Module division multiplexing double-field quantum key distribution system

Abstract

The utility model discloses a mode division multiplexing double-field quantum key distribution system, which comprises a Charlie end and a plurality of user ends, the Charlie end and the plurality of user ends are sequentially connected end to end to form a Sagnac ring structure; the Charlie end comprises a light source LD, a first beam splitter BS1, a second beam splitter BS2, a first mode converter MC1, a second mode converter MC2, a first optical switch OA1, a second optical switch OA2, a mode multiplexer MUX, a circulator CIR, a first single-photon detector PD1 and a second single-photon detector PD2; and the user side comprises a mode demultiplexer DEMUX, an optical signal modulation module and a Faraday mirror FM which are connected in sequence. The utility model discloses a mode division multiplexing double-field quantum key distribution system, which adopts a mode converter and an optical switch to respectively realize mode division multiplexing and time division multiplexing in a Sagnac ring structure, thereby greatly improving the communication capacity.

Description

Technical Field

[0001] The utility model relates to the field of quantum key distribution devices, and particularly to a dual-field quantum key distribution system based on mode division multiplexing. Background Art

[0002] Quantum key distribution (QKD) is the most mature quantum cryptography technology. The first quantum key distribution protocol, the BB84 protocol, has absolute security in theory because it follows the principles of quantum mechanics. However, due to the imperfections of actual devices, various possible loopholes exist. For example, there is no ideal single-photon source. In practice, a strongly attenuated laser is often used to simulate a single-photon source, but such a light source always has a component where a pulse contains multiple photons and is vulnerable to PNS attacks.

[0003] To solve the problem of PNS attacks, researchers proposed the decoy state scheme. Later, due to the imperfections of the detection end devices, various loopholes would occur, and then the measurement device-independent protocol was proposed to completely close the attacks against the detection end. However, these protocols cannot avoid the problem of photon transmission loss, and there is a limit of the key generation rate-distance.

[0004] The core idea of the dual-field quantum key distribution protocol is single-photon interference, and it retains the advantages of the measurement device-independent protocol. Therefore, its transmission loss is reduced by the square root, and finally the key generation rate can break through the key generation rate-distance limit. Although the existing dual-field quantum key distribution technology can achieve a longer transmission distance, the communication capacity is not large enough, and the device structure is complex, and the instruments are expensive, resulting in a high cost in realizing large-scale network deployment. Summary of the Utility Model

[0005] The utility model aims to solve the problem that the communication capacity of the existing dual-field quantum key distribution technology is not large enough, and proposes a dual-field quantum key distribution system based on mode division multiplexing.

[0006] To achieve the above object, the technical solution adopted by the utility model is as follows:

[0007] A dual-field quantum key distribution system based on mode division multiplexing includes a Charlie end and multiple user ends; the Charlie end and the multiple user ends are connected end to end in sequence to form a Sagnac ring structure;

[0008] The Charlie end includes a light source LD, a first beam splitter BS1, a second beam splitter BS2, a first mode converter MC1, a second mode converter MC2, a first optical switch OA1, a second optical switch OA2, a mode multiplexer MUX, a circulator CIR, a first single-photon detector PD1, and a second single-photon detector PD2;

[0009] The client includes a mode demultiplexer DEMUX, an optical signal modulation module, and a Faraday mirror FM that are connected in sequence;

[0010] The output end of the light source LD is respectively connected to the input end of the first mode converter MC1 and the input end of the second mode converter MC2 through the first beam splitter BS1. The output end of the first mode converter MC1 is connected to the input end of the first optical switch OA1, and the output end of the second mode converter MC2 is connected to the input end of the second optical switch OA2. The output ends of the first optical switch OA1 and the second optical switch OA2 are respectively connected to the input end of the mode multiplexer MUX. The output end of the mode multiplexer MUX is connected to the first port of the circulator CIR. The second port of the circulator CIR is connected to the first port of the second beam splitter BS2. The second port of the second beam splitter BS2 is connected to the counterclockwise transmission link of the Sagnac loop, and the third port of the second beam splitter BS2 is connected to the clockwise transmission link of the Sagnac loop. The input end of the first single-photon detector PD1 is connected to the third port of the circulator CIR, and the input end of the second single-photon detector PD2 is connected to the fourth port of the second beam splitter BS2.

[0011] In the above solution, a dual-field light source is fabricated by splitting a single light source into two through the Sagnac loop structure. Since the optical signal passes through the same path, it has good phase and polarization stability, greatly reducing the system complexity. At the same time, mode division multiplexing and time division multiplexing are respectively implemented by using mode converters and optical switches in the Sagnac loop structure, greatly improving the communication capacity.

