Quantum key distribution ring network

Abstract

The invention belongs to the technical field of optical security communication, and discloses a quantum key distribution ring network, which comprises a ring network formed by a central node and N intermediate nodes, when quantum key distribution is carried out between the central node and any intermediate node, random phase modulation is carried out on the central node and any intermediate node to generate symmetric keys; when quantum key distribution is carried out between any two intermediate nodes, random phase modulation is carried out on the two intermediate nodes, the central node does not carry out phase modulation, and after signal transmission and detection are completed, the central node publishes a measurement result and generates a symmetric key. Compared with the prior art, the quantum key distribution between any two nodes in the ring can be realized without a trusted relay, the intermediate node is simple in structure, only phase modulation and light intensity monitoring are needed, a sending end and a receiving end do not need to be arranged at the same time, polarization compensation and phase compensation are not needed, resource consumption is reduced, stability is improved, and the method is suitable for popularization and application. And the deployment and operation cost is greatly reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of optical security communications, and in particular to a quantum key distribution ring network. Background Art

[0002] With the development of science and technology and society, data and communication security are becoming more and more important. Quantum key distribution can provide information-theoretic security for both parties in communication and can be used to ensure the security of data transmission and communication. However, the key generation rate of the current quantum key distribution system cannot meet the growing encryption rate requirements.

[0003] In the existing quantum key distribution networking scheme, the nodes need to perform the quantum key distribution process separately in pairs. Conventional quantum key distribution devices distinguish between the sender and the receiver, so multiple devices need to be deployed at each node, resulting in high networking costs and large occupied volume. In addition, in the conventional ring network structure, quantum key distribution cannot be performed directly between non-adjacent nodes, but the nodes between the two need to be used as trusted relays for secure key transfer. However, the premise of trusted relays 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 be used as a sender and a receiver at the same time. However, the device structure in this scheme is complex, and the channel needs to be compensated for polarization and phase in real time, which increases the complexity and resource consumption of network equipment, and still requires trusted relays. Summary of the invention

[0004] In view of the above defects in the prior art, the present invention proposes a quantum key distribution ring network.

[0005] The technical solution of the present invention is achieved in this way: A quantum key distribution ring network, comprising N intermediate nodes and a central node, where N is an integer not less than 2; Each node contains an input port and an output port; The input ports and output ports of these N+1 adjacent nodes are connected through optical fiber channels to form a ring network. Specifically, each node is connected to each other through optical fiber channels; the output port and input port of the central node are respectively connected to the input port of the intermediate node 1 and the output port of the intermediate node N; the input port and output port of the intermediate node j are respectively connected to the output port of the intermediate node j-1 and the input port of the intermediate node j+1, 2≤j≤N-1; The central node is used to generate a double pulse signal through a laser and an unequal-arm interferometer, and modulate the phase difference between the two sub-pulses in the double pulse signal to 0, π / 2, π or 3π / 2 and then output it to the optical fiber channel; and to make the input double pulse signal enter the unequal-arm interferometer in reverse to interfere, and use a single-photon detector to detect the generated two-way interference results; The intermediate node is used to modulate the phase difference between two sub-pulses in the input double pulse signal to 0, π / 2, π or 3π / 2, and output it after attenuating it to the single photon level; When quantum key distribution is performed between the central node and any intermediate node, the two nodes perform random phase modulation respectively, and after completing signal transmission and detection, basis vector comparison and post-processing operations are performed to generate a symmetric key. When quantum key distribution is performed between any two intermediate nodes, the two perform random phase modulation respectively, and the central node does not perform phase modulation. After completing 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.

[0006] Preferably, the central node comprises a polarization processing module for performing polarization randomization and polarization equalization processing on the input double pulses so that the horizontal polarization component thereof enters the unequal-arm interferometer in the reverse direction.

[0007] Preferably, the intermediate node adopts a polarization-independent phase modulation module to implement a phase modulation function.

