CN113639774B - Quasi-distributed sensing device based on dual-wavelength double-pulse light source - Google Patents
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Abstract
The invention discloses a quasi-distributed sensing device based on a dual-wavelength double-pulse light source, belongs to the field of fiber grating signal demodulation, and particularly relates to a quasi-distributed sensing device based on a dual-wavelength double-pulse light source, which comprises a dual-wavelength double-pulse light source, a quasi-distributed sensing unit and a signal detection and demodulation unit; the dual-wavelength pulse light with the same intensity fluctuation output by the dual-wavelength dual-pulse light source is input into the quasi-distributed sensing unit, and the quasi-distributed sensing unit is connected with signal detection and demodulation. The invention avoids the influence of light source intensity fluctuation and wavelength switching process in the traditional method, reduces the requirement on the stability of the light source, has the characteristics of accurate space positioning and high wavelength resolution of the distributed sensor, and is convenient for implementing a time division multiplexing/wavelength division multiplexing sensing system.
Description
Technical Field
The invention belongs to the field of fiber bragg grating signal demodulation, and relates to a quasi-distributed sensing device based on a dual-wavelength double-pulse light source.
Background
The fiber grating sensor is one of the most widely used fiber wavelength modulation sensors, has the advantages of electromagnetic interference resistance, good electrical insulation performance, corrosion resistance, high sensitivity, large transmission capacity and the like, and is widely applied to structural safety measurement. The conventional fiber grating sensing system obtains the wavelength at the maximum reflectivity of the fiber grating by scanning the wavelength, and requires additional optical devices, such as a tunable filter and a tunable laser, while the spectra of each sensing fiber grating do not overlap, and a tunable filter or a tunable laser with a larger spectral range is required, but the conventional fiber grating sensing system is expensive and not portable. Currently, a fiber grating demodulation method using dual-wavelength pulses has been implemented, which can be used to connect more fiber grating sensors with the same center wavelength in series. However, in the method, a tunable laser is still used as a light source to demodulate the center wavelength of the fiber grating, extra measurement errors are introduced in the intensity fluctuation and wavelength switching process of the laser, the demodulation precision of the center wavelength of the fiber grating is reduced, and it is difficult to realize a time division multiplexing and wavelength division multiplexing fiber grating sensing system at the same time.
Disclosure of Invention
The invention aims to: a quasi-distributed sensing device based on a dual-wavelength double-pulse light source is provided, which is used for realizing fiber bragg grating demodulation with high spatial resolution and high wavelength resolution simultaneously.
The technical scheme adopted by the invention is as follows:
a quasi-distributed sensing device based on a dual-wavelength dual-pulse light source comprises the dual-wavelength dual-pulse light source, dual-wavelength pulse light with the same intensity fluctuation and output by the dual-wavelength dual-pulse light source is input into a quasi-distributed sensing unit, and the quasi-distributed sensing unit converts the change of environmental physical quantities at different spatial positions into the change of reflected light intensity of an optical fiber grating and outputs signals; the output signal of the quasi-distributed sensing unit is detected and demodulated through the signal detection and demodulation unit, so that the change of the environmental physical quantity is obtained.
Further, the dual-wavelength dual-pulse light source comprises a laser, an adjustable attenuator, a polarizer, a polarization controller, a polarization beam splitter, an electro-optic phase modulator and a 1 x 2 coupler;
the output light of the laser is picosecond pulse light, and the central wavelength of the output light is positioned in the reflection spectrum of the fiber grating sensor array; the laser adopts an internal modulation or external modulation distributed feedback laser, a fiber laser or a mode-locked laser.
The polarizer, the polarization controller and the polarization beam splitter are used for separating two beams of double pulse light with the same intensity fluctuation from one beam of pulse light;
the electro-optic phase modulator is used for modulating the wavelength of incident light, is controlled by an external circuit and is synchronous with the output pulse light of the laser.
