Classic-quantum wavelength division multiplexing noise reduction method and system

Abstract

According to the classic-quantum wavelength division multiplexing noise reduction method and system provided by the invention, by using a polarization filtering system, Raman scattering noise generated by classic optical signals in a quantum communication system can be attenuated, and the signal-to-noise ratio and the common-fiber transmission performance are improved; in combination with data post-processing, the polarization coding QKD system can still perform normal decoding after polarization filtering, and the safety of the QKD system is not affected. Through the combination of the polarization filtering system and the traditional filtering noise reduction technology, the requirement for power attenuation of classical optical signals can be reduced to a certain extent, or the requirement for pulse width control and the like of the classical optical signals can be reduced, so that the communication risk of the classical optical signals is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical communication, and particularly relates to a classical-quantum wavelength division multiplexing noise reduction method and system. Background Technique

[0002] The statements in this part only provide background technical information related to the present invention, and do not necessarily constitute prior art.

[0003] Quantum secure communication is a secure communication method different from classical communication. It can generate an information-theoretically secure key that is exactly the same between two communication parties based on quantum key distribution (QKD) technology. This key encrypts classical information in the way of "one-time pad", that is, it can ensure the security of information transmission, so it has received wide attention. There is a prominent problem in the construction of QKD networks, that is, quantum information and classical information need to use different optical fibers to complete the transmission tasks respectively. Therefore, the construction of QKD networks consumes nearly twice as much optical fiber as the construction of general communication networks, thus occupying a large amount of resources of optical fiber communication networks.

[0004] Generally, wavelength division multiplexing technology is used to deploy QKD networks to integrate them with classical communication networks, so as to save a large amount of optical fiber resources and reduce deployment costs. For example, the Chinese invention patent with the publication number CN107465502A and the invention name of a quantum communication method and related device; the Chinese invention patent with the publication number CN110830121A and the invention name of a wavelength division multiplexing system and method for classical channels and quantum channels, as well as foreign literature such as "Coexi stence of High-Bit-RateQuantum Key Di str ibut ion and Data on Opt ica lFi ber", etc. Figure 1 and Figure 2 as shown.

[0005] However, as far as the inventor knows, in the solutions proposed by the above classical-quantum wavelength division multiplexing technology, in the process of co-fiber transmission of classical signals and quantum signals, in order to reduce the influence of classical optical signals on quantum optical signals, many interventions and treatments are often required for classical optical signals. Common treatment methods include: reducing the optical intensity of classical optical signals, narrowing the optical pulse width of classical optical signals, and reallocating the wavelength resources of classical optical signals. Although these intervention means may reduce the influence of classical optical signals on quantum optical signals to a certain extent during transmission in optical fibers, sometimes relying solely on these means cannot reduce the Raman scattering noise generated by classical optical signals to an appropriate level, and even bring more uncertainties to classical signals in the existing network, reducing the quality of classical communication to a certain extent, such as problems such as packet loss and increased bit error rate.

[0006] One of the common methods in most existing technologies to achieve co-fiber transmission of classical and quantum signals is to add an adjustable optical attenuator before co-fiber transmission at the sender to reduce the power of classical optical signals. Although there may be some optical power redundancy for classical optical signals in actual deployment to some extent, this power redundancy is reserved to ensure the normal operation of classical communication in case of abnormal increased losses (such as large fiber bending, some contamination at the end face, etc.) during the classical communication process.

[0007] In order to reduce the interference time of classical optical signals in the time domain, existing technologies have proposed to adjust and compress the pulse width of the optical signals of classical communication devices. This processing method not only has greater risks technically, but also is difficult for operators to organize and implement from the perspective of ensuring the security of classical communication during the specific implementation process. This will involve modifying the drive circuit of classical optical signals, which is more risky than the method of attenuating classical optical power. Therefore, the method of compressing the pulse width of classical optical signals is only researchable in theory and experiments, and is basically inoperable in the case where the existing classical network has been deployed and formed.

