Resonance fluorescence device and method for generating resonance fluorescence

Abstract

The present application provides a resonance fluorescence device and a method for generating resonance fluorescence, comprising: a linear polarization module (100), comprising an incident polarizer (110), a polarization beam splitter (120), and an exit polarizer (130), wherein the polarization beam splitter (120) is optically coated to improve its optical polarization fidelity, the polarization direction of the incident polarizer (110) coincides with the horizontal component of the polarization beam splitter (120), and the polarization direction of the exit polarizer (130) coincides with the vertical component of the polarization beam splitter (120); an objective lens module (200), used for sending the resonance fluorescence to the polarization beam splitter (120), so that the polarization beam splitter (120) splits the resonance fluorescence and sends it to the exit polarizer (130), and the exit polarizer (130) separates the vertical component of the resonance fluorescence; and an optical fiber coupler (300), comprising a first port (310), wherein the first port (310) comprises a first optical fiber collimator and a first single-mode optical fiber.

Description

Technical Field

[0001] The present application relates to the field of resonance fluorescence technology, and in particular to a resonance fluorescence device and a method for generating resonance fluorescence. Background Art

[0002] At present, the filtering method of quantum dot resonant fluorescence single photon source generally adopts the following technical methods: the first method uses two linear polarizers to select linear polarized light to excite quantum dots through the incident polarizer, and the output polarizer selects the polarization angle of orthogonal polarization to filter out the background laser; however, in this scheme, the influence of the beam splitter on the linear polarization degree of the incident excitation light limits the optical filtering ability of the system. In actual use, a certain linear polarization angle needs to be selected to reduce the influence of the beam splitter on the linear polarization degree. The sensitivity of the linear polarization angle makes the filtering ability of the background laser of the system have poor environmental noise tolerance and short-term system stability. The system needs to be readjusted every once in a while. Therefore, the system is generally suitable for quantum dot samples with low surface reflectivity and low requirements for system filtering ability. The second method uses a polarization beam splitter to select a certain p-component linear polarized light to excite quantum dots, and the influence of the optical path on the phase of the excitation light is compensated by a 1 / 4 wave plate. Finally, the s-component linear polarized light is detected by the polarization beam splitter, thereby filtering out the p-component linearly polarized background laser. In this method, the polarization beam splitter can deterministically select the p component in the incident light for excitation and filter out the p component in the outgoing light without selecting a certain linear polarization angle. However, the fidelity of the linear polarized light prepared by the polarization beam splitter and the extinction ratio of the orthogonal polarization are still not as good as those of the linear polarizer due to the limitations of the current manufacturing process. In addition, since only a specific p component linear polarized light can be used for excitation, the application of the system in different polarization excitation schemes is limited. At the same time, the dispersion effect of the 1 / 4 wave plate and the polarization beam splitter is obvious, and a good phase compensation effect can only be maintained within a very narrow spectral range, which in turn limits the filtering ability of the system in a wide spectral band, especially in the application of picosecond pulse resonance fluorescence technology. Summary of the invention

[0003] 1. Technical issues to be resolved

[0004] The present application provides a resonance fluorescence device and a method for generating resonance fluorescence, which can effectively filter background laser and broaden the scope of spectral application.

