Polarization-mode multiplexing quantum key distribution system

Abstract

The utility model discloses a polarization-mode multiplexing quantum key distribution system, which comprises a Bob end and a plurality of Alice ends, the Bob end comprises a laser, a mode conversion module, a mode multiplexer, a mode demultiplexer, a first polarization beam splitter, a second polarization beam splitter, a first beam splitter, a second beam splitter and a Bob phase modulator. The utility model discloses a polarization-mode multiplexing quantum key distribution system, which increases the communication capacity of a QKD (quantum key distribution) system by adopting polarization-mode multiplexing, improves the high security of polarization coding and the high efficiency of mode multiplexing, and can remarkably improve the key generation rate and the transmission distance.

Description

TECHNICAL FIELD

[0001] The utility model relates to quantum information and optical communication technical field, concretely relates to a polarization -mode multiplexed quantum key distribution system. BACKGROUND

[0002] As the next generation of secure communication technology, quantum key distribution (QKD) is actively expanding from point-to-point systems to network architectures. In a QKD network system, it is important to increase the number of users for secure communication conveniently.

[0003] Common multiplexing techniques include time multiplexing and wavelength division multiplexing, which improve the channel utilization of the QKD network system in the time dimension and the frequency dimension, respectively. However, these methods, while increasing the communication rate, also face challenges such as increased system complexity, rising costs, and greater sensitivity to channel conditions, making it difficult to effectively increase the communication capacity.

[0004] Currently, although the wavelength division multiplexing (WDM) architecture can successfully expand the number of channels in the QKD network system without significant system loss, considering factors such as the range of communication wavelengths and crosstalk noise, increasing the number of channels has limitations, resulting in insufficient communication capacity of the QKD network system. SUMMARY

[0005] The utility model discloses in order to solve the current multiplexing technique in QKD network system effectively increases the problem of communication capacity, and proposes a polarization -mode multiplexed quantum key distribution system.

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

[0007] A polarization -mode multiplexed quantum key distribution system, comprising a Bob end and a plurality of Alice ends;

[0008] The Bob end includes a laser, a mode conversion module, a mode multiplexer, a mode demultiplexer, a first polarization beam splitter, a second polarization beam splitter, a first beam splitter, a second beam splitter, and a Bob phase modulator.

[0009] The output end of the laser is connected with the input end of the mode conversion module, the output end of the mode conversion module is connected with the input end of the mode multiplexer, the output end of the mode multiplexer is connected with the input end of the first polarization beam splitter, the output end of the first polarization beam splitter is connected with the input end of the first beam splitter and the input end of the second beam splitter respectively, the first beam splitter is connected with the second polarization beam splitter and the Bob phase modulator bidirectionally respectively, the second beam splitter is connected with the second polarization beam splitter and the Bob phase modulator bidirectionally respectively, the Bob phase modulator is connected with the second polarization beam splitter bidirectionally, and the second polarization beam splitter is connected with a plurality of Alice ends bidirectionally through the mode demultiplexer.

[0010] In the above scheme, the communication capacity of the QKD system is increased by using polarization-mode multiplexing, and the high security of polarization encoding and the high efficiency of mode multiplexing can be combined, so that the unconditional security of quantum key distribution can be maintained, and the key generation rate and transmission distance can be significantly improved.

[0011] Preferably, the mode conversion module comprises a first optical switch, a second optical switch, a first mode converter and a second mode converter.

[0012] The output end of the laser is connected with the input end of the first optical switch and the input end of the second optical switch respectively, the output end of the first optical switch is connected with the input end of the first mode converter, the output end of the second optical switch is connected with the input end of the second mode converter, and the output end of the first mode converter and the output end of the second mode converter are connected with the input end of the mode multiplexer respectively.

[0013] Preferably, the Bob end further comprises a third beam splitter.

[0014] The output end of the laser is connected with the input end of the first optical switch and the input end of the second optical switch through the third beam splitter.

[0015] Preferably, the third beam splitter is a 50:50 beam splitter.

[0016] Preferably, the Alice end comprises a variable optical attenuator, an intensity modulator, an Alice phase modulator and a Faraday mirror connected in sequence.

