Quantum key distribution network based on space division multiplexing

Abstract

The invention provides a quantum key distribution network based on space division multiplexing. Physical links of the network are based on star topology. Each user in the network comprises a transmitting end, and quantum state preparation is carried out according to a double-field quantum key distribution protocol. A transmitting end divides an optical signal into a quantum signal and a strong phase reference signal, and the two paths of signals are coupled to a multi-core optical fiber for transmission through a multi-core fan-in module. A user sends a signal to an untrusted network node through a multi-core optical fiber based on the space division multiplexing technology. The network node integrates a plurality of quantum signal measurement modules and a plurality of reference signal measurement modules, and can realize simultaneous key distribution of multiple pairs of users. The network aims to optimize the implementation of a double-field quantum key distribution network, provides a space division multiplexing-based network scheme, and can improve the transmission capacity, network performance and the like of a quantum channel while realizing phase reference. According to the invention, an alternative scheme is provided for the quantum key distribution network, and the practical process of quantum key distribution is promoted.

Description

Technical Field

[0001] The present invention belongs to the field of quantum communication, and in particular relates to a quantum key distribution network based on space division multiplexing. Background Art

[0002] Quantum key distribution (QKD) allows two users to share a secure symmetric key. Its security is based on the principles of quantum mechanics and rigorous mathematical proofs. Quantum communication based on QKD is developing rapidly and is on the road to practical application. Security is the biggest advantage of QKD, but the deviation between real devices and theoretical models brings security issues to actual systems. Among them, the measurement device-independent QKD protocol eliminates the side channel vulnerability of the detection end and has been widely verified in long-distance and field tests. Recently, the Twin-field quantum key distribution (TF-QKD) protocol has been proposed. This type of protocol breaks the point-to-point relay-free security coding rate limit and has the characteristics of being independent of measurement devices. It is a candidate protocol for building an untrusted relay network.

[0003] At present, QKD networks based on trusted relay nodes have been clearly promoted. The nodes of this type of network know all the keys, so the network nodes must be completely trustworthy. With the development of QKD networks, the efficient deployment and maintenance of the security and reliability of relay nodes is a major challenge. Networks based on untrusted nodes have received widespread attention. There are currently two main types of network solutions, entanglement distribution networks and untrusted node networks based on measurement device-independent QKD protocol extensions. The implementation of entanglement distribution networks requires high-fidelity and high-rate distribution of entangled photons on real optical communication infrastructure. However, the decoherence of entangled photons transmitted in real environments limits the continuous operation of such networks. In comparison, the untrusted node network based on the measurement device-independent QKD protocol extension only requires one transmitter for each user to perform Bell state projection measurements through the detection system of the network node to obtain the same key, which is a network solution with great practical prospects.

[0004] With the rapid growth of network traffic demand, the transmission capacity of ordinary single-mode optical fiber will gradually approach the theoretical limit. Multi-core optical fiber based on space division multiplexing has attracted widespread attention. It transmits multiple optical signals simultaneously in one optical fiber, thereby further improving the communication capacity. It has a typical application prospect in the field of optical fiber communication. In particular, the fusion experiments of QKD and classical optical communication based on multi-core optical fiber have been reported one after another, which has promoted the deployment of the fusion network of QKD and classical optical communication and laid the foundation for the application of QKD technology.

[0005] Without compromising security, network scalability, cost, and security key capacity are key to the practical application of QKD networks. In combination with wavelength division multiplexing or time division multiplexing technology, there have been some excellent works on measuring device-independent QKD networks. However, due to the difficulty and cost of implementing the technology, there are only a handful of untrusted relay networks based on the TF-QKD protocol. Among them, an important task is to feedback the changes in the relative phase of independent links. The existing solution is mainly for each user to obtain link phase information by sending a strong phase reference signal in time. This solution requires additional auxiliary tasks such as delayed feedback, which complicates the system implementation and reduces the transmission bandwidth of quantum signals. In addition, combining wavelength division multiplexing technology can allocate quantum channels of different bands to different user pairs, enabling multiple pairs of users to communicate simultaneously. However, the existing solution still requires time-division multiplexing of strong phase reference signals. How to optimize the network solution to achieve a highly secure, high-performance, low-cost, and scalable multi-user QKD network is an important issue that needs to be faced in building a practical quantum communication network. Summary of the invention

[0006] The present invention proposes a quantum key distribution network based on space division multiplexing. The network adopts a dual-field quantum key distribution protocol and realizes space division multiplexing transmission of quantum signals and strong phase reference signals by applying multi-core optical fibers. Combined with optical devices such as beam splitters, intensity modulators, phase modulators, attenuators, multi-core fan-in and fan-out modules, a high-performance, multi-user interconnected quantum key distribution network is constructed, which further promotes the practical deployment of dual-field quantum key distribution networks.

