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 comprising: a polarization beam splitter, a transmission light path, a first phase modulator and a first high-speed driver; the first high-speed driver is connected with the first phase modulator, and is used for applying a high-frequency modulation signal with a frequency higher than a specified threshold to the first phase modulator; the polarization beam splitter receives an optical pulse through a first port, and splits the optical pulse into a first sub-optical pulse and a second sub-optical pulse; the first phase modulator is used for phase modulating the first sub-optical pulse and the second sub-optical pulse with different modulation efficiencies based on the high-frequency modulation signal; and the polarization beam splitter is further used for combining the first sub-optical pulse and the second sub-optical pulse after phase modulation by the first phase modulator, and outputting the obtained combined optical pulse through the first port. In this way, the purpose of high-stable polarization quantum state encoding of 10GHz or higher speed is achieved.

Description

TECHNICAL FIELD

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

[0002] Quantum communication technology is a frontier and hot field combining quantum physics and information science. 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] The physical implementation of quantum communication systems, such as the physical implementation of quantum key distribution and quantum direct communication, requires encoding and decoding of quantum states. Currently, the encoding and decoding rate of quantum communication systems in practical applications is mainly at the order of 100 megahertz (MHz) and 1 gigahertz (GHz). In order to increase the secure transmission distance of quantum communication and improve the quantum key generation rate or information transmission rate, it is necessary to further break through the 10 GHz high-speed quantum state encoding and decoding technology. In the phase modulation polarization quantum state scheme proposed in Marco Avesani et al. ("Stable, low-error, and calibration-free polarization encoder for free-space quantum communication." Optics Letters 45.17 (2020): 4706-4709), Yang Li et al. ("High-speed robust polarization modulation for quantum key distribution." Optics Letters 44.21 (2019): 5262-5265), Huaxing Xu et al. ("An intrinsic-stabilization polarization encoder for quantum key distribution." Sixth Symposium on Novel Optoelectronic Detection Technology and Applications. Vol. 11455. SPIE, 2020), a phase modulator is arranged in a Sagnac interferometer, and the two light pulses transmitted clockwise and counterclockwise are modulated by time division or only one of them is modulated, so as to realize the encoding of polarization quantum state, which can meet the polarization quantum state encoding and decoding demand of 100 MHz and ~1 GHz.

[0004] However, for the problem of 10 GHz or higher speed polarization quantum state encoding, due to the length of the phase modulator itself, when modulating high-speed quantum states, multiple forward and reverse light pulses will be transmitted at the same time, and it is difficult to modulate two light pulses by time division or only modulate one light pulse by time division, which limits the application of time division in high-speed encoding. At the same time, it is also difficult to modulate the quantum state by connecting two phase modulators in series to reduce the difficulty of modulating the driving circuit design and improve the accuracy of the modulation phase.

[0005] Therefore, it is difficult to implement the modulation of two light pulses or the modulation of only one light pulse at such a high rate by using the traditional time-division method.

[0006] Therefore, how to realize the polarization quantum state encoding at a rate of 10GHz or higher has become a key problem to be solved in quantum communication applications. SUMMARY

[0007] Therefore, the application provides a high-speed polarization encoding device, method and quantum communication system to solve the technical problems in the background art.

[0008] In a first aspect, an embodiment of the application provides a high-speed polarization encoding device, which comprises a polarization beam splitter, a transmission light path, a first phase modulator and a first high-speed driver. The first high-speed driver is connected to the first phase modulator and used to apply a high-frequency modulation signal with a frequency higher than a specified threshold to the first phase modulator. The polarization beam splitter comprises a first port, a second port and a third port. The polarization beam splitter receives a light pulse through the first port and splits the light pulse into a first sub-light pulse and a second sub-light pulse with the same intensity and mutually orthogonal polarization states. The second port and the third port of the polarization beam splitter are connected through the transmission light path. The first phase modulator is arranged in the transmission light path. The first sub-light pulse is output from the second port of the polarization beam splitter and transmitted along the clockwise direction of the transmission light path to the first phase modulator, and then transmitted along the clockwise direction of the transmission light path to the third port of the polarization beam splitter after being modulated by the first phase modulator. The second sub-light pulse is output from the third port of the polarization beam splitter and transmitted along the counterclockwise direction of the transmission light path to the first phase modulator, and then transmitted along the counterclockwise direction of the transmission light path to the second port of the polarization beam splitter after being modulated by the first phase modulator. The first phase modulator is used to modulate the first sub-light pulse and the second sub-light pulse at different modulation efficiencies based on the high-frequency modulation signal. The ratio of the modulation efficiency of the first sub-light pulse to the modulation efficiency of the second sub-light pulse is not less than a preset threshold, so that there is a phase difference between the first sub-light pulse after phase modulation and the second sub-light pulse after phase modulation.

[0009] The polarization beam splitter is further used to combine the first sub-light pulse and the second sub-light pulse after phase modulation by the first phase modulator, obtain a combined light pulse and output the combined light pulse through the first port.

[0010] In a second aspect, the embodiments of the present application provide a high-speed polarization encoding method applied to the high-speed polarization encoding device described above, and the method comprises: receiving one light pulse through a first port of a polarization beam splitter; splitting the received light pulse into a first sub-light pulse and a second sub-light pulse through the polarization beam splitter; causing the first sub-light pulse to be output from a second port of the polarization beam splitter and transmitted to the first phase modulator in a clockwise direction along a transmission light path, and causing the second sub-light pulse to be output from a third port of the polarization beam splitter and transmitted to the first phase modulator in an anticlockwise direction along the transmission light path; using the first phase modulator receiving a high-frequency modulation signal with a frequency higher than a specified threshold, phase-modulating the first sub-light pulse and the second sub-light pulse based on the high-frequency modulation signal at different modulation efficiencies, and transmitting the phase-modulated first sub-light pulse and the phase-modulated second sub-light pulse to the transmission light path in the clockwise direction and the anticlockwise direction respectively, wherein the ratio of the modulation efficiency of the first sub-light pulse to the modulation efficiency of the second sub-light pulse is not less than a preset threshold, so that the phase-modulated first sub-light pulse and the phase-modulated second sub-light pulse have a phase difference; and combining the first sub-light pulse and the second sub-light pulse phase-modulated by the first phase modulator through the polarization beam splitter to obtain a combined light pulse and output the combined light pulse through the first port.

