CN119299097B - Quantum key distribution coding module, sending end and system network - Google Patents
Quantum key distribution coding module, sending end and system network Download PDFInfo
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Abstract
The invention belongs to the technical field of optical secret communication, and discloses a quantum key distribution coding module, a transmitting end and a system network, wherein the coding module comprises a circulator, a stable polarization modulation module and an optical path selection module; the polarization stabilization modulation module is used for carrying out stable polarization modulation on an input optical signal; the optical path selection module is used for enabling the optical signal to select two transmission paths, wherein one path enables the polarization of the optical signal to be unchanged so as to realize discrete variable polarization coding, and the other path only passes through a specific linear polarization component so as to realize continuous variable Gaussian modulation coding. Compared with the prior art, the invention not only can realize polarization coding or Gaussian modulation coding, but also can realize decoy state modulation or pulse generation, thereby integrating discrete variable and continuous variable coding into one transmitting end and realizing flexible reconstruction, and can be applied to different protocols with better compatibility in the application, and reduce the field deployment cost.
Description
Technical Field
The present invention relates to the field of optical secret communication technologies, and in particular, to a quantum key distribution coding module, a transmitting end, and a system network.
Background
Quantum Key Distribution (QKD) has been demonstrated to have information-based security, with an important role in secure communications. The coding schemes of QKD can be divided into two broad categories, discrete Variable (DV) and Continuous Variable (CV). Discrete Variable (DV) and Continuous Variable (CV) protocols each have advantages. The DV-QKD safety proves that the system is mature, the long-distance transmission capability is strong, the transmission distance of the optical fiber BB84 system reaches 421 km, and the transmission distance can reach 1002 km under the double-field scheme. CV-QKD has a high key generation rate (SKR) at short distances, but because of sensitivity to loss, current fiber optic systems are only 203 km apart at maximum.
In the quantum key distribution practical application, a multi-node quantum key distribution system network needs to be constructed, and multiple paths may exist between two nodes, including a relay node connecting one end user and another end user. Thus, depending on the available routes and channel parameters connecting each node, the individual transmission segments may maximize the overall key generation rate by choosing to use either a discrete variable or a continuous variable protocol. At this time, for a specific node, in order to meet whether the DV protocol or the CV protocol can be selected according to the actual link requirements, the conventional method is to deploy two dedicated senders simultaneously, which clearly increases the complexity and cost of the system. With hybrid code senders that can switch between DV and CV, network characteristics can be actively reconfigured in a software-defined manner, thereby increasing its flexibility and improving QKD integration with existing telecommunications infrastructure.
Sabatini M, et al paper Hybrid encoder for DISCRETE AND continuous variable QKD. arxiv:2408.17412, 2024. Sagnac loop structure is adopted, DV polarization coding and CV phase shift keying coding can be respectively realized by adding delay or not, however, extra intensity modulation module is needed to realize decoy state modulation during DV coding, and the complexity of the system is increased. In addition, the security of the former is not perfect due to the phase shift keying coding compared to the gaussian modulation CV protocol, and the security rate is lower than the latter due to the lower key bits per symbol coding.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a quantum key distribution coding module, a sending end and a system network.
The technical scheme of the invention is realized as follows:
A quantum key distribution coding module comprises a first circulator CIR1, a stable polarization modulation module and an optical path selection module,
The CIR1 first port is used as an input port of the coding module;
the second port of the CIR1 and the polarization maintaining optical fiber between one port of the polarization stability modulation module are subjected to 45-degree optical fiber fusion;
The third port of the CIR1 is connected with the input port of the optical path selection module;
The output port of the optical path selection module is used as the output port of the coding module;
the polarization stabilization modulation module is used for carrying out stable polarization modulation on an input optical signal;
The optical path selection module is used for enabling the optical signal to select two transmission paths, wherein one path enables the optical signal to be polarized unchanged to achieve discrete variable polarization coding, and the other path enables continuous variable Gaussian modulation coding only through specific linear polarization components.
Preferably, the polarization stable 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,
The input port of the PBS1 is used as one input port of the polarization stable modulation module;
two output ports of the PBS1 are respectively connected with two input ports of the PBS2 through polarization maintaining optical fibers with different lengths, wherein PM1 is arranged on the longer polarization maintaining optical fiber;
two output ports of PBS2 are connected to FM1 and FM2, respectively.
