Fiber Optic Current Transformer and Current Detection Method Based on Non-Reciprocal Phase Modulation

Abstract

This invention provides a fiber optic current transformer and current detection method based on non-reciprocal phase modulation, relating to the field of electrical measurement technology. The fiber optic current transformer includes a light source, a coupler, a polarizer, a 45° fusion splice, a first 45° Faraday rotator, a phase modulator, a second 45° Faraday rotator, and a fiber optic λ / 4 waveplate arranged and connected sequentially along the optical path. One end of the sensing fiber loop is connected to the fiber optic λ / 4 waveplate, and the other end is connected to a reflector. The output port of the coupler's reflection loop is connected to a photodetector, and the output port of the photodetector is connected to the input port of a lock-in amplifier. The output port of the lock-in amplifier is connected to both the phase modulator and a signal processing module. This solution achieves maximum current sensitivity without relying on a delay fiber, thereby reducing the size, cost, and response time of the fiber optic current sensing system.

Description

Technical Field

[0001] This invention relates to the field of electrical measurement technology, and in particular to an optical fiber current transformer and current detection method based on non-reciprocal phase modulation. Background Technology

[0002] In recent years, with the increase in electrical equipment and global power consumption, all-fiber optic current transformers have gradually become a field of great interest to researchers. Compared with traditional active electronic current transformers represented by air-core coils, fiber optic current transformers have advantages such as resistance to electromagnetic interference, large dynamic range, small size, light weight, and high accuracy, and are gradually becoming important equipment for electrical measurement in the next generation of smart grids.

[0003] Currently, fiber optic current transformers are mostly based on the theory and technology of fiber optic gyroscopes, employing a closed-loop structure to achieve more stable detection accuracy. However, existing fiber optic circuit transformers are all based on transit time-based phase modulation, which is inevitably limited by non-intrinsic frequencies, requiring additional delay fiber to ensure the necessary time delay for modulation. For example, polarization-maintaining fiber of 200m or more is typically used, along with a high-frequency modulation signal. However, the delay fiber is located before the interference point, inevitably resulting in linear birefringence caused by the stress field, which affects the stability of the system. Furthermore, the added delay fiber increases the size, cost, and response time of the fiber optic current sensing system. In addition, the error between the length of the delay fiber and the modulation frequency also affects the phase shift of the phase modulator output, thus reducing the current detection accuracy of the fiber optic current sensing system. Summary of the Invention

[0004] In view of this, and to address the above shortcomings, it is necessary to propose an optical fiber current transformer and current detection method based on non-reciprocal phase modulation, which does not rely on delay fiber, thereby reducing the response time and cost of the optical fiber current sensing system.

[0005] In a first aspect, the present invention provides an optical fiber current transformer based on non-reciprocal phase modulation, comprising: a light source, a coupler, a polarizer, a 45° fusion splice, a first 45° Faraday rotator, a phase modulator, a second 45° Faraday rotator, an optical fiber λ / 4 waveplate, a sensing optical fiber ring, a reflector, a photodetector, a lock-in amplifier, and a signal processing module.

[0006] The light source, coupler, polarizer, 45° fusion splice, first 45° Faraday rotator, phase modulator, second 45° Faraday rotator, and fiber λ / 4 waveplate are sequentially arranged and connected along the optical path. One end of the sensing fiber loop is connected to the fiber λ / 4 waveplate, and the other end is connected to the reflector. The output port of the coupler's reflection loop is connected to the photodetector, the output port of the photodetector is connected to the input port of the lock-in amplifier, and the output port of the lock-in amplifier is connected to the phase modulator and the signal processing module, respectively. The optical components with interconnections are connected by optical fibers, and the optical fiber from the 45° fusion splice to the fiber λ / 4 waveplate is a polarization-maintaining fiber.

