Resonant fiber-optic current sensing system and method of operation

Abstract

The application provides a resonant optical fiber current sensing system and a working method, comprising: a signal generation and detection system, an optical fiber resonant cavity sensing unit, a wave plate unit and an optical modulator unit; the signal generation and detection system is connected with the optical fiber resonant cavity sensing unit, and the optical modulator unit and the wave plate unit are arranged between the signal generation and detection system and the optical fiber resonant cavity sensing unit. The application adopts the optical fiber resonant cavity as a sensitive unit to detect the resonant frequency difference of light caused by the Faraday effect, and compared with the scheme of detecting the phase difference caused by the Faraday effect in the traditional scheme, the sensitivity is higher, and the environmental interference resistance is stronger.

Description

Technical Field

[0001] This invention relates to optical sensing technology, and more specifically, to a resonant fiber optic current sensing system and its operating method. Background Technology

[0002] Fiber optic current sensors are current sensors based on the Faraday effect. During current sensing, light propagates through an optical medium in an electromagnetically generated magnetic field. Different circularly polarized light waves experience different refractive indices, resulting in different phase differences after traveling the same distance. This causes a change in the polarization direction of the synthesized linearly polarized light. By detecting this change in polarization direction, the magnitude and direction of the measured current can be recovered. Compared to electromagnetic and electronic current transformers, fiber optic current sensors can detect both alternating current and direct current. They are not limited by core magnetic saturation, have a fast response speed, and a large dynamic range. The sensing device is composed of optical components, providing strong resistance to environmental electromagnetic interference. Signal transmission through non-conductive optical fibers significantly reduces the difficulty of high-voltage insulation, making it a promising current sensing technology.

[0003] The sensing element of an optical fiber current sensor is the optical fiber. Traditional optical fiber current sensors typically employ methods that directly detect the phase difference between left-handed and right-handed polarized light caused by the Faraday effect, or detect the rotation angle of the polarization plane of linearly polarized light resulting from this phase difference. However, because the Verdet constant of optical fiber is generally small, the Faraday magneto-optical effect is usually weak. Furthermore, due to factors such as ambient temperature drift, the polarization plane rotation angle and corresponding phase difference caused by the Faraday effect are very small and easily masked by noise, significantly limiting the system sensitivity. To improve the accuracy of optical fiber current sensors, more turns of sensing fiber can be used to enhance the Faraday effect. However, increasing the number of turns requires a larger fiber loop, increasing the temperature inhomogeneity within the fiber loop and complicating the deployment of the sensing system. Moreover, the phase difference caused by the Faraday effect within the sensing fiber loop is easily affected by external vibrations and temperature changes on its path through the fiber to the demodulation unit, impacting the detection accuracy and anti-interference capability of the optical fiber current sensing system in practical applications. Summary of the Invention

[0004] In view of the deficiencies in the prior art, the purpose of this invention is to provide a resonant fiber optic current sensing system and its operating method.

[0005] According to the present invention, a resonant fiber optic current sensing system includes: a signal generation and detection system, a fiber optic resonant cavity sensing unit, a waveplate unit, and an optical modulator unit.

[0006] The signal generation and detection system is connected to the fiber optic resonant cavity sensing unit, and the optical modulator unit and the waveplate unit are disposed between the signal generation and detection system and the fiber optic resonant cavity sensing unit.

[0007] Preferably, the signal generation and detection system includes: a low-coherence light source, an optical circulator, a photodetector, a signal processing unit, and a polarizer;

[0008] The three ports of the optical circulator are respectively connected to the low-coherence light source, the photodetector, and the polarizer, and the photodetector is connected to the signal processing unit;

[0009] The polarizer and the signal processing unit are connected to the optical modulator unit.

[0010] Preferably, the fiber optic resonant cavity sensing unit includes: a fiber optic ring resonant unit or a fiber optic linear resonant unit;

[0011] The waveplate unit includes: a first waveplate unit or a second waveplate unit;

[0012] The optical modulator unit includes: a first optical modulator unit or a second optical modulator unit;

[0013] When the fiber optic resonant cavity sensing unit uses the fiber optic ring resonant unit, the fiber optic ring resonant unit is connected to the first waveplate unit, the first waveplate unit is connected to the first optical modulator unit, and the first optical modulator unit is connected to the polarizer and the signal processing unit.

