Superconducting nanowire single-photon detector system capable of expanding array and detection method

Abstract

The invention provides an array-extensible superconducting nanowire single-photon detector system and a detection method, which can be applied to the field of quantum optics. The system comprises a single photon device used for converting light to be detected into pulse signals and sending the pulse signals to a pulse direction discriminator; the pulse direction discriminator is used for discriminating the direction of the pulse signal and sending the discriminated pulse signal to the oscilloscope; the oscilloscope is used for recording the amplitude of the received pulse signal so as to determine the position of a photon in the to-be-detected light in combination with the direction of the pulse signal; the single photon device comprises an SNSPD array and a reading circuit, the SNSPD array is connected with the reading circuit through a row and column multiplexing structure, and the reading circuit comprises a load resistor connected with all pixels in the SNSPD array in series. Therefore, the expandability and the integration level of the system can be improved, and the system has the photon number and spatial resolution capability.

Description

Technical Field

[0001] The present disclosure relates to the field of quantum optics, and more particularly, to a superconducting nanowire single-photon detector system with an expandable array and a detection method thereof. Background Art

[0002] A superconducting nanowire single-photon detector (SNSPD) is a detection device capable of detecting extremely weak optical signals. Compared with traditional semiconductor detectors, SNSPD has advantages such as high detection efficiency, low dark count, low time jitter, and fast response rate, and is widely used in fields such as quantum communication, lidar and remote sensing, biomedicine, and astronomical observation. SNSPD utilizes the property that a superconducting nanowire changes from a superconducting state to a resistive state under single-photon excitation, converts the optical signal into an electrical signal, and reads it out through a readout circuit to achieve the detection of the optical signal.

[0003] With the rapid development of single - photon detection technology, there are still technical problems that need to be overcome urgently in existing superconducting nanowire single - photon detectors. For example, (1) in scenarios that require large - area and high - resolution imaging, each detection unit in the existing superconducting nanowire single - photon detector needs to be matched with a corresponding read - out circuit. However, the existing read - out circuits have deficiencies in integration and cannot integrate multiple matching read - out circuits together, resulting in low integration. This leads to complex read - out circuits and excessive thermal load of the detector. To reduce the thermal load of the detector, the refrigeration system requires a larger cooling capacity and volume, which is difficult to meet the requirements of miniaturization and low thermal power consumption in fields such as astronomical observation, aerospace, etc. In aerospace devices, a refrigeration system with too large a volume and a detector with a high thermal load will limit the installation and operation of aerospace devices. Another example is (2) to meet diverse application requirements, it is necessary to expand the detector array, that is, a large number of detection units need to be used. However, limited by the low integration, using a large number of detection units not only increases the complexity and cost of the system, but also makes it difficult to ensure the uniformity and consistency of the detector. Moreover, due to the difficulty of effectively integrating traditional read - out circuits, adding a large number of detection units will also consume a large amount of time and resources, thus affecting the overall detection performance, which limits the scalability of the array. (3) Existing technologies attempt to expand the effective detection area by increasing the number of detector pixels to meet diverse application requirements. However, the pixels of superconducting nanowire single - photon detectors are very small. Even if the number of pixels is increased, the effective detection area is difficult to increase significantly. Moreover, this method ignores the problems of array scalability and read - out circuit integration, and cannot ensure that the detector has spatial resolution and photon - number resolution capabilities. (4) Most existing single - photon detectors are two - dimensional structures, and superconducting nanowires are distributed in a single plane. When expanding the number of pixels, it is easily restricted by space and difficult to meet the requirements of a large - range field of view, resulting in a decrease in detection efficiency. All these indicate that SNSPD arrays have deficiencies in aspects such as space utilization and function expansion, and the scalability of the array and the integration of read - out circuits need to be improved. Summary of the Invention

[0004] In view of the above problems, the present disclosure provides a scalable array superconducting nanowire single - photon detector system and a detection method for improving the scalability and integration of a single - photon detector system.

[0005] According to the first aspect of the present disclosure, there is provided a scalable array superconducting nanowire single - photon detector system, the system comprising:

[0006] A single - photon device, configured to convert the light to be detected into a pulse signal and send it to a pulse direction discriminator;

[0007] A pulse direction discriminator, configured to discriminate the direction of the pulse signal and send the discriminated pulse signal to an oscilloscope;

[0008] An oscilloscope for recording the amplitude of the received pulse signal, so as to determine the position of photons in the light to be detected in combination with the direction of the discriminated pulse signal;

[0009] Among them, the single-photon device includes an SNSPD array and a readout circuit. The SNSPD array is connected to the readout circuit using a row-column multiplexing structure, and the readout circuit is integrated with load resistors connected in series with each pixel in the SNSPD array.

[0010] According to an embodiment of the present disclosure, the SNSPD array has a three-dimensional spatial structure, including multiple structural layers, a pixel array, a first gold electrode, a second gold electrode, a first peripheral gold electrode, a second peripheral gold electrode, row transmission lines, and column transmission lines; among them,

[0011] The row transmission lines are placed at the bottom of the first structural layer;

[0012] The first peripheral gold electrode and the second peripheral gold electrode are placed at the top of the first structural layer;

[0013] The pixel array, the first gold electrode, the second gold electrode, and the column transmission lines are placed in the second structural layer. According to an embodiment of the present disclosure, the SNSPD array is connected to the readout circuit using a row-column multiplexing structure

[0014] and includes:

[0015] One ends of multiple pixels in the same row in the pixel array are respectively connected to the row transmission line corresponding to the row through the first gold electrode corresponding to the pixel; one end of the row transmission line is connected to a bias power supply, and the other end is connected to the readout circuit through the first peripheral gold electrode;

[0016] The other ends of multiple pixels in the same column are respectively connected to the column transmission line corresponding to the pixel through the second gold electrode corresponding to the pixel. The column transmission line is connected to the load resistor integrated on the readout circuit and connected in series with the pixel corresponding to the column transmission line through the second peripheral gold electrode connected to itself, and is grounded through the load resistor.

[0017] According to an embodiment of the present disclosure, the distances between the first gold electrodes and the distances between the second gold electrodes between each pixel, the conductive contact widths between the first gold electrode and the second gold electrode, and between the first peripheral gold electrode and the second peripheral gold electrode, the nanowire distribution of the pixels in the detection area, the physical properties of the nanowires, and the area of the bypass area outside the detection area are respectively structures that meet the preset performance indicators.

