Optical fiber current sensor feedback phase shift nonlinear correction device, system and method

Abstract

The present invention provides a device for correcting the nonlinear feedback phase shift of a fiber optic current sensor, which is used to perform nonlinear correction on the feedback phase shift output by the output end of the fiber optic current sensor. The device includes a correction coefficient generator, a first multiplier and a second multiplier. The input end of the correction coefficient generator is connected to the output end of the fiber optic current sensor, the output end of the correction coefficient generator is connected to an input end of the first multiplier and the second multiplier is connected to the output end of the fiber optic current sensor, the output end of the first multiplier is connected to an input end of the second multiplier, the second multiplier is connected to the output end of the fiber optic current sensor, and the output end of the second multiplier outputs the corrected feedback phase shift. The present invention also provides a system and method for correcting the nonlinear feedback phase shift of a fiber optic current sensor, which improve the linearity of a flexible fiber optic current sensor within a large dynamic range.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber current sensing, and in particular to a device, system and method for correcting feedback phase shift nonlinearity of an optical fiber current sensor. Background Art

[0002] High current technology is widely used in fields such as metallurgy, electric power, national defense and military industry, and controlled nuclear fusion research. Accurate current measurement is closely related to safe production, energy conservation and emission reduction, product quality control, and major scientific research. The interferometric fiber optic current sensor based on the Faraday magneto-optical effect has the characteristics of high measurement accuracy, large dynamic range, wide frequency response range (can measure AC and DC currents simultaneously), strong resistance to external magnetic field interference, and good portability. It has broad application prospects in the field of high current measurement. Ultra-high current carrying busbars are often difficult to disconnect, requiring high current sensors to be installed in an opening. Flexible fiber optic current sensors encapsulate the sensing optical fiber into a flexible optical cable, which can directly surround the measured current with a certain number of turns without disconnecting the current carrying busbar to form a sensitive loop, which well meets the actual needs of large current online measurement.

[0003] The fiber-optic current sensor uses a reflective Sagnac interferometer as its sensing optical path. A quarter-wave plate converts two orthogonal linearly polarized beams into left-handed and right-handed circularly polarized light. These two orthogonal circularly polarized beams propagate back and forth through a closed-end fiber-optic sensitive loop, generating a phase difference proportional to the measured current. Due to the reciprocity of the optical path structure, the interference intensity of the two signal beams carries only the Faraday phase shift generated by the measured current. This interference intensity is converted into an electrical signal by a photodetector. For signal processing, the sensor employs closed-loop signal detection technology. The detection system demodulates the Faraday phase shift from the interference intensity and generates a feedback phase shift of equal magnitude and opposite sign in real time, locking the system at the quadrature operating point and ensuring high linearity over a wide dynamic range. This feedback phase shift also serves as the sensor output.

[0004] To suppress the influence of linear birefringence caused by fiber bending, flexible fiber optic current sensors usually use elliptical birefringence fiber as the sensing fiber. This fiber is formed by rotating a polarization-maintaining fiber preform while drawing it. Its birefringence axis is distributed helically along the fiber axis, and the pitch is determined by the rotation period and the drawing speed. The two important parameters that describe the characteristics of this fiber are the pitch L and the t and line length L b (beat length of polarization-maintaining fiber in the unrotated state), define η = 2L b / L t .

[0005] The polarization eigenmodes of an elliptically birefringent fiber are two orthogonal elliptically polarized beams. Their ellipticity is related to η. A larger η indicates that the polarization eigenmodes approach circular polarization. Ideally, the polarization eigenmodes of the sensing fiber are left-handed and right-handed circularly polarized. The phase difference detected by the closed-loop sensor system is simply the Faraday phase shift generated by the measured current, and the feedback phase shift is proportional to the measured current. However, in practice, η is not easily achieved, typically ranging from 1 to 5. In this case, the circularly polarized light entering the elliptically birefringent fiber cannot maintain its polarization state. The phase difference detected by the closed-loop sensor system is related not only to the Faraday phase shift generated by the measured current, but also to the linear and circular birefringence determined by the beat length and pitch. The feedback phase shift has a nonlinear relationship with the measured current, and the nonlinearity becomes more pronounced with increasing measured current, seriously affecting the sensor's measurement accuracy over a wide dynamic range.