[0014] When the fiber resonant cavity sensing unit uses the fiber linear resonant unit, the fiber linear resonant unit is connected to the second waveplate unit, the second waveplate unit is connected to the second optical modulator unit, and the second optical modulator unit is connected to the polarizer and the signal processing unit.

[0015] Preferably, the fiber optic ring resonator unit includes: a fiber optic ring resonator cavity, a first optical coupler for the resonator, and a second optical coupler for the resonator;

[0016] The fiber optic ring resonator is configured as a ring fiber connected end to end and wrapped around the periphery of the conductor under test current. The first optical coupler and the second optical coupler of the resonator are fused onto the fiber optic ring resonator.

[0017] Preferably, the first waveplate unit includes: a first waveplate and a second waveplate;

[0018] The first optical coupler of the resonator is connected to the first waveplate, and the second optical coupler of the resonator is connected to the second waveplate.

[0019] Preferably, the first optical modulator unit is a Y-waveguide modulator, and the first optical modulator unit includes: an optical coupler, a first optical modulator, and a second optical modulator;

[0020] The first waveplate is connected to the first optical modulator, the second waveplate is connected to the second optical modulator, and the first optical modulator and the second optical modulator are connected to the optical coupler;

[0021] The optical coupler is connected to the polarizer, and the signal processing unit is connected to the first optical modulator and the second optical modulator.

[0022] Preferably, the fiber optic linear resonant unit includes: a fiber optic linear resonant cavity, a linear cavity optical coupler, a linear cavity first reflector, and a linear cavity second reflector;

[0023] The fiber optic linear resonant cavity is configured as a ring fiber with disconnected ends, which is wrapped around the periphery of the conductor under test current. The first and second reflectors of the linear cavity are respectively installed at the first and second ends of the fiber optic linear resonant cavity, and the linear cavity optical coupler is fused between the first and second ends of the fiber optic linear resonant cavity.

[0024] Preferably, the second waveplate unit includes: a third waveplate;

[0025] The linear cavity optical coupler is connected to the third waveplate.

[0026] Preferably, the second optical modulator unit includes: a third optical modulator;

[0027] The third optical modulator is connected to the third waveplate, the polarizer, and the signal processing unit;

[0028] The third optical modulator is a straight waveguide phase modulator that can be modulated on both axes.

[0029] Preferably, a fusion joint with a 45-degree rotation angle is provided between the third optical modulator and the polarizer.

[0030] Preferably, a method for operating the resonant fiber optic current sensing system includes the following steps:

[0031] Step S1: The signal processing unit generates a sawtooth wave signal with a repetition frequency of 22kHz and applies it to the optical modulator unit, so that the two arms of the optical modulator unit produce frequency shifts of equal magnitude and opposite direction. Changing the amplitude of the sawtooth wave signal can change the magnitude of the frequency shift.

[0032] Simultaneously, a square wave signal synchronized with the sawtooth wave signal is generated as a reference signal for demodulation;

[0033] The signal processing unit acquires the voltage signal output by the photodetector, and uses the voltage signal as a reference signal for synchronous demodulation to obtain a demodulated output signal;

[0034] Step S2: Test the sensing system by gradually changing the voltage amplitude of the sawtooth wave signal on the optical modulator unit, so that the frequency shift difference generated by the two arms is gradually tuned from -275kHz to 275kHz, to simulate the different resonant frequency differences of circularly polarized light in two directions on the fiber ring resonator and the fiber linear resonator under the action of current. At the same time, record the optical power detected by the photodetector and the signal demodulated by the signal processing unit. The signal demodulated by the signal processing unit is proportional to the current to be measured, and the proportionality coefficient is denoted as K.

[0035] Step S3: In open-loop operation mode, within the sensor range, the signal output by the signal processing unit is proportional to the current to be measured. When a current of a certain intensity flows through the conductor of the current to be measured, the magnitude and direction of the current are calculated by the demodulated signal output by the signal processing unit using the proportionality coefficient K.

