Method for representing detection efficiency of sine-gated single-photon detector by using continuous light

Abstract

The invention discloses a method for representing the detection efficiency of a sine-gated single-photon detector by using continuous light. The method comprises the following steps: collecting count values of the single-photon detector under different bias voltages; calculating an initial gate width, an initial average photon number and initial detection efficiency according to the initial over-bias voltage; increasing the bias voltage by a step value, calculating widths of different parts of gate pulse detection efficiency under the voltage, and calculating count values of the different parts; subtracting the count value measured under the bias voltage from the sum of the count values of all the parts to obtain a corrected count value, and calculating the detection efficiency; whether the bias voltage reaches a set maximum value or not is judged, if not, the bias voltage continues to be increased, and meanwhile the detection efficiency is corrected; and if the maximum value is reached, the detection efficiency obtained through processing is used as a final calibration value. The method can correct the detection efficiency when a continuous light source is used, and eliminates the influence of a plurality of voltage intervals, so as to calibrate the maximum detection efficiency of the detector.

Description

Technical Field

[0001] The present invention relates to the technical field of single photon detection, and particularly to a method for characterizing the detection efficiency of a sine-gated single photon detector using continuous light. Background Art

[0002] With the rapid development of optical quantum technology, single photon detection technology is increasingly widely used in fields such as quantum key distribution, quantum optics, astronomical observation, and bioluminescence detection. As a common weak light detection device, an avalanche photodiode (APD) has advantages such as large internal gain, small size, low power consumption, high quantum efficiency, and ease of integration, and is the main development direction for large-scale applications of single photon detectors. According to the magnitude of the reverse bias voltage applied across the APD, the detector can be divided into two operating modes: "linear mode" and "Geiger mode". In the linear mode, the bias voltage across the APD is less than the avalanche voltage, the avalanche amplification factor is small, and it cannot respond to single photons. At this time, the APD can only detect strong light, and the APD will only respond when the incident light power is greater than the threshold power. In the Geiger mode, the bias voltage across the APD is greater than the avalanche voltage, the avalanche amplification factor is large, and the avalanche photodiode can respond to single photons. Usually, single photon detectors operate in the "Geiger mode". A long-lasting avalanche current will generate a large amount of heat, which may cause the APD to burn out. Therefore, a quenching circuit is required to reduce the voltage across the APD below the avalanche breakdown voltage. Quenching circuits are mainly divided into two types according to the operating mode: free-running mode and gated mode. The free-running mode quenches the avalanche by connecting a large resistor in series, which has a simple structure but has problems such as long dead time and low system detection efficiency. In the gated mode, the APD is first biased below the breakdown voltage in direct current. When the optical signal arrives, a synchronized gate pulse is coupled to the APD to make it operate in the Geiger mode. Therefore, a single photon can trigger avalanche breakdown and output a macroscopically measurable pulse, enabling single photon detection only during the period when the gate is open and not detecting single photons during the period when the gate is closed on the entire time axis, achieving controllable dead time and suppressing after-pulses and dark counts, effectively improving the detection efficiency. The gated mode can be further divided into square-wave gating and sine-wave gating according to the waveform. The leading and trailing edges of the square wave are relatively fast, which can better control the duration of the avalanche to reduce the probability of after-pulses. However, in situations where both the frequency and amplitude are relatively high, modulating a square wave is much more difficult than a sine wave, and the spike noise caused by the rapid voltage jump is also stronger. Since the sine wave has a single spectral component, it is not only easier to modulate a high-frequency gate signal, but also the post-processing can be filtered by a variety of filters available on the market, and is often used in situations with relatively high frequencies. Therefore, sine-wave gating is the mainstream direction in the research of high-speed single photon detectors.