Preferably, the polarization stable modulation module comprises a third polarization beam splitter PBS3 and a second polarization modulator PM2,
The input port of the PBS3 is used as one input port of the polarization stable modulation module;
The two output ports of the PBS3 are respectively connected with PM2 through polarization maintaining fibers with different lengths.
Preferably, the optical path selection module comprises a first optical switch OS1, a first polarizer POL1 and a beam splitter BS,
The input port of the OS1 and the output port of the BS are respectively used as the input port and the output port of the optical path selection module;
The two output ports of the OS1 are respectively connected with the two input ports of the BS through polarization maintaining optical fibers with equal lengths;
POL1 is disposed on one of the polarization maintaining fibers.
Preferably, the optical path selection module comprises a second optical switch OS2 and a fourth polarizing beam splitter PBS4,
An input port and an output port of the OS2 are respectively used as an input port and an output port of the optical path selection module;
the other input port and the other output port of the OS2 are connected to the input port and one output port of the PBS4 through polarization maintaining fibers, respectively.
The invention also discloses a quantum key distribution transmitting end, which comprises a laser LD, an optical transmission module, an attenuator VOA and a coding module,
The LD is connected with an input port of the optical transmission module;
the stable polarization modulation module is provided with two ports;
carrying out 45-degree optical fiber fusion on a polarization maintaining optical fiber between one output port of the optical transmission module and the other port of the stable polarization modulation module;
the other output port of the optical transmission module is connected with the input port of the encoding module;
The optical transmission module is used for outputting only horizontally polarized optical signals;
The VOA is connected with an output port of the coding module and is used for adjusting the coded optical signal to a preset light intensity;
The operation mode of the LD may be switched to a pulse mode or a continuous mode;
When the LD works in a pulse mode, the optical path selection module is switched into a path for keeping the polarization of the optical signal unchanged, and the stable polarization modulation module is used for realizing decoy state modulation and polarization coding;
when the LD is operated in a continuous mode, the optical path selection module is switched to a path passing through only a specific linear polarization component, and the stable polarization modulation module is used for realizing pulse generation and Gaussian modulation coding.
Preferably, the optical transmission module comprises a second circulator CIR2, a second polarizer POL2,
The first port, the second port and the third port of the CIR2 are respectively and correspondingly connected with the LD, the other port of the stable polarization modulation module and the input port of the POL 2;
the output port of the POL2 is used as the output port of the optical transmission module;
The polarization passing direction of POL2 is a horizontal polarization direction.
Preferably, the optical transmission module is a fifth polarizing beam splitter PBS5,
One output port and one input port of the PBS5 are respectively and correspondingly connected with the LD and the other port of the stable polarization modulation module;
The other output port of PBS2 serves as the output port of the optical transmission module.
The invention discloses a quantum key distribution system network, which comprises a node A, a node B, a node C, a routing node, a first channel, a second channel and a third channel which are respectively connected with each node and the routing node,
The node A deploys a transmitting end;
The node B deploys a Gaussian modulation continuous variable QKD receiving end;
Node C deploys a polarization encoding QKD receiving end;
the routing node is used to make fibre channel between node a and node B or between node a and node C by switching the optical path.
Compared with the prior art, the invention has the following beneficial effects:
The invention provides a quantum key distribution coding module, a transmitting end and a system network, which can realize polarization coding or Gaussian modulation coding and decoy state modulation or pulse generation by utilizing stable polarization modulation and simple optical switch switching, thereby integrating discrete variable and continuous variable coding into one transmitting end and realizing flexible reconstruction. The quantum key distribution system network can be applied to different protocols with better compatibility, and the field deployment cost is reduced.
Drawings
FIG. 1 is a schematic diagram of a quantum key distribution encoding module according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a second principle of an embodiment of a quantum key distribution encoding module according to the present invention;
FIG. 3 is a schematic diagram of a quantum key distribution transmitting end according to an embodiment of the present invention;
fig. 4 is a schematic diagram of a second principle of an embodiment of a quantum key distribution transmitting end of the present invention;
fig. 5 is a schematic diagram of a network principle of the quantum key distribution system of the present invention.
Detailed Description
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown.