[0011] In a third aspect, the embodiments of the present application provide a quantum communication system, which can comprise the high-speed polarization encoding device described in 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 polarization beam splitter is used to split one received light pulse into a first sub-light pulse transmitted in a clockwise direction along a transmission light path and a second sub-light pulse transmitted in an anticlockwise direction along the transmission light path. The first phase modulator applied with a high-frequency modulation signal is used to phase-modulate the first sub-light pulse and the second sub-light pulse output by the polarization beam splitter at different modulation efficiencies, so that the modulation efficiency of the first sub-light pulse is much higher than the modulation efficiency of the second sub-light pulse, i.e., the first sub-light pulse can be effectively phase-modulated and the second sub-light pulse can be ineffective phase-modulated, so that the phase-modulated first sub-light pulse and the phase-modulated second sub-light pulse have a phase difference. The polarization beam splitter combines the two sub-light pulses phase-modulated at high speed and outputs a combined light pulse, forming different polarization states. In this way, the light paths through which the two sub-light pulses of the polarization beam splitter are transmitted before being combined are completely the same, so that the system has the advantages of self-compensation to environmental interference and high stability against interference, and achieves the purpose of high-stable polarization quantum state encoding at a rate of 10 GHz or higher. BRIEF DESCRIPTION OF DRAWINGS

[0013] In order to more clearly illustrate the technical solutions in the specific embodiments or the prior art of the present application, the drawings needed to be used 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 effort.

[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 structural schematic diagram of a quantum communication system provided by 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 clearer, the present application will be further described below with reference to the drawings. It should be understood that the specific embodiments given herein are for the purpose of explanation and are only exemplary, but are not limiting.

[0020] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application. It will be apparent, however, to one skilled in the art that the present application can be practiced without specific details, which are not necessary to practice the present application. In other instances, well-known steps or procedures are not described in detail in order to avoid obscuring the present application.

[0021] 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, as shown in the figure, the high-speed polarization encoding device can include a polarization beam splitter 101, a transmission light path 102, a first phase modulator 103 and a first high-speed driver 104. Wherein, the polarization beam splitter 101 and the transmission light path 102 can constitute a Sagnac interferometer. Figure 1

[0022] As shown in the figure, the high-speed polarization encoding device can include a polarization beam splitter 101, a transmission light path 102, a first phase modulator 103 and a first high-speed driver 104. Wherein, the polarization beam splitter 101 and the transmission light path 102 can constitute a Sagnac interferometer. Figure 1 ​As shown, the first high-speed driver 104 is connected to the first phase modulator 103. The first high-speed driver 104 is used to apply a high-frequency modulation signal having a frequency higher than a specified threshold to the first phase modulator 103.

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

[0024] In one embodiment, the optical pulse is a high-speed optical pulse, which refers to a high-repetition-rate pulse light, for example, a pulse repetition rate of 10 GHz or higher.

[0025] Polarization beam splitter 101 includes a first port A, a second port B, and a third port C. First port A of polarization beam splitter 101 serves as the input and output ports of the high-speed polarization encoding device. Polarization beam splitter 101 receives a light pulse through first port A and splits the light pulse into a first light pulse and a second light pulse. The first light pulse and the second light pulse have the same intensity and orthogonal polarization states.

[0026] The polarization beam splitter 101 is connected to the transmission optical path 102. Specifically, the second port B of the polarization beam splitter 101 is connected to one port of the transmission optical path 102, and the third port C of the polarization beam splitter 101 is connected to the other port of the transmission optical path 102. In this way, the first-path optical pulse output from the second port B is coupled into the transmission optical path 102, and the second-path optical pulse output from the third port C is coupled into the transmission optical path 102.

[0027] like Figure 1 As shown, the first phase modulator 103 includes three ports: a fourth port D, a fifth port E, and a sixth port F. The fourth port D and the fifth port E are the forward and reverse optical input ports of the first phase modulator 103, respectively, and the sixth port F is an electrical port. The first phase modulator 103 is disposed in the transmission optical path 102. In other words, the first phase modulator 103 is coupled to the transmission optical path via the fourth port D and the fifth port E. It should be noted that the fourth port D can be the forward optical input port, and the fifth port E can be the reverse optical input port.

[0028] The first sub-light pulse is output from the second port B of the polarization beam splitter 101 and transmitted along the clockwise direction of the transmission light path 102 to the first phase modulator 103. After being modulated by the first phase modulator 103, the first sub-light pulse is transmitted along the clockwise direction of the transmission light path 102 to the third port C of the polarization beam splitter 101. The second sub-light pulse is output from the third port C of the polarization beam splitter 101 and transmitted along the counterclockwise direction of the transmission light path 102 to the first phase modulator 103. After being modulated by the first phase modulator 103, the second sub-light pulse is transmitted along the counterclockwise direction of the transmission light path 102 to the second port B of the polarization beam splitter 101.

[0029] That is, the first sub-light pulse output from the second port B of the polarization beam splitter 101 is transmitted along the clockwise direction of the transmission light path 102 and coupled into the first phase modulator 103 through the fourth port D of the first phase modulator 103. After being modulated by the first phase modulator 103, the first sub-light pulse is coupled into the transmission light path 102 through the fifth port E and transmitted along the clockwise direction of the transmission light path 102 to the third port C of the polarization beam splitter 101.

