Optical fiber circular polarization conversion device and optical fiber current measurement device and method

Abstract

The invention discloses an optical fiber circular polarization conversion device and an optical fiber current measuring device and method. The optical fiber circular polarization conversion device comprises a crystal wave plate, a semi-transparent and semi-reflecting mirror and two circular polarization optical fiber collimators. The device can convert incident left-handed and right-handed circularly polarized light signals into circularly polarized light with opposite rotation directions in a reflection light path and a transmission light path of the device. When the device is applied to an optical fiber current measuring device, two independent sensing loops can be formed by using reflected and transmitted light signals of the device respectively. According to the technical scheme, through a novel device structure and a unique polarization state conversion function, the utilization efficiency and the measurement precision of optical signals are effectively improved, and meanwhile the beneficial effects of reducing cost, resisting vibration interference and achieving synchronous measurement of two paths of currents are achieved.

Description

Technical Field

[0001] This application relates to the field of fiber optic sensing technology, specifically to a fiber optic circular polarization converter, a fiber optic current measurement device, and a method. Background Technology

[0002] The field of fiber optic sensing technology is developing rapidly. Fiber optic current sensors (FOCS), based on the Faraday magneto-optical effect and using optical fiber as the sensing medium, hold a crucial position in the field of current measurement. They possess significant advantages such as strong resistance to electromagnetic interference, good electrical insulation, large dynamic range, and small size. They demonstrate enormous application potential in current monitoring in environments with strong electromagnetic interference, such as ultra-high voltage power grids, nuclear physics, and metallurgy, providing new possibilities for current measurement in complex environments and driving the development of related industries.

[0003] In the field of fiber optic current sensors, the conventional approach to current measurement is based on the Faraday magneto-optical effect, using optical fibers as the sensing medium to construct the sensor. The core of the sensor employs a current-sensitive special optical fiber, utilizing its properties to sense changes in the magnetic field generated by the current. However, a single such special optical fiber typically only allows for measurement at a single point, making multiplexing difficult. Furthermore, during the measurement process, this type of sensor faces various challenges from the external environment. For example, mechanical disturbances such as vibration, impact, and compression can act on the sensing fiber, and once the sensing fiber is damaged, specialized equipment is usually required for repair or replacement.

[0004] Existing technologies have significant drawbacks. On the one hand, the core current-sensitive special optical fiber of the sensor is expensive, and a single fiber can typically only achieve measurement at a single point, making reuse difficult and significantly increasing measurement costs. On the other hand, these special optical fibers are extremely sensitive to mechanical disturbances such as vibration, impact, and compression. External stress can cause fiber deformation, altering its birefringence properties and severely affecting the sensor's measurement accuracy. Furthermore, once the sensing fiber is damaged, specialized equipment is usually required for repair or replacement, further increasing the sensor's total lifecycle cost. Summary of the Invention

[0005] To address the technical problems in the prior art, this application provides an optical fiber circular polarization conversion device, an optical fiber current measurement device, and a method.

[0006] The fiber optic circular polarization converter, fiber optic current measurement device, and method provided in this application adopt the following technical solution: A fiber optic circular polarization converter includes: A crystal waveplate; A semi-transparent, semi-reflective mirror disposed on one side of the crystal waveplate; Two circularly polarized fiber collimators are distributed on both sides of the crystal waveplate; One circularly polarized fiber collimator is used to couple the input optical signal and the output optical signal formed by the reflection of the semi-transparent and semi-reflective mirror, and the other circularly polarized fiber collimator is used to couple the output optical signal formed by passing through the crystal waveplate. The input optical signal includes left-hand circularly polarized light and right-hand circularly polarized light. The reflected light signals of the left-hand circularly polarized light and right-hand circularly polarized light are converted into right-hand and left-hand circularly polarized light after passing through the semi-transparent mirror. The transmitted light signals of the left-hand circularly polarized light and right-hand circularly polarized light are converted into right-hand and left-hand circularly polarized light after passing through the crystal waveplate.

[0007] In some embodiments, the fast axis or slow axis of the circularly polarized fiber collimator is aligned at a 45° angle with the fast axis or slow axis of the crystal waveplate.

[0008] In some embodiments, the birefringent phase delay angle of the crystal waveplate is 180°.

[0009] In some embodiments, the fiber circular polarization converter further includes a substrate and a packaged housing; the crystal waveplate is fixed on the substrate, and the circular polarization fiber collimator, the substrate together with the crystal waveplate and the semi-transparent mirror are jointly fixedly installed in the packaged housing.

