Polarization encoding device, method and quantum communication system

Abstract

The present application provides a polarization encoding device, method, and quantum communication system. The device includes: a first polarization operation module, a second polarization operation module, and a third polarization operation module connected in series, wherein the first polarization operation module, the second polarization operation module, and the third polarization operation module each include a polarization control optical path and a phase modulator; the polarization control optical path is used to polarization-split an input optical pulse into two sub-optical pulses, and the phase modulator performs phase modulation on one of the two sub-optical pulses, or performs different phase modulation on the two sub-optical pulses respectively. The angle between the intrinsic polarization states of any two polarization control optical paths can be set according to the requirements of the quantum communication protocol. By combined modulation of the first polarization operation module, the second polarization operation module, and / or the third polarization operation module, multiple polarization states can be modulated in a digital modulation manner to meet the requirements of different quantum communication protocols.

Description

Technical Field

[0001] The present invention relates to the field of quantum communication and optical quantum coding technology, and in particular to a polarization coding device, method and quantum communication system. Background Art

[0002] The physical implementation of quantum communication systems, such as quantum key distribution and direct quantum communication, requires encoding and decoding of quantum states. Quantum communication systems with different protocols have different requirements for quantum state encoding. For example, the BB84 quantum communication protocol requires encoding and decoding of four quantum states using two bases, while reference-frame-independent quantum communication systems require encoding and decoding of six quantum states using three bases or four quantum states using three bases. This requires the design of optical quantum encoding devices compatible with multiple quantum state protocols. Furthermore, a common method for preparing polarization-encoded quantum states is through phase modulation. When preparing multiple quantum states using three bases, a wide variety of phases need to be modulated, making the design of modulator drive circuits very challenging for high-speed modulation. This requires the design of multiple phase modulators for combined modulation using digital modulation.

[0003] Therefore, how to make multiple quantum communication protocols compatible in the same optical quantum coding device and realize the encoding and decoding requirements of multiple quantum states through digital modulation is an urgent problem to be solved. Summary of the Invention

[0004] The present application provides a polarization encoding device, method and quantum communication system to solve the technical problems mentioned in the prior art.

[0005] According to a first aspect of the present application, a polarization encoding device is provided, comprising: a first polarization operation module, a second polarization operation module, and a third polarization operation module connected in series, wherein the first polarization operation module comprises: a first polarization control optical path and a first phase modulator arranged in a transmission optical path of the first polarization control optical path; the first polarization control optical path is used to polarize and split an input optical pulse into two optical sub-pulses, namely a first optical pulse and a second optical pulse, and the first phase modulator is used to phase-modulate the first optical pulse and / or the second optical pulse so that a phase difference α is generated between the two optical pulses, and the first optical pulse and the second optical pulse after passing through the first phase modulator are combined and output through the first polarization control optical path; one of the two eigenpolarization states of the first polarization control optical path is The second polarization operation module includes: a second polarization control optical path and a second phase modulator arranged in the transmission optical path of the second polarization control optical path, the second polarization control optical path is connected in series with the first polarization control optical path, the second polarization control optical path is used to input the optical pulse output by the combined beam of the first polarization control optical path from the input port, and polarization-split it into two sub-optical pulses, namely a third optical pulse and a fourth optical pulse, the second phase modulator is used to phase-modulate the third optical pulse and / or the fourth optical pulse, so that a phase difference β is generated between the two optical pulses, and the third optical pulse and the fourth optical pulse after passing through the second phase modulator are combined and output by the second polarization control optical path; one of the two eigenpolarization states of the second polarization control optical path is The third polarization operation module includes: a third polarization control optical path and a third phase modulator arranged in the transmission optical path of the third polarization control optical path, the third polarization control optical path is connected in series with the first polarization control optical path and the second polarization control optical path, the third polarization control optical path is used to input the optical pulse output by the combined beam of the second polarization control optical path from the input port, and polarize it into two sub-optical pulses, namely the fifth optical pulse and the sixth optical pulse, the third phase modulator is used to phase modulate the fifth optical pulse and / or the sixth optical pulse, so that a phase difference γ is generated between the two optical pulses, and the fifth optical pulse and the sixth optical pulse after passing through the third phase modulator are combined and output through the third polarization control optical path; one of the two eigenpolarization states of the third polarization control optical path is Wherein, by setting the intrinsic polarization state With the eigenpolarization state The angle between them, and the eigenpolarization state With the eigenpolarization state and the phase difference α, phase difference β and phase difference γ are coordinated to meet the requirements of different quantum communication protocols.

[0006] In some embodiments, the first phase modulator includes: a first port, a second port, and a third port, wherein the first port and the second port are respectively a forward input optical port and a reverse input optical port of the first phase modulator, wherein the first path optical pulse is input into the first phase modulator via the first port and output from the second port after passing through the first phase modulator, and the second path optical pulse is input into the first phase modulator via the second port and output from the first port after passing through the first phase modulator, and the third port is an electrical port for applying a modulated electrical signal;

[0007] The second phase modulator includes: a fourth port, a fifth port, and a sixth port, the fourth port and the fifth port being the forward input optical port and the reverse input optical port of the second phase modulator, respectively; the third path optical pulse is input into the second phase modulator via the fourth port and output from the fifth port after passing through the second phase modulator; the fourth path optical pulse is input into the second phase modulator via the fifth port and output from the fourth port after passing through the second phase modulator; the sixth port is an electrical port for applying a modulated electrical signal;

[0008] The third phase modulator includes: a seventh port, an eighth port, and a ninth port. The seventh port and the eighth port are respectively the forward input optical port and the reverse input optical port of the third phase modulator. The fifth optical pulse is input into the third phase modulator via the seventh port and output from the eighth port after passing through the third phase modulator. The sixth optical pulse is input into the third phase modulator via the eighth port and output from the seventh port after passing through the third phase modulator. The ninth port is an electrical port for applying a modulated electrical signal.

[0009] In some embodiments, after applying a high-frequency modulating electrical signal having a frequency higher than a specified threshold, the first phase modulator operates in a non-reciprocal state, and a ratio of a modulation efficiency of a first path optical pulse inputted from a forward input optical port to a modulation efficiency of a second path optical pulse inputted from a reverse input optical port is not less than a preset threshold.

[0010] After applying a high-frequency modulating electrical signal having a frequency higher than a specified threshold, the second phase modulator operates in a non-reciprocal state, and a ratio of a modulation efficiency of a third path optical pulse inputted through the forward input optical port to a modulation efficiency of a fourth path optical pulse inputted through the reverse input optical port is not less than a preset threshold.

[0011] After applying a high-frequency modulating electrical signal having a frequency higher than a specified threshold, the third phase modulator operates in a non-reciprocal state, and a ratio of a modulation efficiency of a fifth path optical pulse input through the forward input optical port to a modulation efficiency of a sixth path optical pulse input through the reverse input optical port is not less than a preset threshold.

[0012] In some embodiments, the first path optical pulse and the second path optical pulse pass through the first phase modulator simultaneously; the third path optical pulse and the fourth path optical pulse pass through the second phase modulator simultaneously; and / or the fifth path optical pulse and the sixth path optical pulse pass through the third phase modulator simultaneously.

[0013] In some embodiments, the intrinsic polarization state and the eigenpolarization state When the angle between them is 1·90°, the eigenpolarization state and the eigenpolarization state The included angle between them is 22.5°±m·45°, or 45°±m·90°, where l and m are integers.

[0014] In some embodiments, the intrinsic polarization state and the eigenpolarization state When the angle between them is 22.5°±a·45° or 45°±a·90°, the eigenpolarization state and the eigenpolarization state The included angle between them is m·90°, or 22.5°±m·45°, or 45°±m·90°, where a and m are integers.

[0015] In some embodiments, the angle between the eigenpolarization state of the first polarization-controlled light path and the eigenpolarization state of the second polarization-controlled light path is achieved by rotating the second polarization-controlled light path, and the angle between the eigenpolarization state of the first polarization-controlled light path and the eigenpolarization state of the third polarization-controlled light path is achieved by rotating the third polarization-controlled light path; and / or,

[0016] The device further comprises: a first polarization state rotator and / or a second polarization state rotator,

[0017] The first polarization state rotator is arranged between the first polarization control light path and the second polarization control light path, and the angle between the intrinsic polarization state of the first polarization control light path and the intrinsic polarization state of the second polarization control light path is adjusted by the first polarization state rotator;

[0018] In some embodiments, the second polarization state rotator is arranged between the second polarization control light path and the third polarization control light path, and the angle between the intrinsic polarization state of the first polarization control light path and the intrinsic polarization state of the third polarization control light path is adjusted by the first polarization state rotator and / or the second polarization state rotator.

[0019] In some embodiments, the polarization state of the light pulse input into the first polarization control light path is Alternatively, the polarization state of the optical pulse input into the first polarization control optical path is Alternatively, the polarization state of the optical pulse input into the first polarization control optical path is or Where k is an integer, and are the two eigenpolarization states of the first polarization control optical path, It can be any value from 0 to 2π.

[0020] In some embodiments, the polarization state of the light pulse input into the first polarization control light path is 45° linear polarization, −45° linear polarization, left-handed circular polarization, or right-handed circular polarization.

[0021] In some embodiments, the phase difference α generated between the first path optical pulse and the second path optical pulse, the phase difference β generated between the third path optical pulse and the fourth path optical pulse, and the phase difference γ generated between the fifth path optical pulse and the sixth path optical pulse are determined according to the requirements of polarization encoding of the quantum communication protocol.

