Optical fiber whole-line equivalent quantitative vibration generation system and generation method, and vibration sensing performance measurement method

Abstract

The invention discloses an optical fiber whole-line equivalent quantitative vibration generation system and method and a vibration sensing performance measurement method. According to the optical fiber whole-line equivalent quantitative vibration generation system and method, a mode of performing frequency modulation on laser pulses is equivalent to applying vibration excitation with the same amplitude to all points of an optical fiber whole line of an optical fiber disc at the same time; quantitative uniform strain is simultaneously applied to the whole section of the tens of kilometers of the optical fiber, excitation is strictly quantitative, the amplitude is accurate and controllable, and the measurement precision of the vibration sensing performance of the optical fiber is greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber sensing, and in particular to an optical fiber full-line equivalent quantitative vibration generation system, a generation method, and a vibration perception performance measurement method. Background Art

[0002] A distributed optical fiber vibration system (hereinafter referred to as a DAS system) collects and analyzes the phase change of Rayleigh scattered light in an optical fiber, and can sense the vibration amplitude information of each point along a fiber of dozens of kilometers, having good application value. To ensure measurement accuracy, it is necessary to measure the vibration response ability of the DAS system during research and development, factory production, certification, and other stages. The vibration intensity in the optical fiber can be expressed by the strain amplitude that changes with time (simply referred to as the dynamic strain amplitude). Since the DAS system has the ability of distributed measurement, that is, it can independently and synchronously sense the vibration changes at different positions of the optical fiber, it is necessary to simultaneously apply vibration to the entire section of the optical fiber within the sensing distance (usually dozens of kilometers) of the DAS system during research and development, performance testing, and other links to judge whether there are differences in the vibration perception capabilities at each location. Also, since the DAS system is oriented to weak vibrations with an amplitude of the order of nε (nanostrain), it is necessary to simultaneously generate a dynamic strain amplitude of this order on a fiber of dozens of kilometers.

[0003] Taking CN110231815A as an example, a common method is that the DAS is connected to an optical fiber coil of dozens of kilometers, and the optical fiber coil is placed on a vibration table. This method is simple to operate. Only by controlling the vibration table, vibration excitation can be simultaneously applied to the entire coil of optical fiber. However, due to the uneven tightness of the optical fiber at each place of the optical fiber coil, it is difficult to create uniform vibration throughout the optical fiber line, and the vibration amplitude is uncontrollable, so it cannot be used for quantitative testing.

[0004] Taking CN105488968A as an example, another common method is that the DAS system is connected to the first optical fiber coil, then connected to an optical fiber expander with a piezoelectric ceramic as the core structure, and finally connected to the second optical fiber coil. By applying a voltage excitation with a certain frequency and a certain amplitude to the optical fiber expander, strain can be applied to the optical fiber in the internal expansion area. This method can accurately control the vibration amplitude (nanostrain value) and excitation frequency generated in the optical fiber, and the strain of the optical fiber in the expansion area is uniform, and can be used for quantitative testing. However, the length of the optical fiber that a single optical fiber expander can stretch is less than 1 km, and it is impossible to simultaneously apply vibration to all the optical fibers within the sensing distance of the DAS system. Summary of the Invention

[0005] In view of this, the present invention provides an optical fiber full-line equivalent quantitative vibration generation system, a generation method, and a vibration perception performance measurement method to solve the problem that uniform vibration cannot be simultaneously applied to each point of the entire optical fiber line.

