阅读说明：本技术 一种光纤磁场传感器及其制备方法 (Optical fiber magnetic field sensor and preparation method thereof ) 是由 龚牧桑 杨朋成 余民 蔡建明 于 2019-08-26 设计创作，主要内容包括：本发明公开一种光纤磁场传感器及其制备方法,包括：光纤和多个金刚石微柱；所述多个金刚石微柱位于所述光纤内部的一端；每个金刚石微柱均含有氮-空位中心；利用该光纤磁场传感器测量磁场时,光纤中包含金刚石微柱的一端被置于待测量磁场的环境中,从光纤的另一端射入预设波长的激光,使得所述氮-空位中心受激发射荧光；向所述光纤中包含金刚石微柱的一端发射预定频率范围的扫频信号,收集荧光,通过分析荧光的强度随着所述扫频信号频率的变化规律,确定待测量磁场的大小。本发明可以在光纤口集成更多的氮-空位中心,灵敏度与样品中氮-空位中心的数量有关,通过氮-空位中心色心密度更大的金刚石微柱样品可以获得更高灵敏度的磁力计。(The invention discloses an optical fiber magnetic field sensor and a preparation method thereof, wherein the preparation method comprises the following steps: an optical fiber and a plurality of diamond micropillars; the plurality of diamond micropillars are positioned at one end of the interior of the optical fiber; each diamond microcolumn contains a nitrogen-vacancy center; when the optical fiber magnetic field sensor is used for measuring a magnetic field, one end of the optical fiber, which comprises the diamond microcolumn, is placed in an environment of the magnetic field to be measured, and laser with a preset wavelength is injected from the other end of the optical fiber, so that the nitrogen-vacancy center is stimulated to emit fluorescence; and emitting a sweep frequency signal in a preset frequency range to one end of the optical fiber, which contains the diamond microcolumn, collecting fluorescence, and determining the size of a magnetic field to be measured by analyzing the change rule of the intensity of the fluorescence along with the frequency of the sweep frequency signal. The invention can integrate more nitrogen-vacancy centers at the optical fiber port, the sensitivity is related to the number of the nitrogen-vacancy centers in the sample, and the magnetometer with higher sensitivity can be obtained by the diamond micro-column sample with higher density of the color centers of the nitrogen-vacancy centers.)

1. a fiber optic magnetic field sensor, comprising: an optical fiber and a plurality of diamond micropillars;

The plurality of diamond micropillars are positioned at one end of the interior of the optical fiber; each diamond microcolumn contains a nitrogen vacancy center;

when the optical fiber magnetic field sensor is used for measuring a magnetic field, one end of the optical fiber, which comprises the diamond microcolumn, is placed in an environment of the magnetic field to be measured, and laser with a preset wavelength is injected from the other end of the optical fiber, so that the center of the nitrogen vacancy is stimulated to emit fluorescence;

And emitting a sweep frequency signal in a preset frequency range to one end of the optical fiber containing the diamond microcolumn, collecting fluorescence emitted by the center of the nitrogen vacancy under the action of the magnetic field environment to be measured and the sweep frequency signal, and determining the size of the magnetic field to be measured by analyzing the change rule of the intensity of the fluorescence along with the frequency of the sweep frequency signal.

2. the fiber optic magnetic field sensor of claim 1, wherein the optical fiber is a multimode fiber or a single mode fiber.

3. The fiber optic magnetic field sensor according to claim 1 or 2, wherein the swept frequency range of the swept frequency signal is 2.8GHz-2.94 GHz.