[0018] According to an embodiment of the present disclosure, the pulse direction discriminator includes a diode and an operational amplifier; among them,

[0019] The diode is used to discriminate the direction of the pulse signal output by the single-photon device;

[0020] The operational amplifier is used to amplify the pulse signal passing through the diode and transmit it to the oscilloscope.

[0021] According to an embodiment of the present disclosure, the system further includes:

[0022] A beam splitter, an optical attenuator, an optical fiber coupler, a refrigerator, and a bias tee connected in sequence; wherein, a single-photon device is integrated in the refrigerator;

[0023] The bias tee is connected to an oscilloscope through a pulse direction discriminator; the bias tee is also connected to a bias power supply;

[0024] The beam splitter is also connected to a first optical power meter;

[0025] The optical fiber coupler is also connected to a second optical power meter.

[0026] According to an embodiment of the present disclosure, the beam splitter is configured to divide the input light into two paths and input one of the paths into the optical attenuator;

[0027] The optical attenuator is configured to adjust the output intensity of the received light;

[0028] The optical fiber coupler is configured to control the light output by the optical attenuator and output the light to be detected;

[0029] The first optical power meter is configured to measure the intensity of the other path of light output by the beam splitter to obtain the intensity of the light input to the optical attenuator;

[0030] The second optical power meter is configured to measure the intensity of one path of light output by the optical fiber coupler to obtain the number of photons in the light to be detected;

[0031] The bias tee is configured to provide a bias power supply for the single-photon device and also to send the pulse signal output by the single-photon device to the pulse direction discriminator.

[0032] According to an embodiment of the present disclosure, the optical fiber coupler includes:

[0033] A neutral density filter, a polarization controller, and an optical fiber splitter connected in sequence;

[0034] The neutral density filter is configured to change the intensity of the light output by the optical attenuator and maintain the color or wavelength of the light output by the optical attenuator;

[0035] The polarization controller is configured to adjust the polarization state of the light output by the neutral density filter to improve the stability and uniformity of the light output;

[0036] The optical fiber splitter is configured to divide the light output by the polarization controller into two paths for output.

[0037] Another aspect of the embodiments of the present disclosure provides a detection method for a superconducting nanowire single photon detector system of a scalable array provided in the first aspect of the present disclosure. The system includes a beam splitter, an adjustable optical attenuator, an optical fiber coupler, a refrigerator, a bias tee, a pulse direction discriminator, and an oscilloscope connected in sequence. Among them, a single photon device is integrated in the refrigerator. The detection method includes:

[0038] The input light is split into two paths by the beam splitter, and the output intensity of one path of light is adjusted by the adjustable attenuator;

[0039] The adjusted light is further split into two paths of light through the regulation of the optical fiber coupler, and one path of light to be detected is incident on the single photon device;

[0040] The light to be detected is converted into a pulse signal by the single photon device and output to the pulse direction discriminator through the bias tee to obtain the direction of the discriminated pulse signal;

[0041] The discriminated pulse signal is sent to the oscilloscope to obtain the amplitude of the discriminated pulse signal;

[0042] According to the direction and amplitude of the discriminated pulse signal, the position of the photon in the light to be detected is determined.

[0043] According to the embodiments of the present disclosure, the detection method further includes:

[0044] Measure the intensity of the other path of light output by the beam splitter through the first optical power meter, and calculate the intensity of the light input to the adjustable optical attenuator according to the preset beam splitting ratio;

[0045] Measure the intensity of the other path of light output by the optical fiber coupler through the second optical power meter;

[0046] Calculate the number of photons in the light to be detected according to the intensity of the light input to the adjustable optical attenuator and the intensity of the light measured by the second optical power meter; where

[0047] The first optical power meter is connected to the beam splitter, and the second optical power meter is connected to the optical fiber coupler.

[0048] According to the embodiments of the present disclosure, the detection method further includes:

[0049] When performing array expansion on the single photon device, complete the array expansion by adding a preset number of pixels in the SNSPD array, adding row and column transmission lines corresponding to the added pixels in the corresponding structural layer, and adding load resistors connected in series with the added pixels in the readout circuit.

[0050] The above one or more embodiments have the following beneficial effects, which can at least partially solve:

[0051] (1) When the single-photon detector system of the present disclosure is expanded in array, it is not necessary to largely change the structure of the readout circuit. Only a load resistor connected in series with the added pixels needs to be added to the readout circuit, thereby improving the scalability of the array. In addition, integrating the load resistor connected in series with the pixels onto the readout circuit can not only increase the detection area, but also reduce the problem of unstable resistance value of the load resistor caused by the actual processing, reduce the impact on the detection efficiency, and thus improve the detection accuracy. This is crucial for the integration level of the system. Integrating the load resistor connected in series with the pixels onto the readout circuit enables the system to still operate stably in a complex environment, reduces the signal loss and misjudgment rate, improves the detection reliability and accuracy, and can better cooperate with other components when integrating a multi-pixel array, reducing the performance degradation and other impacts caused by stability problems.

[0052] (2) The pulse discriminator is used to discriminate the direction of the pulse signal first, and then the oscilloscope is used to display the amplitude of the discriminated pulse signal, avoiding the problem that a large-area SNSPD array requires more oscilloscope channels to obtain the direction and amplitude of the pulse signal, simplifying the photon detection process, and improving the detection efficiency.

[0053] (3) The comprehensive design of structures such as the row-column multiplexing structure, the pulse direction discriminator, and the readout circuit integrated with the load resistor connected in series with the pixels is beneficial to reducing the complexity of the integration level and improving the integration level when the device is expanded such as array expansion or new module addition. Moreover, this comprehensive design also improves the duty cycle of the nanowire. The increase in the duty cycle not only effectively speeds up the detection speed, but also improves the detection accuracy, well meeting the stringent requirements for the processing speed of weak photon signals in fields such as quantum communication and lidar, improving the efficiency of multi-point simultaneous communication, and accelerating the imaging speed of fluorescent photons in the biomedical field in a short time and the detection ability of low surface brightness celestial bodies in the astronomical observation field.

[0054] (4) The detector system can determine the photon position according to the direction and amplitude of the discriminated pulse signal, realizing the spatial resolution ability. In addition, the detector system also includes a first optical power meter and a second optical power meter, and according to the measurement results of the first optical power meter and the second optical power meter, the photon number resolution ability can be realized.