[0007] The light source is used to generate an optical signal; the coupler is used to couple the incident light signal emitted by the light source into the optical fiber and to transmit the reflected light signal to the photodetector; the polarizer is used to convert the input optical signal into linearly polarized light; the 45° fusion splice is used to uniformly distribute the linearly polarized light of the incident optical signal onto the fast and slow axes of the polarization-maintaining fiber; the first 45° Faraday rotator is used to rotate the input optical signal clockwise by 45°; the phase modulator is used to apply phase modulation to the linearly polarized light to generate a controlled initial phase difference between the optical signals transmitted on the fast and slow axes; the second 45° Faraday rotator is used to rotate the input optical signal counterclockwise by 45°; the fiber λ / 4 waveplate is used for... Linearly polarized light on the fast and slow axes is converted into left-handed and right-handed circularly polarized light, respectively, and transmitted to the sensing fiber optic ring. The sensing fiber optic ring is used to wrap around the current-carrying conductor under test, so that the magnetic field generated by the current in the current-carrying conductor causes the two circularly polarized light beams with opposite polarization directions to travel at different speeds. The reflector is used to reflect the transmitted optical signal. The photodetector is used to convert the input optical signal into an electrical signal. The lock-in amplifier is used to generate a signal to drive the phase modulator and to extract and demodulate the first harmonic component of the signal. The signal processing module is used to determine the magnitude of the current in the current-carrying conductor under test based on the demodulated first harmonic component.

[0008] Preferably, the light source is a superluminescent diode with a center wavelength of 1310 nm.

[0009] Preferably, the sensing fiber ring is a helical high birefringence fiber.

[0010] Preferably, the photodetector is used to output a light intensity signal, wherein the output light intensity signal is expressed as:

[0011]

[0012] Among them, I outLet K be the output light intensity signal, K be the responsivity of the photodetector, and I0 be the initial light intensity of the light source. The modulation phase introduced for the phase modulator. Let t be the phase difference caused by the current, τ be the time from when the light source emits the light signal to when the photodetector receives the light signal, A be the amplitude of the AC component, B be the DC component, and V be the amplitude of the DC component. π The half-wave voltage characterizes the phase modulator, ω is the modulation frequency, N is the number of turns of the optical fiber, V is a constant related to the properties of the optical fiber, and I is the current in the current-carrying conductor of the current to be measured.

[0013] Preferably, the lock-in amplifier, when extracting the first harmonic component, includes:

[0014] The light intensity signal output by the photodetector is expanded according to the first-type Bessel function, and the first-order harmonic component is extracted using a demodulation algorithm.

[0015] Preferably, the extracted first-order harmonic components include:

[0016]

[0017] Where S1 represents the first harmonic component of the output optical signal, and J1(·) is the first-order Bessel function.

[0018] Preferably, the fiber λ / 4 waveplate is fabricated by:

[0019] Panda core polarization-maintaining fiber and elliptical core polarization-maintaining fiber are fused together at 45° on the axis.

[0020] After fusion splicing, at a quarter wavelength stage of the elliptical core polarization-maintaining fiber, the resulting elliptical core polarization-maintaining fiber constitutes an optical fiber λ / 4 waveplate.

[0021] Preferably, the modulation frequency of the phase modulator is consistent with the local reference signal frequency of the lock-in amplifier.

[0022] Secondly, the present invention also provides a current detection method, wherein the implementing body of the current measurement method is an optical fiber current transformer based on non-reciprocal phase modulation as described in the first aspect, comprising:

[0023] The sensing fiber loop of the fiber current transformer based on non-reciprocal phase modulation is placed on the current-carrying conductor to be measured.

[0024] Start the fiber optic current transformer based on non-reciprocal phase modulation to enable all components to work and detect the current magnitude of the current-carrying conductor under test.

