An all-fiber current sensor based on linear measurement of wedge interference

Abstract

The application provides an all-fiber current sensor based on linear measurement of sharp wedge interference, linearly polarized light obtained through a polarizer is divided into two mutually orthogonal linearly polarized lights through a coupler, a delay line and a 45-degree fusion splice point, is modulated by an initial phase modulator, is converted into left-handed and right-handed circularly polarized light through a first lambda / 4 wave plate, enters a sensing optical fiber, and a phase difference of the two circularly polarized lights is generated through a Faraday magneto-optic effect; the phase difference is doubled after being reflected by a mirror, is combined into a linearly polarized light through a first lambda / 4 wave plate and a 45-degree fusion splice point, and the phase difference of the circularly polarized light is converted into a rotation of a polarization plane of the linearly polarized light; the rotation of the polarization plane of the linearly polarized light is converted into synchronous translation of a light spot through a coupler, a second lambda / 4 wave plate, a sharp wedge and a polarizer after being twice phase-modulated by a modulator; and linear measurement of a phase delay angle is obtained through positioning of the light spot by an image sensor; the demodulation result of the application is irrelevant to optical power, and is beneficial to separation and compensation of linear birefringence.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrical measurement, and particularly to an all-fiber current sensor based on sharp wedge interference for linear measurement. BACKGROUND

[0002] Current measurement is the basis of power system metering, monitoring, control and protection. With the continuous improvement of power grid voltage level and the continuous increase of transmission capacity, the safety, reliability and accuracy of current transformer are increasingly required. In the application of high voltage, large current and strong power, the traditional electromagnetic current transformer has many shortcomings, such as difficulty in insulation, high manufacturing cost, large size, heavy weight, small dynamic measurement range, magnetic saturation, narrow measurement frequency band, and flammable and explosive, which has been difficult to meet the needs of the development of smart grid. The all-fiber current sensor (FOCT) takes optical fiber as the sensing and transmission medium, has the advantages of reliable insulation, green environmental protection, easy installation, maintenance-free, etc., and represents the development direction of the new generation of current transformer. Since the first proposal of optical fiber magnetic field sensor in 1980, FOCT has gone through more than 40 years of development, and so far it has not been recognized by users. The main reason for the failure of FOCT to be practical is its nonlinear measurement mode, i.e. nonlinear demodulation of light intensity based on Malus law, which has problems such as light power dependence, linear birefringence, aging of electronic and optical devices, etc. SUMMARY

[0003] The application provides a linear fiber optical current transducer (LFOCT) based on wedge interference for linear measurement, which has the characteristics of linear measurement of Faraday magneto-optical rotation angle and optical power independence; light emitted by an LED light source is linearly polarized light through a polarizer, enters a fiber loop through a coupler, realizes beat length matching through a delay line, is divided into two mutually orthogonal linearly polarized lights through a 45-degree fusion splice, is initially phase-modulated through a modulator, is converted into left and right circularly polarized light through a lambda / 4 wave plate 1, and after entering a sensing fiber, the Faraday magneto-optical effect of a primary current causes a phase difference between the two circularly polarized lights; the circularly polarized light is reflected by a mirror at the end of the sensing fiber, and the phase difference is doubled again through the sensing fiber; the two circularly polarized lights are combined into a linearly polarized light through the lambda / 4 wave plate 1, the modulator and the 45-degree fusion splice, and the phase difference of the circularly polarized light is converted into the rotation of the linearly polarized light polarization plane; the rotation of the linearly polarized light polarization plane is converted into the synchronous translation of the light spot through the coupler, the lambda / 4 wave plate 2, the wedge and the polarizer; the phase difference is obtained by positioning the light spot through an image sensor, and the linear birefringence is filtered out through the image sensor based on an algorithm, so that the measured current is obtained; the secondary phase modulation of the modulator avoids polarization mismatch during the transmission of the returned linearly polarized light before reaching the lambda / 4 wave plate 2; and the detection mode is suitable for the measurement of alternating current and direct current.

[0004] The application adopts the following technical scheme.

[0005] A linear fiber optical current transducer based on wedge interference for linear measurement, wherein a detection end of the transducer comprises a sensing fiber; the sensing fiber forms a fiber loop structure; when the transducer performs linear measurement on a measured current transmitted by a power transmission conductor passing through the fiber loop structure, the following steps are included.

