CN111609919A - Optical fiber distributed vibration and loss simultaneous detection system - Google Patents
Optical fiber distributed vibration and loss simultaneous detection system Download PDFInfo
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Abstract
The invention provides an optical fiber distributed vibration and loss simultaneous detection system, wherein the output end of a laser in the system is connected with the input end of a coupler, the first output end of the coupler is connected with the first end of a circulator sequentially through a second modulator, a third modulator and an optical fiber amplifier, the second end of the circulator is connected with one end of an optical fiber, the third end of the circulator is connected with the first input end of a polarization diversity detector, the second output end of the coupler is connected with the second input end of the polarization diversity detector, and the output end of the polarization diversity detector is connected with a processor through an acquisition card. Before the laser signal is transmitted to the optical fiber, the laser signal is modulated into a series of chirped pulse light, so that the polarization states of the chirped pulse light are switched under two orthogonal states, and the polarization diversity detector is adopted for polarization division detection during detection, so that the fading phenomenon existing during vibration detection by adopting a coherent light source can be eliminated, and the loss and distributed vibration of the optical fiber can be measured by utilizing the coherent light source simultaneously.
Description
Technical Field
The invention belongs to the field of optical fiber detection, and particularly relates to an optical fiber distributed vibration and loss simultaneous detection system.
Background
Optical fibers are used as transmission media to play a key role in information transmission in the fields of communication, oil and gas pipelines, power lines, rail transit and the like, and communication optical cables are laid along the lines in the construction process of the pipelines, the power lines, the rail transit and the like for transmitting detection and control signals. The distributed sensing technology utilizes common communication optical fibers, can realize detection of optical fiber channel parameters and multiple physical quantities in the environment where the optical fibers are located, and has the advantages of electromagnetic interference resistance, low cost, wide detection range, real-time monitoring and the like compared with other electrical point type sensors.
In the application field scene, the measurement of optical fiber loss and vibration is particularly important, and the optical fiber loss can be used for detecting the faults of abnormal bending, breaking points and the like of the optical fiber; by using the optical fiber distributed vibration signals, the running state of a pipeline, the wind dance condition of a power line, the running track of a vehicle, external invasion, man-made damage events and the like can be detected. The optical fiber loss detection is generally realized by adopting an Optical Time Domain Reflectometer (OTDR), and the relation of the optical fiber loss along with the distance can be obtained, but the optical fiber loss detection has the defects of low spatial resolution, incapability of realizing the correspondence between a fault point and an actual geographic position and the like under a long distance. The distributed vibration detection of the optical fiber is generally realized by adopting a phase-sensitive optical time domain reflectometry (phi-OTDR), and because a coherent light source is adopted, the test signal of the coherent light source has a fading phenomenon, and faults such as optical fiber microbending loss and the like cannot be intuitively reflected.
Disclosure of Invention
The invention provides an optical fiber distributed vibration and loss simultaneous detection system, which aims to solve the problem that the vibration and loss of an optical fiber cannot be detected simultaneously by adopting the same system at present.
