CN101931488B - Full-time all-pass quantum network router and method for expanding quantum secret communication network - Google Patents

Abstract

The present invention relates to a method for expanding quantum security communication network and a new type of full-time full-pass quantum network router, which is characterized in that, in combination with the characteristics of quantum key distribution, by introducing an optical circulator and a polarization beam splitter, the transmission rate of the optical signal is increased. The degree of freedom enhances the scalability of the quantum secure communication network and reduces its consumption of optical wavelength resources. For a quantum secure communication network with N optical wavelength resources, it can support up to 4N+1 network users. Each port of the quantum network router has an external interface and a plurality of internal interfaces, which are respectively used for connecting with users of the quantum secure communication network and for connecting between internal ports. With the quantum network router of the present invention as the core, a backbone quantum secure communication network that requires all-time and all-pass can be effectively constructed.

Description

Full-time all-pass quantum network router and method for extending quantum secure communication network

technical field

The invention relates to the technical field of quantum secure communication networks, in particular to the quantum key distribution network technology.

Background technique

The concept of quantum key distribution was proposed by Bennett and Brassard in 1984, which provides a perfect solution to the key distribution problem in cryptography. The basic principles of quantum mechanics guarantee the unconditional security of the distributed key. Although the current point-to-point quantum key distribution distance has reached 200 kilometers, from the perspective of practical application, when key distribution is performed among multiple users, the quantum key distribution technology will inevitably develop from point-to-point to a quantum key distribution network, namely Quantum secure communication network.

Existing quantum key distribution networks include quantum key distribution networks based on quantum relays, quantum key distribution networks based on quantum entanglement, quantum key distribution networks based on optical beam splitters, and quantum key distribution networks based on optical switches. network and WDM-based quantum key distribution network, etc. At present, the quantum key distribution network of quantum relay and quantum entanglement is basically in the theoretical research stage, and the single-channel performance of the quantum key distribution network of optical beam splitter decreases sharply with the increase of the number of users, and the scalability is poor. The switch quantum key distribution network needs active switching, and the quantum key distribution network based on optical beam splitter and optical switch cannot realize full-time all-pass between any two users. "Full-time all-pass" means that any two users can communicate at any time, and the backbone network generally requires that any two users of the network can always communicate. For the backbone quantum secure communication network that requires all-time and all-pass, the quantum network router based on the wavelength division multiplexer/demultiplexer proposed by our experimental group is a very promising device (patent number: ZL03132014.7) . In order to enhance the scalability of the quantum secure communication network and reduce its dependence on the optical wavelength, the present invention proposes a novel quantum network router and a method for expanding the quantum secure communication network.

Contents of the invention

The present invention proposes a novel full-time and full-throughput sub-network router, and aims to form a quantum security communication backbone network with the quantum router as the core.

The method for effectively extending the quantum secure communication network proposed by the present invention is based on the characteristics of quantum key distribution and adds an extended degree of freedom. In the phase-encoded quantum key distribution system, the transmission direction, polarization and light wavelength can be used as extended degrees of freedom; in the polarization-encoded quantum key distribution system, the transmission direction and optical wavelength are used as extended degrees of freedom.

The full-time all-through sub-network router of the present invention consists of one, two or three of an optical circulator (CIR), a polarization beam splitter (PBS) and an N-wavelength wavelength division multiplexer/demultiplexer (WDM) There are 14 schemes in total, among which the scheme of quantum network router composed of N wavelength multiplexer/demultiplexer is the same as the patent number ZL03132014.7 of our experimental group, which will not be considered in the present invention. (1) When there is no optical wavelength degree of freedom as a networking solution, if an optical circulator is used alone to form a full-time full-throughput sub-network router, there is one solution that can accommodate up to 3 users; if an optical circulator and polarization beam splitter are used routers to form a full-time full-pass sub-network router. There are 2 schemes, which can accommodate up to 5 users. (2) When the optical wavelength degree of freedom is used as a networking scheme, if an optical circulator and an N-wavelength wavelength division multiplexer are used to form a full-time full-throughput sub-network router, there are two schemes, which can accommodate up to 2N+1 users; Polarization beam splitter and N-wavelength wavelength division multiplexer form a full-time full-throughput sub-network router. There are two schemes, which can accommodate up to 2N users; if an optical circulator, polarization beam splitter and N-wavelength wavelength division multiplexer are used There are 6 schemes to form a full-time and full-pass sub-network router, which can accommodate up to 4N+1 users.

