A calibration method, system and device for low-frequency performance testing of all-fiber detector

Abstract

The present invention provides a calibration method, system and device for testing the low-frequency performance of an all-fiber detector. The method includes: attaching a parallel plate capacitor structure to both ends of the detector probe and applying an AC voltage signal to drive the detector probe to vibrate up and down, causing the optical fiber on the detector probe to deform in an AC form; obtaining the phase change of the optical fiber through a demodulation algorithm, combining the frequency and amplitude of the AC voltage signal, and establishing a first relationship between the phase change and the AC voltage signal; applying an AC voltage signal in a frequency band below 0.1 Hz, and converting the frequency and amplitude of the detector probe based on the first relationship to achieve the test and calibration of the low-frequency performance of the all-fiber detector. The scheme of the present invention is based on parallel plate capacitor excitation, effectively realizing the low-frequency performance test and calibration of the fiber optic seismograph, with high detection accuracy, low detection cost, and simple operation, filling the current technical gap in the low-frequency performance test and calibration of fiber optic interferometer seismographs.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing, and in particular to a calibration method, system and device for low-frequency performance testing of an all-optical fiber detector. Background Art

[0002] Compared with electromechanical seismographs, fiber optic seismographs have advantages such as intrinsic passiveness of the probe, resistance to electromagnetic interference, and easy multiplexing and networking, and are suitable for monitoring natural earthquakes in harsh environments such as the seabed. Fiber optic detectors based on fiber optic interferometry technology have the potential to monitor long-period vibration signals, so interferometric fiber optic seismographs are a hot topic of research at home and abroad, and have achieved certain results. At the same time, corresponding to the calibration method of electromechanical seismograph indicators, the calibration method for fiber optic seismograph indicators also needs to be developed accordingly.

[0003] The test of key performance indicators of ultra-wideband electromechanical seismographs is generally completed by combining the vibration table test (absolute calibration) and the coil excitation test (relative calibration). The existing ultra-low frequency vibration measurement devices in China can only accurately test the frequency band above 0.1Hz, so the vibration table is used to test only the parameters from 0.1Hz to the high frequency band. According to the seismograph inspection regulations of the China Earthquake Administration, the coil excitation test method (sine calibration or step calibration) is adopted for the low-frequency end parameter indicators of ultra-wideband electromechanical seismographs below 0.1Hz; the relative amplitude-frequency characteristics, period, damping and other parameters of the low-frequency end are measured by a high-precision analog signal generator to obtain the amplitude-frequency characteristics of the complete frequency band.

[0004] For ultra-wideband fiber optic seismographs, ultra-low frequency vibration measurement devices can still be used to accurately test the performance indicators of the frequency band above 0.1 Hz. However, its sensor probe is all-fiber passive, and its working principle is also very different from that of electromechanical seismographs. For low frequencies below 0.1 Hz, the relative calibration method of magnetic excitation testing used by electromechanical seismographs is not applicable to ultra-wideband fiber optic seismographs. At present, there is no effective low-frequency performance test calibration technology for fiber optic seismographs. Summary of the invention

[0005] Based on the problems existing in the prior art, the present invention provides a calibration method and control method for low-frequency performance test of an all-fiber detector. The specific scheme is as follows:

[0006] A calibration method for low-frequency performance testing of an all-fiber detector includes the following steps:

[0007] Installing a preset detector probe onto the all-fiber detector to be tested, and attaching a preset parallel plate capacitor structure to both ends of the detector probe;

[0008] Applying an AC voltage signal to the parallel plate capacitor structure to drive the detector probe to vibrate up and down, causing the optical fiber on the detector probe to deform in an AC form;

[0009] Acquire the phase change of the optical fiber by a preset demodulation algorithm, and establish a first relationship between the phase change and the AC voltage signal in combination with the frequency and amplitude of the AC voltage signal;

[0010] An AC voltage signal in a frequency band below 0.1 Hz is applied to the parallel plate capacitor structure to obtain the phase change of the optical fiber under the AC voltage signal in the frequency band, and the frequency and amplitude of the detection probe are converted based on the first relationship to achieve test calibration of the low-frequency performance of the all-fiber detector.

[0011] In a specific embodiment, it also includes: after obtaining the first relationship, applying an AC voltage signal of more than 0.1 Hz to the parallel plate capacitor structure to test and calibrate the high-frequency performance of the all-fiber detector to obtain a first test result; judging whether the first test result and the preset high-frequency performance test result of the all-fiber detector meet the preset test requirements: if so, based on the first relationship, testing and calibrating the low-frequency performance of the all-fiber detector; if not, adjusting the parameters in the test process to re-obtain the first relationship.

[0012] In a specific embodiment, the detection probe includes an inertial mass block, a first compliant cylinder, a second compliant cylinder, a first optical fiber and a second optical fiber; the first optical fiber is wound around the first compliant cylinder to form a first spring body, and the first spring body is equivalent to a spring oscillator structure; the second optical fiber is wound around the second compliant cylinder to form a second spring body, and the second spring body is equivalent to a spring oscillator structure.

