Fiber-optic magnetic field-temperature dual-parameter sensor system based on magneto-optical crystal-grating composite structure

Abstract

The invention relates to an optical fiber magnetic field-temperature dual parameter sensor system based on a magneto-optical crystal-grating composite structure, belonging to the technical field of optical sensors, comprising a magneto-optical crystal-grating composite structure sensing unit, an optical path measurement system, and a magnetic field-temperature dual parameter demodulation system; a narrow-band laser light source emits a narrow-band laser, which is converted into a non-polarized state after passing through a depolarizer, and is incident on a temperature-sensitive optical fiber grating of the magneto-optical crystal-grating composite structure sensing unit through a circulator for reflection and transmission; the reflected light is transmitted to a single-path optical probe; the transmitted light is transmitted to a polarizer through a collimator, enters a polarization beam splitter prism through a magneto-optical crystal and is decomposed into two beams of vertical linear polarized light, and is transmitted to a balanced dual-path optical probe through two collimators; a magnetic field-temperature dual parameter demodulation system performs acquisition management; and the temperature and magnetic field information of a measured point are obtained through a temperature-magnetic field dual parameter demodulation algorithm and magnetic field compensation is performed.

Description

Technical Field

[0001] The invention belongs to the technical field of optical sensors and relates to an optical fiber magnetic field-temperature dual-parameter sensor system based on a magneto-optical crystal-grating composite structure. Background Art

[0002] Magnetic field measurement technology has been widely used in the fields of power industry, aerospace, life sciences, and resource exploration. Considering the application needs in many fields, a variety of magnetic field sensors have been developed, such as fluxgate magnetic field sensors, Hall magnetic field sensors, magnetoresistive magnetic field sensors, and optical fiber magnetic field sensors. As for temperature sensors, as the most common sensor type, common types include thermocouple sensors, thermal resistor sensors, infrared temperature sensors, and optical fiber temperature sensors. Among them, compared with traditional electronic sensors, optical fiber sensors have the advantages of reliable insulation, small size, anti-electromagnetic interference, and anti-chemical corrosion. They have outstanding advantages in special application scenarios such as high electric fields and strong electromagnetic interference. At the same time, both electronic magnetic field sensors and optical fiber magnetic field sensors are susceptible to temperature interference in practical applications, which reduces the accuracy of magnetic field measurement and requires further correction of magnetic field data to remove temperature crosstalk. In the method of temperature compensation for magnetic field perception, the temperature value and magnetic field value are measured synchronously and the initial magnetic field value is accurately compensated using the obtained temperature value, which has become a reliable solution to remove temperature interference and improve the accuracy of magnetic field measurement.

[0003] Current research on sensors mainly focuses on the independent perception of each physical quantity, while the direct combination of two types of sensors is mainly used for the simultaneous perception of magnetic field and temperature dual parameters. This method is relatively simple and can meet the needs of some scenarios. However, for scenarios with small layout space, high spatial resolution requirements, and low cost requirements, combined sensors cannot be used due to their large size and high cost. Therefore, the development of small-sized and low-cost magnetic field-temperature dual parameter sensors has become more necessary. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide an optical fiber magnetic field-temperature dual parameter sensor system based on a magneto-optical crystal-grating composite structure, which synchronously measures magnetic field and temperature information, solves the problem of temperature crosstalk during magnetic field measurement, and has the advantages of high dynamic response, wide-band magnetic field measurement, anti-electromagnetic interference, reliable insulation, etc. It can support the dual parameter measurement of magnetic field (current)-temperature in industries such as electricity, electronics and aviation, and has good technical application prospects and outstanding industrial and economic value.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] An optical fiber magnetic field-temperature dual parameter sensor system based on a magneto-optical crystal-grating composite structure, comprising a magneto-optical crystal-grating composite structure sensing unit, an optical path measurement system, and a magnetic field-temperature dual parameter demodulation system;

[0007] The optical path measurement system includes a narrow-band laser light source, a depolarizer, a circulator, a sensing unit, a single-path optical probe, and a balanced dual-path optical probe; the magneto-optical crystal-grating composite structure sensing unit includes a magneto-optical crystal, a polarizer, a polarization beam splitter prism, a collimator, and a temperature-sensitive fiber grating;

[0008] The narrow-band laser light source emits a narrow-band laser, which is converted into a non-polarized state after passing through a depolarizer, and is incident on a temperature-sensitive fiber grating of a magneto-optical crystal-grating composite structure sensing unit through a circulator for reflection and transmission; wherein the reflected light is transmitted to a single-path optical probe to detect the magnitude of the reflected light; the transmitted light is transmitted to a polarizer through a collimator for polarization, and the polarized light obtained continues to pass through a magneto-optical crystal to rotate its polarization direction under magnetic field modulation, and then enters a polarization beam splitter prism to be decomposed into two beams of vertical linear polarized light, and the two beams of linear polarized light are input into optical fibers through two collimators, and are transmitted to a balanced dual-path optical probe for dual-path light intensity detection;

[0009] The magnetic field-temperature dual-parameter demodulation system performs multi-channel synchronous acquisition of light intensity data of a single-channel optical probe and a balanced dual-channel optical probe through a multi-channel light intensity data acquisition and processing unit, and performs digital filtering, light intensity data conversion, and data synchronous storage management; performs real-time temperature and magnetic field dual-parameter demodulation on the processed multi-channel light intensity data through a temperature-magnetic field dual-parameter demodulation algorithm to obtain temperature and magnetic field information of the measured point; and performs real-time compensation on the uncorrected magnetic field data based on the acquired temperature data through a magnetic field measurement temperature compensation algorithm to obtain an accurate magnetic field value.

