A quantum key distribution coding module, transmitter and system network

Abstract

The present invention belongs to the technical field of optical secure communication, and discloses a quantum key distribution coding module, a transmitter and a system network. The coding module includes a circulator, a stable polarization modulation module and an optical path selection module; the polarization stable modulation module is used to perform stable polarization modulation on the input optical signal; the optical path selection module is used to allow the optical signal to select two transmission paths, one of which keeps the polarization of the optical signal unchanged to achieve discrete variable polarization coding, and the other path only passes a specific linear polarization component to achieve continuous variable Gaussian modulation coding. The present invention also discloses a quantum key distribution transmitter and a system network. Compared with the prior art, the present invention can not only achieve polarization coding or Gaussian modulation coding, but also achieve decoy state modulation or pulse generation, thereby integrating discrete variable and continuous variable coding in one transmitter and achieving flexible reconstruction; it can be better compatible with different protocols in the application, reducing the field deployment cost.

Description

Technical Field

[0001] The present invention relates to the technical field of optical secure communications, and in particular to a quantum key distribution coding module, a transmitting end and a system network. Background Art

[0002] Quantum key distribution (QKD) has been proven to have information-theoretic security and plays an important role in confidential communications. QKD encoding methods can be divided into two categories: discrete variables (DV) and continuous variables (CV). Discrete variable (DV) and continuous variable (CV) protocols each have their own advantages. DV-QKD has proven mature security and strong long-distance transmission capabilities. The transmission distance of the optical fiber BB84 system is 421 kilometers, and it can reach 1002 kilometers under the dual-field scheme. CV-QKD has a high key generation rate (SKR) at short distances, but because it is sensitive to losses, the current longest distance of the optical fiber system is only 203 kilometers.

[0003] In practical applications of quantum key distribution, it is necessary to build a multi-node quantum key distribution system network. There may be multiple paths between two nodes, including relay nodes connecting one end user to another. Therefore, according to the available routes and the channel parameters connecting each node, each transmission segment can maximize the overall key generation rate by choosing to use discrete variable or continuous variable protocols. At this time, for a specific node, in order to be able to choose between DV protocol or CV protocol according to actual link requirements, the conventional method is to deploy two dedicated transmitters at the same time, which undoubtedly increases the complexity and cost of the system. The use of a hybrid coding transmitter that can switch between DV and CV can actively reconfigure network characteristics in a software-defined manner, thereby increasing its flexibility and improving the integration of QKD with existing telecommunications infrastructure.

[0004] Sabatini M, et al. Hybrid encoder for discrete and continuousvariable QKD. arxiv:2408.17412, 2024. Using the Sagnac ring structure, DV polarization coding and CV phase shift keying coding can be realized by adding delay. However, DV coding requires an additional intensity modulation module to realize decoy state modulation, which increases the complexity of the system. In addition, compared with the Gaussian modulation CV protocol, the security proof of the former is not perfect, and the security coding rate is lower than the latter due to the lower key bits encoded per symbol. Summary of the invention

[0005] In view of the above defects in the prior art, the present invention proposes a quantum key distribution encoding module, a transmitter and a system network.

[0006] The technical solution of the present invention is achieved in this way:

[0007] A quantum key distribution encoding module comprises a first circulator CIR1, a stable polarization modulation module, and an optical path selection module.

[0008] The first port of CIR1 is used as the input port of the encoding module;

[0009] The polarization-maintaining fiber between the second port of CIR1 and one port of the polarization-stabilized modulation module is fused at 45°;

[0010] The third port of CIR1 is connected to the input port of the optical path selection module;

[0011] The output port of the optical path selection module serves as the output port of the encoding module;

[0012] The polarization stabilization modulation module is used to perform stable polarization modulation on the input optical signal;

[0013] The optical path selection module is used to enable the optical signal to select two transmission paths, one of which keeps the polarization of the optical signal unchanged to achieve discrete variable polarization encoding, and the other path only passes a specific linear polarization component to achieve continuous variable Gaussian modulation encoding.

[0014] Preferably, the polarization-stabilized modulation module comprises a first polarization beam splitter PBS1, a second polarization beam splitter PBS2, a first polarization modulator PM1, a first Faraday mirror FM1 and a second Faraday mirror FM2.

[0015] The input port of PBS1 serves as an input port of the polarization stabilization modulation module;

[0016] The two output ports of PBS1 and the two input ports of PBS2 are connected respectively through polarization-maintaining optical fibers of different lengths; PM1 is arranged on the longer polarization-maintaining optical fiber;

[0017] The two output ports of PBS2 are connected to FM1 and FM2 respectively.

