CN111412935A - High-repetition-rate quasi-distributed sensing system based on time division multiplexing - Google Patents
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- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- 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
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- 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
- G01D5/35354—Sensor working in reflection
Abstract
The invention discloses a high-repetition rate quasi-distributed sensing system based on time division multiplexing, belonging to the technical field of optical fiber sensing measurement
The range of the repetition period t of the chirp pulse light signal is
And the cross correlation peaks after the reflected light signals of different pulses are subjected to matched filtering are mutually separated in the time domain; the invention ensures that the system has high spatial resolution, simultaneously improves the measurement repetition rate by x times, does not need to modulate pulses with different frequencies, reduces the requirement on a modulator, and reduces the complexity of the system by using single-channel detection.
Description
Technical Field
The invention relates to the technical field of optical fiber sensing measurement, in particular to a high-repetition-rate quasi-distributed sensing system based on time division multiplexing.
Background
The sensor is widely applied to life and production activities of people as a detection device integrating functions of automatic measurement, recording and the like. Compared with the traditional electrical sensor, the optical fiber-based sensor has the unique advantages of portability, corrosion resistance, electromagnetic interference resistance, high temperature resistance, high detection sensitivity and the like, so that the distributed optical fiber sensing is rapidly developed in recent decades.
The phase-sensitive optical time domain reflectometer is a typical distributed optical fiber sensing system, which performs real-time monitoring on external interference by demodulating interference intensity of rayleigh scattered light in an optical fiber, and is concerned about due to its remarkable advantage of ultrahigh sensitivity, but has limited application in some fields due to weak intensity of rayleigh scattered light.
In recent years, an online writing technology for writing an ultra-weak fiber grating (UWFBG) array into a common single mode fiber has been commercialized, and a quasi-distributed measurement system based on a weak reflectivity FBG string is developed since FBGs can provide stable and high reflection intensity. However, no matter the distributed measurement system or the quasi-distributed measurement system, the measurement repetition rate fscanAnd sensing distance L are constrained to satisfy fscan≤c/2nL。
In recent years, there are two main studies for breaking the limitations of measurement repetition rate and sensing distance:
1. a distributed optical fiber sensing technology based on frequency division multiplexing is characterized in that N chirp pulses in different frequency ranges are injected into a sensing optical fiber, scattering signals in each frequency range are respectively demodulated by a frequency domain windowing method, and the scattering signals can respectively recover disturbance information, so that the measurement repetition rate is increased by N times.
2. The distributed optical fiber sensing technology based on positive and negative frequency IQ demodulation injects chirp pulses with positive and negative frequencies into a sensing optical fiber, and the positive frequency and the negative frequency can be separated in a frequency domain, so that signals with the positive and negative frequencies of reflected light information can be separated by applying a Fourier transform technology, and disturbance information can be respectively recovered by the signals, so that the measurement repetition rate is increased by 2 times. However, this approach requires dual channel detection, which increases the complexity of the system.
Disclosure of Invention
The invention aims to: the invention provides a high-repetition rate quasi-distributed sensing system based on time division multiplexing and an implementation method thereof, which solve the technical problem that the repetition rate cannot be improved while the system has high spatial resolution because the measurement repetition rate and the sensing distance are restricted by each other in the existing quasi-distributed measuring system.