[0036] Step S4: In applications requiring a large measurement range, a closed-loop operating mode can be adopted. In this mode, the signal processing unit uses the demodulated output signal as an error signal to adjust the amplitude and phase of the sawtooth wave voltage applied to the optical modulator unit in real time. This ensures that the frequency shift generated by the optical modulator unit completely compensates for the change in the resonant frequency of the circularly polarized light caused by the magnetic field of the current under test. At this time, the voltage amplitude and sign on the optical modulator unit are proportional to the current under test. Multiplying this by the calibration coefficient yields the magnitude and direction of the current under test.

[0037] Open-loop operation mode means that after the measurement system is configured and current is applied to the conductor to be measured, the measured value can be directly read from the demodulated signal without feedback control.

[0038] Closed-loop operation mode refers to the system's controlled output measurement value being returned to the control input in a certain way, based on the open-loop operation mode. That is, a frequency shift signal is applied to the optical modulator unit in real time to compensate for the frequency shift caused by the measured current, so as to realize the function of keeping the demodulated output signal at the original value. This is feedback control.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] This invention uses an optical fiber resonant cavity as the sensitive unit to detect the resonant frequency difference of light caused by the Faraday effect. Compared with the traditional scheme for detecting the phase difference caused by the Faraday effect, it has higher sensitivity and stronger resistance to environmental interference. Attached Figure Description

[0041] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0042] Figure 1 A resonant fiber optic current sensing system with a fiber optic ring resonator;

[0043] Figure 2 A resonant fiber optic current sensing system with a linear resonant cavity in the fiber optic cable;

[0044] Figure 3 The optical power curves detected by the photodetector at different frequency shifts are shown.

[0045] Figure 4 Demodulation output curves at different frequency shifts;

[0046] Figure 5 This represents the average error signal under different DC currents;

[0047] As shown in the figure:

[0048]

[0049] Detailed Implementation

[0050] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0051] Example 1

[0052] This embodiment includes: a signal generation and detection system, an optical fiber resonant cavity sensing unit, a waveplate unit, and an optical modulator unit; the signal generation and detection system includes: a low-coherence light source 1, an optical circulator 2, a photodetector 3, a signal processing unit 4, and a polarizer 5; the three ports of the optical circulator 2 are respectively connected to the low-coherence light source 1, the photodetector 3, and the polarizer 5, the photodetector 3 is connected to the signal processing unit 4, and the polarizer 5 and the signal processing unit 4 are connected to the optical modulator unit. The fiber optic resonant cavity sensing unit includes: a fiber optic ring resonant unit or a fiber optic linear resonant unit; the waveplate unit includes: a first waveplate unit or a second waveplate unit; the optical modulator unit includes: a first optical modulator unit or a second optical modulator unit; when the fiber optic resonant cavity sensing unit uses a fiber optic ring resonant unit, the fiber optic ring resonant unit is connected to the first waveplate unit, the first waveplate unit is connected to the first optical modulator unit, and the first optical modulator unit is connected to the polarizer 5 and the signal processing unit 4; when the fiber optic resonant cavity sensing unit uses a fiber optic linear resonant unit, the fiber optic linear resonant unit is connected to the second waveplate unit, the second waveplate unit is connected to the second optical modulator unit, and the second optical modulator unit is connected to the polarizer 5 and the signal processing unit 4.

[0053] like Figure 1 As shown, the fiber optic ring resonator unit includes: a fiber optic ring resonator cavity 11, a first resonator optical coupler 12, and a second resonator optical coupler 13; the fiber optic ring resonator cavity 11 is configured as a ring fiber connected end to end and surrounds the periphery of the current conductor 14 under test, and the first resonator optical coupler 12 and the second resonator optical coupler 13 are fused onto the fiber optic ring resonator cavity 11. The first waveplate unit includes: a first waveplate 9 and a second waveplate 10; the first resonator optical coupler 12 is connected to the first waveplate 9, and the second resonator optical coupler 13 is connected to the second waveplate 10. The first optical modulator unit includes: an optical coupler 6, a first optical modulator 7, and a second optical modulator 8; the first waveplate 9 is connected to the first optical modulator 7, the second waveplate 10 is connected to the second optical modulator 8, the first optical modulator 7 and the second optical modulator 8 are connected to the optical coupler 6, the optical coupler 6 is connected to the polarizer 5, and the signal processing unit 4 is connected to the first optical modulator 7 and the second optical modulator 8.