[0006] Existing flexible fiber optic current sensors generally have nonlinear problems and cannot guarantee measurement accuracy within a large dynamic range. Summary of the Invention

[0007] One of the technical problems to be solved by the present invention is to provide a correction device for the nonlinear feedback phase shift of a fiber optic current sensor, so that the linear relationship between the feedback phase shift generated by the closed-loop detection module of the flexible fiber optic current sensor and the measured current is restored, thereby improving the linearity of the flexible fiber optic current sensor within a large dynamic range.

[0008] One of the problems of the present invention is achieved as follows:

[0009] A device for correcting the nonlinearity of feedback phase shift of an optical fiber current sensor is provided, for performing nonlinear correction on the feedback phase shift outputted from the output end of the optical fiber current sensor; the device is characterized in that: the device for correcting the nonlinearity of feedback phase shift comprises a correction coefficient generator, a first multiplier and a second multiplier; the input end of the correction coefficient generator is connected to the output end of the optical fiber current sensor, the output end of the correction coefficient generator is connected to an input end of the first multiplier and the other input end of the first multiplier and the other input end of the second multiplier and the other input end of the second multiplier and the output end of the second multiplier outputs the corrected feedback phase shift.

[0010] The second technical problem to be solved by the present invention is to provide a correction system for the nonlinear feedback phase shift of the optical fiber current sensor, so that the linear relationship between the feedback phase shift generated by the closed-loop detection module of the flexible optical fiber current sensor and the measured current is restored, thereby improving the linearity of the flexible optical fiber current sensor within a large dynamic range.

[0011] The second problem of the present invention is achieved as follows:

[0012] A fiber optic current sensor feedback phase shift nonlinearity correction system includes a feedback phase shift nonlinearity test device, a fiber optic current sensor, and a feedback phase shift nonlinearity correction device, wherein the feedback phase shift nonlinearity correction device includes a correction coefficient generator, a first multiplier-adder, and a second multiplier-adder;

[0013] The feedback phase shift nonlinearity testing device is connected to a fiber optic current sensor, the output end of the fiber optic current sensor outputs feedback phase shift, and the output end is respectively connected to the input end of a correction coefficient generator, an input end of a first multiplier and an input end of a second multiplier, the output end of the correction coefficient generator is connected to the other input end of the first multiplier, the output end of the first multiplier is connected to the other input end of the second multiplier, and the output end of the second multiplier outputs the corrected feedback phase shift.

[0014] Furthermore, the feedback phase shift nonlinear test equipment includes a current standard source, a first power line, a second power line and an equal ampere-turn coil, the positive pole of the current standard source is connected to the input end of the first power line, the output end of the first power line is connected to the input end of the equal ampere-turn coil, the output end of the equal ampere-turn coil is connected to the input end of the second power line, the output end of the second power line is connected to the negative pole of the current standard source, the equal ampere-turn coil is wound into M turns, and the optical fiber current sensor is wrapped in the equal ampere-turn coil.

[0015] Furthermore, the fiber optic current sensor includes a flexible sensing optical cable, a sensing optical path and a closed-loop signal detection module. The flexible sensing optical cable is wrapped around an equal ampere-turn coil to form an N-turn fiber optic sensitive ring. The fiber optic sensitive ring is also connected to the closed-loop signal detection module through the sensing optical path. The closed-loop signal detection module outputs a feedback phase shift, and its output end is respectively connected to the correction coefficient generator, the first multiplier and the second multiplier.

[0016] Furthermore, the optical fiber sensitive ring is encapsulated by a panda-type elliptical birefringent optical fiber, a bowtie-type elliptical birefringent optical fiber, an elliptical-core elliptical birefringent optical fiber or an elliptical birefringent photonic crystal optical fiber.

[0017] Furthermore, the optical fiber current sensor is a flexible current sensor.

[0018] The third technical problem to be solved by the present invention is to provide a method for correcting the nonlinearity of the feedback phase shift of the optical fiber current sensor, so that the linear relationship between the feedback phase shift generated by the closed-loop detection module of the flexible optical fiber current sensor and the measured current is restored, thereby improving the linearity of the flexible optical fiber current sensor within a large dynamic range.