[0010] In some embodiments, the semi-reflective mirror is a semi-reflective film deposited on the front surface of the crystal waveplate, or an optical medium that is deposited on optical glass and then bonded to the front surface of the crystal waveplate.

[0011] This application also provides an optical fiber current measurement device, including a photoelectric acquisition unit, the aforementioned optical fiber circular polarization converter, an optical fiber quarter-wave plate, and an optical fiber reflector; The photoelectric acquisition unit is used to generate an initial optical signal and detect and demodulate the returned interference optical signal; One circularly polarized fiber collimator of the fiber circular polarization conversion device is connected to the fiber 1 / 4 waveplate, and the fiber 1 / 4 waveplate forms an optical path connection with the photoelectric acquisition unit. The other circularly polarized fiber collimator is connected to the fiber reflector to form a sensing optical path. In this sensing optical path, the optical signal emitted from the photoelectric acquisition unit is reflected at the semi-transparent mirror and then returned to the photoelectric acquisition unit along the original path after polarization state conversion, thus forming the first sensing loop; the transmitted optical signal formed by passing through the crystal waveplate is transmitted to the fiber optic mirror after polarization state conversion, and then returned to the photoelectric acquisition unit along the original path after reflection, thus forming the second sensing loop.

[0012] In some embodiments, the fiber optic current measuring device further includes a section of linearly polarized optical fiber, one end of which is fused to the fiber optic quarter-wave plate at a 45° axial angle, and the other end is connected to the photoelectric acquisition unit via an optical fiber connector.

[0013] This application also provides a fiber optic current measurement method, applicable to the aforementioned fiber optic current measurement device, and includes the following steps: The first sensor is surrounded around the first conductor current, and the second sensor is surrounded around the second conductor current. A pair of orthogonally linearly polarized lights are emitted by the photoelectric acquisition unit. After being converted into left-hand circularly polarized light and right-hand circularly polarized light by the fiber 1 / 4 waveplate, they enter the first sensing ring and generate a first Faraday phase difference under the magnetic field of the first conductor current. After the optical signal reaches the optical fiber circular polarization converter, a portion of the reflected optical signal is converted into circularly polarized light with the opposite rotation direction and returns along the original path; Another portion of the transmitted light signal is converted into circularly polarized light with opposite rotation direction and enters the second sensing ring. Under the action of the magnetic field of the second conductor current, a second Faraday phase difference is generated. This phase difference is superimposed with the first Faraday phase difference and is reflected by the fiber optic mirror and returns along the original path. The photoelectric acquisition unit uses time-division multiplexing demodulation technology to perform phase detection on the reflected interference light signal and the transmitted interference light signal, respectively, so as to calculate the magnitude of the first conductor current and the second conductor current.

[0014] This application also provides a fiber optic current measurement method, applicable to the aforementioned fiber optic current measurement device, and includes the following steps: The first sensing ring and the second sensing ring are wound together around the same conductor current, and the winding paths of the two sensing rings are consistent but the directions are opposite. The photoelectric acquisition unit emits an optical signal. A portion of the optical signal is transmitted within the first sensing ring and then reflected back by the optical fiber circular polarization converter, forming an interference signal containing a first Faraday phase difference. Another portion of the optical signal passes through the first sensing ring and the second sensing ring in sequence and is reflected back by the optical fiber mirror, forming an interference signal containing a second Faraday phase difference. The photoelectric acquisition unit demodulates the first Faraday phase difference and the second Faraday phase difference to calculate the magnitude of the conductor current; When the sensing ring is subjected to stress interference such as vibration or compression, due to the transmission delay difference of the optical signal in the first and second sensing rings, the same interference will introduce different deviations in the two Faraday phase differences. The photoelectric acquisition unit will issue an alarm based on the measurement error calculated by demodulation and remove abnormal measurement data.

[0015] In some embodiments, by changing the winding direction or number of turns of the first sensing ring while keeping the winding method and number of turns of the second sensing ring constant, a nonlinear relationship curve between the system phase difference and the current measurement value is fitted.

