An all-fiber current sensor based on s-plate for linear measurement

Abstract

The application provides an all-fiber current sensor based on S wave plate linear measurement, which is based on Sagnac effect, Faraday magneto-optic effect and S wave plate; linearly polarized light is obtained through a polarizer, and the linearly polarized light is divided into two mutually orthogonal linearly polarized lights through a delay line and a 45-degree fusion splicing point; the linearly polarized light is modulated by a modulator, and then enters a λ / 4 wave plate and is converted into left-handed and right-handed circularly polarized light; after entering a sensing optical fiber, the measured circuit current magneto-optic effect makes the two circularly polarized lights produce a phase difference; the phase difference is doubled through a fiber end mirror and a sensing optical fiber, and the linearly polarized light is combined into linearly polarized light through a λ / 4 wave plate, a modulator and a 45-degree fusion splicing point; the phase difference of the circularly polarized light is converted into the rotation of the linearly polarized light polarization plane; the linearly polarized light after the secondary modulation passes through an S wave plate and a polarizer in turn, and the rotation of the polarization plane is converted into the synchronous translation of the light spot; the phase difference and the current value are obtained by positioning the light spot through an image sensor; the application has the advantages of optical power independence and linear birefringence complete compensation.

Description

Technical Field

[0001] The present invention relates to the technical field of electric power system current measurement, in particular to an all-optical fiber current sensor for realizing linear measurement based on an S-wave plate. Background Art

[0002] Current transformers are important devices that reflect the operating status of power systems. Their accuracy and reliability are important prerequisites for ensuring system measurement accuracy and the reliability of relay protection devices.

[0003] The electromagnetic current transformers currently used in power systems have exposed some defects that are difficult to ignore, such as difficulty in insulation, easy magnetic saturation, slow response speed, and inability to measure DC current, which seriously hinder the development of new power systems.

[0004] The measurement principle of a fiber optic current transducer (FOCT) is based on the Faraday magneto-optical rotation effect, which states that under the influence of a magnetic field, the plane of polarization of linearly polarized light rotates, and the angle of rotation (i.e., the Faraday magneto-optical rotation angle) is proportional to the magnitude of the magnetic field. Because existing technologies cannot directly measure the Faraday magneto-optical rotation angle, polarization interferometry demodulation is typically used to convert the optical rotation angle into a change in light intensity, and indirectly measure the magnetic field by detecting the light intensity. However, this measurement mode is optical power-dependent and susceptible to fluctuations in optical power. Furthermore, linear birefringence and the Faraday magneto-optical rotation angle are aliased, making them difficult to distinguish and address. These issues have hindered the practical application of FOCT. Summary of the Invention

[0005] The present invention proposes an all-fiber current sensor for linear measurement based on an S-wave plate, which can realize linear demodulation of the Faraday magnetorotation angle and has the advantages of being independent of optical power and fully compensating for linear birefringence.

[0006] The light emitted by the LED light source used in the present invention is converted into linearly polarized light through a polarizer, enters the optical fiber loop through a coupler, achieves beat length matching through a delay line, is split into two mutually orthogonal linearly polarized light beams through a 45° fusion point, undergoes initial phase modulation by a modulator, is converted into left-handed and right-handed circularly polarized light through a λ / 4 wave plate, and enters the sensing optical fiber. The Faraday magneto-optical effect of the primary current causes a phase difference between the two circularly polarized light beams. The circularly polarized light is reflected by a reflector at the end of the sensing optical fiber, and then passes through the sensing optical fiber to double the phase difference. The light is then subjected to secondary phase modulation by the λ / 4 wave plate, the modulator, and the After the 45° welding point, they are merged into a beam of linearly polarized light. At the same time, the phase difference of the circularly polarized light is converted into the rotation of the polarization plane of the linearly polarized light. Through the coupler, S-wave plate, and polarizer, the rotation of the polarization plane of the linearly polarized light is converted into a synchronous translation of the [light spot]. The image sensor locates the light spot to obtain the phase difference. At the same time, the image sensor filters out the linear birefringence based on the algorithm to obtain the current to be measured; the function of the secondary phase modulation of the modulator is to avoid polarization mismatch of the returned linearly polarized light during the transmission process before reaching the S-wave plate; the detection mode is suitable for the measurement of AC current and DC current.

