A fiber-optic magnetic field sensor based on NV color center infrared absorption detection

Abstract

The application discloses a kind of NV color center infrared absorption detection based optical fiber magnetic field sensor, including first diamond crystal and the second diamond crystal being arranged below first diamond crystal, the right side of second diamond crystal is provided with second circulator, the right side of second circulator is provided with second optical fiber filter, the right side of second optical fiber filter is provided with second data processing module, the top of second data processing module is provided with 1042nm laser light source, the top of 1042nm laser light source is provided with 532nm laser light source, the left side central part of 532nm laser light source and 1042nm laser light source is provided with 3dB optical fiber coupler, the top of 3dB optical fiber coupler is provided with first optical fiber filter, the left side of first optical fiber filter is provided with first circulator, the right side of first optical fiber filter is provided with first data processing module.The NV color center infrared absorption detection based optical fiber magnetic field sensor provided by the application has high sensitivity, high photon detection efficiency and can realize magnetic field measurement.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical fiber sensing technology, and particularly to an optical fiber magnetic field sensor based on NV color center infrared absorption detection. BACKGROUND

[0002] At present, the magnetic field sensors based on NV color center spin state fluorescence detection have problems of low photon detection efficiency and background fluorescence interference, and even if the photon collection capacity is improved, the sensitivity cannot reach a high level.

[0003] In order to solve these problems, the method of measuring the magnetic field by detecting the intensity of the fluorescence emitted by the NV color center is changed to the method of measuring the magnetic field by detecting the absorption degree of the infrared light by the NV color center, and this method based on NV color center infrared absorption detection has the advantages of high photon detection efficiency and high measurement sensitivity. SUMMARY

[0004] The purpose of the present application is to provide an optical fiber magnetic field sensor based on NV color center infrared absorption detection, which has high sensitivity, high photon detection efficiency and can realize magnetic field measurement.

[0005] In order to achieve the above-mentioned purpose, the present application provides an optical fiber magnetic field sensor based on NV color center infrared absorption detection, comprising a first diamond crystal and a second diamond crystal arranged below the first diamond crystal, a second circulator is arranged on the right side of the second diamond crystal, a second optical fiber filter is arranged on the right side of the second circulator, a second data processing module is arranged on the right side of the second optical fiber filter, a 1042nm laser light source is arranged above the second data processing module, a 532nm laser light source is arranged above the 1042nm laser light source, a 3dB optical fiber coupler is arranged on the left central part of the 532nm laser light source and the 1042nm laser light source, a first optical fiber filter is arranged above the 3dB optical fiber coupler, a first circulator is arranged on the left side of the first optical fiber filter, and a first data processing module is arranged on the right side of the first optical fiber filter.

[0006] Preferably, the first diamond crystal is provided with a microwave source at the middle part of the second diamond crystal, the microwave source is connected with a microwave waveguide, and the microwave waveguide is wound on the first diamond crystal and the second diamond crystal.

[0007] Preferably, permanent magnets are symmetrically arranged on the upper and lower sides of the first diamond crystal and the second diamond crystal.

[0008] Preferably, the right end of the first diamond crystal is connected with the left end of the first circulator through a first tail fiber, the right end of the first circulator is connected with the left end of the first fiber filter through a third tail fiber, and the right end of the first fiber filter is connected with the left end of the first data processing module through a fifth tail fiber.

[0009] Preferably, the right end of the second diamond crystal is connected with the left end of the second circulator through a second tail fiber, the right end of the second circulator is connected with the left end of the second fiber filter through a fourth tail fiber, and the right end of the second fiber filter is connected with the left end of the second data processing module through a sixth tail fiber.

[0010] Preferably, the lower end of the first circulator is connected with the left end of the 3dB fiber coupler through a seventh tail fiber, the upper end of the second circulator is connected with the left end of the 3dB fiber coupler through an eighth tail fiber, and the eighth tail fiber is below the seventh tail fiber.

[0011] Preferably, the right end of the 3dB fiber coupler is connected with the left end of the 532nm laser light source through a ninth tail fiber, and the right end of the 3dB fiber coupler is connected with the left end of the 1042nm laser light source through a tenth tail fiber, and the tenth tail fiber is below the ninth tail fiber.

