Polarization Encoding Device, Method and Processor Applied to Quantum Key Distribution

Abstract

This application relates to the technical field of quantum communication, and specifically discloses a polarization encoding device applied to quantum key distribution, which includes a light source, PS1, PS2, PS3, PBS, and PMBC; PS1 modulates and outputs polarized light 2 with a polarization state of 0° or 90° based on the polarized light 1 emitted by the light source; PBS outputs the polarized light 2 of 0° and 90° to PS2 and PS3 respectively; PS2 modulates and outputs polarized light 3 with a polarization state of 0° or 90°; PS3 modulates and outputs polarized light 4 with a polarization state of 0° or 90°; PMBC does not rotate the polarization of polarized light 3 and rotates the polarization state of polarized light 4 by 45°. The polarization encoding device provided by this application adopts a new beam splitting method to achieve high-speed and stable modulation of the polarization state of optical pulses, meeting the requirements of high-speed communication systems for rate and bandwidth.

Description

Technical Field

[0001] This application relates to the technical field of quantum communication, and particularly to a polarization encoding device, method, and processor applied to quantum key distribution. Background Art

[0002] Quantum key distribution has information-theoretic security. By applying the basic principles of quantum mechanics, it can resist threats from quantum computers. Encrypted through the "one-time pad" method, it realizes unconditional secure key distribution, and thus is widely used in national defense units, government agencies, research institutions, financial institutions, etc.

[0003] Based on the polarization encoding scheme of the BB84 protocol, four polarization state basis vectors are loaded on the photon state. These four polarization states belong to two groups of conjugate bases. The two polarization states within each group are orthogonal to each other, and the included angle between the two groups of basis vectors is maintained at 45°. The specific implementation schemes of polarization encoding include the multi-laser scheme and the single-laser scheme.

[0004] In the prior art, usually 4 optical paths are first formed by optical devices, and then through 2 polarization beam splitters and a rotation coupler, so that the rotation coupler can output optical signals of 4 polarization states, and these 4 polarization states can correspond to the 4 optical paths one by one, realizing that the optical signals of 4 polarization states can be independently output. This mode may have a series of problems.

[0005] One prior art method for implementing the polarization encoding scheme uses 4 lasers to emit light respectively to modulate four polarization states. Due to certain process differences between the lasers, it is difficult to keep the drive signals completely consistent. There are inevitable differences between multiple lasers (such as spectral shape, central wavelength, and pulse time-domain characteristics, etc.). There is a certain distinguishability between the four polarization states, which does not meet the actual security requirements of quantum communication, and it is difficult to meet the requirements of high-speed communication systems due to the pulse frequency limitation of pulsed lasers.

[0006] Another prior art method for implementing the polarization encoding scheme uses 4 intensity modulators to control the on-off of the optical path. Since a single laser is used to implement polarization encoding, it can avoid the security loopholes of multiple lasers and ensure that the spectral information of the four polarization states is completely consistent. Due to the process differences between the intensity modulators, each intensity modulator also needs to be calibrated separately, the process is complex, and the stability is relatively poor. As long as one of the 4 intensity modulators has a problem, the entire encoding system cannot be used normally. Therefore, the probability of problems occurring during actual deployment is greatly increased compared with a single device, and the total cost of the 4 intensity modulators is high, which is not conducive to practical application and popularization.

[0007] Another polarization encoding scheme in the prior art uses a single laser to implement polarization encoding and controls the passage of four beams of light in a time-gated manner based on the principle of time division multiplexing. Since there are strict requirements for the generation time, stabilization time, cancellation time of signals in the system and their mutual relationships, the timing control is complex. Summary of the Invention

[0008] The present application provides a polarization encoding device applied to quantum key distribution. The polarization encoding device adopts a new beam splitting method to realize high-speed and stable modulation of the polarization state of optical pulses, meeting the requirements of high-speed communication systems for rate and bandwidth.