The technical scheme adopted by the invention is as follows:
the high-repetition rate quasi-distributed sensing system based on time division multiplexing comprises a laser module, a coupler, an optical signal modulation module, a signal detection module, an optical circulator and a signal demodulation module, the optical signal modulation module modulates an optical signal into a chirped pulse optical signal, the output end of the optical signal modulation module is connected with the port 1 of the optical circulator, the port 2 of the optical circulator inputs the chirp pulse optical signal into the sensing optical fiber to be measured and receives the reflected optical signal returned by the sensing optical fiber to be measured, the port 3 of the optical circulator inputs the reflected light signal into a signal detection module, the signal detection module generates beat frequency signals by using the reflected light signal and the local oscillator optical signal input by the coupler, the signal detection module inputs the beat frequency signal into a signal demodulation module for demodulation and output to obtain disturbance information of the reflected light signal;
the width of the main lobe of the chirped pulse light signal after autocorrelation is not more than the interval between two reflecting points in the reflected light signal
Namely:
w1+w2+…+wxl (1) where w is ≦ w1,w2……wxRepresenting the width of the main lobe, x representing the round trip time t of the light traveling in the sensing fiber0The number of pulses driven in, L represents the spacing between the reflection points;
the range of the repetition period t of the chirp pulse light signal is
And mutually separating the cross-correlation peaks of the reflected light signals of different pulses after matched filtering in the time domain, wherein xmaxRepresenting the ratio of the separation L between the reflection points to the average width of the matched filtered cross-correlation peak.
Further, the demodulation step of the beat signal is as follows:
step 1: dividing the beat frequency signal into N groups of data according to a sampling sequence, wherein each group of data comprises x data, and N is an integer which is not zero;
step 2: and solving the disturbance information of the nth group of data, wherein N is a positive integer less than or equal to N.
Further, step 21: generating chirp signals P in a digital domain, wherein the chirp signals P are the same as x chirp pulse signals input into a sensing fiber to be detected;
step 22: and performing matched filtering on the chirp signal P and the beat frequency signal to obtain a cross-correlation peak value M, wherein the formula is as follows:
wherein the content of the first and second substances,
representing cross-correlation operation, M representing a cross-correlation peak value after matching and filtering, and E representing a beat frequency signal;
step 23: and demodulating disturbance information by utilizing the cross-correlation peak value.
In summary, due to the adoption of the technical scheme, the invention has the beneficial effects that:
the invention ensures that the system has high spatial resolution, simultaneously improves the measurement repetition rate by x times, does not need to modulate pulses with different frequencies, reduces the requirement on a modulator, and reduces the complexity of the system by using single-channel detection. For example, when an FBG string spaced 5 meters apart is used as a sensing fiber, the frequency sweep range of a chirp signal is set to 40MHz, and a chirp pulse signal is injected into the fiber, where the pulse interval is 1/4 cycles, so that the system can ensure the spatial resolution of 5 meters and improve the measurement repetition rate by 4 times.
Compared with a distributed optical fiber sensing system based on the frequency division multiplexing technology, the distributed optical fiber sensing system based on the frequency division multiplexing technology has the advantages that because the used chirped pulses are completely the same, the inconsistency of different frequency bands in the frequency division multiplexing on response to a disturbance signal is avoided; in the quasi-distributed system, the spatial resolution is determined by the frequency sweep range of the chirp and the interval between the reflection points, and when the interval between the reflection points is larger than the spatial resolution corresponding to the frequency sweep range of the chirp, the spatial resolution is irrelevant to the frequency sweep range of the chirp signal. The invention ensures high spatial resolution and improves the measurement repetition rate by x times; compared with a distributed optical fiber sensing system based on a positive and negative frequency IQ demodulation technology, the distributed optical fiber sensing system does not need double-channel detection, only needs a single channel, and reduces the complexity of the system.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed 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 for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
FIG. 1 is a system block diagram of a high repetition rate quasi-distributed sensing system based on time division multiplexing provided by the present invention;
FIG. 2 is a schematic diagram of a high repetition rate quasi-distributed sensing system based on time division multiplexing according to an embodiment of the present invention;
FIG. 3 is a flow chart of a high repetition rate quasi-distributed sensing system based on time division multiplexing according to an embodiment of the present invention;
the device comprises a laser module 1, a coupler 2, an optical signal modulation module 3, an optical circulator 4, a sensing optical fiber to be detected 5, a signal detection module 6 and a signal demodulation module 7.
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.