4. the preparation method of the optical fiber magnetic field sensor is characterized by comprising the following steps of:

preparing an aqueous solution containing a plurality of diamond microcolumns; wherein each diamond microcolumn contains a nitrogen vacancy center;

Immersing one end of an optical fiber in the aqueous solution; wherein the optical fiber is hollow;

Drawing air from the other end of the optical fiber such that the aqueous solution is drawn into one end of the optical fiber;

Taking out the optical fiber with one end sucking the aqueous solution from the aqueous solution, and drying to obtain an optical fiber magnetic field sensor; when the optical fiber magnetic field sensor is used for measuring a magnetic field, one end of the optical fiber, which comprises the diamond microcolumn, is placed in an environment of the magnetic field to be measured, and laser with a preset wavelength is injected from the other end of the optical fiber, so that the center of the nitrogen vacancy is stimulated to emit fluorescence; and emitting a sweep frequency signal in a preset frequency range to one end of the optical fiber containing the diamond microcolumn, collecting fluorescence emitted by the center of the nitrogen vacancy under the action of the magnetic field environment to be measured and the sweep frequency signal, and determining the size of the magnetic field to be measured by analyzing the change rule of the intensity of the fluorescence along with the frequency of the sweep frequency signal.

5. The method for preparing the optical fiber magnetic field sensor according to claim 4, wherein the diamond microcolumn containing the nitrogen vacancy center is obtained by the steps of:

Etching a diamond microcolumn on the surface of a diamond sample containing a nitrogen vacancy center, and then removing the etched diamond microcolumn from the surface of the diamond sample to obtain the diamond microcolumn containing the nitrogen vacancy center; or

Carrying out detonation on a massive diamond sample containing a nitrogen vacancy center to obtain micro-nano diamond particles, and introducing the micro-nano diamond particles to a diamond microcolumn containing the nitrogen vacancy center; or

And (3) carrying out ion injection on the nano-diamond sample without the nitrogen vacancy center to form the nitrogen vacancy center, thus obtaining the diamond micro-column containing the nitrogen vacancy center.

6. The method of claim 4, wherein the diamond micro-column is considered to be successfully implanted into the end of the optical fiber when the intensity of the fluorescence changes significantly with the power of the incident laser.

7. The method for manufacturing the fiber-optic magnetic field sensor according to any one of claims 4 to 6, wherein the sweep frequency range of the sweep frequency signal is 2.8GHz-2.94 GHz.

Technical Field

The invention relates to the technical field of weak signal detection, in particular to an optical fiber magnetic field sensor and a preparation method thereof.

Background

the high-precision weak magnetic measurement technology is an important component of modern detection technology, and is widely applied to the fields of aerial potential detection, ocean monitoring, detection of earth water and underwater ferromagnetic substances, earthquake prediction, geomagnetic matching navigation, precise nondestructive monitoring of aerial equipment, nuclear magnetic resonance monitoring in medicine and the like.

There are various schemes for implementing the magnetic detection by using the optical Fiber, including a Fiber magnetic field sensor based on a Mach-Zehnder interferometer, a Fiber magnetic field sensor based on a Michelson interferometer, a Fiber magnetic field sensor based on a Fabry-Perot interferometer, and a magnetic field sensor of a Fiber Bragg Grating (FBG), etc.

Among them, FBG is the most widely used one in current application and research, and a bragg grating is engraved inside an optical fiber so that a part of incident laser light is reflected and transmitted, and information on stress and temperature can be obtained by measuring a wavelength change of the reflected light. However, the magnetic induction itself cannot directly change the fiber grating, so that a medium with strain changing under the action of a magnetic field is generally needed as an aid, and the medium is a magnetostrictive material. The volume or length of such a material changes in an external magnetic field, known as the magnetostrictive effect.

The optical fiber is adhered to the magnetostrictive material or a layer of magnetostrictive material is coated on the surface of the grating, the strain of the magnetostrictive material can be caused by a magnetic field, so that the resonant wavelength of the grating is shifted, and the measurement of the magnetic field is realized by detecting the change of the wavelength. Because the optical fiber has the advantages of small volume and deformability, the optical fiber can be used for carrying out magnetic measurement in a small space which can not be reached by some traditional magnetic measurement equipment.