[0012] Preferably, the optical signal modulation module includes an intensity modulator IM and a phase modulator PM;

[0013] The intensity modulator IM is used to modulate the intensity of the optical signal;

[0014] The phase modulator PM is used to modulate the phase of the optical signal.

[0015] Preferably, the Charlie end further includes a variable optical attenuator VOA;

[0016] The output end of the light source LD is connected to the input end of the first beam splitter BS1 through the variable optical attenuator VOA.

[0017] Preferably, the types of the client include an Alice client and a Bob client.

[0018] Preferably, the Alice client is arranged near the Charlie end in the counterclockwise transmission link of the Sagnac loop, and the Bob client is arranged near the Charlie end in the clockwise transmission link of the Sagnac loop.

[0019] Preferably, there is at least one Alice client and at least one Bob client respectively.

[0020] Preferably, the number of clients is even.

[0021] Preferably, the number of Alice clients is equal to the number of Bob clients.

[0022] Preferably, both the first beam splitter BS1 and the second beam splitter BS2 are 50:50 beam splitters.

[0023] Preferably, the light source LD is a multi-wavelength fiber laser.

[0024] The beneficial technical effects of the present utility model:

[0025] The present utility model provides a mode-division multiplexing dual-field quantum key distribution system. By splitting a light source into two through a Sagnac loop structure to produce a dual-field light source, since the optical signals pass through the same path, it has good phase and polarization stability, greatly reducing the system complexity; at the same time, a mode converter and an optical switch are respectively used in the Sagnac loop structure to achieve mode-division multiplexing and time-division multiplexing, greatly improving the communication capacity. Description of the Drawings

[0026] Figure 1 is a schematic diagram of the overall structure of the present utility model;

[0027] Figure 2 is a schematic diagram of the module connection between the Charlie end and the clients in the present utility model;

[0028] Figure 3 is a schematic diagram of the quantum key distribution process of the present utility model. Detailed Embodiments

[0029] In order to make the purpose, technical solutions and advantages of the present utility model clearer, the following further details the present utility model with reference to embodiments, but the scope of protection required by the present utility model is not limited to the following specific embodiments.

[0030] Embodiment 1

[0031] As Figure 1-2 shown, a mode-division multiplexing dual-field quantum key distribution system includes a Charlie end and multiple clients; the Charlie end and the multiple clients are connected end to end in sequence to form a Sagnac loop structure;

[0032] The Charlie end includes a light source LD, a first beam splitter BS1, a second beam splitter BS2, a first mode converter MC1, a second mode converter MC2, a first optical switch OA1, a second optical switch OA2, a mode multiplexer MUX, a circulator CIR, a first single-photon detector PD1, and a second single-photon detector PD2;

[0033] The user end includes a mode demultiplexer DEMUX, an optical signal modulation module, and a Faraday mirror FM connected in sequence;

[0034] The output end of the light source LD is connected to the input ends of the first mode converter MC1 and the second mode converter MC2 through the first beam splitter BS1 respectively. The output end of the first mode converter MC1 is connected to the input end of the first optical switch OA1, and the output end of the second mode converter MC2 is connected to the input end of the second optical switch OA2. The output ends of the first optical switch OA1 and the second optical switch OA2 are respectively connected to the input end of the mode multiplexer MUX. The output end of the mode multiplexer MUX is connected to the first port of the circulator CIR. The second port of the circulator CIR is connected to the first port of the second beam splitter BS2. The second port of the second beam splitter BS2 is connected to the counterclockwise transmission link of the Sagnac loop, and the third port of the second beam splitter BS2 is connected to the clockwise transmission link of the Sagnac loop. The input end of the first single-photon detector PD1 is connected to the third port of the circulator CIR, and the input end of the second single-photon detector PD2 is connected to the fourth port of the second beam splitter BS2.

[0035] In the specific implementation process, a dual-field light source is fabricated by splitting a single light source into two through the Sagnac loop structure. Since the optical signals pass through the same path, it has good phase and polarization stability, greatly reducing the system complexity. At the same time, mode converters and optical switches are adopted in the Sagnac loop structure to achieve mode division multiplexing and time division multiplexing respectively, greatly improving the communication capacity.

[0036] More specifically, the optical signal modulation module includes an intensity modulator IM and a phase modulator PM;

[0037] The intensity modulator IM is used to modulate the intensity of the optical signal;

[0038] The phase modulator PM is used to modulate the phase of the optical signal.

