A multi-edge-band chirp modulation DAS system and a working method thereof

Abstract

The application discloses a multi-edge-band chirp modulation DAS system and a working method thereof, and relates to the technical field of distributed acoustic sensing. The DAS system comprises a narrow-line-width laser, a fiber coupler, a phase modulator, an electro-optical modulator, an erbium-doped fiber amplifier, a fiber ring, a dense wavelength division multiplexer, an optical-electricity balanced detector, a data acquisition card, an arbitrary waveform generator and a direct current source. The application modulates continuous light with equal amplitude and multiple frequencies by using the phase modulator. The frequency number of the light wave is related to the harmonic number of the microwave modulation signal, and the frequency interval is determined by the base frequency of the microwave modulation signal. The continuous light frequency can be flexibly modulated by adjusting the microwave modulation signal, and the modulation bandwidth is large. The beat frequency signal detected is compressed into a single frequency signal, and then the phase information is demodulated, so that the vibration signal along the sensing fiber can be detected, and the spatial resolution of the system depends on the chirp sweep range, and the spatial resolution is high.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of distributed acoustic sensing technology, in particular to a multi-sideband chirp modulation DAS system and a working method thereof. BACKGROUND

[0002] The distributed acoustic sensing (DAS) technology has unique advantages such as fast measurement speed and high detection sensitivity, but due to the use of high-coherence light sources in the existing system, the position light signal signal-to-noise ratio is extremely low due to the influence of interference effect, which is a "dead zone" for phase demodulation, and the demodulation error is large.

[0003] In order to suppress the phase demodulation error caused by the "dead zone" of the beat frequency signal in the DAS system, researchers have proposed a large number of solutions, such as using special optical fibers such as multi-mode, few-mode and multi-core optical fibers, and scattering enhanced point optical fibers as sensing units, or using multi-frequency, multi-wavelength and multi-phase pulse modulation multiplexing. It is meaningful to continue to improve the existing solutions to obtain better sensing performance. SUMMARY

[0004] In view of the above problems, the present application provides a multi-sideband chirp modulation DAS system and a working method thereof to suppress the phase demodulation error caused by the "dead zone" of the beat frequency signal in the DAS system.

[0005] According to an aspect of the present application, a multi-sideband chirp modulation DAS system is provided, which comprises: a narrow linewidth laser 1, a first optical fiber coupler 2, a phase modulator 3, an electro-optical modulator 4, a first erbium-doped fiber amplifier 5, an optical fiber ring 6, a second erbium-doped fiber amplifier 7, a dense wavelength division multiplexer 8, a second optical fiber coupler 9, an optical-electricity balance detector 10, a data acquisition card 11, an arbitrary waveform generator 12, and a direct current source 13.

[0006] The optical signal output end of the narrow linewidth laser 1 is in communication with the optical signal input end of the first optical fiber coupler 2, and the optical signal output ends of the first optical fiber coupler 2 are in communication with the optical signal input end of the phase modulator 3 and the optical signal input end of the second optical fiber coupler 9, respectively.

[0007] The optical signal output end of the phase modulator 3 is in communication with the optical signal input end of the electro-optical modulator 4, the optical signal output end of the electro-optical modulator 4 is in communication with the optical signal input end of the first erbium-doped fiber amplifier 5, the optical signal output end of the first erbium-doped fiber amplifier 5 is in communication with a No. 1 port 6-1 of the optical fiber ring 6, and a No. 2 port 6-2 of the optical fiber ring 6 is in communication with a sensing optical fiber.

[0008] The third port 6-3 of the optical fiber circulator 6 is in communication with an optical signal input end of a second erbium-doped fiber amplifier 7, an optical signal output end of the second erbium-doped fiber amplifier 7 is in communication with an optical signal input end of a dense wavelength division multiplexer 8, and an optical signal output end of the dense wavelength division multiplexer 8 is in communication with an optical signal input end of a second optical fiber coupler 9;

[0009] An optical signal output end of the second optical fiber coupler 9 is in communication with an optical signal input end of an opto-electric balance detector 10, and an electrical signal output end of the opto-electric balance detector 10 is in communication with a data acquisition card 11;

[0010] A radio frequency output end of an arbitrary waveform generator 12 is in communication with a radio frequency signal input end of the phase modulator 3, a radio frequency signal input end of the electro-optical modulator 4 and a trigger signal input end of the data acquisition card 11 respectively.

