System and method for synchronous discrimination and dynamic dead time control for single photon detectors

Abstract

This invention discloses a synchronous discrimination and dynamic dead-time control system for single-photon detectors, comprising a trigger discrimination module, a fan-out and delay module, a gate signal processing module, a single-photon avalanche diode (SPAD), an avalanche signal extraction module, an avalanche synchronous discrimination module, and a dynamic dead-time processing module connected in sequence. The fan-out and delay module is also connected to the avalanche synchronous discrimination module. This invention solves the problems of large time jitter in existing gated single-photon detectors, the inability of the avalanche signal extraction scheme to distinguish between two distorted avalanche signals, and the inability of the dead-time control scheme to distinguish between the correct avalanche signal and the afterpulse signal.

Description

Technical Field

[0001] This invention relates to the field of weak light detection technology, and in particular to a method for synchronous discrimination and dynamic dead time control for single-photon detectors, which can be applied to fields such as weak light detection, single-photon detection, and quantum key distribution systems. Background Technology

[0002] Key performance indicators for single-photon detectors based on avalanche photodiodes (APDs) include detection efficiency, dark count rate, afterpulse rate, and timing jitter. To reduce the impact of noise and achieve better performance, indium gallium arsenide / indium phosphide (InGaAs / InP) APDs often operate in gated mode, meaning that in addition to the DC bias voltage, the bias voltage across the APD also includes a gate pulse signal of a certain width. Ideally, a gated single-photon detector can only detect single photons within the gate pulse signal; outside the gate pulse signal, it cannot detect single photons, thus suppressing dark count and afterpulse generation and improving the signal-to-noise ratio.

[0003] An APD (Automatic Gate Detector) is essentially a diode with junction capacitance. High-frequency, high-amplitude gate pulse signals are coupled to the output through this junction capacitance, becoming gated differential noise. This noise often exceeds the amplitude of the avalanche signal it generates. Therefore, filters are commonly used in high-speed gated single-photon detectors to remove this noise. However, due to the impedance discontinuity of the filter within the passband, the broadband avalanche signal is broadened to varying degrees, causing distortion. This distortion results in greater time jitter in avalanche signal identification. Furthermore, in high-speed gated single-photon detectors using filtering methods, if two consecutive avalanches occur, the output signal equals the superposition of the two impulse responses. A small amount of the avalanche extraction signal will be broadened into adjacent gate times, incorrectly recording the location of the avalanche signal. If applied to a quantum key distribution (QKD) system, this will increase the error rate and reduce the original key quantity. In severe cases, the communicating parties may be unable to establish secure and reliable communication.

[0004] During an avalanche, some charge carriers are captured due to defects and impurities in the multiplication layer. These captured carriers are released after a period of time, and the resulting avalanche is called a afterpulse. Reducing the afterpulse is crucial for most applications. For low-speed gating systems, an effective method to reduce the afterpulse is to turn off the gate pulse signal after the single-photon avalanche diode (SPAD) detects a photon and generates an effective count. This causes the voltage across the SPAD to drop below the avalanche voltage, thus suppressing unexpected avalanches. The gate pulse signal turn-off time is defined as the dead time. However, for high-speed sinusoidal gating systems, the gate pulse signal cannot be turned off. Therefore, the method used is to stop the detector from counting and outputting the avalanche signal for a period of time after it has been identified and output. This period is defined as the logical dead time, meaning that the SPAD can still avalanche normally during the logical dead time. Existing dead-time control schemes use a fixed dead-time length and cannot actively distinguish between avalanche signals and afterpulse signals. Assuming the time interval between two effective avalanches is T1, and T1 < fixed dead-time length DT, and an afterpulse is generated at the time interval T2 after the second effective avalanche, and (T1+T2) > fixed dead-time length DT, then the second effective avalanche will be mistakenly treated as an afterpulse and suppressed, while the afterpulse generated after the second effective avalanche will be mistakenly treated as an effective avalanche and statistically output, thus forming an incorrect count. As the detection efficiency increases, the probability of this incorrect count will also increase significantly.