[0025] As can be seen from the above technical solution, the fiber optic current transformer based on non-reciprocal phase modulation provided by this solution includes a light source, coupler, polarizer, 45° fusion splice, first 45° Faraday rotator, phase modulator, second 45° Faraday rotator, fiber optic λ / 4 waveplate, sensing fiber ring, reflector, photodetector, lock-in amplifier, and signal processing module. By adding Faraday rotators at both ends of the phase modulator, one optical signal passes through the X-axis of the phase modulator twice, and the other optical signal passes through the Y-axis of the phase modulator twice. Since the phase modulator only modulates the X-axis and not the Y-axis, the modulation phase introduced by the phase modulator only contains a summation term, resulting in a cosine term in the first harmonic component of the output optical signal. Maximum current sensitivity of the fiber optic AC transformer can be achieved without the need for delay fiber and high-frequency modulation. Therefore, this solution does not rely on delay fiber, significantly reducing the cost, size, and detection response time of the fiber optic current transformer. Moreover, the fiber optic current transformer can achieve maximum current sensitivity without the need for additional delay fiber, thereby improving the accuracy of current detection. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of an optical fiber current transformer based on non-reciprocal phase modulation, provided as an embodiment of the present invention.

[0027] In the figure: 1. Light source; 2. Photodetector; 3. Coupler; 4. Polarizer; 5. 45° fusion splice; 6. First 45° Faraday rotator; 7. Phase modulator; 8. Second 45° Faraday rotator; 9. Fiber λ / 4 waveplate; 10. Sensing fiber ring; 12. Mirror; 13. Lock-in amplifier; 14. Signal processing module. Detailed Implementation

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] like Figure 1 As shown, the present invention provides an optical fiber current transformer based on non-reciprocal phase modulation, comprising: a light source 1, a coupler 3, a polarizer 4, a 45° fusion splice 5, a first 45° Faraday rotator 6, a phase modulator 7, a second 45° Faraday rotator 8, an optical fiber λ / 4 waveplate 9, a sensing optical fiber ring 10, a reflector 12, a photodetector 2, a lock-in amplifier 13, and a signal processing module 14;

[0030] Light source 1, coupler 3, polarizer 4, 45° fusion splice 5, first 45° Faraday rotator 6, phase modulator 7, second 45° Faraday rotator 8, and fiber optic λ / 4 waveplate 9 are arranged and connected sequentially along the optical path. One end of sensing fiber loop 10 is connected to fiber optic λ / 4 waveplate 9, and the other end is connected to reflector 12. The output port of the reflection loop of coupler 3 is connected to photodetector 2, and the output port of photodetector 2 is connected to input port of lock-in amplifier 13. The output port of lock-in amplifier 13 is connected to phase modulator 7 and signal processing module 14, respectively. The optical components with interconnected relationships are connected by optical fibers, and the optical fiber from 45° fusion splice 5 to fiber optic λ / 4 waveplate 9 is polarization-maintaining fiber.

[0031] Light source 1 is used to generate optical signals; coupler 3 is used to couple the incident optical signal emitted by light source 1 into the optical fiber and to transmit the reflected optical signal to photodetector 2; polarizer 4 is used to convert the input optical signal into linearly polarized light; 45° fusion splice 5 is used to uniformly distribute the linearly polarized light of the incident optical signal onto the fast and slow axes of the polarization-maintaining fiber; first 45° Faraday rotator 6 is used to rotate the input optical signal clockwise by 45°; phase modulator 7 is used to apply phase modulation to the linearly polarized light to generate a controlled initial phase difference between the optical signals transmitted on the fast and slow axes; second 45° Faraday rotator 8 is used to rotate the input optical signal counterclockwise by 45°; fiber λ / 4 waveplate 9 is used to distribute the linearly polarized light onto the fast and slow axes of the fiber. Linearly polarized light on the axis is converted into left-handed and right-handed circularly polarized light, respectively, and transmitted to the sensing fiber ring 10. The sensing fiber ring 10 is used to wrap around the current-carrying conductor 11 to generate a magnetic field through the current in the current-carrying conductor 11, so that the two circularly polarized light beams with opposite polarization directions are transmitted at different speeds. The reflector 12 is used to reflect the transmitted optical signal. The photodetector 2 is used to convert the input optical signal into an electrical signal. The lock-in amplifier 13 is used to generate a signal to drive the phase modulator 7, as well as to extract and demodulate the first harmonic component of the signal. The signal processing module 14 is used to determine the magnitude of the current in the current-carrying conductor 11 to be measured based on the demodulated first harmonic component.

