Microwave field generating device and photoelectric integrated probe

Abstract

The invention discloses a microwave field generating device and a photoelectric integrated probe, and belongs to the technical field of quantum precision sensing. The photoelectric integrated probe comprises a diamond NV color center probe and a resonance antenna; the diamond NV color center probe is formed by fixing a diamond NV color center crystal at the conical end part of a conical multimode optical fiber; the resonance antenna forms a radiation structure by coaxially welding a same-material sheet at the tail end of a coaxial wire, and the diamond NV color center probe is further fixed at the tail end of the resonance antenna, so that space coupling integration of a microwave field and a light field is realized. According to the invention, the diamond NV color center crystal and the resonant antenna are coaxially packaged, so that a microwave near field and a light field are spatially matched, and electromagnetic coupling optimization, structural symmetry design and miniature packaging technology innovation are combined, so that the mechanical stability and the anti-interference capability of the probe are ensured while the microwave radiation intensity is improved, and the application prospect is wide. Therefore, the sensitivity, the stability and the space adaptability of the NV color center probe are promoted to realize breakthrough improvement.

Description

Technical Field

[0001] The present invention belongs to the technical field of quantum precision sensing, and particularly relates to an optoelectronic integrated probe and a microwave field generating device constructed based on the same. Background Art

[0002] The Nitrogen-Vacancy (NV) color center is an intrinsic point defect system formed by replacing a carbon atom with a nitrogen atom in the diamond lattice and accompanied by an adjacent vacancy. Its unique spin-related photoluminescence characteristics, including long spin coherence time, high optical stability, and biocompatibility at room temperature, make it an ideal carrier for quantum precision measurements (such as magnetic field, temperature, and strain sensing).

[0003] The NV color center forms a spin triplet state between the ground state 3 A2 and the excited state 3 E, and its spin energy levels are m s = +1, m s = 0, m s = -1. Among them, the ground state m s = ±1 energy levels generate a zero-field splitting (D value) of 2.87 GHz due to lattice strain and spin-orbit coupling effects in zero magnetic field. When a microwave field with a matching frequency is applied, the spin transition is excited, accompanied by a significant decrease in fluorescence intensity; through laser pumping to achieve spin polarization and fluorescence readout, the microwave-spin interaction can be converted into an optical intensity signal modulation, that is, the optically detected magnetic resonance (ODMR) technology.

[0004] The current sensing systems based on NV color centers mainly face two core problems. One is that traditional antennas (such as coplanar waveguides, ring resonators) are difficult to meet the requirements of high-sensitivity ODMR measurements for microwave field intensity and stability due to low radiation efficiency and poor near-field uniformity. The other is that NV color centers are usually integrated at the tip or on the surface of the diamond film through micro-nano processing technology, with a split layout from the microwave antenna, resulting in a significant reduction in the spatial coupling efficiency between the microwave field and the spin state. At the same time, the split design is prone to structural fracture of the probe or detachment of the NV color center due to mechanical stress during dynamic measurements. To achieve the synergistic effect of the microwave radiation unit and the NV color center probe, it is urgent to break through the double limitations of spatial coupling efficiency and mechanical stability through structural innovation (such as coaxial packaging, flexible substrate design), construct an integrated sensing probe with both high sensitivity and strong robustness, and redesign the microwave field generating device adapted to it. Summary of the Invention

[0005] The present invention proposes an optoelectronic integrated probe prepared by electromagnetic coupling of a diamond NV - center probe and a resonant antenna to address the problems existing in the prior art, and discloses an adapted measurement and control device. Through electromagnetic coupling optimization, structural symmetry design, and micro - packaging technology innovation, the present application has achieved a breakthrough improvement in the sensitivity, stability, and spatial adaptability of the NV - center probe.

[0006] The technical solution of the present invention is as follows: An optoelectronic integrated probe includes a diamond NV - center probe and a resonant antenna. The diamond NV - center probe is formed by fixing a diamond NV - center crystal at the tapered end of a tapered multimode optical fiber. The resonant antenna is a radiation structure formed by coaxially welding a sheet of the same material at the end of a coaxial wire. The diamond NV - center probe is fixed at the end of the resonant antenna to form a spatial coupling integration of a microwave field and an optical field.

