Interferometric method and apparatus for measuring physical parameters
First Claim
1. A method of measuring at least one selected parameter at a location within a region of interest, which method comprises the steps of:
- launching optical pulses at a plurality of preselected interrogation wavelengths into an optical fiber deployed along the region of interest, reflectors being arrayed along the optical fiber to form an array of sensor elements, an optical path length between the said reflectors being dependent upon the selected parameter;
detecting the returned optical interference signal for each of the preselected wavelengths; and
determining from the optical interference signal an absolute optical path length between two reflectors at the said location, and from the absolute optical path length so determined, the value of the selected parameter at the said location,wherein the step of determining the absolute optical path length comprises carrying out a process in which the derivative of the phase as a function of wavelength is estimated from a subset of the interference signals, using the derivative and an estimated value for the optical path length to estimate the phase relationship between the interference signals, and the phase relationship thus obtained is used to revise the estimated value for the optical path length, the process being repeated for increasing subsets of the remaining wavelengths in sequence, on the basis of the optical path length estimated for the immediately preceding subset in the sequence, thereby to progressively revise the optical path length until it is known to a desired level of accuracy.
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Abstract
A method of measuring a selected physical parameter at a location within a region of interest comprises the steps of: launching optical pulses at a plurality of preselected interrogation wavelengths into an optical fiber (1) deployed along the region of interest, reflectors (20, 21, 2n) being arrayed along the optical fiber (1) to form an array (9) of sensor elements, the optical path length between the said reflectors (2) being dependent upon the selected parameter; detecting the returned optical interference signal for each of the preselected wavelengths; determining from the optical interference signal the absolute optical path length (L) between two reflectors (2) at the said location; and determining from the absolute optical path length (L) the value of the selected parameter at the said location; wherein the step of determining the absolute optical path length (L) comprises carrying out a process in which the phase difference between the interference signals for a pair of the preselected wavelengths is estimated using an estimated value for the optical path length (L), the estimated phase difference is used to estimate the phase at each of those wavelengths, and the phase thus obtained is used to revise the estimated value for the optical path length (L), the process being repeated for some or all remaining wavelength pairs in sequence, on the basis of the optical path length (L) estimated for the immediately preceding pair in the sequence, thereby to progressively revise the optical path length (L) until it is know to a desired level of accuracy.
58 Citations
42 Claims
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1. A method of measuring at least one selected parameter at a location within a region of interest, which method comprises the steps of:
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launching optical pulses at a plurality of preselected interrogation wavelengths into an optical fiber deployed along the region of interest, reflectors being arrayed along the optical fiber to form an array of sensor elements, an optical path length between the said reflectors being dependent upon the selected parameter; detecting the returned optical interference signal for each of the preselected wavelengths; and determining from the optical interference signal an absolute optical path length between two reflectors at the said location, and from the absolute optical path length so determined, the value of the selected parameter at the said location, wherein the step of determining the absolute optical path length comprises carrying out a process in which the derivative of the phase as a function of wavelength is estimated from a subset of the interference signals, using the derivative and an estimated value for the optical path length to estimate the phase relationship between the interference signals, and the phase relationship thus obtained is used to revise the estimated value for the optical path length, the process being repeated for increasing subsets of the remaining wavelengths in sequence, on the basis of the optical path length estimated for the immediately preceding subset in the sequence, thereby to progressively revise the optical path length until it is known to a desired level of accuracy. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. Apparatus for measuring a selected physical parameter at a location within a region of interest, which apparatus comprises:
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an optical fiber for deployment along the region of interest, the optical fiber having reflectors therealong forming an array of sensor elements, an optical path length between the said reflectors being dependent upon the selected parameter; source means operable to launch optical pulses at a plurality of preselected interrogation wavelengths into the said fiber; signal detection means operable to detect the returned optical interference signal for each of the preselected wavelengths; and signal processing means operable to determine from the optical interference signal an absolute optical path length between two reflectors at the said location and to determine from the absolute optical path length the value of the selected parameter at the said location, wherein the said signal processing means is operable to determine the absolute optical path length by carrying out a process in which the derivative of the phase as a function of wavelength is estimated from a subset of the interference signals, using the derivative and an estimated value for the optical path length to estimate the phase relationship between the interference signals, and the phase relationship thus obtained is used to revise the estimated value for the optical path length, the process being repeated for increasing subsets of the remaining wavelengths in sequence, on the basis of the optical path length estimated for the immediately preceding subset in the sequence, thereby to progressively revise the optical path length until it is known to a desired level of accuracy. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42)
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Specification