[0010] Furthermore, the type and structural size of the magneto-optical crystal are selected according to the measured magnetic field variation range and sensitivity requirements, and the key parameters include the Verdet coefficient, transmittance, linear birefringence, and thickness of the magneto-optical crystal;

[0011] The type and parameters of the temperature-sensitive fiber Bragg grating are standardized and prepared according to different temperature change ranges of the measured environment, wherein the key parameters include the central wavelength, the maximum reflectivity, and the bandwidth;

[0012] The temperature-sensitive fiber Bragg grating is integrated and packaged inside the collimator; the magneto-optical crystal, fiber Bragg grating, collimator, polarizer and polarization beam splitter prism are prepared by micro-machining and integrated and packaged in a small glass tube;

[0013] Each device inside the magneto-optical crystal-grating composite structure sensing unit is fixed by heat-conducting optical glue, and the residual air inside is filled; a layer of insulating polymer glue is coated on the outside of the magneto-optical crystal-grating composite structure sensing unit.

[0014] Furthermore, the magneto-optical crystal-fiber Bragg grating composite sensing unit uses the Faraday rotation effect of the magneto-optical crystal and the thermo-optical effect of the fiber Bragg grating to sense the magnetic field-temperature dual parameters;

[0015] The relationship between the central wavelength of the temperature-sensitive fiber Bragg grating and the temperature is as follows:

[0016]

[0017] Wherein, T0 represents the reference temperature value, ξ represents the thermo-optic coefficient of FBG, α represents the thermal expansion coefficient of FBG, α<<ξ, the thermo-optic coefficient and thermal expansion coefficient of FBG depend on the bulk properties of the material, and can be regarded as constants after the material is selected;

[0018] After the narrowband laser is injected into the temperature-sensitive fiber Bragg grating, it is reflected and transmitted. The central wavelength of the temperature-sensitive fiber Bragg grating shifts with the change of temperature due to the thermo-optical effect. The drift of the central wavelength of the light wave changes the transmission intensity and reflection intensity of the narrowband light. When the wavelength center of the narrowband light wave is located in the edge linear interval of the grating reflection spectrum, the relationship between temperature and the reflected light intensity I1 and the transmitted light intensity I2 is expressed as:

[0019] I1=k1T+b1

[0020] I2=k2T+b2

[0021] Among them, k1, k2, b1, b2 are the slope and intercept of the linear relationship between the reflected light intensity, the transmitted light intensity and the temperature T. Based on this expression, the temperature-magnetic field dual parameter demodulation algorithm is used to demodulate the sensor temperature value from the reflected light intensity or the transmitted light intensity.

[0022] The center wavelength, bandwidth, and maximum reflection coefficient of the temperature-sensitive fiber Bragg grating are optimized by multiple parameters, and the influence of different parameters on the temperature measurement linear range, wavelength drift value under unit temperature change, and reflectivity intensity change value are determined, and then the parameters of the temperature-sensitive fiber Bragg grating are comprehensively optimized and actually prepared;

[0023] The magnetic field sensing utilizes the Faraday rotation effect caused by the magneto-optical crystal under the action of the magnetic field. The polarization direction of the linearly polarized light in the magneto-optical crystal rotates in the magneto-optical crystal, and the rotation angle θ is linearly related to the sensed magnetic field B, that is:

[0024] θ=V(T)BL

[0025] Wherein, V(T) is the Verdet coefficient of the magneto-optical crystal with respect to temperature T, and L is the optical length of the magneto-optical crystal;

[0026] The polarization beam splitter is used to convert the rotated linear polarized light into two mutually perpendicular polarized light beams and separate them. Then the two linear polarized light beams are simultaneously input into the balanced dual-path optical detector to measure the light intensity values ​​I of both beams. 2-1 with I 2-2 The polarizing prism is arranged at an angle of 45 degrees with the polarizing direction of the polarizer along the optical axis. The relationship between the light intensity and the optical rotation angle is expressed as:

[0027]

[0028] Based on this relationship, the magnetic field value is calculated through the temperature-magnetic field dual parameter demodulation algorithm.

[0029] Furthermore, the narrow-band laser light source has a function of adjustable central wavelength. The central wavelength of the input narrow-band spectrum is determined according to the reflection spectrum of the temperature-sensitive grating, the relationship between the reflected light intensity or the transmitted light intensity and the temperature, and the ambient temperature change range. The central wavelength of the narrow-band light must be within the short wavelength range to the left of the central wavelength of the grating.