[0013] In a specific embodiment, "applying an AC voltage signal to the parallel plate capacitor structure to drive the detection probe to vibrate up and down, causing the optical fiber on the detection probe to deform in an AC form" includes: applying an AC voltage signal to the parallel plate capacitor structure, the positive and negative poles of the charge of the parallel plate capacitor structure change in an AC manner, causing vibration; the inertial mass block senses the vibration of the parallel plate capacitor structure and produces a relative displacement; the first and second compliant columns are driven by the inertial mass block to deform, thereby causing the first optical fiber and the second optical fiber to produce a phase change due to the deformation, and the first optical fiber and the second optical fiber are deformed in opposite directions.

[0014] In a specific embodiment, the first optical fiber and the second optical fiber form two arms of a Michelson interferometer; when vibration occurs, the first optical fiber and the second optical fiber are stretched and squeezed respectively, so that the two arms of the Michelson interferometer have phase changes in opposite directions; the phase change of the Michelson interferometer is accurately demodulated by a phase generation carrier modulation and demodulation algorithm to obtain the phase change amount of the first optical fiber and the second optical fiber.

[0015] In a specific embodiment, an AC voltage signal in the frequency band of 360s-0.1Hz is applied to the parallel plate capacitor structure to test and calibrate the performance indicators of the all-fiber detector in the frequency band of 360s-0.1Hz; the amplitude of the detection probe is adjusted by changing the amplitude of the AC voltage signal.

[0016] In a specific embodiment, a plurality of node frequencies are selected within a frequency range of 360s-0.1Hz; an AC voltage signal of each node frequency is applied to the parallel plate capacitor structure, and the AC voltage signal of each node frequency has a magnitude relationship in amplitude.

[0017] In a specific embodiment, an AC voltage signal is applied to the parallel plate capacitor structure, and the electric field E is:

[0018]

[0019] The driving force on the inertial mass block, the first spring body, and the second spring body under AC voltage is:

[0020]

[0021] in, is the charge density, Q=CV(t) is the surface charge, C is the capacitance, ε is the equivalent dielectric constant, and V(t) is the voltage of the AC voltage signal.

[0022] In a specific embodiment, the mechanical equation under the action of the driving force F is:

[0023]

[0024] Wherein, h is the height variable of the inertial mass block, γ is the equivalent damping coefficient of the first spring body and the second spring body, and k is the equivalent spring coefficient of the first spring body and the second spring body.

[0025] A calibration system for low-frequency performance testing of an all-fiber detector includes the following:

[0026] A preparation unit, used for installing a preset detector probe on the all-fiber detector to be tested, and adding a preset parallel plate capacitor structure at both ends of the detector probe;

[0027] A driving unit, used for applying an AC voltage signal to the parallel plate capacitor structure to drive the detector probe to vibrate up and down, causing the optical fiber on the detector probe to deform in an AC form;

[0028] A calculation unit, configured to obtain a phase variation of the optical fiber by using a preset demodulation algorithm, and establish a first relationship between the phase variation and the AC voltage signal in combination with the frequency and amplitude of the AC voltage signal;

[0029] The testing unit is used to apply an AC voltage signal in a frequency band below 0.1 Hz to the parallel plate capacitor structure, obtain the phase change of the optical fiber under the AC voltage signal in the frequency band, and convert the frequency and amplitude of the detection probe based on the first relationship to achieve test calibration of the low-frequency performance of the all-fiber detector.

[0030] In a specific embodiment, it also includes:

[0031] A verification unit is used to apply an AC voltage signal of more than 0.1 Hz to the parallel plate capacitor structure after obtaining the first relationship, so as to test and calibrate the high-frequency performance of the all-fiber detector to obtain a first test result; and determine whether the first test result and the preset high-frequency performance test result of the all-fiber detector meet the preset test requirements: if so, based on the first relationship, test and calibrate the low-frequency performance of the all-fiber detector; if not, adjust the parameters in the test process to re-obtain the first relationship.

[0032] A calibration device for low-frequency performance testing of an all-fiber detector, used to implement any of the calibration methods described above, the calibration device comprising:

[0033] The all-fiber detector carries a detector probe on which an optical fiber is wound;

[0034] A parallel plate capacitor structure comprises a first plate body, a second plate body and a circuit unit, wherein the circuit unit connects the first plate body and the second plate body; one end of the detection probe is connected to the first plate body, and the other end is connected to the second plate body;

[0035] A waveform generator, connected to the circuit unit, for applying an AC voltage signal to the parallel plate capacitor structure;

[0036] A coupler connected to the detection probe to form a Michelson interferometer with the detection probe;

[0037] A phase demodulation module is used to obtain the phase change of the optical fiber through a demodulation algorithm;

[0038] The signal acquisition and processing module is connected to the phase demodulation module and is used to calculate the low-frequency performance of the all-fiber detector according to the phase change of the optical fiber.

[0039] In a specific embodiment, the detection probe includes a shell, an inertial mass block, a first compliant cylinder, a second compliant cylinder, a first optical fiber and a second optical fiber; the first optical fiber is wound on the first compliant cylinder to form a first spring body, and the first spring body is equivalent to a spring oscillator structure; the second optical fiber is wound on the second compliant cylinder to form a second spring body, and the second spring body is equivalent to a spring oscillator structure; the first compliant cylinder, the second compliant cylinder, the inertial mass block, the first optical fiber and the second optical fiber are located in the shell.

[0040] In a specific embodiment, the inertial mass block is in a push-pull structure to improve sensing sensitivity; and / or, Faraday rotators are provided at the tail ends of the first optical fiber and the second optical fiber to reduce the polarization fading effect caused by the polarization state in the optical fiber waveguide.

