Reshaping type all-fiber current transformer based on 45-degree tilted fiber grating and signal demodulation method

Abstract

The invention designs a ring-down type all-fiber current transformer based on a 45-degree inclined fiber grating and a signal demodulation method, the ring-down type all-fiber current transformer comprises a fiber ring cavity part and a signal acquisition and processing system, the fiber ring cavity part realizes all-fiber transmission of signals, interference brought by spatial optical coupling is avoided, and the signal acquisition and processing system acquires and processes the signals. A sensing optical signal is modulated by a magnetic field around the optical fiber sensing ring and enters the system again as a sensing signal source, and the power of the sensing optical signal is continuously ring down in a reciprocating circulation process due to indirect interference of a Faraday magneto-optical effect until the sensing optical signal is used up. The demodulation system adopts a time domain demodulation method, and a signal value to be measured is demodulated by measuring the time change of optical power ring-down, so that a test result is not influenced by light source jitter, the system stability is higher, and the detection reliability is improved to a great extent. Meanwhile, compared with an all-fiber-based current transformer system of an electromagnetic transformer, the current transformer system has the advantages of low energy consumption, low cost, accurate measurement, stable performance, safety, reliability, easiness in installation and the like.

Description

Technical Field

[0001] The present invention relates to the technology of all-fiber current transformers and the field of optical signal demodulation, and particularly relates to a ring-down all-fiber current transformer based on a 45° tilted fiber grating and a signal demodulation method. Background Art

[0002] An all-fiber current transformer is a current measurement device based on the Faraday magneto-optical effect and using polarization-maintaining fiber, single-mode fiber, etc. as the measurement and transmission media. Compared with traditional electromagnetic current transformers, it has better anti-electromagnetic interference characteristics, and large currents in wires can be measured using the Faraday magneto-optical effect.

[0003] Currently, one of the main factors affecting the measurement accuracy of all-fiber current transformers is the error caused by light source fluctuations. Such interference will reduce the stability of the system, increase signal noise and decrease the signal-to-noise ratio. Such interference may also cause changes in interference fringes, directly resulting in phase errors, reducing the measurement accuracy, and thus affecting the current measurement results. Therefore, reducing the source of light source errors to improve the stability and accuracy of the measurement system is of great significance.

[0004] In addition, the traditional square-wave modulation differential detection demodulation method obtains the magnitude of the Faraday phase shift by subtracting the light intensity in the negative half-cycle from the light intensity in the positive half-cycle. Such a method is easily affected by the losses of various optical devices in the system and is prone to errors. Therefore, adopting a method that avoids directly demodulating the light intensity is of great significance for improving the system stability and anti-interference performance. Summary of the Invention

[0005] In view of this, the present invention provides a ring-down all-fiber current transformer based on a 45° tilted fiber grating and a signal demodulation method to solve the problem that the existing all-fiber current transformer is vulnerable to unstable light sources, resulting in inaccurate measurement signals.

[0006] The specific technical solutions adopted are as follows:

[0007] A ring-down all-fiber current transformer based on a 45° tilted fiber grating and a signal demodulation method, comprising a fiber optic ring cavity part 1 and a signal acquisition and processing system 2;

[0008] The fiber optic ring cavity part 1 includes a light source 3, a polarization-maintaining fiber coupler 4, a 45° tilted fiber grating 5, a polarization-maintaining fiber coupler 6, a full-fiber quarter-wave plate 7, a current-carrying conductor 8, a fiber optic sensing ring 9, and a full-fiber quarter-wave plate 10; the signal acquisition and processing system 2 includes a photodetector 11, an acquisition card 12, and a computer 13.

[0009] In one embodiment, the light source 3 is connected to the first input end of the polarization-maintaining fiber coupler 4 with 0° axis alignment. The output end of the polarization-maintaining fiber coupler 4 is connected to the input end of the 45° tilted fiber grating 5 with 0° axis alignment. The output end of the 45° tilted fiber grating 5 is connected to the input end of the polarization-maintaining fiber coupler 6 with 0° axis alignment. The second output end of the polarization-maintaining fiber coupler 6 is connected to the input end of the all-fiber quarter-wave plate 7 with 45° axis alignment. The output end of the all-fiber quarter-wave plate 7 is connected to the input end of the fiber sensing loop 9 with 0° axis alignment. The output end of the fiber sensing loop 9 is connected to the input end of the all-fiber quarter-wave plate 10 with 0° axis alignment. The output end of the all-fiber quarter-wave plate 10 is connected to the second input end of the polarization-maintaining fiber coupler 4 with 45° axis alignment in the reverse direction. The fiber sensing loop 9 is used to act on the current-carrying conductor 8. The first output end of the polarization-maintaining fiber coupler 6 is connected to the signal acquisition and processing system 2.

