Phase modulation codec, device and quantum key distribution system

Abstract

The present application relates to a phase modulation codec, a device and a quantum key distribution system, wherein the phase modulation codec comprises a first transmission optical path and a Sagnac ring-phase modulator, wherein the Sagnac ring-phase modulator comprises a first polarization beam splitter rotator provided with a first input port, a first output port and a second output port, wherein the first transmission optical path is connected to the first input port; the second transmission optical path is connected to the first output port and to the second output port; the first phase modulator is connected to the second transmission optical path; the second phase modulator is connected to the second transmission optical path and is symmetrically arranged with the first phase modulator; the first polarization beam splitter rotator, the second transmission optical path, the first phase modulator and the second phase modulator are arranged in a ring shape. The phase modulation codec can realize high-speed modulation of the phase by the codec device or the quantum key distribution system while maintaining the anti-interference of the codec device or the quantum key distribution system.

Description

Technical Field

[0001] The present application relates to the technical field of optical transmission secure communication, and in particular to a phase modulation codec, device and quantum key distribution system. Background Art

[0002] Quantum secure communication technology is a frontier hotspot combining quantum physics and information science. Based on quantum key distribution (QKD) technology and the principle of one-time-one-pad cryptography, quantum secure communication can realize the secure transmission of information in public channels, realize the secure sharing of keys between users, and detect potential eavesdropping behaviors. It can be applied to fields with high security information transmission requirements such as national defense, government affairs, finance, and electricity. Although QKD has undergone a comprehensive development from simple theoretical proof to long-term rigorous experimental verification, QKD technology has not yet been widely used. The existing quantum secure communication network still has some disadvantages (1) low speed, (2) stability needs to be improved, and (3) large size and weight.

[0003] The development of optoelectronic integration technology has brought many advantages to quantum communication devices, such as more complex, more reliable and more scalable quantum devices. In particular, silicon photonics will become the leading platform for future quantum optical technology, achieving miniaturization, low manufacturing cost and compatibility with existing CMOS processes for quantum devices. However, in terms of high-speed modulation of quantum states, the existing effective technologies based on the standard silicon photonic platform are limited. In standard silicon photonic manufacturing, because silicon itself does not have electro-optical nonlinear effects, many silicon-based quantum optical experiments use slower thermo-optic phase modulators to achieve high-fidelity state preparation. The current development of quantum secure communication has exceeded the modulation rate of GHz, which cannot be met by thermo-optic modulation. Although carrier injection or carrier dissipation (CDMs) modulators have the ability of high-speed modulation, there are phase-related losses and modulation saturation problems. The loss and phase modulation depth are strictly limited in the preparation of quantum states for specific applications of quantum secure communication. For example, the loss of CDMs is related to the size of the modulation phase, and there is a problem of phase modulation saturation. These characteristics reduce the fidelity of CDMs in applications.

[0004] Therefore, how to achieve phase modulation stably and efficiently is a hot topic and difficult problem in the application of quantum secure communication based on phase encoding and decoding. Summary of the invention

[0005] The purpose of the present application is to provide a phase modulation codec, device and quantum key distribution system, which can achieve high-speed modulation of the phase by the codec device or quantum key distribution system while maintaining the anti-interference of the codec device or quantum key distribution system.

[0006] To this end, in a first aspect, an embodiment of the present application provides a phase modulation codec, comprising a first transmission optical path and a Sagnac ring-phase modulator connected to each other, the Sagnac ring-phase modulator comprising a first polarization beam splitter rotator, provided with a first input port, a first output port and a second output port, the first transmission optical path being connected to the first input port; a second transmission optical path, one end of which is connected to the first output port and the other end of which is connected to the second output port; a first phase modulator, which is connected to the second transmission optical path; a second phase modulator, which is connected to the second transmission optical path and is symmetrically arranged with the first phase modulator; the first polarization beam splitter rotator, the second transmission optical path, the first phase modulator and the second phase modulator are arranged in a ring shape.

[0007] In a possible implementation, the first transmission optical path and the second transmission optical path are both polarization-maintaining transmission optical paths; the fast axis or the slow axis of the first transmission optical path is 45 degrees to the polarization direction of the first input port; the polarization direction of the second transmission optical path is consistent with the polarization direction of the first output port and the second output port.