[0006] In step S1, left and right circularly polarized light is input to the initial end of the sensing fiber through a first lambda / 4 wave plate, so that the fiber loop outputs a polarized light signal for expressing a measurement result based on Sagnac effect and Faraday magneto-optical effect;

[0007] In step S2, the polarized light signal is processed by a modulator of the transducer, and then the light signal polarization plane sequentially passes through a second lambda / 4 wave plate, a wedge and a polarizer of the transducer, so that the rotation amount of the light polarization plane is converted into the synchronous translation amount of the light spot;

[0008] In step S3, the Faraday magneto-rotation angle of the circularly polarized light input in step S1 when passing through the fiber loop is measured by detecting the translation amount, the current value of the measured line is calculated, and linear measurement of the current of the measured line is realized.

[0009] The sensor further comprises an LED light source, a polarizer, a delay line, a 45° fusion splice, a modulator;

[0010] In step S1, when generating left circularly polarized light and right circularly polarized light, the light emitted by the LED light source is first converted into linearly polarized light by the polarizer and then output by the coupler, and then the linearly polarized light is subjected to beat length matching processing by the delay line, and then the linearly polarized light is split into two mutually orthogonal linearly polarized lights by the 45° fusion splice, and then the two linearly polarized lights are subjected to initial phase modulation by the modulator, and then the first λ / 4 wave plate converts the two linearly polarized lights into left circularly polarized light and right circularly polarized light and inputs the two circularly polarized lights into the sensing optical fiber.

[0011] The to-be-measured line is a power transmission line; and the end of the sensing optical fiber is provided with a mirror;

[0012] In step S1, when the fiber ring is placed at the to-be-measured line, the magnetic field generated by the current of the power transmission line acts on the sensing optical fiber, and the Faraday magneto-optical effect generated thereby causes the polarization planes of the two circularly polarized lights in the fiber ring to rotate and generate a phase difference and a linear birefringence δ; after the two circularly polarized lights with the phase difference reach the end of the sensing optical fiber, the mirror reflects the two circularly polarized lights and inputs the two circularly polarized lights into the fiber ring again, so that the phase difference is doubled, and then a polarized light signal used to express the current measurement result is formed and output from the beginning of the sensing optical fiber.

[0013] In step S2, the polarized light signal output from the beginning of the sensing optical fiber passes through the λ / 4 wave plate, the delay line, and returns to the modulator, and then the modulator adjusts the phase of the polarized light signal for the second time, and then the polarized light signal passes through the 45° fusion splice and the coupler and reaches the second λ / 4 wave plate, and the second λ / 4 wave plate and the polarizer of the sensor convert the rotation amount of the polarization plane of the polarized light signal into the synchronous translation amount of the light spot.

[0014] In step S3, when the sensor detects the translation amount, the phase difference is obtained by locating the light spot by the image sensor, that is, the phase delay angle and the linear birefringence δ is filtered out by the image sensor based on an algorithm, and then the to-be-measured current value is obtained.

[0015] In step S2, the modulator adjusts the phase of the polarized light signal output from the beginning of the sensing optical fiber for the second time, and the adjustment amount is used to avoid polarization mismatch of the returned linearly polarized light before the linearly polarized light reaches the second λ / 4 wave plate.

[0016] The sensor comprises a detection mode suitable for alternating current measurement and direct current measurement.

[0017] In step S3, the Faraday magneto-optical rotation angle of the circularly polarized light when passing through the fiber ring, that is, the rotation angle of the polarization direction of the incident light of the sensing fiber, is the rotation angle of the sensing fiber. The measurement principle is based on Jones matrix theory, and the calculation method includes the following steps: step A1, first ignore the linear birefringence δ of the sensing fiber, and divide the incident linearly polarized light into two mutually orthogonal linearly polarized lights at the 45° fusion splice point. The electric vectors of the two polarized lights are:

[0018]

[0019] The first λ / 4 wave plate is converted into circularly polarized light, and the Jones vector of the first λ / 4 wave plate is:

[0020]

[0021] Step A2, the circularly polarized light passes through the sensing fiber and returns after the mirror at the end of the fiber. The Jones vector of the sensing fiber in the incident light path and the reflected light path is:

[0022]

[0023] Wherein The Jones vector of the mirror is:

