Two-stage polarization encoding device, encoding method and quantum key distribution light source

Abstract

A polarization encoding device includes a two-stage Sagnac ring, specifically including a circulator 1, a polarization beam splitter PBS1, a phase modulator PM1, a circulator 2, a polarization beam splitter PBS2, and a phase modulator PM2, wherein the circulator 1 and the circulator 2 both include a first port a, a second port b, and a third port c; PBS1 and PBS2 both include a first port 1, a second port 2, and a third port 3; the second port 2 and the third port 3 of PBS1 and PBS2 are connected by a polarization-maintaining fiber based on a Sagnac ring to form a bidirectional ring optical path; the input light is connected to the first port a of the circulator 1 through the input fiber, and the input fiber is a polarization-maintaining fiber; the output light is connected to the third port c of the circulator 2 through the output fiber, and the output fiber is a single-mode fiber. The present invention uses a two-channel, single-amplitude pulse signal drive, meets the requirements of preparing four polarization states in a polarization-encoded QKD experiment, avoids the technical difficulties of generating a single-channel, multi-amplitude pulse signal, has low implementation difficulty, and high reliability.

Description

Technical Field

[0001] The present invention relates to the field of optical polarization encoding, and in particular to a polarization encoding device used in a quantum key distribution system, and a method for performing polarization state encoding using the same. Background Art

[0002] As one of the frontier fields of physics today, quantum communication, based on the basic physical principles of quantum mechanics, guarantees the unconditional security of information transmission and is the first development direction of quantum information science towards practical application. The core of quantum communication is quantum key distribution (QKD), which can enable two communicating parties far apart to share unconditionally secure quantum keys. Combined with the "one-time one-pad" encryption method, it can achieve secure communication that has been strictly mathematically proven by information theory. The BB84 protocol is the first QKD protocol proposed by Bennett et al. in 1984 and is also one of the most widely used QKDs to date. In free space and satellite-to-ground QKD experiments, due to the good fidelity of the atmosphere to the polarization state, encoding based on the polarization state is often used. Correspondingly, the polarization state of the QKD light source needs to be modulated to achieve random encoding of the four polarization states of two orthogonal basis vectors.

[0003] There are two main commonly used polarization encoding methods. One is based on a polarization modulator based on lithium nitride crystal or gallium arsenide material. It uses external linear polarized light after a 45-degree rotation axis. The two polarization components H and V are transmitted along the two axes of the modulator crystal respectively. By applying a voltage signal to the modulator, an additional phase difference is introduced between the two polarization components H and V, and interference occurs at the output port of the modulator crystal, resulting in different polarization states. The other is a polarization modulation method based on a circulator + Sagnac ring. By constructing an interference ring with a Sagnacx structure, an additional phase difference is introduced between the clockwise and counterclockwise components through a phase modulator, and finally interference produces different polarization states.

[0004] For the polarization encoding methods that have been reported so far, single-stage polarization encoding schemes are used. In order to generate the four polarization states required for polarization encoding QKD experiments, it is necessary to generate amplitudes of 0, 1 / 2V, and π 、V π , 3 / 2V π There are four voltage value pulse signals, among which V πis the half-wave voltage of the polarization modulator or phase modulator. Considering that the typical half-wave voltage of the modulator is about 5V, pulse signals with amplitudes of 0, 2.5V, 5V, and 7.5V are generated to drive the modulator to prepare the target polarization state. At the same time, in order to ensure the fidelity of the prepared polarization state, low jitter requirements are also put forward for the pulse signal. As the repetition frequency gradually increases from MHz to above GHz, the generation of multi-amplitude, low-jitter, and high-voltage pulse signals has put forward extremely high requirements on driving electronics. The technology is complex, difficult to implement, and has low reliability. This has limited the application prospects of single-stage polarization encoding devices to a certain extent. Summary of the invention

[0005] In view of this, the main purpose of the present invention is to provide a two-stage polarization encoding device, encoding method and quantum key distribution light source, in order to partially solve at least one of the above-mentioned technical problems.