The research result published in 2018 by professor billows of semiconductor institute of academy of sciences in China shows that the magnetic field resolution of the magnetic field sensor prepared by combining the magnetostrictive material Terfenol-D and the fiber bragg grating is 3 mu T, and the magnetic field sensor can be used for measuring weak magnetic fields.

Although 3 μ T is sufficient for some applications, it is not satisfactory in certain more demanding areas. For example, in the measurement of the terrestrial magnetism, the strength of the terrestrial magnetism near the earth surface is 25 muT-65 muT, and the terrestrial magnetism can be measured at a position which cannot be reached by some conventional sensors by using the optical fiber-based magnetic field sensor, but the measurement result is not accurate.

disclosure of Invention

Aiming at the defects of the prior art, the invention aims to solve the technical problem of insufficient sensitivity of the fiber grating magnetic field sensor.

To achieve the above object, in a first aspect, the present invention provides a fiber-optic magnetic field sensor comprising: an optical fiber and a plurality of diamond micropillars;

The plurality of diamond micropillars are positioned at one end of the interior of the optical fiber; each diamond microcolumn contains a nitrogen vacancy center;

When the optical fiber magnetic field sensor is used for measuring a magnetic field, one end of the optical fiber, which comprises the diamond microcolumn, is placed in an environment of the magnetic field to be measured, and laser with a preset wavelength is injected from the other end of the optical fiber, so that the center of the nitrogen vacancy is stimulated to emit fluorescence;

And emitting a sweep frequency signal in a preset frequency range to one end of the optical fiber containing the diamond microcolumn, collecting fluorescence emitted by the center of the nitrogen vacancy under the action of the magnetic field environment to be measured and the sweep frequency signal, and determining the size of the magnetic field to be measured by analyzing the change rule of the intensity of the fluorescence along with the frequency of the sweep frequency signal.

optionally, the optical fiber is a multimode fiber or a single mode fiber.

Optionally, the sweep frequency range of the sweep frequency signal is 2.8GHz-2.94 GHz.

In a second aspect, the present invention provides a method for preparing an optical fiber magnetic field sensor, comprising the following steps:

Preparing an aqueous solution containing a plurality of diamond microcolumns; wherein each diamond microcolumn contains a nitrogen vacancy center;

Immersing one end of an optical fiber in the aqueous solution; wherein the optical fiber is hollow;

Drawing air from the other end of the optical fiber such that the aqueous solution is drawn into one end of the optical fiber;

Taking out the optical fiber with one end sucking the aqueous solution from the aqueous solution, and drying to obtain an optical fiber magnetic field sensor; when the optical fiber magnetic field sensor is used for measuring a magnetic field, one end of the optical fiber, which comprises the diamond microcolumn, is placed in an environment of the magnetic field to be measured, and laser with a preset wavelength is injected from the other end of the optical fiber, so that the center of the nitrogen vacancy is stimulated to emit fluorescence; and emitting a sweep frequency signal in a preset frequency range to one end of the optical fiber containing the diamond microcolumn, collecting fluorescence emitted by the center of the nitrogen vacancy under the action of the magnetic field environment to be measured and the sweep frequency signal, and determining the size of the magnetic field to be measured by analyzing the change rule of the intensity of the fluorescence along with the frequency of the sweep frequency signal.

Alternatively, the diamond microcolumn containing the nitrogen vacancy center is obtained by the following steps:

etching a diamond microcolumn on the surface of a diamond sample containing a nitrogen vacancy center, and then removing the etched diamond microcolumn from the surface of the diamond sample to obtain the diamond microcolumn containing the nitrogen vacancy center; or

Carrying out detonation on a massive diamond sample containing a nitrogen vacancy center to obtain micro-nano diamond particles, and introducing the micro-nano diamond particles to a diamond microcolumn containing the nitrogen vacancy center; or

And (3) carrying out ion injection on the nano-diamond sample without the nitrogen vacancy center to form the nitrogen vacancy center, thus obtaining the diamond micro-column containing the nitrogen vacancy center.

optionally, when the intensity of the fluorescence changes significantly with the power of the incident laser, the diamond micro-column is considered to be successfully implanted into one end of the optical fiber.

