A high-efficiency fiber optic magnetic field sensor based on diamond NV color centers

Abstract

This invention belongs to the field of fiber optic sensor technology and discloses a high-efficiency fiber optic magnetic field sensor based on diamond NV centers. The sensor includes a laser source, an optical path mechanism, a bias permanent magnet, a magnetic field fiber optic sensing mechanism, a microwave waveguide mechanism, a first receiving and conversion mechanism, a second receiving and conversion mechanism, and a third receiving and conversion mechanism. Using this high-efficiency fiber optic magnetic field sensor based on diamond NV centers, the laser emitted by the laser source illuminates the diamond NV center solution injected into the magnetic field fiber optic sensing mechanism through the optical path mechanism. The resulting fluorescence is received by the first and second receiving and conversion mechanisms in a coupled manner, and simultaneously, the generated fluorescence is reflected by the optical path mechanism and received by the third receiving and conversion mechanism. This invention utilizes the coupling between the optical fiber and the diamond NV centers to improve the sensitivity of magnetic field measurement, and the three-path light-receiving scheme improves the fluorescence collection efficiency.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensor technology, and in particular to a high-efficiency fiber optic magnetic field sensor based on diamond NV color centers. Background Technology

[0002] Normally, crystals with regularly arranged atoms do not emit light. However, in reality, the atoms in a crystal can vibrate, creating defects that disrupt the periodicity of the atomic arrangement. This alters the optical properties of the crystal, allowing it to selectively absorb certain wavelengths of visible light and emit detectable fluorescence. These defective sites in a crystal that absorb visible light and emit fluorescence are called color centers. NV color centers are short for nitrogen vacancy luminescent centers. They are formed by replacing a carbon atom with an nitrogen atom in the diamond lattice, creating an nitrogen substitution site, which is then connected to a carbon vacancy lacking a carbon atom.

[0003] Electrons in the NV color center in the ground state 3 A and excited state 3 E contains |m s =0> and |m s =±1> These three spin states, the spin state is |m s Electrons with a wavelength of 0 can be excited from the ground state 3A to the excited state by a pump laser with a wavelength of 532 nm. 3 E, then de-excited back to the ground state. 3 A emits fluorescence, with a spin state of |m s Electrons with a wavelength of ±1 can be drawn from their ground state by a pump laser with a wavelength of 532 nm. 3 A is excited to the excited state. 3 E, during de-excitation, some electrons will directly return to the ground state. 3 A emits fluorescence, and some electrons pass through the singlet state via the ISC (intersystem crossing) mechanism. 1 A, and 1 E returns to the ground state. 3 A, and this process does not emit fluorescence; this is the pathway by which the NV center converts the pump laser into fluorescence. Because the spin state in the NV center is |m s The probability of emitting a fluorescent photon when an electron de-excited by a state with a spin of 0> is higher than that of a spin state with a spin of |m>. s =±1> electrons are large, therefore |m s =0> state is called bright state, |m s The state with ±1 is called the dark state.

[0004] In the absence of an external magnetic field, |m in the ground state of the NV color center sThe electronic energy levels of =±1> are degenerate, and the spin state is |m s =0> and |m s The electron energy level difference between ±1 is 2.87 GHz. When measuring the optically detected magnetic resonance (ODMR) spectrum of the NV center, continuous laser pumping and microwave frequency sweeping are required, along with measuring the intensity of fluorescence emitted by the NV center. When the microwave frequency is 2.87 GHz and the spin state is |m... s =0> and |m s When the energy level difference between electrons with values ​​of ±1 is equal, the spin state is |m s Electrons with a spin state greater than 0 will have their spin state modulated by microwaves to |m s =±1>, because the number of bright electrons and the number of dark electrons in the NV center decreases, the intensity of fluorescence emitted by the NV center under pump laser excitation decreases, resulting in a dip at the microwave frequency of 2.87 GHz in the photodetector magnetic resonance spectrum. In the presence of an external magnetic field, the spin state in the ground state of the NV center is |m s The energy levels of electrons with a spin of ±1 will split due to the Zeeman effect, resulting in a spin state of |m s =0> and |m s The energy difference between electrons with the value = +1> will be greater than 2.87 GHz, and the spin state will be |m s =0> and |m s The energy level difference between electrons with the value =-1> will be less than 2.87 GHz. Therefore, under the excitation of the pump laser, the depression on the photodetector magnetic resonance spectrum of the NV color center will change from one to two, located at two positions with microwave frequencies less than 2.87 GHz and greater than 2.87 GHz, respectively. The magnitude of the magnetic field can be obtained by solving the Hamiltonian equation based on the difference in microwave frequencies between the two depressions.

