Quantum key distribution system and method capable of tolerating high-noise link
By employing ultra-narrow bandwidth configuration and frequency domain filtering at the transmitting and receiving terminals of the QKD device, the problem of noise interference in the quantum key distribution system was solved, enabling long-distance transmission without modifying classical optical communication equipment.
Patent Information
- Application Number
- CN202410961703.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-17
- Publication Date
- 2026-01-20
AI Technical Summary
In existing quantum key distribution systems, the noise interference problem between classical optical signals and quantum optical signals in shared fiber optic links has not been effectively solved, resulting in high demand for the modification of classical optical communication equipment and limiting practical applications.
The QKD device employs an ultra-narrow bandwidth configuration in both the transmitting and receiving terminals. The frequency difference between the quantum optical signal and the classical optical signal is 25 GHz or an integer multiple thereof. Combined with an ultra-narrowband filter, frequency domain filtering is performed in the receiving terminal to control the center wavelength matching and achieve low-loss transmission.
It achieves reduced noise interference and supports long-distance transmission without changing classic optical communication equipment, simplifies engineering applications, and reduces the need for modification of classic optical communication equipment.
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Figure CN121367586A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of quantum information technology, in particular to a quantum key distribution system and method capable of tolerating high-noise links. BACKGROUND
[0002] A quantum key distribution (QKD) system can provide high-level information security protection against high-computing power attacks based on the principles of quantum non-cloning and uncertainty. Due to the very weak signal light in the quantum key distribution process, for example, single-photon level, the weak noise signals in the link have a significant impact on the signal light when the signal light is transmitted from the transmitting terminal to the receiving terminal through the link. Therefore, early quantum key distribution systems often need to use dedicated optical fiber links separately to avoid the impact of other optical signals on the signal light.
[0003] In order to save link resources, related technologies for transmitting classical optical communication signals and quantum key distribution signals in the same link have been developed. At present, the following measures are mainly used to realize the multiplexing of quantum signals and classical signals for optical fiber transmission: first, attenuating the classical optical signal to reduce the noise generated thereby; second, increasing the wavelength interval between the classical optical signal and the quantum optical signal to reduce the noise generated thereby; and third, adding a narrowband filter at the receiving terminal to filter out part of the noise.
[0004] Figure 1 A quantum signal and classical signal multiplexing optical fiber transmission scheme in the prior art is shown, in which an optical intensity self-adaptive adjustment device 110 is arranged in communication connection with the QKD receiving terminal 6 between the classical signal input module 1 and the first wavelength division multiplexer 104, so that the optical intensity self-adaptive adjustment device 110 automatically adjusts the attenuation coefficient to attenuate the classical signal according to the noise feedback information of the QKD receiving terminal 6.
[0005] Figure 2 Another quantum signal and classical signal co-fiber transmission scheme in the prior art is shown, in which a narrowband filter is designed at the receiving terminal to reduce the noise, and a wavelength conversion device is designed at the transmitting terminal to convert the classical signal to a wavelength greatly separated from the quantum signal, for example, to convert the quantum signal to a C-band 1550nm wavelength and the classical signal to an S-band 1310nm or L-band 1625nm wavelength.
[0006] The purpose of transmitting classical optical communication signals and quantum key distribution signals in the same link is to save link resources, and in particular, the quantum key distribution signal hopes to be based on the optical fiber network already laid by classical optical communication, for which the classical optical communication equipment should be modified as little as possible or even not modified at all. Therefore, the existing classical-quantum signal wavelength division multiplexing scheme cannot well meet this demand.
[0007] In the scheme of attenuating the classical optical power, the classical optical communication equipment requires high receiving sensitivity, which is limited in many practical application scenarios, and there is not enough power adjustment space in the existing network.
[0008] For the scheme of reducing noise by increasing the wavelength interval of the classical optical signal and the quantum optical signal, the classical optical communication backbone network often uses the C band, and part of it has also used the L band. Finally, with the increase of bandwidth, it will be a trend to use the C band and the L band at the same time. In this way, if a large wavelength interval of the quantum optical signal and the classical optical signal is pursued, the quantum optical signal needs to be configured in the O band, and the transmission loss of the O band optical signal in the optical fiber will greatly reduce the coding rate distance of the quantum key distribution system. For example, for ordinary single-mode optical fiber, the transmission loss of the C band is about 0.2 dB / km, and the transmission loss of the O band is about 0.35 dB / km. For a system that can tolerate a loss of 20 dB, it can be transmitted for 100 km using the C band, and only 57 km using the O band, which greatly reduces the performance.