[0030] The second sub-light pulse output from the third port C of the polarization beam splitter 101 is transmitted along the counterclockwise direction of the transmission light path 102 and coupled into the first phase modulator 103 through the fifth port E of the first phase modulator 103. After being modulated by the first phase modulator 103, the second sub-light pulse is coupled into the transmission light path 102 through the fourth port D and transmitted along the counterclockwise direction of the transmission light path 102 to the second port B of the polarization beam splitter 101.

[0031] The sixth port F of the first phase modulator 103 is connected with the first high-speed driver 104. The first phase modulator 103 receives the high-frequency modulation signal applied by the first high-speed driver 104 through the sixth port F. The first phase modulator 103 is configured to modulate the first sub-light pulse and the second sub-light pulse with different modulation efficiencies based on the high-frequency modulation signal.

[0032] In some embodiments, the ratio of the modulation efficiency of the first sub-light pulse to the modulation efficiency of the second sub-light pulse is not less than a preset threshold value, so that the phase difference exists between the phase-modulated first sub-light pulse and the phase-modulated second sub-light pulse.

[0033] In some embodiments, the preset threshold value can be not less than 10 decibels (dB). That is, the modulation efficiency of the first phase modulator 103 on the first sub-light pulse is much greater than the modulation efficiency of the first phase modulator 103 on the second sub-light pulse.

[0034] In the embodiment of the present application, the first phase modulator 103 can be made of a lithium niobate crystal, and can be a single-polarization phase modulator or a birefringent phase modulator. The first phase modulator 103 can precisely control the refractive index of the crystal by applying an electric field, thereby achieving modulation of the phase of the light wave. For example, when a high-frequency modulation signal of 10 GHz or more is applied, the efficiency of the first phase modulator 103 in modulating the phase of the optical pulse input from the forward input optical port (for example, the first sub-optical pulse) and the optical pulse input from the reverse input optical port (for example, the second sub-optical pulse) differs greatly, at least 10 times or 100 times or more.

[0035] That is, the modulation efficiency of the first phase modulator 103 on the first sub-optical pulse differs greatly from the modulation efficiency of the first phase modulator 103 on the second sub-optical pulse. Therefore, it can be considered that the first phase modulator 103 can effectively modulate the first sub-optical pulse input from the fourth port D and transmitted forward through the first phase modulator 103 each time, and cannot effectively modulate the phase of the second sub-optical pulse input from the fifth port E and transmitted backward through the first phase modulator 103.

[0036] In the embodiment of the present application, when the two sub-optical pulses pass through the first phase modulator 103 modulated at high speed, the same high-frequency modulation signal is applied to the first sub-optical pulse and the second sub-optical pulse once, that is, the required phase difference between the first sub-optical pulse and the second sub-optical pulse can be formed. And by applying different sizes of high-frequency modulation signals, the phase difference between the first sub-optical pulse and the second sub-optical pulse after being modulated by the first phase modulator 103 is also different, so that the first sub-optical pulse and the second sub-optical pulse produce different polarization states of high-speed modulation when they are combined and output by the polarization beam splitter 101.

[0037] The polarization beam splitter 101 is also used to combine the first sub-optical pulse and the second sub-optical pulse after being phase-modulated by the first phase modulator 103, to obtain a combined optical pulse and output it through the first port A.

[0038] In an embodiment, the first sub-optical pulse and the second sub-optical pulse after being phase-modulated by the first phase modulator 103 are at different phases. The polarization beam splitter 101 can combine the first sub-optical pulse input from the third port C after being phase-modulated by the first phase modulator 103 with the second sub-optical pulse input from the second port B after being phase-modulated by the first phase modulator 103. In the combining process, the polarization beam splitter 101 can combine the two sub-optical pulses into a single combined optical pulse while ensuring that the two sub-optical pulses maintain a specific phase difference.

[0039] In the above embodiment, the received light pulse is split into a first sub-light pulse transmitted in the clockwise direction along the transmission light path 102 and a second sub-light pulse transmitted in the counterclockwise direction along the transmission light path 102 by the polarization beam splitter 101. The first sub-light pulse and the second sub-light pulse output by the polarization beam splitter 101 are phase-modulated at different modulation efficiencies by the first phase modulator 103 to which a high-frequency modulation signal is applied, so that the modulation efficiency of the first sub-light pulse is much higher than that of the second sub-light pulse, i.e., the first sub-light pulse can be effectively phase-modulated, and the second sub-light pulse can be ineffective phase-modulated, so that there is a phase difference between the phase-modulated first sub-light pulse and the phase-modulated second sub-light pulse, forming different polarization states. The polarization beam splitter 101 combines the two high-speed modulated sub-light pulses and outputs a combined light pulse. In this way, the two sub-light pulses of the polarization beam splitter 101 have the same transmission path before being combined, thereby having the advantages of self-compensation to environmental interference and high stability against interference, achieving the purpose of high-stable polarization quantum state encoding at a rate of 10 GHz or higher.

[0040] In some embodiments, the polarization state of the light pulse input into the polarization beam splitter is |H>+e iα |V>, where |H> and |V> are two eigenpolarization states of the polarization beam splitter 101, and a is any value between 0 and 2π.

[0041] Eigenpolarization state generally refers to a polarization state that can be completely transmitted or reflected by an optical device. |H> represents a horizontal polarization state, and |V> represents a vertical polarization state. In an embodiment, the first port A can be a free-space port or a polarization-maintaining fiber port. In the case where the first port A is a polarization-maintaining fiber port, the slow axis and the fast axis of the polarization-maintaining fiber are |H> and |V>, respectively.