[0009] In a first aspect, there is provided a polarization encoding device applied to quantum key distribution, including a light source, a first polarization switch, a second polarization switch, a third polarization switch, a polarization beam splitter and a rotation coupler; wherein,

[0010] The light source is configured to output continuous first polarized light to be encoded to the first polarization switch, and the polarization state of the first polarized light is a first polarization state;

[0011] The first polarization switch is configured to modulate and output second polarized light based on the first polarized light, and the polarization state of the second polarized light is one of the first polarization state and a second polarization state, and the first polarization state and the second polarization state are orthogonal to each other;

[0012] The polarization beam splitter is configured to output the second polarized light in the first polarization state to the second polarization switch, and output the second polarized light in the second polarization state to the third polarization switch;

[0013] The second polarization switch is configured to modulate and output third polarized light to the rotation coupler based on the second polarized light in the first polarization state, and the polarization state of the third polarized light is one of the first polarization state and the second polarization state;

[0014] The third polarization switch is configured to modulate and output fourth polarized light to the rotation coupler based on the second polarized light in the second polarization state, and the polarization state of the fourth polarized light is one of the first polarization state and the second polarization state;

[0015] The polarization state of the third polarized light remains unchanged after being output by the rotation coupler. The rotation coupler is configured to rotate the polarization state of the fourth polarized light. The polarization state of the fourth polarized light in the first polarization state is changed to a third polarization state after rotation, and the polarization state of the fourth polarized light in the second polarization state is a fourth polarization state after rotation. The third polarization state and the fourth polarization state are orthogonal to each other.

[0016] Compared with the prior art, the solution provided by the present application at least includes the following beneficial technical effects:

[0017] The solution provided by this application can achieve high-speed polarization of the polarization state of optical pulses through two-stage polarization switches and a rotation coupler, and finally, an intensity modulator is used to modulate the optical pulses to output high-speed optical pulse polarization states. Using the polarization encoding and decoding device of this application, it is possible to easily achieve high-speed and stable modulation of the polarization state of optical pulses.

[0018] In combination with the first aspect, in certain implementation manners of the first aspect, the polarization encoding device further includes a processor, and the processor is configured to load a first modulation signal to the first polarization switch, where,

[0019] When the first modulation signal is the first signal, the polarization state of the first polarized light is the first polarization state;

[0020] When the first modulation signal is the second signal, the polarization state of the first polarized light is the second polarization state.

[0021] By loading a modulation signal from the processor to the first polarization switch, the polarization state of the first polarized light can be controlled so that the rotation coupler can output laser light with the required polarization direction.

[0022] In combination with the first aspect, in certain implementation manners of the first aspect, the processor is further configured to load a second modulation signal to the second polarization switch, where,

[0023] When the second modulation signal is the first signal, the polarization state of the third polarized light is the first polarization state;

[0024] When the second modulation signal is the second signal, the polarization state of the third polarized light is the second polarization state.

[0025] By loading a modulation signal from the processor to the second polarization switch, the polarization state of the second polarized light can be controlled so that the rotation coupler can output laser light with the required polarization direction. In addition, the signal rules of the modulation signals loaded by the processor on the first polarization switch and the second polarization switch are the same, which is beneficial to simplifying the calculation amount of loading the modulation signals.

[0026] In combination with the first aspect, in certain implementation manners of the first aspect, the processor is further configured to load a third modulation signal to the third polarization switch, where,

[0027] When the third modulation signal is the first signal, the polarization state of the fourth polarized light is the second polarization state;

[0028] When the third modulation signal is the second signal, the polarization state of the fourth polarized light is the first polarization state.

[0029] By loading a modulation signal to the third polarization switch through a processor, the polarization state of the third polarized light can be controlled, so that the rotation coupler can output laser light with the required polarization direction. In addition, the signal rules of the modulation signals loaded by the processor on the first polarization switch, the second polarization switch, and the third polarization switch are the same, which is beneficial to simplifying the calculation amount of the modulation signal loading.

[0030] Combined with the first aspect, in some implementation manners of the first aspect, the polarization encoding device further includes a pulse modulation unit, and the pulse modulation unit is configured to modulate the continuous light from the rotation coupler into pulsed light with a high repetition rate and a narrow pulse width. The pulse modulation unit can be an intensity modulator.

[0031] The continuous light can be modulated into pulsed light meeting the communication requirements through modulation by the intensity modulator, and the modulation signals loaded on the lithium niobate polarization switch and the intensity modulator are calibrated to ensure that there is only one polarization state in one pulsed light.

[0032] Combined with the first aspect, in some implementation manners of the first aspect, the first polarization switch is a lithium niobate polarization switch.

