Polarization encoding apparatus, method and quantum communication system

Abstract

The application provides a polarization encoding device, method and quantum communication system. The device comprises a first polarization operation module and a second polarization operation module connected in series. The first polarization operation module and the second polarization operation module each comprise a polarization control optical path and a phase modulator. The polarization control optical path is used for splitting an input optical pulse into two sub optical pulses. The phase modulator modulates one of the two sub optical pulses or modulates the two sub optical pulses with different phase modulation respectively. The angle between the eigenpolarization states of the two polarization control optical paths can be set according to the encoding requirements of a quantum communication protocol, and a plurality of polarization encoding quantum states of two bases or three bases can be modulated by the combined modulation of the two polarization operation modules, so as to meet the encoding requirements of different quantum communication protocols.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of quantum communication and optical quantum encoding technology, and in particular to a polarization encoding device, a method and a quantum communication system. BACKGROUND

[0002] Quantum communication technology is a frontier and hot field combining quantum physics and information science. Currently, the applications mainly include quantum key distribution and quantum direct communication. Based on physical principles such as Heisenberg uncertainty relation of quantum mechanics and quantum non-cloning theorem, quantum key distribution can securely share keys in real time between communication parties, and quantum direct communication can achieve information transmission, i.e., security. Quantum communication can detect potential eavesdropping behavior of the communication channel, and can be applied to fields such as national defense, government affairs, finance, and power with high security information transmission requirements.

[0003] The physical implementation of a quantum communication system, such as the physical implementation of quantum key distribution and quantum direct communication, requires encoding and decoding of quantum states. Different quantum communication systems of different protocols have different encoding requirements for quantum states, such as the need to implement encoding of two sets of four quantum states for BB84 quantum communication protocol, and the need to implement encoding of three sets of six quantum states or three sets of four quantum states for reference frame independent quantum communication system, and so on.

[0004] How to compatibly support multiple quantum communication protocols in the same optical quantum encoding device and flexibly implement multiple quantum state encoding requirements is an important problem in the current quantum communication application. SUMMARY

[0005] The present application provides a polarization encoding device, a method and a quantum communication system to solve the technical problems mentioned in the prior art.

[0006] According to a first aspect of the present application, a polarization encoding device is provided, comprising: a first polarization operation module and a second 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 a beam splitter of an input light pulse into two sub-light pulses, i.e., a first sub-light pulse and a second sub-light pulse; the first phase modulator is used to perform phase modulation on one of the first sub-light pulse and the second sub-light pulse, or to perform different phase modulations on the first sub-light pulse and the second sub-light pulse, so that a phase difference is generated between the two sub-light pulses , the first sub light pulse and the second sub light pulse after passing through the first phase modulator are output through the first polarization control optical path; the second polarization operation module comprises: 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 for inputting the light pulse output by the first polarization control optical path from the input port, and the light pulse is polarization split into two sub light pulses, which are the third sub light pulse and the fourth sub light pulse respectively, the second phase modulator is used for phase modulating one of the third sub light pulse and the fourth sub light pulse, or phase modulating the third sub light pulse and the fourth sub light pulse differently, so that a phase difference is generated between the two sub light pulses , the third sub light pulse and the fourth sub light pulse after passing through the second phase modulator are output through the second polarization control optical path; wherein the included angle between the eigenpolarization state of the first polarization control optical path and the eigenpolarization state of the second polarization control optical path is set according to the requirement of the quantum communication protocol.

[0007] In some embodiments, the first phase modulator comprises: a first port, a second port and a third port, the first port and the second port are forward input light port and reverse input light port of the first phase modulator respectively, the first sub light pulse is input into the first phase modulator through the first port, and is output by the second port after passing through the first phase modulator, the second sub light pulse is input into the first phase modulator through the second port, and is output by the first port after passing through the first phase modulator, the third port is an electric port for applying a modulation electric signal; the second phase modulator comprises: a fourth port, a fifth port and a sixth port, the fourth port and the fifth port are forward input light port and reverse input light port of the second phase modulator respectively, the third sub light pulse is input into the second phase modulator through the fourth port, and is output by the fifth port after passing through the second phase modulator, the fourth sub light pulse is input into the second phase modulator through the fifth port, and is output by the fourth port after passing through the second phase modulator, the sixth port is an electric port for applying a modulation electric signal.

[0008] In some embodiments, the first phase modulator, when a high frequency modulation electrical signal with a frequency higher than a specified threshold is applied, works in a non-reciprocal state, and the ratio of the modulation efficiency of the first sub light pulse input by the forward input optical port to the modulation efficiency of the second sub light pulse input by the backward input optical port is not less than a preset threshold; the second phase modulator, when a high frequency modulation electrical signal with a frequency higher than a specified threshold is applied, works in a non-reciprocal state, and the ratio of the modulation efficiency of the third sub light pulse input by the forward input optical port to the modulation efficiency of the fourth sub light pulse input by the backward input optical port is not less than a preset threshold.

[0009] In some embodiments, the first sub light pulse and the second sub light pulse pass through the first phase modulator at the same time; and / or the third sub light pulse and the fourth sub light pulse pass through the second phase modulator at the same time.

[0010] In some embodiments, when the quantum communication protocol requirement is two groups of bases, the angle between the eigenpolarization state of the first polarization control optical path and the eigenpolarization state of the second polarization control optical path is , or , or , wherein n is an integer.

[0011] In some embodiments, when the angle between the eigenpolarization state of the first polarization control optical path and the eigenpolarization state of the second polarization control optical path is , wherein n is an integer, 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 , wherein k is an integer, and are two eigenpolarization states of the first polarization control optical path, is an arbitrary value between 0 and 2 π ; the angle between the eigenpolarization state of the first polarization control optical path and the eigenpolarization state of the second polarization control optical path is , or , wherein n is an integer, 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 , wherein k is an integer, and are two eigenpolarizations of the first polarization control optical path, β are any values between 0 and 2. π

[0012] In some embodiments, when the quantum communication protocol requirement is three groups of bases, the angle between the eigenpolarization of the first polarization control optical path and the eigenpolarization of the second polarization control optical path is , or , wherein n is an integer.

[0013] In some embodiments, the polarization state of the optical pulse input into the first polarization control optical path is ; or, the polarization state of the optical pulse input into the first polarization control optical path is ; or, the polarization state of the optical pulse input into the first polarization control optical path is , or , wherein k is an integer, and are two eigenpolarizations of the first polarization control optical path, β are any values between 0 and 2. π

[0014] In some embodiments, the first polarization operation module further comprises a third phase modulator, which is arranged in series with the first phase modulator in the transmission optical path of the first polarization control optical path, and is used to perform phase modulation on one of the first sub-optical pulse and the second sub-optical pulse, or perform different phase modulations on the first sub-optical pulse and the second sub-optical pulse, so that a phase difference between the first sub-optical pulse and the second sub-optical pulse is generated; or the second polarization operation module further comprises a third phase modulator, which is arranged in series with the second phase modulator in the transmission optical path of the second polarization control optical path, and is used to perform phase modulation on one of the third sub-optical pulse and the fourth sub-optical pulse, or perform different phase modulations on the third sub-optical pulse and the fourth sub-optical pulse, so that a phase difference between the third sub-optical pulse and the fourth sub-optical pulse is generated.

[0015] ​​In some embodiments, the third phase modulator comprises a seventh port, an eighth port and a ninth port, the seventh port and the eighth port are forward input optical port and reverse input optical port of the third phase modulator respectively, the ninth port is an electrical port for applying a modulation electrical signal; when a high frequency modulation electrical signal with a frequency higher than a specified threshold is applied, the third phase modulator works in a non-reciprocal state, and the ratio of the modulation efficiency of the optical pulse input by the forward input optical port to the modulation efficiency of the optical pulse input by the reverse input optical port is not less than a preset threshold.

[0016] In some embodiments, the polarization state of the optical pulse input into the first polarization control optical path is 45° linear polarization, -45° linear polarization, left circular polarization or right circular polarization.

