CN110307862B - Fiber grating beat frequency demodulation system based on radio frequency signal bandwidth detection - Google Patents
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- 239000013307 optical fiber Substances 0.000 claims description 9
- 229910052691 Erbium Inorganic materials 0.000 claims description 3
- UYAHIZSMUZPPFV-UHFFFAOYSA-N erbium Chemical group [Er] UYAHIZSMUZPPFV-UHFFFAOYSA-N 0.000 claims description 3
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- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35338—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using other arrangements than interferometer arrangements
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- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
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- G01J3/42—Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry
- G01J3/433—Modulation spectrometry; Derivative spectrometry
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- G—PHYSICS
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- G01R29/00—Arrangements for measuring or indicating electric quantities not covered by groups G01R19/00 - G01R27/00
- G01R29/08—Measuring electromagnetic field characteristics
- G01R29/0864—Measuring electromagnetic field characteristics characterised by constructional or functional features
- G01R29/0878—Sensors; antennas; probes; detectors
- G01R29/0885—Sensors; antennas; probes; detectors using optical probes, e.g. electro-optical, luminescent, glow discharge, or optical interferometers
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R29/00—Arrangements for measuring or indicating electric quantities not covered by groups G01R19/00 - G01R27/00
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Abstract
The invention discloses a fiber grating beat frequency demodulation system based on radio frequency signal bandwidth detection, which comprises a laser pumping source, a wavelength division multiplexer, a static grating, an amplifier, a sensing grating, a photoelectric detector and a radio frequency spectrum analyzer, wherein laser emitted by the laser pumping source sequentially passes through the wavelength division multiplexer, the static grating, the amplifier and the sensing grating to form a resonant cavity; the physical parameters on the sensing grating are modulated into the beat frequency signal in a certain linear relation, and the beat frequency signal is analyzed by the radio frequency spectrum analyzer, so that the size of the physical parameters on the sensing grating can be obtained. The method has higher sensitivity and resolution.
Description
Technical Field
The invention relates to the technical field of grating sensing demodulation systems, in particular to a fiber grating beat frequency demodulation system based on radio frequency signal bandwidth detection.
Background
The optical fiber is an optical fiber made of glass and plastic, and is used as a light conduction tool according to the total reflection principle of light, and is used in the field of optical communication at first; with the development of the fiber grating technology, the fiber technology can be used for the propagation of light wave signals, and simultaneously can modulate the change of external physical parameters into the change of characteristic parameters (such as amplitude, phase, frequency and the like) of the light wave signals in the optical fiber, so that related fiber devices can be used as sensors to monitor the change of various physical quantities.
Through years of researches on the field of optical fiber sensing by scholars at home and abroad, the optical fiber sensing technology tends to be mature; compared with the traditional sensor, the optical fiber sensor has the advantages of simple structure, small volume, light weight, low energy consumption, corrosion resistance, electromagnetic interference resistance, good electrical insulation performance, convenience for reuse and the like, and can be widely applied to the fields of petrochemical industry, aerospace, navigation, intelligent structure monitoring, medical treatment and the like.
The traditional fiber grating sensor is usually a wavelength modulation sensor (which converts the change of physical quantity into the change of wavelength in a spectrum signal), and an expensive set of optical equipment is needed when the spectrum signal is collected, so that real-time dynamic demodulation is difficult. At the same time, its sensitivity and resolution have not been satisfactory.
Disclosure of Invention
In view of the defects of the prior art, the invention aims to provide a fiber grating beat frequency demodulation system based on radio frequency signal bandwidth detection, which has higher sensitivity and resolution and is more convenient to calculate and measure. The technical scheme is as follows:
a fiber grating beat frequency demodulation system based on radio frequency signal bandwidth detection comprises a laser pumping source, a wavelength division multiplexer, a static grating, an amplifier, a sensing grating, a photoelectric detector and a radio frequency spectrum analyzer, wherein laser emitted by the laser pumping source enters the static grating, the amplifier and the sensing grating through the wavelength division multiplexer, the static grating, the amplifier and the sensing grating form a resonant cavity, laser reflected by the static grating and the sensing grating is excited in the resonant cavity, the excited laser is incident to the wavelength division multiplexer and is incident to the photoelectric detector through the wavelength division multiplexer, and lasers with different longitudinal mode frequencies are beat on the photoelectric detector in pairs to form beat frequency signals;
the physical parameters on the sensing grating are modulated into the spectrum bandwidth of the beat frequency signal in a certain linear relation, and the beat frequency signal is analyzed by the radio frequency spectrum analyzer, so that the size of the physical parameters on the sensing grating can be obtained.