The optical circulator can be a commercial optical fiber circulator, or an optical circulator composed of discrete optical elements. Referring to Figure 1, the optical circulator has three optical interfaces 1-1, 1-2, and 1-3. As shown by the arrows, the light can only travel in one direction inside the circulator, and the light entering through the interface 1-1, It can only exit from interface 1-2, the incident light from interface 1-2 can only exit from interface 1-3, and the light entering from interface 1-3 has no exit. Two degrees of freedom, in and out, can be obtained through the optical circulator. The optical circulator is a polarization independent device.

The polarization beam splitter can be a fiber optic polarization beam splitter, or a polarization beam splitter composed of discrete optical elements. The incident light is either linearly polarized or circularly polarized. In the description of the present invention, linearly polarized light is taken as an example, which is equally divided into horizontal polarization and vertical polarization after passing through a polarization beam splitter, thereby obtaining two degrees of freedom.

The N-wavelength wavelength division multiplexer/demultiplexer can be a commercial optical fiber N-wavelength wavelength division multiplexer or an N-wavelength wavelength division multiplexer, or an N-wavelength wavelength division multiplexer composed of discrete optical elements . The light of N wavelengths is input from N input terminals of the wavelength division multiplexer, and is multiplexed to one output terminal for output. The light of N wavelengths is input from one input port of the wave division multiplexer, and is demultiplexed to N output ports corresponding to the wavelengths. Both commercial fiber optic WDM and WDM are reversible optical devices, so they can be regarded as the same device. In the present invention, they are all referred to as N-wavelength wavelength division multiplexer/demultiplexer.

The invention proposes the concept of a quantum network router port, and each port includes an external interface and several internal interfaces. The external interface is used to connect with quantum secure communication network users, and the internal interface is used to connect between ports inside the quantum network router. There is a one-to-one correspondence between the users of the quantum secure communication network and the ports of the quantum network router, and each user has a structure similar to the port of the quantum network router, which is used to multiplex or demultiplex each degree of freedom of the optical signal. The user's external interface is connected to the external interface of the corresponding port of the quantum network router, and several internal interfaces correspond to the transmitting device or receiving device of the quantum key distribution system. Each port is composed of one, two or three optical components such as optical circulator, polarization beam splitter and wavelength division multiplexer/demultiplexer. The number of optical components contained in the internal structure is the same as that in the port The number of connection stages of the optical components is the same, from the outside to the inside, the different optical components are arranged and connected in stages according to the quantity from less to more. It should be noted that the internal structure of each port in a quantum network router can be the same or different, and the internal structure of the user corresponding to the quantum secure communication network can also be the same or different from the internal structure of the port of the quantum network router. Different schemes can separate the various degrees of freedom of the optical signal.

The internal connection of each port of the full-time full-pass sub-network router in the present invention is guaranteed by relevant conclusions in mathematical graph theory. In the full-time all-through sub-network router, if the ports of the router are regarded as vertices, the optical connections connecting each port are regarded as edges, and the degrees of freedom of light are regarded as different colors, and each port is directly connected by optical connections. is a fully connected graph. (a) If there is no optical circulator, only the N-wavelength wavelength division multiplexer/demultiplexer, or the N-wavelength wavelength division multiplexer/demultiplexer and the polarization beam splitter form the port of the router. At this time, it is the same as " The problem described in "Completely Connected Edge Coloring Theory" is exactly the same. When the degree of freedom of light in the quantum network router is D, D+1 (or D) ports can be directly connected, and it is guaranteed that the light transmitted in the internal optical connection with a common port is light with different degrees of freedom, which is It is equivalent to giving each port a unique network address, and it can meet the requirements of all-time and all-pass. (b) If the optical circulator participates in forming the ports of the router, it is completely consistent with the problem described in the "odd-order complete Hamilton graph circuit theory". If the degree of freedom of the optical signal is D before introducing the degree of freedom of the light transmission direction, then there must be D disjoint Hamilton circuits in the quantum network router with 2D+1 ports, and the Hamilton circuits are routed by each The optical connection between the internal interface of the port consists of. The D Hamiltonian circuits correspond to the D degrees of freedom of the optical signal before being introduced into the direction of transmission. Since each router port has two internal interfaces in a Hamilton circuit, the two internal interfaces of the same port in the same Hamilton circuit can be assigned the two degrees of freedom of the transmission directions of ingress and egress respectively. In this way, it is ensured that the light with different degrees of freedom is transmitted in the internal optical connection with a common port, which is equivalent to giving each port a unique network address, and can also meet the requirements of all-time and all-pass.