[0007] Technical solution: A quantum key distribution network based on space division multiplexing, wherein the physical layer of the network is a star topology; the center of the network is an untrusted network node as a detection end, and users are distributed around it, each user holding a transmitter;

[0008] The transmitting end of each user includes a signal generation module, a quantum signal preparation module, a reference signal preparation module and a multi-core fan-in module. The signal generation module includes a narrow linewidth laser and a beam splitter. The light emitted by the narrow linewidth laser is divided into two parts by the beam splitter, and passes through the quantum signal preparation module and the phase reference signal preparation module respectively; the quantum signal preparation module is used to generate a quantum signal encoded by random phase and entrapped state intensity; the reference signal preparation module is used to generate a strong phase reference signal; the multi-core fan-in module couples the encoded quantum signal and reference signal to the multi-core optical fiber and transmits them to the network node.

[0009] The network nodes include a multi-core fan-out module, a reference measurement module and a quantum signal measurement module. The multi-core fan-out module is used to demultiplex the multi-channel optical signals transmitted in the multi-core optical fiber, and split the demultiplexed quantum signals and reference signals into multi-channel signals respectively; the measurement module is divided into quantum signal measurement and reference signal measurement, and the user's multi-channel quantum signals can be combined with quantum signals of different users for single-photon interference measurement; correspondingly, the user's multi-channel reference signals are combined with reference signals of different users for reference signal interference measurement; users can be flexibly combined to realize different logical topologies, such as ring structures and fully interconnected structures.

[0010] Furthermore, the beam splitter in the signal generating module of each user divides the optical signal into two parts, which are used to generate a quantum signal and a strong phase reference signal respectively.

[0011] Furthermore, the quantum signal preparation includes entrapped state intensity modulation and phase modulation, which is applicable to different dual-field quantum key distribution protocols.

[0012] Furthermore, the quantum signal and the strong phase reference signal are coupled into the multi-core optical fiber through a multi-core fan-in module for transmission.

[0013] Furthermore, the multi-channel quantum signals can be combined with quantum signals of different users to perform single-photon interference measurement, and different logical topological structures can be realized through different combinations.

[0014] Furthermore, the multi-path reference signals are combined with reference signals of different users to perform reference signal interference measurement, and the logical topological structure of the reference signals of different users should correspond to the logical topological structure between the user quantum signals.

[0015] Furthermore, the multi-channel quantum signals and multi-channel reference signals need to be split according to the number of users.

[0016] Beneficial effects of the present invention:

[0017] 1. The present invention combines space division multiplexing technology with a dual-field quantum key distribution network using multi-core optical fiber, transmits quantum signals and phase reference signals in different cores respectively, improves the transmission capacity of the quantum channel, and can realize a dual-field quantum key distribution network with high security key capacity;

[0018] 2. The present invention can use polarization beam splitters to connect users with different users, and can realize different network logical topologies, such as ring structures and fully interconnected structures, providing network scalability and flexibility;

[0019] 3. Benefiting from the space-division multiplexing phase reference signal, the present invention does not require time-division multiplexing of quantum signals and strong phase reference signals, thereby reducing the complexity of network implementation and the burden of single-photon detectors detecting strong phase reference signals, laying the foundation for realizing a high-performance, scalable quantum key distribution network. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the present invention together with the specification. Other features, purposes, and advantages of the present invention will become more apparent from the following detailed description of exemplary embodiments with reference to the accompanying drawings.

[0021] Figure 1 The quantum key distribution network architecture of the present invention is shown;

[0022] Figure 2 A physical layer schematic diagram of a dual-field quantum key distribution network according to an embodiment of the present invention is shown;

[0023] Figure 3 The logical topology of the dual-field quantum key distribution network according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0024] In order to more clearly illustrate the technical solution and advantages of the present invention, the specific implementation methods of the present invention will be described in detail below in conjunction with the accompanying drawings. It should be clear that the protection scope of the present invention is not limited to these specific implementation methods. The following examples are intended to help those skilled in the art to deeply understand the present invention, rather than to limit it in any form. Those of ordinary skill in the art can make various changes and improvements based on the understanding of the concept of the present invention, which all belong to the protection scope of the present invention.