According to a first aspect of the embodiments of the present invention, an optical fiber distributed vibration and loss simultaneous detection system is provided, which is characterized by including a laser, a coupler, a first modulator, a second modulator, a third modulator, an optical fiber amplifier, a circulator, an optical fiber, a polarization diversity detector, an acquisition card, and a processor, wherein an output end of the laser is connected to an input end of the coupler, a first output end of the coupler is connected to a first end of the circulator through the second modulator, the third modulator, and the optical fiber amplifier in sequence, a second end of the circulator is connected to one end of the optical fiber, a third end of the circulator is connected to a first input end of the polarization diversity detector, a second output end of the coupler is connected to a second input end of the polarization diversity detector, and an output end of the polarization diversity detector is connected to the processor through the acquisition card;
the first modulator modulates the laser so that the laser provides a laser signal with a periodically-changed center frequency to the coupler;
the coupler divides the laser signals into two paths, the first path of laser signals is transmitted to the second modulator, and the second path of laser signals is transmitted to the polarization diversity detector;
the second modulator modulates the intensity and the frequency of the first path of laser signal to form a series of chirped pulse light with the chirped center frequency changing periodically;
the polarization modulator modulates the polarization state of the chirped pulse light of each frequency band so as to switch the polarization state of the chirped pulse light in two orthogonal states, thereby weakening the polarization fading in coherent demodulation;
the optical amplifier amplifies the chirped pulse light after polarization adjustment, sends the chirped pulse light after amplification to the first end of the circulator, and then sends the chirped pulse light to the optical fiber from the second end of the circulator;
after receiving the chirped pulse light, the optical fiber generates backward-transmitted Rayleigh scattering light, and the Rayleigh scattering light is transmitted to the second end of the circulator and then transmitted to the polarization diversity detector from the third end of the circulator;
the polarization diversity detector beats the second path of laser signals and Rayleigh scattering light to generate two paths of scattering light interference electric signals with mutually orthogonal polarization;
the acquisition card acquires the two paths of scattered light interference electric signals with mutually orthogonal polarization and converts the two paths of scattered light interference electric signals into digital signals;
the processor demodulates the digital signals to obtain scattering complex signals corresponding to each chirped pulse light, obtains loss information of each position on the optical fiber according to the amplitude of the scattering complex signals, and obtains vibration information of each position on the optical fiber according to the phase of the scattering complex signals.
In an optional implementation manner, the first modulator is an optical frequency modulator, an output end of the laser is connected to an input end of the optical frequency modulator, an output end of the optical frequency modulator is connected to an input end of the coupler, the laser is configured to generate an original laser signal, and the optical frequency modulator performs optical frequency modulation on the original laser signal to generate a laser signal with a center frequency that changes periodically and provide the laser signal to the coupler;
or, the first modulator is a current modulator, an output end of the current modulator is connected to a modulation end of the laser, an output end of the laser is connected to an input end of the coupler, and the current modulator is configured to modulate a current of the laser, so that the laser outputs a laser signal whose center frequency changes periodically;
or, the first modulator is a temperature modulator, an output end of the temperature modulator is connected to a modulation end of the laser, an output end of the laser is connected to an input end of the coupler, and the temperature modulator is used for modulating the temperature of the laser, so that the laser outputs a laser signal with a periodically-changing central frequency.
In another alternative implementation, the laser signal periodically varies with respect to the center frequency, and the time duration occupied by each center frequency is the same and continuous in time.
In another optional implementation manner, for the laser signal whose center frequency changes periodically, the bandwidth corresponding to each center frequency is an integer multiple of a set value, the lower limit of the bandwidth of each center frequency is 0, and the duration t0 occupied by each center frequency is greater than 2 × n × L/c, where n represents the refractive index of the optical fiber, L represents the length of the optical fiber, and c represents the speed of light.
In another optional implementation manner, for the chirped pulse light with the chirped center frequency that periodically changes, the bandwidth and the pulse width of each chirped pulse light are the same, and the duration occupied by each chirped center frequency is the same but two adjacent chirped center frequencies are both set at intervals in time.
In another alternative implementation manner, for each path of the scattered light interference electrical signal, each central frequency is equal and occupies the same time duration, but two adjacent central frequencies are arranged at intervals in time, the bandwidth corresponding to each central frequency is equal and the instantaneous frequency in the corresponding frequency band changes with the same set slope along the time.
In another optional implementation manner, for the chirped pulsed light and the scattered light interference electrical signal, the longer the duration occupied by each center frequency is, the better the signal-to-noise ratio is, and the larger the bandwidth corresponding to each center frequency is, the higher the resolution is.
In another optional implementation manner, the processor demodulates the digital signal by using a matched filtering method to obtain a scattering complex signal corresponding to each chirped pulse light.
In another optional implementation manner, for the complex scattering signals demodulated in the corresponding time period, an average value of amplitudes of the complex scattering signals corresponding to the chirped pulsed light with different carrier frequencies and polarization is taken as loss information at the corresponding position on the optical fiber, and differential demodulation is performed on phases of the complex scattering signals to obtain vibration information at the corresponding position on the optical fiber.