[0033] Combined with the first aspect, in some implementation manners of the first aspect, the rotation coupler is a 45° rotation coupler.

[0034] The 45° rotation coupler can rotate the polarized light with polarization directions of 0° and 90° to obtain polarized light with polarization directions of 45° and 135°.

[0035] Combined with the first aspect, in some implementation manners of the first aspect, the polarization encoding device is applied to the BB84 quantum key distribution protocol.

[0036] Combined with the first aspect, in some implementation manners of the first aspect, the input end of the rotation coupler is a polarization-maintaining fiber, and the output end is a single-mode fiber.

[0037] In a second aspect, a polarization encoding method is provided, which is applied to the polarization encoding device in any one of the implementation manners in the first aspect as described above. The polarization encoding method includes:

[0038] Obtain the polarization state corresponding to the signal to be encoded;

[0039] When the polarization state corresponding to the signal to be encoded is the first polarization state, load a first signal to both the first polarization switch and the second polarization switch;

[0040] When the polarization state corresponding to the signal to be encoded is the second polarization state, load the first signal to the first polarization switch and load a second signal to the second polarization switch;

[0041] When the polarization state corresponding to the signal to be encoded is the third polarization state, the second signal is loaded to the first polarization switch, and the first signal is loaded to the third polarization switch;

[0042] When the polarization state corresponding to the signal to be encoded is the fourth polarization state, the second signal is loaded to both the first polarization switch and the third polarization switch;

[0043] Wherein, the first signal indicates that the polarization state of the output polarized light is the same as that of the input polarized light, and the second signal indicates that the polarization state of the output polarized light is orthogonal to that of the input polarized light.

[0044] In a third aspect, a polarization encoding processor is provided, which is characterized in that it is used to execute the method described in any one of the implementation manners in the second aspect above. Description of the Drawings

[0045] Figure 1 It is a schematic structural diagram of a polarization encoding device applied to quantum key distribution provided by an embodiment of the present application;

[0046] Figure 2 It is a schematic flowchart of a polarization encoding method provided by an embodiment of the present application;

[0047] Figure 3 It is a schematic structural diagram of a processor provided by an embodiment of the present application. Detailed Embodiments

[0048] The present application will be further described in detail below with reference to the drawings and specific embodiments.

[0049] An embodiment of the present application discloses a polarization encoding device applied to quantum key distribution. Referring to Figure 1 , it includes a light source, a first polarization switch PS (polarization switching) 1, a second polarization switch PS2, a third polarization switch PS3, a polarization beam splitter (PBS), and a polarization maintaining beam combiner (PMBC).

[0050] The light source can be used to generate linearly polarized continuous light (first polarized light) to be encoded. As an example, the light source can be implemented by means of a laser (such as a continuous laser diode (LD)), and the fully linearly polarized light is transmitted by means of an optical fiber polarizer (such as an in-line polarizor (ILP)). Taking a possible scenario as an example, the continuous laser emits slow-axis light, and the fully linearly polarized light is output via the optical fiber polarizer, so that the slow-axis laser output by the light source is in the 0° direction. That is to say, the polarization state of the first polarized light output by the light source can be a polarization state with a polarization direction of 0°.

[0051] As Figure 1 shown, the laser LD is connected to the first polarization switch PS1 after polarization, so that the first polarized light output by the light source can be input to the first polarization switch PS1. In a possible case, the first polarization switch PS1 can be a lithium niobate polarization switch.

[0052] The first polarization switch PS1 can be used to modulate and output a second polarized light based on the first polarized light from the light source. The polarization state of the second polarized light is one of a first polarization state and a second polarization state, and the first polarization state and the second polarization state are orthogonal to each other.

[0053] When a modulation signal with a specified peak level is loaded onto the polarization switch, the polarization direction of the outgoing light either remains the same as the polarization direction of the original incident light or rotates by 90 degrees. These two directions match the main axis directions of the polarization-maintaining optical fiber and the modulator for the outgoing light, just like a slow-axis / fast-axis switch.

[0054] The first polarization switch PS1 can be loaded with a modulation signal by a processor. In some embodiments, when the modulation signal is "0", the first polarization switch PS1 can be instructed to maintain the original polarization state, that is, the polarization state of the second polarized light is the first polarization state. When the modulation signal is "1", the first polarization switch PS1 can be instructed to rotate the original polarization state by 90°, that is, the polarization state of the second polarized light is the second polarization state.