[0005] Existing fiber optic magnetic field sensors have low sensitivity, large size, and are not convenient for magnetic field measurement. Summary of the Invention

[0006] The purpose of this invention is to solve the problems existing in the prior art.

[0007] To achieve the above objectives, the present invention provides a high-efficiency fiber optic magnetic field sensor based on diamond NV color centers, comprising a laser light source, an optical path mechanism, a bias permanent magnet, a magnetic field fiber optic sensing mechanism, a microwave waveguide mechanism, a first receiving and conversion mechanism, a second receiving and conversion mechanism, and a third receiving and conversion mechanism.

[0008] The laser light source is positioned opposite to the optical path mechanism. One end of the optical path mechanism is positioned opposite to the third receiving and conversion mechanism, and the other end of the optical path mechanism is positioned opposite to the magnetic field fiber optic sensing mechanism. Bias permanent magnets are provided on the upper and lower sides of the magnetic field fiber optic sensing mechanism.

[0009] The magnetic field fiber optic sensing mechanism is connected to the first receiving and conversion mechanism and the second receiving and conversion mechanism respectively on both sides via magnetic field sensing fibers, and the magnetic field sensor fiber is connected to the microwave waveguide mechanism.

[0010] The laser emitted by the laser source shines on the magnetic field fiber optic sensing mechanism through the optical path mechanism, exciting the diamond solution with NV color centers in the magnetic field fiber optic sensing mechanism to produce fluorescence. Part of the fluorescence is received by the first receiving and conversion mechanism and the second receiving and conversion mechanism respectively in a coupled manner, and the other part of the fluorescence is reflected by the optical path mechanism and received by the third receiving and conversion mechanism.

[0011] Preferably, the first receiving and conversion mechanism includes a first optical fiber filter, a first pigtail, and a first single-photon counting module connected in sequence.

[0012] Preferably, the second receiving and conversion mechanism includes a second fiber optic filter, a second pigtail, and a second single-photon counting module connected in sequence.

[0013] Preferably, the third receiving and conversion mechanism includes a filter, a third lens, and a third single-photon counting module arranged sequentially.

[0014] Preferably, the optical path mechanism includes an objective lens, a first reflecting mirror, a first lens, a second lens, a second reflecting mirror, and a dichroic mirror arranged in sequence, with the dichroic mirror positioned opposite to the laser light source.

[0015] Preferably, the magnetic field fiber optic sensing mechanism includes a hollow optical fiber and single-mode optical fibers disposed at both ends of the hollow optical fiber. The two single-mode optical fibers are respectively connected to a first fiber optic filter and a second fiber optic filter, and the hollow optical fiber is disposed opposite to the objective lens.

[0016] Preferably, the microwave waveguide mechanism includes a microwave waveguide and a microwave source, the microwave source being connected to the microwave waveguide, and the microwave waveguide being wound on a hollow optical fiber. The microwave waveguide is made of copper wire.

[0017] Therefore, the present invention has the following beneficial effects:

[0018] (1) It realizes the ability to receive the fluorescence generated by the excitation of diamond solution with NV color center by coupling into the optical fiber, which improves the efficiency of fluorescence collection and the sensitivity of the sensor to measure the magnetic field. At the same time, a third receiving and conversion mechanism is set up to further improve the fluorescence receiving efficiency.

