阅读说明：本技术 用于提取雪崩信号的方法和装置 (Method and apparatus for extracting avalanche signal ) 是由 陈柳平 范永胜 童丽婷 佘祥胜 李南 王其兵 万相奎 于 2021-08-18 设计创作，主要内容包括：本发明提供用于提取雪崩信号的方法和装置,所述方法包括：获取单光子探测器输出的APD信号,所述APD信号包括随着门控信号的上升沿而产生的上尖峰以及随着门控信号的下降沿而产生的下尖峰；确定所述APD信号中的所述上尖峰的延时位置,以通过门控信号的门宽来确定所述APD信号中的所述下尖峰的延时位置；移动符合门信号,以使符合门信号的下降沿的延时位置与所述APD信号中的所述下尖峰的延时位置对齐；将所述APD信号和甄别阈值之间的比较结果与符合门信号进行与运算,以从所述APD信号中提取出雪崩信号。本发明能够有效地避免由门控信号引起的尖峰噪声对雪崩信号提取的影响,从而使得量子通信系统的成码率得到大幅度地提升。(The present invention provides a method and apparatus for extracting an avalanche signal, the method comprising: acquiring an APD signal output by a single photon detector, wherein the APD signal comprises an upper peak generated along with the rising edge of a gating signal and a lower peak generated along with the falling edge of the gating signal; determining a delay location of the upper spike in the APD signal to determine a delay location of the lower spike in the APD signal by gating a gate width of a signal; moving a coincidence gate signal such that a delay position of a falling edge of the coincidence gate signal is aligned with a delay position of the lower spike in the APD signal; and the comparison result between the APD signal and the discrimination threshold value and the coincidence gate signal to extract an avalanche signal from the APD signal. The invention can effectively avoid the influence of spike noise caused by the gating signal on the extraction of the avalanche signal, thereby greatly improving the code rate of the quantum communication system.)

1. A method for extracting an avalanche signal, the method comprising:

acquiring an APD signal output by a single photon detector, wherein the APD signal comprises an upper peak generated along with the rising edge of a gating signal and a lower peak generated along with the falling edge of the gating signal;

determining a delay location of the upper spike in the APD signal to determine a delay location of the lower spike in the APD signal by gating a gate width of a signal;

moving a coincidence gate signal such that a delay position of a falling edge of the coincidence gate signal is aligned with a delay position of the lower spike in the APD signal;

and the comparison result between the APD signal and the discrimination threshold value and the coincidence gate signal to extract an avalanche signal from the APD signal.

2. The method of claim 1, wherein the step of determining the delay location of the up-spike in the APD signal comprises:

adjusting the gate width of a coincidence gate signal to be maximum so as to gradually reduce a discrimination threshold value from the upper part of the APD signal to the lower part of the APD signal according to a preset step length, and counting pulses generated by AND operation of partial signals in the APD signal exceeding the discrimination threshold value and the coincidence gate signal aiming at the discrimination threshold value reduced each time until the pulse count is absent;

adjusting the gate width of the coincidence gate signal to be minimum so as to gradually move the coincidence gate signal from the left side of the APD signal to the right side of the APD signal according to a preset step length, counting pulse counts generated by performing AND operation on pulses generated by partial signals in the APD signal exceeding a discrimination threshold and the coincidence gate signal for each moving coincidence gate signal, and recording a first delay position of the coincidence gate signal when the pulse counts are from absent to present for the first time and a second delay position of the coincidence gate signal when the pulse counts are from present to absent for the first time;

determining a midpoint between the first delay location and the second delay location as a delay location of the up-spike in the APD signal.

3. The method of claim 1, wherein the discrimination threshold is determined based on a peak in an avalanche region adjacent to the lower spike in the APD signal without an avalanche occurrence.

4. The method of claim 3, further comprising:

adjusting the gate width of the coincidence gate signal to be the same as the duration of an avalanche section, gradually reducing a screening threshold value from the upper part of the APD signal to the lower part of the APD signal according to a preset step length, and counting the pulse count generated by AND operation of the pulse generated by the fact that part of signals in the APD signal located in the avalanche section exceeds the screening threshold value and the coincidence gate signal for each reduced screening threshold value until the pulse count is absent.