[0006] In order to achieve the above-mentioned object, as one aspect of the present invention, a polarization encoding device is provided, including a two-stage Sagnac ring, specifically including a circulator 1, a polarization beam splitter PBS1, a phase modulator PM1, a circulator 2, a polarization beam splitter PBS2, and a phase modulator PM2, wherein:

[0007] Circulator 1 and circulator 2 both include a first port a, a second port b and a third port c;

[0008] Both PBS1 and PBS2 include a first port 1, a second port 2 and a third port 3;

[0009] The second port 2 and the third port 3 of PBS1 and PBS2 are connected by a polarization-maintaining fiber based on a Sagnac ring to form a bidirectional ring optical path. By adjusting the length of the polarization-maintaining fiber from PM1 and PM2 to the second port 2 and the third port 3, the delay of the Sagnac ring reaching PM1 and PM2 in the clockwise direction and the counterclockwise direction is different;

[0010] The input light is connected to the first port a of the circulator 1 through the input optical fiber;

[0011] The output light is connected to the third port c of the circulator 2 through the output optical fiber.

[0012] The input light is linearly polarized light input horizontally, and the input optical fiber is rotated by 45° to make the input light linearly polarized at 45°; the input optical fiber is a polarization-maintaining optical fiber, and the output optical fiber is a single-mode optical fiber.

[0013] The ports of the circulator 1 and the circulator 2 are set as follows:

[0014] When the first port a is an input port, the second port b is an output port;

[0015] When the second port b is an input port, the third port c is an output port.

[0016] The ports of PBS1 and PBS2 are set as follows:

[0017] When the first port 1 is an input port, the second port 2 is a reflection output port, and the third port 3 is a transmission output port;

[0018] When the second port 2 is an input port, the first port 1 is a reflection output port;

[0019] When the third port 3 is an input port, the first port 1 is a transmission output port.

[0020] As another aspect of the present invention, there is provided a coding method based on the above polarization coding device, comprising the following steps:

[0021] The input light is a linearly polarized light input horizontally, and the input optical fiber is rotated by 45 degrees to make the input light a 45 degree linearly polarized light, incident on the first port a of the circulator 1, and then output from the second port b of the circulator 1;

[0022] The 45° linear polarized light is output from the second port b of the circulator 1 to the first port 1 of the polarization beam splitter PBS1, and the 45° linear polarized light is evenly split from PBS1 into a first component |H> and a second component |V>, which are output from the reflection end 2 and the transmission end 3 respectively;

[0023] The reflection end 2 of PBS1 realizes fast-axis cutoff of the first component, and then couples it into the slow axis of the polarization-maintaining fiber, propagating clockwise in the bidirectional ring optical path;

[0024] The transmission end 3 of PBS1 realizes fast-axis cutoff of the second component, and then couples it into the slow axis of the polarization-maintaining fiber, propagating counterclockwise in a bidirectional ring optical path;

[0025] The first component is transmitted to port 3 of PBS1 in a clockwise pulse, and the second component is transmitted to port 2 of PBS1 in a counterclockwise pulse; the two pulse components are output through port 1 after interference on PBS1;

[0026] The optical pulse output from port 1 of PBS1 is input to the second port b of circulator 1, and then output from the third port c of circulator 1;

[0027] The optical pulse outputted from the third port c of the circulator 1 is inputted into the first port a of the circulator 2, and then outputted from the second port b of the circulator 2;

[0028] The second port b of the circulator 2 is output to the first port 1 of the polarization beam splitter PBS2, and the polarization components |H> and |V> are separated from PBS2, and the first component |H> and the second component |V> are output from the reflection end 2 and the transmission end 3 respectively;

[0029] The reflection end 2 of PBS2 realizes fast-axis cutoff of the first component, and then couples it into the slow axis of the polarization-maintaining fiber, propagating clockwise in the bidirectional ring optical path;

[0030] The transmission end 3 of PBS2 realizes fast-axis cutoff of the second component, and then couples it into the slow axis of the polarization-maintaining fiber, propagating counterclockwise in a bidirectional ring optical path;

[0031] The first component is transmitted as a clockwise pulse to port 3 of PBS2, and the second component is transmitted as a counterclockwise pulse to port 2 of PBS2; the two pulse components interfere on PBS2 and are output through port 1;

[0032] The pulse light output from port 1 of PBS2 is input to the second port b of circulator 2, and then output from the third port c of circulator 2;

[0033] The third port c of the circulator 2 is output and finally coupled to the output optical fiber and output.

