WO2018059338A1 - 一种编码装置及基于该装置的量子密钥分发设备及系统 - Google Patents

一种编码装置及基于该装置的量子密钥分发设备及系统 Download PDF

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WO2018059338A1
WO2018059338A1 PCT/CN2017/103058 CN2017103058W WO2018059338A1 WO 2018059338 A1 WO2018059338 A1 WO 2018059338A1 CN 2017103058 W CN2017103058 W CN 2017103058W WO 2018059338 A1 WO2018059338 A1 WO 2018059338A1
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Prior art keywords
polarized light
light
psr
sub
polarization
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PCT/CN2017/103058
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English (en)
French (fr)
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梁文烨
苏长征
肖新华
方志方
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华为技术有限公司
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Priority to KR1020197011360A priority Critical patent/KR102151014B1/ko
Priority to JP2019516527A priority patent/JP6729852B2/ja
Priority to EP17854788.1A priority patent/EP3512154B1/en
Publication of WO2018059338A1 publication Critical patent/WO2018059338A1/zh
Priority to US16/364,512 priority patent/US11327233B2/en

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/27—Optical coupling means with polarisation selective and adjusting means
    • G02B6/2753—Optical coupling means with polarisation selective and adjusting means characterised by their function or use, i.e. of the complete device
    • G02B6/2766—Manipulating the plane of polarisation from one input polarisation to another output polarisation, e.g. polarisation rotators, linear to circular polarisation converters
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
    • H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
    • H04L9/0852—Quantum cryptography
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/27—Optical coupling means with polarisation selective and adjusting means
    • G02B6/2746—Optical coupling means with polarisation selective and adjusting means comprising non-reciprocal devices, e.g. isolators, FRM, circulators, quasi-isolators
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/09—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on magneto-optical elements, e.g. exhibiting Faraday effect
    • G02F1/093—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on magneto-optical elements, e.g. exhibiting Faraday effect used as non-reciprocal devices, e.g. optical isolators, circulators
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/70—Photonic quantum communication
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
    • H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
    • H04L9/0852—Quantum cryptography
    • H04L9/0858—Details about key distillation or coding, e.g. reconciliation, error correction, privacy amplification, polarisation coding or phase coding

Definitions

  • the present invention relates to the field of optical communications, and in particular, to an encoding apparatus and a quantum key distribution QKD apparatus and system based on the encoding apparatus.
  • Quantum communication is a communication technology developed on the basis of classical information theory and quantum mechanics.
  • the practical quantum communication technology now mainly refers to Quantum Key Distribution (QKD).
  • QKD Quantum Key Distribution
  • the security of the key depends on the basic principles of quantum mechanics, such as measuring the collapse theory, the principle of non-cloning and uncertainty. Therefore, the key allocated to the communication parties by the QKD system has theoretically proved to be safe.
  • QKD has broad application prospects in the fields of military, national defense, and information security.
  • the existing QKD system is shown in Figure 1.
  • the quantum light source is located at the transmitting end (Alice end) for generating a light pulse.
  • the light pulse is split into two optical pulses P1 and P2 through a beam splitter.
  • P1 takes the short arm, P2.
  • the long arm is taken; after passing through the Faraday Mirror (FM), P1 returns to the beam splitter.
  • FM Faraday Mirror
  • P2 After passing through the modulator and FM, P2 returns to the beam splitter 710, and the two optical pulses P1 and P2 pass through the attenuator in turn.
  • P1 and P2 are sequentially received by the circulator and sent to the beam splitter at the Bob end, the optical pulse P1 is divided into P11 and P12, and the optical pulse P2 is divided into P20 and P22, wherein P11 and P20 take the short arm, P12 and P22 take long arms.
  • P11 and P20 will go through the FM and return to the beam splitter, while P12 and P22 will pass through the modulator and FM, after the information of the Bob end is modulated, and then return to the beam splitter; due to the long arm and short of the Bob and Alice ends
  • the optical path difference of the arms is the same, so P12 and P20 will reach the beam splitter at the same time, where interference occurs, and the interference signal is obtained by the two single photon detectors D1 and D2.
  • the quantum key is obtained by processing the detection results of the two single photon detectors according to the corresponding quantum key distribution protocol.
  • the modulated light pulse (such as P2 at the Alice end and P12 at the Bob end) must pass through the modulator once, and then the FM rotates the polarization direction by 90 degrees before passing through the modulator.
  • High-speed modulators are all polarization-dependent. For example, in normal cases, the insertion loss of TE-polarized light is 6dB, and the insertion loss of TM-polarized light is 30dB. The optical pulse is equivalent to attenuating by 36dB. Big. Therefore, the existing QKD system can only use a low-rate modulator and cannot meet the requirements of high-speed communication.
  • the object of the present invention is to provide an encoding device which can replace the FM and the modulator in the existing QKD system, and solves the problem that the existing QKD system can only adopt a low-rate modulator and cannot meet the requirements of high-speed communication. problem.
  • an encoding apparatus comprising: a polarization splitting rotator PSR, a polarization rotating structure and a tone a PSR having three ports, receiving input signal light from a first port of the PSR, dividing the input signal light into first polarized light and second polarized light, and passing the first polarized light Transmitting, by the second port of the PSR, the polarization rotating structure, the second polarized light to the modulator through a third port of the PSR, wherein the first polarized light and the second The polarized light has the same polarization mode; the polarization rotating structure is configured to rotate the polarization direction of the first polarized light by 180 degrees to obtain the rotated first polarized light, and send the rotated first polarized light to The modulator is configured to modulate the rotated first polarized light to obtain a first signal light, and send the first signal light to a third port of the PSR; Modulating the second polarized light to obtain a second signal
  • the polarization directions of the optical pulses passing through the modulator are the same, and the polarization direction is lower after passing through the modulator. Therefore, the QKD system using the encoding device provided by the embodiment of the present invention can use a high-speed modulator. Meet the requirements of high-speed communication.
  • the optical paths of the two ends of the modulator reaching the PSR are the same, and that the two lights separated from the PSR can reach the modulator at the same time.
  • the time required for the modulator to modulate is shortened.
  • the polarization rotation structure comprises a phase modulator or a dynamic polarization controller.
  • the embodiment of the invention is applicable to Planar Lightwave Circuit (PLC) technology, and is advantageous for miniaturization and integration of the coding device.
  • PLC Planar Lightwave Circuit
  • the second signal light enters Polarized rotating structure.
  • the polarization rotating structure comprises a Faraday crystal and a polarization rotator PR, the Faraday crystal, Having two ports for rotating a polarization direction of light incident from a first port of the Faraday crystal by 90 degrees in a first direction and a second direction of polarization of light incident from a second port of the Faraday crystal
  • the direction is rotated by 90 degrees, wherein the first direction is a clockwise direction or a counterclockwise direction, the second direction is opposite to the first direction
  • the PR has two ports for the PR to be The polarization directions of the incident light of the two ports are all rotated by 90 degrees in the first direction, wherein the first port of the PR is connected to any port of the Faraday crystal.
  • the polarization rotating structure further includes a first polarizing plate and a second polarizing plate, the first polarizing plate Located between the Faraday crystal and the PSR for limiting a polarization direction of light passing through the first polarizing plate to a direction opposite or opposite to a polarization direction of the first polarized light; the second polarization a sheet between the PR and the modulator for limiting a polarization direction of light passing through the second polarizer in a direction opposite or opposite to a polarization direction of the first polarized light, or the A polarizing plate is disposed between the Faraday crystal and the PR for limiting a polarization direction of light passing through the second polarizing plate in a direction perpendicular to a polarization direction of the first polarized light.
  • the polarization rotating structure further includes a first polarizing plate and a second polarizing plate, the first polarizing plate Located between the Faraday crystal and the modulator for limiting a polarization direction of light passing through the first polarizer to a direction opposite or opposite to a polarization direction of the first polarized light; a polarizing plate positioned between the PR and the PSR for limiting a polarization direction of light passing through the second polarizing plate to a direction opposite or opposite to a polarization direction of the first polarized light, or the A polarizing plate is disposed between the Faraday crystal and the PR for limiting a polarization direction of light passing through the second polarizing plate in a direction perpendicular to a polarization direction of the first polarized light.
  • the two polarizing plates can ensure that the rotation angle of the polarization rotating structure is not affected by the temperature and the wavelength of the incident light, and the angle is offset by the angle.
  • the offset is converted into a light intensity offset, which can improve the safety and stability of the system when applied to a QKD system.
  • the PSR, the polarization rotating structure, and the modulator are connected by a polarization maintaining fiber to ensure The polarization state is stabilized in the encoding device.
  • the PSR includes a PBS and a PR
  • the PBS is configured to input the input signal
  • the light is divided into two polarized lights whose polarization directions are perpendicular to each other, and is also used to combine the two polarized lights whose polarization directions are perpendicular to each other to synthesize the output signal light
  • the PR is located between the PBS and the polarization rotating structure or the PBS
  • the polarization direction of the light passing through the PR is rotated by 90 degrees in a first direction, wherein the first direction is a clockwise direction or a counterclockwise direction.
  • a light reflector comprising: a PSR and a polarization rotation structure, the PSR having three ports, receiving input signal light from a first port of the PSR, and dividing the input signal light into a first polarization Light and second polarized light, respectively, transmitting the first polarized light and the second polarized light to the polarization rotating structure through a second port of the PSR and a third port of the PSR, wherein The first polarized light and the second polarized light have the same polarization mode; the polarization rotating structure is configured to rotate the polarization direction of the first polarized light by 180 degrees to obtain a rotated first polarized light, Transmitting the first polarized light to the third port of the PSR, and transmitting the second polarized light to the second port of the PSR; the PSR is further configured to use the rotated first polarization Combining light with the second polarized light to obtain output signal light, and transmitting the output signal light through a first port
  • the embodiment of the invention provides a light reflector with a ring structure, which can be combined with a modulator to form a device with a modulation function, so that the optical pulse passing back and forth through the device only needs to enter the modulator once, and can carry the modulation information and reduce System loss.
  • the polarization rotation structure comprises a phase modulator or a dynamic polarization controller.
  • the embodiments of the invention are applicable to PLC technology and are advantageous for miniaturization and integration of the light reflector.
  • the second polarized light after the first polarized light leaves the polarization rotating structure, the second polarized light enters Polarized rotating structure.
  • the polarization rotation structure comprises a Faraday crystal and a polarization rotator PR, the Faraday crystal having two ports for rotating a polarization direction of light incident from a first port of the Faraday crystal by a first direction by 90 degrees from the Faraday crystal
  • the polarization direction of the incident light of the second port is rotated by 90 degrees in the second direction, wherein the second direction is opposite to the first direction
  • the PR has two ports for the The polarization directions of the light incident on the two ports are each rotated by 90 degrees in the first direction, wherein the first port of the PR is connected to any port of the Faraday crystal.
  • the polarization rotating structure further includes a first polarizing plate and a second polarizing plate, the first polarizing plate Located between the Faraday crystal and the PSR for limiting a polarization direction of light passing through the first polarizing plate to a direction opposite or opposite to a polarization direction of the first polarized light; the second polarization a sheet between the PR and the modulator for limiting a polarization direction of light passing through the second polarizer in a direction opposite or opposite to a polarization direction of the first polarized light, or the A polarizing plate is disposed between the Faraday crystal and the PR for limiting a polarization direction of light passing through the second polarizing plate in a direction perpendicular to a polarization direction of the first polarized light.
  • the polarization rotating structure further includes a first polarizing plate and a second polarizing plate, the first polarizing plate Located between the Faraday crystal and the modulator for limiting a polarization direction of light passing through the first polarizer to a direction opposite or opposite to a polarization direction of the first polarized light; a polarizing plate positioned between the PR and the PSR for limiting a polarization direction of light passing through the second polarizing plate to a direction opposite or opposite to a polarization direction of the first polarized light, or the A polarizing plate is disposed between the Faraday crystal and the PR for limiting a polarization direction of light passing through the second polarizing plate in a direction perpendicular to a polarization direction of the first polarized light.
  • the PSR, the polarization rotating structure, and the modulator are connected by a polarization maintaining fiber to ensure The polarization state of the light reflector is stable.
  • the PSR includes a PBS and PR
  • the PBS is configured to divide the input signal light into two polarized lights whose polarization directions are perpendicular to each other, and to combine two polarized lights whose polarization directions are perpendicular to each other to synthesize the output signal light;
  • the polarization direction of the light passing through the PR is rotated by 90 degrees in a first direction, wherein the first direction is a clockwise direction or a counterclockwise direction.
  • an encoding structure comprising: a beam splitter, a light reflector and an encoding device, the beam splitter for receiving input signal light, dividing the input signal light into first polarized light and second Polarizing light, transmitting the first polarized light to the photo reflector, and transmitting the second polarized light to the encoding device, wherein the beam splitter reaches an optical path of the photo reflector The optical path of the beam splitter reaching the encoding device is different; the light reflector comprises a PSR and a polarization rotating structure, the PSR having three ports, the first polarized light being received from a first port of the PSR, Dividing the first polarized light into a first sub-polarized light and a second sub-polarized light, respectively passing the first sub-polarized light and the second sub-polarized light through a second port of the PSR and the PSR a third port is sent to the polarization rotation structure, wherein polarization modes of the first sub-polarized light
  • the encoding device includes a PSR, a polarization rotating structure and a modulator, the PSR having three ports, receiving second polarized light from a first port of the PSR, and dividing the second polarized light into a third sub-polarized light And transmitting the third sub-polarized light to the polarization rotation structure through the second port of the PSR, and transmitting the fourth sub-polarized light to the third port of the PSR to the The modulator,
  • the coding structure provided by the embodiment of the present invention includes the coding apparatus and the optical reflector according to the first aspect and the second aspect, which has the function of self-compensating polarization dependent loss, and can adopt a high-speed modulator to meet the requirements of high-speed communication.
  • the coding structure further includes two optical delay lines, where the first optical delay line is located in the beam splitter and the optical reflector Between the second optical delay lines is located between the beam splitter and the encoding device, the lengths of the two optical delay lines being different.
  • a fourth aspect provides a quantum key transmitting apparatus, including: a quantum light source, an encoding structure, and an attenuator, wherein the quantum light source is configured to emit a light pulse, and send the optical pulse to the encoding structure;
  • the structure comprises: a beam splitter, a light reflector and an encoding device, the beam splitter for receiving a light pulse, dividing the light pulse into first polarized light and second polarized light, and transmitting the first polarized light Transmitting the second polarized light to the encoding device to the light reflector, wherein the beam splitter reaches an optical path of the light reflector and light of the beam splitter reaching the encoding device
  • the phase difference is N, N is a natural number;
  • the light reflector comprises a PSR and a polarization rotating structure, the PSR has three ports, the first polarized light is received from the first port of the PSR, and the first The polarized light is split into a first sub-polarized light and a second
  • the quantum key transmitting device provided by the embodiment of the invention can self-compensate the polarization dependent loss in the transmitting device, ensure that the two optical pulses sent out have the same polarization direction, and can also adopt a high-speed modulator to meet the requirements of high-speed communication.
