An integrated optical fiber current transformer doped with photonic crystal fiber

Abstract

The embodiment of the present disclosure provides an integrated optical fiber current transformer of doped photonic crystal fiber, including: SLD light source, PIN‑FET detector, on-chip integrated optical chip, polarization-maintaining delay fiber, λ / 4 wave plate, sensor head, and signal processing unit; wherein, the sensor head includes: sensing fiber and optical fiber reflector, and the sensing fiber is wound around the energized conductor to be measured; the on-chip integrated optical chip is integrated with a PLC optical splitter, a phase modulator, and a polarization-maintaining coupler. The present disclosure is conducive to improving the measurement sensitivity and environmental adaptability of the all-optical fiber current sensor; by optimizing the sensing part and the optical device part of the optical fiber current transformer, the accuracy stability and measurement sensitivity of the system sensing are improved, the volume and weight of the system are reduced, and the reliability is improved.

Description

Technical Field

[0001] The present disclosure relates to the technical field of current transformers, and in particular to an integrated optical fiber current transformer doped with photonic crystal fiber. Background Art

[0002] In order to meet the needs of the development of the times, my country is vigorously building a safe, reliable and high-quality smart grid with UHV transmission lines as the backbone, smart substations as the core, digital communications as the means, and economic operation as the goal. Smart grids mainly use advanced sensor measurement technology to automatically monitor and control the power system to achieve the rational allocation of power resources. Among them, current sensors are key equipment in smart grids, playing the role of current monitoring, power distribution, and relay protection. Traditional electromagnetic current sensors (CS) have defects such as low transient measurement accuracy, small nonlinearity and dynamic range, poor insulation safety, and large size that is difficult to install. Therefore, all-fiber current sensors (AFOCS) came into being.

[0003] In actual application, the measurement accuracy and sensitivity of the all-fiber current sensor (AFOCS) are greatly affected by the external ambient temperature. When the external ambient temperature changes, linear birefringence will be generated in the sensing optical fiber, affecting the detection of polarization state changes caused by the current; in addition, the non-ideal symmetry of the light structure and external force squeezing and bending will also cause linear birefringence in the optical fiber. The existing optical fiber current transformer is still large in size and cannot meet the requirements for measurement sensitivity and environmental adaptability.

[0004] Therefore, how to design a lightweight and small-volume structure, as well as improve reliability, measurement sensitivity, and environmental adaptability is a key issue. Summary of the invention

[0005] The present disclosure provides an integrated optical fiber current transformer doped with photonic crystal fiber, which solves the technical problems of the existing optical fiber current transformer of the traditional optical fiber current transformer, such as large volume, inability to meet the requirements of measurement sensitivity and environmental adaptability, and poor measurement accuracy and stability. The present disclosure provides a photonic crystal fiber design scheme with a high Verdet constant suitable for all-optical fiber current sensors, which is conducive to improving the measurement sensitivity and environmental adaptability of all-optical fiber current sensors; by optimizing the sensing part and the optical device part of the optical fiber current transformer, using photonic crystal fiber, a stronger linear birefringence suppression ability than ordinary optical fiber is obtained, and the accuracy and stability of system sensing are improved; by doping the optical fiber with rare earth ions to increase the Verdet coefficient of the optical fiber material, the measurement sensitivity of the system sensing is improved; using integrated optical chips, the volume and weight of the system are reduced, and the reliability is improved, which provides a reference for the subsequent practical application of optical fiber current sensors.

[0006] According to the first aspect of the present disclosure, an integrated optical fiber current transformer of doped photonic crystal fiber is provided, comprising: an SLD light source, a PIN-FET detector, an on-chip integrated optical chip, a polarization-maintaining delay fiber, a λ / 4 wave plate, a sensor head, and a signal processing unit; wherein,

[0007] The sensor head comprises: a sensing optical fiber and an optical fiber reflector, wherein the sensing optical fiber is wound around the energized conductor to be measured;

[0008] The on-chip integrated optical chip integrates a PLC optical splitter, a Y waveguide, and a polarization-maintaining coupler;

