Fiber optic sensor systems
First Claim
1. A fiber optic sensor system, comprising:
- at least one measuring sensor providing a measuring output dependent upon one or more parameters to be measured;
at least one reference sensor providing a reference output for comparison with the measuring output, said reference sensor being provided in a birefringent fiber, such that said reference output has a plurality of different polarisation planes and frequency components;
detecting instrumentation, said detecting instrumentation being adapted to derive a reference beat signal by measuring an optical frequency splitting beat signal between the measuring and reference sensor outputs;
wherein said system is arranged to derive a measurement of one or more parameters using said reference beat signal and said further beat signal.
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Accused Products
Abstract
A fiber optic sensor system comprises at least one measuring sensor 1 providing an optical output dependent upon one or more parameters to be measured, e.g. temperature, and at least one reference sensor 2 providing a reference output for comparison with the measuring sensor output. The reference sensor is provided in a birefringent fiber.
The system includes a detecting means 13,14 whereby a reference beat signal f2 is derived by measuring the optical frequency splitting between frequency components in different polarization planes of the reference sensor output. A further beat signal f3 is generated between the measuring and reference sensor outputs, such beat signals being used to derive a measurement of one or more parameters.
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Citations
67 Claims
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1. A fiber optic sensor system, comprising:
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at least one measuring sensor providing a measuring output dependent upon one or more parameters to be measured;
at least one reference sensor providing a reference output for comparison with the measuring output, said reference sensor being provided in a birefringent fiber, such that said reference output has a plurality of different polarisation planes and frequency components;
detecting instrumentation, said detecting instrumentation being adapted to derive a reference beat signal by measuring an optical frequency splitting beat signal between the measuring and reference sensor outputs;
wherein said system is arranged to derive a measurement of one or more parameters using said reference beat signal and said further beat signal. - View Dependent Claims (3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 17, 18, 19, 20, 21, 22)
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2. A fiber optic sensor system including measuring and reference sensors written into respective optical fibers, in which at least the reference sensor is written into a birefringent fiber, and the system further includes detecting instrumentation which operates by generating a beat frequency derived from the output of the reference sensor.
- 13. A fiber laser sensor system comprising at least two fiber lasers written into respective optical fibers, at least one of which is a birefringent fiber having a birefringence, and detecting instrumentation configured to generate beat signals dependent upon the birefringence of said at least one fiber.
- 23. A system for spectral analysis, comprising a tunable light source for emitting light, wherein a first part of said light from said tunable light source is arranged to pass to an optical device providing a device spectrum to be measured, and a second part of the light is passed to an interferometer which generates a comb spectrum, said comb spectrum being used to provide a linearised frequency scale for measurement of a device spectrum, whereby the effect of noise in the tunable light source is reduced, and a third part of the light from the tunable light source is passed to a birefringent reference grating which provides an absolute wavelength reference.
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27. A fiber optic sensing system comprising at least two passive π
- -phase shifted FBG sensors written into respective fibers, at least one of which is a birefringent fiber, and detecting instrumentation including instrumentation for measuring the frequency splitting between two resonances of the birefringent fiber, the detecting instrumentation being arranged to derive a reference signal using said frequency splitting.
- View Dependent Claims (28, 29, 30)
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31. Detecting instrumentation for use with a fiber optic sensing system, the detecting instrumentation including analysis instrumentation for receiving and analysing optical outputs from at least two fiber optic sensors, wherein said optical outputs have substantially the same nominal operating wavelength, and at least one of the outputs having birefringent components, the analysis instrumentation being arranged to operate by comparing said optical outputs from said at least two fiber optic sensors to derive an output signal indicative of at least one parameter sensed by at least one of the sensors in use.
- 32. A dual parameter fiber optic sensing system, comprising a pair of birefringent optical fibers each having at least one sensor configured to provide a birefringent optical output dependent upon a respective parameter, and detecting instrumentation having signal processing instrumentation adapted to provide an electrical output signal indicative of the birefringence of each of said fiber.
