High-speed polarization encoding device, method and quantum communication system

Abstract

The application provides a high-speed polarization encoding device, method and quantum communication system. The device comprises: an optical beam splitter, which is used for splitting one light pulse input from a first port into two sub-light pulses; a first polarizer, which is used for polarizing the first sub-light pulse output from a second port of the optical beam splitter to output a first polarized sub-light pulse; a second polarizer, which is used for polarizing the second sub-light pulse output from a third port of the optical beam splitter to output a second polarized sub-light pulse; a first phase modulator, which is used for phase-modulating the first polarized sub-light pulse and the second polarized sub-light pulse at different modulation efficiencies based on a modulation signal to obtain a first modulated sub-light pulse and a second modulated sub-light pulse; and the optical beam splitter is further used for combining the two modulated sub-light pulses and outputting the two modulated sub-light pulses through the first port or a fourth port. The application realizes the purpose of high-stable encoding of a polarization quantum state at a speed of 10GHz or more.

Description

TECHNICAL FIELD

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

[0002] The physical implementation of a quantum communication system, such as the physical implementation of quantum key distribution and quantum direct communication, needs to encode and decode quantum states. At present, the rate of encoding and decoding of a quantum communication system in practical application is mainly in the order of 100 megahertz (MHz) and 1 gigahertz (GHz). For the problem of polarization quantum state coding implementation at a speed of 10 GHz or higher, because a phase modulator itself has a certain length, when modulating a high-speed quantum state, multiple forward and reverse light pulses will be transmitted in it at the same time, and a high-speed modulation pulse needs to be generated which is narrow enough, so it is difficult to modulate two light pulses respectively by time division, or to modulate only one light pulse, which limits the application of time division in high-speed coding. At the same time, it is also difficult to modulate the quantum state by connecting two phase modulators to reduce the difficulty of designing the modulation driving circuit and improve the precision of the modulation phase. Therefore, it is difficult to implement the traditional time division method to modulate two light pulses respectively or to modulate only one light pulse at such a high rate.

[0003] Therefore, how to realize polarization quantum state coding at a speed of 10 GHz or higher has become a key problem to be solved in quantum communication applications. SUMMARY

[0004] Therefore, the present application provides a high-speed polarization coding device, a method and a quantum communication system to solve the technical problems in the background art.

[0005] In a first aspect, the embodiments of the present application provide a high-speed polarization coding device, which comprises an optical beam splitter, a first polarizer, a second polarizer, a transmission optical path, a first phase modulator and a first high-speed driver; the first high-speed driver is connected to the first phase modulator and is used to apply a modulation signal with a frequency higher than a specified threshold to the first phase modulator.

[0006] The optical beam splitter comprises a first port, a second port, a third port and a fourth port. The optical beam splitter receives a light pulse through the first port, splits the light pulse into a first light pulse and a second light pulse, and outputs the first light pulse and the second light pulse through the second port and the third port respectively. The polarization state of the first light pulse is the same as that of the second light pulse. The transmission optical path is used to connect the first polarizer and the second polarizer. The first polarizer is connected to the second port of the optical beam splitter and is used to polarize the first light pulse output from the second port and output a first polarized light pulse to the transmission optical path. The polarization state of the first polarized light pulse is The second polarizer is connected with the third port of the optical splitter, and is configured to polarize the second sub-light pulse output from the third port, and output a second polarized sub-light pulse to the transmission light path, wherein a polarization state of the second polarized sub-light pulse is The The are orthogonal to each other.

[0007] The first phase modulator is arranged in the transmission light path, and is configured to perform phase modulation on the first polarized sub-light pulse and the second polarized sub-light pulse at different modulation efficiencies based on a modulation signal, to obtain a first modulated sub-light pulse and a second modulated sub-light pulse; wherein a ratio of the modulation efficiency on the first polarized sub-light pulse to the modulation efficiency on the second polarized sub-light pulse is not less than a preset threshold, so that the first modulated sub-light pulse and the second modulated sub-light pulse have a phase difference.

[0008] The first modulated sub-light pulse and the second modulated sub-light pulse are output from different ports of the first phase modulator respectively, and are transmitted in different directions along the transmission light path, and then input to the third port and the second port of the optical splitter through the second polarizer and the first polarizer respectively.

[0009] The optical splitter is further configured to combine the first modulated sub-light pulse input from the third port and the second modulated sub-light pulse input from the second port, and output the combined light pulse through the first port or the fourth port.

[0010] In a second aspect, the embodiments of the present application provide a high-speed polarization encoding method, which can include: receiving an input optical pulse through a first port of an optical beam splitter; splitting the received input optical pulse into a first sub-optical pulse and a second sub-optical pulse through the optical beam splitter; causing the first sub-optical pulse to be output from a second port of the optical beam splitter, to pass through a first polarizer to be polarized, and to obtain a first polarized sub-optical pulse, and causing the second sub-optical pulse to be output from a third port of the optical beam splitter, to pass through a second polarizer to be polarized, and to obtain a second polarized sub-optical pulse; receiving the first polarized sub-optical pulse and the second polarized sub-optical pulse through different ports of a first phase modulator, and performing phase modulation on the first polarized sub-optical pulse and the second polarized sub-optical pulse at different modulation efficiencies based on a modulation signal, to obtain a first modulated sub-optical pulse and a second modulated sub-optical pulse; wherein a ratio of the modulation efficiency on the first polarized sub-optical pulse to the modulation efficiency on the second polarized sub-optical pulse is not less than a preset threshold, so that the first modulated sub-optical pulse and the second modulated sub-optical pulse have a phase difference; causing the first modulated sub-optical pulse and the second modulated sub-optical pulse to be output from different ports of the first phase modulator respectively, to be transmitted in different directions in a transmission optical path, to pass through the second polarizer and the first polarizer respectively, and to be input to the third port and the second port of the optical beam splitter; and combining the first modulated sub-optical pulse input from the third port and the second modulated sub-optical pulse input from the second port through the optical beam splitter, to obtain a combined optical pulse, and outputting the combined optical pulse through the first port or a fourth port.

[0011] In a third aspect, the embodiments of the present application provide a quantum communication system, which can include the high-speed polarization encoding device according to any of the embodiments of the present application.

[0012] In summary, the high-speed polarization encoding device, method and quantum communication system provided by the embodiments of the present application have at least the following beneficial effects: the light splitter is used to split one received input light pulse into two sub light pulses, and the corresponding polarizer is input from different ports, and the two sub light pulses are polarized by the polarizers with different polarization directions, and two polarized sub light pulses with different polarization states are obtained. In this way, the polarization state of the two sub light pulses can be accurately controlled by the polarizer, so that two polarized sub light pulses with stable relative phase and different polarization states are obtained. The two polarized sub light pulses are transmitted to the first phase modulator in different directions along the transmission light path, and the first phase modulator with a modulation signal with a frequency higher than a specified threshold is used to modulate the first polarized sub light pulse and the second polarized sub light pulse with different modulation efficiencies, so that effective modulation of the first polarized sub light pulse and ineffective modulation of the second polarized sub light pulse can be realized, and the first modulated sub light pulse and the second modulated sub light pulse with a phase difference are obtained. The first modulated sub light pulse and the second modulated sub light pulse are transmitted in different directions along the transmission light path and enter the different ports of the light splitter through the corresponding polarizer. The light splitter combines the two modulated sub light pulses and outputs the combined light pulse through the first port or the fourth port. In this way, the light paths of the two sub light pulses of the light splitter are completely the same when the two sub light pulses are combined, so that the light paths have a self-compensation function to environmental interference, and have the advantages of anti-interference and high stability, and the purpose of high-stable encoding of the polarization quantum state at a speed of 10GHz or higher is achieved. BRIEF DESCRIPTION OF DRAWINGS

[0013] In order to more clearly illustrate the technical solutions in the specific embodiments of the present application or 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 A schematic diagram of a high-speed polarization encoding device provided by an embodiment of the present application is shown;

[0015] Figure 2 A structural schematic diagram of another high-speed polarization encoding device provided by an embodiment of the present application is shown;

[0016] Figure 3 A structural schematic diagram of another high-speed polarization encoding device provided by an embodiment of the present application is shown;

[0017] Figure 4 A flowchart of a high-speed polarization encoding method provided by an embodiment of the present application is shown;

[0018] Figure 5 A schematic structural diagram of a quantum communication system provided in an embodiment of the present application is shown. DETAILED DESCRIPTION

[0019] In order to make the above and other features and advantages of the present application more clear, the present application is further described below with reference to the accompanying drawings. It should be understood that the specific embodiments given herein are for the purpose of explaining to those skilled in the art and are only illustrative and not restrictive.