[0010] In one embodiment, the pulsed light emitted by the light source 3 passes through the polarization-maintaining fiber coupler 4. The light output from the output port of the polarization-maintaining fiber coupler 4 is modulated into linearly polarized light after passing through the 45° tilted fiber grating 5, and then is split into two paths after passing through the polarization-maintaining fiber coupler 6. One path is sent to the signal acquisition and processing system 2, and the other path is sent to the all-fiber quarter-wave plate 7 after passing through the 45° fusion joint to equally divide the linearly polarized light into two orthogonally polarized light beams, converting the two orthogonally polarized light beams into left-handed and right-handed circularly polarized light, which is then sent into the fiber sensing loop 9. Under the Faraday magneto-optical effect, the phase of the circularly polarized light will change, and after passing through the all-fiber quarter-wave plate 10, it becomes linearly polarized light, carrying the Faraday phase difference information generated by the magnetic field as the light source of the second cycle and is sent into the second input end of the polarization-maintaining fiber coupler 4. After passing through the 45° tilted fiber grating 5 again, due to the change in the polarization direction, the light intensity will decay and oscillate, repeating the cycle until the light intensity signal is zero. The photodetector 11 in the signal acquisition and processing system 2 converts the optical pulse signal at the first output port of the polarization-maintaining fiber coupler 6 into an electrical pulse signal, which is sent to the acquisition card 12 for buffering, generating a pulse group signal with a constant interval and exponentially decaying peaks as the delay increases until the signal is zero, and then the acquisition card 12 sends the buffered decaying electrical pulse group signal to the computer 13 for demodulation.

[0011] In one embodiment, the polarized light is transmitted in the fiber sensing loop 9, and the polarization plane rotates under the Faraday magneto-optical effect, causing the light intensity to decay and oscillate after passing through the 45° tilted fiber grating 5 again.

[0012] In one embodiment, the light source 3 uses a pulsed light source with a wavelength of 1550 nm and a pulse width of 20 ns. Its repetition frequency matches the cavity length and provides a high peak power and a stable pulse sequence for the system.

[0013] In one embodiment, the grating period of the 45° tilted fiber grating 5 ranges from 752 to 761 nm, the grating length ranges from 8 to 13 mm, and the tilt angle is 45°. When the tilt angle is 45°, that is, when there is a Brewster angle in the fiber grating, mode coupling of a single polarization state can be achieved. That is, the core mode of the S polarization state radiates out of the fiber at a wavelength-dependent radiation angle, and the core mode of the P polarization state continues to propagate in the fiber through the grating with low loss. Due to the mode coupling characteristics of the single polarization state, the 45° tilted fiber grating can be used as an all-fiber polarizer. The optical transmission path can achieve all-fiber transmission, avoiding the transmission loss caused by spatial optical coupling.

[0014] In one embodiment, signal extraction, fitting, and demodulation processes are performed inside the computer 13. The extraction process is to extract the peak value of each pulse in a pulse group signal with a constant interval and exponentially decaying peaks as the delay increases. The fitting process is to generate an envelope function of y = exp(-A*x) according to the model Exp1p2. The demodulation process measures the loss coefficient in the fiber sensing loop by extracting the change in the decay time, that is, the change in the time required for the light intensity to decay to 1 / e of the initial value, and extracts the Faraday phase shift information through the loss coefficient. Then, the magnitude of the current is demodulated according to the Faraday magneto-optical effect (θ = VNI, where θ is the Faraday rotation angle, V is the Verdet constant, N is the number of turns of the fiber sensing loop, and I is the measured current). -1 when the light intensity decays to 1 / e of the initial value, and the measurement of the loss coefficient in the fiber sensing loop is realized. The method of demodulating by measuring the decay time of the light intensity signal belongs to time-domain demodulation. Therefore, the test results are not affected by the jitter of the light source, the system stability is higher, and it is of great significance to improve the anti-interference performance. It can solve the problem that the measurement signal of the existing all-fiber current transformer is inaccurate due to the interference of the light source stability. In addition, the all-fiber current transformer measurement system has low energy consumption, low cost, high measurement accuracy, stable performance, safe and reliable, and is easy to install, avoiding the disadvantages of high energy consumption, easy occurrence of open circuit and explosion hazards of electromagnetic transformers, and at the same time eliminating the disadvantages of poor stability and easy susceptibility to electromagnetic field interference of electromagnetic transformers.

