CN115790814A - Optical fiber vibration detection system and method thereof - Google Patents
Optical fiber vibration detection system and method thereof Download PDFInfo
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Abstract
The application provides an optical fiber vibration detection system and a method thereof. The optical fiber vibration detection system comprises a chirped pulse light source, a bidirectional coupler, an optical fiber partial reflection point pair, a photoelectric detector and a signal acquisition and processing module, wherein the chirped pulse light source is used for generating chirped pulse light sequences, the output end of the chirped pulse light source is connected with the input end of the bidirectional coupler, the first output end of the bidirectional coupler is connected with the input end of the optical fiber partial reflection point pair, the two partial reflection points in the optical fiber partial reflection point pair are used for respectively reflecting the chirped pulse light to generate two reflected light pulses with mutual time delay, the second output end of the bidirectional coupler is connected with the input end of the photoelectric detector, the output end of the photoelectric detector is connected with the signal acquisition and processing module, and the signal acquisition and processing module is used for acquiring beat frequency interference signals generated by interference of the two reflected light pulses with mutual time delay, solving the phase of the beat frequency interference signals and demodulating the phase of the beat frequency interference signals to obtain optical fiber vibration information.
Description
Technical Field
The application relates to the technical field of optical fiber sensing detection, in particular to an optical fiber vibration detection system and method.
Background
The phenomenon of vibration is seen everywhere in nature and in human production activities. In the fields of large civil engineering structures, aerospace, mechanical manufacturing and the like, the structural body can be damaged in different degrees in the long-term use process, the service life of the structural body is influenced, and even serious personal accidents and economic losses can be caused. In the structural bodies, the vibration condition can usually reflect whether the structural bodies run safely and stably, so that the detection of the vibration has important significance for ensuring the health state of a system and realizing quick and timely equipment maintenance. In addition, in the fields of seismic exploration, pipeline transportation and the like, vibration detection is widely applied, and contributes to life safety and economic activities of people. During the operation of an aircraft engine, the vibration frequency range of the aircraft engine covers several hertz to over several kilohertz, so that high-speed and wide-dynamic-range vibration measurement needs to be realized.
The optical fiber sensor has the characteristics of small inherent volume, light weight, electromagnetic interference resistance, long sensing distance and the like, so that the optical fiber sensor becomes an irreplaceable sensing solution in some application scenes. Optical fiber vibration sensors, a type of optical fiber sensor, have been widely studied and used. According to different working principles, the optical fiber vibration sensor can be mainly classified into intensity demodulation, interference demodulation and wavelength demodulation. The interference type optical fiber vibration sensor is based on the optical interference principle, utilizes the vibration of the external environment to cause the phase change of the transmission light in the optical fiber to realize vibration sensing, and obtains the actual vibration information through phase demodulation. The interference type optical fiber vibration sensor generally adopts a Michelson, mach-Zehnder, fabry-Perot or Sagnac interferometer structure, has the advantages of high sensitivity and high precision, and can realize high-speed demodulation. However, the interference type optical fiber vibration sensor generally has the problems of complex measuring system, high price and the like.
Disclosure of Invention
The application aims to provide an optical fiber vibration detection system and a method thereof, which can realize vibration measurement with high frequency and wide dynamic range.
One aspect of the present application provides a fiber optic vibration detection system. The optical fiber vibration detection system comprises a chirped pulse light source, a bidirectional coupler, an optical fiber partial reflection point pair, a photoelectric detector and a signal acquisition and processing module, wherein the bidirectional coupler is provided with an input end, a first output end and a second output end, the chirped pulse light source is used for generating a chirped pulse light sequence, the output end of the chirped pulse light source is connected with the input end of the bidirectional coupler, the first output end of the bidirectional coupler is connected with the input end of the optical fiber partial reflection point pair, two partial reflection points in the optical fiber partial reflection point pair are used for respectively reflecting the chirped pulse light to generate two reflected light pulses with mutual time delay, the second output end of the bidirectional coupler is connected with the input end of the photoelectric detector, the output end of the photoelectric detector is connected with the signal acquisition and processing module, and the signal acquisition and processing module is used for acquiring beat frequency interference signals generated by interference of the two reflected light pulses with mutual time delay, solving the phase of the beat frequency interference signals and demodulating the optical fiber vibration information by the phase of the beat frequency interference signals.
The optical fiber vibration detection system is low in cost, simple in structure, wide in dynamic frequency response range and high in sensitivity, and is an ideal scheme for achieving high-frequency and wide-dynamic-range vibration measurement.