[0024]

[0025] Step A3, the reflected light passes through the first λ / 4 wave plate to convert into orthogonal linearly polarized light, and the Jones vector of the first λ / 4 wave plate in the return light path is:

[0026]

[0027] After passing through the 45° fusion splice point, the orthogonal linearly polarized light is combined into a linearly polarized light, and the Jones vector of the 45° fusion splice point in the return light path is:

[0028]

[0029] For example, E x After the first λ / 4 wave plate, the sensing fiber, the mirror, the sensing fiber, the first λ / 4 wave plate, and the 45° fusion splice point, the Jones vector of the outgoing linearly polarized light is:

[0030]

[0031] Similarly, the outgoing light vector of E y Is:

[0032]

[0033] E x-out And E y-out Combined into a linearly polarized light, and the superposition amplitude E outRepresented as:

[0034]

[0035] E out The component along the x-axis is The component along the y-axis is E out The angle θ between the polarization plane and the x-axis satisfies the following relationship:

[0036]

[0037] E out The light becomes circularly polarized upon entering the second λ / 4 waveplate. Assuming the azimuth angle between the fast and slow axes of the wedge and the second λ / 4 waveplate is 45°, the linearly polarized light, after passing through the crystal wedge, forms a phase difference distribution, and its Jones matrix becomes...

[0038] After passing through the analyzer, the Jones matrix becomes

[0039]

[0040] At this time, the light intensity distribution is as follows:

[0041]

[0042] The light intensity distribution of the image and the rotation angle of the light vector And it is related to the phase difference φ; φ is related to the wedge angle, and when the wedge angle is constant, φ is a fixed value. When As the fringe position changes, the position of the fringe also changes. Therefore, by detecting the displacement of the fringe, it is possible to... Measurement;

[0043] The displacement Δx of the stripes and Change satisfy:

[0044]

[0045] If we consider the linear birefringence δ of the sensing fiber, the above equation becomes:

[0046]

[0047] After filtering out δ through signal processing, it is achieved via equation (17). Linear measurement.

[0048] The all-fiber current sensor is a linear all-fiber current sensor FOCT, the sensing fiber of which adopts a rotating fiber, the working wavelength of the rotating fiber matches the working wavelength of an image sensor, when the current sensor is used to measure a small current, the length of the rotating fiber is more than several meters, and when the current sensor is used to measure a large current, the length of the rotating fiber is more than several tens of meters.

[0049] When the linear measurement all-fiber current sensor LFOCT based on the Mach-Zehnder interference is used to measure a power transmission line in a substation, the fiber ring of the LFOCT is sleeved on the power transmission line to be measured, so that the magnetic field generated by the current of the power transmission line acts on the sensing fiber, the Faraday magneto-optical effect generated by the magnetic field causes the polarization plane of the polarized light passing through the fiber to rotate; the LFOCT converts the Faraday magneto-rotation angle into linear translation of a light spot image according to a linear demodulation mode, and then directly measures the Faraday magneto-rotation angle by detecting the translation amount of the linear translation, and then obtains the size of the current to be measured according to the corresponding relationship between the Faraday magneto-rotation angle and the current value.

[0050] The LFOCT realizes linear measurement of the Faraday magneto-optical rotation angle and has optical power independence.

[0051] The LFOCT has demodulation results independent of optical power and is beneficial to separation and compensation of linear birefringence. BRIEF DESCRIPTION OF DRAWINGS

[0052] The application will be further described in detail below in combination with the drawings and specific embodiments:

[0053] The accompanying drawings are schematic diagrams of the principles of the application. Figure 1 The accompanying drawings are schematic diagrams of the principles of the application. DETAILED DESCRIPTION

[0054] As shown in the drawings, an all-fiber current sensor based on the Mach-Zehnder interference for linear measurement includes a sensing fiber at a detection end of the sensor; the sensing fiber forms a fiber ring structure, and the sensor includes the following steps when linearly measuring a line to be measured passing through the fiber ring structure;

[0055] Step S1: left-handed circularly polarized light and right-handed circularly polarized light are input to the initial end of the sensing fiber through a first λ / 4 wave plate, so that the fiber ring outputs a polarized light signal for expressing a measurement result based on the Sagnac effect and the Faraday magneto-optical effect;

[0056] Step S2: the polarized light signal is processed by a modulator of the sensor, and then the rotation amount of the light polarization plane is converted into the synchronous translation amount of a light spot by making the light polarization plane pass through a second λ / 4 wave plate, a Mach-Zehnder interferometer and a polarizer of the sensor in turn;

[0057] Step S3, the Faraday magneto-optical rotation angle of the circularly polarized light input in step S1 when passing through the fiber ring is measured by detecting the translation amount, and the current value of the to-be-measured line is calculated to realize linear measurement of the current of the to-be-measured line.

