Multi-sideband chirp modulation DAS system and working method thereof

Abstract

The invention discloses a multi-sideband chirp modulation DAS system and a working method thereof, and relates to the technical field of distributed sound wave sensing. The DAS system comprises a narrow linewidth laser, an optical fiber coupler, a phase modulator, an electro-optical modulator, an erbium-doped optical fiber amplifier, an optical fiber circulator, a dense wavelength division multiplexer, a photoelectric balance detector, a data acquisition card, an arbitrary waveform generator, a direct current source and the like. The phase modulator is used for modulating constant-amplitude multi-frequency continuous light, the frequency number of light waves is related to the harmonic number of a microwave modulation signal, the frequency interval is determined by the fundamental 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; detected beat frequency signals are compressed into single-frequency signals through pulses, phase information of the single-frequency signals is demodulated, vibration signals along the sensing optical fiber can be detected, the spatial resolution of the system depends on the chirp frequency sweeping range, and the spatial resolution is high.

Description

Technical Field

[0001] The present invention relates to the technical field of distributed acoustic wave sensing, and in particular to a multi-sideband chirp-modulated DAS system and a working method thereof. Background Art

[0002] Distributed acoustic sensing (DAS) technology has unique advantages such as fast measurement speed and high detection sensitivity. However, due to the use of high-coherence light sources in existing systems, the interference effect causes the signal-to-noise ratio of the optical signal at the position of coherent cancellation to be extremely low, which is the "dead zone" of phase demodulation and results in a large demodulation error.

[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, scattering-enhanced point optical fibers as sensing units, or using multi-frequency, multi-wavelength, multi-phase pulse modulation multiplexing, etc. It is meaningful to continue to improve the solutions to obtain better sensing performance based on the existing solutions. Summary of the invention

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

[0005] According to one aspect of the present invention, a DAS system with multi-sideband chirp modulation is proposed, which includes: a narrow linewidth laser 1, a first fiber coupler 2, a phase modulator 3, an electro-optic 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;

[0006] 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;

[0007] 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;

[0008] The third port 6-3 of the optical fiber circulator 6 is connected to the optical signal input end of the second erbium-doped fiber amplifier 7, 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, 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;

[0009] 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;

[0010] The radio frequency output end of the arbitrary waveform generator 12 is 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 respectively;

[0011] The output end of the DC source 13 is connected to the bias voltage input end of the electro-optic modulator 4 .

[0012] In one possible implementation, 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.

[0013] In one possible implementation, 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.

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

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

[0016] According to another aspect of the present invention, a working method of a DAS system with multi-sideband chirp modulation is proposed. The working method is implemented based on the DAS system described above; the working method comprises:

[0017] The single-frequency continuous light output by the narrow linewidth laser 1 is divided into two paths, the upper path is used as the detection light of the DAS system, and the lower path is used as the reference light of the DAS system through the first fiber coupler 2;

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

[0019] 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, and then injected into the second fiber coupler 9 together with the downlink reference light for coherent beat frequency. The beat frequency result is photoelectrically converted by the photoelectric balanced detector 10 and recorded by the data acquisition card 11;

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

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

[0022] In one possible implementation, the multi-band chirp signal collected by the data acquisition card 11 is transmitted to a 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; and performing weighted averaging processing on the phase information with the amplitude as the weight.

[0023] In one possible implementation manner, the process of the phase modulator 3 performing equal-amplitude multi-frequency modulation on the added continuous light includes:

[0024] Define 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 expressed as:

[0025]

[0026] Among them, γ k is the modulation index; k is the harmonic order of m(t); φ k is the phase of m(t); t is time;

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

[0028]

[0029] Among them, A is E m(t) amplitude.

[0030] In one possible implementation, the electro-optic modulator 4 converts the equal-amplitude multi-frequency continuous light E m (t) The process of modulating into multi-sideband chirped pulse light includes:

[0031] Define f1 and ΔF as the starting frequency and the sweep bandwidth of the sweep signal loaded on the electro-optic modulator 4 by the arbitrary waveform generator 12; the expression of the sweep signal is as follows:

[0032]

[0033] Among them, A sweep is m sweep (t) amplitude; T P is m sweep (t) width; rect(.) is a rectangle function;

[0034] Then the modulated multi-sideband chirped pulse light E p The expression of (t) is:

[0035]

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

[0037]

[0038] Where N is E m (t) The number of frequencies included.