[0055] (5) The SNSPD array is a three-dimensional spatial structure, and it is not easily restricted by space when expanding the number of pixels, which can meet the requirements of a large range of vision, thereby improving the detection efficiency. Brief Description of the Drawings

[0056] Through the following description of the embodiments of the present disclosure with reference to the drawings, the above content and other objects, features, and advantages of the present disclosure will become clearer. In the drawings:

[0057] Figure 1Schematically shows a structural diagram of a superconducting nanowire single-photon detector system with an expandable array according to an embodiment of the present disclosure;

[0058] Figure 2 Schematically shows a three-dimensional spatial structure diagram of a SNSPD array according to an embodiment of the present disclosure;

[0059] Figure 3 Schematically shows a flowchart of a detection method for a superconducting nanowire single-photon detector system with an expandable array according to an embodiment of the present disclosure;

[0060] Figure 4 Schematically shows a simulation circuit diagram of a superconducting nanowire single-photon detector system of a 3×3 SNSPD array according to an embodiment of the present disclosure;

[0061] Figure 5 Schematically shows a schematic diagram of a pulse signal output by a readout circuit when all pixels in a superconducting nanowire single-photon detector system of a 3×3 SNSPD array according to an embodiment of the present disclosure respond;

[0062] Figure 6 Schematically shows a schematic diagram of a pulse signal output by a readout circuit when no pixel in a certain row or column in a superconducting nanowire single-photon detector system of a 3×3 SNSPD array according to an embodiment of the present disclosure responds;

[0063] Figure 7 Schematically shows a schematic diagram of a pulse signal output by a readout circuit when there are 1, 2, and 3 pixels responding respectively in a certain row in a superconducting nanowire single-photon detector system of a 3×3 SNSPD array according to an embodiment of the present disclosure;

[0064] Figure 8 Schematically shows a schematic diagram of a pulse signal output by a readout circuit when there are 1, 2, and 3 pixels responding respectively in a certain column in a superconducting nanowire single-photon detector system of a 3×3 SNSPD array according to an embodiment of the present disclosure;

[0065] Figure 9 Schematically shows a schematic diagram of a pulse signal output by a readout circuit of a superconducting nanowire single-photon detector system of a 3×3 SNSPD array according to an embodiment of the present disclosure.

[0066] It should be noted that, for clarity, in the drawings used to describe the embodiments of the present disclosure, the size of the overall / local structure or the overall / local area may be enlarged or reduced, that is, these drawings are not drawn according to the actual scale. Detailed implementation manners

[0067] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present disclosure. In the following detailed description, for the sake of explanation, numerous specific details are set forth in order to provide a comprehensive understanding of the embodiments of the present disclosure. However, it is obvious that one or more embodiments can also be implemented without these specific details. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily obscuring the concepts of the present disclosure.

[0068] The terms used herein are merely for describing specific embodiments and are not intended to limit the present disclosure. The terms "including", "comprising", etc. used herein indicate the presence of the described features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0069] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0070] In the case of using expressions such as "at least one of A, B, and C, etc.", generally, it should be interpreted according to the meaning commonly understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include, but is not limited to, a system having only A, only B, only C, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.).

[0071] Embodiments of the present disclosure provide a superconducting nanowire single-photon detector system and a detection method for a scalable array. The system includes: a single-photon device for converting the light to be detected into a pulse signal and sending it to a pulse direction discriminator; a pulse direction discriminator for discriminating the direction of the pulse signal and sending the discriminated pulse signal to an oscilloscope; an oscilloscope for recording the amplitude of the received pulse signal so as to determine the position of the photon in the light to be detected in combination with the discriminated pulse signal direction. Among them, the single-photon device includes an SNSPD array and a readout circuit. The SNSPD array is connected to the readout circuit by a row-column multiplexing structure, and the readout circuit is integrated with load resistors connected in series with each pixel in the SNSPD array.

[0072] When the single - photon detector system of the present disclosure is expanded in an array, it is not necessary to make large - scale changes to the read - out circuit structure. Only a load resistor connected in series with the added pixels needs to be added to the read - out circuit, thereby improving the scalability of the array. The pulse discriminator first discriminates the direction of the pulse signal, and then the oscilloscope is used to display the amplitude of the discriminated pulse signal, avoiding the problem that a large - area SNSPD array requires more oscilloscope channels to obtain the direction and amplitude of the pulse signal, simplifying the photon detection process and improving the detection efficiency. The comprehensive design of structures such as the row - column multiplexing structure, the pulse direction discriminator, and the read - out circuit integrated with the load resistor connected in series with the pixels is beneficial to reducing the complexity of the integration degree and improving the integration degree when the device is expanded such as array expansion or new module addition. Moreover, this comprehensive design also improves the duty cycle of the nanowire. The increase in the duty cycle not only effectively speeds up the detection speed but also improves the detection accuracy, well meeting the stringent requirements for the processing speed of weak photon signals in fields such as quantum communication and lidar, improving the efficiency of multi - point simultaneous communication, accelerating the imaging speed of fluorescent photons in the biomedical field in a short time, and enhancing the detection ability of low - surface - brightness celestial bodies in the astronomical observation field. The detector system can determine the photon position according to the direction and amplitude of the discriminated pulse signal, realizing the spatial resolution ability. In addition, the detector system also includes a first optical power meter and a second optical power meter, and according to the measurement results of the first optical power meter and the second optical power meter, the photon number resolution ability can be realized.

[0073] Figure 1 Schematically shows the structural diagram of a scalable - array superconducting nanowire single - photon detector system according to an embodiment of the present disclosure. As Figure 1 shown, the superconducting nanowire single - photon detector system includes:

[0074] A laser light source, a beam splitter, an adjustable optical attenuator, an optical fiber coupler, a refrigerator, a bias tee, a pulse direction discriminator, and an oscilloscope connected in sequence; wherein, a single - photon device is integrated in the refrigerator, and the bias tee is also connected to a bias power supply;

[0075] Further, the single - photon device includes an SNSPD array and a read - out circuit. The SNSPD array is connected to the read - out circuit using a row - column multiplexing structure, and the read - out circuit is integrated with load resistors connected in series with each pixel in the SNSPD array;

[0076] Further, the optical fiber coupler includes a neutral density filter, a polarization controller, and a 1×2 optical fiber splitter connected in sequence;

[0077] The pulse direction discriminator includes a diode and an operational amplifier connected in sequence;

[0078] The beam splitter is also connected to a first optical power meter, and the 1×2 optical fiber splitter is also connected to a second optical power meter.

