Vernier-sensitized optical fiber microcavity magnetic field measuring device and method

Abstract

The invention discloses a vernier-sensitized optical fiber microcavity magnetic field measuring device and method, and relates to the technical field of optical fiber magnetic field sensing. The device comprises a broadband light source, an optical fiber coupler, an optical fiber microcavity magnetic field sensor and a spectrum analyzer, the broadband light source is used for providing a detection light signal; the optical fiber coupler is used for transmitting the detection optical signal to the optical fiber microcavity magnetic field sensor; the optical fiber microcavity magnetic field sensor detects external magnetic field change information based on an optical fiber Fabry-Perot microcavity principle to obtain a total reflection light signal; the optical fiber coupler is also used for transmitting the total reflected light signal to the spectrum analyzer; the spectrum analyzer demodulates the total reflected light signal and realizes magnetic field measurement based on an optical vernier effect theory; the magnetic field intensity response is used for representing the relation between the wavelength drift amount enveloped by the vernier spectrum and the external magnetic field intensity. The invention aims to realize high-precision magnetic field measurement.

Description

Technical Field

[0001] The present application relates to the field of optical fiber magnetic field sensing technology, and in particular to an optical fiber microcavity magnetic field measurement device and method with vernier-enhanced sensitivity. Background Art

[0002] Fiber optic magnetic field sensors have been widely used in power equipment detection, cable status monitoring and other fields due to their advantages such as corrosion resistance, anti-electromagnetic interference, remote measurement, and adaptability to smart grid needs. Among the many fiber optic magnetic field sensors, fiber optic magnetic field sensors based on new magnetic sensitive materials, magnetic fluids, have attracted widespread attention from researchers at home and abroad due to their superior magneto-optical properties. However, existing fiber optic magnetic fluid sensors have problems such as low sensitivity and difficulty in accurately measuring magnetic field strength due to severe absorption / refractive loss of magnetic fluids. Therefore, it is crucial to achieve high-precision magnetic field measurement. Summary of the invention

[0003] The purpose of the present application is to provide a vernier-sensitized optical fiber microcavity magnetic field measurement device and method, which can achieve high-precision magnetic field measurement.

[0004] To achieve the above objectives, this application provides the following solutions:

[0005] In a first aspect, the present application provides a vernier-sensitized optical fiber microcavity magnetic field measurement device, comprising: a broadband light source, an optical fiber coupler, an optical fiber microcavity magnetic field sensor, and a spectrum analyzer;

[0006] The broadband light source, the optical fiber microcavity magnetic field sensor and the optical spectrum analyzer are all connected to the optical fiber coupler;

[0007] The broadband light source is used to provide a detection light signal;

[0008] The optical fiber coupler is used to transmit the detection light signal to the optical fiber microcavity magnetic field sensor;

[0009] The optical fiber microcavity magnetic field sensor is used to detect external magnetic field change information based on the optical fiber Fabry-Perot microcavity principle to obtain a total reflected light signal;

[0010] The optical fiber coupler is also used to transmit the total reflected light signal to the optical spectrum analyzer;

[0011] The spectrum analyzer is used to demodulate the total reflected light signal and realize magnetic field measurement based on the optical vernier effect theory; the magnetic field intensity response is used to characterize the relationship between the wavelength drift of the vernier spectrum envelope and the external magnetic field intensity; the vernier spectrum envelope is determined based on the total reflected light signal.

[0012] Optionally, the optical fiber microcavity magnetic field sensor specifically comprises: a sensing optical fiber microcavity and a reference optical fiber microcavity;

[0013] The sensing fiber microcavity and the reference fiber microcavity are both connected to the fiber coupler.

[0014] Optionally, the optical fiber coupler is provided with a first port, a second port, a third port and a fourth port;

[0015] The first port is connected to the broadband light source; the second port is connected to the spectrum analyzer; the third port is connected to the sensing fiber microcavity; and the fourth port is connected to the reference fiber microcavity.

[0016] Optionally, the sensing optical fiber microcavity comprises: a first single-mode optical fiber, a first hollow-core optical fiber, a first UV adhesive film, a quartz tube, and a second UV adhesive film;

[0017] The first single-mode optical fiber is fused with the first hollow-core optical fiber; the first UV adhesive film is arranged at the end of the first hollow-core optical fiber; the first single-mode optical fiber is connected to the third port;

[0018] The fusion surface of the first single-mode optical fiber and the first hollow-core optical fiber is a first reflection surface; the critical surface between the air in the first hollow-core optical fiber and the first UV adhesive film is a second reflection surface; the first reflection surface and the second reflection surface constitute a first optical fiber Fabry-Perot interferometer;

[0019] The first optical fiber Fabry-Perot interferometer is arranged inside the quartz tube; the end of the quartz tube is sealed with the second UV adhesive film; the first UV adhesive film and the second UV adhesive film constitute a magnetic fluid cavity, and the magnetic fluid cavity is arranged inside the quartz tube; a magnetic fluid is arranged in the magnetic fluid cavity; wherein the magnetic field directional extension phenomenon of the magnetic fluid inside the magnetic fluid cavity changes with the change of the external magnetic field intensity, thereby changing the force applied to the first UV adhesive film; the force deformation of the first UV adhesive film changes with the change of the external magnetic field intensity, thereby changing the cavity length of the first optical fiber Fabry-Perot interferometer;

[0020] The first single-mode optical fiber is used to receive the detection light signal introduced through the third port, and transmit the detection light signal to the first hollow-core optical fiber; wherein, during the transmission process, a part of the detection light signal is reflected back to the first single-mode optical fiber through the first reflection surface to obtain a first reflected light signal; another part of the detection light signal is transmitted through the first reflection surface, and is reflected back to the first single-mode optical fiber through the second reflection surface in the first optical fiber Fabry-Perot interferometer to obtain a second reflected light signal;

[0021] The first single-mode optical fiber is also used to transmit a first reflected signal to the optical fiber coupler via a third port; the first reflected signal includes: a first reflected light signal and a second reflected light signal.