[0012] Preferably, a layer of metal film is coated on the five side surfaces of the first diamond crystal and the second diamond crystal.

[0013] Preferably, the microwave waveguide is a copper wire.

[0014] Therefore, the optical fiber magnetic field sensor based on NV color center infrared absorption detection has the following beneficial effects:

[0015] (1) The present application measures the magnetic field by detecting the absorption of 1042nm infrared light by the NV color center. In the traditional method of measuring the magnetic field by detecting the fluorescence emitted by the NV color center, the light intensity of the fluorescence emitted by the NV color center is small and the degree of change with the magnetic field is small. In the scheme of measuring the magnetic field based on the infrared absorption of the NV color center, the light intensity of the outgoing light is large and the degree of change with the magnetic field is large, so high photon detection efficiency and high sensitivity of the magnetic field measurement can be achieved.

[0016] (2) The present application divides the laser emitted by the 532nm laser light source and the 1042nm laser light source into two beams with equal intensity through the 3dB fiber coupler, and transmits them to the sensing path and the comparison path respectively, which can eliminate the error caused by the instability of the laser power, and can obtain an infrared light emission rate magnetic resonance spectrum with higher contrast than the traditional fluorescence light detection magnetic resonance spectrum.

[0017] (3) The application obtains the absorption rate of the NV color center to the 1042nm infrared light by comparing the exit light intensity of the sensing path with that of the contrast path, wherein the first diamond crystal in the sensing path is treated by plasma injection to generate NV color center in the preparation of the NV color center, and the second diamond crystal in the contrast path is not treated by plasma injection and does not generate NV color center in the preparation of the NV color center, so that the exit light of the sensing path after filtering is the infrared light after absorption by the NV color center, and the exit light of the contrast path after filtering is the infrared light without absorption by the NV color center, and the ratio of the exit light intensity of the two paths is the exit rate of the infrared light through the diamond crystal, which can significantly reflect the absorption degree of the NV color center to the infrared light.

[0018] (4) The application fixes the diamond crystal by pasting a multimode optical fiber (i.e. the first and second tail fibers) at one end of the diamond crystal, and the probe-type magnetic field sensor is easy to operate and convenient for measuring the magnetic field at different positions.

[0019] (5) The application coats a metal film with a suitable thickness on the side surface and the external end surface of the first and second diamond crystals, so that the laser can be reflected on the side surface and the external end surface of the diamond crystal, which can increase the length of the laser and the diamond NV color center interaction path and improve the collection efficiency of the exit light.

[0020] (6) The application converts the change of the 1042nm infrared light intensity in the exit light which is not easy to observe into the change of the photovoltage which is easy to observe by the data processing module.

[0021] The technical solutions of the application will be further described in detail below with reference to the drawings and embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of the optical fiber magnetic field sensor based on the NV color center infrared absorption detection of the application;

[0023] Figure 2 It is a schematic diagram of the light passing through the diamond crystals of the sensing path and the contrast path of the embodiment of the optical fiber magnetic field sensor based on the NV color center infrared absorption detection of the application;

[0024] Figure 3 It is a schematic diagram of the NV color center energy level of the application;

[0025] Figure 4 It is a structural schematic diagram of the sensing part of the sensing path and the contrast path of the application;

[0026] Figure 5 It is a flowchart of the processing module of the application;

[0027] REFERENCE NUMERALS

[0028] 1. First diamond crystal; 2. First pigtail; 3. First circulator; 4. Third pigtail; 5. First fiber optic filter; 6. Fifth pigtail; 7. First data processing module; 8. 532nm laser source; 9. 1042nm laser source; 10. Seventh pigtail; 11. 3dB fiber optic coupler; 12. Ninth pigtail; 13. Eighth pigtail; 14. Tenth pigtail; 15. Second data processing module; 16. Sixth pigtail; 17. Second fiber optic filter; 18. Fourth pigtail; 19. Second circulator; 20. Second pigtail; 21. Second diamond crystal; 22. Microwave waveguide; 23. Microwave source; 24. Fiber core; 25. Cladding; 26. 532nm laser; 27. 1042nm laser; 28. Fluorescence; 29. ​​Sensing path; 30. Contrast path; 31. Metal thin film; 32. Adhesive; 33. Permanent magnet; 34. Microwave. Detailed Implementation