[0030] Furthermore, the balanced dual-path optical detector measures the respective light intensities of the two input lights and the difference between the two at the same gain, and converts them into three electrical signals for output respectively. The difference between the two is solved by comparing with the external signal, which is used to solve the magneto-optical rotation angle θ and the transmitted light intensity I2.

[0031] Furthermore, the magneto-optical crystal, fiber grating, collimator, polarizer and polarization beam splitter are integrated and packaged in a glass tube, fixed by heat-conducting optical glue, and a layer of insulating polymer glue is coated on the outside of the glass tube.

[0032] Furthermore, the magnetic field-temperature demodulation algorithm calculates the magnetic field and temperature of the actual measured point from the multi-channel light intensity data; wherein, the temperature demodulation algorithm is designed based on the relationship between temperature and the reflected light intensity I1 or the transmitted light intensity I2, and the sizes of the coefficients in the relationship are calculated by combining theory and experiment, and applied to the temperature demodulation algorithm to calculate the actual temperature value from the collected light intensity data; the magnetic field demodulation algorithm is designed based on the relationship between the two-channel light intensity values ​​measured by the balanced dual-channel optical probe and the optical rotation angle, and the magnetic field value to be corrected is solved from the collected two-channel optical fiber data.

[0033] Furthermore, the magnetic field measurement temperature compensation algorithm compensates the uncorrected magnetic field value with the obtained temperature value, brings the measured temperature value into the relationship between the two-way light intensity value and the optical rotation angle, modifies the size of the Verdet coefficient in the original magnetic field demodulation algorithm, and then removes the interference of temperature. The calculated output magnetic field value is the actual magnetic field size.

[0034] Furthermore, the multi-channel light intensity data acquisition and processing unit includes a hardware filtering module, a signal acquisition card, and a data processing module. The hardware filtering module is used to achieve initial noise filtering, and the acquisition card is used to perform multi-channel synchronous acquisition of each light detection data, and then the data processing unit is used to perform digital filtering and data synchronous storage management.

[0035] The beneficial effects of the present invention are:

[0036] (1) The present invention provides a magnetic field-temperature sensor based on a magneto-optical crystal-temperature sensitive grating composite structure, which has the performance of high dynamic response, reliable insulation and anti-electromagnetic interference, and can meet the requirements of accurate measurement of magnetic field-temperature dual parameters in harsh environments such as high electric field, strong electromagnetic interference, and large temperature fluctuations, such as magnetic field (current)-temperature measurement in ultra-high voltage transmission and transformation technology;

[0037] (2) The magneto-optical crystal-grating composite structure sensing unit adopts a single optical path and device integrated packaging design, which realizes the small-size preparation of the magnetic field-temperature dual-parameter sensor with high spatial resolution, facilitating its actual layout and installation;

[0038] (3) The proposed temperature compensation method solves the temperature crosstalk problem of the existing optical fiber magnetic field sensor based on magneto-optical crystal structure. For scenes with a large temperature fluctuation range, it can still accurately correct the measured value of the actual magnetic field to support the accurate measurement of the magnetic field.

[0039] (4) The designed magneto-optical crystal-grating composite structure can realize the magnetic field-temperature dual parameter measurement. The structure can also be extended to the electric field-temperature dual parameter measurement, that is, the magneto-optical crystal is replaced by an electro-optical crystal, and the relevant demodulation algorithm is modified based on the modulation principle of the electro-optical crystal to perceive the electro-optical-temperature dual parameter values.

[0040] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0042] Figure 1 It is a schematic diagram of the sensor structure and its measurement system of the present invention;

[0043] Figure 2 A flow chart is prepared for the sensing unit in the present invention;

[0044] Figure 3 It is a program diagram of the magnetic field-temperature dual parameter demodulation system of the present invention;

[0045] Figure numerals: 1-narrow-band light source; 2-depolarizer; 3-circulator; 4-input end collimator; 5-temperature-sensitive grating; 6-polarizer; 7-magneto-optical crystal; 8-polarization beam splitter; 9-output end collimator A; 10-output end collimator B; 11-thermal conductive optical adhesive; 12-glass tube; 13-polymer outer coating adhesive layer; 14-single-channel optical probe; 15-balanced dual-channel optical probe; 16-multi-channel data acquisition and processing unit; 17-optical fiber; 18-signal line. DETAILED DESCRIPTION

[0046] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0047] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0048] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0049] An optical fiber magnetic field-temperature dual parameter sensor and system based on a magneto-optical crystal-grating composite structure mainly consists of three parts: a magneto-optical crystal-grating composite structure sensing unit, an optical path measurement system, and a magnetic field-temperature dual parameter demodulation system:

[0050] The structure of the magneto-optical crystal-grating composite structure sensor unit is as follows: Figure 1 As shown, it is mainly composed of a magneto-optical crystal 7, a polarizer 6, a polarization beam splitter prism 8, collimators 4-9-10, a temperature-sensitive fiber Bragg grating 5, a glass tube 12, an internal heat-conducting optical adhesive 11, and an external insulating cured adhesive layer 13. The magneto-optical crystal 7 and the temperature-sensitive fiber Bragg grating 5 are in the same optical path, and the transmitted light and the reflected light in the common optical path are used to respectively realize the magnetic field-temperature dual parameter modulation-demodulation. The light first enters the fiber Bragg grating 5 for reflection and transmission, wherein the transmitted light is transmitted to the polarizer 6 through the collimator 4 for polarization, and the polarized light obtained continues to pass through the magneto-optical crystal 7 to rotate in polarization direction under magnetic field modulation, and then the light enters the polarization beam splitter prism 8 to be decomposed into two beams of vertical linear polarized light, and then the two beams of linear polarized light are input into the optical fiber 17 through two collimators 9 and 10;