[0042] Specifically, the polarization state of the light pulse input through the first port A of the polarization beam splitter 101 is |H>+e iα |V>. In an embodiment, a = 0, at this time, the polarization state of the light pulse input into the first port A of the polarization beam splitter 101 is |H>+|V>, i.e., 45° linearly polarized light. The light pulse input through the first port A of the polarization beam splitter 101 is split into a first sub-light pulse and a second sub-light pulse by the polarization beam splitter 101. The polarization state of the first sub-light pulse is |V>, and the polarization state of the second sub-light pulse is |H>.

[0043] In some embodiments, the first phase modulator 103 can include a fast axis and a slow axis. The transmission speed of the two sub-light pulses in the fast axis is higher than that in the slow axis.

[0044] In one embodiment, the first sub light pulse and the second sub light pulse can both be transmitted by the fast axis of the first phase modulator 103 through the first phase modulator 103.

[0045] Specifically, the first sub light pulse output from the second port B of the polarization beam splitter 101 is coupled to the fast axis of the first phase modulator 103 from the forward input optical port (i.e. the fourth port D) of the first phase modulator 103 through the transmission optical path 102, and the first sub light pulse is phase modulated when passing through the fast axis of the first phase modulator 103 and is output along the reverse input optical port (i.e. the fifth port E) of the first phase modulator 103. The second sub light pulse output from the third port C of the polarization beam splitter 101 is coupled to the fast axis of the first phase modulator 103 from the reverse input optical port (i.e. the fifth port E) of the first phase modulator 103 through the transmission optical path 102, and the second sub light pulse is phase modulated when passing through the fast axis of the first phase modulator 103 and is output along the forward input optical port (i.e. the fourth port D) of the first phase modulator 103.

[0046] In another embodiment, the first sub light pulse and the second sub light pulse are both transmitted by the slow axis of the first phase modulator 103 through the first phase modulator 103.

[0047] Specifically, the first sub light pulse output from the second port B of the polarization beam splitter 101 is coupled to the slow axis of the first phase modulator 103 from the forward input optical port (i.e. the fourth port D) of the first phase modulator 103 through the transmission optical path 102, and the first sub light pulse is phase modulated when passing through the slow axis of the first phase modulator 103 and is output along the reverse input optical port (i.e. the fifth port E) of the first phase modulator 103. The second sub light pulse output from the third port C of the polarization beam splitter 101 is coupled to the slow axis of the first phase modulator 103 from the reverse input optical port (i.e. the fifth port E) of the first phase modulator 103 through the transmission optical path 102, and the second sub light pulse is phase modulated when passing through the slow axis of the first phase modulator 103 and is output along the forward input optical port (i.e. the fourth port D) of the first phase modulator 103.

[0048] In the above embodiments, the transmission paths of the first sub light pulse and the second sub light pulse in the transmission optical path 102 and the first phase modulator 103 are consistent, which can ensure that the phase drifts of the two sub light pulses caused by environmental interference when passing through the transmission optical path 102 and the first phase modulator 103 are the same, so that the phase difference between them can be accurately controlled by modulating the first phase modulator 103.

[0049] In some embodiments, the first sub light pulse and the second sub light pulse are transmitted through the first phase modulator 103 at the same time. That is, at a certain time point, both of the two sub light pulses enter the first phase modulator 103 and are simultaneously affected by the high-frequency modulation signal.

[0050] In this way, since the first sub light pulse and the second sub light pulse pass through the same modulation environment at the same time, it can be ensured that the phase difference between the two sub light pulses is accurately controlled.

[0051] In some embodiments, when the first phase modulator 103 is applied to a high-frequency modulation signal with a frequency higher than a specified threshold, at the same time, the first phase modulator 103 can have sub light pulses input from the forward input port and sub light pulses input from the reverse input port.

[0052] In some embodiments, the transmission optical path 102 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.

[0053] The polarization maintaining optical fiber is a special optical fiber that can keep 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 can refer to the path of light propagating in free space, independent of optical fibers or other physical media.

[0054] In some embodiments, when the transmission optical path 102 is a polarization maintaining optical fiber, the two sub light pulses output from the second port B and the third port C of the polarization beam splitter 101 can be coupled to the slow axis of the polarization maintaining optical fiber or the fast axis of the polarization maintaining optical fiber.

[0055] When the transmission optical path 102 is a free space optical path, the two sub light pulses output from the second port B and the third port C of the polarization beam splitter 101 can be coupled to different axes of the first phase modulator 103 through the free space optical path.

[0056] In some embodiments, when the transmission optical path 102 is a free space optical path, the high-speed polarization encoding device can further include a polarization state rotator. Figure 2 Another structure of a high-speed polarization encoding device provided by an embodiment of the present application is shown in a structure diagram, Figure 2 The high-speed polarization encoding device shown is slightly different from Figure 1 As shown in the high-speed polarization encoding device shown, Figure 2 As shown, a polarization state rotator 105 is arranged between the first phase modulator 103 and the polarization beam splitter 101. The polarization state rotator 105 can be used to rotate the polarization state of a sub light pulse passing through the polarization state rotator 105 by 90°. The polarization state rotator 105 can be a half-wave plate or a 90° Faraday rotator.

[0057] It should be noted that the sub-light pulses pass through the polarization state rotator 105 clockwise or counterclockwise, and are rotated by 90 degrees.

[0058] The polarization state rotator 105 can be arranged between the third port C of the polarization beam splitter 101 and the first phase modulator 103 as shown in Figure 2 Thus, the polarization state rotator 105 can rotate the polarization state of the second sub-light pulses by 90°, so that the first sub-light pulses and the second sub-light pulses are coupled to the fast axis or the slow axis of the first phase modulator 103.