[0034] The first component optical pulse outputted clockwise by PBS1 is affected by the electrical signal loaded on PM1 when passing through PM1, and an additional phase When the second component optical pulse outputted counterclockwise by the PBS1 passes through the PM1, the electrical signal loaded on the PM1 is zero, and no additional phase is superimposed.

[0035] The first component optical pulse outputted clockwise by PBS2 is affected by the electrical signal loaded on PM2 when passing through PM2, and an additional phase When the second component optical pulse outputted counterclockwise by PBS2 passes through PM2, the electrical signal loaded on PM2 is zero, and no additional phase is superimposed.

[0036] Wherein, the polarization state of the output pulse light is expressed as When the additional phase and are 0, π and 0, When , the four output quantum states are and Through the combination of two-level polarization encoding, the preparation of the four polarization states required by the BB84 protocol is completed.

[0037] As another aspect of the present invention, a quantum key distribution light source using the above two-stage polarization encoding device is provided, comprising a pulse generator, a laser, an intensity modulator, a polarization encoding device and an attenuator; wherein,

[0038] The pulse generator is used to send out a specific pulse signal to drive the laser, the intensity modulator and the polarization encoding device respectively;

[0039] The laser, driven by the periodic electrical pulses generated by the pulse generator, emits periodic narrow optical pulse signals;

[0040] The intensity modulator modulates the input narrow optical pulse signal under the action of the random pulse generated by the pulse generator to generate the three intensity states of signal state, decoy state and vacuum state required for quantum key distribution;

[0041] The optical signal after intensity modulation enters the polarization encoding device. The polarization encoding device adopts the polarization encoding device as described above. The pulse generator generates two-channel, binary amplitude voltage pulse signals respectively, which act on the first-stage Sagnac ring and the second-stage Sagnac ring of the polarization encoding device respectively, and modulate the input narrow optical pulse signal to generate the four polarization states of +, -, L, and R required for quantum key distribution.

[0042] After polarization encoding, the optical signal passes through an attenuator and is attenuated to the single photon level required for quantum key distribution before being output.

[0043] Based on the above technical solution, it can be seen that the two-stage polarization encoding device, encoding method and quantum key distribution light source of the present invention have at least one of the following beneficial effects compared with the prior art:

[0044] (1) Through the two-stage polarization encoding device scheme, using a two-channel, single-amplitude pulse signal drive, it can meet the requirements of polarization-encoded QKD experiments to prepare four polarization states, avoiding the technical difficulties of generating single-channel, multi-amplitude pulse signals. The technology is simple, easy to implement, and highly reliable.

[0045] (2) The two-stage polarization encoding device solution reduces the demand for the amplitude of the driving electrical pulse signal, which is reduced from the 3 / 2V of the single-stage polarization encoding device. π Reduce to V π (V π is the half-wave voltage of the phase modulator), reducing the pulse amplitude requirements for the drive electronics;

[0046] (3) The polarization modulation scheme based on the two-stage Sagnac loop can avoid the problems of polarization mode delay and poor stability caused by the difference in optical fiber path in the traditional polarization modulator, because the forward and reverse optical components have the same polarization state in the phase modulator and travel through the same length of optical fiber. It also avoids the complex initial polarization state calibration process and has high stability and reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic diagram of the structure and method of the polarization encoding device of the present invention;

[0048] Figure 2 This is a schematic diagram of the application of the polarization encoding device of the present invention in quantum key distribution. DETAILED DESCRIPTION

[0049] Aiming at the traditional single-stage polarization coding scheme, the present invention proposes a two-stage polarization coding device scheme, which is driven by a two-channel, single-amplitude pulse signal and can meet the requirements of preparing four polarization states in the polarization coding QKD experiment, thereby reducing the requirements for the amplitude of the driving electrical pulse signal and avoiding the technical difficulties of generating a single-channel, multi-amplitude pulse signal. The technology is simple, the implementation difficulty is small and the reliability is high.

