Phase modulation polarization encoding and decoding device and quantum key distribution system

Abstract

A phase modulation polarization encoding and decoding device and a quantum key distribution system, the device comprises: an optical transmission device, a birefringent phase modulator, a polarization orthogonal rotation reflection device, and a first and a second polarization-maintaining transmission optical path. The optical transmission device comprises a first, a second and a third port, the first port receives an optical pulse; the second port transmits the optical pulse to the birefringent phase modulator through the first polarization-maintaining transmission optical path, receives the optical pulse transmitted back to the first polarization-maintaining transmission optical path and then transmits it to the third port for output; the birefringent phase modulator has two ports, one port is optically coupled with the second port, and the other port is optically coupled with the polarization orthogonal rotation reflection device; the polarization orthogonal rotation reflection device performs polarization orthogonal rotation reflection on two orthogonal polarization states of the optical pulse; the phase modulator performs phase modulation on one of the optical pulses transmitted from the first and second polarization-maintaining transmission optical paths, or performs different phase modulations. Thus, the polarization state of the optical pulse is modulated more quickly through phase modulation.

Description

Technical Field

[0001] The present invention relates to the technical field of optical transmission secure communication, and in particular to a phase modulation polarization encoding and decoding device and a quantum key distribution system. Background Art

[0002] Quantum secure communication technology is a frontier hotspot combining quantum physics and information science. Based on quantum key distribution technology and the principle of one-time-one-pad cryptography, quantum secure communication can achieve secure information transmission in public channels. Quantum key distribution is based on physical principles such as the Heisenberg uncertainty relation in quantum mechanics and the quantum no-cloning theorem. It can achieve secure key sharing between users and detect potential eavesdropping. It can be applied to fields with high-security information transmission requirements such as national defense, government affairs, finance, and electricity.

[0003] Polarization-encoded quantum key distribution uses two sets of orthogonal polarization states for encoding. With the development of technology and application needs, high-speed quantum key distribution has become a trend. Polarization encoding requires random and high-speed generation of optical pulses in four polarization states. Conventionally, multiple lasers are used, each laser generates a polarization state. However, due to the inconsistency of multiple lasers, such as inconsistent central wavelengths, the security of key distribution is threatened. Realizing high-speed and stable modulation of the polarization state of optical pulses through a single laser is an important issue in the application of polarization-encoded quantum key distribution. Summary of the invention

[0004] The main purpose of the present invention is to propose a phase modulation polarization encoding and decoding device and a quantum key distribution system based on the device to solve the problem of using a single laser to achieve high-speed and stable modulation of the polarization state of an optical pulse in a polarization encoding quantum key distribution system.

[0005] The present invention provides at least the following technical solutions:

[0006] 1. A phase modulation polarization encoding and decoding device, comprising: an optical transmission device, a birefringence phase modulator, a polarization orthogonal rotation reflection device, a first polarization-maintaining transmission optical path optically coupled to the optical transmission device and the birefringence phase modulator, and a second polarization-maintaining transmission optical path optically coupled to the birefringence phase modulator and the polarization orthogonal rotation reflection device, wherein:

[0007] The optical transmission device comprises a first port, a second port and a third port, wherein the first port of the optical transmission device is configured to receive an input optical pulse, the second port of the optical transmission device is configured to transmit the received input optical pulse to the birefringence phase modulator through the first polarization-maintaining transmission optical path, the second port of the optical transmission device is further configured to receive an optical pulse transmitted back through the first polarization-maintaining transmission optical path, and the optical transmission device transmits the optical pulse transmitted back to the second port of the optical transmission device to the third port of the optical transmission device for output;

[0008] The birefringence phase modulator has two ports, one of the two ports is optically coupled to the second port of the optical transmission device through the first polarization-maintaining transmission optical path, and the other of the two ports is optically coupled to the polarization orthogonal rotation reflection device through the second polarization-maintaining transmission optical path;

[0009] The polarization orthogonal rotation reflection device is configured to perform polarization orthogonal rotation reflection on the two orthogonal polarization states of the light pulse output from the birefringence phase modulator to the second polarization-maintaining transmission optical path, so that after being reflected by the polarization orthogonal rotation reflection device, the two orthogonal polarization states of the light pulse of this path are respectively transformed into polarization states orthogonal thereto; wherein,

[0010] The birefringence phase modulator is configured to: perform phase modulation on one of the light pulse transmitted through the first polarization-maintaining transmission optical path and the light pulse transmitted through the second polarization-maintaining transmission optical path, or perform different phase modulation on the light pulse transmitted through the first polarization-maintaining transmission optical path and the light pulse transmitted through the second polarization-maintaining transmission optical path.