[0079] In some embodiments, the laser light source is used to generate pulsed laser light of a specific wavelength required;

[0080] The beam splitter is used to split the input light (i.e., the pulsed laser light generated by the laser) into two paths and input one of the paths into the variable optical attenuator;

[0081] The variable optical attenuator is used to adjust the output intensity of the received light;

[0082] The fiber optic coupler is used to regulate the light output by the variable optical attenuator and output the light to be detected. Through the fiber optic coupler, the light input to the single-photon device can be stabilized, improving the detection stability;

[0083] The cryogenic refrigerator is used to provide the low-temperature environment (0.7 K - 2.2 K) required for testing the single-photon device and reduce the thermal noise, so as to improve the detection performance of the single-photon device and extend the service life of the single-photon device;

[0084] The single-photon device is used to convert the light to be detected output by the fiber optic coupler into a pulse signal and send it to the pulse direction discriminator through a bias tee; further, the SNSPD array is used to convert the light to be detected output by the fiber optic coupler into a pulse signal; the readout circuit is used to read out the pulse signal and send it to the pulse direction discriminator through a bias tee;

[0085] The bias tee is used to provide a bias power supply for the single-photon device and is also used to send the pulse signal output by the single-photon device to the pulse direction discriminator;

[0086] The pulse direction discriminator is used to discriminate the direction of the pulse signal output by the single-photon device and send the discriminated pulse signal to the oscilloscope;

[0087] The oscilloscope records the amplitude of the received pulse signal so as to determine the position of the photons in the light to be detected in combination with the discriminated pulse signal direction.

[0088] In some embodiments, the SNSPD array has a three-dimensional spatial structure, including multiple structural layers, a pixel array, a first gold electrode, a second gold electrode, a first peripheral gold electrode, a second peripheral gold electrode, row transmission lines, and column transmission lines; among them,

[0089] The row transmission lines are placed at the bottom of the first structural layer;

[0090] The first peripheral gold electrode and the second peripheral gold electrode are placed at the top of the first structural layer;

[0091] The pixel array, the first gold electrode, the second gold electrode, and the column transmission lines are placed in the second structural layer;

[0092] Such as Figure 2As shown, the three-dimensional spatial structure includes four structural layers. The material of the first structural layer is SiN. A row transmission line is placed on the lower surface (bottom) of the first structural layer, and a first peripheral gold electrode and a second peripheral gold electrode are placed on the upper surface (top). The material of the second structural layer is SiO2. This structural layer forms an optical cavity, which is divided into two parts. An image sensor array, a first gold electrode, a second gold electrode, and a column transmission line are placed in the middle of the optical cavity. Each pixel in the image sensor array includes a superconducting nanowire. One end of each pixel is respectively connected to the corresponding first gold electrode, and the other end is respectively connected to the column transmission line corresponding to the pixel through the corresponding second gold electrode.

[0093] Furthermore, the other end of the row transmission line is connected to the readout circuit through the first peripheral gold electrode, and the column transmission line is connected to the readout circuit through the second peripheral gold electrode. The third structural layer is a gold substrate structural layer, which is used to reflect the photons not absorbed by the image sensor array back into the optical cavity, extend the propagation path of the photons in the optical cavity, and significantly increase the probability of interaction between the photons and the superconducting nanowires through multiple reflections, thereby improving the absorption efficiency of single photons. The fourth structural layer is a substrate, and its material is Si.

[0094] This three-dimensional spatial structure is not easily restricted by space when expanding the number of pixels, improving the space utilization rate and the scalability of the array. Compared with the two-dimensional spatial structure, the influence between pixels is smaller, and the detection performance of the image sensor array is better.

[0095] Furthermore, the SNSPD array is connected to the readout circuit using a row-column multiplexing structure, including:

[0096] One ends of multiple pixels in the same row in the image sensor array are respectively connected to the row transmission line corresponding to this row through the first gold electrode corresponding to the pixel. One end of the row transmission line is connected to a bias power supply through a bias tee, and the other end is connected to the readout circuit through the first peripheral gold electrode.

[0097] The other ends of multiple pixels in the same column are respectively connected to the column transmission line corresponding to the pixel through the second gold electrode corresponding to the pixel. The column transmission line is connected to a load resistor in series with the pixel corresponding to this column transmission line integrated on the readout circuit through the second peripheral gold electrode connected to itself, and is grounded through the load resistor.

[0098] In some embodiments, the distances between the first gold electrodes and the second gold electrodes between pixels, the conductive contact widths between the first gold electrode and the second gold electrode, and between the first peripheral gold electrode and the second peripheral gold electrode, the nanowire distribution of the pixels in the detection area, the physical properties of the nanowires, and the bypass area outside the detection area are respectively structures that meet the preset performance indicators. This design can improve the scalability of the array.

[0099] For example, to improve the scalability of the array, when designing the SNSPD array, a three-dimensional spatial structure is adopted to reduce the distance between the first gold electrodes and the distance between the second gold electrodes of each pixel, reduce the crosstalk between pixels, and provide a better layout basis for expanding the number of pixels. Also, without changing the total area of a single pixel, the conductive contact width between the first gold electrode and the second gold electrode, between the first peripheral gold electrode and the second peripheral gold electrode, and the area of the bypass region outside the detection area can be reduced, thereby increasing the effective detection area of a single pixel. The effective detection area of a single pixel in the present disclosure can reach more than 62%. The physical properties of the superconducting nanowires can also be optimized, such as reducing the kinetic inductance, decay time, and recovery time of the superconducting nanowires, thereby increasing the duty cycle and achieving the purpose of improving the scalability of the array. The nanowire distribution within the detection area of the pixel can also be optimized, such as increasing the nanowire length and reducing the nanowire width, to increase the active sensing area of a single pixel, thereby improving the scalability of the array and realizing the optimization of performance utilization;

[0100] Further, the charging and discharging processes of the kinetic inductance of the superconducting nanowires in the pixel respectively correspond to the acceleration and deceleration processes of the carriers in the superconducting nanowires. The kinetic inductance of the superconducting nanowires is expressed as follows:

[0101]

[0102] where represents the operating temperature of the superconducting nanowires, represents the vacuum permeability, and its value is 4π×10 -7 H / m, is the magnetic penetration depth, , , are the length, width, and thickness of the superconducting nanowires, respectively;