[0058] The sensor further comprises an LED light source, a polarizer, a delay line, a 45° fusion splice, a modulator;

[0059] In step S1, when generating left circularly polarized light and right circularly polarized light, the light emitted by the LED light source is first converted into linearly polarized light by the polarizer and then output through the coupler, and then the linearly polarized light is subjected to beat length matching processing by the delay line, and then the linearly polarized light is split into two mutually orthogonal linearly polarized lights by the 45° fusion splice, and then the two linearly polarized lights are subjected to initial phase modulation by the modulator, and then the linearly polarized lights are converted into left circularly polarized light and right circularly polarized light by the first λ / 4 wave plate and input into the sensing optical fiber.

[0060] The to-be-measured line is a power transmission line; and the end of the sensing optical fiber is provided with a mirror;

[0061] In step S1, when the fiber ring is placed at the to-be-measured line, the magnetic field generated by the current of the power transmission line acts on the sensing optical fiber, and the Faraday magneto-optical effect generated thereby causes the polarization planes of the two circularly polarized lights in the fiber ring to rotate and generate a phase difference and a linear birefringence δ; after the two circularly polarized lights with the phase difference reach the end of the sensing optical fiber, the phase difference is doubled after the two circularly polarized lights are reflected by the mirror and input into the fiber ring again, and then a polarized light signal used to express the current measurement result is formed and output from the beginning of the sensing optical fiber.

[0062] In step S2, the polarized light signal output from the beginning of the sensing optical fiber passes through the λ / 4 wave plate, the delay line, and returns to the modulator, and then the modulator performs secondary phase adjustment, and then the polarized light signal passes through the 45° fusion splice and the coupler to reach the second λ / 4 wave plate, and the sensor converts the rotation amount of the polarization plane of the polarized light signal into the synchronous translation amount of the light spot by using the second λ / 4 wave plate and the polarizer.

[0063] In step S3, when the sensor detects the translation amount, the phase difference is obtained by locating the light spot by the image sensor, that is, the phase delay angle is obtained by locating the light spot by the image sensor, and then the to-be-measured current value is obtained.

[0064] In step S2, the modulator performs secondary phase adjustment processing on the polarized light signal output from the beginning of the sensing optical fiber, and the adjustment amount is used to avoid polarization mismatch of the returned linearly polarized light before the linearly polarized light reaches the second λ / 4 wave plate.

[0065] The sensor comprises a detection mode suitable for alternating current measurement and direct current measurement.

[0066] In step S3, the Faraday magnetostrictive rotation angle of the circularly polarized light as it passes through the fiber optic loop is the rotation angle of the polarization direction of the incident light in the sensing fiber. Its measurement principle is based on the Jones matrix theory, and the calculation method includes the following steps: Step A1: First, neglecting the linear birefringence δ of the sensing fiber, the incident linearly polarized light is split into two mutually orthogonal linearly polarized beams at a 45° fusion splice. Let the electric vectors of the two polarized beams be:

[0067]

[0068] After being converted into circularly polarized light by the first λ / 4 waveplate, the Jones vector of the first λ / 4 waveplate is:

[0069]

[0070] Step A2: The circularly polarized light passes through the sensing fiber, returns after passing through the mirror at the end of the fiber, and the Jones vectors of the sensing fiber in the incident and reflected light paths are:

[0071]

[0072] in The Jones vector of the reflecting mirror is:

[0073]

[0074] Step A3: The reflected light is converted into orthogonally linearly polarized light after passing through the first λ / 4 waveplate. The Jones vector of the first λ / 4 waveplate in the return optical path is:

[0075]

[0076] After passing through the 45° fusion point, the orthogonally linearly polarized light is combined into a linearly polarized beam. The Jones vector at the 45° fusion point in the return optical path is:

[0077]