Another aspect of the present application provides a method of optical fiber vibration detection. The optical fiber vibration detection method comprises the following steps: generating a chirped pulse light sequence; reflecting the chirped pulse light respectively through two part reflection points in the optical fiber part reflection point pair to generate two reflection light pulses with mutual time delay; the two reflected light pulses which are delayed mutually interfere to generate beat frequency interference signals; solving the phase of the beat frequency interference signal; and demodulating through the phase of the beat frequency interference signal to obtain optical fiber vibration information.
The optical fiber vibration detection method provided by the embodiment of the application has a wide dynamic frequency response range and high sensitivity, and can realize vibration measurement in a high frequency and wide dynamic range.
Drawings
Fig. 1 is a schematic structural diagram of an optical fiber vibration detection system according to an embodiment of the present application.
Fig. 2 is a schematic diagram of three implementation structures of the bidirectional coupler in fig. 1.
Fig. 3 is a schematic diagram of two embodiments of the reflection point pair of the optical fiber in fig. 1.
Fig. 4 is a schematic diagram of two reflected chirped pulses and their beat frequency interference signals of a reflection point pair of a fiber part according to an embodiment of the present application.
FIG. 5 is a flowchart of a method for detecting fiber vibration according to an embodiment of the present application.
Fig. 6 is a flowchart illustrating a phase demodulation process in the optical fiber vibration detection method according to an embodiment of the present application.
Fig. 7 is a schematic diagram illustrating two phase calculation methods in the phase demodulation process according to an embodiment of the present application.
Fig. 8 is a schematic diagram of a phase compensation process in a process of demodulating vibration information of an optical fiber using multiple groups of data points according to an embodiment of the present application and a simulation result of a signal-to-noise ratio enhancement effect of the system.
FIG. 9 shows simulation results of time-domain and frequency-domain vibration information obtained by phase demodulation under 1kHz vibration averaged with one set of data and forty sets of data according to an embodiment of the present application.
Detailed Description
Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus consistent with certain aspects of the present application, as detailed in the appended claims.
The terminology used in the embodiments of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. Unless otherwise defined, technical or scientific terms used in the embodiments of the present application should have the ordinary meaning as understood by those having ordinary skill in the art to which the present application belongs. The terms "first," "second," and the like, as used in the description and in the claims of the present application, do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Also, the use of the terms "a" or "an" and the like do not denote a limitation of quantity, but rather denote the presence of at least one. "plurality" or "a number" means two or more. Unless otherwise specified, "front," "back," "left," "right," "distal," "proximal," "top," and/or "bottom," and the like are for convenience of description and are not limited to a single position or orientation in space. The word "comprising" or "comprises", and the like, means that the element or item listed as preceding "comprising" or "includes" covers the element or item listed as following "comprising" or "includes" and its equivalents, and does not exclude other elements or items. The terms "connected" or "coupled" and the like are not restricted to physical or mechanical connections, but may include electrical connections, whether direct or indirect. As used in the specification of the present application and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.
The embodiment of the application provides an optical fiber vibration detection system 100. Fig. 1 discloses a schematic structural diagram of an optical fiber vibration detection system 100 according to an embodiment of the present application. As shown in fig. 1, an optical fiber vibration detection system 100 according to an embodiment of the present application includes a chirped pulse light source 1, a bidirectional coupler 2, an optical fiber partial reflection point pair 3, a photodetector 4, and a signal acquisition and processing module 5, where the bidirectional coupler 2 has an input end T11, a first output end T12, and a second output end T13. The output end of the chirp pulse light source 1 is connected with the input end T11 of the bidirectional coupler 2, the first output end T12 of the bidirectional coupler 2 is connected with the input end of the optical fiber partial reflection point pair 3, the second output end T13 of the bidirectional coupler 2 is connected with the input end of the photoelectric detector 4, and the output end of the photoelectric detector 4 is connected with the signal acquisition processing module 5.
The chirped pulse light source 1 may be used to generate a chirped pulse light sequence. The output end of the chirped pulse light source 1 is used for outputting the chirped pulse light sequence. The frequency of the light within each chirp varies with time. Each chirped pulse in the chirped pulse light sequence is the same. The pulse repetition frequency of the chirped pulse light sequence is more than twice of the maximum vibration frequency to be measured.
The bidirectional coupler 2 receives the incident chirped pulse light sequence through an input end T11 thereof, transmits the chirped pulse light sequence to the optical fiber partial reflection point pair 3 through a first output end T12, and transmits the optical signal reflected by the optical fiber partial reflection point pair 3 to the photodetector 4 through a second output end T13.