As shown in fig. 1, a quantum key distribution encoding module embodiment one,
Comprises a first circulator CIR1, a stable polarization modulation module and an optical path selection module,
The CIR1 first port is used as an input port of the coding module;
the second port of the CIR1 and the polarization maintaining optical fiber between one port of the polarization stability modulation module are subjected to 45-degree optical fiber fusion;
The third port of the CIR1 is connected with the input port of the optical path selection module;
The output port of the optical path selection module is used as the output port of the coding module;
the polarization stabilization modulation module is used for carrying out stable polarization modulation on an input optical signal;
The optical path selection module is used for enabling the optical signal to select two transmission paths, wherein one path enables the optical signal to be polarized unchanged to achieve discrete variable polarization coding, and the other path enables continuous variable Gaussian modulation coding only through specific linear polarization components.
The polarization stable 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,
The input port of the PBS1 is used as one input port of the polarization stable modulation module;
two output ports of the PBS1 are respectively connected with two input ports of the PBS2 through polarization maintaining optical fibers with different lengths, wherein PM1 is arranged on the longer polarization maintaining optical fiber;
two output ports of PBS2 are connected to FM1 and FM2, respectively.
The optical path selection module comprises a first optical switch OS1, a first polarizer POL1 and a beam splitter BS,
The input port of the OS1 and the output port of the BS are respectively used as the input port and the output port of the optical path selection module;
The two output ports of the OS1 are respectively connected with the two input ports of the BS through polarization maintaining optical fibers with equal lengths;
POL1 is disposed on one of the polarization maintaining fibers.
The specific working process is as follows:
The light pulse with horizontal polarization enters the coding module, passes through the CIR1 and passes through a 45-degree optical fiber fusion point, the polarization state is rotated from horizontal polarization to 45-degree polarization, then the light pulse reaches the PBS1, and the light pulse is polarized and split into a horizontal polarization component and a vertical polarization component with equal amplitude. The horizontal polarization component is directly transmitted, reaches PBS2 and is directly transmitted, reaches FM1 and is reflected, the polarization is rotated by 90 degrees, becomes vertical polarization, reaches PBS2 and is reflected, passes through PM1 and is modulated by phase j1 and then reaches PBS1 and is reflected, the vertical polarization component is reflected, passes through PM1 and is modulated by phase j2 and then reaches PBS2 and is reflected to FM1, the polarization is rotated by 90 degrees after being reflected by the vertical polarization component and becomes horizontal polarization, and the vertical polarization component is directly transmitted from PBS2 and reaches PBS1. Because the two components have the same path length and different passing time of PM1, the two components are emitted from PBS1 at the same time, the polarization is synthesized into an optical pulse, and the polarization state can be written as
,
Wherein, . Then pass through 45 degree optical fiber fusion point polarization to become
,
The polarized light pulse reaches the OS1 through the CIR1, and when the OS1 is switched to the path without the POL1, the light pulse directly exits through the BS, and the coding module is in a polarization coding mode. Regulation ofThe polarization coding can be completed by obtaining 4 polarization states of horizontal polarization (H), right-handed circular polarization (R), vertical polarization (V) and left-handed circular polarization (L).
When OS1 switches to the path with POL1, the vertical polarization component of the light pulse is blocked and the horizontal polarization exits through BS through POL1, at which point the coding module is in gaussian modulation coding mode. The light pulse exiting from BS can be written as
,
Regulation ofRespectively satisfy the followingWherein U and R are random numbers satisfying uniform distribution and Rayleigh distribution, respectively, and the light pulse becomes
,
I.e. the amplitude of the light pulse obeys the rayleigh distribution and the phase obeys the uniform distribution. Thus, the two canonical components of the light pulse can be written as
,
The Box-Muller method shows that two regular components of the light pulse follow Gaussian distribution, and Gaussian modulation coding can be realized.
As shown in fig. 2, a second embodiment of the encoding module:
comprises a first circulator CIR1, a stable polarization modulation module and an optical path selection module,
The CIR1 first port is used as an input port of the coding module;
the second port of the CIR1 and the polarization maintaining optical fiber between one port of the polarization stability modulation module are subjected to 45-degree optical fiber fusion;
The third port of the CIR1 is connected with the input port of the optical path selection module;
The output port of the optical path selection module is used as the output port of the coding module;
the polarization stabilization modulation module is used for carrying out stable polarization modulation on an input optical signal;
The optical path selection module is used for enabling the optical signal to select two transmission paths, wherein one path enables the optical signal to be polarized unchanged to achieve discrete variable polarization coding, and the other path enables continuous variable Gaussian modulation coding only through specific linear polarization components.
