CN104579640A - Real-time delay tracking device and method of quantum communication system - Google Patents

Abstract

The real-time delay tracking device of the quantum communication system includes a control device, a delay device and a single photon detector, wherein the control device is used to control the delay device to generate a certain step-length delay; the delay device is used to generate a delay, And the delay is applied to the clock of the single photon detector, so that the gate pulse generated by the clock delay triggers the single photon detector to detect the incident single photon signal; the single photon detector is used to count and feed back the detected single photon signal In the control device; the control device compares the count accumulation value Y within the predetermined time with the pre-stored count accumulation value X of the single photon signal within the predetermined time, and finds the correct delay direction according to the comparison result, and performs Time-lapse tracking for the next step.

Description

Real-time delay tracking device and method for quantum communication system

technical field

The invention relates to quantum secure communication, specifically, in a quantum secure communication system, aiming at the problem of delay drift in the clock and signal in a single photon detector, a real-time delay tracking method of "short step size and long integration" is used to scan Locate the best delay point, so as to ensure the maximum count of the single photon detector and ensure the coding rate of the quantum key.

Background technique

Quantum secure communication is a hot research field that has developed rapidly in the past 30 years, and it is currently recognized as a communication method that can achieve unconditional security. Since the quantum key distribution technology was proposed by Bennett.C.H and G.Brassard in 1984, it has received extensive attention from the scientific community. Nowadays, many countries are optimistic about the prospects of quantum secure communication. Developed countries such as Europe and the United States have begun to explore high-speed quantum communication and large-scale secure communication networks. my country has also listed it as a key scientific research project for research.

There are many implementation schemes for quantum secure communication systems, including polarization, phase, and entanglement schemes. In the quantum key distribution process, information is loaded onto a single photon, and its quantum properties are used to realize the transmission of information, and the password is screened out through the later base-by-peer operation. In the entire key generation process, an important link is the detection of single photons, because the energy of single photons is extremely low, only on the order of 10-19J, so it is necessary to use ultra-sensitive photons in practical quantum communication systems. Single-photon detection equipment is used for detection, and the performance of single-photon detectors directly determines the quality of core parameters such as coding rate and bit error rate in quantum communication systems.

For now, the most commonly used single-photon detection devices in quantum communication systems are InGaAs-based avalanche photodiodes (APDs). When it works in the "Geiger mode", only when the detection gate pulse appears, the APD enters the avalanche mode to realize the detection of single photons; when there is no gate pulse, the APD works in the linear region, No avalanche occurs. This mode can effectively quench the APD and improve the signal-to-noise ratio of the detector.

Based on this working mode, the single-photon detector only responds to the incident photon within the time of the gate pulse. Therefore, when designing the system, it is necessary to ensure that the gate pulse and the single-photon pulse coincide to obtain the best detection efficiency and coding rate. . However, in practical situations, gate pulses and single-photon pulses are often provided by different channels, and changes in fiber length and refractive index due to environmental temperature, mechanical vibration, etc., will cause the relative delay of gate pulses and single-photon pulses to drift. , this drift will directly lead to a decrease in the counting rate (thereby causing a decrease in the coding rate), and even cause the key distribution process to fail.

At present, the common solution to this problem is to interrupt the communication and re-scan the relative delay of the gate pulse and the single photon pulse to find the best delay point. The disadvantage of this solution is that the communication will be interrupted and the working efficiency of the system will be reduced. The present invention proposes a new scheme for finding the best delay point, which overcomes the disadvantages of the foregoing schemes.

Contents of the invention

The object of the present invention is to provide a real-time delay tracking device and method, which can realize the optimal delay point in real time without interrupting communication.

The present invention establishes a set of schemes for real-time control of single-photon detector gate pulse delay in quantum key distribution, utilizes the characteristics that environmental changes are usually slow-changing processes, and adopts a scheme of "short step length, long integration" for the scanning process , the delay of the detector gate pulse can be scanned without interrupting the communication to find the best delay point. This method can not only keep the count value of the single photon detector at a high level, but also It has the characteristics of real-time tracking.

