A confocal micro-region fluorescence detection system and method based on a super surface light path

Abstract

This application provides a confocal micro-area fluorescence detection system and method based on a metasurface optical path, relating to the fields of quantum optics and fluorescence detection technology. The system includes a laser, a single-photon detector, and a polarization converter, a first metalens, a second metalens, and a metasurface filter, all sequentially arranged and possessing a metasurface structure. The detection laser output from the laser is polarized by the polarization converter, then focused onto the sample under test by the first metalens, exciting fluorescence on the sample and reflecting a portion of the detection laser. The generated fluorescence is then collected and collimated by the second metalens, and further filtered by the wavelength-selective metasurface of the metasurface filter, transmitting the fluorescence to the single-photon detector to collect fluorescence detection data. This system utilizes the wavelength selectivity of the metasurface to achieve optical path adjustment and filtering functions, simplifying the optical path structure, reducing the system's size and weight, and improving its integration and stability.

Description

Technical Field

[0001] This application relates to the fields of quantum optics and fluorescence detection technology, and in particular to a confocal micro-area fluorescence detection system and method based on metasurface optical paths. Background Technology

[0002] Solid-state single-photon sources are core devices in quantum information technologies such as quantum communication and quantum computing. To ensure the stability of quantum system performance, it is necessary to accurately detect the single-photon emission characteristics of solid-state single-photon sources. These characteristics include key performance indicators such as single-photon purity, indistinguishability, and brightness.

[0003] When detecting single-photon emission characteristics, laser scanning confocal microscopy can be used. Based on the high spatial resolution and optical tomography capabilities brought about by the conjugate focusing principle, laser scanning confocal microscopy can accurately characterize key parameters of quantum light sources at the sub-micrometer scale, such as single-photon emission intensity, polarization state, spectral characteristics, and second-order correlation function, thereby evaluating the core performance indicators corresponding to single-photon emission characteristics.

[0004] However, the optical path of laser scanning confocal microscopy systems typically relies on multiple discrete refractive lenses to achieve laser focusing and fluorescence collection, and requires complex filter sets for excitation light suppression and fluorescence screening. This results in a lengthy optical path structure, a large number of components, and complex assembly and adjustment. Consequently, the overall system size is large, and its stability is greatly affected by mechanical alignment, making it difficult to achieve modular integration and portable deployment. This limits its application in scenarios such as on-site detection in quantum experiments, debugging of mobile quantum devices, and on-site characterization of multi-node quantum networks. Summary of the Invention

[0005] In view of this, embodiments of this application provide a confocal micro-area fluorescence detection system and method based on metasurface optical paths to solve the technical problem of the large overall size of the system.

[0006] According to a first aspect of this application, a confocal micro-area fluorescence detection system based on a metasurface optical path is provided, the system comprising: A laser used to output a detection laser; A polarization converter, a first superlens, a second superlens, and a metasurface filter are sequentially arranged along the output optical path of the laser. The polarization converter includes a polarization-converting metasurface for adjusting the polarization state of the detection laser. The first and second superlenses are geometrically phase-based focusing superlenses. The first superlens focuses the polarization-converted detection laser onto the sample to excite fluorescence on the sample. The second superlens collects and collimates the fluorescence. The metasurface filter includes a wavelength-selective metasurface for transmitting the fluorescence. A single-photon detector is disposed in the optical path of the transmitted fluorescence of the metasurface filter; the single-photon detector is used to collect fluorescence detection data.

[0007] In some embodiments, the system further includes: A first fiber collimator is disposed between the laser and the polarization converter; the first fiber collimator is used to collimate the detection laser output by the laser. A second fiber collimator is disposed between the metasurface filter and the single-photon detector; the second fiber collimator is used to collect the fluorescence transmitted by the metasurface filter and couple it to the single-photon detector.

[0008] In some embodiments, the system further includes: A single-mode optical fiber is disposed between the laser and the first fiber collimator, with one end of the single-mode optical fiber connected to the laser and the other end connected to the first fiber collimator; the single-mode optical fiber is used to transmit the detection laser to the first fiber collimator. A multimode fiber is disposed between the second fiber collimator and the single-photon detector; the multimode fiber is used to transmit the fluorescence collected by the second fiber collimator to the single-photon detector.

[0009] In some embodiments, the polarization conversion metasurface of the polarization converter adopts a single-layer dielectric nanoarray structure to convert the linearly polarized collimated Gaussian detection laser beam output by the laser into circularly polarized light through the polarization conversion metasurface.

[0010] In some embodiments, both the first and second superlenses comprise a single-layer dielectric nanoarray structure; the operating wavelength of the first superlens is matched with the detection laser wavelength output by the laser; and the operating wavelength of the second superlens is matched with the fluorescence wavelength generated by the sample under test.