[0005] (II) Technical solution

[0006] In the first aspect, the present application provides a resonance fluorescence device for laser excitation of quantum dots to generate resonance fluorescence for fluorescence detection, the device includes a linear polarization module 100, an objective lens module 200 and an optical fiber coupler 300, wherein: the linear polarization module 100 includes an incident polarizer 110, a polarization beam splitter 120, and an exit polarizer 130, wherein the polarization beam splitter 120 is optically coated to improve its optical polarization fidelity, the polarization direction of the incident polarizer 110 coincides with the horizontal component of the polarization beam splitter 120, and the polarization direction of the exit polarizer 130 coincides with the vertical component of the polarization beam splitter 120, the laser is sequentially transmitted through the incident polarizer 110 and the polarization beam splitter 120. The polarization beam splitter 120 sends the horizontal polarized light of the polarization beam splitter 120 to the objective lens module 200; the objective lens module 200 is used to send the horizontal polarized light to the quantum dots to excite the quantum dots to produce resonant fluorescence, and send the resonant fluorescence to the polarization beam splitter 120, so that the polarization beam splitter 120 splits the resonant fluorescence and sends it to the output polarizer 130, and the output polarizer 130 separates the vertical component of the resonant fluorescence; the optical fiber coupler 300 includes a first port 310, and the first port 310 includes a first optical fiber collimator and a first single-mode optical fiber, wherein the first optical fiber collimator is used to couple the vertical component of the resonant fluorescence to the first single-mode optical fiber to collect the resonant fluorescence.

[0007] Optionally, the linear polarization module 100 further includes a quarter wave plate, which is disposed between the polarization beam splitter 120 and the output polarizer 130 .

[0008] Optionally, the fiber coupler 300 further includes a second port 320 , and the second port 320 includes a second fiber collimator and a second single-mode optical fiber, wherein the second fiber collimator is used to couple the laser from the second single-mode optical fiber to the free space.

[0009] Optionally, the numerical aperture of the objective lens module 200 is 0.4.

[0010] Optionally, the quantum dots are provided in a microcavity quantum dot structure.

[0011] On the other hand, the present application provides a method for generating resonant fluorescence, including: S1, matching the wavelength of the laser with the wavelength of the quantum dots; S2, adjusting the linear polarization module 100 multiple times to obtain multiple adjusted extinction ratios; S3, comparing the multiple adjusted extinction ratios to obtain the optimal extinction ratio.

[0012] Optionally, exciting the quantum dots also generates background laser light. The step S3 to obtain the optimal extinction ratio includes: S31, measuring the first background laser intensity P before the output polarizer 130 background ; S32, obtain the second background laser intensity P in the first single-mode optical fiber collection ; S33, obtain the extinction ratio, the calculation formula of the extinction ratio is:

[0013]

[0014] Optionally, step S32 includes: using a spectrum detector to obtain the number of photons N in the first single-mode optical fiber, the second background laser intensity P collection The calculation formula is:

[0015]

[0016] Wherein, η is the detection efficiency of the spectrometer, and hv is the unit photon energy detected by the spectrometer.

[0017] Optionally, step S2 further includes obtaining signal-to-noise ratios adjusted multiple times, and step S3 further includes comparing the signal-to-noise ratios adjusted multiple times to obtain an optimal signal-to-noise ratio.

[0018] Optionally, the signal-to-noise ratio is calculated as:

[0019]

[0020] Among them, P signal is the true intensity of resonance fluorescence, P signal =PP noise , P noise is the background laser intensity collected in the first single-mode optical fiber, and P is the intensity of the detected resonance fluorescence.

[0021] (III) Beneficial effects

[0022] The present application provides a resonance fluorescence device and a method for generating resonance fluorescence, which have at least the following beneficial effects:

[0023] By selecting a polarization beam splitter with high polarization fidelity, the linear polarization degree of the laser is guaranteed to remain unchanged after passing through the polarization beam splitter, thus overcoming the disadvantage that the linear polarization degree of linear polarized light decreases after passing through an ordinary polarization beam splitter. Therefore, the background laser reflected back from the quantum dot sample can be effectively suppressed after passing through the output polarizer.

[0024] When resonantly exciting microcavity quantum dot samples, using an objective lens module with a smaller numerical aperture can ensure that the collection efficiency of the resonant fluorescence remains unchanged. On the other hand, as the numerical aperture of the objective lens module becomes smaller, the background laser scattered by the surface of the quantum dot sample that can be collected will also be reduced, thereby further improving the filtering ability of the background laser.