[0022] Optionally, the reference fiber microcavity includes a second single-mode fiber, a second hollow-core fiber, and a third single-mode fiber that are fused in sequence; the second single-mode fiber is connected to the fourth port;

[0023] The end of the third single-mode optical fiber is cut at an angle of 45 degrees to 60 degrees;

[0024] The fusion surface of the second single-mode optical fiber and the second hollow-core optical fiber is a third reflection surface; the fusion surface of the second hollow-core optical fiber and the third single-mode optical fiber is a fourth reflection surface; the third reflection surface and the fourth reflection surface constitute a second optical fiber Fabry-Perot interferometer; the second optical fiber Fabry-Perot interferometer has no response to changes in the external magnetic field;

[0025] The second single-mode optical fiber is used to receive the detection light signal introduced through the fourth port, and transmit the detection light signal to the second hollow-core optical fiber; wherein, during the transmission process, a part of the detection light signal is reflected back to the second single-mode optical fiber through the third reflection surface to obtain a third reflected light signal; another part of the detection light signal is transmitted through the third reflection surface, and is reflected back to the second single-mode optical fiber through the fourth reflection surface in the second optical fiber Fabry-Perot interferometer to obtain a fourth reflected light signal;

[0026] The second single-mode optical fiber is also used to transmit the second reflected signal to the optical fiber coupler via the fourth port; the second reflected signal includes: a third reflected light signal and a fourth reflected light signal.

[0027] Optionally, the cavity length of the magnetic fluid cavity ranges from 100 microns to 150 microns.

[0028] In a second aspect, the present application provides a vernier-sensitized optical fiber microcavity magnetic field measurement method, which is implemented by a vernier-sensitized optical fiber microcavity magnetic field measurement device; the vernier-sensitized optical fiber microcavity magnetic field measurement method comprises:

[0029] Acquire a total reflected light signal; the total reflected light signal includes: a first reflected signal and a second reflected signal;

[0030] The total reflected light signal is demodulated, and magnetic field measurement is achieved based on the optical vernier effect theory; the magnetic field intensity response is used to characterize the relationship between the wavelength drift of the vernier spectrum envelope and the external magnetic field intensity; the vernier spectrum envelope is determined based on the total reflected light signal.

[0031] Optionally, the total reflected light signal is demodulated, and magnetic field measurement is achieved based on the optical vernier effect theory, specifically including:

[0032] A four-beam interference model is used to determine the reflection spectrum according to the total reflected light signal; the four-beam interference model includes: a reflection spectrum function;

[0033] determining the magnetic field intensity response of the sensing optical fiber microcavity according to the reflection spectrum;

[0034] Determining a vernier spectrum envelope based on the reflection spectrum; the vernier spectrum envelope changes periodically;

[0035] Determining a vernier sensitization factor; the vernier sensitization factor is determined based on a free spectral range of the vernier spectral envelope;

[0036] The magnetic field intensity response of the vernier spectrum envelope is determined according to the vernier sensitization factor and the magnetic field intensity response of the sensing optical fiber microcavity.

[0037] Optionally, the expression of the reflectance spectrum function specifically includes:

[0038] I sensor =I1+I2;

[0039] I1=A 2 +B 2 +2ABcos(2Φ1);

[0040] I2=C 2 +D 2 +2CDcos(2Φ2);

[0041] Among them, I sensor is the reflection spectrum function; I1 is the reflection spectrum function of the sensing fiber microcavity; I2 is the reflection spectrum function of the reference fiber microcavity; A is the mathematical expression corresponding to the first reflection surface; B is the mathematical expression corresponding to the second reflection surface; Φ1 is the phase difference between the first reflected light signal and the second reflected light signal in the first Fabry-Perot interferometer cavity; C is the mathematical expression corresponding to the third reflection surface; D is the mathematical expression corresponding to the fourth reflection surface; Φ2 is the phase difference between the third reflected light signal and the fourth reflected light signal in the second Fabry-Perot interferometer cavity.

[0042] Optionally, the expression for the magnetic field intensity response of the vernier spectrum envelope is:

[0043] Δλ sensor =M·Δλ=M·3(1-υ)r 4 ·μ0mL MF c.H / 16Eh 3 ;

[0044] Among them, Δλ sensor is the wavelength drift of the vernier spectrum envelope; M is the vernier sensitization factor; Δλ is the wavelength drift of the corresponding reflection spectrum in the magnetic field intensity response of the sensing optical fiber microcavity; υ is the Poisson's ratio of the first UV film; r is the film radius of the first UV film; μ0 is the vacuum magnetic permeability; m is the magnetization intensity of the magnetic fluid; L MF is the cavity length of the magnetic fluid cavity; c is the concentration of the magnetic fluid; H is the external magnetic field strength; E is the Young's modulus of the first UV adhesive film; h is the film thickness of the first UV adhesive film.