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34. A method of sensing a parameter comprising:
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providing a fiber optic measuring sensor having a measuring optical output;
providing a birefringent fiber optic reference sensor having a reference optical output; and
comparing said measuring optical output with said reference optical output, wherein said measuring and reference sensors have substantially the same nominal operating wavelength.
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- 35. A method of sensing a parameter using two or more fiber optic sensors, comprising using an output from a reference sensor provided in a birefringent fiber to derive a beat signal for comparison with an output from a measuring sensor provided in a second fiber.
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46. A method of measuring one or more parameters using a fiber optic sensor system, said sensor system comprising:
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at least one measuring sensor providing an optical output dependent upon said one or more parameters;
at least one reference sensor providing a reference output, wherein the reference sensor is provided in a birefringent fiber such that said reference output has frequency components in different polarisation planes; and
detecting instrumentation;
said method comprising;
deriving a reference beat signal by measuring an optical frequency splitting between said frequency components in different polarisation planes of the reference sensor output;
generating a further beat signal between said measuring and reference sensor outputs; and
using said reference beat signal and said further beat signal to derive a measurement of said one or more parameters. - View Dependent Claims (48, 49, 50, 51, 52)
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47. A method of measuring one or more parameters using a fiber optic sensor system, said sensor system comprising:
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at least one measuring sensor providing an optical output dependent upon said one or more parameters;
at least one reference sensor providing a reference sensor output wherein the reference sensor is provided in a birefringent fiber said method comprising;
deriving a first beat frequency from the reference sensor output;
deriving a second beat frequency from a comparison between the measuring sensor output and the reference sensor output; and
using said first and second beat frequencies to derive an indication of said at least one parameter without the need directly to measure the absolute frequency of either sensor by optical means.
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53. A method of measuring at least one parameter using a fiber laser sensor system having:
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at least two fiber lasers written into respective optical fibers, at least one of said fibers being birefringent and having a birefringence; and
detecting instrumentation;
said method comprising using said detecting instrumentation to generate beat signals dependent upon the birefringence of said at least one birefringent fiber. - View Dependent Claims (54, 55, 56)
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60. A method of spectral analysis comprising:
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providing a tunable light source;
passing a first part of light from said tunable light source to an optical device providing a device spectrum to be measured;
passing a second part of the light from the tunable light source to an interferometer, thereby generating a comb spectrum;
using said comb spectrum to provide a linearised frequency scale for measurement of the device spectrum, whereby the effect of noise in the tunable light source is reduced; and
passing a third part of the light from the tunable light source to a birefringent reference grating, thereby providing an absolute wavelength reference. - View Dependent Claims (61, 62)
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63. A method of sensing using:
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at least two passive π
-phase shifted FBG sensors written into respective fibers, at least one of which is a birefringent fiber;
and detecting instrumentation;
the method comprising;
measuring a frequency splitting between said two resonances of the birefringent fiber; and
said detecting instrumentation using said splitting to derive a reference signal. - View Dependent Claims (64, 65)
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66. A method of deriving an output signal indicative of at least one parameter comprising:
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providing at least two fiber optic sensors providing optical outputs with substantially the same nominal operating wavelength, at least one of said outputs having birefringent components;
receiving and analysing said optical outputs; and
comparing said optical outputs to derive said output signal indicative of the at least one parameter.
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67. A fiber optic sensor system, comprising:
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at least one measuring sensor providing a measuring output dependent upon one or more parameters to be measured;
at least one reference sensor providing a reference output for comparison with the measuring output, said reference sensor being provided in a birefringent fiber, such that said reference output has a plurality of different polarisation planes and frequency components;
detecting instrumentation, said detecting instrumentation being adapted to derive a reference frequency difference signal by measuring an optical frequency splitting between said frequency components, and said detecting instrumentation being adapted also to generate a further frequency difference signal between the measuring and reference sensor outputs;
wherein said system is arranged to derive a measurement of one or more parameters using said reference frequency difference signal and said further frequency difference signal.
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Specification