[0051] The optical path measurement system includes a narrowband laser light source 1, a depolarizer 2, a circulator 3, a sensor unit, a single-path optical probe 14, and a balanced dual-path optical probe 15. The narrowband laser light source 1 emits a narrowband high-power laser, and the narrowband polarized light is converted into a non-polarized state after passing through the depolarizer 2, and is incident on the sensor unit through the circulator 3; the circulator 3 transmits the reflected light of the temperature-sensitive fiber grating 5 to the single-path optical probe 14 to detect the size of the reflected light, and the two beams of transmitted light of the sensor unit will be transmitted to the balanced dual-path optical probe 15 to detect the light intensity of the two paths;

[0052] The magnetic field-temperature dual parameter demodulation system includes a multi-channel light intensity data acquisition and processing unit 16, a temperature-magnetic field dual parameter demodulation algorithm, and a magnetic field measurement temperature compensation algorithm. The flow chart of the entire magnetic field-temperature dual parameter demodulation system is as follows: Figure 3 As shown, the multi-channel light intensity data acquisition and processing unit includes a hardware filtering module, a signal acquisition card, and a data processing and storage module. The hardware filtering module is used to implement initial noise filtering, and the acquisition card is used to perform multi-channel synchronous acquisition of each optical detection data, and then the data processing unit is used to perform digital filtering and data synchronous storage management; the temperature-magnetic field dual parameter demodulation algorithm uses the processed multi-channel light intensity data to perform real-time temperature and magnetic field dual parameter demodulation to obtain the temperature and magnetic field information of the measured point; the magnetic field measurement temperature compensation algorithm uses the acquired temperature data to perform real-time compensation for the uncorrected magnetic field data to obtain a more accurate magnetic field value.

[0053] The type and structural size of the magneto-optical crystal need to be selected according to the measured magnetic field variation range and sensitivity requirements, wherein the key parameters include the Verdet coefficient, transmittance, linear birefringence, thickness, etc. of the magneto-optical crystal; the type and parameters of the temperature-sensitive fiber Bragg grating are standardizedly designed and prepared according to different measured ambient temperature variation ranges, wherein the key parameters include the central wavelength, maximum reflectivity, bandwidth, etc.;

[0054] First, the magneto-optical crystal-grating composite structure sensing unit is made by integrated packaging. The temperature-sensitive fiber Bragg grating is integrated and packaged inside the collimator, which can reduce the size of the sensor and avoid grating damage, and prevent external vibration from interfering with the temperature measurement of the fiber Bragg grating, and can also accurately sense the temperature of the sensor; while the optical devices such as magneto-optical crystal, fiber Bragg grating, collimator, polarizer and polarization beam splitter are prepared into small sizes by micro-machining, and integrated and packaged in a small glass tube, which improves the spatial resolution of the sensor. At the same time, each device is fixed with thermally conductive optical glue, which mainly plays the role of fixing the sensor, filling the internal residual air to avoid air discharge under high field strength, supporting the reliable insulation of the sensor, and also plays the role of uniformly sensing the internal temperature, so that the measured temperature can represent the overall temperature of the sensor. At the same time, in order to enhance the ability of the sensing unit to resist high electric field and strong stress damage, a layer of insulating polymer glue is applied to its outside, which will have high tolerance to electric field strength and mechanical strength after curing.

[0055] The magneto-optical crystal-fiber Bragg grating composite sensing unit mainly uses the Faraday rotation effect of the magneto-optical crystal and the thermo-optical effect of the fiber Bragg grating to sense the magnetic field and temperature dual parameters.

[0056] The central wavelength of the grating shifts with temperature changes due to the thermo-optical effect. The relationship between the central wavelength and temperature is as follows:

[0057]

[0058] Wherein, T0 represents the reference temperature value, ξ represents the thermo-optic coefficient of FBG, and α represents the thermal expansion coefficient of FBG. Generally, α<<ξ. The thermo-optic coefficient and thermal expansion coefficient of FBG are both determined by the bulk properties of the material, so they can be regarded as constants after the material is selected.