[0019] The third problem of the present invention is achieved as follows:

[0020] A method for correcting the nonlinearity of feedback phase shift of a fiber optic current sensor is provided. The method requires providing the above-mentioned nonlinearity correction system for feedback phase shift of a fiber optic current sensor, and comprises the following steps:

[0021] Step 1: The current standard source outputs a standard current i0, which is equivalently amplified by an M-turn equal ampere-turn coil and an N-turn optical fiber sensitive ring to obtain the upper limit equivalent test current I0=MNi0 of the optical fiber current sensor. The feedback phase shift Φ0 output by the optical fiber current sensor at this time is recorded to obtain the scale factor of the optical fiber current sensor:

[0022]

[0023] Step 2: Reduce the equivalent test current in sequence and record the equivalent test current as I n The feedback phase shift Φ of the fiber optic current sensor output is n , calculate the nonlinear error e n , n={1, 2, 3, ...}, and the feedback phase shift nonlinear error curve is obtained e-Φ :

[0024]

[0025] Step 3: Calculate the nonlinear correction coefficient k based on the feedback phase shift nonlinear error curve n and b n , n = {1, 2, 3, ...}, and stored in the correction coefficient generator;

[0026] Step 4: The correction coefficient generator generates a correction coefficient according to the feedback phase shift Φ output by the optical fiber current sensor and the nonlinear correction coefficient k n and b n Output the corresponding feedback coefficients k and b;

[0027] Step 5: predict the nonlinear error e of the feedback phase shift output by the optical fiber current sensor according to a linear function: e=kΦ+b;

[0028] Step 6: Correct and compensate the feedback phase shift Φ output by the optical fiber current sensor according to the nonlinear error e to obtain the corrected feedback phase shift Φ out :Φ out =Φ(1-e);

[0029] Step 7: After correcting the feedback phase shift generated by the closed-loop signal detection module in the optical fiber current sensor, a linear relationship is restored between the corrected feedback phase shift and the measured current in the current-carrying conductor passing through the N-turn optical fiber sensitive ring, thereby improving the linearity of the optical fiber current sensor within a large dynamic range.

[0030] Furthermore, the calculation method of the nonlinear correction coefficient in step 3 is as follows:

[0031] (1) The feedback phase shift nonlinear error curve e-Φ is segmented according to each change of nonlinear error ε, and the coordinates of the corresponding segment points (Φ n , e n ), where e n =ε(n-1), n={1, 2, 3,...};

[0032] (2) Calculate the nonlinear correction coefficient k based on the coordinates of the segmented points n and b n , n = {1, 2, 3, ...}:

[0033]

[0034]

[0035] Furthermore, the correction coefficient generator in step 4 is based on the magnitude of the feedback phase shift Φ output by the optical fiber current sensor, the nonlinear correction coefficient k n and b n Output the corresponding feedback coefficients k and b, specifically:

[0036] a. When |Φ|>Φ0, k=k1, b=-k1Φ0;

[0037] b. When Φ n-1 ≥|Φ|>Φ n When k=k n , b=b n , n = {1, 2, 3, ...};

[0038] c. When Φ p When ≥|Φ|≥0, k=0, b=e p ,(Φ p , e p ) is the segment point closest to the e-axis on the feedback phase shift nonlinear error curve e-Φ.

[0039] The advantages of the present invention are that: through the present invention, a linear relationship is restored between the feedback phase shift generated by the closed-loop signal detection module in the flexible optical fiber current sensor and the measured current, the linearity of the flexible optical fiber current sensor in a large dynamic range is improved, and the measurement accuracy is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0041] Figure 1 The present invention is a schematic structural diagram of a device for correcting nonlinear feedback phase shift of an optical fiber current sensor.

[0042] Figure 2 The present invention is a structural diagram of a fiber optic current sensor feedback phase shift nonlinear correction system.

[0043] Figure 3 It is a structural schematic diagram of the feedback phase shift nonlinear test equipment and the optical fiber current sensor in the present invention.

[0044] Figure 4 This is a flowchart of an execution of a method for correcting nonlinear feedback phase shift of an optical fiber current sensor according to the present invention.

[0045] Description of the numbers in the figure:

[0046] 10-Feedback phase shift nonlinear test equipment, 11-Current standard source, 12-First power line, 13-Second power line, 14-Equal ampere-turn coil, 20-Feedback phase shift nonlinear compensation equipment, 21-Correction coefficient generator, 22-First multiplier-adder, 23-Second multiplier-adder, 30-(Flexible) fiber optic current sensor, 31-Flexible sensing optical cable, 32-Sensing optical path, 33-Closed-loop signal detection module, 34-Fiber optic sensitive ring. DETAILED DESCRIPTION

[0047] To make the present invention more clearly understood, a preferred embodiment is now described in detail below with reference to the accompanying drawings.