5. An apparatus for extracting an avalanche signal, the apparatus comprising:

an APD signal acquisition unit configured to acquire an APD signal output by the single photon detector, the APD signal including an upper peak generated with a rising edge of the gating signal and a lower peak generated with a falling edge of the gating signal;

a peak location determination unit configured to determine a delay location of the upper peak in the APD signal to determine a delay location of the lower peak in the APD signal by gating a gate width of a signal;

a coincidence gate adjustment unit configured to move a coincidence gate signal to align a delay position of a falling edge of the coincidence gate signal with a delay position of the lower spike in the APD signal; and

a screening coincidence unit configured to AND the comparison result between the APD signal and a discrimination threshold with a coincidence gate signal to extract an avalanche signal from the APD signal.

6. The apparatus of claim 5, wherein the spike location determination unit comprises:

the threshold scanning unit is configured to adjust the gate width of a coincidence gate signal to be maximum, gradually reduce a screening threshold from the upper part of the APD signal to the lower part of the APD signal according to a preset step length, and count a pulse count generated by performing an AND operation on a pulse generated by a part of signals in the APD signal exceeding the screening threshold and the coincidence gate signal for each reduced screening threshold until the pulse count is absent;

the coincidence gate scanning unit is configured to adjust the gate width of a coincidence gate signal to be minimum, gradually move the coincidence gate signal from the left side of the APD signal to the right side of the APD signal according to a preset step length, count pulse counts generated by performing AND operation on pulses generated by partial signals in the APD signal exceeding a screening threshold and the coincidence gate signal for each moving coincidence gate signal, and record a first delay position of the coincidence gate signal when the pulse counts are from absence to presence for the first time and a second delay position of the coincidence gate signal when the pulse counts are from presence to absence for the first time; and

a delay position determination calculation configured to determine a midpoint between the first delay position and the second delay position as a delay position of the upper spike in the APD signal.

7. The apparatus of claim 5, wherein the discrimination threshold is determined based on a peak in an avalanche region adjacent to the lower spike in the APD signal without an avalanche occurrence.

8. The apparatus of claim 7, wherein the threshold scanning unit is further configured to adjust a gate width of a coincidence gate signal to be the same as a duration of an avalanche section, to gradually decrease a discrimination threshold from above the APD signal to below the APD signal by a predetermined step size, and to count, for each decreased discrimination threshold, a pulse count resulting from an and operation of a coincidence gate signal with a pulse resulting from a portion of the APD signal located in an avalanche section exceeding the discrimination threshold until the pulse count is from none to none.

9. A computer-readable storage medium having stored thereon a computer program for implementing the method for extracting an avalanche signal according to any one of claims 1 to 4 when the computer program is executed by a processor.

10. A computing device, the computing device comprising:

a processor; and

memory storing a computer program which, when executed by a processor, implements the method for extracting an avalanche signal as claimed in any one of claims 1 to 4.

Technical Field

The present invention relates to the field of quantum communication technology, and in particular, to a method and an apparatus for extracting an avalanche signal in a quantum communication system.

Background

Currently, single photon detectors used in quantum communication systems (such as quantum key distribution systems) mainly detect optical pulses carrying encoded information through Avalanche diodes (APDs).

However, in the APD controlled based on the gating manner, because the existence of the junction capacitance of the APD itself can cause the APD signal to generate the spike noise voltage along with the rising edge and the falling edge of the gating pulse, and the intensity of the spike noise voltage is much larger than that of the avalanche signal triggered by the single photon, the avalanche signal may be annihilated by the spike noise voltage and cannot be extracted, and the yield rate of the quantum communication system is reduced.

Therefore, how to effectively extract the avalanche signal from these spike noise voltages becomes an urgent problem to be solved in the quantum communication system.

Disclosure of Invention

It is an object of the present invention to provide a method and apparatus for extracting an avalanche signal.