[0006] An optical fiber full-line equivalent quantitative vibration generation system, comprising a DAS system detection host, a signal control unit, an optical frequency shifter, and an optical fiber coil. The optical signal output end of the DAS system detection host is connected to the optical input port of the optical frequency shifter. The optical output port of the optical frequency shifter is connected to the optical fiber coil. The radio frequency input port of the optical frequency shifter is connected to the control output end of the signal control unit;

[0007] The DAS system detection host is used to emit laser pulses and analyze the vibration amplitude sensed by the entire optical fiber line according to the phase change of the received backscattered optical signal;

[0008] The signal control unit is used to send a frequency modulation signal to the optical frequency shifter according to the full-line vibration excitation mode selected by the user;

[0009] The optical frequency shifter is used to apply a frequency shift amount to the laser pulse according to the received frequency modulation signal, so as to equivalently apply vibration excitations with equal amplitudes at all points along the entire optical fiber line of the optical fiber coil.

[0010] An optical fiber full-line equivalent quantitative vibration generation method based on the system described in claim 1, specifically including the following steps:

[0011] S1, set up an optical fiber full-line equivalent quantitative vibration generation system;

[0012] S2, the user selects the full-line vibration excitation mode;

[0013] S3, the DAS system detection host emits laser pulses, and at the same time the signal control unit controls the optical frequency shifter to apply a corresponding frequency shift amount to the laser pulse according to the full-line vibration excitation mode selected by the user, so as to equivalently apply vibration excitations with equal amplitudes at all points along the entire optical fiber line of the optical fiber coil.

[0014] Preferably, the calculation formula for the frequency shift amount is:

[0015]

[0016] Among them, Δν(t) is the frequency shift amount applied by the optical frequency shifter to the laser pulse, c is the speed of light in vacuum, λ is the optical wavelength, η is a parameter determined by the optical fiber material, ∈(t) is the vibration amplitude change function corresponding to the full-line vibration excitation mode selected by the user, and t is time.

[0017] Preferably, the optical fiber length of the optical fiber coil is in the range of ten kilometers to one hundred kilometers.

[0018] Preferably, the optical fiber length of the optical fiber coil does not exceed the sensing length of the DAS system detection host.

[0019] An optical fiber full-line vibration sensing performance measurement method based on the system described in claim 1, specifically including the following steps:

[0020] S1. Construct a full-fiber equivalent quantitative vibration generation system;

[0021] S2. The user selects a full-line vibration excitation mode;

[0022] S3. The DAS system detection host emits laser pulses. At the same time, the signal control unit controls the optical frequency shifter to apply a corresponding frequency shift amount to the laser pulses according to the full-line vibration excitation mode selected by the user, so as to equivalently apply vibration excitations with equal amplitudes to all points on the full fiber of the fiber optic disk simultaneously;

[0023] S4. The DAS system detection host analyzes the vibration perception performance of the full fiber according to the received backscattered light signal.

[0024] Preferably, the calculation formula for the frequency shift amount is:

[0025]

[0026] where Δv(t) is the frequency shift amount applied by the optical frequency shifter to the laser pulses, c is the speed of light in vacuum, λ is the optical wavelength, η is a parameter determined by the fiber material, ∈(t) is the vibration amplitude change function corresponding to the full-line vibration excitation mode selected by the user, and t is time.

[0027] Preferably, the fiber length of the fiber optic disk is in the range of ten kilometers to one hundred kilometers.

[0028] Preferably, the fiber length of the fiber optic disk does not exceed the sensing length of the DAS system detection host.

[0029] The beneficial effects of the present invention are:

[0030] 1. By means of frequency modulation of laser pulses, when the DAS system is working, the present invention equivalently applies dynamic strain excitations with equal amplitudes to all points on the full fiber of the fiber optic disk simultaneously, realizes the simultaneous application of vibration excitations with uniform amplitudes and quantitative amounts to each point of a fiber optic disk of dozens of kilometers, and the excitation is strictly quantitative and the amplitude is precisely controllable, which greatly facilitates the performance test and calibration of the DAS system.

[0031] 2. The components of the full-fiber equivalent quantitative vibration generation system of the present invention are all common components, which are easy to obtain, low in cost, and the system link is simple and the operation is convenient, and can improve the measurement efficiency of the fiber vibration perception performance. Description of the Drawings

[0032] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0033] Figure 1 It is the system principle block diagram of the full-line equivalent quantitative vibration generation system for optical fiber.