The pair of fiber partial reflection points 3 includes two fiber partial reflection points. Fig. 4 shows a schematic diagram of two chirped pulses reflected by a pair of partially reflected optical fiber points 3 and their beat interference signals according to an embodiment of the present application. As shown in fig. 4, the two partially reflecting points may partially reflect and partially transmit the incident chirped pulse light, the two chirped pulse lights reflected by the two partially reflecting points have different transmission optical lengths, and when meeting, there is a corresponding time delay Δ τ, the two reflected pulse lights meet, and the overlapping portions interfere to form a beat frequency interference light field, and then the beat frequency interference light field is transmitted to the photodetector 4 through the second output end T13 of the bidirectional coupler 2. The output of the photoelectric detector 4 is a beat frequency interference signal generated by a beat frequency interference optical field, and the signal envelope is similar to the chirp pulse. The density, i.e. the frequency, of the beat frequency interference signal is determined by the chirp amount of the chirped pulse light sequence and the distance between two partially reflecting points in the fiber partially reflecting point pair 3. The spacing of the two partially reflecting points and the amount of chirp in the chirped pulse light sequence should be chosen to satisfy the condition that the frequency of the returned beat frequency interference signal is within the bandwidth of the photodetector 4. The reflection spectrum width of the partial reflection points in the optical fiber partial reflection point pairs 3 covers the wavelength adjustment range of the chirped pulse light source 1 so as to realize the reflection of the chirped pulse light sequence.
The photodetector 4 may be configured to detect interference optical signals of the two chirped pulsed lights reflected by the optical fiber partial reflection point pair 3 output by the second output end T13 of the bidirectional coupler 2, convert the optical signals into electrical signals, and transmit the electrical signals to the signal acquisition and processing module 5.
The signal collecting and processing module 5 can be used to collect and demodulate the electrical signal transmitted by the photodetector 4. The signal acquisition processing module 5 can solve the phase of the beat frequency interference signal, and demodulate the phase of the beat frequency interference signal to obtain the optical fiber vibration information. Each chirp pulse in the chirp pulse light sequence generates interference after being reflected by two partial reflection points, and a frame of beat frequency interference signal is returned. The time interval of each frame of collected beat frequency interference signals corresponds to the time interval of two adjacent chirped pulses of the chirped pulse light sequence. And obtaining the vibration information of the optical fiber to be detected according to the change of the phase of the multiframe beat frequency interference signals along with time.
In an alternative embodiment, the chirped pulse light source 1 can be directly generated by a semiconductor laser for communication through current or temperature modulation, so that the system cost can be greatly reduced. In another alternative embodiment, the chirped pulse light source 1 may also be generated by external frequency modulation from continuous light emitted by a semiconductor laser for communication to output a chirped pulse light sequence. The chirp of the pulses may be linear or non-linear. The chirp may be positive or negative at all times within the pulse, or may be different directions in different parts of the pulse. Ideally, the chirp of the pulse is modulated to be linear, with both the intensity and frequency of the pulse varying linearly with time, as shown in figure 4.
Fig. 2 discloses three embodiments of the bidirectional coupler 2 in fig. 1. As shown in fig. 2 (a), in an alternative embodiment, the bidirectional coupler 2 includes an optical circulator 21, the optical circulator 21 having a first port T21, a second port T22, and a third port T23. The first port T21 of the optical circulator 21 is an input end T11 of the bidirectional coupler 2, the second port T22 of the optical circulator 21 is a first output end T12 of the bidirectional coupler 2, and the third port T23 of the optical circulator 21 is a second output end T13 of the bidirectional coupler 2.
In another alternative embodiment, shown in fig. 2 (b), the bidirectional coupler 2 includes an optical isolator 22 and an optical coupler 23, the optical isolator 22 having an input terminal and an output terminal, the optical coupler 23 having a 2 × 1 structure, and the optical coupler 23 having a first input terminal T31, a second input terminal T32, and an output terminal T33. The input end of the optical isolator 22 is an input end T11 of the bidirectional coupler 2, the output end of the optical isolator 22 is connected to a first input end T31 of the optical coupler 23, an output end T33 of the optical coupler 23 is a first output end T12 of the bidirectional coupler 2, and a second input end T32 of the optical coupler 23 is a second output end T13 of the bidirectional coupler 2. The optical isolator 22 may be used to block the returning optical signal from affecting the chirped pulse light source 1.
In yet another alternative embodiment, as shown in fig. 2 (c), the bidirectional coupler 2 includes an optical isolator 22 and an optical coupler 23, the optical isolator 22 has an input end and an output end, the optical coupler 23 adopts a 2 × 2 structure, the optical coupler 23 has a first input end T31, a second input end T32 and two output ends T33, T34, the input end of the optical isolator 22 is the input end T11 of the bidirectional coupler 2, the output end of the optical isolator 22 is connected to the first input end T31 of the optical coupler 23, the two output ends T33, T34 of the optical coupler 23 are the first output end T12 of the bidirectional coupler 2, and the second input end T32 of the optical coupler 23 is the second output end T13 of the bidirectional coupler 2.