[0022] In some embodiments, the first polarization-controlled optical path, the second polarization-controlled optical path and / or the third polarization-controlled optical path include: a polarization splitting unit and a transmission optical path; the polarization splitting unit includes at least three ports, namely port A, port B and port C; the polarization splitting unit is used to polarization-split the light pulse input from port A into two sub-light pulses, which are output from port B and port C respectively; the intrinsic polarization state of the polarization splitting unit is the intrinsic polarization state of the first polarization-controlled optical path, the second polarization-controlled optical path and / or the third polarization-controlled optical path; and the transmission optical path is used to connect port B and port C of the polarization splitting unit.

[0023] In some embodiments, the polarization beam splitting unit is a polarization beam splitter, and the intrinsic polarization state of the polarization beam splitter is the intrinsic polarization state of the polarization beam splitter.

[0024] In some embodiments, the polarization beam splitting unit includes: a polarization beam splitter, a first polarizer and a second polarizer; the polarization beam splitting unit further includes a port D; the polarization beam splitter includes four ports, namely a first port, a second port, a third port and a fourth port, the first port of the polarization beam splitter is the port A of the polarization beam splitting unit, and the fourth port of the polarization beam splitter is the port D of the polarization beam splitting unit; the second port and the third port of the polarization beam splitter are respectively connected to the port on the first side of the first polarizer and the port on the first side of the second polarizer; the first polarizer is connected to the first polarizer. The ports on the two sides are ports B of the polarization beam splitter unit, and the port on the second side of the second polarizer is port C of the polarization beam splitter unit; the port on the second side of the first polarizer and the port on the second side of the second polarizer are connected through the transmission optical path; the angle between the polarization direction of the first polarizer and an intrinsic polarization state of the polarization beam splitter is θ, and the angle between the polarization direction of the second polarizer and another intrinsic polarization state of the polarization beam splitter is δ; wherein θ, δ≠n·90°, n is an integer; the intrinsic polarization state of the polarization beam splitter is the intrinsic polarization state of the polarization beam splitter.

[0025] In some embodiments, the polarization beam splitting unit comprises: a beam splitter, a first polarizer, and a second polarizer;

[0026] The optical beam splitter includes at least three ports, namely the first port, the second port and the third port. The first port of the optical beam splitter is the port A of the polarization beam splitting unit; the second port and the third port of the optical beam splitter are connected to the port on the first side of the first polarizer and the port on the first side of the second polarizer respectively; the port on the second side of the first polarizer is the port B of the polarization beam splitting unit, and the port on the second side of the second polarizer is the port C of the polarization beam splitting unit; the port on the second side of the first polarizer and the port on the second side of the second polarizer are connected through the transmission optical path. The polarization direction of the first polarizer is The polarization direction of the second polarizer is The polarization direction of the first polarizer The polarizing direction of the second polarizer mutually orthogonal; the polarizing direction of the first polarizer The polarizing direction of the second polarizer is the intrinsic polarization state of the polarization beam splitting unit.

[0027] In some embodiments, the optical beam splitter further includes a fourth port; the polarization beam splitting unit further includes a port D; and the fourth port of the optical beam splitter is the port D of the polarization beam splitting unit.

[0028] In some embodiments, the transmission optical path is a free-space optical path or a polarization-maintaining optical fiber.

[0029] In some embodiments, port B and port C of the polarization beam splitting unit are both coupled to the slow axis of the polarization-maintaining optical fiber or are both coupled to the fast axis of the polarization-maintaining optical fiber.

[0030] In some embodiments, the device further comprises a half-wave plate or a 90-degree Faraday rotator disposed in the transmission optical path.

[0031] According to a second aspect of the present application, a polarization encoding method is provided, comprising: inputting an optical pulse into a first polarization control optical path and polarization splitting the optical pulse into two optical pulses, namely a first optical pulse and a second optical pulse; performing phase modulation on the first optical pulse and / or the second optical pulse by a first phase modulator, so that a phase difference α is generated between the two optical pulses; the first optical pulse and the second optical pulse after passing through the first phase modulator are combined and output through the first polarization control optical path; one of the two eigenpolarization states of the first polarization control optical path is The optical pulse output by the combined beam is input into a second polarization control optical path connected in series with the first polarization control optical path, and is polarized and split into two optical pulses by the second polarization control optical path, namely, a third optical pulse and a fourth optical pulse. The second phase modulator performs phase modulation on the third optical pulse and / or the fourth optical pulse, so that a phase difference β is generated between the two optical pulses. After passing through the second phase modulator, the third optical pulse and the fourth optical pulse are combined and output by the second polarization control optical path; one of the two eigenpolarization states of the second polarization control optical path is The optical pulse output by the combined output of the second polarization-controlled optical path is input into a third polarization-controlled optical path. The third polarization-controlled optical path is connected in series with the first polarization-controlled optical path and the second polarization-controlled optical path. The optical pulse is polarized and split into two optical pulses by the third polarization-controlled optical path, namely, a fifth optical pulse and a sixth optical pulse. The third phase modulator performs phase modulation on the fifth optical pulse and / or the sixth optical pulse, so that a phase difference γ is generated between the two optical pulses. The fifth optical pulse and the sixth optical pulse after passing through the third phase modulator are combined and output by the third polarization-controlled optical path. One of the two eigenpolarization states of the third polarization-controlled optical path is Wherein, by setting the intrinsic polarization state With the eigenpolarization state The angle between them, and the eigenpolarization state With the eigenpolarization state and the angle between them, and the phase difference α, phase difference β and phase difference γ are matched to meet the requirements of different quantum communication protocols.

[0032] In some embodiments, the intrinsic polarization state and the eigenpolarization state When the angle between them is 1·90°, the eigenpolarization state and the eigenpolarization state The included angle between them is 22.5°±m·45°, or 45°±m·90°, where l and m are integers.

[0033] In some embodiments, the intrinsic polarization state and the eigenpolarization state When the angle between them is 22.5°±a·45° or 45°±a·90°, the eigenpolarization state and the eigenpolarization state The included angle between them is m·90°, or 22.5°±m·45°, or 45°±m·90°, where a and m are integers.

[0034] In some embodiments, the polarization state of the light pulse input into the first polarization control light path is Alternatively, the polarization state of the optical pulse input into the first polarization control optical path is Alternatively, the polarization state of the optical pulse input into the first polarization control optical path is or Where k is an integer, and are the two eigenpolarization states of the first polarization control optical path, It can be any value from 0 to 2π.

[0035] In some embodiments, the polarization state of the light pulse input into the first polarization control light path is 45° linear polarization, −45° linear polarization, left-handed circular polarization, or right-handed circular polarization.

[0036] In some embodiments, the phase difference α generated between the first path optical pulse and the second path optical pulse, the phase difference β generated between the third path optical pulse and the fourth path optical pulse, and the phase difference γ generated between the fifth path optical pulse and the sixth path optical pulse are determined according to the requirements of polarization encoding of the quantum communication protocol.

[0037] According to a third aspect of the present application, a quantum communication system is provided, comprising the above-mentioned polarization encoding device.

[0038] In summary, the polarization encoding device, method and quantum communication system provided by the present application have at least the following beneficial effects: the polarization encoding device of the present application includes a first polarization operation module, a second polarization operation module and a third polarization operation module connected in series, wherein each of the first polarization operation module, the second polarization operation module or the third polarization operation module respectively includes a polarization control optical path and a phase modulator; the polarization control optical path is used to polarize and split the input optical pulse into two sub-optical pulses, and the phase modulators in the three polarization operation modules perform combined phase modulation on the two optical pulses, so that the two optical pulses respectively generate phase The phase difference α, phase difference β and phase difference γ are further set according to the requirements of the quantum communication protocol. The angle between the eigenpolarization state of the first polarization-controlled optical path and the eigenstate of the second polarization-controlled optical path is set, and the angle between the eigenstate of the first polarization-controlled optical path and the eigenstate of the third polarization-controlled optical path is set. In combination with the above-mentioned phase difference α, phase difference β and phase difference γ, through the combined modulation of the first polarization operation module, the second polarization operation module and the third polarization operation module, a polarization encoding device can be modulated to produce multiple polarization-encoded quantum states, which is compatible with multiple quantum communication protocols to meet the requirements of different quantum communication protocols.

[0039] Furthermore, by combining the phase modulators in the three polarization operation modules, this application can reduce the number of phase modulations required by a single phase modulator, thereby reducing the difficulty of implementing phase modulation. For example, two phases can be modulated for each of the three phase modulations to achieve the preparation of multiple quantum states. In this case, the phase modulation drive circuit can achieve polarization quantum state encoding through digital modulation, offering advantages such as high-speed modulation and ease of implementation.

[0040] Furthermore, the two paths of polarization-split sub-light pulses in the present application have exactly the same transmission optical path before being combined, and thus have a self-compensation function for environmental interference and the advantages of high anti-interference stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without any creative work.

[0042] Figure 1 A framework diagram of a polarization encoding device provided in an embodiment of the present application;

[0043] Figure 2 A structural diagram of a polarization encoding device according to an embodiment of the present application;

[0044] Figure 3 A structural diagram of a first embodiment of a polarization-controlled optical circuit provided in an embodiment of the present application;

[0045] Figure 4 A structural diagram of a second embodiment of a polarization-controlled optical circuit provided in an embodiment of the present application;

[0046] Figure 5 A structural diagram of a third embodiment of a polarization-controlled optical circuit provided in an embodiment of the present application;

[0047] Figure 6 A structural diagram of a fourth embodiment of a polarization-controlled optical circuit provided in an embodiment of the present application;

[0048] Figure 7 A flowchart of a polarization encoding method provided in an embodiment of the present application. DETAILED DESCRIPTION

[0049] In order to make the above and other features and advantages of the present application more clear, the present application is further described below with reference to the accompanying drawings. It should be understood that the specific embodiments given herein are for the purpose of explaining to those skilled in the art and are only exemplary and not restrictive.