[0011] An output end of a direct current source 13 is in communication with a bias voltage input end of the electro-optical modulator 4.

[0012] In one possible implementation, the narrow line width laser 1 is a polarization maintaining laser, the output power is 10 mW, the wavelength is 1550.12 nm, and the line width is 1 kHz.

[0013] In one possible implementation, the first optical fiber coupler 2 is a 1*2 polarization maintaining coupler, and the splitting ratio is 90:10; and the second optical fiber coupler 9 is a 2*2 coupler, and the splitting ratio is 50:50.

[0014] In one possible implementation, the phase modulator 3 is a polarization maintaining modulator, and the bandwidth is 10 GHz; and the electro-optical modulator 4 is a polarization maintaining modulator, and the bandwidth is 10 GHz and the extinction ratio is 30 dB.

[0015] In one possible implementation, the center transmission wavelength of the dense wavelength division multiplexer 8 is 1550.12 nm, and the 3dB transmission bandwidth is 0.20 nm; the 3dB working bandwidth of the opto-electric balance detector 10 is 5 GHz; and the sampling rate of the data acquisition card 11 is 10 GS / s, and the sampling resolution is 14 bit.

[0016] According to another aspect of the present application, a working method of a multi-edge-band chirp modulation DAS system is provided, and the working method is implemented based on the above-mentioned DAS system; the working method comprises:

[0017] The single frequency continuous light output by the narrow line width laser 1 is divided into two paths by the first optical fiber coupler 2: the upper path is used as the probe light of the DAS system, and the lower path is used as the reference light of the DAS system.

[0018] The continuous light is modulated by the phase modulator 3 into multi-frequency continuous light with equal amplitude, and then is modulated by the electro-optical modulator 4 into multi-sideband chirp pulse light with periodic linear sweep, and then is pre-amplified by the first erbium-doped fiber amplifier 5, and the amplified pulse light is injected into the sensing fiber through the optical fiber circulator 6;

[0019] The back Rayleigh scattering light signal returned by the sensing fiber is pre-amplified by the second erbium-doped fiber amplifier 7 through the optical fiber circulator 6, and then is filtered by the dense wavelength division multiplexer 8 to remove the ASE noise, and then is injected into the second optical fiber coupler 9 together with the downlink reference light to perform coherent beat frequency, the beat frequency result is photoelectrically converted by the photoelectric balanced detector 10, and is recorded by the data acquisition card 11;

[0020] The arbitrary waveform generator 12 is used to control the phase modulator 3 to modulate the continuous light into multi-frequency light with equal amplitude, is used to control the electro-optical modulator 4 to modulate the multi-frequency continuous light with equal amplitude into periodic linear sweep, and is used to control the data acquisition card 11 to collect the beat frequency signal;

[0021] The direct current source 13 is used to provide a bias voltage for the electro-optical modulator 4 to suppress the optical carrier frequency.

[0022] In one possible implementation, the multi-frequency band chirp signal collected by the data acquisition card 11 is transmitted to a computer, and the computer performs the following processing: the multi-frequency band chirp signal is compressed into a plurality of single-frequency signals with different frequencies; and the phase information is weighted and averaged with the amplitude as the weight.

[0023] In one possible implementation, the process of modulating the uplink continuous light into multi-frequency light with equal amplitude by the phase modulator 3 includes:

[0024] f c is the frequency of the continuous light output by the narrow linewidth laser 1, f m is the frequency of the microwave signal loaded on the phase modulator 3 by the arbitrary waveform generator 12, and the microwave signal m(t) is represented as:

[0025]

[0026] wherein γ k is a modulation index; k is the harmonic number of m(t); φ k is the phase of m(t); and t is time;

[0027] The time domain expression E m (t) of the modulated multi-frequency continuous light with equal amplitude is:

[0028]

[0029] wherein A is E mthe amplitude of (t).