[0020] In the following description, many specific details are set forth to provide a thorough understanding of the present application. However, it will be apparent to those skilled in the art that it is not necessary to adopt the specific details to practice the present application. In other cases, well-known steps or operations are not described in detail to avoid obscuring the present application.

[0021] On the one hand, an embodiment of the present application provides a high-speed polarization encoding device. Figure 1 A schematic diagram of a high-speed polarization encoding device provided by an embodiment of the present application is shown in FIG. Figure 1 As shown, the high-speed polarization encoding device may include an optical beam splitter 101, a first polarizer 102, a second polarizer 103, a transmission optical path 104, a first phase modulator 105, and a first high-speed driver 106. The optical beam splitter 101, the first polarizer 102, the second polarizer 103, and the transmission optical path 104 may form a Sagnac interferometer.

[0022] like Figure 1 As shown, the first high-speed driver 106 is connected to the first phase modulator 105. The first high-speed driver 106 is used to apply a modulation signal having a frequency higher than a specified threshold to the first phase modulator 105.

[0023] In one embodiment, the modulation signal higher than the specified threshold may be a high-frequency modulation voltage signal or a modulation current signal of not less than 10 GHz.

[0024] The optical beam splitter 101 includes a first port A, a second port B, a third port C, and a fourth port D. The first port A is the input port of the optical beam splitter 101. The optical beam splitter 101 receives an input optical pulse through the first port A, splits the input optical pulse into a first optical pulse and a second optical pulse, and outputs the first optical pulse and the second optical pulse through the second port B and the third port C. The polarization state of the first optical pulse and the second optical pulse is the same, and the relative phase between the first optical pulse and the second optical pulse is fixed.

[0025] It should be noted that the relative phase between the first path optical pulse and the second path optical pulse can be determined according to the performance of the optical beam splitter.

[0026] In an embodiment, the light pulses are high-speed light pulses, which refer to high repetition rate pulsed light, for example, the pulse repetition rate is 10 GHz or higher.

[0027] The second port B of the optical beam splitter 101 is connected with one end of the first polarizer 102. The second port B is used to input a light sub-pulse (for example, a first light sub-pulse) to the first polarizer 102.

[0028] The third port C of the optical beam splitter 101 is connected with one end of the second polarizer 103. The third port C is used to input a light sub-pulse (for example, a second light sub-pulse) to the second polarizer 103.

[0029] The transmission light path 104 is used to connect the first polarizer 102 and the second polarizer 103. That is, the other end of the first polarizer 102 is connected with the transmission light path 104, and the other end of the second polarizer 103 is connected with the transmission light path 104.

[0030] The first polarizer 102 is used to polarize the first light sub-pulse output from the second port B, and output a first polarized light sub-pulse to the transmission light path 104. The polarization direction of the first polarizer 102 to the first light sub-pulse is The polarization state of the first polarized light sub-pulse is

[0031] In this way, the first light sub-pulse is converted into the first polarized light sub-pulse by the first polarizer 102, and the first polarized light sub-pulse is coupled into the transmission light path 104.

[0032] The second polarizer 103 is used to polarize the second light sub-pulse output from the third port C, and output a second polarized light sub-pulse to the transmission light path 104. The polarization direction of the second polarizer 103 to the second light sub-pulse is The polarization state of the second polarized light sub-pulse is And is orthogonal to .

[0033] In this way, the second light sub-pulse is converted into the second polarized light sub-pulse by the second polarizer 103, and the second polarized light sub-pulse output by the second polarizer 103 is coupled into the transmission light path 104.

[0034] As Figure 1As shown, the first phase modulator 105 is arranged in the transmission light path 104, wherein the first phase modulator 105 is connected between the first polarizer 102 and the second polarizer 103 through the transmission light path 104. The first phase modulator 105 includes three ports, which are a fifth port E, a sixth port F and a seventh port G. The fifth port E and the sixth port F are forward input light ports and reverse input light ports of the first phase modulator 105 respectively, and the seventh port G is an electrical port. The first phase modulator 105 is arranged in the transmission light path 104, that is, the first phase modulator 105 is coupled with the transmission light path 104 through the fifth port E and the sixth port F, and is connected with the first polarizer 102 and the second polarizer 103 respectively. It should be noted that the fifth port E can be a forward input light port or a reverse input light port, and the sixth port F can be a reverse input light port or a forward input light port.

[0035] The first modulated sub-light pulse and the second modulated sub-light pulse are output from different ports of the first phase modulator 105 respectively, and are transmitted in different directions of the transmission light path 104, pass through the second polarizer 103 and the first polarizer 102 respectively, and are input into the third port C and the second port B of the optical beam splitter 101.

[0036] In an embodiment, the first sub-light pulse is output from the second port B of the optical beam splitter 101, is polarized by the first polarizer 102, and is converted into a first polarized sub-light pulse. The first polarized sub-light pulse is transmitted to the first phase modulator 105 through the fifth port E of the first phase modulator 105 in the clockwise direction of the transmission light path 104, is effectively modulated by the first phase modulator 105, and obtains the first modulated sub-light pulse. The first modulated sub-light pulse is output through the sixth port F of the first phase modulator 105 and is transmitted to the second polarizer 103 in the clockwise direction of the transmission light path 104, and is input into the third port C of the optical beam splitter 101 through the second polarizer 103.

[0037] The second sub-light pulse is output from the third port C of the optical beam splitter 101, is polarized by the second polarizer 103, and is converted into a second polarized sub-light pulse. The second polarized sub-light pulse is transmitted to the first phase modulator 105 through the sixth port F of the first phase modulator 105 in the counterclockwise direction of the transmission light path 104, is invalidly modulated by the first phase modulator 105, and obtains the second modulated sub-light pulse. The second modulated sub-light pulse is output through the fifth port E of the first phase modulator 105 and is transmitted to the first polarizer 102 in the counterclockwise direction of the transmission light path 104, and is input into the second port B of the optical beam splitter 101 through the first polarizer 102.

[0038] The seventh port G of the first phase modulator 105 is connected with the first high-speed driver 106. The first phase modulator 105 receives the modulation signal with the frequency higher than the specified threshold value applied by the first high-speed driver 106 through the seventh port G. The first phase modulator 105 is configured to perform phase modulation on the first and second polarized sub-light pulses with different modulation efficiencies based on the modulation signal, to obtain the first and second modulated sub-light pulses, respectively.

[0039] The first modulated sub-light pulse is the first polarized sub-light pulse after phase modulation by the first phase modulator 105, and the second modulated sub-light pulse is the second polarized sub-light pulse after phase modulation by the first phase modulator 105. The ratio of the modulation efficiency of the first polarized sub-light pulse to the modulation efficiency of the second polarized sub-light pulse is not less than a preset threshold value, so that the first and second modulated sub-light pulses have a phase difference.

[0040] In an embodiment, the preset threshold value can be not less than 10 decibels (dB). That is, the modulation efficiency of the first phase modulator 105 on the first polarized sub-light pulse (forward input light port input) is much greater than the modulation efficiency of the first phase modulator 105 on the second polarized sub-light pulse (reverse input light port input).