[0009] For the scheme using a narrow-band filter, since the narrow-band filter needs to be used at the receiving terminal of the quantum key distribution system, it is sensitive to loss, and the increase of the loss of the narrow-band filter will directly cause the performance of the quantum key distribution system to decrease. Therefore, the bandwidth of the narrow-band filter in the existing QKD system is on the order of 10 GHz, and it needs to be combined with measures such as reducing the classical optical power or configuring the classical optical signal and the quantum optical signal on a relatively distant band to reduce noise.
[0010] For example, in the narrow-band filter scheme disclosed in “Dynes J., Tam W., Plews A., et al. Ultra-high bandwidth quantum secured data transmission. Sci Rep 6, 35149 (2016)”, the narrow-band filter uses a bandwidth of 25 GHz, and when using quantum optical signals and classical optical signals in the C band (with an interval of about 20 nm), the classical optical power needs to be reduced. According to the record, it needs to adjust the single-channel power to -25.5 dBm, and a total of 10 channels are used, with a total power of about -15.5 dBm. At present, optical communication backbone network equipment often reaches 80 waves, 110 waves or even more, and the in-fiber optical power reaches +21 dBm or even higher. According to the power limit in the paper, the power of the conventional optical communication equipment needs to be reduced by about 36.5 dB (corresponding to about 4000 times), which is almost impossible to achieve in practical engineering applications.
[0011] For example, in the narrow-band filter scheme disclosed in "Yingqiu Mao, Bi-Xiao Wang, et al. Integrating quantum key distribution with classical communications in backbone fiber network. Opt. Express 26, 6010-6020 (2018)", the narrow-band filter used has a bandwidth of 20 GHz, which does not need to reduce the classical optical power, but needs to configure the quantum optical signal and the classical optical signal at a relatively far wavelength interval to reduce noise (the quantum optical signal is in the O band, the classical optical signal is in the C band, and the wavelength interval is about 240 nm).
[0012] In general, in the classical-quantum signal co-transmission system using the narrow-band filter at present, it is generally believed that a filter bandwidth of the order of 10 GHz needs to be used, and at the same time, the classical signal power needs to be reduced or the classical optical signal and the quantum optical signal need to be configured at a relatively large wavelength interval to reduce noise. The requirement for reducing the classical signal power or configuring the wavelength interval also means that more requirements are put forward for the classical device, which hinders the practical application of the classical-quantum signal co-transmission technology. SUMMARY
[0013] In view of the above problems existing in the prior art, the present application discloses a quantum key distribution system and method, which can provide the QKD system with the ability to tolerate a high-noise link by simultaneously configuring a specific ultra-narrow bandwidth in the QKD device sending terminal and the receiving terminal, especially in the scenario where the classical optical communication device and the QKD device have a small wavelength interval of 25 GHz or an integer multiple thereof, without the need to reduce the classical optical signal power or configure the classical optical signal and the quantum optical signal at a relatively large wavelength interval to reduce noise, without the need to excessively limit the power and wavelength of the classical optical communication device, which can greatly facilitate practical engineering applications, and the quantum optical signal and the classical optical signal can simultaneously achieve a small link attenuation, which is suitable for long-distance scenarios. Thus, the problems that the prior art needs to make many limitations and modifications to the classical optical communication device in practical applications, which hinders practical engineering applications, and the quantum optical signal and the classical optical signal cannot be in the same wavelength band at the same time, which leads to a large link loss of one wavelength band and cannot support long-distance scenario applications, can be well solved.
[0014] Specifically, the first aspect of the present application relates to a quantum key distribution system capable of tolerating a high-noise link, which includes an Alice end and a Bob end.
[0015] The Alice end includes a classical optical communication device, a QKD device sending terminal, and a wavelength division multiplexing component.