  • a fifth aspect provides a quantum key receiving apparatus, including: a circulator, a coding structure, a first single photon detector, and a second single photon detector,
  • the circulator is configured to receive the attenuated third polarized light and the attenuated fourth polarized light from the quantum channel, and send the attenuated third polarized light and the attenuated fourth polarized light to the Code structure
  • the coding structure includes a beam splitter, a light reflector and an encoding device, and the beam splitter is configured to receive the attenuated third polarized light and the attenuated fourth polarized light, and after the attenuating
  • the third polarized light is divided into a first sub-polarized light and a second sub-polarized light
  • the attenuated fourth polarized light is divided into a third sub-polarized light and a fourth sub-polarized light
  • the optical path of the device and the optical path of the beam splitter reaching the encoding device are N, N is a natural number;
  • the light reflector comprises a PSR and a polarization rotation structure, the PSR having three ports, receiving the first sub-polarized light from a first port of the PSR, and dividing the first sub-polarized light into a fifth sub-polarization Light and sixth sub-polarized light, respectively, transmitting the fifth sub-polarized light and the sixth sub-polarized light to the polarization rotating structure through a second port of the PSR and a third port of the PSR, wherein
  • the polarization modes of the fifth sub-polarized light and the sixth sub-polarized light are the same;
  • the polarization rotation structure is configured to rotate the polarization direction of the fifth sub-polarized light by 180 degrees to obtain a fifth sub-polarization after rotation Light, transmitting the rotated fifth sub-polarized light to a third port of the PSR, and transmitting the sixth sub-polarized light to a second port of the PSR;
  • the PSR is further used for The rotated fifth sub-polarized light and the sixth sub-polarized light are combined
  • the encoding device includes a PSR, a polarization rotating structure and a modulator, the PSR having three ports, receiving the second sub-polarized light from a first port of the PSR, and dividing the second sub-polarized light into a first Seven sub-polarized light and eighth sub-polarized light, the seventh sub-polarized light is transmitted to the polarization rotating structure through a second port of the PSR, and the eighth sub-polarized light is passed through a third of the PSR a port is sent to the modulator, wherein a polarization mode of the seventh sub-polarized light and the eighth sub-polarized light is the same; the polarization rotation structure is configured to rotate a polarization direction of the seventh sub-polarized light 180 degrees, the rotated seventh sub-polarized light is obtained, and the rotated seventh sub-polarized light is sent to the modulator; the modulator is configured to perform the rotated seventh sub-polarized light Modulating, obtaining a first signal light, transmitting the first signal light to a third port
  • the beam splitter is further configured to interfere with the second output signal light and the third output signal light to obtain first interference light and second interference light, and the first interference light and the first Two interference lights are respectively sent to the circulator and the second single photon detector;
  • the circulator is further configured to send the first interference light to the first single photon detector
  • Two single photon detectors for detecting the first interference light and the second interference light, respectively.
  • the receiving device provided by the embodiment of the invention has the function of self-compensating the polarization-dependent loss in the receiving device, ensuring that the polarization directions of the two output polarized lights with interference are uniform, enhancing the interference effect, and improving the generation rate of the quantum key.
  • High-speed modulators can also be used to meet the requirements of high-speed communication.
  • a quantum key distribution system comprising: the transmitting device according to the fourth aspect, and the receiving device according to the seventh aspect.
  • a quantum key transmitting apparatus comprising: a beam splitter, a single photon detector, an attenuator and an encoding device, the beam splitter having at least three ports, the first port and the second port being located One side of the beam splitter, the remaining port is located on the other side of the beam splitter, the first port is connected to the attenuator, the second port is connected to the single photon detector, the third a port is coupled to the quantum channel; the beam splitter is configured to receive a light pulse from the quantum channel, and divide the light pulse into a first light pulse and a second light pulse, respectively, transmitted through the first port and the second port; An attenuator, further coupled to the encoding device for attenuating a pulse of light input to the attenuator; the single photon detector for detecting a pulse of light input to the single photon detector, wherein The detection information is used to indicate whether the detected light pulse is attacked by a Trojan; the encoding device includes a polarization
  • a quantum key distribution system comprising: the quantum key placement device according to the seventh aspect, and the receiving device of the existing round-trip QKD system.
  • a remote modulation system comprising a laser, a polarization beam splitter PBS, a remote modulation device and a receiver,
  • the laser is connected to the second port of the PBS for emitting the first polarized light
  • the PBS has three ports for receiving the first polarized light from a second port of the PBS, and transmitting the first polarized light from the first port of the PBS to the far path through a transport channel Terminal modulation device
  • the remote modulation device includes a polarization splitting rotator PSR, a polarization rotating structure and a modulator, the PSR having three ports, receiving input signal light from a first port of the PSR, and the input signal light Dividing into a second polarized light and a third polarized light, transmitting the second polarized light to the polarization rotating structure through a second port of the PSR, and transmitting the third polarized light through a third port of the PSR Giving the modulator, wherein the input signal light is obtained by the first polarized light passing through the transmission channel, and the polarization modes of the second polarized light and the third polarized light are the same; the polarization rotating structure And rotating the polarization direction of the second polarized light by 180 degrees to obtain a rotated second polarized light, and transmitting the rotated second polarized light to the modulator; the modulator is configured to: Modulating the rotated second polarized light to obtain a first signal light, transmitting the first signal light to
  • the PBS is further configured to receive fourth polarized light from a first port of the PBS, and send the fourth polarized light to the receiver through a third port of the PBS, wherein the fourth polarization Light is obtained by the output signal light passing through the transmission channel;
  • the receiver is configured to receive the fourth polarized light.
  • the PBS transmits only the fourth polarized light to the receiver, and only introduces the same noise as the polarization direction of the fourth polarized light, which is equivalent to attenuating the noise by 3 dB.
  • PBS also has a lower insertion loss than the circulator used in existing remote modulation systems.
  • the remote modulation system further includes a beam splitter, configured to receive the first polarized light, and divide the first polarized light into two One copy is sent to the PBS and one copy is sent to the receiver.
  • a beam splitter configured to receive the first polarized light, and divide the first polarized light into two One copy is sent to the PBS and one copy is sent to the receiver.
  • Embodiments of the invention may be applied to a remote coherent modulation system.
  • the polarization directions of the optical pulses passing through the modulator are the same, and the polarization directions are lower after the modulator is applied. Therefore, the QKD system using the encoding device provided by the embodiment of the present invention can be used at a high level. Speed modulator to meet the requirements of high-speed communication.
  • Figure 1 shows a prior art QKD system
  • FIG. 2 shows an encoding apparatus according to an embodiment of the present invention
  • FIG. 3(a) shows an encoding apparatus according to another embodiment of the present invention
  • FIG. 3(b) shows an encoding apparatus according to another embodiment of the present invention
  • FIG. 4(a) shows an encoding apparatus according to another embodiment of the present invention
  • FIG. 4(b) shows an encoding apparatus according to another embodiment of the present invention
  • FIG. 4(c) shows an encoding apparatus according to another embodiment of the present invention.
  • FIG. 5 shows an encoding apparatus according to another embodiment of the present invention.
  • Figure 6 shows a light reflector according to another embodiment of the present invention.
  • FIG. 7 shows an encoding structure provided by another embodiment of the present invention.
  • FIG. 8 shows a quantum key transmitting apparatus according to another embodiment of the present invention.
  • FIG. 9 shows a quantum key receiving device according to another embodiment of the present invention.
  • Figure 10 is a schematic diagram showing changes in the polarization direction of a light pulse
  • Figure 11 shows a QKD system provided by another embodiment of the present invention.
  • FIG. 12 shows a remote modulation system according to another embodiment of the present invention.
  • FIG. 13 shows a remote modulation system according to another embodiment of the present invention.
  • FIG. 14 shows a possible receiver structure in a remote modulation system according to another embodiment of the present invention.
  • An embodiment of the present invention provides an encoding apparatus 200 having a polarization loss self-compensation function without adjusting a polarization state of a light pulse by a PC.
  • the encoding apparatus 200 includes a PSR 210, a polarization rotating structure 220, and a modulator 230.
  • the PSR 210 has three ports that receive input signal light from the first port of the PSR 210 and input the input signal light. Dividing into first polarized light and second polarized light, transmitting the first polarized light to the polarization rotating structure 220 through the second port of the PSR 210, and transmitting the second polarized light to the modulator 230 through the third port of the PSR 210, wherein The polarization modes of one polarized light and the second polarized light are the same.
  • the PSR 210 can be realized by docking the PBS and the polarization maintaining fiber, that is, after the incident light is separated into the TE polarized light and the TM polarized light by the PBS, the polarization directions of the emitted TE polarized light and the TM polarized light are all aligned.
  • the fast axis of the bias fiber is either aligned with the slow axis, rather than the TE aligned with the fast axis, and the TM is aligned with the slow axis.
  • the polarized light emitted from the PSR 210 is aligned in the same axial direction as the polarization maintaining fiber, and thus has the same polarization mode.
  • the PSR 210 has another implementation structure 240, as shown in FIG. 3(a), including a PBS 211 and a PR 212; the PBS 211 is configured to split the input signal light into two polarized lights whose polarization directions are perpendicular to each other; The PR 212 is located between the PBS 211 and the polarization rotating structure 220 for rotating the polarization direction of the light passing through the PR 212 by 90 degrees in the first direction, wherein the first direction is clockwise or counterclockwise.
  • the polarization rotating structure 220 is configured to rotate the polarization direction of the first polarized light by 180 degrees to obtain the rotated first polarized light, and transmit the rotated first polarized light to the modulator 230.
  • an implementation structure 250 of the polarization rotating structure 220 is as shown in FIG. 4(a), which includes a Faraday crystal 221 and a PR 222, and a Faraday crystal 221 having two ports for The polarization direction of the light incident from the first port of the Faraday crystal 221 is rotated by 90 degrees in the first direction, and the polarization direction of the light incident from the second port of the Faraday crystal 221 is rotated by 90 degrees in the second direction, wherein the second direction In contrast to the first direction; the PR 222 has two ports for rotating the polarization directions of the light incident from the two ports of the PR 222 by 90 degrees in the first direction, wherein the first port of the PR 222 and the Faraday crystal Any port of 221 is connected. Therefore, the polarization rotating structure 250 can function to rotate the polarization direction of the light incident from one end of the polarization rotating structure 250 by 180 degrees and the polarization direction of the light incident from the other end by 0 degree.
  • FIG. 4(b) another implementation structure 260 of the polarization rotating structure 220 is as shown in FIG. 4(b), which includes a first polarizing plate 223 and a second polarizing plate 224, and the first polarizing plate 223 is located in the Faraday crystal 221 and the PSR 210.
  • the second polarizing plate 224 is located between the PR 222 and the modulator 230 for The polarization direction of the light passing through the second polarizing plate 224 is defined in the same or opposite direction as the polarization direction of the first polarized light, or the implementation structure 270 as shown in FIG.
  • the position of the first polarizing plate 223 is unchanged,
  • the second polarizing plate 224 is located between the Faraday crystal 221 and the PR 222 for limiting the polarization direction of the light passing through the second polarizing plate 224 in a direction perpendicular to the polarization direction of the first polarized light.
  • the Faraday crystal 221 and the PR 222 are interchanged.
  • the first polarizer 223 may be located between the Faraday crystal 221 and the modulator 230
  • the second polarizer 224 may be located between the PR 222 and the PSR 210, or first.
  • the polarizing plate 223 is located between the Faraday crystal 221 and the modulator 230
  • the second polarizing plate 224 is located between the Faraday crystal 221 and the PR 222.
  • the functions of the two polarizing plates are as shown in FIGS. 4(b) and 4(c).
  • the polarizers are identical.
  • the two polarizing plates can ensure that the rotation angle of the Faraday crystal 221 is not affected by the temperature and the wavelength of the incident light, and the angular shift is converted to the light intensity drift regardless of the angle of the Faraday crystal 221, and the light intensity drifts. It has little effect on the stability of polarization compensation.
  • One degree of offset angle will only produce one in ten million. Light intensity rises and falls.
  • a 1 degree shift in polarization will have a huge impact on the security of the entire system.
  • Eavesdropper EVE can directly use this vulnerability to steal useful information, but the fluctuation of light intensity has little effect on the security of the system. Therefore, applying the embodiment of the present invention to the QKD system can improve the security of the QKD system.
  • the polarization rotation structure 220 has another implementation 280, including a phase modulator (PM) or a dynamic polarization controller (DPC). ).
  • PM phase modulator
  • DPC dynamic polarization controller
  • Tab and Tac are the times required for P1 and P2 to reach the polarization rotation structure 280, respectively, and Tbc is the polarization of the light pulse P1 at the polarization rotation structure 280.
  • the time required for rotation, Wp is the full pulse width of the light pulse P1. It should be noted that although PM or DPC is also related to the wavelength and temperature of the incident light, since it is actively modulated, the control voltage can be adjusted in real time to compensate for the influence of the wavelength and temperature of the incident light.
  • PM is only used to modulate the phase of the optical signal, and it cannot adjust the polarization direction of the optical signal.
  • the polarization direction is rotated by 180 degrees. That is to say, assuming that the plane wave of the optical signal is, the polarization direction is rotated by 180 degrees.
  • the plane wave of the optical signal is also The effect is the same.
  • the PM can only function to adjust the polarization direction of the optical signal when ⁇ phase is modulated. Since the PM can support the modulation rate of the GHz order and is suitable for the PLC technology, the polarization rotating structure 280 using the PM not only satisfies the requirements of high-speed communication, but also facilitates miniaturization and integration of the device.
  • DPC there are two main types, namely, all-optical mechanical type and electro-optical control type.
  • the all-optical mechanical type is generally slow in mechanical control, but it directly acts on the optical fiber and has the advantage of small insertion loss. Suitable for scenarios where speed is not critical.
  • the electro-optic control type includes electro-optic, piezoelectric, magneto-optical, liquid crystal, etc., and the polarization state can be controlled by an applied electric field, and the speed can be up to the order of milliseconds, which is equivalent to the processing speed of the prior art, but the embodiment of the present invention only needs to use DPC respectively.
  • the polarization directions of P1 and P2 can be rotated by 0 degrees and 180 degrees, the control complexity is low, and DPC is also suitable for PLC technology, which is beneficial to the miniaturization and integration of equipment.
  • the PSR 210 and the polarization rotating structure 220 are integrated, optical waveguide connections are used between the devices; if the PSR 210 and the polarization rotating structure 220 are independent devices, the devices are connected by polarization-maintaining fibers. .
  • the modulator 230 is configured to modulate the rotated first polarized light to obtain a first signal light, send the first signal light to a third port of the PSR 210, and further modulate the second polarized light to obtain a first
  • the second signal light transmits the second signal light to the polarization rotating structure 220.
  • the modulator 230 may be an Intensity Modulator (IM), a PM, a Quadrature Phase Shift Keying Modulator (QPSK Modulator), etc., which is not limited in this embodiment of the present invention.
  • IM Intensity Modulator
  • PM PM
  • QPSK Modulator Quadrature Phase Shift Keying Modulator
  • the optical paths of the modulators 230 reaching the PSR 210 are the same, ensuring that the modulator 230 can simultaneously process the two polarized lights separated by the PSR 210, which is advantageous for improving the processing speed.
  • PSR 210, polarization rotation The structure 220 and the modulator 230 are connected by an optical waveguide or a polarization maintaining fiber.
  • the high-speed modulators are all polarization-dependent, and the loss of the TE polarization mode and the TM polarization mode of the incident light are different, and the phase difference is generally more than 20 dB.
  • the loss of the TE polarization mode is about 6dB
  • the loss of the TM polarization mode is about 30dB
  • the loss of 30dB is unacceptable in communication systems, especially in quantum communication systems where the light intensity is very weak.
  • the polarization modes of the two polarized lights split by the PSR 210 are the same, both of which are TE polarized light, and can support a high-speed modulator without worrying about the loss that the communication system cannot bear.
  • the embodiment of the present invention may also allow the two polarized lights split by the PBS 210 to be TM polarized light.
  • the polarization rotation structure 220 is further configured to transmit the second signal light to the second port of the PSR 210.
  • the PR 222 is further configured to receive the first signal light from the third port of the PSR 210, and the polarization direction of the first signal light is in the first direction. Rotating 90 degrees to obtain the rotated first signal light; the Faraday crystal 221 is further configured to rotate the polarization direction of the rotated first signal light by 90 degrees in the second direction to recover the first signal light, wherein the first direction In a clockwise or counterclockwise direction, the second direction is opposite to the first direction.
  • the PSR 210 is further configured to combine the first signal light and the second signal light to obtain an output signal light, and send the output signal light through the first port of the PSR 210, wherein the polarization direction of the output signal light and the input signal The polarization direction of the light is perpendicular.
  • the PSR 240 includes a PBS 211 and a PR 212.
  • the PBS 211 is further configured to combine two signal lights whose polarization directions are perpendicular to each other to output signal light; the PR 212 is located.
  • the polarization direction of the light passing through the PR 212 is rotated by 90 degrees in the first direction, wherein the first direction is a clockwise direction or a counterclockwise direction.