[0008] In a second aspect, an embodiment of the present application provides a phase modulation codec device, comprising a polarization-maintaining beam splitter, a short arm of the codec device, and a long arm of the codec device; the short arm of the codec device is connected to the polarization-maintaining beam splitter, and the long arm of the codec device is connected to the polarization-maintaining beam splitter.

[0009] In a possible implementation manner, the long arm of the codec device includes any one of the phase adjustment codecs described above, and the first transmission optical path of the phase adjustment codec is connected to the polarization-maintaining beam splitter.

[0010] In a possible implementation, the short arm of the encoding and decoding device includes: a third transmission optical path, one end of which is connected to the polarization-maintaining beam splitter; a second polarization beam splitter rotator, which is provided with a second input port, a third output port and a fourth output port, and the second input port is connected to the other end of the third transmission optical path; a fourth transmission optical path, one end of which is connected to the third output port and the other end is connected to the fourth output port, and the fourth transmission optical path and the second polarization beam splitter rotator are arranged in a ring shape.

[0011] In a possible implementation, the third transmission optical path and the fourth transmission optical path are both polarization-maintaining transmission optical paths; the fast axis or the slow axis of the third transmission optical path is 45 degrees to the polarization direction of the second input port; the polarization direction of the fourth transmission optical path is consistent with the polarization directions of the third output port and the fourth output port.

[0012] In a possible implementation manner, the short arm of the codec device includes any one of the phase adjustment codecs described above, and the first transmission optical path of the phase adjustment codec is connected to the polarization-maintaining beam splitter.

[0013] In a possible implementation, the long arm of the encoding and decoding device includes: a fifth transmission optical path, one end of which is connected to the polarization-maintaining beam splitter; a third polarization beam splitter rotator, which is provided with a third input port, a fifth output port and a sixth output port, and the third input port is connected to the other end of the fifth transmission optical path; a sixth transmission optical path, one end of which is connected to the fifth output port and the other end is connected to the sixth output port, and the sixth transmission optical path and the third polarization beam splitter rotator are arranged in a ring shape.

[0014] In a possible implementation, the fifth transmission optical path and the sixth transmission optical path are both polarization-maintaining transmission optical paths; the fast axis or the slow axis of the fifth transmission optical path is 45 degrees to the polarization direction of the third input port; the polarization direction of the sixth transmission optical path is consistent with the polarization directions of the fifth output port and the sixth output port.

[0015] In a third aspect, an embodiment of the present application provides a quantum key distribution system, including the above-mentioned codec or the above-mentioned phase modulation codec device, as a receiving end of the quantum key distribution system, for decoding;

[0016] The above-mentioned codec or the above-mentioned phase modulation codec device is included as the transmitting end of the quantum key distribution system for encoding.

[0017] According to the phase modulation codec, device and quantum key distribution system provided by the embodiment of the present application, the phase modulation codec includes a first transmission optical path and a Sagnac ring-phase modulator connected to each other, the Sagnac ring-phase modulator includes a first polarization beam splitter rotator, a second transmission optical path and a first phase modulator, the first polarization beam splitter rotator is provided with a first input port, a first output port and a second output port, the first transmission optical path is connected to the first input port; one end of the second transmission optical path is connected to the first output port and the other end is connected to the second output port; the first phase modulator is connected to the second transmission optical path; the second phase modulator is connected to the second transmission optical path and is symmetrically arranged with the first phase modulator; the first polarization beam splitter rotator, the second transmission optical path, the first phase modulator and the second phase modulator are arranged in a ring shape. The phase modulation codec can realize high-speed modulation of the phase by the codec device or the quantum key distribution system while maintaining the anti-interference of the codec device or the quantum key distribution system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In addition, in the drawings, the same components are marked with the same reference numerals, and the drawings are not drawn according to the actual scale.

[0019] Figure 1 A schematic diagram showing the structure of a phase modulation codec provided in an embodiment of the present application is shown;

[0020] Figure 2 A schematic diagram showing the structure of a phase modulation encoding and decoding device provided in an embodiment of the present application is shown;

[0021] Figure 3 A schematic diagram of the structure of another phase modulation encoding and decoding device provided in an embodiment of the present application is shown.