[0050] In the following description, many specific details are set forth to provide a thorough understanding of the present application. However, it will be apparent to those skilled in the art that it is not necessary to adopt the specific details to practice the present application. In other cases, well-known steps or operations are not described in detail to avoid obscuring the present application.

[0051] The present application embodiment provides a polarization encoding device, Figure 1 and attached Figure 2 As shown, attached Figure 1 This is the framework diagram of the polarization encoding device, Figure 2 4 is a structural diagram of an embodiment of the polarization encoding device, wherein the device comprises a first polarization operation module 100, a second polarization operation module 200 and a third polarization operation module 300 connected in series.

[0052] In some embodiments, as Figure 2 As shown in, the first polarization operation module 100 includes: a first polarization control optical path and a first phase modulator 205 arranged in the transmission optical path of the first polarization control optical path; the first polarization control optical path is used to polarize and split an input optical pulse into two optical pulses, namely a first optical pulse and a second optical pulse, and the first phase modulator 205 is used to phase modulate the first optical pulse and / or the second optical pulse so that a phase difference α is generated between the two optical pulses. After passing through the first phase modulator 205, the first optical pulse and the second optical pulse are combined and output through the first polarization control optical path; the two eigenpolarization states of the first polarization control optical path are respectively and Represents the horizontal and vertical directions respectively.

[0053] In an exemplary embodiment, the first phase modulator 205 is used to phase modulate the first path optical pulse and / or the second path optical pulse, including: phase modulating one of the first path optical pulse and the second path optical pulse, or performing different phase modulation on the first path optical pulse and the second path optical pulse.

[0054] In an exemplary embodiment, the first phase modulator 205 includes: a first port E, a second port F and a third port N. The first port E and the second port F are respectively the forward input optical port and the reverse input optical port of the first phase modulator 205. The first path optical pulse is input into the first phase modulator 205 through the first port E and output from the second port F after passing through the first phase modulator 205. The second path optical pulse is input into the first phase modulator 205 through the second port F and output from the first port E after passing through the first phase modulator 205. The third port N is an electrical port, connected to the first driver 212, and is used to receive the modulated electrical signal applied by the first driver 212.

[0055] In one embodiment, the first phase modulator 205 is disposed in the first transmission optical path 204. The first transmission optical path 204 is coupled to the slow axes of the first port E and the second port F of the first phase modulator, or is coupled to the fast axes of the first port E and the second port F of the first phase modulator 205. The first phase modulator 205 modulates an optical pulse inputted from one of the first port E and the second port F, or modulates the optical pulses inputted from the first port E and the second port F to different phases.

[0056] In an exemplary embodiment, after applying a high-frequency modulated electrical signal having a frequency higher than a specified threshold, the first phase modulator 205 operates in a non-reciprocal state, and the ratio of the modulation efficiency of the first path optical pulse input by the forward input optical port to the modulation efficiency of the second path optical pulse input by the reverse input optical port is not less than a preset threshold. In one embodiment, the preset threshold can be 10 decibels (dB). The high-frequency modulated signal is, for example, a modulated signal of not less than 10 GHz. Non-reciprocity is a physical concept that describes whether a physical process is equivalent to its inverse process. If they are equivalent, it is called reciprocity; if they are not equivalent, it is called non-reciprocity. In this application, non-reciprocity refers to the fact that light waves exhibit different loss, phase shift and other characteristics when transmitted in two opposite directions in a transmission optical path.

[0057] It is understandable that when a high-frequency modulating electrical signal is applied to the first phase modulator 205, the modulation efficiency of the first phase modulator 205 for the reverse-propagating optical pulse (i.e., the second-path optical pulse) input through the second port F is much lower than the modulation efficiency of the forward-propagating optical pulse (i.e., the first-path optical pulse) input through the first port E. That is, the first phase modulator 205 can effectively phase-modulate the optical pulses propagating forward through the first phase modulator 205 during each high-speed modulation, but cannot effectively phase-modulate the optical pulses propagating backward through the first phase modulator 205. When two optical pulses simultaneously pass through the first phase modulator 205 undergoing high-speed modulation, if the same modulating electrical signal pulse is applied once to both the forward-propagating and reverse-propagating optical pulses, a phase difference can be formed between the first optical pulse and the second optical pulse. If modulating electrical signals of different magnitudes are applied to the first phase modulator 205, the phase differences formed between the first optical pulse and the second optical pulse will be different, thereby modulating and generating optical pulses of different polarization states when the first polarization-controlled optical path is combined and output.

[0058] In some embodiments, the second polarization operation module 200 includes: a second polarization control optical path and a second phase modulator 210 arranged in the transmission optical path of the second polarization control optical path, the second polarization control optical path is connected in series with the first polarization control optical path, the second polarization control optical path is used to input the optical pulse output by the combined beam of the first polarization control optical path from the input port, and polarization-split it into two sub-optical pulses, namely the third optical pulse and the fourth optical pulse, the second phase modulator 210 is used to phase modulate the third optical pulse and / or the fourth optical pulse, so that a phase difference β is generated between the two optical pulses, and the third optical pulse and the fourth optical pulse after passing through the second phase modulator 210 are combined and output by the second polarization control optical path; the two eigenpolarization states of the second polarization control optical path are respectively and

[0059] In an exemplary embodiment, the second phase modulator 210 is used to phase modulate the third path optical pulse and / or the fourth path optical pulse, including: the second phase modulator 210 is used to phase modulate one of the third path optical pulse and the fourth path optical pulse, or to perform different phase modulation on the third path optical pulse and the fourth path optical pulse.

[0060] In an exemplary embodiment, the second phase modulator 210 includes: a fourth port K, a fifth port L and a sixth port M, wherein the fourth port K and the fifth port L are respectively the forward input optical port and the reverse input optical port of the second phase modulator 210, the third path optical pulse is forwardly input into the second phase modulator 210 via the fourth port K, and is output from the fifth port L after passing through the second phase modulator 210, the fourth path optical pulse is reversely input into the second phase modulator 210 via the fifth port L, and is output from the fourth port K after passing through the second phase modulator 210, the sixth port is an electrical port, connected to the second driver 213, and is used to receive the modulated electrical signal applied by the first driver 213.

[0061] In an exemplary embodiment, the second transmission optical paths 209 are coupled to the slow axes of the fourth port K and the fifth port L of the second phase modulator, or are coupled to the fast axes of the fourth port K and the fifth port L of the second phase modulator 210. The second phase modulator 210 performs phase modulation on an optical pulse input from one of the fourth port K and the fifth port L, or performs different phase modulation on the optical pulses input from the fourth port K and the fifth port L.

[0062] In an exemplary embodiment, after applying a high-frequency modulating electrical signal having a frequency higher than a specified threshold, the second phase modulator 210 operates in a non-reciprocal state, and a ratio of a modulation efficiency of a third optical sub-path inputted from a forward input optical port (i.e., the fourth port K) to a modulation efficiency of a fourth optical sub-path inputted from a reverse input optical port (i.e., the fifth port L) is not less than a preset threshold.

[0063] It can be understood that when a high-frequency modulating electrical signal is applied to the second phase modulator 210, the modulation efficiency of the second phase modulator 210 for the reverse-propagating optical pulse (i.e., the fourth optical pulse) input from the fifth port L is much lower than the modulation efficiency of the forward-propagating optical pulse (i.e., the third optical pulse) input from the fourth port K. That is, the second phase modulator 210 can effectively phase-modulate the optical pulse transmitted in the forward direction through the second phase modulator 210 during each high-speed modulation, but cannot effectively phase-modulate the optical pulse transmitted in the reverse direction through the second phase modulator 210. When two optical pulses simultaneously pass through the second phase modulator 210 undergoing high-speed modulation, if the same modulating electrical signal pulse is applied once to the forward and reverse optical pulses, a phase difference can be formed between the third optical pulse and the fourth optical pulse. If modulating electrical signals of different magnitudes are applied to the second phase modulator 210, the phase differences formed between the third optical pulse and the fourth optical pulse are different, thereby modulating and generating optical pulses of different polarization states when the second polarization control optical path is combined and output.

[0064] In an exemplary embodiment, the first polarization-controlled optical path and the second polarization-controlled optical path are connected in series.

[0065] In some embodiments, the third polarization operation module 300 includes: a third polarization control optical path and a third phase modulator 215 arranged in the transmission optical path of the third polarization control optical path, the third polarization control optical path is connected in series with the first polarization control optical path and the second polarization control optical path, the third polarization control optical path is used to input the optical pulse output by the combined beam of the second polarization control optical path from the input port, and polarize it into two sub-optical pulses, namely the fifth optical pulse and the sixth optical pulse, the third phase modulator 215 is used to phase modulate the fifth optical pulse and / or the sixth optical pulse, so that a phase difference γ is generated between the two optical pulses, and the fifth optical pulse and the sixth optical pulse after passing through the third phase modulator 215 are combined and output by the third polarization control optical path; the two eigenpolarization states of the third polarization control optical path are respectively and

[0066] In an exemplary embodiment, the third phase modulator 215 is used to phase modulate the fifth path optical pulse and / or the sixth path optical pulse, including: the third phase modulator 215 is used to phase modulate one of the fifth path optical pulse and the sixth path optical pulse, or to perform different phase modulation on the fifth path optical pulse and the sixth path optical pulse.