[0054] like Figure 2As shown, the fiber optic linear resonant unit includes: a fiber optic linear resonant cavity 18, a linear cavity optical coupler 19, a linear cavity first reflector 20, and a linear cavity second reflector 21. The fiber optic linear resonant cavity 18 is configured as a loop fiber with disconnected ends, surrounding the conductor 14 under test. The linear cavity first reflector 20 and the linear cavity second reflector 21 are respectively installed at the beginning and end of the fiber optic linear resonant cavity 18. The linear cavity optical coupler 19 is fused between the beginning and end of the fiber optic linear resonant cavity 18. The second waveplate unit includes: a third waveplate 17; the linear cavity optical coupler 19 is connected to the third waveplate 17. The second optical modulator unit includes: a third optical modulator 16; the third optical modulator 16 is connected to the third waveplate 17, the polarizer 5, and the signal processing unit 4. A fusion splice 15 with a 45-degree rotation angle is provided between the third optical modulator 16 and the polarizer 5.

[0055] Example 2

[0056] Example 2 is a preferred example of Example 1.

[0057] like Figure 1 and Figure 2 As shown, this embodiment includes: a signal generation and detection system, an optical modulator unit, a waveplate unit, and an optical fiber resonant cavity sensing unit. The signal generation and detection system includes: a low-coherence light source 1, an optical circulator 2, a photodetector 3, a signal processing unit 4, and a polarizer 5.

[0058] The fiber optic resonant cavity sensing unit includes two basic structural types. One is a fiber optic ring resonant cavity 11, which is formed by fusing a first optical coupler 12 and a second optical coupler 13 with a high splitting ratio to the sensing fiber of the fiber optic ring resonant cavity 11. Each of the first optical coupler 12 and the second optical coupler 13 provides a pigtail for connection with the sensing system. The second type is a fiber optic linear resonant cavity 18, which is configured with a first linear cavity mirror 20 and a second linear cavity mirror 21 with high reflectivity at both ends. A linear cavity optical coupler 19 with a high splitting ratio is fused to the middle of the sensing fiber of the fiber optic linear resonant cavity 18. The light is coupled into and out of the fiber optic Fabry-Perot interferometer through a pigtail of the linear cavity optical coupler 19.

[0059] For low-coherence light sources, erbium-doped superfluorescent fiber optic light sources are preferred.

[0060] Optical circulator 2 can be replaced with an optical fiber coupler, but this will increase the loss of optical intensity.

[0061] Polarizer 5 is used to convert the light from the broadband light source into linearly polarized light. If the light emitted by the light source is already linearly polarized, then polarizer 5 is not needed here.

[0062] Polarization-maintaining optical fiber is used to connect polarizer 5 to the quarter-wave plate (wave plate unit).

[0063] In the scheme based on the fiber optic ring resonator 11 structure, the output of the low-coherence light source 1 is connected to the first port of the optical circulator 2. The second port of the optical circulator 2 is sequentially connected to the polarizer 5, the optical coupler 6, the first optical modulator 7, and the second optical modulator 8. The third port of the optical circulator 2 is connected to the photodetector 3. The two output ports of the optical coupler 6 are connected to the two pigtails of the fiber optic ring resonator 11 via the first waveplate 9 and the second waveplate 10, respectively. The optical fiber of the fiber optic ring resonator 11 surrounds the conductor 14 under test. The signal processing unit 4 is connected to the photodetector 3.

[0064] For light propagating clockwise and counterclockwise, due to the filtering effect of the fiber optic ring resonator 11, the light returning to the first waveplate 9 and the second waveplate 10 after passing through the fiber optic ring resonator 11 both have a series of Lorentz-shaped spectral lines. When there is no current in the current-testing conductor 14, the resonant spectral lines of the clockwise and counterclockwise propagating light completely coincide, exhibiting maximum coherence and the strongest output light intensity when they meet. When a certain ampere current flows through the current-testing conductor 14, a magnetic field is generated around it. The clockwise and counterclockwise circularly polarized light in the fiber will experience different refractive indices due to the Faraday effect, producing a resonant frequency difference proportional to the current intensity. The spectral lines transmitted in the two directions no longer coincide, the coherence decreases, the output light intensity decreases, and within a certain range, the magnitude of the interference light intensity is linearly related to the current intensity. When the light from the two propagation directions passes through the first optical modulator 7 and the second optical modulator 8 again, the frequency shift they experience is the same in magnitude but opposite in direction to the frequency shift they experience when passing through the first optical modulator 7 and the second optical modulator 8 for the first time. This compensates for the spectral shift when passing through the first optical modulator 7 and the second optical modulator 8 for the first time, so that the DC component of the interference light intensity represents the coherence of the two light paths. By processing the electrical signal output by the photodetector 3 using the signal processing unit 4, the current intensity signal can be recovered.