[0011] In some embodiments, the wavelength-selective metasurface of the metasurface filter employs a single-layer dielectric nanoarray structure, so that the wavelength-selective metasurface has reflection characteristics for the detection laser band reflected by the sample under test and transmission characteristics for the fluorescence band through the nanostructure resonance characteristics of the wavelength-selective metasurface.

[0012] In some embodiments, the monolayer dielectric nanoarray structure includes a substrate unit and functional units; a plurality of the functional units are disposed on the substrate unit to form a metasurface structure comprising a monolayer dielectric nanoarray.

[0013] In some embodiments, the substrate unit is made of quartz glass; the functional unit is a rectangular titanium dioxide nanopillar; the monolayer dielectric nanoarray structure achieves geometric phase modulation by changing the orientation angle of the rectangular titanium dioxide nanopillar; The single-layer dielectric nanoarray structure is fabricated using electron beam lithography, and the pattern transfer is achieved through reactive ion etching to set multiple functional units on the substrate unit.

[0014] In some embodiments, the system further includes: The housing is a cavity structure made of a rigid material; the polarization converter, the first superlens, the second superlens, and the metasurface filter are fixed in the housing to form an optical axis in the cavity of the housing; The focal length of the first superlens and the second superlens is a first distance; the focal position of the first superlens and the second superlens is offset by a second distance relative to the optical axis; the second distance is less than the first distance.

[0015] According to a second aspect of this application, a confocal micro-area fluorescence detection method based on a metasurface optical path is provided, applied to the system described in the first aspect; the method includes: Acquire fluorescence detection data collected by a single-photon detector; Based on the fluorescence detection data, single-photon performance data of the sample under test in three-dimensional space is established. The single-photon performance data is a set of fluorescence detection data at multiple spatial positions obtained by moving the sample under test with a three-dimensional displacement stage and performing spatial scanning. The optimal sites suitable for quantum technology are selected from the single-photon performance data.

[0016] Based on the above technical solution, this application provides a confocal micro-area fluorescence detection system and method based on a metasurface optical path. The system includes a laser, a single-photon detector, and a polarization converter, a first metalens, a second metalens, and a metasurface filter, all arranged sequentially along the laser output optical path and possessing metasurface structures. The detection laser output from the laser can be polarized by the polarization converter and then focused onto the sample to be tested by the first metalens to generate fluorescence on the sample. The generated fluorescence is then collected and collimated by the second metalens, and the beam is filtered by the wavelength-selective metasurface of the metasurface filter before being transmitted to the single-photon detector to collect fluorescence detection data. The system can utilize the wavelength selectivity of the metasurface to achieve optical path adjustment and filtering functions, simplifying the optical path structure, reducing the system's size and weight, and improving the system's integration and stability.

[0017] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0018] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 A schematic diagram of the structure of a confocal micro-area fluorescence detection system based on metasurface optical path provided in an embodiment of this application; Figure 2 This is a schematic diagram of a single-layer dielectric nanostructure provided in an embodiment of this application; Figure 3 This is a schematic diagram of a single-layer dielectric nanoarray structure provided in an embodiment of this application; Figure 4 This is a schematic diagram of the construction result of the polarization conversion device provided in the embodiments of this application; Figure 5 This is a schematic diagram of focal length and offset distance provided for an embodiment of this application; Figure 6 This is a schematic diagram of the confocal micro-area fluorescence detection method based on metasurface optical path provided in the embodiments of this application. Detailed Implementation

[0019] The present application will be described in detail below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present application can be combined with each other.

[0020] In this embodiment, the confocal micro-area fluorescence detection system based on metasurface optical paths can be used to detect the single-photon emission characteristics of solid-state single-photon sources. A solid-state single-photon source is a device used in quantum information technologies such as quantum communication and quantum computing. Solid-state single-photon sources can emit single photons on demand within solid materials using atomic-scale emitting centers such as quantum dots and crystal defects to form a quantum light source.

[0021] For example, single-photon emission can be achieved in solid-state single-photon sources based on two-dimensional materials such as InAs / GaAs quantum dots, diamond NV centers, silicon carbide centers, WSe2 / h-BN, and organic molecular crystals such as pentacene and DBATT.

[0022] The single-photon emission characteristics of a solid-state single-photon source determine whether the light source can meet the requirements of quantum information technologies such as quantum computing and quantum communication. In some embodiments, the single-photon emission characteristics of a solid-state single-photon source may include core performance indicators such as single-photon purity, indistinguishability, and brightness. Among them, single-photon purity is used to measure the ability of a solid-state single-photon source to emit only one photon at a time, and can be characterized by a second-order correlation function g²(0). The ideal value of single-photon purity is 0.

[0023] Photon indistinguishability measures the quantum state uniformity of photons emitted in successive waves from a solid-state single-photon source. It can be measured by the visibility of interference from the Hong-Ou-Mandel (HOM) effect, with an ideal value of 100% for photon indistinguishability.