Examples
The high-repetition rate quasi-distributed sensing system based on Time-division multiplexing in the embodiment of the invention is mainly realized based on Time-division multiplexing (TDM), and specifically realized based on a chirped pulse phase-sensitive optical Time domain reflectometer based on Time-division multiplexing.
Based on time division multiplexing, as shown in fig. 1, the high repetition rate quasi-distributed sensing system based on time division multiplexing provided in this embodiment includes a laser module 1, the laser module 1 generates an optical signal to a coupler 2, the coupler 2 is an optical coupler 2, the coupler 2 inputs the optical signal into an optical signal modulation module 3 and a signal detection module 6 respectively, the optical signal modulation module 3 modulates the optical signal into a chirped pulse optical signal, an output end of the optical signal modulation module 3 is connected to a port 1 of an optical circulator 4, the port 2 of the optical circulator 4 inputs the chirped pulse optical signal into a sensing fiber 5 to be detected and receives a reflected optical signal returned by the sensing fiber 5 to be detected, a port of the optical circulator 4 inputs the reflected optical signal into the signal detection module 6, the signal detection module 6 generates a beat frequency signal by using the reflected optical signal and a local oscillation optical signal input by the coupler 2, the signal detection module 6 inputs the beat frequency signal into the signal demodulation module 7 for demodulation and output, so as to obtain the disturbance of the reflected light signal.
The optical signal modulation module 3 comprises a waveform generator and an electro-optical modulator. The sensing fiber 5 to be measured is an optical fiber having a series of reflection points along the axial direction, the reflection points may be Fiber Bragg Gratings (FBGs), FP cavities, etc., and the reflection points of this embodiment are Fiber Bragg Gratings (FBGs). The signal detection module 6 comprises an optical mixer and a signal collector.
Wherein, the optical circulator 4(optical circulator) is a multi-port nonreciprocal optical device, which has a light guiding function, and a typical structure thereof has N (N is more than or equal to 3) ports, when light is input from any one port (generally, port 1), the light can be output from the next port (port 2) in the digital sequence with almost no loss, and almost no light is output from the other ports (port 3); by analogy, when light is input from port 2, it can also be output by port 3 with almost no loss, while there is no light output on port 1 or other ports. The optical circulator 4 type may be a transmissive or reflective optical circulator 4.
In this embodiment, the optical signal E generated by the laser module 1L(t) is:
The optical signal modulation module 3 modulates the optical signal EL(t) modulation into chirped pulsed light signal Ep(t) the chirped pulse light signal Ep(t) the width of the main lobe after autocorrelation is no greater than the separation of two reflection points in the reflected light signal
Namely:
w1+w2+…+wxl (5) where w is ≦ w1,w2……wxRepresenting the width of the main lobe, x representing the round trip time t of the light traveling in the sensing fiber0The number of pulses driven in, L represents the spacing between the reflection points;
the range of the repetition period t of the chirp pulse light signal is
And mutually separating the cross-correlation peaks of the reflected light signals of different pulses after matched filtering in the time domain, wherein xmaxRepresenting the ratio of the separation L between the reflection points to the average width of the matched filtered cross-correlation peak.
Firstly finding the range of the repetition period t, and then finding the minimum period value t of the chirped pulse light signals in the range, wherein the minimum period value t is obtained by mutually separating the cross correlation peaks of the reflected light signals of different pulses after matched filtering in the time domain, so that the chirped pulse light signals are obtained
At maximum, substitute the period value t into EpAnd (t) obtaining the final chirp pulse light signal.
The chirped pulse optical signal Ep(t) is:
wherein E is0Which represents the amplitude of the chirp signal and,
indicating the initial phase, tau, of the chirped pulsepThe pulse width is represented, and gamma represents the chirp rate of the chirped pulse light signal;
chirp signal sdigital(t) is:
wherein f ismRepresenting the center frequency of the chirp signal.