[0030] In one possible implementation, the electro-optical modulator 4 modulates the continuous light E m The process of modulating the continuous light E

[0031] Let f1 and ΔF be the start frequency and the sweep bandwidth of the sweep signal loaded on the electro-optical modulator 4 by the arbitrary waveform generator 12, and the expression of the sweep signal is as follows:

[0032]

[0033] where A sweep is the amplitude of (t); T sweep is the width of (t); P is the width of (t); sweep rect(.) is a rectangular function;

[0034] The expression of the modulated multiband-chirped pulse light E p (t) is as follows:

[0035]

[0036] In one possible implementation, the 3dB working bandwidth f BPD of the photoelectric balanced detector 10 satisfies the following relationship:

[0037]

[0038] where N is the number of frequencies contained in E m (t).

[0039] In one possible implementation, the sampling rate S a of the data acquisition card 11 satisfies the following relationship:

[0040]

[0041] The beneficial technical effects of the present application are:

[0042] ​The application provides a multi-sideband chirp modulation DAS system and a working method thereof, which has the following advantages: 1) flexible frequency modulation: the equal-amplitude multi-frequency continuous light is modulated by a phase modulator, the frequency number of the light wave is related to the harmonic number of the microwave modulation signal, and the frequency interval is determined by the base frequency of the microwave modulation signal, so that the continuous light frequency can be flexibly modulated by adjusting the microwave modulation signal, and the modulation bandwidth is large; 2) large dynamic range and high spatial resolution: the long chirp pulse light is injected into the sensing optical fiber DAS system, and the system has a large dynamic range; the beat frequency signal detected is compressed into a single frequency signal, and then the phase information is demodulated, so that the vibration signal along the sensing optical fiber is detected, and the spatial resolution of the system depends on the chirp sweep range, and not on the pulse light width, and the spatial resolution is high. BRIEF DESCRIPTION OF DRAWINGS

[0043] The above and other objects, features and advantages of the present application will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. In the drawings, several embodiments of the present application are illustrated by way of example in which:

[0044] Figure 1 FIG. 1 is a structural schematic diagram of a multi-sideband chirp modulation DAS system according to the present application;

[0045] Figure 2 FIG. 2 is a schematic diagram of multi-frequency continuous light modulated by a phase modulator in an embodiment of the present application;

[0046] Figure 3 FIG. 3 is a schematic diagram of multi-sideband chirp pulse light modulated by a phase modulator and an electro-optical modulator in an embodiment of the present application;

[0047] Figure 4 FIG. 4 is a schematic diagram of up and down sideband chirp modulation of an electro-optical modulator in an embodiment of the present application;

[0048] Figure 5 FIG. 5 is an example diagram of a result of chirp pulse light compressed into a narrow pulse in the shape of a sine function in an embodiment of the present application;

[0049] Figure 6 FIG. 6 is an example diagram of a result of a beat frequency signal after pulse compression in an embodiment of the present application. DETAILED DESCRIPTION

[0050] The principles and spirits of the present application will be described below with reference to several exemplary embodiments. It should be understood that these embodiments are given only to enable those skilled in the art to better understand and implement the present application, and do not limit the scope of the present application in any way. On the contrary, these embodiments are provided to make the disclosure more thorough and complete, and to fully convey the scope of the disclosure to those skilled in the art.