According to an aspect of the invention, there is provided a method for extracting an avalanche signal, the method comprising: acquiring an APD signal output by a single photon detector, wherein the APD signal comprises an upper peak generated along with the rising edge of a gating signal and a lower peak generated along with the falling edge of the gating signal; determining a delay location of the upper spike in the APD signal to determine a delay location of the lower spike in the APD signal by gating a gate width of a signal; moving a coincidence gate signal such that a delay position of a falling edge of the coincidence gate signal is aligned with a delay position of the lower spike in the APD signal; and the comparison result between the APD signal and the discrimination threshold value and the coincidence gate signal to extract an avalanche signal from the APD signal.

According to one embodiment of the present invention, the step of determining the delay location of the up-spike in the APD signal comprises: adjusting the gate width of a coincidence gate signal to be maximum so as to gradually reduce a discrimination threshold value from the upper part of the APD signal to the lower part of the APD signal according to a preset step length, and counting pulses generated by AND operation of partial signals in the APD signal exceeding the discrimination threshold value and the coincidence gate signal aiming at the discrimination threshold value reduced each time until the pulse count is absent; adjusting the gate width of the coincidence gate signal to be minimum so as to gradually move the coincidence gate signal from the left side of the APD signal to the right side of the APD signal according to a preset step length, counting pulse counts generated by performing AND operation on pulses generated by partial signals in the APD signal exceeding a discrimination threshold and the coincidence gate signal for each moving coincidence gate signal, and recording a first delay position of the coincidence gate signal when the pulse counts are from absent to present for the first time and a second delay position of the coincidence gate signal when the pulse counts are from present to absent for the first time; determining a midpoint between the first delay location and the second delay location as a delay location of the up-spike in the APD signal.

According to one embodiment of the invention, the discrimination threshold is determined based on a peak in an avalanche region in the APD signal adjacent to the lower spike in the absence of an avalanche.

According to an embodiment of the invention, the method further comprises: adjusting the gate width of the coincidence gate signal to be the same as the duration of an avalanche section, gradually reducing a screening threshold value from the upper part of the APD signal to the lower part of the APD signal according to a preset step length, and counting the pulse count generated by AND operation of the pulse generated by the fact that part of signals in the APD signal located in the avalanche section exceeds the screening threshold value and the coincidence gate signal for each reduced screening threshold value until the pulse count is absent.

According to another aspect of the present invention, there is provided an apparatus for extracting an avalanche signal, the apparatus comprising: an APD signal acquisition unit configured to acquire an APD signal output by the single photon detector, the APD signal including an upper peak generated with a rising edge of the gating signal and a lower peak generated with a falling edge of the gating signal; a peak location determination unit configured to determine a delay location of the upper peak in the APD signal to determine a delay location of the lower peak in the APD signal by gating a gate width of a signal; a coincidence gate adjustment unit configured to move a coincidence gate signal to align a delay position of a falling edge of the coincidence gate signal with a delay position of the lower spike in the APD signal; and a screening coincidence unit configured to AND the comparison result between the APD signal and a discrimination threshold with a coincidence gate signal to extract an avalanche signal from the APD signal.

According to an embodiment of the present invention, the spike position determining unit includes: the threshold scanning unit is configured to adjust the gate width of a coincidence gate signal to be maximum, gradually reduce a screening threshold from the upper part of the APD signal to the lower part of the APD signal according to a preset step length, and count a pulse count generated by performing an AND operation on a pulse generated by a part of signals in the APD signal exceeding the screening threshold and the coincidence gate signal for each reduced screening threshold until the pulse count is absent; the coincidence gate scanning unit is configured to adjust the gate width of a coincidence gate signal to be minimum, gradually move the coincidence gate signal from the left side of the APD signal to the right side of the APD signal according to a preset step length, count pulse counts generated by performing AND operation on pulses generated by partial signals in the APD signal exceeding a screening threshold and the coincidence gate signal for each moving coincidence gate signal, and record a first delay position of the coincidence gate signal when the pulse counts are from absence to presence for the first time and a second delay position of the coincidence gate signal when the pulse counts are from presence to absence for the first time; and a delay position determination calculation configured to determine a midpoint between the first delay position and the second delay position as a delay position of the upper spike in the APD signal.

According to one embodiment of the invention, the discrimination threshold is determined based on a peak in an avalanche region in the APD signal adjacent to the lower spike in the absence of an avalanche.