[0045] According to the specific embodiments provided in this application, this application has the following technical effects:

[0046] The present application provides a device and method for measuring a fiber microcavity magnetic field with vernier sensitization, the device comprising: a broadband light source, a fiber coupler, a fiber microcavity magnetic field sensor and a spectrum analyzer; the broadband light source is used to provide a detection light signal; the fiber coupler is used to transmit the detection light signal to the fiber microcavity magnetic field sensor; the fiber microcavity magnetic field sensor is based on the fiber Fabry-Perot microcavity principle, detects external magnetic field change information, and obtains a total reflected light signal; the fiber coupler is also used to transmit the total reflected light signal to the spectrum analyzer; the spectrum analyzer demodulates the total reflected light signal, and realizes magnetic field measurement based on the optical vernier effect theory; the magnetic field intensity response is used to characterize the relationship between the wavelength drift of the vernier spectrum envelope and the external magnetic field intensity. The present application realizes vernier effect sensitization by adjusting the parameters of the fiber microcavity magnetic field sensor, and improves the sensor sensitivity by one to two orders of magnitude, thereby realizing high-precision magnetic field measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0048] Figure 1 A structural block diagram of the optical fiber microcavity magnetic field measurement device for vernier sensitization of the present application;

[0049] Figure 2 A structural diagram of the optical fiber microcavity magnetic field measurement device for vernier sensitization of the present application;

[0050] Figure 3 A schematic diagram of the structure of the sensing optical fiber microcavity provided in this application;

[0051] Figure 4 A schematic diagram of the structure of the reference optical fiber microcavity provided in this application;

[0052] Figure 5 The spectrum provided by this application; wherein, Figure 5 (a) is the optical fiber microcavity spectrum. Figure 5 (b) is the reference optical fiber microcavity spectrum. Figure 5 (c) is the optical fiber microcavity magnetic field sensor spectrum;

[0053] Figure 6 The response diagram of the spectrum provided in this application as the intensity of the external magnetic field changes; wherein, Figure 6 (a) is the sensing fiber microcavity. Figure 6 (b) is the reference fiber microcavity;

[0054] Figure 7 This is a response diagram of the spectrum of the sensor provided in this application as the intensity of the external magnetic field changes; wherein, Figure 7 (a) is the response diagram without applied magnetic field. Figure 7 (b) is the response diagram when a 2mT magnetic field is applied.

[0055] Figure numerals: broadband light source-1, optical fiber coupler-2, sensing optical fiber microcavity-3, reference optical fiber microcavity-4, spectrum analyzer-5, optical fiber microcavity magnetic field sensor-6, first single-mode optical fiber-31, first hollow-core optical fiber-32, first UV adhesive film-33, quartz tube-34, second UV adhesive film-35, magnetic fluid cavity-36, second single-mode optical fiber-41, second hollow-core optical fiber-42, third single-mode optical fiber-43. DETAILED DESCRIPTION

[0056] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0057] This application is based on the characteristics of UV film and magnetic fluid, the principle of optical fiber Fabry-Perot microcavity and the theory of optical vernier effect. It utilizes the characteristics of UV film deformation under force and magnetic fluid directional extension with magnetic field. By demodulating the deformation of UV film at the end of sensing optical fiber microcavity, the influence of magnetic fluid absorption / refraction on detection light is effectively avoided, thereby achieving accurate measurement of external magnetic field intensity. In addition, by adjusting the parameters of two optical fiber microcavities, the optical vernier effect is enhanced, thereby significantly improving the sensitivity of the sensor in detecting magnetic field intensity. The optical fiber magnetic field sensor provided by this application has a stable structure and high sensitivity, and can be used for high-precision magnetic field measurement.

[0058] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0059] In an exemplary embodiment, Figure 1 and Figure 2 As shown, a vernier-sensitized optical fiber microcavity magnetic field measuring device is provided. The device comprises: a broadband light source 1, an optical fiber coupler 2, an optical fiber microcavity magnetic field sensor 6 and a spectrum analyzer 5.

[0060] The broadband light source 1, the optical fiber microcavity magnetic field sensor 6 and the spectrum analyzer 5 are all connected to the optical fiber coupler 2; the broadband light source 1 is used to provide a detection light signal; the optical fiber coupler 2 is used to transmit the detection light signal to the optical fiber microcavity magnetic field sensor 6; the optical fiber microcavity magnetic field sensor 6 is used to detect the external magnetic field change information based on the optical fiber Fabry-Perot microcavity principle to obtain the total reflected light signal; the optical fiber coupler 2 is also used to transmit the total reflected light signal to the spectrum analyzer 5.

[0061] The spectrum analyzer 5 is used to demodulate the total reflected light signal and realize magnetic field measurement based on the optical vernier effect theory; the magnetic field intensity response is used to characterize the relationship between the wavelength drift of the vernier spectrum envelope and the external magnetic field intensity; the vernier spectrum envelope is determined based on the total reflected light signal.

[0062] In one embodiment, the optical fiber microcavity magnetic field sensor 6 specifically includes: a sensing optical fiber microcavity 3 and a reference optical fiber microcavity 4 ; the sensing optical fiber microcavity 3 and the reference optical fiber microcavity 4 are both connected to the optical fiber coupler 2 .

[0063] The optical fiber coupler 2 is provided with a first port, a second port, a third port and a fourth port; the first port is connected to the broadband light source 1; the second port is connected to the spectrum analyzer 5; the third port is connected to the sensing optical fiber microcavity 3; and the fourth port is connected to the reference optical fiber microcavity 4.

[0064] As an optional implementation, Figure 3 As shown, the sensing optical fiber microcavity 3 includes: a first single-mode optical fiber 31 , a first hollow-core optical fiber 32 , a first UV adhesive film 33 , a quartz tube 34 and a second UV adhesive film 35 .

[0065] The first single-mode optical fiber 31 is fused with the first hollow-core optical fiber 32 ; the first UV adhesive film 33 is disposed at the end of the first hollow-core optical fiber 32 ; and the first single-mode optical fiber 31 is connected to the third port.

[0066] The fusion surface of the first single-mode optical fiber 31 and the first hollow-core optical fiber 32 is the first reflection surface; the critical surface between the air in the first hollow-core optical fiber 32 and the first UV adhesive film 33 is the second reflection surface; the first reflection surface and the second reflection surface constitute a first optical fiber Fabry-Perot interferometer.

