Quantum state coding device and method and software-defined quantum communication system

Abstract

The invention provides a quantum state coding device and method and a software-defined quantum communication system. The quantum state coding device comprises a polarization coding unit, a first optical coupling unit, a polarization-to-time phase coding unit, a first transmission optical path and a second optical coupling unit, the polarization coding unit is used for carrying out polarization beam splitting, polarization rotation and phase modulation on an input optical pulse and outputting an optical pulse in a polarization coding quantum state; and the polarization-to-time phase coding unit is used for converting the optical pulse of the polarization coding quantum state into an optical pulse of a time phase coding quantum state. And controlling the first optical coupling unit and the second optical coupling unit to output the optical pulse of the polarization coding quantum state or output the optical pulse of the time phase coding quantum state according to the quantum communication coding control instruction. According to the quantum state coding device and the quantum communication system, different coding requirements of the quantum communication system can be met by the same quantum state coding device.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of quantum communication and optical quantum coding technology, and particularly relates to a quantum state coding device, a method and a software-defined quantum communication system. BACKGROUND

[0002] Quantum communication technology is a frontier and hot field combining quantum physics and information science. At present, 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 a communication channel, and can be applied to fields such as national defense, government affairs, finance and power with high security information transmission requirements.

[0003] Physical implementation of a quantum communication system, such as quantum key distribution and quantum direct communication, requires encoding and decoding of quantum states. Commonly used quantum communication coding methods include polarization coding and time-phase coding. A set of quantum communication systems generally selects one of the coding methods, so the system is not universal and cannot be flexibly networked.

[0004] How to implement universal quantum state coding compatible with multiple quantum communication coding methods in an optical quantum coding device is an important problem in quantum communication applications.

[0005] At the same time, current optical quantum coding devices have large insertion loss and crosstalk, and the system noise is relatively large, resulting in a decline in system performance and function. SUMMARY

[0006] The present application aims to provide a quantum state coding device, a method and a software-defined quantum communication system to solve the technical problems mentioned in the prior art.

[0007] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a quantum state encoding device, comprising: a polarization encoding unit, a first optical coupling unit, a polarization-to-time phase encoding unit, a first transmission optical path, and a second optical coupling unit; the polarization encoding unit comprises an input port and an output port, the polarization encoding unit is used for inputting an optical pulse through the input port, generating a polarization-encoded quantum state optical pulse based on the input optical pulse, and outputting through the output port; the polarization encoding unit comprises at least one polarization operation module, each polarization operation module comprises a polarization control optical path and at least one phase modulator arranged in a second transmission optical path of the polarization control optical path; the polarization control optical path is used for polarization beam splitting and polarization rotation of the input optical pulse to obtain a first rotated sub-optical pulse and a second rotated sub-optical pulse; the at least one phase modulator is used for phase modulation of at least one of the first rotated sub-optical pulse and the second rotated sub-optical pulse based on a modulation signal, so that a preset phase difference is generated between the first rotated sub-optical pulse and the second rotated sub-optical pulse; the polarization control optical path is further used for polarization rotation and combining of the first rotated sub-optical pulse and the second rotated sub-optical pulse after the phase difference is generated, and outputting the polarization-encoded quantum state optical pulse generated after the combining; the first optical coupling unit comprises an input port and two output ports, which are a first port, a second port and a third port, respectively; the first port is connected with the output port of the polarization encoding unit; the second optical coupling unit comprises two input ports and an output port, which are a fourth port, a fifth port and a sixth port, respectively; the polarization-to-time phase encoding unit comprises an input port and an output port, and is used for time phase encoding conversion of the input polarization-encoded quantum state optical pulse, and outputting a time phase encoded quantum state optical pulse; the third port of the first optical coupling unit is connected with the input port of the polarization-to-time phase encoding unit, and the output port of the polarization-to-time phase encoding unit is connected with the fifth port of the second optical coupling unit, forming a first optical output branch; the second port of the first optical coupling unit is connected with the fourth port of the second optical coupling unit through the first transmission optical path, forming a second optical output branch; the first optical coupling unit is used for inputting the polarization-encoded quantum state optical pulse output by the polarization encoding unit into the first optical output branch and / or the second optical output branch according to a quantum communication encoding control instruction; the quantum communication encoding control instruction is determined according to the encoding requirement of a quantum communication system; the sixth port of the second optical coupling unit is an output port of the quantum state encoding device, and is used for outputting the polarization-encoded quantum state optical pulse transmitted by the second optical output branch or the time phase encoded quantum state optical pulse transmitted by the first optical output branch according to the quantum communication encoding control instruction.

[0008] The second aspect of the present application provides a quantum state encoding method, which is implemented by using the quantum state encoding device.

[0009] In a third aspect, the present application provides a software-defined quantum communication system, comprising the quantum state encoding apparatus and the encoding control apparatus as described above; the encoding control apparatus is configured to generate a quantum communication encoding control instruction based on the encoding requirement of the quantum communication system, and send the quantum state encoding apparatus.

[0010] In summary, the quantum state encoding apparatus, method and software-defined quantum communication system provided by the present application have at least the following beneficial effects:

[0011] The quantum state encoding apparatus is composed of a polarization encoding unit, a first optical coupling unit, a polarization-to-time phase encoding unit, a first transmission optical path and a second optical coupling unit. The polarization encoding unit can generate polarization-encoded quantum state light pulses through polarization beam splitting, polarization rotation and phase modulation. The polarization control optical path in the polarization encoding unit can realize polarization rotation function, reducing the insertion loss of the apparatus, and one or more phase modulators in the polarization encoding unit can generate one or more phase delays. At the same time, the polarization encoding unit includes an input port and an output port, which can avoid the crosstalk problem caused by the existence of two port outputs and reduce the noise of the apparatus.

[0012] In addition, the polarization-to-time phase encoding unit can convert the polarization-encoded quantum state light pulses into time phase-encoded quantum state light pulses. The first optical coupling unit and the second optical coupling unit can control the output of polarization-encoded quantum state light pulses or time phase-encoded quantum state light pulses according to the quantum communication encoding control instruction. Therefore, the quantum state encoding apparatus provided by the embodiments of the present application can flexibly realize various quantum communication encoding modes of polarization-encoded quantum states and time phase-encoded quantum states, and realize that the same quantum state encoding apparatus can meet different encoding requirements of the quantum communication system. BRIEF DESCRIPTION OF DRAWINGS

[0013] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed in the description of the specific embodiments or the prior art will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0014] Figure 1 The structural block diagram of a quantum state encoding apparatus provided by an embodiment of the present application is shown;

[0015] Figure 2 The structural block diagram of another quantum state encoding apparatus provided by an embodiment of the present application is shown;

[0016] Figure 3 The structural block diagram of a polarization encoding unit provided by an embodiment of the present application is shown;

[0017] Figure 4 A structure schematic diagram of a polarization control optical path provided by an embodiment of the present application is shown.

[0018] Figure 5 A specific structure schematic diagram of a polarization operation module provided by an embodiment of the present application is shown.

[0019] Figure 6 A specific structure schematic diagram of another polarization encoding unit provided by an embodiment of the present application is shown.

[0020] Figures 7 to 9 A specific structure schematic diagram of still another polarization encoding unit provided by an embodiment of the present application is shown.

[0021] Figure 10 A specific structure schematic diagram of a quantum state encoding device provided by an embodiment of the present application is shown.

[0022] Figure 11 A structure schematic diagram of a software-defined quantum communication system provided by an embodiment of the present application is shown. DETAILED DESCRIPTION

[0023] Hereinafter, embodiments of the present application will be described with reference to the accompanying drawings. It should be understood, however, that the description is merely exemplary of the present application, and is not intended to limit the scope of the present application. Furthermore, in the following description, descriptions of well-known structures and techniques are omitted to avoid obscuring the concept of the present application.

[0024] Various structure schematic diagrams according to embodiments of the present application are shown in the accompanying drawings. These diagrams are not drawn to scale, in which certain details are exaggerated for the purpose of clarity, and certain details may be omitted. The shapes of various regions, layers, and their relative sizes and positional relationships shown in the diagrams are merely exemplary, and may deviate in actuality due to manufacturing tolerances or technical limitations, and regions / layers having different shapes, sizes, and relative positions can be additionally designed by those skilled in the art according to actual needs.

[0025] In order to make the technical problems to be solved by the present application, technical solutions and beneficial effects more clearly understood, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely intended to explain the present application, and are not intended to limit the present application.

[0026] In addition, the terms "first", "second", etc. are used only for descriptive purposes and are not to be construed as indicating or implying relative importance or an ordered ranking of the indicated technical features. Thus, features defined with "first", "second" can include one or more of the features explicitly or implicitly. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0027] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integral connection; it can be mechanical connection, or electrical connection; it can be direct connection, or indirect connection through intermediate medium, it can be internal communication of two elements or interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0028] The quantum state encoding device in the existing quantum communication system has the following problems:

[0029] 1. The commonly used quantum communication encoding methods include polarization encoding and time phase encoding. A set of quantum communication system generally selects one of the encoding methods, so that the system is not universal and cannot be flexibly networked, and cannot meet the encoding requirements of quantum states of different quantum communication systems.