[0008] In addition, some existing technologies have proposed to redistribute the wavelength resources of classical signals to reduce the impact of classical optical noise. When building a new classical communication network, wavelength resource allocation may be considered and implemented together. However, when deploying a QKD system in a classical network in a wavelength division multiplexing manner currently, the classical network has often been built and is in operation, and it has already occupied the best communication band, making it difficult to allow the redistribution of its wavelength resources. Therefore, this method is also difficult to be feasible when implementing classical-quantum co-fiber transmission.

[0009] Although some existing technologies have proposed that polarization filtering can be used to reduce the impact of classical optical signals on quantum optical signals, this method is only applicable to non-polarization-encoded QKD systems such as phase encoding and time-phase encoding, because polarization-encoded QKD systems use the polarization state for information encoding, and polarization filtering will affect the normal decoding process of the QKD system and even affect the security of the QKD system. Summary of the Invention

[0010] To solve the above problems, the present invention proposes a classical-quantum wavelength division multiplexing noise reduction method and system. By using a polarization filtering system, the present invention can attenuate the Raman scattering noise generated by classical optical signals in a quantum communication system, improve the signal-to-noise ratio and co-fiber transmission performance; combined with data post-processing, it can enable the polarization-encoded QKD system to still be able to decode normally after polarization filtering without affecting the security of the QKD system.

[0011] By combining the use of a polarization filtering system with traditional filtering and noise reduction techniques, the requirements for the power attenuation of classical optical signals or the requirements for the pulse width control of classical optical signals can be reduced to a certain extent, thereby reducing the communication risks of classical optical signals.

[0012] According to some embodiments, the present invention adopts the following technical solutions:

[0013] A classical-quantum wavelength division multiplexing noise reduction method, comprising the following steps:

[0014] Before detection at the receiving end, perform polarization filtering on the demultiplexed quantum optical signal, allowing only a preset polarization state to pass through;

[0015] In the data post-processing stage, only retain the bit data where the basis vector selection of the sending end and the receiving end is consistent, and the preset polarization state corresponds to the consistent basis vector.

[0016] In the above solution, at the receiving end, after wavelength division demultiplexing, perform polarization filtering on the quantum optical signal separated from the classical optical signal to filter out some noise photons. Then, during decoding and detection, ensure that the quantum states consistent with the preset polarization direction (angle) achieve polarization transmission, and the noise photons in other directions are polarized filtered or attenuated; and in cooperation with the data post-processing process, it can still be normally decoded after polarization filtering without affecting the security of the quantum key distribution system.

[0017] As an alternative implementation, after the quantum optical signal passes through polarization filtering, its signal is:

[0018] Eout = Ein * cosθ

[0019] Where θ is the polarization state angle between the noise photon and the quantum signal light, Ein is the quantum optical signal with noise photons superimposed after wavelength division demultiplexing, and Eout is the signal after polarization filtering with some noise photons filtered out.

[0020] As an alternative implementation, it further includes performing frequency domain / time domain filtering on the signal after polarization filtering.

[0021] As an alternative implementation, it further includes performing optical intensity attenuation on the classical optical signal.

[0022] A classical-quantum wavelength division multiplexing noise reduction system, comprising a polarization filtering system and a processing module provided at the receiving end, wherein:

[0023] The polarization filtering system is used to perform polarization filtering on the demultiplexed quantum optical signal before detection at the receiving end, allowing only a preset polarization state to pass through;

[0024] The processing module is configured to, in the data post - processing stage, only retain the bit data where the basis vector selections of the sender and the receiver are the same, and the preset polarization state corresponds to the basis vector with the same selection.

[0025] As an alternative implementation, the polarization filtering system includes an optical switch and a plurality of polarizers. The polarization states of the polarizers are different, and the polarizers are connected in parallel. The optical switch is used to select the polarizer corresponding to a preset polarization state, and enable the prepared quantum optical signal to pass through the polarizer.

[0026] As an alternative implementation, the polarization filtering system includes a rotatable polarizer. The rotation angles of the polarizer are different, and the selected polarization states are different.

[0027] As an alternative implementation, the polarization states include four types: 0° (H), 90° (V), 45° (P), and 135° (N).

