Fiber current sensor based on nested fiber grating and current detection method thereof

Abstract

The invention discloses a fiber current sensor based on nested fiber bragg grating and a current detection method thereof.The fiber current sensor comprises a base, a shell, a detection interface and a circuit mainboard, the shell is arranged on one side of the base, the detection interface is embedded in the surface of the shell, and an oxygen-free copper pin is arranged in the detection interface; a circuit mainboard is embedded in the shell, a grating writing area and a composite grating structure are arranged on the surface of the circuit mainboard, the oxygen-free copper pin is connected with an external circuit to be measured, and a layer of heating electrode is evaporated on the outer surface of the grating writing area. The measured peak wavelength is combined with Bragg wavelength change, the compensated wavelength is calculated, the compensated wavelength is converted into a current value according to a current-wavelength relation curve or formula of the optical fiber sensor, and the refractive index change caused by temperature change is monitored and compensated by combining the temperature sensor for use. Therefore, errors caused by strain are reduced.

Description

Technical Field

[0001] The invention relates to the technical field of electric power industry, and in particular to an optical fiber current sensor based on an embedded optical fiber grating and a current detection method thereof. Background Art

[0002] Fiber optic sensors can transmit measurement signals over long distances and are suitable for remote or difficult-to-reach monitoring points. After searching, the Chinese patent publication number CN104764926B discloses a fiber optic current sensor based on an embedded fiber grating and a current detection method thereof. Although the fiber optic current sensor based on an embedded fiber grating has the advantages of high sensitivity, fast response speed, small size, simple structure, stable performance, low cost and flexible optical path application, the detection method lacks a step to verify the current detection accuracy of the fiber optic current sensor, which makes the detection result prone to errors. At the same time, the stretching or compression of the optical fiber during detection will produce mechanical strain, which will affect the period of the grating, causing the current detection to be affected by external factors, resulting in accuracy. Summary of the invention

[0003] In view of the shortcomings of the prior art, the present invention provides a fiber optic current sensor based on an embedded fiber grating and a current detection method thereof, which solves the problem that the detection method proposed in the background technology lacks a step for verifying the current detection accuracy of the fiber optic current sensor, which in turn leads to errors in the detection results. At the same time, the stretching or compression of the optical fiber during detection will produce mechanical strain, resulting in affecting the accuracy.

[0004] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0005] A fiber optic current sensor based on embedded fiber gratings comprises a base, a shell, a detection interface and a circuit mainboard, wherein the shell is arranged on one side of the base, the detection interface is embedded on the surface of the shell, oxygen-free copper pins are arranged inside the detection interface, a circuit mainboard is embedded inside the shell, a grating writing area and a composite grating structure are arranged on the surface of the circuit mainboard, the oxygen-free copper pins are connected to an external circuit to be tested, a layer of high-resistance nickel-iron alloy is evaporated on the outer surface of the grating writing area as a heating electrode, the thickness of which is between 150-500nm, and both ends of the heating electrode are respectively led out by oxygen-free copper wires and connected to the oxygen-free copper pins.

[0006] A fiber optic current detection method based on an embedded fiber grating is performed using the fiber optic current sensor, the method comprising:

[0007] S01: Writing the composite grating structure: First, a specific area of ​​the coating layer is stripped off on the optical fiber to serve as the grating writing area; within the grating writing area, a composite grating structure formed by the embedding of a long-period grating and a Bragg grating is written on the fiber core;

[0008] S02: Detecting current: When the external circuit to be tested has current output passing through the heating electrode, the heating electrode heats the grating writing area, causing the peak wavelength of the reflection spectrum or transmission spectrum of the optical fiber current sensor to drift;

[0009] S03: Spectral detection: Detect the reflection spectrum peak wavelength or the transmission spectrum peak wavelength of the optical fiber current sensor by a spectral detection method, and detect the accuracy of the current intensity information of the external circuit to be tested.

[0010] Furthermore, the grating writing method in S01 is:

[0011] a: Fix the optical fiber; fix the clean photosensitive optical fiber on the optical fiber fixture to ensure the stability of the optical fiber position during the subsequent grating writing process;

[0012] b: Grating writing preparation: prepare the equipment required for writing the grating, including the UV laser, grating mask, and place the optical fiber in the appropriate position to receive the grating writing;

[0013] c: Photosensitivity detection: Before writing the grating, the optical fiber is photosensitized to increase the sensitivity of the optical fiber to ultraviolet light, thereby forming the grating structure more effectively;

[0014] d: Writing gratings: Use ultraviolet laser to scan and expose the exposed optical fiber cladding, and write the grating structure into the optical fiber core by precisely controlling the laser power and scanning speed; during the writing process, use a spectrometer to monitor the transmission spectrum or reflection spectrum of the optical fiber in real time;

[0015] e: Subsequent processing: After the grating is written, annealing is performed to stabilize the refractive index change of the grating and ensure the performance of the grating.