  • the PSR 240 may also include a PBS 211 and a PR 212 as shown in FIG. 3(b), wherein the PR 212 is located between the PBS 211 and the modulator 230, and has a function similar to that shown in FIG. 3(a). No longer.
  • the encoding apparatus 200 includes a three-port PSR 210, a polarization rotating structure 220 and a modulator 230.
  • the input signal light is received from the first port of the PSR 210, and the input signal light is divided into the first polarization.
  • Light and second polarized light wherein the polarization modes of the first polarized light and the second polarized light are the same; the polarization direction of the first polarized light is rotated by 180 degrees to obtain the first polarized light after the rotation;
  • the polarized light and the second polarized light are modulated to obtain a first signal light and a second signal light, respectively, and then the first signal light and the second signal light are combined to obtain an output signal light, and the output signal light is passed through the PSR 210.
  • the first port is transmitted, wherein the polarization direction of the output signal light is perpendicular to the polarization direction of the input signal light.
  • the encoding device 200 provided by the embodiment of the present invention can support a high-speed modulator without worrying about introducing loss that the communication system cannot bear, and meeting the requirements of high-speed communication.
  • the embodiment of the present invention further provides a light reflector 600, as shown in FIG. 6, comprising: a PSR 601 and a polarization rotating structure 602,
  • the PSR 601 has three ports, receives input signal light from the first port of the PSR 601, splits the input signal light into first polarized light and second polarized light, and passes the first polarized light and the second polarized light respectively through the PSR 601.
  • the second port and the third port of the PSR 601 are sent to the polarization rotating structure 602, wherein the polarization modes of the first polarized light and the second polarized light are the same;
  • the polarization rotating structure 602 is configured to rotate the polarization direction of the first polarized light by 180 degrees to obtain the rotated first polarized light, and send the rotated first polarized light to the third port of the PSR 601 to convert the second polarized light. Send to the second port of the PSR 601;
  • the PSR 601 is further configured to combine the rotated first polarized light and the second polarized light to obtain an output signal light, and send the output signal light through the first port of the PSR 601, wherein the polarization direction of the output signal light is output. It is perpendicular to the polarization direction of the input signal light.
  • FIG. 7 Another embodiment of the present invention provides an encoding structure 700.
  • the possible structure is as shown in FIG. 7, including: a beam splitter 710, a light reflector 600, and an encoding device 200.
  • the beam splitter 710 is configured to receive the input signal light, divide the input signal light into the first polarized light and the second polarized light, transmit the first polarized light to the light reflector 600, and send the second polarized light to the encoding device 200,
  • the optical path of the beam splitter 710 to the light reflector 600 is different from the optical path of the beam splitter 710 to the encoding device 200.
  • the light reflector 600 includes a PSR 601 and a polarization rotating structure 602.
  • the PSR 601 has three ports, receives first polarized light from the first port of the PSR 601, and splits the first polarized light into a first sub-polarized light and a second sub-polarized light.
  • the polarization rotation structure 602 Transmitting the first sub-polarized light and the second sub-polarized light to the polarization rotation structure 602 through the second port of the PSR 601 and the third port of the PSR 601, respectively, wherein the polarization of the first sub-polarized light and the second sub-polarized light
  • the mode is the same; the polarization rotation structure 602 is configured to rotate the polarization direction of the first sub-polarized light by 180 degrees to obtain the rotated first sub-polarized light, and send the rotated first sub-polarized light to the third port of the PSR 601.
  • the PSR 601 is further configured to combine the rotated first sub-polarized light and the second sub-polarized light to obtain a third polarized light, and the third The polarized light is transmitted through the first port of the PSR 601 to the beam splitter 710, wherein the polarization direction of the third polarized light is perpendicular to the polarization direction of the first polarized light.
  • the encoding device 200 includes a PSR 210, a polarization rotating structure 220 and a modulator 230, a PSR 210 having three ports, receiving a second polarized light from a first port of the PSR 210, and dividing the second polarized light into a third sub-polarized light and a first Four sub-polarized light, the third sub-polarized light is transmitted to the polarization rotating structure 220 through the second port of the PSR 210, and the fourth sub-polarized light is transmitted to the modulator 230 through the third port of the PSR 210, wherein the third sub-polarization The polarization mode of the light and the fourth sub-polarized light is the same; the polarization rotation structure 220 is configured to rotate the polarization direction of the third sub-polarized light by 180 degrees to obtain the rotated third sub-polarized light, and the third sub-polarization after the rotation The light is sent to the modulator 230; the modulator 230 is configured to modulate the rotated third sub-polarized light
  • the third polarized light and the fourth polarized light do not reach the beam splitter 710 at the same time.
  • the encoding structure 700 further includes two optical delay lines 720, the first optical delay line 721 is located between the beam splitter 710 and the light reflector 600, and the second optical delay line 722 is located in the beam splitter 710 and Between the encoding devices 200, the lengths of the first optical delay line 721 and the second optical delay line 722 are different.
  • the encoding structure 700 is the same It can support high-speed modulators and meet the requirements of high-speed communication.
  • FIG. 7 shows a possible coding structure 700, and the position of the optical reflector 600 and the encoding device 200 can also be exchanged, which is not limited in this embodiment.
  • FIG. 8 Another embodiment of the present invention provides a quantum key transmitting device 800, as shown in FIG. 8, comprising: a quantum light source 810, an encoding structure 700, and an attenuator 820.
  • a quantum light source 810 is configured to emit a pulse of light and transmit the pulse of light to the encoding structure 700.
  • the coding structure 700 is a coding structure as shown in FIG. 7.
  • the optical pulse transmitted by the quantum light source is the input signal light of the coding structure 700, and after the same processing is performed on the input signal light, the third polarization light and the fourth polarization light are obtained.
  • the third polarized light and the fourth polarized light are sent to the attenuator 820.
  • the manner of processing the input signal light has been described in detail in the previous embodiments, and details are not described herein again.
  • the light reflector 600 and the encoding device 200 in the encoding structure 700 further include an optical switch or IM.
  • the quantum key transmitting device 800 can support a phase-plus-path encoding six-state quantum key distribution protocol or a reference system. Irrelevant agreement.
  • the attenuator 820 is configured to attenuate the third polarized light and the fourth polarized light to a single photon level, and transmit the attenuated third polarized light and the attenuated fourth polarized light through the quantum channel.
  • the single photon magnitude means that the average number of photons contained in each light pulse is in the single digit, that is, the energy of each light pulse is about 1e-18 or 1e-19 joules.
  • the quantum key transmitting device provided by the embodiment of the invention can support a high-speed modulator to meet the requirements of high-speed communication.
  • FIG. 9 Another embodiment of the present invention provides a quantum key receiving device 900, as shown in FIG. 9, comprising: a circulator 910, an encoding structure 700, a first single photon detector 920, and a second single photon detector 930,
  • the circulator 910 is configured to receive the attenuated third polarized light and the attenuated fourth polarized light from the quantum channel, and send the attenuated third polarized light and the attenuated fourth polarized light to the encoding structure 700, where The polarization directions of the two polarized lights are the same.
  • the coding structure 700 is an encoding structure as shown in FIG. 7, and includes a beam splitter 710, a light reflector 600, and an encoding device 200, wherein the attenuated third polarized light and the attenuated fourth polarized light are both coding structures 700.
  • the input signal light is recorded as the first input signal light and the second input signal light.
  • the beam splitter 710 is configured to receive the two input signal lights, divide the first input signal light into a first sub-polarized light and a second sub-polarized light, and divide the second input signal light into a third sub-polarized light and a fourth sub-polarized Light, transmitting the first sub-polarized light and the third sub-polarized light to the photo reflector 600, and transmitting the second sub-polarized light and the fourth sub-polarized light to the encoding device 200, wherein the beam splitter 710 reaches the photo reflector 600
  • the optical path of the optical path and beam splitter 710 to the encoding device 200 is the same as the corresponding optical path difference in the transmitting device.
  • the light reflector 600 is configured to receive the first sub-polarized light and the third sub-polarized light, and respectively process the two polarized lights to obtain a first output polarized light and a second output polarized light, wherein the first sub-polarized light
  • the third sub-polarized light is the input signal light of the photo reflector 600.
  • the encoding device 200 is configured to receive the second sub-polarized light and the fourth sub-polarized light, respectively processing the two polarized lights to obtain a third output polarized light and a fourth output polarized light, wherein the second sub-polarized light and The fourth sub-polarized light is the input signal light of the encoding device 200, and the specific processing manner has also been described in the previous embodiment. The invention will not be described again here.
  • the beam splitter 710 is further configured to interfere with the second output polarized light and the third output polarized light to obtain the first interference light and the second interference light, and send the first interference light and the second interference light to the circulator 910, respectively. And a second single photon detector 930.
  • the optical path of the beam splitter 710 to the optical reflector 600 is different from the optical path of the beam splitter 710 to the encoding device 200, and the optical path of the beam splitter 710 to the optical reflector 600 is assumed to be shorter.
  • the path of the beam splitter 710 to the light reflector 600 is referred to as a short arm, and the path of the beam splitter 710 to the encoding device 200 is referred to as a long arm, so that the transmitting device will emit two polarized lights.
  • the beam splitter 710 in the encoding structure 700 splits the first polarized light into a first sub-polarized light and a second sub-polarized light, and a second polarization
  • the light is divided into a third sub-polarized light and a fourth sub-polarized light; the first sub-polarized light and the third sub-polarized light travels the short arm, and after passing through the photo reflector 600, respectively obtaining the first output polarized light and the second output polarized light
  • the second sub-polarized light and the fourth sub-polarized light extending arm are passed through the encoding device 200 to obtain a third output polarized light and a fourth output polarized light, respectively.
  • both are the encoding structure 700 shown in FIG. 7, and the optical path difference between the beam splitter 710 to the optical reflector 600 and the encoding device 200 in the receiving device is in the transmitting device.
  • the corresponding optical path differences are consistent, that is, in the transmitting device and the receiving device, light that has passed both the long arm and the short arm will reach the beam splitter at the same time. Therefore, the second output polarized light and the third output polarized light will simultaneously reach the beam splitter 710, and interference occurs at the beam splitter 710, and the first interference light and the second interference light are obtained.
  • the circulator 910 is further configured to transmit the first interference light to the first single photon detector 920.
  • Two single photon detectors are respectively used for detecting the first interference light and the second interference light, and obtaining a quantum key according to a related quantum key distribution protocol.
  • the two output signal lights that interfere with each other need to carry the modulation information of the transmitting device and the receiving device, respectively.
  • the first polarized light since the first polarized light reaches the receiving device first than the second polarized light, the first polarized light moves the short arm in the transmitting device, and the second polarized light moves the long arm in the transmitting device.
  • the second output polarized light will carry the modulation information of the transmitting device, and the third output polarized light will carry the modulation information of the receiving device; assuming that the encoding device 200 is on the long arm, the second output polarization The light will carry the modulation information of the receiving device, and the third output polarized light will carry the modulation information of the transmitting device. Therefore, embodiments of the present invention can ensure that a quantum key is obtained.
  • the embodiment of the invention also has the function of self-compensating polarization-dependent loss, since each beam of light can be divided into two kinds of polarized light whose polarization directions are perpendicular to each other, and the polarization loss is mainly caused by the loss of two polarization directions of light. Inconsistent. Assuming that the input signal light reaches the optical reflector 600 from the beam splitter 710, the TE polarized light loss of the input signal light is 1 dB, and the TM polarized light loss is 3 dB. Therefore, when the input signal light reaches the photo reflector 600, the polarization direction is When the beam splitter 710 is different, as shown in FIG.
  • the input signal light is different from the polarization direction at a at b; if the polarization direction of the output signal light of the light reflector 200 is perpendicular to the polarization direction of the input signal light, The TE polarized light outputting the signal light corresponds to the TM polarized light of the input signal light, and the TM polarized light of the output signal light corresponds to the TE polarized light of the input signal light; therefore, from the input signal light from the beam splitter 710 to the light reflector 600 Then, until the output signal light returns to the beam splitter 710, the optical loss in both polarization directions is 4 dB, and the losses in the two polarization directions are uniform, that is, the polarization loss introduced by the intermediate transmission process is 0, and returns.
  • the output signal light to the beam splitter 710 is perpendicular to the polarization direction of the input signal light from the beam splitter 710. As shown in FIG. 10, the input signal light is perpendicular to the polarization direction at a at d. Due to the output light and output of the encoding device 200 The polarization directions of the incoming light are also perpendicular to each other, so that the loss from the input signal light from the beam splitter 710 to the encoding device 200 to the output signal light back to the beam splitter 710 can be ensured, and the losses in the two polarization directions are uniform.
  • the receiving device provided by the embodiment of the present invention can support a high-speed modulator to meet the requirements of high-speed communication, and can also self-compensate the polarization-dependent loss in the receiving device to ensure that the polarization directions of the two output polarized lights that are interfered are consistent and enhanced.
  • the interference effect is beneficial to increase the quantum key generation rate.
  • Another embodiment of the present invention provides a QKD system, including the quantum key transmitting device 800 and the quantum key receiving device 900 described in the previous embodiments.
  • the specific workflow is as follows:
  • the quantum light source 810 is located in the transmitting device 800 for generating a light pulse.
  • the light pulse passes through the beam splitter 710 and is divided into two polarized lights P1 and P2.
  • the polarized light P1 moves the short arm, and P2 moves the long arm; P1 passes through the light reflection.
  • P2 passes through the encoding device 200 and returns to the beam splitter 710.
  • the two polarized lights P1 and P2 sequentially pass through the attenuator 820, are attenuated to a single photon level, and pass through the quantum channel. It is sent to the receiving device 900, where P2 is modulated with information of the transmitting device in the encoding device 200.
  • P1 and P2 are sequentially received by the circulator 910 and sent to the beam splitter 710, the polarized light P1 is divided into P11 and P12, and the polarized light P2 is divided into P20 and P22, wherein P11 and P20 take the short arm , P12 and P22 take the long arm.
  • P11 and P20 will pass through the light reflector 600 and return to the beam splitter 710, and P12 and P22 will pass through the encoding device 200, after the information of the receiving device is modulated, and then return to the beam splitter 710;
  • the optical path difference of the long arm and the short arm in the transmitting device 800 is the same, so P12 and P20 will arrive at the beam splitter 710 at the same time where interference occurs, and the interference signal is obtained by the two single photon detectors 920 and 930.
  • the quantum key is obtained by processing the detection results of the two single photon detectors according to the corresponding quantum key distribution protocol.
  • the QKD system provided by the embodiment of the invention can support a high-speed modulator to meet the requirements of high-speed communication, and can also self-compensate the polarization-dependent loss in the system to ensure that the polarization directions of the two output polarized lights with interference are uniform, and the interference effect is enhanced. It is beneficial to increase the generation rate of quantum keys.
  • FIG. 11 Another embodiment of the present invention provides a QKD system, as shown in FIG. 11, including an Alice end and a Bob end.
  • the Alice end includes an encoding device 200, an attenuator 1110, a beam splitter 1120, and a single photon detector 1130.
  • the end uses the Bob end of the existing round-trip QKD system;
  • the beam splitter 1120 has at least three ports, the first port and the second port are located on one side of the beam splitter 1120, and the remaining ports are located on the other side of the beam splitter 1120, the first port is connected to the attenuator 1110, the first The two port is connected to the single photon detector 1130, the third port is connected to the quantum channel; the beam splitter 1120 is configured to receive the optical pulse from the quantum channel, and divide the optical pulse into the first optical pulse and the second optical pulse, respectively, through the first The port and the second port are sent out;
  • the attenuator 1110 is further connected to the encoding device 200 for attenuating the light pulse input to the attenuator 220;
  • a single photon detector 1130 for detecting a light pulse input to the single photon detector 1130, wherein the detection information is used to indicate whether the detected light pulse is attacked by a Trojan;
  • the encoding device 200 includes a PSR 210, a polarization rotating structure 220 and a modulator 230.
  • the PSR 210 has three ports, a first port of the PSR 210 is connected to the attenuator 220, and a second port of the PSR 210 is connected to the polarization rotating structure 220, PSR.