[0065] In the scheme based on the fiber optic ring resonator 11 structure, the light output from the polarizer 5 passes through the optical coupler 6, and the two output optical powers are equal. When they pass through the first optical modulator 7 and the second optical modulator 8 respectively, they are frequency modulated, and the magnitude of their frequency shift is the same but the direction is opposite. Preferably, devices such as Y waveguides are used to simultaneously realize the functions of the optical coupler 6, the first optical modulator 7, and the second optical modulator 8.

[0066] In the scheme based on the fiber optic linear resonant cavity 18 structure, the output of the low-coherence light source 1 is connected to the first port of the optical circulator 2. The second port of the optical circulator 2 is sequentially connected to the polarizer 5, the 45-degree fusion splice 15, the third optical modulator 16, the third waveplate 17, and the fiber optic linear resonant cavity 18. The polarization-maintaining fiber between the polarizer 5 and the third optical modulator 16 has a 45-degree rotation angle between their fast and slow axes, i.e., the 45-degree fusion splice 15. The third port of the optical circulator 2 is connected to the photodetector 3. The fiber optic linear resonant cavity 18 surrounds the conductor 14 under test, and the signal processing unit 4 is connected to the photodetector 3.

[0067] The 45-degree fusion between polarizer 5 and the third optical modulator 16 causes the light output from polarizer 5, with a single polarization direction, to enter the third optical modulator 16 in two polarization states with equal power and perpendicular directions after passing through the 45-degree fusion point. In the third optical modulator 16, the light undergoes a frequency shift with equal amplitude and opposite direction. The two mutually perpendicular linearly polarized lights output from the third optical modulator 16 are then converted into left-handed and right-handed circularly polarized light, respectively, after passing through the third waveplate 17 (quarter-wave plate), and labeled as rays A and B. Simultaneously, they are combined by the linear cavity optical coupler 19 and enter the fiber linear resonant cavity 18. Due to the filtering effect of the fiber linear resonant cavity 18, the light returning from the fiber linear resonant cavity 18 to the third waveplate 17 all have a series of Lorentz lines. When there is no current in the conductor 14 under test, the refractive indices experienced by light rays A and B are exactly the same, the resonant spectral lines completely overlap, and the coherence is the maximum. When a certain ampere current flows through the conductor 14 under test, a magnetic field is generated around it, causing light rays A and B to experience different refractive indices due to the Faraday effect, resulting in a resonant frequency difference proportional to the current intensity. The spectral lines transmitted in the two directions no longer overlap, and the coherence decreases. When light rays A and B return from the fiber optic linear resonant cavity 18, their polarization states change to right-handed circularly polarized light and left-handed circularly polarized light, respectively, due to the change in transmission direction. After passing through the third waveplate 17, their polarization states are perpendicular to their initial polarization states. Therefore, when they pass through the third optical modulator 16 again, the frequency shift they experience is the same in magnitude but opposite in direction to the frequency shift they experience when passing through the third optical modulator 16 for the first time. This compensates for the spectral shift when passing through the third optical modulator 16 for the first time, so that the DC component of the interference light intensity characterizes the coherence of the two light paths. By processing the electrical signal output by the photodetector 3 using the signal processing unit 4, the current intensity signal can be recovered.

[0068] The optical modulator unit is used to modulate the frequency of light. Preferably, a sawtooth wave voltage is applied to a straight waveguide phase modulator that can be modulated on both axes to achieve frequency modulation.

[0069] Waveplate units are used for the interconversion of linearly polarized light and circularly polarized light. A quarter-waveplate is preferably made of a section of polarization-maintaining fiber and another section of polarization-maintaining fiber with a length of one-quarter beat.