[0005] At higher operating frequencies and detection efficiencies, the effects of timing jitter and afterpulse on the detection output are particularly prominent in single-photon detectors. Effectively reducing timing jitter and suppressing afterpulse has become a key challenge in improving the performance of single-photon detectors and expanding their application range.

[0006] Furthermore, in high-speed gated single-photon detectors based on filter schemes, existing avalanche signal extraction methods cannot distinguish between two distorted avalanche signals, resulting in incorrect avalanche signal distributions following the peak of the optical pulse distribution, which reduces the performance of the single-photon detector. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to realize a synchronous discrimination and dynamic dead time control system and method for single-photon detectors, so as to solve the problems of large time jitter in existing gated single-photon detectors, the inability of avalanche signal extraction scheme to distinguish between two distorted avalanche signals, and the inability of dead time control scheme to distinguish between the correct avalanche signal and the afterpulse signal.

[0008] To achieve the above objectives, the technical solution adopted by this invention is: a synchronous discrimination and dynamic dead-time control system for single-photon detectors, comprising:

[0009] Trigger discrimination module: used to discriminate the trigger signal of the gated single-photon detector and output the discriminated trigger signal to the fan-out and delay module;

[0010] Fan-out and delay module: This module splits the received trigger signal into two. Each signal is processed by a programmable delay module. One output is a detector door opening signal sent to the door signal processing module, and the other outputs an avalanche synchronization signal sent to the avalanche synchronization discrimination module.

[0011] Gate signal processing module: used to generate gate pulse signals for SPAD and output them to the SPAD cathode;

[0012] Avalanche signal extraction module: Connects to the SPAD anode, extracts the avalanche signal output by the SPAD, and outputs the extracted avalanche signal to the avalanche synchronization identification module;

[0013] Avalanche synchronization identification module: used to receive avalanche extraction signals and avalanche synchronization signals, and send them to the avalanche synchronization output signal to the dynamic dead time processing module;

[0014] Dynamic dead time processing module: used for external probe output.

[0015] The delay module in the fan-out and delay module is used to adjust the relative delay between the detector gate pulse signal and the optical pulse signal to align the detector gate pulse signal and the optical pulse signal, and to adjust the relative delay between the avalanche synchronization signal and the avalanche extraction signal to complete the synchronous discrimination output of the avalanche.

[0016] The gate signal processing module adjusts the amplitude and pulse width of the detector's gate opening signal and filters the gate opening signal in the detector to generate the SPAD gate pulse signal.

[0017] The avalanche synchronization identification module samples the avalanche extraction signal at the rising edge of the avalanche synchronization signal, thereby stabilizing the position of the avalanche synchronization output signal.

[0018] The dynamic dead time processing module is used to perform dead time processing on the avalanche output signal. During the dead time, the avalanche signal will not be effectively counted or output. If the avalanche output signal occurs during the dead time, the timing will restart.

[0019] A method for synchronous discrimination and dynamic dead-time control of single-photon detectors, the synchronous discrimination and control method includes the following steps:

[0020] The single-photon detector emits a gate pulse signal with a period of T;

[0021] The delay of the avalanche synchronization signal is gradually increased by the minimum step size of the delay module, so that the avalanche synchronization signal with increased delay is closer to the stable range of the avalanche extraction signal.

[0022] Each additional delay will trigger a probe output count;

[0023] When the detector output count approaches its maximum value, the avalanche synchronization signal is nearly aligned with the stable range of the avalanche extraction signal.

[0024] Fine-tune the delay of the avalanche synchronization signal to align the delay of the avalanche synchronization signal with that of the avalanche extraction signal;

[0025] The avalanche synchronization output signal after passing through the avalanche synchronization discrimination module has a fixed position and its sequence number is consistent with the gate pulse signal sequence number.

[0026] The fine-tuning of the avalanche synchronization signal delay: the detection output signal appears as a positional fluctuation with an interval of T on the oscilloscope and is defined as a "double line". The delay is slowly increased so that the detection count remains basically unchanged while the "double line" disappears.

