WO2020182055A1 - 量子密钥分发相位编解码器、相应的编解码装置及系统 - Google Patents

量子密钥分发相位编解码器、相应的编解码装置及系统 Download PDF

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Publication number
WO2020182055A1
WO2020182055A1 PCT/CN2020/078048 CN2020078048W WO2020182055A1 WO 2020182055 A1 WO2020182055 A1 WO 2020182055A1 CN 2020078048 W CN2020078048 W CN 2020078048W WO 2020182055 A1 WO2020182055 A1 WO 2020182055A1
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polarization
beam splitter
port
phase
optical
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PCT/CN2020/078048
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English (en)
French (fr)
Inventor
许华醒
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中国电子科技集团公司电子科学研究院
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Priority to US17/593,044 priority Critical patent/US20220173897A1/en
Publication of WO2020182055A1 publication Critical patent/WO2020182055A1/zh

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    • 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
    • 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
    • H04B10/60—Receivers
    • H04B10/61—Coherent receivers
    • H04B10/614—Coherent receivers comprising one or more polarization beam splitters, e.g. polarization multiplexed [PolMux] X-PSK coherent receivers, polarization diversity heterodyne coherent receivers
    • 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 technical field of optical transmission secure communication, in particular to a quantum key distribution phase codec based on polarization orthogonal rotating reflection, a corresponding codec device and a quantum key distribution system including the phase codec.
  • Quantum secure communication technology is a frontier hotspot in the combination of quantum physics and information science. Based on quantum key distribution technology and the principle of one-time encryption, quantum secure communication can realize the secure transmission of information in public channels. Quantum key distribution is based on the Heisenberg uncertainty relationship of quantum mechanics, quantum unclonability theorem and other physical principles. It can realize the secure sharing of keys between users, and can detect potential eavesdropping behaviors. It can be applied to national defense, government affairs, and Finance, electric power and other high security information transmission fields.
  • Terrestrial quantum key distribution is mainly based on fiber channel transmission. Because the phase encoding uses the phase difference between the front and rear optical pulses to encode information, it can be stably maintained during long-distance fiber channel transmission, so it is based on the phase encoding and time bit of the unequal arm interferometer -Phase encoding is the main encoding scheme for quantum key distribution applications.
  • fiber production has non-ideal conditions such as non-circular symmetry of the cross-section and uneven distribution of the core refractive index along the radial direction.
  • the fiber is affected by temperature, strain, and bending in the actual environment, which will produce random birefringence effects.
  • the main purpose of the present invention is to propose a quantum key distribution phase codec based on polarization orthogonal rotating reflection, a corresponding codec device including the phase codec, and a quantum key distribution system to solve phase coding and time bit -The problem of instability of phase decoding interference caused by polarization-induced fading in phase encoding quantum key distribution applications.
  • a quantum key distribution phase codec comprising: a beam splitter, and two reflection devices optically coupled to the beam splitter via two arms, each of the reflection devices is a polarization orthogonal rotating reflection Device, one or each of the two reflection devices includes a polarization beam splitter having an input port and two output ports, and is coupled to the two polarization beam splitters via the input port of the polarization beam splitter In the corresponding arm of the arm, the two output ports of each polarization beam splitter are optically coupled to each other via the transmission optical path.
  • the transmission light is formed by a polarization maintaining fiber twisted by 90 degrees,
  • the light pulses output from the two output ports of the polarization beam splitter are all coupled to the slow axis of the polarization maintaining fiber for transmission or both are coupled to the fast axis of the polarization maintaining fiber for transmission.
  • phase codec according to claim 1, wherein the two reflecting devices are polarization orthogonal rotating reflecting devices of the same structure, or polarization orthogonal rotating reflecting devices of different structures.
  • phase codec according to claim 1, wherein the 90-degree twisted polarization-maintaining fiber comprises a 90-degree twisted or (90+n*180)-degree twisted polarization-maintaining fiber, where n is an integer.
  • each of the two arms is a polarization maintaining optical path
  • the optical devices on the two arms are polarization maintaining optical devices and/or non-birefringent optical devices.
  • phase codec according to any one of the schemes 1-5, wherein the phase codec further comprises a phase modulator, wherein the phase modulator is arranged at the front end of the beam splitter or arranged at all On at least one of the two arms.
  • a DC modulation quantum key distribution phase codec device comprising a pre-splitter and two phase codecs according to any one of schemes 1-6, the two phase codecs are respectively
  • Two sub-optical paths are optically coupled to the front beam splitter, wherein one of the ports of the beam splitter of each phase codec that is not coupled to the two arms of the phase codec is optically coupled to all
  • each of the sub-optical paths is provided with an optical circulator.
  • a quantum key distribution time bit-phase codec device comprising a pre-splitter and a phase codec according to any one of the schemes 1-6, the phase codec passing through a sub-optical path Optically coupled to the pre-splitter, wherein one of the ports of the beam splitter of the phase codec that is not coupled to the two arms is optically coupled to the one sub-optical path.
  • a DC modulation quantum key distribution time bit-phase codec device comprising a pre-splitter and a phase codec according to any one of the schemes 1-6, the phase codec is The sub-optical path is optically coupled to the pre-splitter, wherein one of the ports of the beam splitter of the phase codec that is not coupled to the two arms is optically coupled to the one sub-optical path, wherein the one An optical circulator is provided on the sub-optical path.
  • the coding and decoding device according to claim 8 or 9, further comprising a beam splitter coupled to the pre-splitter via another sub-optical path.
  • a quantum key distribution system including:
  • phase codec according to any one of the solutions 1 to 6 or the codec device according to any one of the solutions 7 to 10, which is arranged at the receiving end of the quantum key distribution system for decoding; and /or
  • phase codec according to any one of the solutions 1 to 6 or the codec device according to any one of the solutions 7 to 10 is arranged at the transmitting end of the quantum key distribution system for encoding.
  • the input optical pulse of any polarization state can be stably coded and decoded, thereby achieving unexpected beneficial effects.
  • stable interference output at the phase decoding interferometer can be realized for input optical pulses of any polarization state, which solves the problem of polarization-induced fading in the application of phase encoding and time bit-phase encoding quantum key distribution, which causes the system to be unstable The problem of work.
  • the invention provides a phase encoding and time bit-phase encoding quantum key distribution and decoding scheme that is easy to implement and apply against polarization-induced fading.
  • FIG. 1 is a schematic diagram of the composition structure of a quantum key distribution phase codec based on polarization orthogonal rotating reflection according to a preferred embodiment of the present invention
  • FIG. 2 is a schematic diagram of the composition structure of a quantum key distribution phase codec based on polarization orthogonal rotating reflection according to another preferred embodiment of the present invention
  • Figure 3 is a schematic diagram of the composition structure of a polarization orthogonal rotating reflection device that can be used in the phase codec of the present invention
  • FIG. 4 is a schematic diagram of the composition structure of another polarization orthogonal rotating reflection device that can be used in the phase codec of the present invention.
  • FIG. 5 is a schematic diagram of the composition structure of another polarization orthogonal rotating reflection device that can be used in the phase codec of the present invention.
  • FIG. 6 is a schematic diagram of the composition structure of a DC modulation quantum key distribution phase encoding and decoding device based on polarization orthogonal rotating reflection according to a preferred embodiment of the present invention
  • FIG. 7 is a schematic diagram of the composition structure of a quantum key distribution time bit-phase encoding and decoding device based on polarization orthogonal rotating reflection according to a preferred embodiment of the present invention
  • FIG. 8 is a schematic diagram of the composition structure of a DC modulation quantum key distribution time bit-phase encoding and decoding device based on polarization orthogonal rotating reflection according to a preferred embodiment of the present invention.
  • the quantum key distribution phase codec based on polarization orthogonal rotating reflection is shown in Fig. 1, and includes the following components: a beam splitter 101, a phase modulator 102, two reflecting devices 103 and 104 .
  • the two reflecting devices 103 and 104 are optically coupled with the beam splitter 101 via two arms (the upper arm and the lower arm in FIG. 1), respectively.
  • the phase modulator 102 is inserted in one of these two arms (in FIG. 1, the upper arm).
  • the two reflection devices 103 and 104 are both polarization orthogonal rotating reflection devices.
  • the polarization orthogonal rotating reflection device refers to a polarization orthogonal rotating reflection of the two orthogonal polarization states of the reflected light pulse, that is, when reflecting the incident light pulse, each of the light pulses is orthogonal
  • a reflection device that transforms the polarization state into a polarization state orthogonal to it. For example, suppose that the two orthogonal polarization states are the x polarization state and the y polarization state, respectively.
  • the x polarization state transmitted along the optical path to a polarization orthogonal rotating reflector is transformed into a polarization orthogonal rotating reflector at the reflector.
  • the polarization state orthogonal to it is the y polarization state, and the y polarization state transmitted along the optical path to the reflection device is converted into the polarization state orthogonal to it, that is, the x polarization state after being reflected by the polarization orthogonal rotation at the reflection device.
  • the beam splitter 101 is used for splitting an incident input optical pulse of any polarization state into two optical pulses for transmission along two arms respectively.
  • the two arms are used to respectively transmit the two optical pulses.
  • the phase modulator 102 is used to phase-modulate the optical pulse (that is, one of the two optical pulses) transmitted by the arm where it is located in accordance with the quantum key distribution protocol.
  • the phase modulation performed by the phase modulator 102 is determined by the quantum key distribution protocol and depends on the specific application. For example, in one possible application, the phase modulator 102 can randomly modulate a 0 degree phase or a 90 degree phase.
  • the phase modulator 102 may be a polarization-independent phase modulator or a birefringent phase modulator.
  • the birefringent phase modulator is adapted to apply different adjustable phase modulations to two orthogonal polarization states passing therethrough.
  • the birefringent phase modulator may be a lithium niobate phase modulator, and by controlling the voltage applied to the lithium niobate crystal, the phase modulation of the two orthogonal polarization states passing through the lithium niobate phase modulator can be modulated. Control and adjust.
  • the reflection devices 103 and 104 are respectively used to reflect the two optical pulses transmitted from the beam splitter 101 through the two arms back to the beam splitter 101 to be combined and output by the beam splitter 101.
  • the two reflection devices 103 and 104 are polarization orthogonal rotating reflection devices, for each of the two optical pulses: when the optical pulse is reflected by the corresponding reflection device of the two reflection devices, the The two orthogonal polarization states of the path light pulse are reflected by polarization orthogonal rotation, so that after reflection by the corresponding reflecting device, each orthogonal polarization state of the path light pulse is transformed into a polarization state orthogonal to it.