[0029] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0031] Example

[0032] like Figure 1 As shown, the present invention provides an optical fiber magnetic field sensor based on infrared absorption detection of NV color centers, including a first diamond crystal 1 and a second diamond crystal 21 disposed below the first diamond crystal 1. The first diamond crystal 1 is processed by mask curing, ion implantation, vacuum annealing and impurity cleaning to generate NV color centers, while the second diamond crystal 21 is not processed by ion implantation and does not generate NV color centers. Thus, the ratio of the intensity of 1042nm infrared light collected from the emitted light of the two diamond crystals is the emissivity of 1042nm infrared light.

[0033] A microwave source 23 is positioned at the midpoint between the first diamond crystal 1 and the second diamond crystal 21. The microwave source 23 is connected to a microwave waveguide 22, which is made of copper wire. The microwave waveguide 22 is wound in a rotating manner around the first and second diamond crystals 1 and 21, transmitting the microwaves emitted by the microwave source 23 to the vicinity of the diamond crystals. Permanent magnets 33 are symmetrically placed on both the upper and lower sides of the first and second diamond crystals 1 and 21 to apply a bias magnetic field and eliminate the influence of internal stress on the NV color center.

[0034] The right side of the second diamond crystal 21 is provided with a second circulator 19, the right end of the second diamond crystal 21 is connected with the left end of the second circulator 19 through a second tail fiber 20, the right side of the second circulator 19 is provided with a second fiber filter 17, the right end of the second circulator 19 is connected with the left end of the second fiber filter 17 through a fourth tail fiber 18, the right side of the second fiber filter 17 is provided with a second data processing module 15, the right end of the second fiber filter 17 is connected with the left end of the second data processing module 15 through a sixth tail fiber 16, the upper side of the second data processing module 15 is provided with a 1042nm laser source 9, the 1042nm laser 27 emitted by the 1042nm laser source 9 will be absorbed by the metastable state 1 E of the electron and jump to the singlet state 1 A1, by detecting the absorption of the diamond NV color center to the 1042nm infrared light, the magnetic field can be measured. The upper side of the 1042nm laser source 9 is provided with a 532nm laser source 8, the 532nm laser 26 emitted by the 532nm laser source 8 can make the electron in the diamond NV color center mainly in the ground state 3 A2 in the form of |m s =0> spin state and metastable state 1 E.

[0035] The left side of the central part of the 532nm laser source 8 and the 1042nm laser source 9 is provided with a 3dB fiber coupler 11, the right end of the 3dB fiber coupler 11 is connected with the left end of the 532nm laser source 8 through a ninth tail fiber 12, the right end of the 3dB fiber coupler 11 is connected with the left end of the 1042nm laser source 9 through a tenth tail fiber 14, and the tenth tail fiber 14 is located below the ninth tail fiber 12. The 532nm laser 26 and the 1042nm laser 27 emitted by the 532nm laser source 8 and the 1042nm laser source 9 will be divided into two beams with equal intensity through the 3dB fiber coupler 11 and transmitted to the first diamond crystal 1 and the second diamond crystal 21 through the optical fiber, and then enter the diamond crystal in a coupled manner. This scheme of using a fiber coupler to divide the laser emitted by the laser source into two beams can eliminate the error caused by the instability of the laser power, and can obtain a higher infrared light emission rate magnetic resonance spectrum than the contrast of the traditional fluorescence magnetic resonance spectrum.