Further, picosecond pulse light output by the laser is divided into two beams of pulse light by the polarization beam splitter, wherein the time delay delta T generated after one beam of pulse passes through the delay optical fiber with the length L is a formula I:
n is the refractive index of the fiber and c is the refractive index of light in vacuum. Another beam of pulse light will generate phase change after passing through the electro-optic phase modulator
Is a formula two:
wherein v is0Center frequency of incident light, gamma is slope of ramp signal, VπIs the half-wave voltage of the modulator,
the initial phase is t is the propagation time of the incident light, and the frequency change Δ v of the pulse light obtained by differentiating the formula two is a formula three:
further, the central wavelength variation Δ λ of the pulsed light with the wavelength λ is a formula four:
further, after the optical signals output by the delay optical fiber and the electro-optical phase modulator are combined by the optical coupler, dual-wavelength dual-pulse light with the wavelength difference delta lambda and the time difference delta T is formed.
Furthermore, the quasi-distributed sensing unit comprises a three-port circulator and a fiber grating sensor array, wherein a first port of the three-port circulator is connected with the output end of the 1-by-2 coupler.
The fiber grating sensor array is a single Gaussian fiber grating, or a series structure formed by a plurality of Gaussian fiber gratings with the same central wavelength, or a parallel structure formed by a plurality of Gaussian fiber gratings with the same central wavelength, or a series-parallel structure formed by a plurality of Gaussian fiber gratings with the same central wavelength.
The signal detection and demodulation unit comprises a single photon detector, a time-to-digital converter and an information processor. The single photon detector is connected with a third port of the three-port circulator.
The single photon detector is composed of an avalanche diode or a superconducting waveguide device, the time-to-digital converter is composed of a single chip microcomputer and/or a programmable logic device and/or a digital signal processing chip and/or an embedded chip and/or a time delay and acquisition device, and the information processor is realized by one or more of the single chip microcomputer and/or the programmable logic device and/or the digital signal processing chip and/or the embedded chip.
The signal detection and demodulation unit detects that the dual-wavelength dipulse photon counts reflected back from the quasi-distributed sensing unit are respectively N1And N2Expressed by formula five and formula six:
wherein λ is1And λ2Respectively wavelength of the dual pulse light, P1And P2Input peak power, λ, for dual wavelength pulsesBIs the reflection center wavelength, omega, of the fiber grating sensorBIs 3dB broadband of the fiber grating sensor, k is a system constant and has the size of
Wherein eta is the detection efficiency of the single photon detector, delta tgateTime gate width for a single photon detector, t1 measurement time, fpulseFor the laser repetition frequency, ε is the attenuation coefficient of the fiber, L is the distance from the circulator to the fiber grating sensor, RmaxBeing optical fibresThe maximum reflectivity of the grating sensor, n is the refractive index of the optical fiber, h is the Planck constant, and c is the propagation speed of light in vacuum.
Further, a sensing signal M can be obtained by a formula five and a formula six, wherein M is represented by a formula seven:
wherein
s is sensitivity, λBIs the central reflection wavelength, P, of the sensing unit1And P2For input peak power of dual wavelength pulse, reflection center wavelength lambda of fiber gratingBDrift amount delta lambda demodulated under external actionBAnd is in linear relation with the change quantity deltam of the sensing signal.
In summary, due to the adoption of the technical scheme, the invention has the beneficial effects that:
1. compared with the traditional detection mode, the frequency-shift device based on the electro-optic modulator is adopted to generate dual-wavelength pulsed light, and the frequency modulation of the input pulsed light is realized by utilizing the phase and frequency relation of the electro-optic phase modulator;
2. the scheme adopts an external modulation mode to generate dual-wavelength light, thereby reducing the requirement of the system on the wavelength interval of the tunable laser and facilitating the implementation of the time division/wavelength division hybrid multiplexing sensing system.
3. The scheme adopts the single photon counter as the detector, and compared with the traditional photoelectric detector, the mode can realize high spatial resolution and high signal-to-noise ratio detection on the single photon; high spatial resolution means that a fibre grating sensor array with smaller spatial separation can be probed.