  • the phase codec in Figure 1 the polarization orthogonal rotating reflection at the polarization orthogonal rotating reflector is used, and the x-polarization state of the input optical pulse is passed through the beam splitter during the beam splitter to the beam splitter combination.
  • the phase difference transmitted by the two arms is exactly equal to the phase difference transmitted by the two arms when the y-polarization state of the optical pulse is split by the beam splitter to combine the beam by the beam splitter.
  • phase modulator 102 is shown as being provided on one of the two arms, it is also possible to provide one phase modulator on each of the two arms. In the case where two phase modulators are provided in this way, the difference between the phases modulated by the two phase modulators is determined by the quantum key distribution protocol, which depends on the specific application.
  • a phase modulator can be provided before the beam splitter 101 for phase modulation of the input optical pulse before the beam splitting according to the quantum key distribution protocol , Or perform phase modulation on the combined output light pulse according to the quantum key distribution protocol.
  • the present invention proposes three creative polarization orthogonal rotating reflection device configurations, namely, the following configuration 1, configuration 2, and configuration 3.
  • the polarization orthogonal rotating reflection device includes a polarization beam splitter having an input port and two output ports, and the two output ports of the polarization beam splitter are optically coupled to each other via a transmission optical path, the The transmission light is formed by a polarization-maintaining fiber, a half-wave plate is arranged on the transmission optical path, and the angle between the polarization direction of the light pulse input to the half-wave plate and the fast axis or the slow axis of the half-wave plate is 45 degrees.
  • the reflection device can be coupled to all by coupling the input port of its polarization beam splitter to one arm of the phase codec. The arm.
  • the polarization orthogonal rotating reflection device includes a polarization beam splitter having an input port and two output ports, and the two output ports of the polarization beam splitter are optically coupled to each other via a transmission optical path, the The transmission light is formed by a polarization-maintaining fiber.
  • the slow axis and the fast axis of the polarization-maintaining fiber respectively maintain the two orthogonal polarization states of the light pulse input to the polarization-maintaining fiber for stable transmission—that is, the polarization state does not change, and the polarization component
  • the two output ports of the beamer and the polarization-maintaining fiber are configured such that the optical pulses output by the two output ports of the polarization beam splitter are both coupled to the slow axis of the polarization-maintaining fiber for transmission or both are coupled to the polarization-maintaining fiber
  • the fast axis of the optical fiber is used for transmission.
  • the optical pulses output by the two output ports of the polarization beam splitter are both coupled to the slow axis of the polarization-maintaining fiber for transmission or both are coupled to the fast axis of the polarization-maintaining fiber for transmission.
  • the polarization-maintaining fiber can be twisted by 90 degrees. Or it can be achieved by twisting (90+n*180) degrees, where n is an integer.
  • the light pulse input from the slow axis of the polarization-maintaining fiber is always transmitted along the slow axis (steady transmission along the slow axis), and the light pulse input from the fast axis of the polarization-maintaining fiber is always along the fast axis.
  • Axis transmission steady transmission along the fast axis.
  • the polarization orthogonal rotating reflection device includes a polarization beam splitter having an input port and two output ports, and the two output ports of the polarization beam splitter are optically coupled to each other via a transmission optical path, the polarization beam splitter
  • the transmission optical route is formed by polarization-maintaining fibers with an odd number of 90-degree fusion splices, and each 90-degree fusion splice is formed by aligning the slow axis of the polarization-maintaining fiber and the fast axis of the polarization-maintaining fiber.
  • the reflection device can be coupled to all by coupling the input port of its polarization beam splitter to one arm of the phase codec. The arm.
  • At least one of the reflection devices 103 and 104 may be a polarization orthogonal rotating reflection device that adopts one of the above-mentioned construction 1, construction 2, and construction 3.
  • the other reflection device may be the above-mentioned configuration 1, configuration 2 and configuration 3.
  • One of the polarization orthogonal rotating reflection devices may also be a polarization orthogonal rotating reflection device of other structures.
  • the polarization orthogonal rotating reflection device of the other configuration may be, for example, a quarter wave plate mirror.
  • the "quarter wave plate mirror” includes a reflector and a quarter wave plate, the reflector being formed integrally with the quarter wave plate at the rear end of the quarter wave plate, wherein The angle between the polarization direction of one of the two orthogonal polarization states of the light pulse input to the quarter wave plate and the fast axis or the slow axis of the quarter wave plate is 45 degrees.
  • the quarter wave plate reflector can be realized by coating a reflector on the crystal surface of the quarter wave plate, or by coating a reflector on the end face of a polarization maintaining fiber with a phase difference of 90 degrees in the fast and slow axis transmission.
  • one or two reflection devices selected from the configuration of configuration 1, configuration 2 and configuration 3 can be adopted by adjusting the length of the two arms and/or adjusting the two reflection devices 103 and 104
  • the transmission optical path realizes the relative delay of the above two optical pulses.
  • the two arms of the phase codec can be configured as polarization maintaining optical paths such as polarization maintaining fiber optical paths, and the two arms on the The optical device is configured as a polarization maintaining optical device and/or a non-birefringent optical device.
  • the polarization maintaining optical path can be a free space optical path or a polarization maintaining fiber optical path.
  • non-birefringent optical device refers to an optical device having the same refractive index for different polarization states (for example, two orthogonal polarization states).
  • polarization maintaining optical devices can also be referred to as polarization maintaining optical devices.
  • the beam splitter 101 of the phase codec may be a polarization maintaining beam splitter.
  • a phase codec according to another preferred embodiment of the present invention is shown in FIG. 2 and includes the following components: a polarization-maintaining beam splitter 203, a phase modulator 204, and polarization orthogonal rotating reflection devices 205 and 206.
  • One of the two ports 201 and 202 on the side of the polarization-maintaining beam splitter 203 is used as the input port of the phase codec.
  • the polarization-maintaining beam splitter 203 and the polarization orthogonal rotating reflection devices 205 and 206 constitute a unequal-arm Michelson interferometer, and the two arms in between are polarization-maintaining fiber optical paths.
  • the phase modulator 204 is inserted into either of the two arms of the unequal-arm Michelson interferometer.
  • the port 201 or 202 of the polarization-maintaining beam splitter 203 can be used as the output port of the phase codec.
  • the optical pulse enters the polarization-maintaining beam splitter 203 through the port 201 or 202 of the polarization-maintaining beam splitter 203 and is divided into two optical pulses by the polarization-maintaining beam splitter 203.
  • One optical pulse from the polarization-maintaining beam splitter 203 is phase-modulated by the phase modulator 204 and then reflected by the polarization orthogonal rotating reflector 205, and the other optical pulse is directly transmitted to the polarization orthogonal rotating reflector 206 through the polarization maintaining fiber. It is reflected back by the polarization orthogonal rotating reflector 206.
  • the two optical pulses reflected back with a relatively delay are combined by the polarization-maintaining beam splitter 203 and output by the port 201 or 202.
  • the phase codec may also include an optical circulator.
  • the optical circulator may be located at the front end of the polarization maintaining beam splitter 203.
  • An incident light pulse of any polarization state can be input from the first port of the optical circulator and output from the second port of the optical circulator to the polarization-maintaining beam splitter 203.
  • the combined output from the polarization-maintaining beam splitter 203 is Input to the second port of the optical circulator and output from the third port of the optical circulator.
  • Fig. 3 shows a schematic diagram of the composition structure of a polarization orthogonal rotating reflection device that can be used in the phase codec of the present invention.
  • the polarization orthogonal rotating reflection device shown in FIG. 3 includes the following components: a polarization beam splitter 302 and a polarization maintaining fiber 303.
  • the polarization beam splitter 302 includes three ports: port A, port B, and port C. Port A, port B, and port C may be called input ports, first output ports, and second output ports, respectively.
  • the port 301 connected to the port A of the polarization beam splitter 302 serves as both an input port and an output port of the reflection device.
  • Port B and port C of the polarization beam splitter 302 are connected by a polarization maintaining fiber 303.
  • the optical pulses output by the port B and the port C of the polarization beam splitter 302 are both coupled to the slow axis transmission of the polarization maintaining fiber 303 or both are coupled to the fast axis transmission of the polarization maintaining fiber.
  • the input optical pulse is input to the polarization beam splitter 302 through the port 301, that is, the port A of the polarization beam splitter 302.
  • the input light pulse can be regarded as composed of two orthogonal polarization states, and the two orthogonal polarization states can be denoted as x polarization state and y polarization state, respectively.
  • the polarization beam splitter 302 polarizes and splits the input optical pulse into the first optical pulse of the x-polarization state and the second optical pulse of the y-polarization state to be output by the port B and the port C of the polarization beam splitter 302 respectively.
  • the first optical pulse of the x-polarization state output by the port B of the polarization beam splitter 302 is coupled to the slow axis of the polarization-maintaining fiber 303 for transmission, and is transmitted along the slow axis of the polarization-maintaining fiber 303 to the port C of the polarization beam splitter 302 ,
  • the first optical pulse at port C is coupled to the polarization beam splitter 302 from the slow axis of the polarization-maintaining fiber 303, and the polarization state of the first optical pulse coupled to the port C of the polarization beam splitter 302 is the y polarization state;
  • the first optical pulse of the y polarization state is output from the port A of the polarization beam splitter 302.
  • the x-polarization component of the input optical pulse input by the port A is converted into the y-polarization state when it is output by the port A after being reflected by the reflecting device.
  • the second optical pulse of the y polarization state output by the port C of the polarization beam splitter 302 is coupled to the slow axis of the polarization maintaining fiber 303 for transmission, and is transmitted along the slow axis of the polarization maintaining fiber 303 to the port B of the polarization beam splitter 302 ,
  • the second optical pulse at port B is coupled to the polarization beam splitter 302 from the slow axis of the polarization maintaining fiber 303, and the polarization state of the second optical pulse coupled to the port B of the polarization beam splitter 302 is the x polarization state;
  • the second optical pulse in the x polarization state is output from the port A of the polarization beam splitter 302.
  • the y polarization state component of the input optical pulse input by the port A is converted into the x polarization state when output by the port A after being reflected by the reflecting device.
  • the reflection device realizes that when the two orthogonal polarization states of the input light pulse are reflected and output by the reflection device, each orthogonal polarization state is transformed into an orthogonal polarization state.
  • the polarization maintaining fiber 303 is used to perform polarization orthogonal rotation on the two orthogonal polarization states, so that the phase between the x polarization state and the y polarization state of the input optical pulse is between the y polarization state and the x polarization state of the output optical pulse. The phase remains the same.
  • Both port B and port C of the polarization beam splitter 302 can be coupled to the fast axis of the polarization maintaining fiber 303, and the above result is not affected.
  • FIG. 4 shows a schematic diagram of the composition structure of another polarization orthogonal rotating reflection device that can be used in the phase codec of the present invention.