[0011] 2. A phase-modulated polarization encoding and decoding device according to Scheme 1, wherein the polarization orthogonal rotation reflection device is a quarter-wave plate reflector, the quarter-wave plate reflector comprises a reflector and a quarter-wave plate, and the reflector is integrally formed with the quarter-wave plate at the rear end of the quarter-wave plate.

[0012] 3. The phase modulation polarization encoding and decoding device according to Scheme 1, wherein the optical transmission device is an optical circulator or an optical coupler.

[0013] 4. The phase-modulation polarization encoding and decoding device according to Solution 2, wherein the first polarization-maintaining transmission optical path is a first polarization-maintaining optical fiber, and / or the second polarization-maintaining transmission optical path is a second polarization-maintaining optical fiber.

[0014] 5. A phase-modulation polarization encoding and decoding device according to Scheme 1 or 3, wherein the optical transmission device is a polarization-maintaining device, and its port is a free space port or a polarization-maintaining fiber port.

[0015] 6. A phase-modulated polarization encoding and decoding device according to Scheme 4, wherein the amplitude components of the light pulse output to the first polarization-maintaining optical fiber via the second port of the optical transmission device projected along the slow axis and the fast axis of the first polarization-maintaining optical fiber are the same in magnitude and the relative phase is an arbitrary phase.

[0016] 7. A phase-modulation polarization encoding and decoding device according to Scheme 6, wherein the optical pulse output to the first polarization-maintaining optical fiber via the second port of the optical transmission device is in a circular polarization state or in a linear polarization state with an angle of 45 degrees with the slow axis or fast axis of the first polarization-maintaining optical fiber.

[0017] 8. A phase-modulation polarization encoding and decoding device according to Scheme 4, wherein the angle between the slow axis of the second polarization-maintaining optical fiber and the slow axis or fast axis of the quarter-wave plate in the quarter-wave plate reflector is 45 degrees.

[0018] 9. A quantum key distribution system, comprising a transmitting end and a receiving end, wherein:

[0019] A phase modulation polarization encoding and decoding device according to any one of schemes 1-8 is provided at the transmitting end for polarization encoding; and / or

[0020] The receiving end is provided with a phase modulation polarization encoding and decoding device according to any one of Schemes 1-8 for polarization decoding or polarization decoding selection.

[0021] 10. The quantum key distribution system according to solution 9, wherein:

[0022] When used for polarization decoding, the receiving end of the quantum key distribution system further includes a polarizer optically coupled to the phase modulation polarization encoding and decoding device and a single photon detector optically coupled to the polarizer; or,

[0023] When used for polarization decoding and base selection, the receiving end of the quantum key distribution system also includes a polarization beam splitter optically coupled to the phase modulation polarization encoding and decoding device and two single-photon detectors optically coupled to the polarization beam splitter.

[0024] The present invention uses a creative configuration to use a birefringent phase modulator to perform phase modulation on one of the optical pulses transmitted through the first polarization-maintaining transmission optical path and the optical pulses transmitted through the second polarization-maintaining transmission optical path, or to perform different phase modulation on the optical pulses transmitted through the first polarization-maintaining transmission optical path and the optical pulses transmitted through the second polarization-maintaining transmission optical path, so that high-speed modulation of the polarization state of the optical pulse can be achieved through phase modulation, and the polarization state modulation achieved by using a polarization orthogonal rotation reflection device is independent of the interference between the first polarization-maintaining transmission optical path and the second polarization-maintaining transmission optical path. The phase modulation polarization encoding and decoding device and the corresponding quantum key distribution system of the present invention can easily achieve the technical effect of high-speed and stable modulation of the polarization state of the optical pulse by modulating the phase, solving the above-mentioned technical problem that it is difficult to modulate the polarization state of the optical pulse at high speed and in a stable manner using a single laser. The present invention provides a solution for a phase modulation polarization encoding and decoding device and a corresponding quantum key distribution system that is easy to implement and apply. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of the composition structure of a phase modulation polarization encoding and decoding device according to a preferred embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the structure of a quantum key distribution system according to a preferred embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram of the composition structure of a quantum key distribution system according to another preferred embodiment of the present invention. DETAILED DESCRIPTION

[0028] Embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to explain the principles of the present invention. For the purpose of clarity and simplicity, detailed descriptions of known functions and structures of the devices described herein will be omitted when they may obscure the subject matter of the present invention.

[0029] According to one aspect of the present invention, a phase modulation polarization encoding and decoding device is provided, which includes: an optical transmission device, a birefringence phase modulator, a polarization orthogonal rotation reflection device, a first polarization-maintaining transmission optical path optically coupled to the optical transmission device and the birefringence phase modulator, and a second polarization-maintaining transmission optical path optically coupled to the birefringence phase modulator and the polarization orthogonal rotation reflection device, respectively.

