Apparatus for deriving measurement signals from fibre optic distributed sensors
First Claim
1. A distributed fibre optic sensor apparatus comprising:
- an optical source, the optical source generating at least first and second optical pulse pairs for launching into an optical fibre, each pulse having a frequency, wherein the first pulses of the pulse pairs have the same frequency and the second pulses of the pulse pairs have the same frequency, andthe pulses generated such that the phase relationship of the pulses of the first pulse pair and the phase relationship of the pulses of the second pulse pair are different by a predetermined relative phase difference wherein;
the pulses of the first and second pulse pairs have a frequency difference between them; and
the first and second pulse pairs are generated so as to be launched into the optical fibre at different times;
such that the time between launch of the first and second pulse pairs corresponds to the time for a relative phase change in a signal at a frequency equal to the frequency difference between the pulses in a pair equal to said predetermined relative phase difference.
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Abstract
The application describes methods and apparatus for distributed fiber sensing, especially distributed acoustic/strain sensing. The method involves launching at least first and second pulse pairs into an optical fiber, the first and second pulse pairs having the same frequency configuration as one another and being generated such that the phase relationship of the pulses of the first pulse pair has a predetermined relative phase difference to the phase relationship of the pulses of the second pulse pair. In one embodiment there is a frequency difference between the pulses in a pulse pair which is related to the launch rate of the pulse pairs. In another embodiment the phase difference between the pulses in a pair is varied between successive launches. In this way an analytic version of the backscatter interference signal can be generated within the baseband of the sensor.
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Citations
62 Claims
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1. A distributed fibre optic sensor apparatus comprising:
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an optical source, the optical source generating at least first and second optical pulse pairs for launching into an optical fibre, each pulse having a frequency, wherein the first pulses of the pulse pairs have the same frequency and the second pulses of the pulse pairs have the same frequency, and the pulses generated such that the phase relationship of the pulses of the first pulse pair and the phase relationship of the pulses of the second pulse pair are different by a predetermined relative phase difference wherein; the pulses of the first and second pulse pairs have a frequency difference between them; and the first and second pulse pairs are generated so as to be launched into the optical fibre at different times; such that the time between launch of the first and second pulse pairs corresponds to the time for a relative phase change in a signal at a frequency equal to the frequency difference between the pulses in a pair equal to said predetermined relative phase difference. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61)
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- 26. A distributed fibre optic sensor apparatus as claimed in 19 wherein the pulses of the first series of pulse pairs have an orthogonal polarisation state to the pulses of the second series of pulse pairs.
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62. A distributed fibre optic sensor apparatus comprising:
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an optical source that launches at least first and second optical pulse pairs of a series pulse pairs into an optical fibre, each pulse having a frequency, wherein each pulse pair has a frequency configuration such that the first pulses of the series of pulse pairs have the same frequency as one another and the second pulses of the series of pulse pairs have the same frequency as one another, the pulses generated such that the phase relationship of the pulses of the first pulse pair and the phase relationship of the pulses of the second pulse pair are different by a predetermined relative phase difference; and a detector that detects radiation which is backscattered within the optical fibre and a processor coupled to said detector to form at least one channel signal comprising samples of the backscatter radiation, the samples acquired at substantially the same time after launch of each pulse pair; and
to demodulate said channel signal to determine a phase value for the relevant section of optical fibre wherein;the pulses of the first and second pulse pairs have a frequency difference between them; and the first and second pulse pairs are generated so as to be launched into the optical fibre at different times; such that the time between launch of the first and second pulse pairs corresponds to the time for a relative phase change in a signal at a frequency equal to the frequency difference between the pulses in a pair equal to said predetermined relative phase difference.
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Specification