[0018] Preferably, the polarization-stabilized modulation module comprises a third polarization beam splitter PBS3 and a second polarization modulator PM2.

[0019] The input port of PBS3 serves as an input port of the polarization stabilization modulation module;

[0020] The two output ports of PBS3 are connected to PM2 through polarization-maintaining optical fibers of different lengths.

[0021] Preferably, the optical path selection module comprises a first optical switch OS1, a first polarizer POL1 and a beam splitter BS.

[0022] The input port of OS1 and the output port of BS serve as the input port and output port of the optical path selection module respectively;

[0023] The two output ports of OS1 are connected to the two input ports of BS through polarization-maintaining optical fibers of equal length;

[0024] POL1 is arranged on one of the polarization-maintaining optical fibers.

[0025] Preferably, the optical path selection module comprises a second optical switch OS2 and a fourth polarization beam splitter PBS4.

[0026] An input port and an output port of OS2 are used as an input port and an output port of the optical path selection module respectively;

[0027] Another input port and another output port of OS2 are connected to an input port and an output port of PBS4 respectively through polarization-maintaining optical fibers.

[0028] The present invention also discloses a quantum key distribution transmitter, including a laser LD, an optical transmission module, an attenuator VOA and a coding module.

[0029] The LD is connected to the input port of the optical transmission module;

[0030] The stable polarization modulation module has two ports;

[0031] Perform 45° fiber fusion splicing of the polarization-maintaining optical fiber between one output port of the optical transmission module and another port of the stable polarization modulation module;

[0032] Another output port of the optical transmission module is connected to the input port of the encoding module;

[0033] The optical transmission module is used for outputting only horizontally polarized optical signals;

[0034] The VOA is connected to the output port of the encoding module and is used to adjust the encoded optical signal to a predetermined light intensity;

[0035] The working mode of LD can be switched to pulse mode or continuous mode;

[0036] When the LD works in the pulse mode, the optical path selection module switches to a path that keeps the polarization of the optical signal unchanged, and the stable polarization modulation module is used to realize decoy state modulation and polarization encoding;

[0037] When the LD works in the continuous mode, the optical path selection module is switched to a path that only passes a specific linear polarization component, and the stable polarization modulation module is used to realize pulse generation and Gaussian modulation encoding.

[0038] Preferably, the optical transmission module comprises a second circulator CIR2, a second polarizer POL2,

[0039] The first port, the second port and the third port of CIR2 are respectively connected to the LD, another port of the stable polarization modulation module and the input port of POL2;

[0040] The output port of POL2 serves as the output port of the optical transmission module;

[0041] The polarization passing direction of POL2 is the horizontal polarization direction.

[0042] Preferably, the optical transmission module is a fifth polarization beam splitter PBS5,

[0043] An output port and an input port of PBS5 correspond to the other port connected to LD and the stable polarization modulation module respectively;

[0044] Another output port of PBS2 serves as an output port of the optical transmission module.

[0045] The present invention discloses a quantum key distribution system network, comprising a node A, a node B, a node C, a routing node, and a first channel, a second channel and a third channel respectively connecting each node and the routing node.

[0046] Node A deploys the sender;

[0047] Node B deploys Gaussian modulation continuous variable QKD receiver;

[0048] Node C deploys the polarization-coded QKD receiver;

[0049] The routing node is used to connect the optical fiber channel between node A and node B or connect the optical fiber channel between node A and node C by switching the optical path.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] The present invention proposes a quantum key distribution coding module, a transmitter and a system network. By using stable polarization modulation and simple optical switch switching, not only polarization coding or Gaussian modulation coding can be realized, but also decoy state modulation or pulse generation can be realized, thereby integrating discrete variable and continuous variable coding in one transmitter and realizing flexible reconstruction. In the application of quantum key distribution system network, it can better be compatible with different protocols and reduce the field deployment cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a schematic diagram of the principle of a quantum key distribution encoding module embodiment 1 of the present invention;

[0053] Figure 2 This is a schematic diagram of the principle of the second embodiment of the quantum key distribution encoding module of the present invention;

[0054] Figure 3 This is a schematic diagram of the principle of a first embodiment of a quantum key distribution transmitting end of the present invention;

[0055] Figure 4 This is a schematic diagram of the principle of the second embodiment of the quantum key distribution sending end of the present invention;

[0056] Figure 5 This is a schematic diagram of the network principle of the quantum key distribution system of the present invention. DETAILED DESCRIPTION

[0057] The present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0058] like Figure 1 As shown, a quantum key distribution encoding module embodiment 1,

[0059] It includes a first circulator CIR1, a stable polarization modulation module, and an optical path selection module,

[0060] The first port of CIR1 is used as the input port of the encoding module;

[0061] The polarization-maintaining fiber between the second port of CIR1 and one port of the polarization-stabilized modulation module is fused at 45°;

[0062] The third port of CIR1 is connected to the input port of the optical path selection module;

[0063] The output port of the optical path selection module serves as the output port of the encoding module;

[0064] The polarization stabilization modulation module is used to perform stable polarization modulation on the input optical signal;

[0065] The optical path selection module is used to enable the optical signal to select two transmission paths, one of which keeps the polarization of the optical signal unchanged to achieve discrete variable polarization encoding, and the other path only passes a specific linear polarization component to achieve continuous variable Gaussian modulation encoding.

