A cable disturbance monitoring system and method based on equivalent sampling and precision delay

Abstract

The application belongs to the technical field of optical cable disturbance monitoring, and particularly relates to an optical cable disturbance monitoring system and method based on equivalent sampling and precise delay, which comprises an optical part, an electrical part and a data processing part, wherein the optical part is electrically connected with the electrical part, the electrical part is electrically connected with the data processing part, and the data processing part adopts an upper computer. The application utilizes the laid optical cable, generates a narrow pulse signal based on an equivalent time sampling method and precise clock control, precise delay control and the like, generates and samples backscattering light through triggering a narrow pulse laser to emit laser and a precise delay module to generate a precise delay at the same time, reconstructs optical fiber disturbance monitoring signals of different positions and high resolution through triggering the laser to emit and sampling the equivalent time for multiple times, and can monitor optical fiber disturbance of different positions.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical cable disturbance monitoring, and particularly relates to an optical cable disturbance monitoring system and method based on equivalent sampling and precise delay. BACKGROUND

[0002] According to different monitoring principles, the distributed optical fiber disturbance detection technology is mainly divided into interference type and scattering type. The interference type mainly includes Michelson interference type, Sagnac type, MZ type, etc. Among them, the Michelson disturbance sensing structure has a relatively short sensing distance and a large positioning error; the basic Sagnac disturbance sensing technology uses the frequency spectrum to obtain a notch point to position the disturbance behavior, and the positioning accuracy is not high, and the disturbance behavior needs to have a relatively wide frequency spectrum range (greater than 20 kHz), so the application range is limited; the MZ type has a long monitoring distance and high positioning accuracy, but the algorithm is relatively complex, and in the double M-Z type optical fiber disturbance sensing structure, two sensing optical fibers and one conducting optical fiber are needed, which wastes resources and is not suitable for long-distance disturbance monitoring.

[0003] The scattering type optical fiber disturbance detection technology mainly includes optical time domain reflection technology OTDR and optical frequency domain reflection technology OFDR. The optical time domain reflection technology has a long monitoring distance and accurate positioning, and has a simple structure and is easy to implement. The optical frequency domain reflection technology has high resolution but a short detection distance.

[0004] Therefore, at present, the OTDR is improved or combined with different interference types to realize high-precision and long-distance optical fiber disturbance testing. For example, the phase-sensitive optical time domain reflection technology φ-OTDR has a simple structure, is easy to implement, has a stable system, accurate positioning, and the ability to simultaneously detect multiple disturbance events, but due to the principle of multi-beam interference, the φ-OTDR is easily disturbed by the external environment, resulting in a large noise.

[0005] In view of the shortcomings of the φ-OTDR distributed optical fiber sensing, many scholars and researchers have improved the technology, and successively proposed the heterodyne detection optical time domain reflectometer C-OTDR, the optical fiber disturbance sensing technology based on Brillouin scattering B-OTDR, the distributed sensing technology based on stimulated Brillouin scattering B-OTDA, and various disturbance sensing technologies combining the interference type optical fiber sensing technology with the φ-OTDR, such as the distributed optical fiber disturbance strain sensor combining the Michelson interferometer with the φ-OTDR, and the φ-OTDR distributed optical fiber disturbance strain sensor of the Mach-Zehnder (M-Z) interference, to improve the system performance indicators such as the effective distance and spatial resolution of the distributed optical fiber disturbance detection. However, the technology is still insufficient in ultra-long distance measurement, and needs to specially lay sensing optical fibers, which increases the cost of the test system. Therefore, it is necessary to study a method for monitoring environmental disturbance and safety by using existing communication optical fibers. SUMMARY

[0006] In order to solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0007] In order to solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0008] A kind of optical cable disturbance monitoring system based on equivalent sampling and precision delay, including optical part, electrical part and data processing part, the optical part is electrically connected with electrical part, the electrical part is electrically connected with data processing part, the data processing part uses host computer.

[0009] The optical part includes narrow pulse laser, electro-optic modulator, optical amplifier, first optical circulator, second optical circulator, pump light source, communication optical fiber, optical filter, photodetector, the optical path direction of the narrow pulse laser is sequentially provided with electro-optic modulator, optical amplifier, first optical circulator, the first optical circulator is connected with second optical circulator by communication optical fiber, the second optical circulator is arranged in the optical path direction of pump light source, the optical path direction of the first optical circulator is provided with optical filter, the optical path direction of the optical filter is provided with photodetector.