[0036] The upper part of the 3dB optical fiber coupler 11 is provided with a first optical fiber filter 5, the left side of the first optical fiber filter 5 is provided with a first circulator 3, the right end of the first circulator 3 is connected with the left end of the first optical fiber filter 5 through a third tail fiber 4, the right side of the first optical fiber filter 5 is provided with a first data processing module 7, the right end of the first optical fiber filter 5 is connected with the left end of the first data processing module 7 through a fifth tail fiber 6, the first data processing module 7 and the second data processing module 15 will convert the change of the 1042nm infrared light intensity emitted from the diamond crystal and passing through the optical fiber filter into the change of the photocurrent first, and then into the change of the photovoltage, and finally collect the photovoltage signal. The right end of the first diamond crystal 1 is connected with the left end of the first circulator 3 through a first tail fiber 2, the lower end of the first circulator 3 is connected with the left end of the 3dB optical fiber coupler 11 through a seventh tail fiber 10, the upper end of the second circulator 19 is connected with the left end of the 3dB optical fiber coupler 11 through an eighth tail fiber 13, and the eighth tail fiber 13 is located below the seventh tail fiber 10.

[0037] A layer of metal film 31 is coated on the five sides of the first diamond crystal 1 and the second diamond crystal 21, and the first diamond crystal 1 and the second diamond crystal 21 are fixed by being pasted with a multimode optical fiber (i.e., the first tail fiber 2 and the second tail fiber 20) on one side. The probe type magnetic field sensor is easy to operate, convenient for measuring the magnetic field at different positions, and a layer of film with a suitable thickness is coated on the remaining surfaces to allow light to be reflected, so that the length of the laser and the diamond NV color center interaction path can be increased and the collection efficiency of the emitted light can be improved.

[0038] The principle of the technical scheme of the application is as follows:

[0039] The electron of the NV color center has three spin states of |m s = 0> and |m s = ±1>, the electron of the NV color center can keep spin state conservation from the ground state 3 A2 to the excited state 3 E, keep spin state conservation from the excited state 3 E to the ground state 3 A2. And in the process of de-excitation, the electron with the spin state of |m s = ±1> can keep spin state conservation by the ISC (intersystem crossing) mechanism to the singlet state 1 A1, then the singlet state 1 A1 emits 1042nm infrared light and jumps to the metastable state 1 E, and finally the metastable state 1 E de-excites back to the ground state 3 A2. Since the NV color center in the ground state 3A2 has lower electron energy and is in a metastable state. 1 Electrons in the electron configuration have a lifetime of 200 ns at room temperature; therefore, under continuous excitation by a 532 nm laser, electrons in the NV color center are primarily in the ground state. 3 The spin state of A2 is |m s =0> or in a metastable state 1 E

[0040] like Figure 2 As shown, this invention uses the infrared absorption detection of diamond NV centers to obtain the infrared emissivity magnetic resonance spectrum measurement magnetic field by comparing the intensity of the 1042nm infrared light emitted from the sensing path with the intensity of the 1042nm infrared light emitted from the upper and lower paths. Microwaves 34 are uniformly distributed above and below the diamond crystal (including the first diamond crystal 1 and the second diamond crystal 21). A 532nm laser 26 and a 1042nm laser 27 are transmitted through the fiber core 24 and coupled into the diamond crystal. The first diamond crystal 1 (which has undergone ion implantation treatment and contains NV centers) absorbs the 1042nm laser 27 under the action of the 532nm laser 6 and microwaves 34 and emits fluorescence 28. The 1042nm laser 27 and fluorescence 28 are collected and transmitted through the fiber core 24. The fiber core 24 and the cladding 25 surrounding the fiber core 24 together constitute the pigtail fiber, and the cladding 25 protects the inner fiber core 24. Because a thin metal film 31 is coated on the side of the diamond crystal, light can be reflected, thereby increasing the path length and improving the light collection efficiency.

[0041] like Figure 3 As shown, the 532nm laser 26 and 1042nm laser 27 emitted by the 532nm laser source 8 and 1042nm laser source 9, respectively, are transmitted to the 3dB fiber coupler 11 and split into two laser beams of equal intensity, which are then transmitted to the first diamond crystal 1 and the second diamond crystal 21, respectively. The 532nm laser 26 can adjust the energy level of electrons in the NV center, while the 1042nm laser 27 can be kept in a metastable state in the NV center. 1 E absorbs an electron and transitions to a singlet state. 1 A1.