[0008] Preferably, the intermediate node further includes a second adjustable attenuator VOA2 and a light intensity monitoring module, the former being used to adjust the output light intensity and the latter being used to monitor the output light intensity in real time.

[0009] Preferably, the light intensity monitoring module of the intermediate node includes a third beam splitter BS3 and a photodetector PD, the input port of BS3 is connected to the output port of VOA2; one output port of BS3 is connected to PD, and the other output port outputs directly.

[0010] Preferably, the central node includes a laser LD, an optical intensity modulator IM, a first circulator CIR1, a first single photon detector SPD1, a second single photon detector SPD2, a first beam splitter BS1, a second beam splitter BS2, a first phase modulator PM1, a first adjustable attenuator VOA1, an optical isolator ISO and a polarization processing module. LD is used to generate optical pulse signals; IM is used to modulate the light intensity of optical pulse signals to generate signal states or decoy states; The two output ports of BS1 and the two input ports of BS2 are connected through optical fibers of unequal lengths to form an unequal-arm interferometer, which is used to generate two sub-pulses emitted from one output port of BS2 from an intensity-modulated optical pulse signal; the two sub-pulses emitted from the other output port of BS2 are isolated by ISO; PM1 is used to randomly modulate the phase difference between the two sub-pulses to be one of 0, π / 2, π, and 3π / 2; VOA1 is used to adjust the output light intensity of the central node; CIR1 is used to transmit the light pulse after light intensity modulation to an input port of BS1, and to transmit the interference result emitted from an input port of BS1 to SPD1; SPD1 and SPD2 are respectively used to detect the interference results emitted from the two input ports of BS1.

[0011] Preferably, the polarization processing module comprises a depolarizer and a polarizer, wherein the depolarizer is used to passively randomize the polarization state of the input optical signal; and the polarizer is used to pass the optical signal of the horizontal polarization component.

[0012] Preferably, the polarization-independent phase modulation module includes a second circulator CIR2, a first polarization beam splitter PBS1, a Faraday rotator FR and a second phase modulator PM2, the second port of CIR2 is connected to the input port of PBS1; the two ports of PM2 are respectively connected to the two output ports of PBS1 through two equal-length polarization-maintaining fibers F1 and F2, forming a first Sagnac ring; wherein, F1 is provided with a FR with a polarization rotation angle of 90°.

[0013] Preferably, the polarization-independent phase modulation module includes a third circulator CIR3, a second polarization beam splitter PBS2, a Faraday mirror FM and a third phase modulator PM3, the second port of CIR3 is connected to an input port of PBS2; an output port of PBS2 is connected to FM through a polarization-maintaining fiber F3; two ports of PM3 are respectively connected to another output port and another input port of PBS2 through a polarization-maintaining fiber F4 and a polarization-maintaining fiber F5, to form a second Sagnac ring; wherein F4=2F3+F5.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The present invention proposes a quantum key distribution ring network, which can realize quantum key distribution between any two nodes in the ring without a trusted relay. The intermediate node has a simple structure and only needs to perform phase modulation and light intensity monitoring. There is no need to set up a transmitting end and a receiving end at the same time, and no polarization compensation and phase compensation are required, which reduces resource consumption, increases stability, and greatly reduces deployment and operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic diagram of the quantum key distribution ring network of the present invention; Figure 2 It is the principle diagram of the central node of the present invention; Figure 3 is a schematic diagram of an intermediate node of the present invention; Figure 4 It is a schematic diagram of the first embodiment of the polarization-independent phase modulation module of the present invention; Figure 5 This is a schematic diagram of the second embodiment of the polarization-independent phase modulation module of the present invention. DETAILED DESCRIPTION

