All-passive quantum key distribution transmitting end chip based on photon integration technology and modulation method

Abstract

The invention discloses an all-passive quantum key distribution transmitting end chip based on a photon integration technology. The transmitting end chip is composed of a laser, a passive intensity modulation module, an intensity detection module, a polarization state passive modulation module, a polarization state detection module, an optical pulse safety truncation module and a data acquisition control unit based on an FPGA. All the modules are connected through optical waveguides. The transmitting end chip is characterized in that a passive modulation architecture is adopted, and the side channel attack risk caused by modulation of an active device is eliminated. The invention further discloses a quantum state modulation method of the all-passive quantum key distribution transmitting end chip. The all-passive quantum key distribution transmitting end chip is combined with a modulation method to realize high-speed, stable and safe quantum state coding. In addition, the transmitting end chip supports polarization coded BB84, MDI-QKD and other protocols, and the anti-interference capability and deployment efficiency of the system are remarkably improved.

Description

Technical Field

[0001] 1. The present invention relates to the field of quantum communication technology, and particularly to a fully passive quantum key distribution transmitter chip based on photon integration technology and a modulation method thereof. Background Art

[0002] 2. Network communication provides a lot of convenience for daily life, but at the same time, it is accompanied by information security problems. With the development of supercomputers and quantum computers, their powerful computing capabilities make the encryption methods based on classical encryption algorithms no longer secure. Quantum key distribution (QKD) can distribute information-theoretically secure keys between two communication parties based on the basic principles of quantum mechanics, and is considered to be the most promising solution for realizing secure communication in the future. Currently, the core challenge of QKD technology lies in how to balance the requirements of security, stability, and integration. Traditional polarization-coded QKD systems rely on discrete optical components (such as lithium niobate intensity / phase modulators) to realize quantum state preparation, but active modulation devices are vulnerable to photorefractive effects, resulting in the risk of side-channel attacks.

[0003] 3. In recent years, photon integration technology has provided a new path for the miniaturization of QKD. Existing integration schemes mostly adopt a hybrid architecture, that is, lasers and modulation units are integrated on a chip, but still rely on active phase modulators or dynamic polarization controllers to maintain coding stability. Therefore, there is an urgent need to develop a fully passive polarization-coded QKD integrated chip, which eliminates the dependence on electro-optic devices through a passive modulation architecture, and combines on-chip polarization stability design to achieve high-precision quantum state output without compensation, and at the same time supports flexible switching of multiple protocols to meet the practical requirements of high security, high stability, and low cost. Summary of the Invention

[0004] 4. Aiming at the deficiencies of the prior art, the present invention provides a fully passive quantum key distribution transmitter chip based on photon integration technology and a modulation method thereof. The passive intensity modulation module and polarization state passive modulation module in the transmitter chip can realize the preparation of decoy states and polarization states without an active modulator. Therefore, this solution can construct a safe, stable, and miniaturized transmitter chip.

[0005] 5. The present invention provides protection for a fully passive quantum key distribution transmitter and modulation method based on photon integration technology, including:

[0006] 6. A fully passive polarization-coded quantum key distribution transmitter chip based on photon integration technology, including: a laser, a passive intensity modulation module, an intensity detection module, a polarization state passive modulation module, a polarization state detection module, an optical pulse safety truncation module, a data acquisition and control unit based on FPGA, a second variable optical attenuator, and a chip-fiber coupler;

[0007] Among them, the passive intensity modulation module is used for random modulation of the intensity of the quantum state; the intensity detection module is used to detect the intensity of the quantum state, and at the same time, the Z-basis polarization state encoding can be determined according to the intensity; the polarization state passive modulation module is used to prepare quantum states with different polarizations; the polarization state detection module is used to determine that the polarization state passive modulation module has prepared the X-basis polarization state; the optical pulse safety truncation module is used to eliminate the redundant pulses associated with the screened quantum states; the data acquisition and control unit based on FPGA is used to record the results of all quantum state detections, screen and determine the positions of the Z-basis and X-basis quantum states; the second variable optical attenuator is used to attenuate the prepared quantum state to the single-photon level, and then transmit it to the quantum channel outside the chip through the chip-fiber coupler.