[0009] The light beam emitted by the SLD light source is input to one end of the PLC optical beam splitter, and is divided into a first light beam and a second light beam after beam splitting; the second light beam is output to the PIN-FET detector; the first light beam is polarized by the Y waveguide to form linear polarized light, and is decomposed into X-axis polarized light and Y-axis polarized light after 45° deflection, and the X-axis polarized light and the Y-axis polarized light are respectively transmitted into the polarization-maintaining delay fiber, the λ / 4 wave plate and the sensor head in an orthogonal mode after passing through the polarization-maintaining coupler, and a phase difference is generated in the sensor fiber under the action of the Faraday magneto-optical effect, and then after being reflected by the fiber reflector, the two light signals carrying the phase information return to the PLC optical beam splitter along the original path, and the third light beam formed after beam splitting interferes with the second light beam and is coupled into the PIN-FET detector and linearly converted into a light intensity voltage signal;

[0010] The signal processing unit is used to control the Y waveguide to achieve phase modulation, receive the light intensity voltage signal output by the PIN-FET detector, and obtain the current value in the conductor by measuring two coherent beams of light.

[0011] Furthermore, the sensing optical fiber of the sensor head is a doped photonic crystal fiber.

[0012] Furthermore,

[0013] The on-chip integrated optical chip is connected to one end of the polarization-maintaining delay optical cable;

[0014] The other end of the polarization-maintaining delay optical cable is connected to the λ / 4 wave plate;

[0015] The other end of the λ / 4 wave plate is fused to the sensing optical fiber of the sensing head.

[0016] Furthermore, the light intensity voltage signal output terminal of the PIN-FET detector is connected to a signal processing unit, and the signal processing unit outputs a superposition signal of a square wave and a step wave and transmits it back to the phase modulator;

[0017] The phase difference of light in the phase modulator satisfies sin4(V·N·I)≈4VNI, and 4V·N·I≤0.5°~1°, V represents the Verdet constant, N represents the number of optical fiber turns wrapped around the wire, and I represents the current value in the wire.

[0018] Furthermore, the doped photonic crystal fiber is a photonic crystal fiber doped with rare earth ions.

[0019] Furthermore, magneto-optical glass with a Verdet constant greater than a certain value is selected and drawn into optical fiber as the sensing optical fiber of the sensor head.

[0020] Furthermore, the phase modulator is a Y-waveguide; and the PLC optical splitter, the phase modulator, and the polarization-maintaining coupler are integrated into the on-chip integrated optical chip using optoelectronic chip design technology.

[0021] Furthermore, the λ / 4 wave plate is a full optical wave plate for converting linear polarization into circular polarization.

[0022] Furthermore, the connection between the two ends of the polarization-maintaining delay optical fiber and the polarization-maintaining coupler and the λ / 4 wave plate is by jumper connection or fusion splicing.

[0023] Compared with the prior art, the above one or more technical solutions disclosed in the present invention have at least the following beneficial effects:

[0024] 1. Provide a photonic crystal fiber design scheme with a high Verdet constant suitable for all-fiber current sensors. Using this fiber to wind the sensitive loop of the current sensor is beneficial to improving the measurement sensitivity and environmental adaptability of the all-fiber current sensor; improving the measurement sensitivity, accuracy stability and reliability of the system;

[0025] 2. The present disclosure adopts an integrated optical chip, which reduces the volume and weight of the system, improves reliability, and provides a reference for the subsequent practical application of optical fiber current sensors;

[0026] 3. Using superluminescent diode (SLD) as the light source can improve the accuracy and sensitivity of the fiber-optic current transformer in testing the current size; the low coherence of SLD, that is, the short coherence length, can avoid the influence of back reflection and scattering in the system;

[0027] 4. By doping the optical fiber with rare earth ions to increase the Verdet coefficient of the optical fiber material, the measurement sensitivity of the system sensor can be improved.

[0028] It should be understood that the contents described in the summary of the invention are not intended to limit the key or important features of the embodiments of the present disclosure, nor are they intended to limit the scope of the present disclosure. Other features of the present disclosure will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] 1. SLD light source; 2. PIN-FET detector; 3. On-chip integrated optical chip; 31. PLC optical splitter; 32. Phase modulator; 33. Polarization-maintaining coupler; 4. Polarization-maintaining delay fiber; 5. λ / 4 wave plate; 6. Sensor head; 61. Sensing fiber; 62. Fiber optic reflector; 7. Signal processing unit.