The invention has the beneficial effects that:
because the prior art adopts a coherent light source when the sensitive optical time domain reflection technology is adopted for vibration detection, the test signal of the coherent light source has a fading phenomenon and cannot reflect the loss of the optical fiber visually, the invention modulates the laser signal before transmitting the laser signal to the optical fiber, modulates the laser signal into a series of chirped pulse light with the chirped center frequency changing periodically, modulates the polarization state of the chirped pulse light of each frequency band so as to switch the polarization state of the chirped pulse light under two orthogonal states, and adopts a polarization diversity detector for polarization division detection during detection, thereby eliminating the fading phenomenon of the test signal existing during the vibration detection by adopting the coherent light source, and realizing the detection of the loss of the optical fiber by utilizing the coherent light source, namely, the invention can simultaneously measure the loss and the distributed vibration of the optical fiber by adopting the same system and the same optical fiber, the test data and the result are consistent, and the field investigation and verification are facilitated.
Secondly, when the prior art adopts the optical time domain reflection technology to detect the optical fiber loss, the spatial resolution is lower at a long distance, and the accurate corresponding relation between the optical fiber loss fault point and the actual geographic position cannot be determined, because the coherent light source can realize distributed vibration detection, and the detection spatial resolution is high, therefore, when the coherent light source is adopted to simultaneously carry out optical fiber vibration and loss detection, the loss information and the vibration information at each position on the optical fiber are obtained by analysis and are based on the same demodulated scattering complex signal, so that the corresponding relation between the optical fiber loss, the vibration and each position on the optical fiber can be established, and the optical fiber loss can be corresponding to each position on the optical fiber even if the spatial resolution of the optical fiber loss detection is higher at a long distance, thereby providing a feedback basis for fault positioning and routing inspection.
Moreover, the second path of laser signals and Rayleigh scattering light are subjected to beat frequency during detection to carry out coherent detection, so that the signal-to-noise ratio and the dynamic range of the system have greater advantages compared with a traditional loss or vibration detection system based on direct detection.
In addition, when the digital signal is demodulated, the processor demodulates the digital signal by adopting a matched filtering method, and combines the chirped pulse light and a matched filtering demodulation scheme, so that the optimal signal-to-noise ratio can be ensured, and the higher spatial resolution can be realized even if the sensing distance is longer. The invention has great significance for fault routing inspection and health monitoring by using the optical fiber.
Drawings
FIG. 1 is a schematic structural diagram of an embodiment of a fiber-optic distributed vibration and loss simultaneous detection system according to the present invention;
FIG. 2 is a schematic structural diagram of another embodiment of the fiber optic distributed vibration and loss simultaneous detection system of the present invention;
FIG. 3 is a schematic structural diagram of a fiber-optic distributed vibration and loss simultaneous detection system according to yet another embodiment of the present invention;
FIG. 4 is a graph of frequency versus time for a laser signal having a periodically varying center frequency in accordance with the present invention;
fig. 5 is a graph of frequency versus time for chirped pulse light with a periodically varying chirp center frequency according to the present invention;
FIG. 6 is an equivalent frequency-time plot of two mutually orthogonal polarized scattered light interference electrical signals of the present invention.
Detailed Description
In order to make the technical solutions in the embodiments of the present invention better understood and make the above objects, features and advantages of the embodiments of the present invention more comprehensible, the technical solutions in the embodiments of the present invention are described in further detail below with reference to the accompanying drawings.
In the description of the present invention, unless otherwise specified and limited, it is to be noted that the term "connected" is to be interpreted broadly, and may be, for example, a mechanical connection or an electrical connection, or a communication between two elements, or may be a direct connection or an indirect connection through an intermediate medium, and a specific meaning of the term may be understood by those skilled in the art according to specific situations.