[0008] 7. As a full-passive polarization encoding quantum key distribution transmitter chip based on photon integration technology according to the present invention, it is characterized in that: the passive intensity modulation module includes a first beam splitter, a second beam splitter and a first optical delay line;

[0009] 8. There are two optical waveguides between the first beam splitter and the second beam splitter; a first optical delay line is provided on the first optical waveguide to connect the first beam splitter and the second beam splitter; the second optical waveguide directly connects the first beam splitter and the second beam splitter.

[0010] 9. As a full-passive polarization encoding quantum key distribution transmitter chip based on photon integration technology according to the present invention, it is characterized in that: the intensity detection module includes a first variable optical attenuator and a first photodetector; the first variable optical attenuator is connected to the first photodetector through an optical waveguide; the first variable optical attenuator is also connected to the second beam splitter; the first photodetector is connected to the data acquisition and control unit based on FPGA.

[0011] 10. As a full-passive polarization encoding quantum key distribution transmitter chip based on photon integration technology according to the present invention, it is characterized in that: the polarization state passive modulation module includes a third beam splitter, a polarization rotation coupler, and a second delay line; there are two optical waveguides between the third beam splitter and the polarization rotation coupler, and a second delay line is provided on the first optical waveguide to connect the third beam splitter and the polarization rotation coupler; the second optical waveguide directly connects the third beam splitter and the polarization rotation coupler; the third beam splitter is also connected to the second beam splitter.

[0012] 11. As a full-passive polarization encoding quantum key distribution transmitter chip based on photon integration technology according to the present invention, it is characterized in that: the polarization rotation coupler is connected to a fourth beam splitter.

[0013] 12. As a full - passive polarization - coding quantum key distribution transmitter chip based on photon integration technology of the present invention, it is characterized in that: the polarization state detection module includes a polarization rotation beam splitter, a fifth beam splitter, a sixth beam splitter, a first phase shifter, a second phase shifter, a third phase shifter, a fourth phase shifter, a second photodetector, and a third photodetector;

[0014] 13. There are two optical waveguides between the polarization rotation beam splitter and the fifth beam splitter. The first optical waveguide is provided with the first phase shifter to connect the polarization rotation beam splitter and the fifth beam splitter, and the second optical waveguide is provided with the second phase shifter to connect the polarization rotation beam splitter and the fifth beam splitter; there are two optical waveguides between the fifth beam splitter and the sixth beam splitter. The first optical waveguide is provided with the third phase shifter to connect the fifth beam splitter and the sixth beam splitter, and the second optical waveguide is provided with the fourth phase shifter to connect the fifth beam splitter and the sixth beam splitter; the polarization rotation beam splitter is also connected to the fourth beam splitter; the sixth beam splitter is respectively connected to the second photodetector and the third photodetector; the second photodetector and the third photodetector are also connected to the data acquisition and control unit based on FPGA.

[0015] As a full - passive polarization - coding quantum key distribution transmitter chip based on photon integration technology of the present invention, it is characterized in that: the optical pulse security truncation module includes a seventh beam splitter, an eighth beam splitter, a fifth phase shifter, and a sixth phase shifter;

[0016] 14. There are two optical waveguides between the seventh beam splitter and the eighth beam splitter. The first optical waveguide is provided with the fifth phase shifter to connect the seventh beam splitter and the eighth beam splitter, and the second waveguide is provided with the sixth phase shifter to connect the seventh beam splitter and the eighth beam splitter; the seventh beam splitter is also connected to the fourth beam splitter; the eighth beam splitter is connected to a second variable optical attenuator and a chip - fiber coupler.

[0017] 15. As a full - passive polarization - coding quantum key distribution transmitter chip based on photon integration technology of the present invention, it is characterized in that: the internal optical devices of the transmitter chip are all connected through optical waveguides, while the first photodetector, the second photodetector, and the third photodetector are respectively connected to the data acquisition and control unit based on FPGA through high - frequency electric wires;

[0018] 16. The full - passive quantum state modulation method is characterized by including the following steps: 17. The laser generates an initial pulse sequence with a fixed frequency, and the pulse sequence is numbered in sequence as: P1, P2, P3, P4,...;