[0030] Specifically, the optical transmission device includes a first port, a second port and a third port. The first port of the optical transmission device is configured to receive an input optical pulse, and the second port of the optical transmission device is configured to transmit the received input optical pulse to the birefringence phase modulator through the first polarization-maintaining transmission optical path. The second port of the optical transmission device is further used to receive an optical pulse transmitted back through the first polarization-maintaining transmission optical path, and the optical transmission device transmits the optical pulse transmitted back to the second port of the optical transmission device to the third port of the optical transmission device for output.

[0031] Preferably, the optical transmission device is an optical circulator or an optical coupler. In addition, preferably, the optical transmission device is a polarization-maintaining device, and the first port, the second port and the third port of the optical transmission device can be free space ports or polarization-maintaining fiber ports.

[0032] The birefringent phase modulator has two ports, one of the two ports is optically coupled to the second port of the optical transmission device through the first polarization-maintaining transmission optical path, and the other of the two ports is optically coupled to the polarization orthogonal rotation reflection device through the second polarization-maintaining transmission optical path.

[0033] The polarization orthogonal rotation reflection device is configured to perform polarization orthogonal rotation reflection on the two orthogonal polarization states of the light pulse output from the birefringence phase modulator to the second polarization-maintaining transmission optical path, so that after reflection by the polarization orthogonal rotation reflection device, the two orthogonal polarization states of the light pulse in this path are respectively transformed into polarization states orthogonal thereto.

[0034] Preferably, the polarization orthogonal rotation reflection device is a quarter wave plate reflector, the quarter wave plate reflector includes a reflector and a quarter wave plate, and the reflector is formed integrally with the quarter wave plate at the rear end of the quarter wave plate. The birefringence phase modulator is configured to: perform phase modulation on one of the light pulse transmitted through the first polarization-maintaining transmission optical path and the light pulse transmitted through the second polarization-maintaining transmission optical path, or perform different phase modulation on the light pulse transmitted through the first polarization-maintaining transmission optical path and the light pulse transmitted through the second polarization-maintaining transmission optical path.

[0035] Preferably, the first polarization-maintaining transmission optical path is a first polarization-maintaining optical fiber, and / or the second polarization-maintaining transmission optical path is a second polarization-maintaining optical fiber.

[0036] Figure 1 FIG. 2 shows a phase modulation polarization encoding and decoding device according to a preferred embodiment of the present invention. Figure 1As shown, the phase modulation polarization encoding and decoding device includes the following components: an optical transmission device 102, a birefringence phase modulator 104, a first polarization-maintaining optical fiber 103 optically coupled to the optical transmission device and the birefringence phase modulator, respectively, a second polarization-maintaining optical fiber 105 optically coupled to the birefringence phase modulator and the polarization orthogonal rotation reflection device, respectively, and a polarization orthogonal rotation reflection device 106 (hereinafter referred to as "reflection device" 106).

[0037] The optical transmission device 102 includes three ports, namely a first port A, a second port B and a third port C. The first port A (i.e., port 101) of the optical transmission device 102 is an input port of the phase modulation polarization encoding and decoding device, and is configured to receive an input optical pulse. The third port C (i.e., port 107) of the optical transmission device 102 is an output port of the phase modulation polarization encoding and decoding device. The second port B of the optical transmission device is configured to transmit the received input optical pulse to the birefringence phase modulator 104 through the first polarization-maintaining optical fiber 103, and the second port B of the optical transmission device is further used to receive the optical pulse transmitted back through the first polarization-maintaining optical fiber 103, and then transmit the transmitted optical pulse back to the third port C of the optical transmission device for output. Specifically, the light pulse input to the first port A of the optical transmission device 102 is output from the second port B of the optical transmission device 102 to the first polarization-maintaining optical fiber 103, and after passing through the birefringence phase modulator 104, is transmitted to the polarization orthogonal rotation reflection device 106 via the second polarization-maintaining optical fiber 105. The polarization orthogonal rotation reflection device 106 returns the phase-modulated light pulse to the first polarization-maintaining optical fiber 103 via the second polarization-maintaining optical fiber 105 after polarization orthogonal rotation reflection, and arrives at the second port B of the optical transmission device 102, and is output from the third port C of the optical transmission device 102.

[0038] Preferably, the optical transmission device 102 may be a three-port optical circulator or a 1×2 optical coupler. Preferably, the optical transmission device 102 is a polarization-maintaining device, and its port is a free space port or a polarization-maintaining optical fiber port.