[0041] In the embodiments of the present application, the first phase modulator 105 can be made of lithium niobate crystal, and can be a single-polarization phase modulator or a birefringent phase modulator. The first phase modulator 105 can accurately control the refractive index of the crystal by applying an electric field, thereby realizing the modulation of the phase of light waves. For example, when a modulation signal of 10 GHz or more is applied, the phase modulation efficiency of the first phase modulator 105 on the forward input light pulse (for example, the first polarized sub-light pulse) and the reverse input light pulse (for example, the second polarized sub-light pulse) is greatly different, at least 10 times or more than 100.

[0042] That is, the modulation efficiency of the first phase modulator 105 on the first polarized sub-light pulse is greatly different from the modulation efficiency of the first phase modulator 105 on the second polarized sub-light pulse. Therefore, it can be considered that the first phase modulator 105 can effectively modulate the first polarized sub-light pulse transmitted in the forward direction input from the fifth port E, and cannot effectively modulate the second polarized sub-light pulse transmitted in the reverse direction input from the sixth port F.

[0043] In the embodiment of the present application, when the two polarized light pulses are input from the positive and negative input optical ports through the high-speed modulated first phase modulator 105 at the same time, the same high-frequency modulation pulse is applied to the first polarized light pulse and the second polarized light pulse, so that the required phase difference is formed between the first modulated light pulse and the second modulated light pulse output by the first phase modulator 105. Different high-frequency modulation pulses are applied to the first modulated light pulse and the second modulated light pulse, so that the phase difference formed between the first modulated light pulse and the second modulated light pulse after the modulation by the first phase modulator 105 is different.

[0044] In an embodiment, the first phase modulator 105 can include a fast axis and a slow axis. The transmission optical path 104 can be coupled with the fast axis or the slow axis of the first phase modulator 105. The two polarized light pulses can be transmitted into and out of the first phase modulator 105 through the slow axis of the first phase modulator 105, or the two polarized light pulses can be transmitted into and out of the first phase modulator 105 through the fast axis of the first phase modulator 105. In this way, it can be ensured that the modulation environment of the two polarized light pulses is the same, and the influence of environmental interference is reduced.

[0045] The first port A or the fourth port D of the optical beam splitter 101 is an output port. The optical beam splitter 101 is also used to combine the first modulated light pulse and the second modulated light pulse, and the combined light pulse is output through the first port A or the fourth port D.

[0046] In an embodiment, the phase of the first modulated light pulse is different from the phase of the second modulated light pulse. The optical beam splitter 101 can combine the first modulated light pulse input from the third port C and the second modulated light pulse input from the second port B, and output the combined light pulse from the first port A or the fourth port D. In the combining process, the optical beam splitter 101 can combine the two modulated light pulses into one light pulse while ensuring that the two modulated light pulses maintain a specific phase difference.

[0047] In the above embodiment, the application adopts an optical beam splitter to split one received input optical pulse into two sub optical pulses, and inputs corresponding polarizers from different ports, and polarizes the two sub optical pulses through two polarizers with different polarization directions to obtain two polarized sub optical pulses with different polarization states. In this way, the polarization states of the two sub optical pulses can be accurately controlled through the polarizer, so as to obtain two polarized sub optical pulses with stable relative phase and different polarization states. The two polarized sub optical pulses are transmitted in different directions along the transmission optical path to the first phase modulator, and the first phase modulator with the applied modulation signal modulates the first polarized sub optical pulse and the second polarized sub optical pulse with different modulation efficiencies, so that effective modulation of the first polarized sub optical pulse and ineffective modulation of the second polarized sub optical pulse can be realized, thereby obtaining the first modulated sub optical pulse and the second modulated sub optical pulse with a phase difference. The first modulated sub optical pulse and the second modulated sub optical pulse are transmitted in different directions along the transmission optical path and enter the different ports of the optical beam splitter through the corresponding polarizers. The optical beam splitter combines the two high-speed modulated sub optical pulses and outputs the combined optical pulse through the first port or the fourth port. In this way, the optical paths of the two sub optical pulses of the optical beam splitter are completely the same when they are combined, thereby having the advantages of self-compensation of environmental interference and high stability against interference, and achieving the purpose of high-stable encoding of the polarization quantum state at a speed of 10GHz or higher.

[0048] In some embodiments, when the first phase modulator 105 applies a high-frequency modulation signal with a frequency higher than a specified threshold, the first phase modulator 105 can have multiple sub optical pulses input from the forward input port and the reverse input port at the same time.

[0049] In some embodiments, in order to make the two modulated sub optical pulses after phase modulation by the first phase modulator 105 pass through the first polarizer 102 and the second polarizer 103 respectively and enter the optical beam splitter, when the first modulated sub optical pulse reaches the second polarizer 103, the polarization state of the first modulated sub optical pulse is the same as the polarization direction of the second polarizer 103.

[0050] When the second modulated sub optical pulse reaches the first polarizer 102, the polarization state of the second modulated sub optical pulse is the same as the polarization direction of the first polarizer 102.

[0051] In an embodiment of the present application, the polarization direction of the first polarizer 102 is 45°, and the polarization direction of the second polarizer 103 is 135°. After the first sub-light pulse passes through the first polarizer 102 and is polarized at 45°, the first sub-light pulse is converted into a first polarized sub-light pulse with a polarization state of 45°. During the transmission of the first polarized sub-light pulse through the transmission optical path 104 and the first phase modulator 105 to the third port C of the optical beam splitter 101, the polarization state is rotated by 90°, so that the first modulated sub-light pulse output by the first phase modulator 105 has a polarization state of 135° when it reaches the second polarizer 103, so that the first modulated sub-light pulse passes through the second polarizer 103 and enters the third port of the optical beam splitter 101.

[0052] In addition, after the second sub-light pulse passes through the second polarizer 103 and is polarized at 135°, the second sub-light pulse is converted into a second polarized sub-light pulse with a polarization state of 135°. During the transmission of the second polarized sub-light pulse through the transmission optical path 104 and the first phase modulator 105 to the second port B of the optical beam splitter 101, the polarization state is rotated by 90°, so that the second modulated sub-light pulse output by the first phase modulator 105 has a polarization state of 45° when it reaches the first polarizer 102, so that the second modulated sub-light pulse passes through the first polarizer 102 and enters the second port B of the optical beam splitter 101.

[0053] It should be noted that there are many ways to change the polarization state, and in the embodiment of the present application, the polarization state of the two modulated sub-light pulses can be changed in a corresponding manner according to the type of the transmission optical path.

[0054] In some embodiments, the transmission optical path 104 can include a wired channel and a wireless channel. The wired channel can include a polarization maintaining optical fiber. The wireless channel can include a free space optical path.

[0055] The polarization maintaining optical fiber is a special optical fiber that can maintain the polarization direction of light unchanged during transmission along the slow axis or fast axis of the polarization maintaining optical fiber. The free space optical path refers to the path of light propagating in free space, independent of optical fibers or other physical media.

[0056] In some embodiments, when the transmission optical path is a polarization maintaining optical fiber with a 90° twist, the first polarizer 102 and the second polarizer 103 are coupled to the fast axis or the slow axis of the polarization maintaining optical fiber.

[0057] The polarization maintaining optical fiber can include two transmission axes, a fast axis and a slow axis. The polarization maintaining optical fiber with a 90° twist means that the fast axis and the slow axis of the polarization maintaining optical fiber have been twisted by 90°. When the light pulse is transmitted along the fast axis or the slow axis of the polarization maintaining optical fiber with a 90° twist, the polarization state of the light pulse is rotated by 90°.

[0058] In some embodiments, the transmission optical path 104 is a free space optical path.Figure 2 Fig. 2 shows a structure diagram of another high-speed polarization encoding device provided by an embodiment of the present application, Figure 2 The high-speed polarization encoding device shown in Fig. 1 and Figure 1 The high-speed polarization encoding device shown in Fig. 2 is slightly different from that shown in Fig. 1. As shown in Fig. 2, Figure 2 As shown in Fig. 2, a polarization state rotator 107 is arranged in the transmission light path 104. The polarization state rotator 107 can be used to rotate the polarization state of the sub-light pulses passing through the polarization state rotator 107 by 90°. The polarization state rotator 107 can be a half-wave plate or a 90° Faraday rotator.