[0016] Furthermore, when writing the grating, the grating period is determined, the refractive index change of the grating is calculated, the diffraction efficiency is calculated, the grating writing depth is determined, the diffraction angle of the grating is calculated, and the thermo-optical effect of the grating is calculated, so as to optimize the grating writing process;

[0017] The diffraction angle of the grating is calculated as: Where m is the diffraction order; Where n0 is the initial refractive index, is the temperature coefficient of refractive index and ΔT is the temperature change.

[0018] Furthermore, the grating writing also includes calculating the light intensity distribution of the grating writing and the laser power and scanning speed of the grating writing, and the formula is:

[0019]

[0020] Where I(x) is the light intensity at position x, and I0 is the incident light intensity;

[0021]

[0022] Wherein, P is the laser power of the writing area; P0 is the laser output power; d is the length of the writing area; and t is the writing time.

[0023] Furthermore, the temperature change in S02 will affect the refractive index of the optical fiber. According to the thermo-optical effect, the relationship between the refractive index n and the temperature T is expressed as:

[0024] n(T)=n0+α(T-T0)

[0025] Where n0 is the initial refractive index, α is the thermo-optic coefficient, T0 is the reference temperature, and the change in refractive index will result in the Bragg wavelength λ of the grating B Drift occurs.

[0026] 8. Furthermore, the relationship between the change of the peak wavelength of the reflection spectrum in S02 is:

[0027] Δλ ref =λ ref -λ ref,0 ;

[0028] Among them, Δλ ref is the shift of the peak wavelength of the reflection spectrum, λ ref is the measured reflection spectrum peak wavelength, λ ref,0 is the peak wavelength of the reflection spectrum when there is no current;

[0029] The transmission spectrum peak wavelength variation relationship is:

[0030] Δλ trans =λ trans -λ trans,0 ;

[0031] Among them, Δλ trans is the shift of the peak wavelength of the transmission spectrum, λ trans,0 is the peak wavelength of the transmission spectrum when there is no current;

[0032] The relationship between the wavelength and the current is: I=k·Δλ+I0, wherein I is the current to be measured, Δλ is the change in the peak wavelength of the reflection spectrum or the change in the peak wavelength of the transmission spectrum, k is a proportional constant, and I0 is a reference current.

[0033] Furthermore, the calculation formula for the drift of the peak wavelength in S02 is:

[0034]

[0035] Where Δλ is the shift of the peak wavelength, Δn is the change in the refractive index, n is the refractive index of the fiber, and λ0 is the original peak wavelength.

[0036] Furthermore, the stretching or compression of the optical fiber in S02 will produce mechanical strain, which will in turn affect the period of the grating, thereby causing the peak wavelength to drift. The relationship between the grating period and the strain is as follows: ΔΛ=∈Λ; wherein ∈ is the strain and Λ is the grating period. It is used in combination with a temperature sensor to monitor and compensate for the refractive index changes caused by temperature changes, thereby reducing the error caused by strain.

[0037] The present invention provides an optical fiber current sensor based on embedded optical fiber Bragg grating and a current detection method thereof. It has the following beneficial effects:

[0038] (1) The present invention uses a spectrometer to measure the reflection or transmission peak wavelength of the optical fiber sensor, combines the measured peak wavelength with the Bragg wavelength change, calculates the compensated wavelength, and converts the compensated wavelength into a current value according to the current-wavelength relationship curve or formula of the optical fiber sensor. The present invention is combined with a temperature sensor to monitor and compensate for the refractive index change caused by temperature change, thereby reducing the error caused by strain.

[0039] (2) In the present invention, when the external circuit to be tested has current output passing through the heating electrode, the heating electrode heats the grating writing area 5, causing the peak wavelength of the reflection spectrum or the transmission spectrum of the optical fiber current sensor to drift, thereby detecting the current. The current detection result is detected by a spectral detection method to detect the peak wavelength of the reflection spectrum or the peak wavelength of the transmission spectrum of the optical fiber current sensor, and the accuracy of the current intensity information of the external circuit to be tested is detected. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a schematic diagram of the overall structure of an optical fiber current sensor based on an embedded optical fiber Bragg grating according to the present invention;

[0041] Figure 2 It is a schematic diagram of the internal structure of a fiber optic current sensor based on an embedded fiber grating according to the present invention;

[0042] Figure 3 The present invention is a schematic flow chart of a fiber optic current detection method based on an embedded fiber optic Bragg grating.

