CN102064884B - Long-distance distributed optical fiber positioning interference structure based on wavelength division multiplexing (WDM) - Google Patents

Abstract

The invention proposes a distributed optical fiber positioning structure and method that can be used for long-distance monitoring, and specifically relates to a distributed optical fiber positioning interference technology based on wavelength division multiplexing, which injects two different wavelengths into the same sensing optical fiber Light, the light is transmitted to the fiber port, the two wavelength components are separated by a wavelength division multiplexing device, and they reach their respective reflection terminals along their own independent fiber paths, and the two light waves form different interferences. The perturbation location information is obtained by comparing the spectral characteristics of the two interferometrically obtained phase signals. The present invention has a simple structure, and the back end has no special requirements for signal processing. Obtaining position information by comparing spectral characteristics not only eliminates the influence of disturbance signal amplitude changes on detection, but also can use the position values obtained at multiple frequency points to average to obtain high positioning accuracy.

Description

Long-distance distributed optical fiber positioning interference system based on wavelength division multiplexing

technical field

The invention belongs to the technical field of optical fiber sensing, and in particular relates to a long-distance distributed optical fiber positioning interference structure. the

Background technique

Maintaining the security of infrastructure is a basic requirement for social stability and rapid economic development. At present, my country's long-distance monitoring of infrastructure such as oil and gas pipelines, power grids, and communication networks is mainly based on some production parameters of the facilities themselves (such as sudden pressure drops, abnormal changes in the liquid level of oil tanks at intermediate stations), manual inspections, and the monitoring of passers-by. reporting, etc. These methods are low in technical content, and generally have defects such as low efficiency, poor real-time performance, long response time, and poor anti-interference ability. Often, the alarm can only be called after the monitoring facilities are damaged, and the practicability is restricted by both natural and human factors. This "remedial" post-mortem detection technology can only reduce but not avoid losses. For the monitoring of long-distance pipelines, especially affected by electromagnetic interference, it is difficult to implement sensor monitoring by means of electricity. Therefore, optical fiber sensing technology will become the main technical means for safety monitoring and prevention of man-made sabotage in industries such as electric power, communication and oil and gas pipelines. the

One of the prior technologies is the monitoring technology based on the all-fiber white light interference system. In this system, the interference signal will be missing at some relevant frequency points, and the location of these disturbances can be judged from these missing frequency points. However, if the disturbance source does not excite the required frequency range, the missing frequency point cannot be obtained, and this judgment method will fail. Figure 1 shows the structure of an all-fiber white light interference system that utilizes missing frequency points for positioning monitoring. The system consists of broadband light source 8, fiber splitter 1, fiber delay line 5, fiber splitter 2, single-core fiber 6, feedback device 3, detectors 9, 10, and signal processing unit 16. The system uses white light for interference . There is a section of single-core optical fiber 6 in the optical path. Using the function of the feedback device 3, the light transmitted from the optical fiber 6 re-enters the optical fiber 6 for transmission after being acted on by the feedback device 3. The obtained interference signal is output from the ports 1b and 1c of 1, and enters the detection Devices 9, 10. 17 are interference units composed of splitters 1, 2 and delay line 5. the

The second prior art solves the problem of the excitation frequency range of the disturbance source in the first prior art. As shown in FIG. 2 , this technology adds a modulation module 15 at the end of the single-core optical fiber 6 . The function of the modulation module 15 is to modulate the external vibration signal to different carrier frequency bands. The specific implementation method is to add two sections of optical fibers 13 and 14 with a certain length difference through the splitter 4. The length difference of the two sections of optical fibers is 1. The time delay is τ ₂ .; Carrier signals of different frequencies are loaded on the two optical fibers through phase modulators 18., 19; feedback devices 11, 12 are added to the tail ends of the two optical fiber paths. In this way, a set of optical fiber interference system is multiplexed by phase generation carrier to obtain two phase signals of the same vibration corresponding to different optical path positions, compare the spectral characteristics of the two phase signals, eliminate the interference of vibration information on position information, and obtain accurate vibration location information.