[0016] In summary, this application includes at least one of the following beneficial technical effects: 1. The fiber optic circular polarization converter, through a combination of a crystal waveplate, a semi-transparent mirror, and a circularly polarized fiber collimator, achieves polarization state conversion of the input optical signal. This polarization state conversion provides the foundation for subsequent fiber optic current measurement, enabling optical signals with different polarization states to carry different information, thereby achieving accurate current measurement. Compared with existing technologies, this device has a novel structure, effectively improving the utilization efficiency and measurement accuracy of the optical signal while reducing costs. 2. The fiber optic current measurement device constructs a unique sensing optical path through a combination of a photoelectric acquisition unit, a fiber optic circular polarization converter, an optical fiber / waveplate, and a fiber optic reflector. The fiber optic circular polarization converter performs polarization state conversion on the optical signal, allowing different sensing rings to carry information about the currents of different conductors. By detecting and demodulating the returned interference optical signal, the magnitude of the current in the corresponding conductor can be accurately measured. Simultaneously, the use of linearly polarized fiber ensures the stability of the optical signal's polarization state, improving the measurement accuracy and reliability. Compared with existing technologies, this device is lower in cost, more resistant to environmental interference such as vibration, and easier to maintain. 3. The fiber optic current measurement method involves winding a first and second sensing ring around different conductors. A fiber optic circular polarization converter is used to convert the polarization state of the optical signal, allowing different optical signals to carry information about the currents in different conductors. Time-division multiplexing demodulation technology is then used to process the returned interference signals, enabling accurate calculation of the magnitudes of the two conductor currents. This method allows for the simultaneous measurement of two currents with a single device, expanding its application range and reducing the cost of multi-point measurements.

[0017] 4. The fiber optic current measurement method utilizes the time delay difference between different optical paths by winding a first sensing ring and a second sensing ring around the same conductor in a specific manner to identify and suppress the influence of environmental interference such as vibration on the measurement results. Simultaneously, the measurement accuracy is further improved by fitting a nonlinear relationship curve. This method achieves highly reliable measurement of the current in a single conductor under harsh environments, solving the problem of sensor sensitivity to vibration and other interference in existing technologies. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of an optical fiber circular polarization converter provided in one embodiment of this application; Figure 2 This is a schematic diagram of the optical fiber current measuring device provided in the embodiments of this application; Figure 3 This is a schematic diagram of the dual-closed optical path conductor current measuring device provided in the embodiments of this application; Figure 4 This is a schematic diagram of the single closed optical path conductor current measuring device provided in the embodiments of this application; Figure 5 This is a schematic diagram of an "8"-shaped loop closure method (with opposite directions of wrapping) provided in an embodiment of this application; Figure 6 This is a schematic diagram of a "B"-type loop closure method (with the same direction of wrapping) provided in an embodiment of this application; Figure 7 This is a schematic diagram of the nonlinear relationship curve between the system phase difference and the current measurement value provided in the embodiments of this application.

[0019] Explanation of reference numerals in the attached figures: 1. Photoelectric acquisition unit; 2. Fiber optic circular polarization converter; 21. Crystal waveplate; 22. Semi-transparent mirror; 23. Circularly polarized fiber collimator; 231. Fiber optic cable; 232. Collimating lens; 24. Substrate; 25. Encapsulation shell; 3. Fiber optic quarter-waveplate; 4. Fiber optic reflector; 5. Linearly polarized fiber; 6. Fiber optic connector; 7. First conductor; 8. Second conductor; 9. Conductor. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. The described embodiments are only possible technical implementations of the present invention, but are not limited thereto. Other embodiments obtained by those skilled in the art in conjunction with the embodiments of the present invention without creative effort are also within the protection scope of the present invention.

[0021] This application mainly adopts a unique circular polarization transformation structure to realize current measurement and anti-interference, achieving the effects of reducing costs, resisting vibration interference, and flexibly measuring current. The following is a further detailed description of this application.

[0022] Example 1

[0023] Please refer to Figure 1 The fiber circular polarization converter 2 provided in this application includes a crystal waveplate 21, a semi-transparent and semi-reflective mirror 22, and two circular polarization fiber collimators 23. The two circular polarization fiber collimators 23 are distributed on both sides of the crystal waveplate 21, and the semi-transparent and semi-reflective mirror 22 is disposed on one side of the crystal waveplate 21. This structure can convert the polarization state of the input optical signal, thus providing a basis for subsequent current measurement. This is because optical signals with different polarization states will carry different information in the subsequent sensing process.

[0024] Specifically, the crystal waveplate 21 is a key component for realizing the polarization state conversion of the optical signal. The crystal waveplate 21 is typically made of a birefringent crystal material, such as quartz or lithium niobate. Its shape is generally a thin sheet, the thickness of which is determined by the required phase delay angle. In this scheme, the birefringent phase delay angle of the crystal waveplate 21 is 180°, equivalent to a half-wave plate. It can be replaced by other optical elements with the same phase delay effect. The fast or slow axis of the crystal waveplate 21 needs to be aligned at a 45° angle with the fast or slow axis of the circularly polarized fiber collimator 23 to ensure effective polarization state conversion of the optical signal when passing through the crystal waveplate 21.