[0059] The main principle of temperature perception is: after narrowband light enters the temperature-sensitive grating, it is reflected and transmitted, and the central wavelength of the grating shifts with the change of temperature due to the thermo-optical effect. The drift of the central wavelength of the light wave further changes the transmission intensity and reflection intensity of the narrowband light. When the wavelength center of the narrowband light wave is located in the edge linear interval of the grating reflection spectrum, the relationship between temperature and the reflected light intensity I1 and the transmitted light intensity I2 can be expressed as:

[0060] I1=k1T+b1

[0061] I2=k2T+b2

[0062] Among them, k1, k2, b1, b2 are the slope and intercept of the linear relationship between the reflected light intensity, the transmitted light intensity and the temperature T. Based on this expression, the subsequent temperature demodulation algorithm is used to demodulate the sensor temperature value from the reflected light intensity or the transmitted light intensity;

[0063] In order to achieve a wide linear temperature measurement range and accurate temperature measurement, multi-parameter optimization selection will be performed on the central wavelength, bandwidth, maximum reflection coefficient and other parameters of the temperature-sensitive grating. The simulation and experimental simulation methods are used to determine the influence of different parameters on the temperature measurement linear range, wavelength drift value and reflectivity intensity change value under unit temperature change, and then comprehensively optimize the parameters of the temperature-sensitive grating and carry out actual preparation;

[0064] The magnetic field sensing mainly utilizes the Faraday rotation effect caused by the magneto-optical crystal under the action of the magnetic field. The polarization direction of the linearly polarized light in the magneto-optical crystal rotates in the magneto-optical crystal, and the rotation angle θ is linearly related to the sensed magnetic field B, that is:

[0065] θ=V(T)BL

[0066] Among them, V(T) is the Verdet coefficient of the magneto-optical crystal with respect to temperature T, and L is the optical length of the magneto-optical crystal. Then, a polarization beam splitter is used to convert the rotated linear polarized light into two mutually perpendicular polarized light beams and separate them. Then, the two linear polarized light beams are simultaneously input into the balanced dual-path optical detector to measure the light intensity values ​​I of the two beams. 2-1 with I 2-2 When the polarizing prism is arranged at an angle of 45 degrees with the polarizing direction of the polarizer along the optical axis, the relationship between the light intensity and the optical rotation angle can be expressed as

[0067]

[0068] Based on this relationship, the design of the subsequent magnetic field demodulation algorithm is supported, and it can be known that the demodulation of the magnetic field is not affected by the change of the total transmitted light intensity, that is, the fiber Bragg grating temperature measurement and the magneto-optical crystal test magnetic field are independent of each other.

[0069] The basic structure of the optical path system in the sensing system has been described in the previous article. The key points include: ① object-oriented adjustment of the central wavelength of the light source; ② detection of multi-path light intensity.

[0070] The narrow-band light source has the function of adjustable central wavelength. In practical application, the central wavelength of the input narrow-band spectrum can be determined according to the reflection spectrum of the temperature-sensitive grating, the relationship between the reflected light intensity (or the transmitted light intensity) and the temperature, and the ambient temperature variation range, so as to obtain the actual best temperature measurement effect; that is, at room temperature (25°C), the central wavelength configuration can meet the maximum linear temperature measurement range; at the same time, considering that the Verdet coefficient of the magneto-optical crystal gradually decreases with increasing temperature, that is, the smaller the signal intensity output under the same magnetic field, the central wavelength of the narrow-band light should be in the short wavelength range to the left of the central wavelength of the grating. In this range, the transmitted light intensity will gradually increase with increasing temperature, which can further compensate for the signal reduction caused by the reduction of the Verdet coefficient, thereby improving the signal-to-noise ratio of the overall measurement;

[0071] The balanced dual-path optical detector can measure the respective light intensities of the two input lights and the difference between the two at the same gain, and convert them into three electrical signals for output respectively. The difference between the two is solved by comparing with the method of making a difference with the external signal. This method has the advantages of low delay and low noise. The output three electrical signals can be used to solve the magneto-optical rotation angle θ and the transmitted light intensity I2.

[0072] The optical path design of the temperature-sensitive grating reflected light transmitted to the optical probe through the circulator is mainly based on the temperature demodulation of the reflected light, but the design of the same reflection branch can also be removed, that is, the temperature is demodulated by the total transmitted light intensity; the temperature demodulation of the total transmitted light intensity mainly depends on the balance of the total light intensity changes of the two-way light obtained by the dual-way optical probe to determine the grating transmission light intensity, and then demodulate the temperature change. For the different optical path designs before and after, the former has better accuracy in temperature measurement and can resist power intensity fluctuations; while the latter can reduce the hardware cost of the newly added circulator and optical probe.

[0073] The software and hardware system of the electronic part of the test system is designed to support the magnetic field-temperature dual parameter demodulation system. Among them, the multi-channel light intensity data acquisition and processing unit is the hardware part, which is responsible for data acquisition, processing and storage. The interface of the multi-channel light intensity data acquisition and processing unit is connected to the two optical probes through a high-frequency signal line, and can synchronously collect the multi-channel output signals of the two optical probes, and perform noise filtering on the initial signal, light intensity data conversion (i.e. converting the electrical signal into each channel of light intensity value), data storage and calculation;

[0074] The magnetic field-temperature demodulation algorithm calculates the magnetic field and temperature of the actual measured point from the multi-channel light intensity data; wherein, the temperature demodulation algorithm is mainly designed based on the relationship between temperature and reflected light intensity I1 (transmitted light intensity I2), and the size of each coefficient in the relationship can be calculated by combining theory and experiment, and applied to the temperature demodulation algorithm, and then the actual temperature value can be calculated from the collected light intensity data; the magnetic field demodulation algorithm is mainly designed based on the relationship between the two-channel light intensity values ​​and the optical rotation angle measured by the balanced two-channel optical probe, and the actual magnetic field value can be solved from the collected two-channel optical fiber data, but because the Verdet coefficient is related to temperature, that is, the obtained magnetic field value is the result of the joint influence of temperature and magnetic field, and the interference of temperature needs to be further removed;