[0032] In this embodiment, based on the all-fiber current transformer, 45° Faraday rotators are added to both ends of the phase modulator 7. This causes X-polarized light, upon passing through the first 45° Faraday rotator 6, to rotate clockwise to the X-axis of the phase modulator 7, which is rotating at a 45° angle to the system reference frame. Then, it passes through the second 45° Faraday rotator 8 and rotates counterclockwise back to its original X-polarization direction before entering the sensing loop. The X-polarized light, after passing through the fiber optic λ / 4 waveplate 9, becomes left-handed circularly polarized light. After passing through the sensing loop, it is reflected by the mirror 12 as right-handed circularly polarized light, and then converted to Y-polarization by the fiber optic λ / 4 waveplate 9. It first rotates counterclockwise to the X-axis of the phase modulator 7, and then clockwise back to Y-polarization. Therefore, this path of light will pass through the X-axis of the phase modulator 7 twice. Similarly, the other path of light, orthogonal to it, will pass through the Y-axis of the phase modulator 7 twice. Since the phase modulator 7 only modulates the X-axis, one path of light will be modulated twice, while the other path will not be modulated. The first harmonic component of the output optical signal is a cosine term, thus eliminating the need for delay fiber and high-frequency modulation to achieve maximum current sensitivity in the fiber optic AC transformer. Furthermore, the elimination of delay fiber makes the system more compact and cost-effective, while also resolving the issue of time-based phase modulation relying on long delay fibers and high modulation frequencies.

[0033] In the fiber optic current transformer based on non-reciprocal phase modulation provided in this embodiment:

[0034] Light source 1 can be a superluminescent diode with a center wavelength of 1310nm, used to provide light source 1 for the sensing system.

[0035] Coupler 3 is used to couple optical signals into optical signals to achieve the distribution and combination of optical power.

[0036] Polarizer 4 is used to convert the input light into linearly polarized light.

[0037] Phase modulator 7 is used to perform initial phase modulation on the optical signal and facilitates subsequent demodulation of the signal using lock-in amplifier 13.

[0038] The Faraday rotator is used to transform the polarization angle of the beam. Specifically, it makes the forward and reverse propagating light pass through the X-axis and Y-axis of the phase modulator 7, respectively, to achieve non-reciprocal phase modulation.

[0039] The fiber λ / 4 waveplate 9 is used to convert the input linearly polarized light into circularly polarized light. It is specifically composed of a section of elliptical core polarization-maintaining fiber. First, the panda core polarization-maintaining fiber and the elliptical core fiber are fused together at 45°. Then, at a quarter wavelength of the elliptical core polarization-maintaining fiber, this section of elliptical core polarization-maintaining fiber constitutes the fiber λ / 4 waveplate 9.

[0040] The sensing fiber ring 10 is a spiral high birefringence fiber.

[0041] The reflector 12 is used to reflect the light beam.

[0042] Photodetector 2 is used for photoelectric conversion and the output of optical signals.

[0043] Specifically, the light intensity signal output by photodetector 2 can be expressed as:

[0044]

[0045] Among them, I out Let K be the output light intensity signal, K be the responsivity of photodetector 2, and I0 be the initial light intensity of light source 1. The modulation phase introduced for phase modulator 7, Let t be the phase difference caused by the current, τ be the time from when the light source 1 emits the light signal to when the photodetector 2 receives the light signal, A be the amplitude of the AC component, B be the DC component, and V be the amplitude of the DC component. π The half-wave voltage of the phase modulator 7 is characterized by ω, the modulation frequency, N, the number of turns of the optical fiber, V, a constant related to the properties of the optical fiber, and I, the current in the current-carrying conductor 11 of the current to be measured.