[0017] In some embodiments, the angle between the eigenpolarization state of the first polarization control optical path and the eigenpolarization state of the second polarization control optical path is achieved by rotating at least one of the two polarization control optical paths; and / or

[0018] The device further comprises a polarization state rotator, which can be a half-wave plate or a Faraday rotator, the polarization state rotator is arranged between the two polarization control optical paths, and the angle between the eigenpolarization states of the two polarization control optical paths is adjusted by the polarization state rotator.

[0019] In some embodiments, the device further comprises an optical isolation unit, which is an optical isolator or an optical circulator, the optical isolation unit is arranged between the first polarization operation module and the second polarization operation module.

[0020] In some embodiments, a phase difference is generated between the first sub-optical pulse and the second sub-optical pulse and a phase difference is generated between the third sub-optical pulse and the fourth sub-optical pulse According to the requirements of polarization encoding of quantum communication protocol.

[0021] In some embodiments, the first polarization control optical path and / or the second polarization control optical path comprises a polarization beam splitting unit and a transmission optical path; the polarization beam splitting unit comprises at least three ports, which are port A, port B and port C respectively; the eigenpolarization state of the polarization beam splitting unit is and the eigenpolarization state of the polarization beam splitting unit is the eigenpolarization state of the first polarization control optical path and / or the second polarization control optical path; the polarization beam splitting unit is used for splitting the optical pulse input by the port A into two sub-optical pulses, which are output by the port B and the port C respectively; the transmission optical path is used for connecting the port B and the port C of the polarization beam splitting unit.

[0022] In some embodiments, the polarization beam splitting unit is a polarizing beam splitter, and the eigenpolarization states of the polarizing beam splitter are the eigenpolarization states of the polarization beam splitting unit.

[0023] In some embodiments, the polarization beam splitting unit comprises a polarizing beam splitter, a first polarizer and a second polarizer; the polarization beam splitting unit further comprises port D; the polarizing beam splitter comprises four ports, which are a first port, a second port, a third port and a fourth port, respectively, the first port of the polarizing beam splitter is port A of the polarization beam splitting unit, and the fourth port of the polarizing beam splitter is port D of the polarization beam splitting unit; the second port and the third port of the polarizing beam splitter are connected with the ports on the first side of the first polarizer and 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 angle between the polarization direction of the first polarizer and one of the eigenpolarization states of the polarizing beam splitter is θ , and the angle between the polarization direction of the second polarizer and the other of the eigenpolarization states of the polarizing beam splitter is δ ; wherein, , n is an integer; and the eigenpolarization states of the polarizing beam splitter are the eigenpolarization states of the polarization beam splitting unit.

[0024] In some embodiments, the polarization beam splitting unit comprises a light beam splitter, a first polarizer and a second polarizer; the light beam splitter comprises at least three ports, which are a first port, a second port and a third port, respectively, and the first port of the light beam splitter is port A of the polarization beam splitting unit; the second port and the third port of the light beam splitter are connected with the ports on the first side of the first polarizer and 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 , and the polarization direction of the second polarizer is ; the polarization direction of the first polarizer is orthogonal to the polarization direction of the second polarizer ; the polarization direction of the first polarizer is parallel to the polarization direction of the second polarizer ; and the polarization direction of the first polarizer and the polarization direction of the second polarizer are the eigenpolarization states of the polarization beam splitting unit.

[0025] In some embodiments, the optical splitter further comprises a fourth port; the polarization splitting unit further comprises a port D; the fourth port of the optical splitter is the port D of the polarization splitting unit.

[0026] In some embodiments, the transmission optical path is a free-space optical path or a polarization maintaining optical fiber.

[0027] In some embodiments, the port B and the port C of the polarization splitting unit are both coupled to a slow axis of the polarization maintaining optical fiber or both coupled to a fast axis of the polarization maintaining optical fiber.

[0028] In some embodiments, the device further comprises a half-wave plate or a 90-degree Faraday rotator disposed in the transmission optical path.

[0029] According to a second aspect of the present application, a polarization encoding method is provided, characterized in that comprising: inputting a light pulse into a first polarization control optical path to split the light pulse into two sub-light pulses, i.e., a first sub-light pulse and a second sub-light pulse; performing phase modulation on at least one of the first sub-light pulse and the second sub-light pulse by a first phase modulator, or performing different phase modulations on the first sub-light pulse and the second sub-light pulse, so that a phase difference is generated between the two sub-light pulses ; the first sub-light pulse and the second sub-light pulse after the first phase modulator are combined and output through the first polarization control optical path; the combined and output light pulse is input into a second polarization control optical path connected in series with the first polarization control optical path, and split into two sub-light pulses, i.e., a third sub-light pulse and a fourth sub-light pulse, through the second polarization control optical path; performing phase modulation on at least one of the third sub-light pulse and the fourth sub-light pulse by a second phase modulator, or performing different phase modulations on the third sub-light pulse and the fourth sub-light pulse, so that a phase difference is generated between the two sub-light pulses ; the third sub-light pulse and the fourth sub-light pulse after the second phase modulator are combined and output through the second polarization control optical path; wherein the included angle between the eigenpolarization state of the first polarization control optical path and the eigenpolarization state of the second polarization control optical path is set according to the requirement of a quantum communication protocol.

[0030] In some embodiments, when the quantum communication protocol requirement is two groups of bases, the included angle between the eigenpolarization state of the first polarization control optical path and the eigenpolarization state of the second polarization control optical path is , or , or , wherein n is an integer.

[0031] In some embodiments, when the quantum communication protocol requires three sets of bases, the angle between the eigenpolarization state of the first polarization control optical path and the eigenpolarization state of the second polarization control optical path is , or , wherein n is an integer.

[0032] In some embodiments, when the angle between the eigenpolarization state of the first polarization control optical path and the eigenpolarization state of the second polarization control optical path is , the polarization state of the optical pulse input into the first polarization control optical path is ; or, the polarization state of the optical pulse input into the first polarization control optical path is , wherein k is an integer, and are two eigenpolarization states of the first polarization control optical path, is any value between 0 and 2 π ; when the angle between the eigenpolarization state of the first polarization control optical path and the eigenpolarization state of the second polarization control optical path is , or , the polarization state of the optical pulse input into the first polarization control optical path is ; or, the polarization state of the optical pulse input into the first polarization control optical path is ; or, the polarization state of the optical pulse input into the first polarization control optical path is , or , wherein k is an integer, and are two eigenpolarization states of the first polarization control optical path, is any value between 0 and 2 π .

[0033] According to a third aspect of the present application, a quantum communication system is provided, comprising the polarization encoding device described above.

[0034] In summary, the polarization encoding device, method and quantum communication system provided by the present application have at least the following beneficial effects:

[0035] The polarization encoding device of the present application comprises a first polarization operation module and a second polarization operation module connected in series, wherein each of the first polarization operation module or the second polarization operation module comprises a polarization control optical path and a phase modulator; the polarization control optical path is used to split the input optical pulse into two sub-optical pulses; the phase modulators in the two polarization operation modules modulate the phase of one of the two sub-optical pulses, or modulate the phases of the two sub-optical pulses respectively, so that the two sub-optical pulses have phase differences andφ further set the angle between the eigenpolarization states of the two polarization control optical paths according to the requirement of the quantum communication protocol, and cooperate the above phase difference and phase difference φ The polarization encoding quantum states of two groups or three groups of bases can be modulated to meet the requirements of different quantum communication protocols, and the complexity of the modulation phase is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the specific embodiments or prior art in the present application, the drawings needed in the description of the specific embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0037] Figure 1 A structural block diagram of a polarization encoding device provided for an embodiment of the present application is provided;

[0038] Figure 2 An embodiment structural diagram of a polarization encoding device provided for an embodiment of the present application is provided;

[0039] Figure 3 A first embodiment structural diagram of a polarization control optical path provided for an embodiment of the present application is provided;

[0040] Figure 4 A second embodiment structural diagram of a polarization control optical path provided for an embodiment of the present application is provided;

[0041] Figure 5 A third embodiment structural diagram of a polarization control optical path provided for an embodiment of the present application is provided;

[0042] Figure 6 A fourth embodiment structural diagram of a polarization control optical path provided for an embodiment of the present application is provided;

[0043] Figure 7 A flowchart of a polarization encoding method provided for an embodiment of the present application is provided. DETAILED DESCRIPTION

[0044] In order to make the above and other features and advantages of the present application clearer, the present application will be further described below with reference to the drawings. It should be understood that the specific embodiments given herein are for the purpose of explanation and are only exemplary, but are not limiting.