  • the polarization orthogonal rotating reflection device shown in FIG. 4 includes the following components: a polarization beam splitter 402, a polarization maintaining fiber 403, and a 90-degree fusion splice 404.
  • the polarization beam splitter 402 includes three ports: port A, port B, and port C. Port A, port B, and port C may be called input ports, first output ports, and second output ports, respectively.
  • the port 401 connected to the port A of the polarization beam splitter 402 serves as both the input port and the output port of the device.
  • Port B and port C of the polarization beam splitter 402 are connected by a polarization maintaining fiber 403.
  • the optical pulse output from the port B of the polarization beam splitter 402 is coupled to the slow axis of the polarization maintaining fiber 403 and the optical pulse output from the port C of the polarization beam splitter 402 is coupled to the fast axis of the polarization maintaining fiber 403, or is split by polarization.
  • the optical pulse output from the port B of the beamer 402 is coupled to the fast axis of the polarization maintaining fiber 403 and the optical pulse output from the port C of the polarization beam splitter 402 is coupled to the slow axis of the polarization maintaining fiber 403.
  • the polarization-maintaining fiber 403 includes a 90-degree fusion splice point 404, which is formed by aligning the slow axis of the polarization-maintaining fiber and the fast axis of the polarization-maintaining fiber.
  • the input optical pulse is input to the polarization beam splitter 402 through the port 401, that is, the port A of the polarization beam splitter 402.
  • the input light pulse can be regarded as composed of two orthogonal polarization states, and the two orthogonal polarization states can be denoted as x polarization state and y polarization state respectively.
  • the polarization beam splitter 402 polarizes and splits the input optical pulse into the first optical pulse of the x-polarization state and the second optical pulse of the y-polarization state to be output by the port B and the port C of the polarization beam splitter 402 respectively.
  • the first optical pulse of the x-polarization state output from port B of the polarization beam splitter 402 is coupled to the slow axis of the polarization-maintaining fiber 403 and transmitted to the 90-degree fusion splice point 404. After passing through the 90-degree fusion splice point 404, it follows the polarization-maintaining fiber
  • the fast axis of 404 is transmitted to port C of the polarization beam splitter 402.
  • the first optical pulse is coupled to the polarization beam splitter 402 by the fast axis of the polarization maintaining fiber 403; it is coupled to the port C of the polarization beam splitter 402.
  • the polarization state of the first optical pulse of the y polarization state is the y polarization state, and the first optical pulse of the y polarization state is output from the port A of the polarization beam splitter 402. That is, the x-polarization state component of the input optical pulse input by the port A is converted into the y-polarization state when it is output by the port A after being reflected by the device.
  • the second optical pulse of the y-polarization state output by the port C of the polarization beam splitter 402 is coupled to the fast axis of the polarization-maintaining fiber 403 and transmitted to the 90-degree fusion splice point 404, after passing through the 90-degree fusion splice point 404, it follows the polarization-maintaining fiber
  • the slow axis of 403 is transmitted to port B of the polarization beam splitter 402.
  • the second optical pulse is coupled to the polarization beam splitter 402 by the slow axis of the polarization maintaining fiber 403; coupled to port B of the polarization beam splitter 402
  • the polarization state of the second optical pulse of the x polarization state is the x polarization state, and the second optical pulse of the x polarization state is output from the port A of the polarization beam splitter 402. That is, the y polarization state component of the input optical pulse input by the port A is converted into the x polarization state when it is output by the port A after being reflected by the device.
  • the polarization orthogonal rotating reflection device realizes that when the two orthogonal polarization states of the input light pulse are reflected and output by the device, each orthogonal polarization state is transformed into a polarization state orthogonal to it.
  • each 90-degree fusion splice point 404 is formed by aligning the slow axis of the polarization maintaining fiber and the fast axis of the polarization maintaining fiber.
  • the above results are not affected, only the first optical pulse and the second optical pulse output by the port B and port C of the polarization beam splitter 402
  • each of the optical pulses is transmitted along the polarization-maintaining fiber 403, it is converted more times between transmission along the slow axis of the polarization-maintaining fiber and transmission along the fast axis of the polarization-maintaining fiber.
  • the polarization-maintaining fiber 403 containing an odd number of 90-degree fusion splices is used to perform polarization orthogonal rotation on the two orthogonal polarization states, so that the phase between the x polarization state and the y polarization state of the input optical pulse is equal to the y of the output optical pulse.
  • the phase between the polarization state and the x polarization state remains the same.
  • Fig. 5 shows a schematic diagram of the composition structure of another polarization orthogonal rotating reflection device that can be used in the phase codec of the present invention.
  • the polarization orthogonal rotating reflection device shown in FIG. 5 includes the following components: a polarization beam splitter 502 and a half-wave plate 503.
  • the polarization beam splitter 502 includes three ports: port A, port B, and port C. Port A, port B, and port C may be called input ports, first output ports, and second output ports, respectively.
  • the port 501 connected to the port A of the polarization beam splitter 502 serves as both the input port and the output port of the device.
  • the port B of the polarization beam splitter 502 is connected to the port D of the half-wave plate 503 through the transmission optical path, and the port C of the polarization beam splitter 502 is connected to the port E of the half-wave plate 503 through the transmission optical path.
  • the transmission optical path connecting the port B of the polarization beam splitter 502 and the port D of the half-wave plate 503 and the transmission optical path connecting the port C of the polarization beam splitter 502 and the port E of the half-wave plate 503 are polarization maintaining optical paths, for example Polarization maintaining fiber optic path.
  • the polarization direction of the polarization state of the light pulse input into the half-wave plate 503 from the port D and the port E of the half-wave plate 503 and the slow axis or the fast axis of the half-wave plate 503 have an angle of 45 degrees.
  • the input optical pulse is input to the polarization beam splitter 502 through the port 501, that is, the port A of the polarization beam splitter 502.
  • the input light pulse can be regarded as composed of two orthogonal polarization states, and the two orthogonal polarization states can be denoted as x polarization state and y polarization state respectively.
  • the polarization beam splitter 502 polarizes and splits the input optical pulse into the first optical pulse of the x-polarization state and the second optical pulse of the y-polarization state to be output by the port B and the port C of the polarization beam splitter 502 respectively.
  • the first optical pulse of the x-polarization state output from the port B of the polarization beam splitter 502 is transmitted to the half-wave plate 503, and the polarization state of the first optical pulse after the polarization orthogonal rotation by the half-wave plate 503 is transformed into the y-polarization state.
  • the first optical pulse of the y-polarization state output by the port E of the half-wave plate 503 is transmitted to the port C of the polarization beam splitter and is input to the polarization beam splitter 502 and output from the port A of the polarization beam splitter 502. In this way, the x-polarization component of the input optical pulse input by the port A is converted into the y-polarization state when it is output by the port A after being reflected by the device.
  • the second optical pulse of the y-polarization state output from the port C of the polarization beam splitter 502 is transmitted to the half-wave plate 503, and the polarization state of the second optical pulse after the polarization orthogonal rotation by the half-wave plate 503 is converted into x-polarization state.
  • the second optical pulse of the x-polarization state output by the port D of the half-wave plate 503 is transmitted to the port B of the polarization beam splitter and is input to the polarization beam splitter 502 and output from the port A of the polarization beam splitter 502.
  • the y polarization state component of the input optical pulse input by the port A is converted into the x polarization state when it is output by the port A after being reflected by the device.
  • the polarization orthogonal rotating reflection device realizes that when the two orthogonal polarization states of the input light pulse are reflected and output by the device, each orthogonal polarization state is transformed into a polarization state orthogonal to it.
  • the half-wave plate 503 is used to rotate the two orthogonal polarization states orthogonally to make the phase between the x polarization state and the y polarization state of the input light pulse and the phase between the y polarization state and the x polarization state of the output light pulse Keep it the same.
  • phase codec of the present invention can be used as a component of a DC modulation quantum key distribution phase codec device, can be used as a component of a quantum key distribution time bit-phase codec device, and can also be used as a DC modulation quantum key Key distribution time bit-a component of the phase codec device.
  • a DC modulation quantum key distribution phase codec device based on polarization orthogonal rotating reflection using the phase codec of the present invention is shown in FIG. 6, and includes the following components: pre-splitter 603, optical circulator 604 And 611, polarization-maintaining beam splitters 605 and 612, DC phase modulators 606 and 613, and polarization orthogonal rotating reflection devices 607, 608, 614, and 615.
  • the polarization-maintaining beam splitter 605, the two polarization-maintaining orthogonal rotating reflection devices 607 and 608, and the two arms between the polarization-maintaining beam splitter 605 and the two polarization orthogonal rotating reflection devices constitute the first polarization-maintaining unequal arm Michael Son interferometer, namely the first phase codec according to the present invention.
  • the two arms of the first phase codec are polarization maintaining fiber optics.
  • the DC phase modulator 606 is located on either of the two arms of the first phase codec.
  • the equal-arm Michelson interferometer is the second phase codec according to the present invention.
  • the two arms of the second phase codec are polarization maintaining fiber optic paths.
  • the DC phase modulator 613 is located on either of the two arms of the second phase codec.
  • the coding and decoding device in FIG. 6 is used for decoding as an example to describe it.
  • One of the two ports 601 and 602 on the side of the front beam splitter 603 (the left side in FIG. 6) is used as the input port of the device.
  • the first port A and the second port B of the optical circulator 604 are respectively connected to an output port of the pre-beam splitter 603 and an input port of the polarization-maintaining beam splitter 605.
  • the optical pulse input to the first phase codec is decoded and then output by one output port 609 of the polarization-maintaining beam splitter 605, or through another output port of the polarization-maintaining beam splitter 605 (that is, all of the polarization-maintaining beam splitter 605).
  • the one input port is transmitted to the port B of the optical circulator 604 and output from the third port C of the optical circulator 604.
  • the first port A and the second port B of the optical circulator 611 are respectively connected to the other output port of the pre-beam splitter 603 and one input port of the polarization-maintaining beam splitter 612.
  • the optical pulse input to the second phase codec is decoded and then output by one output port 616 of the polarization-maintaining beam splitter 612, or through another output port of the polarization-maintaining beam splitter 612 (that is, all of the polarization-maintaining beam splitter 612).
  • the one input port) is transmitted to the port B of the optical circulator 611 and output from the third port C of the optical circulator 611.
  • the optical pulse enters the beam splitter 603 through the port 601 or 602 of the beam splitter 603 and is split by the beam splitter 603 into a first optical pulse and a second optical pulse.
  • the first optical pulse is input through port A of the optical circulator 604 and output to the polarization-maintaining beam splitter 605 through port B of the optical circulator 604.