[0075] The magnetic field measurement temperature compensation algorithm compensates the uncorrected magnetic field value with the obtained temperature value. Since the measured temperature value is equal to the temperature value of the magneto-optical crystal, the determined temperature value is substituted into the relationship between the two-way light intensity value and the optical rotation angle, and the size of the Verdet coefficient in the original magnetic field demodulation algorithm is modified, thereby removing the interference of temperature, and the calculated output magnetic field value is the actual magnetic field size.

[0076] Figure 2 The production flow chart of the magneto-optical crystal-grating composite structure sensing unit is shown. The specific steps are as follows:

[0077] Step 1: The magneto-optical crystal 7, collimators 1-9-10, polarizer 6, polarization beam splitter prism 8 and other optical devices are prepared into small sizes by micro-machining to support the high spatial resolution performance advantage of the sensor;

[0078] Step 2: Since the temperature variation range of the measured environment in the embodiment is 10-90° C., the central wavelength of the temperature-sensitive grating 5 is determined to be 1554.294 nm, the half-wave width is 2 nm, and the reflectivity is 93% as key parameters, and actual preparation is performed;

[0079] Step 3: The grating 5 is further processed and machined, inserted into the collimator and fixed with optical glue so that it is completely encapsulated inside the collimator, which can reduce the size of the sensor, avoid grating damage, and prevent external vibration from interfering with the temperature measurement of the fiber grating 5, and can also accurately sense the temperature of the sensor;

[0080] Step 4: According to the variation range of the measured environmental magnetic field and the resolution requirements of the sensor, the type and structural size of the magneto-optical crystal 7 are selected. In this embodiment, Bi-doped YIG crystal is selected as the target crystal, with a thickness of 0.35 mm and a transmittance of 60%;

[0081] Step 5: Select thermally conductive optical adhesive 11, which mainly plays the role of fixing the sensor, filling the residual air inside to avoid air discharge under high field strength, supporting reliable insulation of the sensor, and also plays the role of uniformly sensing the internal temperature, so that the measured temperature can represent the overall temperature inside the sensor;

[0082] Step 6: Integrate and package optical devices such as magneto-optical crystal 7, fiber grating 5, collimators 4-9-10, polarizer 6 and polarization beam splitter prism 8 into a small glass tube 12, and fix each device with thermal conductive optical glue 11;

[0083] Step 7: Apply a layer of insulating polymer glue 13 on the outside, which will have high electric field strength and mechanical strength after curing to enhance the ability of the sensor unit to resist damage from high electric fields and strong stresses;

[0084] Step 8: Check the appearance and structure of the sensor, and conduct experimental tests on its sensing performance.

[0085] The balanced dual-path optical probe 15 can be used to measure the intensity of each of the two input lights and the difference between the two at the same gain, and convert them into three electrical signals for output respectively. The difference between the two is solved by comparing with the external signal. This method has the advantages of low delay and low noise. The three output electrical signals can be used to solve the magneto-optical rotation angle θ and the transmitted light intensity I2. As for the detection of the reflected light of the temperature-sensitive grating 5, its main support is based on the demodulation of the temperature by the reflected light, but the design of the same reflection branch can also be removed, that is, the total transmitted light intensity is used to demodulate the temperature; at the same time, the total transmitted light intensity can also be used to demodulate the temperature, which mainly depends on the change of the total light intensity of the two lights obtained by the balanced dual-path optical probe 15 to determine the grating transmitted light intensity, and then demodulate the temperature change. This embodiment mainly uses the first optical path design method for temperature measurement, which can resist the intensity fluctuation of the power supply.

[0086] Figure 3 The program diagram of the magnetic field-temperature dual parameter demodulation system is shown, and the specific steps are:

[0087] Step 1: Connect and arrange the actual optical path according to the set optical path structure, and connect the multi-channel optical probe signal output interface with the interface of the acquisition device;

[0088] Step 2: Initialize and configure the narrowband light source 1, the photodetectors 14-15, and the multi-channel light intensity acquisition and processing unit, where the central wavelength of the narrowband light source is 1550nm and the output optical power is 15mw; after completing the initialization configuration, start the device to perform the first measurement cycle;

[0089] Step 3: Filter the multi-channel output signals of the optical detector using the analog filter circuit in the multi-channel light intensity data acquisition and processing unit;

[0090] Step 4: Use the acquisition card in the multi-channel light intensity data acquisition and processing unit to collect multi-channel signals and convert the original analog signals into digital signals to support the later data processing and storage;

[0091] Step 5: Use the data processing module in the multi-channel light intensity data acquisition and processing unit to perform digital filtering on the initial signal, convert the light intensity data (i.e. convert the electrical signal into the light intensity value of each channel), store and calculate the data;