[0078] With E x For example, after passing through the first λ / 4 waveplate, sensing fiber, mirror, sensing fiber, first λ / 4 waveplate, and 45° fusion splice, the Jones vector of the emitted ray polarized light is:

[0079]

[0080] Similarly, E y The emitted light vector is:

[0081]

[0082] E x-out With E y-out The combined beams are linearly polarized and their superimposed amplitude Eout Represented as:

[0083]

[0084] E out The component along the x-axis is The component along the y-axis is E out The angle θ between the polarization plane and the x-axis satisfies the following relationship:

[0085]

[0086] E out The light becomes circularly polarized upon entering the second λ / 4 waveplate. Assuming the azimuth angle between the fast and slow axes of the wedge and the second λ / 4 waveplate is 45°, the linearly polarized light, after passing through the crystal wedge, forms a phase difference distribution, and its Jones matrix becomes...

[0087] After passing through the analyzer, the Jones matrix becomes

[0088]

[0089] At this time, the light intensity distribution is as follows:

[0090]

[0091] The light intensity distribution of the image and the rotation angle of the light vector And it is related to the phase difference φ; φ is related to the wedge angle, and when the wedge angle is constant, φ is a fixed value. When As the fringe position changes, the position of the fringe also changes. Therefore, by detecting the displacement of the fringe, it is possible to... Measurement;

[0092] The displacement Δx of the stripes and Change satisfy:

[0093]

[0094] If we consider the linear birefringence δ of the sensing fiber, the above equation becomes:

[0095]

[0096] After filtering out δ through signal processing, it is achieved via equation (17). Linear measurement.

[0097] The linear measurement based on the sharp wedge interference is realized by the full optical fiber current sensor, i.e. LFOCT, the sensing fiber of which adopts a rotating fiber, the working wavelength of which matches the working wavelength of the image sensor, when the current sensor is used to measure a small current, the length of the rotating fiber is more than several meters, when the current sensor is used to measure a large current, the length of the rotating fiber is more than several tens of meters.

[0098] When the LFOCT is used to measure the transmission line of the transformer substation, the fiber ring of the LFOCT is sleeved on the transmission line of the current to be measured, the magnetic field generated by the current of the transmission line acts on the sensing fiber, the Faraday magneto-optical effect caused by the magnetic field leads to the rotation of the polarization plane of the polarized light passing through the fiber; the LFOCT directly measures the Faraday magneto-rotation angle according to the linear demodulation mode, first converts the Faraday magneto-rotation angle into the linear translation of the spot image, and then detects the translation amount of the linear translation to realize the direct measurement of the Faraday magneto-rotation angle, and then obtains the size of the current to be measured according to the corresponding relationship between the Faraday magneto-rotation angle and the current value.

[0099] Embodiment 1:

[0100] The present example proposes a full optical fiber current sensor based on the linear measurement of the sharp wedge interference, i.e. LFOCT, which is realized based on the Sagnac effect, the Faraday magneto-optical effect and the sharp wedge interference detection method.

[0101] The light emitted by the LED light source adopted by the LFOCT is linearly polarized by a polarizer, and is then divided into two mutually orthogonal linearly polarized lights by a coupler, a delay line, a 45° fusion splice point, is modulated by an initial phase modulator, and is then converted into left-handed and right-handed circularly polarized light by a first λ / 4 wave plate. The Faraday magneto-optical effect of the current causes a phase difference between the two beams of circularly polarized light, and the phase difference is doubled after being reflected by a mirror at the end of the sensing fiber. After the second phase modulation by the first λ / 4 wave plate, the modulator and the 45° fusion splice point, the two beams of circularly polarized light are combined into a linearly polarized light, and the phase difference of the circularly polarized light is converted into the rotation of the polarization plane of the linearly polarized light. Then, through the coupler, the rotation of the polarization plane of the linearly polarized light is converted into the synchronous translation of the spot by the second λ / 4 wave plate, the sharp wedge and the polarizer, and the linear measurement of the phase delay angle is obtained by the image sensor.

[0102] The demodulation result of the present example is independent of the optical power, and is beneficial to the separation and compensation of linear birefringence.