[0007] Furthermore, the resonant antenna is integrally constructed with a beryllium - copper alloy material to form a λ / 4 resonant cavity structure. By adjusting the physical length of the transmission line and the boundary conditions of the end sheet, the resonant frequency is precisely matched to the 2.87 GHz NV - center ground - state transition frequency.

[0008] Furthermore, the diamond NV - center crystal is located at the center of the near - field region of the radiation field at the end of the resonant antenna.

[0009] A microwave - field generating device includes the above - mentioned optoelectronic integrated probe and a measurement and control device. The measurement and control device includes a laser source, a broadband radio - frequency signal microwave source, a pulse - signal generating module, a fluorescence - collecting module, a signal - processing module, and a computer. The laser source and the broadband radio - frequency signal microwave source are electrically connected to the pulse - signal generating module, and are respectively used to drive the fluorescence excitation of the diamond NV - center and the microwave - field modulation.

[0010] Furthermore, the laser source outputs a 532 nm pulsed laser, which is reflected by a long - pass dichroic mirror and then focused by a first objective lens onto the diamond NV - center crystal to excite the diamond NV - center to generate red fluorescence.

[0011] The broadband radio - frequency signal microwave source outputs a microwave signal with a controllable frequency, which is pulse - modulated and amplified by a power amplifier and then coupled to the resonant antenna.

[0012] The fluorescence - collecting module includes an optical - path excitation module and a photodetector, and is used to collect fluorescence and filter out stray light.

[0013] The signal - processing module is connected to the fluorescence - collecting module and is used to convert the fluorescence signal into an electrical signal and generate a detection nuclear magnetic resonance spectrum through a computer, including a front - end processing module and a back - end algorithm module.

[0014] Furthermore, the optical path excitation module includes a first objective lens, a long-pass dichroic mirror, and a long-pass filter. After the red fluorescence generated by the diamond is coupled and introduced through the tapered optical fiber, it is first reflected by the long-pass dichroic mirror and then the stray light is filtered by the long-pass filter. Finally, the optical signal is received by the photodetector.

[0015] Furthermore, the front-end processing module includes a voltage acquisition unit, a signal amplification unit, and a filtering unit. After the photodetector collects the optical signal, it is converted into an electrical signal through the voltage acquisition unit, and then amplified and filtered by the signal amplification unit and the filtering unit in sequence.

[0016] Furthermore, the backend algorithm module extracts the fluorescence amplitude through lock-in amplification and eliminates the background noise based on differential processing.

[0017] Furthermore, the pulse signal generation module provides TTL pulse signals for the first and second RF switches. The second RF switch controls the on / off of the laser pulse, and the first RF switch controls the modulation of the microwave signal.

[0018] Furthermore, the pulse signal generation module generates a subcarrier modulation signal through the third modulation pulse unit, forcing the second half cycle of the microwave radiation sequence to be at a low level, thereby completing the targeted separation of the fluorescence sideband components.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. In the optoelectronic integrated probe disclosed in the present application, the diamond NV center probe is fixed at the end of the resonant antenna. The probe is connected to the resonant antenna unit through a coaxial transmission line to achieve the spatial matching of the microwave near field and the optical field. At the same time, the antenna structure (λ / 4 resonant cavity design) and the NV center positioning process (micrometer-level accuracy) are optimized to form a standing wave field amplification effect at the end of the diamond NV center probe, ensuring the stability of the microwave field environment. While enhancing the microwave radiation intensity, the mechanical stability and anti-interference ability of the probe are ensured, providing a hardware basis for high-precision quantum sensing;

[0021] 2. Aiming at the ground state transition characteristics (2.87 GHz) of the NV center, through the design of the ring resonator and the regulation of the dielectric constant of the dielectric material, the quality factor of the probe is improved, the microwave radiation intensity is enhanced, and the signal-to-noise ratio of the fluorescence signal is significantly improved;

[0022] 3. The resonant antenna is composed of beryllium copper wire of the same material and the end sheet. The latter adopts an axisymmetric design and is processed with a symmetric cavity structure. Combined with the regulation of the feeding phase of the coaxial line, the excitation consistency of the NV center array can be significantly improved, and the edge field distortion effect can be eliminated;

[0023] 4. The optoelectronic integrated probe prepared in the present application has a high integration degree and a small volume, and can adapt to a more refined test environment during magnetic field testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a schematic structural diagram of a resonant antenna;