的值，从而得到外界振动信号在传感光纤上的位置信息。由于计算所用的频率点没有特殊要求，因而可以解决在先技术一中存在频率限制的问题。又由于利用了频谱上若干个点求得

的平均值，消除信号测量的引入的误差所造成的差异性，也大大提高定位的精确性。  By comparing the amplitudes of the two frequency spectrums, the impact of disturbance signal amplitude and frequency component changes on positioning is eliminated. Each frequency point can be obtained

In order to obtain the position information of the external vibration signal on the sensing fiber. Since there is no special requirement for the frequency points used for calculation, the problem of frequency limitation in the first technique can be solved. And due to the use of several points on the frequency spectrum to obtain

The average value of the signal eliminates the difference caused by the error introduced by the signal measurement, and also greatly improves the positioning accuracy.

However, in the second prior art, the demodulation of the signal becomes relatively complicated due to the need to use the phase generation carrier modulation technology, especially the interference signal caused by the disturbance usually has a wide bandwidth. To accurately restore the interference phase, not only the bandpass filter is required The bandwidth of the filter is very wide, and it has high requirements on flatness and phase shift characteristics, and the difficulty and complexity of signal processing are relatively large. the

Contents of the invention

The purpose of the present invention is to propose a distributed optical fiber positioning interference structure based on wavelength division multiplexing that has strong environmental applicability and simple structure and can be used for long-distance distributed monitoring. the

The distributed optical fiber positioning interference structure based on wavelength division multiplexing proposed by the present invention uses wavelength division multiplexing technology, so that the same disturbance can obtain two different interference signals, and the method of comparing the spectral characteristics of the two phase signals can be used to determine The location where the disturbance occurs. Specifically shown in Figure 3. Including: optical fiber interference assembly 20, sensing optical fiber 6, first wavelength division multiplexer 21, first optical fiber 22, second optical fiber 23, first feedback device 11, second feedback device 12; two different wavelengths of light λ ₁ , λ ₂ are injected from the same sensing fiber 6, and these two injected lights are transmitted to the port of the optical fiber along the sensing fiber 6 that is multiplexed, and are separated by the first wavelength division multiplexing device 21, respectively along separate independent paths The first optical fiber 22 and the second optical fiber 23 arrive at respective reflection terminals—the first feedback device 11 and the second feedback device 12; the length difference between the first optical fiber 22 and the second optical fiber 23 of these two independent optical fiber paths is 1 ₃ , resulting in a time delay of τ ₃ .

Among Fig. 3, optical fiber interference assembly 20 and induction optical fiber 6, the first wavelength division multiplexer 21, the first optical fiber 22, the first feedback device 11 jointly form the interference light path of light wave λ ₁ ; Optical fiber interference assembly 20 and induction optical fiber 6, The first wavelength division multiplexer 21, the second optical fiber 23, and the second feedback device 12 jointly form an interference optical path of the light wave _λ2 . The light is input from the optical fiber interference component 20 , and the interference signal is also output from the optical fiber interference component 20 .

The interference signal of light wave λ ₁ carries information about the length of the disturbance point 7 from the feedback device 11, and the interference signal of light wave λ ₂ carries information about the length of the distance between the disturbance point 7 and the feedback device 12. and the length difference of the second optical fiber 23), so that the position of the disturbance point 7 can obtain accurate vibration position information by comparing the spectral characteristics of the phase signal obtained by the interference of the two light waves.