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In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and that for those skilled in the art, other relevant drawings can be obtained according to the drawings without inventive effort, wherein:
FIG. 1 is a schematic diagram of the system of the present invention;
the labels in the figure are: the system comprises a laser 1, an adjustable attenuator 2, a polarizer 3, a polarization controller 4, a polarization beam splitter 5, an electro-optic phase modulator 6, a coupler 7-1 x 2, a three-port circulator 8, a fiber grating sensor array 9, a single photon detector 10, a time-to-digital converter 11 and an information processor 12.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.
Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.
It is noted that relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
The features and properties of the present invention are described in further detail below with reference to examples.
Example one
As shown in fig. 1, the quasi-distributed sensing apparatus based on dual-wavelength dual-pulse light source of the present invention includes a dual-wavelength dual-pulse light source, a quasi-distributed sensing unit, and a signal detection and demodulation unit. The dual-wavelength pulse light with the same intensity fluctuation output by the dual-wavelength dual-pulse light source is input into the quasi-distributed sensing unit, and the quasi-distributed optical sensing unit is connected with signal detection and demodulation.
The dual-wavelength dual-pulse light source is used for generating dual-wavelength pulse photons with the central wavelength within a set range;
in the dual-wavelength double-pulse light source, picosecond pulse light output by a laser is divided into two beams of pulse light through a polarization beam splitter, wherein the time delay delta T generated after one beam of pulse passes through a delay optical fiber with the length of L is a formula I:
n is the refractive index of the fiber and c is the refractive index of light in vacuum. Another beam of pulse light will generate phase change after passing through the electro-optic phase modulator
Is a formula two:
wherein v is0Center frequency of incident light, gamma is slope of ramp signal, VπIs the half-wave voltage of the modulator,
for the initial phase, t is the propagation time of the incident light. And obtaining the frequency change Deltav of the pulsed light as a third formula by differentiating the second formula:
further, the central wavelength variation Δ λ of the pulsed light is given by the formula four:
further, after the optical signals output by the delay optical fiber and the electro-optical phase modulator are combined by the optical coupler, dual-wavelength dual-pulse light with the wavelength difference delta lambda and the time difference delta t is formed.
The quasi-distributed sensing unit is characterized in that the change of the environmental physical quantity at different spatial positions is converted into the change of the reflected light intensity of the fiber bragg grating;
the signal detection and demodulation unit is characterized in that the output signal of the distributed sensing unit is aligned to be detected and demodulated, so that the change of the environmental physical quantity is obtained.
The signal detection and demodulation unit is characterized in that the dual-wavelength dipulse photon counts reflected from the sensing unit are respectively N1And N2Expressed by formula five and formula six
Wherein λ is1And λ2Respectively wavelength of the dual pulse light, P1And P2Input peak power, λ, for dual wavelength pulsesBIs the reflection center wavelength, omega, of the fiber grating sensorBIs 3dB broadband of the fiber grating sensor, k is a system constant and has the size of
Wherein eta is the detection efficiency of the single photon detector, delta tgateTime gate width for a single photon detector, t1 measurement time, fpulseFor the laser repetition frequency, ε is the attenuation coefficient of the fiber, L is the distance from the circulator to the fiber grating sensor, RmaxThe maximum reflectivity of the fiber grating sensor is shown, n is the refractive index of the fiber, h is the Planck constant, and c is the propagation speed of light in vacuum.
Further, a sensing signal M can be obtained by a formula five and a formula six, wherein M is represented by a formula seven:
wherein
s is sensitivity, λBThe central reflection wavelength of the sensing unit, M is the sensing signal, and the reflection central wavelength of the fiber grating is lambdaBDrift amount delta lambda demodulated under external actionBIs linear with the change Δ M of the measurement signal.
Furthermore, because the dual-wavelength dual-pulse light is generated by the same light pulse, the dual-wavelength dual-pulse light has the same intensity fluctuation, and the last item in the formula seven can be a constant, so that the error caused by the fluctuation of the light source is reduced, and the stability of the system is improved.