[0067] The first optical fiber Fabry-Perot interferometer is arranged inside the quartz tube 34; the end of the quartz tube 34 is sealed with the second UV film 35; the first UV film 33 and the second UV film 35 constitute a magnetic fluid cavity 36, and the magnetic fluid cavity 36 is arranged inside the quartz tube 34; a magnetic fluid is arranged in the magnetic fluid cavity 36; wherein, the magnetic field directional extension phenomenon of the magnetic fluid inside the magnetic fluid cavity 36 changes with the change of the external magnetic field intensity, thereby changing the force applied to the first UV film 33; the force deformation of the first UV film 33 changes with the change of the external magnetic field intensity, thereby changing the cavity length of the first optical fiber Fabry-Perot interferometer. Specifically, the cavity length of the magnetic fluid cavity 36 ranges from 100 microns to 150 microns.

[0068] The first single-mode optical fiber 31 is used to receive the detection light signal introduced through the third port, and transmit the detection light signal to the first hollow-core optical fiber 32; wherein, during the transmission process, a part of the detection light signal is reflected back to the first single-mode optical fiber 31 through the first reflection surface to obtain a first reflected light signal; another part of the detection light signal is transmitted through the first reflection surface, and is reflected back to the first single-mode optical fiber 31 through the second reflection surface in the first optical fiber Fabry-Perot interferometer to obtain a second reflected light signal.

[0069] The first single-mode optical fiber 31 is also used to transmit the first reflected signal to the optical fiber coupler 2 via the third port; the first reflected signal includes: a first reflected light signal and a second reflected light signal.

[0070] like Figure 4 As shown, the reference fiber microcavity 4 includes a second single-mode optical fiber 41, a second hollow-core optical fiber 42, and a third single-mode optical fiber 43 which are fused in sequence; the second single-mode optical fiber 41 is connected to the fourth port.

[0071] The end of the third single-mode optical fiber 43 is cut at an angle of 45 degrees to 60 degrees; the fusion surface of the second single-mode optical fiber 41 and the second hollow-core optical fiber 42 is the third reflection surface; the fusion surface of the second hollow-core optical fiber 42 and the third single-mode optical fiber 43 is the fourth reflection surface; the third reflection surface and the fourth reflection surface constitute a second optical fiber Fabry-Perot interferometer; the second optical fiber Fabry-Perot interferometer does not respond to changes in the external magnetic field.

[0072] The second single-mode optical fiber 41 is used to receive the detection light signal introduced through the fourth port, and transmit the detection light signal to the second hollow-core optical fiber 42; wherein, during the transmission process, a part of the detection light signal is reflected back to the second single-mode optical fiber 41 through the third reflection surface to obtain a third reflected light signal; another part of the detection light signal is transmitted through the third reflection surface, and is reflected back to the second single-mode optical fiber 41 through the fourth reflection surface in the second optical fiber Fabry-Perot interferometer to obtain a fourth reflected light signal.

[0073] The second single-mode optical fiber 41 is also used to transmit the second reflected signal to the optical fiber coupler 2 via the fourth port; the second reflected signal includes: a third reflected light signal and a fourth reflected light signal.

[0074] Specifically, Figure 2 As shown, the fiber coupler 2 is provided with a first port, a second port, a third port and a fourth port. The broadband light source 1 is connected to the first port of the fiber coupler 2 to provide a detection light signal. The spectrum analyzer 5 is connected to the second port of the fiber coupler 2 to receive and demodulate the reflected light signal. The sensing fiber microcavity 3 is connected to the third port of the fiber coupler 2 to detect changes in the external magnetic field. The reference fiber microcavity 4 is connected to the fourth port of the fiber coupler 2 and is used as a reference interferometer of the sensing fiber microcavity 3 to achieve optical cursor effect sensitization.

[0075] like Figure 3 As shown, the sensing fiber microcavity 3 includes a first single-mode fiber 31, a first hollow-core fiber 32 and a first UV adhesive film 33. The first single-mode fiber 31 is fused with the first hollow-core fiber 32, and the end of the first hollow-core fiber 32 is provided with the first UV adhesive film 33. The fusion surface of the first single-mode fiber 31 and the first hollow-core fiber 32 is a first reflection surface, and the critical surface between the air in the first hollow-core fiber 32 and the first UV adhesive film 33 is a second reflection surface, and the first reflection surface and the second reflection surface constitute a first fiber Fabry-Perot interferometer. The first fiber Fabry-Perot interferometer and the magnetic fluid cavity are both arranged inside a quartz tube 34, and the end of the quartz tube 34 is sealed with a second UV adhesive film 35. The first UV adhesive film 33 and the second UV adhesive film 35 constitute a magnetic fluid cavity 36. A magnetic fluid is arranged in the magnetic fluid cavity 36.

[0076] The core diameter of the first single-mode optical fiber 31 is in the range of 8 microns to 9 microns, and the outer diameter is 125 microns. The core diameter of the first hollow-core optical fiber 32 is 70 microns, and the outer diameter is 125 microns. The inner diameter of the quartz tube 34 is 125 microns, and the outer diameter is 200 microns. The length of the first hollow-core optical fiber 32 is in the range of 100 microns to 200 microns. The thickness of the first UV film 33 is in the range of 5 microns to 10 microns. The thickness of the second UV film 35 is in the range of 10 microns to 20 microns. The length of the magnetic fluid cavity 36 is in the range of 100 microns to 150 microns.

[0077] like Figure 4 As shown, the reference fiber microcavity 4 includes a second single-mode fiber 41, a second hollow-core fiber 42 and a third single-mode fiber 43. The second single-mode fiber 41, the second hollow-core fiber 42 and the third single-mode fiber 43 are fused in sequence. The end of the third single-mode fiber 43 is cut at an angle of 45 degrees to 60 degrees. The fusion surface of the second single-mode fiber 41 and the second hollow-core fiber 42 is a third reflection surface, and the fusion surface of the second hollow-core fiber 42 and the third single-mode fiber 43 is a fourth reflection surface. The third reflection surface and the fourth reflection surface constitute a second fiber Fabry-Perot interferometer.