As a further improvement of the present invention, the present invention further comprises a fixed platform, a fixed column and a translation column, wherein the fixed column is fixedly connected with the fixed platform, the translation column is slidably connected with the fixed platform, one end of the sensing grating is connected with the fixed column, the other end of the sensing grating is connected with the translation column, and when the physical parameter on the sensing grating changes, the translation column translates, so as to adjust the length of the resonant cavity.
As a further improvement of the invention, a sliding groove is arranged on the fixed table, and a sliding block matched with the sliding groove is arranged at the bottom of the translation column.
As a further improvement of the present invention, when the external physical parameter on the sensing grating does not change, the shortest wavelength of the laser mode excited in the resonant cavity is set as a, and the corresponding frequency is:
where c is the speed at which light propagates in a vacuum,ris the dielectric constant of the optical fiber; let the maximum wavelength of the laser mode excited in the cavity be b, and the corresponding frequency be:
at this time, the bandwidth of the beat signal generated by these two modes is: b ═ fh-fl；
When the external physical parameter on the sensing grating changes, the reflection spectrum drifts, if d is the drift amount of the central wavelength of the sensing grating, the maximum wavelength of the corresponding excited laser mode is b-d, and the frequency is as follows:
at this time, the shortest wavelength of the excited laser mode is still a, and the corresponding frequency is still fhAnd the generated beat frequency signal is: b ═ fh-fl'；
The variation of the beat signal bandwidth is:
as a further improvement of the present invention, the present invention further includes an optical splitting unit and a spectrometer, wherein the reflected laser light enters the wavelength division multiplexer, enters the optical splitting unit, and enters the photodetector and the spectrometer through the optical splitting unit.
As a further improvement of the present invention, the light splitting unit is a 1 × 2 fiber coupler with a splitting ratio of 50: 50.
As a further improvement of the invention, the amplifier is an erbium doped fiber.
As a further improvement of the invention, the laser pumping source is a 980nm laser pumping source.
As a further improvement of the invention, the physical parameters include temperature, stress.
The invention has the beneficial effects that:
the fiber grating beat frequency demodulation system based on the radio frequency signal bandwidth detection can obtain the size of the physical parameter on the sensing grating by modulating the physical parameter on the sensing grating into the frequency spectrum bandwidth of the beat frequency signal in a certain linear relation and analyzing the beat frequency signal through the radio frequency spectrum analyzer.
The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical means of the present invention more clearly understood, the present invention may be implemented in accordance with the content of the description, and in order to make the above and other objects, features, and advantages of the present invention more clearly understood, the following preferred embodiments are described in detail with reference to the accompanying drawings.
Drawings
FIG. 1 is a schematic diagram of a fiber grating beat frequency demodulation system based on radio frequency signal bandwidth detection according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a resonant cavity generating a beat signal in an embodiment of the present invention;
FIG. 3 is a graph of beat signals when no strain is applied to the photosensitive grid in an embodiment of the invention;
FIG. 4 is a plot of the beat signal when strain is applied to the sensing grating in an embodiment of the present invention;
fig. 5 is a graph showing an analysis of the measurement results of the sensor grating in the embodiment of the present invention.
Description of the labeling: 10. a fixed table; 20. fixing a column; 30. and translating the column.
Detailed Description
The present invention is further described below in conjunction with the following figures and specific examples so that those skilled in the art may better understand the present invention and practice it, but the examples are not intended to limit the present invention.
As shown in fig. 1, the fiber grating beat frequency demodulation system based on radio frequency signal bandwidth detection in the embodiment of the present invention includes a laser pump source, a wavelength division multiplexer, a static grating (FBG), an amplifier, a sensing grating (FBG), a photodetector, and a radio frequency spectrum analyzer. In this embodiment, the amplifier is an erbium doped fiber.
Laser that the laser pumping source sent gets into static grating (FBG) through wavelength division multiplexer, amplifier and sensing grating (FBG), static grating (FBG), amplifier and sensing grating (FBG) form the resonant cavity, in the resonant cavity, laser by static grating (FBG) and sensing grating (FBG) reflection is lased simultaneously, laser incident to wavelength division multiplexer by the lasing, and inject photoelectric detector into by wavelength division multiplexer, two liang of beat frequencies formation beat frequency signal of the laser of different longitudinal mode frequencies on photoelectric detector.
The physical parameters on the sensing grating (FBG) are modulated into the spectrum bandwidth of the beat frequency signal in a certain linear relation, and the beat frequency signal is analyzed by a radio frequency spectrum analyzer, so that the size of the physical parameters on the sensing grating (FBG) can be obtained. The physical parameters include temperature, stress, and the like.