[0019] (2) The design of the optical path mechanism: the first lens and the second lens form a lens group to expand the laser beam emitted by the laser source, which can improve the filling rate of the laser when it passes through the objective lens, reduce the light spot on the hollow optical fiber, and improve the efficiency of laser to fluorescence conversion.

[0020] (3) The pump laser and the fluorescence generated by the diamond solution with NV color center are transmitted by optical fiber. Copper wire is selected as microwave waveguide to transmit the microwave emitted by the microwave source to the vicinity of the magnetic field sensing optical fiber. The application of optical fiber and copper wire reduces the overall volume.

[0021] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0022] Figure 1 This is a structural diagram of a high-efficiency fiber optic magnetic field sensor based on diamond NV color centers;

[0023] Figure 2 This is a schematic diagram of a diamond solution with NV color centers that is excited by a laser and emits fluorescence according to the present invention.

[0024] Figure 3 For |m s =±1> Schematic diagram of the splitting of the degenerate energy levels of spin-state NV color center electrons due to the Zeeman effect;

[0025] Figure 4 This is a structural diagram of the magnetic field sensing optical fiber of the present invention;

[0026] Figure 5 This is a structural diagram of a single-photon counting module.

[0027] Figure Labels

[0028] 1. Magnetic field fiber optic sensing mechanism; 2. Objective lens; 3. First reflecting mirror; 4. First lens; 5. Second lens; 6. Second reflecting mirror; 7. Dichroic mirror; 8. Filter; 9. Third lens; 10. Third single-photon counting module; 11. Laser source; 12. Second fiber optic filter; 13. Second pigtail; 14. Second single-photon counting module; 15. Bias permanent magnet; 16. Microwave waveguide; 17. Microwave source; 18. First single-photon counting module; 19. First pigtail; 20. First fiber optic filter; 21. Nanodiamond; 22. Pump laser; 23. Microwave; 24. Fluorescence; 25. Hollow fiber; 26. Single-mode fiber. Detailed Implementation

[0029] Example

[0030] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed when in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0031] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," and "connect" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0032] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0033] refer to Figure 1A high-efficiency fiber optic magnetic field sensor based on diamond NV centers includes a laser source 11, an optical path mechanism, a bias permanent magnet 15, a magnetic field fiber optic sensing mechanism 1, a microwave waveguide mechanism, a first receiving and conversion mechanism, a second receiving and conversion mechanism, and a third receiving and conversion mechanism. The laser source 11 is positioned opposite to the optical path mechanism. The laser source 11 emits a 532nm wavelength laser light that can excite a diamond solution containing NV centers and generate fluorescence 24. The optical path mechanism includes an objective lens 2, a first reflecting mirror 3, a first lens 4, a second lens 5, a second reflecting mirror 6, and a dichroic mirror 7 arranged sequentially. The dichroic mirror 7 is positioned opposite to the laser source 11 and can reflect the laser light emitted by the laser source 11 while allowing the fluorescence 24 emitted by the NV centers to pass through. The focal length ratio of the first lens 4 and the second lens 5 is 2:1. These two lenses can form a lens group to expand the laser beam emitted by the laser source 11. After the laser beam is expanded, the fill rate when passing through the objective lens 2 will be higher, resulting in a smaller spot of laser light illuminating the magnetic field sensing fiber after being focused by the objective lens 2, thereby improving the efficiency of laser-to-fluorescence conversion 24. One end of the optical path mechanism is opposite to the third receiving and conversion mechanism, which includes a filter 8, a third lens 9, and a third single-photon counting module 10 arranged in sequence. The other end of the optical path mechanism is opposite to the magnetic field fiber sensing mechanism 1. The magnetic field fiber sensing mechanism 1 has bias permanent magnets 15 on its upper and lower sides to apply a bias magnetic field to eliminate the influence of internal stress of the diamond crystal on the NV color center. The magnetic field fiber sensing mechanism 1 is connected to the first receiving and conversion mechanism and the second receiving and conversion mechanism on both sides through magnetic field sensing fibers, respectively. The first receiving and conversion mechanism includes a first fiber filter 20, a first pigtail 19, and a first single-photon counting module 18 connected in sequence. The second receiving and conversion mechanism includes a second fiber optic filter 12, a second pigtail 13, and a second single-photon counting module 14 connected in sequence. The magnetic field sensor fiber optic cable is connected to the microwave waveguide mechanism. The laser emitted by the laser source 11 illuminates the magnetic field fiber optic sensing mechanism 1 through the optical path mechanism, exciting the diamond solution with NV color centers inside the magnetic field fiber optic sensing mechanism 1 to generate fluorescence 24. Part of the fluorescence 24 is received by the first receiving and conversion mechanism and the second receiving and conversion mechanism respectively in a coupled manner, and the other part of the fluorescence 24 is reflected by the optical path mechanism and received by the third receiving and conversion mechanism.