  • the third port of 210 is coupled to modulator 230 for receiving input from the first port of PSR 210
  • the light pulse is divided into the first polarized light and the second polarized light, and the polarization direction of the first polarized light is rotated by 90 degrees to obtain a third polarized light, and the first polarized light and the third polarized light are respectively passed.
  • the second port of the PSR 210 and the third port of the PSR 210 are transmitted; the modulator 230 is also coupled to the polarization rotation structure 220 for modulating the light pulses input to the modulator 230; the polarization rotation structure 220 is for The polarization direction of the light pulse entering on one side of the polarization rotation structure 220 is rotated by 180 degrees, and the polarization direction of the light pulse entering from the other side is rotated by 0 degree, wherein the polarization directions of the output light pulse and the input light pulse of the encoding device 200 are perpendicular to each other. .
  • the QKD system provided by the embodiment of the present invention does not need to adopt a PC at the transmitting end, and is not affected by the PC correcting speed, and the system speed is improved.
  • the encoding device 200 can be applied not only as an encoding device of the QKD system, but also as a remote modulation device, in the field of classical light.
  • FIG. 12 Another embodiment of the present invention provides a remote modulation system, as shown in FIG. 12, including: a laser 1200, a PBS 1220, a remote modulation device 1230, and a receiver 1240.
  • a laser 1200 connected to the second port of the PBS 1220 for emitting the first polarized light
  • the light generated by the laser can be either TE polarized light or TM polarized light.
  • the PBS 1220 has three ports for receiving the first polarized light from the second port of the PBS 1220, and transmitting the first polarized light from the first port of the PBS 1220 to the remote modulation device 1230 through the transmission channel;
  • the remote modulation device 1230 including the PSR 1231, the polarization rotation structure 1232, and the modulator 1233, PSR 1231, has three ports, receives input signal light from the first port of the PSR 1231, and divides the input signal light into the second polarization and the first
  • the three polarized light transmits the second polarized light to the polarization rotating structure 1232 through the second port of the PSR 1231, and transmits the third polarized light to the modulator 1233 through the third port of the PSR 1231, wherein the input signal light is the first polarization
  • the polarization mode of the second polarized light and the third polarized light is the same; the polarization rotating structure 1232 is configured to rotate the polarization direction of the second polarized light by 180 degrees to obtain a rotated second polarized light, which will be rotated.
  • the second polarized light is sent to the modulator 1233; the modulator 1233 is configured to modulate the rotated second polarized light to obtain the first signal light, and send the first signal light to the third port of the PSR 1231; For modulating the third polarized light, obtaining the second signal light, and transmitting the second signal light to the polarization rotating structure 1232; the polarization rotating structure 1232 is further configured to send the second signal light To the second port of the PSR 1231; the PSR 1231 is further configured to combine the first signal light and the second signal light to obtain an output signal light, and send the output signal light from the first port of the PSR 1231 to the PBS through the transmission channel. 1220, wherein the polarization direction of the output signal light is perpendicular to the polarization direction of the input signal light;
  • the modulator in the remote modulation device 1230 may be a PM, an IM, a QPSK Modulator, etc., which is not limited in this embodiment of the present invention.
  • the PBS 1220 is further configured to receive fourth polarized light from the first port of the PBS 1220, and transmit the fourth polarized light to the receiver 1240 through the third port of the PBS 1220, wherein the fourth polarized light is the output signal light passing through the transport channel.
  • the receiver 1240 is configured to receive the fourth polarized light.
  • the polarized light generated by the laser 1200 is TE polarized light
  • the first port of the PBS 1220 is connected to the transport channel
  • the second port of the PBS 1220 is the TE polarized port
  • the PBS 1220 is The third port is a TM polarization port.
  • the workflow of the remote modulation system is as follows:
  • the laser 1200 produces TE polarized light that will pass through the second port of the PBS 1220.
  • the transmission channel reaches the remote modulation device 1230.
  • the polarization direction of the TE polarized light changes due to the influence of the transmission channel, and the light reaching the remote modulation device 1230 can be recorded as the input signal light; in the remote modulation device 1230, Modulating the input signal light to obtain an output signal light, and reflecting the output signal light, wherein the polarization direction of the output signal light of the remote modulation device 1230 and the input signal light are perpendicular to each other, and has a function of self-compensating polarization loss.
  • the output signal light when the output signal light returns to the PBS 1220, the polarization direction of the output signal light will be perpendicular to the polarization direction of the TE polarized light emitted from the PBS 1220, that is, the output signal light will become TM polarized light.
  • the specific polarization loss self-compensation principle has been described in the previous embodiments and will not be described herein.
  • the output signal light Since the output signal light becomes TM polarized light when it returns to the PBS 1220 through the transmission channel, the output signal light will be output from the third port of the PBS 1220 to the receiver 1240; in the receiver 1240, the output signal The light is demodulated to extract modulation information.
  • the PBS 1220 transmits only one polarization direction of light to the receiver 1240, and only introduces the same noise as the polarization direction, which is equivalent to attenuating the noise by 3 dB.
  • PBS also has a lower insertion loss than the circulator used in existing remote modulation systems.
  • the modulator in the remote modulation device 1230 is IM
  • the input signal light is intensity modulated
  • the receiver 1240 can demodulate the output signal light by direct detection
  • the remote modulation device 1230 The modulator in the medium is PM, QPSK modulator, etc., and the phase modulation or phase and intensity combination modulation of the input signal light.
  • the receiver 1240 uses the coherent reception mode to demodulate the received light by the local oscillator light; Wherein, the laser 1200, the PBS 1220 and the receiver 1240 are connected by a polarization maintaining fiber or a polarization maintaining waveguide.
  • the remote modulation system further includes a beam splitter 1250 between the laser 1200 and the PBS 1220 for dividing the output light of the laser 1200 into two copies.
  • the PBS 1220 is sent to the receiver 1240 and sent to the receiver 1240 as the local oscillator.