[0016] The present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0017] like Figure 1 As shown, a quantum key distribution ring network includes N intermediate nodes and one central node, where N is an integer not less than 2; Each node contains an input port and an output port; The input ports and output ports of these N+1 adjacent nodes are connected through optical fiber channels to form a ring network. Specifically, each node is connected to each other through optical fiber channels; the output port and input port of the central node are respectively connected to the input port of the intermediate node 1 and the output port of the intermediate node N; the input port and output port of the intermediate node j are respectively connected to the output port of the intermediate node j-1 and the input port of the intermediate node j+1, 2≤j≤N-1; The central node is used to generate a double pulse signal through a laser and an unequal-arm interferometer, and modulate the phase difference between the two sub-pulses in the double pulse signal to 0, π / 2, π or 3π / 2 and then output it to the optical fiber channel; and to make the input double pulse signal enter the unequal-arm interferometer in reverse to interfere, and use a single-photon detector to detect the generated two-way interference results; The intermediate node is used to modulate the phase difference between two sub-pulses in the input double pulse signal to 0, π / 2, π or 3π / 2, and output it after attenuating it to the single photon level; When quantum key distribution is performed between the central node and any intermediate node, the two nodes perform random phase modulation respectively, and after completing signal transmission and detection, basis vector comparison and post-processing operations are performed to generate a symmetric key. When quantum key distribution is performed between any two intermediate nodes, the two perform random phase modulation respectively, and the central node does not perform phase modulation. After completing 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.

[0018] The central node includes a polarization processing module, which is used for performing polarization randomization and polarization equalization processing on the input double pulses, so that the horizontal polarization component thereof enters the unequal-arm interferometer in the reverse direction.

[0019] The intermediate node uses a polarization-independent phase modulation module to achieve phase modulation function.

[0020] The intermediate node also includes a second adjustable attenuator VOA2 and a light intensity monitoring module, the former is used to adjust the output light intensity, and the latter is used to monitor the output light intensity in real time.

[0021] The light intensity monitoring module of the intermediate node includes a third beam splitter BS3 and a photodetector PD. The input port of BS3 is connected to the output port of VOA2; one output port of BS3 is connected to PD, and the other output port is directly output.

[0022] The central node includes a laser LD, an optical intensity modulator IM, a first circulator CIR1, a first single photon detector SPD1, a second single photon detector SPD2, a first beam splitter BS1, a second beam splitter BS2, a first phase modulator PM1, a first adjustable attenuator VOA1, an optical isolator ISO and a polarization processing module. LD is used to generate optical pulse signals; IM is used to modulate the light intensity of optical pulse signals to generate signal states or decoy states; The two output ports of BS1 and the two input ports of BS2 are connected through optical fibers of unequal lengths to form an unequal-arm interferometer, which is used to generate two sub-pulses emitted from one output port of BS2 from an intensity-modulated optical pulse signal; the two sub-pulses emitted from the other output port of BS2 are isolated by ISO; PM1 is used to randomly modulate the phase difference between the two sub-pulses to be one of 0, π / 2, π, and 3π / 2; VOA1 is used to adjust the output light intensity of the central node; CIR1 is used to transmit the light pulse after light intensity modulation to an input port of BS1, and to transmit the interference result emitted from an input port of BS1 to SPD1; SPD1 and SPD2 are respectively used to detect the interference results emitted from the two input ports of BS1.

[0023] The specific working process is as follows: like Figure 2As shown, the laser LD of the central node generates an optical pulse signal, which is modulated into a signal state or a decoy state by IM and then enters the unequal-arm interferometer composed of BS1 and BS2 through CIR1 to generate two dual-pulse signals. One dual-pulse signal is emitted from an output port of BS2, and is randomly phase-modulated by PM1 and attenuated to a single-photon level by VOA1, or directly passes through PM1 and VOA1 without phase modulation and attenuation, and finally is emitted from the output port of the central node; the other dual pulse is emitted from another output port of BS2, is isolated by ISO, and is emitted from the input port of the central node without passing through the polarization output module, so it cannot enter the optical fiber channel and will not affect the quantum key distribution process.