[0017] The second polarization beam splitter is connected with the variable optical attenuator through the mode demultiplexer.

[0018] Preferably, the Alice end further comprises a fourth beam splitter and an Alice single-photon detector.

[0019] The mode demultiplexer is connected with the variable optical attenuator through the fourth beam splitter, and the output end of the fourth beam splitter is connected with the input end of the Alice single-photon detector.

[0020] Preferably, the fourth beam splitter is a 99:1 beam splitter.

[0021] Preferably, the Bob end further comprises a first single-photon detector, a second single-photon detector, a third single-photon detector and a fourth single-photon detector.

[0022] The input end of the first single-photon detector and the input end of the second single-photon detector are respectively connected with the output end of the first beam splitter; the input end of the third single-photon detector and the input end of the fourth single-photon detector are respectively connected with the output end of the second beam splitter.

[0023] Preferably, the Bob end further comprises a first circulator and a second circulator.

[0024] The first port of the first circulator is connected with one output end of the first polarization beam splitter, the second port of the first circulator is connected with one port of the first beam splitter, and the third port of the first circulator is connected with the input end of the second single-photon detector.

[0025] The first port of the second circulator is connected with the other output end of the first polarization beam splitter, the second port of the second circulator is connected with one port of the second beam splitter, and the third port of the second circulator is connected with the input end of the fourth single-photon detector.

[0026] Preferably, the first beam splitter and the second beam splitter are both 50:50 beam splitters.

[0027] The present application has the beneficial technical effects that:

[0028] The present application provides a polarization-mode multiplexing quantum key distribution system, which increases the communication capacity of the QKD system by adopting polarization-mode multiplexing, improves the unconditional security of quantum key distribution by utilizing the high security of polarization coding and the high efficiency of mode multiplexing, and significantly improves the key generation rate and transmission distance. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is a schematic diagram of the overall structure of the present application.

[0030] Figure 2 It is a schematic diagram of the structure of the Alice end and the mode demultiplexer in the present application.

[0031] Wherein, LD: laser; OA1: first optical switch; OA2: second optical switch; MC1: first mode converter; MC2: second mode converter; MUX: mode multiplexer; DUMUX: mode demultiplexer; PBS1: first polarization beamsplitter; PBS2: second polarization beamsplitter; BS1: first beamsplitter; BS2: second beamsplitter; PM1: Bob phase modulator; BS3: third beamsplitter; PD1: first single-photon detector; PD2: second single-photon detector; PD3: third single-photon detector; PD4: fourth single-photon detector; CIR1: first circulator; CIR2: second circulator; VOA: variable optical attenuator; IM: intensity modulator; PM2: Alice phase modulator; FM: Faraday mirror; BS4: fourth beamsplitter; PD5: Alice single-photon detector. Detailed Implementation

[0032] To make the objectives, technical solutions and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the embodiments. However, the scope of protection of this utility model is not limited to the specific embodiments described below.

[0033] Example 1

[0034] like Figure 1 As shown, a polarization-mode multiplexing quantum key distribution system includes a Bob terminal and multiple Alice terminals (Alice1, Alice2, ..., AliceN);

[0035] The Bob terminal includes a laser LD, a mode conversion module, a mode multiplexer MUX, a mode demultiplexer DUMUX, a first polarization beam splitter PBS1, a second polarization beam splitter PBS2, a first beam splitter BS1, a second beam splitter BS2, and a Bob phase modulator PM1.

[0036] The output of the laser LD is connected to the input of the mode conversion module. The output of the mode conversion module is connected to the input of the mode multiplexer MUX. The output of the mode multiplexer MUX is connected to the input of the first polarization beamsplitter PBS1. The output of the first polarization beamsplitter PBS1 is connected to the input of the first beamsplitter BS1 and the input of the second beamsplitter BS2. The first beamsplitter BS1 is bidirectionally connected to the second polarization beamsplitter PBS2 and the Bob phase modulator PM1. The second beamsplitter BS2 is bidirectionally connected to the second polarization beamsplitter PBS2 and the Bob phase modulator PM1. The Bob phase modulator PM1 is bidirectionally connected to the second polarization beamsplitter PBS2. The second polarization beamsplitter PBS2 is bidirectionally connected to multiple Alice terminals through the mode demultiplexer DUMUX.