[0019] 18. Passive intensity modulation method: Through the first beam splitter, the initial pulse sequence is equally divided into two pulse sequences with the same intensity; the first delay line is used to introduce a delay of the light source pulse period (τ) for the two optical pulse sequences; the two pulse sequences interfere again in the second beam splitter, thereby generating a new pulse sequence (the number combinations are P1+P2, P2+P3, P3+P4, P4+P5,...); since the phase of the initial pulse is random, the intensity of the new pulse sequence is also random, thus realizing the random intensity modulation of the quantum state;

[0020] 19. Intensity detection method: The pulse sequence (the number combinations are P1+P2, P2+P3, P3+P4, P4+P5,...) enters the intensity detection module; the function of the first variable optical attenuator is to balance the device insertion loss, so that the detection results of the first photodetector, the second photodetector, and the third photodetector balance the insertion loss introduced by the polarization state passive modulation module and the polarization state detection module; the first photodetector converts the pulsed optical signal into an electrical signal; the data acquisition and control unit based on FPGA acquires the electrical signal to obtain all the intensity information of the pulse sequence;

[0021] 20. Polarization state passive modulation method: Through the third beam splitter, the pulse sequence (the number combinations are P1+P2, P2+P3, P3+P4, P4+P5,...) is equally divided into two identical pulse sequences; the second delay line introduces a delay of period (2τ) for the two separated pulse sequences, and then they are coupled through the polarization rotation coupler, thereby generating a new pulse sequence

[0022] 21. Polarization state detection method: For the polarization state detection of the Z basis, it can be detected by PD1 in the intensity detection module; set the pulse detection threshold as t; when PD1 detects that the intensity of the previous pulse P n +P n+1 is higher than the threshold t and the intensity of the subsequent pulse P n+2 +P n+3 is lower than the threshold t (where n = 1, 2, 3,...), it is the H polarization; when PD1 detects that the intensity of the previous pulse P n +P n+1 is lower than the threshold t and the intensity of the subsequent pulse P n+2 +P n+3When the intensity is higher than the threshold t (where n = 1, 2, 3, …), it is V polarization; if the intensities of the front and rear pulses are both higher than the threshold t, the polarization state detection module is required to perform X-basis decoding; for the polarization state under the X basis vector, first, the orthogonal modes of the polarization state are respectively routed to the first waveguide and the second waveguide through the polarization rotation beam splitter, and then the phase difference is adjusted by the first phase shifter or the second phase shifter so that the two pulse sequences have equal-intensity output after interference at the fifth beam splitter; subsequently, the phase difference is adjusted by the third phase shifter or the fourth phase shifter so that the pulses are split and interfered at the sixth beam splitter. When the pulse intensity detected by PD2 exceeds the threshold t and the pulse intensity detected by PD3 is lower than the threshold t, the current polarization state is determined to be 45°; when the pulse intensity detected by PD3 exceeds the threshold t and the pulse intensity detected by PD2 is lower than the threshold t, the current polarization state is determined to be -45°.

[0023] 22. Optical pulse security truncation strategy: Pulse sequence In the sequence, each pulse is not independent; in order to ensure that eavesdroppers cannot obtain the information of the encoded pulses from the correlated pulses, the optical pulse security truncation module will screen the quantum measurement results that meet the non-correlation conditions, that is The pulse sequence included to transmit it into the quantum channel.

[0024] 23. Compared with the prior art, the beneficial effects of the invention are as follows: 24.1. The intensity modulation and polarization state modulation modules adopted in the present invention abandon the use of active modulators, can remove side-channel attacks against active modulators, and thus significantly improve the security of the communication process while maintaining the efficient operation of the system;

[0025] 25.2. The present invention uses standard devices to design a secure and stable integrated all-passive polarization encoding component, which can develop a quantum key distribution transmitter chip with low cost, low power consumption, scalability, high stability, high integration, and CMOS compatibility.

[0026] 26.3. The present invention uses integration technology, enabling the system to transmit quantum keys at high speed, meeting the requirements of high-rate communication. The QKD system integrated on the chip has a smaller volume, which is convenient for deployment in a limited space, which is very beneficial for mobile devices or application scenarios with limited space. At the same time, the realization of small chips helps to reduce the volume and cost of the quantum communication system and accelerate the practical process of quantum communication technology.