[0010] The electrical part includes precision time base, power amplifier circuit, delay counting circuit, narrow pulse circuit, sampler, signal conditioning filter circuit and acquisition communication module, the precision time base is electrically connected with power amplifier circuit and delay counting circuit respectively, the delay counting circuit is electrically connected with narrow pulse circuit, the narrow pulse circuit is electrically connected with sampler, the sampler is electrically connected with signal conditioning filter circuit, and the signal conditioning filter circuit is electrically connected with acquisition communication module.

[0011] The power amplifier circuit is electrically connected with electro-optic modulator, the sampler is electrically connected with photodetector, and the acquisition communication module is electrically connected with data processing part.

[0012] The pump light source adopts arc pump light source.

[0013] A kind of optical cable disturbance monitoring system based on equivalent sampling and precision delay, including optical part, electrical part and data processing part, the optical part is electrically connected with electrical part, the electrical part is electrically connected with data processing part, the data processing part uses host computer.

[0014] S1, taking a narrow pulse laser as a transmitting light source, modulating into a narrow pulse laser through an electro-optical modulator and amplifying the laser signal through an optical amplifier;

[0015] S2, coupling the light into a communication optical fiber through a first circulator, taking the communication optical fiber as a disturbance sensing carrier, taking a pump light source as a compensation light source to increase scattered light intensity to build an optical fiber disturbance test system, and realizing photoelectric conversion of backscattered light through an optical filter and a photodetector;

[0016] S3, calculating the position of the optical fiber disturbance point by measuring the transmission time of light in the optical fiber from the starting point to the disturbance point;

[0017] S4, generating a frequency-controllable narrow pulse trigger signal through a precise time base, one signal driving an electro-optical modulator after power amplification and narrow pulse compression, realizing adjustment of the ultra-narrow linewidth laser and transmitting narrow pulse laser;

[0018] S5, another pulse signal triggering the sampling switch of the sampler after passing through a delay counting circuit and then being compressed and transformed by a narrow pulse circuit, realizing reconstruction of the backscattered light signal and disturbance analysis;

[0019] S6, after the transient backscattered light signal collected by the sampler passes through a signal conditioning filter circuit for impedance integration transformation, filtering and AD collection, transmitting to the host computer through a USB interface for data storage and processing.

[0020] The method for calculating the position of the optical fiber disturbance point in S3 is:

[0021] Suppose that after injecting pulse light from the incident end of the optical fiber, the time required to receive the backscattered light generated at a distance L from the incident end is t, since the pulse light has transmitted the round trip from the incident end to the reflection point, there is the following relationship:

[0022]

[0023] Thus, the distance of the disturbance position from the incident end is L:

[0024]

[0025] Wherein, n is the refractive index of the optical fiber, c is the speed of light, L is the distance from the starting point of the optical fiber disturbance distance, and t is the time required for the light to transmit from the starting point to the disturbance position and return to the starting point.

[0026] The method for reconstructing the backscattered light signal in S6 is:

[0027] S6.1, the precision time base circuit emits a trigger pulse signal every 20ms+50ns=20000050ns, and 20 trigger pulse signals are generated in succession, 40000 data are collected in total, the time delay between two adjacent trigger pulses is 20000050ns, and the delay of the data corresponding to the serial number in the array in space is τ, that is, 50ns;

[0028] S6.2, the sampling time of the sampler consists of coarse delay and fine delay, that is:

[0029] t=nT+mτ

[0030] Wherein, T is the coarse delay time interval of the sampler sampling; τ is the time interval of the fine delay; m is the mth time of triggering the laser emission pulse laser signal; n is the nth time of sampling within 2ms of the laser round trip after single triggering;

[0031] S6.3, narrow pulse laser signal is emitted every 2ms, and the sampler samples the reflected scattered light signal every time interval T, the time interval T of the coarse delay of the sampler is 1us, and the sampling point number N1 in a single emission period is 2000=2ms / 1us;

[0032] S6.4, the electro-optic modulator in the laser emission circuit and the precision delay circuit are triggered at the same time, the trigger pulse passes through the delay counting circuit to generate a pulse signal every 1us, and the sampling narrow pulse generated by the narrow pulse generating circuit triggers the sampler to sample, and 2000 data points are collected in succession;

[0033] S6.5, the 2000 data points collected by the first triggering and the 2000 data points collected by the second triggering, the nth data point corresponding to the first triggering and the nth data point corresponding to the second triggering, are different by 20000050ns in time, but the position of the optical cable is different by 25ns, that is, the distance of 2.5m is transmitted in time, and the distribution of the forty thousand data points in space is obtained in turn, so as to reconstruct the waveform diagram of the backscattering light signal in space.