[0041] Beneficial effects: The present invention provides a calibration method, system and device for low-frequency performance test of all-fiber geophone, which is based on parallel plate capacitor excitation, effectively realizes low-frequency performance test and calibration of fiber-optic seismograph, has high detection accuracy, low detection cost and simple operation, and fills the technical gap of low-frequency performance test and calibration of all-fiber passive probe of fiber-optic interferometer seismograph. Attach parallel metal plates to the geophone probe and give an alternating voltage signal of 360s-0.1Hz, causing the inertial mass block to vibrate up and down, thereby simulating external vibration signals, and then realizing the low-frequency performance test and calibration of the fiber-optic seismograph. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0043] Figure 1 is a flow chart of the calibration method of the present invention;

[0044] Figure 2 It is a structural diagram of the core shaft type push-pull type compliant cylindrical optical fiber detector of the present invention;

[0045] Figure 3 is a schematic diagram of a parallel plate capacitor structure of the present invention;

[0046] Figure 4 It is a frequency response characteristic curve diagram of the silica gel compliant column under the action of alternating current of the present invention;

[0047] Figure 5 The present invention Figure 4 A partial enlarged view based on the

[0048] Figure 6 is a schematic diagram of a calibration system module of the present invention;

[0049] Figure 7 2 is an example diagram of the calibration device of the present invention.

[0050] Figure markings: A1-preparation unit; A2-driving unit; A3-computing unit; A4-testing unit; A5-verification unit; 1-parallel plate capacitor structure; 2-detection probe; 11-first plate body; 12-second plate body; 13-circuit unit; 21-first compliant column; 22-second compliant column; 23-inertial mass block; 24-first optical fiber; 25-second optical fiber; 26-housing; 27-Faraday rotator; 31-laser light source; 32-isolator; 33-coupler; 34-photodetector; 35-modulator; 36-phase demodulation module; 37-signal acquisition and processing module. DETAILED DESCRIPTION

[0051] 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.

[0052] At present, there is a mature relative calibration method for electromechanical seismographs, namely the coil excitation test method. However, the sensor probe of the fiber optic seismograph is all-fiber passive, which is one of its advantages compared with the electromechanical seismograph, but the coil excitation test method cannot be applied to the fiber optic seismograph, and there is no effective low-frequency performance test calibration solution for the fiber optic seismograph.

[0053] Example 1

[0054] This embodiment proposes a calibration method for low-frequency performance test of all-fiber geophones. Based on the parallel plate capacitor excitation method, it realizes accurate test and calibration of low-frequency performance of fiber-optic seismographs, filling the technical gap of low-frequency performance test and calibration of all-fiber passive probes of fiber-optic interferometer seismographs. The calibration method flow chart is attached to the specification. Figure 1 The specific scheme is as follows:

[0055] A calibration method for low-frequency performance testing of an all-fiber detector comprises the following steps:

[0056] 101. Install a preset detector probe on the all-fiber detector to be tested, and attach a preset parallel plate capacitor structure to both ends of the detector probe;

[0057] 102. Apply an AC voltage signal to the parallel plate capacitor structure to drive the detector probe to vibrate up and down, causing the optical fiber on the detector probe to deform in an AC form;

[0058] 103. Obtain the phase change of the optical fiber by using a preset demodulation algorithm, and establish a first relationship between the phase change and the AC voltage signal in combination with the frequency and amplitude of the AC voltage signal;

[0059] 104. Apply an AC voltage signal in a frequency band below 0.1 Hz to the parallel plate capacitor structure, obtain the phase change of the optical fiber under the AC voltage signal in the frequency band, and convert the frequency and amplitude of the detection probe based on the first relationship to achieve test calibration of the low-frequency performance of the all-fiber detector.

[0060] For the interferometric fiber ultra-wideband seismograph, this embodiment designs a core-shaft push-pull compliant column all-fiber detector probe structure, which is set in the interferometric fiber ultra-wideband seismograph to be tested, and can realize the all-fiber passive detection function. Figure 2 As shown. For the core shaft type push-pull type compliant column all-fiber detector probe structure, this embodiment proposes a calibration method based on parallel plate capacitor excitation test, designs a parallel plate capacitor excitation test structure, connects parallel metal plates to the all-fiber detector to form a capacitor structure, applies a low-frequency alternating voltage (0.1Hz-360s), realizes artificial control of the vibration signal on the probe, and performs low-frequency performance test and calibration of the all-fiber detector probe. The parallel plate capacitor structure is shown in the attached manual. Figure 3 shown.

[0061] Specifically, the core-axis push-pull type compliant cylinder optical fiber detector probe (referred to as the detector probe) includes an inertial mass block, a first compliant cylinder, a second compliant cylinder, a first optical fiber and a second optical fiber. The first optical fiber is wound on the first compliant cylinder to form a first spring body, which is equivalent to a spring oscillator structure; the second optical fiber is wound on the second compliant cylinder to form a second spring body, which is equivalent to a spring oscillator structure.