[0030] The above and other features, advantages and aspects of the embodiments of the present disclosure will become more apparent with reference to the following detailed description in conjunction with the accompanying drawings. The accompanying drawings are used to better understand the present solution and do not constitute a limitation of the present disclosure. In the accompanying drawings, the same or similar reference numerals represent the same or similar elements, among which:

[0031] Figure 1 A schematic diagram showing the Faraday magneto-optical effect of an all-fiber current sensor (AFOCS);

[0032] Figure 2 A schematic diagram of an optical path of an integrated optical fiber current transformer doped with a photonic crystal fiber according to an embodiment of the present disclosure is shown;

[0033] Figure 3 A schematic diagram of an optical path of an integrated optical fiber current transformer of a doped photonic crystal fiber including an internal structure of an on-chip integrated optical chip according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the embodiments of the present disclosure clearer, the technical solution in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0035] In addition, the term "and / or" in this article is only a description of the association relationship between the associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0036] In the present disclosure, the essence of the fiber optic current transformer with an all-fiber structure is measured by utilizing the principle of interference of two beams of light; a magnetic field is generated in the sensing fiber due to the transmission current. When a beam of circularly polarized light passes through the sensing fiber, the phase of the circularly polarized light changes due to the Faraday effect. By measuring the two coherent beams of light, the current value in the conductor can be indirectly measured; and the present disclosure optimizes the sensing part and the optical device part of the fiber optic current transformer, adopts photonic crystal fiber, obtains a stronger linear birefringence suppression capability than ordinary optical fiber, and improves the accuracy and stability of the system sensing; increases the Verdet coefficient of the optical fiber material by doping the optical fiber with rare earth ions, and improves the measurement sensitivity of the system sensing; adopts an integrated optical chip to reduce the volume and weight of the system, improve reliability, and provide a reference for the subsequent practical application of optical fiber current sensors.

[0037] Figure 1 The schematic diagram of the Faraday magneto-optical effect of the all-fiber current sensor (AFOCS) is shown. The all-fiber current sensor (AFOCS) is designed based on the Faraday magneto-optical effect, which is the phenomenon that the polarized light in the sensing fiber rotates the polarization plane due to the magnetic field generated by the current. The angle of polarization rotation is called the Faraday rotation angle, such as Figure 1 shown. Figure 1 In the equation, E represents the polarization plane of the polarized light, H represents the magnetic field strength (A / m), L represents the length of the medium through which the polarized light passes (m), and θ represents the Faraday rotation angle (rad). The magnitude of the Faraday rotation angle is proportional to the magnetic field strength and the cosine value of the magnetic field and the direction of light propagation, and can be described as:

[0038] θ=V∫ L H.dl

[0039] Wherein, V represents the Verdet constant (rad / A).

[0040] In the sensing system, the sensing fiber forms a ring, and the current-carrying wire passes through its center. Since optical fiber always has birefringence, the birefringence of optical fiber objectively exists due to internal residual stress and core diameter asymmetry, as well as external bending, various external stresses and external electromagnetic fields, which will cause instability in the polarization state output of polarized light. In severe cases, it will even completely submerge the artificial polarization state modulation effect, thereby affecting the measurement accuracy. Even if an extremely low birefringence optical fiber is used, there will be the influence of bending birefringence when bending. Therefore, in practical all-fiber current transformers, in order to overcome the influence of fiber birefringence, various measures are often used to minimize the influence of birefringence. High birefringence is an important feature of photonic crystal fiber. Generally, it is made by using a dual-core or multi-core structure, changing the shape of the fiber core or air hole, changing the distribution of air holes, etc. Under the high-mode birefringence characteristics, external interference such as torsion, bending, and stretching will greatly reduce the polarization state of the input polarized light. Therefore, the introduction of photonic crystal fiber in the fiber current transformer system can improve the measurement accuracy and stability of the optical current transformer.