[0043] In the figure, 1. base; 2. shell; 3. detection interface; 4. oxygen-free copper pins; 5. grating writing area; 6. circuit main board; 7. composite grating structure. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] See also Figure 1-2 The embodiment of the present invention provides a technical solution: an optical fiber current sensor based on embedded optical fiber Bragg grating and a current detection method thereof, comprising a base 1, a shell 2, a detection interface 3 and a circuit main board 6, wherein the shell 2 is provided on one side of the base 1, the detection interface 3 is embedded on the surface of the shell 2, an oxygen-free copper pin 4 is provided inside the detection interface 3, a circuit main board 6 is embedded inside the shell 2, a grating writing area 5 and a composite grating structure 7 are provided on the surface of the circuit main board 6, and the oxygen-free copper pin 4 is connected to an external circuit to be tested.

[0046] A layer of high-resistance nickel-iron alloy is evaporated on the outer surface of the grating writing area 5 as a heating electrode with a thickness between 150-500nm, and both ends of the heating electrode are respectively led out by oxygen-free copper wires and connected to the oxygen-free copper pins 4.

[0047] See also Figure 3 , a fiber current detection method based on embedded fiber Bragg grating, using the above fiber current sensor, the method is as follows:

[0048] S01: writing a composite grating structure 7; first, a specific area of ​​the coating layer is stripped off on the optical fiber to serve as a grating writing area 5; in this area, a composite grating structure 7 formed by the embedding of a long period grating and a Bragg grating is written on the fiber core;

[0049] S02: Detecting current; when the external circuit to be tested has current output passing through the heating electrode, the heating electrode heats the grating writing area 5, causing the peak wavelength of the reflection spectrum or transmission spectrum of the optical fiber current sensor to drift;

[0050] S03: Spectral detection: detecting the peak wavelength of the reflection spectrum or the peak wavelength of the transmission spectrum of the optical fiber current sensor by a spectral detection method, and detecting the accuracy of the current intensity information obtained from the external circuit to be tested;

[0051] The grating writing method in S01 is:

[0052] a: Fix the optical fiber; fix the clean photosensitive optical fiber on the optical fiber clamp to ensure the stability of the optical fiber position during the subsequent grating writing process; b: Grating writing preparation; prepare the equipment required for writing the grating, including the ultraviolet laser, grating mask, and place the optical fiber in the appropriate position to receive the grating writing; c: Photosensitivity detection; before writing the grating, photosensitize the optical fiber to improve the sensitivity of the optical fiber to ultraviolet light, so as to more effectively form the grating structure; d: Write the grating; use the ultraviolet laser to scan and expose the exposed optical fiber cladding, and write the grating structure into the optical fiber core by precisely controlling the laser power and scanning speed; during the writing process, use a spectrometer to monitor the transmission spectrum or reflection spectrum of the optical fiber in real time; e: Subsequent processing; after the grating writing is completed, annealing treatment is performed to stabilize the refractive index change of the grating to ensure the performance of the grating.

[0053] When writing the grating, it is necessary to determine the grating period, calculate the refractive index change of the grating, calculate the diffraction efficiency, determine the grating writing depth, calculate the diffraction angle of the grating, calculate the thermo-optical effect of the grating, and optimize the grating writing process.

[0054] The formula for calculating the grating period is: Among them, λ B is the Bragg wavelength, n is the refractive index of the grating, θ B It is Bragg Point;

[0055] The refractive index change of the grating is estimated by the coupling efficiency of the grating and the writing depth of the grating: Where L is the grating writing depth,

[0056] The diffraction efficiency is calculated as: Where α is the coupling coefficient of the grating, and N is the total number of the grating;

[0057] The grating writing depth is estimated by the grating refractive index change and the grating period: L is the gate writing depth;

[0058] The diffraction angle of the grating is calculated as: Where m is the diffraction order; Where n0 is the initial refractive index, is the temperature coefficient of refractive index and ΔT is the temperature change.

[0059] Grating writing also includes calculating the light intensity distribution of grating writing as well as the laser power and scanning speed of grating writing. The formula is:

[0060]

[0061] Where I(x) is the light intensity at position x, and I0 is the incident light intensity;

[0062]

[0063] Wherein, P is the laser power of the writing area; P0 is the laser output power; d is the length of the writing area; and t is the writing time.