[0003] In the field of quantum communication, the detection efficiency of single-photon detectors is a key factor determining the effective communication distance of the system and the quantum key generation rate. Especially with the development of free-space quantum communication technology on space-based and satellite-based platforms, the detection efficiency of detectors is directly related to the overall efficiency of the communication system. Therefore, the accurate characterization of detection efficiency has become the cornerstone for constructing an efficient quantum communication system. When using continuous light to characterize the detection efficiency, since the light intensity remains relatively stable over time, photons exist throughout the time axis. However, with different overbias voltages, the detection efficiency for photons is also different. Therefore, after the bias voltage is determined, the bias voltage can still be divided into several voltage intervals, and different detection efficiencies correspond to different voltage intervals. This results in different detection efficiencies within the response time of a gate pulse, ultimately leading to a reduction in the overall detection efficiency. The existence of this problem has an adverse impact on the performance and application of single-photon detectors. However, currently, there is no relatively perfect technical solution that can effectively solve such problems. Summary of the Invention

[0004] In view of this, to solve the above problems in the prior art, the present invention proposes a method for characterizing the detection efficiency of a sinusoidal gated single-photon detector using continuous light, which can correct the detection efficiency when using a continuous light source, eliminate the influence of the previous several voltage intervals, and calibrate the maximum detection efficiency of the detector.

[0005] The present invention solves the above problems through the following technical means:

[0006] The present invention provides a method for characterizing the detection efficiency of a sinusoidal gated single-photon detector using continuous light, including the following steps:

[0007] Collect the count values of the single-photon detector at different bias voltages;

[0008] Build a gate pulse model in combination with the gate voltage amplitude and the gate frequency;

[0009] Calculate the initial gate width, the initial average photon number, and the initial detection efficiency according to the initial overbias voltage and the gate pulse model;

[0010] Increase the bias voltage by one step value, calculate the widths of different parts of the gate pulse detection efficiency at this bias voltage, and deduce the count values of different parts;

[0011] Subtract the count value measured at this bias voltage from the sum of the count values of different parts deduced according to different detection efficiencies, obtain the corrected count value, and calculate the detection efficiency;

[0012] Determine whether the bias voltage has reached the set maximum value. If not, continue to increase the bias voltage while correcting the detection efficiency. If it has reached the maximum value, the detection efficiency obtained after processing will be used as the final calibration value, which will be used to characterize the performance of the single-photon detector.

[0013] Preferably, collecting the count values of the single-photon detector at different bias voltages specifically includes the following steps:

[0014] Connect the single-photon detection system instruments, set the parameters of each instrument, and turn on the light source and power supply;

[0015] Gradually increase the bias voltage until the single-photon detector detects a single photon, then determine the current bias voltage as the avalanche breakdown voltage;

[0016] Starting from the avalanche breakdown voltage, the bias voltage is gradually increased in a fixed step size, and the current count value is recorded each time after the increase until the set voltage maximum value is reached;

[0017] Disconnect the light source and repeat the previous step to record the count values at different bias voltages.

[0018] Preferably, the single-photon detection system includes:

[0019] A laser for emitting a light source;

[0020] A variable attenuator for attenuating the light source to the single-photon level and then inputting it into the single-photon detector;

[0021] An optical power meter for reading the attenuated optical power after turning on the light source and power supply;

[0022] A synchronous clock generator for outputting a clock with a sinusoidal gating frequency to control the gate pulse trigger of the single-photon detector.

[0023] Preferably, the laser is used to emit a light source with a wavelength of 275 nm.

[0024] Preferably, the laser is an ultraviolet laser.

[0025] Preferably, the sinusoidal gating frequency is 600 MHz.

[0026] Preferably, when building the gate pulse model by combining the gate voltage amplitude and the gate frequency, a sinusoidal gate is used. The gate voltage amplitude is set to A, the gate frequency is set to f, and the gate pulse expression is:

[0027] Y = Acos(2πft) (1)

[0028] Where t represents time.