[0050] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0051] The polarization encoding device disclosed in the present invention is as follows: Figure 1 As shown, it is mainly composed of a two-stage Sagnac ring, including a circulator 1, a polarization beam splitter PBS1, a phase modulator PM1, a circulator 2, a polarization beam splitter PBS2, and a phase modulator PM2, wherein:

[0052] The circulator 1 (2) comprises a first port a, a second port b and a third port c;

[0053] When the first port a is an input port, the second port b is an output port;

[0054] When the second port b is an input port, the third port c is an output port;

[0055] PBS1(2) comprises a first port 1, a second port 2 and a third port 3;

[0056] When the first port 1 is an input port, the second port 2 is a reflection output port, and the third port 3 is a transmission output port;

[0057] When the second port 2 is an input port, the first port 1 is a reflection output port;

[0058] When the third port 3 is an input port, the first port 1 is a transmission output port;

[0059] The second port 2 and the third port 3 of PBS1(2) are connected by a polarization-maintaining fiber based on a Sagnac ring to form a bidirectional ring optical path. By adjusting the length of the polarization-maintaining fiber from PM1(2) to the second port 2 and the third port 3, the delay of Sagnac reaching PM1(2) in the clockwise direction and the counterclockwise direction is different.

[0060] The input light Input is connected to the first port a of the circulator 1 through an input optical fiber, and the input optical fiber is a polarization-maintaining optical fiber;

[0061] The output light Output is connected to the third port c of the circulator 2 through an output optical fiber, and the output optical fiber is a single-mode optical fiber;

[0062] like Figure 1 As shown in the figure, the process of the encoding method based on the above polarization encoding device is shown, which specifically includes the following steps:

[0063] The input light Input is a horizontal input of linearly polarized light. The input optical fiber is rotated 45° to make the input light become 45° linearly polarized light, incident on the first port a of the circulator 1, and then output from the second port b of the circulator 1.

[0064] The 45° linear polarized light is output from the second port b of the circulator 1 to the first port 1 of the polarization beam splitter PBS1, and the 45° linear polarized light is evenly divided from PBS1 into a first component |H> and a second component |V>, which are output from the reflection end 2 and the transmission end 3 respectively.

[0065] The reflection end 2 of PBS1 realizes fast-axis cutoff of the first component, and then couples it into the slow axis of the polarization-maintaining optical fiber, propagating clockwise in a bidirectional ring optical path.

[0066] The transmission end 3 of PBS1 cuts off the fast axis of the second component, and then couples it into the slow axis of the polarization-maintaining optical fiber, propagating counterclockwise in a bidirectional ring optical path.

[0067] When the first component optical pulse output clockwise passes through PM1, it is affected by the electrical signal loaded on PM1, adding an additional phase When the second component optical pulse output counterclockwise passes through PM1, the electrical signal loaded on PM1 is zero, and no additional phase is superimposed.

[0068] The first component is transmitted as a clockwise pulse to port 3 of PBS1, and the second component is transmitted as a counterclockwise pulse to port 2 of PBS1. The two pulse components interfere with each other on PBS1 and are output through port 1.

[0069] The optical pulse output from port 1 of PBS1 is input to the second port b of circulator 1 and then output from the third port c of circulator 1 .

[0070] The optical pulse output from the third port c of the circulator 1 is input to the first port a of the circulator 2 , and then output from the second port b of the circulator 2 .

[0071] The second port b of the circulator 2 is output to the first port 1 of the polarization beam splitter PBS2, and the polarization components |H> and |V> are separated from PBS2, and the first component |H> and the second component |V> are output from the reflection end 2 and the transmission end 3 respectively.

[0072] The reflection end 2 of PBS2 realizes fast-axis cutoff of the first component, and then couples it into the slow axis of the polarization-maintaining optical fiber, propagating clockwise in the bidirectional ring optical path.

[0073] The transmission end 3 of PBS2 realizes fast-axis cutoff of the second component, and then couples it into the slow axis of the polarization-maintaining optical fiber, propagating counterclockwise in a bidirectional ring optical path.

[0074] When the first component optical pulse output clockwise passes through PM2, it is affected by the electrical signal loaded on PM2, adding an additional phase When the second component optical pulse output counterclockwise passes through PM2, the electrical signal loaded on PM2 is zero, and no additional phase is superimposed.

[0075] The first component is transmitted as a clockwise pulse to port 3 of PBS2, and the second component is transmitted as a counterclockwise pulse to port 2 of PBS2. The two pulse components interfere with each other on PBS2 and are output through port 1.

[0076] The polarization state of the output pulse light can be expressed as When the additional phase and are 0, π and 0, When , the four output quantum states are and Through the combination of two-level polarization encoding, the preparation of the four polarization states required by the BB84 protocol is completed.