Referring to fig. 1, a schematic structural diagram of an embodiment of the optical fiber distributed vibration and loss simultaneous detection system of the present invention is shown. The optical fiber distributed vibration and loss simultaneous detection system can comprise a laser, a coupler, a first modulator, a second modulator, a third modulator, an optical fiber amplifier, a circulator, an optical fiber, a polarization diversity detector, an acquisition card and a processor, wherein the output end of the laser is connected with the input end of the coupler, the first output end of the coupler is connected with the first end of the circulator sequentially through the second modulator, the third modulator and the optical fiber amplifier, the second end of the circulator is connected with one end of the optical fiber, the third end of the circulator is connected with the first input end of the polarization diversity detector, the second output end of the coupler is connected with the second input end of the polarization diversity detector, and the output end of the polarization diversity detector is connected with the processor through the acquisition card; the first modulator modulates the laser so that the laser provides a laser signal with a periodically-changed center frequency to the coupler; the coupler divides the laser signals into two paths, the first path of laser signals is transmitted to the second modulator, and the second path of laser signals is transmitted to the polarization diversity detector; the second modulator modulates the intensity and the frequency of the first path of laser signal to form a series of chirped pulse light with the chirped center frequency changing periodically; the polarization modulator modulates the polarization state of the chirped pulse light of each frequency band so as to switch the polarization state of the chirped pulse light in two orthogonal states, thereby weakening the polarization fading in coherent demodulation; the optical amplifier amplifies the chirped pulse light after polarization adjustment, sends the chirped pulse light after amplification to the first end of the circulator, and then sends the chirped pulse light to the optical fiber from the second end of the circulator; after receiving the chirped pulse light, the optical fiber generates backward-transmitted Rayleigh scattering light, and the Rayleigh scattering light is transmitted to the second end of the circulator and then transmitted to the polarization diversity detector from the third end of the circulator; the polarization diversity detector beats the second path of laser signals and Rayleigh scattering light to generate two paths of scattering light interference electric signals with mutually orthogonal polarization; the acquisition card acquires the two paths of scattered light interference electric signals with mutually orthogonal polarization and converts the two paths of scattered light interference electric signals into digital signals; the processor demodulates the digital signals to obtain scattering complex signals corresponding to each chirped pulse light, obtains loss information of each position on the optical fiber according to the amplitude of the scattering complex signals, and obtains vibration information of each position on the optical fiber according to the phase of the scattering complex signals. It should be noted that: the laser signal adopted by the invention can be narrow linewidth laser with long coherence distance and small phase noise.
As shown in fig. 2, the first modulator may be an optical frequency modulator, an output end of the laser is connected to an input end of the optical frequency modulator, an output end of the optical frequency modulator is connected to an input end of the coupler, the laser is configured to generate an original laser signal, and the optical frequency modulator performs optical frequency modulation on the original laser signal to generate a laser signal with a center frequency that changes periodically and provide the laser signal to the coupler. In addition, as shown in fig. 3, the first modulator may also be a current modulator, an output end of the current modulator is connected to a modulation end of the laser, an output end of the laser is connected to an input end of the coupler, and the current modulator is configured to modulate a current of the laser, so that the laser outputs a laser signal whose center frequency changes periodically. The first modulator can also be a temperature modulator, an output end of the temperature modulator is connected with a modulation end of the laser, an output end of the laser is connected with an input end of the coupler, and the temperature modulator is used for modulating the temperature of the laser, so that the laser outputs a laser signal with a periodically-changed central frequency.
In this embodiment, referring to fig. 4, for the laser signal whose center frequency changes periodically, the time duration occupied by each center frequency is the same and is continuous in time, the bandwidth corresponding to each center frequency is an integer multiple of a set value, the lower limit value of the bandwidth of each center frequency is 0, the time duration occupied by each center frequency t0>2 × n × L/c, where n represents the refractive index of the optical fiber, L represents the length of the optical fiber, c represents the speed of light, and the instantaneous frequency in the frequency band corresponding to each center frequency changes linearly with the time lapse. In which each center frequency may be gradually increased in one period, for example, in fig. 4, three center frequencies exist in one period, and the three center frequencies are gradually increased.