[0034] The meanings of the labels in the figure are as follows:

[0035] 100 is the DAS system detection host, 101 is the optical frequency shifter, 102 is the signal control unit, and 103 is the optical fiber reel. Specific embodiments

[0036] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be described through specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are only exemplary and do not intend to limit the scope of the present invention. In addition, in the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention.

[0037] The terms used in this disclosure are only for the purpose of describing specific embodiments and are not intended to limit this disclosure. The singular forms "a", "the", and "said" used in this disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0038] To better understand the technical solutions of the present invention, the present invention will be described in detail below in conjunction with the accompanying drawings.

[0039] The present invention provides a full-line equivalent quantitative vibration generation system for optical fiber, including a DAS system detection host 100, a signal control unit 102, an optical frequency shifter 101, and an optical fiber reel 103. The optical signal output end of the DAS system detection host 100 is connected to the optical input port of the optical frequency shifter 101. The optical output port of the optical frequency shifter 101 is connected to the optical fiber reel 103. The radio frequency input port of the optical frequency shifter 101 is connected to the control output end of the signal control unit 102;

[0040] The DAS system detection host 100 (abbreviated as DAS host) is used to emit laser pulses and analyze the vibration amplitude sensed by the entire optical fiber line according to the phase change of the received backscattered optical signal;

[0041] The signal control unit 102 is used to send a frequency modulation signal to the optical frequency shifter 101 according to the full-line vibration excitation mode selected by the user. The full-line vibration excitation mode includes multiple vibration excitation methods, and each vibration excitation method is stored in the signal control unit in the form of a function of the vibration amplitude changing with time;

[0042] The optical frequency shifter 101 is used to apply a frequency shift amount to the laser pulse according to the received frequency modulation signal, so as to equivalently apply vibration excitation with equal amplitude at each point along the entire length of the optical fiber of the optical fiber coil 103;

[0043] The optical fiber coil 103 serves as the sensing link of the DAS system detection host 100, and its length does not exceed the sensing length of the DAS system detection host. Preferably, the optical fiber of the optical fiber coil is up to dozens of kilometers long, that is, the optical fiber length is in the range of ten kilometers to one hundred kilometers.

[0044] The working principle of the above optical fiber full-line equivalent quantitative vibration generation system is as follows:

[0045] Since the DAS system detection host 100 directly senses the optical phase change caused by vibration, when there is no vibration at the location where the round-trip optical distance on the optical fiber is L, the optical phase φ(L) can be expressed as:

[0046]

[0047] where n eff is the effective refractive index, ν is the optical frequency, and c is the speed of light in vacuum. In a common DAS system, n eff Typical value is 1.4672; ν = c / λ, where λ is the optical wavelength, and the typical value is 1550 nm.

[0048] When no vibration strain is applied to the optical fiber and the optical frequency is increased from ν to ν′ = ν + Δν, the phase increase amount Δφ(L) can be expressed as:

[0049]

[0050] The vibration amplitude sensed by the optical fiber can be represented by the strain borne by the optical fiber. When a strain with a vibration amplitude of ∈ is uniformly applied to the entire section of the optical fiber coil, at the location where the round-trip optical distance on the optical fiber is L, the optical phase increase amount Δφ(L) can be expressed as:

[0051]

[0052] where η is a coefficient determined by the optical fiber material. In a common single-mode optical fiber for communication, η is generally about 0.78.

[0053] Comparing formula (2) and formula (3), it can be seen that only by making

[0054]

[0055] It can generate the same optical phase change as the strain excitation. Since the DAS system senses the optical phase, generating the same optical phase change as the strain excitation means achieving an excitation effect equivalent to generating spatially uniform strain along the entire optical fiber. The vibration excitation of the optical fiber is to apply dynamic strain (the strain amplitude changes with time) to the optical fiber. At this time, it is necessary to make the frequency shift amount change synchronously according to the strain amplitude according to formula (4).