A reflected light signal E at the ith reflection point in the reflected light signalref(tiAnd t) is:
wherein i represents the number of the reflection points, tiDenotes the time delay at the ith reflection point, R (t)i) The reflectivity of the ith reflection point is represented,
indicating the phase of the reflected signal at the ith reflection point.
Beat frequency signal E of reflected light signal and local oscillator light signal at ith reflection point in signal detection module 6B(tiT) is
Wherein, A (t)i) Indicating the amplitude of the signal reflected by the ith reflection point,
representing the phase difference between the local oscillator and the signal.
The beat frequency signal E is demodulated by the signal demodulation module 7B(tiT) obtaining E after Hilbert transformbeat(tiAnd t), demodulating and outputting to obtain disturbance information in the reflected light signal.
The demodulation step of the beat frequency signal is as follows:
step 1: dividing the beat frequency signal into N groups of data according to a sampling sequence, wherein each group of data comprises x data, and N is an integer which is not zero;
step 2: and solving the nth data, wherein N is a positive integer less than or equal to N.
Solving the nth data, wherein the demodulation principle is as follows: when the beat frequency signal is cross-correlated, the peak is matched only when the response function is the same as the original signal, and if the response function is not the same as the original signal, the signal is suppressed. The principle of time division multiplexing is shown in FIG. 2, EpFor a pulse injected into the fiber, M is the cross-correlation peak at the reflection point. Although the reflected light of different pulses are overlapped with each other, the cross correlation peaks of the reflected light signals after matched filtering are separated from each other in the time domain due to the specific interval, so that the reflected light signals of different chirp pulses can be separated, and the disturbance information can be demodulated by the reflected light signals respectively.
The concrete steps of solving the nth data are as follows:
step 21: subjecting the nth data to Hilbert transform to obtain Ebeat(tiT), the formula adopted is:
step 22: generating chirp signals P in a digital domain, wherein the chirp signals P are the same as x chirp pulse signals input into a sensing fiber to be detected;
step 23: the chirp signals P and E are processedbeat(tiAnd t) performing matched filtering to obtain a cross-correlation peak M, wherein the formula is as follows:
S(ti) The cross-correlation peak value of the beat signal and the chirp signal is represented, and E is Ebeat(tiT) represents a beat signal;
step 24: obtaining phase information of the beat frequency signal by utilizing the cross-correlation peak value;
shifting the frequency f towards the basebandmThen, taking the phase can obtain:
wherein the content of the first and second substances,
indicating the phase at which the reflected light signal matches the filter peak,
to represent
The phase after the summation is taken over the phase,
denotes the t-thi+1And tiThe phase difference at the peak of each reflection element.
The integral reflection signal and beat signal only need to be arranged for all i according to the time sequence.
Step 25: and demodulating the disturbance information by using the phase information. The phase difference between the two peak values is linearly related to delta t, so that the cross-correlation peaks after the chirp signal reflected light matched filtering are separated in the time domain according to the phase information of the beat signal, the disturbance information can be respectively demodulated, and the high-repetition-rate quasi-distributed sensing is realized.
The work flow of the invention is shown in figure 3:
s101: the laser modulation module 1 sends an optical signal to the optical signal modulation module through the coupler 2 branch 1, and sends a local oscillator optical signal to the signal detection module 6 through the coupler 2 branch 2;
s102: the optical signal modulation module 3 modulates the optical signal into a chirped pulse optical signal and sends the chirped pulse optical signal to the port 1 of the circulator 4;
s103: the optical circulator 4 sends the chirp pulse optical signal to the sensing optical fiber to be detected through the port 2, and receives a reflected optical signal of the chirp optical signal from the sensing optical fiber to be detected;
s104: the optical circulator 4 sends the reflected light signal to the signal detection module 6 through the port 3;
s105: the signal detection module 6 acquires a reflected light signal and a local oscillation light signal to obtain a beat frequency signal and sends the beat frequency signal to the signal demodulation module 7;
s106: the signal demodulation module 7 demodulates and outputs the beat frequency signal.