[0070] In the scheme based on the fiber optic ring resonator 11 structure, the fiber optic ring resonator 11 is formed by fusing two high-split-ratio 2x2 fiber couplers and sensing fibers of the same specifications and parameters. It is the current-sensitive unit in this embodiment. The fiber optic ring resonator 11 can be a single-mode fiber or a circularly polarized fiber.

[0071] In the scheme based on the fiber linear resonant cavity 18 structure, the fiber linear resonant cavity 18 is composed of a linear cavity optical coupler 19 with a high splitting ratio fused in the middle of an optical fiber with high reflectivity mirrors at both ends. It is the current-sensitive unit in this embodiment. The sensing fiber type can be single-mode fiber or circular fiber. The two high reflectivity linear cavity first mirror 20 and linear cavity second mirror 21 are preferably Faraday mirrors to compensate for the residual birefringence of the optical fiber.

[0072] Photodetector 3 is used to detect optical power.

[0073] The signal processing unit 4 is used to receive the light intensity signal output by the photodetector 3, and after processing, calculate the magnitude and direction information of the current.

[0074] This embodiment relates to two current signal generation and detection systems based on the above-mentioned systems. In one system, low-coherence light is split into two paths by an optical fiber circulator 2, a polarizer 5, an optical coupler 6, a first optical modulator 7, and a second optical modulator 8. The two paths are then converted into circularly polarized light with the same rotation direction by a quarter-wave plate and injected into the sensing unit of the optical fiber ring resonant cavity 11 from two opposite directions. Under the action of the magnetic field generated by the current, the resonant frequencies of the circularly polarized light in the two directions are different. The difference in their resonant frequencies is proportional to the magnitude of the current to be measured. After the two circularly polarized lights return from the resonant cavity, they interfere on the photodetector 3. The intensity of the light signal after interference represents the difference in resonant frequencies, and the magnitude and direction of the current to be measured are calculated.

[0075] In the second current signal generation and detection system based on the above system involved in this embodiment, low-coherence light sequentially passes through fiber optic circulator 2, polarizer 5, 45-degree fusion splice 15, and third optical modulator 16. A quarter-wave plate is used to obtain left-hand circularly polarized light and right-hand circularly polarized light, which are then injected into the sensing unit of fiber optic linear resonant cavity 18 via linear cavity optical coupler 19. Under the action of the magnetic field generated by the current, the two circularly polarized lights with different polarization directions have different resonant frequencies. The difference in their resonant frequencies is proportional to the magnitude of the current to be measured. After returning from the fiber optic linear resonant cavity 18, the two circularly polarized lights interfere on the photodetector 3. The intensity of the light signal after interference characterizes the difference in resonant frequencies, and the magnitude and direction of the current to be measured are calculated.

[0076] Example 3

[0077] More specifically, in one implementation, such as Figure 1 As shown, it includes: a low-coherence light source 1, a circulator 2, a photodetector 3, a signal processing unit 4, a polarizer 5, an optical coupler 6, a first optical modulator 7, a second optical modulator 8, a first waveplate 9, a second waveplate 10, an optical fiber ring resonator 11, a resonator first optical coupler 12, and a resonator second optical coupler 13.

[0078] Low-coherence light source 1 is an erbium-doped superfluorescent fiber light source with a center wavelength of 1550 nm, a spectral bandwidth of 35 nm, and an output low-coherence optical power of 100 mW.

[0079] Polarizer 5 is a device for linear polarization, with slow axis alignment.

[0080] The functions of optical coupler 6, first optical modulator 7 and second optical modulator 8 are realized by Y-waveguide modulator, and the two output arms are respectively connected to the two ports of fiber ring resonator 11.

[0081] Both the first waveplate 9 and the second waveplate 10 are quarter-wave plates made of optical fiber.

[0082] The fiber optic ring resonator 11 is formed by splicing two 99:1 single-mode optical couplers and a single-mode optical fiber with a length of about 1 km, and the coil diameter is 12.6 cm; the free spectral range of this fiber optic ring resonator 11 is 0.205 MHz.