Fig. 3 discloses two embodiments of the fiber pair 3 of fig. 1. In an alternative embodiment, as shown in fig. 3 (a), the two fiber partial reflection points in the fiber partial reflection point pair 3 are two partial reflection fiber gratings 31 and 32 on one fiber, and the incident end of the fiber is connected to the first output end T12 of the bidirectional coupler 2. The reflection spectrum widths of the fiber gratings 31 and 32 cover the wavelength adjustment range of the chirped pulse light source 1. Preferably, the parameters of the two fiber gratings 31, 32 are the same. In practical application, the optical fiber between the two fiber gratings 31 and 32 is adhered to a structural member such as a cantilever arm, and the structural member is connected with a vibration source to convert vibration information into strain of the optical fiber between the two fiber gratings 31 and 32, so that an optical path difference between two reflected light pulses is changed, interference fringes are changed, and detection of the vibration information is realized.
In another alternative embodiment, shown in fig. 3 (b), the two fiber partial reflection points in the pair 3 are two end faces 34, 35 of two closely attached optical fibers with different lengths connected to the output end of one coupler 33. For example, the optical coupler 23 shown in fig. 2 (c) has a 2 × 2 structure, two output ends T33 and T34 of the optical coupler 23 are directly connected to two optical fibers with different lengths, and the end faces 34 and 35 of the two optical fibers are two optical fiber partial reflection points. The two optical fibers of different lengths are closely attached from the output end of the coupler 33, so that the optical paths of the two optical fibers along the transmission direction are consistent except for the portion where the long optical fiber is more than the short optical fiber. In practical application, the longer optical fiber is attached to the shorter optical fiber, the extra part of the longer optical fiber is attached to structural members such as a cantilever beam, the structural members are connected with a vibration source, vibration information is converted into strain of the optical fiber, and further the optical path difference of two reflected light pulses is changed, so that the change of interference fringes is caused, and the detection of the vibration information is realized. If the bidirectional coupler 2 is a structure of the optical isolator 22 and the optical coupler 23, preferably, the optical coupler 23 in the bidirectional coupler 2 adopts a 2 × 2 structure shown in (c) of fig. 2, a first input end T31 of the optical coupler 23 is connected to the optical isolator 22, a second input end T32 is connected to the optical detector, and two output ends T33 and T34 are directly connected to two optical fibers as a pair of partial reflection points.
The optical fiber vibration detection system 100 of the embodiment of the application has the advantages of low cost, simple structure, wide dynamic frequency response range and high sensitivity, and is an ideal scheme for realizing high-frequency and wide-dynamic-range vibration measurement.
The embodiment of the present application further provides an optical fiber vibration detection method based on the optical fiber vibration detection system 100. FIG. 5 discloses a flow chart of a method for detecting fiber vibration according to an embodiment of the present application. As shown in fig. 5, the optical fiber vibration detection method according to an embodiment of the present application may include steps S11 to S15.
In step S11, a chirped pulse light sequence is generated.
In step S12, the chirped pulse light is reflected by two partial reflection points of the fiber partial reflection point pair 3, respectively, to generate two reflected light pulses delayed from each other.
In step S13, the two reflected light pulses delayed from each other interfere to generate a beat frequency interference signal.
In step S14, the phase of the beat frequency interference signal is solved.
In step S15, the fiber vibration information is obtained by demodulating the phase of the beat frequency interference signal.
In some embodiments, the optical fiber vibration detection method of the present application may further include step S16. In step S16, the beat frequency interference signal is preprocessed to obtain a preprocessed beat frequency interference signal. In the case of preprocessing the beat frequency interference signal, in step S14, the phase of the preprocessed beat frequency interference signal may be solved.
The optical fiber vibration detection method of the embodiment of the application provides a vibration demodulation method, the principle of which is based on the phase demodulation process, and two chirped pulse lights reflected by two optical fiber partial reflection points in an optical fiber partial reflection point pair 3 interfere to generate a beat frequency interference signal, as shown in fig. 4. The external vibration causes the distance between the reflection points of the two optical fiber parts to change, and the phase of the beat frequency interference signal also changes along with the change. Therefore, the fiber vibration information can be obtained by demodulating the phase of the beat frequency interference signal.
Fig. 6 discloses a flow chart of a vibration demodulation method in the optical fiber vibration detection method according to an embodiment of the present application.