[0025] Figure 2 is a partial schematic diagram of the end sheet of the resonant antenna;

[0026] Figure 3 is a dimensional drawing of the end sheet of the resonant antenna;

[0027] Figure 4 is a schematic structural diagram of an optoelectronic integrated probe;

[0028] Figure 5 is a schematic block diagram of a measurement and control system based on the optoelectronic integrated probe;

[0029] Figure 6 is a timing diagram of laser pulses, RF signal switching pulses, RF pulse modulation pulses, and electromagnetic wave radiation pulse signals;

[0030] Among them, 1 - diamond NV - color - center crystal, 2 - tapered multimode optical fiber, 3 - coaxial cable, 4 - sheet, 5 - cavity, 6 - robotic arm. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings, but are not limited thereto. Any modification or equivalent replacement of the technical solutions of the present invention, without departing from the spirit and scope of the technical solutions of the present invention, shall be covered by the protection scope of the present invention.

[0032] Embodiment 1

[0033] In order to solve the problems such as the low intensity of the microwave field radiation source and the poor field distribution uniformity in the existing NV - color - center magnetic measurement technology, which lead to a decrease in detection sensitivity, an optoelectronic integrated probe prepared by electromagnetic coupling of a diamond NV - color - center probe and a resonant antenna is disclosed in this embodiment, and the corresponding measurement and control device is also disclosed.

[0034] The optoelectronic integrated probe is jointly integrated by a diamond NV - color - center probe and a resonant antenna. The diamond NV - color - center probe is fixed at the center position of the end of the resonant antenna (structural reference Figure 1 ), and the resonant antenna is used to provide a stable microwave field for the diamond NV - color - center.

[0035] The diamond NV - center probe is formed by fixing the directionally - processed diamond NV - center crystal 1 at the tapered end of the tapered multimode fiber 2. The tapered multimode fiber 2 is a quasi - adiabatic tapered fiber made of multimode fiber. The tip size of the tapered multimode fiber 2 matches the size of the corresponding diamond NV - center particle sample. In this embodiment, the diameter of the diamond particle is 10 μm, and the end - face diameter of the tapered multimode fiber is 20 μm.

[0036] The resonant antenna is formed by coaxially welding a sheet 4 of the same material to the end of the coaxial wire 3. The diameter of the wire is 1000 μm, and the structure of the sheet refers to Figures 2 - 4 . The sheet is in the shape of a teapot and is symmetric about its central axis h. The sheet can be divided into three parts: the upper part, the lower part, and the connecting part. The width a of the upper part of the sheet is 356 μm, the height b of the upper part is 400 μm, the width c of the lower part of the sheet is 950 μm, the height d of the lower part is 1225 μm, the height e of the connecting part is 125 μm. There are two symmetric irregular cavities 5 on the sheet. The upper - part spacing f between the two cavities 5 is 38 μm, and the lower - part spacing g is 200 μm( Figure 3 ).

[0037] The resonant antenna as a whole is constructed with a λ / 4 resonant - cavity structure using a high - conductivity, low - loss beryllium - copper alloy material. By optimizing the physical length of the transmission line (i.e., the physical length of the coaxial wire) and the boundary conditions (the boundary conditions specifically refer to the electrical characteristics at the end of the conductor, the short - circuit end is forced to have zero impedance, and the open - circuit end is forced to have high impedance), efficient resonance in the target frequency band (near 2.87 GHz) is achieved. This design can theoretically achieve precise matching of a specific frequency (such as 2.87 GHz required for the zero - field splitting of the NV - center) by adjusting the cavity size and the dielectric environment. The low - loss characteristics of the beryllium - copper alloy material are expected to significantly improve the energy - storage efficiency of the resonant cavity and the ability to concentrate the local field strength.