[0059] The polarization state rotator 105 can also be arranged between the second port B of the polarization beam splitter 101 and the first phase modulator 103. Thus, the polarization state rotator 105 can rotate the polarization state of the first sub-light pulses by 90°, so that the first sub-light pulses and the second sub-light pulses are coupled to the fast axis or the slow axis of the first phase modulator 103.

[0060] At the same time, the first sub-light pulses pass through the polarization state rotator 105 clockwise, the polarization state changes from |V> to |H>, and the second sub-light pulses pass through the polarization state rotator 105 counterclockwise, the polarization state changes from |H> to |V>, and the second sub-light pulses pass through the free space optical path.

[0061] In an embodiment, when the transmission optical path 102 is a polarization maintaining optical fiber, and the two sub-light pulses output from the second port B and the third port C of the polarization beam splitter 101 are coupled to different axes of the polarization maintaining optical fiber, the high-speed polarization encoding device can be as shown in Figure 2 Thus, the polarization state of the sub-light pulses transmitted along the fast axis of the polarization maintaining optical fiber is rotated by 90° by the polarization state rotator 105 and transmitted along the slow axis of the polarization maintaining optical fiber, and the polarization state of the sub-light pulses transmitted along the slow axis of the polarization maintaining optical fiber is rotated by 90° by the polarization state rotator 105 and transmitted along the fast axis of the polarization maintaining optical fiber.

[0062] In the above embodiment, by arranging the polarization state rotator 105, the first sub-light pulses and the second sub-light pulses pass through the same optical path in the transmission optical path 102 and the first phase modulator 103, so that the phase drift caused by environmental interference of the first sub-light pulses and the second sub-light pulses is the same, and thus the phase difference between them can be accurately controlled by modulating the first phase modulator 103.

[0063] In some embodiments, in order to enable the first phase modulator 103 to effectively phase modulate the second path optical pulse transmitted counterclockwise and not to effectively phase modulate the first path optical pulse transmitted clockwise, the first phase modulator 103 can be reversed and set in the transmission optical path 102, that is, the fifth port E of the first phase modulator 103 is connected to the second port B of the polarization beam splitter 101 through the transmission optical path 102, and the fourth port D of the first phase modulator 103 is connected to the third port C of the polarization beam splitter 101 through the transmission optical path 102.

[0064] In some embodiments, the phase modulated by the first phase modulator 103 can be determined based on the polarization encoding requirements of the quantum communication protocol. For example, in the quantum communication protocol BB84, the modulation requirements are two sets of four basis quantum states, and the phase modulated by the first phase modulator 103 is randomly 0°, 90°, 180°, or 270°.

[0065] In one embodiment, the phase type modulated by the first phase modulator 103 can be considered as the phase difference between the first optical pulse and the second optical pulse after phase modulation, that is, the phase effectively modulated by the first phase modulator 103 on one optical pulse.

[0066] In some embodiments, in order to reduce the types of phases modulated 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 a polarization beam splitter 301 , a transmission optical path 302 , a first phase modulator 303 , a first high-speed driver 304 , a second phase modulator 305 and a second high-speed driver 306 .

[0067] 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 305 and a second high-speed driver 306 .

[0068] Figure 3 The polarization beam splitter 301 in Figure 1 The polarization beam splitter 301 is similar to the polarization beam splitter 101 in FIG. The polarization beam splitter 301 includes a first port A, a second port B, and a third port C. The first port A serves as the input and output ports of the high-speed polarization encoding device. The polarization beam splitter 301 receives an optical pulse through the first port A and splits the optical pulse into a first optical pulse and a second optical pulse. The first optical pulse and the second optical pulse have the same intensity and orthogonal polarization states.

[0069] The second phase modulator 305 can be a phase modulator identical to the first phase modulator 303. The second phase modulator 305 can include three ports, i.e., a seventh port G, an eighth port H, and a ninth port I. Among them, the seventh port G and the eighth port H are forward input optical ports and reverse input optical ports, respectively, and the ninth port I is an electrical port.

[0070] The second phase modulator 305 can be connected in series with the first phase modulator 303 in the transmission optical path 302, i.e., the second phase modulator 305 can be connected in forward direction or in reverse direction with the first phase modulator 303.

[0071] That is, the fifth port E of the first phase modulator 303 is connected to the seventh port G of the second phase modulator 305 through the transmission optical path 302, and the eighth port H of the second phase modulator 305 is connected to the third port C of the polarization beam splitter 301 through the transmission optical path 302. Alternatively, the fifth port E of the first phase modulator 303 is connected to the eighth port H of the second phase modulator 305 through the transmission optical path 302, and the seventh port G of the second phase modulator 305 is connected to the third port C of the polarization beam splitter 301 through the transmission optical path 302.

[0072] The second phase modulator 305 can be used to cooperate with the first phase modulator 303 to phase modulate the first and second sub light pulses.

[0073] That is, the second phase modulator 305 has two functions. One is to serve as a backup phase modulator, in the case that the first phase modulator 303 fails to work, the second phase modulator works to phase modulate the first and second sub light pulses with different modulation efficiencies based on the high-frequency modulation signal applied by the second high-speed driver 306 alone. The other is to serve as a cooperative phase modulator, i.e., in the case that the first phase modulator 303 works, the second phase modulator also works to phase modulate the first and second sub light pulses based on the high-frequency modulation signal applied by each of them, respectively.

[0074] In some embodiments, the second phase modulator 305 can have multiple sub light pulses input from the forward input port and the reverse input port at the same time when the high-frequency modulation signal applied has a frequency higher than a specified threshold, which is the same as the characteristic of the first phase modulator 103.

[0075] In an embodiment, the modulation modes of the first phase modulator 303 and the second phase modulator 305 can include a single modulation mode and a combined modulation mode. The single modulation mode can refer to that the first phase modulator 303 or the second phase modulator 305 performs phase modulation alone. The combined modulation mode can refer to that the first phase modulator 303 and the second phase modulator 305 perform phase modulation cooperatively.