[0025] A single-mode optical fiber with a smaller light aperture is selected to collect the resonant fluorescence signal of quantum dots. On the one hand, it can better collect the resonant fluorescence signal emitted by the quantum dots. On the other hand, since the spatial mode of the background laser does not match the spatial mode of the single-mode optical fiber, it further ensures that the background laser collected in the single-mode optical fiber will be less. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The structure diagram of the resonance fluorescence device according to the embodiment of the present disclosure is schematically shown;

[0027] Figure 2 A schematic diagram showing the steps of a method for generating resonance fluorescence according to an embodiment of the present disclosure;

[0028] Figure 3 A flow chart schematically shows a method for generating resonance fluorescence using continuous laser according to an embodiment of the present disclosure;

[0029] Figure 4 A schematic diagram showing the steps of obtaining an optimal extinction ratio according to an embodiment of the present disclosure;

[0030] Figure 5 A flow chart schematically shows a method for generating resonance fluorescence using pulsed laser according to an embodiment of the present disclosure;

[0031] Figure 6 Schematically shows the resonance fluorescence collected by a conventional resonance fluorescence device according to an embodiment of the present disclosure;

[0032] Figure 7 The diagram schematically shows the resonance fluorescence collected by the resonance fluorescence device according to the embodiment of the present disclosure. DETAILED DESCRIPTION

[0033] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0034] In one embodiment, if Figure 1 As shown, the present disclosure provides a resonance fluorescence device for laser excitation of quantum dots to generate resonance fluorescence for fluorescence detection, the device includes a linear polarization module 100, an objective lens module 200 and an optical fiber coupler 300, wherein:

[0035] The linear polarization module 100 generates background laser light in the process of exciting quantum dots to generate resonant fluorescence, which is used to filter out the background laser light scattered by the quantum dot sample. The linear polarization module 100 includes an incident polarizer 110, a polarization beam splitter 120, and an exit polarizer 130. Since the extinction ratio of the linear polarized light generated by the polarization beam splitter 120 does not reach the level of linear polarization, the incident polarizer 110 and the exit polarizer 130 are required to be in mutually orthogonal polarization directions to further filter out the background laser light. The polarization direction of the incident polarizer 110 coincides with the horizontal (p) component of the polarization beam splitter 120, and the polarization direction of the exit polarizer 130 coincides with the vertical (s) component of the polarization beam splitter 120. In actual application, the horizontal (p) component linear polarized light determined on the polarization beam splitter 120 can be used to excite the quantum dots, and the purpose of filtering out the background laser light can be achieved by detecting the resonant fluorescence of the vertical (s) component linear polarization.

[0036] The laser light passes through the incident polarizer 110 and the polarization beam splitter 120 in sequence, and the horizontally polarized light of the polarization beam splitter 120 is sent to the objective lens module 200 .

[0037] The linear polarization module 100 further includes a quarter wave plate to compensate for the influence of the optical path on the phase of the excitation light. The quarter wave plate is disposed between the polarization beam splitter 120 and the output polarizer 130 .

[0038] The polarization beam splitter 120 is optically coated so that the optical polarization fidelity after wide-band reflection reaches more than 99.9%.

[0039] The objective lens module 200 uses a convex lens with a low numerical aperture, which collects less scattered background laser light while ensuring the ability to collect resonance fluorescence, thereby improving the filtering ability of the background laser light. For example, the aperture of the objective lens module 200 is 0.4, which is used to send horizontal polarized light to the quantum dots to excite the quantum dots to produce resonance fluorescence, and send the resonance fluorescence to the polarization beam splitter 120, so that the polarization beam splitter 120 splits the resonance fluorescence and sends it to the output polarizer 130, and the output polarizer 130 separates the vertical component of the resonance fluorescence. The horizontally polarized light after passing through the polarization beam splitter 120 is sent to the objective lens module 200, and the objective lens module 200 sends the horizontally polarized light to the quantum dots. The quantum dot is located in a microcavity structure. Due to the limitation of the microcavity structure, the emission direction of the resonant fluorescence generated by the quantum dot after being excited is limited to a smaller divergence angle. The use of an objective lens with a smaller numerical aperture will not reduce the system's resonant fluorescence collection efficiency, and it exhibits a better Gaussian mode. The scattered background laser is affected by the surface flatness of the quantum dot sample and will deviate from the Gaussian mode. It can be filtered out based on its deviation from the Gaussian mode. Using an objective lens with a smaller numerical aperture can ensure that the collection efficiency of the resonant fluorescence remains unchanged. On the other hand, due to the smaller numerical aperture of the objective lens, the background laser scattered by the surface of the quantum dot sample that can be collected will also be reduced, further improving the filtering ability of the background laser.