Figure 4 is a specific way to realize this interference structure. the

The optical fiber interference assembly 20 is composed of a first optical fiber splitter 24, a second optical fiber splitter 25, a second wavelength division multiplexer 26, a third wavelength division multiplexer 27, an optical fiber delay line 5, a third optical fiber splitter 28 poses. Wherein, the first optical fiber splitter 24 is an N*M optical fiber splitter (N, M are integers), 24a1, 24a2, ... 24aN are N co-directional ports of the first optical fiber splitter 24, 24b1, 24b2 It belongs to another group of ports in the same direction. The second optical fiber splitter 25 is a P*Q optical fiber splitter (P, Q are integers), 25a1, 25a2, ... 25aP are P co-directional ports of the second optical fiber splitter 25, and 25b1 and 25b2 belong to another A set of ports in the same direction. The second wavelength division multiplexer 26 is a wavelength division multiplexer, 26b, 26c are its independent wavelength ports, and 26a is a multiplexing wavelength port. The third wavelength division multiplexer 27 is another wavelength division multiplexer, 27b, 27c are its independent wavelength ports, and 27a is a multiplexed wavelength port. The third fiber splitter 28 is a fiber splitter whose working wavelength includes λ ₁ and λ ₂ , 28b1 and 28b2 are ports in the same direction, and 28a is a port in the other direction. The first light of wavelength _λ1 is input from 24a1 of the fiber splitter 24, and the light is output from ports 24b1, 24b2; the light of wavelength _λ2 is input from 25a1 of the second fiber splitter 25, and the light is output from ports 25b1, 25b2. Lights with wavelengths λ ₁ and λ ₂ output from ports 24b1 and 25b1 are respectively input from ports 26b and 26c of the second wavelength division multiplexer 26, and the combined light of the two wavelengths is output from port 26a, and multiplexing ports 26a and 28b1 The path between; the light outputted from ports 24b2, 25b2 with wavelengths of λ ₁ and λ ₂ is input from ports 27b, 27c of the third wavelength division multiplexer 27, and the combined light of the two wavelengths is output from port 27a for multiplexing Path between ports 26a and 28b2. The light input from the ports 28b1 and 28b2 is output through 28a and injected into the sensing fiber 6 . In this interference structure, the interference signal produced by the light of wavelength λ ₁ is output from ports 24a1, 24a2, ... 24aN of the first optical fiber splitter 24, and the interference signal produced by the light of wavelength λ ₂ is output from the second optical fiber splitter 25 The ports 25a1, 25a2, ... 25aP of the output. The corresponding phase signals are respectively demodulated from the interference signals generated by λ ₁ and λ ₂ , and the location of the disturbance can be determined by comparing the spectral characteristics of the two phase signals. The specific working principle and calculation process are as follows.

，光在反馈装置R处返回。由于任何一个复杂的振动都可以分解为不同频率的简谐振动的叠加，所以考虑单一频率为

的振动信号。假设在时刻t，由于光弹效应，单一振动角频率为

的振动信号引起的传输光波相位变化为

，则：  As shown in Figure 5, a vibration signal is applied at the disturbance point 7 of the monitoring fiber

, the light returns at the feedback device R. Since any complex vibration can be decomposed into the superposition of simple harmonic vibrations of different frequencies, considering a single frequency as

vibration signal. Assume that at time t, due to the photoelastic effect, the single angular frequency of vibration is

The phase change of the transmitted light wave caused by the vibration signal is

,but:

                           （1）

(1)

为光路中延迟线的长度），单一角频率为ω的振动信号引起的传输光波相位变化为： At time t+τ(

is the length of the delay line in the optical path), the phase change of the transmitted light wave caused by the vibration signal with a single angular frequency ω is:

(2)

，光往返扰动点7的时间为

，则： On one sensing optical fiber, the distance between the disturbance point 7 and the feedback final device R is set to be

, the time for the light to go back and forth to the disturbance point 7 is

,but:

                                         （3）

(3)

是光纤纤芯等效折射率，c是真空中的光速。

，为常数。 In the above formula,

is the equivalent refractive index of the fiber core, and c is the speed of light in vacuum.

, is a constant.

from frequency to The phase difference of the interference light caused by the disturbance is:

（4）

(4)

，对应外界振动信号的大小。 For perturbations at all frequencies, the total phase difference

, corresponding to the magnitude of the external vibration signal.

，即

，则有：  Let this optical path be the path of the light of wavelength λ ₁ , that is, the feedback device R is the feedback device 11, and the distance between the disturbance point 7 and the feedback device 11 is , the time delay generated by the fiber delay line in the interference optical component 20 is

,Right now

, then there are:

               （5）

(5)

，光往返扰动点7的时间为+2

，则有： For the path whose wavelength is λ ₂ , the feedback device R is the feedback device 12, because the delay difference between the optical fiber path 22 and the optical fiber path 23 is

, the time for the light to go back and forth to the disturbance point 7 is +2

, then there are:

        （6）

(6)

For disturbances of all frequencies, the total phase difference corresponding to light waves λ ₁ and λ ₂ are respectively:

                      （7a）

(7a)

                    （7b）

(7b)

The two phase differences are demodulated from the interference light output by the optical fiber splitter 24 and the optical fiber splitter 25 respectively.