[0059] It should be noted that the polarization state rotator 107 can be arranged between the second polarizer 103 and the first phase modulator 105, as shown in Fig. 1. Alternatively, the polarization state rotator 107 can be arranged between the first polarizer 102 and the first phase modulator 105. In addition, whether the sub-light pulses pass through the polarization state rotator 107 clockwise or counterclockwise, they will be rotated by 90 degrees. Figure 2

[0060] In some embodiments, the transmission light path 104 is a polarization maintaining optical fiber that does not twist. When the first polarizer 102 and the second polarizer 103 are coupled to different axes of the polarization maintaining optical fiber, the high-speed polarization encoding device can further include the polarization state rotator 107, as shown in Fig. 2. Figure 2

[0061] In one embodiment, the first polarizer 102 can be coupled to the fast axis of the polarization maintaining optical fiber, and the second polarizer 103 can be coupled to the slow axis of the polarization maintaining optical fiber. That is, the first sub-light pulses output from the second port B of the optical beam splitter 101 pass through the first polarizer 102 to be polarized into first polarized sub-light pulses. The first polarized sub-light pulses are transmitted clockwise along the fast axis of the polarization maintaining optical fiber, enter the first phase modulator 105 from the fifth port E of the first phase modulator 105 to be effectively phase modulated, and obtain first modulated sub-light pulses. The first modulated sub-light pulses are output through the sixth port F of the first phase modulator 105 and transmitted clockwise along the fast axis of the polarization maintaining optical fiber to the polarization state rotator 107, the polarization state rotator 107 rotates the polarization state of the first modulated sub-light pulses by 90° and outputs them and transmits them clockwise along the slow axis of the polarization maintaining optical fiber to the second polarizer 103, and the second polarizer 103 inputs the third port C of the optical beam splitter 101.

[0062] ​​The second sub-light pulse output from the third port C of the optical splitter 101 passes through the second polarizer 103 and is converted into a second polarized sub-light pulse. The second polarized sub-light pulse is transmitted along the slow axis of the polarization maintaining fiber in a counterclockwise direction to the polarization state rotator 107, which rotates the polarization state of the second polarized sub-light pulse by 90° and outputs the second polarized sub-light pulse in a clockwise direction along the fast axis of the polarization maintaining fiber to the first phase modulator 105. The second polarized sub-light pulse enters the first phase modulator 105 from the sixth port F of the first phase modulator 105 and is subjected to ineffective phase modulation in the first phase modulator 105, thereby obtaining a second modulated sub-light pulse. The second modulated sub-light pulse is output from the fifth port E of the first phase modulator 105 and transmitted along the slow axis of the polarization maintaining fiber in a counterclockwise direction to the first polarizer 102, which inputs the second modulated sub-light pulse into the second port B of the optical splitter 101.

[0063] In another embodiment, the first polarizer 102 can be coupled to the slow axis of the polarization maintaining fiber, and the second polarizer 103 can be coupled to the fast axis of the polarization maintaining fiber.

[0064] That is, the first sub-light pulse output from the second port B of the optical splitter 101 passes through the first polarizer 102 and is converted into a first polarized sub-light pulse. The first polarized sub-light pulse is transmitted along the slow axis of the polarization maintaining fiber in a clockwise direction, enters the first phase modulator 105 from the fifth port E of the first phase modulator 105, and is subjected to effective phase modulation in the first phase modulator 105, thereby obtaining a first modulated sub-light pulse. The first modulated sub-light pulse is output from the sixth port F of the first phase modulator 105 and transmitted along the slow axis of the polarization maintaining fiber in a clockwise direction to the polarization state rotator 107, which rotates the polarization state of the first modulated sub-light pulse by 90° and outputs the first modulated sub-light pulse in a counterclockwise direction along the fast axis of the polarization maintaining fiber to the second polarizer 103, which inputs the first modulated sub-light pulse into the third port C of the optical splitter 101.

[0065] That is, the first sub-light pulse output from the second port B of the optical splitter 101 passes through the first polarizer 102 and is converted into a first polarized sub-light pulse. The first polarized sub-light pulse is transmitted along the slow axis of the polarization maintaining fiber in a clockwise direction, enters the first phase modulator 105 from the fifth port E of the first phase modulator 105, and is subjected to effective phase modulation in the first phase modulator 105, thereby obtaining a first modulated sub-light pulse. The first modulated sub-light pulse is output from the sixth port F of the first phase modulator 105 and transmitted along the slow axis of the polarization maintaining fiber in a clockwise direction to the polarization state rotator 107, which rotates the polarization state of the first modulated sub-light pulse by 90° and outputs the first modulated sub-light pulse in a counterclockwise direction along the fast axis of the polarization maintaining fiber to the second polarizer 103, which inputs the first modulated sub-light pulse into the third port C of the optical splitter 101.

[0066] Thus, by setting the polarization state rotator 107, the polarization state of the sub light pulses can be precisely deflected in the transmission optical path, so that the two sub light pulses can completely match the direction of the corresponding polarizer, so that each sub light pulse after deflection can pass through the corresponding polarizer into the port of the optical beam splitter 101 without loss, thereby improving the signal pass rate of the entire transmission optical path and reducing signal loss.

[0067] In some embodiments, the first phase modulator 105 can be reversely arranged in the transmission optical path 104, that is, the fifth port E of the first phase modulator 105 can be connected with the second polarizer 103 through the transmission optical path 104, and the sixth port F of the first phase modulator 105 can be connected with the first polarizer 102 through the transmission optical path 104.

[0068] It should be noted that when the first phase modulator 105 is reversely arranged in the transmission optical path 104, the second sub light pulse can be effectively phase modulated, and the first sub light pulse cannot be effectively phase modulated.

[0069] In some embodiments, in the high-speed polarization encoding device, the polarization state of the input light pulse is in the direction of and The energy of the components in the two directions is equal, and the phase can be arbitrary.

[0070] In an embodiment, when the first port A of the optical beam splitter 101 is connected with the free space optical path, the polarization state of the input light pulse is in the direction of wherein and The polarization direction of the first polarizer and the polarization direction of the second polarizer are respectively, and 0≤α≤2π.

[0071] In another embodiment, the first port A of the optical beam splitter 101 is connected with the polarization maintaining optical fiber, the slow axis of the polarization maintaining optical fiber is the same as the polarization direction of one of the first polarizer and the second polarizer, the fast axis of the polarization maintaining optical fiber is the same as the polarization direction of the other polarizer, and the polarization state of the input light pulse input into the polarization maintaining optical fiber is in the direction of wherein, and The polarization direction of the first polarizer and the polarization direction of the second polarizer are respectively, and 0≤α≤2π.

[0072] In the above embodiment, the slow axis of the polarization maintaining optical fiber can be the same as the polarization direction of the first polarizer 102, and the fast axis of the polarization maintaining optical fiber can be the same as the polarization direction of the second polarizer 103. Alternatively, the fast axis of the polarization maintaining optical fiber can be the same as the polarization direction of the first polarizer 102, and the slow axis of the polarization maintaining optical fiber can be the same as the polarization direction of the second polarizer 103.

[0073] In order to make the two sub light pulses after splitting of the input light pulse pass through the first polarizer 102 and the second polarizer 103 with the same intensity, the slow axis of the polarization maintaining fiber is the same as the polarization direction of one of the first polarizer and the second polarizer, and the fast axis of the polarization maintaining fiber is the same as the polarization direction of the other polarizer.

[0074] It should be noted that the polarization direction of the first polarizer 102 and the polarization direction of the second polarizer 103 are orthogonal. The polarization direction of the slow axis of the polarization maintaining fiber and the polarization direction of the fast axis of the polarization maintaining fiber are orthogonal.