[0028] As an alternative implementation, the processing module is configured to only retain the bit data where the basis vector selections of the sender and the receiver are the same and the polarizer selected by the polarization filtering system corresponds to the basis vector with the same selection.

[0029] As an alternative implementation, the processing module is configured to only retain the bit data where the basis vector selections of the sender and the receiver are the same and the rotation angle of the polarizer rotated by the polarization filtering system corresponds to the basis vector with the same selection.

[0030] A key distribution system includes a receiver, and the receiver includes the above - mentioned classical - quantum wavelength - division multiplexing noise reduction system or adopts the above - mentioned method.

[0031] As an alternative implementation, the receiver includes a demultiplexer, a polarization filtering system, a key distribution receiving end, and a classical communication receiving end. One end of the demultiplexer is connected to the polarization filtering system, the polarization filtering system is connected to the key distribution receiving end, and the other end of the demultiplexer is connected to the classical communication receiving end.

[0032] As a further implementation, the receiver further includes a frequency - domain / time - domain filtering system, and the frequency - domain / time - domain filtering system is arranged between the polarization filtering system and the key distribution receiving end.

[0033] As an alternative implementation, it further includes a sender. The sender includes a key distribution sending end, a classical communication sending end, and a wavelength - division multiplexer. The key distribution sending end and the classical communication sending end are both connected to the wavelength - division multiplexer.

[0034] As a further implementation, the sender further includes an optical attenuator, and the optical attenuator is arranged between the classical communication sending end and the wavelength - division multiplexer.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] Compared with the traditional classical - quantum wavelength - division multiplexing noise reduction technology, the present invention adds a polarization filtering system between the wavelength - division demultiplexing and the QKD receiving end, which plays a strong inhibitory role in the Raman scattering noise formed during the co - fiber transmission in the polarization dimension. Thus, the signal - to - noise ratio of the quantum optical signal relative to the classical noise during co - fiber transmission can be further improved.

[0037] The polarization filtering system adopted by the present invention can be set as a group of polarizers with specific vibration directions or several groups of polarizers with specific vibration directions used in combination with optical switches or rotating polarizers. It has strong operability, simple structure, and low input cost.

[0038] The polarization filtering system of the present invention can be combined with traditional filtering and noise reduction technologies such as time - domain filtering and frequency - domain filtering, reducing the requirement for attenuation of classical light intensity and reducing the risk to classical communication security caused by traditional operation methods (such as attenuating classical optical power).

[0039] By designing the data post - processing process, the present invention can enable the polarization - encoded QKD system to still be able to decode normally after polarization filtering, without affecting the security of the QKD system.

[0040] The polarization filtering system of the present invention only needs to be carried out at the QKD decoding end, without the need to transform classical communication equipment, and polarization devices are relatively mature, so it has high feasibility in actual network formation.

[0041] To make the above - mentioned objects, features, and advantages of the present invention more obvious and understandable, the following specifically gives preferred embodiments and, in conjunction with the accompanying drawings, makes a detailed description as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The accompanying drawings forming a part of this specification are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0043] Figure 1 is a schematic diagram of a classical - quantum wavelength - division multiplexing method and device in the prior art;

[0044] Figure 2 is a schematic diagram of a wavelength - division multiplexing system for a classical channel and a quantum channel in the prior art;

[0045] Figure 3 is a schematic diagram of the polarization states of quantum light and Raman scattered light;

[0046] Figure 4 is a schematic diagram of the polarization filtering noise reduction process;

[0047] Figure 5 It is a schematic diagram of a polarization filtering system based on an optical switch;

[0048] Figure 6 It is a schematic diagram of a polarization filtering system based on a rotating polarizer;

[0049] Figure 7 It is a schematic diagram of a QKD system based on a polarization filtering system and method;

[0050] Figure 8 It is a schematic diagram of a QKD system based on a polarization filtering system and method combined with a frequency domain filtering system;

[0051] Figure 9 It is a schematic diagram of a QKD system based on a polarization filtering system and method combined with a time domain filtering system;