[0078] The core diameter of the second single-mode optical fiber 41 and the third single-mode optical fiber 43 are both in the range of 8 microns to 9 microns, and the outer diameter is 125 microns. The core diameter of the second hollow-core optical fiber 42 is 70 microns, and the outer diameter is 125 microns. The length of the second hollow-core optical fiber 42 is in the range of 100 microns to 200 microns.

[0079] The length difference between the first hollow core optical fiber 32 and the second hollow core optical fiber 42 is in the range of 1 μm to 20 μm.

[0080] Specifically, the working principle of the device mentioned in this application is as follows:

[0081] The detection light signal emitted by the broadband light source 1 enters through the first port of the optical fiber coupler 2. After being split by the optical fiber coupler 2, the incident detection light signal enters the sensing optical fiber microcavity 3 and the reference optical fiber microcavity 4 through the third port and the fourth port of the optical fiber coupler 2 respectively. The reflected light reflected back by the sensing optical fiber microcavity 3 and the reference optical fiber microcavity 4 returns to the optical fiber coupler 2 through the third port and the fourth port of the optical fiber coupler 2 respectively. The total reflected light signal enters the optical spectrum analyzer 5 through the second port of the optical fiber coupler 2, and is received and demodulated by the optical spectrum analyzer 5.

[0082] like Figure 3 As shown, for the sensing fiber microcavity 3, the incident detection light signal is introduced into the first single-mode optical fiber 31 through the third port of the optical fiber coupler 2, and is transmitted to the first hollow-core optical fiber 32 through the first single-mode optical fiber 31. During the transmission process, a portion of the incident detection light signal is reflected back to the first single-mode optical fiber 31 at the first reflection surface. Another portion of the incident detection light signal transmits the first reflection surface, that is, transmits into the first hollow-core optical fiber 32, and is reflected back to the first single-mode optical fiber 31 through the second reflection surface in the first optical fiber Fabry-Perot interferometer. The reflected reflected light signal (first reflected signal), that is, the first reflected light signal and the second reflected light signal, returns to the optical fiber coupler 2 through the third port of the optical fiber coupler 2.

[0083] For the reference fiber microcavity 4, the incident detection light signal is introduced into the second single-mode optical fiber 41 through the fourth port of the fiber coupler 2, and is transmitted to the second hollow-core optical fiber 42 through the second single-mode optical fiber 41; a part of the detection light signal is reflected back to the second single-mode optical fiber at the third reflection surface; another part of the detection light signal is transmitted into the second hollow-core optical fiber 42, that is, transmitted through the third reflection surface, and reflected back to the second single-mode optical fiber 41 through the fourth reflection surface in the second fiber Fabry-Perot interferometer; the reflected light signal (second reflected signal) of the reference fiber microcavity, that is, the third reflected light signal and the fourth reflected light signal, returns to the fiber coupler through the fourth port of the fiber coupler.

[0084] When the external magnetic field intensity changes, for the sensing optical fiber microcavity 3, the magnetic field directional extension phenomenon of the magnetic fluid inside the magnetic fluid cavity 36 changes with the change of the external magnetic field intensity, thereby changing the force applied to the first UV adhesive film 33; the force deformation of the first UV adhesive film 33 changes with the change of the external magnetic field intensity, resulting in the change of the cavity length of the sensing optical fiber microcavity 3, thereby causing the reflection spectrum of the sensing optical fiber microcavity 3 to drift; for the reference optical fiber microcavity 4, its reflection spectrum does not change with the change of the external magnetic field intensity, and has no response to the change of the magnetic field; the optical vernier effect sensitization can be achieved by adjusting the parameters of the two optical fiber microcavities, and finally the reflection spectrum corresponding to the total reflected light signal forms a periodically changing vernier spectrum envelope, and by demodulating the response of the vernier spectrum envelope, the sensitivity of the magnetic field intensity detection can be improved by one to two orders of magnitude.

[0085] Based on the characteristics of UV film and magnetic fluid, the principle of optical fiber Fabry-Perot microcavity and the theory of optical vernier effect, this application proposes a vernier-sensitized optical fiber microcavity magnetic field sensor; this application utilizes the characteristics of UV film deformation under force and magnetic fluid directional extension with magnetic field, and effectively avoids the influence of magnetic fluid absorption / refraction on the detection light signal by demodulating the deformation of the first UV film at the end of the sensing optical fiber microcavity, thereby achieving accurate measurement of the external magnetic field intensity. In addition, this application realizes optical vernier effect sensitization by regulating the parameters of two optical fiber microcavities (sensing optical fiber microcavity and reference optical fiber microcavity), thereby significantly improving the sensor's magnetic field intensity detection sensitivity. The vernier-sensitized optical fiber microcavity magnetic field sensor provided in this application has a stable structure and high sensitivity, and provides a feasible solution for high-precision, stable and reliable detection of external magnetic field intensity.

[0086] In an exemplary embodiment, a method for measuring a magnetic field of an optical fiber microcavity with vernier sensitization is provided, and the method for measuring a magnetic field of an optical fiber microcavity with vernier sensitization is implemented by using a device for measuring a magnetic field of an optical fiber microcavity with vernier sensitization. The method for measuring a magnetic field of an optical fiber microcavity with vernier sensitization comprises:

[0087] Step 100: Acquire a total reflected light signal; the total reflected light signal includes: a first reflected signal and a second reflected signal.

[0088] Step 200: demodulate the total reflected light signal and implement magnetic field measurement based on the optical vernier effect theory; the magnetic field intensity response is used to characterize the relationship between the wavelength drift of the vernier spectrum envelope and the external magnetic field intensity; the vernier spectrum envelope is determined based on the total reflected light signal.