The optical connection can be optical fiber, waveguide, free space or other optical media. Polarization control, collimation, anti-reflection, coupling and other devices can be added to the connection optical path to improve the performance of the optical connection.

The degree of freedom of the transmission direction introduced in the present invention can greatly simplify the connection method between the ports inside the quantum network router. The present invention proposes two simple connection methods. Assuming that the degree of freedom of the optical signal is N (wavelength, or polarization, or wavelength polarization combination) before the freedom of transmission direction is introduced, after adding an optical circulator, a 2N Quantum Router with +1 port. Method 1. Arrange 2N+1 ports in a circle. According to the "odd-order complete Hamilton graph circuit theory", there must be N non-intersecting Hamilton circuits, and assign the aforementioned N degrees of freedom to the N Hamilton circuits. Draw the first Hamilton circuit, starting from the first port (any port can be selected as the first port), and mark the directions of the two edges entering and exiting each port according to the direction of the circuit, that is Input and output degrees of freedom, then draw the second Hamilton circuit, start again with the first port, mark the direction of each port entering and exiting the two edges in the circuit according to the direction of the circuit, and so on It can be analogized up to the Nth Hamilton loop, and the Hamilton loop is composed of the optical connection between the internal interfaces of each port. Method 2: Arrange 2N+1 ports evenly clockwise into a circle, taking the first port (any port can be selected as the first port) as an example, the connection between the port and the center of the circle is called symmetric axis, so, then N ports are distributed on one side of the symmetry axis, which is defined as the left side, and the other N ports are distributed on the other side of the symmetry axis, which is defined as the right side, and the port (ie the first port ) and the N ports on the left side are connected with the aforementioned N degrees of freedom in sequence according to the distance, and these N connections are all marked as the input of the port, and the remaining 2N ports are connected with other ports using the first port The same connection method and sequence are sufficient. The second method is adopted in the following specific implementation manners including the optical circulator.

If the internal structure of the quantum network router port is a combination of a polarization beam splitter and a wavelength division multiplexer/demultiplexer, and the wavelength degree of freedom of the optical signal before adding the polarization beam splitter is N, then the distance between 2N ports The connection method is: each port is connected to other 2N-1 ports using 2N-1 different degrees of freedom.

The quantum network router of the present invention can complete: (1) realize quantum key distribution between any two users connected by the quantum network router; (2) by selecting a suitable quantum key distribution scheme and a suitable quantum network router scheme , the quantum network router will not destroy the nature of the transmitted quantum state; (3) in the entire quantum secure communication network, the network routing address of each user connected to the router is unique; (4) in the entire quantum secure communication network Each user communicates at the same time without interfering with each other; (5) By selecting a suitable quantum router scheme, it can consume less wavelength resources under the same number of users; (6) When the number of network users is fixed , by choosing an appropriate quantum router scheme, the network cost can be saved. Therefore, based on the functions and characteristics of the quantum network router, it is very suitable for backbone quantum secure communication networks that require all-time and all-pass.

The quantum state may be a photon state carrying phase encoding information in phase-encoded quantum key distribution, or a photon state carrying polarization-encoding information in polarization-encoded quantum key distribution, or a photon state carrying information in other schemes.

The full-time full-throughput sub-network router of the present invention increases other degrees of freedom of optical signals by combining the characteristics of quantum key distribution, enhances the scalability of quantum security communication networks, and reduces its consumption of optical wavelength resources. For a quantum secure communication network with N wavelengths, it can guarantee full-time and all-pass quantum secure communication between 4N+1 network users.