的频谱上，对于每一个频率，都有与其相对应的幅值

；在的频谱上，对于每一个频率

，都有与其相对应的幅值

，可得：  exist

on the spectrum of , for each frequency , have corresponding magnitudes

;exist on the spectrum of , for each frequency

, have corresponding magnitudes

,Available:

    （8）

(8)

频率分量引起的相位变化为： According to the photoelastic effect, when the optical fiber is subjected to external stress (assuming no microbending),

The phase change caused by the frequency component is:

                 （9）

(9)

、

为光弹系数，为外界应力

频率的应力分量产生的应变，因此有： in

,

is the photoelastic coefficient, for external stress

The strain produced by the stress component of the frequency is thus:

                                                                          （10）

(10)

but,

                                       （11）

(11)

，通过比较两者频谱上的幅度，都可以求得

的值，从而得到外界振动信号在传感光纤上的位置信息。可利用频谱上若干个点求得

的平均值，消除检测信号不稳定所造成的差异性，也会大大提高定位的精确性。 The left side of (11) is obtained by actual testing, therefore, for each frequency

, by comparing the amplitudes of the two spectrums, we can obtain

In order to obtain the position information of the external vibration signal on the sensing fiber. It can be obtained by using several points on the frequency spectrum

The average value of , eliminating the difference caused by the instability of the detection signal, will also greatly improve the positioning accuracy.

Fig. 6 is yet another implementation of the interference structure. the

The optical fiber interference assembly 20 is composed of a fourth optical fiber splitter 29 , a third optical fiber splitter 28 and an optical fiber delay line 5 . The fourth optical fiber splitter 29 is an R*S optical fiber splitter (R, S are integers), 29a1, 29a2, ... 29aR are R ports in the same direction of the fourth optical fiber splitter 29, 29b1, 29b2 belong to another A set of ports in the same direction. In this manner, all devices in 20 in the optical fiber interference assembly are multiplexed. Port 29b1 is connected to port 28b1 via fiber delay line 5, and port 29b2 is connected to port 28b2. Light input from ports 28b1 and 28b2 is output via port 28a and injected into sensing fiber 6. the

The light containing two wavelength components of _λ1 and _λ2 is input from the port 29a1. The injected light can be generated by one light source, or can be combined by two light sources with wavelengths of _λ1 and _λ2 respectively through a wavelength division multiplexer generated after. The interference generated by the two wavelengths is output from the ports 29a1, 29a2, . . . 29aR. The interference signal containing two wavelengths can be separated by using a wavelength division multiplexer, that is, the interference signal of λ ₁ and the interference signal of λ ₂ are respectively obtained. The phase signal is demodulated from the interference signal generated by λ ₁ and λ ₂ , and the position of the disturbance can be determined according to the two phase signals.

The present invention uses wavelength division multiplexing technology in the interference structure, so that the same disturbance can obtain two different interference signals, and the position of the disturbance can be obtained by comparing the spectral characteristics of the two phase signals. This form has a simple structure and no special means are required for back-end signal processing, which is a major advantage of this structure. the

The invention can obtain disturbance position information by comparing the frequency spectrum characteristics of two phase signals obtained by interference. This method can not only eliminate the influence of disturbance signal amplitude and frequency component changes on positioning, but also use the position values obtained at multiple frequency points to average, eliminate the influence of errors in signal processing, and obtain high positioning accuracy. The method has the advantage of potentially high positioning accuracy. At the same time, because the acquisition of the disturbance position does not depend on the excitation of a special frequency point by the disturbance source, the applicability is stronger and the application prospect is wider. the

The optical fiber used for sensing and positioning in the invention does not need to be closed, does not need to form a loop, is convenient for long-distance laying along the monitoring object, and has strong environmental applicability. the

The distributed optical fiber pipeline monitoring system based on the invention can be widely used in long-distance monitoring in the field of safety monitoring of communication trunk lines, power transmission lines, natural gas pipelines, oil pipelines, and border lines; it can also be applied to large buildings such as dams, tunnels, mines, etc. safety monitoring. the