The polarization stable modulation module comprises a third polarization beam splitter PBS3 and a second polarization modulator PM2,
The input port of the PBS3 is used as one input port of the polarization stable modulation module;
The two output ports of the PBS3 are respectively connected with PM2 through polarization maintaining fibers with different lengths.
The optical path selection module comprises a second optical switch OS2 and a fourth polarizing beam splitter PBS4,
An input port and an output port of the OS2 are respectively used as an input port and an output port of the optical path selection module;
the other input port and the other output port of the OS2 are connected to the input port and one output port of the PBS4 through polarization maintaining fibers, respectively.
The specific working process is as follows:
The light pulse with horizontal polarization enters the coding module, passes through the CIR1 and passes through a 45-degree optical fiber fusion point, the polarization state is rotated from horizontal polarization to 45-degree polarization, then the light pulse reaches the PBS3, and the light pulse is polarized and split into a horizontal polarization component and a vertical polarization component with equal amplitude. Wherein the horizontally polarized component is directly transmitted through the shorter fiber to the PM2 modulated phase j1 and then through the longer fiber to the PBS3 and the vertically polarized component is reflected and then through the longer fiber to the PM2 modulated phase j2 and then through the shorter fiber to the PBS 3. Because the two components have the path length which is the sum of the two optical fiber lengths and the time of passing through PM2 is different, the two components are emitted from PBS3 at the same time, the polarization is synthesized into an optical pulse, and the polarization state can be written as
,
Wherein, . Then pass through 45 degree optical fiber fusion point polarization to become
,
The polarization-modulated light pulses reach OS2 via CIR1, and the coding module is in a polarization coding mode when OS2 switches to a state where the light signal is incident from one of its input ports and directly exits from one of its output ports. At this time by adjustingThe polarization coding can be completed by obtaining 4 polarization states of horizontal polarization (H), right-handed circular polarization (R), vertical polarization (V) and left-handed circular polarization (L).
When OS2 switches to another state, i.e. the optical signal is incident from one of its input ports and exits from the other of its output ports, then the horizontally polarized component passes through PBS4 and finally exits from one of the output ports of OS2, the coding module is in gaussian modulation coding mode. The light pulse can be written as
,
Regulation ofRespectively satisfy the followingWherein U and R are random numbers satisfying uniform distribution and Rayleigh distribution, respectively, and the light pulse becomes
,
I.e. the amplitude of the light pulse obeys the rayleigh distribution and the phase obeys the uniform distribution. Thus, the two canonical components of the light pulse can be written as
,
The Box-Muller method shows that two regular components of the light pulse follow Gaussian distribution, and Gaussian modulation coding can be realized.
As shown in fig. 3, the first transmitting end embodiment:
A quantum key distribution transmitting end comprises an LD, an optical transmission module, an attenuator VOA and a coding module,
The LD is connected with an input port of the optical transmission module;
the stable polarization modulation module is provided with two ports;
carrying out 45-degree optical fiber fusion on a polarization maintaining optical fiber between one output port of the optical transmission module and the other port of the stable polarization modulation module;
the other output port of the optical transmission module is connected with the input port of the encoding module;
The optical transmission module is used for outputting only horizontally polarized optical signals;
The VOA is connected with an output port of the coding module and is used for adjusting the coded optical signal to a preset light intensity;
The operation mode of the LD may be switched to a pulse mode or a continuous mode;
When the LD works in a pulse mode, the optical path selection module is switched into a path for keeping the polarization of the optical signal unchanged, and the stable polarization modulation module is used for realizing decoy state modulation and polarization coding;
when the LD is operated in a continuous mode, the optical path selection module is switched to a path passing through only a specific linear polarization component, and the stable polarization modulation module is used for realizing pulse generation and Gaussian modulation coding.
The polarization stable 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,
The input port of the PBS1 is used as one input port of the polarization stable modulation module;
two output ports of the PBS1 are respectively connected with two input ports of the PBS2 through polarization maintaining optical fibers with different lengths, wherein PM1 is arranged on the longer polarization maintaining optical fiber;
two output ports of PBS2 are connected to FM1 and FM2, respectively.
