OPTICAL SENSOR AND METHOD OF USE

• US 20150192436A1
• Filed: 03/19/2015
• Published: 07/09/2015
• Est. Priority Date: 05/27/2009
• Status: Active Grant

• Current Assignee: Silixa Limited
• Original Assignee: Silixa Limited
• Inventors: Farhadiroushan, Mahmoud, Parker, Tom Richard, Shatalin, Sergey
• Granted Patent: US 9,541,426 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: E21B 47/002 by visual inspection
• CPC Class Codes: E21B 47/0025 generating an image of the borehole wall using down-hole measurements, e.g. acoustic or electric
• CPC Class Codes: E21B 47/107 using acoustic means
• CPC Class Codes: G01D 5/35303 using a reference fibre, e.g. interferometric devices
• CPC Class Codes: G01D 5/35306 using an interferometer arrangement
• CPC Class Codes: G01D 5/35325 using interferometer with two arms in reflection, e.g. Mickelson interferometer
• CPC Class Codes: 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
• CPC Class Codes: G01D 5/35358 using backscattering to detect the measured quantity
• CPC Class Codes: G01D 5/35364 using inelastic backscattering to detect the measured quantity, e.g. using Brillouin or Raman backscattering
• CPC Class Codes: G01D 5/35377 Means for amplifying or modifying the measured quantity
• CPC Class Codes: G01D 5/35383 using multiple sensor devices using multiplexing techniques
• CPC Class Codes: G01F 1/66 by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters
• CPC Class Codes: G01F 1/661 using light
• CPC Class Codes: G01F 1/662 Constructional details
• CPC Class Codes: G01F 1/666 by detecting noise and sounds generated by the flowing fluid
• CPC Class Codes: G01F 1/667 Arrangements of transducers for ultrasonic flowmeters; Circuits for operating ultrasonic flowmeters
• CPC Class Codes: 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
• CPC Class Codes: G01M 11/085 the optical fiber being on or near the surface of the DUT
• CPC Class Codes: G01M 11/331 by using interferometer
• CPC Class Codes: G01M 3/24 using infrasonic, sonic, or ultrasonic vibrations
• CPC Class Codes: G01M 5/0058 : of elongated objects, e.g. pipes, masts, towers or railways
• CPC Class Codes: G01M 5/0066 : by exciting or detecting vibration or acceleration vibration testing of structures G01M7/00
• CPC Class Codes: G01M 5/0091 : by using electromagnetic excitation or detection
• CPC Class Codes: G01V 1/226 : Optoseismic systems
• CPC Class Codes: G01V 1/40 : specially adapted for well-logging

Abstract

An interferometer apparatus for an optical fibre system and method of use is described. The interferometer comprises an optical coupler and optical fibres which define first and second optical paths. Light propagating in the first and second optical paths is reflected back to the optical coupler to generate an interference signal. First, second and third interference signal components are directed towards respective first, second and third photodetectors. The third photodetector is connected to the coupler via a non-reciprocal optical device and is configured to measure the intensity of the third interference signal component directed back towards the input fibre. Methods of use in applications to monitoring acoustic perturbations and a calibration method are described.

Claims

1. An apparatus, comprising:

a pulsed light source;

an optical fibre deployed in an environment to be monitored and arranged to receive pulses of light from the pulsed light source;

an interferometer arranged to receive light backscattered from along the length of the optical fibre as the pulses of light travel along the fibre and to generate an interference signal in dependence thereon, the interference signal comprising first, second, and third interference signal components having phase shifts therebetween;

a first photodetector arranged to measure an intensity of the first interference signal component to provide first intensity data;

a second photodetector arranged to measure an intensity of the second interference signal component to provide second intensity data;

a third photodetector arrange to measure an intensity of the third interference signal component to provide third intensity data; and

a processor time synchronised with the pulsed light source and arranged to;

i) receive the first, second and third intensity data and to determine therefrom any optical phase modulation in the received light; and

ii) identify acoustic perturbations incident along the optical fibre in dependence on the determined optical phase modulation.

2. The apparatus of claim 1, wherein the interferometer further comprises a fourth photodetector arranged to monitor the intensity of the input light from the pulsed light source.

3. The apparatus of claim 1, comprising oversampling the outputs of the photodetectors to provide multiple optical phase angle data over a spatial resolution of the apparatus.

4. The apparatus of claim 3, wherein the outputs of the photodetectors are sampled at least twice over the spatial resolution.

5. The apparatus of claim 3, comprising:

determining a visibility factor from the combined outputs of the photodetectors at each sampled point; and

providing a weighted signal average of optical phase angle data from multiple sample points over the spatial resolution of the apparatus in dependence on the visibility factor.

6. The apparatus of claim 5, comprising:

determining a visibility factor from the combined outputs of the photodetectors at each sampled point; and

adjusting the timing of the digitised samples of the photodetector outputs in dependence on the visibility factor.

7. The apparatus of claim 6, wherein the adjusting the timing of the digitised samples is performed by a digitiser with dynamically varying clock cycles.

8. The apparatus of claim 1, wherein the pulsed light source is a plurality of laser light pulses with a plurality of wavelengths, and wherein the system further comprises wavelength division multiplexed components used to multiplex the plurality of light pulses into the optical fibre.

9. The apparatus of claim 8, wherein the plurality of light pulses are time shifted with respect to each other to control the cross-phase modulation between the plurality of light pulses.

10. The apparatus of claim 1, further comprising calibration circuitry arranged to determine electrical offsets for the photodetectors during a first calibration condition in which no light propagates in the interferometer.

11. The apparatus of claim 1, further comprising calibration circuitry arranged to determine one or more of a photodetector offset, a relative photodetector gain, and/or a coupling ratio of optical paths in the interferometer from the outputs of the photodetectors during a calibration condition in which an incoherent light source inputs incoherent light to the interferometer.