[0055] In a possible case, the slow-axis light emitted by the laser enters the first polarization switch PS1; after being modulated by the loaded modulation signal, it either transmits along the slow axis while maintaining the polarization direction of the original incident light or rotates the polarization direction of the incident light by 90 degrees and transmits along the fast axis. That is to say, the first polarization switch PS1 can output slow-axis laser or fast-axis laser in the polarization-maintaining optical fiber according to the modulation signal, and the slow-axis laser and the fast-axis laser are two orthogonal directions. If the slow-axis laser output by the first polarization switch PS1 is defined as the 0° direction, then the fast-axis laser orthogonal to it is the 90° direction.

[0056] The output port of the first polarization switch PS1 can be connected to the input port of the polarization beam splitter PBS. The two output ports of the polarization beam splitter PBS are respectively connected to the second polarization switch PS2 and the third polarization switch PS3. Thus, after being modulated by the first polarization switch PS1, the light beam can be divided into two paths, and the polarization beam splitter PBS transmits the second polarized light to the second polarization switch PS2 or the third polarization switch PS3 for modulation according to the polarization direction of the second polarized light. The polarization beam splitter PBS can be used to output the second polarized light in the first polarization state to the second polarization switch PS2, and output the second polarized light in the second polarization state to the third polarization switch PS3.

[0057] The second polarization switch PS2 is used to modulate and output the third polarized light based on the second polarized light in the first polarization state, and the polarization state of the third polarized light is one of the first polarization state and the second polarization state.

[0058] The second polarization switch PS2 can be loaded with a modulation signal by a processor. In some embodiments, when the modulation signal is "0", the second polarization switch PS2 can be instructed to maintain the original polarization state, that is, the polarization state of the third polarized light is the first polarization state. When the modulation signal is "1", the second polarization switch PS2 can be instructed to rotate the original polarization state by 90°, that is, the polarization state of the third polarized light is the second polarization state.

[0059] In a possible scenario, the polarization beam splitter PBS transmits the slow-axis laser along the polarization-maintaining fiber to the second polarization switch PS2. The second polarization switch PS2 can generate polarized light in two mutually orthogonal polarization states according to the modulation signal, either output the slow-axis laser that maintains the polarization direction of the original incident light, or rotate it by 90 degrees to obtain the fast-axis laser orthogonal to it. At this time, the output slow-axis laser is in the 0° direction, and the fast-axis laser orthogonal to it is in the 90° direction.

[0060] The third polarization switch PS3 is used to modulate and output the fourth polarized light based on the second polarized light in the second polarization state, and the polarization state of the fourth polarized light is one of the first polarization state and the second polarization state.

[0061] The third polarization switch PS3 can be loaded with a modulation signal by a processor. In some embodiments, when the modulation signal is "0", the third polarization switch PS3 can be instructed to maintain the original polarization state, that is, the polarization state of the fourth polarized light is the second polarization state. When the modulation signal is "1", the third polarization switch PS3 can be instructed to rotate the original polarization state by 90°, that is, the polarization state of the fourth polarized light is the first polarization state.

[0062] It should be noted that the processors for loading adjustment signals for the first polarization switch PS1, the second polarization switch PS2, and the third polarization switch PS3 can be different processors or the same processor.

[0063] In a possible scenario, the polarization beam splitter PBS transmits the fast-axis laser along the polarization-maintaining fiber to the third polarization switch PS3. The third polarization switch PS3 can generate polarized light with two mutually orthogonal polarization states according to the modulation signal. It either outputs the fast-axis laser maintaining the original polarization direction of the incident light or rotates it by 90 degrees to obtain the slow-axis laser orthogonal to it. At this time, the output slow-axis laser is in the 0° direction, and the fast-axis laser orthogonal to it is in the 90° direction.

[0064] The second polarization switch PS2 and the third polarization switch SP3 are respectively connected to the two input ports of the rotation coupler PMBC. The third polarized light output by the second polarization switch PS2 can be input into the rotation coupler PMBC. The fourth polarized light output by the third polarization switch SP3 can be input into the rotation coupler PMBC. The polarization state of the third polarized light remains unchanged after being output by the rotation coupler PMBC. The rotation coupler PMBC is used to rotate the polarization state of the fourth polarized light. The polarization state of the fourth polarized light in the first polarization state changes to the third polarization state after rotation, and the polarization state of the fourth polarized light in the second polarization state is the fourth polarization state after rotation. The third polarization state and the fourth polarization state are mutually orthogonal.