[0089] In one embodiment, the total reflected light signal is demodulated, and the magnetic field measurement is realized based on the optical vernier effect theory, which specifically includes:

[0090] A four-beam interference model is adopted to determine the reflection spectrum according to the total reflected light signal; the four-beam interference model includes: a reflection spectrum function; determining the magnetic field intensity response of the sensing fiber microcavity according to the reflection spectrum; determining the vernier spectrum envelope based on the reflection spectrum; the vernier spectrum envelope changes periodically; determining the vernier sensitivity factor; the vernier sensitivity factor is determined based on the free spectrum range of the vernier spectrum envelope.

[0091] The magnetic field intensity response of the vernier spectrum envelope is determined according to the vernier sensitization factor and the magnetic field intensity response of the sensing optical fiber microcavity.

[0092] The specific expressions of the reflectance spectrum function include:

[0093] I sensor =I1+I2.

[0094] I1=A 2 +B 2 +2ABcos(2Φ1).

[0095] I2=C 2 +D 2 +2CDcos(2Φ2).

[0096] Among them, I sensor is the reflection spectrum function; I1 is the reflection spectrum function of the sensing fiber microcavity; I2 is the reflection spectrum function of the reference fiber microcavity; A is the mathematical expression corresponding to the first reflection surface; B is the mathematical expression corresponding to the second reflection surface; Φ1 is the phase difference between the first reflected light signal and the second reflected light signal in the first Fabry-Perot interferometer cavity; C is the mathematical expression corresponding to the third reflection surface; D is the mathematical expression corresponding to the fourth reflection surface; Φ2 is the phase difference between the third reflected light signal and the fourth reflected light signal in the second Fabry-Perot interferometer cavity.

[0097] The expression of the magnetic field intensity response of the cursor spectrum envelope is:

[0098] Δλ sensor =M·Δλ=M·3(1-υ)r 4 ·μ0mL MF c.H / 16Eh 3 .

[0099] Among them, Δλ sensor is the wavelength drift of the vernier spectrum envelope; M is the vernier sensitization factor; Δλ is the wavelength drift of the corresponding reflection spectrum in the magnetic field intensity response of the sensing optical fiber microcavity; υ is the Poisson's ratio of the first UV film; r is the film radius of the first UV film; μ0 is the vacuum magnetic permeability; m is the magnetization intensity of the magnetic fluid; L MFis the cavity length of the magnetic fluid cavity; c is the concentration of the magnetic fluid; H is the external magnetic field intensity; E is the Young's modulus of the first UV adhesive film; h is the film thickness of the first UV adhesive film.

[0100] The working principle of the sensing fiber microcavity 3 provided in the present application can be analyzed by a double-beam interference model, and its reflection spectrum is as follows: Figure 5 (a) is shown. The reflection spectrum function I1 of the sensing fiber microcavity 3 can be expressed as:

[0101] I1=A 2 +B 2 +2ABcos(2Φ1) (1)

[0102] In formula (1), A=R1 1 / 2 ; B = (1-α1)(1-R1)R2 1 / 2 ;Φ1=2πn1L1 / λ. R1 and R2 are the reflectivities of the first and second reflection surfaces, respectively; α1 is the transmission loss in the cavity of the sensing fiber microcavity; n1 is the refractive index of the medium in the cavity of the sensing fiber microcavity; L1 is the cavity length of the sensing fiber microcavity; λ is the wavelength of the incident detection light signal. A is the mathematical expression corresponding to the first reflection surface; B is the mathematical expression corresponding to the second reflection surface; Φ1 is the phase difference between the two light beams in the first Fabry-Perot interferometer cavity.

[0103] The working principle of the reference optical fiber microcavity 4 provided in this application can be analyzed by a double-beam interference model, and its reflection spectrum is as follows: Figure 5 (b) is shown. The reflection spectrum function I2 of the reference fiber microcavity 4 can be expressed as:

[0104] I2=C 2 +D 2 +2CDcos(2Φ2) (2)

[0105] In formula (2), C = R3 1 / 2 ; D = (1-α2)(1-R3)R4 1 / 2 ;Φ2=2πn2L2 / λ. R3 and R4 are the reflectivities of the third and fourth reflection surfaces, respectively; α2 is the transmission loss in the reference fiber microcavity; n2 is the refractive index of the medium in the reference fiber microcavity; and L2 is the cavity length of the reference fiber microcavity. C is the mathematical expression corresponding to the third reflection surface; D is the mathematical expression corresponding to the fourth reflection surface; Φ2 is the phase difference between the two light beams in the second Fabry-Perot interferometer cavity.

[0106] The vernier-sensitized optical fiber microcavity magnetic field sensor provided in the present application is composed of a sensing optical fiber microcavity 3 and a reference optical fiber microcavity 4 connected in parallel. The working principle can be analyzed by a four-beam interference model. The reflection spectrum is as follows: Figure 5(c) shows the reflection spectrum function of the optical fiber microcavity magnetic field sensor. sensor It can be expressed as:

[0107] I sensor =I1+I2=A 2 +B 2 +C 2 +D 2 +2ABcos(2Φ1)+2CDcos(2Φ2) (3)

[0108] like Figure 5 As shown in (c), due to the dual filtering of the two optical fiber microcavities, the sensor reflection spectrum forms a periodically changing vernier spectrum envelope. The vernier spectrum envelope function of the sensor is envelope It can be expressed as:

[0109] I envelope =2acos[4π(n1L1-n2L2) / λ]+b (4)

[0110] Where a is the amplitude of the cursor spectrum envelope, and b is the DC component of the cursor spectrum envelope.

[0111] The cursor sensitization factor M can be expressed as:

[0112] M=FSR envelope / FSR1=FSR2 / |FSR1-FSR2| (5)

[0113] In formula (5), FSR1 = λ 2 / 2n1L1,FSR2=λ 2 / 2n2L2.

[0114] Among them, FSR envelope is the free spectral range of the sensor’s vernier spectral envelope, FSR1 is the free spectral range of the sensing fiber microcavity, and FSR2 is the free spectral range of the reference fiber microcavity.