[0052] Figure 10 It is a schematic diagram of a QKD system based on a polarization filtering system and method combined with a classical optical intensity attenuation method. Detailed implementation manners

[0053] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0054] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0055] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0056] Embodiment 1

[0057] The classical-quantum wavelength division multiplexing noise reduction method includes the following steps:

[0058] Before detection at the receiving end, perform polarization filtering on the demultiplexed quantum optical signal, and only allow a preset polarization state to pass through;

[0059] In the data post-processing stage, only retain the bit data in which the basis vector selection of the sender and the receiver is consistent, and the preset polarization state corresponds to the consistent basis vector.

[0060] The following is an explanation of the principle: Spontaneous Raman scattering is the inelastic scattered photons generated by the interaction between the incident classical optical signal and the optical fiber. Different from the stimulated Raman scattering effect, the polarization state of the photons generated by spontaneous Raman scattering has no obvious correlation with the polarization state of the incident classical optical signal, and there are some depolarization effects for the polarization state of the scattered photons relative to the incident photons. Therefore, to a certain extent, the polarization state of the Raman scattering noise photons is random, while the polarization state of the quantum optical signal sent by the sender is determined. Therefore, at the receiver of the QKD system, by setting a suitable polarization filtering system, only the specific photon polarization state sent by the sender is allowed to pass through, while other random polarization states are filtered out or attenuated, which can reduce the Raman scattering noise to a certain extent and improve the signal-to-noise ratio.

[0061] Taking the BB84 polarization-coded QKD system as an example, as Figure 3 shown, the polarization state of the quantum optical signal can be one of the four polarization states of 0° (H), 90° (V), 45° (P), and 135° (N), while the polarization state of the Raman scattered light generated by the interaction between the classical optical signal and the optical fiber during transmission is random. Accordingly, before detection at the QKD receiver, by setting a set of polarization filtering systems, as Figure 4 shown, only a specific polarization state is allowed to pass through at a certain moment, while other polarization states are blocked or attenuated, which can reduce a part of the Raman scattering noise from the dimension of polarization filtering. When the polarization state of the Raman scattering noise photons is exactly the same as that of the encoded quantum optical signal at this moment, the polarization filtering system has no filtering effect; when the noise photons are perpendicular to the polarization state of the encoded quantum optical signal at this moment, the noise photons are completely blocked outside the polarization filtering system.

[0062] Generally, the polarization state of the noise photons is between the above two extreme cases. Therefore, the polarization filtering system can attenuate and suppress the noise. The specific filtering process can refer to the following formula:

[0063] Eout = Ein * cosθ

[0064] where θ is the polarization state angle between the noise photons and the quantum signal light, as Figure 4 shown, Ein is the quantum optical signal with noise photons superimposed after demultiplexing. After passing through the polarization filtering system, some noise photons are filtered out and the output is Eout.

[0065] Embodiment 2

[0066] A classical-quantum wavelength division multiplexing noise reduction system based on polarization filtering, for implementing Example 1. Taking the BB84 polarization coding QKD system as an example, it includes a polarization filtering system, which randomly selects one of the four polarizers at 0° (H), 90° (V), 45° (P), and 135° (N) using an optical switch, enabling photons in a specific polarization state to pass through the polarization filtering system, while other polarization states are blocked or attenuated.

[0067] The structural composition of the above polarization filtering system is as Figure 5 shown.

[0068] During actual key distribution, the sender randomly selects one of the two groups of basis vectors (0° (H) / 90° (V) basis vector, 45° (P) / 135° (N) basis vector) for quantum optical signal polarization coding, sending four polarization states of 0° (H), 90° (V), 45° (P), and 135° (N). The polarization filtering system randomly selects one of the four polarizers at 0° (H), 90° (V), 45° (P), and 135° (N) at the position or moment when the quantum optical signal arrives, allowing the prepared quantum optical signal to pass through the polarizer, and the receiver randomly selects one of the two groups of basis vectors (0° (H) / 90° (V) basis vector, 45° (P) / 135° (N) basis vector) for polarization decoding detection to obtain the bit data corresponding to each quantum optical signal.