[0075] In yet another embodiment, the first port A of the optical splitter 101 is connected with the polarization maintaining fiber, and the angle between the slow axis or the fast axis of the polarization maintaining fiber and the polarization direction of the first polarizer 102 is 45°, and the polarization state of the input light pulse input into the polarization maintaining fiber is the same as the slow axis of the polarization maintaining fiber or the same as the fast axis of the polarization maintaining fiber.

[0076] In the above embodiments, in order to make the two sub light pulses after splitting by the optical splitter pass through the polarizer with the same intensity, the polarization direction of the first polarizer 102 can be set to be an angle of 45° with the slow axis or the fast axis of the polarization maintaining fiber.

[0077] Since the polarization direction of the first polarizer 102 and the polarization direction of the second polarizer 103 have an angle of 90°, in another embodiment of the present application, the polarization direction of the second polarizer 103 can be set to be an angle of 45° with the slow axis or the fast axis of the polarization maintaining fiber. In this way, the same technical effect as the above embodiments can be achieved, that is, the two sub light pulses after splitting by the optical splitter can pass through the polarizer with the same intensity.

[0078] In order to make the input light pulse maintain in the polarization maintaining fiber, when the input light pulse enters the first port A of the optical splitter, the polarization state of the input light pulse must be the same as the slow axis or the fast axis of the polarization maintaining fiber.

[0079] In one embodiment, when the polarization direction of the first polarizer and the polarization direction of the second polarizer are 45° and 135° respectively, the input light pulse is a horizontal polarization state or a vertical polarization state.

[0080] In some embodiments, the first phase modulator 105 can include a fast axis and a slow axis. The transmission speed of the two polarized sub light pulses in the fast axis is higher than that in the slow axis.

[0081] In one embodiment, the first polarized sub light pulse and the second polarized sub light pulse can be transmitted through the first phase modulator 105 by the fast axis of the first phase modulator 105.​​​

[0082] Specifically, the first polarized sub light pulse output by the first polarizer 102 is coupled to the fast axis of the first phase modulator 105 through the transmission optical path 104, and the first polarized sub light pulse is phase modulated when passing through the fast axis of the first phase modulator 105 and is output along the reverse input optical port (i.e., the sixth port F) of the fast axis. The second polarized sub light pulse output by the second polarizer 103 is coupled to the fast axis of the first phase modulator 105 through the transmission optical path 104, and the second polarized sub light pulse is phase modulated when passing through the fast axis of the first phase modulator 105 and is output along the forward input optical port (i.e., the fifth port E) of the fast axis.

[0083] In another embodiment, the first polarized sub light pulse and the second polarized sub light pulse are both transmitted by the slow axis of the first phase modulator 105 through the first phase modulator 105.

[0084] Specifically, the first polarized sub light pulse output by the first polarizer 102 is coupled to the fast axis of the first phase modulator 105 through the transmission optical path 104, and the first polarized sub light pulse is phase modulated when passing through the fast axis of the first phase modulator 105 and is output along the reverse input optical port (i.e., the sixth port F) of the fast axis. The second polarized sub light pulse output by the second polarizer 103 is coupled to the fast axis of the first phase modulator 105 through the transmission optical path 104, and the second polarized sub light pulse is phase modulated when passing through the fast axis of the first phase modulator 105 and is output along the forward input optical port (i.e., the fifth port E) of the fast axis.

[0085] In the above embodiment, the transmission paths of the first polarized sub light pulse and the second polarized sub light pulse in the first phase modulator 105 are consistent, which can ensure that the phase drifts caused by environmental interference when the two polarized sub light pulses pass through the transmission optical path 104 and the first phase modulator 105 are the same, so that the phase difference between them can be accurately controlled by the first phase modulator 105, thereby accurately controlling the phase difference between them.

[0086] In some embodiments, the first polarized sub light pulse and the second polarized sub light pulse are transmitted through the first phase modulator 105 at the same time. That is, at a certain time point, both the first polarized sub light pulse and the second polarized sub light pulse enter the first phase modulator 105 and are simultaneously affected by the modulation signal.

[0087] In this way, since the first polarized sub light pulse and the second polarized sub light pulse pass through the same modulation environment at the same time, not only the consistency and accuracy of the phase modulation can be ensured, but also the phase difference between the two sub light pulses can be accurately controlled.

[0088] In some embodiments, the modulation phase of the first phase modulator 105 can be determined based on the polarization encoding requirements of the quantum communication protocol. For example, in the quantum communication protocol BB84, the required modulation phase is 0°, 90°, 180°, or 270°, and the first phase modulator 105 randomly modulates the phase to 0°, 90°, 180°, or 270°.

[0089] In one embodiment, the type of phase modulation performed by the first phase modulator 105 can be considered to be the phase difference between the first polarized optical pulse after phase modulation (i.e., the first modulated optical pulse) and the second polarized optical pulse after phase modulation (i.e., the second modulated optical pulse). In other words, the phase of the polarized optical pulse effectively modulated by the first phase modulator 105.

[0090] In some embodiments, in order to reduce the types of phase modulation by a single phase modulator, multiple phase modulators may be used for combined modulation to achieve polarization state control. Figure 3 A schematic structural diagram of another high-speed polarization encoding device provided in an embodiment of the present application is shown in FIG. Figure 3 As shown, the high-speed polarization encoding device may include an optical beam splitter 301, a first polarizer 302, a second polarizer 303, a transmission optical path 304, a first phase modulator 305, a first high-speed driver 306, a second phase modulator 307 and a second high-speed driver 308.

[0091] compared to Figure 1 The high-speed polarization encoding device shown, Figure 3 The high-speed polarization encoding apparatus shown is further provided with a second phase modulator 307 and a second high-speed driver 308 .

[0092] Figure 3 The optical beam splitter 301 and Figure 1 The optical beam splitter 301 is the same as the optical beam splitter 101 in FIG. The optical beam splitter 301 includes a first port A, a second port B, a third port C, and a fourth port D. The first port A is the input port of the optical beam splitter 301, and the first port A or the fourth port D is the output port of the optical beam splitter 301. The optical beam splitter 301 receives an input optical pulse through the first port A and splits the input optical pulse into a first optical pulse and a second optical pulse. The polarization state of the first optical pulse and the second optical pulse is the same, and the relative phase between the first optical pulse and the second optical pulse is fixed.

[0093] Figure 3 The first polarizer 302 and Figure 1 The structure and function of the first polarizer 102 are the same as those of Figure 3 The second polarizer 303 and Figure 1 The structure and function of the second polarizer 103 are the same.

[0094] The second phase modulator 307 can be a phase modulator identical to the first phase modulator 305. The second phase modulator 307 can include three ports, namely, an eighth port H, a ninth port I, and a tenth port J. The eighth port H and the ninth port I are a forward input optical port and a reverse input optical port, respectively, and the tenth port J is an electrical port.

[0095] In some embodiments, the second phase modulator 307 has the same characteristics as the first phase modulator 305. When a high-frequency modulation signal having a frequency higher than a specified threshold is applied to the second phase modulator 307, there may be multiple sub-optical pulses input from the forward input port and sub-optical pulses input from the reverse input port at the same time.

[0096] The second phase modulator 307 may be connected in series with the first phase modulator 305 in the transmission optical path 304 , that is, the second phase modulator 307 may be connected to the first phase modulator 305 in a forward direction or a reverse direction.

[0097] That is, the sixth port F of the first phase modulator 305 is connected to the eighth port H of the second phase modulator 307 via the transmission optical path 304, and the ninth port I of the second phase modulator 307 is connected to the second polarizer 303 via the transmission optical path 304. Alternatively, the sixth port F of the first phase modulator 305 is connected to the ninth port I of the second phase modulator 307 via the transmission optical path 304, and the eighth port H of the second phase modulator 307 is connected to the second polarizer 303 via the transmission optical path 304.

[0098] The second phase modulator 307 can be used to cooperate with the first phase modulator 305 to perform phase modulation on the first polarization optical pulse and the second polarization optical pulse.