[0039] The birefringent phase modulator 104 has two ports, one of which (eg, Figure 1 The left port in the figure) is optically coupled to the second port B of the optical transmission device through the first polarization-maintaining optical fiber 103, and the other of the two ports (for example, Figure 1 The right side port in the figure) is optically coupled to the polarization orthogonal rotation reflection device 106 through the second polarization-maintaining optical fiber 105.

[0040] The polarization orthogonal rotation reflection device 106 is configured to perform polarization orthogonal rotation reflection on the two orthogonal polarization states of the light pulse output from the birefringence phase modulator to the second polarization-maintaining optical fiber, so that after reflection by the polarization orthogonal rotation reflection device, the two orthogonal polarization states of the light pulse are respectively transformed into polarization states orthogonal thereto, and the phase between the two orthogonal polarization states after reflection is the same as the phase between the two orthogonal polarization states before reflection.

[0041] The birefringence phase modulator 104 is configured to: perform phase modulation on one of the optical pulse transmitted through the first polarization-maintaining optical fiber 103 and the optical pulse transmitted through the second polarization-maintaining optical fiber 105, or perform different phase modulations on the optical pulse transmitted through the first polarization-maintaining optical fiber 103 and the optical pulse transmitted through the second polarization-maintaining optical fiber 105. In other words, the birefringence phase modulator 104 only performs phase modulation on the optical pulse input through one of the two ports of the birefringence phase modulator, or performs different phase modulations on the optical pulses input through the two ports. The birefringence phase modulator 104 is suitable for applying different adjustable phase modulations to the two orthogonal polarization states of the optical pulse passing through it. For example, the birefringence phase modulator can be a lithium niobate birefringence phase modulator, and by controlling the voltage applied to the lithium niobate crystal, the phase modulations respectively experienced by the two orthogonal polarization states passing through the lithium niobate birefringence phase modulator can be controlled and adjusted.

[0042] In this article, the polarization orthogonal rotation reflection device can perform polarization orthogonal rotation reflection on two orthogonal polarization states of an input optical pulse, so that after reflection by the polarization orthogonal rotation reflection device, the two orthogonal polarization states of the optical pulse are respectively transformed into polarization states orthogonal thereto, and the phase between the two orthogonal polarization states after reflection is the same as the phase between the two orthogonal polarization states before reflection. For example, assuming that the two orthogonal polarization states of the input optical pulse are respectively an x ​​polarization state and a y polarization state, the x polarization state of the optical pulse transmitted along the optical path to a polarization orthogonal rotation reflection device is transformed into a polarization state orthogonal thereto, namely, a y polarization state, after polarization orthogonal rotation reflection at the reflection device, and the y polarization state of the optical pulse transmitted along the optical path to the reflection device is transformed into a polarization state orthogonal thereto, namely, an x ​​polarization state, after polarization orthogonal rotation reflection at the polarization orthogonal rotation reflection device, and the phase between the y polarization state and the x polarization state after reflection is the same as the phase between the x polarization state and the y polarization state before reflection.

[0043] Specifically, the polarization orthogonal rotation reflection device 106 can reflect the orthogonal polarization states corresponding to the slow axis and the fast axis of the second polarization-maintaining optical fiber 105 and transform them into polarization states orthogonal thereto. For example, the polarization orthogonal rotation reflection device 106 reflects the light pulse input from the slow axis of the second polarization-maintaining optical fiber 105 and outputs it from the fast axis of the second polarization-maintaining optical fiber 105; the polarization orthogonal rotation reflection device 106 reflects the light pulse input from the fast axis of the second polarization-maintaining optical fiber 105 and outputs it from the slow axis of the second polarization-maintaining optical fiber 105.

[0044] According to a possible configuration, the polarization orthogonal rotation reflection device 106 is a quarter wave plate reflector, the quarter wave plate reflector includes a reflector and a quarter wave plate, and the reflector is integrally formed with the quarter wave plate at the rear end of the quarter wave plate. Preferably, the angle between the slow axis of the second polarization-maintaining optical fiber and the slow axis or fast axis of the quarter wave plate in the quarter wave plate reflector is 45 degrees.