[0024] Brightness measures the effective number of single photons a solid-state single-photon source can generate per second, and it can affect application speed along with extraction efficiency. In addition to indicators such as single-photon purity, indistinguishability, and brightness, single-photon emission characteristics can also include other indicators, such as long-term emission stability and the operating temperature range. These indicators can be comprehensively measured based on corresponding analytical calculation methods.

[0025] It should be noted that in some embodiments of this application, the detection process of single-photon emission characteristics is illustrated using core performance indicators such as single-photon purity, indistinguishability, and brightness as examples. Obviously, the described scheme can also be applied to other indicators, which will not be shown one by one.

[0026] In some embodiments, a laser scanning confocal microscopy system can be used to detect the single-photon emission characteristics of a solid-state single-photon source. Based on the high spatial resolution and optical tomography capabilities brought about by the conjugate focusing principle, the laser scanning confocal microscopy system can accurately characterize key parameters of a quantum light source at the sub-micrometer scale, such as single-photon emission intensity, polarization state, spectral characteristics, and second-order correlation function, thereby evaluating the core performance indicators corresponding to the single-photon emission characteristics.

[0027] The laser scanning confocal microscopy system can include a laser source, a confocal module, and a fluorescence detection device. The laser source can be a solid-state laser to provide excitation light with good monochromaticity and strong directionality. Components such as an acousto-optic tunable filter (AOTF) can be used to precisely control the laser intensity and rapidly switch wavelengths to meet the needs of different fluorescent dyes.

[0028] A confocal module achieves confocal and scanning functions through a series of integrated key components. For example, a confocal module may include a scanning galvanometer, a confocal pinhole, and a beam splitter. The scanning galvanometer, through high-speed oscillation, guides the laser beam to scan the sample point-by-point and line-by-line. The confocal pinhole blocks stray and scattered light from outside the focal plane, allowing only signal light from the focal plane to pass through, thereby improving image clarity and signal-to-noise ratio. The beam splitter, which may include a beam splitter and filters, is responsible for reflecting the excitation light onto the sample and effectively separating the fluorescence emitted by the sample from the excitation light, then distributing the fluorescence signals of different colors to different detection channels according to wavelength.

[0029] Fluorescence detection devices can capture weak fluorescence signals passing through a pinhole using photomultiplier tubes (PMTs) or ultra-sensitive area array detectors, such as GaAsP detectors, and convert them into electrical signals. Fluorescence detection devices can contain multiple independent detection channels for simultaneously acquiring various fluorescence signals.

[0030] Because the optical path of a laser scanning confocal microscopy system relies on multiple discrete refractive lenses to achieve laser focusing and fluorescence collection, and requires complex filter sets for excitation light suppression and fluorescence screening, the optical path structure is lengthy, the number of components is large, and the assembly and adjustment are complex. As a result, the overall system size is large, the stability is greatly affected by mechanical alignment, and it is difficult to achieve modular integration and portable deployment, which limits its application in scenarios such as on-site detection in quantum experiments, debugging of mobile quantum devices, and on-site characterization of multi-node quantum networks.

[0031] Furthermore, the filters in laser scanning confocal microscopy systems suffer from problems such as fixed bandwidth, high angle sensitivity, and limited passband and stopband performance. Their filtering efficiency is easily affected by optical path offset or polarization changes, making it difficult to achieve efficient excitation light suppression and narrowband fluorescence extraction. This leads to a decrease in the signal-to-noise ratio of single-photon detection, which severely affects the detection of weak fluorescence signals and low-noise single-photon counting, thus restricting the accuracy and reliability of solid-state single-photon source performance detection.

[0032] Furthermore, in micro-area fluorescence detection, laser scanning confocal microscopy systems struggle to simultaneously achieve high numerical aperture focusing, polarization-resolved detection, and dynamic spectral filtering within the same optical path. The polarization state and spectral information of solid-state single-photon sources are crucial for their applications in quantum coding and photon interference. Moreover, the fixed function and discrete arrangement of lenses and filters in laser scanning confocal microscopy systems limit the system's flexibility in multi-parameter parallel characterization and rapid reconstruction.

[0033] To address the issue of the system's overall large size, this application provides a confocal micro-area fluorescence detection system based on a metasurface optical path. For example... Figure 1As shown, the system includes: a laser 1, a polarization converter 2, a first superlens 3, a second superlens 4, a metasurface filter 5, and a single-photon detector 6.

[0034] The laser 1 is used to output a detection laser. The laser 1 can be selected based on different application scenarios, such as 405nm, 488nm, 532nm, 561nm, 639nm, etc. Lasers 1 that output different laser types can be based on different laser principles. For example, laser 1 can use a continuous laser source with a wavelength of 532nm to output a linearly polarized collimated detection laser into space. The beam pattern diameter of the detection laser is approximately 2mm. In this embodiment, taking diamond nanoparticles containing NV color centers as an example, fluorescence in the 600-800nm ​​wavelength range can be generated after excitation by this detection laser.