[0040] The optical fiber coupler 300 includes a first port 310, and the first port 310 includes a first optical fiber collimator and a first single-mode optical fiber, wherein the first optical fiber collimator is used to couple the vertical component of the resonant fluorescence to the first single-mode optical fiber to collect the resonant fluorescence, and can filter out the non-Gaussian mode components in the background laser while ensuring the resonant fluorescence collection capability, thereby improving the filtering capability of the background laser. The optical fiber coupler 300 also includes a second port 320, and the second port 320 includes a second optical fiber collimator and a second single-mode optical fiber, wherein the second optical fiber collimator is used to couple the second single-mode optical fiber to free space before the laser enters the incident polarizer 110. As can be seen from the above, in the quantum dot microcavity system, the resonant fluorescence emitted by the quantum dots exhibits a better Gaussian mode. Compared with the resonant fluorescence, the spatial mode of the background laser reflected by the surface of the quantum dots will deviate from the standard Gaussian mode due to the influence of factors such as surface flatness. Therefore, both the first single-mode optical fiber and the second single-mode optical fiber are selected to have smaller light apertures. On the one hand, they can better collect the resonant fluorescence emitted by the quantum dots. On the other hand, since the spatial mode of the background laser does not match the spatial mode of the single-mode optical fiber, it is further ensured that the background laser collected in the first single-mode optical fiber will be less.

[0041] The characteristics of the resonant fluorescence device can be evaluated by parameters such as extinction ratio and signal-to-noise ratio. Among them, the extinction ratio is the ratio of the first background laser intensity before reaching the output polarizer 130 to the second background laser intensity collected in the first single-mode optical fiber. It reflects the filtering ability of the resonant fluorescence device to the background laser. The higher the extinction ratio, the stronger the filtering ability of the system to the background laser. The calculation formula of the extinction ratio ER is as follows:

[0042]

[0043] The first background laser intensity P before the output polarizer 130 is background , the second background laser intensity P in the first single-mode optical fiber collection .

[0044] The signal-to-noise ratio of the fluorescence device is the ratio of the resonance fluorescence intensity collected in the first single-mode optical fiber to the background light intensity in the first single-mode optical fiber, which reflects the purity of the resonance fluorescence collected in the first single-mode optical fiber. The higher the signal-to-noise ratio, the smaller the proportion of the background laser signal collected in the first single-mode optical fiber. The calculation formula is:

[0045]

[0046] Among them, P signal is the true intensity of resonance fluorescence, P signal =PP noise , P noise is the background laser intensity collected in the first single-mode optical fiber, and P is the intensity of the detected resonance fluorescence.

[0047] The ratio of signal-to-noise ratio to extinction ratio can also characterize the quantum quality factor Q. The quality factor of quantum dots reflects, to a certain extent, the average number of photons of the resonant fluorescence signal that can be obtained under unit resonant excitation. The larger the quality factor of quantum dots, the more quantum dot resonant fluorescence signals can be excited per unit resonant excitation. For example, if the extinction ratio of the system is reduced while ensuring that the signal-to-noise ratio of the resonant fluorescence device remains unchanged, the device can also be applied to high-quality quantum dot samples, that is, quantum dots can also obtain strong resonant fluorescence under weaker resonant excitation. In the case of quantum dot samples of the same quality, only by ensuring that the system has a stable extinction ratio can the obtained resonant fluorescence signal have a stable signal-to-noise ratio.