[0034] The method for obtaining the distribution of the forty thousand data points in space in S6.5 is:

[0035] The signal collected by the sampler in sequence after the first triggering of the laser signal emission is:

[0036] [x 1,1 x 1,2 … x 1,2000 ]

[0037] The signal collected by the sampler in sequence after the second triggering of the laser signal emission is:

[0038] [x 2,1 x 2,2… 2,2000 ]

[0039] The nth trigger emits a laser signal, and the sampler sequentially collects signals:

[0040] [x n,1 x n,2 … n,2000 ]

[0041] The 20th trigger emits a laser signal, and the sampler sequentially collects signals:

[0042] [x 20,1 x 20,2 … 20,2000 ]

[0043] Based on the 20th trigger emits a laser narrow pulse signal, based on the different transmission distance of backscattering light, the reconstructed signal with the increase of backscattering light transmission distance is:

[0044] [x 1,1 x 2,1 … 20,1 x 1,2 x 2,2 … 20,2 … 1,2000 x 2.2000 … 20,2000 ]

[0045] Based on the reconstructed 40,000 data, the intensity change curve of backscattering light with transmission distance is drawn.

[0046] The method of analyzing the disturbance of the backscattering light signal in S6 is:

[0047] Suppose there is no disturbance, the backscattering light intensity at different transmission distances is:

[0048] I C =[x 1c,1 x 2c,1 … 20c,1 x 1c,2 x 2c,2 … 20c,2 … 1c,2000 x 2c,2000 … 20c,2000 ]

[0049] In the experiment, the backscattering light signal of the tested optical fiber disturbance is:

[0050] I P =[x 1p,1 x 2p,1 … 20p,1 x1p,2 x 2p,2 … x 20p,2 … x 1p,2000 x 2p.2000 … x 20p,2000

[0051] In order to eliminate the influence of the intensity attenuation of backscattered light with transmission distance, there are:

[0052] I = I P -I C

[0053] Wherein, I is the optical fiber disturbance signal without background interference;

[0054] In the same optical fiber disturbance measurement process, different intensity disturbances at multiple positions are monitored at the same time, and the positions of the disturbance points are determined by measuring the amplitudes of different points and the change rates of the points.

[0055] If it is measured that the kth point has disturbance interference, the transmission time of the kth point from the starting point is:

[0056] t k =k*50ns

[0057] The distance from the starting point is:

[0058]

[0059] Therefore, after eliminating the influence of the attenuation of backscattered light, the time points and amplitudes of the reconstructed optical fiber disturbances can determine the positions and intensities of multiple optical fiber disturbances at the same time.

[0060] Compared with the prior art, the present application has the beneficial effects that:

[0061] The present application utilizes the laid optical cable, generates a narrow pulse signal based on the equivalent time sampling method and precise clock control, precise delay control, etc., generates a fine delay through the fine delay module and the narrow pulse laser emitter triggered at the same time, realizes the generation of backscattered light and the equivalent time sampling of backscattered light, reconstructs the optical fiber disturbance monitoring signal with high resolution at different positions through multiple triggering of the laser emitter and the equivalent time sampling, and can monitor the optical fiber disturbance at different positions. The present application realizes the positioning of the disturbance at different positions on the optical fiber by calculating the time difference between the triggering and the backscattered Rayleigh light, realizes the detection of the fast and long-distance optical fiber perimeter environment disturbance, realizes the prevention of the damage of the optical fiber, and realizes the perimeter security and the monitoring of important facilities by using the optical fiber. BRIEF DESCRIPTION OF DRAWINGS

[0062] ​In order to more clearly illustrate the embodiments or technical solutions of the present application, the drawings needed in the description of the embodiments or prior art will be briefly introduced. Obviously, the drawings in the following description are only exemplary, and for those skilled in the art, other drawings can be derived from the provided drawings without creative labor.