  • the receiver 1240 can adopt the single-bias coherent reception as shown in FIG. 14 compared to the existing coherent receiver.
  • the single-biased coherent receiver has the characteristics of simple structure and small insertion loss, which can bring the advantages of low cost, low power consumption and long transmission distance to the whole system.

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Abstract

本发明公开了一种编码装置，包括：偏振分束旋转器PSR，用于接收输入信号光，将输入信号光分成偏振模式相同的两部分，分别发送给偏振旋转结构和调制器；偏振旋转结构，与PSR和调制器相连，具有从一端进入的光信号偏振方向旋转180度，从另一端进入的光信号偏振方向不变的功能；调制器，用于对输入到调制器的光进行调制；PSR，还用于接收偏振旋转结构和调制器发送的信号光，将两个信号光进行合束，得到输出信号光，将输出信号光发送出去。本发明实施例可以支持高速调制器，满足高速通信的要求。

Description

一种编码装置及基于该装置的量子密钥分发设备及系统
本申请要求于2016年9月27日提交中国专利局、申请号为201610856277.3、申请名称为“一种编码装置及基于该装置的量子密钥分发设备及系统”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本发明涉及光通信领域，特别涉及一种编码装置及基于该编码装置的量子密钥分发QKD设备及系统。
背景技术
量子通信是在经典信息论和量子力学的基础上发展起来的通信技术，现在实用化的量子通信技术主要是指量子密钥分发(Quantum Key Distribution，QKD)。其中，密钥的安全性依赖于量子力学基本原理，例如测量塌缩理论，不可克隆和测不准原理，因此，利用QKD系统分配给通信双方的密钥在理论上已经被证明是安全的，QKD在军事、国防、信息安全等领域拥有广阔的应用前景。
现有的QKD系统如图1所示，量子光源位于发送端(Alice端)，用于产生光脉冲，该光脉冲经过分束器被分成两个光脉冲P1和P2，P1走短臂，P2走长臂；P1经过法拉第旋转镜(Faraday Mirror，FM)之后，返回到分束器，P2经过调制器和FM之后，返回到分束器710，两个光脉冲P1和P2依次经过衰减器，被衰减到单光子量级之后，通过量子信道发送到接收端(Bob端)，其中，P2在经过调制器时被调制了Alice端的信息。
在Bob端中，P1和P2依次被环形器接收，并发送给Bob端的分束器，光脉冲P1被分成P11和P12，光脉冲P2被分成P20和P22，其中，P11和P20走短臂，P12和P22走长臂。P11和P20将经过FM之后，返回到分束器，而P12和P22将经过调制器和FM，被调制了Bob端的信息之后，再返回到分束器；由于Bob端和Alice端的长臂和短臂的光程差相同，故P12和P20将同时到达分束器，在此处发生干涉，干涉信号被两个单光子探测器D1和D2获得。根据相应的量子密钥分配协议处理两个单光子探测器的探测结果，即可得到量子密钥。
然而，在现有的QKD系统中，被调制的光脉冲(如Alice端的P2，Bob端的P12)都要先经过一次调制器，再被FM将偏振方向旋转90度之后再经过一次调制器，而高速的调制器均为偏振相关的，例如，在通常情况下，对TE偏振光的插损为6dB，对TM偏振光的插损为30dB，光脉冲一次往返就相当于衰减了36dB，衰减过大。因此，现有的QKD系统只能采用低速率的调制器，无法满足高速通信的要求。
发明内容
本发明的目的在于提供一种编码装置，该编码装置可以替换掉现有QKD系统中的FM和调制器，解决了现有的QKD系统只能采用低速率的调制器，无法满足高速通信要求的问题。
第一方面，提供一种编码装置，包括：偏振分束旋转器PSR，偏振旋转结构和调 制器，所述PSR，具有三个端口，从所述PSR的第一端口接收输入信号光，将所述输入信号光分成第一偏振光和第二偏振光，将所述第一偏振光通过所述PSR的第二端口发送给所述偏振旋转结构，将所述第二偏振光通过所述PSR的第三端口发送给所述调制器，其中，所述第一偏振光和所述第二偏振光的偏振模式相同；所述偏振旋转结构，用于将所述第一偏振光的偏振方向旋转180度，得到旋转后的第一偏振光，将所述旋转后的第一偏振光发送给所述调制器；所述调制器，用于对所述旋转后的第一偏振光进行调制，得到第一信号光，将所述第一信号光发送到所述PSR的第三端口；还用于对所述第二偏振光进行调制，得到第二信号光，将所述第二信号光发送给所述偏振旋转结构；所述偏振旋转结构，还用于将所述第二信号光发送到所述PSR的第二端口；所述PSR，还用于将所述第一信号光和所述第二信号光进行合束，得到输出信号光，将所述输出信号光通过所述PSR的第一端口发送出去，其中，所述输出信号光的偏振方向与所述输入信号光的偏振方向垂直。
在本发明实施例中，经过调制器的光脉冲的偏振方向一致，均为经过调制器之后损耗较低的偏振方向，故应用本发明实施例提供的编码装置的QKD系统可以使用高速调制器，满足高速通信的要求。
结合第一方面，在第一方面的第一种可能的实现方式中，所述调制器两端到达所述PSR的光程相同，保证从PSR分离的两束光可以同时到达所述调制器，缩短所述调制器进行调制所需的时间。
结合第一方面或第一方面的第一种可能的实现方式，在第一方面的第二种可能的实现方式中，所述偏振旋转结构包括相位调制器或动态偏振控制器。本发明实施例适用于平面光集成(Planar Lightwave Circuit，PLC)技术，有利于该编码装置的小型化集成。
结合第一方面的第二种可能的实现方式，在第一方面的第三种可能的实现方式中，在所述第一偏振光离开所述偏振旋转结构之后，所述第二信号光进入所述偏振旋转结构。
结合第一方面或第一方面的第一种可能的实现方式，在第一方面的第四种可能的实现方式中，所述偏振旋转结构包括法拉第晶体和偏振旋转器PR，所述法拉第晶体，具有两个端口，用于将从所述法拉第晶体的第一端口入射的光的偏振方向按第一方向旋转90度，将从所述法拉第晶体的第二端口入射的光的偏振方向按第二方向旋转90度，其中，所述第一方向为顺时针方向或逆时针方向，所述第二方向与所述第一方向相反；所述PR，具有两个端口，用于将从所述PR的两个端口入射的光的偏振方向均按第一方向旋转90度，其中，所述PR的第一端口与所述法拉第晶体的任一端口相连。
结合第一方面的第四种可能的实现方式，在第一方面的第五种可能的实现方式中，所述偏振旋转结构还包括第一偏振片和第二偏振片，所述第一偏振片位于所述法拉第晶体和所述PSR之间，用于将经过所述第一偏振片的光的偏振方向限定在与所述第一偏振光的偏振方向相同或相反的方向；所述第二偏振片位于所述PR与所述调制器之间，用于将经过所述第二偏振片的光的偏振方向限定在与所述第一偏振光的偏振方向相同或相反的方向，或所述第二偏振片位于所述法拉第晶体与所述PR之间，用于将经过所述第二偏振片的光的偏振方向限定在与所述第一偏振光的偏振方向垂直的方向。
结合第一方面的第四种可能的实现方式，在第一方面的第六种可能的实现方式中，所述偏振旋转结构还包括第一偏振片和第二偏振片，所述第一偏振片位于所述法拉第晶体和所述调制器之间，用于将经过所述第一偏振片的光的偏振方向限定在与所述第一偏振光的偏振方向相同或相反的方向；所述第二偏振片位于所述PR与所述PSR之间，用于将经过所述第二偏振片的光的偏振方向限定在与所述第一偏振光的偏振方向相同或相反的方向，或所述第二偏振片位于所述法拉第晶体与所述PR之间，用于将经过所述第二偏振片的光的偏振方向限定在与所述第一偏振光的偏振方向垂直的方向。
在第一方面的第五种和第六种可能的实现方式中，这两个偏振片可以保证偏振旋转结构的旋转角度不受温度和入射光波长的影响，无论角度如何偏移，都会由角度偏移转变成光强度偏移，应用于QKD系统时，可以提高系统的安全性和稳定性。
结合第一方面的第四种可能的实现方式，在第一方面的第七种可能的实现方式中，所述PSR，所述偏振旋转结构和所述调制器之间采用保偏光纤连接，保证编码装置中偏振状态的稳定。
结合第一方面或第一方面的第一种可能的实现方式，在第一方面的第八种可能的实现方式中，所述PSR包括PBS和PR，所述PBS，用于将所述输入信号光分成偏振方向互相垂直的两个偏振光，还用于将偏振方向互相垂直的两个偏振光合成所述输出信号光；所述PR，位于所述PBS和所述偏振旋转结构之间或所述PBS和所述调制器之间，用于将经过所述PR的光的偏振方向按照第一方向旋转90度，其中，所述第一方向为顺时针方向或逆时针方向。
第二方面，提供一种光反射器，包括：PSR和偏振旋转结构，所述PSR具有三个端口，从所述PSR的第一端口接收输入信号光，将所述输入信号光分成第一偏振光和第二偏振光，将所述第一偏振光和所述第二偏振光分别通过所述PSR的第二端口和所述PSR的第三端口发送给所述偏振旋转结构，其中，所述第一偏振光和所述第二偏振光的偏振模式相同；所述偏振旋转结构，用于将所述第一偏振光的偏振方向旋转180度，得到旋转后的第一偏振光，将所述旋转后的第一偏振光发送到所述PSR的第三端口，将所述第二偏振光发送到所述PSR的第二端口；所述PSR，还用于将所述旋转后的第一偏振光和所述第二偏振光进行合束，得到输出信号光，将所述输出信号光通过所述PSR的第一端口发送出去，其中，所述输出信号光的偏振方向与所述输入信号光的偏振方向垂直。
本发明实施例提供光反射器为环形结构，可以与调制器结合，形成一种带调制功能的装置，让经过该装置往返的光脉冲只需进过一次调制器，即可携带调制信息，降低系统损耗。
结合第二方面，在第二方面的第一种可能的实现方式中，所述偏振旋转结构包括相位调制器或动态偏振控制器。发明实施例适用于PLC技术，有利于该光反射器的小型化集成。
结合第二方面的第一种可能的实现方式，在第二方面的第二种可能的实现方式中，在所述第一偏振光离开所述偏振旋转结构之后，所述第二偏振光进入所述偏振旋转结构。
结合第二方面，在第二方面的第三种可能的实现方式中，所述偏振旋转结构包括 法拉第晶体和偏振旋转器PR，所述法拉第晶体，具有两个端口，用于将从所述法拉第晶体的第一端口入射的光的偏振方向按第一方向旋转90度，将从所述法拉第晶体的第二端口入射的光的偏振方向按第二方向旋转90度，其中，所述第二方向与所述第一方向相反；所述PR，具有两个端口，用于将从所述PR的两个端口入射的光的偏振方向均按第一方向旋转90度，其中，所述PR的第一端口与所述法拉第晶体的任一端口相连。
结合第二方面的第三种可能的实现方式，在第二方面的第四种可能的实现方式中，所述偏振旋转结构还包括第一偏振片和第二偏振片，所述第一偏振片位于所述法拉第晶体和所述PSR之间，用于将经过所述第一偏振片的光的偏振方向限定在与所述第一偏振光的偏振方向相同或相反的方向；所述第二偏振片位于所述PR与所述调制器之间，用于将经过所述第二偏振片的光的偏振方向限定在与所述第一偏振光的偏振方向相同或相反的方向，或所述第二偏振片位于所述法拉第晶体与所述PR之间，用于将经过所述第二偏振片的光的偏振方向限定在与所述第一偏振光的偏振方向垂直的方向。
结合第二方面的第三种可能的实现方式，在第二方面的第五种可能的实现方式中，所述偏振旋转结构还包括第一偏振片和第二偏振片，所述第一偏振片位于所述法拉第晶体和所述调制器之间，用于将经过所述第一偏振片的光的偏振方向限定在与所述第一偏振光的偏振方向相同或相反的方向；所述第二偏振片位于所述PR与所述PSR之间，用于将经过所述第二偏振片的光的偏振方向限定在与所述第一偏振光的偏振方向相同或相反的方向，或所述第二偏振片位于所述法拉第晶体与所述PR之间，用于将经过所述第二偏振片的光的偏振方向限定在与所述第一偏振光的偏振方向垂直的方向。
结合第二方面的第三种可能的实现方式，在第二方面的第六种可能的实现方式中，所述PSR，所述偏振旋转结构和所述调制器之间采用保偏光纤连接，保证光反射器中偏振状态的稳定。
结合第二方面或第二方面的第一种至第六种可能的实现方式中的任一种可能的实现方式，在第一方面的第七种可能的实现方式中，所述PSR包括PBS和PR，所述PBS，用于将所述输入信号光分成偏振方向互相垂直的两个偏振光，还用于将偏振方向互相垂直的两个偏振光合成所述输出信号光；所述PR，位于所述PBS和所述偏振旋转结构之间，用于将经过所述PR的光的偏振方向按照第一方向旋转90度，其中，所述第一方向为顺时针方向或逆时针方向。
第三方面，提供一种编码结构，包括：分束器，光反射器和编码装置，所述分束器，用于接收输入信号光，将所述输入信号光分成第一偏振光和第二偏振光，将所述第一偏振光发送给所述光反射器，将所述第二偏振光发送给所述编码装置，其中，所述分束器到达所述光反射器的光程与所述分束器到达所述编码装置的光程不同；所述光反射器包括PSR和偏振旋转结构，所述PSR具有三个端口，从所述PSR的第一端口接收所述第一偏振光，将所述第一偏振光分成第一子偏振光和第二子偏振光，将所述第一子偏振光和所述第二子偏振光分别通过所述PSR的第二端口和所述PSR的第三端口发送给所述偏振旋转结构，其中，所述第一子偏振光和所述第二子偏振光的偏振模式相同；所述偏振旋转结构，用于将所述第一子偏振光的偏振方向旋转180度，得到旋转后的第一子偏振光，将所述旋转后的第一子偏振光发送到所述PSR的第三端口， 将所述第二子偏振光发送到所述PSR的第二端口；所述PSR，还用于将所述旋转后的第一子偏振光和所述第二子偏振光进行合束，得到第三偏振光，将所述第三偏振光通过所述PSR的第一端口发送到所述分束器，其中，所述第三偏振光的偏振方向与所述第一偏振光的偏振方向垂直；所述编码装置包括PSR，偏振旋转结构和调制器，所述PSR，具有三个端口，从所述PSR的第一端口接收第二偏振光，将所述第二偏振光分成第三子偏振光和第四子偏振光，将所述第三子偏振光通过所述PSR的第二端口发送给所述偏振旋转结构，将所述第四子偏振光通过所述PSR的第三端口发送给所述调制器，其中，所述第三子偏振光和所述第四子偏振光的偏振模式相同；所述偏振旋转结构，用于将所述第三子偏振光的偏振方向旋转180度，得到旋转后的第三子偏振光，将所述旋转后的第三子偏振光发送给所述调制器；所述调制器，用于对所述旋转后的第三子偏振光进行调制，得到第一信号光，将所述第一信号光发送到所述PSR的第三端口；还用于对所述第四子偏振光进行调制，得到第二信号光，将所述第二信号光发送给所述偏振旋转结构；所述偏振旋转结构，还用于将所述第二信号光发送到所述PSR的第二端口；所述PSR，还用于将所述第一信号光和所述第二信号光进行合束，得到第四偏振光，将所述第四偏振光通过所述PSR的第一端口发送到所述分束器，其中，所述第四偏振光的偏振方向与所述第二偏振光的偏振方向垂直；所述分束器，还用于将所述第三偏振光和所述第四偏振光发送出去。
本发明实施例提供的编码结构，包括了第一方面以及第二方面所述的编码装置和光反射器，具有自补偿偏振相关损耗的功能，且可以采用高速调制器，满足高速通信的要求。
结合第三方面，在第三方面的第一种可能的实现方式中，所述编码结构还包括两个光延时线，第一光延时线位于所述分束器和所述光反射器之间，第二光延时线位于所述分束器和所述编码装置之间，所述两个光延时线的长度不同。
第四方面，提供一种量子密钥发送设备，包括：量子光源，编码结构和衰减器，所述量子光源，用于发射光脉冲，将所述光脉冲发送给所述编码结构；所述编码结构包括：分束器，光反射器和编码装置，所述分束器，用于接收光脉冲，将所述光脉冲分成第一偏振光和第二偏振光，将所述第一偏振光发送给所述光反射器，将所述第二偏振光发送给所述编码装置，其中，所述分束器到达所述光反射器的光程与所述分束器到达所述编码装置的光程相差为N，N为自然数；所述光反射器包括PSR和偏振旋转结构，所述PSR具有三个端口，从所述PSR的第一端口接收所述第一偏振光，将所述第一偏振光分成第一子偏振光和第二子偏振光，将所述第一子偏振光和所述第二子偏振光分别通过所述PSR的第二端口和所述PSR的第三端口发送给所述偏振旋转结构，其中，所述第一子偏振光和所述第二子偏振光的偏振模式相同；所述偏振旋转结构，用于将所述第一子偏振光的偏振方向旋转180度，得到旋转后的第一子偏振光，将所述旋转后的第一子偏振光发送到所述PSR的第三端口，将所述第二子偏振光发送到所述PSR的第二端口；所述PSR，还用于将所述旋转后的第一子偏振光和所述第二子偏振光进行合束，得到第三偏振光，将所述第三偏振光通过所述PSR的第一端口发送到所述分束器，其中，所述第三偏振光的偏振方向与所述第一偏振光的偏振方向垂直；所述编码装置包括PSR，偏振旋转结构和调制器，所述PSR，具有三个端口，从所述 PSR的第一端口接收第二偏振光，将所述第二偏振光分成第三子偏振光和第四子偏振光，将所述第三子偏振光通过所述PSR的第二端口发送给所述偏振旋转结构，将所述第四子偏振光通过所述PSR的第三端口发送给所述调制器，其中，所述第三子偏振光和所述第四子偏振光的偏振模式相同；所述偏振旋转结构，用于将所述第三子偏振光的偏振方向旋转180度，得到旋转后的第三子偏振光，将所述旋转后的第三子偏振光发送给所述调制器；所述调制器，用于对所述旋转后的第三子偏振光进行调制，得到第一信号光，将所述第一信号光发送到所述PSR的第三端口；还用于对所述第四子偏振光进行调制，得到第二信号光，将所述第二信号光发送给所述偏振旋转结构；所述偏振旋转结构，还用于将所述第二信号光发送到所述PSR的第二端口；所述PSR，还用于将所述第一信号光和所述第二信号光进行合束，得到第四偏振光，将所述第四偏振光通过所述PSR的第一端口发送到所述分束器，其中，所述第四偏振光的偏振方向与所述第二偏振光的偏振方向垂直；所述分束器，还用于将所述第三偏振光和所述第四偏振光发送给所述衰减器；所述衰减器，用于将所述第三偏振光和所述第四偏振光衰减到单光子量级，通过量子信道将衰减后的第三偏振光和衰减后的第四偏振光发送出去。