The object of the present invention is realized by the following technical solutions:

In the quantum secure communication detection module, the phase delay of the gate pulse of the single photon detector is scanned in a "short step" by using the FPGA to control the delay chip. Because the change of the delay in each step is very small, the change of the detection count value is controlled in a small range, and the influence on the communication coding is very small. Simultaneously, since the detection efficiency of the single photon detector fluctuates within a certain range, and it is difficult to distinguish the change of the detection count due to the delay change of the "short step size", the counting method of "long integral" is also adopted in the present invention, The photon count value accumulated and stored in the FPGA for a long period of time is used for feedback judgment. Long-term cumulative counting can effectively reduce the error caused by noise and jitter, and accurately distinguish the change in counting size before and after the delay change. FPGA compares the two data before and after, and judges the direction of delay adjustment according to the corresponding algorithm, so as to realize the real-time tracking of the maximum count value.

A real-time delay tracking device for a quantum communication system, including a control device, a delay device and a single photon detector, wherein,

The control device is used to control the delay device to generate a certain step-length delay;

The delay device is used to generate a delay, and the delay is applied to the clock of the single photon detector, so that the gate pulse generated by the clock delay triggers the single photon detector to detect the incident single photon signal;

The single photon detector is used to count and feed back the detected single photon signal to the control device;

The control device compares the count accumulation value Y within the predetermined time with the pre-stored count accumulation value X of the single photon signal within the predetermined time, finds the correct delay direction according to the comparison result, and performs the next delay track.

The above-mentioned real-time delay tracking device is characterized in that:

The control device first accumulates the single-photon signal counts within a predetermined time and stores them in the variable X, and then controls the delay device to generate a delay of a certain step length, and then stores the single-photon signal detected by the single-photon detector within the predetermined time. The photon signal counts are accumulated and stored in the variable Y;

The control device compares X and Y, and if Y>X, repeats the previous delay process to continue delay tracking; if Y<X, reverses the delay direction and performs reverse delay tracking.

The above-mentioned real-time delay tracking device is characterized in that:

The control device is FPGA.

The above-mentioned real-time delay tracking device is characterized in that:

The delay device is a delay chip.

The above-mentioned real-time delay tracking device is characterized in that:

The time delay generated by the control device can be forward or reverse.

A real-time delay tracking method for a quantum communication system, characterized in that it comprises the following steps:

The control device pre-stores the cumulative value X of counting incident single-photon signals detected by the single-photon detector within a predetermined time;

The control device controls the delay device to generate a certain step-length delay;

The delay device generates a time delay, and applies the time delay to the clock of the single-photon detector, so that the gate pulse generated by the clock delay triggers the single-photon detector to detect the incident single-photon signal;

The single photon detector counts the detected single photon signal and feeds it back to the control device;

The control device compares the count accumulation value Y within a predetermined time with the pre-stored count accumulation value X, finds the correct delay direction according to the comparison result, and performs the next delay tracking.

The real-time delay tracking method as described above is characterized in that:

The control device first accumulates the single-photon signal counts within a predetermined time and stores them in the variable X, and then controls the delay device to generate a delay of a certain step length, and then stores the single-photon signal detected by the single-photon detector within the predetermined time. The photon signal counts are accumulated and stored in the variable Y;

The control device compares X and Y, and if Y>X, repeats the previous delay process to continue delay tracking; if Y<X, reverses the delay direction and performs reverse delay tracking.

The real-time delay tracking method as described above is characterized in that:

The control device is FPGA.

The real-time delay tracking method as described above is characterized in that:

The delay device is a delay chip.

The above-mentioned real-time delay tracking method is characterized in that the delay generated by the control device can be forward or reverse.

Description of drawings

Fig. 1 is the schematic diagram of the real-time delay tracking device of the quantum communication system of the present invention;

Fig. 2 is a schematic diagram of the real-time delay tracking method of the quantum communication system of the present invention.

Detailed ways

The features of the present invention and other related features will be further described in detail below through embodiments in conjunction with the accompanying drawings.

As shown in Figure 1, the real-time delay tracking device is composed of FPGA, delay chip and single photon detector. The FPGA can control the delay chip to generate a certain step-length delay in forward and reverse directions (the choice of delay should consider the width of the detector gate pulse, too wide will cause the photon count to decrease sharply, and too narrow will lead to insufficient discrimination, combined with In this system, the gate pulse width is 1ns, so 0.01ns is selected), and the gate pulse generated after the delay acts on the clock triggers the single photon detector to detect the incident single photon signal, and the single photon detector feeds back the detection count to the FPGA , the FPGA will accumulate the counts in a long period of time and then compare them to find the correct delay direction and carry out the next delay tracking.