[0045] In the following description, numerous specific details are set forth to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without the specific details. In other instances, well-known steps or procedures have not been described in order to avoid obscuring the present application.

[0046] The embodiment of the present application provides a polarization encoding device. Figure 1 and Figure 2 As shown in the figure, the polarization encoding device comprises a first polarization control optical path and a second polarization control optical path. Figure 1 As shown in the figure, the polarization encoding device comprises a first polarization control optical path and a second polarization control optical path. Figure 2 As shown in the figure, the polarization encoding device comprises a first polarization control optical path and a second polarization control optical path.

[0047] In some embodiments, the first polarization control optical path is used for splitting the input light pulse into two sub light pulses, i.e. a first sub light pulse and a second sub light pulse, and the first phase modulator is used for phase modulating one of the first sub light pulse and the second sub light pulse, or for phase modulating the first sub light pulse and the second sub light pulse differently, so that a phase difference is generated between the two sub light pulses. The first sub light pulse and the second sub light pulse after the first phase modulator are combined and output by the first polarization control optical path.

[0048] In an exemplary embodiment, the first phase modulator comprises a first port E, a second port F and a third port N, the first port E and the second port F are respectively a forward input optical port and a reverse input optical port of the first phase modulator, the first sub light pulse is input into the first phase modulator through the first port E and output from the second port F after passing through the first phase modulator, the second sub light pulse is input into the first phase modulator through the second port F and output from the first port E after passing through the first phase modulator, the third port N is an electrical port connected with the first driver 212, and is used for receiving a modulation electrical signal applied by the first driver 212.

[0049] Figure 2 The structure of the first polarization control optical path and the second polarization control optical path in the polarization encoding device shown in the figure is only a structure of an embodiment, and the first polarization control optical path and the second polarization control optical path described in the present application can respectively adopt the structures as shown in the figures. Figures 3-6The structure of the second polarization control optical path can be the same as or different from the structure of the first polarization control optical path, that is, the two polarization control optical paths can respectively adopt the structure provided in the embodiment of the present application. Figures 3-6 Any of the four structures.

[0050] In an exemplary embodiment, Figure 3 FIG. 1 is a first embodiment of the first polarization control optical path. In this embodiment, the first polarization control optical path includes: a first polarization beam splitting unit and a first transmission optical path 204; the first polarization beam splitting unit includes at least three ports, namely port A, port B and port C; the intrinsic polarization state of the first polarization beam splitting unit is and Polarization state: The intrinsic polarization state of the first polarization beam splitting unit is the intrinsic polarization state of the first polarization-controlled optical path. The first polarization beam splitting unit polarization-splits the optical pulse input from port A into two optical pulses, namely, a first optical pulse and a second optical pulse, which are output from ports B and C, respectively. The first transmission optical path 204 is used to connect ports B and C of the first polarization beam splitting unit and transmit the first optical pulse and the second optical pulse in opposite directions. In this embodiment, the first 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 first polarization beam splitting unit.

[0051] In an exemplary embodiment, Figure 4 FIG. 2 is a second embodiment of the first polarization control optical path. In this embodiment, the first polarization control optical path includes: a first polarization beam splitting unit and a first transmission optical path 204. The intrinsic polarization state of the first polarization beam splitting unit is and The eigenpolarization state of the first polarization beam splitting unit is the first polarization control optical path eigenpolarization state, wherein the first polarization beam splitting unit comprises: a first polarization beam splitter 201, a first polarizer 202, and a second polarizer 203; the first polarization beam splitting unit comprises four ports, namely port A, port B, port C, and port D; the first 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 first polarization beam splitter 201 is the port A of the first polarization beam splitting unit, and the fourth port of the first polarization beam splitter 201 is the port D of the first polarization beam splitting unit; the second port and the third port of the first polarization beam splitter 201 are connected with the port of the first side of the first polarizer 202 and the port of the first side of the second polarizer 203, respectively; the port of the second side of the first polarizer 202 is the port B of the first polarization beam splitting unit, and the port of the second side of the second polarizer 203 is the port C of the first polarization beam splitting unit; the port of the second side of the first polarizer 202 and the port of the second side of the second polarizer 203 are connected through the first transmission optical path 204; the angle between the polarization direction of the first polarizer 202 and one eigenpolarization state of the first polarization beam splitter 201 is , and the angle between the polarization direction of the second polarizer 203 and another eigenpolarization state of the first polarization beam splitter 201 is , wherein , , n is an integer. The angle between the polarization direction of the first polarizer 202 and the polarization direction of the second polarizer 203 is , The eigenpolarization state of the first polarization beam splitter 201 is the eigenpolarization state of the first polarization beam splitting unit in the embodiment.

[0052] In an exemplary embodiment, as shown in Figure 5 , it is a third embodiment of the first polarization control optical path, wherein the first polarization control optical path comprises: a first polarization beam splitting unit and a first transmission optical path 204, the eigenpolarization state of the first polarization beam splitting unit is and The first polarization state is the eigenpolarization state of the first polarization control optical path, wherein the first polarization control optical path comprises: a first polarization beam splitting unit and a first transmission optical path 204, and the eigenpolarization state of the first polarization beam splitting unit is the eigenpolarization state of the first polarization control optical path. The first polarization beam splitting unit comprises: a first optical beam splitter 201, a first polarizer 202, and a second polarizer 203. The first polarization beam splitting unit comprises at least three ports, which are port A, port B, and port C. The first optical beam splitter 201 comprises at least three ports, which are a first port, a second port, and a third port. The first port of the first optical beam splitter 201 is the port A of the first polarization beam splitting unit. The second port and the third port of the first optical beam splitter 201 are connected with the port of the first side of the first polarizer 202 and the port of the first side of the second polarizer 203 respectively. The port of the second side of the first polarizer 202 is the port B of the first polarization beam splitting unit, and the port of the second side of the second polarizer 203 is the port C of the first polarization beam splitting unit. The port of the second side of the first polarizer 202 and the port of 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 is orthogonal to the polarization direction of the second polarizer 203 . In the embodiment, the polarization direction of the first polarizer 202 is , and the polarization direction of the second polarizer 203 is , which are the eigenpolarization state of the first polarization beam splitting unit.

[0053] In an exemplary embodiment, as shown in Figure 6 , it is the fourth embodiment of the first polarization control optical path. In the embodiment, the first polarization control optical path comprises: a first polarization beam splitting unit and a first transmission optical path 204, and the eigenpolarization state of the first polarization beam splitting unit is and The intrinsic polarization state of the first polarization beam splitting unit is the first polarization control optical path intrinsic polarization state, wherein the first polarization beam splitting unit comprises a first optical beam splitter 201, a first polarizer 202 and a second polarizer 203; the first polarization beam splitting unit comprises four ports, which are port A, port B, port C and port D; the first optical beam splitter 201 comprises four ports, which are a first port, a second port, a third port and a fourth port, the first port of the first optical beam splitter 201 is the port A of the first polarization beam splitting unit, and the fourth port of the first optical beam splitter 201 is the port D of the first polarization beam splitting unit; the second port and the third port of the first optical beam splitter 201 are connected with the port of the first side of the first polarizer 202 and the port of the first side of the second polarizer 203 respectively; the port of the second side of the first polarizer 202 is the port B of the first polarization beam splitting unit, and the port of the second side of the second polarizer 203 is the port C of the first polarization beam splitting unit; the port of the second side of the first polarizer 202 and the port of 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 is perpendicular to the polarization direction of the second polarizer 203 ; in the embodiment, the polarization direction of the first polarizer 202 is the intrinsic polarization state of the first polarization beam splitting unit.

[0054] In an embodiment, the first phase modulator 205 is arranged in the first transmission optical path 204, and the first transmission optical path 204 is coupled with the slow axis of the first port E and the second port F of the first phase modulator or is coupled with the fast axis of the first port E and the second port F of the first phase modulator. The first phase modulator 205 modulates the light pulse input from one of the first port E and the second port F or modulates the light pulses input from the first port E and the second port F with different phases.