The optical path selection module comprises a first optical switch OS1, a first polarizer POL1 and a beam splitter BS,
The input port of the OS1 and the output port of the BS are respectively used as the input port and the output port of the optical path selection module;
The two output ports of the OS1 are respectively connected with the two input ports of the BS through polarization maintaining optical fibers with equal lengths;
POL1 is disposed on one of the polarization maintaining fibers.
The optical transmission module comprises a second circulator CIR2 and a second polarizer POL2,
The first port, the second port and the third port of the CIR2 are respectively and correspondingly connected with the LD, the other port of the stable polarization modulation module and the input port of the POL 2;
the output port of the POL2 is used as the output port of the optical transmission module;
The polarization passing direction of POL2 is a horizontal polarization direction.
The specific working process is as follows:
The laser LD works in a gain switch mode, generates light pulses with horizontal polarization, transmits through CIR2, passes through a 45-degree optical fiber fusion point, rotates the polarization state from the horizontal polarization to 45-degree polarization, then reaches PBS1, and is polarized and split into a horizontal polarization component and a vertical polarization component with equal amplitude. The horizontal polarization component is reflected, the polarization of the light reaching the PBS2 is rotated by 90 degrees, the light turns into vertical polarization, the light reaching the PBS2 is transmitted, the light passes through the PM1 to be modulated by the phase j3 and then reaches the PBS1 to be transmitted, the vertical polarization component is directly transmitted, the light passes through the PM1 to be modulated by the phase j4 and then reaches the PBS2 to be transmitted to the PBS2, the polarization of the light turns into horizontal polarization after being reflected by the light turns into horizontal polarization after being rotated by 90 degrees, and the light passes through the PBS1 after being reflected from the PBS2 and is reflected. Because the two components have the same path length and different passing time of PM1, the two components are emitted from PBS1 at the same time, the polarization is synthesized into an optical pulse, and the polarization state can be written as
,
Wherein, . Then pass through 45 degree optical fiber fusion point polarization to become
,
The polarized light pulse reaches POL2 via CIR2, only horizontal polarized component can pass through, and the emergent light intensity is
,
I.e. by adjustingAnd (5) performing light intensity modulation to finish the modulation of the decoy state.
The horizontally polarized light pulse modulated by the decoy state enters the coding module, firstly passes through a CIR1 and passes through a 45-degree optical fiber fusion point, then the polarization state is rotated from the horizontal polarization to the 45-degree polarization, then reaches the PBS1, and is polarized and split into a horizontal polarization component and a vertical polarization component with equal amplitude. The horizontal polarization component is directly transmitted, reaches PBS2 and is directly transmitted, reaches FM1 and is reflected, the polarization is rotated by 90 degrees, becomes vertical polarization, reaches PBS2 and is reflected, passes through PM1 and is modulated by phase j1 and then reaches PBS1 and is reflected, the vertical polarization component is reflected, passes through PM1 and is modulated by phase j2 and then reaches PBS2 and is reflected to FM1, the polarization is rotated by 90 degrees after being reflected by the vertical polarization component and becomes horizontal polarization, and the vertical polarization component is directly transmitted from PBS2 and reaches PBS1. Because the two components have the same path length and different passing time of PM1, the two components are emitted from PBS1 at the same time, the polarization is synthesized into an optical pulse, and the polarization state can be written as
,
Wherein, . Then pass through 45 degree optical fiber fusion point polarization to become
,
The polarized light pulse reaches the OS1 through the CIR1, the OS1 is switched to the path without the POL1, the light pulse directly exits through the BS, and the coding module is in a polarization coding mode. Regulation ofThe polarization coding can be completed by obtaining 4 polarization states of horizontal polarization (H), right-handed circular polarization (R), vertical polarization (V) and left-handed circular polarization (L). And the single photon is attenuated to the single photon magnitude through the VOA and then emitted from the transmitting end.
The laser LD works in a continuous mode to generate continuous light with horizontal polarization, and after the continuous light is transmitted by CIR2 and POL2 through the horizontal polarization component and the transmission process of the light pulse in the stable polarization modulation module is similar to that of the light pulse in the decoy state modulation, the emergent light intensity is that
,
When adjustingThe light intensity reaches the maximum when adjustingThe light intensity is 0, so by setting properPulse modulation can be achieved for the duration of the corresponding electrical signal.