[0038] The integrated assembly of the resonant antenna and the diamond NV - center probe needs to follow the principle of near - field coupling: First, through the micro - operation platform, the NV - center is accurately positioned at the center of the near - field region of the radiation field at the end of the resonant antenna. Here, due to the microwave standing - wave superposition effect, a region with a maximum field strength with a three - dimensional uniform distribution is formed, which can ensure that the NV - center is simultaneously in the peak of the microwave magnetic - field strength and the low - gradient uniform region. To achieve reliable coupling, a microwave - compatible packaging process is used to fix the diamond NV - center crystal at the end of the resonant antenna for matching and positioning, and the microwave energy is efficiently fed in through the coaxial wire. The entire system needs to be calibrated for the voltage standing - wave ratio by means of a vector network analyzer to meet the phase - stability and microwave - power - density threshold requirements for the quantum manipulation of the NV - center.

[0039] To achieve multi - degree - of - freedom azimuth adjustment and precise spatial - position control of the optoelectronic integrated probe, it can be integrated into the end - effector of the robotic arm 6 of the robot, and the spatial azimuth adjustment is realized through multi - axis linkage drive.

[0040] The measurement and control device is composed of a laser source, a broadband radio frequency signal microwave source, a pulse signal generation module, a fluorescence acquisition module, a signal processing module, and a computer working together (refer to Figure 5 ).

[0041] Among them, both the laser source and the broadband radio frequency signal microwave source are connected to the pulse signal generation module in an electrical connection manner, and the latter provides a programmable pulse modulation signal.

[0042] The laser source is used to generate laser pulse signals, and the laser source is connected to a tapered multimode optical fiber. The generated laser is used to excite the diamond NV color center to generate red fluorescence. Since the absorption spectrum of the NV color center is very wide and there are significant absorption peaks between 450 nm and 600 nm, the laser source of a specific wavelength usually generates laser with a wavelength of 510 nm to 540 nm. In this embodiment, a wavelength of 532 nm is preferably used. The pulsed laser output by the laser source is reflected by a long-pass dichroic mirror and then focused by a first objective lens onto the diamond NV color center probe, exciting the diamond NV color center to generate red fluorescence in the wavelength band above 650 nm.

[0043] The broadband radio frequency signal microwave source outputs high-frequency microwave signals through computer program control (the frequency is related to the magnetic field strength to be measured. The stronger the magnetic field strength, the higher the required microwave frequency, and the output power is preferably -60 dBm to 60 dBm). The pulse signal generation module emits pulse signals. The microwave signals are amplified by pulse modulation and a power amplifier and then coupled to a resonant antenna for radiation, and precise microwave field control is achieved by using the electron spin resonance effect of the NV color center.

[0044] The fluorescence acquisition module includes an optical path excitation module and a photodetector, which are used to excite the diamond NV color center to generate red fluorescence and collect it. The optical path excitation module includes a first objective lens, a long-pass dichroic mirror, and a long-pass filter. The tapered multimode optical fiber of the diamond NV color center probe realizes fluorescence conduction through the following path: the red fluorescence generated by the diamond is coupled and introduced through the tapered multimode optical fiber, then reflected by the long-pass dichroic mirror and the stray light is filtered by the long-pass filter, and finally the photodetector completes the reception of the optical signal.

[0045] The signal processing module is connected to the fluorescence acquisition module and is used to convert the optical signal into an electrical signal and perform subsequent signal processing. The signal processing module includes a front-end processing module and a back-end algorithm module; the front-end processing module includes a voltage acquisition unit, a signal amplification unit, and a filtering unit. After the photodetector collects the optical signal, it is first converted into an electrical signal by the voltage acquisition unit, and then amplified and filtered by the signal amplification unit and the filtering unit in sequence, and then lock-in amplification and differential processing are realized through the back-end algorithm module. Finally, the computer generates an optically detected magnetic resonance (ODMR) spectrum with a high signal-to-noise ratio.

[0046] During operation, the core function of the pulse signal generation module is to provide TTL pulse signals for the first and second RF switches. The second RF switch controls the on / off of the laser pulse (corresponding to Figure 6 the laser pulse sequence therein), and the first RF switch controls the microwave signal modulation (refer to Figure 6 the RF signal switch sequence therein). The system implements subcarrier modulation by introducing a third modulation pulse ( Figure 6 the RF pulse modulation sequence therein), forcing the second half cycle of the microwave signal to be at a low level, thereby focusing on the sideband components of the fluorescence signal, significantly improving the signal-to-noise ratio of the ODMR spectrum, providing a strong guarantee for accurate measurement, and the resonant antenna radiates the modulated RF signal in the form of electromagnetic waves directionally.