[0076] The second high-speed driver 306 is connected to the second phase modulator 305, that is, the second phase modulator 305 is connected to the second high-speed driver 306 through the ninth port I. The second high-speed driver 306 is used to apply a high-frequency modulation signal to the second phase modulator. It should be noted that the type and function of the second high-speed driver 306 can be the same as those of the first high-speed driver 304.

[0077] In an embodiment, the first sub-light pulse is transmitted from the second port B of the polarization beam splitter 301 to the third port C of the polarization beam splitter 301 along the clockwise direction of the transmission light path 302, and passes through the first phase modulator 303 and the second phase modulator 305. After being modulated by the first phase modulator 303 and / or the second phase modulator 305, the first sub-light pulse is transmitted to the third port C of the polarization beam splitter 301 along the clockwise direction of the transmission light path 302. The second sub-light pulse is transmitted from the third port C of the polarization beam splitter 301 to the second port B of the polarization beam splitter 301 along the counterclockwise direction of the transmission light path 302, and passes through the first phase modulator 303 and the second phase modulator 305. After being modulated by the first phase modulator 303 and / or the second phase modulator 305, the second sub-light pulse is transmitted to the second port B of the polarization beam splitter 301 along the counterclockwise direction of the transmission light path 302.

[0078] In the above embodiment, by adding the second phase modulator 305, the redundancy of the device can be increased. By cooperatively modulating the two sub-light pulses by the first phase modulator 303 and the second phase modulator 305, a more flexible phase modulation mode can be realized, and the accuracy and speed of phase control can be improved. When the first phase modulator 303 fails to work, the second phase modulator 305 is enabled to perform phase modulation, so that the phase modulation process can be ensured to proceed normally, and the device can avoid interruption.

[0079] In addition, by configuring two phase modulators in the transmission light path 302, and by combined modulation of the two phase modulators to which high-frequency modulation signals are applied, the first high-speed driver and the second high-speed driver can realize the generation of different polarization states by digital high-speed modulation.

[0080] In some embodiments, the random modulation phase of the second phase modulator 305 can be determined according to the requirements of polarization encoding in a quantum communication protocol. For example, the requirements of modulation in the quantum communication protocol BB84 are two groups of four quantum states, and the random modulation phase of the second phase modulator 305 is 0°, 90°, 180° or 270°.

[0081] In some embodiments, the phase modulated by the first phase modulator and the second phase modulator on the first sub-light pulse and the second sub-light pulse is determined according to the requirement of polarization encoding in the quantum communication protocol.

[0082] That is, no matter in the single modulation mode or in the combined modulation mode, the phase difference between the first sub-light pulse and the second sub-light pulse modulated by the first phase modulator and / or the second phase modulator meets the requirement of modulation in the quantum communication protocol. In this way, the high-precision implementation of the quantum communication protocol can be ensured, and the number of states modulated by a single phase modulator can be reduced by setting two phase modulators, thereby improving the flexibility and adaptability of the device.

[0083] In some embodiments, when the first phase modulator 303 and the second phase modulator 305 are connected in series or in reverse series, the phase difference between the first sub-light pulse and the second sub-light pulse after phase modulation is equal to the sum or the difference of the phase modulated by the first phase modulator 303 and the phase modulated by the second phase modulator 305.

[0084] That is, when the first phase modulator 303 and the second phase modulator 305 are connected in series, the phase difference between the first sub-light pulse and the second sub-light pulse after phase modulation is equal to the sum of the phase modulated by the first phase modulator 303 and the phase modulated by the second phase modulator 305.

[0085] When the first phase modulator 303 and the second phase modulator 305 are connected in reverse series, the phase difference between the first sub-light pulse and the second sub-light pulse after phase modulation is equal to the difference of the phase modulated by the first phase modulator 303 and the phase modulated by the second phase modulator 305.

[0086] The phase modulated by the first phase modulator 303 and the second phase modulator 305 on the first sub-light pulse and the second sub-light pulse can be determined according to the requirement of polarization encoding in the quantum communication protocol.

[0087] Based on this, in the combined modulation mode, the number of phases modulated by the first phase modulator 303 can be less than the requirement of modulation in the quantum communication protocol. The number of phases modulated by the second phase modulator 305 can be less than the requirement of modulation in the quantum communication protocol.

[0088] For example, in the quantum communication protocol BB84, the required modulation phase is 0°, 90°, 180° or 270°. When the first phase modulator 303 is connected in series, the phase modulated by the first phase modulator 303 can be 0° or 90°, and the phase modulated by the second phase modulator 305 can be 0° or 180°. When the first phase modulator 303 is connected in reverse series, the phase modulated by the first phase modulator 303 can be 0° or 180°, and the phase modulated by the second phase modulator 305 can be 0° or 90°.

[0089] In an embodiment, the phase modulated by the first phase modulator 303 and the phase modulated by the second phase modulator 305 are determined by the peak value of the high-frequency modulation signal applied by the respective high-speed driver.

[0090] In this way, the combination of the first phase modulator 303 and / or the second phase modulator 305 can not only achieve precise control of the polarization state, but also reduce the number of states modulated by a single phase modulator, thereby reducing the difficulty of implementing the phase modulator driver.

[0091] In some embodiments, the first sub-light pulse and the second sub-light pulse pass through the first phase modulator 303 at the same time, or the first sub-light pulse and the second sub-light pulse pass through the second phase modulator 305 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 high-frequency modulation signal, thereby helping to reduce the phase drift caused by environmental interference and improving the accuracy and reliability of the device.