[0035] The polarization converter 2, the first superlens 3, the second superlens 4, and the metasurface filter 5 can be sequentially arranged along the output optical path of the laser 1. For example, as... Figure 1 As shown, laser 1 is located on the left, emitting a detection laser horizontally to the right. From left to right, polarization converter 2, first metalens 3, second metalens 4, and metasurface filter 5 are arranged sequentially. The sample to be tested is placed between the first metalens 3 and the second metalens 4.

[0036] The polarization converter 2 can be used to adjust the polarization state of the detection laser output from the laser 1, converting the linearly polarized collimated Gaussian beam into circularly polarized light, thus providing a suitable polarization state for subsequent geometric phase control. Therefore, the polarization converter 2 includes a polarization conversion metasurface.

[0037] In some embodiments, the polarization conversion metasurface of the polarization converter 2 adopts a single-layer dielectric nanoarray structure to convert the linearly polarized collimated Gaussian detection laser beam output by the laser into circularly polarized light through the polarization conversion metasurface.

[0038] For example, the polarization converter 2 adopts a single-layer rectangular titanium dioxide (TiO2) nanopillar array structure, which is functionally equivalent to a quarter-wave plate. It can convert the incident linearly polarized collimated light into circularly polarized light after passing through the polarization converter 2, thus preparing for subsequent wavefront modulation based on geometric phase.

[0039] TiO2 has a high refractive index in the visible and near-infrared bands, such as approximately 2.4–2.7, enabling strong light field manipulation at the subwavelength scale, which is beneficial for device miniaturization. Furthermore, it exhibits low absorption loss in the visible to near-infrared region, making it suitable for designing high-efficiency transmissive metasurface devices. Figure 2 , Figure 3As shown, the geometric parameters of the single-layer rectangular titanium dioxide (TiO2) nanopillars can be: length L = 350~550 nm, width W = 150~350 nm, height H = 400~800 nm, and arrangement period T = 400~600 nm.

[0040] In some embodiments, the system further includes a first fiber collimator 7. The first fiber collimator 7 is disposed between the laser 1 and the polarization converter 2, and is used to collimate the detection laser output from the laser 1. That is, the fundamental mode laser output from the laser 1 is collimated by the first fiber collimator 7 and then polarized by the polarization converter 2.

[0041] The detection laser signal can also be transmitted via optical fiber between the first fiber collimator 7 and the laser 1. Specifically, the system also includes a single-mode fiber 8, which is positioned between the laser 1 and the first fiber collimator 7. One end of the single-mode fiber 8 is connected to the laser 1, and the other end is connected to the first fiber collimator 7, used to transmit the detection laser output from the laser 1 to the first fiber collimator 7.

[0042] For example, laser 1 uses a continuous laser source with a wavelength of 532 nm, connected to the first fiber collimator 7 via a single-mode fiber 8 to output linearly polarized collimated laser light into space. Then, a polarization converter 2 converts the incident linearly polarized collimated light into circularly polarized light. If 45° linearly polarized light is incident, the output will be circularly polarized. The polarization converter 2 is constructed as follows: Figure 4 As shown.

[0043] The first superlens 3 is used to focus the polarized detection laser onto the sample to be tested, thereby exciting fluorescence on the sample. Therefore, the first superlens 3 is a focusing superlens based on geometric phase. While the detection laser is focused onto the sample to be tested and excited to generate fluorescence, the sample also reflects part of the detection laser.

[0044] In some embodiments, the first superlens 3 comprises a single-layer dielectric nanoarray structure, and the operating wavelength of the first superlens 3 matches the detection laser wavelength output by the laser 1, so that the first superlens 3 can focus the detection laser output by the laser 1. For example, the first superlens 3 performs wavefront modulation based on the geometric phase principle, and its superatomic structure is similar to that of the polarization converter 2, also employing a single-layer rectangular TiO2 nanopillar. According to the geometric phase principle, when circularly polarized light is incident on the TiO2 nanopillar, the cross-polarized component in its outgoing light will acquire an additional phase, which is equal to twice the structural orientation angle.

[0045] Therefore, complete phase coverage within the range of 0 to 2π can be achieved by rotating the orientation of the structure. That is, the geometric phase of a monolayer dielectric nanoarray structure is achieved through changes in the orientation angle of rectangular titanium dioxide nanopillars. Compared to other phase modulation methods, geometric phase modulation originates from the geometric relationship of structural rotation, rather than a resonance effect. It maintains stable performance over a wider wavelength range, and phase modulation is relatively independent of the structure's size and shape parameters, facilitating separate optimization of amplitude and phase.