[0030] 2. The preparation of polarization encoded or time phase encoded quantum states usually uses a phase modulator, however, the phase modulator is susceptible to environmental influences, resulting in phase drift, which requires real-time feedback compensation or temperature control measures, making it difficult for the quantum communication system to work stably and efficiently.

[0031] 3. In practical applications, the encoding rate of the quantum communication system is mainly 100MHz and 1GHz, however, in order to increase the quantum communication safe transmission distance and improve the quantum key generation rate or information transmission rate, quantum states with a speed of 10GHz or higher need to be encoded.

[0032] 4. The current quantum communication system generally supports the encoding of two groups of four quantum states, and it is difficult to support multiple quantum communication protocols such as BB84 and reference frame independent in a set of quantum communication system. The quantum communication system needs to support three groups of four quantum state encoding or three groups of six quantum state encoding.

[0033] In order to solve the above problems, the present application provides a quantum state encoding device, Figure 1A structure block diagram of a quantum state encoding device provided by an embodiment of the present application is shown, and the device comprises a polarization encoding unit 100, a first optical coupling unit 200, a polarization-to-time phase encoding unit 300, a first transmission optical path 400, and a second optical coupling unit 500.

[0034] Figure 2 A structure block diagram of another quantum state encoding device provided by an embodiment of the present application is shown, and as shown in the figure, the polarization encoding unit 100 comprises one input port and one output port. The polarization encoding unit 100 is configured to input light pulses through the input port, generate polarization-encoded quantum state light pulses based on the input light pulses, and output the polarization-encoded quantum state light pulses through the output port. Figure 2

[0035] The first optical coupling unit 200 comprises one input port and two output ports, i.e., a first port G, a second port H, and a third port I. The first port G is connected to the output port of the polarization encoding unit 100.

[0036] The second optical coupling unit 500 comprises two input ports and one output port, i.e., a fourth port H', a fifth port I', and a sixth port G'.

[0037] The polarization-to-time phase encoding unit 300 comprises one input port P and one output port Q, and is configured to perform time phase encoding conversion on the input polarization-encoded quantum state light pulses, and output time phase encoded quantum state light pulses.

[0038] The input port of the polarization-to-time phase encoding unit 300 is configured to receive the polarization-encoded quantum state light pulses input by the first optical coupling unit, and the output port of the polarization-to-time phase encoding unit 300 is configured to output the time phase encoded quantum state light pulses after the time phase encoding conversion by the polarization-to-time phase encoding unit 300.

[0039] It should be noted that the time phase encoding described in the present application comprises phase encoding, i.e., the time phase encoding is an encoding composed of any combination of X phase basis, Y phase basis, and Z time basis quantum states.

[0040] In an embodiment of the present application, the third port I of the first optical coupling unit 200 is connected to the input port P of the polarization-to-time phase encoding unit 300, and the output port Q of the polarization-to-time phase encoding unit 300 is connected to the fifth port I' of the second optical coupling unit 500, forming a first optical output branch.

[0041] The second port H of the first optical coupling unit 200 is connected to the fourth port H' of the second optical coupling unit 500 through the first transmission optical path 400, forming a second optical output branch.

[0042] ​The first light coupling unit 200 is configured to input the polarized encoded quantum state light pulse output by the polarized encoding unit 100 into the first light output branch and / or the second light output branch according to the quantum communication encoding control instruction.

[0043] The sixth port G' of the second light coupling unit is an output port of the quantum state encoding device, configured to output the polarized encoded quantum state light pulse transmitted by the second light output branch or the time-phase encoded quantum state light pulse transmitted by the first light output branch according to the quantum communication encoding control instruction.

[0044] It should be noted that the quantum communication encoding control instruction can be determined according to the quantum communication system encoding requirement, and can be issued by programmable control software.

[0045] For example, when the first light coupling unit and the second light coupling unit are both optical switches, according to the quantum communication system encoding requirement, the quantum communication system runs the control software through the upper computer (control circuit unit or processor unit) to issue the quantum communication encoding control instruction to configure the gating state of the optical switch, so as to realize the selective output of the polarized encoded quantum state light pulse or the time-phase encoded quantum state light pulse.

[0046] In the above embodiment, the quantum state encoding device is composed of the polarized encoding unit 100, the first light coupling unit 200, the polarization-to-time-phase encoding unit 300, the first transmission light path 400 and the second light coupling unit 500. The polarized encoding unit 100 can generate a polarized encoded quantum state light pulse, and the polarization-to-time-phase encoding unit 300 can convert the polarized encoded quantum state light pulse into a time-phase encoded quantum state light pulse. The first light coupling unit 200 and the second light coupling unit 500 can control the output of the polarized encoded quantum state light pulse or the time-phase encoded quantum state light pulse according to the quantum communication encoding control instruction. In this way, the same quantum state encoding device can meet the different encoding requirements of the quantum communication system to realize the encoding output of the multi-form quantum state light pulse, and the encoding requirements of the quantum communication system are met. The application can also realize the quantum communication security requirement, reduce the number of lasers used, and reduce the weight and power consumption of the quantum communication transmitter. The polarized encoded quantum state of the application has strong stability and can meet the demand for polarized encoded quantum state and time-phase encoded quantum state in space quantum communication application.

[0047] Figure 3 A structure block diagram of a polarized encoding unit provided by an embodiment of the application is shown in FIG. 1. Figure 3As shown, the polarization encoding unit 100 comprises at least one polarization operation module 110. Each polarization operation module 110 comprises a polarization control optical path 111 and at least one phase modulator 112 arranged in the second transmission optical path of the polarization control optical path. That is, the polarization operation module 110 comprises one polarization control optical path 111 and one or more phase modulators 112.

[0048] In an embodiment of the present application, the polarization control optical path 111 comprises one input port and one output port. The input port of the polarization control optical path 111 serves as the input port of the polarization operation module 110, and the output port of the polarization control optical path 111 serves as the output port of the polarization operation module 110.

[0049] The polarization control optical path 111 is configured to perform polarization splitting and polarization rotation on the input optical pulse to obtain first and second rotated sub optical pulses. The at least one phase modulator 112 is configured to perform phase modulation on at least one of the first and second rotated sub optical pulses based on a modulation signal, so that a preset phase difference is generated between the first and second rotated sub optical pulses. The polarization control optical path 111 is further configured to perform polarization rotation and combination on the first and second rotated sub optical pulses with the generated phase difference, and output the optical pulse of the polarization encoded quantum state generated after the combination.

[0050] In an embodiment of the present application, the first and second rotated sub optical pulses are obtained by performing polarization rotation on two sub optical pulses obtained by polarization splitting of the input optical pulse.

[0051] In an embodiment of the present application, the polarization control optical path 111 performs polarization splitting and polarization rotation on the input optical pulse to obtain first and second rotated sub optical pulses. The one or more phase modulators 112 can perform phase modulation on the first rotated sub optical pulse, or perform phase modulation on the second rotated sub optical pulse, or perform phase modulation on the first and second rotated sub optical pulses, so that a preset phase difference meeting the requirements of the quantum communication system is generated between the two rotated sub optical pulses. The first and second rotated sub optical pulses output by the one or more phase modulators 112 are subjected to polarization rotation and combination in the polarization control optical path 111 to obtain the optical pulse of the polarization encoded quantum state. The output port of the polarization control optical path 111 outputs the optical pulse of the polarization encoded quantum state generated after the combination.

[0052] In an embodiment of the present application, the two eigenpolarizations of the polarization control optical path 111, i.e., the two eigenpolarizations of the polarization beam splitter 31, are and respectively represent horizontal direction and vertical direction. The eigenpolarization state of the polarization control optical path 111 is the eigenpolarization state of the polarization operation module 110.

[0053] In the above embodiment, the polarization encoding unit 100, the first optical coupling unit 200, the polarization-to-time phase encoding unit 300, the first transmission optical path 400, and the second optical coupling unit 500 are used to form the quantum state encoding device. The polarization encoding unit 100 can generate a polarization encoded quantum state optical pulse through polarization beam splitting, polarization rotation, and phase modulation. The polarization control optical path in the polarization encoding unit 100 can realize the polarization rotation function, reduce the insertion loss of the device, and one or more phase modulators in the polarization encoding unit 100 can generate one or more phase delays. At the same time, the polarization encoding unit 100 includes one input port and one output port, which can avoid the crosstalk problem caused by the existence of two port outputs and reduce the noise of the device.