[0069] In the QKD data post-processing stage, only the bit data where the basis vector selections of the sender and the receiver are consistent and the polarizer selected by the polarization filtering system corresponds to the consistent basis vector (the 0° (H) polarizer and 90° (V) polarizer correspond to the 0° (H) / 90° (V) basis vector, the 45° (P) polarizer and 135° (N) polarizer correspond to the 45° (P) / 135° (N) basis vector) is retained. At this time, through the combination of polarization filtering and data post-processing, while reducing noise, the secure key generation of the QKD system is achieved.

[0070] Example 3

[0071] A classical-quantum wavelength division multiplexing noise reduction system based on polarization filtering, for implementing Example 1. Taking the BB84 polarization coding QKD system as an example, it includes a polarization filtering system, which randomly rotates a rotating polarizer to one of the four angles of 0° (H), 90° (V), 45° (P), and 135° (N), enabling photons in a specific polarization state to pass through the polarization filtering system, while other polarization states are blocked or attenuated.

[0072] The structural composition of the above polarization filtering system is as Figure 6 shown.

[0073] The sender randomly selects one of two sets of basis vectors (0°(H) / 90°(V) basis vectors, 45°(P) / 135°(N) basis vectors) to perform polarization encoding on the quantum optical signal, sending four polarization states: 0°(H), 90°(V), 45°(P), and 135°(N). The polarization filtering system randomly rotates the polarizer to one of the four angles: 0°(H), 90°(V), 45°(P), 135°(N) at the position or moment when the quantum optical signal arrives, allowing the prepared quantum optical signal to pass through the polarizer, and the receiver randomly selects one of two sets of basis vectors (0°(H) / 90°(V) basis vectors, 45°(P) / 135°(N) basis vectors) for polarization decoding detection to obtain the bit data corresponding to each quantum optical signal.

[0074] In the post-processing stage of QKD data, only the bit data where the basis vector selections of the sender and the receiver are consistent and the angle of the polarizer rotated by the polarization filtering system corresponds to the consistent basis vector (the polarizer rotated 0°(H), the polarizer rotated 90°(V) corresponds to the 0°(H) / 90°(V) basis vector, the polarizer rotated 45°(P), the polarizer rotated 135°(N) corresponds to the 45°(P) / 135°(N) basis vector) is retained. At this time, through the combination of polarization filtering and the data post-processing process, while reducing noise, the secure key generation of the QKD system is achieved.

[0075] Example 4

[0076] A classical-quantum wavelength division multiplexing noise reduction system based on polarization filtering. For a QKD system using polarization encoding, only need to set up a polarization filtering system after demultiplexing at the receiving end and before entering the decoder for decoding, and then combine the data post-processing process to achieve secure key generation of QKD.

[0077] Example 5

[0078] A QKD system, as Figure 7 shown, mainly includes a QKD sender, a wavelength division multiplexer and a demultiplexer, an optical fiber transmission channel, a polarization filtering system, a QKD receiver, a classical communication sender, and a classical communication receiver.

[0079] The classical-quantum wavelength division multiplexing noise reduction system mentioned in the above embodiments is mainly placed at the QKD receiver, as Figure 7As shown in the figure, the specific filtering process is set as follows: After the quantum optical signal passes through the wavelength division multiplexer, it is separated from the classical optical signal. Then, the quantum optical signal passes through the polarization filtering system to filter out some noise photons, and then enters the QKD receiver for decoding, and a single-photon detector is used to detect the quantum optical signal. For a polarization-encoded QKD system, under the action of the system synchronization clock, the quantum state consistent with the polarization direction (angle) of the selected (rotated) polarizer in the polarization filtering system can achieve polarization transmission, and the noise photons in other directions can achieve polarization filtering or attenuation.

[0080] Embodiment Six

[0081] A QKD system that combines the solution mentioned in the present invention with the existing frequency-domain filtering technology can achieve a higher signal-to-noise ratio of the QKD system.