[0103] For an SNSPD array with a detection area of 30μm×30μm for a single pixel, a superconducting nanowire thickness of 7nm, a superconducting nanowire width of 100nm, a superconducting nanowire length of 0.302nm, a nanowire spacing of 200nm, a nanowire width duty cycle of 1 / 3, a load resistance of 50Ω in series for the pixel, and the nanowires designed with an optimal 180-degree turn scheme, the calculated kinetic inductance of the superconducting nanowires is 2.655 pH, and this value is better than the kinetic inductance value of the nanowires in traditional single-photon detectors; where the nanowire width duty cycle is the ratio of the nanowire width to the sum of the nanowire width and the nanowire spacing;

[0104] For the detection process of a single pixel, it can be equivalent to a process composed of the kinetic inductance The equivalent circuit consists of the time-varying resistance Rn(t) generated after the superconducting nanowire absorbs the incident photons and the load resistance Z0 in series with the pixel. After the pixel absorbs the incident photons, a resistance barrier will be formed, triggering the phase transition of the nanowire from the superconducting state to the normal state and generating a transient voltage pulse. The time taken for the transient voltage pulse to drop from the peak to a preset ratio of the peak is the decay time, and the time taken for the nanowire to recover from the normal state to the superconducting state is the recovery time;

[0105] Decay time The expression is as follows:

[0106]

[0107] Recovery time The expression is as follows:

[0108]

[0109] By optimizing the physical properties of the superconducting nanowire and the distribution of the nanowires in the detection area of the pixel, the duty cycle and detection area of the nanowire can be improved.

[0110] In some embodiments, the row-column multiplexing structure uses the same bias power supply to supply power to each pixel in the SNSPD array. When a certain pixel absorbs photons, pulse signals with opposite directions will be generated in the row and column directions where the pixel is located. These pulse signals are finally read out through the readout circuit. This readout method can reduce the time loss caused by the switching and initialization of the readout circuit, improve the duty cycle, thus making the expansion of the array more convenient and improving the scalability and integration;

[0111] Integrating the load resistance in series with the pixel onto the readout circuit can not only expand the distribution area of the nanowires in the pixel, thus effectively increasing the detection area, but also reduce the problem of unstable resistance value of the load resistance brought by the actual processing process, reduce the impact on the detection efficiency, thereby improving the detection accuracy. This is crucial for the integration of the system. Integrating the load resistance in series with the pixel onto the readout circuit enables the system to still operate stably in a complex environment, reduce the signal loss and misjudgment rate, improve the detection reliability and accuracy, and can work better with other components when integrating a multi-pixel array, reducing the performance degradation and other impacts caused by stability problems.

[0112] In some embodiments, the neutral density filter is used to change the light intensity output by the variable optical attenuator. For example, it uniformly reduces the light intensity output by the variable optical attenuator and keeps the color or wavelength of the light output by the variable optical attenuator;

[0113] The polarization controller is used to adjust the polarization state of the light output by the neutral density filter, so as to improve the stability and uniformity of the light output, and avoid the change of the polarization of the light caused by noise or vibration;

[0114] The 1×2 optical fiber splitter is used to split the light output by the polarization controller into two paths. One path outputs the light to be detected and is incident on the single-photon device, and the other path measures the intensity of the light in this path through the second optical power meter.

[0115] In some embodiments, the first optical power meter is used to measure the intensity of the other path of light output by the beam splitter to obtain the intensity of the light input to the variable optical attenuator;

[0116] The second optical power meter is used to measure the intensity of one path of light output by the optical fiber splitter to obtain the number of photons in the light to be detected.

[0117] In some embodiments, the diode is used to discriminate the direction of the pulse signal output by the single-photon device;

[0118] The operational amplifier is used to amplify the pulse signal passing through the diode and transmit it to the oscilloscope. The operational amplifier includes a fast response circuit, which can greatly increase the duty cycle and quickly transmit the received pulse signal to the oscilloscope within an extremely short time. Its signal processing speed can reach the nanosecond level, greatly shortening the signal amplification time.

[0119] In some embodiments, for a large-area SNSPD array, more oscilloscope channels are required to obtain the direction and amplitude of the pulse signal. This not only has a high cost but also a very low detection efficiency. The present disclosure uses a pulse direction discriminator composed of a diode and an operational amplifier to determine the direction of the pulse signal, avoiding this problem, simplifying the photon detection process, improving the detection efficiency, and also facilitating the integration of the single-photon detector system. For example, when expanding the SNSPD array or adding new signal processing modules and other device expansions, through the integration of the pulse direction discriminator of the present disclosure for single-photon detection, etc., the complexity of integration can be effectively reduced, and the integration degree and scalability can be improved.

[0120] In some embodiments, by cleverly integrating the physical characteristics of the superconducting nanowire, the row-column multiplexing structure, and the fast response circuit in the pulse direction discriminator, the duty cycle of the nanowire is greatly improved, well meeting the stringent requirements for the processing speed of weak photon signals in fields such as quantum communication and lidar. The improvement of the duty cycle not only effectively speeds up the detection speed but also improves the detection accuracy, and this integrated architecture is easy to be compatible with other modules, significantly improving the integration degree.

[0121] Figure 3Schematically shown is a flowchart of a detection method for a superconducting nanowire single-photon detector system of a scalable array according to an embodiment of the present disclosure. The method 300 includes:

[0122] S310, splitting the input light into two paths through a beam splitter, and adjusting the output intensity of one path of light through an adjustable attenuator.

[0123] In some embodiments, the method 300 further includes:

[0124] Measuring the other path of light output by the beam splitter with a first optical power meter, and calculating the light intensity input to the adjustable optical attenuator according to a preset beam splitting ratio;

[0125] Specifically, assuming the preset beam splitting ratio is A, the light intensity measured by the first optical power meter is B1, and the light intensity input to the adjustable optical attenuator is B2, then A = B1 / B2. Therefore, the light intensity input to the adjustable optical attenuator can be obtained according to the value measured by the first optical power meter and the preset beam splitting ratio.

[0126] S320, the adjusted light is split into two paths of light through the regulation of a fiber optic coupler, and one path of light to be detected is incident on a single-photon device.

[0127] In some embodiments, the method 300 further includes:

[0128] Measuring the light intensity of the other path of light output by the fiber optic coupler with a second optical power meter;

[0129] Calculating the number of photons in the light to be detected according to the light intensity input to the adjustable optical attenuator and the light intensity measured by the second optical power meter, to achieve the ability of photon number resolution;

[0130] Specifically, the number of photons incident on the single-photon device in the light to be detected per unit time The calculation formula is as follows:

[0131]

[0132] Wherein, is the optical power incident on the single-photon device per unit time, and this value can be obtained according to the light intensity input to the adjustable optical attenuator and the light intensity measured by the second optical power meter, 、 are the wavelength and the speed of light of the light incident on the single-photon device respectively, is Planck's constant.