[0039] More specifically, the Charlie end further includes a variable optical attenuator VOA;

[0040] The output end of the light source LD is connected to the input end of the first beam splitter BS1 through the variable optical attenuator VOA.

[0041] More specifically, the types of the user terminals include an Alice user terminal and a Bob user terminal.

[0042] In the specific implementation process, there are n Alice user terminals, namely Alice 1, Alice 2,..., Alice n; and there are n Bob user terminals, namely Bob 1, Bob 2,..., Bob n.

[0043] More specifically, the Alice user terminal is arranged near the Charlie end in the counterclockwise transmission link of the Sagnac loop, and the Bob user terminal is arranged near the Charlie end in the clockwise transmission link of the Sagnac loop.

[0044] More specifically, there is at least one Alice user terminal and at least one Bob user terminal respectively.

[0045] More specifically, the number of the user terminals is even.

[0046] More specifically, the number of the Alice user terminals is equal to the number of the Bob user terminals.

[0047] More specifically, both the first beam splitter BS1 and the second beam splitter BS2 are 50:50 beam splitters.

[0048] More specifically, the light source LD is a multi-wavelength fiber laser.

[0049] In the specific implementation process, the multi-wavelength fiber laser emits lasers of multiple wavelengths, which are attenuated to appropriate powers by a variable optical attenuator VOA. Subsequently, the optical signals enter the first mode converter MC1 and the second mode converter MC2 respectively through the first beam splitter BS1 and are converted into different modes (for example, the first mode converter MC1 converts the optical signal into the L01 mode, and the second mode converter MC2 converts the optical signal into the L11 mode). The first optical switch OA1 and the second optical switch OA2 select to let the optical signal pass through in different time slices through time-division multiplexing.

[0050] The optical signal enters the few-mode fiber through the mode multiplexer MUX, and then is divided into two beams of light with the same intensity through the circulator CIR and the second beam splitter BS2. One beam enters the counterclockwise transmission link of the Sagnac loop, and the other beam enters the clockwise transmission link of the Sagnac loop. Among them, the optical signal entering the counterclockwise transmission link of the Sagnac loop is not modulated when passing through the Alice user terminal and is modulated when passing through the Bob user terminal; the optical signal entering the clockwise transmission link of the Sagnac loop is not modulated when passing through the Bob user terminal and is modulated when passing through the Alice user terminal.

[0051] The client selects the optical signal of the corresponding mode through the mode demultiplexer DEMUX, and modulates the intensity and phase of the optical signal of the corresponding mode through the intensity modulator IM and the phase modulator PM respectively. Different users select different modes of optical signals. That is, the Alice client and the Bob client that select the same optical signal mode are a pair of users (both communication parties). When the communicating client selects the X basis, the intensity modulator IM modulates the optical signal to the v intensity, and the phase modulator PM randomly modulates the optical signal to the 0 or π phase; when the communicating client selects the Z basis, the intensity modulator IM randomly modulates the optical signal to the μ intensity or the pulse in the vacuum state, and the phase modulator PM randomly modulates the optical signal to any phase between 0 and 2π. This embodiment adopts the SNS-TF-QKD protocol, which can immunize against attacks on detectors and has a high coding rate in long-distance communication.

[0052] The Faraday mirror FM reflects the modulated optical signal and makes the polarization state of the reflected optical signal perpendicular to that of the incident optical signal. The optical signals in the clockwise transmission link and the optical signals in the counterclockwise transmission link finally return to the second beam splitter BS2 at Charlie's end for single-photon interference, and the interference results are detected by the first single-photon detector PD1 and the second single-photon detector PD2.

[0053] Embodiment 2

[0054] As Figure 3 shown, the quantum key distribution process of a mode-division multiplexed dual-field quantum key distribution system is as follows:

[0055] S1: Generate an optical signal at Charlie's end and perform the first beam splitting on the optical signal;

[0056] S2: Convert the two optical signals obtained by the first beam splitting into different modes respectively and transmit them in a time-division multiplexing manner;

[0057] S3: Perform the second beam splitting on the optical signal of each mode, and let one beam enter the counterclockwise transmission link of the Sagnac loop and the other beam enter the clockwise transmission link of the Sagnac loop;

[0058] S4: Modulate the optical signal entering the counterclockwise transmission link through the Bob client;

[0059] Modulate the optical signal entering the clockwise transmission link through the Alice client;

[0060] In actual implementation, the user terminal selects the optical signal of the corresponding mode through the mode demultiplexer DEMUX, and modulates the intensity and phase of the optical signal of the corresponding mode through the intensity modulator IM and the phase modulator PM respectively. Different users select different modes of optical signals, that is, the Alice user terminal and the Bob user terminal that select the same optical signal mode are a pair of users (both communication parties).