[0062] Preferably, a compliant cylinder is made of silicone and an optical fiber is wound thereon, which can not only reduce the equivalent elastic coefficient but also have good low-frequency response characteristics. An inertial mass block is added in the middle of the compliant cylinder. Preferably, the inertial mass block is a metal block, such as an inertial brass mass block. Further preferably, the inertial mass block is designed as a push-pull structure, which can improve the sensing sensitivity. Preferably, a Faraday rotator is designed at the tail end of the sensing optical fiber to reduce the polarization fading effect caused by the polarization state in the optical fiber waveguide. The silicone compliant cylinder and the wound optical fiber constitute a spring oscillator structure; the inertial brass mass block can sense the vibration of the shell and produce relative displacement.

[0063] The changes in the internal structure of the detector probe specifically include: applying an AC voltage signal to the parallel plate capacitor structure, the positive and negative poles of the charge of the parallel plate capacitor structure change in an alternating manner, and generating an AC Coulomb force together with the inertial mass block, causing the inertial mass block to vibrate up and down; the first and second compliant columns are driven by the inertial mass block to deform, thereby causing the first optical fiber and the second optical fiber to produce a phase change due to the deformation, and the deformation directions of the first and second optical fibers are opposite. For passive probes, an alternating capacitance mode is adopted to excite the inertial mass block on the probe to vibrate up and down, so that the compliant column is "squeezed" and "stretched", causing the phase change caused by the "compression" and "extension" deformation of the wound optical fiber. The up and down vibration of the detector probe is also to better meet the test requirements. Preferably, the alternating electrical signal is set to 360s-0.1Hz, and the performance indicators of the 360s-0.1Hz frequency band of the fiber optic seismometer can be tested and calibrated.

[0064] The low-frequency performance test and calibration of the mandrel-type push-pull compliant column detector probe can be completed by only using an arbitrary waveform generator to give the parallel plate capacitor structure a low-frequency alternating voltage signal. No complicated auxiliary equipment and instruments are required, which is simple and easy to operate with low testing cost.

[0065] The parallel plate capacitor excitation test and calibration technology is designed to effectively realize the low-frequency performance test and calibration of the fiber optic seismometer. Specifically, the signal output by the arbitrary waveform generator is used as the AC drive signal of the parallel plate capacitor; the positive and negative poles of the parallel plate charge change in an alternating manner, driving the inertial mass block to vibrate up and down, driving the silicone compliant cylinder of the wound optical fiber, which is equivalent to the spring body, to "squeeze" or "stretch", causing the optical fiber length to deform in an alternating manner, and its change frequency is equivalent to the AC drive signal output by the waveform generator.

[0066] Instructions attached Figure 3 A parallel plate capacitor structure is provided, comprising a first plate body, a second plate body and a circuit unit, wherein the circuit unit connects the first plate body and the second plate body; one end of a detection probe is connected to the first plate body, and the other end is connected to the second plate body. The parallel plate capacitor structure is fully compatible with a mandrel-type push-pull compliant column structure, and only requires metal parallel plates to be added at both ends, which is simple and easy to operate, and is efficient and accurate.

[0067] The calibration method of this embodiment needs to first confirm the relationship between the AC voltage signal and the optical fiber phase change, and name this relationship as the first relationship. Therefore, after obtaining the first relationship, it is necessary to confirm whether the relationship is accurate. The calibration method also includes: after obtaining the first relationship, applying an AC voltage signal of more than 0.1 Hz to the parallel plate capacitor structure to perform a high-frequency performance test calibration on the all-fiber detector to obtain a first test result; judging whether the first test result and the preset high-frequency performance test result of the all-fiber detector meet the preset test requirements: if so, based on the first relationship, perform a low-frequency performance test calibration on the all-fiber detector; if not, adjust the parameters during the test and re-acquire the first relationship.

[0068] In order to verify the feasibility of measuring the first relationship, an AC voltage signal at a high frequency point above 0.1 Hz can be selected to perform a performance test on the all-fiber detector, and the vibration table absolute calibration test method can be used to perform an index test at the same frequency. The results of the two methods are compared to verify the effectiveness and accuracy of the sample solution. The preset test requirement is whether the first test result and the high-frequency performance test result are the same within the preset accuracy requirement. Only when the first test result is the same as the high-frequency performance test result can it be determined that the first relationship is correct. When the first relationship is incorrect, it is necessary to adjust the relevant parameters in the test process and re-acquire the first relationship until the correct first relationship is obtained.

[0069] The first optical fiber and the second optical fiber form two arms of the Michelson interferometer (i.e., the sensing arm and the reference arm); when vibration occurs, the first optical fiber and the second optical fiber are stretched and squeezed, so that the two arms of the Michelson interferometer have phase changes in opposite directions. The phase change of the Michelson interferometer is accurately demodulated by the phase generation carrier modulation and demodulation algorithm to obtain the phase change of the first optical fiber and the second optical fiber.

[0070] Preferably, the first optical fiber and the second optical fiber are connected to a coupler, and the coupler and the detection probe form a Michelson interferometer. The silicone compliant cylinder wrapped with the sensing optical fiber at the upper and lower positions of the inertial mass block of the detection probe senses the external vibration signal, and the deformation of the compliant cylinder causes the deformation of the wrapped optical fiber. The upper and lower sections of the wrapped optical fiber form the two arms of the Michelson interferometer. When the vibration signal comes, due to the up and down vibration of the inertial mass block, the upper and lower sections of the optical fiber are stretched and squeezed respectively, so that the two arms of the interferometer have phase changes in opposite directions. The phase change amount can be obtained by the phase generation carrier modulation and demodulation algorithm, and then the external vibration signal is measured.