  • the polarization maintaining beam splitter 605 splits the input first optical pulse into two first sub optical pulses.
  • One first sub-light pulse is phase-modulated by the DC phase modulator 606 and then reflected by the polarization orthogonal rotating reflection device 607, and the other first sub-light pulse is directly transmitted to the polarization orthogonal rotating reflection device 608 through the polarization maintaining fiber
  • the polarization orthogonal rotating reflector 608 reflects back.
  • the two first sub-light pulses reflected back with relative delay are combined by the polarization-maintaining beam splitter 605 and output by port 609, or output to port B of optical circulator 604 and transmitted to port C and output by port 610 .
  • the second optical pulse is input through the port A of the optical circulator 611 and output to the polarization maintaining beam splitter 612 through the port B of the optical circulator 611.
  • the polarization maintaining beam splitter 612 splits the input second optical pulse into two second sub optical pulses.
  • One second sub-light pulse is phase-modulated by the DC phase modulator 613 and then reflected back by the polarization orthogonal rotating reflector 614, and the other second sub-light pulse is directly transmitted to the polarization orthogonal rotating reflector 615 via the polarization maintaining fiber.
  • the polarization orthogonal rotating reflector 615 reflects back.
  • the two second sub-light pulses reflected back with relatively delay are combined by the polarization-maintaining beam splitter 612 and output by the port 616, or output to the port B of the optical circulator 611 and transmitted to the port C and output by the port 617 .
  • the DC phase modulators 606 and 613 cause the DC phase modulation by one of the first phase codec and the second phase codec to be 90 degrees different from the DC phase modulation by the other.
  • the coding and decoding device of FIG. 6 is used for coding as an example to describe it.
  • One port 609 of the polarization maintaining beam splitter 605, the third port C of the optical circulator 604, one port 616 of the polarization maintaining beam splitter 612, and the third port C of the optical circulator 611 are used as input ports of the device.
  • the first port A and the second port B of the optical circulator 604 are respectively connected to one port of the pre-splitter 603 and the other port of the polarization-maintaining beam splitter 605.
  • the optical pulse input from the third port C of the optical circulator 604 is input to the first phase codec via the second port B of the optical circulator 604.
  • the optical pulses input from the one port 609 of the polarization-maintaining beam splitter 605 and the third port C of the optical circulator 604 are encoded by the first phase codec and output by the polarization-maintaining beam splitter 605 to the optical circulator 604.
  • the second port B is transmitted from the first port A of the optical circulator 604 to the pre-splitter 603.
  • the first port A and the second port B of the optical circulator 611 are respectively connected to the other port of the pre-beam splitter 603 and the other port of the polarization-maintaining beam splitter 612.
  • the optical pulse input from the third port C of the optical circulator 611 is input to the second phase codec via the second port B of the optical circulator 611.
  • the optical pulses input from the one port 616 of the polarization-maintaining beam splitter 612 and the third port C of the optical circulator 612 are encoded by the second phase codec and output by the polarization-maintaining beam splitter 612 to the optical circulator 611.
  • the second port B is transmitted from the first port A of the optical circulator 611 to the pre-splitter 603.
  • One of the two ports 601 and 602 on the side of the pre-splitter 603 (the left side in FIG. 6) is used as the output port of the device.
  • Optical pulses input from the one port 609 of the polarization-maintaining beam splitter 605, the third port C of the optical circulator 604, the one port 616 of the polarization-maintaining beam splitter 612, and the third port C of the optical circulator 611 After encoding, four kinds of phase encoding are realized respectively, and the encoded optical pulses are combined by the beam splitter 603 and output by the port 601 or 602.
  • a quantum key distribution time bit-phase codec device based on polarization orthogonal rotating reflection using the phase codec of the present invention is shown in Fig. 7, and includes the following components: beam splitters 703 and 704, polarization maintaining splitters A beamer 707, a phase modulator 708, and polarization orthogonal rotating reflection devices 709 and 710.
  • the polarization-maintaining beam splitter 707, the two polarization-maintaining orthogonal rotating reflectors 709 and 710, and the two arms between the polarization-maintaining beam splitter 707 and the two polarization orthogonal rotating reflectors form a polarization-maintaining unequal-arm Michelson interference
  • the instrument is the phase codec according to the present invention.
  • the two arms are polarization maintaining fiber optic paths.
  • the phase modulator 708 is located on either of the two arms of the phase codec.
  • the codec device of FIG. 7 is used for decoding as an example to describe it.
  • the beam splitter 703 serves as a front beam splitter, and one of the two ports 701 and 702 on one side thereof is used as the input port of the device.
  • the beam splitter 704 splits one optical pulse from the beam splitter 703 and outputs it through the port 705 or 706.
  • the optical pulse input to the PM unequal-arm Michelson interferometer is decoded and output from the port 711.
  • the input optical pulse enters the beam splitter 703 through the port 701 or 702 of the beam splitter 703, and is divided into two optical pulses for transmission by the beam splitter 703.
  • One optical pulse from the beam splitter 703 is input to the beam splitter 704, and is split by the beam splitter 704 and then output via the port 705 or 706 for time bit decoding.
  • Another optical pulse from the beam splitter 703 is input to the polarization-maintaining beam splitter 707, and is split into two sub-light pulses by the polarization-maintaining beam splitter 707.
  • One sub-light pulse is randomly modulated by the phase modulator 708 to 0 degrees or 180 degrees, and then reflected by the polarization orthogonal rotating reflector 709, and the other sub-light pulse is directly transmitted to the polarization orthogonal rotating reflector 710 through the polarization maintaining fiber
  • the polarization orthogonal rotating reflector 710 reflects back.
  • the two sub-light pulses that have been reflected back with relative delay are combined by the polarization-maintaining beam splitter 707 and then output by the port 711.
  • the beam splitter 704 is optional. It is possible for the pre-splitter 703 to directly output the above-mentioned optical pulse for time bit decoding.
  • the coding and decoding apparatus of FIG. 7 is used for coding as an example to describe it.
  • the ports 705 and 706 of the beam splitter 704 and the port 711 of the polarization maintaining beam splitter 707 serve as input ports of the device.
  • the optical pulses input from the ports 705 and 706 are combined by the beam splitter 704 and output to the pre-beam splitter 703 to realize time bit encoding.
  • the optical pulse input from the port 711 is encoded by the polarization-maintaining unequal-arm Michelson interferometer, and then output by the polarization-maintaining beam splitter 707 to the pre-beam splitter 703, during which two phase encodings are realized by the modulation phase modulator 708.
  • One of the ports 701 and 702 of the pre-splitter 703 serves as the output port of the device.
  • the beam splitter 703 combines the optical pulse output from the beam splitter 704 and the optical pulse output from the polarization-maintaining beam splitter 707, and then outputs the optical pulse through the port 701 or 702.
  • the beam splitter 704 is optional, and it is possible to directly use the port of the beam splitter 703 connected to the beam splitter 704 as an input port for time bit encoding.
  • a DC modulation quantum key distribution time bit-phase codec device based on polarization orthogonal rotating reflection using the phase codec of the present invention is shown in Fig. 8, and includes the following components: beam splitters 803 and 804, optical ring Shaper 807, polarization-maintaining beam splitter 808, DC phase modulator 809, and polarization orthogonal rotating reflection devices 810 and 811.
  • the polarization-maintaining beam splitter 808, the two polarization-maintaining orthogonal rotating reflectors 810 and 811, and the two arms between the polarization-maintaining beam splitter 808 and the two polarization orthogonal rotating reflectors form a polarization-maintaining unequal-arm Michelson interference
  • the instrument is the phase codec according to the present invention.
  • the two arms are polarization maintaining fiber optic paths.
  • the DC phase modulator 809 is located on either of the two arms of the phase codec.
  • the coding and decoding device of FIG. 8 is used for decoding as an example to describe it.
  • the beam splitter 803 serves as a front beam splitter, and one of the two ports 801 and 802 on one side thereof serves as the input port of the device.
  • the beam splitter 804 splits one optical pulse from the beam splitter 803 and outputs it through the port 805 or 806.
  • the optical pulse input from the first port A of the optical circulator 807 is output from the second port B of the optical circulator 807, and the optical pulse input from the second port B of the optical circulator 807 is output from the third port C of the optical circulator 807. Output.
  • the optical pulse input to the unequal-arm Michelson interferometer is decoded and output by port 812, or is transmitted to the second port B of the optical circulator 807 through another output port of the polarization-maintaining beam splitter 808 and then from the optical circulator
  • the third port C of 807 is output from port 813 after output.
  • the input optical pulse enters the beam splitter 803 through the port 801 or 802 of the beam splitter 803, and is split into two optical pulses for transmission by the beam splitter 803.
  • One optical pulse from the beam splitter 803 is input to the beam splitter 804, and is split by the beam splitter 804 and then output by the port 805 or 806 for time bit decoding.
  • Another optical pulse from the beam splitter 803 is input through the first port A of the optical circulator 807 and output from the second port B of the optical circulator 807 to the polarization-maintaining beam splitter 808.
  • the polarization maintaining beam splitter 808 splits the other optical pulse into two sub optical pulses.
  • One sub-light pulse is modulated by the DC phase modulator 809 with a phase of 0 degrees or 180 degrees and then reflected by the polarization orthogonal rotating reflector 810, and the other sub-light pulse is directly transmitted to the polarization orthogonal rotating reflector 811 through the polarization maintaining fiber. It is reflected back by the polarization orthogonal rotating reflector 811.
  • the reflected two relatively delayed sub-light pulses are combined by the polarization-maintaining beam splitter 808 and then output by the port 812, or are transmitted to the second port B of the optical circulator 807 and are transmitted by the third port of the optical circulator 807 After C is output, it is output by port 813.
  • the beam splitter 804 is optional. It is possible for the pre-splitter 803 to directly output the above-mentioned optical pulse for time bit decoding.
  • the coding and decoding device of FIG. 8 is used for coding as an example to describe it.
  • the ports 805 and 806 of the beam splitter 804, the port 812 of the polarization maintaining beam splitter 808, and the third port C of the optical circulator 807 are used as input ports of the device.
  • the optical pulse input from the third port C of the optical circulator 807 is output from the second port B of the optical circulator 807, and the optical pulse input from the second port B of the optical circulator 807 is output from the first port A of the optical circulator 807.
  • the optical pulses input from the ports 805 and 806 are combined by the beam splitter 804 and output to the pre-beam splitter 803 to realize time bit encoding.
  • the optical pulse input from the port 812 and the optical pulse input from the third port C of the optical circulator 807 and output from the second port B of the optical circulator 807 to the polarization-maintaining beam splitter 808 are passed through the polarization-maintaining unequal arm Michelson
  • the polarization-maintaining beam splitter 808 outputs to the second port B of the optical circulator 807 and transmits to the pre-beam splitter 803 via the first port A of the optical circulator 807.