[0037] In the implementation process, the communication capacity of the QKD system is increased by using polarization-mode multiplexing, and the high security of polarization encoding and the high efficiency of mode multiplexing can be combined, so that the unconditional security of quantum key distribution can be maintained, and the key generation rate and transmission distance can be significantly improved.

[0038] Embodiment 2

[0039] A polarization-mode multiplexed quantum key distribution system includes a Bob end and multiple Alice ends (Alice1, Alice2,..., AliceN);

[0040] The Bob end includes a laser LD, a mode conversion module, a mode multiplexer MUX, a mode demultiplexer DUMUX, a first polarization beam splitter PBS1, a second polarization beam splitter PBS2, a first beam splitter BS1, a second beam splitter BS2, and a Bob phase modulator PM1.

[0041] The output end of the laser LD is connected with the input end of the mode conversion module, the output end of the mode conversion module is connected with the input end of the mode multiplexer MUX, the output end of the mode multiplexer MUX is connected with the input end of the first polarization beam splitter PBS1, the output end of the first polarization beam splitter PBS1 is connected with the input end of the first beam splitter BS1 and the input end of the second beam splitter BS2 respectively, the first beam splitter BS1 is bidirectionally connected with the second polarization beam splitter PBS2 and the Bob phase modulator PM1 respectively, the second beam splitter BS2 is bidirectionally connected with the second polarization beam splitter PBS2 and the Bob phase modulator PM1 respectively, the Bob phase modulator PM1 is bidirectionally connected with the second polarization beam splitter PBS2, and the second polarization beam splitter PBS2 is bidirectionally connected with the multiple Alice ends through the mode demultiplexer DUMUX.

[0042] More specifically, the mode conversion module includes a first optical switch OA1, a second optical switch OA2, a first mode converter MC1, and a second mode converter MC2.

[0043] The output end of the laser LD is connected with the input end of the first optical switch OA1 and the input end of the second optical switch OA2 respectively, the output end of the first optical switch OA1 is connected with the input end of the first mode converter MC1, the output end of the second optical switch OA2 is connected with the input end of the second mode converter MC2, and the output end of the first mode converter MC1 and the output end of the second mode converter MC2 are connected with the input end of the mode multiplexer MUX respectively.

[0044] More specifically, the Bob end further includes a third beam splitter BS3.

[0045] The output end of the laser LD is connected with the input end of the first optical switch OA1 and the input end of the second optical switch OA2 respectively through a third beam splitter BS3.

[0046] More specifically, the third beam splitter BS3 is a 50:50 beam splitter.

[0047] More specifically, as shown in the figure, the Alice end comprises a variable optical attenuator VOA, an intensity modulator IM, an Alice phase modulator PM2 and a Faraday mirror FM connected in sequence. Figure 2

[0048] The second polarization beam splitter PBS2 is connected with the variable optical attenuator VOA through a mode demultiplexer DUMUX.

[0049] More specifically, the Alice end further comprises a fourth beam splitter BS4 and an Alice single-photon detector PD5.

[0050] The mode demultiplexer DUMUX is connected with the variable optical attenuator VOA through the fourth beam splitter BS4, and the output end of the fourth beam splitter BS4 is connected with the input end of the Alice single-photon detector PD5.

[0051] More specifically, the fourth beam splitter BS4 is a 99:1 beam splitter.

[0052] More specifically, the Bob end further comprises a first single-photon detector PD1, a second single-photon detector PD2, a third single-photon detector PD3 and a fourth single-photon detector PD4.

[0053] The input end of the first single-photon detector PD1 and the input end of the second single-photon detector PD2 are connected with the output end of the first beam splitter BS1 respectively; the input end of the third single-photon detector PD3 and the input end of the fourth single-photon detector PD4 are connected with the output end of the second beam splitter BS2 respectively.

[0054] More specifically, the Bob end further comprises a first circulator CIR1 and a second circulator CIR2.

[0055] The first port of the first circulator CIR1 is connected with one of the output ends of the first polarization beam splitter PBS1, the second port of the first circulator CIR1 is connected with one of the ports of the first beam splitter BS1, and the third port of the first circulator CIR1 is connected with the input end of the second single-photon detector PD2.