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

[0040]

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

[0042] The present invention proposes a multi-sideband chirp-modulated DAS system and a working method thereof, which have the following advantages: 1) Flexible frequency modulation: a phase modulator is used to modulate equal-amplitude multi-frequency continuous light, the frequency number of the light wave is related to the harmonic order of the microwave modulation signal, and the frequency interval is determined by the fundamental frequency of the microwave modulation signal, so 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: a sensing optical fiber DAS system is injected with long chirp pulse light, which has a large dynamic range; the detected beat frequency signal is compressed into a single-frequency signal through pulse compression, and then its phase information is demodulated to realize the detection of vibration signals along the sensing optical fiber, and the spatial resolution of the system depends on the chirp sweep frequency range, but not on the pulse light width, and the spatial resolution is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The above and other objects, features and advantages of the exemplary embodiments of the present invention will become readily understood by reading the following detailed description with reference to the accompanying drawings. In the accompanying drawings, several embodiments of the present invention are shown in an exemplary and non-limiting manner, in which:

[0044] Figure 1 A schematic structural diagram of a DAS system with multi-sideband chirp modulation according to the present invention;

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

[0046] Figure 3 Schematic diagram of a multi-sideband chirped pulse light jointly modulated by a phase modulator and an electro-optical modulator in an embodiment of the present invention;

[0047] Figure 4 Schematic diagram of chirp modulation of upper and lower sidebands of an electro-optic modulator in an embodiment of the present invention;

[0048] Figure 5 This is an example diagram of the result of chirped pulse light being compressed into a narrow pulse in the shape of a sinc function in an embodiment of the present invention;

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

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

[0051] The embodiment of the present invention provides 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-optic 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, 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, 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 6-4 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-optic 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 central 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 operating 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 bits.

[0059] Another embodiment of the present invention provides a working method of a DAS system with multi-sideband chirp modulation, and the working method is implemented based on the DAS system with multi-sideband chirp modulation described above; the working method includes:

[0060] The single-frequency continuous light output by the narrow linewidth laser 1 is divided into two paths, an upper path and an lower path, by the first optical fiber coupler 2; the upper path is the detection light of the DAS system; the lower path is the reference light of the DAS system; the upper path continuous light is modulated into multi-frequency continuous light of equal amplitude by the phase modulator 3, and then periodically linearly swept modulated into multi-sideband chirped pulse light by the electro-optical modulator 4, and then power pre-amplified by the first erbium-doped fiber amplifier 5, and the amplified pulse light is injected into the sensing optical fiber through the optical fiber circulator 6; the back Rayleigh scattered light signal in the sensing optical fiber is injected into the second erbium-doped fiber amplifier 7 through the optical fiber circulator 6 for power pre-amplification, and the ASE noise is filtered out by the dense wavelength division multiplexer 8, and then injected into the second optical fiber coupler 9 together with the lower path reference light for coherent beat frequency, and the beat frequency result is photoelectrically converted 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 modulate the continuous light with equal amplitude and multiple frequencies, and to control the electro-optic modulator 4 to perform periodic linear frequency sweep modulation on the multi-frequency continuous light with equal amplitude into a multi-sideband chirped pulse light; at the same time, it 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-optic modulator 4 to suppress the optical carrier frequency.

[0061] The collected multi-band chirp signals are pulse compressed into multiple single-frequency signals of different frequencies, and the phase information is weighted and averaged with the amplitude as the weight, ultimately achieving the suppression of the coherent fading "dead zone" in the DAS system.

[0062] Figure 2 A schematic diagram of the phase modulator 3 in the system modulating multi-frequency continuous light; Figure 3 Schematic diagram of the phase modulator 3 and the electro-optic modulator 4 jointly modulating the multi-sideband chirped pulse light; it can be seen that the modulated multi-frequency continuous light is equal-amplitude multi-sideband light; the modulated multi-sideband chirped pulse light is linearly swept on both sides of each frequency.

[0063] Figure 4It is a schematic diagram of the upper and lower sideband chirp modulation of the electro-optical modulator 4 in the system; the lower sideband light extends the frequency of the optical signal from low to high, while the upper sideband light extends the frequency of the optical signal from high to low.

[0064] Figure 5 It is the result of chirped pulse light being compressed into a narrow pulse in the shape of a sinc function. At this time, the spatial resolution of the system depends on the half-width of the main lobe of the sinc function, that is, on the frequency range of the chirped pulse light.

[0065] Figure 6 This is the result of pulse compression of the beat frequency signal. 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 performing equal-amplitude multi-frequency modulation on the continuous light is as follows:

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

[0068]

[0069] Where γ is the modulation index; k is the harmonic order of m(t); φ k is 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. The time domain expression E m (t) is:

[0071]

[0072] Where A is E m (t) amplitude.

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

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

[0075]

[0076] Among them, A sweep is m sweep(t) amplitude; T P2 is m sweep (t) width; 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-optic modulator 4, E m (t) is modulated into multi-sideband chirped pulse light E p (t), the expression is:

[0078]

[0079] In this embodiment, preferably, the 3dB working bandwidth f of the photoelectric balanced detector 10 BPD Satisfies the following relationship:

[0080]

[0081] Where N is E m (t) The number of frequencies included.

[0082] In this embodiment, preferably, the sampling rate S of the data acquisition card 11 is a 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 with the amplitude as the weight, finally realizing the suppression of the coherent fading "dead zone" in the DAS system.