[0007] The present invention adopts the following technical solutions.

[0008] An all-fiber current sensor for linear measurement based on an S-wave plate, wherein the detection end of the sensor includes a sensing fiber; the sensing fiber forms a fiber ring structure, and the sensor performs linear measurement on a circuit to be measured passing through the fiber ring structure, comprising the following steps:

[0009] Step S1, inputting left-handed circularly polarized light and right-handed circularly polarized light into the starting end of the sensing optical fiber, so that the optical fiber ring outputs a polarized light signal for expressing the measurement result based on the Sagnac effect and the Faraday magneto-optical effect;

[0010] Step S2: Process the polarized light signal with the modulator of the sensor, and then make the polarization plane of the light signal pass through the S-wave plate and analyzer of the sensor in sequence, so as to convert the rotation of the polarization plane of the light into the synchronous translation of the light spot;

[0011] Step S3: Measure the Faraday magnetorotation angle of the circularly polarized light input in step S1 when it passes through the optical fiber ring by detecting the translation amount, calculate the current value of the circuit to be measured, and realize linear measurement of the current of the circuit to be measured.

[0012] The sensor also includes a light source, a coupler, a polarizer, a delay line, a 45° fusion point, a modulator, and a λ / 4 wave plate;

[0013] In step S1, when generating left-handed circularly polarized light and right-handed circularly polarized light, the light emitted by the light source is first converted into linearly polarized light by a polarizer and then output through a coupler. The linearly polarized light is then beat-length matched by a delay line and then split into two mutually orthogonal linearly polarized beams at a 45° fusion point. Subsequently, the two beams of polarized light are initially phase-modulated by a modulator, and then converted into left-handed circularly polarized light and right-handed circularly polarized light by a λ / 4 wave plate and input into the sensing optical fiber.

[0014] The line to be tested is a power transmission line; a reflector is provided at the end of the sensing optical fiber;

[0015] In step S1, when the optical fiber ring is placed on the transmission line, the magnetic field generated by the current in the transmission line acts on the sensing optical fiber. The resulting Faraday magneto-optical effect causes the polarization planes of the two circularly polarized light beams in the optical fiber ring to rotate, resulting in a phase difference. With linear birefringence δ; after the two circularly polarized lights with phase difference reach the end of the sensing optical fiber, they are reflected by the reflector and input into the optical fiber ring again to double the phase difference, forming a polarized light signal emitted from the starting end of the sensing optical fiber for expressing the current measurement result.

[0016] In step S2, the polarized light signal output from the starting end of the sensing fiber returns to the modulator through the λ / 4 wave plate and delay line. After secondary phase adjustment by the modulator, it passes through the 45° fusion point and coupler to reach the S wave plate. The sensor uses the S wave plate and polarizer to convert the rotation of the polarization plane of the polarized light signal into a synchronous translation of the light spot.

[0017] In step S3, when the sensor detects the translation amount, the image sensor locates the light spot to obtain the phase difference, that is, the image sensor locates the light spot to obtain the phase delay angle At the same time, the image sensor filters out the linear birefringence δ based on the algorithm, thereby obtaining the current value to be measured.

[0018] In step S2, the modulator performs secondary phase adjustment on the polarized light signal output from the beginning of the sensing fiber. This is to avoid polarization mismatch in the reflected linearly polarized light before it reaches the S-wave plate.

[0019] The sensor includes detection modes suitable for AC current measurement and DC current measurement.

