Fiber-optic sensor for measuring direct-current electric field strength, and direct-current electric field strength measurement apparatus and measurement method

Abstract

A fiber-optic sensor for measuring direct-current electric field strength, the fiber-optic sensor comprising an equal-strain cantilever beam (1), wherein a metal conductor (2) is fixed on a free end of the equal-strain cantilever beam (1); the upper and lower surfaces of the metal conductor (2) are respectively an upper charge induction surface and a lower charge induction surface, with the surface area of the upper charge induction surface being larger than the surface area of the lower charge induction surface; and an interference optical fiber (3) in a Michelson interferometer configuration is also fixedly connected to the equal-strain cantilever beam (1). A direct-current electric field strength measurement apparatus, which comprises a laser source, a circulator, a spectrometer and a sensor. After the components are connected, a quadratic function relationship between a direct-current electric field strength value and the strength value of a same interference peak in an output spectrum is determined; a corresponding database is established on the basis of the quadratic function relationship; the direct-current electric field strength measurement apparatus is used to test a direct-current electric field to be tested, so as to obtain a corresponding interference-peak strength value in a corresponding output spectrum; and on the basis of corresponding data in the database, a direct-current electric field strength value of said direct-current electric field is obtained.

Description

Optical fiber DC electric field intensity detection sensor, DC electric field intensity detection device and detection method TECHNICAL FIELD

[0001] The present application relates to the technical field of sensors, in particular to an optical fiber DC electric field intensity detection sensor, a DC electric field intensity detection device and a detection method. BACKGROUND

[0002] Electric field sensors play an important role in the fields of electric power and national defense. With the rapid development of electric power technology, high-voltage direct current transmission systems have become an important part of modern power grid structures. Therefore, accurate monitoring of direct current and static electric fields has attracted widespread attention.

[0003] Existing electric field sensors are divided into traditional electronic sensors and optical electric field sensors. The former has high sensitivity, but its sensitivity to electromagnetic environment cannot be ignored. In contrast, optical electric field sensors have excellent performance in strong electric field measurement due to their passive characteristics and wide frequency band. In recent years, with the integration of material science and optical technology, lithium niobate has become a research hotspot due to its excellent electro-optic effect. An integrated optical electric field sensor is prepared by preparing an optical waveguide on a lithium niobate crystal through titanium diffusion, thereby realizing the measurement of electric field. The integration and efficiency of the electric field sensor are realized, however, the charge accumulation effect of lithium niobate crystal in direct current electric field limits its application in strong direct current electric field measurement.

[0004] In 2020, a servo motor mechanism was introduced to dynamically rotate the lithium niobate sensor, successfully modulating the direct current electric field into an alternating current electric field for measurement, effectively overcoming the charge accumulation problem, thereby realizing the measurement of direct current electric field. However, this method also brings new challenges, such as the complexity of optical fiber rotation connection and system stability. In 2022, a design scheme of integrating a rotating shield electrode on a lithium niobate electro-optic (EO) sensor was proposed, which not only solves the problem of optical fiber rotation connection, but also has good linear characteristics in the range of 4-220kV / m direct current electric field. However, the introduction of the rotating shield electrode also brings problems such as increased noise, mechanical loss, and dependence on power stability, affecting the overall performance of the sensor. In view of the high cost and complex preparation of lithium niobate material, as well as the limitations of existing technologies in direct current electric field measurement, some new electric field sensors combining electrically sensitive materials with optical fibers have gradually become a new research direction. The earliest one uses electrostrictive material combined with optical fiber mode interference, through the strain of electrostrictive material caused by electric field to cause the change of output interference, thereby analyzing the output light to obtain the measured electric field value. There are also liquid crystal electro-optic effect and optical fiber grating, photonic crystal fiber to realize low electric field measurement.

[0005] Although these methods show potential in low electric field and alternating current electric field measurements, their application in direct current and high electric field environments still needs further optimization. In summary, the research of fiber-optic electric field sensors has great significance for the development of the field of electric field monitoring, and key problems in the prior art need to be solved urgently. SUMMARY

[0006] In view of the above problems in the prior art, the technical problem to be solved by the present application is to provide a fiber-optic direct current electric field strength detection sensor with fast detection speed, high sensitivity and high accuracy.