  • the optical pulses input from the port 812 of the polarization-maintaining beam splitter 808 and the third port C of the optical circulator 807 are encoded to realize two kinds of phase encoding respectively.
  • One of the ports 801 and 802 of the beam splitter 803 serves as the output port of the device.
  • the beam splitter 803 combines the optical pulses output from the beam splitter 804 and the optical pulses output from the first port A of the optical circulator 807 and then outputs them through the port 801 or 802.
  • the beam splitter 804 is optional, and it is possible to directly use the port of the beam splitter 803 connected to the beam splitter 804 as an input port for time bit encoding.
  • phase modulator is shown in FIGS. 1-2 and 6-8, it is possible that the phase codec and codec device of the present invention do not include the phase modulator.
  • beam splitter and “beam combiner” can be used interchangeably, and beam splitters can also be referred to and used as beam combiners, and vice versa.
  • polarization-maintaining fiber optical path refers to the optical path that uses polarization-maintaining fiber to transmit light pulses or the optical path formed by polarization-maintaining fiber connection.
  • the receiving end of the quantum key distribution system can be configured with the phase codec or corresponding codec device based on the polarization orthogonal rotating reflection of the present invention as described above for decoding.
  • the phase codec or corresponding codec device based on the polarization orthogonal rotation reflection of the present invention as described above can also be configured at the transmitting end of the quantum key distribution system for coding.
  • the phase codec or corresponding codec device of the present invention when it is used at the receiving end or the transmitting end of a quantum key distribution system, it may include the exemplarily described above in conjunction with FIGS. 1-2 and 6-8. Phase modulator or not including phase modulator.
  • the phase codec or codec used for at least one of the receiving end and the transmitting end may include a phase modulator.

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Abstract

本发明提出一种量子密钥分发相位编解码器及相应的编解码装置和系统。该相位编解码器包括：分束器、分别经两个臂与分束器光耦合的两个偏振正交旋转反射装置、设置于两个臂中之一上的相位调制器。两个反射装置中之一或每个反射装置包括具有输入端口和两个输出端口的偏振分束器，并经偏振分束器的输入端口耦合至相应的臂，每个偏振分束器的两个输出端口经扭转90度的保偏光纤彼此光耦合使得所述两个输出端口输出的光脉冲均耦合至保偏光纤的慢轴传输或均耦合至保偏光纤的快轴传输。本发明使得能够对任意偏振态的输入光脉冲稳定地进行编解码干涉，解决了相位编码及时间比特-相位编码量子密钥分发应用中偏振诱导衰落造成系统无法稳定工作的问题。

Description

量子密钥分发相位编解码器、相应的编解码装置及系统 技术领域
本发明涉及光传输保密通信技术领域，尤其涉及一种基于偏振正交旋转反射的量子密钥分发相位编解码器、包括该相位编解码器的相应编解码装置和量子密钥分发系统。
背景技术
量子保密通信技术是量子物理与信息科学相结合的前沿热点领域。基于量子密钥分发技术和一次一密密码原理，量子保密通信可在公开信道实现信息的安全传输。量子密钥分发基于量子力学海森堡不确定关系、量子不可克隆定理等物理原理，能够实现在用户之间安全地共享密钥，并可以检测到潜在的窃听行为，可应用于国防、政务、金融、电力等高安全信息传输需求的领域。
地面量子密钥分发主要基于光纤信道传输，因为相位编码采用前后光脉冲的相位差来编码信息，在长距离光纤信道传输过程中能够稳定保持，所以基于不等臂干涉仪的相位编码和时间比特-相位编码是量子密钥分发应用的主要编码方案。然而，光纤制作存在截面非圆对称、纤芯折射率沿径向不均匀分布等非理想情况，并且光纤在实际环境中受温度、应变、弯曲等影响，会产生随机双折射效应。因此，光脉冲经长距离光纤传输以及经不等臂干涉仪两臂光纤传输后，通过不等臂干涉仪进行相位解码干涉时存在偏振诱导衰落的问题，导致解码干涉不稳定，造成误码率升高。若使用纠偏设备，会增加系统复杂度和成本，且对于架空光缆、路桥光缆等强干扰情况难以实现稳定应用。
对于量子密钥分发相位编码以及时间比特-相位编码方案，如何稳定高效地进行干涉解码是基于现有光缆基础设施进行量子保密通信应用的热点和难题。
发明内容
本发明的主要目的在于提出一种基于偏振正交旋转反射的量子密钥分发相位编解码器、包括该相位编解码器的相应编解码装置和量子密钥分发系统，以解决相位编码以及时间比特-相位编码量子密钥分发应用中偏振诱导衰落引起的相位解码干涉不稳定的难题。
本发明提供至少以下技术方案：
1.一种量子密钥分发相位编解码器，包括：分束器、分别经两个臂与所述分束器光耦合的两个反射装置，每个所述反射装置为偏振正交旋转反射装置，所述两个反射装置中之一或每个所述反射装置包括具有输入端口和两个输出端口的偏振分束器，并经所述偏振分束器的输入端口耦合至所述两个臂中的相应臂，其中每个偏振分束器的两个输出端口经传输光路彼此光耦合，对于至少一个包括偏振分束器的反射装置：其传输光路由扭转90度的保偏光纤形成，使得由其偏振分束器的两个输出端口输出的光脉冲均耦合至所述保偏光纤的慢轴进行传输或均耦合至所述保偏光纤的快轴进行传输。
2.根据方案1所述的相位编解码器，其中，所述两个反射装置为相同构造的偏振正交旋转反射装置，或为不同构造的偏振正交旋转反射装置。
3.根据方案1所述的相位编解码器，其中，所述扭转90度的保偏光纤包括扭转90度或扭转(90+n*180)度的保偏光纤，其中n为整数。
4.根据方案1所述的相位编解码器，其中，所述分束器是保偏分束器。
5.根据方案1所述的相位编解码器，其中，所述两个臂各为偏振保持光路，所述两个臂上的光器件为偏振保持光器件和/或非双折射光器件。
6.根据方案1-5中任一所述的相位编解码器，其中，所述相位编解码器还包括相位调制器，其中所述相位调制器设置于所述分束器前端或设置于所述两个臂中至少之一上。
7.一种直流调制量子密钥分发相位编解码装置，包括前置分束器和两个根据方案1-6中任一所述的相位编解码器，两个所述相位编解码器分别经两条子光路光耦合至所述前置分束器，其中每个所述相位编解码器的分束器的未耦合至该相位编解码器的所述两个臂的端口之一光耦合至所述两条子光路中的相应子光路，每条所述子光路上设置有一个光环形器。
8.一种量子密钥分发时间比特-相位编解码装置，包括前置分束器和一个根据方案1-6中任一所述的相位编解码器，所述相位编解码器经一条子光路光耦合至所述前置分束器，其中所述相位编解码器的分束器的未耦合至所述两个臂的端口之一光耦合至所述一条子光路。
9.一种直流调制量子密钥分发时间比特-相位编解码装置，包括前置分束器和一个根据方案1-6中任一所述的相位编解码器，所述相位编解码器经一条子光路光耦合至所述前置分束器，其中所述相位编解码器的分束器的未耦合至所述两个臂的端口之一光耦合至所述一条子光路，其中所述一条子光路上设置有一个光环形器。
10.根据方案8或9所述的编解码装置，还包括经另一条子光路耦合至所述前置分束器的分束器。
11.一种量子密钥分发系统，包括：
根据方案1～6中任一所述的相位编解码器或根据方案7～10中任一所述的编解码装置，其设置在所述量子密钥分发系统的接收端，用于解码；和/或
根据方案1～6中任一所述的相位编解码器或根据方案7～10中任一所述的编解码装置，其设置在所述量子密钥分发系统的发射端，用于编码。