[0056] Based on the above principle, the method for generating equivalent quantitative vibration along the entire optical fiber of the present invention specifically includes the following steps:

[0057] S1, construct the above-mentioned system for generating equivalent quantitative vibration along the entire optical fiber;

[0058] S2, the user selects the full-line vibration excitation mode.

[0059] S3, the DAS system detection host 100 emits laser pulses, and at the same time the signal control unit 102 controls the optical frequency shifter 101 to apply a corresponding frequency shift amount to the laser pulses according to the full-line vibration excitation mode selected by the user, so as to equivalently apply vibration excitations with equal amplitudes at each point along the entire optical fiber of the optical fiber coil 103.

[0060] The calculation formula for the frequency shift amount is:

[0061]

[0062] where Δν(t) is the frequency shift amount applied by the optical frequency shifter to the laser pulse, c is the speed of light in vacuum, λ is the optical wavelength, η is a parameter determined by the optical fiber material, ∈(t) is the vibration amplitude change function corresponding to the full-line vibration excitation mode selected by the user, and t is time.

[0063] For example, assume that there are five full-line vibration excitation modes, namely ∈ 1 (t), ∈ 2 (t), ∈ 3 (t), ∈ 4 (t), ∈ 5 (t), and the full-line vibration excitation mode selected by the user is ∈ 1 (t), and ∈ 1 (t) represents applying a vibration (set artificially) with a duration of 10 seconds, a vibration frequency of 43 Hz, and a vibration amplitude of A 1 to the entire optical fiber coil, with the vibration amplitude uniformly distributed in space;

[0064] The DAS system detection host 100 emits laser pulses, and at the same time the signal control unit 102 calculates the frequency shift amount Δv that the optical frequency shifter needs to apply to the laser pulse according to the full-line vibration excitation mode ∈ 1 (t)1 (t) and send a frequency modulation signal to the optical frequency shifter 101. The optical frequency shifter 101 applies a frequency shift amount Δv to the laser pulse according to the received frequency modulation signal. 1 (t). The frequency-shifted laser pulse is input into the optical fiber of the optical fiber reel 103, which is equivalent to simultaneously applying a vibration excitation with an amplitude of A at all points along the entire length of the optical fiber of the optical fiber reel 103. 1

[0065] The present invention also provides a method for measuring the vibration sensing performance of the entire optical fiber based on the above-mentioned system, which specifically includes the following steps:

[0066] S1, construct an equivalent quantitative vibration generation system for the entire optical fiber;

[0067] S2, the user selects the vibration excitation mode for the entire line;

[0068] S3, the DAS system detection host 100 emits a laser pulse, and at the same time, the signal control unit 102 controls the optical frequency shifter 101 to apply a corresponding frequency shift amount to the laser pulse according to the vibration excitation mode selected by the user, so as to be equivalent to simultaneously applying vibration excitations with equal amplitudes at all points along the entire length of the optical fiber of the optical fiber reel 103;

[0069] S4, the DAS system detection host 100 analyzes the vibration sensing performance of the entire optical fiber according to the received backscattered light signal, that is, after the DAS system detection host 100 receives the backscattered light signal, it demodulates the optical signal and calculates the phase change amount Δφ(L) at each position on the optical fiber respectively. According to the phase change amounts Δφ(L) at each position, further analyze whether the performance of the DAS system detection host meets the standard.

[0070] For example, if the phase change amounts Δφ(L) at each position are the same or very close, it indicates that the vibration sensing ability of this DAS system at all points along the optical fiber is basically consistent and meets the design requirements; if the phase change amount Δφ(L) at a certain position is significantly different from the phase change amounts at other positions, it indicates that the vibration sensing ability of the DAS system at this position is abnormal and further investigation of the abnormality is required.

