Device and method for avoiding coherent fading in DVS system

Abstract

The invention discloses a device and method for avoiding coherent fading in a DVS system, and relates to the technical field of optical fiber sensing. The device comprises two 1 * N optical switches and N delay optical fibers, wherein N is greater than or equal to 2; wherein the com end of one of the 1 * N optical switches is connected with the output end of the DVS system, and the com end of the other 1 * N optical switch is connected with a target optical cable to be tested; each time-delay optical fiber is arranged between the two 1 * N optical switches, and two ends of each time-delay optical fiber are respectively connected with the 1 * N optical switches at the corresponding positions. Signal measurement can be carried out through the device, the DVS system is prevented from being influenced by coherent fading, and the vibration position of the target optical cable can be positioned more accurately and efficiently.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, and in particular to a device and method for avoiding coherent fading in a DVS system. Background Art

[0002] With the development of society and the advancement of science and technology, fiber optic sensing technology has been widely used in various fields of society. The DVS system is an application based on fiber optic sensing technology, which is mainly used to locate the vibration position of the optical cable.

[0003] By tapping the optical cable, the DVS system can quickly locate the vibration position of the target optical cable. This positioning is not only lossless to the optical cable, but also highly efficient and accurate. However, due to the randomness of the phase change, polarization state change and Rayleigh scattering of the optical signal in the optical cable, the DVS system will have different positioning effects at certain positions of the target optical cable at different times or under different conditions when measuring the target optical cable. This weakening of the detection signal intensity caused by the phase fluctuation of the interference field is called coherent fading. Coherent fading will cause the DVS to have a large difference in vibration signals over time or even no response at the same position of the target optical cable when locating the vibration position of the target optical cable, or a large difference in vibration signals or even no response at different positions of the target optical cable at the same time under the same vibration conditions. Summary of the invention

[0004] The object of the present invention is to provide a device and method for avoiding coherent fading in a DVS system, which can avoid the DVS system from being affected by coherent fading and improve the positioning accuracy and positioning efficiency of the vibration position of the target optical cable.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A device for avoiding coherent fading in a DVS system comprises: two 1xN optical switches and N time-delay optical fibers, N≥2; a com end of one of the 1xN optical switches is connected to an output end of a DVS system, and a com end of another 1xN optical switch is connected to a target optical cable to be tested; each of the time-delay optical fibers is arranged between the two 1xN optical switches, and both ends of each of the time-delay optical fibers are respectively connected to the 1xN optical switches at corresponding positions.

[0007] Optionally, the lengths of the delay optical fibers are different and do not repeat periodically.

[0008] Optionally, the length difference between each two of the delay optical fibers is greater than the maximum resolution of the DVS system.

[0009] Optionally, the number of the delay optical fibers is set to 8.

[0010] Optionally, the lengths of the delay optical fibers are respectively set to: 25m, 33m, 51m, 87m, 102m, 233m, 527m and 1005m.

[0011] The present invention also provides a method for avoiding coherent fading in a DVS system, which is applied to the above-mentioned device, comprising:

[0012] A device for avoiding coherent fading in a DVS system is constructed by using two 1xN optical switches and N delay optical fibers, recording the length of each delay optical fiber, and performing time stamp correction between each delay optical fiber and the corresponding 1xN optical switch channel;

[0013] Switch the channels of the 1xN optical switch according to the set switching mode, and perform single or multiple measurements on the DVS system to obtain single or multiple measurement data under the corresponding channel;

[0014] During the completion of a cycle, the signal quality of each channel is evaluated, and each measurement data is weighted. After the cycle ends, the weighted average signal is calculated according to the weights of each signal, and the interpolation algorithm is used to compensate for the data of the area with poor evaluation results within the cycle; wherein, the evaluation process is: the signal amplitude is normalized, and when the normalized value is greater than 0.8, the signal quality is determined to be excellent, when the normalized value is less than or equal to 0.8 and greater than or equal to 0.5, the signal quality is determined to be general, and when the normalized value is less than 0.5, the signal quality is determined to be poor.

[0015] Optionally, the set switching mode includes a sequential switching mode or a random switching mode; wherein the sequential switching mode is: sequentially switching all channels once or multiple times as a cycle; the random switching mode is: randomly switching a set number of channels as a cycle.

[0016] Optionally, in the set switching mode, the channel switching time interval of the 1xN optical switch is greater than a single measurement time of the DVS system.