[0007] To solve the above technical problems, the present application adopts the following technical solutions:

[0008] A fiber-optic direct current electric field strength detection sensor, comprising an equal-strain cantilever beam, a metal conductor fixedly connected to a free end of the equal-strain cantilever beam, the metal conductor being a circumferentially symmetrical structure, the upper and lower surfaces of the metal conductor being an upper charge induction surface and a lower charge induction surface respectively, the surface area of the upper charge induction surface being larger than that of the lower charge induction surface, an interference optical fiber fixedly connected to the upper surface or the lower surface of the equal-strain cantilever beam, the interference optical fiber extending along a direction parallel to the axis of the equal-strain cantilever beam, the projections of the axis of the interference optical fiber, the axis of the equal-strain cantilever beam and the symmetry axis of the metal conductor in the vertical direction all lying on the same straight line, the interference optical fiber being a Michelson interference structure optical fiber, and the reflection end of the interference optical fiber facing the side where the metal conductor is located.

[0009] As an optimization, the interference optical fiber comprises a single-mode optical fiber, a multi-mode optical fiber and a multi-core optical fiber, the single-mode optical fiber and the multi-core optical fiber being fused to the two ends of the multi-mode optical fiber respectively, so that the interference optical fiber forms a Michelson interference structure.

[0010] As an optimization, a silver film is plated on the end face of the reflection end of the interference optical fiber, ultraviolet glue I is cured on the reflection end of the interference optical fiber, and the silver film is encapsulated in the ultraviolet glue I.

[0011] As an optimization, the interference optical fiber is cured on the equal-strain cantilever beam by ultraviolet glue II.

[0012] As an optimization, the equal-strain cantilever beam is in an isosceles triangular structure, and the metal conductor and the interference optical fiber are respectively arranged on the upper surface or the lower surface of the equal-strain cantilever beam.

[0013] As an optimization, the metal conductor is in a hemispherical structure.

[0014] As an optimization, the metal conductor is in a hollow structure.

[0015] A direct current electric field intensity detection device, comprising a laser source, a circulator, a light intensity detection device and a sensor, the sensor being the optical fiber direct current electric field intensity detection sensor of any one of claims 1 to 7, the output end of the laser being connected with the input end of the circulator, the output end I of the circulator being connected with one end of the interference optical fiber away from the direction of the silver film, and the output end II of the circulator being connected with the input end of the light intensity detection device.

[0016] A direct current electric field intensity detection method, using the direct current electric field intensity detection device to detect the direct current electric field intensity in the environment, placing the optical fiber direct current electric field intensity detection sensor in the direct current electric field, obtaining the light intensity detection value under the direct current electric field intensity, determining the quadratic function relationship between the direct current electric field intensity value and the light intensity detection value, establishing the database of the direct current electric field intensity value and the light intensity detection value according to the quadratic function relationship, the database having the direct current electric field intensity value and the corresponding light intensity detection value, using the direct current electric field intensity detection device to detect the direct current electric field to be detected to obtain the corresponding light intensity detection value, and obtaining the direct current electric field intensity value of the direct current electric field to be detected according to the corresponding light intensity detection value in the database.

[0017] As optimization, the quadratic function relationship between the direct current electric field intensity value and the light intensity detection value is determined by the following way: obtaining a plurality of sample environments with direct current electric field intensity values, respectively using the direct current electric field intensity detection device to detect to obtain the corresponding light intensity detection value, and according to each light intensity detection value, using a nonlinear quadratic polynomial to fit the direct current electric field intensity value and the light intensity detection value, so as to determine the quadratic function relationship between the direct current electric field intensity value and the light intensity detection value.