[0029] Preferably, in calculating the initial gate width, the initial average photon number, and the initial detection efficiency based on the initial over-bias voltage and the gate pulse model, the value by which the bias voltage is increased for the first time by a fixed step ΔV on the basis of the avalanche breakdown voltage V B is the initial over-bias voltage V1, i.e., V1 = V B + ΔV. At this time, the recorded count value and the dark count value are N1 and N d1 respectively; L1 is the distance between the two intersections of the waveform and the coordinate axes, i.e., the initial gate width; It can be easily obtained from Equation (1):

[0030]

[0031] where A - V1 represents the sine value corresponding to this over-bias voltage on the gate pulse;

[0032] The energy E of a single photon is given by the relationship between wavelength and energy:

[0033]

[0034] where h represents Planck's constant, c represents the speed of light, and λ represents the wavelength used;

[0035] The optical power P is measured at the optical power meter, and the average photon number n per second is expressed as:

[0036]

[0037] The average photon number n per second is multiplied by the gate width to obtain the average photon number n1 corresponding to the gate width:

[0038] n1 = L1 × n (5)

[0039] Combining the above numerical values, the expression for the initial detection efficiency of the single-photon detector is obtained:

[0040]

[0041] where p s1 and p d1 represent the counting rate and the dark counting rate under the initial bias voltage respectively, and are given by the following equations:

[0042]

[0043] .

[0045] Preferably, the bias voltage is increased by one step value, and the widths of different parts of the gate pulse detection efficiency at this voltage are calculated. Among the count values of different parts deduced, if the bias voltage has increased to the i-th time at this time, i > 1, the over-bias voltage should be expressed as:

[0046] V i = V B + iΔV (9)

[0047] V B is the avalanche breakdown voltage, and ΔV is the step value; different overbias voltages correspond to different detection efficiencies. Therefore, the overbias voltages in the range from 0 to V i are divided into [0, V1], [V1, V2], [V2, V3], ……, [V i-1 , V i these i voltage intervals, and the span of each voltage interval is ΔV; however, in a certain interval [V x , V x+1 , the corresponding detection efficiency is still continuously changing. According to the idea of calculus, when ΔV takes a very small value, that is, the span within each interval is very small, the change in the detection efficiency is also very small. Thus, it can be considered that the detection efficiency is approximately constant within this interval. Therefore, the detection efficiency value η x at a certain point in this interval can be used to represent the detection efficiency of the entire interval; for the i voltage intervals divided previously, there are i different detection efficiencies corresponding from η1 to η i ;

[0048] The waveform curve when the overbias voltage is V i from the inside to the outside represents the cases where the overbias voltages are V1, V2, V3, ……, V i-1 , V i ; points a1, a1′, a2, a′2, ……, a i-1 , a i ′ -1 respectively correspond to the points on the gate pulse curve representing V i when the overbias voltages are V1, V2, ……, V i-1 ; line segments a1 a1′, a2 a′2, ……, a i-1 a i ′ -1 represent the widths occupied by each overbias voltage value on the gate pulse curve representing V i ; it can be clearly seen on the waveform curve that there are i voltage intervals in total, but only the detection efficiency corresponding to the i-th voltage interval is ultimately required. Therefore, it is necessary to eliminate the influence generated by the first to the (i - 1)-th intervals;

[0049] The width occupied by the curve representing the overbias voltage V i can be expressed by referring to the form of the formula, specifically as:

[0050]

[0051] Next, from line segment a1 a1′ to line segment ai-1 a i ′ -1 The specific calculation method for the width occupied by each line segment is as follows:

[0052]

[0053] Therefore, referring to Equation (5), the average number of photons contained in the first voltage interval to the (i - 1)-th voltage interval is:

[0054]

[0055] Combining the average number of photons in each interval and the calculation formula for the detection efficiency of the single-photon detector, the actual count value from the first voltage interval to the (i - 1)-th voltage interval is inversely deduced, and the calculation method is given by the following expression:

[0056]

[0057] where η x represents the detection efficiency corresponding to the x-th voltage interval within the range from the first voltage interval to the (i - 1)-th voltage interval.