[0015] The present invention has at least the following beneficial effects: By constructing a fiber optic ring cavity circulation system, the present invention generates a pulse group signal with a constant interval and exponentially decaying peaks as the delay increases. By extracting the time required for the signal intensity to decay to 1 / e of the initial value, the measurement of the loss coefficient in the fiber sensing loop is realized. The method of demodulating by measuring the decay time of the optical intensity signal belongs to time-domain demodulation. Therefore, the test results are not affected by the jitter of the light source, the system stability is higher, and it is of great significance to improve the anti-interference performance. It can solve the problem that the measurement signal of the existing all-fiber current transformer is inaccurate due to the interference of the light source stability. -1 In addition, the all-fiber current transformer measurement system has low energy consumption, low cost, high measurement accuracy, stable performance, safe and reliable, and is easy to install, avoiding the disadvantages of high energy consumption, easy occurrence of open circuit and explosion hazards of electromagnetic transformers, and at the same time eliminating the disadvantages of poor stability and easy susceptibility to electromagnetic field interference of electromagnetic transformers. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic structural diagram of a decay-type all-fiber current transformer and a signal demodulation method based on a 45° tilted fiber grating provided by the present invention;

[0017] Figure 2 is a flowchart of the internal processing of the acquisition card;

[0018] Figure 3 is the internal computer demodulation processing flow chart;

[0019] Figure 1 In it, 1 is the fiber optic ring cavity part, 2 is the signal acquisition and processing system, 3 is the light source, 4 is the polarization maintaining fiber optic coupler I, 5 is the 45° tilted fiber grating, 6 is the polarization maintaining fiber optic coupler II, 7 is the all-fiber quarter-wave plate I, 8 is the current-carrying conductor, 9 is the fiber optic sensing ring, 10 is the all-fiber quarter-wave plate II, 11 is the photodetector, 12 is the acquisition card, and 13 is the computer. Specific implementation mode

[0020] This embodiment provides a ring-down type all-fiber current transformer based on a 45° tilted fiber grating and a signal demodulation method. As Figure 1 shown, it includes the fiber optic ring cavity part 1 and the signal acquisition and processing system 2. This embodiment provides a ring-down type all-fiber current transformer based on a 45° tilted fiber grating and a signal demodulation method by extracting the ring-down time, that is, the time required for the light intensity to decay to e -1 of the initial value to realize the measurement of the loss coefficient in the fiber optic sensing ring, avoiding the influence of light source jitter and improving the system stability.

[0021] The fiber optic ring cavity part 1 includes a light source 3, a polarization maintaining fiber optic coupler I 4, a 45° tilted fiber grating 5, a polarization maintaining fiber optic coupler II 6, an all-fiber quarter-wave plate I 7, a current-carrying conductor 8, a fiber optic sensing ring 9, and an all-fiber quarter-wave plate II 10; the signal acquisition and processing system 2 includes a photodetector 11, an acquisition card 12, and a computer 13.

[0022] In this embodiment, the light source 3 uses a pulsed light source with a wavelength of 1550 nm and a pulse width of 20 ns. The grating period range of the 45° tilted fiber grating 5 is 752 - 761 nm, the grating length range is 8 - 13 mm, and the tilt angle is 45°. Among them, when the tilt angle is 45°, that is, when the fiber grating has a Brewster angle, single-polarization mode coupling can be realized, that is, the core mode of the S polarization state radiates out of the fiber with a wavelength-dependent radiation angle, and the core mode of the P polarization state continues to propagate in the fiber with low loss through the grating. Due to the single-polarization mode coupling characteristic, the 45° tilted fiber grating can be used as an all-fiber polarizer. The optical transmission path can achieve all-fiber transmission, avoiding the transmission loss caused by spatial optical coupling.

[0023] The all-fiber current transformer is mainly assembled by splicing the tail fibers of optical devices and circuit connection. As Figure 1 shown, the light source 3 is connected to the first input end of the polarization maintaining fiber optic coupler I 4 with 0° axis alignment, that is, the tail fiber of the light source 3 is fusion spliced with the fiber of the first input end of the polarization maintaining fiber optic coupler I 4 with 0° axis alignment.

[0024] The polarization-maintaining fiber coupler 4 has two input ends and one output end. Among them, the first input end is port a, the second input end is port c, and the output end is port b. The polarization-maintaining fiber coupler 6 has one input end and two output ends. Among them, the input end is port e, the first output end is port f, and the second output end is port k.