[0016] The Bob end comprises a classical optical communication device, a QKD device receiving terminal and a demultiplexing component;
[0017] The QKD device transmitting terminal comprises an ultra-narrowband signal forming module and a quantum state modulation module, the ultra-narrowband signal forming module is configured to make the quantum optical signal have a first bandwidth lower than 1GHz;
[0018] The QKD device receiving terminal comprises a second ultra-narrowband filter, a quantum state demodulation module, a single-photon detection module and a control unit, the second ultra-narrowband filter has a second bandwidth lower than 1GHz and is configured to filter the quantum optical signal, and the control unit is configured to control the center wavelength of the second ultra-narrowband filter to match the center wavelength of the quantum optical signal.
[0019] Further, the frequency of the classical optical signal output by the classical optical communication device differs from the frequency of the quantum optical signal by 25GHz or an integer multiple thereof.
[0020] Preferably, the ultra-narrowband signal forming module comprises a narrow-linewidth laser, which has the first bandwidth.
[0021] Preferably, the ultra-narrowband signal forming module comprises a laser light source and a first ultra-narrowband filter, the first ultra-narrowband filter has the first bandwidth and is configured to make the quantum optical signal have the first bandwidth by filtering.
[0022] Preferably, the ultra-narrowband filter comprises a phase-shifted grating.
[0023] Preferably, the first bandwidth is set to 20MHz-1GHz, and the second bandwidth is set to 20MHz-1GHz.
[0024] Further, the control unit is configured to control the center wavelength of the second ultra-narrowband filter to make the detection count of the single-photon detection module about the quantum optical signal reach a preset threshold or a maximum value.
[0025] Preferably, the second ultra-narrowband filter is integrated with a temperature controller, and the control unit is configured to control the temperature controller.
[0026] The second aspect of the present application relates to a quantum key distribution method tolerable to a high-noise link, comprising the following steps:
[0027] At the Alice end, a quantum optical signal with a first bandwidth is generated by a QKD device sending terminal, and the quantum optical signal and a classical optical signal output by a classical optical communication device are output to an optical fiber channel by wavelength division multiplexing using a wavelength division multiplexing component, wherein the first bandwidth is set to be lower than 1 GHz; and
[0028] At the Bob end, the classical optical signal and the quantum optical signal are demultiplexed by a demultiplexing component and transmitted to a classical optical communication device and a QKD device receiving terminal, respectively, and the quantum optical signal is filtered by a second ultra-narrow band filter with a second bandwidth before single-photon detection in the QKD device receiving terminal, the second bandwidth being set to be lower than 1 GHz; and
[0029] The center wavelength of the second ultra-narrow band filter is controlled according to the detection count of the single-photon detection module on the quantum optical signal, so that the detection count reaches a preset threshold or a maximum value.
[0030] Further, the frequency difference between the classical optical signal and the quantum optical signal is set to 25 GHz or an integer multiple thereof.
[0031] Preferably, the center wavelength of the second ultra-narrow band filter is controlled by controlling the temperature of the second ultra-narrow band filter.
[0032] Preferably, the quantum key distribution method of the present application can be implemented by means of the above-mentioned quantum key distribution system. BRIEF DESCRIPTION OF DRAWINGS
[0033] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings.
[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, brief descriptions will be given below for the drawings needed in the embodiments or prior art descriptions. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.
[0035] Figure 1 A quantum signal and classical signal multiplexing optical fiber transmission scheme in the prior art is schematically shown;
[0036] Figure 2 Another quantum signal and classical signal multiplexing optical fiber transmission scheme in the prior art is schematically shown;
[0037] Figure 3 A quantum key distribution system of the present application which can tolerate a high-noise link is schematically shown. DETAILED DESCRIPTION
[0038] In the following, exemplary embodiments of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are provided by way of example in order to convey the spirit of the present application to those skilled in the art to which the present application pertains. Therefore, the present application is not limited to the embodiments disclosed herein.
[0039] Figure 3 A quantum key distribution (QKD) system of the present application tolerating high-noise link is schematically shown, which includes an Alice side and a Bob side connected through a fiber channel.
[0040] As shown in Figure 3 , a classical optical communication device, a QKD device sending terminal and a wavelength division multiplexing component are provided in the Alice side, wherein the classical optical signal output by the classical optical communication device and the quantum optical signal output by the QKD device sending terminal can be transmitted in a wavelength division multiplexing manner through the fiber channel towards the Bob side via the wavelength division multiplexing component (for example, the classical quantum wavelength division component shown in Figure 3 ).