[0045] In one embodiment, the amplitude components of the light pulse outputted from the second port B of the optical transmission device 102 along the slow axis and the fast axis of the first polarization-maintaining optical fiber are the same in magnitude and the relative phase is an arbitrary phase. The following is an example of the light pulses whose amplitude components along the slow axis and the fast axis of the first polarization-maintaining optical fiber are the same in magnitude and the relative phase is an arbitrary phase. Assume that the polarized light transmitted along the slow axis and the fast axis of the polarization-maintaining optical fiber are in the x polarization state and the y polarization state, respectively, and are represented by The amplitude of the light pulse can be expressed as Where A and B represent the amplitude of the x polarization state and the y polarization state respectively and A=B, the relative phase is an arbitrary phase. Therefore, the amplitude component projected onto the slow axis of the polarization-maintaining fiber is A, and the amplitude component projected onto the fast axis of the polarization-maintaining fiber is The two amplitude components have the same magnitude and an arbitrary relative phase. Preferably, the optical pulse outputted through the second port B of the optical transmission device 102 is in a circular polarization state or a linear polarization state with an angle of 45 degrees with the slow axis or fast axis of the first polarization-maintaining optical fiber.

[0046] If the optical transmission device 102 which is an optical circulator is replaced by a 1×2 optical coupler, the above results are not affected.

[0047] The working process of the phase modulation polarization encoding and decoding device of the present invention will be described below in conjunction with a specific embodiment.

[0048] A linearly polarized light pulse is input into the phase modulation polarization encoding and decoding device via port 101 (i.e., the first port A of the optical transmission device 102), and then output to the first polarization-maintaining optical fiber 103 via the second port B of the optical transmission device 102. The polarization state of the light pulse input into the first polarization-maintaining optical fiber 103 has an angle of 45 degrees with the slow axis of the first polarization-maintaining optical fiber 103. The light pulse input into the first polarization-maintaining optical fiber 103 can be divided into a first component light pulse and a second component light pulse (for example, a horizontal component and a vertical component). The first component light pulse and the second component light pulse can be transmitted to the birefringence phase modulator 104, for example, along the slow axis and the fast axis of the first polarization-maintaining optical fiber 103, respectively. Assume that the first component light pulse is transmitted along the slow axis of the birefringent phase modulator 104 and output to the second polarization-maintaining fiber 105 for transmission along the slow axis, and then the first component light pulse continues to be transmitted along the slow axis of the second polarization-maintaining fiber 105 to the polarization orthogonal rotation reflection device 106 and after being reflected by the polarization orthogonal rotation reflection device 106, it is respectively returned along the fast axis of the second polarization-maintaining fiber 105, the fast axis of the phase modulator 104, and the fast axis of the first polarization-maintaining fiber 103 for transmission in sequence, and is output to the second port B of the optical transmission device 102, and then output from the third port C of the optical transmission device 102. Assume that the second component light pulse is transmitted along the fast axis of the birefringence phase modulator 104 and output to the fast axis of the second polarization-maintaining fiber 105 for transmission, and then the second component light pulse continues to be transmitted along the fast axis of the second polarization-maintaining fiber 105 to the polarization orthogonal rotation reflection device 106 and after being reflected by the polarization orthogonal rotation reflection device 106, it is respectively transmitted back along the slow axis of the second polarization-maintaining fiber 105, the slow axis of the phase modulator 104, and the slow axis of the first polarization-maintaining fiber 103 in sequence, and is output to the second port B of the optical transmission device 102, and then output from the third port C of the optical transmission device 102.

[0049] Only when the optical pulse is inputted into the birefringence phase modulator 104 for transmission from the first polarization-maintaining optical fiber 103, or only when the optical pulse is inputted into the birefringence phase modulator 104 for transmission from the second polarization-maintaining optical fiber 105, the phase modulation is performed on the birefringence phase modulator 104. In other words, the birefringence phase modulator only modulates the optical pulse that passes through the birefringence phase modulator once. Thus, the function of modulating the polarization state of the optical pulse can be achieved by modulating the phase difference between the two components (two orthogonal polarization state components) of the optical pulse. Alternatively, in an alternative embodiment, when the optical pulse is inputted into the birefringence phase modulator 104 for transmission from the first polarization-maintaining optical fiber 103, and when the optical pulse is inputted into the birefringence phase modulator 104 for transmission from the second polarization-maintaining optical fiber 105, the birefringence phase modulator 104 performs different phase modulations on the two components respectively, thereby achieving the function of modulating the polarization state of the optical pulse.

[0050] Since the polarization orthogonal rotation reflection device 106 is a device that can perform polarization orthogonal rotation reflection on the two polarization states of the input optical pulse, the phase difference (inherent when not modulated) between the two components of the optical pulse caused by the slow axis and the fast axis of the birefringence phase modulator 104, the first polarization-maintaining optical fiber 103 and the second polarization-maintaining optical fiber 105 and the insertion loss inconsistency can be automatically compensated. Therefore, the polarization modulation of the optical pulse is only related to the phase difference generated by the phase modulation of the two components (two orthogonal polarization state components) of the optical pulse by the birefringence phase modulator 104, so that stable polarization state modulation can be achieved. By using the birefringence phase modulator 104 to phase modulate one of the optical pulse transmitted through the first polarization-maintaining optical fiber 103 and the optical pulse transmitted through the second polarization-maintaining optical fiber 105, or by performing different phase modulation on the optical pulse transmitted through the first polarization-maintaining optical fiber 103 and the optical pulse transmitted through the second polarization-maintaining optical fiber 105, the birefringence phase modulator 104 can be used to perform high-speed modulation of the phase difference between the two orthogonal polarization states of the optical pulse, thereby achieving high-speed polarization state modulation.