[0048] Another embodiment of the present disclosure provides a method for generating resonance fluorescence by exciting quantum dots based on the above resonance fluorescence device, which can be used for continuously resonantly exciting quantum dots to generate resonance fluorescence, such as Figure 2 and Figure 3 As shown, the method includes:

[0049] S1, matching the wavelength of the laser with the wavelength of the quantum dots;

[0050] The parameters of the laser controller are calculated by collecting information about the wavelength (frequency) of quantum dots and the wavelength (frequency) of the laser, and then the wavelength of the laser is matched with the wavelength of the quantum dots, and then the filtering is adjusted. In order to distinguish the resonant fluorescence signal from the background laser signal, the laser frequency and the quantum dot frequency need to be detuned to a certain extent during the adjustment process, for example, 10GHz.

[0051] S2, adjusting the linear polarization module 100 multiple times to obtain multiple adjusted extinction ratios;

[0052] Each time the adjustment is made, the linear polarization module 100 can be adjusted first. In order to perform filtering adjustment more quickly, a strong power laser (such as 100 μW) is first used to roughly adjust the device. In the process of rough adjustment, the angle of the polarizer with the minimum transmitted light intensity is mainly found by observing the background laser signal collected in the first single-mode optical fiber and adjusting the angles of the incident polarizer 110 and the output polarizer 130. Since the position of the optimal extinction ratio of the linear polarizer changes with the change of the optical wavelength, for quantum dots of different wavelengths, the polarization angle of the polarizer can be further optimized by observing the background laser signal after extinction to match the linear polarization angle of the optimal extinction ratio. Then the device is fine-tuned, and the signal can be detected by a high-sensitivity spectrometer, and the influence of the linear polarization angle on the extinction ratio within the milliradian range can be observed, so as to find the linear polarization angle corresponding to the highest system extinction ratio. Among them, the first background laser intensity before the output polarizer 130 can be directly measured by a light intensity detector, and the first background laser intensity collected in the first single-mode optical fiber can obtain the corresponding photon number information N in the spectrometer.

[0053] S3, compare the extinction ratios adjusted multiple times to obtain the optimal extinction ratio.

[0054] Among them, Figure 4 As shown, obtaining the optimal extinction ratio includes:

[0055] S31, measuring the first background laser intensity P before the output polarizer 130 background ;

[0056] S32, obtaining a second background laser intensity P in the first single-mode optical fiber collection ; A spectrum detector can be used to obtain the number of photons N in the first single-mode optical fiber and the second background laser intensity P collection The calculation formula is:

[0057] Wherein, η is the detection efficiency of the spectrometer, and hv is the unit photon energy detected by the spectrometer.

[0058] S33, obtain the extinction ratio, the calculation formula of the extinction ratio is:

[0059]

[0060] The above step S2 also includes obtaining the signal-to-noise ratio of multiple adjustments, and step S3 also includes comparing the signal-to-noise ratio of multiple adjustments to obtain the optimal signal-to-noise ratio. The calculation formula of the signal-to-noise ratio is:

[0061]

[0062] Among them, P signal is the true intensity of resonance fluorescence, P signal =PP noise , P noise is the background laser intensity collected in the first single-mode optical fiber, and P is the intensity of the detected resonance fluorescence.

[0063] By repeatedly comparing the extinction ratio, signal-to-noise ratio and the linear polarization angles of the incident polarizer 110 and the output polarizer 130 of the device, the optimal filtering capability of the resonant fluorescence device is finally achieved.

[0064] In this resonant fluorescence device, the polarization beam splitter has little effect on the polarization of the excitation light. Through filtering by the linear polarization module 100, the spectral bandwidth of the optimal extinction ratio is wide, and it is not particularly sensitive to the influence of environmental vibration, etc. The adjusted system extinction ratio and signal-to-noise ratio can maintain long-term stability. However, when resonantly exciting new quantum dots, due to the randomness of the wavelength of the quantum dots, it is necessary to readjust according to the wavelength of the quantum dots.