[0051] The embodiment of the present invention proposes a DAS system with multi-sideband chirp modulation, such as Figure 1 As shown, the system includes: a narrow linewidth laser 1, a first fiber coupler 2, a phase modulator 3, an electro-optical modulator 4, a first erbium-doped fiber amplifier 5, a fiber circulator 6, a second erbium-doped fiber amplifier 7, a dense wavelength division multiplexer 8, a second fiber coupler 9, a photoelectric balanced detector 10, a data acquisition card 11, an arbitrary waveform generator 12, and a DC source 13;

[0052] The optical signal output end of the narrow linewidth laser 1 is connected to the optical signal input end of the first optical fiber coupler 2, and the optical signal output end of the first optical fiber coupler 2 is connected to the optical signal input end of the phase modulator 3 and the optical signal input end of the second optical fiber coupler 9 respectively. The optical signal output end of the phase modulator 3 is connected to the optical signal input end of the electro-optical modulator 4, and the optical signal output end of the electro-optical modulator 4 is connected to the optical signal input end of the first erbium-doped fiber amplifier 5. The optical signal output end of the first erbium-doped fiber amplifier 5 is connected to the first port 6-1 of the optical fiber circulator 6, the second port 6-2 of the optical fiber circulator 6 is connected to the sensing optical fiber 7, and the third port 6-3 of the optical fiber circulator 6 is connected to the second port 6-1 of the second erbium-doped fiber amplifier 7. The optical signal input end is connected, the optical signal output end of the second erbium-doped fiber amplifier 7 is connected to the optical signal input end of the dense wavelength division multiplexer 8, the optical signal output end of the dense wavelength division multiplexer 8 is connected to the optical signal input end of the second optical fiber coupler 9, the optical signal output end of the second optical fiber coupler 9 is connected to the optical signal input end of the photoelectric balance detector 10, the electrical signal output end of the photoelectric balance detector 10 is connected to the data acquisition card 11, and the RF output end of the arbitrary waveform generator 12 is simultaneously connected to the RF signal input end of the phase modulator 3, the RF signal input end of the electro-optical modulator 4 and the trigger signal input end of the data acquisition card 11; the output end of the DC source 13 is connected to the bias voltage input end of the electro-optical modulator 4.

[0053] In this embodiment, preferably, the narrow linewidth laser 1 is a polarization-maintaining laser with an output power of 10 mW, a wavelength of 1550.12 nm, and a linewidth of 1 kHz.

[0054] In this embodiment, preferably, the first optical fiber coupler 2 is a 1×2 polarization-maintaining coupler with a splitting ratio of 90:10; and the second optical fiber coupler 9 is a 2×2 coupler with a splitting ratio of 50:50.

[0055] In this embodiment, preferably, the phase modulator 3 is a polarization-maintaining modulator with a bandwidth of 10 GHz; the electro-optical modulator 4 is a polarization-maintaining modulator with a bandwidth of 10 GHz and an extinction ratio of 30 dB.

[0056] In this embodiment, preferably, the center transmission wavelength of the dense wavelength division multiplexer 8 is 1550.12 nm, and the 3dB transmission bandwidth is 0.20 nm.

[0057] In this embodiment, preferably, the 3dB working bandwidth of the photoelectric balance detector 10 is 5 GHz.

[0058] In this embodiment, preferably, the sampling rate of the data acquisition card 11 is 10 GS / s, and the sampling resolution is 14 bit.

[0059] Another embodiment of the present application provides a working method of a multi-edge-band chirp-modulated DAS system, which is realized based on the multi-edge-band chirp-modulated DAS system described above; the working method comprises the following steps:

[0060] The single-frequency continuous light output by the narrow-linewidth laser 1 is divided into an upper path and a lower path through the first optical fiber coupler 2; the upper path is the probe light of the DAS system, and the lower path is the reference light of the DAS system; the continuous light in the upper path is modulated into multi-frequency continuous light with equal amplitude by the phase modulator 3, and then is modulated into multi-edge-band chirp pulse light by the electro-optical modulator 4 through periodic linear sweep modulation, and then is pre-amplified by the first erbium-doped fiber amplifier 5; the pulse light after amplification is injected into the sensing optical fiber through the optical fiber circulator 6; the backscattering Rayleigh scattering light signal in the sensing optical fiber is injected into the second erbium-doped fiber amplifier 7 through the optical fiber circulator 6 for pre-amplification, and then the ASE noise is filtered out by the dense wavelength division multiplexer 8, and then the pulse light is injected into the second optical fiber coupler 9 together with the reference light in the lower path for coherent beat frequency, the beat frequency result is converted into photoelectricity by the photoelectric balance detector 10, and then is recorded by the data acquisition card 11. The arbitrary waveform generator 12 is used for controlling the phase modulator 3 to modulate the continuous light into multi-frequency light with equal amplitude, and is used for controlling the electro-optical modulator 4 to modulate the multi-frequency continuous light with equal amplitude into multi-edge-band chirp pulse light through periodic linear sweep modulation; at the same time, the data acquisition card 11 is used for collecting the beat frequency signal. The direct current source 13 is used for providing a bias voltage for the electro-optical modulator 4, so as to realize suppression of the optical carrier frequency.