[0054] In addition, the polarization-to-time phase encoding unit 300 can convert the polarization encoded quantum state optical pulse into a time phase encoded quantum state optical pulse. The first optical coupling unit 200 and the second optical coupling unit 500 can control the output of the polarization encoded quantum state optical pulse or the output of the time phase encoded quantum state optical pulse according to the quantum communication encoding control instruction. Therefore, the quantum state encoding device provided in the embodiment of the present application can flexibly realize various quantum communication encoding modes of polarization encoded quantum states and time phase encoded quantum states, and realize that the same quantum state encoding device can meet different encoding requirements of the quantum communication system.

[0055] Figure 4 The structure of the polarization control optical path provided in the embodiment of the present application is shown in the structure diagram of the polarization control optical path as shown in the figure. Figure 4 As shown in the figure, the polarization control optical path 111 includes a polarization beam splitter 31, a first Faraday rotator 32, a second Faraday rotator 33, and a second transmission optical path 34.

[0056] In an embodiment of the present application, in the polarization control optical path 111, the polarization beam splitter 31 is connected with the first Faraday rotator 32 and the second Faraday rotator 33, and the first Faraday rotator 32 and the second Faraday rotator 33 are connected through the second transmission optical path 34.

[0057] That is, the polarization beam splitter 31 is connected with the first Faraday rotator 32 and the second Faraday rotator 33. In addition, the first Faraday rotator 32, the at least one phase modulator 112, and the second Faraday rotator 33 are connected in series through the second transmission optical path 34.

[0058] In an embodiment of the present application, the polarization beam splitter 31 is used to receive an input optical pulse and split the polarization of the input optical pulse into a first sub-optical pulse and a second sub-optical pulse.

[0059] The first Faraday rotator 32 is configured to perform polarization rotation on the first sub light pulse to output a first rotated sub light pulse. The second Faraday rotator 34 is configured to perform polarization rotation on the second sub light pulse to output a second rotated sub light pulse.

[0060] The at least one phase modulator 112 is configured to perform phase modulation on at least one of the first rotated sub light pulse and the second rotated sub light pulse based on a modulation signal, so that a preset phase difference is generated between the first rotated sub light pulse and the second rotated sub light pulse.

[0061] The first Faraday rotator 32 is further configured to perform polarization rotation on the second rotated sub light pulse output by the at least one phase modulator 112 to obtain a polarization-rotated second rotated sub light pulse.

[0062] The second Faraday rotator 33 is further configured to perform polarization rotation on the first rotated sub light pulse output by the at least one phase modulator 112 to obtain a polarization-rotated first rotated sub light pulse.

[0063] The polarization beam splitter 31 is further configured to combine the polarization-rotated first rotated sub light pulse and the polarization-rotated second rotated sub light pulse to output a polarization-encoded quantum state light pulse generated after the combination.

[0064] In an embodiment of the present application, the first sub light pulse and the second sub light pulse split by the polarization beam splitter 31 are output from different ports, respectively pass through different Faraday rotators, and the polarization states are rotated to obtain the first rotated sub light pulse and the second rotated sub light pulse. One or more phase modulators 112 can perform phase modulation on the first rotated sub light pulse, or perform phase modulation on the second rotated sub light pulse, or perform phase modulation on the first rotated sub light pulse and the second rotated sub light pulse, so that a preset phase difference meeting the requirements of a quantum communication system is generated between the two rotated sub light pulses. The first rotated sub light pulse and the second rotated sub light pulse output by the one or more phase modulators 112 pass through different Faraday rotators again, the polarization states are rotated, and are input into the polarization beam splitter 31 from different ports for combination. The polarization beam splitter 31 outputs the polarization-encoded quantum state light pulse generated after the combination from a port without input of the light pulse. The different Faraday rotators include the first Faraday rotator 32 and the second Faraday rotator 33.

[0065] In an embodiment of the present application, the second transmission optical path 34 can be a free-space optical path or a polarization maintaining optical fiber. The polarization maintaining optical fiber is a special optical fiber which can keep the polarization direction of light unchanged during the transmission along the slow axis or the fast axis of the polarization maintaining optical fiber. The free-space optical path can refer to the path of light propagating in free space, and is independent of optical fibers or other physical media.

[0066] Figure 5 A specific structure schematic diagram of a polarization operation module provided by an embodiment of the present application is shown in FIG. 3. As shown in FIG. 3, the polarization beam splitter 31 includes four ports, i.e., a first port A, a second port B, a third port C and a fourth port D. The first port A of the polarization beam splitter 31 is an input port of the polarization control optical path 111, and the fourth port D of the polarization beam splitter 31 is an output port of the polarization control optical path. Figure 5

[0067] The second port B and the third port C of the polarization beam splitter are connected with the port of the first side of the first Faraday rotator 32 and the port of the first side of the second Faraday rotator 33, respectively.

[0068] The port of the second side of the first Faraday rotator 32 and the port of the second side of the second Faraday rotator 33 are connected through the second transmission optical path 34.

[0069] It should be noted that, Figure 5 Only one phase modulator 112 is shown.

[0070] In some embodiments of the present application, the first Faraday rotator 32 is a 45°+a·90° Faraday rotator, and the second Faraday rotator 33 is a 45°+b·90° Faraday rotator, where a and b are integers.

[0071] In an embodiment of the present application, the first Faraday rotator 32 and the second Faraday rotator 33 can be used to rotate the first sub-optical pulse and the second sub-optical pulse by 45°, respectively, and to rotate the second rotated sub-optical pulse and the first rotated sub-optical pulse output from the phase modulator 112 by 45° again, respectively.

[0072] In some embodiments of the present application, the rotation direction of the first Faraday rotator 32 can be clockwise or counterclockwise. The rotation direction of the second Faraday rotator 33 can be clockwise or counterclockwise.

[0073] In an embodiment of the present application, the rotation direction of the first Faraday rotator 32 can be the same as the rotation direction of the second Faraday rotator 33, or the rotation direction of the first Faraday rotator 32 can be opposite to the rotation direction of the second Faraday rotator 33.

[0074] ​Specifically, when the rotation direction of the first Faraday rotator 32 is clockwise, the rotation direction of the second Faraday rotator 33 can be clockwise. Or, when the rotation direction of the first Faraday rotator 32 is counterclockwise, the rotation direction of the second Faraday rotator 33 can be counterclockwise.

[0075] When the rotation direction of the first Faraday rotator 32 is clockwise, the rotation direction of the second Faraday rotator 33 can be counterclockwise. Or, when the rotation direction of the first Faraday rotator 32 is counterclockwise, the rotation direction of the second Faraday rotator 33 can be clockwise.

[0076] In an embodiment of the present application, the polarization state direction of the first route of the rotated sub-light pulses output by the second port of the first Faraday rotator 32 is perpendicular or parallel to the polarization state direction of the second route of the rotated sub-light pulses output by the second port of the second Faraday rotator 33.

[0077] That is, the first Faraday rotator 32 and the second Faraday rotator 33 are arranged in such a way that the polarization state direction of the first route of the rotated sub-light pulses output by the first Faraday rotator 32 is perpendicular or parallel to the polarization state direction of the second route of the rotated sub-light pulses output by the second Faraday rotator 33.

[0078] In an embodiment of the present application, when the second transmission light path is a polarization maintaining optical fiber, the ports on the second side of the first Faraday rotator 32 and the ports on the second side of the second Faraday rotator 33 output the first route of the rotated sub-light pulses and the second route of the rotated sub-light pulses to the slow axis of the polarization maintaining optical fiber or to the fast axis of the polarization maintaining optical fiber.

[0079] In this way, without additional devices, each route of the sub-light pulses is transmitted along the same axis of the polarization maintaining optical fiber after passing through the two Faraday rotators, so that the light pulse component of the vertical polarization state output by the second port B is still of the vertical polarization state when input by the port C. In addition, the light pulse component of the horizontal polarization state output by the third port C is still of the horizontal polarization state when input by the port B.

[0080] In another embodiment of the present application, the second transmission light path 34 is a free space light path, and the polarization direction of the first route of the rotated sub-light pulses after passing through the first Faraday rotator 32 is parallel to the polarization direction of the second route of the rotated sub-light pulses after passing through the second Faraday rotator 33.

[0081] In another embodiment of the present application, when the second transmission optical path is a polarization maintaining fiber, and the first route of the rotator light pulse and the second route of the rotator light pulse output from the port of the second side of the first Faraday rotator 32 and the port of the second side of the second Faraday rotator 33 are coupled to different axes of the polarization maintaining fiber respectively, the polarization control optical path 111 further comprises a 90° polarization rotator.