[0133] S330, converting the light to be detected into a pulse signal through a single-photon device and outputting it to a pulse direction discriminator through a bias tee, to obtain the direction of the discriminated pulse signal.

[0134] In some embodiments, the pulse direction discriminator discriminates the direction of the pulse signal by the following method:

[0135] For the Figure 1 pulse direction discriminator as shown, only the pulse signal with a positive direction can pass through the diode and be amplified by the operational amplifier, while the negative pulse signal is filtered out and cannot be displayed by the oscilloscope as a negative pulse signal;

[0136] If the Figure 1 positive and negative poles of the diode in are placed in the opposite direction, the pulse direction discriminator can only pass through the negative pulse signal, amplify it and display it by the oscilloscope, while the positive pulse signal cannot pass through the pulse direction discriminator.

[0137] In some embodiments, the direction of the pulse signal can be predicted in advance by the diode, thereby reducing the number of channels of the oscilloscope and improving the detection efficiency.

[0138] S340, Send the discriminated pulse signal to the oscilloscope and obtain the amplitude of the discriminated pulse signal.

[0139] S350, Determine the position of the photon in the light to be detected according to the direction and amplitude of the discriminated pulse signal.

[0140] In some embodiments, according to the pulse signals output by the readout circuit when all pixels in the simulated single-photon device respond, the pulse signals output by the readout circuit when there is no pixel response in a certain row or column, the pulse signals output by the readout circuit when there are 1, 2, 3... all pixels in a certain row respond, and the pulse signals output by the readout circuit when there are 1, 2, 3... all pixels in a certain column respond, determine which of the above situations the direction and amplitude of the discriminated pulse signal belong to, and determine the position of the responding pixel according to the judgment result, and determine the position of the photon in the light to be detected based on the position of the responding pixel to achieve spatial resolution ability;

[0141] Specifically, taking a 3×3 pixel array as an example, a simulation circuit is constructed for it, as Figure 4As shown, one end of pixel 1, pixel 2, and pixel 3 are respectively connected to row transmission line 1 (abbreviated as row 1). One end of row 1 is connected to a voltage source, and the other end outputs signal 1. The other end of pixel 1 is connected to column transmission line 1 (abbreviated as column 1) through load resistor 1 (abbreviated as load 1). The other end of pixel 2 is connected to column transmission line 2 (abbreviated as column 2) through load resistor 2 (abbreviated as load 2). The other end of pixel 3 is connected to column transmission line 3 (abbreviated as column 3) through load resistor 3 (abbreviated as load 3). The input impedance (resistor 1, resistor 2, resistor 3) of the matching readout circuit is set on row 1. One end of pixel 4, pixel 5, and pixel 6 are respectively connected to row transmission line 2 (abbreviated as row 2). One end of row 2 is connected to a voltage source, and the other end outputs signal 2. The other end of pixel 4 is connected to column transmission line 1 through load resistor 4 (abbreviated as load 4). The other end of pixel 5 is connected to column transmission line 2 through load resistor 5 (abbreviated as load 5). The other end of pixel 6 is connected to column transmission line 3 through load resistor 6 (abbreviated as load 6). The input impedance (resistor 4, resistor 5, resistor 6) of the matching readout circuit is set on row 2. One end of pixel 7, pixel 8, and pixel 9 are respectively connected to row transmission line 3 (abbreviated as row 3). One end of row 3 is connected to a voltage source, and the other end outputs signal 3. The other end of pixel 7 is connected to column transmission line 1 through load resistor 7 (abbreviated as load 7). The other end of pixel 8 is connected to column transmission line 2 through load resistor 8 (abbreviated as load 8). The other end of pixel 9 is connected to column transmission line 3 through load resistor 9 (abbreviated as load 9). The input impedance (resistor 7, resistor 8, resistor 9) of the matching readout circuit is set on row 3. The end of column 1 outputs signal 4 and is grounded through resistor 10, and resistor 10 is in parallel with inductor 1. The end of column 2 outputs signal 5 and is grounded through resistor 11, and resistor 11 is in parallel with inductor 2. The end of column 3 outputs signal 6 and is grounded through resistor 12, and resistor 12 is in parallel with inductor 3. Among them, inductor 1 represents the equivalent inductance of pixel 1, pixel 4, and pixel 7 located in the first column. Inductor 2 represents the equivalent inductance of pixel 2, pixel 5, and pixel 8 located in the second column. Inductor 3 represents the equivalent inductance of pixel 3, pixel 6, and pixel 9 located in the third column.

[0142] In Figure 4 the structure shown, the schematic diagram of the pulse signals of output signals 1 - 6 when simulating all pixels responding is as Figure 5 shown. The directions of the pulse signals in output signals 1 - 3 are all positive, and the amplitudes of the pulse signals increase in sequence as output signal 1, output signal 3, and output signal 2. The directions of the pulse signals in output signals 4 - 6 are all negative, and the absolute values of the amplitudes of the pulse signals increase in sequence as output signal 4, output signal 5, and output signal 6.

[0143] In Figure 4 the structure shown, the schematic diagram of the pulse signals of output signals 1 - 6 when simulating no pixel response in a certain row or column is as Figure 6As shown, output signal 1 is the pulse signal output by row 1 when each pixel in row 1 has no response and other pixels have responses. Output signal 2 is the pulse signal output by row 2 when each pixel in row 2 has no response and other pixels have responses. Output signal 3 is the pulse signal output by row 3 when each pixel in row 3 has no response and other pixels have responses. Output signal 4 is the pulse signal output by column 1 when each pixel in column 1 has no response and other pixels have responses. Output signal 5 is the pulse signal output by column 2 when each pixel in column 2 has no response and other pixels have responses. Output signal 6 is the pulse signal output by column 3 when each pixel in column 3 has no response and other pixels have responses. The directions of the pulse signals in output signals 1 - 3 are all negative, and the amplitudes of the pulse signals are, from small to large, output signal 1, output signal 3, and output signal 2. The directions of the pulse signals in output signals 4 - 6 are all positive, and the amplitudes of the pulse signals are, from small to large, output signal 4, output signal 5, and output signal 6;