[0025] The semi-reflective mirror 22 is used to split the input optical signal in two, reflecting one part and transmitting the other. It can be a semi-reflective film deposited on the front surface of the crystal waveplate 21, resulting in a compact structure and reduced device size. Alternatively, it can be an optical medium deposited on optical glass and then bonded to the front surface of the crystal waveplate 21. This approach allows for the selection of different optical glass and coating processes to meet varying optical performance requirements. The special construction of the semi-reflective mirror 22 lies in the design of its semi-reflective film, which precisely controls the ratio of reflected to transmitted light.

[0026] A circularly polarized fiber collimator 23 is used to couple the input optical signal and the corresponding reflected and transmitted optical signals. It typically consists of an optical fiber 231 and a collimating lens 232. The optical fiber 231 transmits the optical signal, and the collimating lens 232 collimates the diverging light output from the optical fiber 231 into parallel light. The circularly polarized fiber collimator 23 can be fabricated using circularly polarized preserving fiber or low birefringence fiber, etc. Alternatively, it can be any other optical device with similar coupling and collimation functions. Two circularly polarized fiber collimators 23 are connected to opposite sides of a crystal waveplate 21, one for coupling the input optical signal and the reflected optical signal, and the other for coupling the transmitted optical signal. Their connection to the crystal waveplate 21 is typically achieved through high-precision mechanical positioning and optical adhesive bonding to ensure the stability and accuracy of the optical path.

[0027] When the input optical signal includes both left-handed and right-handed circularly polarized light, the reflected light signals of the left-handed and right-handed circularly polarized light are converted to right-handed and left-handed circularly polarized light after passing through the semi-transparent mirror 22. Similarly, the transmitted light signals of the left-handed and right-handed circularly polarized light are converted to right-handed and left-handed circularly polarized light after passing through the crystal waveplate 21. This polarization conversion is achieved based on the optical properties of the crystal waveplate 21 and the semi-transparent mirror 22. The birefringence of the crystal waveplate 21 causes a change in the phase of the optical signal, thus leading to the polarization conversion. The reflection and transmission effects of the semi-transparent mirror 22 also affect the polarization state of the optical signal.

[0028] The fiber optic circular polarization converter 2 also includes a substrate 24 and a housing 25. The substrate 24 is used to fix the crystal waveplate 21 and is typically made of a material with good flatness and stability, such as a ceramic substrate or a glass substrate. The shape of the substrate 24 is generally rectangular or circular, and its size is determined according to the size of the crystal waveplate 21. The housing 25 is used to protect the internal optical components. It can be made of metal or plastic, or a high-permeability material, and has a certain degree of sealing and anti-interference capability. The circular polarization fiber collimator 23, the substrate 24, together with the crystal waveplate 21 and the semi-transparent mirror 22, are fixedly installed in the housing 25. This encapsulation method ensures the stability and reliability of the device and reduces the influence of the external environment on the device performance.

[0029] The implementation principle of this embodiment is as follows: The fiber circular polarization converter 2, through the combination of a crystal waveplate 21, a semi-transparent mirror 22, and a circularly polarized fiber collimator 23, realizes the polarization state conversion of the input optical signal. This polarization state conversion provides the basis for subsequent fiber current measurement, enabling optical signals with different polarization states to carry different information, thereby achieving accurate current measurement. Compared with the prior art, this device has a novel structure, effectively improving the utilization efficiency and measurement accuracy of the optical signal while reducing costs.

[0030] Example 2

[0031] The difference between this embodiment and the previous embodiment lies in the implementation method of the semi-transparent and semi-reflective mirror 22. In this embodiment, the semi-transparent and semi-reflective mirror 22 is an optical medium that is deposited on optical glass and then bonded to the front surface of the crystal waveplate 21. This method allows for the selection of different optical glass and coating processes according to specific application requirements to obtain better optical performance.

[0032] Optical glass possesses excellent optical uniformity and transmittance, and different types of optical glass exhibit varying refractive indices and dispersion characteristics. By selecting a suitable optical glass, the optical performance of the semi-reflective mirror 22 can be optimized. When depositing a semi-reflective film on the optical glass, methods such as physical vapor deposition and chemical vapor deposition can be employed, and the thickness and composition of the film can be controlled as needed to achieve different reflection and transmission ratios.

[0033] When bonding the optical glass coated with a semi-reflective film to the front surface of the crystal waveplate 21, a high-precision bonding process is required to ensure the fit and stability between the two. Optical adhesive can be used for bonding, as it has good optical properties and bonding strength, ensuring accurate optical path connection between the semi-transparent mirror 22 and the crystal waveplate 21.