[0067] In some embodiments, the third phase modulator 215 includes: a seventh port T, an eighth port U, and a ninth port X. The seventh port T and the eighth port U are respectively the forward input optical port and the reverse input optical port of the third phase modulator 215. The fifth optical pulse is input into the third phase modulator 215 via the seventh port T and output from the eighth port U after passing through the third phase modulator 215. The sixth optical pulse is input into the third phase modulator 215 via the eighth port U and output from the seventh port T after passing through the third phase modulator 215. The ninth port X is an electrical port connected to the third driver 216 for receiving the modulated electrical signal applied by the third driver 216.

[0068] The third transmission optical path 214 is coupled to the slow axes of the seventh port T and the eighth port U of the third phase modulator 215, or is coupled to the fast axes of the seventh port T and the eighth port U of the third phase modulator 215. The third phase modulator 215 modulates an optical pulse inputted from either the seventh port T or the eighth port U, or performs different phase modulation on the optical pulses inputted from the seventh port T and the eighth port U.

[0069] In an exemplary embodiment, after applying a high-frequency modulating electrical signal having a frequency higher than a specified threshold, the third phase modulator 215 operates in a non-reciprocal state, and a ratio of a modulation efficiency of a fifth optical sub-path inputted from a forward input optical port (i.e., the seventh port T) to a modulation efficiency of a sixth optical sub-path inputted from a reverse input optical port (i.e., the eighth port U) is not less than a preset threshold.

[0070] It is understandable that when a high-frequency modulating electrical signal is applied to the third phase modulator 215, the modulation efficiency of the third phase modulator 215 for the reverse-propagating optical pulse (i.e., the sixth optical pulse) input from the eighth port U is much lower than the modulation efficiency of the forward-propagating optical pulse (i.e., the fifth optical pulse) input from the seventh port T. That is, the third phase modulator 215 can effectively phase-modulate the optical pulses propagating forward through the third phase modulator 215 during each high-speed modulation, but cannot effectively phase-modulate the optical pulses propagating backward through the third phase modulator 215. When two optical pulses simultaneously pass through the high-speed modulating third phase modulator 215, if the same modulating electrical signal pulse is applied once to both the forward-propagating and reverse-propagating optical pulses, a phase difference can be formed between the fifth optical pulse and the sixth optical pulse. If modulating electrical signals of different magnitudes are applied to the third phase modulator 215, the phase differences formed between the fifth optical pulse and the sixth optical pulse are different, thereby modulating and generating optical pulses of different polarization states when the third polarization-controlled optical path is combined and output.

[0071] It should be noted that in the embodiment of the present application, when a high-frequency modulation signal having a frequency higher than a predetermined threshold is applied to the first phase modulator 205, the second phase modulator 210, and the third phase modulator 215, there may be multiple sub-optical pulses input from the forward input optical port and multiple sub-optical pulses input from the reverse input optical port at the same time.

[0072] It should be noted that Figure 2 The structures of the first polarization control optical path, the second polarization control optical path, and the third polarization control optical path in the polarization encoding device shown in FIG are only one embodiment. The first polarization control optical path, the second polarization control optical path, and the third polarization control optical path described in this application can be respectively adopted as follows: Figures 3 to 6 The structures of the three polarization control light paths can be the same or different. That is, the three polarization control light paths can respectively adopt the structures provided in the embodiment of the present application. Figures 3 to 6 Any of the four structures.

[0073] In an exemplary embodiment, Figure 3 FIG. 1 is a first embodiment of a polarization control optical path. In this embodiment, the polarization control optical path includes: a polarization beam splitting unit and a transmission optical path 204; the polarization beam splitting unit includes at least three ports, namely port A, port B and port C; the intrinsic polarization state of the polarization beam splitting unit is and The intrinsic polarization state of the polarization beam splitting unit is the intrinsic polarization state of the polarization control optical path. The polarization beam splitting unit polarization-splits the optical pulse input from port A into two sub-optical pulses, which are output from port B and port C, respectively. Transmission optical path 204 is used to connect port B and port C of the polarization beam splitting unit. In this embodiment, the polarization beam splitting unit is a polarization beam splitter, and the intrinsic polarization state of the polarization beam splitter is the intrinsic polarization state of the polarization beam splitter.

[0074] In an exemplary embodiment, Figure 4 The second embodiment of the polarization control optical path is shown in FIG. Figure 3 The difference between the illustrated embodiments is that, in this embodiment, the polarization beam splitting unit comprises: a polarization beam splitter 201, a first polarizer 202 and a second polarizer 203; the polarization beam splitting unit further comprises a port D; the polarization beam splitter 201 comprises four ports, namely a first port, a second port, a third port and a fourth port, the first port of the polarization beam splitter 201 is the port A of the polarization beam splitter unit, the fourth port of the polarization beam splitter 201 is the port D of the polarization beam splitter unit; the second port B and the third port C of the polarization beam splitter 201 are connected to the port on the first side of the first polarizer 202 and the port on the second polarizer 203 respectively. 3; the port on the second side of the first polarizer 202 is port B of the polarization beam splitter unit, and the port on the second side of the second polarizer 203 is port C of the polarization beam splitter unit; the port on the second side of the first polarizer 202 and the port on the second side of the second polarizer 203 are connected via a first transmission optical path 204; the angle between the polarization direction of the first polarizer 202 and one of the intrinsic polarization states of the polarization beam splitter 201 is θ, and the angle between the polarization direction of the second polarizer 203 and another of the intrinsic polarization states of the polarization beam splitter 201 is δ; where θ and δ ≠ n·90°, and n is an integer. The angle between the polarization directions of the first polarizer 202 and the second polarizer 203 is ω, where 0 ≤ ω ≤ 2π. In this embodiment, the intrinsic polarization state of the polarization beam splitter 201 is the intrinsic polarization state of the polarization beam splitter unit.

[0075] In some embodiments, the first polarizer 202 may be bonded to the second port of the polarization beam splitter 201 , and the second polarizer 203 may be bonded to the third port of the polarization beam splitter 201 .

[0076] In an exemplary embodiment, Figure 5 The third embodiment of the polarization control optical path is shown in FIG. Figure 3The difference between the embodiments shown is that, in this embodiment, the polarization beam splitting unit includes: a beam splitter 201, a first polarizer 202 and a second polarizer 203; the beam splitter 201 includes at least three ports, namely a first port, a second port and a third port, the first port of the beam splitter 201 is port A of the polarization beam splitting unit; the second port and the third port of the beam splitter 201 are connected to the port on the first side of the first polarizer 202 and the port on the first side of the second polarizer 203 respectively; the port on the second side of the first polarizer 202 is port B of the polarization beam splitting unit, and the port on the second side of the second polarizer 203 is port C of the polarization beam splitting unit; the port on the second side of the first polarizer 202 and the port on the second side of the second polarizer 203 are connected via a first transmission optical path 204. The polarization direction of the first polarizer 202 is The polarization direction of the second polarizer 203 is The polarization direction of the first polarizer 202 The polarization direction of the second polarizer 203 mutually orthogonal; the polarization direction of the first polarizer 202 The polarization direction of the second polarizer 203 is the eigenpolarization state of the polarization beam splitting unit.

[0077] In an exemplary embodiment, Figure 6 As shown, it is the fourth embodiment of the polarization control optical path. In this embodiment, the polarization beam splitting unit includes: an optical beam splitter 201, a first polarizer 202 and a second polarizer 203; the polarization beam splitting unit also includes a port D; the optical beam splitter 201 includes four ports, namely a first port, a second port, a third port and a fourth port. The first port of the optical beam splitter 201 is port A of the polarization beam splitting unit, and the fourth port of the optical beam splitter 201 is port D of the polarization beam splitting unit; the second port and the third port of the optical beam splitter 201 are respectively connected to the port on the first side of the first polarizer 202 and the port on the first side of the second polarizer 203; the port on the second side of the first polarizer 202 is port B of the polarization beam splitting unit, and the port on the second side of the second polarizer 203 is port C of the polarization beam splitting unit; the port on the second side of the first polarizer 202 and the port on the second side of the second polarizer 203 are connected through the first transmission optical path 204. The polarization direction of the first polarizer 202 is The polarization direction of the second polarizer 203 is The polarization direction of the first polarizer 202 The polarization direction of the second polarizer 203 mutually orthogonal; the polarization direction of the first polarizer 202 The polarization direction of the second polarizer 203 is the eigenpolarization state of the polarization beam splitting unit.

[0078] In some embodiments, the transmission optical path includes a first transmission optical path 204, a second transmission optical path 209, and a third transmission optical path 214. The transmission optical paths may be free space optical paths or polarization-maintaining optical fibers. In an exemplary embodiment, both ports of the polarization beam splitting unit are coupled to the slow axis of the polarization-maintaining optical fiber or to the fast axis of the polarization-maintaining optical fiber. Figure 4 Taking the polarization control optical path shown in as an example, the first transmission optical path 204 is a polarization-maintaining optical fiber. In this case, port B and port C of the polarization beam splitting unit are both coupled to the slow axis of the polarization-maintaining optical fiber or are both coupled to the fast axis of the polarization-maintaining optical fiber.

[0079] In an exemplary embodiment, the device further includes a half-wave plate or a 90-degree Faraday rotator arranged in the transmission optical path. The half-wave plate or the 90-degree Faraday rotator can be used to control the polarization state of the two sub-light pulses when they are transmitted in the transmission optical path, so that the transmission paths of the two sub-light pulses in the transmission optical path and the phase modulator remain consistent, which can ensure that the phase drift caused by environmental interference of the two sub-light pulses is the same, so that the phase difference between them can be accurately controlled by modulating the phase modulator.

[0080] In some embodiments, the first phase modulator 205 , the second phase modulator 210 , and / or the third phase modulator 215 may be single polarization phase modulators or birefringence phase modulators.