[0024] The central node can distribute quantum keys with any intermediate node, and any two intermediate nodes can also distribute quantum keys. The following are explained separately: (1) Quantum key distribution is performed between the central node and any intermediate node j. The dual pulse signal generated by the central node is randomly phase-modulated by PM1, and VOA1 attenuates the light intensity to the single-photon level, obtaining four phase-encoded quantum states. , in, The two sub-pulse temporal states randomly modulated by PM1 and There are 4 phase differences between them.

[0025] After passing 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, the quantum state enters the input port of the intermediate node j.

[0026] like Figure 3 As shown, the quantum state is firstly modulated by a polarization-independent phase modulation module to the time state Random Phase Modulation , then passes through VOA2 without attenuation, and after passing through the fiber channel and other intermediate nodes between the output port of 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 , After passing through the optical fiber channel, the polarization of the quantum state will change with environmental factors. After entering the input port of the central node, the polarization of the quantum state is first randomized by the polarization processing module, and then a horizontally polarized quantum state is generated after polarization, and then enters the unequal-arm interferometer in the reverse direction through the ISO. and The components of the unequal-arm interferometer reach the two output ports of BS1 at the same time through the long arm and short arm of the unequal-arm interferometer. The two interfere on BS1, generating two interference results emitted from the two input ports of BS1 respectively. , This process is the standard process of the phase-coded BB84 protocol. After completing signal transmission and detection, both parties perform basis vector comparison and post-processing operations to generate a symmetric key. At the intermediate node, a portion of the quantum state passes through BS3 and enters the photodetector PD for detection. The light intensity passing through the intermediate node is monitored in real time to monitor whether there is an eavesdropper injecting Trojan light.

[0027] (2) Quantum key distribution is performed between intermediate nodes i and j. like Figure 2 As shown, the double pulse signal generated by the central node is randomly phase-modulated by PM1, and VOA1 is not phase-modulated and not attenuated, and then emitted from the output port of the central node and enters the optical fiber channel.

[0028] The double pulse signal reaches the intermediate node i after passing through several optical fiber channels and intermediate nodes. Figure 3 As shown, the quantum state first passes through the polarization-independent phase modulation module to adjust its time state. Modulate the random phase, then pass VOA2 to attenuate the light intensity to the single photon level, and obtain four phase-encoded quantum states , in, The two sub-pulse temporal states randomly modulated by PM1 and There are 4 phase differences between them.

[0029] After passing through the optical fiber channel and several intermediate nodes, the quantum state enters the input port of the intermediate node j, and the time state is first adjusted by the polarization-independent phase modulation module. Random Phase Modulation , then passes through VOA2 without attenuation, passes through the optical fiber channel and other intermediate nodes, and reaches the input port of the central node. The quantum state becomes , After passing through the optical fiber channel, the polarization of the quantum state will change with environmental factors. After entering the input port of the central node, the polarization of the quantum state is first randomized by the polarization processing module, and then a horizontally polarized quantum state is generated after polarization, and then enters the unequal-arm interferometer in the reverse direction through the ISO. and The components of the unequal-arm interferometer reach the two output ports of BS1 at the same time through the long arm and short arm of the unequal-arm interferometer. The two interfere on BS1, generating two interference results emitted from the two input ports of BS1 respectively. , This process is the standard process of the phase-coded BB84 protocol. After completing signal transmission and detection, both parties perform basis vector comparison and post-processing operations to generate a symmetric key. At the intermediate node, a portion of the quantum state passes through BS3 and enters the photodetector PD for detection. The light intensity passing through the intermediate node is monitored in real time to monitor whether there is an eavesdropper injecting Trojan light.

[0030] like Figure 4 As shown, the first embodiment of the polarization-independent phase modulation module: The polarization-independent phase modulation module includes a second circulator CIR2, a first polarization beam splitter PBS1, a Faraday rotator FR and a second phase modulator PM2. The second port of CIR2 is connected to the input port of PBS1; the two ports of PM2 are respectively connected to the two output ports of PBS1 through two equal-length polarization-maintaining fibers F1 and F2, forming a first Sagnac ring; wherein F1 is provided with a FR with a polarization rotation angle of 90°.