[0027] The dynamic dead time control method includes the following steps:

[0028] Upon detecting an avalanche synchronization output signal, a high level is output and timing begins;

[0029] The timing length is the dead time length DT set by the user;

[0030] If an avalanche synchronization output signal is detected again within the timing range, the timing length is reset to zero and timing restarts.

[0031] If no avalanche synchronization output signal is detected within the entire time period DT, a low level is output, completing one full dead time processing cycle.

[0032] During dynamic dead time control,

[0033] When the avalanche synchronization output signal generates an avalanche 'a', the detector outputs a high level, and the dead time timing module starts timing.

[0034] If a follow-up pulse a occurs after avalanche a, and the time interval between avalanche a and follow-up pulse a is t1, and t1 < DT, then the dead time timing module is reset to zero and the timing starts again.

[0035] If avalanche b occurs after avalanche a, and the time interval between avalanche a and avalanche b is t2, and t2 < DT, then the dead time timing module is reset to zero and the timing starts again.

[0036] If a follow-up pulse b appears after avalanche b, and the time interval between avalanche b and follow-up pulse b is t3, and t3 < DT, then the dead time timing module continues to reset and restart timing until the dead time timing module completes timing for a time length of DT, and the detector outputs a low level.

[0037] The present invention has the following beneficial effects:

[0038] 1. By using the avalanche synchronization discrimination module, the position of the detection output signal is fixed at the rising edge of the synchronization signal, which greatly improves the time jitter performance of the gated single-photon detector.

[0039] 2. By using the avalanche synchronization discrimination module, the sequence number of the detection output signal is made to correspond with the gate signal sequence number, thereby improving the performance of the gated single-photon detector in systems such as QKD that are sensitive to the location of avalanche signals.

[0040] 3. By using dynamic dead-time processing technology, the correct avalanche signal and afterpulse signal are actively distinguished, optimizing the existing dead-time control scheme and improving the afterpulse performance of the gated single-photon detector. Attached Figure Description

[0041] The following is a brief explanation of the content represented by each figure in this specification:

[0042] Figure 1 This is a block diagram of a method for synchronous discrimination and dynamic dead time control of single-photon detectors.

[0043] Figure 2 , 3 This is a flowchart illustrating the synchronous discrimination method used in single-photon detectors.

[0044] Figure 4 This is a logic timing diagram for dynamic dead-time control of a single-photon detector. Detailed Implementation

[0045] The following description, with reference to the accompanying drawings, details the specific implementation of the present invention, including the shape and structure of each component, the relative positions and connections between the parts, the function and working principle of each part, the manufacturing process, and the operation and use methods, to help those skilled in the art to have a more complete, accurate, and in-depth understanding of the inventive concept and technical solution of the present invention.

[0046] like Figure 1 As shown, the synchronization discrimination and dynamic dead time control system for a single-photon detector includes a trigger discrimination module, a fan-out and delay module, a gate signal processing module, a single-photon avalanche diode (SPAD), an avalanche signal extraction module, an avalanche synchronization discrimination module, and a dynamic dead time processing module connected in sequence. The fan-out and delay module is also connected to the avalanche synchronization discrimination module.

[0047] The following is a detailed description of the function of each module:

[0048] The trigger discrimination module is used to discriminate the trigger signal of the gated single-photon detector and output the discriminated trigger signal to the fan-out and delay module.

[0049] The fan-out and delay module splits the received trigger signal into two. Each signal is processed by a programmable delay module: one outputs a detector gate opening signal to the gate signal processing module, and the other outputs an avalanche synchronization signal to the avalanche synchronization discrimination module. The delay modules adjust the relative delay between the detector gate pulse signal and the optical pulse signal to align them, and also adjust the relative delay between the avalanche synchronization signal and the avalanche extraction signal, thus completing the avalanche synchronization discrimination output.

[0050] The gate signal processing module is used to adjust the amplitude and pulse width of the detector gate signal. The high-speed gated single-photon detector includes filtering of the gate signal to generate the SPAD gate pulse signal, which is then output to the SPAD cathode.

[0051] The avalanche signal extraction module is used to identify and extract the avalanche signal output by SPAD, and output the extracted avalanche signal to the avalanche synchronization identification module.