[0041] Figure 2 FIG. 1 shows an optical path schematic diagram of an integrated optical fiber current transformer doped with a photonic crystal fiber according to an embodiment of the present disclosure. Figure 2 As shown, an integrated optical fiber current transformer doped with photonic crystal fiber includes: an SLD light source 1, a PIN-FET detector 2, an on-chip integrated optical chip 3, a polarization-maintaining delay fiber 4, a λ / 4 wave plate 5, a sensor head 6, and a signal processing unit 7; wherein,

[0042] The sensor head comprises: a sensing optical fiber 61 and an optical fiber reflector 62, wherein the sensing optical fiber 61 is wound around the current-carrying conductor to be measured;

[0043] Figure 3 The optical path principle diagram of an integrated optical fiber current transformer of a doped photonic crystal fiber including the internal structure of an on-chip integrated optical chip according to an embodiment of the present disclosure is shown. Figure 3 As shown, the on-chip integrated optical chip 3 integrates a PLC optical splitter 31, a phase modulator 32, and a polarization-maintaining coupler 33;

[0044] The light beam emitted by the SLD light source 1 is input to one end of the PLC optical beam splitter 31, and is divided into a first light beam and a second light beam after beam splitting; the second light beam is output to the PIN-FET detector 2; the first light beam is polarized by the phase modulator 32 to form linear polarized light, and is decomposed into X-axis polarized light and Y-axis polarized light by 45° deflection, and then phase biased, the X-axis polarized light and the Y-axis polarized light are respectively transmitted through the polarization-maintaining coupler 33 in an orthogonal mode into the polarization-maintaining delay fiber 4, the λ / 4 wave plate 5 and the sensor Head 6, wherein after passing through the λ / 4 wave plate 5, the X-axis polarized light and the Y-axis polarized light are respectively converted into right-handed circularly polarized light and left-handed circularly polarized light and enter the sensing optical fiber 61, and are acted upon by the Faraday magneto-optical effect in the sensing optical fiber 61 to produce a phase difference Δθ=2V·N·I, and then after being reflected by the optical fiber reflector 62, the right-handed circularly polarized light is converted into left-handed circularly polarized light, and the left-handed circularly polarized light is converted into right-handed circularly polarized light, and the two light beams carrying the phase information return along the original path, and the two light beams after the conversion are acted upon by the Faraday magneto-optical effect again through the sensing optical fiber 61 to produce a doubled phase difference After the conversion, the right-handed circularly polarized light and the left-handed circularly polarized light are restored to the X-axis polarized light and the Y-axis polarized light after passing through the λ / 4 wave plate 5 again. The two light signals carrying the phase information return to the PLC optical beam splitter 31 along the original path. After the third light beam is formed after the beam splitting, it interferes with the second light beam and couples into the PIN-FET detector 2 and is linearly converted into a light intensity voltage signal.

[0045] The signal processing unit 7 is used to control the phase modulator to achieve phase modulation, and to receive the light intensity voltage signal output by the PIN-FET detector 2 and obtain the current value in the wire by measuring two coherent light beams.

[0046] According to this embodiment, by measuring two coherent beams of light, the current value in the conductor can be indirectly measured; and by integrating discrete optical devices into an optical chip, the size of the device is reduced; the fiber-optic current transformer device uses all-fiber connection to avoid electromagnetic interference. This integrated design scheme reduces the volume and weight of the system with a lightweight and small structure and improves reliability. At the same time, the use of photonic crystal fiber obtains a stronger linear birefringence suppression ability than ordinary optical fiber, thereby improving the accuracy and stability of system sensing.

[0047] Preferably, in the present disclosure, the sensing optical fiber 61 of the sensing head 6 is a doped photonic crystal optical fiber, such as Figure 2 and Figure 3As shown in , the dotted part represents the doped photonic crystal fiber. Replacing the traditional sensing fiber with the doped photonic crystal fiber is an innovation of the present disclosure. The technical advancement of this technical solution lies in that the photonic crystal fiber is used to obtain a stronger linear birefringence suppression capability than ordinary optical fiber, thereby improving the accuracy and stability of the system sensing.

[0048] Further preferably, the doped photonic crystal fiber is a photonic crystal fiber doped with rare earth ions. By doping rare earth ions in the preparation process of photonic crystal fiber, the Verdet constant of the optical fiber material is increased, and the measurement sensitivity and environmental adaptability of the optical fiber current sensor can be improved.