[0031] The specific working process is as follows: The quantum state of arbitrary polarization enters the input port of PBS1 through CIR2 and is divided into a horizontal polarization component and a vertical polarization component. The horizontal polarization component enters the first Sagnac loop and propagates in a counterclockwise direction, passing through PM2 and FR in turn, and is modulated by a phase φ. The vertical polarization component enters the first Sagnac loop and propagates in a clockwise direction, passing through FR and PM2 in turn. Since the lengths of polarization-maintaining fibers F1 and F2 are equal, the vertical polarization component is also modulated by a phase φ. The two polarization components return to PBS1 at the same time for polarization beam combining. Since both have passed through polarization-maintaining fibers F1 and F2, the phases modulated by PM2 are the same, and the phases between the two polarization components are consistent. Due to the optical rotation effect of FR, the polarization is rotated 90° after polarization beam combining compared to the incident phase, and is finally output through CIR2 with a phase modulated to φ. Therefore, polarization-independent phase modulation can be achieved.

[0032] like Figure 5 As shown, the second embodiment of the polarization-independent phase modulation module: The polarization-independent phase modulation module includes a third circulator CIR3, a second polarization beam splitter PBS2, a Faraday mirror FM and a third phase modulator PM3. The second port of CIR3 is connected to an input port of PBS2; an output port of PBS2 is connected to FM through a polarization-maintaining fiber F3; two ports of PM3 are connected to another output port and another input port of PBS2 through a polarization-maintaining fiber F4 and a polarization-maintaining fiber F5, respectively, to form a second Sagnac ring; wherein F4=2F3+F5.

[0033] The specific working process is as follows: The quantum state of arbitrary polarization enters an input port of PBS2 through CIR2 and is divided into a horizontal polarization component and a vertical polarization component. The horizontal polarization component is transmitted from PBS2 to FM, and is reflected and polarized by 90°. It is reflected again when it reaches PBS2, enters the second Sagnac loop and propagates in the counterclockwise direction, and is modulated by phase φ through PM3. The vertical polarization component is reflected by PBS2 and enters the second Sagnac loop and propagates in the clockwise direction. It is phase modulated by PM3 and reaches PBS2 and is reflected. It is reflected again when it reaches FM, and finally transmitted from PBS2. Since the length relationship between polarization-maintaining fiber F3, polarization-maintaining fiber F4, and polarization-maintaining fiber F5 satisfies F4=2F3+F5, the vertical polarization component is also modulated by phase φ. The two polarization components return to PBS2 at the same time for polarization beam combining. Since the polarization-maintaining fiber paths they pass through are the same and the phases modulated by PM3 are the same, the phases between the two polarization components are consistent. After polarization beam combining, the polarization is rotated by 90° compared to the incident phase, and finally output through CIR3 with the phase modulated to φ. Therefore, polarization-independent phase modulation can be achieved.

[0034] It can be seen from the various embodiments of the present invention that the present invention proposes a quantum key distribution ring network, which can realize quantum key distribution between any two nodes in the ring without a trusted relay. The intermediate node has a simple structure and only needs to perform phase modulation and light intensity monitoring. There is no need to set up the transmitting end and the receiving end at the same time, and there is no need for polarization compensation and phase compensation, which reduces resource consumption, increases stability, and greatly reduces deployment and operating costs.

Claims

1. A quantum key distribution ring network, characterized in that: including a central node and N intermediate nodes each having an input port and an output port, where N is an integer not less than 2; The input ports and output ports of these N+1 adjacent nodes are connected via optical fiber channels to form a ring network; The central node is used to generate a double pulse signal through a laser and an unequal-arm interferometer, and modulate the phase difference between the two sub-pulses in the double pulse signal to 0, π / 2, π or 3π / 2 and then output it to the optical fiber channel; and to make the input double pulse signal enter the unequal-arm interferometer in reverse to interfere, and use a single-photon detector to detect the generated two-way interference results; The intermediate node is used to modulate the phase difference between two sub-pulses in the input double pulse signal to 0, π / 2, π or 3π / 2, and output it after attenuating it to the single photon level; When quantum key distribution is performed between the central node and any intermediate node, the two nodes perform random phase modulation respectively, and after completing signal transmission and detection, basis vector comparison and post-processing operations are performed to generate a symmetric key. When quantum key distribution is performed between any two intermediate nodes, the two perform random phase modulation respectively, and the central node does not perform phase modulation. After completing 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 according to claim 1, characterized in that: The central node includes a polarization processing module for performing polarization randomization and polarization processing on the input double pulses so that the horizontal polarization components thereof enter the unequal-arm interferometer in the reverse direction.