[0081] A phase difference α is generated between the first optical pulse and the second optical pulse, a phase difference β is generated between the third optical pulse and the fourth optical pulse, and a phase difference γ is generated between the fifth optical pulse and the sixth optical pulse. These can be determined according to the requirements of polarization coding of the quantum communication protocol.

[0082] Based on the present application, the polarization state of the optical pulse can be modulated by modulating three phase modulators: for example, the first phase modulator 205 can randomly modulate four phase states of 0°, 45°, 90°, or 135°; or randomly modulate four phase states of 45°, 90°, 135°, or 180°; or randomly modulate two phase states of 0° or 180°; or randomly modulate two phase states of 90° or 270°; or randomly modulate four phase states of 0°, 90°, 180°, or 270°. The second phase modulator 210 can have multiple modulation modes, such as randomly modulating two phase states of 0° or 180°; or randomly modulating two phase states of 0° or 90°; or randomly modulating two phase states of 90° or 270°; or randomly modulating four phase states of 0°, 90°, 180°, or 270°. The third phase modulator 215 can have multiple modulation modes, such as randomly modulating two phase states of 0° or 180°; or randomly modulating two phase states of 0° or 90°; or randomly modulating two phase states of 90° or 270°; or randomly modulating four phase states of 0°, 90°, 180° or 270°.

[0083] In this application, by setting the intrinsic polarization state With the eigenpolarization state The angle between them, and the eigenpolarization state With the eigenpolarization state and the phase difference α, phase difference β and phase difference γ are coordinated to meet the requirements of different quantum communication protocols.

[0084] In an exemplary embodiment, the intrinsic polarization state and the eigenpolarization state When the angle between them is 1·90°, the eigenpolarization state and the eigenpolarization state The included angle between them can be 22.5°±m·45°, or 45°±m·90°, where l and m are integers.

[0085] In an exemplary embodiment, the intrinsic polarization state and the eigenpolarization state When the angle between them is 22.5°±a·45°, the eigenpolarization state and the eigenpolarization state The angle between them can be m·90°, or 22.5°±m·45°, or 45°±m·90°, where a and m are integers.

[0086] In an exemplary embodiment, the intrinsic polarization state and the eigenpolarization state When the angle between them is 45°±a·90°, the eigenpolarization state and the eigenpolarization state The angle between them can be m·90°, or 22.5°±m·45°, or 45°±m·90°, where a and m are integers.

[0087] In an exemplary embodiment, the angle between the intrinsic polarization state of the first polarization control light path and the intrinsic polarization state of the second polarization control light path can be achieved by rotating the second polarization control light path, and the angle between the intrinsic polarization state of the first polarization control light path and the intrinsic polarization state of the third polarization control light path can be achieved by rotating the third polarization control light path; and / or, the device further includes: a first polarization state rotator and / or a second polarization state rotator, the first polarization state rotator is arranged between the first polarization control light path and the second polarization control light path, and the angle between the intrinsic polarization state of the first polarization control light path and the intrinsic polarization state of the second polarization control light path is adjusted by the first polarization state rotator; the second polarization state rotator is arranged between the second polarization control light path and the third polarization control light path, and the angle between the intrinsic polarization state of the first polarization control light path and the intrinsic polarization state of the third polarization control light path is adjusted by the first polarization state rotator and / or the second polarization state rotator; the first polarization state rotator and / or the second polarization state rotator can be a half-wave plate or a Faraday rotator.

[0088] In some embodiments, the device further includes two optical isolation units, which are optical isolators or optical circulators. The two optical isolation units are respectively arranged between any two adjacent polarization operation modules to isolate the optical signal transmitted back from the latter polarization operation module to the previous polarization operation module, thereby reducing signal interference and crosstalk.

[0089] In an exemplary embodiment, the polarization state of the light pulse input into the first polarization control light path is Alternatively, the polarization state of the optical pulse input into the first polarization control optical path is Alternatively, the polarization state of the optical pulse input into the first polarization control optical path is or Where k is an integer, and are the two eigenpolarization states of the first polarization control optical path, It can be any value from 0 to 2π.

[0090] In an exemplary embodiment, the polarization state of the light pulse input into the first polarization control optical path is 45° linear polarization, −45° linear polarization, left-handed circular polarization, or right-handed circular polarization.

[0091] By using the polarization encoding device described in the present application, through the combined modulation of the first phase modulator, the second phase modulator and the third phase modulator, and setting the intrinsic polarization state angles of the three polarization control light paths according to the requirements of the quantum communication protocol, a variety of combinations of polarization-encoded quantum states can be prepared, including: horizontal and vertical polarization bases ±45° polarization base or left-right circular polarization basis

[0092] For example, when the eigenpolarization state x of the first polarization control light path is equal to the eigenpolarization state x of the second polarization control light path The angle is 22.5°±m·45°, where m is an integer; the first polarization control optical path eigenpolarization state With the third polarization control optical path eigenpolarization state The angle is 45°±n·90°, where n is an integer; and the first polarization control optical path, the second polarization control optical path and the third polarization control optical path all use a polarization beam splitting unit composed of a four-port polarization beam splitter and two optical polarizers; at this time, the first polarization control optical path inputs The polarization state remains unchanged and the input The polarization state also remains unchanged at output, that is, the relationship between the input and output of the first polarization control optical path is: (The negative sign is taken into account The polarization state is reflected twice by the polarization beam splitter); the second polarization control light path will input The polarization state remains unchanged and the input The polarization state also remains unchanged at the output, that is, the relationship between the input and output of the second polarization control optical path is: (The negative sign is taken into account The polarization state is reflected twice by the polarization beam splitter); the third polarization control optical path will input The polarization state remains unchanged and the input The polarization state also remains unchanged at the output, that is, the relationship between the input and output of the third polarization control optical path is: (The negative sign is taken into account When the polarization state of the light pulse input into the first polarization control optical path is 45° linear polarization, if the first phase modulator randomly modulates 0°, 90° or 180°, that is, the phase difference α is modulated to 0°, 90° or 180°, the second phase modulator modulates 0° (that is, no modulation), that is, the phase difference β is modulated to 0°, and the third phase modulator randomly modulates 0° or 180°, that is, the phase difference γ is modulated to 0° or 180°, then a ±45° polarization-based optical system can be prepared. and left-right circular polarization basis Two groups of four polarization states;

[0093] If the first phase modulator randomly modulates 0° or 180°, that is, the phase difference α is modulated to 0° or 180°, the second phase modulator randomly modulates 0° or 180°, that is, the phase difference β is modulated to 0° or 180°, and the third phase modulator modulates 0° (that is, no modulation), that is, the phase difference γ is modulated to 0°, then a horizontal and vertical polarization matrix can be prepared. and ±45° polarization base Two groups of four polarization states.

[0094] If the first phase modulator randomly modulates 0° or 180°, the second phase modulator modulates 180°, and the third phase modulator randomly modulates 0° or 90°, a horizontal and vertical polarization matrix can be prepared. and left-right circular polarization basis Two groups of four polarization states;

[0095] If the first phase modulator is randomly modulated to 0° or 180°, the second phase modulator is randomly modulated to 0° or 180°, and the third phase modulator is randomly modulated to 0° or 90°, then a horizontal and vertical polarization matrix can be prepared. ±45° polarization base and left-right circular polarization basis Three groups of six polarization states.

[0096] If the first phase modulator is randomly modulated to 0° or 90°, the second phase modulator is randomly modulated to 0° or 180°, and the third phase modulator is modulated to 0°, then a horizontal and vertical polarization matrix can be prepared. ±45° polarization base and left-right circular polarization basis Three groups of basis and four polarization states

[0097] In some embodiments, according to the requirements of quantum communication, the polarization encoding device of the present application can also implement a polarization decoding process.

[0098] The polarization encoding device of the present application includes a first polarization operation module, a second polarization operation module, and a third polarization operation module connected in series, wherein each of the first polarization operation module, the second polarization operation module, or the third polarization operation module respectively includes a polarization control optical path and a phase modulator; the polarization control optical path is used to polarization-split an input optical pulse into two sub-optical pulses, and the phase modulators in the three polarization operation modules perform combined phase modulation on the two sub-optical pulses, so that the two optical pulses respectively produce a phase difference α, a phase difference β, and a phase difference γ. Further, according to the requirements of the quantum communication protocol, the angle between the eigenpolarization state of the first polarization control optical path and the eigenstate of the second polarization control optical path, as well as the angle between the eigenstate of the first polarization control optical path and the eigenstate of the third polarization control optical path are set. In combination with the above-mentioned phase difference α, phase difference β, and phase difference γ, through the combined modulation of the first polarization operation module, the second polarization operation module, and the third polarization operation module, a polarization encoding device can modulate multiple polarization-encoded quantum states, which is compatible with multiple quantum communication protocols to meet the requirements of different quantum communication protocols.

[0099] In addition, the present application applies a high-frequency modulated electrical signal with a frequency higher than a specified threshold to the first phase modulator, the second phase modulator and / or the third phase modulator, so that the modulation efficiency of the first phase modulator, the second phase modulator and / or the third phase modulator for the optical pulse input through the reverse input optical port is much lower than the modulation efficiency of the optical pulse input through the forward input optical port; the first phase modulator, the second phase modulator and / or the third phase modulator can effectively phase modulate the sub-optical pulse input through the forward input optical port, but cannot effectively phase modulate the sub-optical pulse input through the reverse input optical port. Therefore, when the sub-optical pulse input through the forward input optical port and the sub-optical pulse input through the reverse input optical port simultaneously pass through the high-speed modulated first phase modulator, the second phase modulator and / or the third phase modulator, it is only necessary to apply the same modulated electrical signal once to the two sub-optical pulses to form a phase difference between the two sub-optical pulses; by applying modulated electrical signals of different sizes to the first phase modulator, the second phase modulator and / or the third phase modulator, the phase differences formed between the two sub-optical pulses are different, and polarization quantum state encoding at 10 GHz or higher speed can be achieved.