[0046] The first superlens 3 functions as a converging lens. In some embodiments, the focal length of the first superlens 3 is a first distance; the focal position of the first superlens 3 is offset from the optical axis by a second distance, and the second distance is less than the first distance.

[0047] For example, such as Figure 5 As shown, the first superlens 3 is designed with a focal length of 20 mm, and the focal point is offset downwards by approximately 10 mm relative to the optical axis to accommodate the layout of the actual sample stage. Furthermore, the phase distribution on the surface of the first superlens 3 is calculated using a multifocal formula. The beam converged by the first superlens 3 can be focused onto the surface of the sample under test through the observation hole, with a spot radius of approximately 1.185 μm at the focal point. When the sample under test is irradiated by this excitation light, it produces fluorescence with a wavelength range of 600-800 nm. Simultaneously, part of the excitation light is reflected, and both are received by the second superlens 4 through the same observation hole.

[0048] The second superlens 4 is also a geometric phase-based focusing superlens, and the second superlens 4 is used to collect and collimate fluorescence to transmit the collected and collimated fluorescence to the metasurface filter 5.

[0049] In some embodiments, the second superlens 4 also includes a monolayer dielectric nanoarray structure, and the operating wavelength of the second superlens 4 matches the fluorescence wavelength generated by the sample under test, so that the fluorescence generated by the sample under test can be collected and collimated by the second superlens 4. For example, the second superlens 4 can functionally serve as a collecting lens to focus the fluorescence generated after the sample point is excited.

[0050] Similarly, the focal length of the second superlens 4 can also be the first distance, and the focal position of the second superlens 4 is offset from the optical axis by a second distance, where the second distance is less than the first distance. For example, the focal lengths of both the first superlens 3 and the second superlens 4 are 15-25 mm, and the focal position is offset downwards by 8-12 mm relative to the optical axis. Then, for the second superlens 4, its focal length is 20 mm, and the focal point is designed to be offset downwards by 10 mm to ensure a conjugate relationship with the excitation optical path and satisfy the confocal imaging condition.

[0051] The metasurface filter 5 is used to transmit fluorescence and reflect a portion of the detection laser reflected by the sample under test. Therefore, the metasurface filter 5 includes a wavelength-selective metasurface. In some embodiments, the wavelength-selective metasurface of the metasurface filter 5 employs a monolayer dielectric nanoarray structure to achieve reflection characteristics in the detection laser band reflected by the sample under test and transmission characteristics in the fluorescence band through the nanostructure resonance properties of the wavelength-selective metasurface.

[0052] For example, the metasurface filter 5 employs a metasurface structure with wavelength selectivity, its basic unit still being a single-layer rectangular TiO2 nanopillar. Through the arrangement and resonant characteristics of the nanostructure, it functions as a bandpass filter. Specifically, for 532 nm excitation light, the metasurface filter 5 exhibits high reflectivity, thus suppressing it; while for the target fluorescence band (600-800 nm), it has high transmittance, effectively preserving the fluorescence signal. Therefore, the metasurface filter 5 can achieve efficient bandpass filtering and can replace filter components.

[0053] As can be seen, the polarization converter 2, the first superlens 3, the second superlens 4 and the metasurface filter 5 described in the above embodiments are all composed of a single-layer dielectric nanostructure array, that is, they all contain metasurface structures, thereby forming a detection optical path for confocal micro-area fluorescence detection based on the combination of metasurface structure devices.

[0054] In some embodiments, the monolayer dielectric nanoarray structure includes a substrate unit and functional units; multiple functional units are disposed on the substrate unit to form a metasurface structure containing a monolayer dielectric nanoarray. The substrate unit may be made of quartz glass; the functional units are rectangular titanium dioxide nanopillars. The geometric phase of the monolayer dielectric nanoarray structure is controlled by varying the orientation angle of the rectangular titanium dioxide nanopillars.

[0055] For example, the substrate material of the monolayer dielectric nanostructure array is quartz glass with a thickness of 1 mm. Quartz glass has good light transmittance and stability, making it suitable for optical path transmission in the visible and near-infrared bands. The dielectric nanostructure is a rectangular or elliptical titanium dioxide nanopillar. Titanium dioxide has a high refractive index (2.4–2.7) in the visible and near-infrared bands, which can achieve strong light field modulation at the subwavelength scale.

[0056] The titanium dioxide nanopillars have a length L = 350–550 nm, a width W = 150–350 nm, a height H = 400–800 nm, and an arrangement period T = 400–600 nm. The orientation angle of the titanium dioxide nanopillars varies continuously within the range of 0°–180°. According to the geometric phase principle, complete geometric phase modulation from 0° to 2π can be achieved, satisfying the wavefront modulation requirements of the superlens.