[0025] Figure 1 The quantum key distribution network architecture of the present invention is shown;

[0026] The present invention is a quantum key distribution network based on space division multiplexing. Figure 1As shown. The user's transmitting end includes a signal generation module, a quantum signal preparation module, a reference signal preparation module and a multi-core fan-in module. The signal generation module includes a narrow linewidth laser and a beam splitter. The narrow linewidth laser is used to generate light with a linewidth of kilohertz. The beam splitter is used to divide the optical signal into two parts, which are used to generate quantum signals and strong phase reference signals respectively. The quantum signal preparation module is used to generate quantum signals encoded with random phase and entrapped state intensity. The reference signal preparation module is used to generate strong phase reference signals. The multi-core fan-in module couples the encoded quantum signal and reference signal to the multi-core optical fiber and transmits them to the untrusted relay network node. The network node includes a multi-core fan-out module, a quantum signal measurement module and a reference signal measurement module. The multi-core fan-out module is used to demultiplex the multi-channel optical signals transmitted in the multi-core optical fiber, and to split the demultiplexed quantum signals and reference signals into multi-channel signals respectively. The quantum signal measurement module is used to combine the multi-channel quantum signals between users, and the quantum signals of different users are combined to perform single-photon interference measurement. The reference signal measurement module is used to combine the multi-channel reference signals of users, and the reference signals of different users are combined to perform reference signal interference measurement.

[0027] The technical solution of the present invention is now further described in conjunction with the accompanying drawings and embodiments.

[0028] Figure 2 A physical layer schematic diagram of a dual-field quantum key distribution network according to an embodiment of the present invention is shown;

[0029] Depend on Figure 2 As shown, the transmitting end held by the user includes a signal generation module, a quantum signal preparation module, a reference signal preparation module and a multi-core fan-in module. The laser in the signal generation module in the transmitting end emits laser light, which is divided into two optical signals through a 50:50 beam splitter. One of the optical signals is sent to the quantum signal modulation module for encoding. First, it is pulsed light prepared and modulated by three-intensity decoy states in the intensity modulation module, and then randomly phase modulated in the phase modulation module. Then, the optical signal is attenuated to the single photon level by a variable optical attenuator (VOA) to generate a quantum signal. The final electronic polarization controller (EPC) is used for polarization feedback. Another optical signal passes through the reference signal preparation module to generate a strong phase reference signal, and the EPC is used for polarization feedback. The multi-core fan-in module couples the quantum signal and the reference signal and sends them to the multi-core optical fiber for transmission. Different from obtaining link phase information by sending a strong phase reference signal in time-sharing, we use an independent optical signal to transmit link phase information, and also use an independent measurement module to measure the strong reference signal at the network node, which reduces the complexity of network implementation and the burden of single-photon detectors to detect strong phase reference signals.

[0030] The untrusted relay network center of this embodiment includes a multi-core fan-out module, N(N-1) / 2 quantum signal measurement modules and a reference signal measurement module, such as Figure 2 As shown in the figure, the multi-core fan-out module demultiplexes the incoming optical signal into two signals, a quantum signal and a reference signal, and then splits the quantum signal and the reference signal into multiple signals through a polarization beam splitter. The quantum signal measurement module includes a beam splitter and two single-photon detectors, which record effective detection events based on the single-photon Bell state measurement results and obtain a security key after post-processing.

[0031] In this embodiment, a dual-field quantum key distribution protocol of sending and not sending is adopted. This protocol has the characteristic of being independent of the measurement device and effectively resists quantum hacker attacks on the detection end.

[0032] The network users of this embodiment implement dual-field quantum key distribution with or without sending according to the following steps:

[0033] Step 1: Before the protocol starts, the user sends strong light to the network node to compensate for the path phase difference.

[0034] Step 2: The user's transmitter uses a linewidth laser to generate an optical signal. The optical signal passes through the intensity modulation module (IMs, Intensity modulators) and the phase modulation module (PMs, Phasemodulators) in the quantum signal preparation module to generate phase-randomized optical pulse signals of different intensities. Finally, the optical pulse signal is attenuated to the single photon level through the VOA and sent to the network node. Among them, the user independently chooses whether to perform entrapped state modulation or signal state modulation on the optical pulse signal. If entrapped state modulation is chosen, the user randomly prepares an optical pulse with an intensity of μ∈{0, μ1, μ2} (0, μ1, μ2 represent the intensities of the vacuum state, weak entrapped state, and strong entrapped state, respectively) and a phase of ρ∈[0,2π). If signal state modulation is chosen, the user randomly prepares an optical pulse with an intensity of μ′∈{μ Z ,0}(μ Z , 0 represents sending and not sending, and the corresponding probabilities are ε and 1-ε), and the phase is ρ∈[0,2π). The sending and not sending of a user are recorded as bits 0 and 1, respectively. The sending and not sending of another user connected to the same quantum signal measurement module are recorded as bits 1 and 0, respectively.