[0071] The Michelson interferometer is the most common type of optical interferometer. Its principle is that an incident light beam is split into two beams by a beam splitter and then reflected back by the corresponding plane mirror. Because the two beams have the same frequency, the same vibration direction and a constant phase difference (i.e., they meet the interference condition), interference can occur. The different optical paths of the two beams in the interference can be achieved by adjusting the length of the interference arm and changing the refractive index of the medium, thereby forming different interference patterns.

[0072] Preferably, an AC voltage signal in the frequency band of 360s-0.1Hz is applied to the parallel plate capacitor structure to test and calibrate the performance indicators of the all-fiber detector in the frequency band of 360s-0.1Hz; the amplitude of the detection probe is adjusted by changing the amplitude of the AC voltage signal. Multiple node frequencies are selected in the frequency band of 360s-0.1Hz, and AC voltage signals of each node frequency are applied to the parallel plate capacitor structure, and the AC voltage signals of each node frequency have a size relationship in amplitude. For example, several key node frequencies between 360s-0.1Hz of the applied AC voltage frequency are set, such as 360s, 300s, 200s, 100s, 50s, 20s, and 10s, and their amplitudes are modulated from small to large.

[0073] As attached Figure 1 As shown, applying an AC voltage In the parallel plate capacitor structure and acting on the inertial mass block (mass m, area A). The height variable of the inertial mass block is h, the equivalent damping coefficient of the silicone compliant cylinder wrapped by the optical fiber is γ, the equivalent spring coefficient is k, and the equivalent dielectric constant is ε; when an AC voltage signal is applied to the parallel plate capacitor structure, the electric field E is:

[0074]

[0075] The driving force on the inertial mass block, the first spring body, and the second spring body under AC voltage is:

[0076]

[0077] in, is the charge density, Q=CV(t) is the surface charge, C is the capacitance, ε is the equivalent dielectric constant, and V(t) is the voltage of the AC voltage signal. The mechanical equation under the driving force F is:

[0078]

[0079] Wherein, h is the height variable of the inertial mass block, γ is the equivalent damping coefficient of the first spring body and the second spring body, and k is the equivalent spring coefficient of the first spring body and the second spring body. The function h(t) or h(ω) of the height change of the inertial mass block over time is obtained by formulas (1) and (2), which directly corresponds to the relationship between the length change (i.e., phase change) of the wound optical fiber and the time change. Wherein, (the frequency f = 2π / ω can be set to less than 0.1 Hz, up to 360s).

[0080] The phase change of the optical fiber is obtained by the phase generation carrier modulation and demodulation algorithm suitable for the optical fiber Michelson interference structure. V(t) gives the detection probe a vibration signal, causing the phase change of the wound optical fiber; if V(t) is a signal with a frequency of 360s-0.1Hz, the vibration frequency of the sensor probe is 360s-0.1Hz; and the amplitude of V(t) is directly related to the amplitude of the sensor probe. The frequency and amplitude of V(t) are read out, and the frequency and amplitude of the sensor probe vibration can be obtained by determining the conversion relationship, and then the low-frequency response characteristics of the all-fiber passive probe can be detected.

[0081] Preferably, the calibration method of this embodiment can achieve low-frequency response characteristic measurement including: testing and calibrating key indicators such as the operating frequency, responsiveness, and dynamic range of the all-fiber detector. Simulation analysis proves that the scheme of the present invention can effectively measure the performance of the all-fiber detector probe and is an effective means of testing the low-frequency performance of the fiber optic seismic detector. Figure 4 The frequency response characteristic curve of the silicone rubber cylinder with various parameters set under AC is attached in the manual. Figure 5 For attachment Figure 4 A local enlarged view (0.001Hz-100Hz).

[0082] This embodiment provides a calibration method for low-frequency performance test of an all-fiber geophone. Based on parallel plate capacitor excitation, the low-frequency performance test and calibration of the fiber-optic seismograph is effectively realized. The detection accuracy is high, the detection cost is low, and the operation is simple. It fills the technical gap of low-frequency performance test and calibration of all-fiber passive probes of fiber-optic interferometer seismographs. A parallel metal plate is attached to the geophone probe and an alternating voltage signal of 360s-0.1Hz is given to cause the inertial mass block to vibrate up and down, thereby simulating an external vibration signal, thereby realizing the low-frequency performance test and calibration of the fiber-optic seismograph.

[0083] Example 2

[0084] This embodiment provides a calibration system for testing the low-frequency performance of an all-fiber detector. The calibration method of Embodiment 1 is systematized. The module diagram of the calibration system is shown in the attached manual. Figure 6 The specific plan is as follows:

[0085] A calibration system for low-frequency performance testing of an all-fiber detector includes the following:

[0086] A preparation unit A1 is used to install a preset detector probe on the all-fiber detector to be tested, and to attach a preset parallel plate capacitor structure to both ends of the detector probe;

[0087] The driving unit A2 is used to apply an AC voltage signal to the parallel plate capacitor structure to drive the detector probe to vibrate up and down, causing the optical fiber on the detector probe to deform in an AC form;

[0088] The calculation unit A3 is used to obtain the phase change of the optical fiber by using a preset demodulation algorithm, and establish a first relationship between the phase change and the AC voltage signal in combination with the frequency and amplitude of the AC voltage signal;

[0089] The test unit A4 is used to apply an AC voltage signal in a frequency band below 0.1 Hz to the parallel plate capacitor structure, obtain the phase change of the optical fiber under the AC voltage signal in the frequency band, and convert the frequency and amplitude of the detection probe based on the first relationship to realize the test calibration of the low-frequency performance of the all-fiber detector.