[0144] In Figure 4 the structure shown, the schematic diagrams of the pulse signals of output signal 1 when a certain row (taking row 1 as an example) has 1, 2, and 3 pixels responding respectively are as Figure 7 shown. When row 1 has 1, 2, and 3 pixels responding respectively, the directions of the pulse signals of output signal 1 are all positive, and the amplitudes are, from small to large, only 1 response, any 2 of them responding, and all 3 responding;

[0145] In Figure 4 the structure shown, the schematic diagrams of the pulse signals of output signal 4 when a certain column (taking column 1 as an example) has 1, 2, and 3 pixels responding respectively are as Figure 8 shown. When column 1 has 1, 2, and 3 pixels responding respectively, the directions of the pulse signals of output signal 4 are all negative, and the absolute values of the amplitudes are, from small to large, only 1 response, any 2 of them responding, and all 3 responding;

[0146] If the single - photon detection system of the present disclosure has a 3×3 pixel array structure, and the obtained output signals 1 - 6 are as Figure 9 shown, then based on the above simulation results and the results shown in Figure 9 it can be concluded that the responding pixels are pixel 1, pixel 3, and pixel 7. Specifically, Figure 9 the pulse direction and amplitude of output signal 1 in Figure 7 match the situation of any 2 pixels responding in Figure 6 the pulse direction and amplitude of output signal 2 match the situation where there is no pixel response in row two in Figure 7 the pulse direction and amplitude of output signal 3 match the situation where only 1 pixel responds in Figure 8For any two pixel responses, the pulse direction and amplitude of the output signal 5 conform to Figure 6 For the case where none of the pixels respond, the pulse direction and amplitude of the output signal 6 conform to Figure 8 For the case where only 1 pixel responds, it is concluded that pixels 1, 3, and 7 respond, and the other pixels do not respond;

[0147] Based on the positions of the responding pixels 1, 3, and 7, the photon position can be determined, realizing the spatial resolution ability;

[0148] Furthermore, Figures 5 - 9 In each of the figures, the abscissa represents the response time in ns, and the ordinate represents the response amplitude in .

[0149] In some embodiments, the single-photon detection system of the present disclosure does not affect the spatial resolution ability when expanding the pixel array, and can flexibly expand the pixel array according to different requirements.

[0150] In some embodiments, method 300 further includes:

[0151] When expanding the single-photon device into an array, by adding a preset number of pixels in the SNSPD array, adding row and column transmission lines corresponding to the added pixels in the corresponding structural layer, and adding load resistors connected in series with the added pixels in the readout circuit, the array expansion is completed;

[0152] For example, if the single-photon device of the present disclosure is a 3×3 pixel array and now it is desired to expand it into a 5×5 pixel array, in addition to adding 16 pixels, only 2 row transmission lines, 2 column transmission lines, and load resistors connected in series with these 16 pixels need to be added in the readout circuit, without the need for large-scale expansion of the readout circuit, improving the array scalability and integration.

[0153] It should be noted that some steps of the above method can be executed alone or in combination, and can be executed in parallel or sequentially, not limited to the specific operation sequence shown in the figure.

[0154] According to an embodiment of the present disclosure, a superconducting nanowire single-photon detector system and a detection method for a scalable array are provided. The system includes: a single-photon device for converting the light to be detected into a pulse signal and sending it to a pulse direction discriminator; a pulse direction discriminator for discriminating the direction of the pulse signal and sending the discriminated pulse signal to an oscilloscope; an oscilloscope for recording the amplitude of the received pulse signal, so as to determine the position of photons in the light to be detected in combination with the discriminated pulse signal direction. Among them, the single-photon device includes an SNSPD array and a readout circuit. The SNSPD array is connected to the readout circuit by a row-column multiplexing structure, and the readout circuit is integrated with load resistors connected in series with each pixel in the SNSPD array. When the array of the single-photon detector system of the present disclosure is expanded, it is not necessary to largely change the structure of the readout circuit. Only load resistors connected in series with the added pixels need to be added to the readout circuit, thereby improving the scalability of the array. By using the pulse discriminator to first discriminate the direction of the pulse signal and then using the oscilloscope to display the amplitude of the discriminated pulse signal, the problem that a large-area SNSPD array requires more oscilloscope channels to obtain the pulse signal direction and amplitude is avoided, the photon detection process is simplified, and the detection efficiency is improved. The comprehensive design of structures such as the row-column multiplexing structure, the pulse direction discriminator, and the readout circuit integrated with load resistors connected in series with pixels is beneficial to reducing the complexity of integration and improving the integration when the device is expanded such as array expansion or addition of new modules. Moreover, this comprehensive design also improves the duty cycle of the nanowire. The increase in the duty cycle not only effectively speeds up the detection speed but also improves the detection accuracy, well meeting the stringent requirements for the processing speed of weak photon signals in fields such as quantum communication and lidar, improving the efficiency of multi-point simultaneous communication, and accelerating the imaging speed of fluorescent photons in the biomedical field in a short time and the detection ability of low surface brightness celestial bodies in the astronomical observation field. The detector system can determine the photon position according to the direction and amplitude of the discriminated pulse signal, realizing spatial resolution ability. In addition, the detector system further includes a first optical power meter and a second optical power meter. According to the measurement results of the first optical power meter and the second optical power meter, photon number resolution ability can be realized.

[0155] The above system part includes modules respectively used to execute the steps of any one of the method embodiments described above. Moreover, the implementation manners, the technical problems solved, the functions realized, and the technical effects achieved by the corresponding steps in the method part embodiments are respectively the same as or similar to those of the modules / units / sub-units, etc. in the system part embodiments, and will not be elaborated here.

[0156] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods according to various embodiments of the present disclosure. In this regard, each block in the flowchart or block diagram may represent a module, a segment of a program, or a portion of code, which contains one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions noted in the blocks may occur in a different order than that noted in the accompanying drawings. For example, two consecutive blocks shown may actually be executed substantially in parallel, and they may sometimes be executed in the reverse order, depending on the functions involved. It should also be noted that each block in the block diagram or flowchart, and combinations of blocks in the block diagram or flowchart, can be implemented by a dedicated hardware-based system that performs the specified functions or operations, or by a combination of dedicated hardware and computer instructions.

[0157] Those skilled in the art will appreciate that the features described in the various embodiments of the present disclosure can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in the present disclosure. In particular, without departing from the spirit and teachings of the present disclosure, the features described in the various embodiments of the present disclosure can be combined and / or combined in various ways. All such combinations and / or combinations fall within the scope of the present disclosure.