本发明通过创造性的构造，使得能够对任意偏振态的输入光脉冲稳定地进行编解码干涉，由此实现了意想不到的有益效果。利用本发明的方案，对于任意偏振态的输入光脉冲可以实现在相位解码干涉仪处的稳定干涉输出，解决了相位编码以及时间比特-相位编码量子密钥分发应用中偏振诱导衰落造成系统无法稳定工作的问题。本发明提供了一种易于实现和应用的抗偏振诱导衰落的相位编码以及时间比特-相位编码量子密钥分发解码方案。
附图说明
图1为本发明一优选实施例的基于偏振正交旋转反射的量子密钥分发相位编解码器的组成结构示意图；
图2为本发明另一优选实施例的基于偏振正交旋转反射的量子密钥分发相位编解码器的组成结构示意图；
图3为可用于本发明的相位编解码器的一种偏振正交旋转反射装置的组成结构 示意图；
图4为可用于本发明的相位编解码器的另一种偏振正交旋转反射装置的组成结构示意图；
图5为可用于本发明的相位编解码器的另一种偏振正交旋转反射装置的组成结构示意图；
图6为本发明一优选实施例的基于偏振正交旋转反射的直流调制量子密钥分发相位编解码装置的组成结构示意图；
图7为本发明一优选实施例的基于偏振正交旋转反射的量子密钥分发时间比特-相位编解码装置的组成结构示意图；
图8为本发明一优选实施例的基于偏振正交旋转反射的直流调制量子密钥分发时间比特-相位编解码装置的组成结构示意图。
具体实施方式
下面结合附图来具体描述本发明的优选实施例，其中，附图构成本申请一部分，并与本发明的实施例一起用于阐释本发明的原理。为了清楚和简化目的，当其可能使本发明的主题模糊不清时，对本文所描述的器件的已知功能和结构的详细具体说明将省略。
本发明一优选实施例的基于偏振正交旋转反射的量子密钥分发相位编解码器如图1所示，包括以下组成部分：分束器101、相位调制器102、两个反射装置103和104。
两个反射装置103和104分别经两个臂(图1中的上臂和下臂)与分束器101光耦合。相位调制器102插入这两个臂中之一(在图1中，为上臂)上。
根据本发明，两个反射装置103和104均为偏振正交旋转反射装置。
这里，偏振正交旋转反射装置是指一种能够对所反射的光脉冲的两个正交偏振态作偏振正交旋转反射、即在反射入射的光脉冲时将该光脉冲的每个正交偏振态变换成与其正交的偏振态的反射装置。举例而言，假设这两个正交偏振态分别为x偏振态和y偏振态，沿光路传输到一个偏振正交旋转反射装置的x偏振态在反射装置处经偏振正交旋转反射后变换成与其正交的偏振态即y偏振态，沿光路传输到该 反射装置的y偏振态在反射装置处经偏振正交旋转反射后变换成与其正交的偏振态即x偏振态。
分束器101用于将入射的任意偏振态的一路输入光脉冲分束为两路光脉冲以分别沿两个臂传输。
两个臂用于分别传输所述两路光脉冲。
相位调制器102用于对其所在的臂传输的光脉冲(即，两路光脉冲之一)按照量子密钥分发协议进行相位调制。相位调制器102进行的相位调制由量子密钥分发协议确定，取决于具体的应用。例如，在一种可能的应用中，相位调制器102可随机调制0度相位或90度相位。
相位调制器102可以为偏振无关相位调制器或者双折射相位调制器。双折射相位调制器适于对通过其的两个正交偏振态施加不同的可调的相位调制。例如，双折射相位调制器可以为铌酸锂相位调制器，通过控制施加至铌酸锂晶体的电压，可以对通过该铌酸锂相位调制器的两个正交偏振态各自所经受的相位调制进行控制和调整。
反射装置103和104分别用于将来自分束器101的经所述两个臂传输来的所述两路光脉冲反射回分束器101以由分束器101合束输出。
由于两个反射装置103和104均为偏振正交旋转反射装置，对于所述两路光脉冲中的每一路光脉冲：该路光脉冲经所述两个反射装置中的相应反射装置反射时该路光脉冲的两个正交偏振态作偏振正交旋转反射，使得经由所述相应反射装置的反射后，该路光脉冲的每个正交偏振态变换成与其正交的偏振态。如此，对于图1的相位编解码器，利用偏振正交旋转反射装置处的偏振正交旋转反射，输入光脉冲的x偏振态在分束器分束至分束器合束的过程中经所述两个臂传输的相位差恰好等于该光脉冲的y偏振态在分束器分束至分束器合束的过程中经所述两个臂传输的相位差。
尽管图1中，仅一个相位调制器102被示出为设置于两个臂中之一上，但在两个臂上各设置一个相位调制器也是可能的。在如此设置有两个相位调制器的情况下，两个相位调制器所调制的相位之差由量子密钥分发协议确定，取决于具体的应用。另外，代替在两个臂中之一或两者上设置相位调制器，可以在分束器101之前 设置相位调制器，用于对分束前的输入光脉冲按照量子密钥分发协议进行相位调制，或者对合束后的输出光脉冲按照量子密钥分发协议进行相位调制。
本发明提出了三种创造性的偏振正交旋转反射装置构造，即下文所述的构造1、构造2和构造3。
根据构造1，偏振正交旋转反射装置包括偏振分束器，该偏振分束器具有输入端口和两个输出端口，该偏振分束器的两个输出端口经一条传输光路彼此光耦合，所述传输光路由保偏光纤形成，该传输光路上设置有半波片，输入该半波片的光脉冲的极化方向与该半波片的快轴或慢轴的夹角为45度。具有构造1的偏振正交旋转反射装置在用于本发明的相位编解码器时，可通过将其偏振分束器的输入端口耦合至相位编解码器的一个臂来将该反射装置耦合至所述臂。
根据构造2，偏振正交旋转反射装置包括偏振分束器，该偏振分束器具有输入端口和两个输出端口，该偏振分束器的两个输出端口经一条传输光路彼此光耦合，所述传输光路由保偏光纤形成，所述保偏光纤的慢轴和快轴分别保持输入该保偏光纤的光脉冲的两个正交偏振态稳定传输——即偏振态不变，且该偏振分束器的两个输出端口和该保偏光纤构造成使得，由该偏振分束器的两个输出端口输出的光脉冲均耦合至该保偏光纤的慢轴进行传输或均耦合至该保偏光纤的快轴进行传输。这里，由该偏振分束器的两个输出端口输出的光脉冲均耦合至该保偏光纤的慢轴进行传输或均耦合至该保偏光纤的快轴进行传输可通过保偏光纤扭转90度或者扭转(90+n*180)度实现，其中n为整数。无论保偏光纤扭转或者不扭转，从保偏光纤的慢轴输入的光脉冲始终沿着慢轴传输(沿着慢轴稳定传输)，从保偏光纤的快轴输入的光脉冲始终沿着快轴传输(沿着快轴稳定传输)。具有构造2的偏振正交旋转反射装置在用于本发明的相位编解码器时，可通过将其偏振分束器的输入端口耦合至相位编解码器的一个臂来将该反射装置耦合至所述臂。
根据构造3，偏振正交旋转反射装置包括偏振分束器，该偏振分束器具有输入端口和两个输出端口，该偏振分束器的两个输出端口经一条传输光路彼此光耦合，所述传输光路由包含奇数个90度熔接点的保偏光纤形成，每个90度熔接点由保偏光纤慢轴与保偏光纤快轴对准熔接而成。具有构造3的偏振正交旋转反射装置在用 于本发明的相位编解码器时，可通过将其偏振分束器的输入端口耦合至相位编解码器的一个臂来将该反射装置耦合至所述臂。
回到图1的相位编解码器，反射装置103和104中至少之一可以为采用上述构造1、构造2和构造3中之一的偏振正交旋转反射装置。在反射装置103和104中的一个反射装置为采用上述构造1、构造2和构造3中之一的偏振正交旋转反射装置时，另一个反射装置可以为采用上述构造1、构造2和构造3中之一的偏振正交旋转反射装置，也可以为其他构造的偏振正交旋转反射装置。所述其他构造的偏振正交旋转反射装置可以是例如四分之一波片反射镜。“四分之一波片反射镜”包括反射镜和四分之一波片，所述反射镜在所述四分之一波片后端与所述四分之一波片一体地形成，其中输入该四分之一波片的光脉冲的两个正交偏振态之一的极化方向与该四分之一波片的快轴或慢轴的夹角为45度。四分之一波片反射镜可以通过在四分之一波片晶体表面镀反射镜实现，亦可通过在快慢轴传输相位相差90度的保偏光纤端面镀反射镜实现。
对于图1的相位编解码器，可以通过调节两个臂的长度和/或调节两个反射装置103和104中采用选自构造1、构造2和构造3的构造的一个或两个反射装置中的传输光路，实现上述两路光脉冲的相对延时。
在反射装置采用选自构造1、构造2和构造3的构造的情况下，可以将相位编解码器的两个臂配置为偏振保持光路例如保偏光纤光路，且将所述两个臂上的光器件配置为偏振保持光器件和/或非双折射光器件。如此，对于分束得到的两路光脉冲中的每一路光脉冲：可以保持该路光脉冲的两个正交偏振态在分束器分束至相应反射装置反射期间保持不变，且在所述相应反射装置反射至所述分束器合束期间保持不变。通常，偏振保持光路可以是自由空间光路或保偏光纤光路。本文中，“非双折射光器件”是指对于不同的偏振态(例如，两个正交偏振态)具有相同折射率的光器件。另外，偏振保持光器件也可称为保偏光器件。
此外，相位编解码器的分束器101可以为保偏分束器。
本发明另一优选实施例的一种相位编解码器如图2所示，包括以下组成部分：保偏分束器203、相位调制器204，以及偏振正交旋转反射装置205和206。
保偏分束器203一侧的两个端口201和202之一作为相位编解码器的输入端口。保偏分束器203与偏振正交旋转反射装置205和206构成不等臂迈克尔逊干涉仪，其间的两个臂为保偏光纤光路。相位调制器204插入不等臂迈克尔逊干涉仪的两臂中的任一臂。保偏分束器203的端口201或202可作为相位编解码器的输出端口。
工作时，光脉冲经保偏分束器203的端口201或202进入保偏分束器203并由保偏分束器203分成两路光脉冲。来自保偏分束器203的一路光脉冲经相位调制器204进行相位调制后由偏振正交旋转反射装置205反射回来，另一路光脉冲直接经保偏光纤传输至偏振正交旋转反射装置206并由偏振正交旋转反射装置206反射回来。经相对延时的反射回来的两路光脉冲经保偏分束器203合束后由端口201或202输出。
在保偏分束器203的输入端口和输出端口之一为同一端口的情况下，相位编解码器还可以包括光环形器。该光环形器可以位于保偏分束器203前端。入射的任意偏振态的一路输入光脉冲可从光环形器的第一端口输入并从光环形器的第二端口输出至保偏分束器203，来自保偏分束器203的合束输出被输入至光环形器的第二端口并从光环形器的第三端口输出。
图3示出了可用于本发明的相位编解码器的一种偏振正交旋转反射装置的组成结构示意图。
图3所示的偏振正交旋转反射装置包括以下组成部分：偏振分束器302、保偏光纤303。
偏振分束器302包括端口A、端口B、端口C三个端口。端口A、端口B、端口C可分别称为输入端口、第一输出端口、第二输出端口。与偏振分束器302的端口A相连的端口301既作为反射装置的输入端口也作为反射装置的输出端口。偏振分束器302的端口B和端口C通过保偏光纤303连接。由偏振分束器302的端口B和端口C输出的光脉冲均耦合至保偏光纤303的慢轴传输或均耦合至该保偏光纤的快轴传输。