[0055] ​In an exemplary embodiment, the first phase modulator 205 is configured to operate in a non-reciprocal state when a high frequency modulation signal with a frequency higher than a specified threshold is applied to the first phase modulator 205, and the ratio of the modulation efficiency of the first sub light pulse input from the forward input optical port to the modulation efficiency of the second sub light pulse input from the backward input optical port is not less than a preset threshold. In one embodiment, the preset threshold can be 10 decibels (dB). Non-reciprocity is a physical concept that describes whether a certain physical process is equal to its inverse process. If equal, it is called reciprocal; if not equal, it is called non-reciprocal. In this application, non-reciprocity refers to the fact that light waves exhibit different loss, phase shift, and other characteristics when transmitted in opposite directions in an optical device. The high frequency modulation signal is, for example, a modulation signal of not less than 10 GHz.

[0056] It can be understood that when a high frequency modulation signal is applied to the first phase modulator 205, the modulation efficiency of the backward transmission light pulse (i.e., the second sub light pulse) input from the second port F by the first phase modulator 205 is much lower than the modulation efficiency of the forward transmission light pulse (i.e., the first sub light pulse) input from the first port E by the first phase modulator 205. That is, the first phase modulator 205 can effectively modulate the phase of the light pulse transmitted in the forward direction through the first phase modulator 205, but cannot effectively modulate the phase of the light pulse transmitted in the backward direction through the first phase modulator 205. When the two sub light pulses pass through the high frequency modulated first phase modulator 205 at the same time, if the same modulation signal pulse is applied to the two sub light pulses transmitted in the forward direction and in the backward direction, a phase difference can be formed between the first sub light pulse and the second sub light pulse; if different modulation signals are applied to the first phase modulator 205, the phase difference formed between the first sub light pulse and the second sub light pulse is different, so that different polarization states of light pulses are generated when the light pulses are combined and output.

[0057] In an exemplary embodiment, the first polarization operation module further comprises a third phase modulator, which is arranged in series with the first phase modulator 205 in the transmission optical path of the first polarization control optical path, and is configured to modulate the phase of one of the first sub light pulse and the second sub light pulse, or to modulate the phases of the first sub light pulse and the second sub light pulse differently, so that a phase difference is generated between the first sub light pulse and the second sub light pulse. .

[0058] In an example embodiment, the third phase modulator comprises a seventh port, an eighth port and a ninth port, the seventh port and the eighth port are a forward input optical port and a reverse input optical port of the third phase modulator respectively, the ninth port is an electrical port for applying a modulation electrical signal; when a high frequency modulation electrical signal with a frequency higher than a specified threshold is applied, the third phase modulator works in a non-reciprocal state, and a ratio of a modulation efficiency of an optical pulse input by the forward input optical port to a modulation efficiency of an optical pulse input by the reverse input optical port is not less than a preset threshold.

[0059] In some embodiments, the second polarization operation module 200 comprises a second polarization control optical path and a second phase modulator 210 arranged in a 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 for inputting the optical pulse combined and output by the first polarization control optical path from an input port, and splitting the polarization of the optical pulse into two sub optical pulses, which are a third sub optical pulse and a fourth sub optical pulse respectively, the second phase modulator 210 is used for phase modulating one of the third sub optical pulse and the fourth sub optical pulse, or phase modulating the third sub optical pulse and the fourth sub optical pulse differently, so that a phase difference is generated between the two sub optical pulses. φ The third sub optical pulse and the fourth sub optical pulse after passing through the second phase modulator are combined and output by the second polarization control optical path.

[0060] In an example embodiment, the second phase modulator 210 comprises a fourth port K, a fifth port L and a sixth port M, the fourth port K and the fifth port L are a forward input optical port and a reverse input optical port of the second phase modulator respectively, the third sub optical pulse is input into the second phase modulator 210 by the fourth port K in a forward direction, and is output by the fifth port L after passing through the second phase modulator 210, the fourth sub optical pulse is input into the second phase modulator 210 by the fifth port L in a reverse direction, and is output by the fourth port K after passing through the second phase modulator 210, the third port is an electrical port connected with the second driver 213, and is used for receiving a modulation electrical signal applied by the second driver 213.

[0061] In an example embodiment, the second polarization control optical path comprises a second polarization splitting unit and a second transmission optical path 209; the second polarization splitting unit comprises at least three ports, which are a port G, a port H and a port I (the functions of the port G, the port H and the port I in the present application are equivalent to the functions of the corresponding port A, the port B and the port C respectively); the eigenpolarization state of the second polarization splitting unit is and The second polarization state is the eigenpolarization state of the second polarization control optical path; the second polarization beam splitting unit splits the light pulse input from the port G into two sub-light pulses, which are the third sub-light pulse and the fourth sub-light pulse, and are output from the port H and the port I, respectively; and the second transmission optical path 209 is used to connect the port H and the port I of the second polarization beam splitting unit and to transmit the third sub-light pulse and the fourth sub-light pulse in opposite directions. In this embodiment, the second polarization beam splitting unit is a polarization beam splitter, and the eigenpolarization state of the polarization beam splitter is the eigenpolarization state of the second polarization beam splitting unit.

[0062] In an exemplary embodiment, the second polarization beam splitting unit comprises a second polarization beam splitter 206, a third polarizer 207, and a fourth polarizer 208; the polarization beam splitting unit further comprises a port J; the second polarization beam splitter 206 comprises four ports, which are a first port, a second port, a third port, and a fourth port, the first port of the second polarization beam splitter 206 is the port G of the second polarization beam splitting unit, and the fourth port of the second polarization beam splitter 206 is the port J of the second polarization beam splitting unit; the second port and the third port of the second polarization beam splitter 206 are connected to the port of the first side of the third polarizer 207 and the port of the first side of the fourth polarizer 208, respectively; the port of the second side of the third polarizer 207 is the port H of the second polarization beam splitting unit, and the port of the second side of the fourth polarizer 208 is the port I of the second polarization beam splitting unit; the port of the second side of the third polarizer 207 and the port of the second side of the fourth polarizer 208 are connected through the second transmission optical path 209; the angle between the polarization direction of the third polarizer 207 and the eigenpolarization state of the second polarization beam splitter 206 is θ , and the angle between the polarization direction of the fourth polarizer 208 and the other eigenpolarization state of the second polarization beam splitter 206 is δ ; wherein, , n is an integer, and the angle between the polarization direction of the third polarizer 207 and the polarization direction of the fourth polarizer 208 is , The eigenpolarization state of the second polarization beam splitter 206 in this embodiment is the eigenpolarization state of the second polarization beam splitting unit.

[0063] In an example embodiment, the second polarization beam splitting unit comprises a second optical beam splitter, a third polarizer and a fourth polarizer; the second optical beam splitter comprises at least three ports, which are a fifth port, a sixth port and a seventh port respectively, the fifth port of the second optical beam splitter is the port G of the second polarization beam splitting unit; the sixth port and the seventh port of the second optical beam splitter are connected with the port of the first side of the third polarizer and the port of the first side of the fourth polarizer respectively; the port of the second side of the third polarizer is the port H of the second polarization beam splitting unit, and the port of the second side of the fourth polarizer is the port I of the second polarization beam splitting unit; the port of the second side of the third polarizer and the port of the second side of the fourth polarizer are connected through a second transmission optical path. The polarization direction of the third polarizer is , the polarization direction of the fourth polarizer is ; the polarization direction of the third polarizer is orthogonal to the polarization direction of the fourth polarizer ; in this embodiment, the polarization direction of the third polarizer and the polarization direction of the fourth polarizer are the eigenpolarizations of the second polarization beam splitting unit.