[0103] In this example, the sensing fiber of LFOCT is a spun fiber. The spun fiber has three working wavelengths: 600-900 nm, 900-1100 nm, and 1300-1600 nm. LFOCT uses the spun fiber with a working wavelength of 600-900 nm to match the working wavelength of the image sensor (such as CMOS). In addition, the length of the sensing fiber varies from several meters to tens of hundreds of meters according to the rated current. Generally, the length of the sensing fiber is several meters when the rated current is large, and the length of the sensing fiber is tens of meters to hundreds of meters when the rated current is small.

[0104] In practical applications (such as substations), the fiber loop of LFOCT is usually wrapped around the power transmission line carrying the current to be measured. The current of the power transmission line generates a magnetic field and acts on the sensing fiber, producing a Faraday magneto-optical effect, which causes the polarization plane of the polarized light passing through the fiber to rotate. According to the linear demodulation mode, FOCT converts the Faraday magneto-rotation angle into a linear translation of the spot image, and the direct measurement of the Faraday magneto-rotation angle can be realized by detecting the translation, thereby obtaining the size of the current to be measured.

[0105] Embodiment 2:

[0106] In this example, the all-fiber current sensor based on the tip-pit interference detection polarization method realizes linear measurement, wherein:

[0107] The light emitted by the [LED light source] becomes linearly polarized light through the [polarizer], enters the fiber loop through the [coupler], realizes beat length matching through the [delay line], is divided into two mutually orthogonal linearly polarized lights through the [45°] fusion splice, is initially phase-modulated through the [modulator], is converted into left and right circularly polarized light through the [λ / 4 wave plate 1], and 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 [mirror] at the end of the sensing fiber, and then the phase difference is doubled through the [sensing fiber], and after the [λ / 4 wave plate 1], [modulator] secondary phase modulation and [45°] fusion splice, it is combined into a 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. The [modulator] is secondary phase-modulated, passes through the [coupler], and the rotation of the polarization plane of the linearly polarized light is converted into the synchronous translation of the [spot] through the [λ / 4 wave plate 2], [tip-pit] and [polarizer]. The phase difference is obtained by positioning the spot with the [image sensor], and the direct current to be measured is obtained by filtering out linear birefringence based on the algorithm with the [image sensor].

[0108] The function of the [modulator] secondary phase modulation is to avoid polarization mismatch during the transmission of the returned linearly polarized light before it reaches the [λ / 4 wave plate 2].

[0109] The detection mode of the product described in this example is suitable for the measurement of alternating current and direct current.

[0110] All other embodiments obtained by a person skilled in the art based on the specific embodiments of the present application without creative labor fall within the scope of the present application.

Claims

1. An all-fiber current sensor based on wedge interferometer for linear measurement, characterized by: Linear measurement of all-fiber current sensor based on wedge-interference detection polarization method is realized; The linearly polarized light is obtained by the polarizer, and then enters the fiber loop through the coupler, and the beat length is matched through the delay line, and the 45° fusion splice point divides the linearly polarized light into two mutually orthogonal linearly polarized lights, and the initial phase modulation is realized through the modulator, and then the left-handed and right-handed circularly polarized light is obtained through the λ / 4 wave plate 1, and after entering the sensing fiber, the Faraday magneto-optic effect of the primary current causes the phase difference of the two circularly polarized lights, and after the reflection of the mirror at the end of the sensing fiber, the phase difference is doubled through the sensing fiber, and then the linearly polarized light is obtained through the λ / 4 wave plate 1, the modulator and the 45° fusion splice point, and the phase difference of the circularly polarized light is converted into the rotation of the polarization plane of the linearly polarized light, and then the rotation of the polarization plane of the linearly polarized light is converted into the synchronous translation of the light spot through the coupler, the λ / 4 wave plate 2, the wedge and the polarizer, and the phase difference is obtained by positioning the light spot through the image sensor, and then the linear birefringence is filtered out through the image sensor based on the algorithm, and the current to be measured is obtained. The fast and slow axes of the wedge and the azimuth angle of the second input / 4 wave plate are 45°.

2. The all-fiber current sensor based on wedge interference for linear measurement according to claim 1, characterized in that: The function of the second phase modulation of the modulator is to avoid the polarization mismatch in the transmission process of the returned linearly polarized light before reaching the λ / 4 wave plate 2.

3. The all-fiber current sensor based on the wedge interference to realize linear measurement according to claim 1 or 2, characterized in that: The detection mode is suitable for the measurement of alternating current and direct current.

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