[0018] Compared with the prior art, the present application has the following beneficial effects: the sensor structure is simple, the detection of the direct current electric field intensity in the environment is convenient and reliable, the measured electric field can be directly analyzed according to the light intensity change, the detection sensitivity is high, the stability is good, the repeatability is good, the measurement of the direct current electric field intensity can be met, and the application prospect is good. BRIEF DESCRIPTION OF DRAWINGS

[0019] Fig. 1 is a structural schematic view of the optical fiber direct current electric field intensity detection sensor in the embodiment of the present application;

[0020] Fig. 2 is a bending strain diagram of a cantilever beam under 0.5kV / mm and 1kV / mm in the embodiment of the present application;

[0021] Fig. 3 is a light propagation field and light intensity distribution diagram in the interference optical fiber in the embodiment of the present application;

[0022] Fig. 4 is a spectrum response diagram of the corresponding interference peak of the sensor free end under different displacements in the embodiment of the present application;

[0023] Fig. 5 is a fitting curve diagram of the free end of the sensor and the reflected light intensity at different displacements in the embodiment of the present application;

[0024] Fig. 6 is a spectral response diagram of the corresponding interference peaks detected by the sensor at different direct current field intensity values in the embodiment of the present application;

[0025] Fig. 7 is a fitting curve diagram of different direct current field intensity values and the corresponding interference peak intensity values in the embodiment of the present application;

[0026] Fig. 8 is a fitting result diagram of the light intensity and the electric field at different times in the embodiment of the present application;

[0027] Fig. 9 is a spectral response diagram of two different interference peaks at different temperatures in the embodiment of the present application;

[0028] Fig. 10 is a linear fitting curve diagram of the wavelength of two different interference peaks changing with temperature at different temperatures in the embodiment of the present application. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0030] The fiber direct current field intensity detection sensor in the specific embodiment includes an equal-strain cantilever beam 1, a metal conductor 2 is fixedly connected to the free end of the equal-strain cantilever beam 1, the metal conductor 2 is a circumferentially symmetrical structure, the upper and lower surfaces of the metal conductor 2 are respectively an upper charge induction surface and a lower charge induction surface, the surface area of the upper charge induction surface is greater than that of the lower charge induction surface, an interference optical fiber 3 is fixedly connected to the upper surface or the lower surface of the equal-strain cantilever beam 1, the interference optical fiber 3 is arranged in extension along the direction parallel to the axis of the equal-strain cantilever beam 1, the projections of the axis of the interference optical fiber 3, the axis of the equal-strain cantilever beam 1 and the symmetry axis of the metal conductor 2 along the vertical direction are all located on the same straight line, the interference optical fiber 3 is a Michelson interference structure optical fiber, and the reflection end of the interference optical fiber 3 faces the side direction where the metal conductor 2 is located.

[0031] In the embodiment, the interference optical fiber 3 comprises a single-mode optical fiber, a multi-mode optical fiber and a multi-core optical fiber, the single-mode optical fiber and the multi-core optical fiber are respectively fused at two ends of the multi-mode optical fiber, so that the interference optical fiber 3 forms a Michelson interference structure.

[0032] In the embodiment, a silver film is plated on the reflection end face of the interference optical fiber 3, the interference optical fiber 3 is cured with the ultraviolet glue I, and the silver film is encapsulated in the ultraviolet glue I.

[0033] In the embodiment, the interference optical fiber 3 is cured on the equal-strain cantilever beam 1 by the ultraviolet glue II.

[0034] In the embodiment, the equal-strain cantilever beam 1 is in an isosceles triangular structure, and the metal conductor 2 and the interference optical fiber 3 are respectively arranged on the upper surface of the equal-strain cantilever beam 1.

[0035] In the embodiment, the metal conductor 2 is in a hemispherical structure.

[0036] In the embodiment, the metal conductor 2 is in a hollow structure.

[0037] A direct-current electric field intensity detection device comprises a laser source, a circulator, a light intensity detection device and a sensor, the sensor is the optical fiber direct-current electric field intensity detection sensor, the output end of the laser is connected with the input end of the circulator, the output end I of the circulator is connected with one end of the interference optical fiber which is located in the direction away from the silver film, and the output end II of the circulator is connected with the input end of the light intensity detection device. The light intensity detection device can be a spectrometer, or a power meter and a photodiode. In the embodiment, the light intensity detection device adopts a spectrometer to detect the corresponding interference peak intensity value in the output spectrum diagram.