[0052] The avalanche synchronization discrimination module is used to receive the avalanche extraction signal and the avalanche synchronization signal. It samples the avalanche extraction signal at the rising edge of the avalanche synchronization signal to stabilize the position of the avalanche synchronization output signal.

[0053] The dynamic dead time processing module is used to perform dead time processing on the avalanche output signal. During the dead time, the avalanche signal will not be effectively counted or output. If the avalanche output signal occurs during the dead time, the timing will restart. Therefore, it is called the dynamic dead time processing module.

[0054] The workflow of the avalanche synchronization identification method is as follows: Figure 2 As shown, the detector trigger signal frequency, i.e., the gate pulse signal period, is T. Since the location and intensity of avalanches are random, the location and width of the avalanche extraction signal are variable, and there may be avalanche extraction signals with a width of twice or more than the gate opening period, such as... Figure 3 The avalanche extraction signal is shown by the dashed line.

[0055] The avalanche synchronization identification method first increases the delay of the avalanche synchronization signal by the minimum step size of the delay module. As the delay increases, the avalanche synchronization signal gets closer to the stable range of the avalanche extraction signal, such as... Figure 3As shown by the solid line portion of the avalanche extraction signal, the detection output count increases accordingly. When the detection output count approaches its maximum value, the avalanche synchronization signal is basically aligned with the stable range of the avalanche extraction signal. However, due to the presence of an avalanche extraction signal that has broadened to twice its period, the detection output signal can be clearly seen on the oscilloscope to exhibit positional fluctuations at intervals of T. This phenomenon is called "double lines." At this point, a fine-tuning of the avalanche synchronization signal delay is performed. The delay is slowly increased so that the detection count remains basically unchanged while the "double lines" disappear. Thus, the delay alignment between the avalanche synchronization signal and the avalanche extraction signal is achieved. The position of the avalanche synchronization output signal after passing through the avalanche synchronization discrimination module is fixed, and its sequence number is consistent with the gate pulse signal sequence number.

[0056] The core of the dynamic dead time control method is: after detecting an avalanche synchronization output signal, output a high level and start timing. The timing length is the dead time length DT set by the user. If an avalanche synchronization output signal is detected again within the timing range, the timing length is reset to zero and timing starts again until no avalanche synchronization output signal is detected within the entire time length DT, at which point a low level is output, completing a complete dead time processing.

[0057] The logic timing of the dynamic dead time handling module is as follows: Figure 4 As shown, when the avalanche synchronization output signal generates an avalanche 'a', the detector outputs a high level, and the dead time timing module starts timing. A follow-up pulse 'a' is likely to be generated immediately after avalanche 'a'. The time interval between avalanche 'a' and the follow-up pulse 'a' is denoted as t1, where t1 < DT. Therefore, the dead time timing module is reset and restarts timing. If a second avalanche 'b' is generated when the dead time timing module reaches t2, and t2 < DT, the dead time timing module is reset again and restarts timing. A follow-up pulse 'b' is likely to be generated immediately after the second avalanche 'b'. The time interval between avalanche 'b' and the follow-up pulse 'b' is denoted as t3, where t3 < DT. Therefore, the dead time timing module continues to be reset and restarts timing until the dead time timing module completes timing for a duration of DT, at which point the detector outputs a low level. Therefore, the width of the detector output signal, i.e., the actual dead time length τ = t1 + t2 + t3 + DT. The advantage of this scheme is that it still responds to the avalanche output signal within the dead time range, and the subsequent pulse signal is generated following the avalanche signal. Therefore, based on this scheme, the first avalanche output signal after the dead time ends must be a valid avalanche, thus enabling the distinction between the avalanche signal and the subsequent pulse signal.

[0058] The present invention has been described above with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution to other situations without modification, are all within the protection scope of the present invention.