[0064] Temperature changes in S02 will affect the refractive index of the optical fiber. According to the thermo-optical effect, the relationship between the refractive index n and the temperature T can be expressed as:

[0065] n(T)=n0+α(T-T0)

[0066] Where n0 is the initial refractive index, α is the thermo-optic coefficient, T0 is the reference temperature, and the change in refractive index will result in the Bragg wavelength λ of the grating B Drift occurs.

[0067] The relationship between the peak wavelength change of the reflection spectrum in S02 is: Δλ ref =λ ref -λ ref,0 ; where Δλ ref is the shift of the peak wavelength of the reflection spectrum, λ ref is the measured reflection spectrum peak wavelength, λ ref,0 is the peak wavelength of the reflection spectrum when there is no current; the change relationship of the peak wavelength of the transmission spectrum is: Δλ trans =λ trans -λ trans,0 ; where Δλ trans is the shift of the peak wavelength of the transmission spectrum, λ trans,0 It is the peak wavelength of the transmission spectrum when there is no current. The relationship between wavelength and current is: I=k·Δλ+I0, where I is the current to be measured, Δλ is the wavelength change (reflection or transmission), k is the proportional constant, and I0 is the reference current.

[0068] The calculation formula for the drift of the peak wavelength in S02 is:

[0069]

[0070] Where Δλ is the shift of the peak wavelength, Δn is the change in the refractive index, n is the refractive index of the fiber, and λ0 is the original peak wavelength.

[0071] In S02, if the optical fiber is stretched or compressed, it will produce mechanical strain, which will affect the period of the grating, causing the peak wavelength to drift. The relationship between the grating period and the strain is as follows: ΔΛ=∈Λ; where ∈ is the strain and Λ is the grating period. The reflection or transmission peak wavelength λ of the optical fiber sensor is measured using a spectrometer. meas , combining the measured peak wavelength with the Bragg wavelength change to calculate the compensated wavelength, λ comp:λ comp =λ meas -Δλ B , according to the current-wavelength relationship curve or formula of the optical fiber sensor, the compensated wavelength is converted into the current value, I:I=f(λ comp ), f is the current-to-wavelength conversion function, which is used in conjunction with a temperature sensor to monitor and compensate for the refractive index change caused by temperature changes, thereby reducing the error caused by strain.

[0072] Table 1 shows the response of the fiber optic current sensor at different current values:

[0073] Table 1

[0074]

[0075] By observing the trend of the peak wavelength changing with the current value, the sensitivity of the sensor can be calculated, which is the ratio of the wavelength change to the current change. For example, from 0.5A to 3.0A, the wavelength changes from 1550.2nm to 1551.7nm, a change of 1.5nm, indicating that the sensor has a good response to the current change. The good response of the sensor to the current change indicates its high sensitivity, which means that even a small current change can be detected by the sensor. The data provided also shows that the sensor can maintain a consistent response at different current levels, which indicates its good repeatability and stability.

[0076] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the attached claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any figure mark in the claims should not be regarded as limiting the claims involved.

[0077] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. An optical fiber current sensor based on an embedded optical fiber Bragg grating, characterized in that: The invention comprises a base (1), a shell (2), a detection interface (3) and a circuit main board (6), wherein the shell (2) is arranged on one side of the base (1), the detection interface (3) is embedded on the surface of the shell (2), an oxygen-free copper pin (4) is arranged inside the detection interface (3), the shell (2) is embedded inside the circuit main board (6), a grating writing area (5) and a composite grating structure (7) are arranged on the surface of the circuit main board (6), the oxygen-free copper pin (4) is connected to an external circuit to be tested, a layer of high-resistance nickel-iron alloy is evaporated on the outer surface of the grating writing area (5) as a heating electrode, the thickness of which is between 150 and 500 nm, and the two ends of the heating electrode are respectively led out by oxygen-free copper wires and connected to the oxygen-free copper pin (4).

2. A fiber current detection method based on embedded fiber Bragg grating, characterized in that: The method is performed using the optical fiber current sensor of claim 1, wherein the method comprises: S01: writing a composite grating structure (7): first, stripping a specific area of ​​the coating layer on the optical fiber to serve as a grating writing area (5); within the grating writing area (5), writing a composite grating structure (7) formed by embedding a long period grating and a Bragg grating on the fiber core; S02: Detecting current: When the external circuit to be tested has current output passing through the heating electrode, the heating electrode heats the grating writing area (5), causing the peak wavelength of the reflection spectrum or transmission spectrum of the optical fiber current sensor to drift; S03: Spectral detection: Detect the reflection spectrum peak wavelength or the transmission spectrum peak wavelength of the optical fiber current sensor by a spectral detection method, and detect the accuracy of the current intensity information of the external circuit to be tested.