[0046] As can be seen from the above formula, in the fiber optic current transformer based on this scheme, since the X-axis is modulated twice and the Y-axis is not modulated, the modulation phase introduced by its corresponding phase modulator 7 is: For traditional fiber optic current transformers, since each of the two optical paths undergoes modulation once, the modulation phase introduced by the corresponding phase modulator 7 is... Therefore, the first harmonic component obtained by this scheme is a cosine quantity, while the first harmonic component obtained by the traditional scheme is a sine quantity. This scheme can make the cosine quantity 1 without delay fiber and high-frequency modulation, thus enabling the fiber optic current transformer to achieve maximum sensitivity.

[0047] The lock-in amplifier 13 is used to generate a signal to drive the phase modulator 7, and to extract and demodulate the first harmonic component of the light intensity signal.

[0048] When extracting the first harmonic component, the lock-in amplifier 13 first expands the light intensity signal output by the photodetector 2 according to the first kind of Bessel function, and then extracts the first harmonic component through a related demodulation algorithm. Finally, the following can be obtained:

[0049]

[0050] Since the phase shift introduced by the Faraday effect is relatively small, when the modulated DC component is also relatively small, then:

[0051]

[0052] Where S1 represents the first harmonic component of the output optical signal, and J1(·) is the first-order Bessel function.

[0053] As can be seen from the above first-order harmonic components, when there is no delay fiber and high-frequency modulation, Therefore, Therefore, simply selecting an appropriate modulation voltage A is sufficient to achieve maximum current sensitivity. Simultaneously, by adjusting the value of B, the system can always operate in the linear region near zero.

[0054] The signal processing module 14 is used for signal display, data storage and processing.

[0055] The signal processing module 14 uses the first harmonic component mentioned above to calculate the magnitude of the current I on the carrier wire to be measured.

[0056] like Figure 1 As shown, in the fiber optic current transformer based on non-reciprocal phase modulation provided by this invention, the superluminescent diode serving as light source 1 provides a stable continuous output spectrum near 1310 nm. Coupler 3 couples the optical signal emitted by light source 1 into the optical fiber. Polarizer 4 converts the incident light into linearly polarized light, and 45° fusion splice 5 evenly distributes the incident light onto the fast and slow axes of the polarization-maintaining fiber for transmission. First 45° Faraday rotator 6 rotates the light 45° clockwise, and the subsequent polarization-maintaining fiber also rotates 45° clockwise to ensure that there is no crosstalk between the fast and slow axes. Phase modulator 7 applies a certain phase modulation to the linearly polarized light, so that the light propagating along the fast and slow axes generates a controlled initial phase difference. The modulated light is then rotated counterclockwise to its original direction by second 45° Faraday rotator 8.

[0057] After passing through the second 45° Faraday rotator 8, the light enters the fiber λ / 4 waveplate 9 via a 45° fusion splice. The two linearly polarized beams along the fast and slow axes become left-handed and right-handed circularly polarized beams, respectively, and enter the sensing fiber ring 10 surrounding the current-carrying conductor 11 to be measured. Due to the Faraday effect caused by the magnetic field generated by the transmitted current, the two circularly polarized beams with opposite polarization directions propagate at different speeds, resulting in a phase difference between the two beams that is related to the current magnitude. After being reflected by the mirror 12, the polarization modes of the two beams are interchanged, i.e., the left-handed beam becomes right-handed, and the right-handed beam becomes left-handed. Thus, they are again subject to the Faraday effect, and due to the non-reciprocity of the Faraday effect, the phase difference between the two beams caused by the magnetic field is doubled. After passing through the fiber λ / 4 waveplate 9, the two circularly polarized beams with opposite polarization directions become orthogonally linearly polarized beams with interchanged modes, i.e., the original fast-axis polarized beam is converted to the slow-axis polarized beam, and the original slow-axis polarized beam is converted to the fast-axis polarized beam. Due to the non-reciprocity of the Faraday rotator, the light on the fast axis that you want to propagate will pass through the same axis as the light on the slow axis that is propagating in the forward direction. This will cause the incident light of each polarization to pass through the X-axis or Y-axis of the phase modulator 7 twice before the final interference. The light that passes through the X-axis twice is modulated twice, while the light that passes through the Y-axis twice is not modulated.