As shown in fig. 6, the vibration demodulation method may include the steps of:
in step S21: and filtering and denoising the beat frequency interference signal. And filtering the beat frequency interference signal, and removing useless high-frequency noise on the beat frequency interference signal by using a low-pass filter.
Firstly, fourier transform is carried out on the beat frequency interference signal, the bandwidth range of the beat frequency interference signal is observed in a frequency domain, and then high-frequency noise outside the bandwidth range is removed by using a low-pass filter.
In step S22: and normalizing the filtered beat frequency interference signal.
The normalization process may be to normalize the filtered beat frequency interference signal with respect to the envelope of the incident chirped pulse light; or extracting an envelope from the filtered beat frequency interference signal and normalizing the envelope relative to the extracted envelope.
For example, the envelope L of the beat interference signal S can be obtained by the hilbert transform, as follows:
L＝|Hilbert(S)|
and normalizing the beat frequency interference signal through S/L.
In step S23: and removing the direct current component in the normalized beat frequency interference signal.
The steps S21 to S23 all belong to the process of preprocessing the beat frequency interference signal mentioned in the step S16.
In step S24, the beat frequency interference signal (if the beat frequency interference signal is preprocessed, the preprocessed beat frequency interference signal is subjected to hilbert transform), and a linear phase variation law of the beat frequency interference signal with time is obtained.
The phase values of the beat frequency interference signal can be obtained by hilbert transform as follows:
in step S25, according to the linear phase variation law obtained in step S24, each data point required for solving the phase value of a specific point can be found on the beat frequency interference signal by an operation such as interpolation.
In step S26, the phase of a specific point on the beat interference signal is obtained by solving the signal intensity of each data point found in step S25. This process is referred to as a phase calculation process.
In step S27: the optical fiber vibration information is obtained from the time-dependent change curve of the phase value obtained in step S26.
The vibration demodulation method of the embodiment of the application can demodulate the optical fiber vibration information through two optional vibration demodulation implementation modes.
A first vibration demodulation implementation may demodulate vibration information by calculating the phase change over time of a single fixed point on the beat frequency interference signal.
With continued reference to fig. 6, step S25 may include step S251. In step 251, a set of data points required to solve for the phase value can be found on each frame of the beat frequency interference signal by an operation such as interpolation according to the linear phase variation rule obtained in step S24.
Step S26 may include step S261 and step S262. In step S261, the phase value of a single fixed point on the beat frequency interference signal is obtained by solving the signal strength of a set of data points per frame.
Step S261 may include step S2611 or step S2612, and in step S261, the phase value of a single fixed point on each frame of beat frequency interference signal may be calculated by two alternative methods, that is, step S2611 or step S2612.
Referring to fig. 7, in step S2611, a first calculation method is adopted, where a set of data points includes three points with 120 ° phase difference, and the phase value of a single fixed point on each frame of beat frequency interference signal is obtained through calculation of signal intensities of the three points with 120 ° phase difference on each frame of beat frequency interference signal.
Suppose that the signal intensities of three points with 120 ° phase difference are respectively recorded as S 11 ，S 12 ，S 13 ：
Wherein A is the amplitude of the signal,
is S 12 The phase value of the dot. A fixed point on the beat frequency interference signal, such as S, can be solved by the calculation of the signal intensity of the three points as described in the following formula 12 Phase value of a point
Can be calculated from the following formula:
in step S2612, a second calculation method is adopted, where a set of data points includes two points with a phase difference of 90 degrees, and the phase value of a single fixed point on each frame of beat frequency interference signal is obtained by solving through the calculation of the signal intensities of the two points with a phase difference of 90 degrees on each frame of beat frequency interference signal.
Suppose that the signal intensities of two points with 90 ° phase difference are respectively recorded as S 21 ，S 22 ：
Then, the phase value of a fixed point on the beat interference signal
Can be calculated from the following formula:
the phase value of the same fixed point on each frame of beat frequency interference signal can be obtained through the two phase calculation processes.
In step S262, the phase values of a single fixed point on each frame of beat frequency interference signal obtained by the solution in step S261 are listed together, so that the time-dependent change curve of the phase of the single fixed point can be obtained.
Step S27 may include step S271. In step S271, the fiber vibration information may be calculated from the phase-versus-time variation curve of the single fixed point obtained in step S262.
A second implementation of vibration demodulation may be to accumulate average demodulated vibration information by calculating the variation of the phase of a plurality of fixed points on the beat frequency interference signal over time.