[0063] The structures, proportions, sizes, etc. shown in the specification are only used to cooperate with the content disclosed in the specification, so that those skilled in the art can understand and read, and are not used to limit the conditions that the present application can be implemented, so they do not have technical significance. Any modification of structure, change of proportion relationship or adjustment of size, without affecting the effect and purpose that the present application can produce, should still fall within the scope of the technical content disclosed by the present application.

[0064] Figure 1 The system structure diagram of the present application is shown in Figure 1.

[0065] Figure 2 The disturbance signal measurement principle diagram based on equivalent sampling of the present application is shown in Figure 2.

[0066] Figure 3 The method diagram for eliminating scattering light attenuation of the present application is shown in Figure 3.

[0067] Wherein: 1 is the optical part, 101 is a narrow pulse laser, 102 is an electro-optical modulator, 103 is an optical amplifier, 104 is a first optical circulator, 105 is a second optical circulator, 106 is a pump light source, 107 is a communication optical fiber, 108 is an optical filter, 109 is a photoelectric detector, 2 is an electrical part, 201 is a precision time base, 202 is a power amplification circuit, 203 is a delay counting circuit, 204 is a narrow pulse circuit, 205 is a sampler, 206 is a signal conditioning filter circuit, 207 is a communication module, 3 is a data processing part. DETAILED DESCRIPTION

[0068] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely. Obviously, the described embodiments are only some of the embodiments of the present application, and are not all the embodiments. These descriptions are only to further illustrate the features and advantages of the present application, and are not to limit the claims of the present application; based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0069] The specific embodiments of the present application will be further described in detail below in combination with the drawings and examples. The following examples are used to illustrate the present application, but not to limit the scope of the present application.

[0070] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0071] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0072] In this embodiment, as Figure 1 As shown, in the optical section 1, the disturbance fiber serves as both a communication fiber 107 and a disturbance detection fiber, eliminating the need for a dedicated sensing fiber and saving resources. The narrow-pulse laser 101 employs a 3kHz ultra-narrow linewidth laser to generate continuous laser light. The electro-optic modulator 102 modulates and controls the narrow pulse generated by the precision time base 201, producing a narrow-pulse laser. After being amplified by the optical amplifier 103, the laser light is coupled into the communication fiber 107 via an optical coupler. When the laser light is subjected to disturbances such as vibration or deformation in the communication fiber 107, backscattered light of varying intensities is generated. The backscattered light is transmitted through the fiber and coupled to the optical filter 108 and photodetector 109 via the first optical circulator 104, converting the optical signal into an electrical signal.

[0073] When a light source is injected into the incident end of the communication optical fiber 107, backscattered Rayleigh light of varying intensities is generated during propagation due to external disturbances, deformation, and bending of the fiber. This backscattered light returns to the incident end and is coupled to the photodetector 109 via the first optical circulator 104 for photoelectric conversion. Let t be the time required from the injection of pulsed light into the incident end of the communication optical fiber 107 to the receipt of the backscattered light generated at a distance L from the incident end. Since the pulsed light travels a round trip from the incident end to the reflection point in the communication optical fiber 107, the following relationship holds:

[0074]

[0075] Therefore, the distance between the disturbance location and the incident end can be calculated as L:

[0076]

[0077] Wherein, n is the refractive index of the optical fiber, c is the speed of light, L is the distance of the starting point of the optical fiber disturbance distance; t is the time required for the light to transmit from the starting point to the disturbance position and return to the starting point. As can be seen from formula (1) and (2), by measuring the transmission time of the light from the starting point to the disturbance point in the optical fiber, the position of the disturbance point of the optical fiber can be calculated. When the incident light propagates in the communication optical fiber 107, the Rayleigh backscattered light will produce an attenuation or mutation due to the breakpoint, joint and other optical fiber structure problems. Therefore, the change of the scattering light intensity is determined based on the change of the scattering light intensity, the time of light transmission is determined, and the detection of the disturbance position is realized.