[0058] After the two beams return, they interfere with each other via polarizer 4, and then reach photodetector 2 via coupler 3. Photodetector 2 converts the optical signal into an electrical signal and outputs a light intensity signal. The lock-in amplifier 13 then acquires the signal and extracts the first harmonic component. The signal processing module 14 further calculates the magnitude of the current under test based on the first harmonic component. Throughout the detection process, the modulation frequency of phase modulator 7 and the local reference signal frequency of lock-in amplifier 13 remain consistent, thus achieving the extraction of the first harmonic component signal.

[0059] Furthermore, this embodiment of the invention also provides a current detection method, wherein the implementing entity of the current measurement method is an optical fiber current transformer based on non-reciprocal phase modulation as described in any of the above embodiments, comprising:

[0060] The sensing fiber ring 10 of the fiber current transformer based on non-reciprocal phase modulation is fitted onto the current-carrying conductor 11 to be tested.

[0061] Start the fiber optic current transformer based on non-reciprocal phase modulation to enable all components to work and detect the current magnitude of the current-carrying conductor 11 under test.

[0062] As can be seen from the above embodiments, the fiber optic current transformer and current detection method based on non-reciprocal phase modulation provided by the present invention have at least the following beneficial effects:

[0063] 1. The system is composed of all-fiber devices, with no spatial optical path, simple structure and strong stability.

[0064] 2. By adopting a reflective structure and a phase-generated carrier modulation scheme, the sensitivity is improved while having high demodulation accuracy and anti-interference capability.

[0065] 3. Linear measurement of ultra-large currents can be achieved by adjusting the phase introduced by the bias compensation current of the phase demodulator.

[0066] 4. No long polarization-maintaining delay fiber is required, reducing the response time and cost of the linear birefringence system.

[0067] The device and method embodiments of the present invention are based on the same inventive concept. For detailed description, please refer to the method embodiments, which will not be repeated here.

[0068] The modules or units in the device of this invention can be merged, divided, and deleted according to actual needs. The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. Those skilled in the art will understand that implementing all or part of the processes of the above embodiments and making equivalent changes according to the claims of this invention still fall within the scope of the invention.