[0066] The polarization-stabilized modulation module includes a first polarization beam splitter PBS1, a second polarization beam splitter PBS2, a first polarization modulator PM1, a first Faraday mirror FM1 and a second Faraday mirror FM2.

[0067] The input port of PBS1 serves as an input port of the polarization stabilization modulation module;

[0068] The two output ports of PBS1 and the two input ports of PBS2 are connected respectively through polarization-maintaining optical fibers of different lengths; PM1 is arranged on the longer polarization-maintaining optical fiber;

[0069] The two output ports of PBS2 are connected to FM1 and FM2 respectively.

[0070] The optical path selection module includes a first optical switch OS1, a first polarizer POL1 and a beam splitter BS.

[0071] The input port of OS1 and the output port of BS serve as the input port and output port of the optical path selection module respectively;

[0072] The two output ports of OS1 are connected to the two input ports of BS through polarization-maintaining optical fibers of equal length;

[0073] POL1 is arranged on one of the polarization-maintaining optical fibers.

[0074] The specific working process is as follows:

[0075] The horizontally polarized light pulse enters the encoding module, first passes through CIR1 and passes through the 45° fiber fusion point, and the polarization state is rotated from horizontal polarization to 45° polarization, and then reaches PBS1, where it is polarized and split into horizontal polarization components and vertical polarization components of equal amplitude. The horizontal polarization component is directly transmitted, and is also directly transmitted when it reaches PBS2. It is reflected when it reaches FM1, and its polarization is rotated 90° to become vertical polarization. It is reflected when it reaches PBS2, and is modulated by phase j1 when it passes through PM1, and then it is reflected when it reaches PBS1; the vertical polarization component is reflected, and is modulated by phase j2 when it passes through PM1, and then it reaches PBS2 and is reflected to FM1. After being reflected by it, its polarization is rotated 90° to become horizontal polarization, and it is directly transmitted from PBS2 to PBS1. Since the two components have the same path length but different time passing through PM1, they are emitted from PBS1 at the same time, and the polarization is synthesized into one light pulse. The polarization state can be written as

[0076] ,

[0077] in, Then, after passing through the 45° fiber splicing point, the polarization becomes

[0078] ,

[0079] The polarization modulated optical pulse reaches OS1 via CIR1. When OS1 switches to a path without POL1, the optical pulse is emitted directly through BS. At this time, the encoding module is in polarization encoding mode. , four polarization states can be obtained: horizontal polarization (H), right-hand circular polarization (R), vertical polarization (V), and left-hand circular polarization (L), thus completing polarization coding.

[0080] When OS1 switches to the path with POL1, the vertical polarization component of the optical pulse is blocked, and the horizontal polarization passes through POL1 and is emitted from the BS. At this time, the encoding module is in Gaussian modulation encoding mode. The optical pulse emitted from the BS can be written as

[0081] ,

[0082] adjust Satisfy , where U and R are random numbers that satisfy uniform distribution and Rayleigh distribution respectively, and the light pulse becomes

[0083] ,

[0084] That is, the amplitude of the optical pulse follows the Rayleigh distribution, and the phase follows the uniform distribution. Therefore, the two regular components of the optical pulse can be written as

[0085] ,

[0086] From the Box-Muller method, it can be seen that the two regular components of the optical pulse obey the Gaussian distribution, and Gaussian modulation coding can be realized.

[0087] like Figure 2 As shown, the second embodiment of the encoding module:

[0088] It includes a first circulator CIR1, a stable polarization modulation module, and an optical path selection module,

[0089] The first port of CIR1 is used as the input port of the encoding module;

[0090] The polarization-maintaining fiber between the second port of CIR1 and one port of the polarization-stabilized modulation module is fused at 45°;

[0091] The third port of CIR1 is connected to the input port of the optical path selection module;

[0092] The output port of the optical path selection module serves as the output port of the encoding module;

[0093] The polarization stabilization modulation module is used to perform stable polarization modulation on the input optical signal;

[0094] The optical path selection module is used to enable the optical signal to select two transmission paths, one of which keeps the polarization of the optical signal unchanged to achieve discrete variable polarization encoding, and the other path only passes a specific linear polarization component to achieve continuous variable Gaussian modulation encoding.