[0022] Description of reference numerals:

[0023] 1. The first transmission optical path;

[0024] 2. Sagnac ring-phase modulator; 21. first polarization beam splitter rotator; 211. first input port; 212. first output port; 213. second output port; 22. second transmission optical path; 23. first phase modulator; 24. second phase modulator;

[0025] 3. Polarization-maintaining beam splitter; 4. Short arm of the codec device; 41. Third transmission optical path; 42. Second polarization beam splitter rotator; 421. Second input port; 422. Third output port; 423. Fourth output port; 43. Fourth transmission optical path; 5. Long arm of the codec device; 51. Fifth transmission optical path; 52. Third polarization beam splitter rotator; 521. Third input port; 522. Fifth output port; 523. Sixth output port; 53. Sixth transmission optical path. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0027] like Figures 1 to 3As shown, an embodiment of the present application provides a phase modulation codec, including a first transmission optical path 1 and a Sagnac ring-phase modulator 2 connected to each other, the Sagnac ring-phase modulator 2 including a first polarization beam splitter rotator 21, a second transmission optical path 22, a first phase modulator 23 and a second phase modulator 24, the first polarization beam splitter rotator 21 is provided with a first input port 211, a first output port 212 and a second output port 213, the first transmission optical path 1 is connected to the first input port 211; one end of the second transmission optical path 22 is connected to the first output port 212 and the other end is connected to the second output port 213; the first phase modulator 23 is connected to the second transmission optical path 22; the second phase modulator 24 is connected to the second transmission optical path 22 and is symmetrically arranged with the first phase modulator 23; the first polarization beam splitter rotator 21, the second transmission optical path 22, the first phase modulator 23 and the second phase modulator 24 are arranged in a ring shape.

[0028] In some optional examples, the first transmission optical path 1 and the second transmission optical path 22 are both polarization-maintaining transmission optical paths; the fast axis or slow axis of the first transmission optical path 1 is 45 degrees to the polarization direction of the first input port 211; the polarization direction of the second transmission optical path 22 is consistent with the polarization directions of the first output port 212 and the second output port 213.

[0029] During operation, the input optical pulse from the first transmission optical path 1 is input into the first polarization beam splitter rotator 21 through the first input port 211. The input optical pulse can be regarded as consisting of two orthogonal polarization states, which can be respectively recorded as x polarization state and y polarization state. The x polarization state is split by the first polarization beam splitter rotator 21 and output from the second output port 213, enters the second transmission optical path 22, and propagates in the clockwise direction. The y polarization state is split by the first polarization beam splitter rotator 21 and rotated into the x polarization state, output from the first output port 212, enters the second transmission optical path 22, and propagates in the counterclockwise direction.

[0030] The x-ray pulse propagating in the clockwise direction is phase-modulated by the second phase modulator 24 and the first phase modulator 23 successively, inputted from the first output port 212 , and transformed into the y polarization state after polarization rotation and then enters the first polarization beam splitter rotator 21 .

[0031] The x-ray pulse propagating in the counterclockwise direction is phase-modulated by the first phase modulator 23 and the second phase modulator 24 successively, and then input into the first polarization beam rotator 21 through the second output port 213 .

[0032] In this way, the x polarization state component of the input optical pulse inputted from the first input port 211 is transformed into the y polarization state when it is outputted from the first input port 211 after being transformed by the device. The y polarization state component of the input optical pulse inputted from the first input port 211 is transformed into the x polarization state when it is outputted from the first input port 211 after being transformed by the device.

[0033] And the x polarization state and y polarization state inputted from the first input port 211 are both x polarization states in the device, and arrive at the second phase modulator 24 and the first phase modulator 23 respectively in the clockwise and counterclockwise directions for phase modulation. The anti-interference high-speed phase modulation codec realizes that when the two orthogonal polarization states of the input optical pulse are reflected and outputted by the device, each orthogonal polarization state is transformed into a polarization state orthogonal thereto, so that the phase between the x polarization state and the y polarization state of the input optical pulse is kept the same as the phase between the y polarization state and the x polarization state of the output optical pulse. At the same time, the device structure in which the first phase modulator 23 and the second phase modulator 24 are symmetrically placed is adopted, so that the x polarization state (clockwise propagation x polarization state) and the y polarization state (counterclockwise propagation x polarization state) of the input optical pulse can be modulated at the same time, that is, in each encoding and decoding process, the modulation voltage of the first phase modulator 23 and the second phase modulator 24 remains unchanged and only needs to be maintained for the shortest time, thereby maximizing the modulation speed of the device.