[0064] In an example embodiment, the second polarization beam splitting unit comprises a second optical beam splitter, a third polarizer and a fourth polarizer; the second polarization beam splitting unit further comprises a port J; the second optical beam splitter comprises four ports, which are a fifth port, a sixth port, a seventh port and an eighth port respectively, the fifth port of the second optical beam splitter is the port G of the second polarization beam splitting unit, and the eighth port of the second optical beam splitter is the port J of the second polarization beam splitting unit; the sixth port and the seventh port of the second optical beam splitter are connected with the port of the first side of the third polarizer and the port of the first side of the fourth polarizer respectively; the port of the second side of the third polarizer is the port H of the second polarization beam splitting unit, and the port of the second side of the fourth polarizer is the port I of the second polarization beam splitting unit; the port of the second side of the third polarizer and the port of the second side of the fourth polarizer are connected through a second transmission optical path. The polarization direction of the third polarizer is , the polarization direction of the fourth polarizer is ; the polarization direction of the third polarizer is orthogonal to the polarization direction of the fourth polarizer ; in this embodiment, the polarization direction of the third polarizer and the polarization direction of the fourth polarizer are the eigenpolarizations of the second polarization beam splitting unit.

[0065] For example, the second phase modulator 210 is arranged in the second transmission light path 209, and the second transmission light path 209 is coupled with the slow axis of the fourth port K and the fifth port L of the second phase modulator 210 or coupled with the fast axis of the fourth port K and the fifth port L of the second phase modulator 210. The second phase modulator 210 modulates one of the light pulses input from the fourth port K and the fifth port L or different phase modulates the two light pulses input from the fourth port K and the fifth port L.

[0066] In an example embodiment, when a high-frequency modulation signal with a frequency higher than a specified threshold is applied to the second phase modulator 210, the second phase modulator 210 works in a non-reciprocal state, and the ratio of the modulation efficiency of the third sub-light pulse input from the forward input optical port (i.e., the fourth port K) to the modulation efficiency of the fourth sub-light pulse input from the reverse input optical port (i.e., the fifth port L) is not less than a preset threshold.

[0067] It can be understood that when the high-frequency modulation signal is applied to the second phase modulator 210, the modulation efficiency of the reverse transmission light pulse (i.e., the fourth sub-light pulse) input from the fifth port L is much lower than the modulation efficiency of the forward transmission light pulse (i.e., the third sub-light pulse) input from the fourth port K. That is, the second phase modulator 210 can effectively perform phase modulation on the light pulse transmitted forward through the second phase modulator 210 and cannot effectively perform phase modulation on the light pulse transmitted backward through the second phase modulator 210. When the two sub-light pulses pass through the high-frequency modulated second phase modulator 210 at the same time, if the same modulation signal pulse is applied to the two sub-light pulses transmitted forward and backward, a phase difference can be formed between the third sub-light pulse and the fourth sub-light pulse; if different modulation signals are applied to the second phase modulator 210, the phase difference formed between the third sub-light pulse and the fourth sub-light pulse is different, so that different polarization states of light pulses are generated when the light pulses are combined and output.

[0068] In an example embodiment, the second polarization operation module further comprises a third phase modulator arranged in series with the second phase modulator 210 in the transmission light path of the second polarization control light path, for phase modulating one of the third sub-light pulse and the fourth sub-light pulse or different phase modulating the third sub-light pulse and the fourth sub-light pulse, so that a phase difference is generated between the third sub-light pulse and the fourth sub-light pulse. .

[0069] As can be seen from the above description, in some embodiments, for example, when the quantum communication protocol requires three groups of bases, two phase modulators in series can be arranged in the first polarization operation module or the second polarization operation module, and the optical pulses are modulated by the three phase modulators in the polarization encoding device to meet the quantum communication protocol requirement of three groups of bases.

[0070] It should be noted that, no matter the first phase modulator 205, the second phase modulator 210, or the third phase modulator, when a high-frequency modulation signal with a frequency higher than a specified threshold is applied, there can be multiple forward input optical ports and backward input optical ports inputting sub-optical pulses at the same time.

[0071] In an exemplary embodiment, the first polarization control optical path and the second polarization control optical path are connected in series.

[0072] In an exemplary embodiment, a phase difference is generated between the first sub-optical pulse and the second sub-optical pulse ， and a phase difference is generated between the third sub-optical pulse and the fourth sub-optical pulse According to the requirement of quantum communication protocol polarization encoding.

[0073] In some embodiments, the angle between the eigenpolarization state of the first polarization control optical path and the eigenpolarization state of the second polarization control optical path is set according to the quantum communication protocol requirement.

[0074] In an exemplary embodiment, when the quantum communication protocol requirement is two groups of bases, the angle between the eigenpolarization state of the first polarization control optical path and the eigenpolarization state of the second polarization control optical path is , or , or , wherein n is an integer.

[0075] In an exemplary embodiment, when the angle between the eigenpolarization state of the first polarization control optical path and the eigenpolarization state of the second polarization control optical path is , the polarization state of the optical pulse input into the first polarization control optical path is ; or, the polarization state of the optical pulse input into the first polarization control optical path is , wherein k is an integer, and are two eigenpolarization states of the first polarization control optical path, is an arbitrary value between 0 and 2 π .

[0076] In an example embodiment, the eigenpolarization states of the first polarization control optical path and the eigenpolarization states of the second polarization control optical path satisfy , 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, the polarization state of the light pulse input into the first polarization control optical path is , or , wherein k is an integer, and are two eigenpolarization states of the first polarization control optical path, β is an arbitrary value between 0 and 2 π .

[0077] In an example embodiment, when the quantum communication protocol requirement is three groups of bases, the eigenpolarization states of the first polarization control optical path and the eigenpolarization states of the second polarization control optical path satisfy , or , wherein n is an integer.

[0078] In an example embodiment, 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 , wherein k is an integer, and are two eigenpolarization states of the first polarization control optical path, β is an arbitrary value between 0 and 2 π .

[0079] In an example 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.

[0080] When the eigenpolarization states of the first polarization control optical path and the eigenpolarization states of the second polarization control optical path satisfy , or , or , phase modulation can be achieved to obtain a phase difference is 0°, 45°, 90° or 135°, or 45°, 90°, 135° or 180°, or 0° or 180°, or 0° or 90°, or 90° or 270°, or 0°, 90°, 180° or 270°; the phase difference 0° or 180°, or 0° or 90°, or 90° or 270°, or 0°, 90°, 180° or 270°.

[0081] In some embodiments, the angle between the eigenpolarization state of the first polarization control optical path and the eigenpolarization state of the second polarization control optical path can be achieved by rotating at least one of the two polarization control optical paths; and / or

[0082] The device further comprises a polarization state rotator, which can be a half- wave plate or a Faraday rotator, disposed between the two polarization control optical paths (i.e. between the two polarization operation modules), to adjust the angle between the eigenpolarization states of the two polarization control optical paths.

[0083] In some embodiments, the device further comprises an optical isolation unit, which can be an optical isolator or an optical circulator, disposed between the first polarization operation module and the second polarization operation module, to isolate the optical signal from the second polarization operation module back to the first polarization operation module, to reduce signal interference and crosstalk.

[0084] In some embodiments, the transmission optical path is a free-space optical path or a polarization maintaining optical fiber.

[0085] In an exemplary embodiment, the port B and the port C of the polarization beam splitting unit are both coupled to the slow axis of the polarization maintaining optical fiber or both coupled to the fast axis of the polarization maintaining optical fiber.

[0086] For example, the first transmission optical path 204 is a polarization maintaining optical fiber, and in this case, the second port and the third port of the first polarization beam splitter 201 are both coupled to the slow axis of the polarization maintaining optical fiber or both coupled to the fast axis of the polarization maintaining optical fiber.

[0087] In an exemplary embodiment, the first polarization control optical path and / or the second polarization control optical path further comprises a half-wave plate or a 90-degree Faraday rotator disposed in the transmission optical path, to rotate the polarization state of the passing sub-pulses by 90°, so that both of the two sub-pulse optical paths are coupled to the slow axis of the polarization maintaining optical fiber or both coupled to the fast axis of the polarization maintaining optical fiber.

[0088] In some embodiments, the first polarization control optical path and / or the second polarization control optical path is a Sagnac interferometer.

[0089] In some embodiments, the first phase modulator 205, the second phase modulator 210 and / or the third phase modulator can be a single-polarization phase modulator or a birefringent phase modulator.