本发明实施例提供的量子密钥发送设备，可以自补偿发送设备中的偏振相关损耗，保证发送出去的两个光脉冲具有相同的偏振方向，还可以采用高速调制器，满足高速通信的要求。
第五方面，提供一种量子密钥接收设备，包括：环形器，编码结构，第一单光子探测器和第二单光子探测器，
所述环形器，用于从量子信道接收衰减后的第三偏振光和衰减后的第四偏振光，将所述衰减后的第三偏振光和所述衰减后的第四偏振光发送给所述编码结构；
所述编码结构包括分束器，光反射器和编码装置，所述分束器，用于接收所述衰减后的第三偏振光和所述衰减后的第四偏振光，将所述衰减后的第三偏振光分成第一子偏振光和第二子偏振光，将所述衰减后的第四偏振光分成第三子偏振光和第四子偏振光，将所述第一子偏振光和所述第三子偏振光发送给所述光反射器，将所述第二子偏振光和所述第四子偏振光发送给所述编码装置，其中，所述分束器到达所述光反射器的光程与所述分束器到达所述编码装置的光程相差为N，N为自然数；
所述光反射器包括PSR和偏振旋转结构，所述PSR具有三个端口，从所述PSR的第一端口接收所述第一子偏振光，将所述第一子偏振光分成第五子偏振光和第六子偏振光，将所述第五子偏振光和第六子偏振光分别通过所述PSR的第二端口和所述PSR的第三端口发送给所述偏振旋转结构，其中，所述第五子偏振光和所述第六子偏振光的偏振模式相同；所述偏振旋转结构，用于将所述第五子偏振光的偏振方向旋转180度，得到旋转后的第五子偏振光，将所述旋转后的第五子偏振光发送到所述PSR的第三端口，将所述第六子偏振光发送到所述PSR的第二端口；所述PSR，还用于将所述旋转后的第五子偏振光和所述第六子偏振光进行合束，得到第一输出偏振光，将所述第一输出偏振光通过所述PSR的第一端口发送到所述分束器，其中，所述第一输出偏振光的偏振方向与所述第一子偏振光的偏振方向垂直；所述光反射器对所述第三子偏振光做同样处理，得到第二输出偏振光，将所述第二输出偏振光通过所述PSR的 第一端口发送给所述分束器，其中，所述第二输出偏振光的偏振方向与所述第三子偏振光的偏振方向垂直；
所述编码装置包括PSR，偏振旋转结构和调制器，所述PSR，具有三个端口，从所述PSR的第一端口接收所述第二子偏振光，将所述第二子偏振光分成第七子偏振光和第八子偏振光，将所述第七子偏振光通过所述PSR的第二端口发送给所述偏振旋转结构，将所述第八子偏振光通过所述PSR的第三端口发送给所述调制器，其中，所述第七子偏振光和所述第八子偏振光的偏振模式相同；所述偏振旋转结构，用于将所述第七子偏振光的偏振方向旋转180度，得到旋转后的第七子偏振光，将所述旋转后的第七子偏振光发送给所述调制器；所述调制器，用于对所述旋转后的第七子偏振光进行调制，得到第一信号光，将所述第一信号光发送到所述PSR的第三端口；还用于对所述第八子偏振光进行调制，得到第二信号光，将所述第二信号光发送给所述偏振旋转结构；所述偏振旋转结构，还用于将所述第二信号光发送到所述PSR的第二端口；所述PSR，还用于将所述第一信号光和所述第二信号光进行合束，得到第三输出偏振光，将所述第三输出偏振光通过所述PSR的第一端口发送到所述分束器，其中，所述第三输出偏振光的偏振方向与所述第二子偏振光的偏振方向垂直；所述编码装置对所述第四子偏振光做同样处理，得到第四输出偏振光，将所述第四输出偏振光通过所述PSR的第一端口发送给所述分束器，其中，所述第四输出偏振光的偏振方向与所述第二子偏振光的偏振方向垂直；
所述分束器，还用于让所述第二输出信号光和所述第三输出信号光发生干涉，得到第一干涉光和第二干涉光，将所述第一干涉光和所述第二干涉光分别发送给所述环形器和所述第二单光子探测器；
所述环形器，还用于将所述第一干涉光发送给所述第一单光子探测器；
两个单光子探测器，分别用于对所述第一干涉光和所述第二干涉光进行检测。
本发明实施例提供的接收设备，具有自补偿接收设备中的偏振相关损耗的功能，保证发生干涉的两个输出偏振光的偏振方向一致，增强干涉效果，有利于提高量子密钥的生成率，还可以采用高速调制器，满足高速通信的要求。
第六方面，提供一种量子密钥分发系统，包括：如第四方面所述的发送设备以及如第七五面所述的接收设备。
第七方面，提供一种量子密钥发送设备，包括：分束器，单光子探测器，衰减器和编码装置，所述分束器，具有至少三个端口，第一端口和第二端口位于所述分束器的一侧，其余端口位于所述分束器的另一侧，所述第一端口连接所述衰减器，所述第二端口连接所述单光子探测器，所述第三端口连接量子信道；所述分束器用于从所述量子信道接收光脉冲，将所述光脉冲分成第一光脉冲和第二光脉冲，分别通过第一端口和第二端口发送出去；所述衰减器，还与所述编码装置相连，用于对输入到所述衰减器的光脉冲进行衰减；所述单光子探测器，用于检测输入到所述单光子探测器的光脉冲，其中，所述检测信息用于指示检测的光脉冲是否受到木马攻击；所述编码装置，包括偏振分束旋转器PSR，偏振旋转结构和调制器，所述PSR具有三个端口，所述PSR的第一端口与所述衰减器相连，所述PSR的第二端口与所述偏振旋转结构相连，所述PSR的第三端口与所述调制器相连，用于从所述PSR的第一端口接收输入光脉冲，将 输入光脉冲分为第一偏振光和第二偏振光，将所述第一偏振光的偏振方向旋转90度，得到第三偏振光，将所述第一偏振光和所述第三偏振光分别通过所述PSR的第二端口和所述PSR的第三端口发送出去；所述调制器还与所述偏振旋转结构相连，用于对输入到所述调制器的光脉冲进行调制；所述偏振旋转结构，用于将从所述偏振旋转结构一侧进入的光脉冲的偏振方向旋转180度，从另一侧进入的光脉冲的偏振方向旋转0度，其中，所述编码装置的输出光脉冲和输入光脉冲的偏振方向互相垂直。
第八方面，提供一种量子密钥分发系统，包括：如第七方面所述的量子密钥放设备，以及现有的往返式QKD系统的接收设备。
第九方面，提供一种远端调制系统，包括激光器，偏振分束器PBS，远端调制装置和接收器，
所述激光器，与所述PBS的第二端口相连，用于发射第一偏振光；
所述PBS，具有三个端口，用于从所述PBS的第二端口接收所述第一偏振光，将所述第一偏振光从所述PBS的第一端口通过传输信道发送给所述远端调制装置；
所述远端调制装置，包括偏振分束旋转器PSR，偏振旋转结构和调制器，所述PSR，具有三个端口，从所述PSR的第一端口接收输入信号光，将所述输入信号光分成第二偏振光和第三偏振光，将所述第二偏振光通过所述PSR的第二端口发送给所述偏振旋转结构，将所述第三偏振光通过所述PSR的第三端口发送给所述调制器，其中，所述输入信号光为所述第一偏振光经过所述传输信道所得，所述第二偏振光和所述第三偏振光的偏振模式相同；所述偏振旋转结构，用于将所述第二偏振光的偏振方向旋转180度，得到旋转后的第二偏振光，将所述旋转后的第二偏振光发送给所述调制器；所述调制器，用于对所述旋转后的第二偏振光进行调制，得到第一信号光，将所述第一信号光发送到所述PSR的第三端口；还用于对所述第三偏振光进行调制，得到第二信号光，将所述第二信号光发送给所述偏振旋转结构；所述偏振旋转结构，还用于将所述第二信号光发送到所述PSR的第二端口；所述PSR，还用于将所述第一信号光和所述第二信号光进行合束，得到输出信号光，将所述输出信号光从所述PSR的第一端口通过所述传输信道发送给所述PBS，其中，所述输出信号光的偏振方向与所述输入信号光的偏振方向垂直；
所述PBS，还用于从所述PBS的第一端口接收第四偏振光，将所述第四偏振光通过所述PBS的第三端口发送给所述接收器，其中，所述第四偏振光为所述输出信号光经过所述传输信道所得；
所述接收器，用于对所述第四偏振光进行接收。
本发明实施例提供的远端调制系统，所述PBS只将第四偏振光发送给所述接收器，也只会引入与第四偏振光的偏振方向相同的噪声，相当于将噪声衰减了3dB，此外，PBS也比现有远端调制系统采用的环形器的插损更低。
结合第九方面，在第九方面的第一种可能的实现方式中，所述远端调制系统还包括分束器，用于接收所述第一偏振光，将所述第一偏振光分成两份，一份发送给所述PBS，一份发送给所述接收器。本发明实施例可以应用于远端相干调制系统。
在本发明实施例中，经过调制器的光脉冲的偏振方向一致，均为经过调制器之后损耗较低的偏振方向，故应用本发明实施例提供的编码装置的QKD系统可以使用高 速调制器，满足高速通信的要求。
附图说明
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动性的前提下，还可以根据这些附图获得其他的附图。
图1示出现有的一种QKD系统；
图2示出本发明一实施例提供的编码装置；
图3(a)示出本发明另一实施例提供的编码装置；
图3(b)示出本发明另一实施例提供的编码装置；
图4(a)示出本发明另一实施例提供的编码装置；
图4(b)示出本发明另一实施例提供的编码装置；
图4(c)示出本发明另一实施例提供的编码装置；
图5示出本发明另一实施例提供的编码装置；
图6示出本发明另一实施例提供的光反射器；
图7示出本发明另一实施例提供的编码结构；
图8示出本发明另一实施例提供的量子密钥发送设备；
图9示出本发明另一实施例提供的量子密钥接收设备；
图10为光脉冲的偏振方向的变化示意图；
图11示出本发明另一实施例提供的QKD系统；
图12示出本发明另一实施例提供的远端调制系统；
图13示出本发明另一实施例提供的远端调制系统；
图14示出本发明另一实施例提供的远端调制系统中一种可能的接收器结构。
具体实施方式
下面将结合本发明实施例中的附图，对本发明实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例是本发明的一部分实施例，而不是全部实施例。基于本发明中的实施例，本领域普通技术人员在没有做出创造性劳动的前提下所获得的所有其他实施例，都应属于本发明的保护范围。
以下描述中，为了说明而不是为了限定，提出了诸如特定系统结构、接口、技术之类的具体细节，以便透彻理解本发明。然而，本领域的技术人员应当清楚，在没有这些具体细节的其它实施例中也可以实现本发明。在其它情况中，省略对众所周知的装置、电路以及方法的详细说明，以免不必要的细节妨碍本发明的描述。
当本发明实施例提及“第一”、“第二”、“第三”、“第四”等序数词时，除非根据上下文其确实表达顺序之意，否则应当理解为仅仅是起区分之用。
本发明实施例提供一种无需PC调节光脉冲的偏振态，即可具有偏振损耗自补偿功能的编码装置200，如图2所示，编码装置200包括PSR 210，偏振旋转结构220和调制器230，
PSR 210具有三个端口，从PSR 210的第一端口接收输入信号光，将输入信号光 分成第一偏振光和第二偏振光，将第一偏振光通过PSR 210的第二端口发送给偏振旋转结构220，第二偏振光通过PSR 210的第三端口发送给调制器230，其中，第一偏振光和第二偏振光的偏振模式相同。
其中，PSR 210可以利用PBS和保偏光纤快慢轴对接实现，也就是说，在入射光被PBS分成TE偏振光和TM偏振光之后，出射的TE偏振光和TM偏振光的偏振方向全部对准保偏光纤的快轴或者全部对准慢轴，而不是TE对准快轴，TM对准慢轴。此时，从PSR 210出射的偏振光对准保偏光纤相同的轴方向，故具有相同的偏振模式。
可选地，PSR 210还有另一种实现结构240，如图3(a)所示，包括PBS 211和PR 212；PBS 211用于将输入信号光分成偏振方向互相垂直的两个偏振光；PR 212位于PBS 211和偏振旋转结构220之间，用于将经过PR 212的光的偏振方向按照第一方向旋转90度，其中，第一方向为顺时针方向或逆时针方向。
需要说明的是，在本发明所有实施例中，偏振方向的变化，都为逆着光传播方向观察所得。
偏振旋转结构220，用于将第一偏振光的偏振方向旋转180度，得到旋转后的第一偏振光，将旋转后的第一偏振光发送到调制器230。
可选地，作为另一个实施例，偏振旋转结构220的一种实现结构250如图4(a)所示，其包括法拉第晶体221和PR 222，法拉第晶体221，具有两个端口，用于将从法拉第晶体221的第一端口入射的光的偏振方向按第一方向旋转90度，将从法拉第晶体221的第二端口入射的光的偏振方向按第二方向旋转90度，其中，第二方向与第一方向相反；PR 222，具有两个端口，用于将从PR 222的两个端口入射的光的偏振方向均按第一方向旋转90度，其中，PR 222的第一端口与法拉第晶体221的任一端口相连。因此，该偏振旋转结构250可以起到将从偏振旋转结构250一端入射的光的偏振方向旋转180度，从另一端入射的光的偏振方向旋转0度的功能。
进一步地，偏振旋转结构220的另一种实现结构260如图4(b)所示，其包括第一偏振片223和第二偏振片224，第一偏振片223位于法拉第晶体221和PSR 210之间，用于将经过第一偏振片223的光的偏振方向限定在与第一偏振光的偏振方向相同或相反的方向；第二偏振片224位于PR 222与调制器230之间，用于将经过第二偏振片224的光的偏振方向限定在与第一偏振光的偏振方向相同或相反的方向，或如图4(c)所示的实现结构270，第一偏振片223位置不变，第二偏振片224位于法拉第晶体221与PR 222之间，用于将经过第二偏振片224的光的偏振方向限定在与第一偏振光的偏振方向垂直的方向。
或者，法拉第晶体221和PR 222互换位置，换句话说，第一偏振片223可以位于法拉第晶体221和调制器230之间，第二偏振片224位于PR 222与PSR 210之间，或第一偏振片223位于法拉第晶体221和调制器230之间，第二偏振片224位于法拉第晶体221与PR 222之间，两个偏振片的功能与图4(b)和图4(c)所示的偏振片一致。
其中，这两个偏振片可以保证法拉第晶体221的旋转角度不受温度和入射光波长的影响，不管法拉第晶体221的角度如何漂移，都会由角度偏移转换到光强度漂移，这种光强度漂移对偏振补偿的稳定性影响很小，一度的偏移角只会产生千万分之一的 光强涨落。在QKD系统中，偏振方向偏移1度就会对整个系统的安全性产生巨大影响，窃听者EVE可以直接利用这个漏洞窃取到有用信息，但光强的涨落对于系统的安全性几乎没有影响，因此，将本发明实施例应用于QKD系统中，可以提高QKD系统的安全性。
可选地，作为另一个实施例，如图5所示，偏振旋转结构220还有另一种实现方式280，包括相位调制器(Phase Modulator，PM)或动态偏振控制器(Dynamic Polarization Controler，DPC)。
假设从偏振旋转结构280两端入射的光脉冲记为P1和P2，P1的偏振方向被旋转180度，P2的偏振方向不变。由于PM或DPC均为主动控制器，不能同时处理两端入射的光信号，这就要求P2到达偏振旋转结构280时，P1已经处理完成，完全离开偏振旋转结构280。因此，要满足如下关系Tac≥Tab+Tbc+Wp，如图7所示，Tab和Tac分别是P1和P2到达偏振旋转结构280所需的时间，Tbc是光脉冲P1在偏振旋转结构280进行偏振旋转所需的时间，Wp是光脉冲P1的全脉宽。需要说明的是，虽然PM或DPC也跟入射光波长和温度有关，但由于是主动调制，可以实时的调整控制电压，补偿掉入射光波长和温度的影响。
一般意义上，PM只用于调制光信号的相位，并不能调节光信号的偏振方向，但是如果给一个光信号加一个π相位的调制，则相当于偏振方向旋转了180度。也就是说，假设光信号的平面波为，偏振方向旋转180度变为
Figure PCTCN2017103058-appb-000001
而给该光信号加一个π相位的调制之后，该光信号的平面波也为
Figure PCTCN2017103058-appb-000002
两者效果是一样的。需要注意的是，只有在调制π相位时，PM才可以起到调节光信号偏振方向的功能。由于PM可以做到支持GHz量级的调制速率，且适用于PLC技术，故采用PM的偏振旋转结构280不仅满足高速通信的需求，还有利于设备的小型化集成。
至于DPC，主要分为两种，分别为全光机械型和电光控制型，其中，全光机械型由于一般采用机械控制，速度较慢，但其直接作用于光纤，有插入损耗小的优势，适用于对速度要求不高的场景。而电光控制型包括电光、压电、磁光、液晶等类型，通过外加电场控制偏振态，速度可以达到毫秒量级，与现有技术的处理速度相当，但本发明实施例只需要利用DPC分别对P1和P2的偏振方向旋转0度和180度即可，控制复杂度较低，而且DPC也适用于PLC技术，有利于设备的小型化集成。
需要说明的是，如果PSR 210和偏振旋转结构220集成在一起，则上述器件之间采用光波导连接；如果PSR 210和偏振旋转结构220为独立的器件，则上述器件之间采用保偏光纤连接。
调制器230，用于对旋转后的第一偏振光进行调制，得到第一信号光，将第一信号光发送到PSR 210的第三端口；还用于对第二偏振光进行调制，得到第二信号光，将第二信号光发送到偏振旋转结构220。
具体的，调制器230可以为强度调制器(Intensity Modulator，IM)，PM，正交相移键控调制器(Quadrature Phase Shift Keying Modulator，QPSK Modulator)等，本发明实施例对此不做限定。
可选地，调制器230两端到达PSR 210的光程相同，保证调制器230可以同时处理被PSR 210分开的两束偏振光，有利于提高处理速度。具体的，PSR 210，偏振旋转 结构220以及调制器230之间采用光波导或保偏光纤连接。