[0038] A detection method of a direct-current electric field intensity, the direct-current electric field intensity detection device is used to detect the direct-current electric field intensity in the environment, the optical fiber direct-current electric field intensity detection sensor is placed in the direct-current electric field, the light intensity detection value under the direct-current electric field intensity is obtained, the quadratic function relationship between the direct-current electric field intensity value and the light intensity detection value is determined, the database of the direct-current electric field intensity value and the light intensity detection value is established according to the quadratic function relationship, the direct-current electric field intensity value of the direct-current electric field to be detected is obtained according to the corresponding light intensity detection value in the database after the direct-current electric field to be detected is detected by the direct-current electric field intensity detection device.

[0039] In the specific embodiment, the quadratic function relationship between the direct current electric field intensity value and the light intensity detection value is determined by the following method: obtaining a plurality of sample environments with direct current electric field intensity values, respectively detecting the corresponding light intensity detection values by using the direct current electric field intensity detection device, and fitting the direct current electric field intensity value and the light intensity detection value by using a nonlinear quadratic polynomial according to each light intensity detection value, so as to determine the quadratic function relationship between the direct current electric field intensity value and the light intensity detection value.

[0040] An interferometric fiber assembly is prepared by using optical fiber fusion technology. First, the coating layers of single-mode fiber (SMF), multi-mode fiber (MMF) and four-core fiber (FCF) are removed. Then, the end face is accurately cut by using an optical fiber cutting machine to ensure the flatness of the end face. Next, one end of a 5mm long MMF is fused with an SMF by using a full-automatic optical fiber fusion machine, and the other end of the MMF is fused with a 40mm long FCF, thereby obtaining a Michelson fiber interference structure. The four cores of the FCF are arranged in a square array, and the diameters of the core and the cladding are 9um and 125um respectively. The spacing between the cores is 42um. In order to enhance the reflectivity of the end face of the FCF, a layer of silver film is plated on the end face of the FCF by silver mirror reaction. In order to prevent the silver film from being oxidized, the silver film is packaged and protected by using ultraviolet curing glue.

[0041] The cantilever beam assembly is selected from a hard PVC plate with a thickness of 0.2mm and is cut into an isosceles triangle. The width (w) of the fixed end of the isosceles cantilever beam is set to 30mm, and the center axis length (L) is 55mm. A copper hollow hemisphere with a diameter of 6mm is fixed on the free end of the isosceles cantilever beam. In order to realize the stable combination of the interferometric fiber and the cantilever beam, the interferometric fiber is also fixed on the center axis of the isosceles cantilever beam by using ultraviolet curing glue.

[0042] A uniform electric field is formed between the two copper plates connected to the positive electrode and the ground, respectively. The copper hollow hemisphere is displaced by the electrostatic force in the electric field, thereby causing the cantilever beam to deform and further causing the fiber to bend. According to electrodynamic theory, the electrostatic force acting on the copper hollow hemisphere in the electrostatic field is:

[0043] ε0 is the dielectric constant of air, R is the radius of the hollow conductor hemisphere, and E is the intensity of the uniform electric field.

[0044] According to material mechanics, when the copper hemisphere at the end of the isosceles cantilever beam is affected by the electrostatic force F, the maximum deflection (tip displacement) of the isosceles cantilever beam is:

[0045] L is the length of the cantilever beam, σ is the elastic modulus of the fiber, and γ is the moment of inertia of the fiber. The electrostatic force causes the cantilever beam to bend and deform, thereby causing the fiber to bend.

[0046] Four-core fiber excite cladding modes and core modes, when the light is transmitted in the fiber, there will be optical path difference and phase difference between the core mode and the cladding mode. According to the mode interference theory, it is known that:

[0047] In the formula, I co is the light intensity of the core mode, is the light intensity of the m-order cladding mode. is the phase difference between the core mode and the m-order cladding mode.