[0049] Generally speaking, glass materials with magneto-optical effects can be divided into two categories, namely diamagnetic glass and paramagnetic glass. The atoms in diamagnetic glass do not have permanent electron orbital magnetic moments, so under the action of a magnetic field, they can only produce extremely small induced magnetic moments opposite to the direction of the magnetic field. Ordinary optical glass belongs to this category. After Faraday discovered the magneto-optical effect using heavy lead borosilicate, he studied glasses containing various metal ions for a long time, but the Verdet constant of diamagnetic glass is generally small. During the research, it was found that glasses containing rare earth ions are paramagnetic because the outermost 5s and 5p electron shells of the rare earth ions are in a saturated state and have a shielding effect. Glass containing Pr 3+ , Tb 3+ 、Dy 3+ 、Er3 + Plasma paramagnetic magneto-optical glass generally has a very high Verdet constant.

[0050] The higher the concentration of rare earth ion doping, the larger the constant Verdet constant becomes, and the two are proportional. Therefore, the Verdet coefficient of the photonic crystal fiber doped with rare earth ions introduced in the present disclosure becomes larger, which can effectively improve the measurement sensitivity of the all-fiber current sensor.

[0051] In order to improve the sensitivity of the rotation angle measurement, the embodiment of the present disclosure selects magneto-optical glass with a large Verdet constant (for example, greater than a certain value) to be drawn into an optical fiber as the sensing optical fiber 61 of the sensor head 6 .

[0052] Furthermore,

[0053] The on-chip integrated optical chip 3 is connected to one end of the polarization-maintaining delay optical cable 4;

[0054] The other end of the polarization-maintaining delay optical cable 4 is connected to the λ / 4 wave plate 5;

[0055] The other end of the λ / 4 wave plate 5 is fused to the sensing optical fiber 61 of the sensor head 6 .

[0056] Furthermore, the light intensity voltage signal output terminal of the PIN-FET detector 2 is connected to the signal processing unit 7, and the signal processing unit 7 outputs a superposition signal of a square wave and a step wave and transmits it back to the phase modulator 2;

[0057] The phase difference of light in the phase modulator 32 satisfies sin4(V·N·I)≈4V·N·I, and 4V·N·I≤0.5°~1°, V represents the Verdet constant, N represents the number of turns of optical fiber wrapped around the wire, and I represents the current value in the wire.

[0058] Furthermore, the phase modulator 32 is a Y waveguide, which is used to polarize, split and phase modulate the optical signal output by the light source 11. In this embodiment, the phase modulator 32 integrates the functions of a polarizer and phase modulation. Since the polarization characteristics of the light working in the optical fiber current transformer are most ideally polarized light, the light from the light source after passing through the polarizer is required to be ideal linearly polarized light. In order to obtain a higher degree of polarization, a polarizer should be used as a polarizer to produce linearly polarized light. This system uses an integrated optical waveguide polarizer as a polarizer; the function of phase modulation is that in the detection system, the circuit can realize square wave modulation and superimposed non-reciprocal phase difference on the phase of the light wave. This modulation method has a large bandwidth and a low modulation voltage, and can also realize dynamic closed-loop detection.

[0059] Furthermore, the PLC optical splitter 31, the phase modulator 32, and the polarization-maintaining coupler 33 are integrated into the on-chip integrated optical chip 3 by using the optoelectronic chip design technology. In this embodiment, the integrated optical chip is used to reduce the volume and weight of the system and improve reliability.

[0060] Furthermore, the λ / 4 wave plate 5 is a full optical wave plate for converting linear polarization into circular polarization.

[0061] In this embodiment, the λ / 4 wave plate 5 converts linear polarization into circular polarization; this is achieved by causing two mutually perpendicular linear polarizations of the polarized light to produce a relative λ / 4 wave plate 5 phase delay; an all-fiber wave plate is used, which is made by cutting an appropriate length of polarization-maintaining fiber and fusing two sections of polarization-maintaining fiber at a suitable axis angle.

[0062] Furthermore, the connection between the two ends of the polarization-maintaining delay optical fiber 4 and the polarization-maintaining coupler 3 and the λ / 4 wave plate 5 is performed by jumper connection or fusion splicing.