[0057] In some embodiments, the monolayer dielectric nanoarray structure is fabricated using electron beam lithography, and multiple functional units are transferred onto the substrate unit through reactive ion etching. For example, the polarization converter 2, the first superlens 3, the second superlens 4, and the metasurface filter 5 are all monolayer dielectric nanostructure arrays, using quartz glass as the substrate and rectangular TiO2 nanopillars as functional units. The layout is precisely fabricated using electron beam lithography, and the pattern transfer is achieved through reactive ion etching.

[0058] Therefore, by integrating multiple optical functions such as polarization conversion, focusing, and wavelength selective filtering onto metasurface elements, a small, compact, easy-to-integrate, and stable metasurface optical path system for confocal micro-area fluorescence detection can be constructed. This effectively alleviates the technical problems of large size, complex structure, and high assembly difficulty of detection systems, and is particularly suitable for applications such as solid-state single-photon source detection technology.

[0059] The single-photon detector 6 is used to collect fluorescence detection data. The single-photon detector 6 can be placed in the fluorescence light path transmitted by the metasurface filter 5, and can detect the single-photon-level light signal of the transmitted fluorescence.

[0060] For example, the single-photon detector 6 may include detectors such as a photomultiplier tube (PMT), a single-photon avalanche diode (SPAD), and a superconducting nanowire single-photon detector (SNSPD). Taking a photomultiplier tube as an example, a photomultiplier tube can acquire fluorescence detection data based on the external photoelectric effect and secondary electron emission. After a photon excites an electron, the electron is amplified through multiple stages to obtain fluorescence detection data.

[0061] In some embodiments, the system further includes a second fiber collimator 9 disposed between the metasurface filter 5 and the single-photon detector 6. The second fiber collimator 9 is used to collect and couple the fluorescence transmitted by the metasurface filter 5 to the single-photon detector 6.

[0062] Optical signals can be transmitted between the second fiber collimator 9 and the single-photon detector 6 via a multimode fiber 10. In some embodiments, the system further includes a multimode fiber 10, which is disposed between the second fiber collimator 9 and the single-photon detector 6, and is used to transmit the fluorescence collected by the second fiber collimator 9 to the single-photon detector 6.

[0063] For example, the fluorescence signal retained by the metasurface filter 5 can be collected by the second fiber collimator 9 and coupled into the multimode fiber 10. The multimode fiber 10 then transmits the fluorescence signal to the single-photon detector 6 to complete the final detection of the signal.

[0064] In some embodiments, the system further includes a housing. The housing is a cavity structure made of a rigid material. The polarization converter 2, the first superlens 3, the second superlens 4, and the metasurface filter 5 are all fixed within the housing to form an optical axis within the cavity of the housing.

[0065] For example, the outer shell is made of a lightweight rigid material to fix the relative positions of the polarization converter 2, the first superlens 3, the second superlens 4 and the metasurface filter 5, ensuring the optical path alignment accuracy, while improving the system's vibration resistance and reducing assembly difficulty.

[0066] By applying the technical solutions of the above embodiments, in the confocal micro-area fluorescence detection system based on metasurface optical paths described in the above embodiments, the laser 1 outputs a fundamental mode laser, which is collimated by the first fiber collimator 7, and then sequentially undergoes polarization conversion by the polarization converter 2 and excitation light focusing by the first superlens 3, converging to illuminate the sample to be tested. The excitation light reflected from the sample to be tested and the excited fluorescence are collected and collimated by the second superlens 4, and after being filtered by the metasurface filter 5, the excitation light is efficiently suppressed (reflected), and only the fluorescence is transmitted, which is finally collected by the second fiber collimator 9 and coupled to the single-photon detector 6 for detection.

[0067] The system can use a metalens to replace the traditional refractive lens. The metalens has a planar structure, and its thickness can be reduced to the subwavelength level, shortening the optical path length, reducing the system's size and weight, and facilitating integration and portable packaging. Furthermore, the wavelength selectivity of the metasurface filter achieves filtering, eliminating the need for the filter array required in a confocal system, reducing the number of optical components, simplifying optical path design, and lowering assembly difficulty and system cost. In addition, the entire system uses planar optical components, which facilitates precise coupling with fiber optic systems and is beneficial for modular packaging. Simultaneously, the geometric phase modulation characteristics of the metalens are less affected by environmental factors, improving the system's vibration resistance and alignment tolerance, ensuring long-term stable operation.

[0068] According to the confocal micro-area fluorescence detection system based on metasurface optical path described in the above embodiments, some embodiments of this application also provide a confocal micro-area fluorescence detection method based on metasurface optical path. The method can be combined with a three-dimensional precision displacement stage for spatial scanning to establish single-photon performance data of the sample under test in three-dimensional space, thereby screening out the best sites suitable for quantum technology.