[0065] In some embodiments, the rotation coupler PMBC is a 45° rotation coupler PMBC. Since there is a 45° angle between the first path of 0° and 90° and the second path of 45° and 135° among the four polarization states required by the BB84 quantum key distribution protocol, after combining the beams using the 45° rotation coupler PMBC, the modulation of the required polarization direction can be completed.

[0066] The 45° rotation coupler PMBC couples and outputs two input paths: it only couples and outputs one path, and for the other path, it first performs a 45° polarization rotation and then couples and outputs. In a possible scenario, the 45° rotation coupler PMBC only couples and outputs the fast-axis laser and the slow-axis laser input by the second polarization switch PS2, and the polarization directions of the slow-axis laser and the fast-axis laser remain 0° and 90°. For the fast-axis laser and the slow-axis laser input by the third polarization switch PS3, the 45° rotation coupler PMBC first performs a 45° polarization rotation, and the polarization directions of the slow-axis laser and the fast-axis laser rotate from 0° and 90° to 45° and 135°, and then they are coupled and output with the fast-axis laser and the slow-axis laser output by the second polarization switch PS2. It can be seen that the 45° rotation coupler PMBC performs polarization rotation on the directions of the fast-axis laser and the slow-axis laser output by the third polarization switch PS3 on the premise of ensuring the orthogonal polarization directions of the fast-axis laser and the slow-axis laser output by the second polarization switch PS2. Finally, there is a 45° polarization angle between the two sets of laser pulses output by the second polarization switch PS2 and the third polarization switch PS3, and at the output end of the 45° rotation coupler PMBC, lasers with polarization directions of 0°, 90°, 45°, and 135° are respectively output.

[0067] The polarization encoding device further includes a pulse modulation unit, and the pulse modulation unit is used to modulate the continuous light from the rotation coupler PMBC into pulsed light with a high repetition rate and a narrow pulse width. In some embodiments, the pulse modulation unit includes an intensity modulator (IM), which is configured to modulate the continuous light into pulsed light with a high repetition rate and a narrow pulse width. The output port of the rotation coupler PMBC is connected to the intensity modulator IM. The laser output by the rotation coupler PMBC through rotation and coupling can be pulse-modulated by the intensity modulator IM. As Figure 1 shown, the output end of the 45° rotation coupler PMBC outputs continuous polarized light, and the continuous light can be modulated into pulsed light meeting the communication requirements through modulation by the intensity modulator IM. The input end of the rotation coupler PMBC can be a polarization-maintaining optical fiber, and the output end can be a single-mode optical fiber.

[0068] As can be seen from the above description, by modulating the first polarization switch PS1 and combining it with the passive device polarization beam splitter PBS, the optical path selection function can be achieved; and by modulating the first polarization switch PS1, the second polarization switch PS2, and the third polarization switch PS3 and combining it with the passive device polarization rotation coupler PMBC, 4 encoding states are finally output. The first polarization switch PS1 is individually loaded with a modulation signal, and only one of the second polarization switch PS2 and the third polarization switch PS3 has light passing through at the same time. A modulation signal is loaded on the second polarization switch PS2 or the third polarization switch PS3. When the modulation signal is 0, the polarized light of the polarization switch is output in the original polarization direction; when the modulation signal is 1, the polarization direction of the polarized light of the polarization switch rotates 90 degrees and is output. By loading modulation signals on the first polarization switch PS1, the second polarization switch PS2, and the third polarization switch PS3, the 4 encoding states required by the BB84 protocol can be prepared, as shown in Table 1 below. The modulation signals loaded on the polarization switch PS and the intensity modulator IM are calibrated to ensure that there is only one polarization state within one pulsed light.

[0069] Table 1: Quantum state encoding table of the polarization encoding device

[0070]

[0071] Figure 2 The schematic flowchart of a polarization encoding method provided by an embodiment of the present application is shown, and this polarization encoding method can be applied to the polarization encoding device provided by the embodiment of the present application.

[0072] S1: Obtain the polarization state corresponding to the signal to be encoded. In some embodiments, the polarization state corresponding to the signal to be encoded can correspond to one of the following 4 polarization directions: 0°, 90°, 45°, 135°.