[0048] If there are many interference peaks in the interference spectrum, it is known that the sensor has multiple modes participating in interference, that is:

[0049] L is the length of the sensing area, and Δn eff is the difference between the effective refractive index of the cladding mode and the core film. According to the interference principle, when , the wavelength of the interference trough is determined by the following formula:

[0050] The free spectral range of the interference spectrum is:

[0051] According to the stress optical effect, when the fiber is bent, compression is generated inside and tension is generated outside, which changes the difference between the effective refractive index and causes the modulation of the phase difference of the Michelson structure and the reflection intensity. The derivative of the length L and the curvature C of the fiber bending describes:

[0052] The sensitivity of the intensity change caused by the curvature:

[0053] Therefore, the metal hemisphere is driven by the electrostatic force in the electric field to bend the cantilever beam, thereby changing the curvature of the optical fiber, forcing the structure of the optical fiber to bend and deform, causing the leakage of the cladding mode of the optical fiber, and causing the intensity of the interference spectrum of the Michelson interference of the optical fiber to change. The change is used to measure the electric field.

[0054] In order to verify the elastic deformation of the equal-strain cantilever beam caused by the electrostatic force of the sensor under a certain electric field intensity, the finite element simulation software is used to simulate the equal-strain cantilever beam component in the sensor structure in the application. Through simulation analysis, the mechanical response of the sensor under the action of the electric field is revealed. Table 1 is the related parameters of the equal-strain cantilever beam.

[0055] Table 1

[0056] The DC electric field strength generated between the two electrode plates is set to a range of 0.5 kV / mm to 1 kV / mm, and the electrostatic force generated under different electric field strengths is calculated using formula (1.1). Figures 2(a) and 2(b) show the bending strain distribution of the cantilever beam under the action of the electrostatic force under the electric field strengths of 0.5 kV / mm and 1 kV / mm. It can be seen that when one end of the equal strain cantilever beam is fixed, the displacement of the conductor hemisphere end reaches the maximum, and under the electric field strengths of 0.5 kV / mm and 1 kV / mm, the maximum displacement of the free end caused by the electrostatic force is (a) 0.5978 mm and (b) 1.0119 mm, respectively.

[0057] As shown in FIG. 3, the light propagation field and light intensity distribution in the SMF-MMF-FCF structure are simulated by using the beam propagation method. The fiber model is gradually constructed along the Z-axis direction with the virtual light source as the center. The environmental settings and related parameters of the interference fiber structure are shown in Table 2. FIGS. 3(a) and 3(b) show the light field distribution of the sensor along the XZ and YZ axes. Since the core of the entire FCF is uniformly distributed, the light field distribution along the XZ and YZ axes is the same. As shown in FIG. 3(c), the light field distribution along the XY axis is shown. The light field distribution of the center and the four cores of the FCF is more obvious. The light is transmitted in the core of the SMF into the MMF, the MMF acts as a coupler, the MMF couples the light into the FCF, thereby generating an interference effect.

[0058] Table 2

[0059] In order to verify the influence of the interference fiber on the Michelson interference fiber reflection spectrum when it is subjected to bending deformation, a fiber free end displacement control device is used to control the bending deformation of the cantilever beam. In the initial state of the experiment, the interference fiber is kept in a horizontal position, at this time the recorded displacement is 0 mm. By adjusting the displacement of the free end of the interference fiber, the displacement interval is set to 0.25 mm. During the experiment, the spectral data under different displacement amounts are recorded. As shown in FIGS. 4 and 5, within the displacement range of 0 mm to 1.25 mm, it is observed that the reflection intensity gradually decreases with the increase of the displacement amount. Through quadratic polynomial fitting analysis, the fitting degree is 0.99254. Combined with the finite element simulation results, the maximum displacement of the cantilever beam is 1.0119 mm, which does not exceed the regular range obtained in the experiment. Therefore, it can be concluded that the sensor shows a regular response relationship within the electric field range of 0 kV / mm to 1 kV / mm.