工作时，输入光脉冲经端口301也即偏振分束器302的端口A输入偏振分束器302。输入光脉冲可以看作由两个正交偏振态构成，所述两个正交偏振态可分别 记为x偏振态和y偏振态。偏振分束器302将输入光脉冲偏振分束为x偏振态的第一路光脉冲和y偏振态的第二路光脉冲，以分别由偏振分束器302的端口B和端口C输出。由偏振分束器302的端口B输出的x偏振态的第一路光脉冲耦合至保偏光纤303的慢轴传输，并沿保偏光纤303的慢轴传输至偏振分束器302的端口C，在端口C处第一路光脉冲由保偏光纤303的慢轴耦合至偏振分束器302，耦合至偏振分束器302的端口C的第一路光脉冲的偏振态为y偏振态；y偏振态的第一路光脉冲由偏振分束器302的端口A输出。也即实现由端口A输入的输入光脉冲的x偏振态分量在由反射装置反射后由端口A输出时变换为y偏振态。由偏振分束器302的端口C输出的y偏振态的第二路光脉冲耦合至保偏光纤303的慢轴传输，并沿保偏光纤303的慢轴传输至偏振分束器302的端口B，在端口B处第二路光脉冲由保偏光纤303的慢轴耦合至偏振分束器302，耦合至偏振分束器302的端口B的第二路光脉冲的偏振态为x偏振态；x偏振态的第二路光脉冲由偏振分束器302的端口A输出。也即实现由端口A输入的输入光脉冲的y偏振态分量在由反射装置反射后由端口A输出时变换为x偏振态。反射装置实现输入光脉冲的两个正交偏振态由反射装置反射输出时每个正交偏振态均变换为与其正交的偏振态。利用上述的保偏光纤303对两个正交偏振态作偏振正交旋转，使得输入光脉冲的x偏振态和y偏振态之间的相位与输出光脉冲的y偏振态和x偏振态之间的相位保持相同。
偏振分束器302的端口B和端口C可均耦合至保偏光纤303的快轴，上述结果不受影响。
图4示出了可用于本发明的相位编解码器的另一种偏振正交旋转反射装置的组成结构示意图。
图4所示的偏振正交旋转反射装置包括以下组成部分：偏振分束器402、保偏光纤403，以及90度熔接点404。
偏振分束器402包括端口A、端口B、端口C三个端口。端口A、端口B、端口C可分别称为输入端口、第一输出端口、第二输出端口。与偏振分束器402的端口A相连的端口401既作为装置的输入端口也作为装置的输出端口。偏振分束器402的端口B和端口C通过保偏光纤403连接。由偏振分束器402的端口B输出的光脉冲耦合至保偏光纤403的慢轴且由偏振分束器402的端口C输出的光 脉冲耦合至保偏光纤403的快轴，或者由偏振分束器402的端口B输出的光脉冲耦合至保偏光纤403的快轴且由偏振分束器402的端口C输出的光脉冲耦合至保偏光纤403的慢轴。保偏光纤403包含90度熔接点404，90度熔接点404由保偏光纤慢轴与保偏光纤快轴对准熔接而成。
工作时，输入光脉冲经端口401也即偏振分束器402的端口A输入偏振分束器402。输入光脉冲可以看作由两个正交偏振态构成，所述两个正交偏振态可分别记为x偏振态和y偏振态。偏振分束器402将输入光脉冲偏振分束为x偏振态的第一路光脉冲和y偏振态的第二路光脉冲，以分别由偏振分束器402的端口B和端口C输出。由偏振分束器402的端口B输出的x偏振态的第一路光脉冲耦合至保偏光纤403的慢轴并被传输至90度熔接点404，经过90度熔接点404后沿保偏光纤404的快轴传输至偏振分束器402的端口C，在端口C处第一路光脉冲由保偏光纤403的快轴耦合至偏振分束器402；耦合至偏振分束器402的端口C的第一路光脉冲的偏振态为y偏振态，y偏振态的第一路光脉冲由偏振分束器402的端口A输出。也即实现由端口A输入的输入光脉冲的x偏振态分量在由装置反射后由端口A输出时变换为y偏振态。由偏振分束器402的端口C输出的y偏振态的第二路光脉冲耦合至保偏光纤403的快轴并被传输至90度熔接点404，经过90度熔接点404后沿保偏光纤403的慢轴传输至偏振分束器402的端口B，在端口B处第二路光脉冲由保偏光纤403的慢轴耦合至偏振分束器402；耦合至偏振分束器402的端口B的第二路光脉冲的偏振态为x偏振态，x偏振态的第二路光脉冲由偏振分束器402的端口A输出。也即实现由端口A输入的输入光脉冲的y偏振态分量在由装置反射后由端口A输出时变换为x偏振态。该偏振正交旋转反射装置实现输入光脉冲的两个正交偏振态由该装置反射输出时每个正交偏振态均变换为与其正交的偏振态。
尽管图4中示出了仅一个90度熔接点404，但这只是示例性的，保偏光纤403可以包含任意的奇数个90度熔接点。每个90度熔接点由保偏光纤慢轴与保偏光纤快轴对准熔接而成。在保偏光纤403包含多于1个的奇数个90度熔接点的情况下，上述结果不受影响，只是由偏振分束器402的端口B和端口C输出的第一 路光脉冲和第二路光脉冲各自沿保偏光纤403传输时更多次在沿保偏光纤慢轴传输与沿保偏光纤快轴传输之间变换，变换的次数等于90度熔接点的数目。
采用上述的包含奇数个90度熔接点的保偏光纤403对两个正交偏振态作偏振正交旋转，使得输入光脉冲的x偏振态和y偏振态之间的相位与输出光脉冲的y偏振态和x偏振态之间的相位保持相同。
偏振分束器402的端口B耦合至保偏光纤403的快轴且偏振分束器402的端口C耦合至保偏光纤403的慢轴时，上述结果不受影响。
图5示出了可用于本发明的相位编解码器的另一种偏振正交旋转反射装置的组成结构示意图。
图5所示的偏振正交旋转反射装置包括以下组成部分：偏振分束器502、半波片503。
偏振分束器502包括端口A、端口B、端口C三个端口。端口A、端口B、端口C可分别称为输入端口、第一输出端口、第二输出端口。与偏振分束器502的端口A相连的端口501既作为装置的输入端口也作为装置的输出端口。偏振分束器502的端口B通过传输光路与半波片503的端口D连接，偏振分束器502的端口C通过传输光路与半波片503的端口E连接。将偏振分束器502的端口B与半波片503的端口D连接的传输光路以及将偏振分束器502的端口C与半波片503的端口E连接的传输光路均为偏振保持光路，例如保偏光纤光路。由半波片503的端口D和端口E输入半波片503的光脉冲的偏振态的极化方向与半波片503的慢轴或快轴的夹角为45度。
工作时，输入光脉冲经端口501也即偏振分束器502的端口A输入偏振分束器502。输入光脉冲可以看作由两个正交偏振态构成，所述两个正交偏振态可分别记为x偏振态和y偏振态。偏振分束器502将输入光脉冲偏振分束为x偏振态的第一路光脉冲和y偏振态的第二路光脉冲，以分别由偏振分束器502的端口B和端口C输出。由偏振分束器502的端口B输出的x偏振态的第一路光脉冲传输至半波片503，经半波片503作偏振正交旋转后的第一路光脉冲偏振态变换为y偏振态。由半波片503的端口E输出的y偏振态的第一路光脉冲传输至偏振分束器的端口C并被输入偏振分束器502，并由偏振分束器502的端口A输出。如此，实现由端口 A输入的输入光脉冲的x偏振态分量在由装置反射后由端口A输出时变换为y偏振态。由偏振分束器502的端口C输出的y偏振态的第二路光脉冲传输至半波片503，经半波片503作偏振正交旋转后的第二路光脉冲偏振态变换为x偏振态。由半波片503的端口D输出的x偏振态的第二路光脉冲传输至偏振分束器的端口B并被输入偏振分束器502，并由偏振分束器502的端口A输出。如此，实现由端口A输入的输入光脉冲的y偏振态分量在由装置反射后由端口A输出时变换为x偏振态。该偏振正交旋转反射装置实现输入光脉冲的两个正交偏振态由该装置反射输出时每个正交偏振态均变换为与其正交的偏振态。采用半波片503对两个正交偏振态作偏振正交旋转，使得输入光脉冲的x偏振态和y偏振态之间的相位与输出光脉冲的y偏振态和x偏振态之间的相位保持相同。
本发明的相位编解码器可用作直流调制量子密钥分发相位编解码装置的组成部分，可用作量子密钥分发时间比特-相位编解码装置的组成部分，也可用作直流调制量子密钥分发时间比特-相位编解码装置的组成部分。
利用本发明的相位编解码器的一种基于偏振正交旋转反射的直流调制量子密钥分发相位编解码装置如图6所示，包括以下组成部分：前置分束器603、光环形器604和611、保偏分束器605和612、直流相位调制器606和613，以及偏振正交旋转反射装置607、608、614和615。
保偏分束器605、两个偏振正交旋转反射装置607和608以及保偏分束器605与这两个偏振正交旋转反射装置之间的两个臂组成第一保偏不等臂迈克尔逊干涉仪，即根据本发明的第一相位编解码器。第一相位编解码器的两个臂为保偏光纤光路。直流相位调制器606位于第一相位编解码器的两臂中的任一臂上。
类似地，保偏分束器612、两个偏振正交旋转反射装置614和615以及保偏分束器612与这两个偏振正交旋转反射装置之间的两个臂组成第二保偏不等臂迈克尔逊干涉仪，即根据本发明的第二相位编解码器。第二相位编解码器的两个臂为保偏光纤光路。直流相位调制器613位于第二相位编解码器的两臂中的任一臂上。
下面，以图6的编解码装置用于进行解码为例对其进行示例描述。
前置分束器603一侧(图6中为左侧)的两个端口601和602之一作为装置的输入端口。光环形器604的第一端口A和第二端口B分别连接前置分束器603 的一个输出端口和保偏分束器605的一个输入端口。输入第一相位编解码器的光脉冲解码后由保偏分束器605的一个输出端口609输出，或经保偏分束器605的另一输出端口(即，保偏分束器605的所述一个输入端口)传输至光环形器604的端口B并从光环形器604的第三端口C输出。光环形器611的第一端口A和第二端口B分别连接前置分束器603的另一个输出端口和保偏分束器612的一个输入端口。输入第二相位编解码器的光脉冲解码后由保偏分束器612的一个输出端口616输出，或经保偏分束器612的另一输出端口(即，保偏分束器612的所述一个输入端口)传输至光环形器611的端口B并从光环形器611的第三端口C输出。
工作时，光脉冲经分束器603的端口601或602进入分束器603并由分束器603分束为第一路光脉冲和第二路光脉冲。第一路光脉冲经光环形器604的端口A输入并由光环形器604的端口B输出至保偏分束器605。保偏分束器605将输入的第一路光脉冲分束为两路第一子光脉冲。一路第一子光脉冲经直流相位调制器606进行相位调制后由偏振正交旋转反射装置607反射回来，另一路第一子光脉冲直接经保偏光纤传输至偏振正交旋转反射装置608并由偏振正交旋转反射装置608反射回来。经相对延时的反射回来的两路第一子光脉冲经保偏分束器605合束后由端口609输出，或者被输出至光环形器604的端口B并传输至端口C由端口610输出。第二路光脉冲经光环形器611的端口A输入并由光环形器611的端口B输出至保偏分束器612。保偏分束器612将输入的第二路光脉冲分束为两路第二子光脉冲。一路第二子光脉冲经直流相位调制器613进行相位调制后由偏振正交旋转反射装置614反射回来，另一路第二子光脉冲直接经保偏光纤传输至偏振正交旋转反射装置615并由偏振正交旋转反射装置615反射回来。经相对延时的反射回来的两路第二子光脉冲经保偏分束器612合束后由端口616输出，或者被输出至光环形器611的端口B并传输至端口C由端口617输出。直流相位调制器606和613导致第一相位编解码器和第二相位编解码器中的一个所作的直流相位调制相对于另一个所作的直流相位调制相差90度。