Optionally, the sweep frequency range of the sweep frequency signal is 2.8GHz-2.94 GHz.

Generally, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:

The optical fiber magnetic field sensor and the preparation method thereof provided by the invention can integrate more nitrogen vacancy centers at an optical fiber port, and the sensitivity and the nitrogen-vacancy centers in a sampleIs related to the quantity ofWhere δ B is characteristic of the minimum detectable magnetic field strength, g_sis Landau factor, mu_BIs the Bohr magneton constant, R is a constant, η is the detection efficiency, t is the time,characterizing the system coherence time, N represents the number of spins, which are provided by the nitrogen-vacancy center. In a given NV system, g_s、μ_B、R、η、t、All fixed, diamond microcolumn samples with greater density of color centers (greater N) in the nitrogen-vacancy center allow for higher sensitivity magnetometers (smaller δ B), while our method provides higher fluorescence collection efficiency.

Drawings

FIG. 1 is a schematic diagram of the structure of nitrogen-vacancy centres in diamond provided by the present invention;

FIG. 2 is a schematic diagram of the energy level structure of nitrogen-vacancy centres provided by the present invention;

FIG. 3 is a schematic view of the fluorescence collection of a detector formed by coupling a diamond microcolumn containing nitrogen-vacancy centers with an optical fiber according to the present invention;

FIG. 4 is a schematic view of fluorescence collection of a detector formed by coupling a micro-nano diamond containing nitrogen-vacancy centers and an optical fiber according to the present invention;

FIG. 5 is a schematic diagram of the optical fiber combined with the microwave wire to realize magnetic field measurement;

FIG. 6 is a schematic diagram of the present invention for implementing magnetic field measurement by using the optical fiber structure of surface etched microwave wire.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

The invention aims to solve the problem of insufficient sensitivity of a fiber grating magnetic field sensor and provides a method for utilizing an optical fiber, a diamond microcolumn containing a nitrogen-vacancy center and micro-nano diamond particles to manufacture a detector, which is simple in manufacturing device, small and exquisite in detecting head, high in stability and high in detection efficiency and is suitable for various complex environments.

The present invention proposes measuring the magnetic field using a Nitrogen-vacancy center (NVcenter) in the diamond. The nitrogen-vacancy centres are formed by adjacent carbon vacancies after replacement of a carbon atom in the diamond lattice by a nitrogen atom, as shown in FIG. 1, and are predominantly NV0 and NV^-Two charge states exist, and nitrogen-vacancy centres are referred to herein as NV unless otherwise specified^-。

Energy level structure diagram of nitrogen-vacancy center referring to fig. 2, if laser light within a predetermined wavelength range is irradiated on the nitrogen-vacancy center, electrons at the nitrogen-vacancy center can be excited to an excited state, photons of a predetermined wavelength are radiated when the electrons transit down from the excited state to generate a fluorescence effect, and if the electrons indirectly return to a ground state through the right energy level of fig. 2, photons of 1024nm are emitted. In the absence of an external magnetic field, the |1> and |1> states of the ground state are degenerate, their energy level difference from the |0> state is 2.87GHz, and in the presence of the magnetic field to be detected, the Zeeman effect causes the degeneracy of the ground states |1> and |1> to be broken, and the two energy levels start to split.

the magnitude of the magnetic field can be detected by an Optical Detected Magnetic Resonance (ODMR) experiment. ODMR experiments excite the transitions of ground state electrons at |0> and |1> and |0> and |1> when the frequency of the signal exactly matches the difference in the nitrogen-vacancy central energy level by applying a frequency sweeping signal to the nitrogen-vacancy center, and the electrons are not fully pumped to the excited state, resulting in a significant decrease in fluorescence. By analyzing the emitted fluorescence, an ODMR spectrum can be plotted relating to the magnetic field and the intensity of the fluorescence, from which external magnetic field information can be derived. The magnetic field detection sensitivity of the nitrogen-vacancy center can also be improved through more complicated experiments, and the diamond is non-toxic and harmless to biological cells, so that the nitrogen-vacancy center can also be utilized to carry out related measurement on biological cell samples.