[0063] Optionally, in some embodiments, the polarization-maintaining delay fiber 4 uses a single-mode fiber whose polarization state remains unchanged along the length of the fiber, achieving an intrinsic birefringence that is much greater than the internal and external perturbation birefringence used, thereby making the polarization state of the transmitted light insensitive to external disturbances, thereby maintaining the stability of the polarization state.

[0064] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps recorded in this disclosure can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solutions disclosed in this disclosure can be achieved, and this document does not limit this.

[0065] The above specific implementations do not constitute a limitation on the protection scope of the present disclosure. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

1. An integrated optical fiber current transformer doped with photonic crystal fiber, characterized in that it comprises: SLD light source (1), PIN-FET detector (2), on-chip integrated optical chip (3), polarization-maintaining delay fiber (4), λ / 4 wave plate (5), sensor head (6), signal processing unit (7); wherein, The sensing head (6) comprises: a sensing optical fiber (61) and an optical fiber reflector (62), wherein the sensing optical fiber (61) is wound around the conductor to be measured; The sensing optical fiber (61) of the sensing head (6) is a doped photonic crystal fiber; the doped photonic crystal fiber is a photonic crystal fiber doped with rare earth ions; magneto-optical glass having a Verdet constant greater than a certain value is selected to be drawn into an optical fiber as the sensing optical fiber (61) of the sensing head (6); The on-chip integrated optical chip (3) is integrated with a PLC optical splitter (31), a phase modulator (32), and a polarization-maintaining coupler (33); The λ / 4 wave plate (5) is a fully optical wave plate used to convert linearly polarized light into circularly polarized light; The light beam emitted by the SLD light source (1) is input to one end of the PLC optical splitter (31), and is divided into a first light beam and a second light beam after beam splitting; the second light beam is output to the PIN-FET detector (2); the first light beam is polarized by the phase modulator (32) to form linear polarized light, and is decomposed into X-axis polarized light and Y-axis polarized light after 45° deflection, the X-axis polarized light and the Y-axis polarized light are respectively transmitted through the polarization-maintaining coupler (33) in an orthogonal mode and sequentially enter the polarization-maintaining delay fiber (4), the λ / 4 wave plate (5) and the sensor head (6), and a phase difference is generated in the sensing fiber (61) due to the Faraday magneto-optical effect, and then after being reflected by the fiber reflector (62), the two light signals carrying the phase information return to the PLC optical splitter (31) along the original path, and the third light beam formed after beam splitting interferes with the second light beam and is coupled into the PIN-FET detector (2) and linearly converted into a light intensity voltage signal; The signal processing unit (7) is used to control the phase modulator to realize phase modulation, and to receive the light intensity voltage signal output by the PIN-FET detector (2) and obtain the current value in the wire by measuring two coherent light beams.

2. The optical fiber current transformer according to claim 1, wherein: The on-chip integrated optical chip (3) is connected to one end of the polarization-maintaining delay optical fiber (4); The other end of the polarization-maintaining delay optical fiber (4) is connected to the λ / 4 wave plate (5); The other end of the λ / 4 wave plate (5) is fused to the sensing optical fiber (61) of the sensing head (6).

3. The optical fiber current transformer according to claim 1, wherein: The light intensity voltage signal output end of the PIN-FET detector (2) is connected to a signal processing unit (7), and the signal processing unit (7) outputs a superposition signal of a square wave and a step wave and transmits it back to the phase modulator (32); The phase difference of light in the phase modulator (32) satisfies sin4(V·N·I)≈4VNI, and 4 V·N·I≤0.5°~1°, V represents the Verdet constant, N represents the number of turns of the optical fiber wound around the wire, and I represents the current value in the wire.

4. The optical fiber current transformer according to claim 1, wherein: The phase modulator (32) is a Y-waveguide; and the PLC optical splitter (31), the phase modulator (32), and the polarization-maintaining coupler (33) are integrated into the on-chip integrated optical chip (3) by using optoelectronic chip design technology.

5. The optical fiber current transformer according to claim 1, wherein: The connection between the two ends of the polarization-maintaining delay optical fiber (4) and the polarization-maintaining coupler (33) and the λ / 4 wave plate (5) is achieved by jumper connection or fusion splicing.

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