[0058] Preferably, subtract the count value measured at this bias voltage from the sum of the count values of different parts deduced according to different detection efficiencies to obtain the corrected count value, and calculate that in the detection efficiency, if the overbias voltage increases to V i and the recorded count value is N i , the corrected count value and count rate are:

[0059]

[0060]

[0061] Finally, the corrected detection efficiency is:

[0062]

[0063] where n i-1 represents the average number of photons contained in the gate width corresponding to the i-th voltage interval [V i-1 , V i . Referring to Equation (5), we have:

[0064] n i-1 = L i-1 × n(18)

[0065] The η i calculated at this time represents that the overbias voltage is in the i-th voltage interval [V i-1 , V iThe detection efficiency at this time. After the above steps, the influence of the 1st to the (i - 1)th voltage intervals on the detection efficiency has been eliminated; thus, the correction of the detection efficiency at the over - bias voltage of V i is completed.

[0066] Compared with the prior art, the beneficial effects of the present invention at least include:

[0067] The present invention first collects the count values of the single - photon detector at different bias voltages. For the above - collected data, a set of algorithms is written using MATLAB software to calculate the initial gate width, the initial average number of photons, and the initial detection efficiency. On this basis, the bias voltage is gradually increased with a fixed step size. Each time it is increased, the widths of different parts of the detection efficiency at this bias voltage value are calculated, and the count values of different width parts are deduced. The count value at this bias voltage is subtracted from the sum of the count values deduced for different detection efficiency parts to complete the correction of the count value. The detection efficiency is calculated using the corrected count value to complete the correction of the detection efficiency. The above process is repeated until the voltage increases to the set maximum value, and the actual detection efficiency of the detector is characterized. The present invention can correct the detection efficiency when using a continuous light source, eliminate the influence of several previous voltage intervals, and calibrate the maximum detection efficiency of the detector. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0069] Figure 1 is the block diagram of the single - photon detection system used in the present invention;

[0070] Figure 2 is the single - photon counting data acquisition flowchart under the method of the present invention;

[0071] Figure 3 is the flowchart of the detection efficiency correction method proposed by the present invention;

[0072] Figure 4 is the gate pulse waveform diagram used in the method of the present invention;

[0073] Figure 5 is the waveform schematic diagram when the over - bias voltage is set to the initial value.

[0074] Figure 6 is the waveform schematic diagram when the over - bias voltage is set to V i at this time. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0075] To make the above objects, features, and advantages of the present invention more apparent and understandable, the technical solutions of the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0076] As Figure 1 and Figure 2 shown, the block diagram of the single-photon detection system and the single-photon counting acquisition flowchart used in this embodiment are given. The specific steps for collecting the count values of the single-photon detector at different bias voltages are as follows:

[0077] Step 21: Connect the instruments, set all the parameters, and turn on the light source and the power supply. The layout and connection of the instruments are as Figure 1 shown. In this embodiment, the wavelength of the light source used is 275 nm, emitted by an ultraviolet laser. The synchronous clock generator is used to output a 600 MHz clock to control the gate pulse trigger of the single-photon detector. In this embodiment, a sinusoidal gate with a gating frequency of 600 MHz is used. The variable attenuator attenuates the light emitted by the ultraviolet laser to the single-photon level and then inputs it into the single-photon detector. After turning on the light source and the power supply, the attenuated optical power P can be read at the optical power meter. The optical power used in this embodiment is -71.55 dBm.

[0078] Step 22: Increase the bias voltage and observe the reading until there is a count value, and determine the avalanche breakdown voltage V B . In this embodiment, the avalanche breakdown voltage V B is 145.38 V.