[0034] The implementation principle of this embodiment is as follows: a semi-reflective mirror 22 is realized by depositing a semi-reflective film on optical glass and then bonding it to the front surface of the crystal waveplate 21. This allows for optimization of optical performance according to specific needs and improves the control accuracy of the reflection and transmission ratio of the semi-reflective mirror 22. This method increases the design flexibility of the semi-reflective mirror 22, enabling the fiber optic circular polarization converter 2 to better adapt to different application scenarios, and further improves the performance and reliability of the device.

[0035] Example 3

[0036] Please refer to Figure 2 The fiber optic current measurement device provided in this application includes a photoelectric acquisition unit 1, a fiber optic circular polarization converter 2, a fiber optic quarter-wave plate 3, and a fiber optic reflector 4. The photoelectric acquisition unit 1 is used to generate an initial optical signal and detect and demodulate the returned interference optical signal. One circular polarization fiber collimator 23 of the fiber optic circular polarization converter 2 is connected to the fiber optic quarter-wave plate 3, and an optical path connection is formed between the fiber optic quarter-wave plate 3 and the photoelectric acquisition unit 1. The other circular polarization fiber collimator 23 is connected to the fiber optic reflector 4 to form a sensing optical path. This structure can realize the measurement of current, achieving the effects of reducing costs, expanding measurement functions, and improving measurement reliability. This is because the device, through its unique optical path design and polarization state conversion, can realize the measurement of current in multiple conductors and anti-vibration interference measurement.

[0037] Specifically, the photoelectric acquisition unit 1 is the core control and signal processing component of the entire device. It typically includes a light source, a detector, and a demodulation circuit. The light source generates the initial light signal and generally uses a laser source, such as a semiconductor laser, which offers advantages such as stable output power and good monochromaticity. The detector detects the returned interference light signal; common types include photodiodes and avalanche photodiodes. The demodulation circuit processes and demodulates the electrical signal output from the detector to obtain the required current information. Through optical path connections with other components, the photoelectric acquisition unit 1 can accurately acquire and process light signals.

[0038] The fiber optic quarter-wave plate 3 is used to convert the linearly polarized light emitted by the photoelectric acquisition unit 1 into circularly polarized light. It is typically made of a crystalline material with birefringence, such as quartz. The fiber optic quarter-wave plate 3 is a thin sheet, the thickness of which is determined by the required phase delay angle. In this scheme, it converts linearly polarized light into circularly polarized light, providing a suitable optical signal for subsequent sensing processes. The fiber optic quarter-wave plate 3 is optically connected to the photoelectric acquisition unit 1 via optical fiber, typically through fusion splicing, to ensure low loss and stability of the optical path.

[0039] The fiber optic reflector 4 is used to reflect the transmitted light signal, allowing it to return along its original path. It can be a reflector formed by coating a reflective film on the end of the fiber, a reflector constructed using optical elements such as a reflecting prism, or a fiber optic Faraday reflector. The reflectivity of the fiber optic reflector 4 needs to be designed according to specific application requirements to ensure sufficient light signal returns to the photoelectric acquisition unit 1. It is connected to another circularly polarized fiber collimator 23 of the fiber optic circular polarization converter 2, and the connection method is also through high-precision mechanical positioning and optical adhesive bonding.

[0040] In the sensing optical path, the optical signal emitted from the photoelectric acquisition unit 1 is reflected at the semi-transparent mirror 22 and, after polarization state conversion, returns to the photoelectric acquisition unit 1 along the original path to form the first sensing loop. The transmitted optical signal, formed by passing through the crystal waveplate 21, is transmitted to the fiber optic mirror 4 after polarization state conversion, and after reflection, returns to the photoelectric acquisition unit 1 along the original path to form the second sensing loop. These two sensing loops can be used to sense the magnetic fields generated by different conductor currents, thereby realizing the measurement of multiple conductor currents.

[0041] The device also includes a section of linearly polarized optical fiber 5, one end of which is fused to the fiber optic quarter-wave plate 3 at a 45° axial angle, and the other end is connected to the photoelectric acquisition unit 1 via an optical fiber connector 6. The linearly polarized optical fiber 5 is used to maintain the linear polarization characteristics of the optical signal, reducing polarization state changes during transmission. It is typically made of fiber materials with high birefringence, such as panda-type polarization-maintaining fiber. The optical fiber connector 6 allows for a detachable connection between the linearly polarized optical fiber 5 and the photoelectric acquisition unit 1, facilitating device installation and maintenance.