Description of drawings

Fig. 1 is a schematic diagram of an embodiment of a single port made up of optical circulators in a 3-port quantum network router;

Fig. 2 is the schematic diagram of an embodiment of the connection mode between 3 ports of the 3-port quantum network router;

Fig. 3 is a schematic diagram of an embodiment of a single port made up of a polarization beam splitter and a 2-wavelength wavelength division multiplexer/demultiplexer in a 4-port quantum network router;

Fig. 4 is a second embodiment schematic diagram of a single port made up of a polarization beam splitter and a 2-wavelength wavelength division multiplexer/demultiplexer in a 4-port quantum network router;

Fig. 5 is the schematic diagram of the embodiment of the connection mode between the 4 ports of the 4-port quantum network router composed of polarization beam splitter and 2-wavelength wavelength division multiplexing/demultiplexing device;

Fig. 6 is a schematic diagram of an embodiment of a single port made up of an optical circulator and a polarization beam splitter in a 5-port quantum network router;

Fig. 7 is a second embodiment schematic diagram of a single port made up of an optical circulator and a polarization beam splitter in a 5-port quantum network router;

Fig. 8 is a schematic diagram of an embodiment of a single port made up of an optical circulator and a 2-wavelength wavelength division multiplexer/demultiplexer in a 5-port quantum network router;

Fig. 9 is a schematic diagram of a second embodiment of a single port made up of an optical circulator and a 2-wavelength wavelength division multiplexer/demultiplexer in a 5-port quantum network router;

Fig. 10 is a schematic diagram of an embodiment of a connection mode between 5 ports of a 5-port quantum network router;

Fig. 11 is a schematic diagram of an embodiment of a single port composed of an optical circulator and an N-wavelength wavelength division multiplexer/demultiplexer in a 2N+1 port quantum network router;

12 is a schematic diagram of a second embodiment of a single port composed of an optical circulator and an N-wavelength wavelength division multiplexer/demultiplexer in a 2N+1 port quantum network router;

Fig. 13 is a schematic diagram of an embodiment of a single port composed of a polarization beam splitter and an N-wavelength wavelength division multiplexer/demultiplexer in a 2N-port quantum network router;

14 is a schematic diagram of a second embodiment of a single port composed of a polarization beam splitter and an N-wavelength wavelength division multiplexer/demultiplexer in a 2N-port quantum network router;

Fig. 15 is a schematic diagram of an embodiment of a single port composed of an optical circulator, a polarization beam splitter and an N-wavelength wavelength division multiplexer/demultiplexer in a 4N+1 port quantum network router;

Fig. 16 is a schematic diagram of a second embodiment of a single port composed of an optical circulator, a polarization beam splitter and an N-wavelength wavelength division multiplexer/demultiplexer in a 4N+1 port quantum network router;

17 is a schematic diagram of a third embodiment of a single port composed of an optical circulator, a polarization beam splitter and an N-wavelength wavelength division multiplexer/demultiplexer in a 4N+1 port quantum network router;

Fig. 18 is a schematic diagram of a fourth embodiment of a single port composed of an optical circulator, a polarization beam splitter and an N-wavelength wavelength division multiplexer/demultiplexer in a 4N+1 port quantum network router;

Fig. 19 is a schematic diagram of a fifth embodiment of a single port composed of an optical circulator, a polarization beam splitter and an N-wavelength wavelength division multiplexer/demultiplexer in a 4N+1 port quantum network router;

Fig. 20 is a schematic diagram of a sixth embodiment of a single port composed of an optical circulator, a polarization beam splitter and an N-wavelength wavelength division multiplexer/demultiplexer in a 4N+1 port quantum network router.

Fig. 21 is a schematic diagram of an embodiment of the connection mode between 9 ports composed of an optical circulator, a polarization beam splitter and a 2-wavelength wavelength division multiplexer/demultiplexer in a 9-port quantum network router.

Detailed ways

The implementation manner of the technical solution of the present invention will be specifically described below in conjunction with the accompanying drawings.

