A Quantum Key Distribution Ring Network without an Interferometer

Abstract

The present invention belongs to the technical field of optical secure communication, and discloses a quantum key distribution ring network without an interferometer. When quantum key distribution is carried out between the central node and any intermediate node in the network, both of them perform subcarrier signal modulation and add a random phase to generate a symmetric key. When quantum key distribution is carried out between any two intermediate nodes, the central node does not perform phase modulation, and the two intermediate nodes respectively perform subcarrier signal modulation and add 4 random phases. After signal transmission and detection are completed, the central node announces the measurement results, and then a symmetric key is generated. Compared with the prior art, the present invention can realize quantum key distribution between any two nodes in the ring without a trusted relay, only needs to perform phase modulation and optical intensity monitoring, does not need to use an interferometer, does not need to set the transmitter and receiver at the same time, and does not need polarization compensation and phase compensation, reducing resource consumption, increasing stability, and greatly reducing the deployment and operation costs.

Description

Technical Field

[0001] The present invention relates to the technical field of optical secure communication, and particularly to a quantum key distribution ring network without an interferometer. Background Art

[0002] With the development of technology and society, data and communication security have become increasingly important. Quantum key distribution can provide information-theoretic security for both communication parties and can be used to ensure the security of data transmission and communication. However, the key generation rate of current quantum key distribution systems cannot meet the growing demand for encryption rates.

[0003] In existing quantum key distribution networking solutions, quantum key distribution processes need to be carried out separately between each pair of nodes. Conventional quantum key distribution devices distinguish between the sending end and the receiving end. Therefore, multiple devices need to be deployed at each node, and most of them adopt a phase encoding scheme that requires an interferometer for encoding and decoding or a polarization encoding scheme that requires real-time polarization compensation, resulting in a relatively high networking cost and a large occupied volume. In addition, in a conventional ring network structure, direct quantum key distribution cannot be carried out between non-adjacent nodes. Instead, the nodes between them need to be used as trusted relays for secure key transmission. However, the prerequisite for a trusted relay is that the nodes are trusted, which greatly limits the actual security. Patent CN 115883089 B proposes a ring network structure, in which the same quantum key distribution device is deployed at each network node, which can serve as both the sending end and the receiving end at the same time. However, the device structure in this scheme is complex, and real-time polarization compensation and phase compensation for the channel are required, increasing the complexity of network devices and resource consumption, and still requiring a trusted relay. Summary of the Invention

[0004] In view of the above-mentioned defects in the prior art, the present invention proposes a quantum key distribution ring network without an interferometer.

[0005] The technical solution of the present invention is implemented as follows:

[0006] A quantum key distribution ring network without an interferometer includes N intermediate nodes and a central node, where N is an integer not less than 2;

[0007] Each node includes an input port and an output port;

[0008] The input ports and output ports between these N + 1 adjacent nodes are connected by optical fiber channels to form a ring network. Specifically: each pair of nodes is connected by an optical fiber channel; among them, the output port and the input port of the central node are respectively connected to the input port of intermediate node 1 and the output port of intermediate node N; the input port and the output port of intermediate node j are respectively connected to the output port of intermediate node j - 1 and the input port of intermediate node j + 1, where 2 ≤ j ≤ N - 1;

[0009] The central node is used to generate a narrow linewidth pulsed optical signal, and can perform subcarrier signal modulation on the pulsed optical signal and attenuate it to the single-photon level; and is used to filter the pulsed optical signal input to its incident port, and use single-photon detectors to detect the carrier signal and subcarrier signal generated by the filtering.

[0010] The intermediate node is used to perform carrier signal modulation on the input pulsed optical signal, and output it after attenuating it to the single-photon level.

[0011] When quantum key distribution is performed between the central node and any one of the intermediate nodes, both perform subcarrier signal modulation and add a random phase; after signal transmission and detection, operations such as basis vector comparison and post-processing are performed to generate a symmetric key.

[0012] When quantum key distribution is performed between any two intermediate nodes, the central node does not perform phase modulation, and the two intermediate nodes respectively perform subcarrier signal modulation and add random phases of 0, π / 2, π, and 3π / 2; after signal transmission and detection, the central node announces the measurement results, and then the two intermediate nodes perform operations such as basis vector comparison and post-processing to generate a symmetric key.

[0013] Preferably, the central node includes a laser LD, an amplitude modulator AM, a first phase modulator PM1, a first variable optical attenuator VOA1, a circulator CIR, an optical fiber filter OF, a first single-photon detector SPD1, and a second single-photon detector SPD2, and is used to generate a narrow linewidth continuous optical signal with a central frequency of ω.