[0034] The magnetic field fiber optic sensing mechanism 1 includes a hollow optical fiber 25 and single-mode optical fibers 26 disposed at both ends of the hollow optical fiber 25. A section of hollow optical fiber approximately 5mm long is selected, and all coating is removed from this section. A portion of both ends of this section is cut off using a fiber optic cleaver to make the fiber end faces flat. Two single-mode optical fibers 26 approximately 20cm long are selected, and 3cm of coating is removed from both ends of these two single-mode optical fibers 26. First, one end of the hollow optical fiber 25 is welded to one of the single-mode optical fibers 26 using a fiber optic welding machine. Then, a diamond solution with NV color centers, which has undergone ultrasonic homogenization treatment, is filled into the hollow optical fiber 25 without leaving air bubbles using a fine dropper. Finally, the other end of the hollow optical fiber 25 is vertically welded to the other single-mode optical fiber 26 using a fiber optic welding machine, thus completing the fabrication of the magnetic field fiber optic sensing mechanism 1 and realizing the encapsulation of the diamond solution with NV color centers. Both ends of the single-mode fiber 26 are fitted with fiber optic connectors and connected to the first fiber optic filter 20 and the second fiber optic filter 12, respectively. The hollow fiber 25 is positioned opposite to the objective lens 2.

[0035] The microwave waveguide mechanism includes a microwave waveguide 16 and a microwave source 17. The microwave source 17 is connected to the microwave waveguide 16. A copper wire about 10cm long and 0.5mm thick is selected as the microwave waveguide 16, and the microwave waveguide 16 is evenly wound 10 turns on the hollow optical fiber.

[0036] Implementation principle as follows Figure 2 As shown, the laser emitted by the laser source 11 is reflected and then shines through the objective lens 2 onto the diamond NV center solution in the hollow optical fiber. This excites the diamond solution containing the NV centers in the hollow optical fiber, causing it to emit fluorescence 24. Part of the fluorescence 24 is coupled into the single-mode fibers 26 on both sides of the hollow optical fiber for transmission, and is finally received by the first single-photon counting module 18 and the second single-photon counting module 14, respectively. Another part of the fluorescence 24 is reflected by the objective lens 2 and received by the first single-photon counting module 18. In the absence of an external magnetic field, the |m of the NV centers... s =±1> states are degenerate. A dip appears in the photodetector magnetic resonance spectrum of the fluorescence emitted by the NV color center under continuous laser and microwave spin modulation. In the presence of an external magnetic field, the |m... s =±1>State as Figure 3 As shown, the NV color center will split due to the Zeeman effect. The fluorescence 24 emitted by the light detector magnetic resonance spectrum under continuous laser and microwave spin modulation will show two symmetrical depressions about the previous depression. The magnitude of the magnetic field at the sensor can be obtained by solving the Hamiltonian equation based on the difference in microwave frequency between the two depressions.