[0042] The two beams of light emitted from the first diamond crystal 1 and the second diamond crystal 21 are respectively filtered out by the first fiber optic filter 5 and the second fiber optic filter 17, removing all light except for the 1042nm infrared light. The two beams of light after passing through the fiber optic filters are then respectively... Figure 5 The first data processing module 7 and the second data processing module 15 shown absorb and convert the data into a photovoltage signal and collect it into a computer.

[0043] In the absence of external magnetic field, the NV color center is continuously pumped by 532nm and 1042nm laser and swept by microwave, and the absorption of 1042nm infrared light in the outgoing light is detected, because the electron in the metastable state 1 E of the NV color center can absorb 1042nm infrared light to jump to singlet state 1 A1, and the electron in the metastable state 1 E comes from the electron with spin state |m s =±1> through ISC mechanism and de-excitation, so when the frequency of the microwave is equal to the energy level difference between the electron with spin state |m 3 =0> and |m s =±1> in the ground state s A2, the electron with spin state |m 3 =0> in the ground state s A2 is regulated to |m s =±1> by the microwave, at this time the population of the electron with spin state |m 3 =±1> in the ground state s A2 increases, and then the number of the electron in the metastable state 1 E also increases through ISC mechanism de-excitation, so that the absorption of 1042nm infrared light by the NV color center is enhanced, and in addition, the energy level of the electron with spin state |m 3 =±1> in the ground state s A2 will be split due to Zeeman effect under the action of the bias magnetic field, so two recesses will appear on the microwave sweep spectrum of the outgoing rate of 1042nm infrared light.

[0044] In the presence of external magnetic field, the energy level of the |m s =±1> state of the NV color center will be further split due to Zeeman effect, and the distance between the two recesses in the magnetic resonance spectrum of the outgoing rate of infrared light obtained by the NV color center under the action of continuous 532nm and 1042nm laser and microwave will increase, and the size of the magnetic field at the sensor can be obtained by solving the Hamiltonian equation according to the difference between the microwave frequencies of the two recesses on the spectrum.

[0045] According to the above principle and structure, the present application can be realized in the following ways:

[0046] In order to obtain the outgoing rate of 1042nm infrared light, the diamond crystal for the sensing path and the comparison path is designed and prepared, the diamond crystal for the sensing path is treated by ion implantation, the diamond crystal for the comparison path is not treated by ion implantation, and a thin film with appropriate thickness is plated on the side surface and the external end surface of the diamond crystal, and finally the prepared diamond crystal is connected to the magnetic field sensing system, as shown in Figure 1 The specific operation steps are as follows:

[0047] S1. Select two pieces of diamond crystal with appropriate thickness and end surface area. First, fix the diamond crystal on the glue spreader by vacuum suction and drop the appropriate amount of mask glue on its surface. A uniform mask layer can be obtained on the surface of the diamond crystal by the selective centrifugal treatment of the glue spreader. Then, heat the sample by the drying machine to solidify the mask. Finally, draw the designed mask pattern on the mask by the photoetching machine.

[0048] S2. Perform nitrogen ion implantation on the diamond crystal for the sensing path by the ion implanter, and do not perform ion implantation on the diamond crystal for the comparison path.

[0049] S3. Perform vacuum annealing on the sample by the vacuum annealing equipment. First, perform vacuum treatment by the equipment, then slowly heat the equipment to a high temperature and keep it for a period of time, and finally slowly cool the equipment to room temperature.

[0050] S4. Clean the organic impurities on the surface of the sample by the organic solution, and clean the inorganic impurities on the surface of the sample by the acidic solution.

[0051] S5. Coat a thin film with appropriate thickness on the side of the diamond crystal by the coating machine.

[0052] S6. Uniformly apply a high refractive index adhesive to one side of each of the two diamond crystals, and stick the first fiber tail 2 to one side of the first diamond crystal 1 for the sensing path, and stick the second fiber tail 20 to one side of the second diamond crystal 21 for the comparison path, as shown in Figure 4 .

[0053] S7. Select a piece of copper wire with appropriate length and thickness as the microwave waveguide 22, connect the microwave waveguide 22 to the microwave source 23, and then uniformly wrap several turns of the microwave waveguide 22 on the first diamond crystal 1 and the second diamond crystal 21, respectively.