Description of drawings

Figure 1 shows the structure of an all-fiber white light interference system that utilizes missing frequency points for positioning monitoring. The system consists of broadband light source 8, fiber splitter 1, fiber delay line 5, fiber splitter 2, single-core fiber 6, feedback device 3, detectors 9, 10, and signal processing unit 16. The system uses white light for interference . There is a section of single-core optical fiber 6 in the optical path. Using the function of the feedback device 3, the light transmitted from the optical fiber 6 re-enters the optical fiber 6 after being acted on by the feedback device 3. The obtained interference signal is output from the ports 1b and 1c of 1 and enters the detection Devices 9, 10. 17 are interference units composed of splitters 1, 2 and delay line 5. the

Figure 2 is a structure of an optical fiber positioning and monitoring system based on phase generation and carrier multiplexing technology. 15 is modulation module modulation module 15, and 4 is splitter, and 13,14 are optical fibers, and the time delay that the length difference of two sections of optical fibers is 1 generation is τ _2. , 18.,19 are phase modulators, and 11,12 are feedback device.

Fig. 3 is a distributed optical fiber positioning interference structure based on wavelength division multiplexing proposed by the present invention. 20 is an optical fiber interference component, 6 is an induction optical fiber, 21 is a first wavelength division multiplexer, 22 and 23 are respectively a first and a second optical fiber, 11 and 12 are respectively a first and a second feedback device. The light is input from the optical fiber interference component 20 , and the interference signal is also output from the optical fiber interference component 20 . the

Fig. 4 is a specific implementation of the interference structure of the present invention. 24 is an N*M fiber optic splitter (N, M are integers), 24a1, 24a2, ... 24aN are N co-directional ports of the fiber optic splitter 24, and 24b1, 24b2 belong to another group of co-directional ports. 25 is a P*Q fiber optic splitter (P, Q are integers), 25a1, 25a2, ... 24aP are P co-directional ports of the fiber optic splitter 25, 25b1, 25b2 belong to another group of co-directional ports. 26 is a wavelength division multiplexer, 26b, 26c are its independent wavelength ports, and 26a is a multiplexing wavelength port. 27 is another wavelength division multiplexer, 27b and 27c are its independent wavelength ports, and 27a is a multiplexed wavelength port. 28 is a fiber optic splitter whose working wavelength includes λ ₁ and λ ₂ , 28b1 and 28b2 are its ports in the same direction, and 28a is a port in the other direction.

Fig. 5 is a schematic diagram of a disturbance point 7 existing on the monitoring line. the

Fig. 6 is yet another specific implementation of the interference structure of the present invention. 29 is an R*S fiber optic splitter (R and S are integers), 29a1, 29a2, ... 29aR are R co-directional ports of the fiber optic splitter 29, and 29b1 and 29b2 belong to another group of co-directional ports. the

Detailed ways

The present invention is further described below by way of examples. Use the interference structure shown in Figure 4. The light sources are superluminescent diodes (SLD) with center wavelengths of 1300nm (λ ₁ ) and 1550nm (λ ₂ ) produced by the 44 Research Institute of Electronics Group Corporation. Fiber coupler and wavelength division multiplexer are produced by Wuhan Institute of Posts and Telecommunications. Fiber splitter 24 uses a 3*3 equal split coupler with a working wavelength of 1300nm, fiber splitter 25 uses a 3*3 split coupler with a working wavelength of 1550nm, and fiber splitter 28 uses a 2*2 split double window Optical fiber coupler, wavelength division multiplexer 21, 26, 27 is the wavelength division multiplexer of 1300nm, 1550nm. The 1300nm light is input from the port 24a1, and the formed interference signal is taken out from the ports 24a2 and 24a3; the 1550nm light is input through the port 25a1, and the formed interference signal is taken out from the ports 25a2 and 25a3. The InGaAs photodetector model GT322C500 produced by 44 is used to convert the light interference signal into an electrical signal. The electrical signal is collected into the computer through the National Instruments company data acquisition card PCI-6122 for signal processing. The monitoring line is laid near the pipeline that needs to be monitored, and the optical fiber interference module needs to be placed in a soundproof device to shield external interference. The results show that the accurate perturbation position can be obtained conveniently.