接下来，以图6的编解码装置用于进行编码为例对其进行示例描述。
保偏分束器605的一个端口609、光环形器604的第三端口C、保偏分束器612的一个端口616、光环形器611的第三端口C作为装置的输入端口。光环形器 604的第一端口A和第二端口B分别连接前置分束器603的一个端口和保偏分束器605的另一个端口。从光环形器604的第三端口C输入的光脉冲经光环形器604的第二端口B输入第一相位编解码器。从保偏分束器605的所述一个端口609、光环形器604的第三端口C输入的光脉冲经第一相位编解码器编码后由保偏分束器605输出至光环形器604的第二端口B并由光环形器604的第一端口A传输至前置分束器603。光环形器611的第一端口A和第二端口B分别连接前置分束器603的另一个端口和保偏分束器612的另一个端口。从光环形器611的第三端口C输入的光脉冲经光环形器611的第二端口B输入第二相位编解码器。从保偏分束器612的所述一个端口616、光环形器612的第三端口C输入的光脉冲经第二相位编解码器编码后由保偏分束器612输出至光环形器611的第二端口B并由光环形器611的第一端口A传输至前置分束器603。前置分束器603一侧(图6中为左侧)的两个端口601和602之一作为装置的输出端口。由保偏分束器605的所述一个端口609、光环形器604的第三端口C、保偏分束器612的所述一个端口616、光环形器611的第三端口C输入的光脉冲经编码后分别实现四种相位编码，编码后的光脉冲经分束器603合束后由端口601或602输出。
利用本发明的相位编解码器的一种基于偏振正交旋转反射的量子密钥分发时间比特-相位编解码装置如图7所示，包括以下组成部分：分束器703和704、保偏分束器707、相位调制器708，以及偏振正交旋转反射装置709和710。
保偏分束器707、两个偏振正交旋转反射装置709和710以及保偏分束器707与这两个偏振正交旋转反射装置之间的两个臂组成保偏不等臂迈克尔逊干涉仪，即根据本发明的相位编解码器。所述两个臂为保偏光纤光路。相位调制器708位于相位编解码器的两臂中的任一臂上。
下面，以图7的编解码装置用于进行解码为例对其进行示例描述。
分束器703作为前置分束器，其一侧的两个端口701和702之一作为装置的输入端口。分束器704将来自分束器703的一路光脉冲分束后由端口705或706输出。输入保偏不等臂迈克尔逊干涉仪的光脉冲经解码后由端口711输出。
工作时，输入光脉冲经分束器703的端口701或702进入分束器703，并由分束器703分成两路光脉冲进行传输。来自分束器703的一路光脉冲输入至分束器 704，并由分束器704分束后经端口705或706输出用于进行时间比特解码。来自分束器703的另一路光脉冲输入至保偏分束器707，并由保偏分束器707分束为两路子光脉冲。一路子光脉冲经相位调制器708随机调制0度或180度相位后由偏振正交旋转反射装置709反射回来，另一路子光脉冲直接经保偏光纤传输至偏振正交旋转反射装置710并由偏振正交旋转反射装置710反射回来。经相对延时的反射回来的两路子光脉冲经保偏分束器707合束后由端口711输出。
这里，需要说明的是，分束器704是可选的。由前置分束器703将上述一路光脉冲直接输出用于进行时间比特解码是可能的。
接下来，以图7的编解码装置用于进行编码为例对其进行示例描述。
分束器704的端口705和706以及保偏分束器707的端口711作为装置的输入端口。从端口705和706输入的光脉冲由分束器704合束后输出至前置分束器703，实现时间比特编码。从端口711输入的光脉冲经保偏不等臂迈克尔逊干涉仪编码后由保偏分束器707输出至前置分束器703，其间通过调制相位调制器708实现两种相位编码。前置分束器703的端口701和702之一作为装置的输出端口。分束器703将由分束器704输出的光脉冲和由保偏分束器707输出的光脉冲合束后由端口701或702输出。
分束器704是可选的，直接将分束器703的与分束器704连接的端口作为输入端口用于进行时间比特编码是可能的。
利用本发明的相位编解码器的一种基于偏振正交旋转反射的直流调制量子密钥分发时间比特-相位编解码装置如图8所示，包括以下组成部分：分束器803和804、光环形器807、保偏分束器808、直流相位调制器809，以及偏振正交旋转反射装置810和811。
保偏分束器808、两个偏振正交旋转反射装置810和811以及保偏分束器808与这两个偏振正交旋转反射装置之间的两个臂组成保偏不等臂迈克尔逊干涉仪，即根据本发明的相位编解码器。所述两个臂为保偏光纤光路。直流相位调制器809位于相位编解码器的两臂中的任一臂上。
下面，以图8的编解码装置用于进行解码为例对其进行示例描述。
分束器803作为前置分束器，其一侧的两个端口801和802之一作为装置的输入端口。分束器804将来自分束器803的一路光脉冲分束后由端口805或806输出。从光环形器807的第一端口A输入的光脉冲由光环形器807的第二端口B输出，从光环形器807的第二端口B输入的光脉冲由光环形器807的第三端口C输出。输入保偏不等臂迈克尔逊干涉仪的光脉冲经解码后由端口812输出，或者经保偏分束器808的另一输出端口传输至光环形器807的第二端口B并从光环形器807的第三端口C输出后由端口813输出。
工作时，输入光脉冲经分束器803的端口801或802进入分束器803，并由分束器803分束成两路光脉冲进行传输。来自分束器803的一路光脉冲输入至分束器804，并由分束器804分束后由端口805或806输出用于进行时间比特解码。来自分束器803的另一路光脉冲经光环形器807的第一端口A输入并从光环形器807的第二端口B输出至保偏分束器808。保偏分束器808将该另一路光脉冲分束为两路子光脉冲。一路子光脉冲经直流相位调制器809调制0度相位或180度相位后由偏振正交旋转反射装置810反射回来，另一路子光脉冲直接经保偏光纤传输至偏振正交旋转反射装置811并由偏振正交旋转反射装置811反射回来。反射回来的经相对延时的两路子光脉冲经保偏分束器808合束后由端口812输出，或者被传输至光环形器807的第二端口B并由光环形器807的第三端口C输出后由端口813输出。
这里，需要说明的是，分束器804是可选的。由前置分束器803将上述一路光脉冲直接输出用于进行时间比特解码是可能的。
接下来，以图8的编解码装置用于进行编码为例对其进行示例描述。
分束器804的端口805和806、保偏分束器808的端口812，以及光环形器807的第三端口C作为装置的输入端口。从光环形器807的第三端口C输入的光脉冲由光环形器807的第二端口B输出，从光环形器807的第二端口B输入的光脉冲由光环形器807的第一端口A输出。从端口805和806输入的光脉冲由分束器804合束后输出至前置分束器803，实现时间比特编码。从端口812输入的光脉冲以及由光环形器807的第三端口C输入并由光环形器807的第二端口B输出至保偏分束器808的光脉冲，经保偏不等臂迈克尔逊干涉仪编码后由保偏分束器808输出至光环形器807的第二端口B并经光环形器807的第一端口A传输至前置分束 器803。由保偏分束器808的端口812、光环形器807的第三端口C输入的光脉冲经编码后分别实现两种相位编码。分束器803的端口801和802之一作为装置的输出端口。分束器803将由分束器804输出的光脉冲和从光环形器807的第一端口A输出的光脉冲合束后由端口801或802输出。
分束器804是可选的，直接将分束器803的与分束器804连接的端口作为输入端口用于进行时间比特编码是可能的。
尽管图1-2和图6-8中示出了相位调制器，但本发明的相位编解码器和编解码装置不包括相位调制器是可能的。
本文中，术语“分束器”和“合束器”可互换使用，分束器亦可称为和用作合束器，反之亦然。本文中，“保偏光纤光路”是指采用保偏光纤传输光脉冲的光路或保偏光纤连接形成的光路。
可以在量子密钥分发系统的接收端配置如上文所述的本发明的基于偏振正交旋转反射的相位编解码器或相应的编解码装置，用于解码。另外，也可以在量子密钥分发系统的发射端配置如上文所述的本发明的基于偏振正交旋转反射的相位编解码器或相应的编解码装置，用于编码。对于本发明的相位编解码器或相应的编解码装置，其在用于量子密钥分发系统的接收端或发射端时，可以包括如上文结合图1-2和图6-8示例性描述的相位调制器或不包括相位调制器。另外，在量子密钥分发系统的接收端和发射端均采用本发明的相位编解码器或编解码装置的情况下，用于接收端和发射端中至少之一的相位编解码器或编解码装置可包括相位调制器。
通过具体实施方式的说明，应当可对本发明为达成预定目的所采取的技术手段及功效有更加深入且具体的了解，然而所附图示仅是提供参考与说明之用，并非用来对本发明加以限制。

Claims (10)

  1. 一种量子密钥分发相位编解码器，包括：分束器、分别经两个臂与所述分束器光耦合的两个反射装置，每个所述反射装置为偏振正交旋转反射装置，所述两个反射装置中至少之一包括具有输入端口和两个输出端口的偏振分束器，并经所述偏振分束器的输入端口耦合至所述两个臂中的相应臂，其中每个偏振分束器的两个输出端口经传输光路彼此光耦合，对于至少一个包括偏振分束器的反射装置：其传输光路由扭转90度的保偏光纤形成，使得由其偏振分束器的两个输出端口输出的光脉冲均耦合至所述保偏光纤的同一个轴进行传输。
  2. 根据权利要求1所述的相位编解码器，其中，所述两个反射装置为相同构造的偏振正交旋转反射装置。
  3. 根据权利要求1所述的相位编解码器，其中，所述两个反射装置为不同构造的偏振正交旋转反射装置。
  4. 根据权利要求1所述的相位编解码器，其中，所述保偏光纤的所述同一个轴是所述保偏光纤的慢轴。
  5. 根据权利要求1所述的相位编解码器，其中，所述保偏光纤的所述同一个轴是所述保偏光纤的快轴。
  6. 根据权利要求1所述的相位编解码器，其中，所述扭转90度的保偏光纤包括扭转(90+n*180)度的保偏光纤，其中n为整数。
  7. 根据权利要求1所述的相位编解码器，其中，所述分束器是保偏分束器。
  8. 根据权利要求1所述的相位编解码器，其中，所述两个臂各为偏振保持光路，所述两个臂上的光器件为偏振保持光器件。
  9. 根据权利要求1所述的相位编解码器，其中，所述相位编解码器还包括相位调制器，其中所述相位调制器设置于所述两个臂中至少之一上。
  10. 一种量子密钥分发系统，包括：
    根据权利要求1所述的相位编解码器，其设置在所述量子密钥分发系统的接收端，用于解码；或
    根据权利要求1所述的相位编解码器，其设置在所述量子密钥分发系统的发射端，用于编码。
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