Figures 1 and 2 are quantum network router schemes without wavelength multiplexer/demultiplexer, that is, when there is no wavelength degree of freedom, only using optical circulators for 3-user networking. In this scheme, the router includes 3 ports 1, 2, and 3 correspond to three users 1, 2, and 3, respectively. The structure of each port is shown in Figure 1, which is composed of an optical circulator 1-4, wherein the light entering from the port 1-1 can only exit from the port 1-2, and the light entering from the port 1-2 can only Can emit from interface 1-3. Interface 1-2 is an external interface, which is directly connected to the user corresponding to this port. Interfaces 1-1 and 1-3 are two internal interfaces, respectively connected to corresponding internal interfaces of the other two ports. Figure 2 shows the connection mode between the three ports of the router. When quantum key distribution is performed between user 1 and user 2, the quantum state is sent by user 1, passes through port 1 of the quantum network router to port 2, and finally reaches User 2; when the quantum key is distributed between user 2 and user 3, the quantum state is sent by user 2, through the quantum network router port 2 to port 3, and finally reaches user 3; the quantum key is distributed between user 3 and user 1 During distribution, the quantum state is sent by user 3, goes through port 3 of the quantum network router to port 1, and finally reaches user 1. Finally, the quantum key distribution of all users is completed.

表示水平偏振，“β”表示竖直偏振。图4是应用于4端口量子网络路由器的、由一个偏振分束器和两个2波长波分复用/解复用器组成的单个端口示意图，图示结构有波长λ1水平偏振、波长λ1竖直偏振、波长λ2水平偏振和波长λ2竖直偏振四个自由度，对于4端口量子网络路由器来说，从当前端口向其它三个端口寻址只需取其中三个自由度即可，例如可以取前三个自由度。图5示出了采用如图3、4所示的端口结构时量子网络路由器各端口的连接方法：每个端口利用3个不同的自由度连接至另外3个端口。其中，线型5-1代表波长λ1水平偏振，线型5-2代表波长λ1竖直偏振，线型5-3代表波长λ2或波长λ2水平偏振。量子态以波长λ1水平偏振为路由地址，通过量子网络路由器的端口1和端口4将用户1和用户4连接起来，通过量子网络路由器的端口2和端口3将用户2和用户3连接起来；即，端口1和端口4分别以波长λ1水平偏振彼此寻址，而端口2和端口3也分别以波长λ1水平偏振彼此寻址。量子态以波长λ1竖直偏振为路由地址，通过量子网络路由器的端口1和端口3将用户1和用户3连接起来，通过量子网络路由器的端口2和端口4将用户2和用户4连接起来。量子态以波长λ2(图3结构)或者波长λ2水平偏振(图4结构)为路由地址，通过量子网络路由器的端口1和端口2将用户1和用户2连接起来，通过量子网络路由器的端口3和端口4将用户3和用户4连接起来。其原理同端口1、4，及2、3的连接。Figure 3, Figure 4 and Figure 5 are schemes of a 4-port quantum network router composed of a polarization beam splitter and a 2-wavelength wavelength division multiplexer/demultiplexer. Among them, the polarization and the wavelength can respectively provide two degrees of freedom, and a total of four degrees of freedom can be formed. However, only three degrees of freedom are required to support a 4-user network. Figure 3 is a schematic diagram of a single port composed of a 2-wavelength wavelength division multiplexer/demultiplexer and a polarization beam splitter applied to a 4-port quantum network router, where the three degrees of freedom are the wavelength λ1 horizontal polarization, The wavelength λ1 is vertically polarized and the wavelength λ2, the port can be addressed to the other three ports of the router using the above three degrees of freedom. 3-1 shows a single structure of a 2-wavelength wavelength division multiplexer/demultiplexer, which can be extended to N wavelengths. 3-2 shows the single structure of the polarizing beam splitter, where