[0090] The verification unit A5 is used to apply an AC voltage signal of more than 0.1 Hz to the parallel plate capacitor structure after obtaining the first relationship, so as to test and calibrate the high-frequency performance of the all-fiber detector to obtain a first test result; determine whether the first test result and the preset high-frequency performance test result of the all-fiber detector meet the preset test requirements: if so, based on the first relationship, test and calibrate the low-frequency performance of the all-fiber detector; if not, adjust the parameters in the test process to re-obtain the first relationship.

[0091] As attached Figure 1 As shown, applying an AC voltage In the inertial mass block (mass is m, area is A). The mass block height variable is h, the equivalent damping coefficient of the silicone compliant cylinder wrapped with the optical fiber is γ, the equivalent spring coefficient is k, and the equivalent dielectric constant is ε; applying an AC voltage signal to the parallel plate capacitor structure, the electric field E is:

[0092]

[0093] The driving force on the inertial mass block, the first spring body, and the second spring body under AC voltage is:

[0094]

[0095] in, is the charge density, Q=CV(t) is the surface charge, C is the capacitance, ε is the equivalent dielectric constant, and V(t) is the voltage of the AC voltage signal. The mechanical equation under the driving force F is:

[0096]

[0097] Wherein, h is the height variable of the inertial mass block, γ is the equivalent damping coefficient of the first spring body and the second spring body, and k is the equivalent spring coefficient of the first spring body and the second spring body. The function h(t) or h(ω) of the height change of the inertial mass block over time is obtained by formulas (1) and (2), which directly corresponds to the relationship between the length change (i.e., phase change) of the wound optical fiber and the time change. Wherein, (the frequency f = 2π / ω can be set to less than 0.1 Hz, up to 360s).

[0098] The phase change of the wound sensing fiber is obtained by the phase generation carrier modulation and demodulation algorithm suitable for the optical fiber Michelson interference structure. V(t) gives the detection probe a vibration signal, causing the phase change of the wound optical fiber; if V(t) is a signal with a frequency of 360s-0.1Hz, the vibration frequency of the sensing probe is 360s-0.1Hz; and the amplitude of V(t) is directly related to the amplitude of the sensing probe. The frequency and amplitude of V(t) are read out, and the frequency and amplitude of the vibration of the sensing probe can be obtained by determining the conversion relationship, and then the low-frequency response characteristics of the all-fiber passive probe can be detected.

[0099] Preferably, the low-frequency response characteristic measurement that can be achieved by the calibration method of this embodiment includes: testing and calibrating key indicators such as the operating frequency, responsiveness, and dynamic range of the all-fiber detector.

[0100] This embodiment provides a calibration system for low-frequency performance testing of an all-fiber detector, which systematizes the calibration method for low-frequency performance testing of an all-fiber detector in Embodiment 1 to make it more practical.

[0101] Example 3

[0102] This embodiment provides a calibration device for low-frequency performance testing of an all-fiber detector, which can implement the calibration method of Embodiment 1. The specific scheme is as follows:

[0103] A calibration device for low-frequency performance testing of an all-fiber detector, comprising:

[0104] The all-fiber detector carries a detector probe 2 on which an optical fiber is wound;

[0105] The parallel plate capacitor structure 1 comprises a first plate body 11, a second plate body 12 and a circuit unit 13, wherein the circuit unit 13 connects the first plate body 11 and the second plate body 12; one end of the detection probe 2 is connected to the first plate body 11, and the other end is connected to the second plate body 12;

[0106] a waveform generator, connected to the circuit unit, for applying an AC voltage signal to the parallel plate capacitor structure;

[0107] The coupler 33 is connected to the detection probe 2 and forms a Michelson interferometer with the detection probe 2;

[0108] A phase demodulation module 36, used to obtain the phase change of the optical fiber through a demodulation algorithm;

[0109] The signal acquisition and processing module 17 is connected to the phase demodulation module 36 and is used to calculate the low-frequency performance of the all-fiber detector according to the phase change of the optical fiber.

[0110] The detector probe is as shown in the instruction manual. Figure 2 As shown, it includes a housing 26, an inertial mass block 23, a first compliant cylinder 21, a second compliant cylinder 22, a first optical fiber 24 and a second optical fiber 25; the first optical fiber 24 is wound on the first compliant cylinder 21 to form a first spring body, which is equivalent to a spring oscillator structure; the second optical fiber 25 is wound on the second compliant cylinder 22 to form a second spring body, which is equivalent to a spring oscillator structure; the first compliant cylinder 21, the second compliant cylinder 22, the inertial mass block 23, the first optical fiber 24 and the second optical fiber 25 are located in the housing 26. The upper and lower parts of the housing 26 are respectively provided with aluminum bases to achieve electrical connection with the parallel plate capacitor 1 structure.