[0056] ​The first port of the second circulator CIR2 is connected with another output end of the first polarization beam splitter PBS1, the second port of the second circulator CIR2 is connected with one port of the second beam splitter BS2, and the third port of the second circulator CIR2 is connected with the input end of the fourth single-photon detector PD4.

[0057] More specifically, the first beam splitter BS1 and the second beam splitter BS2 are both 50:50 beam splitters.

[0058] In the specific implementation, the laser LD emits a pulse signal, the pulse signal is split into two beams of equal intensity signal light by the third beam splitter BS3, the two beams of signal light pass through the first optical switch OA1 and the second optical switch OA2 respectively, and then pass through the first mode converter MC1 and the second mode converter MC2 respectively to convert into different modes, and are multiplexed in a few-mode fiber by the mode multiplexer MUX;

[0059] Then the signal light is split into horizontally polarized light and vertically polarized light by the first polarization multiplexer, wherein:

[0060] The horizontally polarized light is transmitted to the first circulator CIR1, and then split into two beams of equal intensity signal light by the first beam splitter BS1, one of which is directly transmitted to the second polarization beam splitter PBS2, and the other is transmitted to the second polarization beam splitter PBS2 after passing through the Bob phase modulator PM1;

[0061] The vertically polarized light is transmitted to the second circulator CIR2, and then split into two beams of equal intensity signal light by the second beam splitter BS2, one of which is directly transmitted to the second polarization beam splitter PBS2, and the other is transmitted to the second polarization beam splitter PBS2 after passing through the Bob phase modulator PM1;

[0062] Then the signal light output by the second polarization beam splitter PBS2 is transmitted to different Alice ends by the mode demultiplexer DUMUX;

[0063] In the Alice end, one end of the fourth beam splitter BS4 with a proportion of 1 is connected with the input end of the Alice single-photon detector PD5, and through the fourth beam splitter BS4, a small part of the light signal is transmitted to the Alice single-photon detector PD5 for monitoring the light signal; one end of the fourth beam splitter BS4 with a proportion of 99 is connected with the variable optical attenuator VOA, so that most of the light signal is transmitted to the variable optical attenuator VOA, and then passes through the intensity modulator IM and the Alice phase modulator PM2 for intensity and phase modulation (in this embodiment, the intensity and phase modulation of the light signal adopts the BB84 protocol), and finally is reflected back to the second polarization beam splitter PBS2 of the Bob end by the Faraday mirror FM;

[0064] The originally horizontally polarized light becomes vertically polarized light after passing through the Faraday mirror FM, half of the light is transmitted through the Bob phase modulator PM1 to be phase modulated, and the other half is directly transmitted to the second beam splitter BS2, and finally the two beams of light interfere at the second beam splitter BS2, and the interference result is detected by the third single-photon detector PD3 and the fourth single-photon detector PD4;

[0065] The originally vertically polarized light becomes horizontally polarized light after passing through the Faraday mirror FM, half of the light is transmitted through the Bob phase modulator PM1 to be phase modulated, and the other half is directly transmitted to the first beam splitter BS1, and finally the two beams of light interfere at the first beam splitter BS1, and the interference result is detected by the first single-photon detector PD1 and the second single-photon detector PD2.

[0066] The complete quantum key distribution process is as follows:

[0067] Step one: the light signal emitted by the laser LD is divided into two beams of light with the same intensity, and is converted into different modes for multiplexing;

[0068] Step two: the light signal passes through the polarization beam splitter and is divided into horizontally polarized light signals and vertically polarized light signals, which enter different M-Z interferometers (composed of beam splitters, phase modulators and polarization beam splitters) respectively, and then are demultiplexed and transmitted to different Alice ends (Alice1, Alice2,..., AliceN);

[0069] Step three: the Alice end modulates the light signal in intensity and phase, and transmits the modulated signal back to the Bob end;

[0070] Step four: the Bob end modulates the signal through the M-Z interferometer and performs interference detection;

[0071] Step five: the bit error rate is calculated, if the bit error rate exceeds the threshold, the communication is discarded; if the bit error rate is within the threshold, the post-processing process is performed to extract the final key.