[0034] By designing the phase modulation structure of the mirror-symmetrical first phase modulator 23 and the second phase modulator 24 in the Sagnac ring, the high-speed modulation of the phase of the codec device or the quantum key distribution system can be achieved while maintaining the anti-interference of the codec device or the quantum key distribution system. The present invention can be used to design and implement the all-optical integration of the codec device or the quantum key distribution system, can avoid the modulation saturation problem related to the existing phase modulation in the standard silicon photonics manufacturing, realize the high-speed quantum state modulation with a modulation depth above the π phase, and help to realize the miniaturization of the quantum key distribution device or system.

[0035] In some optional examples, a phase modulation codec device includes a polarization maintaining beam splitter 3, a codec device short arm 4 and a codec device long arm 5; the codec device short arm 4 is connected to the polarization maintaining beam splitter 3, and the codec device long arm 5 is connected to the polarization maintaining beam splitter 3.

[0036] Two ports I and O on one side of the polarization-maintaining beam splitter 3 are used as input and output ports of the phase encoding and decoding device, respectively, and I and O are interchangeable. The polarization-maintaining beam splitter 3, the encoding and decoding device long arm 5 and the encoding and decoding device short arm 4 form an unequal-arm Michelson interferometer.

[0037] The long arm 5 of the codec device includes any one of the above-mentioned phase modulation codecs, and the first transmission optical path 1 of the phase modulation codec is connected to the polarization-maintaining beam splitter 3 .

[0038] Furthermore, the short arm 4 of the encoding and decoding device includes a third transmission optical path 41, a second polarization beam splitter rotator 42 and a fourth transmission optical path 43, and one end of the third transmission optical path 41 is connected to the polarization-maintaining beam splitter 3; the second polarization beam splitter rotator 42 is provided with a second input port 421, a third output port 422 and a fourth output port 423, and the second input port 421 is connected to the other end of the third transmission optical path 41; one end of the fourth transmission optical path 43 is connected to the third output port 422 and the other end is connected to the fourth output port 423, and the fourth transmission optical path 43 and the second polarization beam splitter rotator 42 are arranged in a ring shape.

[0039] The third transmission optical path 41 and the fourth transmission optical path 43 are both polarization-maintaining transmission optical paths; the fast axis or slow axis of the third transmission optical path 41 is 45 degrees to the polarization direction of the second input port 421; the polarization direction of the fourth transmission optical path 43 is consistent with the polarization direction of the third output port 422 and the fourth output port 423.

[0040] During operation, the optical pulse enters the polarization-maintaining beam splitter 3 through the port I of the polarization-maintaining beam splitter 3 and is divided by the polarization-maintaining beam splitter 3 into two optical pulses that enter the first transmission optical path 1 and the third transmission optical path 41 respectively. The optical pulse from the first transmission optical path 1 is transformed by the first polarization beam splitter rotator 21 in the long arm 5 of the phase modulation codec device and phase modulated by the first phase modulator 23 and the second phase modulator 24, and then returns to the first transmission optical path 1 and then returns to the polarization-maintaining beam splitter 3. The optical pulse from the third transmission optical path 41 is transformed by the second polarization beam splitter rotator 42 in the short arm 4 of the phase modulation codec device, and then returns to the third transmission optical path 41 and then returns to the polarization-maintaining beam splitter 3. The optical pulses from the first transmission optical path 1 and the third transmission optical path 41 that return after a relative delay are combined by the polarization-maintaining beam splitter 3 and output from port O.

[0041] In some optional examples, the short arm 4 of the codec device includes the above-mentioned phase modulation codec, and the first transmission optical path 1 of the phase modulation codec is connected to the polarization-maintaining beam splitter 3 .