[0079] Step 23: Starting from the avalanche breakdown voltage V B , the voltage is gradually increased in a fixed step size ΔV, and the count value of the device is recorded each time it is increased until the set maximum voltage value is reached. When the voltage is increased for the i-th time, the corresponding overbias voltage expression is V i =V B +iΔV, and the corresponding count value is N i . In this embodiment, ΔV = 0.4 V, the finally set maximum value is 152.10 V, and a total of 17 data are recorded.

[0080] Step 24: Disconnect the light source and repeat Step 23. At this time, the dark count at different bias voltages is recorded. The dark count corresponding to the i-th increase in voltage is N di .

[0081] As Figure 3As shown, the flowchart of the detection efficiency correction method in this embodiment is given. For the data collected above, a set of algorithms are written using MATLAB software. First, the initial gate width, initial average photon number, and initial detection efficiency are calculated. On this basis, the bias voltage is gradually increased with a fixed step size ΔV. Each time it is increased, the widths of different parts of the detection efficiency at this bias voltage value are calculated, and the count values of different width parts are deduced. Subtract the sum of the count values deduced from different detection efficiency parts from the count value at this bias voltage to complete the correction of the count value. Use the corrected count value to calculate the detection efficiency to complete the correction of the detection efficiency. Repeat the above process until the voltage increases to the set maximum value to characterize the actual detection efficiency of the detector. The specific working process is as follows:

[0082] Step 31: Build a gate pulse model in combination with the gate voltage amplitude and gate frequency. In this experiment, sinusoidal gating is adopted. The gate voltage amplitude is set to A, and the gate frequency is set to f. For the convenience of subsequent calculations, the gate pulse expression is:

[0083] Y = Acos(2πft) (1)

[0084] where t represents time, with the unit of seconds. The gating waveform is as Figure 4 shown.

[0085] Step 32: Calculate the initial gate width, initial average photon number, and initial detection efficiency according to the initial over-bias voltage. The value of the bias voltage increased for the first time on the basis of the avalanche breakdown voltage V B with a fixed step size is the initial over-bias voltage, that is, V1 = V B + ΔV. At this time, the recorded count value and the dark count value are N1 and N d1 . respectively. The waveform at this time is as Figure 5 shown. L1 is the distance between the two intersections of the waveform and the coordinate axes, that is, the initial gate width. It can be easily obtained from Equation (1):

[0086]

[0087] where A - V1 represents the sine value corresponding to this over-bias voltage on the gate pulse.

[0088] The energy of a single photon is given by the relationship between wavelength and energy:

[0089]

[0090] where h represents Planck's constant, which is 6.626×10^34 J·s, c represents the speed of light, which is 3×10^8 m / s, and λ represents the wavelength of 275 nm used in this embodiment.

[0091] According to the optical power P measured in Step 21, the average number of photons per second is expressed as:

[0092]

[0093] The average number of photons per second n is multiplied by the gate width to obtain the average number of photons corresponding to the gate width. As Figure 5 shown, the average number of photons contained in the waveform is:

[0094] n1 = L1 × n (5)

[0095] Combining the above values, the expression for the initial detection efficiency of the detector can be obtained:

[0096]

[0097] where p s1 and p d1 represent the counting rate and the dark counting rate under the initial bias voltage respectively, and are given by the following equations:

[0098]

[0099]

[0100] Step 33: Increase the bias voltage by a step value, calculate the widths of different parts of the gate pulse detection efficiency at this voltage, and deduce the count values of different parts. If the bias voltage has increased to the i-th time (i > 1) at this time, the over-bias voltage should be expressed as:

[0101] V i = V B + iΔV (9)

[0102] V B is the avalanche breakdown voltage, and ΔV is the step value. As mentioned before, different over-bias voltages correspond to different detection efficiencies. Therefore, the over-bias voltages in the range from 0 to V i can be divided into i voltage intervals: [0, V1], [V1, V2], [V2, V3], ……, [V i-1 , V i , and the span of each voltage interval is ΔV. However, in a certain interval [V x , V x+1 , its corresponding detection efficiency is still continuously changing. According to the idea of calculus, when ΔV takes a very small value, that is, the span within each interval is very small, the change in the detection efficiency is also very small. Thus, it can be considered that the detection efficiency is approximately constant within this interval. Therefore, the detection efficiency value η x at a certain point in this interval can be used to represent the detection efficiency of the entire interval. For the i voltage intervals divided above, there are i different detection efficiencies corresponding from η1 to η i .