[0014] AM is used to modulate the continuous optical signal into a pulsed optical signal.

[0015] PM1 is used to perform subcarrier signal modulation on the pulsed optical signal.

[0016] VOA1 is used to attenuate the phase-modulated pulsed optical signal to the single-photon level.

[0017] CIR is used to transmit the pulsed optical signal incident on the input port of the central node to OF, and the carrier optical signal reflected by OF.

[0018] SPD1 and SPD2 are respectively used to detect the subcarrier optical signal and carrier optical signal transmitted from OF.

[0019] Preferably, the signals for subcarrier modulation by the central node and the intermediate nodes are , where Ω is the subcarrier frequency, t is time, and it satisfies the modulation signal amplitude , and the random phases of each node satisfy .

[0020] Preferably, the intermediate node includes a phase modulation module, a second variable optical attenuator VOA2, and an optical intensity monitoring module. The phase modulation module is used for phase modulation of the signal modulated by the subcarrier. VOA2 is used to adjust the output optical intensity. The optical intensity monitoring module is used to monitor the output optical intensity in real time.

[0021] Preferably, the optical intensity monitoring module of the intermediate node includes a beam splitter BS and a photodetector PD. The input port of BS is connected to the output port of VOA2; one output port of BS is connected to PD, and the other output port outputs directly.

[0022] Preferably, the phase modulation module includes a first polarization beam splitter PBS1, a second polarization beam splitter PBS2, a second phase modulator PM2, and a third phase modulator PM3. The two output ports of PBS1 and the two input ports of PBS2 are respectively connected by a polarization maintaining fiber. The lengths of the two polarization maintaining fibers are equal, and PM2 and PM3 are respectively arranged on them.

[0023] Preferably, the phase modulation module includes a fourth phase modulator PM4 and a fifth phase modulator PM5. Both of them can work in a biaxial manner, and the output port of PM4 and the input port of PM5 are aligned with a 90° polarization rotation.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention proposes a quantum key distribution ring network without an interferometer. Without a trusted relay, quantum key distribution between any two nodes in the ring can be realized. The structure of each node is simple, only phase modulation and optical intensity monitoring are required, no interferometer is needed, no need to set a transmitting end and a receiving end at the same time, and no polarization compensation and phase compensation are required, reducing resource consumption, increasing stability, and greatly reducing the deployment and operation costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is the schematic diagram of the quantum key distribution ring network without an interferometer of the present invention;

[0027] Figure 2 is the schematic diagram of the central node of the present invention;

[0028] Figure 3 is the schematic diagram of the subcarrier signal in the frequency domain of the present invention;

[0029] Figure 4 is the schematic diagram of the intermediate node of the present invention;

[0030] Figure 5 is the schematic diagram of the first embodiment of the phase modulation module of the present invention;

[0031] Figure 6 is the schematic diagram of the second embodiment of the phase modulation module of the present invention. Detailed implementation manners

[0032] The present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0033] As Figure 1 shown, a quantum key distribution ring network without an interferometer includes N intermediate nodes and a central node, where N is an integer not less than 2;

[0034] Each node includes an input port and an output port;

[0035] The input ports and output ports between these N + 1 adjacent nodes are connected by optical fiber channels to form a ring network. Specifically: each pair of nodes is connected by optical fiber channels; among them, the output port and input port of the central node are respectively connected to the input port of intermediate node 1 and the output port of intermediate node N; the input port and output port of intermediate node j are respectively connected to the output port of intermediate node j - 1 and the input port of intermediate node j + 1, where 2 ≤ j ≤ N - 1;

[0036] The central node is used to generate a narrow linewidth pulsed optical signal, and can perform subcarrier signal modulation on the pulsed optical signal and attenuate it to the single - photon level; and is used to filter the pulsed optical signal input to its incident port, and use a single - photon detector to detect the carrier signal and subcarrier signal generated by the filtering;

[0037] The intermediate node is used to perform carrier signal modulation on the input pulsed optical signal, and output it after attenuating it to the single - photon level;

[0038] When quantum key distribution is performed between the central node and any one of the intermediate nodes, both of them perform subcarrier signal modulation and add a random phase; after signal transmission and detection, operations such as basis vector comparison and post - processing are performed to generate a symmetric key;

[0039] When quantum key distribution is performed between any two intermediate nodes, the central node does not perform phase modulation, and the two intermediate nodes respectively perform subcarrier signal modulation and add random phases of 0, π / 2, π, 3π / 2; after signal transmission and detection, the central node announces the measurement results, and then the two intermediate nodes perform operations such as basis vector comparison and post - processing to generate a symmetric key.