[0061] The multi-frequency band chirp signal collected is compressed into a plurality of single-frequency signals with different frequencies, and the amplitude size is used as a weight, and the phase information is processed through weighted average, so as to finally realize suppression of the coherent fading "dead zone" in the DAS system.

[0062] Figure 2 A schematic diagram of the phase modulator 3 modulating the multi-frequency continuous light in the system is shown in FIG. 4; Figure 3 A schematic diagram of the phase modulator 3 and the electro-optical modulator 4 jointly modulating the multi-edge-band chirp pulse light is shown in FIG. 5; it can be seen that the modulated multi-frequency continuous light is equal-amplitude multi-edge-band light; and the modulated multi-edge-band chirp pulse light is linearly swept on both sides of each frequency.

[0063] Figure 4The schematic diagram of the up and down sideband chirp modulation of the electro-optical modulator 4; the down sideband light expands the frequency of the optical signal from low to high, and the up sideband light expands the frequency of the optical signal from high to low.

[0064] Figure 5 The result of the chirp pulse light compressed into a narrow pulse in the shape of a sine function, at this time, the spatial resolution of the system depends on the main lobe half-width of the sine function, that is, depends on the frequency range of the chirp pulse light.

[0065] Figure 6 The result of the beat signal after pulse compression, it can be seen that the compression result is a single frequency signal.

[0066] In this embodiment, preferably, the process of the phase modulator 3 modulating the continuous light into equal-amplitude multi-frequency modulation is as follows:

[0067] Firstly, define f c The frequency of the continuous light output by the narrow linewidth laser 1; f m The microwave frequency loaded on the phase modulator 3 by the arbitrary waveform generator 12; the microwave modulation signal m(t) can be expressed as:

[0068]

[0069] Wherein, γ is the modulation index; k is the harmonic number of m(t); φ k The phase of m(t); t is time.

[0070] When m(t) is loaded on the phase modulator 3, the single-frequency continuous light is modulated into equal-amplitude multi-frequency continuous light, and the time-domain expression E m (t) is:

[0071]

[0072] Wherein, A is the amplitude of E m (t).

[0073] In this embodiment, preferably, the process of the electro-optical modulator 4 modulating the equal-amplitude multi-frequency continuous light E m (t) into multi-sideband chirp pulse light is as follows:

[0074] Define f1 and ΔF as the sweep signal m sweep (t) loaded on the electro-optical modulator 4 by the arbitrary waveform generator 12; f sweep The expression of m sweep (t) is as follows:

[0075]

[0076] Wherein, A sweepAmplitude of (t); T P2 m sweep Width of (t); f m Should be greater than or equal to 2ΔF; rect(.) is a rectangular function.

[0077] When m sweep (t) is loaded on the electro-optical modulator 4, E m (t) is modulated into a multi-sideband chirp pulse light E p (t), the expression is:

[0078]

[0079] In this embodiment, preferably, the 3dB operating bandwidth f BPD of the photoelectric balance detector 10 satisfies the following relationship:

[0080]

[0081] Wherein, N is the number of frequencies contained in E m (t).

[0082] In this embodiment, preferably, the sampling rate S a of the data acquisition card 11 satisfies the following relationship:

[0083]

[0084] The beat frequency signal collected by the data acquisition card 11 once can obtain 2N signals with different frequencies after pulse compression, and the phase information is weighted and averaged, and finally the suppression of the coherent fading "dead zone" in the DAS system is realized.