[0095] The polarization-stabilized modulation module includes a third polarization beam splitter PBS3 and a second polarization modulator PM2.

[0096] The input port of PBS3 serves as an input port of the polarization stabilization modulation module;

[0097] The two output ports of PBS3 are connected to PM2 through polarization-maintaining optical fibers of different lengths.

[0098] The optical path selection module includes a second optical switch OS2 and a fourth polarization beam splitter PBS4.

[0099] An input port and an output port of OS2 are used as an input port and an output port of the optical path selection module respectively;

[0100] Another input port and another output port of OS2 are connected to an input port and an output port of PBS4 respectively through polarization-maintaining optical fibers.

[0101] The specific working process is as follows:

[0102] The horizontally polarized light pulse enters the encoding module, first passes through CIR1 and the 45° fiber fusion point, and the polarization state is rotated from horizontal polarization to 45° polarization, and then reaches PBS3, where it is polarized and split into horizontal polarization components and vertical polarization components of equal amplitude. The horizontal polarization component is directly transmitted, passes through a shorter optical fiber to PM2 and is modulated by phase j1, and then passes through a longer optical fiber to PBS3 and is reflected; the vertical polarization component is reflected, passes through a longer optical fiber to PM2 and is modulated by phase j2, and then passes through a shorter optical fiber to PBS3 and is directly transmitted. Since the path lengths of the two components are the sum of the lengths of the two optical fibers, and the time they pass through PM2 is different, the two components are emitted from PBS3 at the same time, and the polarization is synthesized into a light pulse. The polarization state can be written as

[0103] ,

[0104] in, Then, after passing through the 45° fiber splicing point, the polarization becomes

[0105] ,

[0106] The polarization modulated optical pulse reaches OS2 via CIR1. When OS2 switches to the state where the optical signal is directly emitted from one of its output ports after being incident from one of its input ports, the encoding module is in polarization encoding mode. , four polarization states can be obtained: horizontal polarization (H), right-hand circular polarization (R), vertical polarization (V), and left-hand circular polarization (L), thus completing polarization coding.

[0107] When OS2 switches to another state, that is, the optical signal is incident from one of its input ports and emitted from another output port, then the horizontal polarization component passes through PBS4 and finally emitted from one output port of OS2, the encoding module is in Gaussian modulation encoding mode. The optical pulse can be written as

[0108] ,

[0109] adjust Satisfy , where U and R are random numbers that satisfy uniform distribution and Rayleigh distribution respectively, and the light pulse becomes

[0110] ,

[0111] That is, the amplitude of the optical pulse follows the Rayleigh distribution, and the phase follows the uniform distribution. Therefore, the two regular components of the optical pulse can be written as

[0112] ,

[0113] From the Box-Muller method, it can be seen that the two regular components of the optical pulse obey the Gaussian distribution, and Gaussian modulation coding can be realized.

[0114] like Figure 3 As shown, the first embodiment of the sending end:

[0115] A quantum key distribution transmitter includes an LD, an optical transmission module, an attenuator VOA and a coding module.

[0116] The LD is connected to the input port of the optical transmission module;

[0117] The stable polarization modulation module has two ports;

[0118] Perform 45° fiber fusion splicing of the polarization-maintaining optical fiber between one output port of the optical transmission module and another port of the stable polarization modulation module;

[0119] Another output port of the optical transmission module is connected to the input port of the encoding module;

[0120] The optical transmission module is used for outputting only horizontally polarized optical signals;

[0121] The VOA is connected to the output port of the encoding module and is used to adjust the encoded optical signal to a predetermined light intensity;

[0122] The working mode of LD can be switched to pulse mode or continuous mode;

[0123] When the LD works in the pulse mode, the optical path selection module switches to a path that keeps the polarization of the optical signal unchanged, and the stable polarization modulation module is used to realize decoy state modulation and polarization encoding;

[0124] When the LD works in the continuous mode, the optical path selection module is switched to a path that only passes a specific linear polarization component, and the stable polarization modulation module is used to realize pulse generation and Gaussian modulation encoding.

[0125] The polarization-stabilized modulation module includes a first polarization beam splitter PBS1, a second polarization beam splitter PBS2, a first polarization modulator PM1, a first Faraday mirror FM1 and a second Faraday mirror FM2.