[0065] Pulse resonant excitation can produce a deterministic quantum dot resonant fluorescence single-photon source, so in practical applications, pulse resonant excitation of quantum dots is more likely to be used. Unlike continuous resonant excitation quantum dot filtering, the spectrum of pulsed laser is very wide. Pulse resonant excitation quantum dot filtering must not only ensure the extinction ratio of the device when the quantum dots resonate, but also ensure the best signal-to-noise ratio of the device within the entire pulse laser spectrum range. Figure 5 As shown, the process of filtering the pulse resonantly excited quantum dots can be as follows:

[0066] After the device performs the above continuous resonant excitation quantum dot filtering adjustment, the device extinction ratio reaches the highest during resonance. The laser is then switched to a pulsed resonant laser. In order to fine-tune the signal-to-noise ratio of the device, the resonant fluorescence signal and the background laser signal are calculated on the spectrum detector based on their different spectrum widths, and then the signal-to-noise ratio of the device is calculated. By comparing the changes in the linear polarization angle and the device signal-to-noise ratio, the linear polarization angle corresponding to the optimal signal-to-noise ratio is obtained. Compared with traditional quantum dot resonant fluorescence devices, the device in the present application can achieve a better quantum dot pulsed resonant fluorescence signal-to-noise ratio. Figure 6Schematic diagram showing the resonance fluorescence collected by a conventional resonance fluorescence device. Figure 7 The schematic diagram shows the spectral signal collected by the resonance fluorescence device in the present application. Figure 6 and Figure 7 In the figure, the solid line is the pulse resonance fluorescence signal read out by the spectrometer, and the dotted line is the pulse resonance background laser signal. It can be seen that the background laser signal is significantly reduced in the modified resonance fluorescence device, and the signal-to-noise ratio of the quantum dot resonance fluorescence signal to the background laser is significantly improved.

[0067] This method is not only applicable to resonant fluorescence filtering based on microcavity quantum dots, but also to other single-photon source systems with better quality factors, such as single-photon source systems based on single-atomic layer materials.

[0068] In summary, the present application first replaces the polarization beam splitter in the prior art with a polarization beam splitter with high polarization fidelity to ensure that the linear polarization degree of the laser remains unchanged after passing through the polarization beam splitter, and overcomes the disadvantage that the linear polarization degree of the linear polarized light decreases after passing through the ordinary polarization beam splitter. Therefore, the background laser reflected back by the quantum dot sample can be effectively suppressed after passing through the output polarizer. Secondly, without losing the quantum dot resonant fluorescence collection efficiency, an objective lens module with a lower numerical aperture is selected. For a quantum dot system with a planar structure, since the emission angle of the quantum dot fluorescence is very large, selecting an objective lens module with a high numerical aperture can effectively improve the resonant fluorescence collection efficiency of the quantum dots. In a microcavity quantum dot system, due to the modulation effect of the microcavity, the emission direction of the quantum dot resonant fluorescence is limited to a smaller divergence angle, so using an appropriate objective lens module with a smaller numerical aperture will not reduce the resonant fluorescence collection efficiency of the system. When resonantly exciting microcavity quantum dot samples, using an objective lens module with a smaller numerical aperture can ensure that the collection efficiency of the resonant fluorescence remains unchanged. On the other hand, as the numerical aperture of the objective lens module becomes smaller, the background laser scattered by the surface of the quantum dot sample can be collected. Reduced, thereby further improving the filtering ability of the background laser. Thirdly, a single-mode fiber with a smaller aperture is selected to collect the quantum dot resonant fluorescence signal. In the microcavity quantum dot system, the resonant fluorescence emitted by the quantum dots exhibits a better Gaussian mode. Compared with the resonant fluorescence, the spatial mode of the background laser reflected from the surface of the quantum dot sample will deviate from the standard Gaussian mode due to factors such as surface flatness. By using a single-mode fiber with a smaller aperture, on the one hand, the resonant fluorescence signal emitted by the quantum dots can be better collected. On the other hand, since the spatial mode of the background laser does not match the spatial mode of the single-mode fiber, it is further ensured that the background laser collected in the single-mode fiber will be less.