[0042] The implementation principle of this embodiment is as follows: This fiber optic current measurement device, through the combination of a photoelectric acquisition unit 1, a fiber optic circular polarization converter 2, a fiber optic quarter-wave plate 3, and a fiber optic reflector 4, constitutes a unique sensing optical path. The fiber optic circular polarization converter 2 performs polarization state conversion on the optical signal, enabling different sensing rings to carry information about the currents of different conductors. By detecting and demodulating the returned interference optical signal, the magnitude of the current in the corresponding conductor can be accurately measured. Simultaneously, the use of linearly polarized fiber 5 ensures the stability of the polarization state of the optical signal, improving the accuracy and reliability of the measurement. Compared with existing technologies, this device has lower cost, can resist environmental interference such as vibration, and is easy to maintain.

[0043] Example 4

[0044] Please refer to Figure 3 , Figure 5 and Figure 6 The fiber optic current measurement method provided in this application includes the following steps: S1, the first sensing ring is wound around the current in the first conductor 7, and the second sensing ring is wound around the current in the second conductor 8. During the winding process, suitable winding tools, such as a winding machine, are required to ensure winding accuracy and stability. The number of turns and the tightness of the winding need to be adjusted according to the specific measurement requirements. Generally, more turns result in higher measurement sensitivity, but also increase the length of the optical fiber and its loss.

[0045] S2, a pair of orthogonally linearly polarized light rays emitted by the photoelectric acquisition unit 1 are converted into left-handed and right-handed circularly polarized light rays by the fiber optic quarter-wave plate 3 before entering the first sensing ring. Under the influence of the magnetic field of the current in the first conductor 7, a first Faraday phase difference is generated. The light source in the photoelectric acquisition unit 1 generates orthogonally linearly polarized light, which is converted into circularly polarized light by the fiber optic quarter-wave plate 3. The magnetic field generated by the current in the first conductor 7 causes the optical signal passing through the first sensing ring to undergo Faraday rotation, thereby generating a phase difference.

[0046] S3, after the optical signal reaches the fiber optic circular polarization converter 2, a portion of the reflected optical signal is converted into circularly polarized light with the opposite rotation direction and returns along the original path. The semi-transparent mirror 22 and the crystal waveplate 21 in the fiber optic circular polarization converter 2 perform polarization state conversion on the optical signal, and the reflected optical signal carries information about the current of the first conductor 7.

[0047] S4. Another portion of the transmitted light signal is converted into circularly polarized light with opposite rotation and enters the second sensing ring. Under the influence of the magnetic field of the current in the second conductor 8, a second Faraday phase difference is generated. This phase difference is superimposed with the first Faraday phase difference, reflected by the fiber optic mirror 4, and returns along the original path. The transmitted light signal is subjected to the magnetic field of the current in the second conductor 8 in the second sensing ring, generating a second Faraday phase difference, which is then superimposed with the first Faraday phase difference, carrying information about the two conductor currents.

[0048] S5, the photoelectric acquisition unit 1 employs time-division multiplexing demodulation technology to perform phase detection on the reflected interference light signal and the transmitted interference light signal, respectively, thereby calculating the magnitude of the current in the first conductor 7 and the second conductor 8. Time-division multiplexing demodulation technology can process different interference light signals separately by controlling the time sequence of the control signal, thus accurately separating the information of the two conductor currents.

[0049] The implementation principle of this embodiment is as follows: This fiber optic current measurement method involves winding a first sensing ring and a second sensing ring around different conductors, respectively. A fiber optic circular polarization converter 2 is used to convert the polarization state of the optical signal, allowing different optical signals to carry information about the currents of different conductors. By processing the returned interference optical signals using time-division multiplexing demodulation technology, the magnitudes of the two conductor currents can be accurately calculated. This method enables a single device to simultaneously measure two currents, expanding the application range and reducing the cost of multi-point measurements.

[0050] For example, when measuring two currents I a and I b At that time, the minimum current that the system can measure is I. min =I b -I a The maximum current is I max =I a +I b This effectively expands the system's measurement range. Specifically, such as... Figure 7 As shown in the figure, this graph illustrates the nonlinear relationship between the system phase difference θ and the measured current value I. The continuous current value I can be uniformly quantized into a finite number of discrete values, with a step size equal to the current I in the conductor of the second sensing loop. b The resulting phase difference change. This can be explained by the formula θ=φ(I a ,I b )=φ(I a +NI b (Where N is the step size) The measured value can be obtained. At a phase difference of π / 2, the sensor operates at the point of maximum slope, and the corresponding current value at this moment is the current I in the wires of the first sensing loop. a The actual current value is obtained, thereby improving measurement accuracy.