[0060] The sensor was tested in a direct current electric field at an experimental ambient temperature of 25°C and a humidity of 40%. First, the full range was divided by an equal interval of 50 V / mm, the electric field between the electrodes was increased from small to large, and the reflected spectrum data of the Michelson interferometric fiber and the applied electric field intensity value were recorded by the spectrometer. Until the high-voltage electrode began to discharge, it was found that the electrode began to discharge when the applied electric field intensity was 1.1 kV / mm, and the sensor could not realize normal electric field intensity measurement, thereby establishing that the highest measurement electric field intensity of the sensor was 1 kV / mm. According to the range measured by the sensor, the sensor was tested multiple times according to the calibration procedure, as shown in FIG. 6, and the experimental data showed that the spectral intensity change was nonlinearly related to the electric field intensity, and therefore a nonlinear quadratic polynomial was used to fit the data, as shown in FIG. 7. The fitting degree was 0.99789, which ensured that the sensor could have good measurement accuracy, and multiple experiments showed that the fiber direct current electric field intensity detection sensor in the embodiment could realize the measurement of the electric field intensity between 0 kV / mm and 1 kV / mm. The sensitivity of the maximum electric field intensity measurement value was 11.728 dBm / (kV / mm), and the resolution was 100 V / mm.

[0061] For sensor applications, hysteresis is a very important indicator. In the embodiment, the electric field intensity was applied at an interval of 0.15 kV / mm from 0 kV / mm to 0.9 kV / mm and from 0.9 kV / mm to 0 kV / mm, respectively, and the fitting result is shown in FIG. 8(a). It can be observed that the change in light intensity during the measurement of increasing and decreasing electric field cycles is almost consistent and there is only a slight difference in sensitivity between the two processes, which indicates that the sensor has a low hysteresis effect in electric field measurement.

[0062] In addition, in order to test the measurement repeatability of the sensor, another separate cycle measurement was performed after 72 hours, and the electric field intensity was applied at an interval of 0.15 kV / mm from 0 kV / mm to 0.9 kV / mm and from 0.9 kV / mm to 0 kV / mm, respectively. The results showed that the sensor had repeatability, as shown in FIG. 8(b). The calculated electric field sensitivity was stable at about 13.86249 dBm / (kV / mm), and the data result graphs in the two time periods showed that the sensor had a certain stability.

[0063] To study the temperature response, the sensor structure was placed on the heating stage, and the temperature measurement was carried out by increasing the temperature from 30°C to 70°C at an interval of 10°C, and the spectral data was recorded using the optical spectrum analyzer. In the experiment, the sensing structure was fixed on the heating platform, and no electric field and external force was applied to the interference optical fiber. When the temperature changes, the diameter, length and effective refractive index of the interference optical fiber will change due to the thermal expansion effect and the thermo-optic effect. Therefore, the phase will also change under the influence of temperature, which will cause the wavelength of the interference spectrum to move. During the process of slowly increasing the temperature from 30°C to 70°C at an interval of 10°C, the reflection spectrum was tracked using the spectral analysis, and the reflection spectrum of the two different interference peaks at different temperature points was recorded by the optical spectrum analyzer (OSA).

[0064] Through the spectral analysis of the sensing structure, it can be observed that the interference spectrum moves to the long wave direction with the increase of temperature. As shown in FIG. 9(a) and FIG. 9(b), two spectral fringes Dip1 and Dip2 are selected for the characteristic analysis of the wavelength drift with temperature change. FIG. 10(a) and FIG. 10(b) show the linear fitting curves of the wavelength of the two spectral dips with temperature change. It is found that the wavelength of the two dips moves linearly to the long wave direction with the increase of temperature. The temperature sensitivity of Dip1 and Dip2 is 48 pm / °C, and the linearity is 0.9908 and 0.9976 respectively, and both of the two spectra have good linearity.

[0065] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit the technical solutions. Those of ordinary skill in the art should understand that those who modify or equivalently replace the technical solutions of the present application without departing from the purpose and scope of the technical solutions should be covered in the scope of the claims of the present application.