[0111] Preferably, a compliant cylinder is made of silicone and an optical fiber is wound thereon, which can not only reduce the equivalent elastic coefficient but also have good low-frequency response characteristics. An inertial mass block is added in the middle of the compliant cylinder. Preferably, the inertial mass block 23 is a metal block, such as an inertial brass mass block. Further preferably, the inertial mass block 23 is designed as a push-pull structure, which can improve the sensing sensitivity. Preferably, a Faraday rotator 27 is designed at the tail end of the sensing optical fiber to reduce the polarization fading effect caused by the polarization state in the optical fiber waveguide. The silicone compliant cylinder and the wound optical fiber constitute a spring oscillator structure; the inertial brass mass block senses the vibration of the shell and produces relative displacement.

[0112] Instructions attached Figure 7An example of a calibration device is given, including a laser light source 31, an isolator 32, a coupler 33, a photodetector 34, a modulator 35, a phase demodulation module 36, a signal acquisition and processing module 37, a detection probe 2 and a parallel plate capacitor structure 1. The laser light source 31 uses a narrow linewidth laser light source, which is a distributed feedback (DFB) laser with a wavelength of about 1550nm, and outputs continuous light with a pulse width of 10kHz to subsequent components; the subsequent components include an isolator 32, a coupler 33, a photodetector 34, a modulator 35, a phase demodulation module 36, a signal acquisition and processing module 37, etc. The coupler 33 is connected to the first optical fiber 24 and the second optical fiber 25 respectively, and the first optical fiber 24 and the second optical fiber 25 are used as a sensing arm and a reference arm respectively. The photodetector 34 is connected to the coupler 33 and the phase demodulation module 36 respectively, and the phase demodulation module 36 performs phase demodulation according to the output result of the modulator 35 and the result of the coupler 33, obtains the phase change of the optical fiber, and outputs it to the signal acquisition and processing module 37. The signal acquisition and processing module 37 calculates the low-frequency performance of the all-fiber detector according to the phase change of the optical fiber.

[0113] The most important of these is the Michelson interferometer composed of a coupler 33 and a detection probe 2. The silicone compliant cylinder wrapped around the sensing optical fiber in the detection probe 2 senses the external vibration signal, and causes the deformation of the wrapped optical fiber through the deformation of the compliant cylinder. The upper and lower sections of the wrapped optical fiber form the two arms of the Michelson interferometer. When the vibration signal comes, due to the up and down vibration of the inertial mass block, the upper and lower sections of the wrapped optical fiber are stretched and squeezed respectively, so that the two arms of the interferometer have phase changes in opposite directions. The phase change can be obtained by the phase generation carrier modulation and demodulation algorithm, and then the external vibration signal can be measured.

[0114] The present invention provides a calibration method, system and device for low-frequency performance test of all-fiber geophone, which is based on parallel plate capacitor excitation, effectively realizes low-frequency performance test and calibration of fiber-optic seismograph, has high detection accuracy, low detection cost and simple operation, and fills the technical gap of low-frequency performance test and calibration of all-fiber passive probe of fiber-optic interferometer seismograph. Parallel metal plates are added to the geophone probe and an alternating voltage signal of 360s-0.1Hz is given to cause the inertial mass block to vibrate up and down, thereby simulating external vibration signals, and then realizing the test and calibration of low-frequency performance of fiber-optic seismograph.

[0115] It should be understood by those skilled in the art that the modules of the present invention described above can be implemented using a general-purpose computing system, they can be concentrated on a single computing system, or distributed on a network composed of multiple computing systems, optionally, they can be implemented using program codes executable by a computer system, so that they can be stored in a storage system and executed by the computing system, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. Thus, the present invention is not limited to any specific combination of hardware and software.

[0116] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

[0117] The above disclosure is only a few specific implementation scenarios of the present invention, but the present invention is not limited thereto, and any changes that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A calibration method for low-frequency performance testing of an all-fiber detector, characterized in that: These include: Installing a preset detector probe onto the all-fiber detector to be tested, and attaching a preset parallel plate capacitor structure to both ends of the detector probe; An AC voltage signal is applied to the parallel plate capacitor structure, and the positive and negative poles of the charge of the parallel plate capacitor structure are alternating, causing vibration; the inertial mass block senses the vibration of the parallel plate capacitor structure and produces relative displacement; the first compliant column and the second compliant column are driven by the inertial mass block to deform, thereby causing the first optical fiber and the second optical fiber to produce a phase change due to the deformation, and the first optical fiber and the second optical fiber are deformed in opposite directions; Acquire the phase change of the optical fiber by a preset demodulation algorithm, and establish a first relationship between the phase change and the AC voltage signal in combination with the frequency and amplitude of the AC voltage signal; Applying an AC voltage signal in a frequency band below 0.1 Hz to the parallel plate capacitor structure, obtaining a phase change of the optical fiber under the AC voltage signal in the frequency band, and converting the frequency and amplitude of the detector probe based on the first relationship to achieve low-frequency performance test calibration of the all-fiber detector; The detection probe includes an inertial mass block, a first compliant cylinder, a second compliant cylinder, a first optical fiber and a second optical fiber; the first optical fiber is wound on the first compliant cylinder to form a first spring body, and the first spring body is equivalent to a spring oscillator structure; the second optical fiber is wound on the second compliant cylinder to form a second spring body, and the second spring body is equivalent to a spring oscillator structure.