[0103] The waveform when the overbias voltage is V i is as shown in Figure 6 . The curves from the inside to the outside represent the cases where the overbias voltages are V1, V2, V3, ……, V i-1 , V i . The points a1, a1′, a2, a′2, ……, a i-1 , a i ′ -1 correspond to the respective points on the gate pulse curve representing V i when the overbias voltages are V1, V2, ……, V i-1 . The line segments a1 a1′, a2 a′2, ……, a i-1 a i ′ -1 represent the widths occupied by the respective overbias voltage values on the gate pulse curve representing V i . It can be clearly seen on Figure 6 that there are a total of i voltage intervals, but only the detection efficiency corresponding to the i-th voltage interval is ultimately required. Therefore, it is necessary to eliminate the influence generated in the 1st to the (i - 1)-th intervals.

[0104] The width occupied by the curve representing the overbias voltage V i can be expressed by referring to the form of the formula, specifically as:

[0105]

[0106] Next, the specific calculation method for the widths occupied by the line segments from a1 a1′ to the line segment a i-1 a i ′ -1 is as follows:

[0107]

[0108] Therefore, referring to Equation (5), the average number of photons contained in the 1st voltage interval to the (i - 1)-th voltage interval is:

[0109]

[0110] Combining the average number of photons in each interval and the calculation formula for the detection efficiency of the single-photon detector, the actual count values in the 1st voltage interval to the (i - 1)-th voltage interval are deduced backward, and the calculation method is given by the following expression:

[0111]

[0112] where η x represents the detection efficiency corresponding to the x-th voltage interval within the range of the 1st voltage interval to the (i - 1)-th voltage interval.

[0113] Step 34: Subtract the count value measured at this bias voltage from the sum of the count values of each part to obtain the corrected count value, and calculate the detection efficiency. If the over-bias voltage increases to V i and the recorded count value is N i , the corrected count value and count rate are:

[0114]

[0115]

[0116] Finally, the corrected detection efficiency is:

[0117]

[0118] where n i-1 represents the average number of photons contained in the gate width corresponding to the i-th voltage interval [V i-1 , V i . Referring to Equation (5), we have:

[0119] n i-1 = L i-1 × n(18)

[0120] At this time, the calculated η i represents the detection efficiency when the over-bias voltage is in the i-th voltage interval [V i-1 , V i . Through the above steps, the influence of the 1st to the (i - 1)-th voltage intervals on the detection efficiency has been eliminated. Thus, the correction of the detection efficiency when the over-bias voltage is V i is completed.

[0121] Step 35: Determine whether the bias voltage has reached the set maximum value. If not, continue to increase the bias voltage, and correct the detection efficiency by referring to the methods in Step 33 and Step 34. If the maximum value has been reached, the detection efficiency obtained after processing will be used as the final calibration value, which will be used to characterize the performance of the detector.

[0122] Finally, the correction effect achieved by applying the above correction method in this embodiment is given, and the specific values are shown in the following table. In this embodiment, the bias voltage starts from 145.78 V and gradually increases to 152.10 V in a fixed step of 0.4 V. When the maximum voltage setting is reached, the detection efficiency increases from 12.94% to 37.30%. As shown in Table 1.

[0123] Table 1

[0124]

[0125]

[0126] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation to the scope of the patent for the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention shall be subject to the appended claims.