[0020] In step S3, the Faraday magnetorotation angle of the circularly polarized light when it passes through the optical fiber ring is the rotation angle of the polarization direction of the incident light of the sensing optical fiber. The measurement principle is based on the Jones matrix theory, and the calculation method includes the following steps: Step A1, first, ignoring the linear birefringence δ of the sensing optical fiber, the linearly polarized light incident on the sensing optical fiber is split into two mutually orthogonal linear polarized light beams through the 45° fusion point, and the electric vectors of the two polarized light beams are assumed to be:

[0021]

[0022] After being converted into circularly polarized light by the λ / 4 wave plate, the Jones vector of the λ / 4 wave plate is:

[0023]

[0024] Step A2: The circularly polarized light passes through the sensing fiber, passes through the reflector at the end of the fiber, and returns to the input end of the sensing fiber and exits. The Jones vector of the sensing fiber in the incident light path and the reflected light path is:

[0025]

[0026] in The Jones vector of the reflector is:

[0027]

[0028] Step A3: The light emitted from the sensing fiber is converted into orthogonal linearly polarized light through a λ / 4 wave plate. The Jones vector of the λ / 4 wave plate in the return optical path is:

[0029]

[0030] After passing through the 45° splice, the orthogonal linearly polarized light beams are combined into a beam of linearly polarized light. The Jones vector of the 45° splice in the return optical path is:

[0031]

[0032] E x For example, after passing through the λ / 4 wave plate, sensing fiber, reflector, sensing fiber, λ / 4 wave plate, and 45° fusion point, the Jones vector of the outgoing polarized light is:

[0033]

[0034] Similarly, E y The outgoing light vector is:

[0035]

[0036] E x-out With E y-out After being synthesized into a beam of linearly polarized light, its superimposed amplitude E out Expressed as:

[0037]

[0038] E out The component along the x-axis is The component along the y-axis is E outThe angle θ between the polarization plane and the x-axis satisfies the following relationship:

[0039]

[0040] Step A3: Assume the Jones matrix of the S wave plate is:

[0041]

[0042] E out After entering the S-wave plate and analyzer, it becomes:

[0043]

[0044] At this time, the output light intensity distribution is

[0045]

[0046] When the following conditions are met, the output light intensity is extremely small

[0047]

[0048] The detection range and the abscissa x of the S wave plate are limited by the following conditions

[0049]

[0050] Assume that n = 0 in formula (16), then the range of the minimum coordinate x of the spot and the polarization angle of the incident light satisfies

[0051] That is, the minimum value x of the light spot and the rotation angle of the incident light satisfy a linear relationship;

[0052] Step A4: Measure the rotation angle of the incident light polarization direction by locating the dark fringe minimum. Figure 2 for Simulated image of the intensity distribution of the emitted light spot when it changes.

[0053] The all-fiber current sensor is a linear FOCT, and its sensing fiber uses a rotating fiber. The operating wavelength of the rotating fiber matches the operating wavelength of the image sensor. When the current sensor is used to measure small currents, the length of the rotating fiber is more than several meters. When the current sensor is used to measure large currents, the length of the rotating fiber is more than tens of meters.

[0054] When linear FOCT is used to measure transmission lines in substations, the optical fiber loop of the linear FOCT is placed inside the transmission line to be measured. The magnetic field generated by the current in the transmission line acts on the sensing optical fiber. The Faraday magneto-optical effect generated by the magnetic field causes the polarization plane of the polarized light passing through the optical fiber to rotate. Based on the linear demodulation mode, the linear FOCT first converts the Faraday magnetorotation angle into a linear translation of the light spot image. The linear translation is then detected to directly measure the Faraday magnetorotation angle. The magnitude of the measured current is then determined based on the corresponding relationship between the Faraday magnetorotation angle and the current value.