The pulse modulated horizontal polarized light pulse enters the coding 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, and the coding module is in gaussian modulation coding mode. The light pulse exiting from BS can be written as
,
Regulation ofRespectively satisfy the followingWherein U and R are random numbers satisfying uniform distribution and Rayleigh distribution, respectively, and the light pulse becomes
,
I.e. the amplitude of the light pulse obeys the rayleigh distribution and the phase obeys the uniform distribution. Thus, the two canonical components of the light pulse can be written as
,
The Box-Muller method shows that two regular components of the light pulse follow Gaussian distribution, and Gaussian modulation coding can be realized. And the light is attenuated to the set light intensity through the VOA and then emitted from the transmitting end.
As shown in fig. 4, a second transmitting-end embodiment:
A quantum key distribution transmitting end comprises an LD, an optical transmission module, an attenuator VOA and a coding module,
The LD is connected with an input port of the optical transmission module;
the stable polarization modulation module is provided with two ports;
carrying out 45-degree optical fiber fusion on a polarization maintaining optical fiber between one output port of the optical transmission module and the other port of the stable polarization modulation module;
the other output port of the optical transmission module is connected with the input port of the encoding module;
The optical transmission module is used for outputting only horizontally polarized optical signals;
The VOA is connected with an output port of the coding module and is used for adjusting the coded optical signal to a preset light intensity;
The operation mode of the LD may be switched to a pulse mode or a continuous mode;
When the LD works in a pulse mode, the optical path selection module is switched into a path for keeping the polarization of the optical signal unchanged, and the stable polarization modulation module is used for realizing decoy state modulation and polarization coding;
when the LD is operated in a continuous mode, the optical path selection module is switched to a path passing through only a specific linear polarization component, and the stable polarization modulation module is used for realizing pulse generation and Gaussian modulation coding.
The polarization stable modulation module comprises a third polarization beam splitter PBS3 and a second polarization modulator PM2,
The input port of the PBS3 is used as one input port of the polarization stable modulation module;
The two output ports of the PBS3 are respectively connected with PM2 through polarization maintaining fibers with different lengths.
The optical path selection module comprises a second optical switch OS2 and a fourth polarizing beam splitter PBS4,
An input port and an output port of the OS2 are respectively used as an input port and an output port of the optical path selection module;
the other input port and the other output port of the OS2 are connected to the input port and one output port of the PBS4 through polarization maintaining fibers, respectively.
The optical transmission module is a fifth polarizing beam splitter PBS5,
One output port and one input port of the PBS5 are respectively and correspondingly connected with the LD and the other port of the stable polarization modulation module;
The other output port of PBS2 serves as the output port of the optical transmission module.
The specific working process is as follows:
The laser LD works in a gain switch mode, generates light pulses with horizontal polarization, transmits through the PBS5, passes through a 45-degree optical fiber fusion point, rotates the polarization state from the horizontal polarization to the 45-degree polarization, then reaches the PBS3, and is polarized and split into a horizontal polarization component and a vertical polarization component with equal amplitude. Wherein the horizontally polarized component is reflected by the PBS3, reaches the PM2 modulated phase j3 through the shorter fiber and then reaches the PBS3 through the longer fiber, and the vertically polarized component is transmitted, reaches the PM2 modulated phase j4 through the longer fiber and then reaches the PBS3 through the shorter fiber and is reflected. Because the two components have the path length which is the sum of the two optical fiber lengths and the time of passing through PM2 is different, the two components are emitted from PBS3 at the same time, the polarization is synthesized into an optical pulse, and the polarization state can be written as
,
Wherein, . Then pass through 45 degree optical fiber fusion point polarization to become
,
The polarization-modulated light pulse reaches PBS5, whose vertically polarized component is reflected to CIR1, at an intensity of
,
I.e. by adjustingAnd (5) performing light intensity modulation to finish the modulation of the decoy state.