[0092] Step 6: Use the temperature demodulation algorithm to calculate the actual temperature value from the collected light intensity data, where the temperature demodulation algorithm is mainly designed based on the relationship between temperature and reflected light intensity I1 (transmitted light intensity I2), and the size of each coefficient in the relationship can be calculated by combining theory and experiment;

[0093] Step 7: Use a magnetic field demodulation algorithm to solve the actual magnetic field value from the collected two-way optical fiber data. The algorithm is mainly designed based on the relationship between the two-way light intensity value and the optical rotation angle measured by the balanced dual-way optical detector;

[0094] Step 8: Design a temperature compensation algorithm for magnetic field measurement, and use the obtained temperature value to compensate the uncorrected magnetic field value. Since the measured temperature value is equal to the temperature value of the magneto-optical crystal, the determined temperature value is brought into the relationship between the two-way light intensity value and the optical rotation angle, and the size of the Verdet coefficient in the original magnetic field demodulation algorithm is modified, thereby removing the interference of temperature, and the calculated output magnetic field value is the actual magnetic field size;

[0095] Step 9: Determine whether to exit the operation? If yes, end the measurement; if no, proceed to the next measurement cycle and start again from step 3;

[0096] Step 10: End.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. An optical fiber magnetic field-temperature dual parameter sensor system based on a magneto-optical crystal-grating composite structure, characterized in that: It includes a magneto-optical crystal-grating composite structure sensing unit, an optical path measurement system, and a magnetic field-temperature dual parameter demodulation system; The optical path measurement system includes a narrow-band laser light source, a depolarizer, a circulator, a sensing unit, a single-path optical probe, and a balanced dual-path optical probe; the magneto-optical crystal-grating composite structure sensing unit includes a magneto-optical crystal, a polarizer, a polarization beam splitter prism, a collimator, and a temperature-sensitive fiber grating; The narrow-band laser light source emits a narrow-band laser, which is converted into a non-polarized state after passing through a depolarizer, and is incident on a temperature-sensitive fiber grating of a magneto-optical crystal-grating composite structure sensing unit through a circulator for reflection and transmission; wherein the reflected light is transmitted to a single-path optical probe to detect the magnitude of the reflected light; the transmitted light is transmitted to a polarizer through a collimator for polarization, and the polarized light obtained continues to pass through a magneto-optical crystal to rotate its polarization direction under magnetic field modulation, and then enters a polarization beam splitter prism to be decomposed into two beams of vertical linear polarized light, and the two beams of linear polarized light are input into optical fibers through two collimators, and are transmitted to a balanced dual-path optical probe for dual-path light intensity detection; The magnetic field-temperature dual parameter demodulation system performs multi-channel synchronous acquisition of light intensity data of single-channel optical probes and balanced dual-channel optical probes through a multi-channel light intensity data acquisition and processing unit, and performs digital filtering, light intensity data conversion, and data synchronous storage management; the processed multi-channel light intensity data is subjected to real-time temperature and magnetic field dual parameter demodulation through a temperature-magnetic field dual parameter demodulation algorithm to obtain temperature and magnetic field information of the measured point; And through the magnetic field measurement temperature compensation algorithm, based on the acquired temperature data, the uncorrected magnetic field data is compensated in real time to obtain an accurate magnetic field value; The type and structural size of the magneto-optical crystal are selected according to the measured magnetic field variation range and sensitivity requirements, and the key parameters include the Verdet coefficient, transmittance, linear birefringence, and thickness of the magneto-optical crystal; The type and parameters of the temperature-sensitive fiber Bragg grating are standardized and prepared according to different temperature change ranges of the measured environment, wherein the key parameters include the central wavelength, the maximum reflectivity, and the bandwidth; The temperature-sensitive fiber Bragg grating is integrated and packaged inside the collimator; the magneto-optical crystal, fiber Bragg grating, collimator, polarizer and polarization beam splitter prism are prepared by micro-machining and integrated and packaged in a small glass tube; Each device inside the magneto-optical crystal-grating composite structure sensing unit is fixed by heat-conducting optical glue, and the residual air inside is filled; a layer of insulating polymer glue is coated on the outside of the magneto-optical crystal-grating composite structure sensing unit.