[0077] The optical pulse output from the port 1 of PBS2 is input to the second port b of the circulator 2 and then output from the third port c of the circulator 2 .

[0078] The third port c of the circulator 2 is output and finally coupled to the output optical fiber Output and output.

[0079] Based on the polarization encoding device proposed above, a quantum key distribution light source can be realized and applied in quantum key distribution. Figure 2 As shown, the light source mainly includes a pulse generator, a laser, an intensity modulator, a polarization encoding device, an attenuator and other parts:

[0080] The pulse generator is used to send out specific pulse signals to drive the laser, intensity modulator and polarization encoding device respectively.

[0081] Driven by the periodic electrical pulses generated by the pulse generator, the laser emits a periodic narrow optical pulse signal.

[0082] Under the action of the random pulses generated by the pulse generator, the intensity modulator modulates the input narrow optical pulse signal to generate three intensity states required for quantum key distribution: signal state, decoy state, and vacuum state.

[0083] The intensity modulated optical signal enters the polarization encoding device. The polarization encoding device adopts the two-stage polarization encoding scheme proposed in this patent. The pulse generator generates two-channel, binary amplitude voltage pulse signals, which act on the first-stage Sagnac ring and the second-stage Sagnac ring of the polarization encoding device, respectively, to modulate the input narrow optical pulse signal and generate the four polarization states of +, -, L, and R required for quantum key distribution.

[0084] After intensity modulation and polarization encoding, the optical signal passes through an attenuator and is attenuated to the single photon level required for quantum key distribution before being output.

[0085] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A polarization encoding device, characterized in that: It includes a two-stage Sagnac ring, specifically including a circulator 1, a polarization beam splitter PBS1, a phase modulator PM1, a circulator 2, a polarization beam splitter PBS2, and a phase modulator PM2, wherein: Circulator 1 and circulator 2 both include a first port a, a second port b and a third port c; Both PBS1 and PBS2 include a first port 1, a second port 2 and a third port 3; The second port 2 and the third port 3 of PBS1 and PBS2 are connected by a polarization-maintaining fiber based on a Sagnac ring to form a bidirectional ring optical path. By adjusting the length of the polarization-maintaining fiber from PM1 and PM2 to the second port 2 and the third port 3, the delay of the Sagnac ring reaching PM1 and PM2 in the clockwise direction and the counterclockwise direction is different; The input light is connected to the first port a of the circulator 1 through the input optical fiber; The output light is connected to the third port c of the circulator 2 through the output optical fiber; The input light is a linearly polarized light input horizontally, and the input optical fiber is rotated by 45 degrees to make the input light a 45 degree linearly polarized light, incident on the first port a of the circulator 1, and then output from the second port b of the circulator 1; The 45° linear polarized light is output from the second port b of the circulator 1 to the first port 1 of the polarization beam splitter PBS1, and the 45° linear polarized light is evenly split from PBS1 into a first component |H> and a second component |V>, which are output from the reflection end 2 and the transmission end 3 respectively; The optical pulse outputted from the third port c of the circulator 1 is inputted into the first port a of the circulator 2, and then outputted from the second port b of the circulator 2; The second port b of the circulator 2 is output to the first port 1 of the polarization beam splitter PBS2, and the polarization components |H> and |V> are separated from PBS2, and the first component |H> and the second component |V> are output from the reflection end 2 and the transmission end 3 respectively.

2. The polarization encoding device according to claim 1, characterized in that: The input optical fiber is a polarization-maintaining optical fiber, and the output optical fiber is a single-mode optical fiber.

3. The polarization encoding device according to claim 1, characterized in that: The ports of the circulator 1 and the circulator 2 are set as follows: When the first port a is an input port, the second port b is an output port; When the second port b is an input port, the third port c is an output port.

4. The polarization encoding device according to claim 1, characterized in that: The port settings of PBS1 and PBS2 are: When the first port 1 is an input port, the second port 2 is a reflection output port, and the third port 3 is a transmission output port; When the second port 2 is an input port, the first port 1 is a reflection output port; When the third port 3 is an input port, the first port 1 is a transmission output port.