Indicates horizontal polarization, "β" indicates vertical polarization. Figure 4 is a schematic diagram of a single port composed of a polarization beam splitter and two 2-wavelength wavelength division multiplexing/demultiplexing devices applied to a 4-port quantum network router. Direct polarization, wavelength λ2 horizontal polarization, and wavelength λ2 vertical polarization are four degrees of freedom. For a 4-port quantum network router, only three of the degrees of freedom are needed to address from the current port to the other three ports. For example, Take the first three degrees of freedom. Fig. 5 shows the connection method of each port of the quantum network router when the port structure shown in Fig. 3 and Fig. 4 is adopted: each port is connected to other 3 ports with 3 different degrees of freedom. Wherein, line 5-1 represents horizontal polarization at wavelength λ1, line 5-2 represents vertical polarization at wavelength λ1, and line 5-3 represents horizontal polarization at wavelength λ2 or wavelength λ2. The quantum state takes the horizontal polarization of wavelength λ1 as the routing address, connects user 1 and user 4 through port 1 and port 4 of the quantum network router, and connects user 2 and user 3 through port 2 and port 3 of the quantum network router; that is , port 1 and port 4 address each other with horizontal polarization of wavelength λ1, respectively, and port 2 and port 3 address each other with horizontal polarization of wavelength λ1, respectively. The quantum state takes the vertical polarization of wavelength λ1 as the routing address, connects user 1 and user 3 through port 1 and port 3 of the quantum network router, and connects user 2 and user 4 through port 2 and port 4 of the quantum network router. The quantum state uses wavelength λ2 (structure in Figure 3) or wavelength λ2 horizontal polarization (structure in Figure 4) as the routing address, connects user 1 and user 2 through port 1 and port 2 of the quantum network router, and connects user 1 and user 2 through port 3 of the quantum network router And port 4 connects user3 and user4. The principle is the same as the connection of ports 1, 4, and 2, 3.

Fig. 6, Fig. 7, Fig. 8, Fig. 9 and Fig. 10 are schemes in which an optical circulator and a polarization beam splitter or an optical circulator and a 2-wavelength wavelength division multiplexer/demultiplexer form a 5-port quantum network router. Figures 6-9 show the internal structure of a single port in a 5-port quantum network router. Due to the addition of an optical circulator, only two polarization states or two wavelengths of light are required to support a 5-user network. Fig. 6 is a schematic diagram of a single port composed of an optical circulator and two polarization beam splitters. Fig. 7 is a schematic diagram of a single port composed of two optical circulators and a polarization beam splitter. Fig. 8 is a schematic diagram of a single port composed of an optical circulator and two 2-wavelength wavelength division multiplexers/demultiplexers. Fig. 9 is a schematic diagram of a single port composed of two optical circulators and a 2-wavelength wavelength division multiplexer/demultiplexer. Figure 10 shows the connection method of each port of the quantum network router when the port structure shown in Figure 6-9 is adopted: the line type 10-1 represents the wavelength λ1 or horizontal polarization, and the line type 10-2 represents λ2 or vertical polarization . When quantum key distribution is performed between user 1 and user 2, the quantum state is sent by user 1, and the wavelength λ1 (structure in Figure 8 and figure 9) or horizontal polarization (structure in figure 6 and figure 7) is used as the routing address through the quantum network router port 1 to port 2, and finally reaches user 2; when quantum key distribution is performed between user 1 and user 3, the quantum state is sent by user 1, with wavelength λ2 (structure in Fig. , Figure 7 structure) is the routing address via the quantum network router port 1 to port 3, and finally reaches user 3; when the quantum key is distributed between user 1 and user 4, the quantum state is sent by user 4 with wavelength λ2 (Figure 8 , Figure 9 structure) or vertical polarization (Figure 6, Figure 7 structure) is the routing address through the quantum network router port 4 to port 1, and finally reaches user 1; when the quantum key is distributed between user 1 and user 5, the quantum The state is sent by user 5, with wavelength λ1 (structure in Fig. 8 and Fig. 9) or horizontal polarization (structure in Fig. 6 and Fig. 7) as the routing address, via quantum network router port 5 to port 1, and finally reaches user 1. Quantum key distribution among user 2, user 3, user 4 and user 5 can be deduced by analogy.

Fig. 11 and Fig. 12 are schemes in which an optical circulator and an N-wavelength wavelength division multiplexer/demultiplexer form a 2N+1 port quantum network router. With the addition of circulators, N wavelengths can support 2N+1 user quantum security communication network. Fig. 11 is a schematic diagram of a single port composed of a circulator and two N-wavelength wavelength division multiplexers/demultiplexers. Fig. 12 is a schematic diagram of a single port composed of N circulators and an N wavelength division multiplexer/demultiplexer. The connections between the ports of the 2N+1 port quantum network router are similar to those shown in Figure 10.