[0041] Correspondingly, a classical optical communication device, a QKD device receiving terminal and a wavelength division demultiplexing component (for example, the classical quantum wavelength division demultiplexing component shown in Figure 3 ) can be provided in the Bob side. Therefore, the classical optical signal and the quantum optical signal reaching the Bob side in a wavelength division multiplexing manner through the same fiber channel can be wavelength division demultiplexed in the wavelength division demultiplexing component, so as to be transmitted to the classical optical communication device and the QKD device receiving terminal, respectively.
[0042] Unlike the existing manner of only providing a narrow-band filter with a bandwidth of the order of ten gigahertz at the QKD device receiving terminal, the present application firstly proposes a manner of simultaneously configuring an ultra-narrow bandwidth at the QKD device sending terminal and the receiving terminal for the QKD scheme of transmitting in a wavelength division multiplexing manner through the channel, thereby providing the QKD system with the ability to tolerate high-noise link.
[0043] Specifically referring to Figure 3 , in the QKD device sending terminal of the present application, in addition to a quantum state modulation module for modulating a quantum state on an optical signal, an ultra-narrow-band signal forming module is specially provided for making the quantum optical signal finally output by the QKD device sending terminal have a first bandwidth. In the present application, the first bandwidth is set to an ultra-narrow bandwidth (which has a spectral width of about 8 pm) lower than 1 GHz.
[0044] Figure 3 A preferred example of the ultra-narrow-band signal forming module is shown, which includes a light source (for example, a laser) and a first ultra-narrow-band filter, wherein the first ultra-narrow-band filter has the above-mentioned first bandwidth.
[0045] In Figure 3In the example shown in FIG. 1, the light signal output by the light source can be provided with modulation by the quantum state modulation module, and then provided with frequency domain filtering with ultra-narrow bandwidth by the first ultra-narrow band filter, so as to obtain an ultra-narrow bandwidth corresponding to the first bandwidth, thereby allowing the QKD device sending terminal to finally output a quantum light signal with ultra-narrow bandwidth.
[0046] In another example (not shown) of the present application, a narrow linewidth laser with the first bandwidth can be used as the light source, and the ultra-narrow band signal forming module of the present application can be implemented by directly outputting a light signal with the first bandwidth, thereby allowing the QKD device sending terminal to finally output a quantum light signal with ultra-narrow bandwidth.
[0047] In the QKD device receiving terminal of the present application, in addition to the quantum state demodulation module for demodulating the quantum light signal and the single photon detection module (which is in the form of a single photon detector, for example) for detecting the quantum light signal, a second ultra-narrow band filter is also provided, as shown in Figure 3 .
[0048] In the present application, the second ultra-narrow band filter can have a second bandwidth and be configured to filter the quantum light signal in the frequency domain. The second bandwidth can be set to an ultra-narrow bandwidth lower than 1 GHz.
[0049] Continuing to refer to Figure 3 In the QKD device receiving terminal of the present application, a control unit is also provided, which is configured to control the center wavelength of the second ultra-narrow band filter to form an optimal match (e.g., consistent) with the center wavelength of the quantum light signal, thereby eliminating the system impact caused by the change of the center wavelength of the light signal of the QKD device sending terminal and the drift of the center wavelength of the ultra-narrow band filter of the QKD device receiving terminal.
[0050] As a preferred example, the control unit can control the second ultra-narrow band filter to adjust its center wavelength according to the detection result (e.g., detection count of the quantum light signal) of the single photon detection module in a preset strategy, so as to eliminate the impact of the change of the center wavelength of the light signal of the QKD sending terminal and the drift of the center wavelength of the ultra-narrow band filter of the receiving terminal on the system. For example, the control unit can monitor the detection count reported by the single photon detector, and control the center wavelength of the second ultra-narrow band filter by using an optimization algorithm such as a climbing algorithm, until the detection count of the single photon detector reaches a set threshold or a maximum value, which means that the center wavelengths of the two are in an optimal match state (e.g., consistent).
[0051] Further, a temperature controller can be integrated in the second ultra-narrow band filter to allow control of the center wavelength of the second ultra-narrow band filter by controlling the temperature. In this case, the control unit can control the center wavelength of the second ultra-narrow band filter by controlling the temperature controller of the second ultra-narrow band filter.