As shown in fig. 5, for the chirped pulse light whose chirped center frequency changes periodically, the bandwidth and pulse width of each chirped pulse light are the same, and the duration occupied by each chirped center frequency is the same but two adjacent chirped center frequencies are both set at intervals in time. As shown in fig. 5, the sum of the time duration occupied by each chirp center frequency and the time interval between each chirp center frequency and the next adjacent chirp center frequency is equal to t0, the time intervals between two adjacent chirp center frequencies may be equal, and the instantaneous frequencies in the frequency band corresponding to each center frequency change with the same set slope over time, for example, change with an upward slope over time in fig. 5. It should be noted that: the frequency-time curves of the chirped pulse light in fig. 5 respectively represent different polarization states by a solid line and a dashed line, wherein the polarization states of the chirped pulse light corresponding to two chirped center frequencies adjacent in time are different.
Referring to fig. 6, a dashed line represents a frequency-time graph of one scattered light interference electrical signal, and a solid line represents another scattered light interference electrical signal, wherein the two scattered light interference electrical signals have different polarization states and orthogonal polarizations. For each path of scattered light interference electrical signal, each center frequency is equal and the occupied time length is the same, but two adjacent center frequencies are arranged at intervals in time (may be arranged at equal intervals or may be arranged at unequal intervals), the bandwidth corresponding to each center frequency is equal and the instantaneous frequency in the corresponding frequency band changes with the same set slope along the time, for example, changes with an upward slope along the time in fig. 6. For one path of scattered light interference electrical signal (for example, as shown by a dotted line), a center frequency belonging to the other path of scattered light interference electrical signal (as shown by a solid line) exists between two adjacent center frequencies in terms of time, the center frequency existing between the two center frequencies is respectively arranged at intervals with the two center frequencies, the time length occupied by one center frequency in one path of scattered light interference electrical signal plus the time interval occupied by the center frequency with the adjacent center frequency belonging to the other path of scattered light interference electrical signal is equal to t0, the center frequencies of the two paths of scattered light interference electrical signals are equal, and the time lengths occupied by the two paths of scattered light interference electrical signals are the same. For the chirped pulse light and the scattered light interference electric signal, the longer the duration occupied by each central frequency is, the better the signal-to-noise ratio is, and the larger the bandwidth corresponding to each central frequency is, the higher the resolution is.
After the acquisition card transmits the digital signals to the processor, the processor can demodulate the digital signals by adopting a matched filtering method to obtain scattering complex signals corresponding to each chirped pulse light. For the scattered complex signals demodulated in the corresponding time period, the average value of the amplitudes of the scattered complex signals corresponding to the chirped pulse lights with different carrier frequencies and polarizations can be taken as loss information of the corresponding position on the optical fiber, and because the phase change of the scattered complex signals is in direct proportion to the vibration intensity received by the optical fiber, the phase of the scattered complex signals can be differentially demodulated to obtain the vibration information of the corresponding position on the optical fiber.
It can be seen from the above embodiments that, since the prior art adopts a coherent light source when vibration detection is performed by using a sensitive optical time domain reflection technology, the test signal of which has a fading phenomenon and cannot reflect the optical fiber loss visually, the present invention modulates a laser signal before transmitting the laser signal to an optical fiber, modulates the laser signal into a series of chirped pulse lights whose chirped center frequencies change periodically, modulates the polarization states of the chirped pulse lights of each frequency band to switch the polarization states of the chirped pulse lights in two orthogonal states, and performs polarization division detection by using a polarization diversity detector during detection, thereby eliminating the fading phenomenon of the test signal when vibration detection is performed by using the coherent light source, so that the coherent light source can be used to perform optical fiber loss detection, that is, the present invention uses the same system and the same optical fiber, the loss and distributed vibration of the optical fiber can be measured simultaneously, and the test data and the test result are consistent, so that the field investigation and verification are facilitated. Secondly, when the prior art adopts the optical time domain reflection technology to detect the optical fiber loss, the spatial resolution is lower at a long distance, and the accurate corresponding relation between the optical fiber loss fault point and the actual geographic position cannot be determined, because the coherent light source can realize distributed vibration detection, and the detection spatial resolution is high, therefore, when the coherent light source is adopted to simultaneously carry out optical fiber vibration and loss detection, the loss information and the vibration information at each position on the optical fiber are obtained by analysis and are based on the same demodulated scattering complex signal, so that the corresponding relation between the optical fiber loss, the vibration and each position on the optical fiber can be established, and the optical fiber loss can be corresponding to each position on the optical fiber even if the spatial resolution of the optical fiber loss detection is higher at a long distance, thereby providing a feedback basis for fault positioning and routing inspection. Moreover, the second path of laser signals and Rayleigh scattering light are subjected to beat frequency during detection to carry out coherent detection, so that the signal-to-noise ratio and the dynamic range of the system have greater advantages compared with a traditional loss or vibration detection system based on direct detection. In addition, when the digital signal is demodulated, the processor demodulates the digital signal by adopting a matched filtering method, and combines the chirped pulse light and a matched filtering demodulation scheme, so that the optimal signal-to-noise ratio can be ensured, and the higher spatial resolution can be realized even if the sensing distance is longer. The invention has great significance for fault routing inspection and health monitoring by using the optical fiber.
