SYSTEM AND METHOD FOR USING COHERENTLY LOCKED OPTICAL OSCILLATOR WITH BRILLOUIN FREQUENCY OFFSET FOR FIBER-OPTICS-BASED DISTRIBUTED TEMPERATURE AND STRAIN SENSING APPLICATIONS
First Claim
1. A system for distributed temperature and strain sensing along a length of an infrastructure being inspected, the system comprising:
- a first optical source with a narrow linewidth for launching a probe signal into a sensing fiber coupled to the infrastructure, wherein the probe signal is backscattered from the infrastructure with a Brillouin frequency shift;
a second optical source with a narrow linewidth used as a local oscillator producing a local oscillation signal, wherein the first optical source and the second optical source are coherently locked with a predefined frequency offset with respect to each other, the predefined frequency offset being in the order of the Brillouin frequency shift, and wherein the first optical source and the second optical source are included in an optical phase lock loop (OPLL) system; and
a balanced heterodyne receiver for narrow band detection at radio frequency (RF) bandwidth that receives an optical signal generated by coherent mixing of the backscattered probe signal with the Brillouin frequency shift and the local oscillation signal, and produces an output indicative of one or both of a measured temperature and a measured strain.
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Abstract
Systems and methods are disclosed for distributed temperature and strain sensing along a length of an infrastructure. Two optical sources, such as, external cavity lasers with a narrow linewidth, are used for launching a probe signal into a sensing fiber coupled to the infrastructure, and for producing a local oscillation signal, respectively. The optical sources are coherently locked with a predefined frequency offset with respect to each other, the predefined frequency offset being in the order of the Brillouin frequency shift. The optical sources are included in an optical phase lock loop (OPLL) system. A balanced heterodyne receiver for narrow band detection at radio frequency (RF) bandwidth receives an optical signal generated by coherent mixing of a backscattered probe signal with the Brillouin frequency shift and the local oscillation signal, and produces an output indicative of one or both of a measured temperature and a measured strain.
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Citations
18 Claims
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1. A system for distributed temperature and strain sensing along a length of an infrastructure being inspected, the system comprising:
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a first optical source with a narrow linewidth for launching a probe signal into a sensing fiber coupled to the infrastructure, wherein the probe signal is backscattered from the infrastructure with a Brillouin frequency shift; a second optical source with a narrow linewidth used as a local oscillator producing a local oscillation signal, wherein the first optical source and the second optical source are coherently locked with a predefined frequency offset with respect to each other, the predefined frequency offset being in the order of the Brillouin frequency shift, and wherein the first optical source and the second optical source are included in an optical phase lock loop (OPLL) system; and a balanced heterodyne receiver for narrow band detection at radio frequency (RF) bandwidth that receives an optical signal generated by coherent mixing of the backscattered probe signal with the Brillouin frequency shift and the local oscillation signal, and produces an output indicative of one or both of a measured temperature and a measured strain. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method for distributed temperature and strain sensing along a length of an infrastructure being inspected, the method comprising:
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launching a probe signal from a first optical source with a narrow linewidth into a sensing fiber coupled to the infrastructure; routing a backscattered probe signal generated by reflection of the probe signal from the infrastructure with a Brillouin frequency shift to a balanced heterodyne receiver configured for narrow band detection at radio frequency (RF) bandwidth; producing a local oscillation signal from a second optical source with a narrow linewidth used as a local oscillator, wherein the first optical source and the second optical source are coherently locked with a predefined frequency offset with respect to each other, the predefined frequency offset being in the order of the Brillouin frequency shift, and wherein the first optical source and the second optical source are included in an optical phase lock loop (OPLL) system; routing the local oscillation signal to the balanced heterodyne receiver; coherently mixing the backscattered probe signal with the Brillouin frequency shift and the local oscillation signal at the balanced heterodyne receiver; and producing an output indicative of one or both of a measured temperature and a measured strain. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18)
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Specification