3. The quantum key distribution ring network according to claim 1, characterized in that: The intermediate node uses a polarization-independent phase modulation module to achieve phase modulation function.

4. The quantum key distribution ring network according to claim 3, characterized in that: The intermediate node also includes a second adjustable attenuator VOA2 and a light intensity monitoring module, the former is used to adjust the output light intensity, and the latter is used to monitor the output light intensity in real time.

5. The quantum key distribution ring network according to claim 4, characterized in that: The light intensity monitoring module of the intermediate node includes a third beam splitter BS3 and a photodetector PD. The input port of BS3 is connected to the output port of VOA2; one output port of BS3 is connected to PD, and the other output port is directly output.

6. The quantum key distribution ring network according to claim 1, 2, 3 or 4, characterized in that: The central node includes a laser LD, an optical intensity modulator IM, a first circulator CIR1, a first single photon detector SPD1, a second single photon detector SPD2, a first beam splitter BS1, a second beam splitter BS2, a first phase modulator PM1, a first adjustable attenuator VOA1, an optical isolator ISO and a polarization processing module. LD is used to generate optical pulse signals; IM is used to modulate the light intensity of optical pulse signals to generate signal states or decoy states; The two output ports of BS1 and the two input ports of BS2 are connected through optical fibers of unequal lengths to form an unequal-arm interferometer, which is used to generate two sub-pulses emitted from one output port of BS2 from an intensity-modulated optical pulse signal; the two sub-pulses emitted from the other output port of BS2 are isolated by ISO; PM1 is used to randomly modulate the phase difference between the two sub-pulses to be one of 0, π / 2, π, and 3π / 2; VOA1 is used to adjust the output light intensity of the central node; CIR1 is used to transmit the light pulse after light intensity modulation to an input port of BS1, and to transmit the interference result emitted from an input port of BS1 to SPD1; SPD1 and SPD2 are respectively used to detect the interference results emitted from the two input ports of BS1.

7. The quantum key distribution ring network according to claim 6, characterized in that: The polarization processing module includes a depolarizer and a polarizer. The depolarizer is used to passively randomize the polarization state of the input optical signal; the polarizer is used to pass the optical signal of the horizontal polarization component.

8. The quantum key distribution ring network according to claim 3, 4 or 5, characterized in that: The polarization-independent phase modulation module includes a second circulator CIR2, a first polarization beam splitter PBS1, a Faraday rotator FR and a second phase modulator PM2. The second port of CIR2 is connected to the input port of PBS1; the two ports of PM2 are respectively connected to the two output ports of PBS1 through two equal-length polarization-maintaining fibers F1 and F2, forming a first Sagnac ring; wherein F1 is provided with a FR with a polarization rotation angle of 90°.

9. The quantum key distribution ring network according to claim 2, 3 or 4, characterized in that: The polarization-independent phase modulation module includes a third circulator CIR3, a second polarization beam splitter PBS2, a Faraday mirror FM and a third phase modulator PM3. The second port of CIR3 is connected to an input port of PBS2; an output port of PBS2 is connected to FM through a polarization-maintaining fiber F3; two ports of PM3 are connected to another output port and another input port of PBS2 through a polarization-maintaining fiber F4 and a polarization-maintaining fiber F5, respectively, to form a second Sagnac ring; wherein F4=2F3+F5.

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