[0078] In order to obtain the disturbance position of the optical fiber and identify the disturbance source, it is necessary to sample the backscattering Rayleigh light signal in real time within a period. When the monitoring test length of the communication optical fiber 107 is equal to 200km, and the spatial resolution of the disturbance is greater than 5m, the AD converter is required to have high conversion speed and high resolution. However, the current AD conversion chip is difficult to meet the requirements. The embodiment takes the sampler 205 as the core and takes the equivalent time sampling method as the theoretical basis, and realizes the reconstruction of the backscattering light signal and the disturbance analysis by means of the transient equivalent time sampling of the optical fiber disturbance signal by the sampler 205. The working process is as shown in Figure 2 .

[0079] According to formula (1), the transmission time of the scattering light generated by a single pulse laser can be calculated according to the length of the communication optical fiber 107, the speed of light propagation and the refractive index of the optical cable. When the length of the optical cable is 200km and the refractive index of the optical cable is 1.544, the round-trip time of the light propagating in the 200km long optical cable is 2ms. In order to satisfy the non-overlapping of the scattering light generated by the adjacent two light pulses, the interval time T of the two light pulses is set to 2ms in the embodiment.

[0080] In the embodiment, the precise time base module is used to generate pulse signals under the action of an external clock. The pulse signals trigger the laser to emit narrow pulse laser signals and trigger the delay timing circuit to delay sample the backscattering light signals at the same time.

[0081] One pulse signal triggers the electro-optical modulator 102 to generate pulse laser after power amplification and narrow pulse compression, and the pulse laser passes through the first circulator 104 and is coupled into the communication optical fiber 107. The scattering light with intensity change returns to the starting point and is coupled to the photodetector 109. The transmission time of the scattering light is known from formula (1).

[0082] To detect scattered light and overcome the need for a high-speed AD converter, the pulse trigger signal generated by the precision time base 201 triggers the delay counting circuit 203 to delay the pulse signal. For every delay time T, i.e., 1µs, the delay counting circuit generates a pulse signal and increments the count by 1. To enable rapid opening and closing of the sampler gate, the delayed pulse signal is compressed and amplified by the narrow pulse circuit 204 before triggering the sampler 205 to perform rapid equivalent sampling of the backscattered light signal. Counting 2000 times can achieve data acquisition at 50m intervals within a 200km range.

[0083] Because of its transient characteristics, the equivalent sampled signal cannot be directly converted by an analog-to-digital converter (AD). Therefore, the signal needs to be converted into a 50kHz low-frequency signal by impedance integration transformation through the signal conditioning and filtering circuit 206. After filtering and acquisition by the AD converter, the signal is transmitted to the host computer.

[0084] To achieve a 5m spatial resolution for disturbance positioning, the sampling data of the fiber optic disturbance signal needs to be improved. Therefore, this embodiment proposes that a precise time base 201 transmits a trigger pulse signal at intervals of (20ms + 50ns = 20000050ns), continuously generating 20 trigger pulse signals. A total of 40,000 data points are collected. The time delay between two adjacent trigger pulses is 20000050ns, and the spatial delay of the corresponding data in the acquisition array is τ, i.e., 50ns.

[0085] Therefore, the sampling time of sampler 205 consists of two parts: a coarse delay and a fine delay, namely:

[0086] t=nT+mτ (3)

[0087] T: coarse delay time interval for sampling by sampler 205; τ: fine delay time interval; m: laser pulse signal triggered by the mth laser emission; n: nth sampling within 2ms round trip of the laser after a single trigger.

[0088] In this embodiment, a narrow pulse laser signal is emitted every 2ms, and the sampler 205 samples the reflected scattered light signal every time interval T. The time interval T of each coarse delay of the sampler 205 is 1us, and the number of sampling points in a single emission cycle is N1 = 2ms / 1us = 2000 times.

[0089] To meet the 5m spatial resolution for disturbance positioning, the fine delay step delay time is 50ns. Therefore, the number of fine delays is 1us / 50ns = 20 times. That is, by transmitting 20 pulse signals with an interval of (20ms + 50ns = 20000050ns), 40,000 data points are sampled in about 40ms to complete one sampling of the disturbance signal.