[0115] When the external magnetic field intensity H changes, for the sensing optical fiber microcavity 3, the magnetic field directional extension phenomenon of the magnetic fluid inside the magnetic fluid cavity 36 changes with the change of the external magnetic field intensity H, thereby changing the force P applied to the first UV adhesive film 33. The force deformation of the first UV adhesive film 33 changes with the change of the external magnetic field intensity H, resulting in a change in the cavity length L1 of the sensing optical fiber microcavity 3, thereby causing the reflection spectrum of the sensing optical fiber microcavity 3 to drift. Figure 6 As shown in (a), the reflection spectrum of the sensing optical fiber microcavity 3 blue shifts with the increase of the external magnetic field intensity H. The relationship between the wavelength drift Δλ of the reflection spectrum of the sensing optical fiber microcavity 3 and the external magnetic field intensity H can be expressed as:

[0116] Δλ=3(1-υ)r4 ·μ0mL MF c.H / 16Eh 3 (6)

[0117] Wherein, υ is the Poisson's ratio of the first UV film; r is the film radius of the first UV film; μ0 is the vacuum magnetic permeability; m is the magnetization intensity of the magnetic fluid; L MF is the cavity length of the magnetic fluid cavity; c is the concentration of the magnetic fluid; H is the external magnetic field intensity; E is the Young's modulus of the first UV adhesive film; h is the film thickness of the first UV adhesive film.

[0118] like Figure 6 As shown in (b), for the reference optical fiber microcavity 4, its reflection spectrum has no obvious drift and has no response to changes in the external magnetic field.

[0119] like Figure 7 (a) and Figure 7 As shown in (b), the vernier spectrum envelope of the optical fiber sensor provided by the present application is red-shifted with the increase of the external magnetic field intensity H, and the spectrum drift is M times the spectrum drift of the sensing optical fiber microcavity 3. The magnetic field intensity response of the vernier spectrum envelope of the optical fiber sensor provided by the present application, that is, the wavelength drift of the vernier spectrum envelope Δλ sensor The relationship with the external magnetic field strength H can be expressed as:

[0120] Δλ sensor =M·Δλ=M·3(1-υ)r 4 ·μ0mL MF c.H / 16Eh 3 (7)

[0121] It can be seen from formula (7) that by demodulating the response of the sensor's vernier spectrum envelope, the sensitivity of magnetic field intensity detection can be increased by M times, thereby achieving high-precision, stable and reliable measurement of changes in external magnetic field intensity.

[0122] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0123] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A vernier-sensitized optical fiber microcavity magnetic field measurement device, characterized in that: The vernier-sensitized optical fiber microcavity magnetic field measuring device comprises: a broadband light source, an optical fiber coupler, an optical fiber microcavity magnetic field sensor and a spectrum analyzer; The broadband light source, the optical fiber microcavity magnetic field sensor and the optical spectrum analyzer are all connected to the optical fiber coupler; The broadband light source is used to provide a detection light signal; The optical fiber coupler is used to transmit the detection light signal to the optical fiber microcavity magnetic field sensor; The optical fiber microcavity magnetic field sensor is used to detect external magnetic field change information based on the optical fiber Fabry-Perot microcavity principle to obtain a total reflected light signal; The optical fiber coupler is also used to transmit the total reflected light signal to the optical spectrum analyzer; The spectrum analyzer is used to demodulate the total reflected light signal and realize magnetic field measurement based on the optical vernier effect theory; the magnetic field intensity response is used to characterize the relationship between the wavelength drift of the vernier spectrum envelope and the external magnetic field intensity; the vernier spectrum envelope is determined based on the total reflected light signal.

2. The optical fiber microcavity magnetic field measurement device with vernier sensitization according to claim 1, characterized in that: The optical fiber microcavity magnetic field sensor specifically comprises: a sensing optical fiber microcavity and a reference optical fiber microcavity; The sensing fiber microcavity and the reference fiber microcavity are both connected to the fiber coupler.

3. The optical fiber microcavity magnetic field measuring device with vernier sensitization according to claim 2, characterized in that: The optical fiber coupler is provided with a first port, a second port, a third port and a fourth port; The first port is connected to the broadband light source; the second port is connected to the spectrum analyzer; the third port is connected to the sensing fiber microcavity; and the fourth port is connected to the reference fiber microcavity.

4. The optical fiber microcavity magnetic field measurement device with vernier sensitization according to claim 3, characterized in that: The sensing optical fiber microcavity comprises: a first single-mode optical fiber, a first hollow-core optical fiber, a first UV adhesive film, a quartz tube and a second UV adhesive film; The first single-mode optical fiber is fused with the first hollow-core optical fiber; the first UV adhesive film is arranged at the end of the first hollow-core optical fiber; the first single-mode optical fiber is connected to the third port; The fusion surface of the first single-mode optical fiber and the first hollow-core optical fiber is a first reflection surface; the critical surface between the air in the first hollow-core optical fiber and the first UV adhesive film is a second reflection surface; the first reflection surface and the second reflection surface constitute a first optical fiber Fabry-Perot interferometer; The first optical fiber Fabry-Perot interferometer is arranged inside the quartz tube; the end of the quartz tube is sealed with the second UV adhesive film; the first UV adhesive film and the second UV adhesive film constitute a magnetic fluid cavity, and the magnetic fluid cavity is arranged inside the quartz tube; a magnetic fluid is arranged in the magnetic fluid cavity; wherein the magnetic field directional extension phenomenon of the magnetic fluid inside the magnetic fluid cavity changes with the change of the external magnetic field intensity, thereby changing the force applied to the first UV adhesive film; the force deformation of the first UV adhesive film changes with the change of the external magnetic field intensity, thereby changing the cavity length of the first optical fiber Fabry-Perot interferometer; The first single-mode optical fiber is used to receive the detection light signal introduced through the third port, and transmit the detection light signal to the first hollow-core optical fiber; wherein, during the transmission process, a part of the detection light signal is reflected back to the first single-mode optical fiber through the first reflection surface to obtain a first reflected light signal; another part of the detection light signal is transmitted through the first reflection surface, and is reflected back to the first single-mode optical fiber through the second reflection surface in the first optical fiber Fabry-Perot interferometer to obtain a second reflected light signal; The first single-mode optical fiber is also used to transmit a first reflected signal to the optical fiber coupler via a third port; the first reflected signal includes: a first reflected light signal and a second reflected light signal.