[0027] 27.4. The design of the present invention is an integrated passive quantum state encoding component that can perform polarization encoding and phase encoding. These components can be compatible with a variety of QKD protocols, including the BB84 protocol and the MDI-QKD protocol. The multi-protocol QKD system improves the adaptability, flexibility, and simplicity of the system, as well as enhances the versatility of the system.

[0028] 28.5. The all-passive solution of the present invention solves the security problem at the source end. At the same time, combined with the measurement device-independent QKD protocol, a high-security quantum key distribution chip system can be constructed. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] 29. To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings. Among them:

[0030] 30. Figure 1 A full-passive quantum key distribution transmitter chip and modulation method based on photon integration technology according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] 31. To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the following will further elaborate on the specific embodiments of the present invention with reference to the drawings in the specification. However, it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0032] 32. To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention. Unless otherwise clearly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "having" etc. will be understood to include the stated elements or components, without excluding other elements or other components.

[0033] 33. Additionally, to better illustrate the present invention, numerous specific details are given in the following detailed description. Those skilled in the art should understand that the present invention can be implemented without some of these specific details. In some instances, methods, means, and elements well-known to those skilled in the art are not described in detail to highlight the gist of the present invention.

[0034] 34. Embodiment 1: As Figure 1 , this embodiment provides a fully passive polarization-encoded quantum key distribution transmitter chip based on photon integration technology, including: 35. Laser LD1, passive intensity modulation module 2, intensity detection module 3, polarization state passive modulation module 4, fourth beam splitter 5, polarization state detection module 6, optical pulse security truncation module 7, second variable optical attenuator 8, chip-fiber coupler 9, FPGA-based data acquisition and control unit 10, first beam splitter 201, second beam splitter 202, first delay line 203, first variable optical attenuator 301, first photodetector 302, third beam splitter 401, polarization rotation coupler 402, second delay line 403, polarization rotation beam splitter 601, fifth beam splitter 602, sixth beam splitter 603, second photodetector 604, third photodetector 605, first phase shifter 606, second phase shifter 607, third phase shifter 608, fourth phase shifter 609, seventh beam splitter 701, eighth beam splitter 702, fifth phase shifter 703, sixth phase shifter 704; wherein, the passive intensity modulation module 2 is used to prepare a quantum state with random intensity; the intensity detection module 3 is used to detect the intensity of the pulse sequence; the polarization state passive modulation module 4 is used to prepare a polarization-encoded quantum state; the polarization state detection module 6 is used to detect the polarization state of the pulse sequence; the optical pulse security truncation module 7 is used to screen out quantum states that meet specific conditions.

[0035] 36. Based on the above embodiment, the laser LD1 is connected to the passive intensity modulation module 2, the passive intensity modulation module 2 is respectively connected to the intensity detection module 3 and the polarization state passive modulation module 4, the polarization state passive modulation module 4 is connected to the fourth beam splitter 5, the fourth beam splitter 5 is respectively connected to the polarization state detection module 6 and the optical pulse security truncation module 7, the optical pulse security truncation module 7 is connected to the second variable optical attenuator 8, and the second variable optical attenuator 8 is connected to the chip-fiber coupler 9;

[0036] 37. Based on the above embodiment, the passive intensity modulation module 2 includes a first beam splitter 201, a second beam splitter 202, and a first delay line 203; wherein, the input end of the first beam splitter 201 is connected to the laser LD1, the two output ends of the first beam splitter 201 are respectively connected to the two input ends of the second beam splitter 202 through two optical arms, and a first delay line 203 is provided on one of the optical arms. Finally, the two output ends of the second beam splitter 202 are respectively connected to the intensity detection module 3 and the polarization state passive modulation module 4;

[0037] 38. Based on the above embodiments, the intensity detection module 3 includes a first variable optical attenuator 301, a first photodetector 302, and an FPGA-based data acquisition and control unit 10; wherein, the input end of the first variable optical attenuator 301 is connected to an output end of the second beam splitter 202, the output end of the first variable optical attenuator 301 is connected to the first photodetector 302, and finally the first photodetector 302 is connected to the FPGA-based data acquisition and control unit 10;