[0040] As Figure 2 shown, the central node includes a laser LD, an amplitude modulator AM, a first phase modulator PM1, a first variable optical attenuator VOA1, a circulator CIR, an optical fiber filter OF, a first single - photon detector SPD1, and a second single - photon detector SPD2, and is used to generate a narrow linewidth continuous optical signal with a central frequency of ω;

[0041] AM is used to modulate a continuous optical signal into a pulsed optical signal;

[0042] PM1 is used to modulate a subcarrier signal onto the pulsed optical signal;

[0043] VOA1 is used to attenuate the phase-modulated pulsed optical signal to the single-photon level;

[0044] CIR is used to transmit the pulsed optical signal incident on the input port of the central node to OF, and to transmit the carrier optical signal reflected by OF;

[0045] SPD1 and SPD2 are respectively used to detect the subcarrier optical signal and the carrier optical signal transmitted from OF.

[0046] The signals for subcarrier modulation at the central node and the intermediate nodes are , where Ω is the subcarrier frequency, t is time, and the modulation signal amplitude satisfies , and the random phase at each node satisfies .

[0047] The intermediate node includes a phase modulation module, a second variable optical attenuator VOA2, and an optical intensity monitoring module. The phase modulation module is used for phase modulation of the signal for subcarrier modulation. VOA2 is used to adjust the output optical intensity. The optical intensity monitoring module is used to monitor the output optical intensity in real time.

[0048] The optical intensity monitoring module of the intermediate node includes a beam splitter BS and a photodetector PD. The input port of BS is connected to the output port of VOA2. One output port of BS is connected to PD, and the other output port outputs directly.

[0049] The specific working process is as follows:

[0050] As Figure 2 shown, the laser LD at the central node generates a narrow-linewidth continuous optical signal with a central frequency of ω, which is modulated into a pulsed optical signal by the amplitude modulator AM.

[0051] Quantum key distribution can be carried out between the central node and any one of the intermediate nodes, and also between any two intermediate nodes. The following is a separate explanation:

[0052] (1) For quantum key distribution between the central node and any one intermediate node j,

[0053] The pulsed optical signal generated by the central node is modulated with a subcarrier signal by PM1 , where the additional random phase satisfies , and then the intensity of the subcarrier signal is attenuated to the single-photon level by VOA1, and the obtained optical signal is

[0054] ,

[0055] Its schematic diagram in the frequency domain is as shown in Figure 3 , including a carrier signal with a central frequency of ω and two sub-carrier signals with frequencies of ω±Ω. Among them, the carrier signal serves as a strong reference signal, and the intensity of the sub-carrier signal is of the order of single photons and serves as a quantum state.

[0056] After the quantum state passes through the optical fiber channel and other intermediate nodes between the output port of the central node and the input port of the intermediate node j, it enters the input port of the intermediate node j.

[0057] As shown in Figure 4 , at the intermediate node j, the quantum state first undergoes sub-carrier signal modulation through a phase modulation module , where the additional random phase satisfies . Subsequently, it passes through VOA2 without attenuation, and after passing through the optical fiber channel and other intermediate nodes between the output port of the intermediate node j and the input port of the central node, it reaches the input port of the central node, and the quantum state becomes

[0058] ,

[0059] where η is the total loss of the channel and the losses of each intermediate node. It can be seen that the spectrum of the quantum state contains a carrier signal and a sub-carrier signal.

[0060] When , constructive interference occurs. After the quantum state passes through the CIR and is filtered by the OF, the sub-carrier signal enters SPD1, and the carrier signal enters SPD2. At this time, SPD1 responds and a bit 1 is obtained; when , destructive interference occurs, the sub-carrier signal is 0. After the quantum state passes through the CIR and is filtered by the OF, no sub-carrier signal enters SPD1, and the carrier signal enters SPD2. At this time, SPD1 does not respond and a bit 0 is obtained.

[0061] After both parties complete signal transmission and detection, operations such as basis vector comparison and post-processing are performed to generate a symmetric key. At the intermediate node, the quantum state is split into a part through the BS and enters the photodetector PD for detection, and the optical intensity passing through the intermediate node is monitored in real time, and it can be monitored whether there is a Trojan horse light injected by an eavesdropper.