[0025] The pigtail at the output end of the light source 3 is fusion-spliced with the fiber of port a of the polarization-maintaining fiber coupler 4 with 0° axis alignment. The fiber of port b of the polarization-maintaining fiber coupler 4 is fusion-spliced with the input fiber of the 45° tilted fiber grating 5 with 0° axis alignment. The pigtail at the output end of the 45° tilted fiber grating 5 is fusion-spliced with the fiber of port e of the polarization-maintaining fiber coupler 6 with 0° axis alignment. The port f of the polarization-maintaining fiber coupler 6 is connected to the photodetector 11 in the signal acquisition and processing system 2 for outputting a modulated optical signal to the signal acquisition and processing system 2. The fiber of port k is fusion-spliced with the input fiber of the all-fiber quarter-wave plate 1 with 45° axis alignment, and then a quarter beat length of the rear wave plate fiber is intercepted. The output fiber of the all-fiber quarter-wave plate 1 is fusion-spliced with the input fiber of the fiber sensing ring 9 with 0° axis alignment. The output fiber of the fiber sensing ring 9 is fusion-spliced with the input fiber of the all-fiber quarter-wave plate 2 10 with 0° axis alignment, and then a quarter beat length of the wave plate fiber is intercepted. The output fiber of the all-fiber quarter-wave plate 2 10 is fusion-spliced with the fiber of port c of the polarization-maintaining fiber coupler 4 in the opposite direction with 45° axis alignment. The fiber sensing ring 9 acts on the current-carrying conductor 8 for detecting the current signal of the current-carrying conductor 8.

[0026] The pulsed light emitted by the light source 3 becomes linearly polarized light after passing through the 45° tilted fiber grating 5. After passing through the polarization-maintaining fiber coupler 6, it is divided into two paths. One path is sent from the first output end to the signal acquisition and processing system 2. The other path divides the linearly polarized light into two orthogonally polarized linearly polarized light beams after passing through the 45° point and is sent into the all-fiber quarter-wave plate 1 to convert the two orthogonally polarized linearly polarized light beams into left-handed and right-handed circularly polarized light, which is then sent into the fiber sensing ring 9. Under the Faraday magneto-optical effect, the phase of the circularly polarized light will change. After passing through the all-fiber quarter-wave plate 2 10 and the 45° point in the opposite direction, it becomes linearly polarized light and is sent into the second input end of the polarization-maintaining fiber coupler 4 as the light source for the second cycle. After passing through the 45° tilted fiber grating 5, the polarization direction changes due to the rotation of the polarization plane, resulting in optical intensity decay.

[0027] The photodetector 11 converts the optical pulse signal containing phase difference information output from the port f of the polarization-maintaining fiber coupler 6 into an electrical pulse signal and caches it in the acquisition card 12, generating a pulse group signal with a constant interval and exponentially decaying peaks as the delay increases, and sending it to the computer 13 for demodulation.

[0028] In this embodiment, as Figure 2The processing flow inside the acquisition card 12 shown includes A / D conversion and caching. The acquisition card 12 mainly converts analog electrical signals into digital signals and caches the data.

[0029] In this embodiment, as Figure 3 the processing flow inside the computer 13 described includes extraction, fitting, and demodulation. The computer 13 mainly extracts the peak value of each pulse and fits the envelope function for a pulse group signal whose peaks exponentially decay with the increase of time delay at a constant interval. By extracting the decay time, that is, the time required for the light intensity to decay to e -1 of the initial value, the measurement of the loss coefficient in the fiber optic sensing loop is realized.

[0030] Compared with the prior art, the advantages of the present invention are as follows:

[0031] The present invention generates a pulse group signal whose peaks exponentially decay with the increase of time delay at a constant interval by constructing a fiber optic ring cavity circulation system. The change of the decay time of the pulse group signal reflects the loss coefficient in the fiber optic sensing loop. By measuring the decay time of the pulse signal intensity, that is, the time required for the intensity to decay to e -1 of the initial value for sensing. The demodulation method belongs to time-domain demodulation. Therefore, the test results are not affected by the jitter of the light source, the system stability is higher, which is of great significance for improving the anti-interference performance, and can solve the problem that the detection of the existing all-fiber current transformer is interfered by the light source stability and the measurement signal is inaccurate.

[0032] The above-described embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A ring-down type all-fiber current transformer based on 45° tilted fiber Bragg grating and a signal demodulation method, characterized in that: It comprises an optical fiber ring cavity part (1) and a signal acquisition and processing system (2); The fiber ring cavity part (1) comprises a light source (3), a polarization-maintaining fiber coupler (4), a 45° tilted fiber grating (5), a polarization-maintaining fiber coupler (6), an all-fiber quarter-wave plate (7), a current-carrying conductor (8), a fiber sensing ring (9), and an all-fiber quarter-wave plate (10); the signal acquisition and processing system (2) comprises a photoelectric detector (11), an acquisition card (12), and a computer (13).