[0042] Furthermore, the long arm 5 of the encoding and decoding device includes a fifth transmission optical path 51, a third polarization beam splitter rotator 52 and a sixth transmission optical path 53, and one end of the fifth transmission optical path 51 is connected to the polarization-maintaining beam splitter 3; the third polarization beam splitter rotator 52 is provided with a third input port 521, a fifth output port 522 and a sixth output port 523, and the third input port 521 is connected to the other end of the fifth transmission optical path 51; one end of the sixth transmission optical path 53 is connected to the fifth output port 522 and the other end is connected to the sixth output port 523, and the sixth transmission optical path 53 and the third polarization beam splitter rotator 52 are arranged in a ring shape.

[0043] The fifth transmission optical path 51 and the sixth transmission optical path 53 are both polarization maintaining transmission optical paths; the fast axis or slow axis of the fifth transmission optical path 51 is 45 degrees to the polarization direction of the third input port 521; the polarization direction of the sixth transmission optical path 52 is consistent with the polarization direction of the fifth output port 522 and the sixth output port 523.

[0044] During operation, the optical pulse enters the polarization-maintaining beam splitter 3 through the port I of the polarization-maintaining beam splitter 3 and is divided by the polarization-maintaining beam splitter 3 into two optical pulses that enter the first transmission optical path 1 and the fifth transmission optical path 51 respectively. The optical pulse from the first transmission optical path 1 is transformed by the first polarization beam splitter rotator 21 in the short arm 4 of the encoding and decoding device and phase modulated by the first phase modulator 23 and the second phase modulator 24, and then returns to the first transmission optical path 1 and then returns to the polarization-maintaining beam splitter 3. The optical pulse from the fifth transmission optical path 51 is transformed by the third polarization beam splitter rotator 52 in the long arm 5 of the encoding and decoding device, and then returns to the third transmission optical path 51 and then returns to the polarization-maintaining beam splitter 3. The optical pulses from the first transmission optical path 1 and the fifth transmission optical path 51 that return after a relative delay are combined by the polarization-maintaining beam splitter 3 and output from port O.

[0045] A quantum key distribution system includes the above-mentioned codec or phase modulation codec device as a receiving end of the quantum key distribution system for decoding; and includes the above-mentioned codec or phase modulation codec device as a transmitting end of the quantum key distribution system for encoding.

[0046] It should be noted that the phrases "one embodiment", "an embodiment", "an exemplary embodiment", "some embodiments", etc. mentioned in the specification indicate that the described embodiments may include certain features, structures or characteristics, but not every embodiment may include the certain features, structures or characteristics. In addition, such phrases do not necessarily refer to the same embodiment. In addition, when describing certain features, structures or characteristics in conjunction with an embodiment, it is within the knowledge of those skilled in the art to implement such features, structures or characteristics in conjunction with other embodiments, whether explicitly or not explicitly described.

[0047] It should be easily understood that “on,” “above,” and “over” in the present disclosure should be interpreted in the broadest manner, so that “on” not only means “directly on something,” but also includes the meaning of “on something” with intervening features or layers therebetween, and “above” or “over” not only includes the meaning of “above” or “over,” but also may include the meaning of “above” or “over something” with no intervening features or layers therebetween (i.e., directly on something).

[0048] In addition, spatially relative terms, such as "below," "below," "beneath," "above," "above," etc., may be used herein for ease of description to describe the relationship of one element or feature relative to other elements or features as shown in the figures. Spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation shown in the figures. The device may have other orientations (rotated 90 degrees or at other orientations), and the spatially relative descriptors used herein may likewise be interpreted accordingly.