With continued reference to fig. 6, step S25 may include step S252. In step S252, according to the linear phase variation rule obtained in step S24, a plurality of groups, for example, n (n > 1) groups of data points, which are required for solving the phase value, can be found on each frame of the beat frequency interference signal by an operation such as interpolation.
Step S26 may include steps S263 to S266. In step S263, the phase values of a plurality of fixed points on each frame of the beat frequency interference signal are obtained by solving the signal strength of the plurality of sets of data points in each frame.
Wherein, step S263 may include step S2631 or step S2632, and in step S263, the phase values of a plurality of fixed points on each frame of the beat frequency interference signal may be calculated by two alternative methods of step S2631 or step S2632.
Referring to fig. 7, in step S2631, a first calculation method is adopted, where each of the multiple sets of data points includes three points with a phase difference of 120 degrees, and the phase value of one fixed point in each set of beat frequency interference signals is obtained by performing calculation on the signal strength of the three points in each set (for example, as shown in the above formula (1)), and the phase values of the multiple sets of fixed points in each frame are combined together, so as to obtain the phase values of multiple fixed points in each frame.
In step S2632, a second calculation method is adopted, where a group of data points includes two points with a phase difference of 90 degrees, the phase value of one fixed point in each group on each frame of beat frequency interference signal is obtained by solving through an operation of signal strengths of the two points in each group (for example, as shown in the above formula (2)), and the phase values of multiple groups of fixed points in each frame are combined together, so as to obtain the phase values of multiple fixed points in each frame.
The phases of n fixed points on each frame of beat frequency interference signal can be calculated by using n groups of data points on each frame of beat frequency interference signal and utilizing the two phase calculation processes.
In step S264, phase values of a plurality of (e.g., n) fixed points on each frame of beat frequency interference signal obtained by the solution in step S263 are respectively listed together, so as to obtain a time-dependent change curve of the phase of the plurality of (e.g., n) fixed points, that is, a time-dependent change curve of a plurality of groups (e.g., n groups) of phases is obtained.
Assuming that the number of the multiple sets of data points is n, the obtained n sets of phase variation curves with time can be respectively recorded as
In step S265, the plurality of sets of time-dependent phase change curves obtained in step S264 are each subjected to phase compensation.
For example, in the n sets of data points, the phase differences between each point in the next n-1 set of data points and the corresponding point in the first set of data points are each
The subsequent n-1 groups of phase change curves with time are respectively phase-shifted relative to the first group of phase change curves with time
Phase compensation is achieved as shown in fig. 8 (a), i.e.:
wherein, obtained
The n groups of phase change curves with time after phase compensation are obtained.
In step S266, the multiple sets of phase variation curves over time after the phase compensation in step S265 are subjected to cumulative average denoising to obtain cumulative average phase variation curves over time.
For example, n groups of phase variation curves with time are subjected to cumulative average denoising, which is shown as follows:
therefore, a curve of the variation of the accumulated average denoised phase along with the time can be obtained
Step S27 may include step S272. In step S272, the fiber vibration information may be calculated from the time-dependent change curve of the phase after the cumulative averaging obtained in step S266.
With the second implementation of vibration demodulation, the relationship between the snr of the system and the average data point group obtained through simulation is shown in (b) of fig. 8, and it can be seen that the snr of the system can be improved by more than 6dB by using multiple data groups.
Fig. 9 discloses simulation results of time-domain and frequency-domain vibration information obtained by phase demodulation under 1kHz vibration obtained by averaging one set of data and forty sets of data according to an embodiment of the present application, where (a) in fig. 9 shows the time-domain vibration information and (b) in fig. 9 shows the frequency-domain vibration information. As can be seen from fig. 9, the system can reduce the noise floor of the system through multiple sets of data phase compensation and averaging processes, and obtain more accurate vibration information. Namely, partial noise can be eliminated by demodulation in a mode of accumulating and averaging a plurality of groups of phase change curves, and the signal-to-noise ratio of a system demodulation result is improved.
The optical fiber vibration detection method provided by the embodiment of the application has a wide dynamic frequency response range and high sensitivity, and can realize vibration measurement in a high frequency and wide dynamic range.
The above description is only exemplary of the present application and should not be taken as limiting the present application, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the scope of protection of the present application.