Therefore, compared with the prior art, the high repetition rate quasi-distributed sensing implementation method based on time division multiplexing in the embodiment of the invention has the following advantages: compared with a distributed optical fiber sensing system based on the frequency division multiplexing technology, due to the fact that the used chirped pulses are completely the same, inconsistency of different frequency bands in the frequency division multiplexing on response of disturbance signals is avoided; in the quasi-distributed system, the spatial resolution is determined by the frequency sweep range of the chirp and the interval between the reflection points, and when the interval between the reflection points is larger than the spatial resolution corresponding to the frequency sweep range of the chirp, the spatial resolution is irrelevant to the frequency sweep range of the chirp signal. The invention ensures high spatial resolution and improves the measurement repetition rate by x times; compared with a distributed optical fiber sensing system based on a positive and negative frequency IQ demodulation technology, the distributed optical fiber sensing system does not need double-channel detection, only needs a single channel, and reduces the complexity of the system.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (3)
1. The high-repetition-rate quasi-distributed sensing system based on time division multiplexing comprises a laser module (1), a coupler (2), an optical signal modulation module (3), a signal detection module (6), an optical circulator (4) and a signal demodulation module (7), wherein the optical signal modulation module (3) modulates optical signals into chirp pulse optical signals, the output end of the optical signal modulation module (3) is connected with a port 1 of the optical circulator (4), the chirp pulse optical signals are input into a sensing optical fiber (5) to be detected by a port 2 of the optical circulator (4) and received by reflected light signals returned by the sensing optical fiber (5) to be detected, the reflected light signals are input into the signal detection module (6) by the port 3 of the optical circulator (4), and the reflected light signals and local oscillation optical signals input by the coupler (2) are utilized by the signal detection module (6) to generate beat frequency signals, the signal detection module (6) inputs the beat frequency signal into a signal demodulation module (7) for demodulation and output to obtain disturbance information of the reflected light signal;
wherein the width of the main lobe of the chirped pulse light signal after autocorrelation is not greater than the interval between two reflection points in the reflected light signal
Namely:
w1+w2+…+wxl (1) where w is ≦ w1,w2……wxRepresenting the width of the main lobe, x representing the round trip time t of the light traveling in the sensing fiber0The number of pulses driven in, L represents the spacing between the reflection points;
the range of the repetition period t of the chirp pulse light signal is
And mutually separating the cross-correlation peaks of the reflected light signals of different pulses after matched filtering in the time domain, wherein xmaxRepresenting the ratio of the separation L between the reflection points to the average width of the matched filtered cross-correlation peak.
2. The time division multiplexing based high repetition rate quasi-distributed sensing system of claim 1, wherein: the demodulation step of the beat frequency signal is as follows:
step 1: dividing the beat frequency signal into N groups of data according to a sampling sequence, wherein each group of data comprises x data, and N is an integer which is not zero;
step 2: and solving the disturbance information of the nth group of data, wherein N is a positive integer less than or equal to N.
3. The time division multiplexing based high repetition rate quasi-distributed sensing system of claim 2, wherein: the concrete steps of solving the nth data are as follows:
step 21: generating chirp signals P in a digital domain, wherein the chirp signals P are the same as x chirp pulse signals input into a sensing fiber to be detected;
step 22: and performing matched filtering on the chirp signal P and the beat frequency signal to obtain a cross-correlation peak value M, wherein the formula is as follows:
wherein the content of the first and second substances,
representing cross-correlation operation, M representing a cross-correlation peak value after matching and filtering, and E representing a beat frequency signal;
step 23: and demodulating disturbance information by utilizing the cross-correlation peak value.
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| CN116105777A (en) * | 2023-04-11 | 2023-05-12 | 广东海洋大学 | Quasi-distributed Fabry-Perot interference optical fiber sensor and signal demodulation method thereof |
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