[0035] Step 3: The network node records the response of the detector in the quantum signal measurement module. Events with only one detector response are recorded as valid events, and the detection results are announced. The two users connected to the same quantum signal measurement module retain the corresponding data according to the results announced by the network node and abandon the invalid data.

[0036] Step 4: Two users of the same quantum signal measurement module announce information about the signal window and the decoy window. If the effective detection is that both users choose the event under the signal window, it will be used as their respective original keys; if the effective detection is that both users choose the time under the decoy window, the two users announce the intensity and phase.

[0037] Step 5: The user randomly samples bits from part of the signal window for testing, calculates the quantum bit error rate, and uses the data from the decoy window to calculate the lower bound of the single-photon event ratio and the signal bit error rate. Finally, error correction is performed using error correction code technology, and post-processing is performed using privacy amplification to obtain a secure key.

[0038] In the dual-field quantum key distribution network system of this embodiment, a fully connected, no trusted node, three-user dual-field quantum key distribution network is proposed and demonstrated. Its logical topology is as follows: Figure 3 As shown, a multi-core optical fiber is used as a physical link connecting the transmitter and the network node. In addition, a polarization beam splitter can be used to connect users to other users, and different network logical topologies, such as a ring structure and a fully connected structure, can be realized, providing network scalability and flexibility; in addition, the present invention benefits from the space-division multiplexing phase reference signal, and does not require time-division multiplexing of quantum signals and strong phase reference signals, which reduces the complexity of network implementation and the burden of single-photon detectors detecting strong phase reference signals, laying the foundation for realizing a high-performance, scalable quantum key distribution network.

Claims

1. A quantum key distribution network based on space division multiplexing, characterized in that: The physical layer of the network is a star topology; each user in the network has a transmitter, which sends a signal to an untrusted relay node, and the node gathers multiple measurement modules; The transmitting end of each user includes a signal generation module, a quantum signal preparation module, a reference signal preparation module and a multi-core fan-in module; the signal generation module includes a narrow linewidth laser and a beam splitter, the narrow linewidth laser is used to generate light with a linewidth of kilohertz, the beam splitter divides the light emitted by the laser into two parts, which pass through the quantum signal preparation module and the phase reference signal preparation module respectively; the quantum signal preparation module is used to generate a quantum signal encoded by random phase and decoy state intensity; the reference signal preparation module is used to generate a strong phase reference signal; the multi-core fan-in module couples the encoded quantum signal and the reference signal to the multi-core The optical fiber is used for transmitting the multi-channel optical signals to the network node; the network node comprises a multi-core fan-out module, a reference signal measurement module and a quantum signal measurement module; the multi-core fan-out module is used for demultiplexing the multi-channel optical signals transmitted in the multi-core optical fiber, and splitting the demultiplexed quantum signals and reference signals into multi-channel signals respectively; the measurement module is divided into quantum signal measurement and reference signal measurement, the multi-channel quantum signals of the user can be combined with the quantum signals of different users for single-photon interference measurement, and correspondingly, the multi-channel reference signals of the user can be combined with the reference signals of different users for reference signal interference measurement; users can be flexibly combined to realize different logical topological structures.

2. A quantum key distribution network based on space division multiplexing according to claim 1, characterized in that: The beam splitter in the signal generation module of each user divides the optical signal into two parts, which are used to generate a quantum signal and a strong phase reference signal respectively.

3. A quantum key distribution network based on space division multiplexing according to claim 1, characterized in that: The quantum signal preparation includes decoy state intensity modulation and phase modulation, and is suitable for different dual-field quantum key distribution protocols.

4. A quantum key distribution network based on space division multiplexing according to claim 1, characterized in that: The quantum signal and the strong phase reference signal are coupled into the multi-core optical fiber through a multi-core fan-in module for transmission.

5. The quantum key distribution network based on space division multiplexing according to claim 1, characterized in that: The multi-channel quantum signals can be combined with quantum signals of different users to perform single-photon interference measurement, and different logical topological structures can be realized through different combination forms.

6. A quantum key distribution network based on space division multiplexing according to claim 1, characterized in that: The multi-path reference signal is combined with reference signals of different users to perform reference signal interference measurement, and the reference signal combination between users corresponds to the quantum signal combination, providing a reliable relative phase reference for the optical fiber link.

7. A quantum key distribution network based on space division multiplexing according to claim 5 and claim 6, characterized in that: The number of the multi-path quantum signals and the multi-path reference signals is related to the number of network users and the logical topology structure.

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