Claims (1)

1. A long-distance distributed optical fiber positioning interference system based on wavelength division multiplexing, characterized in that the interference system includes: optical fiber interference components, sensing optical fibers, first wavelength division multiplexers, first optical fibers, second optical fibers, first Feedback device, second feedback device; two different wavelengths of light λ ₁ and λ ₂ are injected from the same sensing fiber, and the two injected lights are transmitted to the port of the fiber along the multiplexed sensing fiber, and are transmitted by the first The wavelength division multiplexer is separated, respectively along the first optical fiber and the second optical fiber of the independent path to reach the respective reflection terminals - the first feedback device and the second feedback device; the first optical fiber and the second optical fiber of these two independent optical fiber paths The length difference between them is l ₃ , and the resulting time delay is τ ₃ ; wherein, the optical fiber interference component and the sensing fiber, the wavelength division multiplexer, the first optical fiber, and the first feedback device form an interference optical path of light wave λ ₁ ; the optical fiber interference component Form the interference optical path of light wave λ ₂ with induction optical fiber, wavelength division multiplexer, the second optical fiber, the second feedback device; Light is input from optical fiber interference assembly, and interference signal is also exported from optical fiber interference assembly; Wherein: The optical fiber interference assembly is composed of a first optical fiber splitter, a second optical fiber splitter, a second wavelength division multiplexer, a third wavelength division multiplexer, an optical fiber delay line, and a third optical fiber splitter; wherein, The first fiber optic splitter is an N*2 fiber optic splitter, N is an integer, 24a1, 24a2, ... 24aN are N co-directional ports of the first fiber optic splitter, 24b1, 24b2 are the first fiber optic splitters Another group of ports in the same direction; the second optical fiber splitter is a P*2 optical fiber splitter, P is an integer, 25a1, 25a2, ... 25aP are P co-directional ports of the second optical fiber splitter, 25b1, 25b2 Another group of ports in the same direction of the second optical fiber splitter; the second wavelength division multiplexer is a wavelength division multiplexer, 26b, 26c are its independent wavelength ports, and 26a is a multiplexing wavelength port; the third wavelength division multiplexer The multiplexer is another wavelength division multiplexer, 27b and 27c are its independent wavelength ports, and 27a is a multiplexing wavelength port; the third optical fiber splitter is an optical fiber splitter whose working wavelength includes λ ₁ and λ ₂ , 28b1 and 28b2 are ports in the same direction, and 28a is another direction port; the light of wavelength λ ₁ is input from the port 24a1 of the first optical fiber splitter, and is output from ports 24b1 and 24b2; the light of wavelength λ ₂ is split from the second optical fiber input from port 25a1 of the multiplexer, and output from ports 25b1 and 25b2; light with wavelengths λ ₁ and λ ₂ output from ports 24b1 and 25b1 are respectively input from ports 26b and 26c of the second wavelength division multiplexer, and the two wavelengths are merged The light output from the port 26a, the path between the multiplexing ports 26a and 28b1; the light output from the ports 24b2, 25b2 with wavelengths λ ₁ , λ ₂ are input from the ports 27b, 27c of the third wavelength division multiplexer, and the two The light with combined wavelengths is output from port 27a, and the path between ports 27a and 28b2 is multiplexed; the light input from ports 28b1 and 28b2 is output through port 28a, and injected into the induction fiber; in this interference system, the light with wavelength λ ₁ The generated interference signal is output from the ports 24a1, 24a2, ... 24aN of the first optical fiber splitter, and the interference signal generated by the light of wavelength λ ₂ is output from the ports 25a1, 25a2, ... 25aP of the second optical fiber splitter; Alternatively, the optical fiber interference component is composed of a fourth optical fiber splitter, a third optical fiber splitter and a fiber delay line; the fourth optical fiber splitter is an R*2 optical fiber splitter, R is an integer, 29a1, 29a2 , ... 29aR are R co-directional ports of the fourth optical fiber splitter, and 29b1, 29b2 are another group of co-directional ports of the fourth optical fiber splitter; in this way, all devices in the optical fiber interference component are multiplexed; Port 29b1 is connected to port 28b1 through a fiber delay line, port 29b2 is connected to port 28b2, and the light input from ports 28b1 and 28b2 is output through port 28a and injected into the sensing optical fiber; Light containing two wavelength components of _λ1 and _λ2 is input from the port 29a1, and interference signals generated by the two wavelengths are output from the ports 29a1, 29a2, . . . 29aR.

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