2. The optical fiber magnetic field-temperature dual parameter sensor system based on the magneto-optical crystal-grating composite structure according to claim 1 is characterized in that: The magneto-optical crystal-fiber Bragg grating composite sensing unit uses the Faraday rotation effect of the magneto-optical crystal and the thermo-optical effect of the fiber Bragg grating to sense the magnetic field-temperature dual parameters; The relationship between the central wavelength of the temperature-sensitive fiber Bragg grating and the temperature is as follows: Wherein, T0 represents the reference temperature value, ξ represents the thermo-optic coefficient of FBG, α represents the thermal expansion coefficient of FBG, α<<ξ, the thermo-optic coefficient and thermal expansion coefficient of FBG depend on the bulk properties of the material, and can be regarded as constants after the material is selected; After the narrowband laser is injected into the temperature-sensitive fiber Bragg grating, it is reflected and transmitted. The central wavelength of the temperature-sensitive fiber Bragg grating shifts with the change of temperature due to the thermo-optical effect. The drift of the central wavelength of the light wave changes the transmission intensity and reflection intensity of the narrowband light. When the wavelength center of the narrowband light wave is located in the edge linear interval of the grating reflection spectrum, the relationship between temperature and the reflected light intensity I1 and the transmitted light intensity I2 is expressed as: I1=k1T+b1 I2=k2T+b2 Among them, k1, k2, b1, b2 are the slope and intercept of the linear relationship between the reflected light intensity, the transmitted light intensity and the temperature T. Based on this expression, the temperature-magnetic field dual parameter demodulation algorithm is used to demodulate the sensor temperature value from the reflected light intensity or the transmitted light intensity. The center wavelength, bandwidth, and maximum reflection coefficient of the temperature-sensitive fiber Bragg grating are optimized by multiple parameters, and the influence of different parameters on the temperature measurement linear range, wavelength drift value under unit temperature change, and reflectivity intensity change value are determined, and then the parameters of the temperature-sensitive fiber Bragg grating are comprehensively optimized and actually prepared; The magnetic field sensing utilizes the Faraday rotation effect caused by the magneto-optical crystal under the action of the magnetic field. The polarization direction of the linearly polarized light in the magneto-optical crystal rotates in the magneto-optical crystal, and the rotation angle θ is linearly related to the sensed magnetic field B, that is: θ=V(T)BL Wherein, V(T) is the Verdet coefficient of the magneto-optical crystal with respect to temperature T, and L is the optical length of the magneto-optical crystal; The polarization beam splitter is used to convert the rotated linear polarized light into two mutually perpendicular polarized light beams and separate them. Then the two linear polarized light beams are simultaneously input into the balanced dual-path optical detector to measure the light intensity values ​​I of both beams. 2-1 with I 2-2 The polarizing prism is arranged at an angle of 45 degrees with the polarizing direction of the polarizer along the optical axis. The relationship between the light intensity and the optical rotation angle is expressed as: Based on this relationship, the magnetic field value is calculated through the temperature-magnetic field dual parameter demodulation algorithm.

3. The optical fiber magnetic field-temperature dual parameter sensor system based on the magneto-optical crystal-grating composite structure according to claim 1 is characterized in that: The narrow-band laser light source has a function of adjustable central wavelength. The central wavelength of the input narrow-band spectrum is determined according to the reflection spectrum of the temperature-sensitive grating, the relationship between the reflected light intensity or the transmitted light intensity and the temperature, and the ambient temperature change range. The central wavelength of the narrow-band light must be within the short wavelength range to the left of the central wavelength of the grating.

4. The optical fiber magnetic field-temperature dual parameter sensor system based on the magneto-optical crystal-grating composite structure according to claim 1 is characterized in that: The balanced dual-path optical detector measures the respective light intensities of the two input lights and the difference between the two at the same gain, and converts them into three electrical signals for output respectively. The difference between the two is solved by comparing and subtracting the external signal, which is used to solve the magneto-optical rotation angle θ and the transmitted light intensity I2.

5. The optical fiber magnetic field-temperature dual parameter sensor system based on the magneto-optical crystal-grating composite structure according to claim 1 is characterized in that: The magneto-optical crystal, optical fiber grating, collimator, polarizer and polarization beam splitter prism are integrated and packaged in a glass tube, fixed by heat-conducting optical glue, and a layer of insulating polymer glue is coated on the outside of the glass tube.

6. The optical fiber magnetic field-temperature dual parameter sensor system based on the magneto-optical crystal-grating composite structure according to claim 1 is characterized in that: The magnetic field-temperature demodulation algorithm calculates the magnetic field and temperature of the actual measured point from multi-channel light intensity data; wherein the temperature demodulation algorithm is designed based on the relationship between temperature and reflected light intensity I1 or transmitted light intensity I2, and the size of each coefficient in the relationship is calculated by combining theory and experiment, and applied to the temperature demodulation algorithm to calculate the actual temperature value from the collected light intensity data; the magnetic field demodulation algorithm is designed based on the relationship between the two-channel light intensity values ​​measured by a balanced dual-channel optical probe and the optical rotation angle, and the magnetic field value to be corrected is solved from the collected two-channel optical fiber data.

7. The optical fiber magnetic field-temperature dual parameter sensor system based on the magneto-optical crystal-grating composite structure according to claim 1 is characterized in that: The magnetic field measurement temperature compensation algorithm compensates the uncorrected magnetic field value with the obtained temperature value, brings the measured temperature value into the relationship between the two-way light intensity value and the optical rotation angle, modifies the size of the Verdet coefficient in the original magnetic field demodulation algorithm, and then removes the interference of temperature. The calculated output magnetic field value is the actual magnetic field size.

8. The optical fiber magnetic field-temperature dual parameter sensor system based on the magneto-optical crystal-grating composite structure according to claim 1 is characterized in that: The multi-channel light intensity data acquisition and processing unit includes a hardware filtering module, a signal acquisition card, and a data processing module. The hardware filtering module is used to filter out initial noise, and the acquisition card is used to perform multi-channel synchronous acquisition of each light detection data, and then the data processing unit is used to perform digital filtering and data synchronous storage management.

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