[0048] like Figure 1 As shown, a nonlinear correction device for feedback phase shift of a fiber optic current sensor of the present invention is used to perform nonlinear correction on the feedback phase shift output by the output end of a fiber optic current sensor 30. The nonlinear correction device 20 for feedback phase shift includes a correction coefficient generator 21, a first multiplier 22, and a second multiplier 23. The input end of the correction coefficient generator 21 is connected to the output end of the fiber optic current sensor 30, the output end of the correction coefficient generator 21 is connected to an input end of the first multiplier 22, the other input end of the first multiplier 22 is connected to the output end of the fiber optic current sensor 30, the output end of the first multiplier 22 is connected to an input end of the second multiplier 23, the other input end of the second multiplier 23 is connected to the output end of the fiber optic current sensor 30, and the output end of the second multiplier 23 outputs the corrected feedback phase shift. The fiber optic current sensor 30 is a flexible fiber optic current sensor.

[0049] like Figure 2 and Figure 3 As shown, a feedback phase shift nonlinearity correction system for a fiber optic current sensor of the present invention includes a feedback phase shift nonlinearity testing device 10, a fiber optic current sensor 30, and a feedback phase shift nonlinearity correction device 20. The fiber optic current sensor 30 is a flexible fiber optic current sensor. The feedback phase shift nonlinearity correction device 20 includes a correction coefficient generator 21, a first multiplier-adder 22, and a second multiplier-adder 23.

[0050] The feedback phase shift nonlinearity testing device 10 is connected to a fiber optic current sensor 30. The output end of the fiber optic current sensor 30 outputs the feedback phase shift. The output end of the fiber optic current sensor 30 is respectively connected to the input end of the correction coefficient generator 21, one input end of the first multiplier 22, and one input end of the second multiplier 23. The output end of the correction coefficient generator 21 is connected to the other input end of the first multiplier 22, the output end of the first multiplier 22 is connected to the other input end of the second multiplier 23, and the output end of the second multiplier 23 outputs the corrected feedback phase shift.

[0051] The correction coefficient generator 21 includes a nonlinear correction coefficient memory, which can automatically retrieve the memory and output corresponding feedback coefficients k and b according to the size of the feedback phase shift Φ output by the closed-loop signal detection module 33 of the flexible optical fiber current sensor 30;

[0052] The first multiplier-adder 22 receives the feedback coefficients k and b output by the correction coefficient generator 21 and the feedback phase shift Φ output by the closed-loop signal detection module 33 of the flexible optical fiber current sensor 30, predicts the nonlinear error e of the feedback phase shift according to a linear function, and obtains the nonlinear error e after performing addition, subtraction, multiplication and / or division on the feedback phase shift Φ and the feedback coefficients k and b;

[0053] The second multiplier 23 receives the nonlinear error e output by the first multiplier 22 and compensates for the feedback phase shift Φ output by the closed-loop signal detection module 33 to obtain the final output Φ out After completing the addition, subtraction, multiplication and / or division calculations of the feedback phase shift Φ and the nonlinear error e, the final output Φ is obtained. ou .

[0054] Preferably, the feedback phase-shift nonlinear test device 10 includes a current standard source 11, a first power line 12, a second power line 13, and an equal-ampere-turn coil 14. The positive electrode of the current standard source 11 is connected to the input end of the first power line 12, the output end of the first power line 12 is connected to the input end of the equal-ampere-turn coil 14, the output end of the equal-ampere-turn coil 14 is connected to the input end of the second power line 13, and the output end of the second power line 13 is connected to the negative electrode of the current standard source 11. The equal-ampere-turn coil 14 is wound into M turns, and the optical fiber current sensor 30 is wrapped around the equal-ampere-turn coil 14.

[0055] The fiber optic current sensor 30 includes a flexible sensing cable 31, a sensing optical path 32, and a closed-loop signal detection module 33. The flexible sensing cable 31 is wrapped around the equal ampere-turn coil 14 to form an N-turn fiber optic sensitive ring 34. The fiber optic sensitive ring 34 is a flexible fiber optic sensitive ring. The fiber optic sensitive ring 34 is also connected to the closed-loop signal detection module 33 through the sensing optical path 32. The closed-loop signal detection module 33 outputs a feedback phase shift, and its output end is respectively connected to the correction coefficient generator 21, the first multiplier 22, and the second multiplier 23.

[0056] The optical fiber sensitive ring 34 is formed by encapsulating a panda-type elliptical birefringent optical fiber, a bowtie-type elliptical birefringent optical fiber, an elliptical core-type elliptical birefringent optical fiber or an elliptical birefringent photonic crystal optical fiber.