[0158] The embodiments of the present disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present disclosure. Although the embodiments have been described separately above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. The scope of the present disclosure is defined by the appended claims and their equivalents. Without departing from the scope of the present disclosure, those skilled in the art can make various substitutions and modifications, and all such substitutions and modifications should fall within the scope of the present disclosure.

Claims

1. A superconducting nanowire single photon detector system with an extensible array, characterized in that, The system includes: A single-photon device, configured to convert the light to be detected into a pulse signal and send it to a pulse direction discriminator; The pulse direction discriminator, configured to discriminate the direction of the pulse signal and send the discriminated pulse signal to an oscilloscope; The oscilloscope, configured to record the amplitude of the received pulse signal, so as to determine the position of photons in the light to be detected in combination with the discriminated pulse signal direction; Wherein, the single-photon device includes an SNSPD array and a readout circuit, the SNSPD array is connected to the readout circuit by a row-column multiplexing structure, and the readout circuit is integrated with load resistors connected in series with each pixel in the SNSPD array.

2. The system according to claim 1, wherein The SNSPD array has a three-dimensional spatial structure, including multiple structural layers, a pixel array, a first gold electrode, a second gold electrode, a first peripheral gold electrode, a second peripheral gold electrode, row transmission lines, and column transmission lines; wherein, The row transmission lines are disposed at the bottom of the first structural layer; The first peripheral gold electrode and the second peripheral gold electrode are disposed at the top of the first structural layer; The pixel array, the first gold electrode, the second gold electrode, and the column transmission lines are disposed in the second structural layer.

3. The system according to claim 2, wherein The SNSPD array is connected to the readout circuit by a row-column multiplexing structure, including: One ends of multiple pixels in the same row in the pixel array are respectively connected to the row transmission line corresponding to the row through the first gold electrode corresponding to the pixel; one end of the row transmission line is connected to a bias power supply, and the other end is connected to the readout circuit through the first peripheral gold electrode; The other ends of multiple pixels in the same column are respectively connected to the column transmission line corresponding to the pixel through the second gold electrode corresponding to the pixel, the column transmission line is connected to the load resistor integrated on the readout circuit and connected in series with the pixel corresponding to the column transmission line through the second peripheral gold electrode connected to itself, and is grounded through the load resistor.

4. The system according to claim 3, wherein The distances between the first gold electrodes and the second gold electrodes between the pixels, the conductive contact widths between the first gold electrode and the second gold electrode and between the first peripheral gold electrode and the second peripheral gold electrode, the nanowire distribution of the pixels in the detection area, the physical properties of the nanowires, and the bypass area outside the detection area are respectively structures that meet preset performance indicators.

5. The system according to claim 1, characterized in that The pulse direction discriminator includes a diode and an operational amplifier; wherein, The diode is configured to discriminate the direction of the pulse signal output by the single-photon device; The operational amplifier is configured to amplify the pulse signal passing through the diode and transmit it to the oscilloscope.

6. The system according to claim 1, characterized in that The system further includes: a beam splitter, an adjustable optical attenuator, an optical fiber coupler, a refrigerator, and a bias tee connected in sequence; wherein, the single-photon device is integrated in the refrigerator; The bias tee is connected to the oscilloscope through the pulse direction discriminator; the bias tee is also connected to a bias power supply; The beam splitter is also connected to a first optical power meter; The optical fiber coupler is also connected to a second optical power meter.

7. The system according to claim 6, wherein The beam splitter is configured to divide the input light into two paths and input one of the paths into the adjustable optical attenuator; The adjustable optical attenuator is configured to adjust the output intensity of the received light; The optical fiber coupler is used to regulate the light output by the tunable optical attenuator and output the light to be detected; The first optical power meter is used to measure the intensity of the other path of light output by the beam splitter to obtain the intensity of the light input to the tunable optical attenuator; The second optical power meter is used to measure the intensity of one path of light output by the optical fiber coupler to obtain the number of photons in the light to be detected; The bias tee is used to provide a bias power supply for the single-photon device and also to send the pulse signal output by the single-photon device to the pulse direction discriminator.

8. The system according to claim 7, wherein The optical fiber coupler includes: A neutral density filter, a polarization controller, and an optical fiber splitter connected in sequence; The neutral density filter is used to change the intensity of the light output by the tunable optical attenuator and maintain the color or wavelength of the light output by the tunable optical attenuator; The polarization controller is used to adjust the polarization state of the light output by the neutral density filter to improve the stability and uniformity of the light output; The optical fiber splitter is used to split the light output by the polarization controller into two paths for output.

9. A detection method for a superconducting nanowire single-photon detector system of a scalable array according to any one of claims 1-8, characterized in that, The system includes a beam splitter, a tunable optical attenuator, an optical fiber coupler, a refrigerator, a bias tee, a pulse direction discriminator, and an oscilloscope connected in sequence, wherein a single-photon device is integrated in the refrigerator. The method includes: Dividing the input light into two paths by the beam splitter, and adjusting the output intensity of one path of light through the tunable attenuator; The adjusted light is divided into two paths of light through the regulation of the optical fiber coupler, and one path of the light to be detected is incident on the single-photon device; Converting the light to be detected into a pulse signal by the single-photon device and outputting it to the pulse direction discriminator through the bias tee to obtain the direction of the discriminated pulse signal; Sending the discriminated pulse signal to the oscilloscope to obtain the amplitude of the discriminated pulse signal; Determining the position of the photons in the light to be detected according to the direction and amplitude of the discriminated pulse signal.

10. The method according to claim 9, wherein The method further includes: Measuring the intensity of the other path of light output by the beam splitter by the first optical power meter, and calculating the intensity of the light input to the tunable optical attenuator according to a preset beam splitting ratio; Measuring the intensity of the other path of light output by the optical fiber coupler by the second optical power meter; Calculating the number of photons in the light to be detected according to the intensity of the light input to the tunable optical attenuator and the intensity of the light measured by the second optical power meter; wherein, The first optical power meter is connected to the beam splitter, and the second optical power meter is connected to the optical fiber coupler.

11. The method according to claim 9, wherein The method further includes: When performing array expansion on the single-photon device, complete the array expansion by adding a preset number of pixels in the SNSPD array, adding row and column transmission lines corresponding to the added pixels in the corresponding structural layer, and adding load resistors connected in series with the added pixels in the readout circuit.

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