[0017] Optionally, the calculation formula for the normalization process is:

[0018]

[0019] Among them, A i is the signal amplitude of the i-th channel, and max(A) is the maximum amplitude of all channels.

[0020] Optionally, the calculation formula for the signal weighting is:

[0021]

[0022] in, is the normalized value of the i-th channel signal, is the normalized value of the j-th channel signal, j=1...N, N is the total number of channels.

[0023] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0024] The present invention discloses a device and method for avoiding coherent fading in a DVS system. The device comprises two 1xN optical switches and N time-delay optical fibers, where N is greater than or equal to 2; the com end of one of the 1xN optical switches is connected to the output end of the DVS system, and the com end of the other 1xN optical switch is connected to the target optical cable to be measured; each of the time-delay optical fibers is arranged between the two 1xN optical switches, and the two ends of each of the time-delay optical fibers are respectively connected to the 1xN optical switches at corresponding positions. When the DVS locates the vibration position of the target optical cable, due to coherent fading, the vibration signal at the same position of the target optical cable varies greatly with time or even does not respond, or the vibration signal at different positions of the target optical cable varies greatly or even does not respond under the same vibration conditions at the same time. Therefore, the present invention performs signal measurement through the device, which can avoid the DVS system from being affected by coherent fading, and locate the vibration position of the target optical cable more accurately and efficiently. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0026] Figure 1 The schematic diagram of the structure of the device for avoiding coherent fading in the DVS system of the present invention is shown.

[0027] Reference numerals:

[0028] 1. DVS system; 2. 1xN optical switch; 3. Delay optical fiber; 4. Target optical cable. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] The object of the present invention is to provide a device and method for avoiding coherent fading in a DVS system, which can avoid the DVS system from being affected by coherent fading and improve the positioning accuracy and positioning efficiency of the vibration position of the target optical cable.

[0031] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] like Figure 1 As shown, the present invention provides a device for avoiding coherent fading in a DVS system 1, comprising: two 1xN optical switches 2 and N delay optical fibers 3, N≥2; a com end of one of the 1xN optical switches 2 is connected to an output end of the DVS system 1, and a com end of another 1xN optical switch 2 is connected to a target optical cable 4 to be tested; each of the delay optical fibers 3 is arranged between the two 1xN optical switches 2, and both ends of each of the delay optical fibers 3 are respectively connected to the 1xN optical switches 2 at corresponding positions.

[0033] As a specific implementation method, the lengths of the delay optical fibers 3 are different from each other and should be as random as possible to avoid periodic repeated interference. The minimum length of the delay optical fibers 3 depends on the line width of the laser of the DVS system 1, and the minimum difference between the lengths of the delay optical fibers 3 should be greater than the maximum resolution of the DVS system 1.

[0034] When the length of the optical fiber changes, the phase relationship of the return light from different scattering points will change. The optical switch changes the total optical path of the system by connecting extended optical fibers of different lengths, so that the original coherent fading points are redistributed, thereby avoiding the situation where the signal at certain points is always weak.

[0035] In this embodiment, the 1xN optical switch 2 is set to a 1x8 optical switch, the number of delay optical fibers 3 is 8, and the lengths are 25m, 33m, 51m, 87m, 102m, 233m, 527m and 1005m, respectively corresponding to channels 1-8 of the 1xN optical switch 2.

[0036] In addition, the present invention also provides a method for avoiding coherent fading in a DVS system 1, comprising the following steps:

[0037] S1: A device for avoiding coherent fading in a DVS system 1 is constructed using two 1xN optical switches 2 and N delay optical fibers 3.

[0038] S2: Record the length of the delay optical fiber 3 and enter it into the system, correspond it with the 1xN optical switch 2 channels and calibrate the timestamp to ensure that the data of each measurement is aligned in time.

[0039] S3: After the 1xN optical switch 2 switches channels sequentially or randomly and becomes stable, the DVS system 1 starts single measurement or multiple measurements and obtains single or multiple measurement data under the channel.

[0040] S4: Sequentially switch all channels once or multiple times as a cycle, or randomly switch a certain number of channels as a cycle. During the completion of a cycle, evaluate the signal quality of each channel, assign signal weights to each point, and calculate the weighted average signal after the cycle ends. If there is an area with poor signal quality within a cycle, use an interpolation algorithm to compensate the signal.