[0062] Although the polarization of the quantum state will change with factors such as the environment after passing through the optical fiber channel, the central node only needs to perform filtering and detection operations, which have nothing to do with the polarization state. Therefore, polarization compensation is not required.

[0063] (2) Quantum key distribution is carried out between the intermediate node i and the intermediate node j.

[0064] As shown in Figure 2As shown, the pulsed optical signal generated by the central node passes through PM1 and VOA1 without phase modulation and attenuation, and exits from the output port of the central node, enters the optical fiber channel, and reaches the intermediate node i after passing through several optical fiber channels and intermediate nodes.

[0065] As Figure 4 shown, at the intermediate node i, the pulsed optical signal undergoes subcarrier signal modulation through the phase modulation module , where the additional random phase satisfies , and then the subcarrier signal intensity is attenuated to the single-photon level through VOA2, and the obtained optical signal is

[0066] ,

[0067] Its schematic diagram in the frequency domain is as Figure 3 shown, including a carrier signal with a central frequency of ω and two subcarrier signals with frequencies of ω±Ω. Among them, the carrier signal serves as a strong reference signal, and the subcarrier signal intensity is at the single-photon level and serves as a quantum state.

[0068] After the quantum state passes through the optical fiber channel and several intermediate nodes, it enters the input port of the intermediate node j. The quantum state first undergoes subcarrier signal modulation through the phase modulation module , where the additional random phase satisfies , and then passes through VOA2 without attenuation. After passing through the optical fiber channel and other intermediate nodes, it reaches the input port of the central node, and the quantum state becomes

[0069] ,

[0070] where η is the total loss of the channel and the losses of each intermediate node. It can be seen that the spectrum of the quantum state contains a carrier signal and a subcarrier signal.

[0071] When , constructive interference occurs. After the quantum state passes through the CIR and is filtered by the OF, the subcarrier signal enters the SPD1, and the carrier signal enters the SPD2. At this time, the SPD1 responds and obtains bit 1; when , destructive interference occurs, the subcarrier signal is 0, and after the quantum state passes through the CIR and is filtered by the OF, no subcarrier signal enters the SPD1, and the carrier signal enters the SPD2. At this time, the SPD1 does not respond and obtains bit 0.

[0072] After both parties complete signal transmission and detection, they perform operations such as basis vector comparison and post-processing to generate a symmetric key. At the intermediate node, a part of the quantum state is split off by the BS and enters the photodetector PD for detection, and the optical intensity passing through the intermediate node is monitored in real time, and it can be monitored whether there is a Trojan horse light injected by an eavesdropper.

[0073] Although the polarization of the quantum state changes with factors such as the environment after passing through the optical fiber channel, the central node only needs to perform filtering and detection operations, which are independent of the polarization state. Therefore, polarization compensation is not required.

[0074] As Figure 5 shown, Embodiment 1 of the phase modulation module:

[0075] The phase modulation module includes a first polarization beam splitter PBS1, a second polarization beam splitter PBS2, a second phase modulator PM2, and a third phase modulator PM3. The two output ports of PBS1 and the two input ports of PBS2 are respectively connected by a polarization-maintaining optical fiber. The lengths of the two polarization-maintaining optical fibers are equal, and PM2 and PM3 are respectively arranged on them.

[0076] The specific working process is as follows:

[0077] A quantum state with arbitrary polarization enters the input port of PBS1 and is divided into a horizontal polarization component and a vertical polarization component. The two components respectively pass through the corresponding PM3 and PM2, and at the same time, subcarrier signal modulation is performed. . Since the two components pass through polarization-maintaining optical fibers of equal length and the same phase modulation, the same phase change is generated. Therefore, the polarization state remains unchanged after polarization combination at PBS2, and polarization-independent subcarrier phase modulation can be achieved.

[0078] As Figure 6 shown, Embodiment 2 of the phase modulation module:

[0079] The phase modulation module includes a fourth phase modulator PM4 and a fifth phase modulator PM5. Both can work in a biaxial manner, and the output port of PM4 and the input port of PM5 are aligned with a 90° polarization rotation.

[0080] The specific working process is as follows:

[0081] A quantum state with arbitrary polarization enters the input port of PM4. Its horizontal polarization component and vertical polarization component respectively enter PM4 and become TE polarization mode and TM polarization mode. After the two components perform subcarrier signal modulation, due to the birefringence effect, the additional phases of the two polarization modes are different. Therefore, the obtained subcarrier signals can be respectively written as and . Subsequently, after passing through a 90° polarization rotation and entering PM5, after the same subcarrier modulation, the phases of the two polarization components can be respectively written as and . It can be seen that the two polarization components are modulated by the same phase. Let , and polarization-independent subcarrier phase modulation can be achieved.