Fig. 13 and Fig. 14 are schemes in which a 2N-port quantum network router is composed of a polarization beam splitter and an N-wavelength wavelength division multiplexer. The total degree of freedom of polarization and wavelength is 2N, which can support a quantum secure communication network with up to 2N users. Figure 13 is a schematic diagram of a single port composed of an N-wavelength wavelength division multiplexer and N-1 polarization beam splitters. Since it supports 2N user quantum security communication networks, 2N-1 degrees of freedom are required, so only N-1 polarizing beam splitters. Figure 14 is a schematic diagram of a single port composed of a polarization beam splitter and two N-wavelength wavelength division multiplexers. Since it supports 2N user quantum security communication networks, only 2N-1 degrees of freedom are required, so it is discarded in actual networking. One degree of freedom is not required. The connections between the ports of the 2N-port quantum network router are similar to those shown in FIG. 5 .

Fig. 15, Fig. 16, Fig. 17, Fig. 18, Fig. 19 and Fig. 20 are schemes in which a 4N+1 port quantum network router is composed of an optical circulator, a polarization beam splitter and an N-wavelength wavelength division multiplexer. The total degree of freedom of the polarization beam splitter and the N-wavelength wavelength division multiplexer is 2N. Due to the addition of the optical circulator, the quantum network router can support 4N+1 users. Fig. 15 is a schematic diagram of a single port composed of an optical circulator, two N-wavelength wavelength division multiplexers/demultiplexers and 2N polarization beam splitters. Fig. 16 is a schematic diagram of a single port composed of an optical circulator, two polarization beam splitters and four N-wavelength wavelength division multiplexers/demultiplexers. Fig. 17 is a schematic diagram of a single port composed of an N-wavelength wavelength division multiplexer/demultiplexer, N optical circulators, and 2N polarization beam splitters. Fig. 18 is a schematic diagram of a single port composed of an N wavelength division multiplexer/demultiplexer, N polarization beam splitters and 2N optical circulators. Fig. 19 is a schematic diagram of a single port composed of a polarization beam splitter, two optical circulators and four N-wavelength wavelength division multiplexers/demultiplexers. Fig. 20 is a schematic diagram of a single port composed of a polarization beam splitter, two N-wavelength wavelength division multiplexers/demultiplexers, and 2N optical circulators.

Figure 21 takes a 9-port quantum network router composed of an optical circulator, a polarization beam splitter, and a 2-wavelength wavelength division multiplexer/demultiplexer as an example, showing how the ports of the 4N+1-port quantum network router are connected. Two wavelengths and two polarizations constitute four degrees of freedom of wavelength λ1 horizontal polarization, wavelength λ1 vertical polarization, wavelength λ2 horizontal polarization and wavelength λ2 vertical polarization. Due to the addition of optical circulators, it can support 9-user quantum communication network. A single port of the router can adopt any internal structure as shown in Fig. 15, Fig. 16, Fig. 17, Fig. 18, Fig. 19 and Fig. 20, where N=2, and there are 6 possible structures in total. The nine ports can adopt the same or different internal structures, and it is only necessary to separate each degree of freedom of the optical signal. Wherein the line type 21-1 represents the horizontal polarization of the wavelength λ1, the line type 21-2 represents the vertical polarization of the wavelength λ1, the line type 21-3 represents the horizontal polarization of the wavelength λ2, and the line type 21-4 represents the vertical polarization of the wavelength λ2. When the quantum key is distributed between user 1 and user 2, the quantum state is sent by user 1, with the wavelength λ1 horizontal polarization as the routing address, through the quantum network router port 1 to port 2, and finally reaches user 2; user 1 and user 3 When performing quantum key distribution between users, the quantum state is sent by user 1, with the vertical polarization of wavelength λ1 as the routing address, through the quantum network router port 1 to port 3, and finally reaches user 3; the quantum state between user 1 and user 4 When the key is distributed, the quantum state is sent by user 1, with the wavelength λ2 horizontal polarization as the routing address, through the quantum network router port 1 to port 4, and finally reaches user 4; when the quantum key is distributed between user 1 and user 5, The quantum state is sent by user 1, with the vertical polarization of wavelength λ2 as the routing address, through the quantum network router port 1 to port 5, and finally reaches user 5; when the quantum key is distributed between user 1 and user 6, the quantum state is determined by the user 6, with the vertical polarization of wavelength λ2 as the routing address, through the quantum network router port 6 to port 1, and finally to user 1; when the quantum key is distributed between user 1 and user 7, the quantum state is sent by user 7, and the The wavelength λ2 is horizontally polarized as the routing address, which passes through the quantum network router port 7 to port 1, and finally reaches user 1; when the quantum key is distributed between user 1 and user 8, the quantum state is sent by user 8, and is vertically polarized with wavelength λ1 is the routing address, through the quantum network router port 8 to port 1, and finally reaches user 1; when the quantum key is distributed between user 1 and user 9, the quantum state is sent by user 9, and the wavelength λ1 horizontal polarization is used as the routing address, via Quantum network router port 9 to port 1, and finally reach user 1, user 2, user 3, user 4, user 5, user 6, user 7, user 8 and user 9 for quantum key distribution and so on.