[0082] For example, the first route of the rotator light pulse output from the port of the second side of the first Faraday rotator 32 is coupled to the fast axis transmission of the polarization maintaining fiber, and the second route of the rotator light pulse output from the port of the second side of the second Faraday rotator 33 is coupled to the slow axis transmission of the polarization maintaining fiber. Alternatively, the first route of the rotator light pulse output from the port of the second side of the first Faraday rotator 32 is coupled to the slow axis transmission of the polarization maintaining fiber, and the second route of the rotator light pulse output from the port of the second side of the second Faraday rotator 33 is coupled to the fast axis transmission of the polarization maintaining fiber.

[0083] Since the slow axis direction and the fast axis direction of the polarization maintaining fiber are 90° apart, it is necessary to set a 90° polarization rotator to convert the polarization state of the two routes of the rotator light pulse between the fast axis direction and the slow axis direction, so that the two routes of the rotator light pulse pass through the same optical path when transmitted in the second transmission optical path, ensuring the stable operation of the quantum encoding optical path, and avoiding the influence of phase drift caused by environmental interference on the phase modulator.

[0084] In another embodiment of the present application, when the polarization direction of the first route of the rotator light pulse after passing through the first Faraday rotator 32 is perpendicular to the polarization direction of the second route of the rotator light pulse after passing through the second Faraday rotator 33, and the second transmission optical path 34 is a free space optical path, the polarization control optical path 111 further comprises a 90° polarization rotator.

[0085] In the above two embodiments, the 90° polarization rotator is arranged in the second transmission optical path. The 90° polarization rotator is used to rotate the polarization state of the two routes of the rotator light pulse passing through by 90°.

[0086] In an embodiment of the present application, the 90° polarization rotator is a half-wave plate or a 90° Faraday rotator.

[0087] In order to illustrate the change of the polarization state of the light pulse in the polarization control optical path, two cases are taken as examples for illustration.

[0088] Assuming that the second transmission optical path 34 is a polarization maintaining optical fiber, the first Faraday rotator 32 is a clockwise 45° rotation Faraday rotator, the second Faraday rotator 33 is a counterclockwise 45° rotation Faraday rotator, and the ports on the second side of the first Faraday rotator 32 and the second Faraday rotator 33 output the first and second rotated optical pulses, which are both coupled to the slow axis of the polarization maintaining optical fiber: the optical pulse input into the polarization control optical path is split into a first sub-optical pulse with vertical polarization and a second sub-optical pulse with horizontal polarization by the polarization beam splitter 31, which are output from the ports B and C of the polarization beam splitter 31, respectively. The first sub-optical pulse with vertical polarization is rotated clockwise by 45° by the first Faraday rotator 32 to become a first rotated optical pulse with 45° polarization, which is coupled to the slow axis of the polarization maintaining optical fiber 34 and transmitted to the second Faraday rotator 33 in a clockwise direction. When the first rotated optical pulse is input into the second Faraday rotator 33, the polarization state is 45°, and after passing through the second Faraday rotator 33, it is rotated counterclockwise by 45°, and the polarization state becomes 90°, i.e., vertical polarization, which is input into the polarization beam splitter 31 from the port C of the polarization beam splitter 31 and reflected to the port D. The second sub-optical pulse with horizontal polarization is rotated counterclockwise by 45° by the second Faraday rotator 33 to become a second rotated optical pulse with 45° polarization, which is coupled to the slow axis of the polarization maintaining optical fiber 34 and transmitted to the first Faraday rotator 32 in a counterclockwise direction. When the second rotated optical pulse is input into the first Faraday rotator 32, the polarization state is 45°, and after passing through the first Faraday rotator 32, it is rotated clockwise by 45°, and the polarization state becomes 0°, i.e., horizontal polarization, which is input into the polarization beam splitter 31 from the port B of the polarization beam splitter 31 and transmitted to the port D. The first rotated optical pulse with vertical polarization reflected to the port D and the second rotated optical pulse with horizontal polarization transmitted to the port D are output after being combined. In addition, by modulating the phase difference between the two combined rotated optical pulses by the phase modulator 112, the polarization state of the combined optical pulse can be modulated.

[0089] Suppose the second transmission optical path 34 is a free-space optical path, the first Faraday rotator 32 and the second Faraday rotator 33 are both counterclockwise 45°-rotating Faraday rotators, and the second transmission optical path is provided with a 90°-rotating half-wave plate as a 90°-polarization rotator. In this case, the input-polarization-controlled optical pulse is split into a first-path sub-optical pulse with vertical polarization and a second-path sub-optical pulse with horizontal polarization by the polarization beam splitter 31, and the two sub-optical pulses are output from the port B and the port C of the polarization beam splitter 31 respectively. The first-path sub-optical pulse with vertical polarization is rotated counterclockwise by 45° by the first Faraday rotator 32 to become a first-path rotated sub-optical pulse with 135° polarization, and is transmitted to the 90°-rotating half-wave plate through the free-space optical path. After the transmission, the polarization state of the first-path rotated sub-optical pulse is changed to 45°. Then, the first-path rotated sub-optical pulse is transmitted to the second Faraday rotator 33 through the free-space optical path. When the first-path rotated sub-optical pulse is input into the second Faraday rotator 33, the polarization state of the first-path rotated sub-optical pulse is 45°. After the first-path rotated sub-optical pulse passes through the second Faraday rotator 33, the polarization state of the first-path rotated sub-optical pulse is rotated counterclockwise by 45°, and the polarization state of the first-path rotated sub-optical pulse is changed to 90°, i.e. vertical polarization. The first-path rotated sub-optical pulse is input into the polarization beam splitter 31 from the port C of the polarization beam splitter 31, and is reflected to the port D. The second-path sub-optical pulse with horizontal polarization is rotated counterclockwise by 45° by the second Faraday rotator 33 to become a second-path rotated sub-optical pulse with 45° polarization, and is transmitted to the 90°-rotating half-wave plate through the free-space optical path. After the transmission, the polarization state of the second-path rotated sub-optical pulse is changed to 135°. Then, the second-path rotated sub-optical pulse is transmitted to the first Faraday rotator 32 through the free-space optical path. When the second-path rotated sub-optical pulse is input into the first Faraday rotator 32, the polarization state of the second-path rotated sub-optical pulse is 135°. After the second-path rotated sub-optical pulse passes through the first Faraday rotator 32, the polarization state of the second-path rotated sub-optical pulse is rotated counterclockwise by 45°, and the polarization state of the second-path rotated sub-optical pulse is changed to 180°, i.e. horizontal polarization. The second-path rotated sub-optical pulse is input into the polarization beam splitter 31 from the port B of the polarization beam splitter 31, and is transmitted to the port D. The first-path rotated sub-optical pulse with vertical polarization reflected to the port D and the second-path rotated sub-optical pulse with horizontal polarization transmitted to the port D are combined and output. In addition, the phase difference between the two combined rotated sub-optical pulses can be modulated by the phase modulator 112, so that the polarization state of the combined optical pulse can be modulated.

[0090] In an embodiment of the present application, the phase modulator 112 comprises a forward input optical port E and a reverse input optical port F. The phase modulator 112 is configured to modulate the phase of at least one rotated sub-optical pulse based on a modulation signal, so that a preset phase difference is generated between the two rotated sub-optical pulses.

[0091] In an embodiment of the present application, the transmission optical paths (the second transmission optical path 34) connected to the phase modulator 112 are all coupled with the slow axis of the forward input optical port and the slow axis of the reverse input optical port of the phase modulator 112, or are all coupled with the fast axis of the forward input optical port and the fast axis of the reverse input optical port of the phase modulator 112.

[0092] In addition, it can be understood that the phase modulator 112 further comprises an electrical port for receiving a modulation signal.

[0093] In an embodiment of the present application, the phase modulator 112 can effectively modulate the spin sublight pulses input from the forward input optical port and the backward input optical port when a low-frequency modulation signal (for example, a modulation signal with a frequency less than 1 GHz) is applied. When a high-frequency modulation signal (for example, a modulation signal with a frequency not less than 10 GHz) with a frequency higher than a specified threshold is applied, the phase modulator 112 works in a non-reciprocal state, and the ratio of the modulation efficiency of the spin sublight pulses input from the forward input optical port to the modulation efficiency of the spin sublight pulses input from the backward input optical port is greater than a preset threshold, that is, only the spin sublight pulses input from the forward input optical port are effectively phase-modulated, and the spin sublight pulses input from the backward input optical port are not effectively phase-modulated, which can also be regarded as not being modulated. In addition, when a high-frequency modulation signal with a frequency higher than the specified threshold is applied, at the same time, the phase modulator 112 can have multiple spin sublight pulses input from the forward input optical port and multiple spin sublight pulses input from the backward input optical port. The preset threshold can be 10 decibels.

[0094] In an embodiment of the present application, the second transmission optical path 34 connected to the phase modulator 112 is coupled to the slow axis of the forward input optical port and the slow axis of the backward input optical port of the phase modulator 112, or is coupled to the fast axis of the forward input optical port and the fast axis of the backward input optical port of the phase modulator 112.