[0069] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A resonance fluorescence device for laser excitation of quantum dots to generate resonance fluorescence for fluorescence detection, the device comprising a linear polarization module (100), an objective lens module (200) and an optical fiber coupler (300), wherein: A linear polarization module (100), comprising an incident polarizer (110), a polarization beam splitter (120), and an exit polarizer (130), wherein the polarization beam splitter (120) is optically coated to improve its optical polarization fidelity, the polarization direction of the incident polarizer (110) coincides with the horizontal component of the polarization beam splitter (120), the polarization direction of the exit polarizer (130) coincides with the vertical component of the polarization beam splitter (120), the laser sequentially passes through the incident polarizer (110) and the polarization beam splitter (120), and the horizontally polarized light of the polarization beam splitter (120) is sent to the objective lens module (200), and the linear polarization module (100) further comprises a quarter wave plate, which is arranged between the polarization beam splitter (120) and the exit polarizer (130); An objective lens module (200) is used to send the horizontally polarized light to the quantum dots to excite the quantum dots to generate resonance fluorescence, and to send the resonance fluorescence to the polarization beam splitter (120), so that the polarization beam splitter (120) splits the resonance fluorescence and sends it to the output polarizer (130), and the output polarizer (130) separates the vertical component of the resonance fluorescence; The optical fiber coupler (300) comprises a first port (310), wherein the first port (310) comprises a first optical fiber collimator and a first single-mode optical fiber, wherein the first optical fiber collimator is used to couple the vertical component of the resonance fluorescence to the first single-mode optical fiber to collect the resonance fluorescence, and the optical fiber coupler (300) further comprises a second port (320), wherein the second port (320) comprises a second optical fiber collimator and a second single-mode optical fiber, wherein the second optical fiber collimator is used to couple the laser from the second single-mode optical fiber to free space.

2. The resonance fluorescence device according to claim 1, wherein the numerical aperture of the objective lens module (200) is 0.

4.

3. The resonance fluorescence device according to claim 1, wherein the quantum dots are arranged in a microcavity quantum dot structure.

4. A method for generating resonance fluorescence, based on the resonance fluorescence device according to any one of claims 1 to 3, comprising: S1, matching the wavelength of the laser with the wavelength of the quantum dot; S2, adjusting the linear polarization module (100) multiple times to obtain a multiple-adjusted extinction ratio; S3, comparing the extinction ratios adjusted multiple times to obtain an optimal extinction ratio.

5. According to the method of claim 4, exciting the quantum dots also generates background laser light, and obtaining the optimal extinction ratio in step S3 comprises: S31, measuring the first background laser intensity in front of the output polarizer (130) ; S32, obtaining a second background laser intensity in the first single-mode optical fiber ; S33, obtaining an extinction ratio, wherein the calculation formula of the extinction ratio is: 。 6. According to the method of claim 5, the step S32 comprises: The number of photons N in the first single-mode optical fiber and the intensity of the second background laser are obtained by using a spectrum detector. The calculation formula is: in, is the detection efficiency of the spectrometer, is the unit photon energy detected by the spectrometer.

7. According to the method of claim 4, the step S2 further comprises obtaining a signal-to-noise ratio of multiple adjustments, and the step S3 further comprises comparing the signal-to-noise ratios of the multiple adjustments to obtain an optimal signal-to-noise ratio.

8. According to the method of claim 7, the calculation formula of the signal-to-noise ratio is: in, is the true intensity of the resonance fluorescence, , is the background laser intensity collected in the first single-mode optical fiber, is the intensity of the detected resonance fluorescence.

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