Claims

1. A fiber optic current transformer based on non-reciprocal phase modulation, characterized in that, include: Light source, coupler, polarizer, 45° fusion splice, first 45° Faraday rotator, phase modulator, second 45° Faraday rotator, optical fiber Waveplates, sensing fiber optic rings, mirrors, photodetectors, lock-in amplifiers, and signal processing modules; The light source, coupler, polarizer, 45° fusion splice, first 45° Faraday rotator, phase modulator, second 45° Faraday rotator, and optical fiber are described. Waveplates are sequentially arranged and connected along the optical path, and one end of the sensing fiber optic loop is connected to the optical fiber. One end of the waveplate is connected to the other end, and the other end is connected to the reflector; the output port of the coupler's reflection circuit is connected to the photodetector, the output port of the photodetector is connected to the input port of the lock-in amplifier, and the output port of the lock-in amplifier is connected to the phase modulator and the signal processing module respectively; the optical components with interconnections are connected by optical fibers, and the 45° fusion splice point is connected to the optical fiber. The optical fiber at the waveplate is a polarization-maintaining fiber; The light source is used to generate optical signals, and the coupler is used to couple the incident light signal emitted by the light source into the optical fiber and to transmit the reflected light signal to the photodetector. The polarizer is used to convert the input optical signal into linearly polarized light. The 45° fusion splice is used to uniformly distribute the linearly polarized light of the incident optical signal onto the fast and slow axes of the polarization-maintaining fiber. The first 45° Faraday rotator is used to rotate the input optical signal clockwise by 45°. The phase modulator is used to apply phase modulation to the linearly polarized light so that the optical signals transmitted on the fast and slow axes generate a controlled initial phase difference. The second 45° Faraday rotator is used to rotate the input optical signal counterclockwise by 45°. A waveplate is used to convert linearly polarized light on the fast axis and slow axis into left-handed and right-handed circularly polarized light, respectively, and transmit them to the sensing fiber ring; the sensing fiber ring is used to wrap around the current-carrying conductor to be measured, so that the magnetic field generated by the current in the current-carrying conductor produces the Faraday effect, causing the two circularly polarized beams with opposite polarization directions to transmit at different speeds; the mirror is used to reflect the transmitted optical signal; The photodetector is used to convert the input optical signal into an electrical signal; the lock-in amplifier is used to generate a signal to drive the phase modulator and to extract and demodulate the first harmonic component of the signal; the signal processing module is used to determine the magnitude of the current in the current-carrying conductor under test based on the demodulated first harmonic component. The photodetector is used to output a light intensity signal, wherein the output light intensity signal is represented as: ； in, Let K be the output light intensity signal, and K be the responsivity of the photodetector. The initial light intensity of the light source. The modulation phase introduced for the phase modulator. The phase difference is caused by the current, and t is time. Let A be the time from when the light is emitted by the light source to when the light signal is received by the photodetector, and let B be the amplitude of the AC component and the DC component. Characterizing the half-wave voltage of the phase modulator, Where is the modulation frequency, N is the number of turns of the optical fiber, V is a constant related to the properties of the optical fiber, and I is the current in the current-carrying conductor of the current to be measured.

2. The fiber optic current transformer based on non-reciprocal phase modulation according to claim 1, characterized in that, The light source is a superluminescent diode with a center wavelength of 1310 nm.

3. The fiber optic current transformer based on non-reciprocal phase modulation according to claim 1, characterized in that, The sensing fiber ring is a helical high birefringence fiber.

4. The fiber optic current transformer based on non-reciprocal phase modulation according to claim 1, characterized in that, The lock-in amplifier, when extracting the first harmonic component, includes: The light intensity signal output by the photodetector is expanded according to the first-type Bessel function, and the first-order harmonic component is extracted using a demodulation algorithm.

5. The fiber optic current transformer based on non-reciprocal phase modulation according to claim 4, characterized in that, The extracted first-order harmonic components include: ； in, Characterizing the first harmonic component of the output optical signal It is a first-order Bessel function.

6. The fiber optic current transformer based on non-reciprocal phase modulation according to claim 1, characterized in that, The optical fiber Methods for preparing wave plates include: Panda core polarization-maintaining fiber and elliptical core polarization-maintaining fiber are fused together at 45° on the axis. After fusion splicing, at the quarter-wavelength stage of the elliptical core polarization-maintaining fiber, the resulting elliptical core polarization-maintaining fiber constitutes an optical fiber. Wave plate.

7. The fiber optic current transformer based on non-reciprocal phase modulation according to claim 1, characterized in that, The modulation frequency of the phase modulator is consistent with the local reference signal frequency of the lock-in amplifier.

8. A current detection method, characterized in that, The main body for implementing this current detection method is the fiber optic current transformer based on non-reciprocal phase modulation as described in any one of claims 1-7, comprising: The sensing fiber loop of the fiber current transformer based on non-reciprocal phase modulation is placed on the current-carrying conductor to be measured. Start the fiber optic current transformer based on non-reciprocal phase modulation to enable all components to operate and detect the current magnitude of the current-carrying conductor under test.

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