According to the formulawhere δ B is characteristic of the minimum detectable magnetic field strength, g_sIs Landau factor, mu_BIs the Bohr magneton constant, R is a constant, η is the detection efficiency, t is the time,characterizing the system coherence time, N represents the number of spins, which are provided by the nitrogen-vacancy center. In a given NV system, g_s、μ_B、R、η、t、diamond micropillar samples, all fixed, with a greater density of color centers (greater N) in the nitrogen-vacancy center, can achieve a magnetometer with higher sensitivity (smaller δ B).

The device can move an objective lens through a positioning table, excite laser with a preset wavelength (usually 532nm) on the surface of a sample point by point, and collect fluorescence intensity of each point, wherein the fluorescence intensity is high, namely fluorescence effect exists, and possibly nitrogen-vacancy center exists. The problem can be solved skillfully by embedding the diamond columns or particles with the micron level into the hollow optical fiber, the nitrogen-vacancy center at the other end of the optical fiber can be directly excited by injecting exciting light (usually 532nm) from one section of the optical fiber by using a laser, and the measurement of a magnetic field can be carried out by applying specific microwave to the external environment. The device does not need to use a positioning table which is high-precision equipment, diamond micro-columns or nano-diamond particles containing nitrogen-vacancy centers are loaded into an optical fiber (called a port as a detection end) in advance, only laser needs to be injected from the other end in actual use, fluorescence is collected at the same end or the other end, and the position of the detection end can be freely changed as long as the stability of the injection end is ensured.

specifically, the preparation of the diamond microcolumn is an existing mature technology, and the diamond microcolumn containing the nitrogen-vacancy center can be obtained by etching the diamond microcolumn on the surface of a diamond sample containing the nitrogen-vacancy center and then removing the microcolumn from the surface of the diamond, wherein the diameter of the microcolumn can be from hundreds of nanometers to tens of micrometers.

the preparation process of the micro-nano diamond particles is mature, micro-nano diamond particles can be obtained by carrying out detonation on a massive diamond sample containing a nitrogen-vacancy center, and the nitrogen-vacancy center can also be formed by carrying out ion injection on a nano diamond sample without the nitrogen-vacancy center.

The optical fiber can be a single-mode optical fiber or a multimode optical fiber, the diameter of the single-mode optical fiber is about 10 micrometers generally, and the diameter of the multimode optical fiber is 50 micrometers-100 micrometers. Single mode optical fibres are recommended.

The diamond micro-column or micro-nano diamond particles are implanted and fixed from one end of the optical fiber, microwaves are applied to the detection end, laser with specific wavelength (usually 532nm) can be irradiated from the other end, and fluorescence emitted by a nitrogen-vacancy center is collected from the same side or the other side, so that measurement can be realized.

in order to apply microwave pulse, (1) using an independent microwave waveguide, approaching the probe end from the outside to apply microwave pulse to the nitrogen-vacancy center inside the probe end; (2) coupling a microwave waveguide in the coating layer of the optical fiber, and applying microwave pulses to the detection end through the microwave waveguide; (3) and winding a waveguide wire on the surface of the optical fiber to apply microwave pulses to the detection end.

The detector of the invention can maintain the stability and portability of the device while measuring with high precision, and the probe of the sensor can be placed at a position which is not easy to reach by guiding the optical fiber to realize high-precision measurement. Such as nondestructive detection of aerospace equipment or high-precision measurement of extreme environments such as water bottom, ground bottom and the like, and can also guide the optical fiber to carry out measurement in a cell environment. The detector can operate stably for a long time due to the stability of the fluorescence emitted from the nitrogen-vacancy central structure.