[0052] With the QKD device sending terminal and the QKD device receiving terminal structure described above, the quantum optical signal carrying quantum state information can pass through the second ultra-narrow band filter with low loss when it reaches the QKD device receiving terminal, and the noise tolerance of the system is greatly improved, making it possible to tolerate high noise links in the QKD system. Therefore, in the QKD system of the present application, a small wavelength interval can be used between the QKD device sending terminal and the classical optical communication device (i.e., the quantum optical signal and the classical optical signal), and the power and wavelength of the classical optical communication device do not need to be limited too much, thereby avoiding many problems existing in the prior art that hinder practical engineering applications.
[0053] On this basis, the applicant has further found that setting the wavelength interval between the QKD device sending terminal and the classical optical communication device (i.e., the quantum optical signal and the classical optical signal) to 25 GHz (about 0.2 nm) or an integer multiple of 25 GHz is particularly suitable for the specific ultra-narrow bandwidth configuration in the QKD device sending terminal and the QKD device receiving terminal described above. In this case, the optical fiber channel in the QKD system can cause small attenuation to the classical optical signal and the quantum optical signal at the same time, and is particularly suitable for long-distance application scenarios.
[0054] In a further preferred example, the first and second bandwidths can be set to 20 MHz-1 GHz.
[0055] As a preferred example, the first and / or second ultra-narrow band filter can be in the form of a phase-shifted grating.
[0056] Based on the technical information provided above, those skilled in the art can realize that the QKD system of the present application, on the basis of adopting a frequency domain filtering mode, no longer needs to reduce the power of the classical light signal or configure the classical light signal and the quantum light signal on two wave bands with a large interval to reduce noise, so as to realize a satisfactory quantum key distribution process. That is, when the quantum key distribution system of the present application is adopted, the power and wavelength of the classical light communication equipment do not need to be limited too much, which greatly facilitates practical engineering application, and the wavelength interval of the QKD equipment and the classical light communication equipment does not need to be large, and both can simultaneously realize small link attenuation, suitable for long distance scenarios. Thus, the problems that the power of the classical light communication equipment needs to be attenuated or the classical light communication wavelength and the QKD equipment wavelength need to be configured on a large wavelength interval in the prior art, resulting in the need for more restrictions and modifications of the classical light communication equipment in practical application and hindering practical engineering application, and the problems that the classical light signal and the quantum light signal cannot be in the same wave band at the same time, resulting in large link loss of one wave band and inability to support long distance scenarios, can be well solved.
[0057] At this point, those skilled in the art can realize that the present application also proposes a quantum key distribution method that can tolerate a high noise link, which is especially suitable for being implemented by means of the QKD system described above.
[0058] Specifically, the quantum key distribution method of the present application can include a signal generation and transmission process, a signal reception and demodulation process, and a feedback control process.
[0059] In the signal generation and transmission process, the QKD equipment sending terminal at the Alice end can generate a quantum light signal with a first bandwidth, and output the quantum light signal and a classical light signal output by the classical light communication equipment into the same optical fiber channel in a wavelength division multiplexing manner by means of a wavelength division multiplexing component to be transmitted to the Bob end, wherein the first bandwidth is set to an ultra-narrow bandwidth lower than 1 GHz, and is preferably 20 MHz-1 GHz.
[0060] As a preferred example, the wavelength interval between the classical light signal and the quantum light signal can be set to 25 GHz or an integer multiple thereof.
[0061] In the signal reception and demodulation process, when the quantum light signal and the classical light signal arrive at the Bob end in a wavelength division multiplexing manner, the classical light signal and the quantum light signal can be demultiplexed by a demultiplexing component and transmitted to the classical light communication equipment and the QKD equipment receiving terminal, respectively. Further, before single-photon detection of the quantum light signal is performed by a single-photon detection module, the quantum light signal is filtered in the frequency domain by means of a second ultra-narrow band filter with a second bandwidth, wherein the second bandwidth is set to an ultra-narrow bandwidth lower than 1 GHz, and is preferably 20 MHz-1 GHz.
[0062] Meanwhile, in the feedback control process, the second ultra-narrow band filter can be controlled to adjust its center wavelength according to the detection result (e.g., the detection count of the quantum optical signal) of the single-photon detection module, according to a preset strategy, so as to eliminate the influence of the change of the center wavelength of the quantum optical signal and the drift of the center wavelength of the second ultra-narrow band filter. For example, the detection count reported by the single-photon detector can be monitored, and an optimization algorithm such as a hill-climbing algorithm can be used to control the adjustment of the center wavelength of the second ultra-narrow band filter until the detection count of the single-photon detector reaches a set threshold or a maximum value, which means that the center wavelengths of the two are in an optimal matching state (e.g., consistent).