Claims

1. An optical fiber DC electric field strength detection sensor, characterized by: The equal-strain cantilever beam is fixedly connected with a metal conductor at a free end of the equal-strain cantilever beam, the metal conductor has a circularly symmetrical structure, upper and lower surfaces of the metal conductor are respectively an upper charge induction surface and a lower charge induction surface, a surface area of the upper charge induction surface is larger than that of the lower charge induction surface, an interferometric fiber is fixedly connected to an upper surface or a lower surface of the equal-strain cantilever beam, the interferometric fiber is arranged in an extending direction parallel to an axis of the equal-strain cantilever beam, projections of the axis of the interferometric fiber, the axis of the equal-strain cantilever beam and an axis of symmetry of the metal conductor in a vertical direction are all located on the same straight line, the interferometric fiber is a Michelson interferometric fiber, and a reflection end of the interferometric fiber faces a side where the metal conductor is located.

2. The optical fiber DC electric field strength detection sensor according to claim 1, characterized in that: The interferometric fiber includes a single-mode fiber, a multi-mode fiber and a multi-core fiber, the single-mode fiber and the multi-core fiber are respectively fused to two ends of the multi-mode fiber, so that the interferometric fiber forms a Michelson interferometric structure.

3. The optical fiber DC electric field strength detection sensor according to claim 1, characterized in that: A silver film is plated on an end face of the reflection end of the interferometric fiber, the reflection end of the interferometric fiber is cured with ultraviolet glue I, and the silver film is encapsulated in the ultraviolet glue I.

4. The optical fiber DC electric field strength detection sensor according to claim 1, characterized in that: The interferometric fiber is cured on the equal-strain cantilever beam by ultraviolet glue II.

5. The optical fiber DC electric field strength detection sensor according to claim 1, characterized in that: The equal-strain cantilever beam has an isosceles triangular structure, and the metal conductor and the interferometric fiber are respectively arranged on the upper surface or the lower surface of the equal-strain cantilever beam.

6. The optical fiber DC electric field strength detection sensor according to claim 1, characterized by: The metal conductor has a hemispherical structure.

7. The optical fiber DC electric field strength detection sensor according to claim 1, characterized by: The metal conductor has a hollow structure.

8. A direct current field strength detection device, characterized by: The DC electric field intensity detection device includes a laser source, a circulator, a light intensity detection device and a sensor, the sensor is the optical fiber DC electric field intensity detection sensor in any one of claims 1 to 7, an output end of the laser is connected with an input end of the circulator, an output end I of the circulator is connected with one end of the interferometric fiber which is located in a direction away from the silver film, and an output end II of the circulator is connected with an input end of the light intensity detection device.

9. A method of detecting direct current field strength, characterized by: The DC electric field intensity detection device in claim 8 is used to detect a DC electric field intensity in an environment, the optical fiber DC electric field intensity detection sensor is placed in the DC electric field, an optical intensity detection value under the DC electric field intensity is obtained, a quadratic function relationship between the DC electric field intensity value and the optical intensity detection value is determined, a database of the DC electric field intensity value and the optical intensity detection value is established according to the quadratic function relationship, the database has the DC electric field intensity value and the corresponding optical intensity detection value, a corresponding optical intensity detection value is obtained after the DC electric field intensity detection device detects a to-be-detected DC electric field, and the DC electric field intensity value of the to-be-detected DC electric field is obtained according to the corresponding optical intensity detection value in the database.

10. The method of detecting the strength of a direct current electric field according to claim 9, characterized by: The quadratic function relationship between the DC electric field intensity value and the optical intensity detection value is determined by the following method: a plurality of sample environments with DC electric field intensity values are obtained, corresponding optical intensity detection values are obtained after the DC electric field intensity detection device detects the sample environments respectively, and a non-linear quadratic polynomial is used to fit the DC electric field intensity value and the optical intensity detection value according to each optical intensity detection value, so as to determine the quadratic function relationship between the DC electric field intensity value and the optical intensity detection value.

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