[0071] It should be clear that the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

Claims

1. An optical fiber full-line equivalent quantitative vibration generation system, characterized in that: It includes a DAS system detection host, a signal control unit, an optical frequency shifter and an optical fiber disk, wherein the optical signal output end of the DAS system detection host is connected to the optical input port of the optical frequency shifter, the optical output port of the optical frequency shifter is connected to the optical fiber disk, and the radio frequency input port of the optical frequency shifter is connected to the control output end of the signal control unit; The DAS system detection host is used to emit laser pulses and analyze the vibration amplitude sensed by the entire optical fiber line based on the phase change of the received backscattered light signal; The signal control unit is used to send a frequency modulation signal to the optical frequency shifter according to the full-line vibration excitation mode selected by the user; The optical frequency shifter is used to apply a frequency shift amount to the laser pulse according to the received frequency modulation signal, so as to be equivalent to simultaneously applying vibration excitation of equal amplitude to all points along the entire optical fiber of the optical fiber disk.

2. A method for generating equivalent quantitative vibration of the entire optical fiber line based on the system of claim 1, characterized in that: The specific steps include: S1, establish an equivalent quantitative vibration generation system for the entire optical fiber line; S2, the user selects the full-line vibration excitation mode; S3, the DAS system detects the laser pulse emitted by the host, and at the same time, the signal control unit controls the optical frequency shifter to apply the corresponding frequency shift amount to the laser pulse according to the full-line vibration excitation mode selected by the user, so as to be equivalent to applying vibration excitation of equal amplitude to all points along the entire optical fiber of the optical fiber disk at the same time.

3. The method for generating equivalent quantitative vibration of the entire optical fiber according to claim 2, characterized in that: The calculation formula of the frequency shift amount is: Among them, Δη(t) is the frequency shift applied by the optical frequency shifter to the laser pulse, c is the speed of light in vacuum, λ is the wavelength of light, η is the parameter determined by the optical fiber material, ∈(t) is the vibration amplitude change function corresponding to the full-line vibration excitation mode selected by the user, and t is time.

4. The method for generating equivalent quantitative vibration of the entire optical fiber according to claim 2, characterized in that: The optical fiber length of the optical fiber reel is in the range of ten kilometers to one hundred kilometers.

5. The method for generating equivalent quantitative vibration of the entire optical fiber according to claim 2 or 4, characterized in that: The optical fiber length of the optical fiber disk does not exceed the sensing length of the DAS system detection host.

6. A method for measuring the full-line vibration perception performance of optical fiber based on the system of claim 1, characterized in that: The specific steps include: S1, establish an equivalent quantitative vibration generation system for the entire optical fiber line; S2, the user selects the full-line vibration excitation mode; S3, the DAS system detects the laser pulse emitted by the host, and the signal control unit controls the optical frequency shifter to apply a corresponding frequency shift to the laser pulse according to the full-line vibration excitation mode selected by the user, so as to be equivalent to applying vibration excitation of equal amplitude to all points along the entire optical fiber of the optical fiber disk at the same time; S4, the DAS system detection host analyzes the vibration sensing performance of the entire optical fiber line based on the backscattered light signals it receives.

7. The method for measuring the full-line vibration perception performance of optical fiber according to claim 6, characterized in that: The calculation formula of the frequency shift amount is: Among them, Δν(t) is the frequency shift applied by the optical frequency shifter to the laser pulse, c is the speed of light in a vacuum, λ is the wavelength of light, η is a parameter determined by the optical fiber material, ∈(t) is the vibration amplitude change function corresponding to the full-line vibration excitation mode selected by the user, and t is time.

8. The method for measuring the full-line vibration perception performance of optical fiber according to claim 6, characterized in that: The optical fiber length of the optical fiber reel is in the range of ten kilometers to one hundred kilometers.

9. The method for measuring the full-line vibration perception performance of optical fiber according to claim 6 or 8, characterized in that: The optical fiber length of the optical fiber disk does not exceed the sensing length of the DAS system detection host.

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