Claims

1. A synchronous discrimination and dynamic dead-time control system for single-photon detectors, characterized in that, include: Trigger discrimination module: used to discriminate the trigger signal of the gated single-photon detector and output the discriminated trigger signal to the fan-out and delay module; Fan-out and delay module: This module splits the received trigger signal into two. Each signal is processed by a programmable delay module. One output is a detector door opening signal sent to the door signal processing module, and the other outputs an avalanche synchronization signal sent to the avalanche synchronization discrimination module. Gate signal processing module: used to generate gate pulse signals for SPAD and output them to the SPAD cathode; Avalanche signal extraction module: Connects to the SPAD anode, extracts the avalanche signal output by the SPAD, and outputs the extracted avalanche signal to the avalanche synchronization identification module; Avalanche synchronization identification module: used to receive avalanche extraction signals and avalanche synchronization signals, and send them to the avalanche synchronization output signal to the dynamic dead time processing module; Dynamic dead time processing module: used for outward detection output; The avalanche synchronization discrimination module samples the avalanche extraction signal at the rising edge of the avalanche synchronization signal to stabilize the position of the avalanche synchronization output signal. The dynamic dead time processing module is used to perform dead time processing on the avalanche output signal. During the dead time, the avalanche signal will not be effectively counted or output. If the avalanche output signal occurs during the dead time, the timing will restart.

2. The synchronous discrimination and dynamic dead-time control system for single-photon detectors according to claim 1, characterized in that: The delay module in the fan-out and delay module is used to adjust the relative delay between the detector gate pulse signal and the optical pulse signal to align the detector gate pulse signal and the optical pulse signal, and to adjust the relative delay between the avalanche synchronization signal and the avalanche extraction signal to complete the synchronous discrimination output of the avalanche.

3. The synchronous discrimination and dynamic dead-time control system for single-photon detectors according to claim 1, characterized in that: The gate signal processing module adjusts the amplitude and pulse width of the detector's gate opening signal and filters the gate opening signal in the detector to generate the SPAD gate pulse signal.

4. The control method for synchronous discrimination and dynamic dead-time control system of single-photon detector based on any one of claims 1-3, characterized in that, The synchronous screening and control method includes the following steps: The single-photon detector emits a gate pulse signal with a period of T; The delay of the avalanche synchronization signal is gradually increased by the minimum step size of the delay module, so that the avalanche synchronization signal with increased delay is closer to the stable range of the avalanche extraction signal. Each additional delay will trigger a probe output count; When the detector output count reaches its maximum value, the avalanche synchronization signal reaches the stable range aligned with the avalanche extraction signal. Fine-tune the delay of the avalanche synchronization signal to align the delay of the avalanche synchronization signal with that of the avalanche extraction signal; The avalanche synchronization output signal after passing through the avalanche synchronization discrimination module has a fixed position and its sequence number is consistent with the gate pulse signal sequence number.

5. The control method according to claim 4, characterized in that: The fine-tuning of the avalanche synchronization signal delay: the detection output signal appears as a positional fluctuation with an interval of T on the oscilloscope and is defined as a "double line". Increasing the delay makes the detection count remain unchanged while the "double line" disappears.

6. The control method according to claim 4 or 5, characterized in that, The dynamic dead time control method includes the following steps: Upon detecting an avalanche synchronization output signal, a high level is output and timing begins; The timing length is the dead time length DT set by the user; If an avalanche synchronization output signal is detected again within the timing range, the timing length is reset to zero and timing restarts. If no avalanche synchronization output signal is detected within the entire time period DT, a low level is output, completing one full dead time processing cycle.

7. The control method according to claim 6, characterized in that: During dynamic dead time control, When the avalanche synchronization output signal generates an avalanche 'a', the detector outputs a high level, and the dead time timing module starts timing. If a follow-up pulse a occurs after avalanche a, and the time interval between avalanche a and follow-up pulse a is t1, and t1 < DT, then the dead time timing module is reset to zero and the timing starts again. If avalanche b occurs after avalanche a, and the time interval between avalanche a and avalanche b is t2, and t2 < DT, then the dead time timing module is reset to zero and the timing starts again.

8. The control method according to claim 7, characterized in that: If a follow-up pulse b appears after avalanche b, and the time interval between avalanche b and follow-up pulse b is t3, and t3 < DT, then the dead time timing module continues to reset and restart timing until the dead time timing module completes timing for a time length of DT, and the detector outputs a low level.

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