In this embodiment, the system further includes a fixed platform 10, a fixed column 20 and a translation column 30, the fixed column 20 is fixedly connected to the fixed platform 10, the translation column 30 is slidably connected to the fixed platform 10, one end of the sensing grating (FBG) is connected to the fixed column 20, the other end of the sensing grating (FBG) is connected to the translation column 30, and when the physical parameter on the sensing grating (FBG) changes, the translation column 30 translates, thereby adjusting the length of the resonant cavity. Preferably, a sliding groove is formed in the fixed table 10, and a sliding block matched with the sliding groove is arranged at the bottom of the translation column 30.
Preferably, the system further comprises a light splitting unit and a spectrometer, the reflected laser light is incident to the light splitting unit after being incident to the wavelength division multiplexer, and is respectively incident to the photodetector and the spectrometer by the light splitting unit. In this embodiment, the spectroscopic unit is a 1 × 2 fiber coupler with a spectroscopic ratio of 50: 50. The spectrometer is used for observing the optical signal.
As shown in fig. 2, when the external physical parameter on the sensing grating (FBG) is not changed, the shortest wavelength of the laser mode excited in the resonant cavity is set as a, and the corresponding frequency is:
where c is the speed at which light propagates in a vacuum,ris the dielectric constant of the optical fiber; let the maximum wavelength of the laser mode excited in the cavity be b, and the corresponding frequency be:
at this time, the bandwidth of the beat signal generated by these two modes is: b ═ fh-fl；
When the external physical parameter on the sensing grating (FBG) changes, the reflection spectrum drifts, d is the drift amount of the central wavelength of the sensing grating (FBG), the maximum wavelength of the corresponding excited laser mode is b-d, and the frequency is as follows:
at this time, the shortest wavelength of the excited laser mode is still a, and the corresponding frequency is still fhAnd the generated beat frequency signal is: b ═ fh-fl'；
The variation of the beat signal bandwidth is:
when the external physical parameter on the sensing grating (FBG) changes, the bandwidth of the beat frequency signal is reduced along with the translation of the reflection spectrum of the sensing grating (FBG); according to the linear relation between the bandwidth of the beat frequency signal and the central wavelength of the sensing grating (FBG), the change of the additional physical parameter sensed on the sensing grating (FBG) is modulated into the change of the bandwidth of the beat frequency signal, and the real-time monitoring can be realized through a radio frequency spectrum analyzer.
In the embodiment, the laser pumping source is a 980nm laser pumping source, the length of the erbium-doped fiber in the resonant cavity is 8.0m, and the absorption coefficient at 1532.0nm is 6.1 dB/m; the reflection bandwidth of the static grating is 0.24nm with a reflectivity of 90.0% and the center wavelength is 1550.21nm, the reflection bandwidth of the sensing grating is 0.25nm with a reflectivity of 89.7% and the center wavelength is 1550.43 nm.
As shown in fig. 3, in order to obtain a beat signal measured by a radio frequency spectrum analyzer when no strain is applied to the photosensitive grating, it can be seen from fig. 3(a) that the bandwidth of the beat signal is 7.0GHz when no strain is applied; and the beat frequency signal of the 1.00GHz to 1.05GHz band is shown in fig. 3(b), and the frequency band includes two modes of beat frequency signals: the beat frequency signals of the long longitudinal modes and the beat frequency signals of the polarization modes can be measured, the interval between the beat frequency signals of the two long longitudinal modes can be measured to be 10.1MHz, and the corresponding whole cavity length can be known to be 11.98m according to theoretical analysis of the beat frequency signals.
As shown in fig. 4, in order to obtain beat signals obtained by applying strains of 60 μ and 100 μ to the photosensitive grating, respectively, it can be seen from fig. 4(a) that the bandwidth of the beat signal is 4.0GHz when strain of 60 μ is applied, compared with the beat signal of 3.0GHz bandwidth when strain is not applied; from FIG. 4(b) it can be seen that the beat signal has a bandwidth of 2.0GHz when 100 μ strain is applied, compared to a beat signal with no strain applied, which has a reduced bandwidth of 5.0 GHz; it can be seen that the bandwidth of the beat signal gradually decreases with increasing applied stress.
In order to further discuss the transformation relationship between the bandwidth of the beat frequency signal and the applied strain, strain from 0 to 140 μ is respectively applied to the photosensitive grating in a step size of 20 μ in the experiment, and the transformation of the beat frequency signal bandwidth is recorded and the measured experimental data is subjected to linear fitting, and the experimental result is shown in fig. 5 (a); the results of analyzing the experimental error and calculating the bandwidth of each group of measured beat signals according to the linear relationship obtained by fitting the experimental data are shown in fig. 5(b), and it can be seen that the average maximum error is within ± 0.94 μ, the measured maximum strain is ± 140.0 μ, and the demodulation accuracy of the system is about 0.6%.