[0090] The schematic diagram of the backscattering light signal collection principle based on the sampler 205 is shown in FIG. 2. Figure 2

[0091] In the embodiment, the electro-optical modulator in the laser emission circuit and the precision delay circuit are triggered simultaneously. The time interval of the two triggering signals is 20000050 ns. The trigger pulse is sent to the delay counting circuit 203, and a pulse signal is generated every 1 us. The sampling narrow pulse generated by the narrow pulse circuit 204 triggers the sampler 205 to perform sampling, and 2000 data points are collected continuously. Figure 2

[0092] The 2000 data points collected by the first trigger and the 2000 data points collected by the second trigger are different by 20000050 ns in time, but different by 25 ns in the position of the optical cable, i.e., the distance of 2.5 m transmitted in time. By analogy, the distribution of the 40000 data points in space can be obtained, so that the waveform diagram of the backscattering light signal in space can be reconstructed.

[0093] The signal collected by the sampler 205 in sequence when the laser signal is triggered for the first time is:

[0094] [x 1,1 x 1,2 … x 1,2000 ]

[0095] The signal collected by the sampler 205 in sequence when the laser signal is triggered for the second time is:

[0096] [x 2,1 x 2,2 … x 2,2000 ]

[0097] The signal collected by the sampler 205 in sequence when the laser signal is triggered for the nth time is:

[0098] [x n,1 x n,2 … x n,2000 ]

[0099] The signal collected by the sampler 205 in sequence when the laser signal is triggered for the 20th time is:

[0100] [x 20,1 x 20,2 … x 20,2000 ]

[0101] Based on the 20 times of triggering the laser narrow pulse signal, and based on the different transmission distances of the backscattering light, the signal reconstructed along with the increase of the transmission distance of the backscattering light is:

[0102] [x 1,1 ​​x 2,1 … x 20,1 x 1,2 x 2,2 … x 20,2 … x 1,2000 x 2.2000 … x 20,2000 ]

[0103] Based on the reconstruction of 40,000 data can be drawn backscattered light intensity curve with the transmission distance changes.

[0104] Scattered light intensity changes with time formula:

[0105] I(t k ) = ∑a i exp[j2πv0(t k -τ i )] (4)

[0106] It is known that the farther the light transmission distance, the light intensity is exponentially decayed with time. But when the fiber is disturbed by the signal interference, the backscattered light generated by the disturbance increases. Therefore, the backscattered light waveform intensity change analysis of 40,000 data points reconstructed disturbance position.

[0107] When the change rate of adjacent data is equal to the decay rate of backscattered light signal, no disturbance occurs; when the change rate of adjacent data is not equal to the decay rate of backscattered light signal at that point, there is a disturbance near that position. When a disturbance occurs at a certain position, the intensity near the point increases with the increase of the transmission distance, and when it increases to a certain value, it decays from the maximum value, and the decay rate is greater than the light intensity decay rate at that distance.

[0108] Based on the above analysis, in order to reduce the influence of backscattered light intensity decay with transmission distance. Before the experiment, first by laser emitting pulse width, intensity of the same laser, based on the principle of equivalent sampling, at the same rate and delay interval to collect its intensity at different transmission distances, based on the 40,000 data points collected to reconstruct the backscattered light intensity curve, and store the 40,000 data in the order of scattering light transmission distance from small to large. The 40,000 data are used to correct the decay effect of backscattered light.

[0109] Suppose no disturbance occurs, the backscattered light intensity at different transmission distances is

[0110] I C = [x 1c,1 x 2c,1 … x 20c,1 x 1c,2 x 2c,2 … x 20c,2… 1c,2000 x 2c,2000 … 20c,2000 ]

[0111] In the experiment, the backscattered light signal of the fiber disturbance that is tested can be:

[0112] I P =[x 1p,1 x 2p,1 … 20p,1 x 1p,2 x 2p,2 … 20p,2 … 1p,2000 x 2p.2000 … 20p,2000 ]

[0113] In order to eliminate the influence of the intensity attenuation of the backscattered light with the transmission distance, there is:

[0114] I=I P -I C (5)

[0115] Wherein, I is the fiber disturbance signal without the background interference.

[0116] According to the signal amplitude of different points of the tested fiber disturbance signal I, it can be judged whether the point has disturbance or not, and the greater the amplitude is, the greater the disturbance intensity is. For example, as shown in the following table. Figure 3

[0117] In the same fiber disturbance measurement process, disturbances with different intensities in multiple positions can be monitored simultaneously. The position of the disturbance point can be determined by measuring the amplitude of different points and the change rate of the point.

