the pulsed optical signal being backscattered and/or reflected along the length of the optical sensing fiber, the backscattered and/or reflected light being constrained by the optical sensing fiber such that it propagates therealong in a second direction opposite the first direction, wherein acoustic perturbations generated by the acoustic signal of the acoustic source incident along the length of the optical sensing fiber cause the optical sensing fiber to expand and contract such that the backscattered and/or reflected light is modulated; receiving the backscattered and/or reflected light from along the length of the optical sensing fiber; and processing the received backscattered and/or reflected light to measure the phase, frequency and amplitude data of the received backscattered and/or reflected light to provide quantitative measurements of the acoustic perturbations along the length of the optical sensing fiber to thereby measure the strength of the acoustic signal generated by the acoustic source. ### Claim 19 (depends on 18) A method according to claim 18, wherein the processing comprises measuring the backscattered and/or reflected light received from each contiguous section of optical sensing fiber along its length based on the time taken for the pulsed optical signal to propagate along the length of the optical fiber in the first direction, and the time taken for the backscattered and/or reflected light to propagate back in the second direction, to thereby map the received backscattered and/or reflected light to a respective section of optical fiber. ### Claim 20 A dam or dyke comprising: an optical fiber distributed acoustic sensing system, the optical fiber distributed acoustic sensing system comprising an optical sensing fiber deployed in use along the dam or dyke and arranged to receive an input optical signal and propagate the received optical signal along its length; and an acoustic source located within a body of fluid contained by the dam or dyke, or within the dam or dyke itself; wherein the optical fiber distributed acoustic sensing system is arranged to process light backscattered and/or reflected from along the optical sensing fiber as the optical signal travels therealong, the light being backscattered and/or reflected in dependence on acoustic signals incident along the length of the optical sensing fiber, the backscattered and/or reflected light being processed to determine a relative optical phase modulation along at least one section of the optical sensing fiber to thereby measure a strength of an acoustic signal generated by the acoustic source, and to determine areas of seepage in the dam or dyke based thereon; wherein the optical fiber distributed acoustic sensing system is arranged to detect a louder acoustic signal in areas of seepage, wherein areas of seepage provide low acoustic impedance paths for acoustic wave transmission.