According to one embodiment of the invention, the threshold scanning unit is further configured to adjust the gate width of the coincidence gate signal to be the same as the duration of an avalanche section, to gradually decrease the screening threshold from above the APD signal to below the APD signal by a predetermined step size, and to count, for each decreased screening threshold, the pulse count generated by and-ing the pulse generated by the partial signal of the APD signal located in the avalanche section with the coincidence gate signal until the pulse count is from none to none.

According to another aspect of the invention, a computer readable storage medium is provided, having stored thereon a computer program which, when being executed by a processor, carries out the method for extracting an avalanche signal as previously described.

According to another aspect of the present invention, there is provided a computing device comprising: a processor; and a memory storing a computer program which, when executed by the processor, implements a method for extracting an avalanche signal as described previously.

The method and the device for extracting the avalanche signal according to the exemplary embodiment of the invention can not only extract the avalanche signal from the APD signal without adding new investment (such as other optical devices or electric devices), but also effectively avoid the influence of spike noise caused by the gating signal on the extraction of the avalanche signal, thereby greatly improving the rate of finished code of the quantum communication system.

Drawings

The above objects and features of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings.

Fig. 1 shows a flow chart of a method for extracting an avalanche signal according to an exemplary embodiment of the present invention.

FIG. 2 shows a schematic diagram of an APD signal including an up spike and a down spike, according to an exemplary embodiment of the present invention.

FIG. 3 shows a schematic diagram for determining the delay location of an up-spike in an APD signal according to an exemplary embodiment of the invention.

FIG. 4 illustrates another schematic diagram for determining a delay location of an up-spike in an APD signal according to an exemplary embodiment of the invention.

Fig. 5 shows a schematic diagram for aligning the delay position of a falling edge of a coincidence gate signal with the delay position of a lower spike in an APD signal in accordance with an exemplary embodiment of the present invention.

Fig. 6 shows a schematic diagram for determining a discrimination threshold based on a peak in an avalanche region adjacent to a lower peak in an APD signal without an avalanche occurrence in accordance with an exemplary embodiment of the present invention.

Fig. 7 illustrates a block diagram of an apparatus for extracting an avalanche signal according to an exemplary embodiment of the present invention.

Fig. 8 shows a signal timing diagram of an apparatus for extracting an avalanche signal according to an exemplary embodiment of the present invention.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Fig. 1 shows a flow chart of a method for extracting an avalanche signal according to an exemplary embodiment of the present invention. The method shown in fig. 1 may operate as an algorithm in a computing device such as, but not limited to, a quantum communication system.

Referring to fig. 1, the method shown in fig. 1 may include the following steps.

At step 101, APD signals output by the single photon detectors may be acquired, which may include an up-spike with a rising edge of the gating signal and a down-spike with a falling edge of the gating signal.

FIG. 2 shows a schematic diagram of an APD signal 1020 including an upper spike P1 and a lower spike P2, according to an exemplary embodiment of the invention.

In addition, even in the absence of a bias voltage, the APD signal 1020 generates an upper peak P1 with the rising edge of the gating signal 1010 and a lower peak P2 with the falling edge of the gating signal 1010, and the upper peak P1 and the lower peak P2 are different from each other in delay time by the gate width W1 of the gating signal 1010.

At step 102, the delay location of an upper peak in the APD signal can be determined to determine the delay location of a lower peak in the APD signal by gating the gate width of the signal.

In one example, the gate width of the coincidence gate signal can be adjusted to a maximum to gradually decrease the discrimination threshold from below the APD signal in an upward direction of the APD signal by a predetermined step size, and for each decreased discrimination threshold, counting the pulse count resulting from the and operation of the pulse resulting from a portion of the APD signal exceeding the discrimination threshold with the coincidence gate signal until the pulse count is never available; adjusting the gate width of the coincidence gate signal to be minimum so as to gradually move the coincidence gate signal from the left side of the APD signal to the right side of the APD signal according to a preset step length, counting pulses generated by AND operation of partial signals in the APD signal exceeding a discrimination threshold value and the coincidence gate signal aiming at the coincidence gate signal moving each time, and recording a first delay position of the coincidence gate signal when the pulse counting is firstly carried out and a second delay position of the coincidence gate signal when the pulse counting is firstly carried out; a midpoint between the first delay location and the second delay location is determined as a delay location of an upper peak in the APD signal.