[0072] According to the disclosure and teaching of the above description, those skilled in the art of the present application can also make changes and modifications to the above embodiments. Therefore, the present application is not limited to the specific embodiments disclosed and described above, and some modifications and changes of the present application should fall within the protection scope of the claims of the present application. In addition, although some specific terms are used in the present specification, these terms are only for convenience and do not constitute any limitation on the present application.

Claims

1. A polarization-mode multiplexed quantum key distribution system, characterized by, The Bob end and the plurality of Alice ends are connected by a quantum channel. The Bob end comprises a laser, a mode conversion module, a mode multiplexer, a mode demultiplexer, a first polarization beam splitter, a second polarization beam splitter, a first beam splitter, a second beam splitter and a Bob phase modulator. The output end of the laser is connected with the input end of the mode conversion module, the output end of the mode conversion module is connected with the input end of the mode multiplexer, the output end of the mode multiplexer is connected with the input end of the first polarization beam splitter, the output end of the first polarization beam splitter is connected with the input end of the first beam splitter and the input end of the second beam splitter respectively, the first beam splitter is connected with the second polarization beam splitter and the Bob phase modulator bi-directionally respectively, the second beam splitter is connected with the second polarization beam splitter and the Bob phase modulator bi-directionally respectively, the Bob phase modulator is connected with the second polarization beam splitter bi-directionally, and the second polarization beam splitter is connected with the plurality of Alice ends bi-directionally through the mode demultiplexer.

2. The polarization-mode-coupled quantum key distribution system according to claim 1, wherein, The mode conversion module comprises a first optical switch, a second optical switch, a first mode converter and a second mode converter. The output end of the laser is connected with the input end of the first optical switch and the input end of the second optical switch respectively, the output end of the first optical switch is connected with the input end of the first mode converter, the output end of the second optical switch is connected with the input end of the second mode converter, and the output end of the first mode converter and the output end of the second mode converter are connected with the input end of the mode multiplexer respectively.

3. The polarization-mode-coupled quantum key distribution system according to claim 2, wherein, The Bob end further comprises a third beam splitter. The output end of the laser is connected with the input end of the first optical switch and the input end of the second optical switch through the third beam splitter.

4. The polarization-mode-coupled quantum key distribution system according to claim 3, wherein, The third beam splitter is a 50:50 beam splitter.

5. The polarization-mode-coupled quantum key distribution system according to claim 1, wherein, The Alice end comprises a variable optical attenuator, an intensity modulator, an Alice phase modulator and a Faraday mirror connected in sequence. The second polarization beam splitter is connected with the variable optical attenuator through the mode demultiplexer.

6. The polarization-mode-coupled quantum key distribution system according to claim 5, wherein, The Alice end further comprises a fourth beam splitter and an Alice single-photon detector. The mode demultiplexer is connected with the variable optical attenuator through the fourth beam splitter, and the output end of the fourth beam splitter is connected with the input end of the Alice single-photon detector.

7. The polarization-mode-coupled quantum key distribution system according to claim 6, wherein, The fourth beam splitter is a 99:1 beam splitter.

8. The polarization-mode-coupled quantum key distribution system according to claim 1, wherein, The Bob end further comprises a first single-photon detector, a second single-photon detector, a third single-photon detector and a fourth single-photon detector. The input end of the first single-photon detector and the input end of the second single-photon detector are connected with the output end of the first beam splitter respectively, and the input end of the third single-photon detector and the input end of the fourth single-photon detector are connected with the output end of the second beam splitter respectively.

9. The polarization-mode-coupled quantum key distribution system according to claim 8, wherein, The Bob end further comprises a first circulator and a second circulator. The first port of the first circulator is connected with one of the output ends of the first polarization beam splitter, the second port of the first circulator is connected with one of the ports of the first beam splitter, and the third port of the first circulator is connected with the input end of the second single-photon detector. The first port of the second circulator is connected with another output end of the first polarization beam splitter, the second port of the second circulator is connected with one port of the second beam splitter, and the third port of the second circulator is connected with the input end of the fourth single-photon detector.

10. The polarization-mode-coupled quantum key distribution system according to claim 1, wherein, The first beam splitter and the second beam splitter are both 50:50 beam splitters.

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