Further, the dual-wavelength dual-pulse light source comprises a laser 1, an adjustable attenuator 2, a polarizer 3, a polarization controller 4, a polarization beam splitter 5, an electro-optic phase modulator 6 and a 1 × 2 coupler 7.
The laser 1 outputs picosecond pulse light, the central wavelength of the output light is located in the reflection spectrum of the fiber grating sensor array 9, and the picosecond pulse light comprises a distributed feedback laser adopting internal modulation or external modulation, a fiber laser, a mode-locked laser and the like.
The polarizer 3, the polarization controller 4 and the polarization beam splitter 5 are used for splitting one pulse light into two double pulse lights with the same intensity fluctuation;
the electro-optic phase modulator 6 is used for modulating the wavelength of incident light, and the electro-optic phase modulator 6 is controlled by an external circuit and is synchronized with the output pulse light of the laser 1.
Further, the quasi-distributed sensing unit comprises a three-port optical circulator 8 and a fiber grating sensor array 9, wherein a first port of the three-port optical circulator 8 is connected with the output end of the 1-by-2 coupler 7. The fiber grating sensor array 9 is a single gaussian fiber grating or a series structure composed of a plurality of gaussian fiber gratings with the same central wavelength, or a parallel structure composed of a plurality of gaussian fiber gratings with the same central wavelength, or a series-parallel structure composed of a plurality of gaussian fiber gratings with the same central wavelength.
Further, the signal detection and demodulation unit includes a single photon detector 10, a time-to-digital converter 11 and an information processor 12. The single photon detector 10 is connected to the third port of the three-port optical circulator 8. The single photon detector 10 is composed of an avalanche diode or a superconducting waveguide device, the time-to-digital converter 11 is composed of a single chip microcomputer and/or a programmable logic device and/or a digital signal processing chip and/or an embedded chip and/or a time delay and fetch device, and the information processor 12 is realized by one or more of the single chip microcomputer and/or the programmable logic device and/or the digital signal processing chip and/or the embedded chip.
Based on the system, the quasi-distributed sensing device based on the dual-wavelength double-pulse light source comprises the following steps:
the method comprises the following steps: the output laser of laser instrument 1 is the picosecond pulsed light, and the polarizer 3 and polarization controller 4 and polarization beam splitter 5 are incitted in proper order to the pulsed light after 2 attenuations of attenuator, divide into two bundles of two pulsed lights that have the same intensity fluctuation in with a beam of pulsed light, and wherein a beam of pulse produces time delay delta T after the delay fiber that length is L and is:
n is the refractive index of the fiber and c is the refractive index of light in vacuum. Another beam of pulse light will generate phase change after passing through the electro-optic phase modulator
The formula II is as follows:
wherein v is0Center frequency of incident light, gamma is slope of ramp signal, VπIs the half-wave voltage of the modulator,
for the initial phase, t is the propagation time of the incident light. And obtaining the frequency change Deltav of the pulsed light as a third formula by differentiating the second formula:
further, the central wavelength variation Δ λ of the pulsed light is given by the formula four:
further, after the optical signals output by the delay optical fiber and the electro-optical phase modulator are combined by the optical coupler, dual-wavelength dual-pulse light with the wavelength difference delta lambda and the time difference delta t is formed.