[0082] A QKD system that combines traditional frequency-domain filtering (spectrum), such as Figure 8 As shown in the figure, the quantum optical signal and the classical optical signal are transmitted through the same optical fiber through the wavelength division multiplexer at the sending end. During the transmission process, the stronger classical optical signal interacts with the optical fiber to generate Raman scattering noise photons. Its polarization state is random, and a part of the Raman scattering noise photons are in the same wavelength band as the quantum optical signal. After demultiplexing, they are strung into the QKD channel. In order to reduce the influence of these noise photons on the QKD signal-to-noise ratio, first filter out a part of the noise that is inconsistent with the quantum light polarization through the polarization filtering system, and then further filter out the out-of-band noise of the quantum light through the traditional frequency-domain filtering system, which can achieve a higher QKD signal-to-noise ratio.

[0083] Other settings can be the same as those in Embodiment Five.

[0084] Embodiment Seven

[0085] A QKD system that combines polarization filtering with traditional time-domain filtering, such as Figure 9 As shown in the figure, by combining polarization filtering with the existing time-domain filtering technology, a higher signal-to-noise ratio of the QKD system can also be achieved.

[0086] The quantum optical signal and the classical optical signal are transmitted through the same optical fiber through the wavelength division multiplexer at the sending end. During the transmission process, the stronger classical optical signal interacts with the optical fiber to generate Raman scattering noise photons. Its polarization state is random, and the Raman scattering noise is uniformly distributed in time. After demultiplexing, a part of the noise photons are strung into the QKD channel. According to the time distribution characteristics of the noise photons, the time-domain filtering system can first filter out the noise outside the gate width by controlling the gate width of the single-photon detector at the receiving end, and then combine with the polarization filtering system to filter out the noise photons with inconsistent polarization. In this way, a higher QKD signal-to-noise ratio is achieved.

[0087] Other settings can be the same as those in Embodiment Five.

[0088] Example 8

[0089] A QKD system that combines polarization filtering with the traditional classical optical intensity attenuation noise reduction technology. As Figure 10 shown, the quantum optical signal and the classical optical signal are co-fiber transmitted through a wavelength division multiplexer at the transmitting end. To weaken the interaction between the classical light with stronger signal and the optical fiber and reduce the generated Raman scattering noise photons, the optical intensity of the classical light is attenuated before multiplexing. After demultiplexing and before entering the QKD receiving end, the polarization filtering system is combined to filter out the noise photons with inconsistent polarization. Through this solution, the requirement for optical intensity attenuation in the traditional optical intensity attenuation scheme can be reduced. For example, originally, to achieve classical-quantum co-fiber transmission, the classical optical intensity needed to be attenuated by 3 dB. By combining the polarization filtering technology, only 1-2 dB of classical optical intensity attenuation is required. While achieving a high QKD signal-to-noise ratio, the communication risk of the classical light is reduced, ensuring the normal operation of classical optical communication.

[0090] The above Examples 2-8 are QKD systems proposed by combining the proposed polarization filtering system alone or with several typical traditional filtering and noise reduction technologies. When actually networking, according to the actual signal-to-noise ratio requirements, it can be a combination of the above two or more filtering and noise reduction technologies, which will not be elaborated one by one here.

[0091] Those skilled in the art should understand that the embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0092] The present invention is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram can be implemented by computer program instructions, and the combination of the processes and / or blocks in the flowchart and / or block diagram can also be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate a device for realizing the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0093] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce a manufacture including an instruction means that implements the function specified in one or more of the flows Figure 1 one or more of the flows and / or boxes Figure 1 specified in one or more of the boxes.

[0094] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, whereby the instructions executed on the computer or other programmable apparatus provide steps for implementing the function specified in one or more of the flows Figure 1 one or more of the flows and / or boxes Figure 1 specified in one or more of the boxes.

[0095] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made by those skilled in the art without creative efforts within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A classical-quantum wavelength division multiplexing noise reduction method, characterized in that, It includes the following steps: Before detection at the receiving end, perform polarization filtering on the demultiplexed quantum optical signal, allowing only a preset polarization state to pass through; In the data post-processing stage, only retain the bit data where the basis vector selections of the sending end and the receiving end are consistent, and the preset polarization state corresponds to the consistent basis vector.