[0055] The present invention can realize linear demodulation of the Faraday rotation angle, and its measurement result is independent of optical power, is conducive to the separation compensation of linear birefringence, can realize distortion-free harmonic measurement, and has the advantages of optical power independence, complete linear birefringence compensation, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0057] Attachment Figure 1 It is a schematic diagram of the principle of the present invention;

[0058] Attachment Figure 2 It is a schematic diagram of a simulated image of the output light spot of the linear all-fiber current transformer of the present invention. DETAILED DESCRIPTION

[0059] As shown in the figure, an all-fiber current sensor for linear measurement based on an S-wave plate is provided. The detection end of the sensor includes a sensing fiber; the sensing fiber forms a fiber ring structure. When the sensor performs linear measurement on a circuit to be measured passing through the fiber ring structure, the sensor includes the following steps:

[0060] Step S1, inputting left-handed circularly polarized light and right-handed circularly polarized light into the starting end of the sensing optical fiber, so that the optical fiber ring outputs a polarized light signal for expressing the measurement result based on the Sagnac effect and the Faraday magneto-optical effect;

[0061] Step S2: Process the polarized light signal with the modulator of the sensor, and then make the polarization plane of the light signal pass through the S-wave plate and analyzer of the sensor in sequence, so as to convert the rotation of the polarization plane of the light into the synchronous translation of the light spot;

[0062] Step S3: Measure the Faraday magnetorotation angle of the circularly polarized light input in step S1 when it passes through the optical fiber ring by detecting the translation amount, calculate the current value of the circuit to be measured, and realize linear measurement of the current of the circuit to be measured.

[0063] The sensor also includes a light source, a coupler, a polarizer, a delay line, a 45° fusion point, a modulator, and a λ / 4 wave plate;

[0064] In step S1, when generating left-handed circularly polarized light and right-handed circularly polarized light, the light emitted by the light source is first converted into linearly polarized light by a polarizer and then output through a coupler. The linearly polarized light is then beat-length matched by a delay line and then split into two mutually orthogonal linearly polarized beams at a 45° fusion point. Subsequently, the two beams of polarized light are initially phase-modulated by a modulator, and then converted into left-handed circularly polarized light and right-handed circularly polarized light by a λ / 4 wave plate and input into the sensing optical fiber.

[0065] The line to be tested is a power transmission line; a reflector is provided at the end of the sensing optical fiber;

[0066] In step S1, when the optical fiber ring is placed at the line to be measured, the magnetic field generated by the current in the transmission line acts on the sensing optical fiber. The resulting Faraday magneto-optical effect causes the polarization planes of the two circularly polarized light beams in the optical fiber ring to rotate, resulting in a phase difference. With linear birefringence δ; after the two circularly polarized lights with phase difference reach the end of the sensing optical fiber, they are reflected by the reflector and input into the optical fiber ring again to double the phase difference, forming a polarized light signal emitted from the starting end of the sensing optical fiber for expressing the current measurement result.

[0067] In step S2, the polarized light signal output from the starting end of the sensing fiber returns to the modulator through the λ / 4 wave plate and delay line. After secondary phase adjustment by the modulator, it passes through the 45° fusion point and coupler to reach the S wave plate. The sensor uses the S wave plate and polarizer to convert the rotation of the polarization plane of the polarized light signal into a synchronous translation of the light spot.

[0068] In step S3, when the sensor detects the translation amount, the image sensor locates the light spot to obtain the phase difference, that is, the image sensor locates the light spot to obtain the phase delay angle At the same time, the image sensor filters out the linear birefringence δ based on the algorithm, thereby obtaining the current value to be measured.

[0069] In step S2, the modulator performs secondary phase adjustment on the polarized light signal output from the beginning of the sensing fiber. This is to avoid polarization mismatch in the reflected linearly polarized light before it reaches the S-wave plate.

[0070] The sensor includes detection modes suitable for AC current measurement and DC current measurement.