The fiber grating beat frequency demodulation system based on the radio frequency signal bandwidth detection can obtain the size of the physical parameter on the sensing grating by modulating the physical parameter on the sensing grating into the frequency spectrum bandwidth of the beat frequency signal in a certain linear relation and analyzing the beat frequency signal through the radio frequency spectrum analyzer.
The above embodiments are merely preferred embodiments for fully illustrating the present invention, and the scope of the present invention is not limited thereto. The equivalent substitution or change made by the technical personnel in the technical field on the basis of the invention is all within the protection scope of the invention. The protection scope of the invention is subject to the claims.
Claims (9)
1. A fiber grating beat frequency demodulation system based on radio frequency signal bandwidth detection is characterized by comprising a laser pumping source, a wavelength division multiplexer, a static grating, an amplifier, a sensing grating, a photoelectric detector and a radio frequency spectrum analyzer, wherein laser emitted by the laser pumping source enters the static grating, the amplifier and the sensing grating through the wavelength division multiplexer, the static grating, the amplifier and the sensing grating form a resonant cavity, laser reflected by the static grating and the sensing grating is excited in the resonant cavity, the excited laser is incident to the wavelength division multiplexer and is incident to the photoelectric detector through the wavelength division multiplexer, and lasers with different longitudinal mode frequencies are beaten pairwise on the photoelectric detector to form beat frequency signals;
the physical parameters on the sensing grating are modulated into the spectrum bandwidth of the beat frequency signal in a certain linear relation, and the beat frequency signal is analyzed by the radio frequency spectrum analyzer, so that the size of the physical parameters on the sensing grating can be obtained.
2. The fiber grating beat frequency demodulation system based on radio frequency signal bandwidth detection according to claim 1, further comprising a fixed stage, a fixed column and a translation column, wherein the fixed column is fixedly connected with the fixed stage, the translation column is slidably connected with the fixed stage, one end of the sensing grating is connected with the fixed column, the other end of the sensing grating is connected with the translation column, and when the physical parameter on the sensing grating changes, the translation column translates, thereby adjusting the length of the resonant cavity.
3. The fiber grating beat frequency demodulation system based on radio frequency signal bandwidth detection according to claim 2, wherein a sliding groove is arranged on the fixed platform, and a sliding block matched with the sliding groove is arranged at the bottom of the translation column.
4. The fiber grating beat frequency demodulation system based on radio frequency signal bandwidth detection according to claim 1, wherein when the external physical parameter on the sensing grating is not changed, the shortest wavelength of the laser mode excited in the resonant cavity is set as a, and the corresponding frequency is:
where c is the speed at which light propagates in a vacuum,ris the dielectric constant of the optical fiber; let the maximum wavelength of the laser mode excited in the cavity be b, and the corresponding frequency be:
at this time, the bandwidth of the beat signal generated by these two modes is: b ═ fh-fl；
When the external physical parameter on the sensing grating changes, the reflection spectrum drifts, if d is the drift amount of the central wavelength of the sensing grating, the maximum wavelength of the corresponding excited laser mode is b-d, and the frequency is as follows:
at this time, the shortest wavelength of the excited laser mode is still a, and the corresponding frequency is still fhAnd the generated beat frequency signal is: b ═ fh-fl'；
The variation of the beat signal bandwidth is:
5. the fiber grating beat frequency demodulation system based on radio frequency signal bandwidth detection according to claim 1, further comprising an optical splitting unit and a spectrometer, wherein the laser light is incident to the wavelength division multiplexer, then incident to the optical splitting unit, and then incident to the photodetector and the spectrometer by the optical splitting unit respectively.
6. The fiber grating beat frequency demodulation system based on radio frequency signal bandwidth detection according to claim 5, wherein the light splitting unit has a splitting ratio of 50:50 of a 1 x 2 fiber coupler.
7. The fiber grating beat frequency demodulation system based on bandwidth detection of radio frequency signals according to claim 1 wherein said amplifier is an erbium doped fiber.
8. The fiber grating beat frequency demodulation system based on radio frequency signal bandwidth detection according to claim 1, wherein the laser pump source is a 980nm laser pump source.
9. The fiber grating beat frequency demodulation system based on bandwidth detection of radio frequency signals according to claim 1 wherein the physical parameters comprise temperature, stress.
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| CN102128639B (en) * | 2010-12-24 | 2012-06-27 | 中国计量学院 | Spontaneous Brillouin scattered light time-domain reflectometer on basis of double laser frequency locking |
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