[0090] In some embodiments, the first polarizer 202 can be bonded with the second port B of the polarization beam splitter 201, and the second polarizer 203 can be bonded with the third port C of the polarization beam splitter 201.

[0091] In some embodiments, the directions of the two eigenpolarizations of the first polarization beam splitter 201 and are horizontal and vertical directions, respectively.

[0092] According to the polarization encoding device of the application, when the angle between the eigenpolarization of the first polarization control optical path and the eigenpolarization of the second polarization control optical path is , by combined modulation of the first phase modulator arranged in the first polarization control optical path and the second phase modulator arranged in the second polarization control optical path, the polarization encoding device can prepare two sets of four polarization states of ±45° polarization bases and left and right circular polarization bases .

[0093] For example, assuming that the first polarization control optical path and the second polarization control optical path both use a polarization beam splitting unit composed of a four-port polarization beam splitter and two polarizers, the first polarization control optical path outputs the input eigenpolarization unchanged, and the input eigenpolarization is also output unchanged, i.e., the relationship between the input and the output of the first polarization control optical path is (the negative sign is due to the fact that the polarization state passes through the polarization beam splitter twice); the second polarization control optical path also outputs the input eigenpolarization unchanged. When the polarization state of the light pulse input into the first polarization control optical path is 45° linear polarization (i.e., ), if the first phase modulator randomly modulates 0° or 180°, i.e., the phase difference is modulated to 0° or 180°, and the second phase modulator randomly modulates 0° or 90°, i.e., the phase difference is modulated to 0° or 90°, then two sets of four polarization states of ±45° polarization bases and left and right circular polarization bases can be prepared.

[0094] When the angle between the eigenpolarization of the first polarization control optical path and the eigenpolarization of the second polarization control optical path is , by combined modulation of the first phase modulator arranged in the first polarization control optical path and the second phase modulator arranged in the second polarization control optical path, the polarization encoding device can prepare two sets of four polarization states of horizontal and vertical polarization bases and ±45° polarization bases ; or can prepare two sets of four polarization states of horizontal and vertical polarization bases​ and left-right circular polarization basis Two groups of four polarization states; or ±45° polarization base can be prepared and left-right circular polarization basis Two groups of four polarization states; or horizontal and vertical polarization bases can be prepared 、±45° polarization base and left-right circular polarization basis Three groups of six polarization states; or the polarization encoding device can prepare horizontal and vertical polarization base 、±45° polarization base and left-right circular polarization basis There are three groups of basis and four polarization states, each group of basis contains at least one polarization state, and so on.

[0095] For example, assuming that both the first polarization control optical path and the second polarization control optical path use a polarization beam splitting unit consisting of a four-port polarization beam splitter and two polarizers, the first polarization control optical path will input The intrinsic polarization state remains unchanged and the input The intrinsic polarization state also remains unchanged at the output, that is, the relationship between the input and output of the first polarization control optical path is: (The negative sign takes into account The polarization state is reflected twice by the polarization beam splitter); the second polarization control light path will output the input eigenpolarization state unchanged. When the polarization state of the light pulse input to the first polarization control light path is 45° linear polarization (i.e. ), if the first phase modulator randomly modulates 0°, 90°, 180° or 270°, that is, the phase difference The modulation is 0°, 90°, 180° or 270°, and the second phase modulator modulates 0° (ie no modulation), then a ±45° polarization-based and left-right circular polarization basis Two groups of four polarization states; if the first phase modulator randomly modulates 0°, 90° or 180°, that is, the phase difference The phase difference is modulated to 0°, 90° or 180°, and the second phase modulator randomly modulates 90° or 270°. Modulation is 90° or 270°, then horizontal and vertical polarization can be prepared. and ±45° polarization base Two groups of four polarization states; if the first phase modulator randomly modulates 90° or 270° and the second phase modulator modulates 0° or 90°, horizontal and vertical polarization bases can be prepared. and left-right circular polarization basis two sets of four polarization states; if the first phase modulator randomly modulates 0°, 90°, 180° or 270°, and the second phase modulator randomly modulates 0° or 90°, then the horizontal-vertical polarization basis , ±45° polarization basis and left-right circular polarization basis three sets of six polarization states; if the first phase modulator randomly modulates 0°, 90° or 180°, and the second phase modulator randomly modulates 0° or 90°, then the horizontal-vertical polarization basis , ±45° polarization basis and left-right circular polarization basis three sets of four polarization states.

[0096] According to the polarization encoding device of the present application, when the included angle between the eigenpolarization state of the first polarization control light path and the eigenpolarization state of the second polarization control light path is , the polarization encoding device can prepare the horizontal-vertical polarization basis and ±45° polarization basis two sets of four polarization states; or the polarization encoding device can prepare the horizontal-vertical polarization basis and left-right circular polarization basis two sets of four polarization states; or the polarization encoding device can prepare the ±45° polarization basis and left-right circular polarization basis two sets of four polarization states; or the polarization encoding device can prepare the horizontal-vertical polarization basis , ±45° polarization basis and left-right circular polarization basis three sets of six polarization states; or the polarization encoding device can prepare the horizontal-vertical polarization basis , ±45° polarization basis and left-right circular polarization basis three sets of four polarization states, each set of basis containing at least one polarization state, and so on.

[0097] For example, assuming that the first polarization control light path and the second polarization control light path both use a polarization splitting unit composed of a four-port polarization beam splitter and two polarizers, at this time the first polarization control light path keeps the input eigenpolarization state unchanged and outputs, and the input eigenpolarization state of the second polarization control light path is also kept unchanged and outputs, that is, the relationship between the input and output of the first polarization control light path is (the negative sign takes into account The second polarization control optical path keeps the eigenpolarization state input thereto unchanged and outputs it. When the polarization state of the light pulse input into the first polarization control optical path is 45° linear polarization (i.e. ), if the first phase modulator randomly modulates 0°, 90°, 180° or 270°, and the second phase modulator modulates 0° (i.e. no modulation), the polarization bases of ±45° polarization and left and right circular polarization bases of two groups of four polarization states can be prepared. If the first phase modulator randomly modulates 0° or 180°, and the second phase modulator randomly modulates 0° or 180°, the polarization bases of horizontal and vertical polarization and ±45° polarization bases of two groups of four polarization states can be prepared. If the first phase modulator randomly modulates 0°, 90° or 180°, and the second phase modulator randomly modulates 0° or 180°, the polarization bases of horizontal and vertical polarization , ±45° polarization bases and left and right circular polarization bases of three groups of six polarization states can be prepared. If the first phase modulator randomly modulates 0°, 90° or 180°, and the second phase modulator randomly modulates 0° or 180°, the polarization bases of horizontal and vertical polarization , ±45° polarization bases and left and right circular polarization bases of three groups of four polarization states can be prepared. If three phase modulators are arranged in the polarization encoding device (for example, two phase modulators are arranged in series in the first polarization operation module), if the first phase modulator randomly modulates 0° or 90°, the third phase modulator randomly modulates 0° or 180°, and the second phase modulator randomly modulates 0° or 180°, the polarization bases of horizontal and vertical polarization , ±45° polarization bases and left and right circular polarization bases

[0098] of three groups of six polarization states can be prepared. From the above description, it can be seen that the polarization encoding device described in the embodiments of the present application contains two phase modulators in the first polarization operation module and the second polarization operation module when the quantum communication protocol requires two groups of bases, and four polarization states can be modulated in a digital modulation manner through combined modulation. When the quantum communication protocol requires three groups of bases, six polarization states can be modulated in a digital modulation manner through combined modulation of three phase modulators.

[0099] In some embodiments, the polarization encoding device of the present application can also be used for polarization decoding process according to the requirements of quantum communication.

[0100] The polarization encoding device of the present application comprises a first polarization operation module and a second polarization operation module connected in series, wherein each of the first polarization operation module or the second polarization operation module comprises a polarization control optical path and a phase modulator; the polarization control optical path is used for polarization beam splitting of the input optical pulse into two sub optical pulses; the phase modulators in the two polarization operation modules modulate the phase of one of the two sub optical pulses or modulate the phases of the two sub optical pulses respectively, so that the two sub optical pulses generate phase difference and phase difference φ Further, the angle between the eigenpolarization states of the two polarization control optical paths is set according to the requirements of the quantum communication protocol, and the phase difference and phase difference φ can be modulated to generate a variety of polarization encoding quantum states of two groups or three groups of bases to meet the requirements of different quantum communication protocols and reduce the complexity of phase modulation.