[0049] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A phase modulation encoding and decoding device, characterized in that: The phase modulation codec device comprises a polarization-maintaining beam splitter, a codec device short arm and a codec device long arm; the codec device long arm is connected to the polarization-maintaining beam splitter, and comprises a first transmission optical path and a Sagnac ring-phase modulator connected to each other, and the Sagnac ring-phase modulator comprises: A first polarization beam splitter rotator is provided with a first input port, a first output port and a second output port, and the first transmission optical path is connected to the first input port; a second transmission optical path, one end of which is connected to the first output port and the other end of which is connected to the second output port; A first phase modulator connected to the second transmission optical path; a second phase modulator, connected to the second transmission optical path and symmetrically arranged with the first phase modulator; The first polarization beam splitter rotator, the second transmission optical path, the first phase modulator and the second phase modulator are arranged in a ring shape; Wherein, the short arm of the encoding and decoding device includes: The third transmission optical path, one end of which is connected to the polarization-maintaining beam splitter: A second polarization beam splitter rotator is provided with a second input port, a third output port and a fourth output port, wherein the second input port is connected to the other end of the third transmission optical path; A fourth transmission optical path has one end connected to the third output port and the other end connected to the fourth output port, and the fourth transmission optical path and the second polarization beam splitter rotator are arranged in a ring shape.

2. The phase modulation encoding and decoding device according to claim 1, characterized in that: The first transmission optical path and the second transmission optical path are both polarization-maintaining transmission optical paths; the fast axis or the slow axis of the first transmission optical path is 45 degrees to the polarization direction of the first input port; the polarization direction of the second transmission optical path is consistent with the polarization directions of the first output port and the second output port; The third transmission optical path and the fourth transmission optical path are both polarization-maintaining transmission optical paths; the fast axis or slow axis of the third transmission optical path is 45 degrees to the polarization direction of the second input port; the polarization direction of the fourth transmission optical path is consistent with the polarization directions of the third output port and the fourth output port.

3. The phase modulation encoding and decoding device according to claim 1, characterized in that: The first transmission optical path of the long arm of the encoding and decoding device is connected to the polarization-maintaining beam splitter.

4. A phase modulation encoding and decoding device, characterized in that: It includes a polarization-maintaining beam splitter, a short arm of a codec device and a long arm of a codec device; the short arm of the codec device is connected to the polarization-maintaining beam splitter, and includes a first transmission optical path and a Sagnac ring-phase modulator connected to each other, and the Sagnac ring-phase modulator includes: A first polarization beam splitter rotator is provided with a first input port, a first output port and a second output port, and the first transmission optical path is connected to the first input port; a second transmission optical path, one end of which is connected to the first output port and the other end of which is connected to the second output port; A first phase modulator connected to the second transmission optical path; a second phase modulator, connected to the second transmission optical path and symmetrically arranged with the first phase modulator; The first polarization beam splitter rotator, the second transmission optical path, the first phase modulator and the second phase modulator are arranged in a ring shape; Wherein, the long arm of the encoding and decoding device includes: A fifth transmission optical path, one end of which is connected to the polarization-maintaining beam splitter: A third polarization beam splitter rotator is provided with a third input port, a fifth output port and a sixth output port, wherein the third input port is connected to the other end of the fifth transmission optical path; A sixth transmission optical path has one end connected to the fifth output port and the other end connected to the sixth output port, and the sixth transmission optical path and the third polarization beam splitter rotator are arranged in a ring shape.

5. The phase modulation encoding and decoding device according to claim 4, characterized in that: The first transmission optical path and the second transmission optical path are both polarization-maintaining transmission optical paths; the fast axis or the slow axis of the first transmission optical path is 45 degrees to the polarization direction of the first input port; the polarization direction of the second transmission optical path is consistent with the polarization directions of the first output port and the second output port; The fifth transmission optical path and the sixth transmission optical path are both polarization-maintaining transmission optical paths; the fast axis or slow axis of the fifth transmission optical path is 45 degrees to the polarization direction of the third input port; the polarization direction of the sixth transmission optical path is consistent with the polarization direction of the fifth output port and the sixth output port.

6. The phase modulation encoding and decoding device according to claim 4, characterized in that: The first transmission optical path of the short arm of the encoding and decoding device is connected to the polarization-maintaining beam splitter.

7. A quantum key distribution system, characterized in that: The encoding and decoding device according to any one of claims 1 to 3 or the phase modulation encoding and decoding device according to any one of claims 4 to 6 is used as a receiving end of a quantum key distribution system for decoding; It includes the encoding and decoding device according to any one of claims 1 to 3 or the phase modulation encoding and decoding device according to any one of claims 4 to 6, which is used as the transmitting end of a quantum key distribution system for encoding.

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