2. The calibration method according to claim 1, characterized in that: Also includes: After obtaining the first relationship, applying an AC voltage signal of more than 0.1 Hz to the parallel plate capacitor structure to test and calibrate the high frequency performance of the all-fiber detector to obtain a first test result; Determine whether the first test result and the preset high-frequency performance test result of the all-fiber detector meet the preset test requirements: If yes, based on the first relationship, the low-frequency performance of the all-fiber detector is tested and calibrated; If not, adjust the parameters during the test to re-obtain the first relationship.

3. The calibration method according to claim 1, characterized in that: The first optical fiber and the second optical fiber form two arms of a Michelson interferometer; When vibration occurs, the first optical fiber and the second optical fiber are stretched and squeezed respectively, so that the two arms of the Michelson interferometer have phase changes in opposite directions; The phase variation of the Michelson interferometer is accurately demodulated by using a phase generation carrier modulation and demodulation algorithm to obtain the phase variation of the first optical fiber and the second optical fiber.

4. The calibration method according to claim 1, characterized in that: Applying an AC voltage signal in the frequency band of 360s-0.1Hz to the parallel plate capacitor structure to test and calibrate the performance index of the all-fiber detector in the frequency band of 360s-0.1Hz; The amplitude of the detection probe is adjusted by changing the amplitude of the AC voltage signal.

5. The calibration method according to claim 4, characterized in that: Select multiple node frequencies within the 360s-0.1Hz frequency band; An alternating voltage signal of each node frequency is applied to the parallel plate capacitor structure, and the alternating voltage signal of each node frequency has a magnitude relationship in amplitude.

6. The calibration method according to claim 1, characterized in that: When an AC voltage signal is applied to the parallel plate capacitor structure, the electric field E is: The driving force on the inertial mass block, the first spring body, and the second spring body under AC voltage is: in, is the charge density, is the surface charge, is the capacitor, The equivalent dielectric constant is, is the voltage of the AC voltage signal.

7. The calibration method according to claim 6, characterized in that: In driving force The mechanical equation under action is: in, is the height variable of the inertial mass block, is the equivalent damping coefficient of the first spring body and the second spring body, is the equivalent spring coefficient of the first spring body and the second spring body.

8. A calibration system for low-frequency performance testing of an all-fiber detector, characterized in that: The method for implementing the calibration method according to any one of claims 1 to 7 comprises the following: A preparation unit, used for installing a preset detector probe on the all-fiber detector to be tested, and adding a preset parallel plate capacitor structure at both ends of the detector probe; A driving unit, used for applying an AC voltage signal to the parallel plate capacitor structure to drive the detector probe to vibrate up and down, causing the optical fiber on the detector probe to deform in an AC form; A calculation unit, configured to obtain a phase variation of the optical fiber by using a preset demodulation algorithm, and establish a first relationship between the phase variation and the AC voltage signal in combination with the frequency and amplitude of the AC voltage signal; The testing unit is used to apply an AC voltage signal in a frequency band below 0.1 Hz to the parallel plate capacitor structure, obtain the phase change of the optical fiber under the AC voltage signal in the frequency band, and convert the frequency and amplitude of the detection probe based on the first relationship to achieve test calibration of the low-frequency performance of the all-fiber detector.

9. The calibration system according to claim 8, characterized in that: Also includes: A verification unit, configured to apply an AC voltage signal of 0.1 Hz or higher to the parallel plate capacitor structure after acquiring the first relationship, so as to test and calibrate the high frequency performance of the all-fiber detector and obtain a first test result; Determine whether the first test result and the preset high-frequency performance test result of the all-fiber detector meet the preset test requirements: If yes, based on the first relationship, the low-frequency performance of the all-fiber detector is tested and calibrated; If not, adjust the parameters during the test to re-obtain the first relationship.

10. A calibration device for low-frequency performance testing of an all-fiber detector, characterized in that: Used to implement the calibration method according to any one of claims 1 to 7, the calibration device comprises: The all-fiber detector carries a detector probe on which an optical fiber is wound; A parallel plate capacitor structure comprises a first plate body, a second plate body and a circuit unit, wherein the circuit unit connects the first plate body and the second plate body; one end of the detection probe is connected to the first plate body, and the other end is connected to the second plate body; A waveform generator, connected to the circuit unit, for applying an AC voltage signal to the parallel plate capacitor structure; A coupler connected to the detection probe to form a Michelson interferometer with the detection probe; A phase demodulation module is used to obtain the phase change of the optical fiber through a demodulation algorithm; The signal acquisition and processing module is connected to the phase demodulation module and is used to calculate the low-frequency performance of the all-fiber detector according to the phase change of the optical fiber.

11. The calibration device according to claim 10, characterized in that: The detector probe comprises a shell, an inertial mass block, a first compliant column, a second compliant column, a first optical fiber and a second optical fiber; The first optical fiber is wound around the first compliant cylinder to form a first spring body, and the first spring body is equivalent to a spring oscillator structure; The second optical fiber is wound around the second compliant cylinder to form a second spring body, and the second spring body is equivalent to a spring oscillator structure; The first compliant cylinder, the second compliant cylinder, the inertial mass, the first optical fiber and the second optical fiber are located in the housing.

12. The calibration device according to claim 11, characterized in that: The inertial mass block is in a push-pull structure to improve the sensing sensitivity; And / or, Faraday rotators are arranged at the tail ends of the first optical fiber and the second optical fiber to reduce the polarization fading effect caused by the polarization state in the optical fiber waveguide.

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