Next, a process of determining the delay position of the up spike will be described in detail with reference to fig. 3 and 4.

Fig. 3 shows a schematic diagram for determining the delay location of an upper spike P1 in an APD signal 1020, in accordance with an exemplary embodiment of the present invention. FIG. 4 illustrates another schematic diagram for determining the delay location of the upper spike P1 in the APD signal 1020, according to an exemplary embodiment of the invention.

Referring to fig. 3, the gate width W2 of the coincidence gate signal 1040 may be adjusted to be maximum such that the gate width W2 of the coincidence gate signal 1040 is greater than the gate width W1 of the gating signal 1010 and envelopes the gate width W1 of the gating signal 1010. The discrimination Threshold may be set to an amplitude m0 (such as, but not limited to, 2200 mv), and then gradually decreased from below the APD signal 1020 in an upward direction of the APD signal 1020 by a predetermined step size (such as, but not limited to, 5 mv), when the discrimination Threshold is decreased from an amplitude m0 to an amplitude m1, a portion of the APD signal 1020 first exceeds the discrimination Threshold to produce a very narrow pulse 1030 (as shown in fig. 4), the pulse 1030 produces a pulse 1050 count by anding with the coincidence gate signal, the pulse 1050 count may change from "0" to "1" as the discrimination Threshold is decreased, the change in the pulse 1050 count indicating that the discrimination Threshold is near or at the top of the upper spike P1 in the APD signal 1020.

Referring to fig. 4, when the discrimination Threshold is near the top of the upper spike P1 in the APD signal 1020, the coincidence gate signal 1040 can be set to the minimum delay position X0 and the gate width W2 of the coincidence gate signal 1040 can be adjusted to a minimum. With the discrimination Threshold maintained at the amplitude m1, the coincidence gate signal 1040 may be moved in steps from the left side of the APD signal 1020 to the right side of the APD signal 1020 in predetermined steps (such as, but not limited to, 11 ps), when the coincidence gate signal 1040 moves from the delay position X0 to about the delay position X1, a portion of the APD signal 1020 first exceeds the discrimination Threshold, thereby producing a very narrow pulse 1030, the pulse 1030 generates a pulse 1050 count by anding the coincidence gate signal 1040, the pulse 1050 count may change from "0" to "1" about the delay position X1 as the coincidence gate signal moves, a change in the pulse 1050 count indicates that the coincidence gate signal 1040 is near or at the left edge of the upper spike P1, and at the same time, the delay position X1 of the coincidence gate signal 1040 may be recorded. As the coincidence gate signal 1040 moves from the delay position X1 to about the delay position X2, some of the APD signals 1020 continue to exceed the discrimination Threshold and continue to produce extremely narrow pulses 1030, the pulses 1030 produce a pulse 1050 count by and-ing the coincidence gate signal 1040, the pulse 1050 count may change from a "1" to a "0" about the delay position X2 as the coincidence gate signal 1040 moves, the change in the pulse 1050 count indicating that the coincidence gate signal 1040 is near or at the right-hand edge of the upper spike P1, and at the same time, the delay position X2 of the coincidence gate signal 1040 may be recorded. Next, the midpoint between delay position X1 and delay position X2 may be calculated based on the set of delay positions X1 and X2 recorded at amplitude m1 to estimate the delay position of the upper spike P1 in the APD signal 1020. Furthermore, in order to obtain a more accurate delay position of the upper peak P1, the Threshold may also be adjusted (increased or decreased) repeatedly with a very small margin based on the amplitude m1 to obtain the delay positions X1 and X2 recorded at a plurality of amplitudes, so as to calculate midpoints between the plurality of delay positions X1 and X2, and an average value of the midpoints may be determined as the delay position of the upper peak P1 in the APD signal 1020.

Further, after determining the delay location of the upper peak P1 in the APD signal 1020, the delay location of the gate width W1 of the gating signal 1010 one time away from the delay location of the upper peak P1 in the APD signal 1020 may be determined as the delay location of the lower peak P2 in the APD signal 1020.