需要说明的是，高速调制器都是偏振相关的，对入射光的TE偏振模式和TM偏振模式的损耗是不同的，相差一般在20个dB以上，通常情况下，TE偏振模式的损耗约为6dB，TM偏振模式的损耗约为30dB，而30dB的损耗在通信系统中，尤其在光强很弱的量子通信系统中是无法接受的。在本发明实施例中，PSR 210分出的两束偏振光偏振模式相同，均为TE偏振光，可以支持高速调制器，不用担心引入通信系统无法承受的损耗。
应理解，如果编码装置200采用特殊的对TM偏振光损耗低的调制器，本发明实施例也可以让PBS 210分出的两束偏振光均为TM偏振光。
偏振旋转结构220，还用于将第二信号光发送到PSR 210的第二端口。
可选地，以图4(a)所示的偏振旋转结构250为例，PR 222还用于从PSR 210的第三端口接收第一信号光，将第一信号光的偏振方向按第一方向旋转90度，得到旋转后的第一信号光；法拉第晶体221还用于将旋转后的第一信号光的偏振方向沿第二方向旋转90度，恢复出第一信号光，其中，第一方向为顺时针方向或逆时针方向，第二方向与第一方向相反。
PSR 210，还用于将第一信号光和第二信号光进行合束，得到输出信号光，将输出信号光通过PSR 210的第一端口发送出去，其中，输出信号光的偏振方向与输入信号光的偏振方向垂直。
可选地，作为另一个实施例，PSR 240包括PBS 211和PR 212，如图3(a)所示，PBS 211还用于将偏振方向互相垂直的两个信号光合成输出信号光；PR 212位于PBS 211和偏振旋转结构220之间，用于将经过PR 212的光的偏振方向按照第一方向旋转90度，其中，第一方向为顺时针方向或逆时针方向。
另外，PSR 240也可如图3(b)所示，包括PBS 211和PR 212，其中，PR 212位于PBS 211和调制器230之间，功能与图3(a)所示结构类似，在此不再赘述。
综上所述，本发明实施例提供的编码装置200包括三端口的PSR 210，偏振旋转结构220和调制器230；从PSR 210的第一端口接收输入信号光，将输入信号光分成第一偏振光和第二偏振光，其中，第一偏振光和第二偏振光的偏振模式相同；将第一偏振光的偏振方向旋转180度，得到旋转后的第一偏振光；对旋转后的第一偏振光和第二偏振光进行调制，分别得到第一信号光和第二信号光，再对第一信号光和第二信号光进行合束，得到输出信号光，将输出信号光通过PSR 210的第一端口发送出去，其中，输出信号光的偏振方向与输入信号光的偏振方向垂直。
本发明实施例提供的编码装置200可以支持高速调制器，无需担心引入通信系统无法承受的损耗，满足高速通信的要求。
本发明实施例还提供一种光反射器600，如图6所示，包括：PSR 601和偏振旋转结构602，
PSR 601具有三个端口，从PSR 601的第一端口接收输入信号光，将输入信号光分成第一偏振光和第二偏振光，将第一偏振光和第二偏振光分别通过PSR 601的第二端口和PSR 601的第三端口发送给偏振旋转结构602，其中，第一偏振光和第二偏振光的偏振模式相同；
偏振旋转结构602，用于将第一偏振光的偏振方向旋转180度，得到旋转后的第一偏振光，将旋转后的第一偏振光发送到PSR 601的第三端口，将第二偏振光发送到PSR 601的第二端口；
PSR 601，还用于将旋转后的第一偏振光和第二偏振光进行合束，得到输出信号光，将输出信号光通过PSR 601的第一端口发送出去，其中，输出信号光的偏振方向与输入信号光的偏振方向垂直。
本发明另一实施例提供一种编码结构700，其可能的结构如图7所示，包括：分束器710，光反射器600和编码装置200，
分束器710，用于接收输入信号光，将输入信号光分成第一偏振光和第二偏振光，将第一偏振光发送给光反射器600，将第二偏振光发送给编码装置200，其中，分束器710到达光反射器600的光程与分束器710到达编码装置200的光程不同。
光反射器600包括PSR 601和偏振旋转结构602，PSR 601具有三个端口，从PSR 601的第一端口接收第一偏振光，将第一偏振光分成第一子偏振光和第二子偏振光，将第一子偏振光和第二子偏振光分别通过PSR 601的第二端口和PSR 601的第三端口发送给偏振旋转结构602，其中，第一子偏振光和第二子偏振光的偏振模式相同；偏振旋转结构602，用于将第一子偏振光的偏振方向旋转180度，得到旋转后的第一子偏振光，将旋转后的第一子偏振光发送到PSR 601的第三端口，将第二子偏振光发送到PSR 601的第二端口；PSR 601，还用于将旋转后的第一子偏振光和第二子偏振光进行合束，得到第三偏振光，将第三偏振光通过PSR 601的第一端口发送到分束器710，其中，第三偏振光的偏振方向与第一偏振光的偏振方向垂直。
编码装置200包括PSR 210，偏振旋转结构220和调制器230，PSR 210，具有三个端口，从PSR 210的第一端口接收第二偏振光，将第二偏振光分成第三子偏振光和第四子偏振光，将第三子偏振光通过PSR 210的第二端口发送给偏振旋转结构220，将第四子偏振光通过PSR 210的第三端口发送给调制器230，其中，第三子偏振光和第四子偏振光的偏振模式相同；偏振旋转结构220，用于将第三子偏振光的偏振方向旋转180度，得到旋转后的第三子偏振光，将旋转后的第三子偏振光发送给调制器230；调制器230，用于对旋转后的第三子偏振光进行调制，得到第一信号光，将第一信号光发送到PSR 210的第三端口；还用于对第四子偏振光进行调制，得到第二信号光，将第二信号光发送给偏振旋转结构220；偏振旋转结构220，还用于将第二信号光发送到PSR 210的第二端口；PSR 210，还用于将第一信号光和第二信号光进行合束，得到第四偏振光，将第四偏振光通过PSR 210的第一端口发送到分束器710，其中，第四偏振光的偏振方向与第二偏振光的偏振方向垂直；分束器710，还用于将第三偏振光和第四偏振光发送出去。
具体的，由于分束器710到达光反射器600的光程与分束器710到达编码装置200的光程不同，故第三偏振光和第四偏振光不会同时到达分束器710。
可选地，该编码结构700还包括两个光延时线720，第一光延时线721位于分束器710和光反射器600之间，第二光延时线722位于分束器710和编码装置200之间，其中，第一光延时线721和第二光延时线722的长度不同。
在本发明实施例中，由于采用光反射器600和编码装置200，故编码结构700同 样可以支持高速调制器，可以满足高速通信的要求。
应理解，图7示出了一种可能的编码结构700，光反射器600与编码装置200的位置也可以调换，本实施例对此不做限定。
本发明另一实施例提供一种量子密钥发送设备800，如图8所示，包括：量子光源810，编码结构700和衰减器820，
量子光源810，用于发射光脉冲，将光脉冲发送给编码结构700。
编码结构700为如图7所示的编码结构，量子光源发送的光脉冲即为编码结构700的输入信号光，对该输入信号光做同样处理之后，得到第三偏振光和第四偏振光，将第三偏振光和第四偏振光发送给衰减器820。对该输入信号光的处理方式在之前实施例已经详细描述过，本发明实施例在此不再赘述。
具体的，编码结构700中的光反射器600和编码装置200还包括光开关或IM，此时，该量子密钥发送设备800可以支持相位加路径编码的六态量子密钥分发协议或参考系无关协议。
衰减器820，用于将第三偏振光和第四偏振光衰减到单光子量级，通过量子信道将衰减后的第三偏振光和衰减后的第四偏振光发送出去。
其中，单光子量级指平均每个光脉冲包含的光子数在个位数，即每个光脉冲的能量约为1e-18或1e-19焦耳左右。
本发明实施例提供的量子密钥发送设备，可以支持高速调制器，满足高速通信的要求。
本发明另一实施例提供一种量子密钥接收设备900，如图9所示，包括：环形器910，编码结构700，第一单光子探测器920和第二单光子探测器930，
环形器910，用于从量子信道接收衰减后的第三偏振光和衰减后的第四偏振光，将衰减后的第三偏振光和衰减后的第四偏振光发送给编码结构700，其中，两个偏振光的偏振方向相同。
编码结构700为如图7所示的编码结构，包括分束器710，光反射器600和编码装置200，其中，衰减后的第三偏振光和衰减后的第四偏振光均为编码结构700的输入信号光，记为第一输入信号光和第二输入信号光。
分束器710用于接收这两个输入信号光，将第一输入信号光分成第一子偏振光和第二子偏振光，将第二输入信号光分成第三子偏振光和第四子偏振光，将第一子偏振光和第三子偏振光发送给光反射器600，将第二子偏振光和第四子偏振光发送给编码装置200，其中，分束器710到达光反射器600的光程与分束器710到达编码装置200的光程差与发送设备中相应的光程差相同。
光反射器600，用于接收第一子偏振光和第三子偏振光，分别对这两束偏振光进行处理，得到第一输出偏振光和第二输出偏振光，其中，第一子偏振光和第三子偏振光均为光反射器600的输入信号光，具体的处理方式在之前实施例已经描述过，本发明在此不再赘述。
编码装置200，用于接收第二子偏振光和第四子偏振光，分别对这两束偏振光进行处理，得到第三输出偏振光和第四输出偏振光，其中，第二子偏振光和第四子偏振光均为编码装置200的输入信号光，具体的处理方式在之前实施例也已经描述过，本 发明在此不再赘述。
分束器710，还用于让第二输出偏振光和第三输出偏振光发生干涉，得到第一干涉光和第二干涉光，将第一干涉光和第二干涉光分别发送给环形器910和第二单光子探测器930。
具体的，在编码结构700中，分束器710到达光反射器600的光程与分束器710到达编码装置200的光程不同，假设分束器710到达光反射器600的光程较短，则将分束器710到光反射器600的路径称为短臂，将分束器710到编码装置200的路径称为长臂，故发送设备将发出两个偏振光。在接收设备中，假设第一偏振光比第二偏振光先到达，编码结构700中的分束器710将第一偏振光分为第一子偏振光和第二子偏振光，将第二偏振光分为第三子偏振光和第四子偏振光；第一子偏振光和第三子偏振光走短臂，经过光反射器600之后，分别得到第一输出偏振光和第二输出偏振光，第二子偏振光和第四子偏振光走长臂，经过编码装置200之后，分别得到第三输出偏振光和第四输出偏振光。由于接收设备和发送设备中的编码结构完全相同，均为如图7所示的编码结构700，接收设备中分束器710到光反射器600和编码装置200的光程差与发送设备中的相应光程差一致，也就是说，在发送设备和接收设备中，既走过长臂也走过短臂的光将同时到达分束器。因此，第二输出偏振光和第三输出偏振光将同时到达分束器710，在分束器710处发生干涉，得到第一干涉光和第二干涉光。
环形器910，还用于将第一干涉光发送给第一单光子探测器920。
两个单光子探测器，分别用于对第一干涉光和第二干涉光进行检测，根据相关的量子密钥分配协议，得到量子密钥。
需要说明的是，如果想从第一干涉光和第二干涉光中得到量子密钥，发生干涉的两个输出信号光需要分别携带发送设备和接收设备的调制信息。在本发明实施例中，由于第一偏振光比第二偏振光先到达接收设备，故第一偏振光在发送设备中走短臂，第二偏振光在发送设备中走长臂。假设编码装置200在短臂上，则第二输出偏振光将携带发送设备的调制信息，第三输出偏振光将携带接收设备的调制信息；假设编码装置200在长臂上，则第二输出偏振光将携带接收设备的调制信息，第三输出偏振光将携带发送设备的调制信息。因此，本发明实施例可以保证获得量子密钥。
另外，本发明实施例还具有自补偿偏振相关损耗的功能，由于每束光都可以分为偏振方向互相垂直的两种偏振光来看，而偏振损耗主要就是由光的两个偏振方向的损耗不一致导致的。假设输入信号光从分束器710到达光反射器600的过程中，该输入信号光的TE偏振光损耗1dB，TM偏振光损耗3dB，故该输入信号光到达光反射器600时，偏振方向与在分束器710时不同，如图10所示,输入信号光在b处与a处偏振方向不同；如果光反射器200的输出信号光的偏振方向与输入信号光的偏振方向垂直，此时输出信号光的TE偏振光对应于输入信号光的TM偏振光，输出信号光的TM偏振光对应于输入信号光的TE偏振光；因此，从输入信号光从分束器710到光反射器600，再到输出信号光返回分束器710这整个过程，两个偏振方向的光损耗均为4dB，两个偏振方向的损耗一致，也就是说，由中间传输过程引入的偏振损耗为0，返回到分束器710的输出信号光与从分束器710出发的输入信号光的偏振方向垂直，如图10所示，输入信号光在d处与a处偏振方向垂直。由于经过编码装置200的输出光和输 入光的偏振方向也相互垂直，故也可以保证从输入信号光从分束器710到编码装置200，再到输出信号光返回分束器710这整个过程，两个偏振方向的损耗一致。
因此，本发明实施例提供的接收设备，可以支持高速调制器，满足高速通信的要求，还可以自补偿接收设备中的偏振相关损耗，保证发生干涉的两个输出偏振光的偏振方向一致，增强干涉效果，有利于提高量子密钥的生成率。
本发明另一实施例提供一种QKD系统，包括：之前实施例描述的量子密钥发送设备800和量子密钥接收设备900。具体的工作流程如下：
量子光源810位于发送设备800中，用于产生光脉冲，该光脉冲经过分束器710，被分成两个偏振光P1和P2，偏振光P1走短臂，P2走长臂；P1经过光反射器600之后，返回到分束器710，P2经过编码装置200之后，返回到分束器710，两个偏振光P1和P2依次经过衰减器820，被衰减到单光子量级之后，通过量子信道发送到接收设备900，其中，P2在编码装置200中被调制了发送设备的信息。
在接收设备900中，P1和P2依次被环形器910接收，并发送给分束器710，偏振光P1被分成P11和P12，偏振光P2被分成P20和P22，其中，P11和P20走短臂，P12和P22走长臂。P11和P20将经过光反射器600之后，返回到分束器710，而P12和P22将经过编码装置200，被调制了接收设备的信息之后，再返回到分束器710；由于接收设备900和发送设备800中长臂和短臂的光程差相同，故P12和P20将同时到达分束器710，在此处发生干涉，干涉信号被两个单光子探测器920和930获得。根据相应的量子密钥分配协议处理两个单光子探测器的探测结果，即可得到量子密钥。
应理解，光反射器600和编码装置200对偏振光的处理过程在之前的实施例已经详细描述过，本发明实施例在此不再赘述。
本发明实施例提供的QKD系统，可以支持高速调制器，满足高速通信的要求，还可以自补偿系统中的偏振相关损耗，保证发生干涉的两个输出偏振光的偏振方向一致，增强干涉效果，有利于提高量子密钥的生成率。
本发明另一实施例提供一种QKD系统，如图11所示，包括Alice端和Bob端，该Alice端包括编码装置200，衰减器1110，分束器1120和单光子探测器1130，该Bob端采用现有的往返式QKD系统的Bob端；
分束器1120，具有至少三个端口，第一端口和第二端口位于分束器1120的一侧，其余端口位于分束器1120的另一侧，该第一端口连接衰减器1110，该第二端口连接单光子探测器1130，该第三端口连接量子信道；分束器1120用于从量子信道接收光脉冲，将该光脉冲分成第一光脉冲和第二光脉冲，分别通过该第一端口和该第二端口发送出去；
衰减器1110，还与编码装置200相连，用于对输入到衰减器220的光脉冲进行衰减；
单光子探测器1130，用于检测输入到单光子探测器1130的光脉冲，其中，该检测信息用于指示检测的光脉冲是否受到木马攻击；
编码装置200，包括PSR 210，偏振旋转结构220和调制器230，PSR 210具有三个端口，PSR 210的第一端口与衰减器220相连，PSR 210的第二端口与偏振旋转结构220相连，PSR 210的第三端口与调制器230相连，用于从PSR 210的第一端口接收输 入光脉冲，将输入光脉冲分为第一偏振光和第二偏振光，将第一偏振光的偏振方向旋转90度，得到第三偏振光，将第一偏振光和第三偏振光分别通过PSR 210的第二端口和PSR 210的第三端口发送出去；调制器230还与偏振旋转结构220相连，用于对输入到调制器230的光脉冲进行调制；偏振旋转结构220，用于将从偏振旋转结构220一侧进入的光脉冲的偏振方向旋转180度，从另一侧进入的光脉冲的偏振方向旋转0度，其中，编码装置200的输出光脉冲和输入光脉冲的偏振方向互相垂直。
本发明实施例提供的QKD系统与现有的往返式QKD系统相比，在发送端无需采用PC，也就不受PC纠偏速度的影响，系统速率获得提升。
另外，编码装置200不仅可以作为QKD系统的编码装置，应用于量子通信领域，也可以作为远端调制装置，应用于经典光领域。
本发明另一实施例提供一种远端调制系统，如图12所示，包括：激光器1200，PBS 1220，远端调制装置1230和接收器1240，
激光器1200，与PBS 1220的第二端口相连，用于发射第一偏振光；
需要说明的是，激光器产生的光既可以为TE偏振光，也可以为TM偏振光。
PBS 1220，具有三个端口，用于从PBS 1220的第二端口接收第一偏振光，将第一偏振光从PBS 1220的第一端口通过传输信道发送给远端调制装置1230；
远端调制装置1230，包括PSR 1231，偏振旋转结构1232和调制器1233，PSR 1231，具有三个端口，从PSR 1231的第一端口接收输入信号光，将输入信号光分成第二偏振光和第三偏振光，将第二偏振光通过PSR 1231的第二端口发送给偏振旋转结构1232，将第三偏振光通过PSR 1231的第三端口发送给调制器1233，其中，输入信号光为第一偏振光经过传输信道所得，第二偏振光和第三偏振光的偏振模式相同；偏振旋转结构1232，用于将第二偏振光的偏振方向旋转180度，得到旋转后的第二偏振光，将旋转后的第二偏振光发送给调制器1233；调制器1233，用于对旋转后的第二偏振光进行调制，得到第一信号光，将第一信号光发送到PSR 1231的第三端口；还用于对第三偏振光进行调制，得到第二信号光，将第二信号光发送给偏振旋转结构1232；偏振旋转结构1232，还用于将第二信号光发送到PSR 1231的第二端口；PSR 1231，还用于将第一信号光和第二信号光进行合束，得到输出信号光，将输出信号光从PSR 1231的第一端口通过传输信道发送给PBS 1220，其中，输出信号光的偏振方向与输入信号光的偏振方向垂直；