[0057] like Figure 4 As shown, a method for correcting the nonlinearity of feedback phase shift of a fiber optic current sensor according to the present invention is provided. The method requires providing the above-mentioned nonlinearity correction system for feedback phase shift of a fiber optic current sensor, and comprises the following steps:

[0058] Step 1: The current standard source 11 outputs a standard current i0, which is equivalently amplified by the M-turn equal ampere-turn coil and the N-turn fiber optic sensitive loop to obtain the upper limit of the range equivalent test current I0 = MNi0 for the fiber optic current sensor 30. The equivalent amplification of the current by the equal ampere-turn coil 14 and the fiber optic sensitive loop 34 reduces the power requirement of the current standard source 11. Under the action of this equivalent test current, the feedback phase shift Φ0 output by the fiber optic current sensor 30 is recorded to obtain the scale factor of the fiber optic current sensor 30:

[0059]

[0060] Step 2: Reduce the equivalent test current in sequence and record the equivalent test current as I n The feedback phase shift Φ output by the optical fiber current sensor 30 is n , calculate the nonlinear error e n , n={1, 2, 3, ...}, and the feedback phase shift nonlinear error curve is obtained e-Φ :

[0061]

[0062] Step 3: Calculate the nonlinear correction coefficient k based on the feedback phase shift nonlinear error curve n and b n , n = {1, 2, 3, ...}, and stored in the correction coefficient generator 21; the nonlinear correction coefficient is calculated as follows:

[0063] (1) The feedback phase shift nonlinear error curve e-Φ is segmented according to each change of nonlinear error ε, and the coordinates of the corresponding segment points (Φn , e n ), where e n =ε(n-1), n={1, 2, 3,...};

[0064] (2) Calculate the nonlinear correction coefficient k based on the coordinates of the segmented points n and b n , n = {1, 2, 3, ...}:

[0065]

[0066]

[0067] Step 4: The correction coefficient generator 21 generates a correction coefficient according to the feedback phase shift Φ output by the optical fiber current sensor 30 and the nonlinear correction coefficient k n and b n Output the corresponding feedback coefficients k and b; specifically:

[0068] a. When |Φ|>Φ0, k=k1, b=-k1Φ0;

[0069] b. When Φ n-1 ≥|Φ|>Φ n When k=k n , b=b n , n = {1, 2, 3, ...};

[0070] c. When Φ p When ≥|Φ|≥0, k=0, b=e p ,(Φ p , e p ) is the segment point closest to the e-axis on the feedback phase shift nonlinear error curve e-Φ;

[0071] Step 5: predict the nonlinear error e of the feedback phase shift output by the optical fiber current sensor 30 according to a linear function:

[0072] e=kΦ+b; (5)

[0073] Step 6: Correct and compensate the feedback phase shift Φ output by the optical fiber current sensor 30 according to the nonlinear error e to obtain the corrected feedback phase shift Φ out :

[0074] Φ out =Φ(1-e) (6)

[0075] Step 7: After correcting the feedback phase shift generated by the closed-loop signal detection module 33 in the fiber optic current sensor 30, a linear relationship is restored between the corrected feedback phase shift and the measured current in the current-carrying conductor (not shown) passing through the N-turn fiber optic sensitive ring 34, thereby improving the linearity of the fiber optic current sensor 30 within a large dynamic range.

[0076] The advantages of the present invention are as follows:

[0077] The present invention restores the linear relationship between the feedback phase shift generated by the closed-loop signal detection module 33 in the flexible fiber optic current sensor 30 and the measured current, thereby improving the linearity of the flexible fiber optic current sensor 30 within a large dynamic range and the measurement accuracy.