[0095] In an embodiment of the present application, multiple phase modulators 112 can be arranged on the second transmission optical path 112. The modulation modes of the multiple phase modulators 112 can include a single modulation mode and a combined modulation mode. The single modulation mode can mean that one of the multiple phase modulators 112 performs phase modulation alone, and the other phase modulators 112 act as backup modulators, and in the case of damage to one phase modulator, another phase modulator is enabled. The combined modulation mode can mean that the multiple phase modulators 112 cooperatively perform phase modulation.

[0096] In an embodiment of the present application, the multiple phase modulators 112 can be connected in various ways, for example, in forward series, in reverse series, or in mixed forward and reverse series.

[0097] In the case of forward series connection of the multiple phase modulators 112, the phase difference between the first spin sublight pulses and the second spin sublight pulses modulated by the multiple phase modulators 112 is equal to the sum of the phases modulated by the multiple phase modulators 112.

[0098] In the case of reverse series connection of the two phase modulators 112, the phase difference between the first spin sublight pulses and the second spin sublight pulses modulated by the two phase modulators 112 is equal to the difference between the phases modulated by the two phase modulators 112.

[0099] In the case of the plurality of phase modulators 112 being connected in series in the forward direction or in the reverse direction, the phase difference between the first and second rotated sub light pulses modulated by the plurality of phase modulators 112 is equal to the phase mixing operation result of the plurality of phase modulators 112.

[0100] In an embodiment of the present application, when the first and second phase modulators 112 modulate the same rotated sub light pulse, the phase difference between the first and second rotated sub light pulses modulated by the phase modulators is equal to the sum of the phase modulated by the first phase modulator 112 and the phase modulated by the second phase modulator 112.

[0101] In another embodiment of the present application, when the first phase modulator 112 modulates one of the first and second rotated sub light pulses and the second phase modulator 112 modulates the other of the first and second rotated sub light pulses, the phase difference between the first and second rotated sub light pulses modulated by the phase modulators is equal to the difference between the phase modulated by the first phase modulator 112 and the phase modulated by the second phase modulator 112.

[0102] The phases modulated by the plurality of phase modulators 112 on the first and second rotated sub light pulses can be determined according to the requirements of polarization encoding in the quantum communication protocol.

[0103] Based on this, when there are a plurality of phase modulators, the types of the phases modulated by each phase modulator 112 can be less than the required modulated phases in the quantum communication protocol.

[0104] For example, the required types of the modulated phases in the quantum communication protocol BB84 are 0°, 90°, 180° or 270°, and two phase modulators 112 are provided. In the case of being connected in series in the forward direction, the phase modulated by the first phase modulator 112 can be 0° or 90°, and the phase modulated by the second phase modulator 112 can be 0° or 180°. In the case of being connected in series in the reverse direction, the phase modulated by the first phase modulator 112 can be 0° or 180°, and the phase modulated by the second phase modulator 112 can be 0° or 90°.

[0105] In this way, the combination of the plurality of phase modulators 112 not only can realize polarization state control, but also can reduce the types of the phases modulated by a single phase modulator, thereby reducing the difficulty of implementing the phase modulator driver.

[0106] In some embodiments, the first and second rotator light pulses are transmitted through a phase modulator 112 at the same time. In this way, by passing through the same phase modulator at the same time, it can be ensured that the two rotator light pulses can be modulated by the same modulation signal, thereby helping to reduce the phase drift caused by environmental interference and improving the accuracy and reliability of the device.

[0107] In some embodiments, the polarization encoding unit 100 comprises at least one polarization operation module 110 and a first quarter wave plate and a second quarter wave plate. The first quarter wave plate is arranged before the input port of the first polarization operation module in the at least one polarization operation module, and the second quarter wave plate is arranged after the output port of the last polarization operation module in the at least one polarization operation module.

[0108] An embodiment of the present application relates to the first quarter wave plate for converting the input light pulse comprising the left circularly polarized component and the right circularly polarized component into the light pulse comprising two orthogonal linearly polarized components. The second quarter wave plate is used to convert the combined light pulse comprising two orthogonal linearly polarized components into the light pulse comprising the left circularly polarized component and the right circularly polarized component. In this way, the adjustable phase delay of the left and right circularly polarized states of light can be realized, that is, the adjustable circular birefringence function is realized.

[0109] The structure composed of the at least one polarization operation module 110, the first quarter wave plate and the second quarter wave plate is also a kind of adjustable circular birefringence module, which can modulate the polarization state of the input light pulse and realize the function of polarization encoding.

[0110] In some embodiments, the angle between one of the two eigenpolarization states of the first quarter wave plate 120 and one of the two eigenpolarization states of the polarization beam splitter of the first polarization operation module 110 is 45°+c·90°. In some embodiments, the angle between one of the two eigenpolarization states of the first quarter wave plate 120 and one of the two eigenpolarization states of the polarization beam splitter of the first polarization operation module 110 is 45°+c·90°.

[0111] In some embodiments, the angle between one of the two eigenpolarization states of the second quarter wave plate 130 and one of the two eigenpolarization states of the polarization beam splitter of the last polarization operation module 110 is 45°+d·90°, where c and d are integers. In some embodiments, the angle between one of the two eigenpolarization states of the second quarter wave plate 130 and one of the two eigenpolarization states of the polarization beam splitter of the last polarization operation module 110 is 45°+d·90°, where c and d are integers.

[0112] Taking the polarization encoding unit 100 comprising one polarization operation module 110 as an example, Figure 6 a specific structure diagram of another polarization encoding unit provided by an embodiment of the present application is shown, as Figure 6 shown, the first quarter wave plate 120 is arranged before the first port A of the polarization beam splitter 31. The second quarter wave plate 130 is arranged after the fourth port D of the polarization beam splitter 31.​​

[0113] one of the two eigenpolarizations of the first quarter wave plate 120 one of the two eigenpolarizations of the polarization beam splitter of the polarization operation module 110 the included angle of which is 45°+c·90°.

[0114] one of the two eigenpolarizations of the second quarter wave plate one of the two eigenpolarizations of the polarization beam splitter of the polarization operation module 110 the included angle of which is 45°+d·90°, where c and d are integers.

[0115] In the above embodiment, the first port A of the polarization beam splitter 31 receives the light pulse containing the two orthogonal linear polarization components converted by the first quarter wave plate 120, and the polarization beam splitter 31 splits the light pulse containing the two orthogonal linear polarization components into two sub light pulses, i.e., a first sub light pulse and a second sub light pulse. The first sub light pulse is output from the second port B, passes through the first Faraday rotator 32, and is transmitted along the clockwise direction of the second transmission light path, passes through the phase modulator 112 and the second Faraday rotator 33, and is input into the polarization beam splitter 31 from the third port C. The second sub light pulse is output from the third port C, passes through the second Faraday rotator 33, and is transmitted along the counterclockwise direction of the second transmission light path, passes through the phase modulator 112 and the first Faraday rotator 32, and is input into the polarization beam splitter 31 from the second port B. The polarization beam splitter 31 combines the two sub light pulses with a phase difference and outputs from the fourth port D. The light pulse output from the fourth port D is converted into a light pulse containing a left-handed circular polarization component and a right-handed circular polarization component by the second quarter wave plate 130.

[0116] In some embodiments, when the polarization encoding unit 100 includes at least two polarization operation modules 110, the included angle between the eigenpolarizations of two adjacent polarization operation modules 110 is l·22.5°, where l is an integer.

[0117] In an embodiment of the present application, when the included angle between the eigenpolarizations of two adjacent polarization operation modules 110 is l·22.5°, the included angle between the eigenpolarizations of the two polarization operation modules 110 can be realized by rotating at least one of the two polarization control light paths.

[0118] In another embodiment of the present application, the polarization encoding unit 100 further includes a polarization state rotator. The polarization state rotator is arranged between the two polarization operation modules 110, and the included angle between the eigenpolarizations of the two polarization control light paths is adjusted by the polarization state rotator.

[0119] In yet another embodiment of the present application, the angle between the eigen polarization states of the two polarization operation modules 110 can be achieved by rotating at least one of the two polarization control optical paths and by adjusting the polarization state rotators in coordination.

[0120] In yet another embodiment of the present application, the polarization encoding unit 100 further comprises two polarization state rotators. The two polarization state rotators are respectively arranged at the front end and the rear end of one of the two polarization operation modules 110, and the angle between the eigen polarization states of the two polarization control optical paths is adjusted by the two polarization state rotators.

[0121] In one example, one of the two polarization state rotators achieves a polarization state rotation angle γ, and the other of the two polarization state rotators achieves a polarization state rotation angle -γ.

[0122] In some embodiments, Figure 7 A specific structure of another polarization encoding unit 100 provided by an embodiment of the present application is shown in a specific structure schematic diagram as shown in Figure 7 As shown, the polarization encoding unit 100 can include at least one polarization operation module 110 and at least one adjustable birefringence module 140. The at least one adjustable birefringence module 140 is in series with the at least one polarization operation module 110.