[0092] 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 305 and the third port C of the polarization beam splitter 301. The polarization state rotator has the same effect as the Figure 2 The polarization state rotator has the same effect as the polarization state rotator shown, and will not be described here for brevity.

[0093] In some embodiments, Figure 1 The high-speed polarization encoding device shown and Figure 3 The high-speed polarization encoding device shown can also include an optical transmission device and a second transmission light path between the optical transmission device and the polarization beam splitter 101. The optical transmission device is connected to the first port A of the polarization beam splitter 101.

[0094] The optical transmission device can include three ports, i.e., a tenth port, an eleventh port, and a twelfth port. The tenth port of the optical transmission device is configured to receive an optical pulse. The eleventh port of the optical transmission device is configured to transmit the received optical pulse to the polarization beam splitter 101 through a second transmission optical path. The eleventh port of the optical transmission device is further configured to receive a combined optical pulse transmitted back through the second transmission optical path. The optical transmission device transmits the combined optical pulse transmitted back to the eleventh port of the optical transmission device to the twelfth port of the optical transmission device for output.

[0095] In an embodiment, the optical transmission device can include, but is not limited to, a 1x2 circulator or a 1x2 optical coupler.

[0096] In an embodiment, the high-speed polarization encoding device can also be used for high-speed polarization decoding.

[0097] Another aspect of the embodiments of the present application provides a high-speed polarization encoding method, which can be applied to any of the high-speed polarization encoding devices of the embodiments of the present application. Figure 4 The method is only applied to the high-speed polarization encoding device shown in the embodiment. Figure 1 The high-speed polarization encoding device shown in the embodiment is taken as an example for description. Figure 4 A flowchart of a high-speed polarization encoding method provided by the embodiments of the present application is shown in FIG. 4. As shown in FIG. 4, the high-speed polarization encoding method can include the following steps. Figure 4

[0098] S41, receiving an optical pulse through a first port A of the polarization beam splitter 101.

[0099] S42, splitting the received optical pulse into a first sub-optical pulse and a second sub-optical pulse through the polarization beam splitter 101.

[0100] S43, outputting the first sub-optical pulse from a second port B of the polarization beam splitter 101 and transmitting the first sub-optical pulse to the first phase modulator 103 in a clockwise direction of the transmission optical path 102, and outputting the second sub-optical pulse from a third port C of the polarization beam splitter 101 and transmitting the second sub-optical pulse to the first phase modulator 103 in an anticlockwise direction of the transmission optical path.

[0101] S44, using the first phase modulator 103 receiving a high-frequency modulation signal with a frequency higher than a specified threshold to modulate the first sub-optical pulse and the second sub-optical pulse based on the high-frequency modulation signal with different modulation efficiencies, and transmitting the phase-modulated first sub-optical pulse and the phase-modulated second sub-optical pulse to the transmission optical path 102 in the clockwise direction and the anticlockwise direction, respectively.

[0102] ​The ratio of the modulation efficiency of the first phase modulator 103 on the first sub-light pulse to the modulation efficiency on the second sub-light pulse is not less than a preset threshold. The phase-modulated first sub-light pulse and the phase-modulated second sub-light pulse have a phase difference.

[0103] S45, the first sub-light pulse and the second sub-light pulse after phase modulation by the first phase modulator 103 are combined by the polarization beam splitter 101 to obtain a combined light pulse and output by the first port A.

[0104] In the above embodiment, the received light pulse is split into the first sub-light pulse transmitted in the clockwise direction along the transmission light path 102 and the second sub-light pulse transmitted in the counterclockwise direction along the transmission light path 102 by the polarization beam splitter 101. The first sub-light pulse and the second sub-light pulse output by the polarization beam splitter 101 are phase-modulated by the first phase modulator 103 applied with a high-frequency modulation signal with different modulation efficiencies, so that the modulation efficiency of the first sub-light pulse is much higher than that of the second sub-light pulse, that is, the first sub-light pulse can be effectively phase-modulated, and the second sub-light pulse can be ineffective phase-modulated, so that the phase-modulated first sub-light pulse and the phase-modulated second sub-light pulse have a phase difference. The polarization beam splitter 101 combines and outputs the combined light pulse of the two sub-light pulses transmitted through the high-speed modulation light path, forming different polarization states. In this way, the two sub-light pulses of the polarization beam splitter 101 have the same transmission light path when combined, thereby having the advantages of self-compensation to environmental interference and high stability against interference, achieving the purpose of high-stable polarization quantum state encoding at a rate of 10GHz or higher.

[0105] In some embodiments, the method can further include that the first sub-light pulse and the second sub-light pulse are transmitted to the first phase modulator 103 by the fast axis of the first phase modulator 103, or are transmitted to the first phase modulator 103 by the slow axis of the first phase modulator 103.

[0106] In some embodiments, the method can further include that the first sub-light pulse and the second sub-light pulse are phase-modulated by the second phase modulator 305 in cooperation with the first phase modulator 303.

[0107] In some embodiments, the method can further include that the phase of the first sub-light pulse and the second sub-light pulse modulated by the first phase modulator 303 and the second phase modulator 305 is determined according to the requirement of polarization encoding of the quantum communication protocol.

[0108] In some embodiments, the polarization state of the light pulse is |H>+e iα|V>, where |H> and |V> are the two eigenpolarizations of the polarizing beam splitter 101, and a is an arbitrary value between 0 and 2π.

[0109] In some embodiments, when a is 0, the light pulse is a 45° linearly polarized light.

[0110] In some embodiments, the method can further include: receiving a light pulse through a tenth port of the optical transmission device; transmitting the received light pulse through a second transmission light path to the polarizing beam splitter 101 through an eleventh port of the optical transmission device; receiving the combined light pulse transmitted through the second transmission light path through the eleventh port of the optical transmission device; and transmitting the combined light pulse transmitted back to the eleventh port of the optical transmission device to a twelfth port of the optical transmission device for output.