The light pulse with the horizontal polarization after being modulated by the decoy state enters the coding module, firstly passes through the CIR1 and passes through a 45-degree optical fiber fusion point, then the polarization state is rotated from the horizontal polarization to the 45-degree polarization, then reaches the PBS3, and is polarized and split into a horizontal polarization component and a vertical polarization component with equal amplitude. Wherein the horizontally polarized component is directly transmitted through the shorter fiber to the PM2 modulated phase j1 and then through the longer fiber to the PBS3 and the vertically polarized component is reflected and then through the longer fiber to the PM2 modulated phase j2 and then through the shorter fiber to the PBS 3. Because the two components have the path length which is the sum of the two optical fiber lengths and the time of passing through PM2 is different, the two components are emitted from PBS3 at the same time, the polarization is synthesized into an optical pulse, and the polarization state can be written as
,
Wherein, . Then pass through 45 degree optical fiber fusion point polarization to become
,
The polarization-modulated light pulses reach OS2 via CIR1, and the coding module is in a polarization coding mode when OS2 switches to a state where the light signal is incident from one of its input ports and directly exits from one of its output ports. At this time by adjustingThe polarization coding can be completed by obtaining 4 polarization states of horizontal polarization (H), right-handed circular polarization (R), vertical polarization (V) and left-handed circular polarization (L). And the single photon is attenuated to the single photon magnitude through the VOA and then emitted from the transmitting end.
The laser LD works in a continuous mode to generate continuous light with horizontal polarization, and after the continuous light is transmitted by the light pulse in the stable polarization modulation module similar to the light pulse in the decoy state modulation and the vertical polarization component is reflected by the PBS5, the light intensity reaching the CIR1 is that
,
When adjustingThe light intensity is 0 when adjustingThe light intensity reaches the maximum, so by setting the properPulse modulation can be achieved for the duration of the corresponding electrical signal.
The pulse modulated horizontal polarized light pulse enters the coding module through CIR1, and enters OS2 after the polarization modulation process. When OS2 switches to another state, i.e. the optical signal is incident from one of its input ports and exits from the other of its output ports, then the horizontally polarized component passes through PBS4 and finally exits from one of the output ports of OS2, the coding module is in gaussian modulation coding mode. The light pulse can be written as
,
Regulation ofRespectively satisfy the followingWherein U and R are random numbers satisfying uniform distribution and Rayleigh distribution, respectively, and the light pulse becomes
,
I.e. the amplitude of the light pulse obeys the rayleigh distribution and the phase obeys the uniform distribution. Thus, the two canonical components of the light pulse can be written as
The Box-Muller method shows that two regular components of the light pulse follow Gaussian distribution, and Gaussian modulation coding can be realized.
As shown in fig. 5, a quantum key distribution system network includes a node a, a node B, a node C, a routing node, and first, second and third channels respectively connecting each node with the routing node,
The node A deploys any one of the sending ends 6-8;
The node B deploys a Gaussian modulation continuous variable QKD receiving end;
Node C deploys a polarization encoding QKD receiving end;
the routing node is used to make fibre channel between node a and node B or between node a and node C by switching the optical path.
The specific working process is as follows:
The node A, the node B and the node C are respectively connected with the routing node, wherein a first channel from the node A to the routing node is shorter than a second channel from the node B to the routing node, and a third channel from the node C to the routing node is longer.
When the fibre channel between node a and node B is on, node a is connected to node B via the first channel and the second channel. Because the channel length is shorter, the QKD transmitting end of the control node A is switched to a Gaussian modulation coding mode, the node B deploys a Gaussian modulation continuous variable QKD receiving end, and the two form a point-to-point continuous variable quantum key distribution system, so that Gaussian modulation continuous variable protocol quantum key distribution can be carried out.
When the fibre channel between node a and node C is on, node a is connected to node C via the first channel and the third channel. Because the channel length is longer, the QKD transmitting end of the control node A is switched into a polarization coding mode, the node C deploys a polarization coding QKD receiving end, and the two form a point-to-point polarization coding quantum key distribution system, so that the polarization coding BB84 protocol quantum key distribution can be performed.
By reconstructing the coding module structure of the QKD transmitting end deployed by the node A, the switching between the Gaussian modulation coding and the polarization coding can be realized without deploying two sets of independent Gaussian modulation coding transmitting ends and polarization coding transmitting ends on the node A.
By integrating the embodiment of the invention, the invention provides a quantum key distribution coding module, a transmitting end and a network, and stable polarization modulation and simple optical switch switching are utilized, so that not only can polarization coding or Gaussian modulation coding be realized, but also decoy state modulation or pulse generation can be realized, and therefore, discrete variable and continuous variable coding are integrated in one transmitting end, and flexible reconstruction is realized. The quantum key distribution system network can be applied to different protocols with better compatibility, and the field deployment cost is reduced.
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