[0123] It should be noted that the adjustable birefringence module 140 can be arranged before the polarization operation module 110, or arranged after the polarization operation module 110, or arranged between the two polarization operation modules 110. The polarization operation module 110 can be arranged between the two adjustable birefringence modules 140.

[0124] The adjustable birefringence module 140 involved in the present application is a functional module that controls the phase delay of two orthogonal polarization states of light. The structure of the adjustable birefringence module can be the same as that of the polarization operation module 110, or can be different from that of the polarization operation module 110.

[0125] The adjustable birefringence module 140 can be a functional module that controls the phase delay of two orthogonal polarization states of light by adjusting the birefringence size or the principal axis through an external field (electric field, magnetic field, stress), or a functional module that can modulate the phase of different polarization states formed by the combination of optical devices.

[0126] In an embodiment of the present application, the adjustable birefringence module 140 is an adjustable linear birefringence module or an adjustable circular birefringence module. The adjustable linear birefringence module is a functional module that controls the phase delay of two orthogonal linear polarization states of light. The adjustable circular birefringence module is a functional module that controls the phase delay of left-handed circular polarization state and right-handed circular polarization state of light.

[0127] In an embodiment of the present application, when the polarization encoding unit 100 comprises at least one polarization operation module 110 and one adjustable linear birefringence module, the angle between the polarization operation module 110 in series with the adjustable linear birefringence module and the eigenpolarization state of the adjustable linear birefringence module is also: l·22.5°.

[0128] In some embodiments, one polarization operation module 110, the first quarter wave plate 120 and the second quarter wave plate 130 can realize the function of an adjustable circular birefringence module. The polarization operation module 110 can realize the function of an adjustable linear birefringence.

[0129] In an embodiment of the present application, the polarization encoding unit 100 comprises one polarization operation module 110, the first quarter wave plate 120, the second quarter wave plate 130 and at least one adjustable linear birefringence module.

[0130] The polarization operation module 110 and the arrangement of the two quarter wave plates are consistent with the arrangement of the polarization operation module 110 and the first quarter wave plate and the second quarter wave plate as described above, which will not be repeated here.

[0131] The adjustable linear birefringence module can be arranged before the first quarter wave plate 120 or arranged after the second quarter wave plate 130, as shown in Figures 8 to 9 .

[0132] In an embodiment of the present application, the polarization encoding unit 100 comprises one polarization operation module 110, the first quarter wave plate 120, the second quarter wave plate 130 and at least one adjustable circular birefringence module.

[0133] The adjustable circular birefringence module can be arranged before the first quarter wave plate 120 or arranged after the second quarter wave plate 130.

[0134] In an embodiment of the present application, the polarization encoding unit 100 comprises one polarization operation module 110, the first quarter wave plate 120, the second quarter wave plate 130, at least one adjustable circular birefringence module and at least one adjustable linear birefringence module.

[0135] The adjustable circular birefringence module is arranged before the first quarter wave plate 120 or after the second quarter wave plate 130. The adjustable linear birefringence module can be arranged between the first quarter wave plate and the adjustable circular birefringence module, between the second quarter wave plate and the adjustable circular birefringence module, between the polarization operation module 110 and the first quarter wave plate or between the polarization operation module 110 and the second quarter wave plate.

[0136] In an embodiment of the present application, the polarization state of the optical pulse input into the polarization encoding unit 100 (i.e. the input optical pulse) is

[0137] In another embodiment of the present application, the polarization state of the optical pulse input into the polarization encoding unit 100 (i.e. the input optical pulse) is

[0138] In some of the above embodiments, n is an integer, and are the two eigenpolarization states of the first polarization beam splitter 31 in the polarization encoding unit 100, and β is an arbitrary value between 0 and 2π.

[0139] For example, the polarization state of the optical pulse input into the polarization operation module can be 45° linear polarization, -45° linear polarization, left-handed circular polarization or right-handed circular polarization.

[0140] In some embodiments, the first optical coupling unit 200 is an optical coupler, and the second optical coupling unit 500 is an optical switch. The optical coupler can be a free-space crystal coupler or a fiber coupler, which is used to split the optical pulse. The optical switch can be used to select the encoded quantum state transmitted through one of the optical output branches by being connected or disconnected.

[0141] Since the first port G of the first optical coupling unit 200 is connected to the output port of the polarization encoding unit 100, the second port H is connected to one end of the first transmission optical path 400, and the third port I is connected to the input port of the polarization rotation time phase encoding unit 300. Therefore, when the first optical coupling unit 200 is an optical coupler, it can be used to input the polarization encoded quantum state optical pulse output by the polarization encoding unit 100 through the first port G, and split the polarization encoded quantum state optical pulse into two sub optical pulses, which are respectively input into the first optical output branch and the second optical output branch through the third port I and the second port H.

[0142] In the present embodiment, the second optical coupling unit 500 is used to select the polarization encoded quantum state optical pulse output by the second optical output branch or the time phase encoded quantum state optical pulse output by the first optical output branch according to the quantum communication encoding control instruction. In an embodiment, the second optical coupling unit 500 is an optical switch, which can be used to flexibly switch the connection between the second optical output branch and the first optical output branch according to the quantum communication encoding control instruction, so as to select the polarization encoded quantum state optical pulse output by the second optical output branch or the time phase encoded quantum state optical pulse output by the first optical output branch.

[0143] In the above embodiment, the light pulses of the polarization encoded quantum state are split into two paths by the first light coupling unit, and then sent into the first light output branch and the second light output branch respectively. The second light coupling unit can switch the connected light output branch according to the encoding requirement of the quantum communication system. In this way, the quantum states with different encoding modes can be selectively outputted, and the flexibility and adaptability of the quantum communication system are improved. The advantages of the two encoding modes can be fully utilized to ensure the adaptability of the quantum state to the communication channel and improve the security and reliability of the quantum communication system. In addition, new encoding modes can be integrated to support new communication protocols and higher performance quantum state transmission.

[0144] In some other embodiments, the first light coupling unit 200 is an optical switch, and the second light coupling unit 500 is an optical switch.

[0145] Since the first port G of the first light coupling unit 200 is connected to the output port of the polarization encoding unit 100, the second port H is connected to the input port of the first transmission light path 400, and the third port I is connected to the input port of the polarization and time phase encoding unit 300. Therefore, when the first light coupling unit 200 is an optical switch, the light pulses of the polarization encoded quantum state can be selectively inputted into the first light output branch or the second light output branch based on the quantum communication encoding control instruction.

[0146] In an embodiment of the present application, the first light coupling unit 200 can select the corresponding light output branch to be connected according to the quantum communication encoding control instruction, and input the light pulses of the polarization encoded quantum state outputted by the polarization encoding unit 100 into the corresponding light output branch. That is, when the quantum communication encoding control instruction is an instruction corresponding to outputting the polarization encoded quantum state, the first light coupling unit 200 selects the second light output branch to be connected, and inputs the light pulses of the polarization encoded quantum state into the second light output branch. When the quantum communication encoding control instruction is an instruction corresponding to outputting the time phase encoded quantum state, the first light coupling unit 200 selects the first light output branch to be connected, and inputs the light pulses of the polarization encoded quantum state into the first light output branch.

[0147] In the present embodiment, the second light coupling unit 500 is an optical switch, which can connect the first light output branch or the second light output branch according to the quantum communication encoding control instruction, that is, connect the first light output branch outputting the light pulses of the time phase encoded quantum state, or connect the second light output branch outputting the light pulses of the polarization encoded quantum state.

[0148] It should be noted that, in general, the second optical coupling unit 500 selects the same optical output branch as the first optical coupling unit 200. Specifically, the first optical coupling unit 200 and the second optical coupling unit 500 select the same optical output branch based on the quantum communication encoding control instruction, that is, the first optical coupling unit 200 selects the first optical output branch based on the quantum communication encoding control instruction, and the second optical coupling unit 500 also selects the first optical output branch based on the quantum communication encoding control instruction. When the first optical coupling unit 200 and the second optical coupling unit 500 are both connected to the first transmission light path, the second optical coupling unit 500 outputs the time-phase encoding quantum state light pulse transmitted by the first optical output branch.

[0149] Alternatively, the first optical coupling unit 200 selects the second optical output branch based on the quantum communication encoding control instruction, and the second optical coupling unit 500 also selects the second optical output branch based on the quantum communication encoding control instruction. When the first optical coupling unit 200 and the second optical coupling unit 500 are both connected to the second optical output branch, the second optical coupling unit 500 outputs the polarization encoding quantum state light pulse transmitted by the second optical output branch.