[0061] S5: Send the modulated optical signal back to the Charlie terminal for single-photon interference to obtain an interference result;

[0062] S6: The two user terminals performing communication perform basis comparison and calculate the bit error rate;

[0063] S7: Determine whether the bit error rate is lower than a preset threshold;

[0064] If so, perform error correction and privacy amplification to obtain the final quantum key;

[0065] If not, discard all information bits of this transmission and return to step S1.

[0066] According to the disclosure and teachings of the above specification, those skilled in the art to which the present utility model pertains can also make changes and modifications to the above embodiments. Therefore, the present utility model is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the utility model should also fall within the protection scope of the claims of the present utility model. In addition, although some specific terms are used in this specification, these terms are only for convenience and do not constitute any limitation to the present utility model.

Claims

1. A mode-division multiplexed dual-field quantum key distribution system, characterized in that It includes a Charlie terminal and multiple user terminals; the Charlie terminal and the multiple user terminals are connected end to end in sequence to form a Sagnac loop structure; The Charlie terminal includes a light source LD, a first beam splitter BS1, a second beam splitter BS2, a first mode converter MC1, a second mode converter MC2, a first optical switch OA1, a second optical switch OA2, a mode multiplexer MUX, a circulator CIR, a first single-photon detector PD1, and a second single-photon detector PD2; The user terminal includes a mode demultiplexer DEMUX, an optical signal modulation module, and a Faraday mirror FM connected in sequence; The output end of the light source LD is connected to the input ends of the first mode converter MC1 and the second mode converter MC2 respectively through the first beam splitter BS1. The output end of the first mode converter MC1 is connected to the input end of the first optical switch OA1. The output end of the second mode converter MC2 is connected to the input end of the second optical switch OA2. The output ends of the first optical switch OA1 and the second optical switch OA2 are respectively connected to the input end of the mode multiplexer MUX. The output end of the mode multiplexer MUX is connected to the first port of the circulator CIR. The second port of the circulator CIR is connected to the first port of the second beam splitter BS2. The second port of the second beam splitter BS2 is connected to the counterclockwise transmission link of the Sagnac loop, and the third port of the second beam splitter BS2 is connected to the clockwise transmission link of the Sagnac loop. The input end of the first single-photon detector PD1 is connected to the third port of the circulator CIR, and the input end of the second single-photon detector PD2 is connected to the fourth port of the second beam splitter BS2.

2. The dual-field quantum key distribution system for mode division multiplexing according to claim 1, wherein The optical signal modulation module includes an intensity modulator IM and a phase modulator PM; The intensity modulator IM is used to modulate the intensity of the optical signal; The phase modulator PM is used to modulate the phase of the optical signal.

3. A mode-division multiplexed dual-field quantum key distribution system according to claim 1, wherein The Charlie terminal also includes a variable optical attenuator VOA; The output end of the light source LD is connected to the input end of the first beam splitter BS1 through the variable optical attenuator VOA.

4. A mode-division multiplexing dual-field quantum key distribution system according to claim 1, characterized in that, The types of the user terminals include an Alice user terminal and a Bob user terminal.

5. A mode-division multiplexed dual-field quantum key distribution system according to claim 4, characterized in that, The Alice user terminal is arranged close to the Charlie terminal in the counterclockwise transmission link of the Sagnac loop, and the Bob user terminal is arranged close to the Charlie terminal in the clockwise transmission link of the Sagnac loop.

6. A mode-division multiplexing dual-field quantum key distribution system according to claim 4, characterized in that There is at least one Alice user terminal and at least one Bob user terminal respectively.

7. A mode-division multiplexing dual-field quantum key distribution system according to claim 4, characterized in that The number of user terminals is even.

8. A mode-division multiplexed dual-field quantum key distribution system according to claim 7, characterized in that, The number of Alice user terminals is equal to the number of Bob user terminals.

9. A mode-division multiplexed dual-field quantum key distribution system according to claim 1, wherein Both the first beam splitter BS1 and the second beam splitter BS2 are 50:50 beam splitters.

10. A mode-division multiplexing dual-field quantum key distribution system according to claim 1, characterized in that, The light source LD is a multi-wavelength fiber laser.

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