[0038] 39. Based on the above embodiments, the polarization state passive modulation module 4 includes a third beam splitter 401, a polarization coupler 402, and a second optical delay line 403; wherein, the input end of the third beam splitter 401 is connected to the other output end of the second beam splitter 202, the two output ends of the third beam splitter 401 are respectively connected to the two input ends of the polarization rotation coupler 402 through two optical arms, and a second optical delay line 403 is provided on one of the optical arms. Finally, the output end of the polarization rotation coupler 402 is connected to the fourth beam splitter 5;

[0039] 40. Based on the above embodiments, the polarization state detection module 6 includes a polarization rotation beam splitter 601, a fifth beam splitter 602, a sixth beam splitter 603, a second photodetector 604, a third photodetector 605, a first phase shifter 606, a second phase shifter 607, a third phase shifter 608, a fourth phase shifter 609, and an FPGA-based data acquisition and control unit 10; wherein, the input end of the polarization rotation beam splitter 601 is connected to an output end of the fourth beam splitter 5, the two output ends of the polarization beam splitter 601 are respectively connected to the two input ends of the fifth beam splitter 602 through two optical arms, and the first phase shifter 606 and the second phase shifter 607 are respectively provided on the two optical arms. The two output ends of the fifth beam splitter 602 are respectively connected to the two input ends of the sixth beam splitter 603 through two optical arms, and the third phase shifter 608 and the fourth phase shifter 609 are respectively provided on the two optical arms. The two output ends of the sixth beam splitter 603 are respectively connected to the second photodetector 604 and the third photodetector 605, and finally the second photodetector 604 and the third photodetector 605 are connected to the FPGA-based data acquisition and control unit 10;

[0040] 41. Based on the above embodiments, the optical pulse safety truncation module 7 includes a seventh beam splitter 701, an eighth beam splitter 702, a fifth phase shifter 703, and a sixth phase shifter 704; wherein, the input end of the seventh beam splitter 701 is connected to the other output end of the fourth beam splitter 5, the two output ends of the seventh beam splitter 701 are respectively connected to the two input ends of the eighth beam splitter 702 through two optical arms, and the fifth phase shifter 703 and the sixth phase shifter 704 are respectively provided on the two optical arms. Finally, the output end of the eighth beam splitter 702 is connected to the second variable optical attenuator 8;

[0041] Example 2: Polarization Encoding BB84 and MDI-QKD Protocol Polarization State Preparation

[0042] 43. Step S1: Turn on laser LD1 and set the time interval of the pulsed light to τ; laser LD1 generates a pulsed light sequence with random phases;

[0043] 44. Step S2: Turn on the data acquisition control unit to perform data acquisition;

[0044] 45. Step S3: Detect the polarization state of the Z basis through PD1 in the intensity detection module;

[0045] 46. Step S4: Detect the polarization state of the X basis through PD2 and PD3 in the intensity detection module;

[0046] 47. Step S5: Turn on the optical pulse secure truncation module to securely truncate the optical pulses that do not meet the condition of optical pulse independence;

[0047] 48. Optical pulse secure truncation: The pulse sequence entering the optical pulse secure truncation module To meet the condition of optical pulse independence, select the pulse sequence from for retention, and perform secure truncation on all optical pulses in except so that they cannot enter the quantum channel.

[0048] 49. Detection of the polarization state of the Z basis: Set the pulse detection threshold to t. When PD1 detects that the intensity of the front pulse P n +P n+1 , n = 1, 2, 3,... exceeds the threshold t and the intensity of the rear pulse P n+2 +P n+3 , n = 1, 2, 3,... is lower than the threshold t, it is the H polarization; when PD1 detects that the intensity of the front pulse P n +P n+1 , n = 1, 2, 3,... is lower than the threshold t and the intensity of the rear pulse P n+2 +P n+3 , n = 1, 2, 3,... is higher than the threshold t, it is the V polarization. If the intensities of both the front and rear pulses are higher than the threshold, the polarization state detection module is required for X basis decoding.

[0049] ​50. Detection of the polarization state of the X basis: When the pulse intensity detected by PD2 exceeds the threshold t and the pulse intensity detected by PD3 is lower than the threshold t, the current polarization state is determined to be 45°; when the pulse intensity detected by PD3 exceeds the threshold t and the pulse intensity detected by PD2 is lower than the threshold t, the current polarization state is determined to be -45°.