5. The optical fiber microcavity magnetic field measuring device with vernier sensitization according to claim 3, characterized in that: The reference optical fiber microcavity comprises a second single-mode optical fiber, a second hollow-core optical fiber and a third single-mode optical fiber which are fused in sequence; the second single-mode optical fiber is connected to the fourth port; The end of the third single-mode optical fiber is cut at an angle of 45 degrees to 60 degrees; The fusion surface of the second single-mode optical fiber and the second hollow-core optical fiber is a third reflection surface; the fusion surface of the second hollow-core optical fiber and the third single-mode optical fiber is a fourth reflection surface; the third reflection surface and the fourth reflection surface constitute a second optical fiber Fabry-Perot interferometer; the second optical fiber Fabry-Perot interferometer has no response to changes in the external magnetic field; The second single-mode optical fiber is used to receive the detection light signal introduced through the fourth port, and transmit the detection light signal to the second hollow-core optical fiber; wherein, during the transmission process, a part of the detection light signal is reflected back to the second single-mode optical fiber through the third reflection surface to obtain a third reflected light signal; another part of the detection light signal is transmitted through the third reflection surface, and is reflected back to the second single-mode optical fiber through the fourth reflection surface in the second optical fiber Fabry-Perot interferometer to obtain a fourth reflected light signal; The second single-mode optical fiber is also used to transmit the second reflected signal to the optical fiber coupler via the fourth port; the second reflected signal includes: a third reflected light signal and a fourth reflected light signal.

6. The optical fiber microcavity magnetic field measuring device with vernier sensitization according to claim 4, characterized in that: The cavity length of the magnetic fluid cavity ranges from 100 microns to 150 microns.

7. A method for measuring magnetic field of an optical fiber microcavity with vernier sensitization, characterized in that: The vernier-sensitized optical fiber microcavity magnetic field measurement method is implemented by using the vernier-sensitized optical fiber microcavity magnetic field measurement device described in any one of claims 1 to 6; The vernier-sensitized optical fiber microcavity magnetic field measurement method comprises: Acquire a total reflected light signal; the total reflected light signal includes: a first reflected signal and a second reflected signal; The total reflected light signal is demodulated, and magnetic field measurement is achieved based on the optical vernier effect theory; the magnetic field intensity response is used to characterize the relationship between the wavelength drift of the vernier spectrum envelope and the external magnetic field intensity; the vernier spectrum envelope is determined based on the total reflected light signal.

8. The method for measuring magnetic field of an optical fiber microcavity with vernier sensitization according to claim 7, characterized in that: The total reflected light signal is demodulated, and magnetic field measurement is achieved based on the optical vernier effect theory, specifically including: A four-beam interference model is used to determine the reflection spectrum according to the total reflected light signal; the four-beam interference model includes: a reflection spectrum function; determining the magnetic field intensity response of the sensing optical fiber microcavity according to the reflection spectrum; Determining a vernier spectrum envelope based on the reflection spectrum; the vernier spectrum envelope changes periodically; Determining a vernier sensitization factor; the vernier sensitization factor is determined based on a free spectral range of the vernier spectral envelope; The magnetic field intensity response of the vernier spectrum envelope is determined according to the vernier sensitization factor and the magnetic field intensity response of the sensing optical fiber microcavity.

9. The method for measuring magnetic field of an optical fiber microcavity with vernier sensitization according to claim 8, characterized in that: The expression of the reflectance spectrum function specifically includes: I sensor =I1+I2; I1=A 2 +B 2 +2ABcos(2Φ1); I2=C 2 +D 2 +2CDcos(2Φ2); Among them, I sensor is the reflection spectrum function; I1 is the reflection spectrum function of the sensing fiber microcavity; I2 is the reflection spectrum function of the reference fiber microcavity; A is the mathematical expression corresponding to the first reflection surface; B is the mathematical expression corresponding to the second reflection surface; Φ1 is the phase difference between the first reflected light signal and the second reflected light signal in the first Fabry-Perot interferometer cavity; C is the mathematical expression corresponding to the third reflection surface; D is the mathematical expression corresponding to the fourth reflection surface; Φ2 is the phase difference between the third reflected light signal and the fourth reflected light signal in the second Fabry-Perot interferometer cavity.

10. The method for measuring magnetic field of an optical fiber microcavity with vernier sensitization according to claim 8, characterized in that: The expression of the magnetic field intensity response of the cursor spectrum envelope is: Dl sensor =M·Δλ=M·3(1-υ)r 4 ·μ0mL MF c·H / 16Eh 3 ; Among them, Δλ sensor is the wavelength drift of the vernier spectrum envelope; M is the vernier sensitization factor; Δλ is the wavelength drift of the corresponding reflection spectrum in the magnetic field intensity response of the sensing optical fiber microcavity; υ is the Poisson's ratio of the first UV film; r is the film radius of the first UV film; μ0 is the vacuum magnetic permeability; m is the magnetization intensity of the magnetic fluid; L MF is the cavity length of the magnetic fluid cavity; c is the concentration of the magnetic fluid; H is the external magnetic field intensity; E is the Young's modulus of the first UV adhesive film; h is the film thickness of the first UV adhesive film.

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