The dual-wavelength pulse enters the fiber grating sensor array 9 from a first port of the circulator 8, the fiber grating sensor array 9 is connected with a second port of the circulator 8, and the dual-wavelength pulse enters the single photon detector 10 through a third port of the circulator 8 after being reflected by the fiber grating sensor array 9;
step two: the time-to-digital converter 11 measures the single photon count value reaching the single photon detector 10; the single photon count values arriving at the single photon detector 10 are respectively N1And N2Expressed by formula five and formula six:
wherein λ is1And λ2Respectively wavelength of the dual pulse light, P1And P2Input peak power, λ, for dual wavelength pulsesBIs the reflection center wavelength, omega, of the fiber grating sensorBIs 3dB broadband of the fiber grating sensor, k is a system constant and has the size of
Wherein eta is the detection efficiency of the single photon detector, delta tgateTime gate width for a single photon detector, t1 measurement time, fpulseFor the laser repetition frequency, ε is the attenuation coefficient of the fiber, L is the distance from the circulator to the fiber grating sensor, RmaxThe maximum reflectivity of the fiber grating sensor is shown, n is the refractive index of the fiber, h is the Planck constant, and c is the propagation speed of light in vacuum.
Step three: the information processor 12 obtains a measurement signal according to the single photon counting value measured by the time-to-digital converter 11, and obtains the measurement signal change quantity of the two reflected pulse lights reaching the single photon detector 10 according to the measurement signal; before the information processor 12 obtains the measurement signal according to the photon count value measured by the time-to-digital converter 11, the single photon count value is converted into a linear representation in a logarithmic mode, and the conversion formula is as follows:
wherein the content of the first and second substances,
m is sensing signal, reflection center wavelength lambda of optical fiber gratingBDrift amount delta lambda demodulated under external actionBIs linear with the change Δ M of the measurement signal, s is the sensitivity, which can be written as equation eight,
Δ λ is the wavelength difference modulated by the electro-optic phase modulator 6. Lambda [ alpha ]BLinear with the change of M, so that the reflection center wavelength lambda of the fiber grating sensor array 9BLinear demodulation is possible according to the variation of the demodulation signal M. Because the dual-wavelength dual-pulse light source can output dual pulse light with the same intensity fluctuation, the last item of the formula seven can be simplified into a constant, thereby reducing the error caused by the fluctuation of the light source and improving the measurement precision of the system.
Step four: and demodulating the drift amount of the reflection center wavelength of the fiber grating sensor array 9 according to the measurement signal variation, and further accurately measuring the physical quantity of the fiber grating sensor array 9 according to the demodulated drift amount of the reflection center wavelength of the fiber grating sensor array 9.
Through the steps one to four, the influence of the wavelength switching process and the intensity fluctuation of the light source is avoided due to the characteristic that the frequency shift device does not need to directly modulate the light source, so that the method has higher demodulation precision, the requirement on the stability of the light source is reduced, and the implementation difficulty of the time division multiplexing/wavelength division multiplexing sensing system is reduced.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and should not be taken as limiting the scope of the present invention, and any modifications, equivalents and improvements made by those skilled in the art within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (6)
1. The utility model provides a quasi-distributed sensing device based on dual wavelength dipulse light source which characterized in that: the dual-wavelength double-pulse optical fiber grating sensor comprises a dual-wavelength double-pulse optical source, wherein dual-wavelength pulse light with the same intensity fluctuation and output by the dual-wavelength double-pulse optical source is input into a quasi-distributed sensing unit, and the quasi-distributed sensing unit converts the change of environmental physical quantities at different spatial positions into the change of reflected light intensity of an optical fiber grating and outputs signals; the output signal of the quasi-distributed sensing unit is detected and demodulated through a signal detection and demodulation unit, so that the change of the environmental physical quantity is obtained;
the dual-wavelength dual-pulse light source comprises a laser (1), an adjustable attenuator (2), a polarizer (3), a polarization controller (4), a polarization beam splitter (5), an electro-optic phase modulator (6) and a 1 x 2 coupler (7);
the output light of the laser (1) is picosecond pulse light, and the central wavelength of the output light is positioned in the reflection spectrum of the fiber grating sensor array (9);
the polarizer (3), the polarization controller (4) and the polarization beam splitter (5) are used for separating two beams of double pulse light with the same intensity fluctuation from one beam of pulse light;
the electro-optic phase modulator (6) is used for modulating the wavelength of incident light, and the electro-optic phase modulator (6) is controlled by an external circuit and is synchronous with the output pulse light of the laser (1);
the laser (1) adopts an internal modulation or external modulation distributed feedback laser, a fiber laser or a mode-locked laser;
picosecond pulse light output by the laser (1) is divided into two beams of pulse light through the polarization beam splitter (5), wherein the time delay delta T generated after one beam of pulse passes through the delay optical fiber with the length of L is a formula I:
n is the refractive index of the optical fiber, c is the refractive index of light in vacuum; the other beam of pulse light passes through the electro-optic phase modulator (6) and then generates phase change
Is a formula two:
wherein v is0Is the center frequency of the incident light, gamma is the slope of the ramp signal, VπIs the half-wave voltage of the modulator,
is the initial phase, t is the propagation time of the incident light; and obtaining the frequency change Deltav of the pulsed light as a third formula by differentiating the second formula:
further, the central wavelength variation Δ λ of the pulsed light with the wavelength λ is a formula four:
further, after the optical signals output by the delay optical fiber and the electro-optical phase modulator are combined by the optical coupler, dual-wavelength dual-pulse light with the wavelength difference delta lambda and the time difference delta T is formed.