[0126] The input port of PBS1 serves as an input port of the polarization stabilization modulation module;

[0127] The two output ports of PBS1 and the two input ports of PBS2 are connected respectively through polarization-maintaining optical fibers of different lengths; PM1 is arranged on the longer polarization-maintaining optical fiber;

[0128] The two output ports of PBS2 are connected to FM1 and FM2 respectively.

[0129] The optical path selection module includes a first optical switch OS1, a first polarizer POL1 and a beam splitter BS.

[0130] The input port of OS1 and the output port of BS serve as the input port and output port of the optical path selection module respectively;

[0131] The two output ports of OS1 are connected to the two input ports of BS through polarization-maintaining optical fibers of equal length;

[0132] POL1 is arranged on one of the polarization-maintaining optical fibers.

[0133] The optical transmission module includes a second circulator CIR2 and a second polarizer POL2.

[0134] The first port, the second port and the third port of CIR2 are respectively connected to the LD, another port of the stable polarization modulation module and the input port of POL2;

[0135] The output port of POL2 serves as the output port of the optical transmission module;

[0136] The polarization passing direction of POL2 is the horizontal polarization direction.

[0137] The specific working process is as follows:

[0138] The laser LD works in the gain switching mode, generating a horizontally polarized light pulse. After passing through CIR2, it passes through the 45° fiber fusion point, and the polarization state is rotated from horizontal polarization to 45° polarization, and then reaches PBS1, where it is polarized and split into a horizontal polarization component and a vertical polarization component with equal amplitudes. The horizontal polarization component is reflected, and is also reflected when it reaches PBS2. When it reaches FM2, its polarization is rotated 90° and becomes vertical polarization, and it is transmitted through PBS2, and is modulated by phase j3 through PM1, and then is transmitted through PBS1; the vertical polarization component is directly transmitted, and is modulated by phase j4 through PM1, and then reaches PBS2 and is transmitted to FM2. After being reflected by it, its polarization is rotated 90° and becomes horizontal polarization, and it is directly reflected from PBS2 and reaches PBS1 and is reflected. Since the two components have the same path length but different time passing through PM1, they are emitted from PBS1 at the same time, and their polarizations are synthesized into one light pulse. The polarization state can be written as

[0139] ,

[0140] in, Then, after passing through the 45° fiber splicing point, the polarization becomes

[0141] ,

[0142] The polarization modulated light pulse reaches POL2 via CIR2, and only the horizontal polarization component can pass through. The outgoing light intensity is

[0143] ,

[0144] By adjusting Perform light intensity modulation to complete the modulation of the decoy state.

[0145] The horizontally polarized light pulse modulated by the decoy state enters the encoding module, first passes through CIR1 and passes through the 45° fiber fusion point, the polarization state is rotated from horizontal polarization to 45° polarization, and then reaches PBS1, where it is polarized and split into horizontal polarization components and vertical polarization components of equal amplitude. The horizontal polarization component is directly transmitted, and is also directly transmitted when it reaches PBS2. It is reflected when it reaches FM1, and its polarization is rotated 90° to become vertical polarization. It is reflected when it reaches PBS2, and is modulated by phase j1 through PM1, and then it is reflected when it reaches PBS1; the vertical polarization component is reflected, and is modulated by phase j2 through PM1, and then it reaches PBS2 and is reflected to FM1. After being reflected by it, its polarization is rotated 90° to become horizontal polarization, and it is directly transmitted from PBS2 to PBS1. Since the two components have the same path length but different time passing through PM1, they are emitted from PBS1 at the same time, and the polarization is synthesized into a light pulse. The polarization state can be written as

[0146] ,

[0147] in, Then, after passing through the 45° fiber splicing point, the polarization becomes

[0148] ,

[0149] The polarization modulated optical pulse reaches OS1 via CIR1. At this time, OS1 switches to a path without POL1, and the optical pulse is emitted directly through BS. At this time, the encoding module is in polarization encoding mode. , four polarization states can be obtained: horizontal polarization (H), right-hand circular polarization (R), vertical polarization (V), and left-hand circular polarization (L), that is, polarization encoding is completed. After being attenuated to the single photon level by the VOA, it is emitted from the transmitter.

[0150] The laser LD works in continuous mode, generating horizontally polarized continuous light. After a transmission process similar to that of the light pulse in the stable polarization modulation module during the decoy state modulation, and after passing through the horizontal polarization component through CIR2 and POL2, the output light intensity is

[0151] ,

[0152] When adjusting When the light intensity reaches the maximum, When the light intensity is 0, by setting the appropriate The corresponding electrical signal duration can realize pulse modulation.