[0101] In addition, by applying a high-frequency modulation electrical signal with a frequency higher than a specified threshold to the first phase modulator and / or the second phase modulator, the modulation efficiency of the first phase modulator and / or the second phase modulator on the backward transmission optical pulse is much lower than the modulation efficiency on the forward transmission optical pulse; the first phase modulator and / or the second phase modulator can effectively modulate the phase of the forward transmission optical pulse, but cannot effectively modulate the phase of the backward transmission optical pulse, so that when the forward transmission optical pulse and the backward transmission optical pulse pass through the high-frequency modulation first phase modulator and / or the second phase modulator, only one same modulation electrical signal needs to be applied to the two optical pulses to form a phase difference between the two optical pulses; by applying modulation electrical signals with different sizes to the first phase modulator and / or the second phase modulator, the phase difference between the two sub optical pulses is different, and polarization quantum state encoding at a speed of 10GHz or more can be realized.

[0102] In addition, the two sub optical pulses of the polarization beam splitter in the polarization control optical path have the same optical path from polarization beam splitting to beam combining, have a self-compensation function for environmental interference, and have the advantages of anti-interference and high stability. The present application provides an implementation scheme of a high-speed polarization quantum state encoding device which is easy to implement and apply and compatible with a variety of quantum communication protocols.

[0103] The polarization encoding method provided by the embodiments of the present application can be executed by the polarization encoding device and system provided by the embodiments of the present application.

[0104] The accompanying drawings are referred to in the description of the present application. Figure 7As shown, the present application provides a polarization encoding method, which can be implemented by the polarization encoding device of the above-mentioned embodiments, and the method comprises steps 710-720.

[0105] In step 710, one light pulse is input into a first polarization control optical path to split into two sub light pulses, i.e., a first sub light pulse and a second sub light pulse. One of the first sub light pulse and the second sub light pulse is phase modulated by a first phase modulator, or the first sub light pulse and the second sub light pulse are phase modulated differently, so that a phase difference is generated between the two sub light pulses. The first sub light pulse and the second sub light pulse after the first phase modulator are combined and output by the first polarization control optical path.

[0106] For example, with reference to Figure 2The structure shown, a light pulse is input into the polarization encoding device through the first port A of the first polarization beam splitter 201, and the first polarization beam splitter 201 splits the input light pulse into a first sub light pulse and a second sub light pulse, which are output through the port B and the port C respectively. The first sub light pulse is transmitted in the clockwise direction through the first polarizer 202, the first polarization maintaining fiber 204, the first phase modulator 205, the second polarizer 203 to the port C of the first polarization beam splitter 201 after being output through the port B of the first polarization beam splitter 201, and is output through the port D after being reflected by the first polarization beam splitter 201; the second sub light pulse is transmitted in the counterclockwise direction through the second polarizer 203, the first polarization maintaining fiber 204, the first phase modulator 205, the first polarizer 202 to the port B of the first polarization beam splitter 201 after being output through the port C of the first polarization beam splitter 201, and is output through the port D after being transmitted by the first polarization beam splitter 201; the first sub light pulse and the second sub light pulse are combined and output through the port D of the first polarization beam splitter 201 to the second polarization control optical path. In operation, the first phase modulator 205 modulates the light pulse input through one of the port E and the port F; or modulates the light pulses input through the port E and the port F with different phases; or when the first sub light pulse and the second sub light pulse pass through the first phase modulator 205 at the same time, a high-frequency modulation electric signal is applied to the first phase modulator 205, such as a 10GHz high-frequency modulation electric signal pulse. Although the first sub light pulse and the second sub light pulse pass through the first phase modulator 205 at the same time and the same modulation electric signal is applied, because the first phase modulator 205 modulates the first sub light pulse input through the port E in the forward direction and transmits through the first phase modulator 205 effectively, and does not modulate the second sub light pulse input through the port F in the reverse direction and transmits through the first phase modulator 205 effectively, a phase difference is formed between the first sub light pulse and the second sub light pulse; different modulation electric signals are applied to the first phase modulator 205, and the phase difference formed between the two sub light pulses is different, so that the two sub light pulses produce different polarization states of high-speed modulation when they are combined and output through the first polarization beam splitter 201. The first phase modulator 205 can have multiple modulation modes, such as randomly modulating four phase states of 0°, 45°, 90° or 135°; or randomly modulating four phase states of 45°, 90°, 135° or 180°; or 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°.

[0107] In step 720, the light pulses output in the beam combination are input into a second polarization control optical path connected in series with the first polarization control optical path, and the light pulses are polarization split into two sub light pulses, i.e., a third sub light pulse and a fourth sub light pulse, by the second polarization control optical path. One of the third sub light pulse and the fourth sub light pulse is phase modulated by a second phase modulator, or the third sub light pulse and the fourth sub light pulse are phase modulated differently, so that a phase difference is generated between the two sub light pulses. The third sub light pulse and the fourth sub light pulse after passing through the second phase modulator are output in the beam combination by the second polarization control optical path. The angle between the eigenpolarization state of the first polarization control optical path and the eigenpolarization state of the second polarization control optical path is set according to the requirements of the quantum communication protocol.

[0108] For example, with reference to Figure 2The light pulses output from the port D of the first polarization beam splitter 201 are input to the second polarization control optical path through the port G of the second polarization beam splitter 206 according to the shown structure. The second polarization beam splitter 206 splits the input light pulses into third and fourth sub light pulses which are output from the ports H and I respectively. The third sub light pulse is transmitted in the clockwise direction through the third polarizer 207, the second polarization maintaining fiber 209, the second phase modulator 210, and the fourth polarizer 208 after being output from the port H of the second polarization beam splitter 206, and is output from the port J of the second polarization beam splitter 206 after being reflected by the second polarization beam splitter 206. The fourth sub light pulse is transmitted in the counterclockwise direction through the fourth polarizer 208, the second polarization maintaining fiber 209, the second phase modulator 210, and the third polarizer 207 after being output from the port I of the second polarization beam splitter 206, and is output from the port J of the second polarization beam splitter 206 after being transmitted by the second polarization beam splitter 206. The third and fourth sub light pulses are combined and output from the port J of the second polarization beam splitter 206. During operation, the second phase modulator 210 modulates the light pulses input from one of the ports K and L, or modulates the light pulses input from the ports K and L with different phases, or applies a high-frequency modulation signal to the second phase modulator 210 when the third and fourth sub light pulses pass through the second phase modulator 210, such as a 10 GHz high-frequency modulation signal. Although the third and fourth sub light pulses pass through the second phase modulator 210 and the same modulation signal is applied, the second phase modulator 210 effectively modulates the phase of the third sub light pulse which is transmitted in the forward direction and input from the port K, and does not effectively modulate the phase of the fourth sub light pulse which is transmitted in the reverse direction and input from the port L, thereby forming a phase difference between the third and fourth sub light pulses. The second phase modulator 210 applies modulation signals with different sizes, and the phase difference between the two sub light pulses is different, so that the two sub light pulses have different polarization states which are modulated at high speed when they are combined and output from the second polarization beam splitter 206. 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°.

[0109] In an exemplary embodiment, the quantum communication protocol requirement is that the angle between the eigenpolarization state of the first polarization control optical path and the eigenpolarization state of the second polarization control optical path is , or , or , where n is an integer.

[0110] In an example embodiment, when the quantum communication protocol requires three groups of bases, the angle between the eigenpolarization state of the first polarization control optical path and the eigenpolarization state of the second polarization control optical path is , or , wherein n is an integer.

[0111] In an example embodiment, when the angle between the eigenpolarization state of the first polarization control optical path and the eigenpolarization state of the second polarization control optical path is , the polarization state of the optical pulse input into the first polarization control optical path is ; or, the polarization state of the optical pulse input into the first polarization control optical path is , wherein k is an integer, and are two eigenpolarization states of the first polarization control optical path, is any value between 0 and 2 π .