In one example, a narrow linewidth laser with a center wavelength of 1550.12nm and a linewidth of 100Hz emits a continuous laser signal, an optical frequency modulator modulates the laser frequency into steps as shown in fig. 4, the period t0 of the steps is equal to the transit time of an optical pulse in an optical fiber, the interval of the frequency steps is 100MHz, the number of the steps is 20, a coupler divides the laser into two paths according to a splitting ratio of 1:1, the upper branch is signal light, and the lower branch is reference light. The continuous laser is modulated into chirped pulse light with the chirped signal center frequency of 200MHz, the chirped range of 150MHz and the time width of 1 microsecond by the modulator in the upper branch path, then the polarization state of the chirped pulse light is switched in two orthogonal states by the third modulator, the modulated chirped pulse light is amplified by the optical fiber amplifier and then injected into the optical fiber through the circulator, and the optical fiber is a long-distance common single-mode optical fiber. The scattered light and the reference light enter a polarization diversity detector, two paths of orthogonal polarization electric signals are collected by an acquisition card, and the sampling rate of the acquisition card is 1 Gsa/s.
In another example, laser frequency modulation can be achieved by current regulation, the center frequency of the laser and the current can be approximately in a linear relationship, and laser frequency modulation as shown in fig. 4 can be achieved by outputting a stepped signal through the current modulator, and the laser frequency interval is 500 MHz. The subsequent modulation and processing are the same as in the above example and will not be described again.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
It will be understood that the invention is not limited to the precise arrangements described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the invention is to be controlled solely by the appended claims.
Claims (9)
1. An optical fiber distributed vibration and loss simultaneous detection system is characterized by comprising a laser, a coupler, a first modulator, a second modulator, a third modulator, an optical fiber amplifier, a circulator, an optical fiber, a polarization diversity detector, an acquisition card and a processor, wherein the output end of the laser is connected with the input end of the coupler, the first output end of the coupler is connected with the first end of the circulator sequentially through the second modulator, the third modulator and the optical fiber amplifier, the second end of the circulator is connected with one end of the optical fiber, the third end of the circulator is connected with the first input end of the polarization diversity detector, the second output end of the coupler is connected with the second input end of the polarization diversity detector, and the output end of the polarization diversity detector is connected with the processor through the acquisition card;
the first modulator modulates the laser so that the laser provides a laser signal with a periodically-changed center frequency to the coupler;
the coupler divides the laser signals into two paths, the first path of laser signals is transmitted to the second modulator, and the second path of laser signals is transmitted to the polarization diversity detector;
the second modulator modulates the intensity and the frequency of the first path of laser signal to form a series of chirped pulse light with the chirped center frequency changing periodically;
the polarization modulator modulates the polarization state of the chirped pulse light of each frequency band so as to switch the polarization state of the chirped pulse light in two orthogonal states, thereby weakening the polarization fading in coherent demodulation;
the optical amplifier amplifies the chirped pulse light after polarization adjustment, sends the chirped pulse light after amplification to the first end of the circulator, and then sends the chirped pulse light to the optical fiber from the second end of the circulator;
after receiving the chirped pulse light, the optical fiber generates backward-transmitted Rayleigh scattering light, and the Rayleigh scattering light is transmitted to the second end of the circulator and then transmitted to the polarization diversity detector from the third end of the circulator;
the polarization diversity detector beats the second path of laser signals and Rayleigh scattering light to generate two paths of scattering light interference electric signals with mutually orthogonal polarization;
the acquisition card acquires the two paths of scattered light interference electric signals with mutually orthogonal polarization and converts the two paths of scattered light interference electric signals into digital signals;
the processor demodulates the digital signals to obtain scattering complex signals corresponding to each chirped pulse light, obtains loss information of each position on the optical fiber according to the amplitude of the scattering complex signals, and obtains vibration information of each position on the optical fiber according to the phase of the scattering complex signals.