[0083] The specific steps of this embodiment are as follows:

[0084] Step 1: The signal processing unit 4 generates a sawtooth wave signal with a repetition frequency of 22kHz and applies it to the Y-waveguide modulator (first optical modulator unit), causing the two arms of the Y-waveguide modulator to generate frequency shifts of equal magnitude but opposite direction. Changing the amplitude of the sawtooth wave signal can change the magnitude of the frequency shift. At the same time, a square wave signal synchronized with the sawtooth wave signal is generated as a reference signal for demodulation. The signal processing unit 4 acquires the voltage signal output by the photodetector 3 and uses the square wave signal as a reference signal for synchronous demodulation to obtain the demodulated output signal.

[0085] Step 2: Test the sensing system by gradually changing the voltage amplitude of the sawtooth wave signal on the Y-waveguide modulator, so that the frequency shift difference generated by the two arms is gradually tuned from -275kHz to 275kHz, to simulate the different resonant frequency differences of circularly polarized light in two directions on the fiber ring resonator 11 and the fiber linear resonator 18 under the action of current. At the same time, record the optical power detected by the photodetector 3 and the signal demodulated output of the signal processing unit. The signal demodulated output of the signal processing unit 4 is proportional to the current to be measured, and the proportionality coefficient is denoted as K; Figure 3 and Figure 4As shown, the system can respond to current and has a good linear relationship in the frequency shift range of [-5kHz, 5kHz].

[0086] Step 3: In open-loop operation mode, within the sensor range, the signal output by the demodulated signal unit is proportional to the current to be measured. When the current to be measured conductor 14 is energized, the magnitude and direction of the current are calculated by the demodulated signal output by the signal processing unit 4 using the proportional coefficient K. The resulting calibration coefficient is 10.9A / mV, and the measurement range exceeds 1000A.

[0087] Figure 5 The average error signal test results under open-loop conditions show that the current measurement accuracy is better than 0.2%.

[0088] Step 4: In applications requiring a large measurement range, a closed-loop operating mode can be used. In this mode, the signal processing unit 4 uses the demodulated output signal as an error signal to adjust the amplitude and phase of the sawtooth wave voltage applied to the Y-waveguide modulator in real time. This ensures that the frequency shift generated by the Y-waveguide modulator fully compensates for the change in the resonant frequency of the circularly polarized light caused by the magnetic field of the current under test. At this time, the voltage amplitude and sign on the Y-waveguide modulator are proportional to the current under test. Multiplying this by the calibration coefficient yields the magnitude and direction of the current under test.

[0089] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0090] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A resonant fiber optic current sensing system, characterized in that, include: Signal generation and detection system, fiber optic resonant cavity sensing unit, waveplate unit, and optical modulator unit; The signal generation and detection system is connected to the fiber optic resonant cavity sensing unit, and the optical modulator unit and the waveplate unit are disposed between the signal generation and detection system and the fiber optic resonant cavity sensing unit. The signal generation and detection system includes: a low-coherence light source (1), an optical circulator (2), a photodetector (3), a signal processing unit (4), and a polarizer (5). The three ports of the optical circulator (2) are respectively connected to the low coherence light source (1), the photodetector (3) and the polarizer (5), and the photodetector (3) is connected to the signal processing unit (4). The polarizer (5) and the signal processing unit (4) are connected to the optical modulator unit; The fiber optic resonant cavity sensing unit includes: a fiber optic ring resonant unit or a fiber optic linear resonant unit. The waveplate unit includes: a first waveplate unit or a second waveplate unit; The optical modulator unit includes: a first optical modulator unit or a second optical modulator unit; When the fiber resonant cavity sensing unit adopts the fiber ring resonant unit, the fiber ring resonant unit is connected to the first waveplate unit, the first waveplate unit is connected to the first optical modulator unit, and the first optical modulator unit is connected to the polarizer (5) and the signal processing unit (4). When the fiber resonant cavity sensing unit adopts the fiber linear resonant unit, the fiber linear resonant unit is connected to the second waveplate unit, the second waveplate unit is connected to the second optical modulator unit, and the second optical modulator unit is connected to the polarizer (5) and the signal processing unit (4). The fiber optic ring resonant unit includes: a fiber optic ring resonant cavity (11), a first resonator optical coupler (12), and a second resonator optical coupler (13). The fiber optic ring resonator (11) is configured as a ring fiber connected end to end and surrounds the periphery of the current conductor (14) under test. The first optical coupler (12) and the second optical coupler (13) of the resonator are fused onto the fiber optic ring resonator (11). The fiber optic linear resonant unit includes: a fiber optic linear resonant cavity (18), a linear cavity optical coupler (19), a linear cavity first reflector (20), and a linear cavity second reflector (21). The fiber optic linear resonant cavity (18) is configured as a ring fiber with disconnected ends and surrounds the conductor (14) under test. The first reflector (20) and the second reflector (21) of the linear cavity are respectively installed at the first and second ends of the fiber optic linear resonant cavity (18). The linear cavity optical coupler (19) is fused between the first and second ends of the fiber optic linear resonant cavity (18).