[0100] In addition, the two sub-light pulses of polarization splitting in the polarization control optical path pass through exactly the same optical path before polarization splitting and beam combining, and have a self-compensation function for environmental interference, and have the advantages of high anti-interference stability.

[0101] Furthermore, by combining the phase modulators in the three polarization operation modules, this application can reduce the number of phases modulated by a single phase modulator, thereby reducing the difficulty of implementing phase modulation. For example, two phases can be modulated for each of the three phase modulations, enabling the preparation of multiple quantum states. In this case, the phase modulation drive circuit can implement polarization quantum state encoding using digital modulation, offering advantages such as high-speed modulation and ease of implementation. Therefore, this application provides a polarization encoding device that is easy to implement and apply and compatible with multiple quantum communication protocols.

[0102] The polarization encoding method provided in the embodiment of the present application can be performed by the polarization encoding device provided in the embodiment of the present application, and the device can be configured in an electronic device.

[0103] Refer to the attached Figure 7 As shown, the present application provides a polarization encoding method, which can be implemented by the polarization encoding device of the above embodiment. The method includes steps 710-730.

[0104] Step 710: Input an optical pulse into the first polarization-controlled optical path and polarize-split it into two optical pulses, namely, a first optical pulse and a second optical pulse. The first optical pulse and / or the second optical pulse are phase-modulated by a first phase modulator so that a phase difference α is generated between the two optical pulses. After passing through the first phase modulator, the first optical pulse and the second optical pulse are combined and output through the first polarization-controlled optical path. One of the two eigenpolarization states of the first polarization-controlled optical path is

[0105] For example, refer to Figure 2In the structure shown, a light pulse is input into the polarization encoding device via the first port (i.e., polarization beam splitter port A) of the polarization beam splitter 201 of the first polarization control optical path. The polarization beam splitter 201 polarization-splits the input light pulse into a first light pulse and a second light pulse, which are output from the second port and the third port, respectively. After the first light pulse is output from the second port of the polarization beam splitter 201, it is transmitted in a clockwise direction to the third port of the polarization beam splitter 201 and is reflected by the polarization beam splitter 201 and output from the fourth port (i.e., polarization beam splitter port D). After the second light pulse is output from the third port of the polarization beam splitter 201, it is transmitted in a counterclockwise direction to the second port of the polarization beam splitter 201 and is transmitted by the polarization beam splitter 201 and output from the fourth port (i.e., polarization beam splitter port D). The first light pulse and the second light pulse are combined at the fourth port of the polarization beam splitter 201 and output to the second polarization control optical path. During operation, the first phase modulator 205 modulates the sub-optical pulses inputted from one of the ports E and F; or performs different phase modulation on the sub-optical pulses inputted from the ports E and F; or when the first optical pulse and the second optical pulse pass through the first phase modulator 205 at the same time, a high-frequency modulation electrical signal with a frequency higher than a specified threshold is applied to the first phase modulator 205, such as a 10 GHz high-frequency modulation electrical signal pulse. Although the first optical pulse and the second optical pulse are subjected to the same modulation electrical signal when passing through the first phase modulator 205, the first phase modulator 205 is different from the first phase modulator 205. During high-speed modulation, the first optical pulse input from port E and transmitted forward through the first phase modulator 205 is effectively phase modulated, while the second optical pulse input from port F and transmitted backward through the first phase modulator 205 is not effectively phase modulated, thereby forming a phase difference between the first optical pulse and the second optical pulse; different magnitudes of modulated electrical signals are applied to the first phase modulator 205, resulting in different phase differences between the two optical pulses, thereby causing the two optical pulses to produce different polarization states of high-speed modulation when they are combined and output by the polarization beam splitter 201. According to the requirements of the quantum communication protocol, the first phase modulator 205 can have multiple modulation modes, such as random modulation of four phase states of 0°, 45°, 90° or 135°; or random modulation of four phase states of 45°, 90°, 135° or 180°; or random modulation of two phase states of 0° or 180°; or random modulation of two phase states of 90° or 270°; or random modulation of four phase states of 0°, 90°, 180° or 270°, and so on.

[0106] Step 720: The combined optical pulse output is input into a second polarization-controlled optical path connected in series with the first polarization-controlled optical path. The optical pulse is polarized and split into two optical pulses, namely, a third optical pulse and a fourth optical pulse, by the second polarization-controlled optical path. The third optical pulse and the fourth optical pulse are phase-modulated by a second phase modulator so that a phase difference β is generated between the two optical pulses. The third optical pulse and the fourth optical pulse after passing through the second phase modulator are combined and output by the second polarization-controlled optical path. One of the two eigenpolarization states of the second polarization-controlled optical path is

[0107] For example, still referring to Figure 2 In the illustrated structure, the first polarization-controlled optical path is input from the optical pulse output from the fourth port of polarization beam splitter 201 to the second polarization-controlled optical path via the first port of polarization beam splitter 206. Polarization beam splitter 206 polarizes the input optical pulse into a third optical pulse and a fourth optical pulse, which are output from the second and third ports, respectively. After being output from the second port of polarization beam splitter 206, the third optical pulse is transmitted in a clockwise direction to the third port of polarization beam splitter 206, reflected by polarization beam splitter 206, and output from the fourth port. After being output from the third port of polarization beam splitter 206, the fourth optical pulse is transmitted in a counterclockwise direction to the second port of polarization beam splitter 206, transmitted by polarization beam splitter 206, and output from the fourth port. The third and fourth optical pulses are then combined and output at the fourth port of polarization beam splitter 206.

[0108] A high-frequency modulating electrical signal having a frequency higher than a specified threshold, such as a 10 GHz high-frequency modulating electrical signal pulse, is applied to the second phase modulator 210. Although the third and fourth optical pulses are subjected to the same modulating electrical signal when passing through the second phase modulator 210, the second phase modulator 210 effectively phase-modulates the third optical pulse input from port K and transmitted forward through the second phase modulator 210 during high-speed modulation, while not effectively phase-modulating the fourth optical pulse input from port L and transmitted backward through the second phase modulator 210. As a result, a phase difference is formed between the third and fourth optical pulses. When modulating electrical signals of different magnitudes are applied to the second phase modulator 210, different phase differences are formed between the two optical pulses, resulting in different polarization states of the two optical pulses being modulated at high speed when the two optical pulses are combined and output by the polarization beam splitter 206. According to the requirements of the quantum communication protocol, the second phase modulator 210 can have multiple modulation modes, such as random modulation of two phase states of 0° or 180°; or random modulation of two phase states of 0° or 90°; or random modulation of two phase states of 90° or 270°; or random modulation of four phase states of 0°, 90°, 180° or 270°, and so on.

[0109] Step 730: The optical pulse output by the combined output of the second polarization-controlled optical path is input into a third polarization-controlled optical path. The third polarization-controlled optical path is connected in series with the first polarization-controlled optical path and the second polarization-controlled optical path. The optical pulse is polarized and split into two optical pulses by the third polarization-controlled optical path, namely, a fifth optical pulse and a sixth optical pulse. The third phase modulator performs phase modulation on the fifth optical pulse and / or the sixth optical pulse, so that a phase difference γ is generated between the two optical pulses. The fifth optical pulse and the sixth optical pulse after passing through the third phase modulator are combined and output by the third polarization-controlled optical path. One of the two eigenpolarization states of the third polarization-controlled optical path is Wherein, by setting the intrinsic polarization state With the eigenpolarization state The angle between them, and the eigenpolarization state With the eigenpolarization state and the phase difference α, phase difference β and phase difference γ are coordinated to meet the requirements of different quantum communication protocols.

[0110] For example, still referring to Figure 2 In the illustrated structure, the second polarization-controlled optical path is input from the optical pulse output from the fourth port of polarization beam splitter 206 to the third polarization-controlled optical path via the first port of polarization beam splitter 219. Polarization beam splitter 219 polarizes and splits the input optical pulse into a fifth optical pulse and a sixth optical pulse, which are output from the second and third ports, respectively. After being output from the second port of polarization beam splitter 219, the fifth optical pulse is transmitted in a clockwise direction to the third port of polarization beam splitter 219, reflected by polarization beam splitter 219, and output from the fourth port. After being output from the third port of polarization beam splitter 219, the sixth optical pulse is transmitted in a counterclockwise direction to the second port of polarization beam splitter 219, transmitted by polarization beam splitter 219, and output from the fourth port. The fifth and sixth optical pulses are then combined and output at the fourth port of polarization beam splitter 219.

[0111] The third phase modulator 215 modulates the optical pulse input from one of the ports T and U; or performs different phase modulation on the optical pulses input from the ports T and U; or when the fifth optical pulse and the sixth optical pulse pass through the third phase modulator 215, a high-frequency modulation voltage is applied to the third phase modulator 215, such as a 10 GHz high-frequency modulation voltage pulse. Although the same modulation voltage is applied to the fifth optical pulse and the sixth optical pulse when passing through the third phase modulator 215, the third phase modulator 215 modulates the optical pulse from the port T and the port U at high frequency. The fifth optical pulse transmitted forward from port T through the third phase modulator 215 undergoes effective phase modulation, while the sixth optical pulse transmitted backward from port U through the third phase modulator 215 does not undergo effective phase modulation, thereby forming a phase difference between the fifth and sixth optical pulses. Applying different modulation voltages to the third phase modulator 215 results in different phase differences between the two optical pulses, thereby causing the two optical pulses to generate different polarization states of high-frequency modulation when combined and output by the polarization beam splitter 219. Depending on the requirements of the quantum communication protocol, the third phase modulator 215 can have multiple modulation modes, such as random modulation of two phase states of 0° or 180°; or random modulation of two phase states of 0° or 90°; or random modulation of two phase states of 90° or 270°; or random modulation of four phase states of 0°, 90°, 180°, or 270°, etc.