2. The fiber distributed vibration and loss simultaneous detection system according to claim 1, wherein the first modulator is an optical frequency modulator, an output end of the laser is connected to an input end of the optical frequency modulator, an output end of the optical frequency modulator is connected to an input end of the coupler, the laser is used for generating an original laser signal, and the optical frequency modulator performs optical frequency modulation on the original laser signal to generate a laser signal with a periodically-changing center frequency and provide the laser signal to the coupler;
or, the first modulator is a current modulator, an output end of the current modulator is connected to a modulation end of the laser, an output end of the laser is connected to an input end of the coupler, and the current modulator is configured to modulate a current of the laser, so that the laser outputs a laser signal whose center frequency changes periodically;
or, the first modulator is a temperature modulator, an output end of the temperature modulator is connected to a modulation end of the laser, an output end of the laser is connected to an input end of the coupler, and the temperature modulator is used for modulating the temperature of the laser, so that the laser outputs a laser signal with a periodically-changing central frequency.
3. The fiber optic distributed simultaneous vibration and loss detection system of claim 1, wherein the laser signal periodically varying for said center frequency occupies the same time duration and is continuous in time for each center frequency.
4. The optical fiber distributed vibration and loss simultaneous detection system according to claim 3, wherein for the laser signal with the center frequency varying periodically, the bandwidth corresponding to each center frequency is an integer multiple of a set value, the lower limit of the bandwidth of each center frequency is 0, and the occupied time period t0 of each center frequency is greater than 2 × n × L/c, where n represents the refractive index of the optical fiber, L represents the length of the optical fiber, and c represents the speed of light.
5. The fiber distributed vibration and loss simultaneous detection system according to claim 1, wherein for the chirped pulse light with the chirped center frequency periodically changing, the bandwidth and pulse width of each chirped pulse light are the same, and the duration occupied by each chirped center frequency is the same but the two adjacent chirped center frequencies are both set at intervals in time.
6. The fiber optic distributed vibration and loss simultaneous detection system according to any one of claims 3 to 5, wherein for each scattered light interference electrical signal, each center frequency is equal and occupies the same time period, but two adjacent center frequencies are spaced apart in time, the bandwidth corresponding to each center frequency is equal and the instantaneous frequency in the corresponding frequency band changes with the same set slope along the time.
7. The fiber optic distributed vibration and loss simultaneous detection system according to claim 6, wherein for the chirped pulsed light and the scattered light interference electrical signal, the longer the duration occupied by each center frequency, the better the signal-to-noise ratio, and the larger the bandwidth corresponding to each center frequency, the higher the resolution.
8. The fiber distributed vibration and loss simultaneous detection system according to claim 1, wherein the processor demodulates the digital signal by using a matched filtering method to obtain a scattered complex signal corresponding to each chirped pulse light.
9. The optical fiber distributed vibration and loss simultaneous detection system according to claim 1, wherein for the scattered complex signals demodulated in the corresponding time period, an average value of amplitudes of the scattered complex signals corresponding to the chirped pulsed light with different carrier frequencies and polarizations is taken as loss information at the corresponding position on the optical fiber, and a phase of the scattered complex signals is differentially demodulated to obtain vibration information at the corresponding position on the optical fiber.
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