5. A coding method using the polarization coding device according to any one of claims 1 to 4, characterized in that: The following steps are involved: The input light is a linearly polarized light input horizontally, and the input optical fiber is rotated by 45 degrees to make the input light a 45 degree linearly polarized light, incident on the first port a of the circulator 1, and then output from the second port b of the circulator 1; The 45° linear polarized light is output from the second port b of the circulator 1 to the first port 1 of the polarization beam splitter PBS1, and the 45° linear polarized light is evenly split from PBS1 into a first component |H> and a second component |V>, which are output from the reflection end 2 and the transmission end 3 respectively; The reflection end 2 of PBS1 realizes fast-axis cutoff of the first component, and then couples it into the slow axis of the polarization-maintaining fiber, propagating clockwise in the bidirectional ring optical path; The transmission end 3 of PBS1 realizes fast-axis cutoff of the second component, and then couples it into the slow axis of the polarization-maintaining fiber, propagating counterclockwise in a bidirectional ring optical path; The first component is transmitted as a clockwise pulse to port 3 of PBS1, and the second component is transmitted as a counterclockwise pulse to port 2 of PBS1; The two pulse components interfere on PBS1 and are output through port 1; The optical pulse output from port 1 of PBS1 is input to the second port b of circulator 1, and then output from the third port c of circulator 1; The optical pulse outputted from the third port c of the circulator 1 is inputted into the first port a of the circulator 2, and then outputted from the second port b of the circulator 2; The second port b of the circulator 2 is output to the first port 1 of the polarization beam splitter PBS2, and the polarization components |H> and |V> are separated from PBS2, and the first component |H> and the second component |V> are output from the reflection end 2 and the transmission end 3 respectively; The reflection end 2 of PBS2 realizes fast-axis cutoff of the first component, and then couples it into the slow axis of the polarization-maintaining fiber, propagating clockwise in the bidirectional ring optical path; The transmission end 3 of PBS2 realizes fast-axis cutoff of the second component, and then couples it into the slow axis of the polarization-maintaining fiber, propagating counterclockwise in a bidirectional ring optical path; The first component is transmitted as a clockwise pulse to port 3 of PBS2, and the second component is transmitted as a counterclockwise pulse to port 2 of PBS2; The two pulse components interfere on PBS2 and are output through port 1; The pulse light output from port 1 of PBS2 is input to the second port b of circulator 2, and then output from the third port c of circulator 2; The third port c of the circulator 2 is output and finally coupled to the output optical fiber and output.

6. The encoding method according to claim 5, characterized in that: The first component optical pulse outputted clockwise by PBS1 is affected by the electrical signal loaded on PM1 when passing through PM1, and an additional phase When the second component optical pulse outputted counterclockwise by PBS1 passes through PM1, the electrical signal loaded on PM1 is zero, and no additional phase is superimposed.

7. The encoding method according to claim 5, characterized in that: The first component optical pulse outputted clockwise by PBS2 is affected by the electrical signal loaded on PM2 when passing through PM2, and an additional phase When the second component optical pulse output counterclockwise by PBS2 passes through PM2, the electrical signal loaded on PM2 is zero, and no additional phase is superimposed.

8. The encoding method according to claim 5, characterized in that: The polarization state of the output pulse light is expressed as , when the additional phase and They are 0, and 0, When , the four output quantum states are , , and ; Through the combination of two-level polarization encoding, the preparation of the four polarization states required by the BB84 protocol is completed.

9. A quantum key distribution system using the polarization encoding device according to any one of claims 1 to 4, characterized in that: The system comprises a pulse generator, a laser, an intensity modulator, a polarization encoding device and an attenuator; wherein, The pulse generator is used to send out a specific pulse signal to drive the laser, the intensity modulator and the polarization encoding device respectively; The laser, driven by the periodic electrical pulses generated by the pulse generator, emits periodic narrow optical pulse signals; The intensity modulator modulates the input narrow optical pulse signal under the action of the random pulse generated by the pulse generator to generate the three intensity states of signal state, decoy state and vacuum state required for quantum key distribution; The optical signal after intensity modulation enters the polarization encoding device, and the polarization encoding device adopts the polarization encoding device as described in any one of claims 1 to 4. The pulse generator generates two-channel, binary amplitude voltage pulse signals respectively, which act on the first-stage Sagnac ring and the second-stage Sagnac ring of the polarization encoding device respectively, and modulate the input narrow optical pulse signal to generate the four polarization states of +, -, L, and R required for quantum key distribution; After polarization encoding, the optical signal passes through an attenuator and is attenuated to the single photon level required for quantum key distribution before being output.

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