[0069] The method can be applied to the confocal micro-area fluorescence detection system based on metasurface optical paths, or to an electronic device that establishes a communication connection with the system and has data processing capabilities. The electronic device includes, but is not limited to, computers, servers, mobile terminals, smart wearable devices, and industrial control computers. For ease of description, the system is used as the execution subject of the method in this embodiment. It should be understood that the method can also be applied to other types of execution subjects, which are not shown one by one in this embodiment. Figure 6 As shown, the method includes: S101. Acquire fluorescence detection data collected by the single-photon detector; S102. Establish single-photon performance data of the sample under test in three-dimensional space based on fluorescence detection data; S103. Select the best sites suitable for quantum technology from single-photon performance data.

[0070] To achieve fluorescence detection of the sample under test, the system first acquires fluorescence detection data collected by a single-photon detector. Then, based on the fluorescence detection data, it establishes single-photon performance data of the sample in three-dimensional space. This single-photon performance data is a set of fluorescence detection data obtained by moving the sample under test using a three-dimensional displacement stage and performing spatial scanning at multiple spatial locations. Finally, the optimal sites suitable for quantum technology are selected from the single-photon performance data.

[0071] For example, during detection, fluorescence detection data collected by a single-photon detector can be obtained first. That is, the system can be used to scan the sample point by point, and the luminescence intensity and time information of each spatial location can be recorded by a single-photon detector.

[0072] The sample to be tested is a diamond nanoparticle sample containing NV color centers. The sample is placed on a three-dimensional displacement stage of the system. A 532nm laser 1 is used as the excitation source, and its power is controlled by an acousto-optic tunable filter (AOTF), set to 100μW. The detection laser generated by laser 1 is collimated by a first fiber collimator 7, then polarized by a polarization converter 2, and focused by a first superlens 3, converging onto the sample. The excitation light reflected from the sample and the excited fluorescence are collected and collimated by a second superlens 4, filtered by a metasurface filter 5, and the excitation light is efficiently suppressed, with only fluorescence transmitted. Finally, the fluorescence is collected by a second fiber collimator 9 and coupled to a single-photon detector 6 for detection.

[0073] The system's data processing module can control the movement of a three-dimensional displacement stage via computer commands, enabling the laser focus to perform a grating scan on the sample surface. With a scanning range of 20μm × 20μm and a resolution of 100 × 100 pixels, a total of 10,000 points need to be acquired. Within the dwell time (e.g., 50 microseconds) of each pixel, the single-photon detector 6 records all arriving photons and generates a time series, i.e., fluorescence detection data. The fluorescence detection data may include photon arrival time stamps to record the precise arrival time of each photon. The data processing module then associates and saves the spatial coordinates (X, Y) of each pixel with its corresponding photon count and time series data, forming a raw data file of fluorescence detection data.

[0074] Then, based on the fluorescence detection data, single-photon performance data of the sample under test in three-dimensional space is established. By processing the collected raw data, physical parameters that characterize the emitter's performance are extracted and mapped onto three-dimensional space. Therefore, a confocal fluorescence intensity map (grayscale image) can be generated based on the total photon count of each pixel. The confocal fluorescence intensity map can clearly show the location of all emitting points in the sample; the brighter the point, the stronger the emission from the emitter at that location.

[0075] To confirm whether a bright spot is a true single-photon source, its second-order correlation function g needs to be calculated. 2 (0). For the photon arrival time data of each bright spot region in the fluorescence detection data, the time difference distribution will be statistically analyzed, and g will be calculated. 2 (0) value. If g 2 If (0) < 0.5, then it can be determined that it is a single-photon emission.

[0076] Then, in the spatial dimension (X, Y), a performance label is generated for each pixel, containing the photon count rate of that point to reflect brightness; the calculated g 2 The (0) value reflects the single-photon purity, and the spectral information reflects the emission wavelength. Furthermore, in the depth dimension (Z), an optical slice containing three-dimensional information can be obtained by stepping along the Z-axis using a three-dimensional displacement stage, thereby establishing a single-photon performance database of the sample in three-dimensional space (X, Y, Z).

[0077] Then, the best sites suitable for quantum technology are selected from the single-photon performance data. That is, according to the specific needs of quantum technology, such as quantum computing requiring high brightness and indistinguishable photons, and quantum communication requiring communication bands, the screening conditions are set, and the optimal single emitter is selected from the database.

[0078] For example, assuming the goal is to find a high-quality single-photon source for optical quantum computing, the core criterion would be: extremely high single-photon purity, g 2(0) < 0.05; High brightness, saturated photon count rate > 1,000,000 counts / s; Spectral stability, no drift in emission wavelength around 637 nm. Then, the constructed database is automatically analyzed. It first excludes all g... 2 (0)>0.05 emission points, then sort the remaining candidate points from high to low brightness, and finally remove the points with unstable spectrum.