[0118] If it is measured that the kth point has disturbance interference, the transmission time of the kth point from the starting point is:

[0119] t k =k×50ns

[0120] The position from the starting point is:

[0121]

[0122] Therefore, after eliminating the influence of the backscattered light attenuation, the time point and amplitude of the reconstructed fiber disturbance can determine the positions and intensities of multiple fiber disturbances simultaneously.

[0123] The above only describes the preferred embodiments of the present application in detail, but the present application is not limited to the above-mentioned embodiments, and various changes can be made within the knowledge possessed by those skilled in the art without departing from the purpose of the present application, and all the changes shall be included in the protection scope of the present application.​

Claims

1. A fiber optic cable disturbance monitoring system based on equivalent sampling and precise time delay, characterized in that: The system includes an optical section (1), an electrical section (2), and a data processing section (3). The optical section (1) is electrically connected to the electrical section (2), and the electrical section (2) is electrically connected to the data processing section (3). The data processing section (3) is a host computer. The optical section (1) includes a narrow pulse laser (101), an electro-optic modulator (102), an optical amplifier (103), a first optical circulator (104), a second optical circulator (105), a pump source (106), a communication optical fiber (107), an optical filter (108), and a photodetector (109). The narrow pulse laser (101) has the electro-optic modulator (102), the optical amplifier (103), and the first optical circulator (104) arranged sequentially in the optical path direction. The first optical circulator (104) is connected to the second optical circulator (105) through the communication optical fiber (107). The second optical circulator (105) is located at the pump source (106). In the optical path direction of the first optical circulator (104), an optical filter (108) is provided in the optical path direction, and a photodetector (109) is provided in the optical path direction of the optical filter (108); the electrical part (2) includes a precision time base (201), a power amplifier circuit (202), a delay counting circuit (203), a narrow pulse circuit (204), a sampler (205), a signal conditioning filter circuit (206), and an acquisition and communication module (207). The precision time base (201) is electrically connected to the power amplifier circuit (202) and the delay counting circuit (203), respectively. The delay counting circuit (203) is electrically connected to the narrow pulse circuit (204). The narrow pulse circuit (204) is electrically connected to the sampler (205). The sampler (205) is electrically connected to the signal conditioning filter circuit (206). The signal conditioning filter circuit (206) is electrically connected to the acquisition and communication module (207).

2. The optical cable disturbance monitoring system based on equivalent sampling and precise time delay according to claim 1, characterized in that: The power amplifier circuit (202) is electrically connected to the electro-optic modulator (102), the sampler (205) is electrically connected to the photodetector (109), and the acquisition and communication module (207) is electrically connected to the data processing section (3).

3. The optical cable disturbance monitoring system based on equivalent sampling and precise time delay according to claim 1, characterized in that: The pump light source (106) is an arc pump light source.

4. A monitoring method for an optical cable disturbance monitoring system based on equivalent sampling and precise time delay according to any one of claims 1-3, characterized in that: Includes the following steps: S1. A narrow pulse laser is used as the emission source, which is modulated into a narrow pulse laser by an electro-optic modulator and then amplified by an optical amplifier; S2. The light is coupled into the communication optical fiber through the first circulator. The communication optical fiber is used as the disturbance sensing carrier, and the pump light source is used as the compensation light source to increase the intensity of the scattered light to build an optical fiber disturbance test system. The photoelectric conversion of the backscattered light is realized through optical filter and photodetector. S3. Calculate the location of the fiber disturbance point by measuring the propagation time of light in the fiber from the starting point to the disturbance point. S4. A precision time base generates a frequency-controllable narrow pulse trigger signal. One signal is amplified and compressed into a narrow pulse to drive an electro-optic modulator, thereby adjusting the ultra-narrow linewidth laser and emitting a narrow pulse laser. S5. Another pulse signal passes through a delay counting circuit and then through a narrow pulse circuit to compress and transform the pulse signal before triggering the sampling switch of the sampler, thereby realizing fast equivalent time sampling of backscattered light. S6. The transient backscattered light signal acquired by the sampler is subjected to impedance integration transformation, filtering, and AD acquisition by the signal conditioning and filtering circuit. It is then transmitted to the host computer via USB interface for data storage and processing, thereby realizing the reconstruction and disturbance analysis of the backscattered light signal.