2. The ring-down type all-fiber current transformer and signal demodulation method based on 45° tilted fiber Bragg grating according to claim 1 is characterized in that: The light source (3) is connected to the first input end of the polarization-maintaining fiber coupler (4) at 0°, the output end of the polarization-maintaining fiber coupler (4) is connected to the input end of the 45°-tilted fiber grating (5) at 0°, the output end of the 45°-tilted fiber grating (5) is connected to the input end of the polarization-maintaining fiber coupler (6) at 0°, the second output end of the polarization-maintaining fiber coupler (6) is connected to the input end of the all-fiber quarter-wave plate (7) at 45°, and the all-fiber quarter-wave plate (7) is connected to the input end of the all-fiber quarter-wave plate (7) at 45°. The output end of the optical fiber sensor ring (7) is connected to the input end of the optical fiber sensor ring (9) at 0°, the output end of the optical fiber sensor ring (9) is connected to the input end of the second all-optical fiber quarter wave plate (10) at 0°, the output end of the second all-optical fiber quarter wave plate (10) is connected to the second input end of the first polarization-maintaining optical fiber coupler (4) at 45° in the opposite direction, the optical fiber sensor ring (9) is used to act on the current-carrying conductor (8), and the first output end of the second polarization-maintaining optical fiber coupler (6) is connected to the signal acquisition and processing system (2).

3. The ring-down type all-fiber current transformer and signal demodulation method based on 45° tilted fiber Bragg grating according to claim 1, characterized in that: The pulse light emitted by the light source (3) passes through the polarization-maintaining fiber coupler 1 (4), and the light output from the output port of the polarization-maintaining fiber coupler 1 (4) passes through the 45° tilted fiber grating (5) and is modulated into linearly polarized light. The light then passes through the polarization-maintaining fiber coupler 2 (6) and is divided into two paths. One path is sent to the signal acquisition and processing system (2), and the other path passes through the 45° docking point and is equally divided into two orthogonal linearly polarized lights and sent to the all-fiber quarter wave plate 1 (7), so that the two orthogonal linearly polarized lights are converted into left-handed and right-handed circularly polarized lights and sent to the optical fiber sensor ring (9). Under the Faraday magneto-optical effect, the phase of the circularly polarized light changes. The light passes through the all-fiber quarter wave plate 2 (10) and becomes linearly polarized light. The light carries the Faraday phase difference information generated by the magnetic field and is sent to the second input end of the polarization-maintaining fiber coupler 1 (4) as the light source of the second cycle. The light intensity decays due to the change in polarization direction after passing through the 45° tilted fiber grating (5) again. The cycle is repeated until the light intensity signal is zero. The photoelectric detector (11) in the signal acquisition and processing system (2) converts the optical pulse signal of the first output port of the second polarization-maintaining optical fiber coupler (6) into an electrical pulse signal, and sends it to the acquisition card (12) for buffering, thereby generating a pulse group signal with a constant interval and a peak value that decays exponentially with time delay. After the signal is zero, the acquisition card (12) sends the buffered decaying electrical pulse group signal to the computer (13) for demodulation.

4. The ring-down type all-fiber current transformer and signal demodulation system based on 45° tilted fiber Bragg grating according to claim 1 is characterized in that: The light source (3) is a pulse light source with a wavelength of 1550nm and a pulse width of 200ns, the repetition frequency of which matches the cavity length, and provides the system with high peak power and a stable pulse sequence.

5. The ring-down type all-fiber current transformer and signal demodulation method based on 45° tilted fiber Bragg grating according to claim 1, characterized in that: The grating period range of the 45° inclined optical fiber grating (5) is 752-761 nm, the grating length range is 8-13 mm, and the inclination angle is 45°.

6. The ring-down type all-fiber current transformer and signal demodulation method based on 45° tilted fiber Bragg grating according to claim 1, characterized in that: The computer (13) performs signal extraction, fitting and demodulation processes. The extraction process is to extract the peak value of each pulse in the pulse group signal with constant interval and increasing peak value ring-down with delay. The fitting process is to generate an envelope function y=exp(-A*x) based on the Exp1p2 model. The demodulation process adopts the time domain demodulation method to extract the ring-down time, that is, the time when the light intensity decays to the initial value e -1 The time required for measuring the loss coefficient in the optical fiber sensing loop is used to extract the Faraday phase shift information through the loss coefficient, and then the current size is demodulated according to the Faraday magneto-optical effect.

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