It should be understood that although fig. 3 and 4 show schematic diagrams for determining the delay location of an up-spike in an APD signal in accordance with exemplary embodiments of the present invention, the examples shown in the schematic diagrams are merely illustrative and the present invention is not limited thereto.

Returning again to fig. 1, at step 103, the coincidence gate signal can be moved to align the delay position of the falling edge of the coincidence gate signal with the delay position of the lower spike in the APD signal.

Fig. 5 illustrates a schematic diagram for aligning the delay position of the falling edge of the coincidence gate signal 1040 with the delay position of the lower spike P2 in the APD signal 1020, in accordance with an exemplary embodiment of the present invention.

At step 104, the comparison between the APD signal and the discrimination threshold can be anded with the coincidence gate signal to extract an avalanche signal from the APD signal.

In one example, the discrimination threshold can be determined based on a peak within an avalanche region adjacent to a lower spike in the APD signal without an avalanche occurrence.

In this example, the gate width of the coincidence gate signal can be adjusted to be the same as the duration of the avalanche section, so that the discrimination threshold is gradually decreased from above the APD signal to below the APD signal in a predetermined step, and the pulse count resulting from the and operation of the coincidence gate signal with the pulses resulting from the partial signal of the APD signal located in the avalanche section exceeding the discrimination threshold is counted for each decreased discrimination threshold until the pulse count is never reached.

Fig. 6 shows a schematic diagram of determining a discrimination Threshold based on a peak P3 within an avalanche Section adjacent to a lower peak in an APD signal without avalanche occurrence according to an exemplary embodiment of the present invention.

Referring to fig. 6, where the delay position of the falling edge of the coincidence-gate signal 1040 is aligned with the delay position of the lower spike P2 in the APD signal 1020, the gate width W2 of the coincidence-gate signal 1040 may be adjusted to be the same as the duration of the avalanche Section so that the coincidence-gate signal 1040 coincides with the avalanche Section. The discrimination Threshold, may be set to an amplitude m0 (such as, but not limited to, 50 mv) as previously described, and then gradually decreased in predetermined steps (such as, but not limited to, 5 mv) from below the APD signal 1020 in an upward direction of the APD signal 1020, when the discrimination Threshold, decreases from an amplitude m0 to an amplitude m2, a portion of the signal in the APD signal 1020 located in the avalanche Section first exceeds the discrimination Threshold, thereby producing an extremely narrow pulse 1030, the pulse 1030 producing a pulse 1050 count by anding with the coincidence gate signal 1040, the pulse 1050 count may change from "0" to "1" as the discrimination Threshold, the change in the pulse 1050 count indicating that the discrimination Threshold, is near or located in the avalanche Section peak P3.

It should be understood that although fig. 6 shows a schematic diagram for determining the discrimination Threshold based on the peak value P3 in the avalanche section adjacent to the lower peak in the APD signal without avalanche, according to an exemplary embodiment of the present invention, the example shown in the schematic diagram is merely illustrative, and the present invention is not limited thereto.

In addition, in an example, both the gating signal and the coincidence gate signal can be synchronized with an encoding clock of the quantum communication system, which can synchronize the gating signal and the coincidence gate signal with optical pulses transmitted in the quantum communication system to provide a reliable discrimination range for the extraction of the avalanche signal.

Fig. 7 illustrates a block diagram of an apparatus for extracting an avalanche signal according to an exemplary embodiment of the present invention. Fig. 8 shows a signal timing diagram of an apparatus for extracting an avalanche signal according to an exemplary embodiment of the present invention. The apparatus shown in fig. 7 may be integrated in a computing device such as, but not limited to, a quantum communication system.

Referring to fig. 7, the apparatus 100 for extracting an avalanche signal according to an exemplary embodiment of the present invention may include at least an APD signal acquisition unit 701, a spike position determination unit 702, a coincidence gate adjustment unit 703, and a screening coincidence unit 704.