[0112] In an exemplary embodiment, the intrinsic polarization state and the eigenpolarization state When the angle between them is 1·90°, the eigenpolarization state and the eigenpolarization state The included angle between them is 22.5°±m·45°, or 45°±m·90°, where l and m are integers.

[0113] In an exemplary embodiment, the intrinsic polarization state and the eigenpolarization state When the angle between them is 22.5°±a·45°, the eigenpolarization state and the eigenpolarization state The included angle between them is m·90°, or 22.5°±m·45°, or 45°±m·90°, where a and m are integers.

[0114] In an exemplary embodiment, the intrinsic polarization state and the eigenpolarization state When the angle between them is 45°±a·90°, the eigenpolarization state and the eigenpolarization state The included angle between them is m·90°, or 22.5°±m·45°, or 45°±m·90°, where a and m are integers.

[0115] In some embodiments, the polarization state of the light pulse input into the first polarization control light path is Alternatively, the polarization state of the optical pulse input into the first polarization control optical path is Alternatively, the polarization state of the optical pulse input into the first polarization control optical path is or Where k is an integer, and are the two eigenpolarization states of the first polarization control optical path, It can be any value from 0 to 2π.

[0116] In some embodiments, the polarization state of the light pulse input into the first polarization control light path is 45° linear polarization, −45° linear polarization, left-handed circular polarization, or right-handed circular polarization.

[0117] In some embodiments, the phase difference α generated between the first path optical pulse and the second path optical pulse, the phase difference β generated between the third path optical pulse and the fourth path optical pulse, and the phase difference γ generated between the fifth path optical pulse and the sixth path optical pulse are determined according to the requirements of polarization encoding of the quantum communication protocol.

[0118] The polarization encoding method of the present application is based on a first polarization operation module, a second polarization operation module, and a third polarization operation module connected in series, wherein each of the first polarization operation module, the second polarization operation module, or the third polarization operation module respectively includes a polarization control optical path and a phase modulator; the polarization control optical path is used to polarization-split an input optical pulse into two sub-optical pulses, and the phase modulators in the three polarization operation modules perform combined phase modulation on the two sub-optical pulses, so that the two optical pulses produce phase differences α, β, and γ, respectively. Further, according to the requirements of the quantum communication protocol, the angle between the eigenpolarization state of the first polarization control optical path and the eigenstate of the second polarization control optical path, as well as the angle between the eigenstate of the first polarization control optical path and the eigenstate of the third polarization control optical path are set. In combination with the above-mentioned phase differences α, β, and γ, through the combined modulation of the first polarization operation module, the second polarization operation module, and the third polarization operation module, a polarization encoding device can modulate multiple polarization states, compatible with multiple quantum communication protocols, to meet the requirements of different quantum communication protocols.

[0119] In addition, the present application applies a high-frequency modulated electrical signal with a frequency higher than a specified threshold to the first phase modulator, the second phase modulator and / or the third phase modulator, so that the modulation efficiency of the first phase modulator, the second phase modulator and / or the third phase modulator for the optical pulse input through the reverse input optical port is much lower than the modulation efficiency of the optical pulse input through the forward input optical port; the first phase modulator, the second phase modulator and / or the third phase modulator can effectively phase modulate the sub-optical pulse input through the forward input optical port, but cannot effectively phase modulate the sub-optical pulse input through the reverse input optical port. Therefore, when the sub-optical pulse input through the forward input optical port and the sub-optical pulse input through the reverse input optical port simultaneously pass through the high-speed modulated first phase modulator, the second phase modulator and / or the third phase modulator, it is only necessary to apply the same modulated electrical signal once to the two sub-optical pulses to form a phase difference between the two sub-optical pulses; by applying modulated electrical signals of different sizes to the first phase modulator, the second phase modulator and / or the third phase modulator, the phase differences formed between the two sub-optical pulses are different, and polarization quantum state encoding at 10 GHz or higher speed can be achieved.

[0120] In addition, the two sub-light pulses of polarization splitting in the polarization control optical path pass through exactly the same optical path from polarization splitting to beam combining, have a self-compensation function for environmental interference, and have the advantages of high anti-interference stability.

[0121] In addition, the present application reduces the types of modulation phases through combined modulation of the phase modulators in the three polarization operation modules, thereby reducing the difficulty of implementing the modulation phase. Therefore, the present application provides an implementation solution for a high-speed polarization encoding device that is easy to implement and apply and is compatible with multiple quantum communication protocols.

[0122] According to the present application, a quantum communication system is provided, comprising the above-mentioned polarization encoding device.

[0123] It should be understood that the specific features, operations, and details described hereinabove with respect to the apparatus of the present application may also be similarly applied to the method and system of the present application, or vice versa. In addition, each step of the method of the present application described above may be performed by a corresponding component or unit of the apparatus or system of the present application.

[0124] The various technical features described above can be combined arbitrarily. Although not all possible combinations of these technical features are described, any combination of these technical features should be considered to be covered by this specification as long as such combination does not conflict.

[0125] 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 them. 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 polarization encoding device, characterized in that: include: A first polarization operation module, a second polarization operation module and a third polarization operation module connected in series, The first polarization operation module includes: a first polarization control optical path and a first phase modulator arranged in the transmission optical path of the first polarization control optical path; the first polarization control optical path is used to polarization-split an input optical pulse into two optical pulses, namely a first optical pulse and a second optical pulse; the first phase modulator is used to phase-modulate the first optical pulse and / or the second optical pulse so that a phase difference α is generated between the two optical pulses; the first optical pulse and the second optical pulse after passing through the first phase modulator are combined and output through the first polarization control optical path; one of the two eigenpolarization states of the first polarization control optical path is The second polarization operation module includes: a second polarization control optical path and a second phase modulator arranged in the transmission optical path of the second polarization control optical path, the second polarization control optical path is connected in series with the first polarization control optical path, the second polarization control optical path is used to input the optical pulse output by the combined beam of the first polarization control optical path from the input port, and polarization-split it into two sub-optical pulses, namely a third optical pulse and a fourth optical pulse, the second phase modulator is used to phase-modulate the third optical pulse and / or the fourth optical pulse, so that a phase difference β is generated between the two optical pulses, and the third optical pulse and the fourth optical pulse after passing through the second phase modulator are combined and output by the second polarization control optical path; one of the two eigenpolarization states of the second polarization control optical path is The third polarization operation module includes: a third polarization control optical path and a third phase modulator arranged in the transmission optical path of the third polarization control optical path, the third polarization control optical path is connected in series with the first polarization control optical path and the second polarization control optical path, the third polarization control optical path is used to input the optical pulse output by the combined beam of the second polarization control optical path from the input port, and polarize it into two sub-optical pulses, namely the fifth optical pulse and the sixth optical pulse, the third phase modulator is used to phase modulate the fifth optical pulse and / or the sixth optical pulse, so that a phase difference γ is generated between the two optical pulses, and the fifth optical pulse and the sixth optical pulse after passing through the third phase modulator are combined and output through the third polarization control optical path; one of the two eigenpolarization states of the third polarization control optical path is Wherein, by setting the intrinsic polarization state With the eigenpolarization state The angle between them, and the eigenpolarization state With the eigenpolarization state and the phase difference α, phase difference β and phase difference γ are coordinated to meet the requirements of different quantum communication protocols.

2. The device according to claim 1, characterized in that The first phase modulator includes: a first port, a second port, and a third port, wherein the first port and the second port are respectively a forward input optical port and a reverse input optical port of the first phase modulator, wherein the first path optical pulse is input into the first phase modulator via the first port and output from the second port after passing through the first phase modulator, and the second path optical pulse is input into the first phase modulator via the second port and output from the first port after passing through the first phase modulator, and the third port is an electrical port for applying a modulated electrical signal; The second phase modulator includes: a fourth port, a fifth port, and a sixth port, the fourth port and the fifth port being the forward input optical port and the reverse input optical port of the second phase modulator, respectively; the third path optical pulse is input into the second phase modulator via the fourth port and output from the fifth port after passing through the second phase modulator; the fourth path optical pulse is input into the second phase modulator via the fifth port and output from the fourth port after passing through the second phase modulator; the sixth port is an electrical port for applying a modulated electrical signal; The third phase modulator includes: a seventh port, an eighth port, and a ninth port. The seventh port and the eighth port are respectively the forward input optical port and the reverse input optical port of the third phase modulator. The fifth optical pulse is input into the third phase modulator via the seventh port and output from the eighth port after passing through the third phase modulator. The sixth optical pulse is input into the third phase modulator via the eighth port and output from the seventh port after passing through the third phase modulator. The ninth port is an electrical port for applying a modulated electrical signal.

3. The device according to claim 2, characterized in that After a high-frequency modulating electrical signal having a frequency higher than a specified threshold is applied to the first phase modulator, the first phase modulator operates in a non-reciprocal state, and a ratio of a modulation efficiency of a first path optical pulse inputted through the forward input optical port to a modulation efficiency of a second path optical pulse inputted through the reverse input optical port is not less than a preset threshold; After applying a high-frequency modulating electrical signal having a frequency higher than a specified threshold, the second phase modulator operates in a non-reciprocal state, and a ratio of a modulation efficiency of a third path optical pulse inputted through the forward input optical port to a modulation efficiency of a fourth path optical pulse inputted through the reverse input optical port is not less than a preset threshold. After applying a high-frequency modulating electrical signal having a frequency higher than a specified threshold, the third phase modulator operates in a non-reciprocal state, and a ratio of a modulation efficiency of a fifth path optical pulse input through the forward input optical port to a modulation efficiency of a sixth path optical pulse input through the reverse input optical port is not less than a preset threshold.