[0063] Similarly, a temperature controller can be integrated in the second ultra-narrow band filter, so as to allow the control of the center wavelength of the second ultra-narrow band filter by controlling the temperature.
[0064] Although the present application has been described in connection with the embodiments thereof with reference to the drawings, it will be apparent to those skilled in the art that the embodiments are only exemplary and are used to illustrate the principles of the present application, and do not limit the scope of the present application, and various combinations, modifications and equivalent replacements of the above embodiments can be made without departing from the spirit and scope of the present application.
Claims
1. A quantum key distribution system tolerable to high-noise link, comprising an Alice side and a Bob side; the Alice side comprising a classical optical communication device, a QKD device sending terminal and a wavelength division multiplexing component; the Bob side comprising a classical optical communication device, a QKD device receiving terminal and a wavelength division demultiplexing component; wherein the QKD device sending terminal comprising an ultra-narrowband signal forming module and a quantum state modulation module, the ultra-narrowband signal forming module being configured to make the quantum optical signal have a first bandwidth lower than 1 GHz; the QKD device receiving terminal comprising a second ultra-narrowband filter, a quantum state demodulation module, a single-photon detection module and a control unit, wherein the second ultra-narrowband filter has a second bandwidth lower than 1 GHz and is configured to filter the quantum optical signal, and the control unit is configured to control the center wavelength of the second ultra-narrowband filter to match the center wavelength of the quantum optical signal.
2. The quantum key distribution system of claim 1, wherein, The frequency of the classical optical signal output by the classical optical communication device differs from the frequency of the quantum optical signal by 25 GHz or an integer multiple thereof.
3. The quantum key distribution system of claim 1 or 2, wherein, The ultra-narrowband signal forming module comprises a narrow-linewidth laser having the first bandwidth; or the ultra-narrowband signal forming module comprises a laser light source and a first ultra-narrowband filter, the first ultra-narrowband filter having the first bandwidth and being configured to make the quantum optical signal have the first bandwidth by filtering.
4. The quantum key distribution system of claim 1 or 2, wherein, The ultra-narrowband filter comprises a phase-shifted grating.
5. The quantum key distribution system of claim 1 or 2, wherein, The first bandwidth is set to 20 MHz-1 GHz, and the second bandwidth is set to 20 MHz-1 GHz.
6. The quantum key distribution system of claim 1 or 2, wherein, The control unit is configured to control the center wavelength of the second ultra-narrowband filter to make the detection count of the single-photon detection module about the quantum optical signal reach a preset threshold or a maximum value.
7. The quantum key distribution system of any one of claims 1-2 and 6, wherein, The second ultra-narrowband filter is integrated with a temperature controller, and the control unit is configured to control the temperature controller. 8.A quantum key distribution method tolerable to high-noise link, comprising the following steps: At the Alice side, generating a quantum optical signal having a first bandwidth by using a QKD device sending terminal, and outputting the quantum optical signal and a classical optical signal output by a classical optical communication device to an optical fiber channel by using a wavelength division multiplexing component, wherein the first bandwidth is set to be lower than 1 GHz; and At the Bob side, demultiplexing the classical optical signal and the quantum optical signal by using a wavelength division demultiplexing component and transmitting them to a classical optical communication device and a QKD device receiving terminal respectively, and filtering the quantum optical signal by using a second ultra-narrowband filter having a second bandwidth before single-photon detection in the QKD device receiving terminal, wherein the second bandwidth is set to be lower than 1 GHz; and According to the detection count of the single-photon detection module about the quantum optical signal, the center wavelength of the second ultra-narrowband filter is controlled to make the detection count reach a preset threshold or a maximum value.
9. The quantum key distribution method of claim 8, wherein, a frequency difference between the classical optical signal and the quantum optical signal is set to 25 GHz or an integer multiple thereof; and / or, a center wavelength is controlled by controlling a temperature of the second ultra-narrow band filter.
10. The quantum key distribution method of claim 8, implemented with the quantum key distribution system of any one of claims 1-7.