[0085] The present invention proposes a multi-sideband chirp-modulated DAS system and a working method thereof, which have the following advantages: 1) Flexible frequency modulation: a phase modulator is used to modulate equal-amplitude multi-frequency continuous light, the frequency number of the light wave is related to the harmonic order of the microwave modulation signal, and the frequency interval is determined by the fundamental frequency of the microwave modulation signal, so 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: a sensing optical fiber DAS system is injected with long chirp pulse light, which has a large dynamic range; the detected beat frequency signal is compressed into a single-frequency signal through pulse compression, and then its phase information is demodulated to realize the detection of vibration signals along the sensing optical fiber, and the spatial resolution of the system depends on the chirp sweep frequency range, but not on the pulse light width, and the spatial resolution is high.

[0086] Although the spirit and principle of the present invention have been described with reference to several specific embodiments, it should be understood that the present invention is not limited to the disclosed specific embodiments, and the division of various aspects does not mean that the features in these aspects cannot be combined to benefit, and such division is only for the convenience of expression. The present invention is intended to cover various modifications and equivalent arrangements included in the spirit and scope of the attached claims.

Claims

1. A DAS system with multi-sideband chirp modulation, characterized in that: include: Narrow linewidth laser (1), first optical fiber coupler (2), phase modulator (3), electro-optic modulator (4), first erbium-doped optical fiber amplifier (5), optical fiber circulator (6), second erbium-doped optical fiber amplifier (7), dense wavelength division multiplexer (8), second optical fiber coupler (9), photoelectric balanced detector (10), data acquisition card (11), arbitrary waveform generator (12), direct current 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 direct current source (13) is connected to the bias voltage input end of the electro-optic modulator (4).

2. The DAS system with multi-sideband chirp modulation according to claim 1, 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.

3. The DAS system with multi-sideband chirp modulation according to claim 1, 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.

4. The DAS system with multi-sideband chirp modulation according to claim 1, 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.

5. The DAS system with multi-sideband chirp modulation according to claim 1, 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 working 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.

6. A method for operating a DAS system with multi-sideband chirp modulation, characterized in that: The working method is implemented based on the DAS system described in any one of claims 1 to 5; 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, through a first optical fiber coupler (2): the upper path is used as detection light of the DAS system, and the lower path is used as reference light of the DAS system; The added continuous light is modulated into multi-frequency continuous light of equal amplitude by a phase modulator (3), and then modulated into multi-sideband chirped pulse light by periodic linear frequency sweeping by an electro-optic modulator (4), and then power pre-amplified by a first erbium-doped fiber amplifier (5), and the amplified pulse light is injected into the sensing fiber through a fiber circulator (6); The backscattered Rayleigh light signal returned by the sensing optical fiber is then injected into the second erbium-doped optical fiber amplifier (7) through the optical fiber circulator (6) for power pre-amplification, and then filtered out ASE noise through the dense wavelength division multiplexer (8), and then injected into the second optical fiber coupler (9) together with the downlink reference light for coherent frequency beat, and the frequency beat result is photoelectrically converted by the photoelectric balanced 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, to control the electro-optic modulator (4) to perform periodic linear frequency sweep modulation on the equal-amplitude multi-frequency continuous light, and to control the data acquisition card (11) to collect the beat frequency signal; The direct current source (13) is used to provide a bias voltage for the electro-optic modulator (4) to achieve suppression of the optical carrier frequency.

7. The working method of a DAS system with multi-sideband chirp modulation according to claim 6, characterized in that: The multi-band chirp signal collected by the data acquisition card (11) is transmitted to a computer, and the computer performs the following processing: compressing the multi-band chirp signal into a plurality of single-frequency signals with different frequencies through pulse compression; and performing weighted averaging processing on the phase information with the amplitude as the weight.

8. The working method of a DAS system with multi-sideband chirp modulation according to claim 7, characterized in that: The process of the phase modulator (3) performing equal-amplitude multi-frequency modulation on the added continuous light includes: Define 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 expressed as: Among them, γ k is the modulation index; k is the harmonic order of m(t); φ k is the phase of m(t); t is time; Then the time domain expression of modulated equal-amplitude multi-frequency continuous light is E m (t) is: Where A is E m (t) amplitude.

9. The working method of a multi-sideband chirp modulation DAS system according to claim 8, characterized in that: The electro-optic modulator (4) converts the equal-amplitude multi-frequency continuous light E m (t) The process of modulating into multi-sideband chirped pulse light includes: f1 and ΔF are defined as the starting frequency and the sweep bandwidth of the sweep signal loaded on the electro-optic modulator (4) by the arbitrary waveform generator (12); the expression of the sweep signal is as follows: Among them, A sweep is m sweep (t) amplitude; T P is m sweep (t) width; rect(.) is a rectangle function; Then the modulated multi-sideband chirped pulse light E p The expression of (t) is:

10. The working method of a DAS system with multi-sideband chirp modulation according to claim 9, characterized in that: The 3dB working bandwidth f of the photoelectric balanced detector (10) BPD Satisfies the following relationship: Where N is E m (t) the number of frequencies included; The sampling rate S of the data acquisition card (11) a Satisfies the following relationship:

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