[0050] 51. Among them, the encoding of the four polarization quantum states of H, V, 45°, and -45° is randomly selected.

Claims

1. A fully passive polarization-encoded quantum key distribution transmitter chip based on photon integration technology, comprising: A laser, a passive intensity modulation module, an intensity detection module, a polarization state passive modulation module, a polarization state detection module, an optical pulse safety truncation module, a data acquisition and control unit based on FPGA, a second variable optical attenuator, and a chip-fiber coupler; Among them, the passive intensity modulation module is used for random modulation of the intensity of the quantum state; the intensity detection module is used to detect the intensity of the quantum state, and at the same time, the polarization state encoding of the Z-basis vector can be determined according to the intensity; the polarization state passive modulation module is used to prepare quantum states with different polarizations; the polarization state detection module is used to determine that the polarization state passive modulation module has prepared the X-basis polarization state; the optical pulse safety truncation module is used to eliminate the redundant pulses associated with the screened quantum states; the data acquisition and control unit based on FPGA is used to record the results of all quantum state detections, screen and determine the positions of the Z-basis and X-basis quantum states; the second variable optical attenuator is used to attenuate the prepared quantum state to the single-photon level, and then transmit it to the quantum channel outside the chip through the chip-fiber coupler.

2. The all-passive polarization-encoded quantum key distribution transmitter chip based on photon integration technology according to claim 1, characterized in that: The passive intensity modulation module includes a first beam splitter, a second beam splitter, and a first optical delay line; There are two optical waveguides between the first beam splitter and the second beam splitter. A first optical delay line is provided on the first optical waveguide to connect the first beam splitter and the second beam splitter; the second optical waveguide directly connects the first beam splitter and the second beam splitter.

3. A fully passive polarization-coded quantum key distribution transmitter chip based on photon integration technology according to claim 1, characterized in that: The intensity detection module includes a first variable optical attenuator and a first photodetector; the first variable optical attenuator is connected to the first photodetector through an optical waveguide; the first variable optical attenuator is also connected to the second beam splitter; the first photodetector is connected to the data acquisition and control unit based on FPGA.

4. The all-passive polarization encoding quantum key distribution transmitter chip based on photon integration technology according to claim 1, characterized in that: The polarization state passive modulation module includes a third beam splitter, a polarization rotation coupler, and a second delay line; there are two optical waveguides between the third beam splitter and the polarization rotation coupler. A second delay line is provided on the first optical waveguide to connect the third beam splitter and the polarization rotation coupler; the second optical waveguide directly connects the third beam splitter and the polarization rotation coupler; the third beam splitter is also connected to the second beam splitter.

5. The all-passive polarization-encoded quantum key distribution transmitter chip based on photon integration technology according to claim 1, characterized in that: The polarization rotation coupler is connected to a fourth beam splitter.

6. The all-passive polarization coding quantum key distribution transmitter chip based on photon integration technology according to claim 1, characterized in that: The polarization state detection module includes a polarization rotation beam splitter, a fifth beam splitter, a sixth beam splitter, a first phase shifter, a second phase shifter, a third phase shifter, a fourth phase shifter, a second photodetector, and a third photodetector; There are two optical waveguides between the polarization rotation beam splitter and the fifth beam splitter. The first optical waveguide is provided with the first phase shifter to connect the polarization rotation beam splitter and the fifth beam splitter, and the second optical waveguide is provided with the second phase shifter to connect the polarization rotation beam splitter and the fifth beam splitter; there are two optical waveguides between the fifth beam splitter and the sixth beam splitter. The first optical waveguide is provided with the third phase shifter to connect the fifth beam splitter and the sixth beam splitter, and the second optical waveguide is provided with the fourth phase shifter to connect the fifth beam splitter and the sixth beam splitter; the polarization rotation beam splitter is also connected to the fourth beam splitter; the sixth beam splitter is respectively connected to the second photodetector and the third photodetector; the second photodetector and the third photodetector are also connected to the FPGA-based data acquisition and control unit.