[0099] It should be noted that in the implementation of the two phase modulators cooperative modulation, the two phase modulators are connected in series in the transmission optical path, and the same Figure 3 Taking the structure shown in as an example, if the two sub-light pulses are allowed to pass through the first phase modulator 305 at the same time, then for the first phase modulator 305, when the second polarized light pulse is input, the second polarized light pulse has already passed through the second phase modulator 307. At this time, the second polarized light pulse input to the first phase modulator 305 is the second modulated sub-light pulse after phase modulation; similarly, if the two sub-light pulses are allowed to pass through the second phase modulator 307 at the same time, then for the second phase modulator 307, when the first polarized light pulse is input, the first polarized light pulse has already passed through the first phase modulator 305. At this time, the first polarized light pulse input to the second phase modulator 307 is the first modulated sub-light pulse after phase modulation.

[0100] That is, the second phase modulator 307 has two functions. One is a backup phase modulator. In the case that the first phase modulator 305 cannot work due to a fault, the second phase modulator works to phase-modulate the first and second polarized sub light pulses with different modulation efficiencies based on the high-speed modulation signal applied by the second high-speed driver 308 alone. The other is a cooperative phase modulator. In the case that the first phase modulator 305 works, the second phase modulator 307 also works to phase-modulate the first and second polarized sub light pulses based on the high-speed modulation signals applied by the first and second high-speed drivers 306 and 308 respectively.

[0101] In an embodiment, the modulation modes of the first and second phase modulators 305 and 307 can include a single modulation mode and a combined modulation mode. The single modulation mode can mean that the first or second phase modulator 305 or 307 phase-modulates alone. The combined modulation mode can mean that the first and second phase modulators 305 and 307 phase-modulate cooperatively.

[0102] The second high-speed driver 308 is connected to the second phase modulator 307, i.e., the second phase modulator 307 is connected to the second high-speed driver 308 through the tenth port J. The second high-speed driver 308 is used to apply a modulation signal with a frequency higher than a specified threshold to the second phase modulator 307. It should be noted that the type and role of the second high-speed driver 308 can be the same as those of the first high-speed driver 306.

[0103] In an embodiment, the first sub light pulse is output from the second port B of the optical beam splitter 301, is polarized by the first polarizer 302, is transmitted in the clockwise direction of the transmission light path 304 through the first and second phase modulators 305 and 307, is modulated by the first and / or second phase modulators 305 and 307, and is transmitted in the clockwise direction of the transmission light path 304 to the third port C of the optical beam splitter 301. The second sub light pulse is output from the third port C of the optical beam splitter 301, is polarized by the second polarizer 303, is transmitted in the counterclockwise direction of the transmission light path 304 through the first and second phase modulators 305 and 307, is modulated by the first and / or second phase modulators 305 and 307, and is transmitted in the counterclockwise direction of the transmission light path 304 to the second port B of the optical beam splitter 301.

[0104] In the above embodiments, by adding the second phase modulator 307, the redundancy of the device can be increased, and by the first phase modulator 305 and the second phase modulator 307 cooperating to modulate two polarized light pulses, a more complex phase modulation mode can be realized, and the precision and speed of phase control can be improved. When the first phase modulator 305 fails to work, the second phase modulator 307 is enabled to perform phase modulation, so as to ensure the normal progress of the phase modulation process and avoid interruption of the device.

[0105] In addition, by configuring two phase modulators in the transmission optical path 304, and by the combination of the two phase modulators being applied with a modulation signal with a frequency higher than a specified threshold, the first high-speed driver 306 and the second high-speed driver 308 can be enabled to generate different polarization states through digital high-speed modulation.

[0106] In some embodiments, the random modulation phase of the second phase modulator 307 can be determined according to the requirements of polarization encoding of the quantum communication protocol. For example, in the BB84 quantum communication protocol, the requirements of modulation are two groups of four quantum states, and the random modulation phase of the second phase modulator 307 is 0°, 90°, 180° or 270°.

[0107] In some embodiments, the modulation phases of the first phase modulator and the second phase modulator to the first polarized light pulse and the second polarized light pulse are determined according to the requirements of polarization encoding of the quantum communication protocol.

[0108] That is, no matter in the single modulation mode or in the combined modulation mode, the phase difference between the first modulated light pulse and the second modulated light pulse after being modulated by the first phase modulator and / or the second phase modulator meets the requirements of modulation in the quantum communication protocol. In this way, the high-precision implementation of the quantum communication protocol can be ensured, and by setting two modulators, the number of modulation phase states of a single phase modulator is reduced, and the flexibility and adaptability of the device are improved.

[0109] In some embodiments, when the first phase modulator 305 and the second phase modulator 307 are in forward series or reverse series, the phase difference between the first polarized light pulse and the second polarized light pulse after being modulated is equal to the sum or difference of the modulation phase of the first phase modulator 305 and the modulation phase of the second phase modulator 307.

[0110] That is, when the first phase modulator 305 and the second phase modulator 307 are in forward series, the phase difference between the first modulated light pulse and the second modulated light pulse after being modulated is equal to the sum of the modulation phase of the first phase modulator 305 and the modulation phase of the second phase modulator 307.

[0111] When the first phase modulator 305 and the second phase modulator 307 are connected in reverse series, the phase difference between the first modulated sub-light pulse and the second modulated sub-light pulse is equal to the difference between the phase modulated by the first phase modulator 305 and the phase modulated by the second phase modulator 307.

[0112] The phases modulated by the first phase modulator and the second phase modulator on the first polarized sub-light pulse and the second polarized sub-light pulse can be determined according to the requirements of the polarization encoding of the quantum communication protocol.

[0113] Based on this, in the combined modulation mode, the types of the phases modulated by the first phase modulator 305 can be less than the required phases modulated in the quantum communication protocol. The types of the phases modulated by the second phase modulator 307 can be less than the required phases modulated in the quantum communication protocol.

[0114] For example, the required types of the modulated phases in the quantum communication protocol BB84 are 0°, 90°, 180°, or 270°. When connected in forward series, the phase modulated by the first phase modulator 305 can be 0° or 90°, and the phase modulated by the second phase modulator 307 can be 0° or 180°. When connected in reverse series, the phase modulated by the first phase modulator 305 can be 0° or 180°, and the phase modulated by the second phase modulator 307 can be 0° or 90°.

[0115] In an embodiment, the phase modulated by the first phase modulator 305 and the phase modulated by the second phase modulator 307 are both determined by the size of the modulation signal applied by the respective high-speed driver.

[0116] In this way, by combined modulation of the first phase modulator 305 and / or the second phase modulator 307, not only can the polarization state be controlled, but also the types of the phases modulated by a single phase modulator can be reduced, thereby reducing the difficulty of implementing the phase modulator driver.

[0117] In some embodiments, the first polarized sub-light pulse and the second polarized sub-light pulse are transmitted through the first phase modulator 305 at the same time, or the first polarized sub-light pulse and the second polarized sub-light pulse are transmitted through the second phase modulator 307 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 sub-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.

[0118] In addition, Figure 3 The high-speed polarization encoding device shown can also be provided with a polarization state rotator. The polarization state rotator can be arranged between the second phase modulator 307 and the third port C of the optical beam splitter 301. The function of the polarization state rotator is the same as that of the polarization state rotator 306. Figure 2The polarization state rotator shown has the same effect, which will not be described here for brevity.

[0119] In an embodiment, the high-speed polarization encoding device can also be used for high-speed polarization decoding.

[0120] Another aspect of the embodiments of the present application provides a high-speed polarization encoding method, which is applied to any one of the high-speed polarization encoding devices in the embodiments of the present application. Figure 4 A flowchart of a high-speed polarization encoding method provided by the embodiments of the present application is shown in FIG. 4. Figure 4 As shown in the figure, the high-speed polarization encoding method can include the following steps.