[0071] In step S3, the Faraday magnetorotation angle of the circularly polarized light when it passes through the optical fiber ring is the rotation angle of the polarization direction of the incident light of the sensing optical fiber. The measurement principle is based on the Jones matrix theory, and the calculation method includes the following steps: Step A1, first, ignoring the linear birefringence δ of the sensing optical fiber, the linearly polarized light incident on the sensing optical fiber is split into two mutually orthogonal linear polarized light beams through the 45° fusion point, and the electric vectors of the two polarized light beams are assumed to be:

[0072]

[0073] After being converted into circularly polarized light by the λ / 4 wave plate, the Jones vector of the λ / 4 wave plate is:

[0074]

[0075] Step A2: The circularly polarized light passes through the sensing fiber, passes through the reflector at the end of the fiber, and returns to the input end of the sensing fiber and exits. The Jones vector of the sensing fiber in the incident light path and the reflected light path is:

[0076]

[0077] in The Jones vector of the reflector is:

[0078]

[0079] Step A3: The light emitted from the sensing fiber is converted into orthogonal linearly polarized light through a λ / 4 wave plate. The Jones vector of the λ / 4 wave plate in the return optical path is:

[0080]

[0081] After passing through the 45° splice, the orthogonal linearly polarized light beams are combined into a beam of linearly polarized light. The Jones vector of the 45° splice in the return optical path is:

[0082]

[0083] E x For example, after passing through the λ / 4 wave plate, sensing fiber, reflector, sensing fiber, λ / 4 wave plate, and 45° fusion point, the Jones vector of the outgoing polarized light is:

[0084]

[0085] Similarly, E y The outgoing light vector is:

[0086]

[0087] E x-out With E y-out After being synthesized into a beam of linearly polarized light, its superimposed amplitude E out Expressed as:

[0088]

[0089] E out The component along the x-axis is The component along the y-axis is E outThe angle θ between the polarization plane and the x-axis satisfies the following relationship:

[0090]

[0091] Step A3: Assume the Jones matrix of the S wave plate is:

[0092]

[0093] E out After entering the S-wave plate and analyzer, it becomes:

[0094]

[0095] At this time, the output light intensity distribution is

[0096]

[0097] When the following conditions are met, the output light intensity is extremely small

[0098]

[0099] The detection range and the abscissa x of the S wave plate are limited by the following conditions

[0100]

[0101] Assume that n = 0 in formula (16), then the range of the minimum coordinate x of the spot and the polarization angle of the incident light satisfies

[0102] That is, the minimum value x of the light spot and the rotation angle of the incident light satisfy a linear relationship;

[0103] Step A4: Measure the rotation angle of the incident light polarization direction by locating the dark fringe minimum. Figure 2 for Simulated image of the intensity distribution of the emitted light spot when it changes.

[0104] The all-fiber current sensor for linear measurement based on an S-wave plate, i.e., a linear FOCT, uses a rotating fiber as its sensing fiber. The operating wavelength of the rotating fiber matches the operating wavelength of the image sensor. When the current sensor is used to measure small currents, the length of the rotating fiber is more than several meters. When the current sensor is used to measure large currents, the length of the rotating fiber is more than tens of meters.

[0105] When linear FOCT is used to measure transmission lines in substations, the optical fiber loop of the linear FOCT is placed inside the transmission line to be measured. The magnetic field generated by the current in the transmission line acts on the sensing optical fiber. The Faraday magneto-optical effect generated by the magnetic field causes the polarization plane of the polarized light passing through the optical fiber to rotate. Based on the linear demodulation mode, the linear FOCT first converts the Faraday magnetorotation angle into a linear translation of the light spot image. The linear translation is then detected to directly measure the Faraday magnetorotation angle. The magnitude of the measured current is then determined based on the corresponding relationship between the Faraday magnetorotation angle and the current value.