[0082] Based on each embodiment of the present invention, the present invention proposes a quantum key distribution ring network without an interferometer. Without a trusted relay, quantum key distribution between any two nodes within the ring can be achieved. The structure of each node is simple, only requiring phase modulation and optical intensity monitoring, without the use of an interferometer, without simultaneously setting a transmitter and a receiver, and without polarization compensation and phase compensation, reducing resource consumption, increasing stability, and greatly reducing the deployment and operation costs.

Claims

1. A quantum key distribution ring network without an interferometer, characterized in that, It includes N intermediate nodes and a central node, where N is an integer not less than 2; Each node includes an input port and an output port; The input ports and output ports of these N + 1 adjacent nodes are connected by optical fiber channels to form a ring network; The central node is used to generate a narrow linewidth pulsed optical signal, and can modulate the pulsed optical signal with a subcarrier signal and attenuate it to the single - photon level. The modulated pulsed optical signal is output from the output port of the central node to the intermediate nodes; and is used to filter the pulsed optical signal input to its incident port, and use single - photon detectors to detect the carrier signal and subcarrier signal generated by the filtering; The intermediate node is used to modulate the input pulsed optical signal with a carrier signal and output it after attenuating it to the single - photon level; When quantum key distribution is carried out between the central node and any one intermediate node, both perform subcarrier signal modulation and add a random phase; after signal transmission and detection, basis vector comparison and post - processing operations are carried out to generate a symmetric key; When quantum key distribution is carried out between any two intermediate nodes, the central node does not perform phase modulation. The two intermediate nodes respectively perform subcarrier signal modulation and add random phases of 0, π / 2, π, 3π / 2; after signal transmission and detection, the central node announces the measurement results, and then the two intermediate nodes perform basis vector comparison and post - processing operations to generate a symmetric key.

2. The quantum key distribution ring network without an interferometer according to claim 1, characterized in that, The central node includes a laser LD, an amplitude modulator AM, a first phase modulator PM1, a first variable optical attenuator VOA1, a circulator CIR, an optical fiber filter OF, a first single - photon detector SPD1, and a second single - photon detector SPD2, and is used to generate a narrow linewidth continuous optical signal with a central frequency of ω; AM is used to modulate the continuous optical signal into a pulsed optical signal; PM1 is used to modulate the pulsed optical signal with a subcarrier signal; VOA1 is used to attenuate the phase - modulated pulsed optical signal to the single - photon level; CIR is used to transmit the pulsed optical signal incident on the input port of the central node to OF, and transmit the carrier optical signal reflected by OF to SPD2; SPD1 and SPD2 are respectively used to detect the subcarrier optical signal and carrier optical signal transmitted by OF.

3. The quantum key distribution ring network without an interferometer according to claim 1, characterized in that The signals modulated by the central node and intermediate nodes with subcarriers are , where Ω is the subcarrier frequency, t is time, and the modulation signal amplitude satisfies . The random phases of each node satisfy .

4. The quantum key distribution ring network without an interferometer according to claim 2, wherein The intermediate node includes a phase modulation module, a second variable optical attenuator VOA2, and an optical intensity monitoring module connected in sequence. The phase modulation module is used for phase modulation of the signal for subcarrier modulation. VOA2 is used to adjust the output optical intensity, and the optical intensity monitoring module is used to monitor the output optical intensity in real time.

5. The quantum key distribution ring network without an interferometer according to claim 4, characterized in that The optical intensity monitoring module of the intermediate node includes a beam splitter BS and a photodetector PD. The input port of BS is connected to the output port of VOA2; one output port of BS is connected to PD, and the other output port is directly output.

6. The quantum key distribution ring network without an interferometer according to claim 4, characterized in that, The phase modulation module includes a first polarization beam splitter PBS1, a second polarization beam splitter PBS2, a second phase modulator PM2, and a third phase modulator PM3. The two output ports of PBS1 and the two input ports of PBS2 are respectively connected by a polarization - maintaining optical fiber. The lengths of the two polarization - maintaining optical fibers are equal, and PM2 and PM3 are respectively arranged on them.

7. The quantum key distribution ring network without an interferometer according to claim 4, characterized in that The phase modulation module includes a fourth phase modulator PM4 and a fifth phase modulator PM5, both of which can operate in two axes, and the output port of PM4 is aligned with the input port of PM5 with a 90° polarization rotation.

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