[0079] Through the above steps, the system ultimately generates a list of candidate sites and marks the coordinates of the optimal site on the confocal image with special markers, such as red markers indicating X=12.5μm, Y=8.3μm. This allows the three-dimensional displacement stage to be moved to precise coordinates for subsequent fine spectral measurements or quantum optics experiments to ultimately confirm its performance.

[0080] By applying the technical solutions of the above embodiments, the confocal micro-area fluorescence detection method based on metasurface optical path provided by the above embodiments can perform spatial scanning by combining a three-dimensional precision displacement stage after the single-photon detector completes the signal detection, so as to establish single-photon performance data of the sample under test in three-dimensional space, thereby screening out the best site suitable for quantum technology.

[0081] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0082] The embodiments described above are merely examples of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the protection scope of this application.

Claims

1. A confocal micro-area fluorescence detection system based on metasurface optical path, characterized in that, The system includes: A laser used to output a detection laser; A polarization converter, a first superlens, a second superlens, and a metasurface filter are sequentially arranged along the output optical path of the laser. The polarization converter includes a polarization-converting metasurface for adjusting the polarization state of the detection laser. The first and second superlenses are geometrically phase-based focusing superlenses. The first superlens focuses the polarization-converted detection laser onto the sample to excite fluorescence on the sample. The second superlens collects and collimates the fluorescence. The metasurface filter includes a wavelength-selective metasurface for transmitting the fluorescence. A single-photon detector is disposed in the optical path of the transmitted fluorescence of the metasurface filter; the single-photon detector is used to collect fluorescence detection data.

2. The system according to claim 1, characterized in that, The system also includes: A first fiber collimator is disposed between the laser and the polarization converter; the first fiber collimator is used to collimate the detection laser output by the laser. A second fiber collimator is disposed between the metasurface filter and the single-photon detector; the second fiber collimator is used to collect the fluorescence transmitted by the metasurface filter and couple it to the single-photon detector.

3. The system according to claim 2, characterized in that, The system also includes: A single-mode optical fiber is disposed between the laser and the first fiber collimator, with one end of the single-mode optical fiber connected to the laser and the other end connected to the first fiber collimator; the single-mode optical fiber is used to transmit the detection laser to the first fiber collimator. A multimode fiber is disposed between the second fiber collimator and the single-photon detector; the multimode fiber is used to transmit the fluorescence collected by the second fiber collimator to the single-photon detector.

4. The system according to claim 1, characterized in that, The polarization conversion metasurface of the polarization converter adopts a single-layer dielectric nanoarray structure to convert the linearly polarized collimated Gaussian detection laser beam output by the laser into circularly polarized light.

5. The system according to claim 1, characterized in that, Both the first and second superlenses comprise a single-layer dielectric nanoarray structure; the operating wavelength of the first superlens matches the detection laser wavelength output by the laser; and the operating wavelength of the second superlens matches the fluorescence wavelength generated by the sample under test.

6. The system according to claim 1, characterized in that, The wavelength-selective metasurface of the metasurface filter adopts a single-layer dielectric nanoarray structure. Through the nanostructure resonance characteristics of the wavelength-selective metasurface, it has reflection characteristics for the detection laser band reflected by the sample under test and transmission characteristics for the fluorescence band.

7. The system according to any one of claims 4, 5, and 6, characterized in that, The monolayer dielectric nanoarray structure includes a substrate unit and functional units; a plurality of the functional units are disposed on the substrate unit to form a metasurface structure containing a monolayer dielectric nanoarray.

8. The system according to claim 7, characterized in that, The substrate unit is made of quartz glass; the functional unit is a rectangular titanium dioxide nanopillar; the monolayer dielectric nanoarray structure achieves geometric phase modulation by changing the orientation angle of the rectangular titanium dioxide nanopillar; The single-layer dielectric nanoarray structure is fabricated using electron beam lithography, and the pattern transfer is achieved through reactive ion etching to set multiple functional units on the substrate unit.

9. The system according to claim 1, characterized in that, The system also includes: The housing is a cavity structure made of a rigid material; the polarization converter, the first superlens, the second superlens, and the metasurface filter are fixed in the housing to form an optical axis in the cavity of the housing; The focal length of the first superlens and the second superlens is a first distance; the focal position of the first superlens and the second superlens is offset by a second distance relative to the optical axis; the second distance is less than the first distance.

10. A confocal micro-area fluorescence detection method based on metasurface optical path, characterized in that, Applied to the system according to any one of claims 1-9; the method comprises: Acquire fluorescence detection data collected by a single-photon detector; Based on the fluorescence detection data, single-photon performance data of the sample under test in three-dimensional space is established. The single-photon performance data is a set of fluorescence detection data at multiple spatial positions obtained by moving the sample under test with a three-dimensional displacement stage and performing spatial scanning. The optimal sites suitable for quantum technology are selected from the single-photon performance data.

Images