[0121] S41, receiving an input optical pulse through a first port A of an optical beam splitter 101.

[0122] S42, splitting the received input optical pulse into a first sub-optical pulse and a second sub-optical pulse through the optical beam splitter 101.

[0123] S43, outputting the first sub-optical pulse from a second port B of the optical beam splitter 101, and obtaining a first polarized sub-optical pulse by polarizing the first sub-optical pulse through a first polarizer 102, and outputting the second sub-optical pulse from a third port C of the optical beam splitter 101, and obtaining a second polarized sub-optical pulse by polarizing the second sub-optical pulse through a second polarizer 103.

[0124] S44, receiving the first polarized sub-optical pulse and the second polarized sub-optical pulse through different ports of a first phase modulator 105, and phase-modulating the first polarized sub-optical pulse and the second polarized sub-optical pulse at different modulation efficiencies based on a modulation signal, to obtain a first modulated sub-optical pulse and a second modulated sub-optical pulse.

[0125] The ratio of the modulation efficiency of the first phase modulator 105 on the first polarized sub-optical pulse to the modulation efficiency of the first phase modulator 105 on the second polarized sub-optical pulse under a high-speed modulation signal is not less than a preset threshold, so that the first modulated sub-optical pulse and the second modulated sub-optical pulse have a phase difference.

[0126] S45, outputting the first modulated sub-optical pulse and the second modulated sub-optical pulse from different ports of the first phase modulator 105 respectively, transmitting in different directions in a transmission optical path 104, passing through the second polarizer 103 and the first polarizer 102 respectively, and inputting into the third port C and the second port B of the optical beam splitter 101.

[0127] S46, combining the first modulated sub-optical pulse input from the third port C and the second modulated sub-optical pulse input from the second port B through the optical beam splitter 101, and outputting the combined optical pulse through the first port A or the fourth port D.

[0128] In the above embodiment, the application adopts an optical beam splitter to split one received input optical pulse into two sub optical pulses, and inputs corresponding polarizers from different ports, and polarizes the two sub optical pulses through two polarizers with different polarization directions to obtain two polarized sub optical pulses with different polarization states. In this way, the polarization states of the two sub optical pulses can be accurately controlled through the polarizers, so that two polarized sub optical pulses with stable relative phase and different polarization states are obtained. The two polarized sub optical pulses are transmitted in different directions along the transmission optical path to the first phase modulator, and the first phase modulator with an applied modulation signal modulates the first polarized sub optical pulse and the second polarized sub optical pulse with different modulation efficiencies, so that effective modulation of the first polarized sub optical pulse and ineffective modulation of the second polarized sub optical pulse can be realized, thereby obtaining the first modulated sub optical pulse and the second modulated sub optical pulse with a phase difference. The first modulated sub optical pulse and the second modulated sub optical pulse are transmitted in different directions along the transmission optical path to enter different ports of the optical beam splitter through corresponding polarizers. The optical beam splitter combines the two sub optical pulses modulated at high speed and outputs the combined optical pulse through the first port or the fourth port. In this way, the optical paths of the two sub optical pulses of the optical beam splitter are completely the same when they are combined, thereby having the advantages of self-compensation of environmental interference and high stability against interference, and achieving the purpose of high-stable encoding of the polarization quantum state at a speed of 10GHz or higher.

[0129] In some embodiments, the method can further include that the first sub optical pulse and the second sub optical pulse are transmitted to the first phase modulator 105 by the fast axis of the first phase modulator 105, or are transmitted to the first phase modulator 105 by the slow axis of the first phase modulator 105.

[0130] In some embodiments, the method can further include that when the first modulated sub optical pulse reaches the second polarizer 103, the polarization state of the first modulated sub optical pulse is the same as the polarization direction of the second polarizer 103.

[0131] When the second modulated sub optical pulse reaches the first polarizer 102, the polarization state of the second modulated sub optical pulse is the same as the polarization direction of the first polarizer 102.

[0132] In some embodiments, the method can include that the transmission optical path 104 is a free space optical path or a polarization maintaining optical fiber.

[0133] In some embodiments, the method can include that when the transmission optical path 104 is a polarization maintaining optical fiber, the first polarizer 102 and the second polarizer 103 are coupled to the fast axis or the slow axis of the polarization maintaining optical fiber.

[0134] In some embodiments, the method can further include: when the transmission optical path is a free-space optical path, or the first polarizer 102 and the second polarizer 103 are coupled to different axes of a polarization maintaining optical fiber respectively, rotating the polarization state of the sub-light pulses passing through the polarization state rotator 107 by 90° by the polarization state rotator 107.

[0135] In some embodiments, the method can further include: the polarization state of the input light pulse input to the first port A of the optical beam splitter 101 is wherein, and are the polarization directions of the first polarizer 102 and the second polarizer 103 respectively, and 0≤α≤2π.

[0136] In some embodiments, when the first port A of the optical beam splitter 101 is connected to a polarization maintaining optical fiber, and the slow axis of the polarization maintaining optical fiber is the same as the polarization direction of one of the first polarizer 102 and the second polarizer 103, and the fast axis of the polarization maintaining optical fiber is the same as the polarization direction of the other polarizer, the polarization state of the input light pulse is set to wherein, and are the polarization directions of the first polarizer 102 and the second polarizer 103 respectively, and 0≤α≤2π.

[0137] In some embodiments, when the first port A of the optical beam splitter 101 is connected to a polarization maintaining optical fiber, and the angle between the slow axis or the fast axis of the polarization maintaining optical fiber and the polarization direction of the first polarizer 102 is 45°, the polarization state of the input light pulse input to the polarization maintaining optical fiber is the same as the slow axis of the polarization maintaining optical fiber or the same as the fast axis of the polarization maintaining optical fiber.

[0138] In some embodiments, the method can include: phase modulating the first polarized sub-light pulses and the second polarized sub-light pulses by the second phase modulator 307 in cooperation with the first phase modulator 305.

[0139] In some embodiments, the method can further include: the first polarized sub-light pulses and the second polarized sub-light pulses are transmitted through the first phase modulator 305 at the same time, or the first polarized sub-light pulses and the second polarized sub-light pulses are transmitted through the second phase modulator 307 at the same time.

[0140] In another aspect, the embodiments of the present application provide a quantum communication system, Figure 5 Fig. 1 shows a structure schematic diagram of a quantum communication system provided by the embodiments of the present application, as shown in the figure, the quantum communication system 500 can include the high-speed polarization encoding device 501 described in any of the embodiments of the present application. Figure 5

[0141] ​​It should be appreciated that all the specific features, operations and details described above in relation to the device of the present application can be similarly applied to the method and system of the present application, or vice versa. In addition, each step of the method of the present application described above can be performed by the corresponding component or unit of the device or system of the present application.

[0142] It should be understood that each module / unit of the device of the present application can be implemented in whole or in part by software, hardware, firmware, or a combination thereof. Each module / unit can be embedded in a processor of an electronic device in hardware or firmware form, or independent of the processor, or stored in a memory of the electronic device in software form to be invoked by the processor to perform the operations of each module / unit. Each module / unit can be implemented as an independent component or module, or two or more modules / units can be implemented as a single component or module.

[0143] Each of the technical features described above can be combined arbitrarily. Although all possible combinations of these technical features are not described, any combination of these technical features should be considered to be covered by the present specification, as long as there is no contradiction in such a combination.