Claims (24)
1. An optical fiber vibration detection system, characterized by: the optical fiber vibration detection device comprises a chirped pulse light source, a bidirectional coupler, an optical fiber partial reflection point pair, a photoelectric detector and a signal acquisition and processing module, wherein the bidirectional coupler is provided with an input end, a first output end and a second output end, the chirped pulse light source is used for generating a chirped pulse light sequence, the output end of the chirped pulse light source is connected with the input end of the bidirectional coupler, the first output end of the bidirectional coupler is connected with the input end of the optical fiber partial reflection point pair, two partial reflection points in the optical fiber partial reflection point pair are used for respectively reflecting the chirped pulse light to generate two reflected light pulses with mutual time delay, the second output end of the bidirectional coupler is connected with the input end of the photoelectric detector, the output end of the photoelectric detector is connected with the signal acquisition and processing module, and the signal acquisition and processing module is used for acquiring beat frequency interference signals generated by interference of the two reflected light pulses with mutual time delay, solving the phase of the beat frequency interference signals and demodulating and acquiring optical fiber vibration information by the phase of the beat frequency interference signals.
2. The fiber optic vibration detection system of claim 1 wherein: the chirped pulse light source is directly generated by a semiconductor laser for communication through modulation in a current or temperature modulator.
3. The fiber optic vibration detection system of claim 1 wherein: the chirped pulse light source is generated by continuous light emitted by a semiconductor laser for communication through external frequency modulation.
4. The fiber optic vibration detection system of claim 1 wherein: the bidirectional coupler comprises an optical circulator, wherein the optical circulator is provided with a first port, a second port and a third port, the first port of the optical circulator is an input end of the bidirectional coupler, the second port of the optical circulator is a first output end of the bidirectional coupler, and the third port of the optical circulator is a second output end of the bidirectional coupler.
5. The fiber optic vibration detection system of claim 1 wherein: bidirectional coupler includes optical isolator and optical coupler, optical isolator has input and output, optical coupler has first input, second input and output, optical isolator's input does bidirectional coupler's input, optical isolator's output is connected optical coupler's first input, optical coupler's output does bidirectional coupler's first output, optical coupler's second input does bidirectional coupler's second output.
6. The fiber optic vibration detection system of any one of claims 1 to 5 wherein: the two optical fiber partial reflection points in the optical fiber partial reflection point pair are two partial reflection optical fiber gratings on one optical fiber, the optical fiber between the two optical fiber gratings is adhered to a structural member connected with a vibration source, and the incident end of the optical fiber is connected with the first output end of the bidirectional coupler.
7. The fiber optic vibration detection system of claim 6 wherein: the parameters of the two fiber gratings are the same.
8. The fiber optic vibration detection system of any of claims 1-3, wherein: two optical fiber partial reflection points in the optical fiber partial reflection point pair are two tail end faces of two optical fibers which are tightly attached and have different lengths, and the part of the two optical fibers, which is more than the longer optical fiber, is adhered to a structural member connected with a vibration source.
9. The fiber optic vibration detection system of claim 8 wherein: bidirectional coupler includes optical isolator and optical coupler, optical isolator has input and output, optical coupler has first input, second input and two outputs, optical isolator's input does bidirectional coupler's input, optical isolator's output is connected optical coupler's first input, two outputs of optical coupler do bidirectional coupler's first output, optical coupler's second input does bidirectional coupler's second output, two output lug connection of optical coupler are two optic fibre.
10. The fiber optic vibration detection system of claim 1 wherein: the reflection spectrum width of the partial reflection point in the optical fiber partial reflection point pair covers the wavelength adjusting range of the chirped pulse light source.
11. The fiber optic vibration detection system of claim 1 wherein: each chirped pulse in the chirped pulse light sequence is the same, and the pulse repetition frequency of the chirped pulse light sequence is more than twice of the maximum vibration frequency to be measured.
12. The fiber optic vibration detection system of claim 1 wherein: the frequency of the beat frequency interference signal is determined by the chirp quantity of the chirped pulse light sequence and the distance between two partial reflection points in the optical fiber partial reflection point pair, and the frequency of the beat frequency interference signal is within the bandwidth of the photoelectric detector.
13. An optical fiber vibration detection method is characterized in that: the method comprises the following steps:
generating a chirped pulse light sequence;
the chirped pulse light is respectively reflected by two partial reflection points in the optical fiber partial reflection point pair to generate two reflection light pulses with mutual time delay;
the two reflected light pulses which are delayed mutually interfere to generate beat frequency interference signals;
solving the phase of the beat frequency interference signal; and
and demodulating through the phase of the beat frequency interference signal to obtain optical fiber vibration information.
14. The optical fiber vibration detecting method according to claim 13, wherein: further comprising:
preprocessing the beat frequency interference signal to obtain a preprocessed beat frequency interference signal,
wherein the solving for the phase of the beat frequency interference signal comprises: and solving the phase of the preprocessed beat frequency interference signal.
15. The optical fiber vibration detecting method according to claim 14, wherein: the preprocessing the beat frequency interference signal comprises:
filtering and denoising the beat frequency interference signal;
normalizing the filtered beat frequency interference signal; and
and removing the direct current component in the normalized beat frequency interference signal.