[0041] As a specific implementation, the signal in the above description refers to the signal after the original signal is processed. After the original signal is bandpass filtered, baseline corrected and smoothed to reduce noise, the desired signal is obtained by integrating the amplitude change rate and the single-point change rate within multiple frames. The signal quality is evaluated by the signal amplitude. The signal amplitude is collected at the same position in each channel, and the signal amplitude is used as a direct indicator of signal quality. A larger signal amplitude indicates a better signal quality.

[0042] The calculation of the amplitude change rate within the above multiple frames is based on the continuous frame S t+1 -S t and interval frame S t+2 -S t , S t+3 -S t , S t+4 -S t ...weights are assigned to the differential values ​​according to the signal-to-noise ratio, and smoothing and threshold filtering are performed after weighting; the integral of the single-point rate of change is calculated by accumulating the same point for a fixed time t after the above processing, and the value of t depends on the system sampling rate and system performance requirements.

[0043] The weight of signal weighting is directly determined by the signal amplitude. First, the signal amplitudes of all channels are normalized. A i is the signal amplitude of the i-th channel, max(A) is the maximum amplitude of all channels, and weight Calculate the weighted average signal of each point by weight The signal quality criteria are as follows: For excellence, For general, The interpolation algorithm uses linear interpolation to compensate for points with poor signal amplitude. For points with poor signal amplitude, the weighted average of channels with better signal quality is used for compensation.

[0044] S5: Repeat steps S3 and S4.

[0045] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0046] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A device for avoiding coherent fading in a DVS system, characterized in that: include: Two 1xN optical switches and N delay optical fibers, N ≥ 2; the com end of one of the 1xN optical switches is connected to the output end of the DVS system, and the com end of the other 1xN optical switch is connected to the target optical cable to be tested; each of the delay optical fibers is arranged between the two 1xN optical switches, and both ends of each of the delay optical fibers are respectively connected to the 1xN optical switches at corresponding positions.

2. The device for avoiding coherent fading in a DVS system according to claim 1, characterized in that: The lengths of the delay optical fibers are different and do not repeat periodically.

3. The device for avoiding coherent fading in a DVS system according to claim 1, characterized in that: The length difference between each two of the delay optical fibers is greater than the maximum resolution of the DVS system.

4. The device for avoiding coherent fading in a DVS system according to claim 1, characterized in that: The number of the delay optical fibers is set to 8.

5. The device for avoiding coherent fading in a DVS system according to claim 4, characterized in that: The lengths of the delay optical fibers are respectively set to: 25m, 33m, 51m, 87m, 102m, 233m, 527m and 1005m.

6. A method for avoiding coherent fading in a DVS system, applied to the device as claimed in any one of claims 1 to 5, characterized in that: include: A device for avoiding coherent fading in a DVS system is constructed by using two 1xN optical switches and N delay optical fibers, recording the length of each delay optical fiber, and performing time stamp correction between each delay optical fiber and the corresponding 1xN optical switch channel; Switch the channels of the 1xN optical switch according to the set switching mode, and perform single or multiple measurements on the DVS system to obtain single or multiple measurement data under the corresponding channel; During the completion of a cycle, the signal quality of each channel is evaluated, and each measurement data is weighted. After the cycle ends, the weighted average signal is calculated according to the weights of each signal, and the interpolation algorithm is used to compensate for the data of the area with poor evaluation results within the cycle; wherein, the evaluation process is: the signal amplitude is normalized, and when the normalized value is greater than 0.8, the signal quality is determined to be excellent, when the normalized value is less than or equal to 0.8 and greater than or equal to 0.5, the signal quality is determined to be general, and when the normalized value is less than 0.5, the signal quality is determined to be poor.

7. The method for avoiding coherent fading in a DVS system according to claim 6, characterized in that: The set switching mode includes a sequential switching mode or a random switching mode; wherein the sequential switching mode is: sequentially switching all channels once or multiple times as a cycle; the random switching mode is: randomly switching a set number of channels as a cycle.

8. The device for avoiding coherent fading in a DVS system according to claim 6, characterized in that: In the set switching mode, the channel switching time interval of the 1xN optical switch is greater than a single measurement time of the DVS system.

9. The device for avoiding coherent fading in a DVS system according to claim 6, characterized in that: The calculation formula for the normalization process is: Among them, A i is the signal amplitude of the i-th channel, and max(A) is the maximum amplitude of all channels.

10. The device for avoiding coherent fading in a DVS system according to claim 6, characterized in that: The calculation formula of the signal weighting is: in, is the normalized value of the i-th channel signal, is the normalized value of the j-th channel signal, j=1...N, N is the total number of channels.

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