In the apparatus shown in fig. 7, the APD signal acquisition unit 701 may be configured to acquire an APD signal 1020 output by the single photon detector, which may include an upper spike P1 generated with a rising edge of the gating signal 1010 and a lower spike P2 generated with a falling edge of the gating signal 1010; the spike position determination unit 702 may be configured to determine the delay position of the upper spike P1 in the APD signal 1020 to determine the delay position of the lower spike P2 in the APD signal 1020 by gating the gate width W1 of the signal 1010; the coincidence-gate adjustment unit 703 can be configured to move the coincidence-gate signal 1040 to align the delay position of the falling edge of the coincidence-gate signal 1040 with the delay position of the lower spike P2 in the APD signal 1020; the screening coincidence unit 704 can be configured to AND the comparison between the APD signal 1020 and the screening Threshold with the coincidence gate signal 1040 to extract an avalanche signal from the APD signal 1020.

In the apparatus 100 for extracting an avalanche signal shown in fig. 7, the spike position determining unit 702 may include a threshold value scanning unit, a coincidence gate scanning unit, and a delay position calculating unit (not shown). In this example, the Threshold scanning unit can be configured to adjust the gate width of the coincidence gate signal 1040 to a maximum, to progressively decrease the discrimination Threshold from below the APD signal 1020 in an upward direction of the APD signal 1020 by a predetermined step size, and to count, for each decreased discrimination Threshold, pulses 1030 resulting from an and operation of a portion of the APD signal 1020 that exceeds the discrimination Threshold with the pulses 1050 resulting from the coincidence gate signal 1040 until the pulses 1050 count is never present; the coincidence gate scan unit can be configured to minimize the gate width of the coincidence gate signal 1040, to move the coincidence gate signal 1040 stepwise in predetermined steps from the left side of the APD signal 1020 to the right side of the APD signal 1020, and to count, for each moved coincidence gate signal, a pulse 1050 count resulting from an and operation of a pulse 1030 resulting from a fraction of the APD signal 1020 exceeding a discrimination Threshold with the coincidence gate signal 1040, to record a first delay position where the coincidence gate signal 1040 counts from none to none at the pulse 1050 for the first time and a second delay position where the coincidence gate signal 1040 counts from presence to none at the pulse 1050 for the first time; the delay position calculation unit may be configured to determine a midpoint between the first delay position and the second delay position as the delay position of the upper spike P1 in the APD signal 1020.

In the apparatus 100 for extracting an avalanche signal shown in fig. 7, the discrimination Threshold may be determined based on a peak P3 within an avalanche Section adjacent to the lower spike P2 in the APD signal 1020 in the absence of an avalanche. In an example, the Threshold scan unit can be further configured to adjust the gate width W2 of the coincidence gate signal 1040 to be the same as the duration of the avalanche Section, to gradually decrease the discrimination Threshold by a predetermined step from below the APD signal 1020 in an upward direction of the APD signal 1020, and to count, for each decreased discrimination Threshold, pulses 1030 resulting from an and operation of a portion of the APD signal 1020 with the coincidence gate signal 1040 until the pulse 1050 counts from none to none.

It can be seen that the method and apparatus for extracting an avalanche signal according to the exemplary embodiments of the present invention can not only extract an avalanche signal from an APD signal without adding new investment (such as other optical devices or electrical devices), but also effectively avoid the influence of spike noise caused by a gate control signal on the extraction of the avalanche signal, so that the rate of the quantum communication system is greatly increased.

There may also be provided a computer-readable storage medium storing a computer program according to an exemplary embodiment of the present invention. The computer readable storage medium stores a computer program which, when executed by a processor, causes the processor to perform a method for extracting an avalanche signal according to the present invention. The computer readable recording medium is any data storage device that can store data read by a computer system. Examples of the computer-readable recording medium include: read-only memory, random access memory, read-only optical disks, magnetic tapes, floppy disks, optical data storage devices, and carrier waves (such as data transmission through the internet via wired or wireless transmission paths).

There may also be provided, in accordance with an exemplary embodiment of the present invention, a computer apparatus. The computer device may include a processor and a memory. The memory is for storing a computer program. The computer program is executed by a processor causing the processor to execute a computer program of a method for extracting an avalanche signal according to the present invention.

While the present application has been shown and described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made to these embodiments without departing from the spirit and scope of the present application as defined by the following claims.