2. The quasi-distributed sensing device based on dual-wavelength double-pulse light source as claimed in claim 1, wherein: the quasi-distributed sensing unit comprises a three-port circulator (8) and a fiber grating sensor array (9), wherein a first port of the three-port circulator (8) is connected with the output end of a 1-x 2 coupler (7).
3. The quasi-distributed sensing device based on dual-wavelength double-pulse light source as claimed in claim 2, wherein: the fiber grating sensor array (9) is a single Gaussian fiber grating, or a series structure formed by a plurality of Gaussian fiber gratings with the same central wavelength, or a parallel structure formed by a plurality of Gaussian fiber gratings with the same central wavelength, or a series-parallel structure formed by a plurality of Gaussian fiber gratings with the same central wavelength.
4. The quasi-distributed sensing device based on dual-wavelength double-pulse light source as claimed in claim 2, wherein: the signal detection and demodulation unit comprises a single-photon detector (10), a time-to-digital converter (11) and an information processor (12), and the single-photon detector (10) is connected with a third port of the three-port circulator (8).
5. The quasi-distributed sensing device according to claim 4, wherein: the single photon detector (10) is composed of an avalanche diode or a superconducting waveguide device, the time-to-digital converter (11) is composed of a single chip microcomputer and/or a programmable logic device and/or a digital signal processing chip and/or an embedded chip and/or a time delay and taking device, and the information processor (12) is realized by one or more of the single chip microcomputer and/or the programmable logic device and/or the digital signal processing chip and/or the embedded chip.
6. The quasi-distributed sensing device according to claim 4, wherein: the signal detection and demodulation unit detects that the dual-wavelength dipulse photon counts reflected back from the quasi-distributed sensing unit are respectively N1And N2Expressed by formula five and formula six:
wherein the content of the first and second substances,1and λ2Respectively wavelength of the dual pulse light, P1And P2Input peak power, λ, for dual wavelength pulsesBIs the reflection center wavelength, omega, of the fiber grating sensorBIs 3dB broadband of the fiber grating sensor, k is a system constant and has the size of
Wherein eta is the detection efficiency of the single photon detector, delta tgateTime gate width for a single photon detector, t1 measurement time, fpulseFor the laser repetition frequency, ε is the attenuation coefficient of the fiber, L is the distance from the circulator to the fiber grating sensor, RmaxThe maximum reflectivity of the fiber grating sensor is shown, n is the refractive index of the fiber, h is the Planck constant, and c is the propagation speed of light in vacuum;
further, a sensing signal M can be obtained by a formula five and a formula six, wherein M is represented by a formula seven:
wherein
s is sensitivity, λBIs the central reflection wavelength, P, of the sensing unit1And P2For input peak power of dual wavelength pulse, reflection center wavelength lambda of fiber gratingBDrift amount delta lambda demodulated under external actionBIs linear with the change Δ M of the measurement signal.
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