[0051] Example 5

[0052] Please refer to Figure 4 The fiber optic current measurement method provided in this application includes the following steps: S1, the first and second sensing rings are wound together around the same conductor 9, with the winding paths of the two sensing rings being consistent and in opposite directions. A figure-eight winding method can be used during winding, and winding tools should be used to ensure the winding is standardized. This winding method allows the Faraday effect generated by the same current to be superimposed in a specific way in the two signals.

[0053] S2, an optical signal is emitted by the photoelectric acquisition unit 1. Part of the optical signal is transmitted within the first sensing ring and reflected back by the fiber optic circular polarization converter 2, forming an interference signal containing a first Faraday phase difference. The other part of the optical signal passes through the first and second sensing rings in sequence and is reflected back by the fiber optic reflector 4, forming an interference signal containing a second Faraday phase difference. The optical signal is subjected to the magnetic field of the current in the conductor 9 in different sensing rings, producing corresponding Faraday phase differences.

[0054] S3, the photoelectric acquisition unit 1 demodulates the first Faraday phase difference and the second Faraday phase difference to calculate the magnitude of the current in conductor 9. The demodulation circuit in the photoelectric acquisition unit 1 calculates the corresponding phase difference based on the received interference signal and calculates the magnitude of the current in conductor 9 using an algorithm.

[0055] S4. When the sensing ring is subjected to stress interference such as vibration or compression, due to the transmission delay difference of the optical signal in the first and second sensing rings, the same interference will introduce different deviations in the two Faraday phase differences. The photoelectric acquisition unit 1 will issue an alarm based on the measurement error calculated by demodulation and remove abnormal measurement data. Since the optical path lengths of the reflected signal and the transmitted-reflected signal are different, the phase noise caused by vibration and other interference on the two signals is asynchronous. The photoelectric acquisition unit 1 will determine whether interference exists by comparing the instantaneous deviation of the two measurement results and remove abnormal data.

[0056] S5. By changing the winding direction or number of turns of the first sensing ring while keeping the winding method and number of turns of the second sensing ring constant, a nonlinear relationship curve between the system phase difference and the measured current value is fitted to improve measurement accuracy. Multiple experiments can be conducted to change the winding parameters of the first sensing ring, record the corresponding phase difference and current measurement values, and then use mathematical methods to fit the nonlinear relationship curve. In actual measurements, the measurement results are then corrected based on this curve.

[0057] The implementation principle of this embodiment is as follows: This fiber optic current measurement method utilizes the time delay difference between different optical paths by winding a first sensing ring and a second sensing ring around the same conductor 9 in a specific manner to identify and suppress the influence of environmental interference such as vibration on the measurement results. Simultaneously, the measurement accuracy is further improved by fitting a nonlinear relationship curve. This method achieves highly reliable measurement of the current in a single conductor 9 under harsh environments, solving the problem of sensor sensitivity to vibration and other interference in existing technologies.

[0058] The specific embodiments described above do not constitute a limitation on the scope of protection of this application. Any other corresponding changes and modifications made based on the technical concept of this application should be included within the scope of protection of this application.

Claims

1. A fiber optic circular polarization converter (2), characterized in that, include: A crystal waveplate (21); A semi-transparent and semi-reflective mirror (22) disposed on one side of the crystal waveplate (21); Two circularly polarized fiber collimators (23) are distributed on both sides of the crystal waveplate (21); One circularly polarized fiber collimator (23) is used to couple the input optical signal and the output optical signal formed by the reflection of the semi-transparent mirror (22), and the other circularly polarized fiber collimator (23) is used to couple the output optical signal formed by passing through the crystal waveplate (21). The input optical signal includes left-hand circularly polarized light and right-hand circularly polarized light. After the reflected light signals of the left-hand circularly polarized light and right-hand circularly polarized light are processed by the semi-transparent mirror (22), the polarization state is converted into right-hand and left-hand circularly polarized light. After the transmitted light signals of the left-hand circularly polarized light and right-hand circularly polarized light are processed by the crystal waveplate (21), the polarization state is converted into right-hand and left-hand circularly polarized light.

2. The fiber optic circular polarization converter (2) according to claim 1, characterized in that, The fast or slow axis of the circularly polarized fiber collimator (23) is aligned at a 45° angle with the fast or slow axis of the crystal waveplate (21).

3. The fiber optic circular polarization converter (2) according to claim 1, characterized in that, The birefringence phase delay angle of the crystal waveplate (21) is 180°.

4. The fiber optic circular polarization converter (2) according to claim 1, characterized in that, It also includes a substrate (24) and a packaged housing (25); the crystal waveplate (21) is fixed on the substrate (24), and the circularly polarized fiber collimator (23), the substrate (24) together with the crystal waveplate (21) and the semi-transparent and semi-reflective mirror (22) are fixedly installed in the packaged housing (25).