[0085] The present application provides a multi-sideband chirp modulation DAS system and its working method, which has the following advantages: 1) flexible frequency modulation: using a phase modulator to modulate continuous light with equal amplitude and multiple frequencies, the number of frequencies of the light wave is related to the harmonic number of the microwave modulation signal, and the frequency interval is determined by the fundamental frequency of the microwave modulation signal, so that the continuous light frequency can be flexibly modulated by adjusting the microwave modulation signal, and the modulation bandwidth is large; 2) large dynamic range and high spatial resolution: by injecting long chirp pulse light into the sensing optical fiber DAS system, it has a large dynamic range; the beat frequency signal detected is pulse compressed into a single frequency signal, and then the phase information is demodulated to detect the vibration signal along the sensing optical fiber, and the spatial resolution of the system depends on the chirp sweep range, not the pulse light width, so the spatial resolution is high.

[0086] While the principles and spirit of the application have been described with reference to several specific embodiments, it is to be understood that the application is not limited to the specific embodiments disclosed, and that the division of the aspects is not meant to imply that features from these aspects cannot be combined to benefit, but is merely for ease of presentation. The application is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the claims appended hereto.

Claims

1. A method for operating a DAS system with multi-sideband chirp modulation, characterized in that: The working method comprises: The single-frequency continuous light output by the narrow linewidth laser (1) is divided into two paths, an upper path and an lower path, via a first optical fiber coupler (2): the upper path serves as a detection light of the DAS system, and the lower path serves as a reference light of the DAS system; The incoming continuous light is modulated into a multi-frequency continuous light of equal amplitude by a phase modulator (3), and then modulated into a multi-sideband chirped pulse light by a periodic linear frequency sweep by an electro-optical modulator (4), and then power pre-amplified by a first erbium-doped fiber amplifier (5). The amplified pulse light is injected into the sensing fiber through a fiber circulator (6); The backscattered Rayleigh light signal returned by the sensing fiber is then injected into the second erbium-doped fiber amplifier (7) through the fiber circulator (6) for power pre-amplification, and then filtered out ASE noise through the dense wavelength division multiplexer (8). It is then injected into the second fiber coupler (9) together with the downlink reference light for coherent frequency beat. The beat frequency result is converted into photoelectricity by the photoelectric balance detector (10) and recorded by the data acquisition card (11); The arbitrary waveform generator (12) is used to control the phase modulator (3) to perform equal-amplitude multi-frequency modulation on the continuous light, is used to control the electro-optical modulator (4) to perform periodic linear frequency sweep modulation on the equal-amplitude multi-frequency continuous light, and is used to control the data acquisition card (11) to collect the beat frequency signal; The DC source (13) is used to provide a bias voltage for the electro-optical modulator (4) to suppress the optical carrier frequency; The multi-band chirp signal collected by the data acquisition card (11) is transmitted to the computer, and the computer performs the following processing: compressing the multi-band chirp signal into multiple single-frequency signals of different frequencies through pulse compression; performing weighted averaging processing on the phase information with the amplitude as the weight; The process of the phase modulator (3) performing equal-amplitude multi-frequency modulation on the added continuous light includes: definition is the frequency of the continuous light output by the narrow linewidth laser (1), is the frequency of the microwave signal loaded on the phase modulator (3) by the arbitrary waveform generator (12), and the microwave signal Expressed as: in, is the modulation index; k is harmonic order; for The phase of ; t is the time; Then the time domain expression of the modulated equal-amplitude multi-frequency continuous light is for: ； in, for Amplitude; The electro-optic modulator (4) converts the equal-amplitude multi-frequency continuous light The process of modulating into multi-sideband chirped pulse light includes: definition and are the starting frequency and sweep bandwidth of the sweep signal loaded by the arbitrary waveform generator (12) on the electro-optical modulator (4); the expression of the sweep signal is as follows: in, for Amplitude; for width; ; is a rectangular function; The modulated multi-sideband chirped pulse light The expression is: 。 2. The operating method of a DAS system with multi-sideband chirp modulation according to claim 1, characterized in that: 3dB operating bandwidth of the photoelectric balanced detector (10) Satisfies the following relationship: ； Where N is the number of frequencies included; Sampling rate of the data acquisition card (11) Satisfies the following relationship: 。 3. The operating method of a DAS system with multi-sideband chirp modulation according to claim 1 or 2, characterized in that: The DAS system for realizing the multi-sideband chirp modulation of the working method comprises: a narrow linewidth laser (1), a first optical fiber coupler (2), a phase modulator (3), an electro-optical modulator (4), a first erbium-doped optical fiber amplifier (5), an optical fiber circulator (6), a second erbium-doped optical fiber amplifier (7), a dense wavelength division multiplexer (8), a second optical fiber coupler (9), a photoelectric balanced detector (10), a data acquisition card (11), an arbitrary waveform generator (12), and a DC source (13); The optical signal output end of the narrow linewidth laser (1) is connected to the optical signal input end of the first optical fiber coupler (2), and the optical signal output end of the first optical fiber coupler (2) is respectively connected to the optical signal input end of the phase modulator (3) and the optical signal input end of the second optical fiber coupler (9); The optical signal output end of the phase modulator (3) is connected to the optical signal input end of the electro-optical modulator (4), the optical signal output end of the electro-optical modulator (4) is connected to the optical signal input end of the first erbium-doped fiber amplifier (5), the optical signal output end of the first erbium-doped fiber amplifier (5) is connected to the first port (6-1) of the optical fiber circulator (6), and the second port (6-2) of the optical fiber circulator (6) is connected to the sensing optical fiber; The third port (6-3) of the optical fiber circulator (6) is connected to the optical signal input end of the second erbium-doped optical fiber amplifier (7), the optical signal output end of the second erbium-doped optical fiber amplifier (7) is connected to the optical signal input end of the dense wavelength division multiplexer (8), and the optical signal output end of the dense wavelength division multiplexer (8) is connected to the optical signal input end of the second optical fiber coupler (9); The optical signal output end of the second optical fiber coupler (9) is connected to the optical signal input end of the photoelectric balance detector (10), and the electrical signal output end of the photoelectric balance detector (10) is connected to the data acquisition card (11); The radio frequency output end of the arbitrary waveform generator (12) is respectively connected to the radio frequency signal input end of the phase modulator (3), the radio frequency signal input end of the electro-optical modulator (4), and the trigger signal input end of the data acquisition card (11); The output end of the DC source (13) is connected to the bias voltage input end of the electro-optical modulator (4).