Fig. 2 is the working flowchart of real-time delay tracking device, specifically as follows:

When an external real-time delay tracking request is input into FPGA, the whole system starts to work. FPGA first accumulates the photon counts within a certain period of time (the selection of the integration time needs to consider the speed of delay drift, and the detection efficiency jitter range of the detector itself, combined with this system, and the integration time of 3 minutes is selected) and then stored in the variable X , and then delay the delay direction by 0.01ns, and count the photon count within 3 minutes and store it in the variable Y, and compare X and Y in the FPGA chip. If Y>X, it means that the maximum detection count point is at After the delay direction at this time, the current delay direction is correct. Repeat the previous delay process and continue to delay backward to approach the best delay point; once Y<X is found, it means the maximum detection count point In the reverse direction of the original delay direction, the current delay direction is wrong, so reverse the delay direction and delay by 0.01ns.

The optimal delay point is a theoretical value, that is, the point at which the relative deviation between the clock and the signal is 0, and the detector can obtain a maximum count at this point. But because the relative time drift of the clock and the signal is a dynamic process, the function realized by the present invention is to make the relative deviation of the clock and the signal continuously decrease until approaching the minimum deviation value (i.e. the optimum value) by judging the inequality. The final result is that the deviation value will oscillate around 0 point (ie the optimal value).

Because the optimal delay point changes in real time, it is necessary to continuously adjust the delay during the whole tracking process. Finally, the gate pulse delay of the detector will oscillate around the actual optimal delay point, and at the optimal delay point Tracking is carried out when the time point drifts, so that the single photon detector can always maintain a good detection count rate and ensure the coding stability of the quantum key distribution process.

Claims (10)

1. A real-time time-delay tracking device of a quantum communication system, comprising a control device, a time-delay device and a single photon detector, wherein, The control device is used to control the delay device to generate a certain step-length delay; The delay device is used to generate a delay, and the delay is applied to the clock of the single photon detector, so that the gate pulse generated by the clock delay triggers the single photon detector to detect the incident single photon signal; The single photon detector is used to count and feed back the detected single photon signal to the control device; The control device compares the count accumulation value Y within the predetermined time with the pre-stored count accumulation value X of the single photon signal within the predetermined time, finds the correct delay direction according to the comparison result, and performs the next delay track. 2. The real-time delay tracking device as claimed in claim 1, characterized in that: The control device first accumulates the single-photon signal counts within a predetermined time and stores them in the variable X, and then controls the delay device to generate a delay of a certain step length, and then stores the single-photon signal detected by the single-photon detector within the predetermined time. The photon signal counts are accumulated and stored in the variable Y; The control device compares X and Y, and if Y>X, repeats the previous delay process to continue delay tracking; if Y<X, reverses the delay direction and performs reverse delay tracking. 3. The real-time delay tracking device according to any one of claims 1-2, characterized in that: The control device is FPGA. 4. The real-time delay tracking device as claimed in claim 3, characterized in that: The delay device is a delay chip. 5. The real-time delay tracking device according to any one of claims 1-2, characterized in that: The time delay generated by the control device can be forward or reverse. 6. A real-time delay tracking method of a quantum communication system, characterized in that it comprises the steps: The control device pre-stores the cumulative value X of counting incident single-photon signals detected by the single-photon detector within a predetermined time; The control device controls the delay device to generate a certain step-length delay; The delay device generates a time delay, and applies the time delay to the clock of the single-photon detector, so that the gate pulse generated by the clock delay triggers the single-photon detector to detect the incident single-photon signal; The single photon detector counts the detected single photon signal and feeds it back to the control device; The control device compares the count accumulation value Y within a predetermined time with the pre-stored count accumulation value X, finds the correct delay direction according to the comparison result, and performs the next delay tracking. 7. The real-time delay tracking method as claimed in claim 6, characterized in that: The control device first accumulates the single-photon signal counts within a predetermined time and stores them in the variable X, then controls the delay device to generate a certain step-length delay, and then stores the single-photon signal detected by the single-photon detector within the predetermined time. The photon signal counts are accumulated and stored in the variable Y; The control device compares X and Y, and if Y>X, repeats the previous delay process to continue delay tracking; if Y<X, reverses the delay direction and performs reverse delay tracking. 8. The real-time delay tracking method according to any one of claims 6-7, characterized in that: The control device is FPGA. 9. The real-time delay tracking method according to claim 8, characterized in that: The delay device is a delay chip. 10. The real-time delay tracking method according to any one of claims 6-7, characterized in that the delay generated by the control device can be forward or reverse.