5. The fiber optic circular polarization converter (2) according to claim 1, characterized in that, The semi-reflective mirror (22) is a semi-reflective film deposited on the front surface of the crystal waveplate (21), or an optical medium that is deposited on optical glass and then bonded to the front surface of the crystal waveplate (21).

6. A fiber optic current measuring device, characterized in that, It includes a photoelectric acquisition unit (1), an optical fiber circular polarization conversion device (2) as described in any one of claims 1 to 5, an optical fiber quarter-wave plate (3), and an optical fiber reflector (4); The photoelectric acquisition unit (1) is used to generate an initial optical signal and detect and demodulate the returned interference optical signal. One circular polarization fiber collimator (23) of the fiber circular polarization conversion device (2) is connected to the fiber 1 / 4 wave plate (3), and the fiber 1 / 4 wave plate (3) forms an optical path connection with the photoelectric acquisition unit (1). The other circular polarization fiber collimator (23) is connected to the fiber reflector (4) to form a sensing optical path. In this sensing optical path, the light signal emitted from the photoelectric acquisition unit (1) is reflected at the semi-transparent mirror (22) and then returns to the photoelectric acquisition unit (1) along the original path after polarization state conversion, which is used to form the first sensing ring; the transmitted light signal formed by passing through the crystal waveplate (21) is transmitted to the fiber optic mirror (4) after polarization state conversion, and then returns to the photoelectric acquisition unit (1) along the original path after reflection, which is used to form the second sensing ring.

7. The fiber optic current measuring device according to claim 6, characterized in that, It also includes a section of linearly polarized optical fiber (5), one end of which is fused to the fiber 1 / 4 waveplate (3) at 45° with the axis, and the other end is connected to the photoelectric acquisition unit (1) through an optical fiber connector (6).

8. A method for measuring fiber optic current, characterized in that, The method is applicable to the fiber optic current measuring device as described in claim 6 or 7, and includes the following steps: The first sensor is surrounded around the current of the first conductor (7), and the second sensor is surrounded around the current of the second conductor (8). A pair of orthogonally linearly polarized lights are emitted by the photoelectric acquisition unit (1), which are converted into left-hand circularly polarized light and right-hand circularly polarized light by the fiber 1 / 4 waveplate (3) and then enter the first sensing ring. Under the action of the magnetic field of the current in the first conductor (7), a first Faraday phase difference is generated. After the optical signal reaches the optical fiber circular polarization converter (2), a portion of the reflected optical signal is converted into circularly polarized light with the opposite rotation direction and returns along the original path; Another part of the transmitted light signal is converted into circularly polarized light with opposite rotation direction and enters the second sensing ring. Under the action of the magnetic field of the current in the second conductor (8), a second Faraday phase difference is generated. After the phase difference is superimposed with the first Faraday phase difference, it is reflected by the fiber optic mirror (4) and returns along the original path. The photoelectric acquisition unit (1) uses time-division multiplexing demodulation technology to perform phase detection on the reflected interference light signal and the transmitted interference light signal, respectively, so as to calculate the magnitude of the current in the first conductor (7) and the second conductor (8).

9. A method for measuring fiber optic current, characterized in that, The method is applicable to the fiber optic current measuring device as described in claim 6 or 7, and includes the following steps: The first sensing ring and the second sensing ring are wound together around the current of the same conductor (9), and the winding paths of the two sensing rings are consistent and the directions are opposite. The photoelectric acquisition unit (1) emits a light signal. A portion of the light signal is transmitted in the first sensing ring and then reflected back by the optical fiber circular polarization converter (2) to form an interference signal containing a first Faraday phase difference. Another portion of the light signal passes through the first sensing ring and the second sensing ring in sequence and is reflected back by the optical fiber reflector (4) to form an interference signal containing a second Faraday phase difference. The photoelectric acquisition unit (1) demodulates the first Faraday phase difference and the second Faraday phase difference to calculate the magnitude of the current in the conductor (9); When the sensing ring is subjected to stress interference such as vibration or compression, due to the transmission delay difference of the optical signal in the first and second sensing rings, the same interference will introduce different deviations in the two Faraday phase differences. The photoelectric acquisition unit (1) will issue an alarm based on the measurement error calculated by demodulation and remove abnormal measurement data.

10. The fiber optic current measurement method according to claim 9, characterized in that, By changing the winding direction or number of turns of the first sensing ring while keeping the winding method and number of turns of the second sensing ring unchanged, a nonlinear relationship curve between the system phase difference and the current measurement value is fitted.

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