[0037] The laser source 11 and microwave source 17 are turned on. Simultaneously, while the magnetic field fiber optic sensing mechanism 1 performs a microwave frequency sweep, the fluorescence 24 emitted by the diamond solution containing the NV color center is received through the first single-photon counting module 18, the second single-photon counting module 14, and the third single-photon counting module 10. The structure of the single-photon counting module is as follows: Figure 5 As shown, the photomultiplier tube converts the received fluorescent 24 photons into photoelectron pulses. These photoelectron pulses are linearly amplified by an amplifier. A discriminator removes noise pulses from the amplified photoelectron pulses and shapes them into standard pulses. A counter counts the output standard pulses. Finally, the data acquisition card imports the time-related data obtained from the counter into a computer via a data cable. After data processing, the data is converted into a photodetector magnetic resonance spectrum related to microwave frequency. By solving the Hamiltonian equation based on the difference in microwave frequency between the two depressions in the obtained photodetector magnetic resonance spectrum, the magnitude of the magnetic field at the sensor can be obtained.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A high-efficiency optical fiber magnetic field sensor based on diamond NV color centers, characterized in that: The application relates to a laser light source, an optical path mechanism, a bias permanent magnet, a magnetic field optical fiber sensing mechanism, a microwave waveguide mechanism, a first receiving conversion mechanism, a second receiving conversion mechanism and a third receiving conversion mechanism. The laser light source is arranged opposite to the optical path mechanism, one end of the optical path mechanism is arranged opposite to the third receiving conversion mechanism, and the other end of the optical path mechanism is arranged opposite to the magnetic field optical fiber sensing mechanism; bias permanent magnets are arranged on the upper side and the lower side of the magnetic field optical fiber sensing mechanism. The magnetic field sensing optical fibers on the two sides of the magnetic field optical fiber sensing mechanism are connected with the first receiving conversion mechanism and the second receiving conversion mechanism respectively, and the magnetic field sensing optical fibers are connected with the microwave waveguide mechanism. Laser emitted by the laser light source is irradiated on the magnetic field optical fiber sensing mechanism through the optical path mechanism, and the fluorescent light generated by the diamond solution with NV color centers in the magnetic field optical fiber sensing mechanism is excited; a part of the fluorescent light is received by the first receiving conversion mechanism and the second receiving conversion mechanism in a coupling mode, and the other part of the fluorescent light is reflected by the optical path mechanism and received by the third receiving conversion mechanism. The optical path mechanism comprises an objective lens, a first reflector, a first lens, a second lens, a second reflector and a dichroic mirror which are sequentially arranged, and the dichroic mirror is arranged opposite to the laser light source.

2. The high-efficiency optical fiber magnetic field sensor based on diamond NV color centers according to claim 1, characterized in that: The first receiving conversion mechanism comprises a first optical fiber filter, a first tail fiber and a first single-photon counting module which are sequentially connected.

3. The high-efficiency optical fiber magnetic field sensor based on diamond NV color centers according to claim 2, characterized in that: The second receiving conversion mechanism comprises a second optical fiber filter, a second tail fiber and a second single-photon counting module which are sequentially connected.

4. The high-efficiency optical fiber magnetic field sensor based on diamond NV color centers according to claim 3, characterized in that: The third receiving conversion mechanism comprises an optical filter, a third lens and a third single-photon counting module which are sequentially arranged.

5. The high-efficiency optical fiber magnetic field sensor based on diamond NV color centers according to claim 4, characterized in that: The magnetic field optical fiber sensing mechanism comprises a hollow optical fiber and single-mode optical fibers arranged at the two ends of the hollow optical fiber, the two single-mode optical fibers are connected with the first optical fiber filter and the second optical fiber filter respectively, and the hollow optical fiber is arranged opposite to the objective lens.

6. The high-efficiency optical fiber magnetic field sensor based on diamond NV color centers according to claim 5, characterized in that: The microwave waveguide mechanism comprises a microwave waveguide and a microwave source, the microwave source is connected with the microwave waveguide, and the microwave waveguide is arranged around the hollow optical fiber.

7. The high-efficiency optical fiber magnetic field sensor based on diamond NV color centers according to claim 6, characterized in that: The microwave waveguide is a copper wire.

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