3. The optical fiber current detection method based on nested fiber Bragg grating according to claim 2, characterized in that: The grating writing method in S01 is: a: Fix the optical fiber; fix the clean photosensitive optical fiber on the optical fiber fixture to ensure the stability of the optical fiber position during the subsequent grating writing process; b: Grating writing preparation; Prepare the equipment needed to write the grating, including the UV laser, grating mask, and place the optical fiber in the appropriate position to receive the grating writing; c: Photosensitivity detection: Before writing the grating, the optical fiber is photosensitized to increase the sensitivity of the optical fiber to ultraviolet light, thereby forming the grating structure more effectively; d: Writing gratings: Use ultraviolet laser to scan and expose the exposed optical fiber cladding, and write the grating structure into the optical fiber core by precisely controlling the laser power and scanning speed; during the writing process, use a spectrometer to monitor the transmission spectrum or reflection spectrum of the optical fiber in real time; e: Subsequent processing: After the grating is written, annealing is performed to stabilize the refractive index change of the grating and ensure the performance of the grating.

4. The optical fiber current detection method based on nested fiber Bragg grating according to claim 2, characterized in that: When writing the grating, the grating period is determined, the refractive index change of the grating is calculated, the diffraction efficiency is calculated, the writing depth of the grating is determined, the diffraction angle of the grating is calculated, and the thermo-optical effect of the grating is calculated, so as to optimize the grating writing process; The diffraction angle of the grating is calculated as: Where m is the diffraction order; Where n0 is the initial refractive index, is the temperature coefficient of refractive index and ΔT is the temperature change.

5. The optical fiber current detection method based on nested fiber Bragg grating according to claim 2, characterized in that: The grating writing also includes calculating the light intensity distribution of the grating writing and the laser power and scanning speed of the grating writing, and the formula is: Where I(x) is the light intensity at position x, and I0 is the incident light intensity; Wherein, P is the laser power of the writing area; P0 is the laser output power; d is the length of the writing area; and t is the writing time.

6. The optical fiber current detection method based on nested fiber Bragg grating according to claim 2, characterized in that: The temperature change in S02 will affect the refractive index of the optical fiber. According to the thermo-optical effect, the relationship between the refractive index n and the temperature T is expressed as: n(T)=n0+α(T-T0) Where n0 is the initial refractive index, α is the thermo-optic coefficient, T0 is the reference temperature, and the change in refractive index will result in the Bragg wavelength λ of the grating B Drift occurs.

7. The optical fiber current detection method based on nested fiber Bragg grating according to claim 2, characterized in that: The relationship between the peak wavelength change of the reflection spectrum in S02 is: Dl ref =λ ref -l ref,0 ; Among them, Δλ ref is the shift of the peak wavelength of the reflection spectrum, λ ref is the measured peak wavelength of the reflection spectrum, λ ref,0 is the peak wavelength of the reflection spectrum when there is no current; The transmission spectrum peak wavelength variation relationship is: Dl trans =λ trans -l trans,0 ; Among them, Δλ trans is the shift of the peak wavelength of the transmission spectrum, λ trans,0 is the peak wavelength of the transmission spectrum when there is no current; The relationship between the wavelength and the current is: I=k·Δλ+I0, wherein I is the current to be measured, Δλ is the change in the peak wavelength of the reflection spectrum or the change in the peak wavelength of the transmission spectrum, k is a proportional constant, and I0 is a reference current.

8. The optical fiber current detection method based on nested fiber Bragg grating according to claim 2, characterized in that: The calculation formula for the drift of the peak wavelength in S02 is: Where Δλ is the shift of the peak wavelength, Δn is the change in the refractive index, n is the refractive index of the fiber, and λ0 is the original peak wavelength.

9. The optical fiber current detection method based on nested fiber Bragg grating according to claim 2, characterized in that: The stretching or compression of the optical fiber in S02 will produce mechanical strain, which will in turn affect the period of the grating, thereby causing the peak wavelength to drift. The relationship between the grating period and the strain is as follows: ΔΛ=∈Λ; where ∈ is the strain and Λ is the grating period. It is used in combination with a temperature sensor to monitor and compensate for the refractive index change caused by temperature change, thereby reducing the error caused by strain.

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