[0073] S2: When the polarization state corresponding to the signal to be encoded is the first polarization state, load the first signal on both the first polarization switch PS1 and the second polarization switch PS2. In one possible scenario, the first polarization state can correspond to the 0° polarization direction.

[0074] S3: When the polarization state corresponding to the signal to be encoded is the second polarization state, load the first signal on the first polarization switch PS1 and load the second signal on the second polarization switch PS2. In one possible scenario, the first polarization state can correspond to the 90° polarization direction.

[0075] S4: When the polarization state corresponding to the signal to be encoded is the third polarization state, load the second signal on the first polarization switch PS1 and load the first signal on the third polarization switch PS3. In one possible scenario, the first polarization state can correspond to the 135° polarization direction.

[0076] S5: When the polarization state corresponding to the signal to be encoded is the fourth polarization state, the second signal is loaded to both the first polarization switch PS1 and the third polarization switch PS3. In a possible scenario, the first polarization state may correspond to a polarization direction of 45°.

[0077] Among them, the first signal indicates that the polarization state of the output polarized light is the same as that of the input polarized light, and the second signal indicates that the polarization state of the output polarized light is orthogonal to that of the input polarized light. The first signal can be "0", and the second signal can be "1".

[0078] The embodiment of the present application also provides a processor for executing the method as Figure 2 shown.

[0079] According to Figure 3 shown, generally, an FPGA, a DSP, or an ARM can be selected as the processor. The three input / output (I / O) interfaces of the processor are respectively connected to the first polarization switch PS1, the second polarization switch PS2, the third polarization switch PS3, and the intensity modulator IM. Specifically, when connecting, I / O port 1 is connected to the first polarization switch PS1, and the output modulation signal 1 modulates PS1; I / O port 2 is connected to the second polarization switch PS2 and the third polarization switch PS3, and the output modulation signal 2 modulates PS2 and PS3 simultaneously; I / O port 3 is connected to the intensity modulator IM, and the output modulation signal 3 modulates IM.

[0080] As can be seen from the above description, the first polarization switch PS1 is loaded with the modulation signal 1. When the modulation signal 1 is "0", the polarized light enters the second polarization switch PS2 while maintaining the 0° polarization direction, and at this time, no light passes through the third polarization switch PS3. The second polarization switch PS2 can be loaded with the modulation signal 2. When the loaded modulation signal 2 is "0", the polarized light enters the 45-degree rotation coupler PMBC while maintaining the 0° polarization direction. When the loaded modulation signal 2 is "1", the polarized light rotates 90 degrees and then enters the 45-degree rotation coupler PMBC while maintaining the 90° polarization direction, and the 45-degree rotation coupler PMBC directly couples and outputs the laser with a polarization direction of 0° or 90°.

[0081] When the modulation signal 1 is "1", the polarized light rotates 90 degrees and then enters the third polarization switch PS3 while maintaining the 90° polarization direction. At this time, no light passes through the second polarization switch PS2. The third polarization switch PS3 can load the modulation signal 2. When the loaded modulation signal 2 is "0", the polarized light enters the 45-degree rotation coupler PMBC while maintaining the 90° polarization direction. When the loaded modulation signal 2 is "1", the polarized light rotates 90 degrees and then enters the 45-degree rotation coupler PMBC while maintaining the 0° polarization direction. The 45-degree rotation coupler PMBC first performs a 45° polarization rotation, and the polarization direction rotates from 0° and 90° to 45° and 135°, and then performs coupled output.

[0082] The processor can load the modulation signal 3 in the intensity modulator IM to modulate the continuous light output by the rotation coupler PMBC into pulsed light with a high repetition rate and a narrow pulse width. Thus, the four encoding states required by the BB84 protocol can be prepared, as shown in Table 1 above.

[0083] This application is a quantum key distribution polarization encoding device based on polarization switches, which can realize the high-speed polarization of the polarization state of optical pulses through two-stage polarization switches and rotation couplers, and finally realize the modulation of optical pulses by an intensity modulator to output the polarization state of high-speed optical pulses. Using the polarization encoding and decoding device of this application, it is possible to easily realize the polarization state modulation of high-speed and stable optical pulses.