2. The classical-quantum wavelength division multiplexing noise reduction method according to claim 1, characterized in that the quantum After the optical signal passes through polarization filtering, its signal is: Eout = Ein * cosθ Where θ is the polarization state angle between the noise photon and the quantum signal photon, Ein is the quantum optical signal with noise photons superimposed after demultiplexing, and Eout is the signal after polarization filtering where some noise photons are filtered out.

3. A classical-quantum wavelength division multiplexing noise reduction method according to claim 1 or 2, characterized in that, It also includes performing frequency-domain / time-domain filtering on the signal after polarization filtering.

4. A classical-quantum wavelength division multiplexing noise reduction method according to claim 1 or 2, characterized in that, It also includes performing optical intensity attenuation on the classical optical signal.

5. A classical-quantum wavelength division multiplexing noise reduction system, characterized in that, It includes a polarization filtering system and a processing module provided at the receiving end, where: The polarization filtering system is used to perform polarization filtering on the demultiplexed quantum optical signal before detection at the receiving end, allowing only a preset polarization state to pass through; The processing module is used to only retain the bit data where the basis vector selections of the sending end and the receiving end are consistent, and the preset polarization state corresponds to the consistent basis vector in the data post-processing stage.

6. A classical-quantum wavelength division multiplexing noise reduction system according to claim 5, characterized in that, The polarization filtering system includes an optical switch and multiple polarizers. The polarization states of the polarizers are different, and the polarizers are connected in parallel. The optical switch is used to select the polarizer corresponding to a preset polarization state to allow the prepared quantum optical signal to pass through the polarizer.

7. A classical-quantum wavelength division multiplexing noise reduction system according to claim 5, characterized in that, The polarization filtering system includes a rotatable polarizer. The rotation angles of the polarizer are different, and the selected polarization states are different.

8. A classical-quantum wavelength division multiplexing noise reduction system according to any one of claims 5-7, characterized in that, The polarization states include four types: 0° (H), 90° (V), 45° (P), and 135° (N).

9. A classical-quantum wavelength division multiplexing noise reduction system according to claim 6, characterized in that, The processing module is used to only retain the bit data where the basis vector selections of the sending end and the receiving end are consistent and the polarizer selected by the polarization filtering system corresponds to the consistent basis vector.

10. A classical-quantum wavelength division multiplexing noise reduction system according to claim 7, characterized in that, The processing module is used to only retain the bit data where the basis vector selections of the sending end and the receiving end are consistent and the rotation angle of the polarizer rotated by the polarization filtering system corresponds to the consistent basis vector.

11. A key distribution system, characterized in that It includes a receiving end, and the receiving end includes the classical-quantum wavelength division multiplexing noise reduction system according to any one of claims 5-10 or adopts the classical-quantum wavelength division multiplexing noise reduction method according to any one of claims 1-4.

12. A key distribution system according to claim 11, characterized in that, The receiving end includes a demultiplexer, a polarization filtering system, a key distribution receiving end, and a classical communication receiving end. One end of the demultiplexer is connected to the polarization filtering system, the polarization filtering system is connected to the key distribution receiving end, and the other end of the demultiplexer is connected to the classical communication receiving end.

13. A key distribution system according to claim 12, characterized in that, The receiving end further includes a frequency-domain / time-domain filtering system, and the frequency-domain / time-domain filtering system is provided between the polarization filtering system and the key distribution receiving end.

14. A key distribution system according to claim 11, 12 or 13, characterized in that, It also includes a sending end, and the sending end includes a key distribution sending end, a classical communication sending end, and a wavelength division multiplexer. The key distribution sending end and the classical communication sending end are both connected to the wavelength division multiplexer.

15. A key distribution system according to claim 14, characterized in that, The sending end further includes an optical attenuator, and the optical attenuator is provided between the classical communication sending end and the wavelength division multiplexer.

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