Claims

1. A method for characterizing the detection efficiency of a sinusoidally gated single-photon detector using continuous light, characterized in that: The steps include: Collect the count values ​​of the single photon detector under different bias voltages; Build a gate pulse model by combining the gate voltage amplitude and gate frequency; Calculate the initial gate width, initial average photon number and initial detection efficiency based on the initial over-bias voltage and gate pulse model; Increase the bias voltage by a step value, calculate the width of different parts of the gate pulse detection efficiency under the bias voltage, and deduce the count values ​​of different parts; Subtracting the count value measured under the bias voltage from the sum of the count values ​​of different parts calculated according to different detection efficiencies to obtain a corrected count value, and calculating the detection efficiency; Determine whether the bias voltage has reached the set maximum value. If not, continue to increase the bias voltage and correct the detection efficiency at the same time; If the maximum value has been reached, the detection efficiency obtained after processing will be used as the final calibration value, which will be used to characterize the performance of the single-photon detector.

2. The method for characterizing the detection efficiency of a sinusoidally gated single-photon detector using continuous light according to claim 1, characterized in that: Collecting the count values ​​of the single photon detector under different bias voltages specifically includes the following steps: Connect the single photon detection system instrument, set the instrument parameters, and turn on the light source and power supply; Gradually increase the bias voltage until the single photon detector detects a single photon, then determine that the current bias voltage is the avalanche breakdown voltage; Starting from the avalanche breakdown voltage, the bias voltage is gradually increased in fixed steps, and the current count value is recorded after each increase until the set maximum voltage is reached; Disconnect the light source, repeat the previous step, and record the count values ​​under different bias voltages.

3. The method for characterizing the detection efficiency of a sinusoidally gated single-photon detector using continuous light according to claim 2, characterized in that: The single photon detection system comprises: Laser, used to emit light; A variable attenuator, used to attenuate the light source to a single-photon level before inputting it into a single-photon detector; Optical power meter, used to read the attenuated optical power after turning on the light source and power supply; The synchronous clock generator is used to output a clock of a sinusoidal gate gating frequency to control the gate pulse triggering of the single photon detector.

4. The method for characterizing the detection efficiency of a sinusoidally gated single-photon detector using continuous light according to claim 3, characterized in that: The laser is used to emit a light source with a wavelength of 275 nm.

5. The method for characterizing the detection efficiency of a sinusoidally gated single-photon detector using continuous light according to claim 3, characterized in that: The laser is an ultraviolet laser.

6. The method for characterizing the detection efficiency of a sinusoidally gated single-photon detector using continuous light according to claim 3, characterized in that: The gating frequency of the sinusoidal gate is 600 MHz.

7. The method for characterizing the detection efficiency of a sinusoidally gated single-photon detector using continuous light according to claim 1, characterized in that: In the gate pulse model built by combining the gate voltage amplitude and the gate frequency, sinusoidal gating is used, the gate voltage amplitude is set to A, the gate frequency is set to f, and the gate pulse expression is: Y=Acos(2πft) (1) Here, t represents time.

8. The method for characterizing the detection efficiency of a sinusoidally gated single-photon detector using continuous light according to claim 7, characterized in that: According to the initial over-bias voltage and gate pulse model, the initial gate width, initial average photon number and initial detection efficiency are calculated. The bias voltage is at the avalanche breakdown voltage V B The first increase in the fixed step length ΔV is the initial over-bias voltage V1, that is, V1 = V B +ΔV, the count value and dark count value recorded at this time are N1 and N d1 ; L1 is the distance between the two intersection points of the waveform and the coordinate axis, that is, the initial gate width; From formula (1), it is easy to get: Wherein, A-V1 represents the sine value of the over-bias voltage corresponding to the gate pulse; The energy E of a single photon is given by the relationship between wavelength and energy: Among them, h represents Planck's constant, c represents the speed of light, and λ represents the wavelength used; The optical power P is measured at the optical power meter, and the average number of photons per second n is expressed as: The average number of photons per second n is multiplied by the gate width to obtain the average number of photons n1 corresponding to the gate width: n1=L1×n (5) Combining the above values, the expression of the initial detection efficiency of the single-photon detector is obtained: Among them, p s1 and p d1 They represent the count rate and dark count rate under the initial bias voltage, respectively, and are given by the following formula:

9. The method for characterizing the detection efficiency of a sinusoidally gated single-photon detector using continuous light according to claim 8, characterized in that: Increase the bias voltage by a step value, calculate the width of different parts of the gate pulse detection efficiency under this voltage, and deduce the count values ​​of different parts. If the bias voltage is increased to the i-th time, i>1, the over-bias voltage should be expressed as: V i =V B +iΔV (9) V B is the avalanche breakdown voltage, ΔV is the step value; different over-bias voltages correspond to different detection efficiencies, so the range from 0 to V i The over-bias voltage in the range is divided into [0, V1], [V1, V2], [V2, V3], ..., [V i-1 ,V i ], each voltage interval has a span of ΔV; however, in a certain interval [V x ,V x+1 ], the corresponding detection efficiency still changes continuously. According to the idea of ​​calculus, when ΔV is very small, that is, the span in each interval is very small, the change of detection efficiency is also very small, so it can be considered that the detection efficiency is approximately constant in this interval. Therefore, the detection efficiency value η at a certain point in this interval can be used. x To represent the detection efficiency of the entire interval; for the i voltage intervals divided previously, there are corresponding i There are i different detection efficiencies; Over bias voltage is V i The waveform curves from inside to outside represent the over-bias voltages V1, V2, V3, ..., V i-1 ,V i The situation; points a1, a1′, a2, a′2, …, a i-1 ,a i ' -1 Corresponding to the V i On the gate pulse curve, the over-bias voltages are V1, V2, ..., V i-1 Each point when the line segment a1 a1′, a2 a′2, …, a i-1 a i ' -1 It means that each over-bias voltage value represents V i The width of the gate pulse curve; it is clearly seen on the waveform curve that there are i voltage intervals in total, but only the detection efficiency corresponding to the i-th voltage interval is ultimately required, so it is necessary to eliminate the influence of the 1st to i-1th intervals; Represents over-bias voltage V i The width of the curve can be expressed in the form of a reference formula, specifically: Next, line segment a1 a1′ to line segment a i-1 a i ' -1 The specific calculation method of the width of each line segment is: Therefore, referring to formula (5), the average number of photons contained in the 1st voltage interval to the i-1th voltage interval is: Combining the average number of photons in each interval with the calculation formula of the detection efficiency of the single-photon detector, the actual count value from the 1st voltage interval to the i-1th voltage interval is deduced, and the calculation method is given by the following expression: Among them, η x It represents the detection efficiency corresponding to the xth voltage interval in the range from the 1st voltage interval to the (i-1)th voltage interval.

10. The method for characterizing the detection efficiency of a sinusoidally gated single-photon detector using continuous light according to claim 9, characterized in that: Subtract the count value measured under the bias voltage from the sum of the count values ​​of different parts calculated according to different detection efficiencies to obtain the corrected count value, and calculate the detection efficiency. i The count value recorded when i , the corrected count value and count rate are: Finally, the corrected detection efficiency is: Among them, n i-1 Indicates the i-th voltage interval [V i-1 ,V i ] The average number of photons contained in the gate width corresponding to , referring to formula (5) is: n i-1 =L i-1 ×n (18) The calculated η i Indicates that the over-bias voltage is in the ith voltage interval [V i-1 ,V i ], after the above steps, the influence of the voltage range from 1 to i-1 on the detection efficiency has been eliminated; so far, the detection efficiency of the over-bias voltage V i Correction of detection efficiency when .

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