[0051] Another aspect of the present invention provides a quantum key distribution system, including a transmitting end and a receiving end, wherein: the above-mentioned phase modulation polarization encoding and decoding device is arranged at the transmitting end for polarization encoding; and / or the above-mentioned phase modulation polarization encoding and decoding device is arranged at the receiving end for polarization decoding or polarization decoding selection.

[0052] In one embodiment, when used for polarization decoding, the receiving end of the quantum key distribution system also includes a polarizer optically coupled to the phase modulation polarization encoding and decoding device and a single photon detector optically coupled to the polarizer; or, when used for polarization decoding base selection, the receiving end of the quantum key distribution system also includes a polarization beam splitter optically coupled to the phase modulation polarization encoding and decoding device and two single photon detectors optically coupled to the polarization beam splitter.

[0053] Figure 2 A schematic diagram showing the composition structure of a quantum key distribution system according to a preferred embodiment of the present invention. Figure 2 The quantum key distribution system shown in the figure includes the following components: a laser 201, an intensity modulator 202, a polarization encoder 203, an attenuator 204, a quantum channel 205, a polarization controller 206, a polarization decoding base selection device 207, a polarization beam splitter 208, and single photon detectors 209 and 210.

[0054] Specifically, a laser 201, an intensity modulator 202, a polarization encoder 203 and an attenuator 204 are arranged at the transmitting end of the quantum key distribution system, wherein: the laser 201 is used to generate a light pulse; the intensity modulator 202 is used to randomly modulate the intensity of the light pulse generated by the laser 201 to generate a decoy state; the polarization encoder 203 is the above-mentioned phase modulation polarization encoding and decoding device, which can be used to polarization encode the light pulse; the attenuator 204 is used to attenuate the light pulse to a single photon state output.

[0055] The quantum channel 205 is arranged between the transmitting end and the receiving end of the quantum key distribution system for transmitting single photon optical pulses. The quantum channel 205 can be an optical propagation channel composed of an optical waveguide, an optical fiber, free space, a discrete optical element, a planar waveguide optical element, a fiber optical element, or any combination of two or more of the above.

[0056] A polarization controller 206, a polarization decoding base selection device 207, a polarization beam splitter 208, and single-photon detectors 209 and 210 are arranged at the receiving end of the quantum key distribution system, wherein: the polarization controller 206 is used to adjust the polarization state of the single-photon light pulse; the polarization decoding base selection device 207 is the above-mentioned phase modulation polarization encoding and decoding device, which can be used to perform polarization decoding and base selection on the single-photon light pulse; the polarization beam splitter 208 is used to output the single-photon light pulse to the single-photon detector after polarization beam splitting, and together with the polarization decoding base selection device 207, constitutes a polarization decoding device; the single-photon detectors 209 and 210 are used to detect the single-photon light pulse output by the polarization beam splitter 208, and perform quantum key distribution according to the detection results and the quantum key distribution protocol.

[0057] In operation, at the transmitting end, the laser 201 emits a light pulse into the intensity modulator 202, and the intensity modulator 202 randomly modulates the intensity of the light pulse to generate a signal state and a decoy state and outputs it to the polarization encoder 203. The polarization encoder 203 randomly encodes the light pulse in four polarization states (for example, encoding to ±45 degree linear polarization state and left / right circular polarization state) and then outputs it to the attenuator 204. The attenuator 204 attenuates the encoded light pulse into a single photon light pulse (for example, attenuates to an average of 0.1 photons per pulse) and then outputs it to the quantum channel 205. The quantum channel 205 can be a single-mode optical fiber or free space, and the single-photon light pulse is transmitted to the receiving end through the quantum channel 205 for polarization decoding.