7. The all-passive polarization-coded quantum key distribution transmitter chip based on photon integration technology according to claim 1, characterized in that: The optical pulse safety truncation module includes a seventh beam splitter, an eighth beam splitter, a fifth phase shifter, and a sixth phase shifter; There are two optical waveguides between the seventh beam splitter and the eighth beam splitter. The first optical waveguide is provided with the fifth phase shifter to connect the seventh beam splitter and the eighth beam splitter, and the second waveguide is provided with the sixth phase shifter to connect the seventh beam splitter and the eighth beam splitter; the seventh beam splitter is also connected to the fourth beam splitter; the eighth beam splitter is connected with a second variable optical attenuator and a chip-fiber coupler.

8. A full-passive polarization-encoding quantum key distribution transmitter chip based on photon integration technology according to claims 1-7, characterized in that: The connections of the optical devices inside the transmitter chip are all through optical waveguides. Different modules can be monolithically integrated or integrated on the transmitter chip in a heterogeneous integration manner; while the first photodetector, the second photodetector, and the third photodetector are respectively connected to the FPGA-based data acquisition and control unit through high-frequency wires.

9. A fully passive quantum state modulation method based on claims 1-8, characterized in that, It includes the following steps: (1) The laser generates an initial pulse sequence with a fixed frequency, and the pulse sequence is numbered in sequence as P1, P2, P3, P4,...; (2) Passive intensity modulation method: After passing through the first beam splitter, the initial pulse sequence is equally divided into two pulse sequences with the same intensity; the first delay device is used to introduce a delay of the light source pulse period (τ) for the two optical pulse sequences; the two pulse sequences interfere again in the second beam splitter, thereby generating a new pulse sequence (number combination is P1+P2, P2+P3, P3+P4, P4+P5,...); since the phases of the initial pulses are random, the intensity of the new pulse sequence is also random, thus realizing the random intensity modulation of the quantum state. (3) Intensity detection method: The pulse sequence (number combination is P1+P2, P2+P3, P3+P4, P4+P5,...) enters the intensity detection module; the role of the first variable optical attenuator is to balance the device insertion loss, so that the detection results of the first photodetector, the second photodetector, and the third photodetector balance the insertion losses introduced by the polarization state passive modulation module and the polarization state detection module. The first photodetector converts the pulsed optical signal into an electrical signal; the FPGA-based data acquisition and control unit acquires the electrical signal to obtain all the intensity information of the pulse sequence; (4) Polarization state passive modulation method: After passing through the third beam splitter, the pulse sequence (number combinations are P1+P2, P2+P3, P3+P4, P4+P5,...) is equally divided into two identical pulse sequences; The second delay generator introduces a delay of period (2τ) to two separate pulse sequences, and then couples them through the polarization rotation coupler, thereby generating a new pulse sequence (5) Polarization state detection method: For the polarization state detection of the Z basis, it can be detected by PD1 in the intensity detection module; set the pulse detection threshold to t; when PD1 detects the pre-pulse P n +P n+1 with an intensity higher than the threshold t and the post-pulse P n+2 +P n+3 with an intensity lower than the threshold t (where n = 1, 2, 3,...), it is the H polarization; when PD1 detects the pre-pulse P n +P n+1 with an intensity lower than the threshold t and the post-pulse P n+2 +P n+3 with an intensity higher than the threshold t (where n = 1, 2, 3,...), it is the V polarization; if the intensities of both the pre- and post-pulses are higher than the threshold t, then the polarization state detection module is required for the decoding of the X basis; for the polarization state under the X basis vector, first, the orthogonal modes of the polarization state are respectively routed to the first waveguide and the second waveguide through the polarization rotation beam splitter, and then the phase difference is adjusted by the first phase shifter or the second phase shifter so that the two pulse sequences have equal-intensity output after interference at the fifth beam splitter; then, the phase difference is adjusted by the third phase shifter or the fourth phase shifter so that the pulses are split and interfered at the sixth beam splitter. When the pulse intensity detected by PD2 exceeds the threshold t and the pulse intensity detected by PD3 is lower than the threshold t, the current polarization state is determined to be 45°; when the pulse intensity detected by PD3 exceeds the threshold t and the pulse intensity detected by PD2 is lower than the threshold t, the current polarization state can be determined to be -45°; (6) Optical pulse safety truncation module: The pulse sequence entering the optical pulse safety truncation module To meet the condition that optical pulses are independent of each other, select the pulse sequence for retention, and perform safety truncation on all optical pulses in except so that they cannot enter the quantum channel. ​

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