2. The resonant fiber optic current sensing system according to claim 1, characterized in that, The first waveplate unit includes: a first waveplate (9) and a second waveplate (10); The first optical coupler (12) of the resonator is connected to the first waveplate (9), and the second optical coupler (13) of the resonator is connected to the second waveplate (10).

3. The resonant fiber optic current sensing system according to claim 2, characterized in that, The first optical modulator unit includes: an optical coupler (6), a first optical modulator (7), and a second optical modulator (8); The first waveplate (9) is connected to the first optical modulator (7), the second waveplate (10) is connected to the second optical modulator (8), and the first optical modulator (7) and the second optical modulator (8) are connected to the optical coupler (6). The optical coupler (6) is connected to the polarizer (5), and the signal processing unit (4) is connected to the first optical modulator (7) and the second optical modulator (8).

4. The resonant fiber optic current sensing system according to claim 1, characterized in that, The second waveplate unit includes: a third waveplate (17); The linear cavity optical coupler (19) is connected to the third waveplate (17).

5. The resonant fiber optic current sensing system according to claim 4, characterized in that, The second optical modulator unit includes: a third optical modulator (16); The third optical modulator (16) is connected to the third waveplate (17), the polarizer (5), and the signal processing unit (4). A fusion point (15) with a 45-degree rotation angle is provided between the third optical modulator (16) and the polarizer (5).

6. A method of operating the resonant fiber optic current sensing system according to any one of claims 2-5, characterized in that, Includes the following steps: Step S1: The signal processing unit (4) generates a sawtooth wave signal and applies it to the optical modulator unit, so that the two arms of the optical modulator unit generate frequency shifts of equal magnitude and opposite direction. Changing the amplitude of the sawtooth wave signal can change the magnitude of the frequency shift. Simultaneously, a square wave signal synchronized with the sawtooth wave signal is generated as a reference signal for demodulation; The signal processing unit (4) collects the voltage signal output by the photodetector (3), and uses the voltage signal as a reference signal to perform synchronous demodulation to obtain the demodulated output signal; Step S2: Test the sensing system by gradually changing the voltage amplitude of the sawtooth wave signal on the optical modulator unit, so that the frequency shift difference generated by the two arms is gradually tuned, so as to simulate the different resonant frequency differences of circularly polarized light in two directions on the fiber ring resonator (11) and the fiber linear resonator (18) under the action of current. At the same time, record the optical power detected by the photodetector (3) and the signal demodulated by the signal processing unit (4). The signal demodulated by the signal processing unit (4) is proportional to the current to be measured, and the proportionality coefficient is denoted as K. Step S3: In open-loop operation mode, within the sensor range, the signal output by the signal processing unit (4) is proportional to the current to be measured. When the current to be measured conductor (14) is energized, the magnitude and direction of the current are calculated by the demodulated signal output by the signal processing unit (4) using the proportional coefficient K. Step S4: In situations requiring a large measurement range, a closed-loop working mode can be adopted. At this time, the signal processing unit (4) uses the demodulated output signal as an error signal to adjust the amplitude and phase of the sawtooth wave voltage applied to the optical modulator unit in real time, so that the frequency shift generated by the optical modulator unit completely compensates for the change in the resonant frequency of the circularly polarized light caused by the magnetic field of the current under test. At this time, the voltage amplitude and sign on the optical modulator unit are proportional to the current under test. Multiplying by the calibration coefficient yields the magnitude and direction of the current under test.

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