[0084] Although this application is disclosed above in preferred embodiments, it is not used to limit this application. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of this application. Therefore, the protection scope of this application should be subject to the scope defined by the claims of this application.

Claims

1. A polarization encoding device applied to quantum key distribution, characterized in that, It includes a light source, a first polarization switch, a second polarization switch, a third polarization switch, a polarization beam splitter, and a rotation coupler; wherein, The light source is used to output continuous first polarized light to be encoded to the first polarization switch, and the polarization state of the first polarized light is the first polarization state; The first polarization switch is used to modulate and output second polarized light based on the first polarized light, and the polarization state of the second polarized light is one of the first polarization state and the second polarization state, and the first polarization state and the second polarization state are orthogonal to each other; The polarization beam splitter is used to output the second polarized light in the first polarization state to the second polarization switch, and output the second polarized light in the second polarization state to the third polarization switch; The second polarization switch is used to modulate and output third polarized light to the rotation coupler based on the second polarized light in the first polarization state, and the polarization state of the third polarized light is one of the first polarization state and the second polarization state; The third polarization switch is used to modulate and output fourth polarized light to the rotation coupler based on the second polarized light in the second polarization state, and the polarization state of the fourth polarized light is one of the first polarization state and the second polarization state; The polarization state of the third polarized light remains unchanged after being output by the rotation coupler. The rotation coupler is used to rotate the polarization state of the fourth polarized light. The polarization state of the fourth polarized light in the first polarization state changes to the third polarization state after rotation, and the polarization state of the fourth polarized light in the second polarization state is the fourth polarization state after rotation. The third polarization state and the fourth polarization state are orthogonal to each other.

2. The polarization encoding device according to claim 1, wherein The polarization encoding device further includes a processor, and the processor is used to load a first modulation signal to the first polarization switch, wherein, When the first modulation signal is the first signal, the polarization state of the first polarized light is the first polarization state; When the first modulation signal is the second signal, the polarization state of the first polarized light is the second polarization state.

3. The polarization encoding device according to claim 2, wherein The processor is further used to load a second modulation signal to the second polarization switch, wherein, When the second modulation signal is the first signal, the polarization state of the third polarized light is the first polarization state; When the second modulation signal is the second signal, the polarization state of the third polarized light is the second polarization state.

4. The polarization encoding device according to claim 2, wherein The processor is further used to load a third modulation signal to the third polarization switch, wherein, When the third modulation signal is the first signal, the polarization state of the fourth polarized light is the second polarization state; When the third modulation signal is the second signal, the polarization state of the fourth polarized light is the first polarization state.

5. The polarization encoding device according to claim 1, wherein The polarization encoding device further includes a pulse modulation unit, and the pulse modulation unit is used to modulate the continuous light from the rotation coupler into pulsed light with a high repetition rate and a narrow pulse width.

6. The polarization encoding device according to claim 1, wherein The first polarization switch is a lithium niobate polarization switch.

7. The polarization encoding device according to claim 1, wherein The rotation coupler is a 45° rotation coupler.

8. The polarization encoding device according to claim 1, wherein The polarization encoding device is applied to the BB84 quantum key distribution protocol.

9. The polarization encoding device according to claim 1, wherein The input end of the rotation coupler is a polarization-maintaining fiber, and the output end is a single-mode fiber.

10. A polarization encoding method, characterized in that, Applied to the polarization encoding device according to any one of claims 1 to 9, the polarization encoding method includes: Obtaining the polarization state corresponding to the signal to be encoded; When the polarization state corresponding to the signal to be encoded is the first polarization state, loading the first signal to both the first polarization switch and the second polarization switch; When the polarization state corresponding to the signal to be encoded is the second polarization state, loading the first signal to the first polarization switch and loading the second signal to the second polarization switch; When the polarization state corresponding to the signal to be encoded is the third polarization state, loading the second signal to the first polarization switch and loading the first signal to the third polarization switch; When the polarization state corresponding to the signal to be encoded is the fourth polarization state, loading the second signal to both the first polarization switch and the third polarization switch; Wherein, the first signal indicates that the polarization state of the output polarized light is the same as the polarization state of the input polarized light, and the second signal indicates that the polarization state of the output polarized light is orthogonal to the polarization state of the input polarized light.

11. A polarization encoding processor, characterized in that, For executing the method according to claim 10.

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