[0058] At the receiving end, the single-photon light pulse is input to the polarization controller 206, and the polarization controller 206 is used to compensate for the change in polarization state caused by the influence of the quantum channel and the birefringence of the optical path at the transmitting end and the receiving end before the polarization decoding of the single-photon light pulse. The single-photon light pulse output from the polarization controller 206 is input to the polarization decoding base selection device 207 for polarization decoding base selection (for example, a diagonal basis corresponding to the encoding of the ±45 degree linear polarization state and a circular polarization basis corresponding to the left / right circular polarization state are selected). The single-photon light pulse output from the polarization decoding base selection device 207 is input to the polarization beam splitter 208 for polarization beam splitting, and the light pulse after polarization beam splitting by the polarization beam splitter 208 is input to the single-photon detector 209 or 210 for result detection. Both the polarization encoder 203 and the polarization decoding base selection device 207 can be combined with the above Figure 1 The described phase modulation bias encoding and decoding device is implemented, and polarization encoding and polarization decoding bases are selected for optical pulses respectively according to the quantum key distribution protocol, so as to distribute keys according to the quantum key distribution protocol.

[0059] Figure 3 A schematic diagram showing the composition structure of a quantum key distribution system according to a preferred embodiment of the present invention. Figure 3 The quantum key distribution system shown in the figure includes the following components: a laser 301, an intensity modulator 302, a polarization encoder 303, an attenuator 304, a quantum channel 305, a polarization controller 306, a polarization decoder 307, a polarizer 308, and a single photon detector 309.

[0060] Specifically, similar to Figure 2 At the transmitter, Figure 3 In the figure, the laser 301, the intensity modulator 302, the polarization encoder 303 and the attenuator 304 are arranged at the transmitting end of the quantum key distribution system, wherein the laser 301 is used to generate a light pulse; the intensity modulator 302 is used to randomly perform intensity modulation on the light pulse generated by the laser 301 to generate a decoy state; the polarization encoder 303 is the above-mentioned phase modulation polarization encoding and decoding device, which is used to perform polarization encoding on the light pulse; and the attenuator 304 is used to attenuate the light pulse to a single-photon state output.

[0061] Similar to Figure 2 The quantum channel 305 is arranged between the transmitting end and the receiving end of the quantum key distribution system for transmitting single photon light pulses. The quantum channel 305 can also be an optical waveguide, an optical fiber, a free space, a discrete optical element, a planar waveguide optical element, a fiber optical element, or a light propagation channel composed of any two or more of the above.

[0062] A polarization controller 306, a polarization decoder 307, a polarizer 308, and a single-photon detector 309 are arranged at the receiving end of the quantum key distribution system, wherein: the polarization controller 306 is used to adjust the polarization state of the single-photon light pulse; the polarization decoder 307 is the above-mentioned phase modulation polarization encoding and decoding device, which is used to perform polarization decoding on the single-photon light pulse; the polarizer 308 is used to polarize and output the single-photon light pulse; the single-photon detector 309 is used to detect the single-photon light pulse output by the polarizer 308, and perform quantum key distribution according to the detection result and the quantum key distribution protocol.

[0063] At work, similar to Figure 2 At the transmitter, Figure 3 At the transmitting end in the embodiment, the laser 301 emits a light pulse into the intensity modulator 302, and the intensity modulator 302 randomly modulates the intensity of the light pulse to generate a signal state and a decoy state and outputs them to the polarization encoder 303. The polarization encoder 303 randomly encodes the light pulse in four polarization states (for example, encoding to ±45 degree linear polarization state and left / right circular polarization state) and then outputs it to the attenuator 304. The attenuator 304 attenuates the encoded light pulse into a single photon light pulse (for example, attenuates to an average of 0.1 photons per pulse) and then outputs it to the quantum channel 305. The quantum channel 305 can be a single-mode optical fiber or free space, and the single-photon light pulse is transmitted to the receiving end through the quantum channel 305 for polarization decoding.

[0064] At the receiving end, the single-photon light pulse is input to the polarization controller 306, and the polarization controller 306 is used to compensate for the change in polarization state caused by the influence of the quantum channel and the birefringence of the optical path at the transmitting end and the receiving end before the polarization decoding of the single-photon light pulse. The single-photon light pulse output from the polarization controller 306 is input to the polarization decoder 307 for polarization decoding (for example, the ±45 degree linear polarization state and the corresponding left / right circular polarization state are decoded). The single-photon light pulse output from the polarization decoder 307 is input to the polarizer 308 for polarization, and the light pulse polarized by the polarizer 308 is input to the single-photon detector 309 for detection. The polarization encoder 303 and the polarization decoder 307 respectively perform polarization encoding and polarization decoding on the light pulse according to the quantum key distribution protocol, and perform key distribution according to the quantum key distribution protocol.

[0065] In this article, the transmission optical path formed by "polarization-maintaining optical fiber" refers to an optical path that uses polarization-maintaining optical fiber to transmit optical pulses or an optical path formed by connecting polarization-maintaining optical fibers.