[0112] In an example embodiment, when the angle between the eigenpolarization state of the first polarization control optical path and the eigenpolarization state of the second polarization control optical path is , or , the polarization state of the optical pulse input into the first polarization control optical path is ; or, the polarization state of the optical pulse input into the first polarization control optical path is ; or, the polarization state of the optical pulse input into the first polarization control optical path is , or , wherein k is an integer, and are two eigenpolarization states of the first polarization control optical path, is any value between 0 and 2 π .

[0113] The polarization encoding method of the present application, through phase modulation of one of the two sub-optical pulses in the two polarization operation modules in series by the phase modulator, or different phase modulation of the two sub-optical pulses respectively, makes the two sub-optical pulses respectively generate phase difference and phase difference φ , further sets the angle between the eigenpolarization states of the two polarization control optical paths according to the quantum communication protocol requirement, cooperates with the above-mentioned phase difference and phase difference φ , modulates a plurality of polarization encoding quantum states of two groups of bases or three groups of bases through the combination modulation of the two phase modulators, to meet the requirements of different quantum communication protocols, and reduces the complexity of the modulation phase.

[0114] According to the present application, a quantum communication system is provided, comprising the polarization encoding device described above.

[0115] It should be understood that the specific features, operations and details described above in relation to the device of the present application can 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 can be performed by the corresponding components or units of the device or system of the present application.

[0116] The technical features described above can be combined arbitrarily. Although all possible combinations of the technical features are not described, any combination of the technical features should be considered to be covered by the present specification, as long as there is no contradiction in such a combination.

[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the above embodiments, or make equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions 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 and a second polarization operation module are connected in series, wherein 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 sub-pulses, namely a first optical pulse and a second optical pulse, and the first phase modulator is used to phase-modulate one of the first optical pulse and the second optical pulse, or to perform different phase modulations on the first optical pulse and the second optical pulse, so that a phase difference is generated between the two optical pulses. , the first path optical pulse and the second path optical pulse after passing through the first phase modulator are combined and output through the first polarization control optical path; 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 polarize it into two sub-optical pulses, namely a third optical pulse and a fourth optical pulse, and the second phase modulator is used to phase modulate one of the third optical pulse and the fourth optical pulse, or to perform different phase modulation on the third optical pulse and the fourth optical pulse, so that a phase difference is generated between the two optical pulses φ , the third path optical pulse and the fourth path optical pulse after passing through the second phase modulator are combined and output through the second polarization control optical path; The angle between the intrinsic polarization state of the first polarization-controlled optical path and the intrinsic polarization state of the second polarization-controlled optical path is set according to the requirements of the quantum communication protocol; When the quantum communication protocol requires two bases, the angle between the intrinsic polarization state of the first polarization control optical path and the intrinsic polarization state of the second polarization control optical path is ,or ,or ,in n is an integer; When the quantum communication protocol requires three bases, the angle between the intrinsic polarization state of the first polarization control optical path and the intrinsic polarization state of the second polarization control optical path is ,or ,in n is an integer.

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 are respectively the forward input optical port and the reverse input optical port of the second phase modulator. The third path optical pulse is input into the second phase modulator through 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 through 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.

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 a high-frequency modulating electrical signal having a frequency higher than a specified threshold is applied to the second phase modulator, the second phase modulator operates in a non-reciprocal state, and a ratio of a modulation efficiency of a third path optical pulse input through the forward input optical port to a modulation efficiency of a fourth 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; and / or The third path optical pulse and the fourth path optical pulse pass through the second phase modulator simultaneously.

5. The device according to any one of claims 1 to 4, characterized in that 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 When n is an integer, 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 , in, k is an integer, and are the two eigenpolarization states of the first polarization control optical path, 0~2 π Any value of 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 ,or When n is an integer, 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 , in, k is an integer, and are the two eigenpolarization states of the first polarization control optical path, β 0~2 π Any value of .

6. The device according to any one of claims 1 to 4, 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.

7. The device according to any one of claims 1 to 4, characterized in that The first polarization operation module further includes: a third phase modulator, which is arranged in the transmission optical path of the first polarization control optical path and is connected in series with the first phase modulator, and is used to perform phase modulation on one of the first optical pulse and the second optical pulse, or to perform different phase modulation on the first optical pulse and the second optical pulse, so that a phase difference is generated between the first optical pulse and the second optical pulse ;or The second polarization operation module further includes: a third phase modulator, which is arranged in the transmission optical path of the second polarization control optical path and is connected in series with the second phase modulator, and is used to perform phase modulation on one of the third optical pulse and the fourth optical pulse, or to perform different phase modulation on the third optical pulse and the fourth optical pulse, so that a phase difference is generated between the third optical pulse and the fourth optical pulse .

8. The device according to claim 7, characterized in that The third phase modulator includes: a seventh port, an eighth port, and a ninth port. The seventh port and the eighth port are respectively a forward optical input port and a reverse optical input port of the third phase modulator. The ninth port is an electrical port for applying a modulated electrical signal. After applying a high-frequency modulated 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 for an optical pulse input through the forward optical input port to a modulation efficiency for an optical pulse input through the reverse optical input port is not less than a preset threshold.

9. The device according to any one of claims 1 to 4, characterized in that The angle between the intrinsic polarization state of the first polarization-controlled light path and the intrinsic polarization state of the second polarization-controlled light path is achieved by rotating at least one of the two polarization-controlled light paths; and / or The device further comprises a polarization state rotator, which is arranged between the two polarization control light paths and is used to adjust the angle between the intrinsic polarization states of the two polarization control light paths.

10. The device according to any one of claims 1 to 4, characterized in that The device further includes an optical isolation unit, which is an optical isolator or an optical circulator, and is disposed between the first polarization operation module and the second polarization operation module.

11. The device according to claim 1, characterized in that The first polarization control optical path and / or the second polarization control optical path comprises: 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 intrinsic polarization state of the polarization beam splitting unit is and Polarization state, the intrinsic polarization state of the polarization beam splitting unit is the intrinsic polarization state of the first polarization control optical path and / or the second polarization control optical path; 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 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 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 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 an intrinsic polarization state of the polarization beam splitter is θ , the angle between the polarization direction of the second polarizer and another intrinsic polarization state of the polarization beam splitter is δ ;in, , n is an integer; the eigenpolarization state of the polarization beam splitter is the eigenpolarization state of the polarization beam splitting unit.

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, and the polarization direction of the first polarizer is , the polarization direction of the second polarizer is ; The polarizing 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 light path and polarized and split into two light pulses, namely a first light pulse and a second light pulse. A first phase modulator performs phase modulation on at least one of the first light pulse and the second light pulse, or performs different phase modulation on the first light pulse and the second light pulse, so that a phase difference is generated between the two light pulses. , the first path optical pulse and the second path optical pulse after passing through the first phase modulator are combined and output through the first polarization control optical path; 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, namely a third optical pulse and a fourth optical pulse, by the second polarization control optical path. The second phase modulator performs phase modulation on at least one of the third optical pulse and the fourth optical pulse, or performs different phase modulation on the third optical pulse and the fourth optical pulse, so that a phase difference is generated between the two optical pulses. , the third path optical pulse and the fourth path optical pulse after passing through the second phase modulator are combined and output through the second polarization control optical path; The angle between the intrinsic polarization state of the first polarization-controlled optical path and the intrinsic polarization state of the second polarization-controlled optical path is set according to the requirements of the quantum communication protocol; When the quantum communication protocol requires two bases, the angle between the intrinsic polarization state of the first polarization control optical path and the intrinsic polarization state of the second polarization control optical path is ,or ,or ,in n is an integer; When the quantum communication protocol requires three bases, the angle between the intrinsic polarization state of the first polarization control optical path and the intrinsic polarization state of the second polarization control optical path is ,or ,in n is an integer.

20. The method according to claim 19, characterized in that 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 When n is an integer, 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 , in, k is an integer, and are the two eigenpolarization states of the first polarization control optical path, 0~2 π Any value of 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 ,or When n is an integer, 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 , in, k is an integer, and are the two eigenpolarization states of the first polarization control optical path, 0~2 π Any value of .

21. 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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