[0153] The horizontally polarized light pulse after pulse modulation enters the encoding module through CIR1, and enters OS1 after the polarization modulation process. At this time, OS1 switches to the path with POL1, the vertical polarization component of the light pulse is blocked, and the horizontal polarization passes through POL1 and exits through BS. At this time, the encoding module is in Gaussian modulation encoding mode. The light pulse emitted from BS can be written as

[0154] ,

[0155] adjust Satisfy , where U and R are random numbers that satisfy uniform distribution and Rayleigh distribution respectively, and the light pulse becomes

[0156] ,

[0157] That is, the amplitude of the optical pulse follows the Rayleigh distribution, and the phase follows the uniform distribution. Therefore, the two regular components of the optical pulse can be written as

[0158] ,

[0159] From the Box-Muller method, we know that the two regular components of the optical pulse obey Gaussian distribution, which can realize Gaussian modulation coding. After being attenuated to the set light intensity by VOA, it is emitted from the transmitter.

[0160] like Figure 4 As shown, the second embodiment of the sending end:

[0161] A quantum key distribution transmitter includes an LD, an optical transmission module, an attenuator VOA and a coding module.

[0162] The LD is connected to the input port of the optical transmission module;

[0163] The stable polarization modulation module has two ports;

[0164] Perform 45° fiber fusion splicing of the polarization-maintaining optical fiber between one output port of the optical transmission module and another port of the stable polarization modulation module;

[0165] Another output port of the optical transmission module is connected to the input port of the encoding module;

[0166] The optical transmission module is used for outputting only horizontally polarized optical signals;

[0167] The VOA is connected to the output port of the encoding module and is used to adjust the encoded optical signal to a predetermined light intensity;

[0168] The working mode of LD can be switched to pulse mode or continuous mode;

[0169] When the LD works in the pulse mode, the optical path selection module switches to a path that keeps the polarization of the optical signal unchanged, and the stable polarization modulation module is used to realize decoy state modulation and polarization encoding;

[0170] When the LD works in the continuous mode, the optical path selection module is switched to a path that only passes a specific linear polarization component, and the stable polarization modulation module is used to realize pulse generation and Gaussian modulation encoding.

[0171] The polarization-stabilized modulation module includes a third polarization beam splitter PBS3 and a second polarization modulator PM2.

[0172] The input port of PBS3 serves as an input port of the polarization stabilization modulation module;

[0173] The two output ports of PBS3 are connected to PM2 through polarization-maintaining optical fibers of different lengths.

[0174] The optical path selection module includes a second optical switch OS2 and a fourth polarization beam splitter PBS4.

[0175] An input port and an output port of OS2 are used as an input port and an output port of the optical path selection module respectively;

[0176] Another input port and another output port of OS2 are connected to an input port and an output port of PBS4 respectively through polarization-maintaining optical fibers.

[0177] The optical transmission module is a fifth polarization beam splitter PBS5.

[0178] An output port and an input port of PBS5 correspond to the other port connected to LD and the stable polarization modulation module respectively;

[0179] Another output port of PBS2 serves as an output port of the optical transmission module.

[0180] The specific working process is as follows:

[0181] The laser LD works in the gain switching mode, generating a horizontally polarized light pulse. After passing through PBS5 and passing through the 45° fiber fusion point, the polarization state rotates from horizontal polarization to 45° polarization, and then reaches PBS3, where it is polarized and split into a horizontal polarization component and a vertical polarization component with equal amplitudes. The horizontal polarization component is reflected by PBS3, passes through a shorter optical fiber to reach PM2 and is modulated by phase j3, and then passes through a longer optical fiber to reach PBS3 for transmission; the vertical polarization component is transmitted, passes through a longer optical fiber to reach PM2 and is modulated by phase j4, and then passes through a shorter optical fiber to reach PBS3 and is reflected. Since the path lengths of the two components are the sum of the lengths of the two optical fibers, and the time they pass through PM2 is different, the two components are emitted from PBS3 at the same time, and the polarization is synthesized into a light pulse. The polarization state can be written as

[0182] ,

[0183] in, Then, after passing through the 45° fiber splicing point, the polarization becomes

[0184] ,

[0185] The polarization modulated light pulse reaches PBS5, and its vertical polarization component is reflected to CIR1 with a light intensity of

[0186] ,

[0187] By adjusting Perform light intensity modulation to complete the modulation of the decoy state.