The present invention has been exemplarily described above in conjunction with the accompanying drawings. Obviously, the specific implementation of the present invention is not limited by the above methods, as long as the various improvements of the method concept and technical solutions of the present invention are adopted, or directly applied to other Occasions, all within the protection scope of the present invention.

Claims (6)

1. A method for expanding a quantum secure communication network, characterized in that: by introducing the transmission direction of light, the degree of freedom of the optical signal is increased, thereby expanding the capacity of the quantum secure communication network, wherein, the light is introduced by introducing an optical circulator The degree of freedom of the transmission direction expands the original wavelength freedom N to 2N, which can support 2N+1 users; Assuming that the degree of freedom of the optical signal is N wavelengths before the degree of freedom of the transmission direction is introduced, after adding an optical circulator, a quantum router with 2N+1 ports can be constructed: Method 1. Arrange 2N+1 ports in a circle. According to the theory of odd-order complete Hamiltonian graph circuits, there must be N non-intersecting Hamilton circuits. Assign the aforementioned N degrees of freedom to these N Hamilton circuits, and draw For the first Hamilton circuit, starting from the first port, mark the directions of the two edges of each port in and out according to the direction of the circuit, that is, the input and output degrees of freedom, and then draw the second Hamilton circuit, Taking the first port as the starting point again, mark the entry and exit directions of the two edges of each port in the circuit according to the direction of the circuit, and so on until the Nth Hamilton circuit; or, Method 2: Arrange 2N+1 ports uniformly clockwise into a circle, and the line connecting the first port and the center of the circle is called the symmetry axis, then the N ports are distributed on one side of the symmetry axis, which is defined as the left side , and the other N ports are distributed on the other side of the symmetry axis, which is defined as the right side. The first port and the N ports on the left are connected with the aforementioned N degrees of freedom in sequence according to the distance, and the N The connection is marked as the input of the port, and the other 2N ports are connected to other ports using the same connection method and sequence as the first port. 2. The method for expanding the quantum secure communication network according to claim 1, wherein any port can be selected as the first port. 3. A quantum network router for realizing the method according to claim 1, characterized in that: Including N ports; Each port includes an external interface connected to the corresponding user, and N-1 internal interfaces; Each internal interface of each port is respectively connected to corresponding internal interfaces of the remaining N-1 ports; The internal structure of each port contains one of the following optics or combinations of optics optical circulator, A combination of an optical circulator and a wavelength division multiplexer/demultiplexer. 4. The quantum network router according to claim 3, the external interface of each port is connected with the external interface of the corresponding user. 5. The quantum network router according to claim 3, wherein N=3, and the internal structure of each port includes an optical circulator. 6. quantum network router according to claim 3, wherein N=2K+1 (K≥3), the internal structure of each port comprises a circulator and two K wavelength wavelength division multiplexing/demultiplexing devices, Or K circulators and a K wavelength division multiplexer/demultiplexer.

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