16. The optical fiber vibration detecting method according to claim 15, wherein: the normalizing the filtered beat frequency interference signal comprises:
the filtered beat frequency interference signal is normalized with respect to the envelope of the incident chirped pulse light.
17. The optical fiber vibration detecting method according to claim 15, wherein: the normalizing the filtered beat frequency interference signal comprises:
and extracting an envelope from the filtered beat frequency interference signal, and normalizing relative to the extracted envelope.
18. The optical fiber vibration detection method according to claim 13, wherein: the solving for the phase of the beat frequency interference signal comprises:
performing Hilbert change on the beat frequency interference signal to obtain a phase linear change rule of the beat frequency interference signal along with time;
searching each data point required for solving a phase value on the beat frequency interference signal according to the obtained phase linear change rule; and
and solving to obtain the phase of the beat frequency interference signal through the searched signal intensity of each data point.
19. The optical fiber vibration detecting method according to claim 18, wherein: the searching for each data point required for solving a phase value on the beat frequency interference signal according to the obtained linear phase change rule comprises: searching a group of data points required for solving a phase value on each frame of the beat frequency interference signal according to the obtained phase linear change rule,
wherein the obtaining the phase of the beat frequency interference signal by solving the found signal strength of each data point comprises:
solving and obtaining the phase value of a single fixed point on the beat frequency interference signal of each frame through the searched signal intensity of the group of data points of each frame; and
obtaining a time-dependent change curve of the phase of the single fixed point according to the phase value of the single fixed point on each frame of beat frequency interference signal obtained by solving,
wherein the obtaining of the optical fiber vibration information through the demodulation of the phase of the beat frequency interference signal comprises: and calculating the vibration information of the optical fiber according to the change curve of the phase of the single fixed point along with the time.
20. The optical fiber vibration detecting method according to claim 19, wherein: the set of data points comprises three points with phases different by 120 degrees, and solving to obtain a phase value of a single fixed point of the beat frequency interference signal per frame by finding the signal strength of the set of data points per frame comprises:
and solving the phase value of the single fixed point on each frame of the beat frequency interference signal through the operation of the signal intensity of the three points of each frame.
21. The optical fiber vibration detection method according to claim 19, wherein: the set of data points comprises two points with a phase difference of 90 degrees, and solving to obtain a phase value of a single fixed point of the beat frequency interference signal per frame by finding the signal strength of the set of data points per frame comprises:
and solving the phase value of the single fixed point on each frame of the beat frequency interference signal through the calculation of the signal intensity of the two points per frame.
22. The optical fiber vibration detecting method according to claim 18, wherein: the searching for each data point required for solving a phase value on the beat frequency interference signal according to the obtained linear phase change rule comprises: searching a plurality of groups of data points required for solving phase values on each frame of the beat frequency interference signal according to the obtained linear phase change rule,
wherein the obtaining the phase of the beat frequency interference signal by solving the found signal intensity of each data point comprises:
solving and obtaining phase values of a plurality of fixed points on the beat frequency interference signal of each frame through the searched signal intensity of the plurality of groups of data points of each frame;
obtaining a plurality of groups of phase variation curves along with time according to the phase values of the plurality of fixed points on each frame of beat frequency interference signal obtained by solving;
respectively carrying out phase compensation on the change curves of the multiple groups of phases along with time; and
accumulating and average denoising the multiple groups of phase variation curves with time after phase compensation to obtain the phase variation curves with time after accumulating and averaging,
wherein the obtaining of the optical fiber vibration information through the demodulation of the phase of the beat frequency interference signal comprises: and calculating to obtain the optical fiber vibration information through the change curve of the accumulated and averaged phase along with the time.
23. The optical fiber vibration sensing method according to claim 22, wherein: each of the plurality of sets of data points includes three points with a phase difference of 120 degrees, and the obtaining the phase values of a plurality of fixed points on the beat frequency interference signal by solving the signal strength of each frame of the plurality of sets of data points includes:
and solving the phase values of a plurality of fixed points on the beat frequency interference signal of each frame through the calculation of the signal intensity of the three points in each frame of the plurality of groups.
24. The optical fiber vibration detecting method according to claim 22, wherein: each of the multiple sets of data points includes two points that are 90 degrees out of phase, and the obtaining the phase values of the multiple fixed points on the beat frequency interference signal by solving the signal strength of each frame of the multiple sets of data points includes:
and solving the phase values of a plurality of fixed points on the beat frequency interference signal of each frame through the calculation of the signal intensity of the two points in each frame of the plurality of groups.
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