[0188] The horizontally polarized light pulse modulated by the entrapped state enters the encoding module, first passes through CIR1 and the 45° fiber fusion point, the polarization state is rotated from horizontal polarization to 45° polarization, and then reaches PBS3, where it is polarized and split into horizontal polarization components and vertical polarization components of equal amplitude. The horizontal polarization component is directly transmitted, passes through a shorter optical fiber to PM2 and is modulated with a phase j1, then passes through a longer optical fiber to PBS3 and is reflected; the vertical polarization component is reflected, passes through a longer optical fiber to PM2 and is modulated with a phase j2, then passes through a shorter optical fiber to PBS3 and is directly transmitted. Since the path lengths of the two components are the sum of the lengths of the two optical fibers, and the time they pass through PM2 is different, the two components are emitted from PBS3 at the same time, and the polarization is synthesized into a light pulse. The polarization state can be written as

[0189] ,

[0190] in, Then, after passing through the 45° fiber splicing point, the polarization becomes

[0191] ,

[0192] The polarization modulated optical pulse reaches OS2 via CIR1. When OS2 switches to the state where the optical signal is directly emitted from one of its output ports after being incident from one of its input ports, the encoding module is in polarization encoding mode. , four polarization states can be obtained: horizontal polarization (H), right-hand circular polarization (R), vertical polarization (V), and left-hand circular polarization (L), that is, polarization encoding is completed. After being attenuated to the single photon level by the VOA, it is emitted from the transmitter.

[0193] The laser LD works in continuous mode, generating horizontally polarized continuous light. After a transmission process similar to that of the light pulse in the stable polarization modulation module during the decoy state modulation, and after the vertical polarization component is reflected by PBS5, the light intensity reaching CIR1 is

[0194] ,

[0195] When adjusting When the light intensity is 0, The light intensity reaches its maximum when the The corresponding electrical signal duration can realize pulse modulation.

[0196] After pulse modulation, the horizontal polarized light pulse enters the encoding module through CIR1, and enters OS2 after the polarization modulation process. When OS2 switches to another state, that is, the optical signal is incident from one of its input ports and emitted from another output port, then the horizontal polarization component passes through PBS4 and finally emits from one output port of OS2. At this time, the encoding module is in Gaussian modulation encoding mode. The optical pulse can be written as

[0197] ,

[0198] adjust Satisfy , where U and R are random numbers that satisfy uniform distribution and Rayleigh distribution respectively, and the light pulse becomes

[0199] ,

[0200] That is, the amplitude of the optical pulse follows the Rayleigh distribution, and the phase follows the uniform distribution. Therefore, the two regular components of the optical pulse can be written as

[0201]

[0202] From the Box-Muller method, it can be seen that the two regular components of the optical pulse obey the Gaussian distribution, and Gaussian modulation coding can be realized.

[0203] like Figure 5 , a quantum key distribution system network, comprising a node A, a node B, a node C, a routing node, and a first channel, a second channel and a third channel respectively connecting each node and the routing node,

[0204] Node A deploys any of 6-8 senders;

[0205] Node B deploys Gaussian modulation continuous variable QKD receiver;

[0206] Node C deploys the polarization-coded QKD receiver;

[0207] The routing node is used to connect the optical fiber channel between node A and node B or connect the optical fiber channel between node A and node C by switching the optical path.

[0208] The specific working process is as follows:

[0209] Node A, node B, and node C are connected to the routing node respectively, wherein the first channel from node A to the routing node and the second channel from node B to the routing node are shorter, and the third channel from node C to the routing node is longer.

[0210] When the optical fiber channel between node A and node B is connected, that is, node A is connected to node B through the first channel and the second channel. Due to the short channel length, the QKD transmitter of node A is controlled to switch to Gaussian modulation coding mode, and node B deploys Gaussian modulation continuous variable QKD receiver. The two form a point-to-point continuous variable quantum key distribution system, which can perform Gaussian modulation continuous variable protocol quantum key distribution.

[0211] When the optical fiber channel between node A and node C is connected, that is, node A is connected to node C through the first channel and the third channel. Due to the long channel length, the QKD transmitter of node A is controlled to switch to polarization encoding mode, and node C deploys polarization encoding QKD receiver. The two form a point-to-point polarization encoding quantum key distribution system, which can perform polarization encoding BB84 protocol quantum key distribution.

[0212] By reconstructing the coding module structure of the QKD transmitter deployed at node A, switching between Gaussian modulation coding and polarization coding can be achieved without deploying two separate Gaussian modulation coding transmitters and polarization coding transmitters at node A.

[0213] It can be seen from the embodiments of the present invention that the present invention proposes a quantum key distribution coding module, a transmitter and a network, which can realize polarization coding or Gaussian modulation coding, and can also realize entrapped state modulation or pulse generation by using stable polarization modulation and simple optical switch switching, thereby integrating discrete variable and continuous variable coding in one transmitter and realizing flexible reconstruction. In the application of quantum key distribution system network, it can better be compatible with different protocols and reduce the cost of field deployment.