[0106] Example:

[0107] This example proposes an all-fiber current sensor for linear measurement based on an S-wave plate. This sensor is based on the Sagnac effect, the Faraday magneto-optical effect, and an S-wave plate. The technical principle is as follows: Light from a light source passes through a polarizer to generate linear polarization. This is then split into two orthogonal linearly polarized beams by a delay line and a 45° fusion splice. After initial phase modulation by a modulator, the light enters a λ / 4 wave plate and is converted into left-handed and right-handed circularly polarized light. Upon entering the sensing fiber, the Faraday magneto-optical effect of the primary current creates a phase difference between the two circularly polarized beams. After reflection from a reflector at the end of the sensing fiber, the circularly polarized light is doubled by the sensing fiber. The light then undergoes secondary phase modulation by the λ / 4 wave plate, a modulator, and a 45° fusion splice, reuniting the two beams into a single linearly polarized beam. This phase difference is then converted into a rotation of the linearly polarized light's plane of polarization. The light then passes through an S-wave plate and an analyzer, converting the rotation into a synchronous translation of the light spot. An image sensor locates the light spot and determines the phase difference.

[0108] The device in this example realizes the linear demodulation of Faraday magneto-optical rotation angle, and has the advantages of independent measurement results and optical power, being conducive to the separation compensation of linear birefringence, and realizing distortion-free harmonic measurement.

[0109] In this example, the linear FOCT uses a spun fiber as the sensing fiber. Spun fibers operate at wavelengths of 600-900 nm, 900-1100 nm, and 1300-1600 nm. LFOCT uses a spun fiber with an operating wavelength of 600-900 nm to match the operating wavelength of image sensors (such as CMOS). Furthermore, depending on the rated current, the sensing fiber length can range from several meters to tens or hundreds of meters. Generally, for higher rated currents, the sensing fiber length is several meters; for lower rated currents, the length can range from tens to hundreds of meters.

[0110] In this example, when used in a substation, the linear FOCT fiber loop is placed inside the transmission line under test. The current in the transmission line generates a magnetic field that acts on the sensing fiber, producing the Faraday magneto-optical effect, which rotates the plane of polarization of the polarized light passing through the fiber. Using the linear demodulation mode, the linear FOCT converts the Faraday magnetorotation angle into a linear translation of the spot image. By detecting this translation, the Faraday magnetorotation angle can be directly measured, thereby obtaining the magnitude of the current under test.

Claims

1. An all-fiber current sensor for linear measurement based on an S-wave plate, characterized by: All-fiber current sensor based on S-wave plate for linear measurement; The light emitted by the LED light source is converted into linearly polarized light through a polarizer, enters the optical fiber loop through a coupler, achieves beat length matching through a delay line, and is split into two mutually orthogonal beams of linearly polarized light through a 45° fusion point. After initial phase modulation by a modulator, it is converted into left-handed and right-handed circularly polarized light through a λ / 4 wave plate. After entering the sensing fiber, the Faraday magneto-optical effect of the primary current causes a phase difference between the two beams of circularly polarized light. The circularly polarized light is reflected by the reflector at the end of the sensing fiber, and then doubled by the sensing fiber. After passing through the λ / 4 wave plate, secondary phase modulation by the modulator, and a 45° fusion point, it is merged into a beam of linearly polarized light. At the same time, the phase difference of the circularly polarized light is converted into a rotation of the polarization plane of the linearly polarized light. The rotation of the polarization plane of the linearly polarized light is converted into a synchronous translation of the light spot through a coupler, an S wave plate, and an analyzer. The image sensor locates the light spot to obtain the phase difference. At the same time, the image sensor filters out the linear birefringence based on an algorithm to obtain the current to be measured. The Jones matrix of the S waveplate is:

2. The all-fiber current sensor for linear measurement based on an S-wave plate according to claim 1, characterized in that: The function of the secondary phase modulation of the modulator is to avoid polarization mismatch of the returned linearly polarized light during its transmission before reaching the S-wave plate.

3. The all-fiber current sensor for linear measurement based on an S-wave plate according to claim 1 or 2, characterized in that: The detection mode is suitable for measuring AC current and DC current.

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