[0054] S8. Place a pair of permanent magnets 24 on the upper and lower sides of the first diamond crystal 1 and the second diamond crystal 21, respectively.

[0055] After the above steps are completed,

[0056] Turn on the 532 nm laser light source 1, the 1042 nm laser light source 2, and the microwave source 23. While sweeping the microwave frequency on the first diamond crystal 1 and the second diamond crystal 21, receive the exit light filtered by the fiber filter on the sensing path and the comparison path by the first data processing module 8 and the second data processing module 9, respectively, convert it into a photovoltage signal, and collect it into the computer. Plot the collected data as an infrared light exit rate magnetic resonance spectrum. According to the difference in microwave frequency between the two depressions on the spectrum, solve the Hamiltonian equation, and obtain the magnetic field strength at the sensor.

[0057] Therefore, the application adopts the above structure to provide an optical fiber magnetic field sensor based on NV color center infrared absorption detection, which has high sensitivity, high photon detection efficiency and can realize magnetic field measurement.

[0058] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, but not to limit them. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can still be modified or replaced by equivalents, and these modifications or replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A fiber-optic magnetic field sensor based on NV color center infrared absorption detection, characterized by: The first diamond crystal and the second diamond crystal are provided below the first diamond crystal, the right side of the second diamond crystal is provided with a second circulator, the right side of the second circulator is provided with a second fiber filter, the right side of the second fiber filter is provided with a second data processing module, the upper side of the second data processing module is provided with a 1042nm laser light source, the upper side of the 1042nm laser light source is provided with a 532nm laser light source, the left central part of the 532nm laser light source and the 1042nm laser light source is provided with a 3dB fiber coupler, the upper side of the 3dB fiber coupler is provided with a first fiber filter, the left side of the first fiber filter is provided with a first circulator, the right side of the first fiber filter is provided with a first data processing module, and a layer of metal film is coated on the five sides of the first diamond crystal and the second diamond crystal.

2. The fiber-optic magnetic field sensor based on NV color center infrared absorption detection according to claim 1, characterized in that: The first diamond crystal is provided with a microwave source away from the middle part of the second diamond crystal, and the microwave source is connected with a microwave waveguide.

3. The fiber-optic magnetic field sensor based on NV color center infrared absorption detection according to claim 2, characterized in that: The upper and lower sides of the first diamond crystal and the second diamond crystal are symmetrically provided with permanent magnets.

4. The fiber-optic magnetic field sensor based on NV color center infrared absorption detection according to claim 3, characterized in that: The right end of the first diamond crystal is connected with the left end of the first circulator through a first tail fiber, the right end of the first circulator is connected with the left end of the first fiber filter through a third tail fiber, and the right end of the first fiber filter is connected with the left end of the first data processing module through a fifth tail fiber.

5. The fiber-optic magnetic field sensor based on NV color center infrared absorption detection according to claim 4, characterized in that: The right end of the second diamond crystal is connected with the left end of the second circulator through a second tail fiber, the right end of the second circulator is connected with the left end of the second fiber filter through a fourth tail fiber, and the right end of the second fiber filter is connected with the left end of the second data processing module through a sixth tail fiber.

6. The fiber-optic magnetic field sensor based on NV color center infrared absorption detection according to claim 5, characterized in that: The lower end of the first circulator is connected with the left end of the 3dB fiber coupler through a seventh tail fiber, the upper end of the second circulator is connected with the left end of the 3dB fiber coupler through an eighth tail fiber, and the eighth tail fiber is located below the seventh tail fiber.

7. The fiber-optic magnetic field sensor based on NV color center infrared absorption detection according to claim 6, characterized in that: The right end of the 3dB fiber coupler is connected with the left end of the 532nm laser light source through a ninth tail fiber, and the right end of the 3dB fiber coupler is connected with the left end of the 1042nm laser light source through a tenth tail fiber, and the tenth tail fiber is located below the ninth tail fiber.

8. The fiber-optic magnetic field sensor based on NV color center infrared absorption detection according to claim 7, characterized in that: The microwave waveguide is a copper wire.

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