4. The device according to claim 3, characterized in that The first path optical pulse and the second path optical pulse pass through the first phase modulator simultaneously; The third path optical pulse and the fourth path optical pulse pass through the second phase modulator simultaneously; and / or The fifth path optical pulse and the sixth path optical pulse pass through the third phase modulator simultaneously.

5. The device according to claim 1, characterized in that Eigenpolarization state and the eigenpolarization state When the angle between them is 1·90°, the eigenpolarization state and the eigenpolarization state The included angle between them is 22.5°±m·45°, or 45°±m·90°, where l and m are integers.

6. The device according to claim 1, characterized in that Eigenpolarization state and the eigenpolarization state When the angle between them is 22.5°±a·45° or 45°±a·90°, the eigenpolarization state and the eigenpolarization state The included angle between them is m·90°, or 22.5°±m·45°, or 45°±m·90°, where a and m are integers.

7. The device according to claim 1, characterized in that The angle between the eigenpolarization state of the first polarization-controlled optical path and the eigenpolarization state of the second polarization-controlled optical path is achieved by rotating the second polarization-controlled optical path, and the angle between the eigenpolarization state of the first polarization-controlled optical path and the eigenpolarization state of the third polarization-controlled optical path is achieved by rotating the third polarization-controlled optical path; and / or, The device further comprises: a first polarization state rotator and / or a second polarization state rotator, The first polarization state rotator is arranged between the first polarization control light path and the second polarization control light path, and the angle between the intrinsic polarization state of the first polarization control light path and the intrinsic polarization state of the second polarization control light path is adjusted by the first polarization state rotator; The second polarization state rotator is arranged between the second polarization control light path and the third polarization control light path, and the angle between the intrinsic polarization state of the first polarization control light path and the intrinsic polarization state of the third polarization control light path is adjusted by the first polarization state rotator and / or the second polarization state rotator.

8. The device according to claim 1, characterized in that The device further comprises two optical isolation units, which are optical isolators or optical circulators. The two optical isolation units are respectively arranged between any two adjacent polarization operation modules.

9. The device according to claim 1, 5 or 6, characterized in that The polarization state of the light pulse input into the first polarization control optical path is or, The polarization state of the light pulse input into the first polarization control optical path is or, The polarization state of the light pulse input into the first polarization control optical path is or Where k is an integer, and are the two eigenpolarization states of the first polarization control optical path, It can be any value from 0 to 2π.

10. The device according to claim 9, characterized in that The polarization state of the light pulse input into the first polarization control optical path is 45° linear polarization, −45° linear polarization, left-hand circular polarization or right-hand circular polarization.

11. The device according to claim 1, characterized in that The first polarization-controlled optical path, the second polarization-controlled optical path and / or the third polarization-controlled optical path include: a polarization beam splitting unit and a transmission optical path; The polarization beam splitting unit comprises at least three ports, namely port A, port B and port C; the polarization beam splitting unit is used to polarization-split the light pulse input from port A into two sub-light pulses, which are output from port B and port C respectively; the intrinsic polarization state of the polarization beam splitting unit is the intrinsic polarization state of the first polarization-controlled light path, the second polarization-controlled light path and / or the third polarization-controlled light path; The transmission optical path is used to connect port B and port C of the polarization beam splitting unit.

12. The device according to claim 11, characterized in that The polarization beam splitting unit is a polarization beam splitter, and the intrinsic polarization state of the polarization beam splitter is the intrinsic polarization state of the polarization beam splitting unit.

13. The device according to claim 11, characterized in that The polarization beam splitting unit comprises: a polarization beam splitter, a first polarizer and a second polarizer; The polarization beam splitting unit further comprises a port D; The polarization beam splitter includes four ports, namely a first port, a second port, a third port and a fourth port. The first port of the polarization beam splitter is port A of the polarization beam splitting unit, and the fourth port of the polarization beam splitter is port D of the polarization beam splitting unit; the second port and the third port of the polarization beam splitter are respectively connected to the port on the first side of the first polarizer and the port on the first side of the second polarizer; the port on the second side of the first polarizer is port B of the polarization beam splitting unit, and the port on the second side of the second polarizer is port C of the polarization beam splitting unit; the port on the second side of the first polarizer and the port on the second side of the second polarizer are connected through the transmission optical path, the angle between the polarization direction of the first polarizer and one intrinsic polarization state of the polarization beam splitter is θ, and the angle between the polarization direction of the second polarizer and another intrinsic polarization state of the polarization beam splitter is δ; wherein θ, δ≠n·90°, n is an integer; the intrinsic polarization state of the polarization beam splitter is the intrinsic polarization state of the polarization beam splitter.

14. The device according to claim 11, characterized in that The polarization beam splitting unit comprises: a beam splitter, a first polarizer and a second polarizer; The optical beam splitter comprises at least three ports, namely a first port, a second port and a third port. The first port of the optical beam splitter is port A of the polarization beam splitting unit; the second port and the third port of the optical beam splitter are connected to the port on the first side of the first polarizer and the port on the first side of the second polarizer respectively; the port on the second side of the first polarizer is port B of the polarization beam splitting unit, and the port on the second side of the second polarizer is port C of the polarization beam splitting unit; the port on the second side of the first polarizer and the port on the second side of the second polarizer are connected through the transmission optical path; the polarization direction of the first polarizer is The polarization direction of the second polarizer is The polarization direction of the first polarizer The polarizing direction of the second polarizer mutually orthogonal; the polarizing direction of the first polarizer The polarizing direction of the second polarizer is the intrinsic polarization state of the polarization beam splitting unit.

15. The device according to claim 14, characterized in that The optical beam splitter further comprises a fourth port; The polarization beam splitting unit further comprises a port D; The fourth port of the optical beam splitter is the port D of the polarization beam splitting unit.

16. The device according to claim 11, characterized in that The transmission optical path is a free space optical path or a polarization-maintaining optical fiber.

17. The device according to claim 16, characterized in that Port B and port C of the polarization beam splitting unit are both coupled to the slow axis of the polarization-maintaining optical fiber or are both coupled to the fast axis of the polarization-maintaining optical fiber.

18. The device according to claim 16, characterized in that The device further includes a half-wave plate or a 90-degree Faraday rotator arranged in the transmission light path.

19. A polarization encoding method, characterized in that: include: A light pulse is input into the first polarization control optical path and polarization-split into two light pulses, namely the first light pulse and the second light pulse. The first phase modulator performs phase modulation on the first light pulse and / or the second light pulse, so that a phase difference α is generated between the two light pulses. After passing through the first phase modulator, the first light pulse and the second light pulse are combined and output through the first polarization control optical path; one of the two eigenpolarization states of the first polarization control optical path is The optical pulse output by the combined beam is input into a second polarization control optical path connected in series with the first polarization control optical path, and is polarized and split into two optical pulses by the second polarization control optical path, namely, a third optical pulse and a fourth optical pulse. The second phase modulator performs phase modulation on the third optical pulse and / or the fourth optical pulse, so that a phase difference β is generated between the two optical pulses. After passing through the second phase modulator, the third optical pulse and the fourth optical pulse are combined and output by the second polarization control optical path; one of the two eigenpolarization states of the second polarization control optical path is The optical pulse output by the combined output of the second polarization-controlled optical path is input into a third polarization-controlled optical path. The third polarization-controlled optical path is connected in series with the first polarization-controlled optical path and the second polarization-controlled optical path. The optical pulse is polarized and split into two optical pulses by the third polarization-controlled optical path, namely, a fifth optical pulse and a sixth optical pulse. The third phase modulator performs phase modulation on the fifth optical pulse and / or the sixth optical pulse, so that a phase difference γ is generated between the two optical pulses. The fifth optical pulse and the sixth optical pulse after passing through the third phase modulator are combined and output by the third polarization-controlled optical path. One of the two eigenpolarization states of the third polarization-controlled optical path is Wherein, by setting the intrinsic polarization state With the eigenpolarization state The angle between the intrinsic polarization state x and the eigenpolarization state and the phase difference α, phase difference β and phase difference γ are coordinated to meet the requirements of different quantum communication protocols.

20. The method according to claim 19, wherein Eigenpolarization state and the eigenpolarization state When the angle between them is 1·90°, the eigenpolarization state and the eigenpolarization state The included angle between them is 22.5°±m·45°, or 45°±m·90°, where l and m are integers.

21. The method according to claim 19, wherein Eigenpolarization state and the eigenpolarization state When the angle between them is 22.5°±a·45° or 45°±a·90°, the eigenpolarization state and the eigenpolarization state The included angle between them is m·90°, or 22.5°±m·45°, or 45°±m·90°, where a and m are integers.

22. The method according to any one of claims 19 to 21, characterized in that The polarization state of the light pulse input into the first polarization control optical path is or, The polarization state of the light pulse input into the first polarization control optical path is or, The polarization state of the light pulse input into the first polarization control optical path is or Where k is an integer, and are the two eigenpolarization states of the first polarization control optical path, It can be any value from 0 to 2π.

23. The method according to claim 22, characterized in that The polarization state of the light pulse input into the first polarization control optical path is 45° linear polarization, −45° linear polarization, left-hand circular polarization or right-hand circular polarization.

24. A quantum communication system, characterized in that: The polarization encoding device comprises the polarization encoding device according to any one of claims 1 to 18.

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