[0066] Through the description of the specific implementation methods, one should be able to have a more in-depth and specific understanding of the technical means and effects adopted by the present invention to achieve the predetermined purpose. However, the accompanying drawings are only for reference and illustration purposes and are not intended to limit the present invention.

Claims

1. A phase modulation polarization encoding and decoding device, comprising: An optical transmission device, a birefringent phase modulator, a polarization orthogonal rotation reflection device, a first polarization-maintaining transmission optical path optically coupled to the optical transmission device and the birefringent phase modulator, and a second polarization-maintaining transmission optical path optically coupled to the birefringent phase modulator and the polarization orthogonal rotation reflection device, wherein: The optical transmission device comprises a first port, a second port and a third port, wherein the first port of the optical transmission device is configured to receive an input optical pulse, the second port of the optical transmission device is configured to transmit the received input optical pulse to the birefringence phase modulator through the first polarization-maintaining transmission optical path, the second port of the optical transmission device is further configured to receive an optical pulse transmitted back through the first polarization-maintaining transmission optical path, and the optical transmission device transmits the optical pulse transmitted back to the second port of the optical transmission device to the third port of the optical transmission device for output; The birefringence phase modulator has two ports, one of the two ports is optically coupled to the second port of the optical transmission device through the first polarization-maintaining transmission optical path, and the other of the two ports is optically coupled to the polarization orthogonal rotation reflection device through the second polarization-maintaining transmission optical path; The polarization orthogonal rotation reflection device is configured to perform polarization orthogonal rotation reflection on the two orthogonal polarization states of the light pulse output from the birefringence phase modulator to the second polarization-maintaining transmission optical path, so that after being reflected by the polarization orthogonal rotation reflection device, the two orthogonal polarization states of the light pulse of this path are respectively transformed into polarization states orthogonal thereto; wherein, The birefringence phase modulator is configured to: perform phase modulation on one of the light pulse transmitted through the first polarization-maintaining transmission optical path and the light pulse transmitted through the second polarization-maintaining transmission optical path, or perform different phase modulation on the light pulse transmitted through the first polarization-maintaining transmission optical path and the light pulse transmitted through the second polarization-maintaining transmission optical path.

2. The phase modulation polarization encoding and decoding device according to claim 1, wherein: The polarization orthogonal rotation reflection device is a quarter wave plate reflector, which includes a reflector and a quarter wave plate, and the reflector is integrally formed with the quarter wave plate at the rear end of the quarter wave plate.

3. The phase modulation polarization encoding and decoding device according to claim 1, wherein: The optical transmission device is an optical circulator or an optical coupler.

4. The phase modulation polarization encoding and decoding device according to claim 2, wherein: The first polarization-maintaining transmission optical path is a first polarization-maintaining optical fiber, and / or the second polarization-maintaining transmission optical path is a second polarization-maintaining optical fiber.

5. The phase modulation polarization encoding and decoding device according to claim 1 or 3, wherein: The optical transmission device is a polarization-maintaining device, and its port is a free space port or a polarization-maintaining optical fiber port.

6. The phase modulation polarization encoding and decoding device according to claim 4, wherein: The amplitude components of the light pulse output to the first polarization-maintaining optical fiber via the second port of the optical transmission device projected along the slow axis and the fast axis of the first polarization-maintaining optical fiber are the same in magnitude and the relative phase is an arbitrary phase.

7. The phase modulation polarization encoding and decoding device according to claim 6, wherein: The optical pulse output to the first polarization-maintaining optical fiber via the second port of the optical transmission device is in a circular polarization state or in a linear polarization state with an angle of 45 degrees with the slow axis or the fast axis of the first polarization-maintaining optical fiber.

8. The phase modulation polarization encoding and decoding device according to claim 4, wherein: The angle between the slow axis of the second polarization-maintaining optical fiber and the slow axis or the fast axis of the quarter-wave plate in the quarter-wave plate reflector is 45 degrees.

9. A quantum key distribution system, comprising a transmitting end and a receiving end, wherein: A phase modulation polarization encoding and decoding device according to any one of claims 1 to 8 is provided at the transmitting end for polarization encoding; and / or The receiving end is provided with a phase modulation polarization encoding and decoding device according to any one of claims 1 to 8 for polarization decoding or polarization decoding base selection.

10. The quantum key distribution system according to claim 9, wherein: When used for polarization decoding, the receiving end of the quantum key distribution system further includes a polarizer optically coupled to the phase modulation polarization encoding and decoding device and a single photon detector optically coupled to the polarizer; or, When used for polarization decoding and base selection, the receiving end of the quantum key distribution system also includes a polarization beam splitter optically coupled to the phase modulation polarization encoding and decoding device and two single-photon detectors optically coupled to the polarization beam splitter.

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