[0150] In the above embodiment, the first optical coupling unit 200 and the second optical coupling unit 500 can be connected to the same optical output branch according to the quantum communication encoding control instruction, so that the encoding quantum state matching the quantum communication protocol can be output, and the flexibility and adaptability of the quantum communication system are improved. In addition, the advantages of the two encoding methods can be fully utilized to ensure the adaptability of the quantum state to the communication channel in the quantum communication process, and the security and reliability of the quantum communication system are improved. In addition, it is convenient to integrate new encoding methods, thereby supporting new communication protocols and higher performance quantum state transmission.

[0151] In some embodiments, the first optical coupling unit 200 is an optical switch, and the second optical coupling unit 500 is an optical coupler.

[0152] In the embodiment of the present application, the first optical coupling unit 200 includes one input port and two output ports. The first optical coupling unit 200 can freely switch the connected port based on the quantum communication encoding control instruction, so as to be connected to the first optical output branch or the second optical output branch.

[0153] The optical coupler corresponding to the second optical coupling unit 500 can include two input ports and one output port, and each input port can correspond to connect one optical output branch. The optical coupler is used to couple and output the time-phase encoding quantum state light pulse transmitted by the first optical output branch or the polarization encoding quantum state light pulse transmitted by the second optical output branch.

[0154] Specifically, when the first optical coupling unit 200 communicates with the first optical output branch through the output port I based on the quantum communication encoding control instruction, the first optical coupling unit 200 inputs the polarized encoded quantum state light pulse output by the polarization encoding unit 100 to the first optical output branch through the output port I. At this time, the first optical output branch inputs the polarized encoded quantum state light pulse output by the first optical coupling unit 200, and outputs the time phase encoded quantum state light pulse converted by the polarization conversion time phase encoding unit 300. The input and output of the second optical output branch are both empty. The second optical coupling unit 500 couples the outputs of the two optical output branches, and the output coupling quantity is the time phase encoded quantum state light pulse of the first optical output branch.

[0155] When the first optical coupling unit 200 communicates with the second optical output branch through the output port H based on the quantum communication encoding control instruction, the first optical coupling unit 200 inputs the polarized encoded quantum state light pulse output by the polarization encoding unit 100 to the second optical output branch through the output port H. At this time, the second optical output branch receives the polarized encoded quantum state light pulse input by the first optical coupling unit 200 and outputs it, and the input and output of the first optical output branch are both empty. The second optical coupling unit 500 couples the outputs of the two optical output branches, and the output coupling quantity is the polarized encoded quantum state light pulse of the second optical output branch.

[0156] In the above embodiment, the polarization encoded quantum state can be output to the optical output branch matched with the encoding requirement of the quantum communication system through the first optical coupling unit 200, and then the quantum state required by the quantum communication system encoding can be output through the second optical coupling unit 500. In this way, the flexibility and adaptability of the quantum communication system are improved. And the advantages of the two encoding methods can be fully utilized to ensure the adaptability of the quantum state to the communication channel in the communication process and improve the security and reliability of the quantum communication system. In addition, it is convenient to integrate new encoding methods, thereby supporting new communication protocols and higher performance quantum state transmission.

[0157] In some embodiments, the polarization conversion time phase encoding unit 300 can include a third optical coupling unit, a fourth optical coupling unit, a third transmission optical path and a fourth transmission optical path. The third optical coupling unit includes at least three ports, one input port and two output ports; the fourth optical coupling unit includes at least three ports, two input ports and one output port, the two output ports of the third optical coupling unit are connected with the two input ports of the fourth optical coupling unit through the third transmission optical path and the fourth transmission optical path; the third transmission optical path and the fourth transmission optical path are not equal in optical path.

[0158] Figure 10 A specific structure schematic diagram of a quantum state encoding device provided by an embodiment of the present application is shown as follows: Figure 10As shown, the polarization encoding unit 100 includes two polarization operation modules. The polarization-to-time phase encoding unit 300 adopts the above structure.

[0159] In an embodiment of the present application, the third optical coupling unit is a polarization beam splitter, and the fourth optical coupling unit is a polarization beam combiner.

[0160] In another embodiment of the present application, the third optical coupling unit is a polarization beam splitter, and the fourth optical coupling unit is an optical coupler.

[0161] In yet another embodiment of the present application, the third optical coupling unit is an optical coupler, and the fourth optical coupling unit is a polarization beam combiner.

[0162] In yet another embodiment of the present application, the third optical coupling unit is an optical coupler, and the fourth optical coupling unit is an optical coupler, and the polarization-to-time phase encoding unit 300 further includes: two polarizers respectively arranged on the third transmission optical path and the fourth transmission optical path, and the polarization directions of the two polarizers are orthogonal to each other.

[0163] In some embodiments, the third transmission optical path or the fourth transmission optical path is a 90° twisted polarization maintaining optical fiber, or the polarization-to-time phase encoding unit 300 of the present application further includes: a 90° polarization state rotator arranged on the third transmission optical path or the fourth transmission optical path, for rotating the polarization state of the passing sub-light pulse by 90°.

[0164] In some embodiments, when the third optical coupling unit and the fourth optical coupling unit are the same polarization beam splitter, the polarization-to-time phase encoding unit 300 further includes: two mirrors, two output ports of the polarization beam splitter are respectively connected with one end of the third transmission optical path and one end of the fourth transmission optical path, and the two mirrors are respectively connected with the other end of the third transmission optical path and the other end of the fourth transmission optical path.

[0165] In some embodiments, the two mirrors can be polarization state rotating mirrors.

[0166] In one embodiment, when the polarization beam splitter includes three ports, the input port can also serve as an output port of the polarization-to-time phase encoding unit 300, for outputting the polarization-to-time phase encoded light pulse; at this time, the polarization-to-time phase encoding unit further includes an optical coupling unit arranged in front of the polarization beam splitter, and the optical coupling unit can be an optical coupler or an optical circulator.

[0167] In another embodiment, when the two mirrors are polarization state rotation mirrors, for example, the two mirrors are quarter-wave plate mirrors or 90° Faraday rotation mirrors, the polarization beam splitter can further comprise a fourth port; the fourth port of the polarization beam splitter is an output port of the polarization-to-time-phase encoding unit 300.

[0168] In some embodiments, the third optical coupling unit and the fourth optical coupling unit are the same optical coupler, and the polarization-to-time-phase encoding unit 300 further comprises: two mirrors and two polarizers, two output ports of the optical coupler are connected to one end of the third transmission light path and one end of the fourth transmission light path respectively, the two mirrors are connected to the other end of the third transmission light path and the other end of the fourth transmission light path respectively; the two polarizers are arranged on the third transmission light path and the fourth transmission light path respectively, and the polarizing directions of the two polarizers are orthogonal to each other.

[0169] In some embodiments, when the optical coupler comprises three ports, the input port can also serve as an output port of the polarization-to-time-phase encoding unit 300, for outputting the polarization-to-time-phase encoded light pulse; at this time, the polarization-to-time-phase encoding unit 300 further comprises an optical coupling unit arranged in front of the optical coupler, and the optical coupling unit can be an optical coupler or an optical circulator.

[0170] In some embodiments, the optical coupler can further comprise a fourth port; the fourth port of the optical coupler is an output port of the polarization-to-time-phase encoding unit 300.

[0171] In some embodiments, the polarization-to-time-phase encoding unit 300 can further comprise a polarizer; the polarizer is arranged at the output port of the polarization-to-time-phase encoding unit 300, for polarizing the output light pulse.

[0172] In any of the above embodiments, the quantum state encoding device of the present application further comprises: a quarter-wave plate and / or a polarization state rotator arranged between the polarization encoding unit 100 and the polarization-to-time-phase encoding unit 300, and the polarization state rotator is a half-wave plate or a Faraday rotator.

[0173] In some embodiments, according to the requirements of quantum communication, the quantum state encoding device of the present application can also be used to realize the quantum state decoding process.

[0174] According to the present application, a quantum state encoding method is provided, and the method is realized by using the quantum state encoding device described above.

[0175] In another aspect, the present application provides a software-defined quantum communication system, Figure 11A structure schematic diagram of a software-defined quantum communication system provided by an embodiment of the present application is shown in FIG. 11. As shown in FIG. 11, the software-defined quantum communication system 1100 can include the quantum state encoding device 1101 and the encoding control device 1102 described above; the encoding control device 1102 is configured to generate a quantum communication encoding control instruction based on a quantum communication system encoding requirement, and send the quantum state encoding device 1101. Figure 11

[0176] The quantum communication system can be a discrete variable quantum communication system or a continuous variable quantum communication system, and can include a BB84 protocol, a reference frame independent protocol, an MDI protocol, a TF protocol, and the like.

[0177] It should be understood that the specific features, operations, and details described above with respect to the device of the present application can be similarly applied to the method and system of the present application, or vice versa.

[0178] 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.