4. The operating method of a multi-sideband chirp-modulated DAS system according to claim 3, characterized in that: The narrow linewidth laser (1) is a polarization-maintaining laser with an output power of 10 mW, a wavelength of 1550.12 nm, and a linewidth of 1 kHz.

5. The operating method of a multi-sideband chirp modulation DAS system according to claim 3, characterized in that: The first optical fiber coupler (2) is a 1×2 polarization-maintaining coupler with a splitting ratio of 90:10; the second optical fiber coupler (9) is a 2×2 coupler with a splitting ratio of 50:

50.

6. The operating method of a DAS system with multi-sideband chirp modulation according to claim 3, characterized in that: The phase modulator (3) is a polarization-maintaining modulator with a bandwidth of 10 GHz; the electro-optical modulator (4) is a polarization-maintaining modulator with a bandwidth of 10 GHz and an extinction ratio of 30 dB.

7. The operating method of a DAS system with multi-sideband chirp modulation according to claim 3, characterized in that: The central transmission wavelength of the dense wavelength division multiplexer (8) is 1550.12 nm, and the 3dB transmission bandwidth is 0.20 nm; the 3dB operating bandwidth of the photoelectric balance detector (10) is 5 GHz; the sampling rate of the data acquisition card (11) is 10 GS / s, and the sampling resolution is 14 bits.

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