具体的，远端调制装置1230中的调制器可以为PM，IM，QPSK Modulator等，本发明实施例对此不做限定。
PBS 1220，还用于从PBS 1220的第一端口接收第四偏振光，将第四偏振光通过PBS 1220的第三端口发送给接收器1240，其中，第四偏振光为输出信号光经过传输信道所得；
接收器1240，用于对第四偏振光进行接收。
在本发明实施例提供的远端调制系统中，假设激光器1200产生的偏振光为TE偏振光，PBS 1220的第一端口与传输信道相连，PBS 1220的第二端口为TE偏振端口，PBS 1220的第三端口为TM偏振端口，该远端调制系统的工作流程如下：
激光器1200产生TE偏振光，该TE偏振光到达PBS 1220的第二端口后，将通过 传输信道到达远端调制装置1230，由于传输信道的影响，该TE偏振光的偏振方向会发生变化，可将到达远端调制装置1230的光记为输入信号光；在远端调制装置1230中，对输入信号光进行调制，得到输出信号光，将该输出信号光反射回去，其中，由于远端调制装置1230的输出信号光和输入信号光的偏振方向互相垂直，具有自补偿偏振损耗的功能，即在该输出信号光返回到PBS 1220时，该输出信号光的偏振方向将与从PBS 1220发射的TE偏振光的偏振方向互相垂直，也就是说，该输出信号光将变为TM偏振光。具体的偏振损耗自补偿原理在之前的实施例已经描述过，在此不再赘述。
由于该输出信号光通过该传输信道返回PBS 1220时，变为TM偏振光，故该输出信号光将从PBS 1220的第三端口输出，到达接收器1240；在接收器1240中，对该输出信号光进行解调，提取调制信息。
综上所述，本发明实施例提供的远端调制系统，PBS 1220只将一个偏振方向的光发送给接收器1240，也只会引入与该偏振方向相同的噪声，相当于将噪声衰减了3dB，此外，PBS也比现有远端调制系统采用的环形器的插损更低。
需要说明的是，如果远端调制装置1230中的调制器为IM，则对输入信号光进行强度调制，接收器1240可以采用直接检测的方式对输出信号光进行解调，如果远端调制装置1230中的调制器为PM，QPSK modulator等，则对输入信号光进行相位调制或相位及强度联合调制，此时，接收器1240将采用相干接收的方式，利用本振光对接收光进行解调；其中，激光器1200，PBS 1220和接收器1240之间采用保偏光纤或保偏波导连接。
可选地，如图13所示，该远端调制系统还包括分束器1250，该分束器1250在激光器1200和PBS 1220之间，用于将激光器1200的输出光分成两份，一份发送给PBS1220，另一份发送给接收器1240，作为本振光。
此时，由于接收器1240接收的输出信号光具有确定的偏振方向，不需要双偏振接收，因此，相比现有的相干接收器，接收器1240可以采用如图14所示的单偏相干接收器，单偏相干接收器具有结构简单、插损小的特点，该特点可以给整个系统带来成本低、功耗低、传输距离长的好处。
以上所述，仅为本发明的具体实施方式，但本发明的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本发明揭露的技术范围内，可轻易想到变化或替换，都应涵盖在本发明的保护范围之内。因此，本发明的保护范围应以所述权利要求的保护范围为准。

Claims (15)

  1. 一种编码装置，其特征在于，包括：偏振分束旋转器PSR，偏振旋转结构和调制器，
    所述PSR，具有三个端口，从所述PSR的第一端口接收输入信号光，将所述输入信号光分成第一偏振光和第二偏振光，将所述第一偏振光通过所述PSR的第二端口发送给所述偏振旋转结构，将所述第二偏振光通过所述PSR的第三端口发送给所述调制器，其中，所述第一偏振光和所述第二偏振光的偏振模式相同；
    所述偏振旋转结构，用于将所述第一偏振光的偏振方向旋转180度，得到旋转后的第一偏振光，将所述旋转后的第一偏振光发送给所述调制器；
    所述调制器，用于对所述旋转后的第一偏振光进行调制，得到第一信号光，将所述第一信号光发送到所述PSR的第三端口；还用于对所述第二偏振光进行调制，得到第二信号光，将所述第二信号光发送给所述偏振旋转结构；
    所述偏振旋转结构，还用于将所述第二信号光发送到所述PSR的第二端口；
    所述PSR，还用于将所述第一信号光和所述第二信号光进行合束，得到输出信号光，将所述输出信号光通过所述PSR的第一端口发送出去，其中，所述输出信号光的偏振方向与所述输入信号光的偏振方向垂直。
  2. 根据权利要求1所述的编码装置，其特征在于，所述调制器两端到达所述PSR的光程相同。
  3. 根据权利要求1或2所述的编码装置，其特征在于，所述偏振旋转结构包括相位调制器或动态偏振控制器。
  4. 根据权利要求3所述的编码装置，其特征在于，在所述第一偏振光离开所述偏振旋转结构之后，所述第二信号光进入所述偏振旋转结构。
  5. 根据权利要求1或2所述的编码装置，其特征在于，所述偏振旋转结构包括法拉第晶体和偏振旋转器PR，
    所述法拉第晶体，具有两个端口，用于将从所述法拉第晶体的第一端口入射的光的偏振方向按第一方向旋转90度，将从所述法拉第晶体的第二端口入射的光的偏振方向按第二方向旋转90度，其中，所述第一方向为顺时针方向或逆时针方向，所述第二方向与所述第一方向相反；
    所述PR，具有两个端口，用于将从所述PR的两个端口入射的光的偏振方向均按所述第一方向旋转90度，其中，所述PR的第一端口与所述法拉第晶体的任一端口相连。
  6. 根据权利要求5所述的编码装置，其特征在于，所述偏振旋转结构还包括第一偏振片和第二偏振片，
    所述第一偏振片位于所述法拉第晶体和所述PSR之间，用于将经过所述第一偏振片的光的偏振方向限定在与所述第一偏振光的偏振方向相同或相反的方向；
    所述第二偏振片位于所述PR与所述调制器之间，用于将经过所述第二偏振片的光的偏振方向限定在与所述第一偏振光的偏振方向相同或相反的方向，或
    所述第二偏振片位于所述法拉第晶体与所述PR之间，用于将经过所述第二偏振片的光的偏振方向限定在与所述第一偏振光的偏振方向垂直的方向。
  7. 根据权利要求6所述的编码装置，其特征在于，所述偏振旋转结构还包括第一偏振片和第二偏振片，
    所述第一偏振片位于所述法拉第晶体和所述调制器之间，用于将经过所述第一偏振片的光的偏振方向限定在与所述第一偏振光的偏振方向相同或相反的方向；
    所述第二偏振片位于所述PR与所述PSR之间，用于将经过所述第二偏振片的光的偏振方向限定在与所述第一偏振光的偏振方向相同或相反的方向，或
    所述第二偏振片位于所述法拉第晶体与所述PR之间，用于将经过所述第二偏振片的光的偏振方向限定在与所述第一偏振光的偏振方向垂直的方向。
  8. 根据权利要求5所述的编码装置，其特征在于，所述PSR，所述调制器和所述偏振旋转结构之间采用保偏光纤连接。
  9. 根据权利要求1或2所述的编码装置，其特征在于，所述PSR包括偏振分束器PBS和PR，
    所述PBS，用于将所述输入信号光分成偏振方向互相垂直的两个偏振光，还用于将偏振方向互相垂直的两个偏振光合成所述输出信号光；
    所述PR，位于所述PBS和所述偏振旋转结构之间或所述PBS和所述调制器之间，用于将经过所述PR的光的偏振方向按照第一方向旋转90度，其中，所述第一方向为顺时针方向或逆时针方向。
  10. 一种光反射器，其特征在于，包括：PSR和偏振旋转结构，
    所述PSR具有三个端口，从所述PSR的第一端口接收输入信号光，将所述输入信号光分成第一偏振光和第二偏振光，将所述第一偏振光和所述第二偏振光分别通过所述PSR的第二端口和所述PSR的第三端口发送给所述偏振旋转结构，其中，所述第一偏振光和所述第二偏振光的偏振模式相同；
    所述偏振旋转结构，用于将所述第一偏振光的偏振方向旋转180度，得到旋转后的第一偏振光，将所述旋转后的第一偏振光发送到所述PSR的第三端口，将所述第二偏振光发送到所述PSR的第二端口；
    所述PSR，还用于将所述旋转后的第一偏振光和所述第二偏振光进行合束，得到输出信号光，将所述输出信号光通过所述PSR的第一端口发送出去，其中，所述输出信号光的偏振方向与所述输入信号光的偏振方向垂直。
  11. 一种编码结构，其特征在于，包括：分束器，光反射器和编码装置，
    所述分束器，用于接收输入信号光，将所述输入信号光分成第一偏振光和第二偏振光，将所述第一偏振光发送给所述光反射器，将所述第二偏振光发送给所述编码装置，其中，所述分束器到达所述光反射器的光程与所述分束器到达所述编码装置的光程不同；
    所述光反射器，包括PSR和偏振旋转结构，所述PSR具有三个端口，从所述PSR的第一端口接收所述第一偏振光，将所述第一偏振光分成第一子偏振光和第二子偏振光，将所述第一子偏振光和所述第二子偏振光分别通过所述PSR的第二端口和所述PSR的第三端口发送给所述偏振旋转结构，其中，所述第一子偏振光和所述第二子偏振光的偏振模式相同；所述偏振旋转结构，用于将所述第一子偏振光的偏振方向旋转180度，得到旋转后的第一子偏振光，将所述旋转后的第一子偏振光发送到所述PSR 的第三端口，将所述第二子偏振光发送到所述PSR的第二端口；所述PSR，还用于将所述旋转后的第一子偏振光和所述第二子偏振光进行合束，得到第三偏振光，将所述第三偏振光通过所述PSR的第一端口发送到所述分束器，其中，所述第三偏振光的偏振方向与所述第一偏振光的偏振方向垂直；
    所述编码装置，包括PSR，偏振旋转结构和调制器，所述PSR，具有三个端口，从所述PSR的第一端口接收第二偏振光，将所述第二偏振光分成第三子偏振光和第四子偏振光，将所述第三子偏振光通过所述PSR的第二端口发送给所述偏振旋转结构，将所述第四子偏振光通过所述PSR的第三端口发送给所述调制器，其中，所述第三子偏振光和所述第四子偏振光的偏振模式相同；所述偏振旋转结构，用于将所述第三子偏振光的偏振方向旋转180度，得到旋转后的第三子偏振光，将所述旋转后的第三子偏振光发送给所述调制器；所述调制器，用于对所述旋转后的第三子偏振光进行调制，得到第一信号光，将所述第一信号光发送到所述PSR的第三端口；还用于对所述第四子偏振光进行调制，得到第二信号光，将所述第二信号光发送给所述偏振旋转结构；所述偏振旋转结构，还用于将所述第二信号光发送到所述PSR的第二端口；所述PSR，还用于将所述第一信号光和所述第二信号光进行合束，得到第四偏振光，将所述第四偏振光通过所述PSR的第一端口发送到所述分束器，其中，所述第四偏振光的偏振方向与所述第二偏振光的偏振方向垂直；
    所述分束器，还用于将所述第三偏振光和所述第四偏振光发送出去。
  12. 根据权利要求11所述的编码结构，其特征在于，所述编码结构还包括两个光延时线，第一光延时线位于所述分束器和所述光反射器之间，第二光延时线位于所述分束器和所述编码装置之间，所述两个光延时线的长度不同。
  13. 一种量子密钥发送设备，其特征在于，包括：量子光源，编码结构和衰减器，
    所述量子光源，用于发射光脉冲，将所述光脉冲发送给所述编码结构；
    所述编码结构包括：分束器，光反射器和编码装置，所述分束器，用于接收光脉冲，将所述光脉冲分成第一偏振光和第二偏振光，将所述第一偏振光发送给所述光反射器，将所述第二偏振光发送给所述编码装置，其中，所述分束器到达所述光反射器的光程与所述分束器到达所述编码装置的光程相差为N，N为自然数；所述光反射器包括PSR和偏振旋转结构，所述PSR具有三个端口，从所述PSR的第一端口接收所述第一偏振光，将所述第一偏振光分成第一子偏振光和第二子偏振光，将所述第一子偏振光和所述第二子偏振光分别通过所述PSR的第二端口和所述PSR的第三端口发送给所述偏振旋转结构，其中，所述第一子偏振光和所述第二子偏振光的偏振模式相同；所述偏振旋转结构，用于将所述第一子偏振光的偏振方向旋转180度，得到旋转后的第一子偏振光，将所述旋转后的第一子偏振光发送到所述PSR的第三端口，将所述第二子偏振光发送到所述PSR的第二端口；所述PSR，还用于将所述旋转后的第一子偏振光和所述第二子偏振光进行合束，得到第三偏振光，将所述第三偏振光通过所述PSR的第一端口发送到所述分束器，其中，所述第三偏振光的偏振方向与所述第一偏振光的偏振方向垂直；所述编码装置包括PSR，偏振旋转结构和调制器，所述PSR，具有三个端口，从所述PSR的第一端口接收第二偏振光，将所述第二偏振光分成第三子偏振光和第四子偏振光，将所述第三子偏振光通过所述PSR的第二端口发送给所述偏振 旋转结构，将所述第四子偏振光通过所述PSR的第三端口发送给所述调制器，其中，所述第三子偏振光和所述第四子偏振光的偏振模式相同；所述偏振旋转结构，用于将所述第三子偏振光的偏振方向旋转180度，得到旋转后的第三子偏振光，将所述旋转后的第三子偏振光发送给所述调制器；所述调制器，用于对所述旋转后的第三子偏振光进行调制，得到第一信号光，将所述第一信号光发送到所述PSR的第三端口；还用于对所述第四子偏振光进行调制，得到第二信号光，将所述第二信号光发送给所述偏振旋转结构；所述偏振旋转结构，还用于将所述第二信号光发送到所述PSR的第二端口；所述PSR，还用于将所述第一信号光和所述第二信号光进行合束，得到第四偏振光，将所述第四偏振光通过所述PSR的第一端口发送到所述分束器，其中，所述第四偏振光的偏振方向与所述第二偏振光的偏振方向垂直；所述分束器，还用于将所述第三偏振光和所述第四偏振光发送给所述衰减器；
    所述衰减器，用于将所述第三偏振光和所述第四偏振光衰减到单光子量级，通过量子信道将衰减后的第三偏振光和衰减后的第四偏振光发送出去。
  14. 一种量子密钥接收设备，其特征在于，包括：环形器，编码结构，第一单光子探测器和第二单光子探测器，
    所述环形器，用于从量子信道接收衰减后的第三偏振光和衰减后的第四偏振光，将所述衰减后的第三偏振光和所述衰减后的第四偏振光发送给所述编码结构；
    所述编码结构包括分束器，光反射器和编码装置，所述分束器，用于接收所述衰减后的第三偏振光和所述衰减后的第四偏振光，将所述衰减后的第三偏振光分成第一子偏振光和第二子偏振光，将所述衰减后的第四偏振光分成第三子偏振光和第四子偏振光，将所述第一子偏振光和所述第三子偏振光发送给所述光反射器，将所述第二子偏振光和所述第四子偏振光发送给所述编码装置，其中，所述分束器到达所述光反射器的光程与所述分束器到达所述编码装置的光程相差为N，N为自然数；所述光反射器包括PSR和偏振旋转结构，所述PSR具有三个端口，从所述PSR的第一端口接收所述第一子偏振光，将所述第一子偏振光分成第五子偏振光和第六子偏振光，将所述第五子偏振光和第六子偏振光分别通过所述PSR的第二端口和所述PSR的第三端口发送给所述偏振旋转结构，其中，所述第五子偏振光和所述第六子偏振光的偏振模式相同；所述偏振旋转结构，用于将所述第五子偏振光的偏振方向旋转180度，得到旋转后的第五子偏振光，将所述旋转后的第五子偏振光发送到所述PSR的第三端口，将所述第六子偏振光发送到所述PSR的第二端口；所述PSR，还用于将所述旋转后的第五子偏振光和所述第六子偏振光进行合束，得到第一输出偏振光，将所述第一输出偏振光通过所述PSR的第一端口发送到所述分束器，其中，所述第一输出偏振光的偏振方向与所述第一子偏振光的偏振方向垂直；所述光反射器对所述第三子偏振光做同样处理，得到第二输出偏振光，将所述第二输出偏振光通过所述PSR的第一端口发送给所述分束器，其中，所述第二输出偏振光的偏振方向与所述第三子偏振光的偏振方向垂直；所述编码装置包括PSR，偏振旋转结构和调制器，所述PSR，具有三个端口，从所述PSR的第一端口接收所述第二子偏振光，将所述第二子偏振光分成第七子偏振光和第八子偏振光，将所述第七子偏振光通过所述PSR的第二端口发送给所述偏振旋转结构，将所述第八子偏振光通过所述PSR的第三端口发送给所述调制器，其中，所述 第七子偏振光和所述第八子偏振光的偏振模式相同；所述偏振旋转结构，用于将所述第七子偏振光的偏振方向旋转180度，得到旋转后的第七子偏振光，将所述旋转后的第七子偏振光发送给所述调制器；所述调制器，用于对所述旋转后的第七子偏振光进行调制，得到第一信号光，将所述第一信号光发送到所述PSR的第三端口；还用于对所述第八子偏振光进行调制，得到第二信号光，将所述第二信号光发送给所述偏振旋转结构；所述偏振旋转结构，还用于将所述第二信号光发送到所述PSR的第二端口；所述PSR，还用于将所述第一信号光和所述第二信号光进行合束，得到第三输出偏振光，将所述第三输出偏振光通过所述PSR的第一端口发送到所述分束器，其中，所述第三输出偏振光的偏振方向与所述第二子偏振光的偏振方向垂直；所述编码装置对所述第四子偏振光做同样处理，得到第四输出偏振光，将所述第四输出偏振光通过所述PSR的第一端口发送给所述分束器，其中，所述第四输出偏振光的偏振方向与所述第二子偏振光的偏振方向垂直；所述分束器，还用于让所述第二输出信号光和所述第三输出信号光发生干涉，得到第一干涉光和第二干涉光，将所述第一干涉光和所述第二干涉光分别发送给所述环形器和所述第二单光子探测器；
    所述环形器，还用于将所述第一干涉光发送给所述第一单光子探测器；
    两个单光子探测器，分别用于对所述第一干涉光和所述第二干涉光进行检测。
  15. 一种量子密钥分发系统，其特征在于，包括：如权13所述的量子密钥发送设备以及如权14所述的量子密钥接收设备。
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