[0144] 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: it 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 high-speed polarization encoding device, characterized in that: include: An optical beam splitter, a first polarizer, a second polarizer, a transmission optical path, a first phase modulator, and a first high-speed driver; The first high-speed driver is connected to the first phase modulator and is configured to apply a modulation signal having a frequency higher than a specified threshold to the first phase modulator; The optical beam splitter includes a first port, a second port, a third port, and a fourth port. The optical beam splitter receives an input optical pulse through the first port, splits the input optical pulse into a first optical pulse and a second optical pulse, and outputs the first optical pulse and the second optical pulse through the second port and the third port, respectively. The polarization state of the first optical pulse and the second optical pulse is the same. The transmission optical path is used to connect the first polarizer and the second polarizer; The first polarizer is connected to the second port of the optical beam splitter, and is used to polarize the first path of sub-light pulses output from the second port, and output the first path of polarized sub-light pulses to the transmission optical path. The polarization state of the first path of polarized sub-light pulses is ; The second polarizer is connected to the third port of the optical beam splitter, and is used to polarize the second path of sub-light pulses output from the third port, and output the second path of polarized sub-light pulses to the transmission optical path. The polarization state of the second path of polarized sub-light pulses is , With the mutually orthogonal; The first phase modulator is disposed in the transmission optical path and is configured to perform phase modulation on the first polarized optical pulse and the second polarized optical pulse at different modulation efficiencies based on the modulation signal to obtain a first modulated optical sub-pulse and a second modulated optical sub-pulse; wherein a ratio of the modulation efficiency of the first polarized optical pulse to the modulation efficiency of the second polarized optical pulse is not less than a preset threshold, so that a phase difference exists between the first modulated optical sub-pulse and the second modulated optical sub-pulse; The first modulated optical sub-pulse and the second modulated optical sub-pulse are respectively output from different ports of the first phase modulator, transmitted along different directions of the transmission optical path, respectively pass through the second polarizer and the first polarizer, and are input to the third port and the second port of the optical beam splitter; The optical beam splitter is further configured to combine the first modulated optical sub-pulse and the second modulated optical sub-pulse, and output the obtained combined optical pulse through the first port or the fourth port.

2. The device according to claim 1, characterized in that When the first modulated light sub-pulse reaches the second polarizer, the polarization state of the first modulated light sub-pulse is the same as the polarization direction of the second polarizer; When the second-path modulated light sub-pulses arrive at the first polarizer, the polarization state of the second-path modulated light sub-pulses is the same as the polarization direction of the first polarizer.

3. The device according to claim 2, characterized in that The transmission optical path is a free space optical path or a polarization-maintaining optical fiber.

4. The device according to claim 3, characterized in that The transmission optical path is a polarization-maintaining optical fiber with a 90° twist, and the first polarizer and the second polarizer are both coupled to the fast axis or the slow axis of the polarization-maintaining optical fiber.

5. The device according to claim 3, characterized in that The transmission optical path is the free space optical path, or the first polarizer and the second polarizer are respectively coupled to different axes of the polarization-maintaining optical fiber. The device also includes a polarization state rotator for rotating the polarization state of the sub-light pulse passing through the polarization state rotator by 90°.

6. The device according to claim 1, characterized in that When the first port of the optical beam splitter is connected to a polarization-maintaining fiber, the slow axis of the polarization-maintaining fiber is the same as the polarization direction of one of the first polarizer and the second polarizer, and the fast axis of the polarization-maintaining fiber is the same as the polarization direction of the other polarizer, the polarization state of the input light pulse is ,in, and are the polarizing directions of the first polarizer and the second polarizer, respectively, .

7. The device according to claim 1, characterized in that include: The first port of the optical beam splitter is connected to a polarization-maintaining optical fiber, and when the polarization state of the input light pulse is the same as the slow axis of the polarization-maintaining optical fiber or the fast axis of the polarization-maintaining optical fiber, the angle between the slow axis or the fast axis of the polarization-maintaining optical fiber and the polarization direction of the first polarizer is 45°.

8. The device according to any one of claims 1 to 7, characterized in that The apparatus further includes a second phase modulator and a second high-speed driver, The second phase modulator is provided in the transmission optical path, and is connected in series with the first phase modulator, and is used to cooperate with the first phase modulator to phase modulate the first polarized optical pulse and the second polarized optical pulse; The second high-speed driver is connected to the second phase modulator and is configured to apply a modulation signal having a frequency higher than a specified threshold to the second phase modulator.

9. The device according to claim 8, characterized in that The first polarized optical pulse and the second polarized optical pulse are transmitted through the first phase modulator at the same time, or the first polarized optical pulse and the second polarized optical pulse are transmitted through the second phase modulator at the same time.

10. A high-speed polarization encoding method, characterized in that: Applied to the polarization encoding device according to any one of claims 1 to 9, the method comprises: receiving an input optical pulse through a first port of the optical beam splitter; Splitting the received input optical pulse into a first path optical pulse and a second path optical pulse by the optical beam splitter; The first path of light pulses is output from the second port of the optical beam splitter and polarized by a first polarizer to obtain a first path of polarized light pulses; and the second path of light pulses is output from the third port of the optical beam splitter and polarized by a second polarizer to obtain a second path of polarized light pulses; The first polarized optical pulse and the second polarized optical pulse are received by different ports of a first phase modulator, and phase-modulated at different modulation efficiencies are performed on the first polarized optical pulse and the second polarized optical pulse based on the modulation signal to obtain a first modulated optical sub-pulse and a second modulated optical sub-pulse; wherein a ratio of the modulation efficiency of the first polarized optical pulse to the modulation efficiency of the second polarized optical pulse is not less than a preset threshold value, so that a phase difference exists between the first modulated optical sub-pulse and the second modulated optical sub-pulse; The first modulated optical sub-pulse and the second modulated optical sub-pulse are respectively output from different ports of the first phase modulator, transmitted along different directions in the transmission optical path, respectively passed through the second polarizer and the first polarizer, and input to the third port and the second port of the optical beam splitter; The first modulated optical sub-pulse input from the third port and the second modulated optical sub-pulse input from the second port are combined through the optical beam splitter, and the obtained combined optical pulse is output through the first port or the fourth port.

11. The method according to claim 10, characterized in that include: When the first modulated light sub-pulse reaches the second polarizer, the polarization state of the first modulated light sub-pulse is the same as the polarization direction of the second polarizer; When the second-path modulated light sub-pulses arrive at the first polarizer, the polarization state of the second-path modulated light sub-pulses is the same as the polarization direction of the first polarizer.

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

13. The method according to claim 12, characterized in that When the transmission optical path is the polarization-maintaining optical fiber, the first polarizer and the second polarizer are both coupled to the fast axis or the slow axis of the polarization-maintaining optical fiber.

14. The method according to claim 12, characterized in that Also includes: When the transmission optical path is the free space optical path, or the first polarizer and the second polarizer are respectively coupled to different axes of the polarization-maintaining optical fiber, the polarization state of the sub-light pulse passing through the polarization state rotator is rotated by 90°.

15. The method according to claim 10, characterized in that When the first port of the optical beam splitter is connected to a polarization-maintaining fiber, the slow axis of the polarization-maintaining fiber is the same as the polarization direction of one of the first polarizer and the second polarizer, and the fast axis of the polarization-maintaining fiber is the same as the polarization direction of the other polarizer, the polarization state of the input light pulse is set to ,in, and are the polarizing directions of the first polarizer and the second polarizer, respectively, .

16. The method according to claim 10, characterized in that When the first port of the optical beam splitter is connected to a polarization-maintaining optical fiber, and the polarization state of the input light pulse is the same as the slow axis of the polarization-maintaining optical fiber or the fast axis of the polarization-maintaining optical fiber, the angle between the slow axis or the fast axis of the polarization-maintaining optical fiber and the polarization direction of the first polarizer is set to 45°.

17. The method according to any one of claims 10 to 16, characterized in that: The polarization encoding device includes a second phase modulator, which is arranged in the transmission optical path and connected in series with the first phase modulator. The method includes: The first polarized optical pulse and the second polarized optical pulse are phase-modulated by the second phase modulator in cooperation with the first phase modulator.

18. The method according to claim 17, characterized in that include: The first polarized optical pulse and the second polarized optical pulse are transmitted through the first phase modulator at the same time, or the first polarized optical pulse and the second polarized optical pulse are transmitted through the second phase modulator at the same time.

19. A quantum communication system, characterized in that: The device comprises a high-speed polarization encoding device as claimed in any one of claims 1 to 9.

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