[0111] In another aspect, the embodiments of the present application provide a quantum communication system, Figure 5 FIG. 5 shows a structure schematic diagram of a quantum communication system according to an embodiment of the present application. Figure 5 As shown in FIG. 5, the quantum communication system 500 can include the high-speed polarization encoding device 501 according to any of the embodiments of the present application.

[0112] It should be understood that the specific features, operations and details described above in relation to the device of the present application can be similarly applied to the method and system of the present application, or vice versa. In addition, each step of the method of the present application can be performed by the corresponding components or units of the device or system of the present application.

[0113] 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 such a combination does not result in a contradiction.

[0114] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and such 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: a polarization beam splitter, 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 high-frequency modulation signal having a frequency higher than a specified threshold to the first phase modulator; The polarization beam splitter includes a first port, a second port, and a third port. The polarization beam splitter receives a light pulse through the first port and splits the light pulse into a first light pulse and a second light pulse. The first light pulse and the second light pulse have the same intensity and orthogonal polarization states. The second port and the third port of the polarization beam splitter are connected via the transmission optical path. The first phase modulator is arranged in the transmission optical path. The first path of light pulses is output from the second port of the polarization beam splitter and transmitted to the first phase modulator along the clockwise direction of the transmission optical path. After being modulated by the first phase modulator, the light pulses are transmitted to the third port of the polarization beam splitter along the clockwise direction of the transmission optical path. The second path of light pulses is output from the third port of the polarization beam splitter and transmitted to the first phase modulator along the counterclockwise direction of the transmission optical path. After being modulated by the first phase modulator, the light pulses are transmitted to the second port of the polarization beam splitter along the counterclockwise direction of the transmission optical path. The first phase modulator is configured to perform phase modulation on the first optical pulse and the second optical pulse at different modulation efficiencies based on the high-frequency modulation signal; wherein a ratio of the modulation efficiency of the first optical pulse to the modulation efficiency of the second optical pulse is not less than a preset threshold, so that a phase difference exists between the phase-modulated first optical pulse and the phase-modulated second optical pulse; The polarization beam splitter is further configured to combine the first path optical pulse and the second path optical pulse phase-modulated by the first phase modulator to obtain a combined optical pulse and output the combined optical pulse through the first port.

2. The device according to claim 1, characterized in that The first phase modulator includes a fast axis and a slow axis; The first path optical pulse and the second path optical pulse are both transmitted to the first phase modulator through the fast axis of the first phase modulator, or are both transmitted to the first phase modulator through the slow axis of the first phase modulator.

3. The device according to claim 1, characterized in that The transmission optical path is a polarization-maintaining optical fiber or a free-space optical path.

4. The device according to claim 3, characterized in that The second port and the third port of the polarization beam splitter are both coupled to the slow axis of the polarization-maintaining optical fiber, or are both coupled to the fast axis of the polarization-maintaining optical fiber.

5. The device according to claim 1 or 3, characterized in that The apparatus further includes a polarization rotator disposed between the first phase modulator and the polarization beam splitter; The polarization state rotator is used to rotate the polarization state of a path of optical pulses passing through the polarization state rotator by 90°.

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

7. The device according to claim 6, characterized in that The phases of the first path optical pulse and the second path optical pulse modulated by the first phase modulator and the second phase modulator are determined according to the requirements of polarization encoding of the quantum communication protocol.

8. The device according to claim 1, characterized in that The first path optical pulse and the second path optical pulse are transmitted simultaneously through the first phase modulator.

9. The device according to claim 1, characterized in that The polarization state of the optical pulse is ,in and are the two eigenpolarization states of the polarization beam splitter, for ~ Any value of .

10. The device according to claim 9, characterized in that In the When it is 0, the optical pulse is 45° linearly polarized light.

11. A high-speed polarization encoding method, characterized in that: Applied to the polarization encoding device according to any one of claims 1 to 10, the method comprising: receiving an optical pulse through the first port of the polarization beam splitter; Splitting the received optical pulse into the first path optical pulse and the second path optical pulse by the polarization beam splitter; The first path of optical pulses is output from the second port of the polarization beam splitter and transmitted to the first phase modulator along the clockwise direction of the transmission optical path, and the second path of optical pulses is output from the third port of the polarization beam splitter and transmitted to the first phase modulator along the counterclockwise direction of the transmission optical path; Using the first phase modulator that receives a high-frequency modulation signal having a frequency higher than a specified threshold, phase-modulating the first optical pulse and the second optical pulse at different modulation efficiencies based on the high-frequency modulation signal, and transmitting the phase-modulated first optical pulse and the second optical pulse to a transmission optical path in a clockwise direction and a counterclockwise direction, respectively, wherein a ratio of the modulation efficiency of the first optical pulse to the modulation efficiency of the second optical pulse is not less than a preset threshold, so that a phase difference exists between the phase-modulated first optical pulse and the phase-modulated second optical pulse; The first optical pulse and the second optical pulse phase-modulated by the first phase modulator are combined by the polarization beam splitter to obtain a combined optical pulse, which is output through the first port.

12. The method according to claim 11, 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 second phase modulator cooperates with the first phase modulator to phase modulate the first path optical pulses and the second path optical pulses.

13. The method according to claim 12, characterized in that include: The phases modulated by the first phase modulator and the second phase modulator on the first path optical pulse and the second path optical pulse are determined according to the requirements of polarization encoding of the quantum communication protocol.

14. The method according to claim 11, characterized in that include: The polarization state of the optical pulse is ,in and are the two eigenpolarization states of the polarization beam splitter, for ~ Any value of .

15. The method according to claim 14, characterized in that include: In the When it is 0, the optical pulse is 45° linearly polarized light.

16. 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 10.

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