[0047] The pulsed laser output by the laser source excites the diamond NV color center to generate red fluorescence. After being coupled and introduced through a tapered multimode fiber, it is successively reflected by a long-pass dichroic mirror and filtered by a long-pass filter to remove stray light. Finally, the optical signal is received by a photodetector, then converted into an electrical signal by a voltage acquisition unit, and successively amplified and filtered by a signal amplification unit and a filtering unit. After that, lock-in amplification and differential processing are implemented through a backend algorithm module, and finally a high signal-to-noise ratio ODMR spectrum is generated by a computer.

[0048] The above are only embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be similarly included in the patent protection scope of the present invention.

Claims

1. An optoelectronic integrated probe, characterized in that, It includes a diamond NV center probe and a resonant antenna; The diamond NV center probe is formed by fixing a diamond NV center crystal at the tapered end of a tapered multimode optical fiber; The resonant antenna is a radiation structure formed by coaxially welding a sheet of the same material at the end of a coaxial wire; The diamond NV center probe is fixed at the end of the resonant antenna to form a spatial coupling integration of a microwave field and an optical field.

2. The optoelectronic integrated probe according to claim 1, wherein The resonant antenna is entirely constructed of beryllium copper alloy material to form a λ / 4 resonant cavity structure. By adjusting the physical length of the transmission line and the boundary conditions of the end sheet, the resonant frequency is precisely matched to the 2.87 GHz NV center ground state transition frequency.

3. An optoelectronic integrated probe as claimed in claim 1, wherein, The diamond NV center crystal is located at the center of the near-field region of the radiation field at the end of the resonant antenna.

4. A microwave field generating device, characterized in that, It includes the optoelectronic integrated probe described in any one of claims 1-3 and a measurement and control device. The measurement and control device includes a laser source, a broadband radio frequency signal microwave source, a pulse signal generation module, a fluorescence collection module, a signal processing module, and a computer; The laser source and the broadband radio frequency signal microwave source are electrically connected and connected to the pulse signal generation module, respectively used to drive the fluorescence excitation of the diamond NV center and the modulation of the microwave field.

5. A microwave field generating device according to claim 4, characterized in that The laser source outputs a 532 nm pulsed laser. After being reflected by a long-pass dichroic mirror, it is focused by a first objective lens onto the diamond NV center crystal to excite the diamond NV center to generate red fluorescence; The broadband radio frequency signal microwave source outputs a controllable frequency microwave signal. After being pulse-modulated and amplified by a power amplifier, it is coupled to the resonant antenna; The fluorescence collection module includes an optical path excitation module and a photodetector, and is used to collect fluorescence and filter out stray light; The signal processing module is connected to the fluorescence collection module, and is used to convert the fluorescence signal into an electrical signal and generate a detection nuclear magnetic resonance spectrum through a computer, including a front-end processing module and a back-end algorithm module.

6. A microwave field generating device according to claim 5, characterized in that, The optical path excitation module includes a first objective lens, a long-pass dichroic mirror, and a long-pass filter. The red fluorescence generated by the diamond is coupled and introduced through a tapered optical fiber, and then sequentially reflected by the long-pass dichroic mirror and filtered out stray light by the long-pass filter. Finally, the photodetector completes the reception of the optical signal.

7. A microwave field generating device according to claim 5, characterized in that, The front-end processing module includes a voltage acquisition unit, a signal amplification unit, and a filtering unit. After the photodetector collects the optical signal, it is converted into an electrical signal through the voltage acquisition unit, and then sequentially amplified and filtered by the signal amplification unit and the filtering unit.

8. A microwave field generating device according to claim 5, characterized in that, The back-end algorithm module extracts the fluorescence amplitude through lock-in amplification and eliminates background noise based on differential processing.

9. A microwave field generating device according to claim 5, characterized in that, The pulse signal generation module provides TTL pulse signals for the first and second radio frequency switches. The second radio frequency switch controls the on / off of the laser pulse, and the first radio frequency switch controls the modulation of the microwave signal.

10. A microwave field generating device according to claim 5, characterized in that, The pulse signal generation module generates a subcarrier modulation signal through a third modulation pulse unit, forcing the second half cycle of the microwave radiation sequence to be at a low level, thereby completing the targeted separation of the fluorescence sideband components.

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