[0078] Although the specific embodiments of the present invention are described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and are not intended to limit the scope of the present invention. Equivalent modifications and changes made by those skilled in the art in accordance with the spirit of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for correcting nonlinearity of feedback phase shift in a fiber optic current sensor, characterized by: The method needs to provide a fiber optic current sensor feedback phase shift nonlinearity correction system, the system includes a feedback phase shift nonlinearity test device, the feedback phase shift nonlinearity test device includes a current standard source, a first power line, a second power line and an equal ampere-turn coil, the positive pole of the current standard source is connected to the input end of the first power line, the output end of the first power line is connected to the input end of the equal ampere-turn coil, the output end of the equal ampere-turn coil is connected to the input end of the second power line, the output end of the second power line is connected to the negative pole of the current standard source, the equal ampere-turn coil is wound into M turns, the fiber optic current sensor is wrapped in the equal ampere-turn coil, the fiber optic current sensor includes a flexible sensing optical cable, a sensing optical path and a closed-loop signal detection module, and the flexible sensing optical cable is wrapped around the equal ampere-turn coil to form an N-turn optical fiber sensitive ring; The method comprises the following steps: Step 1: The current standard source outputs a standard current i0, which is equivalently amplified by an M-turn equal ampere-turn coil and an N-turn optical fiber sensitive ring to obtain the upper limit equivalent test current I0=MNi0 of the optical fiber current sensor. The feedback phase shift Φ0 output by the optical fiber current sensor at this time is recorded to obtain the scale factor of the optical fiber current sensor: Step 2: Reduce the equivalent test current in sequence and record the equivalent test current as I n The feedback phase shift Φ of the fiber optic current sensor output is n , calculate the nonlinear error e n , n={1, 2, 3, ...}, and the feedback phase shift nonlinear error curve is obtained e-Φ : Step 3: Calculate the nonlinear correction coefficient k based on the feedback phase shift nonlinear error curve n and b n , n = {1, 2, 3, ...}, and stored in the correction coefficient generator; Step 4: The correction coefficient generator generates a correction coefficient according to the feedback phase shift Φ output by the optical fiber current sensor and the nonlinear correction coefficient k n and b n Output the corresponding feedback coefficients k and b; Step 5: predict the nonlinear error e of the feedback phase shift output by the optical fiber current sensor according to a linear function: e=kΦ+b; Step 6: Correct and compensate the feedback phase shift Φ output by the optical fiber current sensor according to the nonlinear error e to obtain the corrected feedback phase shift Φ out :Φ out =Φ(1-e); Step 7: After correcting the feedback phase shift generated by the closed-loop signal detection module in the optical fiber current sensor, a linear relationship is restored between the corrected feedback phase shift and the measured current in the current-carrying conductor passing through the N-turn optical fiber sensitive ring, thereby improving the linearity of the optical fiber current sensor within a large dynamic range.

2. The method for correcting nonlinearity of feedback phase shift of an optical fiber current sensor according to claim 1, wherein: The calculation method of the nonlinear correction coefficient in step 3 is as follows: (1) The feedback phase shift nonlinear error curve e-Φ is segmented according to each change of nonlinear error ε, and the coordinates of the corresponding segment points (Φ n , e n ), where e n =ε(n-1), n={1, 2, 3,...}; (2) Calculate the nonlinear correction coefficient k based on the coordinates of the segmented points n and b n , n = {1, 2, 3, ...}:

3. The method for correcting nonlinear feedback phase shift of an optical fiber current sensor according to claim 2, wherein: The correction coefficient generator in step 4 is based on the feedback phase shift Φ output by the optical fiber current sensor, the nonlinear correction coefficient k n and b n Output the corresponding feedback coefficients k and b, specifically: a. When |Φ|>Φ0, k=k1, b=-k1Φ0; b. When Φ n-1 ≥|Φ|>Φ n k = k n b = b n n = {1, 2, 3,...}; c. When Φ p When ≥|Φ|≥0, k=0, b=e p ,(Φ p , e p ) is the segment point closest to the e-axis on the feedback phase shift nonlinear error curve e-Φ.

4. The method for correcting nonlinear feedback phase shift of an optical fiber current sensor according to claim 1, wherein: The system also includes a fiber optic current sensor and a feedback phase shift nonlinear correction device, wherein the feedback phase shift nonlinear correction device includes a correction coefficient generator, a first multiplier and a second multiplier; The feedback phase shift nonlinearity testing device is connected to a fiber optic current sensor, the output end of the fiber optic current sensor outputs feedback phase shift, and the output end is respectively connected to the input end of a correction coefficient generator, an input end of a first multiplier and an input end of a second multiplier, the output end of the correction coefficient generator is connected to the other input end of the first multiplier, the output end of the first multiplier is connected to the other input end of the second multiplier, and the output end of the second multiplier outputs the corrected feedback phase shift.

5. The method for correcting nonlinearity of feedback phase shift of an optical fiber current sensor according to claim 4, characterized in that: The optical fiber sensitive ring is also connected to a closed-loop signal detection module through a sensing optical path. The closed-loop signal detection module outputs a feedback phase shift, and its output end is respectively connected to a correction coefficient generator, a first multiplier and a second multiplier.

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