[0179] 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 replacement for part 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 quantum state encoding device, characterized in that: include: A polarization encoding unit, a first optical coupling unit, a polarization-to-temporal phase encoding unit, a first transmission optical path, and a second optical coupling unit; The polarization encoding unit comprises an input port and an output port, wherein the polarization encoding unit is configured to input a light pulse through the input port, generate a light pulse in a polarization-encoded quantum state based on the input light pulse, and output the light pulse through the output port; The polarization encoding unit includes at least one polarization operation module, each of which includes a polarization control optical path and at least one phase modulator arranged in a second transmission optical path of the polarization control optical path; The polarization control optical path is used to perform polarization splitting and polarization rotation on the input optical pulse to obtain a first path of rotating sub-optical pulses and a second path of rotating sub-optical pulses; The at least one phase modulator is configured to perform phase modulation on at least one of the first rotating optical sub-pulse and the second rotating optical sub-pulse based on a modulation signal, so as to generate a preset phase difference between the first rotating optical sub-pulse and the second rotating optical sub-pulse; The polarization control optical path is further used to perform polarization rotation and combine the first rotating sub-light pulse and the second rotating sub-light pulse that generate the phase difference, and output the polarization-encoded quantum state optical pulse generated after the combination; The first optical coupling unit comprises an input port and two output ports, namely a first port, a second port and a third port, wherein the first port is connected to the output port of the polarization coding unit; The second optical coupling unit comprises two input ports and one output port, namely a fourth port, a fifth port and a sixth port; The polarization-to-time phase encoding unit includes an input port and an output port, and is used to perform time phase encoding conversion on the input polarization-encoded quantum state light pulse and output the time phase encoded quantum state light pulse; The third port of the first optical coupling unit is connected to the input port of the polarization-to-temporal phase encoding unit, and the output port of the polarization-to-temporal phase encoding unit is connected to the fifth port of the second optical coupling unit to form a first optical output branch; The second port of the first optical coupling unit is connected to the fourth port of the second optical coupling unit through the first transmission optical path to form a second optical output branch; The first optical coupling unit is configured to input the optical pulse of the polarization-encoded quantum state output by the polarization encoding unit into the first optical output branch and / or the second optical output branch according to a quantum communication coding control instruction, wherein the quantum communication coding control instruction is determined according to a coding requirement of a quantum communication system; The sixth port of the second optical coupling unit is the output port of the quantum state encoding device, which is used to output the polarization-encoded quantum state optical pulse transmitted by the second optical output branch or the time phase-encoded quantum state optical pulse transmitted by the first optical output branch according to the quantum communication coding control instruction.

2. The device according to claim 1, characterized in that The polarization control optical path includes a polarization beam splitter, a first Faraday rotator, a second Faraday rotator, and a second transmission optical path; The polarization beam splitter is connected to the first Faraday rotator and the second Faraday rotator respectively, and the first Faraday rotator and the second Faraday rotator are connected via a second transmission optical path; The polarization beam splitter is used to receive an input optical pulse and polarization-split it into a first optical pulse and a second optical pulse; The first Faraday rotator is used to perform polarization rotation on the first path of sub-light pulses and output the first path of rotated sub-light pulses; The second Faraday rotator is used to perform polarization rotation on the second path of sub-light pulses and output the second path of rotated sub-light pulses; The first Faraday rotator is further configured to perform polarization rotation on the second rotating optical sub-pulse output by the at least one phase modulator to obtain a polarization-rotated second rotating optical sub-pulse; The second Faraday rotator is further configured to perform polarization rotation on the first rotating optical sub-pulse output by the at least one phase modulator to obtain a polarization-rotated first rotating optical sub-pulse; The polarization beam splitter is further used to combine the first polarization-rotated rotating sub-light pulse and the second polarization-rotated rotating sub-light pulse that generate a phase difference, and output the polarization-encoded quantum state light pulse generated after the combination.

3. The device according to claim 2, characterized in that 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 the input port of the polarization control light path, and the fourth port of the polarization beam splitter is the output port of the polarization control light path; The second port and the third port of the polarization beam splitter are connected to the port on the first side of the first Faraday rotator and the port on the first side of the second Faraday rotator, respectively; The port on the second side of the first Faraday rotator and the port on the second side of the second Faraday rotator are connected through the second transmission optical path.

4. The device according to claim 1, characterized in that The first Faraday rotator is a 45°+a·90° Faraday rotator, and the second Faraday rotator is a 45°+b·90° Faraday rotator, wherein a and b are integers.

5. The device according to claim 4, characterized in that The polarization direction of the first rotated sub-light pulse outputted from the second port of the first Faraday rotator is perpendicular or parallel to the polarization direction of the second rotated sub-light pulse outputted from the second port of the second Faraday rotator.

6. The device according to claim 5, characterized in that The second transmission optical path is a free space optical path or a polarization-maintaining optical fiber.

7. The device according to claim 6, characterized in that The first path of rotated sub-light pulses and the second path of rotated sub-light pulses outputted from the port on the second side of the first Faraday rotator and the port on the second side of the second Faraday rotator are both coupled to the slow axis of the polarization-maintaining fiber or are both coupled to the fast axis of the polarization-maintaining fiber.

8. The device according to claim 6, characterized in that When the first path of rotated sub-light pulses and the second path of rotated sub-light pulses output from the port on the second side of the first Faraday rotator and the port on the second side of the second Faraday rotator are respectively coupled to different axes of the polarization-maintaining optical fiber, the polarization control optical path further includes a 90° polarization rotator, which is arranged in the second transmission optical path. The 90° polarization rotator is a half-wave plate or a 90° Faraday rotator.

9. The device according to claim 6, characterized in that When the second transmission optical path is a free-space optical path, and the polarization state direction of the first rotated sub-light pulse output by the second port of the first Faraday rotator is perpendicular to the polarization state direction of the second rotated sub-light pulse output by the second port of the second Faraday rotator, the polarization control optical path further includes a 90° polarization rotator, which is arranged in the second transmission optical path, and the 90° polarization rotator is a half-wave plate or a 90° Faraday rotator.

10. The device according to any one of claims 1 to 5, characterized in that: The polarization operation unit further includes a first quarter-wave plate and a second quarter-wave plate; the first quarter-wave plate is arranged before the input port of the first polarization operation module in the at least one polarization operation module, and the second quarter-wave plate is arranged after the output port of the last polarization operation module in the at least one polarization operation module.

11. The device according to claim 10, characterized in that One of the two eigenpolarization states of the first quarter-wave plate One of the two eigenpolarization states of the polarization beam splitter of the first polarization operation module The angle between them is 45° + c·90°; One of the two eigenpolarization states of the second quarter-wave plate One of the two eigenpolarization states of the polarization beam splitter of the last polarization operation module The angle between them is 45°+d·90°, where c and d are integers.

12. The device according to claim 1, characterized in that The polarization encoding unit further comprises at least one adjustable birefringence module, which is connected in series with the at least one polarization operation module. The adjustable birefringence module is an adjustable linear birefringence module or an adjustable circular birefringence module.

13. The device according to claim 1 or 12, characterized in that When the polarization encoding unit includes at least two polarization operation modules, the angle between the intrinsic polarization states of the two adjacent polarization operation modules is: 1·22.5°, where 1 is an integer; Alternatively, when the polarization encoding unit includes at least one polarization operation module and one adjustable linear birefringence module, the angle between the intrinsic polarization state of the polarization operation module connected in series with the adjustable linear birefringence module and the adjustable linear birefringence module is: 1·22.5°, where 1 is an integer.

14. The device according to claim 13, characterized in that The angle between the intrinsic polarization states of the two adjacent polarization operation modules is achieved by rotating at least one of the two polarization control light paths; and / or The polarization encoding unit further includes a polarization state rotator, which is arranged between the two polarization operation modules and is used to adjust the angle between the intrinsic polarization states of the two polarization control light paths.

15. The device according to claim 1 or 12, characterized in that The polarization state of the optical pulse input to the polarization encoding unit is Alternatively, the polarization state of the optical pulse input to the polarization encoding unit is Where n is an integer, and are the two eigenpolarization states of the first polarization beam splitter in the polarization encoding unit, and β is any value from 0 to 2π.

16. The device according to claim 1, characterized in that The first optical coupling unit is an optical coupler, and the second optical coupling unit is an optical switch.

17. The device according to claim 1, characterized in that The first optical coupling unit is an optical switch, and the second optical coupling unit is an optical switch or an optical coupler.

18. A quantum state encoding method, characterized in that: Quantum state encoding is achieved by applying the quantum state encoding device described in any one of claims 1 to 17.

19. A software-defined quantum communication system, characterized in that: A quantum state encoding device and an encoding control device comprising any one of claims 1 to 17; The coding control device is used to generate quantum communication coding control instructions based on the coding requirements of the quantum communication system and send them to the quantum state coding device.

Images