5. The monitoring method of the optical cable disturbance monitoring system based on equivalent sampling and precise time delay according to claim 4, characterized in that: The method for calculating the location of the fiber optic disturbance point in S3 is as follows: Let t be the time required from the injection of pulsed light from the incident end of the optical fiber to the reception of the backscattered light generated by the pulsed light at a distance L from the incident end. Since the pulsed light travels a round trip from the incident end to the reflection point in the optical fiber, the following relationship holds: Therefore, the distance between the disturbance location and the incident end can be calculated as L: in, denoted as the refractive index of the optical fiber, c as the speed of light, L as the distance from the starting point to the disturbance in the optical fiber, and t as the time required for light to travel from the starting point to the disturbance location and back to the starting point.

6. The monitoring method of the optical cable disturbance monitoring system based on equivalent sampling and precise time delay according to claim 4, characterized in that: The method for reconstructing the backscattered light signal in S6 includes the following steps: S6.1, Precision time base circuit at each interval A trigger pulse signal is emitted at regular intervals, generating 20 consecutive trigger pulse signals. A total of 40,000 data points are collected. The time delay between two consecutive trigger pulses is 200,000.50 ns. The spatial delay of the data at the corresponding index in the collected array is... That is, 50ns; S6.2 The sampling time of the sampler consists of two parts: a coarse delay and a fine delay, namely: in, This is the coarse delay time interval for the sampler to collect samples; The time interval for fine delay; For the first The laser emission pulse signal is triggered by the next laser pulse. The first laser pulse within 2ms round trip after a single trigger Second sampling; S6.

3. A narrow pulse laser signal is emitted every 2ms. The sampler samples the reflected scattered light signal every time interval T. The time interval T of each coarse delay of the sampler is 1us. The number of sampling points in a single emission cycle is N1 = 2ms / 1us = 2000 times. S6.4 Simultaneously trigger the electro-optic modulator and precision delay circuit in the laser emission circuit. The trigger pulse is passed through the delay counting circuit, and a pulse signal is generated every 1us delay. The sampler is then sampled by the narrow pulse generated by the narrow pulse generation circuit, and 2000 data points are continuously collected. S6.5 The 2000 data points collected in the first trigger and the 2000 data points collected in the second trigger have a time difference of 20000050ns for the corresponding nth data point, but a time difference of 25ns for the transmission distance of the optical cable, i.e., 2.5m. And so on, to obtain the spatial distribution of 40,000 data points, thereby reconstructing the spatial waveform of the backscattered light signal.

7. The monitoring method of the optical cable disturbance monitoring system based on equivalent sampling and precise time delay according to claim 4, characterized in that: The method for obtaining the spatial distribution of 40,000 data points in S6.5 is as follows: The first laser signal is triggered, and the sampler sequentially acquires the following signals: The second laser signal was triggered, and the sampler sequentially acquired the following signals: The signals sequentially acquired by the sampler during the nth triggering of the laser signal emission are: The 20th trigger of laser signal emission resulted in the following signals being sequentially acquired by the sampler: Based on 20 triggered narrow-pulse laser signals, and considering the different backscattered light propagation distances, the reconstructed signal increasing with the backscattered light propagation distance is as follows: Based on the reconstructed 40,000 data points, the intensity variation curve of backscattered light as a function of transmission distance was plotted.

8. The monitoring method of the optical cable disturbance monitoring system based on equivalent sampling and precise time delay according to claim 4, characterized in that: The method for analyzing backscattered light signal perturbation in S6 is as follows: Assuming no disturbance occurs, the backscattered light intensity at different transmission distances is: In the experiment, the backscattered light signal of the tested fiber optic disturbance was: To eliminate the effect of backscattered light intensity attenuation with transmission distance, we have: in, To remove background interference from fiber optic disturbance signals; During the same fiber optic disturbance measurement, disturbances of different intensities are monitored at multiple locations simultaneously. The location of the disturbance point is determined by measuring the amplitude and rate of change at different points. If measurements indicate that there is disturbance at point k, then the transmission time from point k to the starting point is: The distance from the starting point is: Therefore, after eliminating the effect of backscattered light attenuation, the time point and amplitude of the reconstructed fiber disturbance can simultaneously determine the location and intensity of multiple fiber disturbances.

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