Claims

1. A quantum key distribution encoding module, characterized in that: It includes a first circulator CIR1, a polarization stabilization modulation module, and an optical path selection module, The first port of CIR1 is used as the input port of the encoding module; The polarization-maintaining fiber between the second port of CIR1 and one port of the polarization-stabilized modulation module is fused at 45°; The third port of CIR1 is connected to the input port of the optical path selection module; The output port of the optical path selection module serves as the output port of the encoding module; The polarization stabilization modulation module is used to perform stable polarization modulation on the input optical signal; The optical path selection module is used to enable the optical signal to select two transmission paths, one of which keeps the polarization of the optical signal unchanged to achieve discrete variable polarization encoding, and the other path only passes a specific linear polarization component to achieve continuous variable Gaussian modulation encoding. The polarization-stabilized modulation module includes a first polarization beam splitter PBS1, a second polarization beam splitter PBS2, a first polarization modulator PM1, a first Faraday mirror FM1 and a second Faraday mirror FM2. The input port of PBS1 serves as an input port of the polarization stabilization modulation module; The two output ports of PBS1 and the two input ports of PBS2 are connected respectively through polarization-maintaining optical fibers of different lengths; PM1 is arranged on the longer polarization-maintaining optical fiber; The two output ports of PBS2 are connected to FM1 and FM2 respectively. The optical path selection module includes a first optical switch OS1, a first polarizer POL1 and a beam splitter BS. The input port of OS1 and the output port of BS serve as the input port and output port of the optical path selection module respectively; The two output ports of OS1 are connected to the two input ports of BS through polarization-maintaining optical fibers of equal length; POL1 is arranged on one of the polarization-maintaining optical fibers.

2. The quantum key distribution encoding module according to claim 1, characterized in that: The polarization-stabilized modulation module includes a third polarization beam splitter PBS3 and a second polarization modulator PM2. The input port of PBS3 serves as an input port of the polarization stabilization modulation module; The two output ports of PBS3 are connected to PM2 through polarization-maintaining optical fibers of different lengths.

3. The quantum key distribution encoding module according to claim 1, characterized in that: The optical path selection module includes a second optical switch OS2 and a fourth polarization beam splitter PBS4. An input port and an output port of OS2 are used as an input port and an output port of the optical path selection module respectively; Another input port and another output port of OS2 are connected to an input port and an output port of PBS4 respectively through polarization-maintaining optical fibers.

4. A quantum key distribution transmitter, characterized in that: It comprises a laser LD, an optical transmission module, an attenuator VOA and one of the encoding modules in claims 1-3, The LD is connected to the input port of the optical transmission module; The polarization-stabilized modulation module has two ports; Performing 45° fiber fusion splicing of a polarization-maintaining optical fiber between an output port of an optical transmission module and another port of a polarization-stabilized modulation module; Another output port of the optical transmission module is connected to the input port of the encoding module; The optical transmission module is used for outputting only horizontally polarized optical signals; The VOA is connected to the output port of the encoding module and is used to adjust the encoded optical signal to a predetermined light intensity; The working mode of LD can be switched to pulse mode or continuous mode; When the LD works in the pulse mode, the optical path selection module switches to a path that keeps the polarization of the optical signal unchanged, and the polarization stabilization modulation module is used to realize decoy state modulation and polarization coding; When the LD works in the continuous mode, the optical path selection module switches to a path that only passes a specific linear polarization component, and the polarization stabilization modulation module is used to realize pulse generation and Gaussian modulation encoding. The optical transmission module includes a second circulator CIR2 and a second polarizer POL2. The first port, the second port and the third port of CIR2 are respectively connected to the LD, another port of the polarization stabilization modulation module and the input port of POL2; The output port of POL2 serves as the output port of the optical transmission module; The polarization passing direction of POL2 is the horizontal polarization direction.

5. The quantum key distribution transmitter according to claim 4, characterized in that: The optical transmission module is a fifth polarization beam splitter PBS5. An output port and an input port of PBS5 correspond to the other port connected to LD and polarization stabilization modulation module respectively; Another output port of PBS2 serves as an output port of the optical transmission module.

6. A quantum key distribution system network, characterized in that: It includes a node A, a node B, a node C, a routing node, and a first channel, a second channel, and a third channel respectively connecting each node and the routing node. Node A deploys one of the transmitters in claims 4-5; Node B deploys Gaussian modulation continuous variable QKD receiver; Node C deploys the polarization-coded QKD receiver; The routing node is used to connect the optical fiber channel between node A and node B or connect the optical fiber channel between node A and node C by switching the optical path.

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