CN111901050A - Phase modulation polarization encoding and decoding device and quantum key distribution system - Google Patents
Phase modulation polarization encoding and decoding device and quantum key distribution system Download PDFInfo
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- 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
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- 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
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- H04B10/516—Details of coding or modulation
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Abstract
A phase modulation polarization codec device and a quantum key distribution system, the device comprising: the optical transmission device comprises a first port, a second port and a third port, and the first port receives optical pulses; the second port transmits the optical pulse to the birefringent phase modulator through the first polarization-maintaining transmission optical path, receives the optical pulse transmitted back to the first polarization-maintaining transmission optical path and then transmits the optical pulse to the third port for output; the birefringent phase modulator has two ports, one of which is optically coupled to the second port and the other of which is optically coupled to the polarization quadrature rotating reflective device; the polarization orthogonal rotation reflection device carries out polarization orthogonal rotation reflection on two orthogonal polarization states of the light pulse; the phase modulator phase-modulates one of the optical pulses transmitted from the first and second polarization maintaining transmission optical paths, or differently phase-modulates the same. Thereby modulating the polarization state of the optical pulses more quickly by phase modulation.
Description
Technical Field
The invention relates to the technical field of optical transmission secret communication, in particular to a phase modulation polarization coding and decoding device and a quantum key distribution system.
Background
The quantum secret communication technology is a leading-edge hotspot field combining quantum physics and information science. Based on quantum key distribution technology and one-time pad cipher principle, quantum secret communication can realize the safe transmission of information in public channel. The quantum key distribution is based on the physical principles of quantum mechanics Heisebauer uncertain relation, quantum unclonable theorem and the like, the secret key can be safely shared among users, potential eavesdropping behavior can be detected, and the quantum key distribution method can be applied to the fields of high-safety information transmission requirements of national defense, government affairs, finance, electric power and the like.
The polarization encoding quantum key distribution adopts two groups of orthogonal polarization states for encoding, along with the technical development and application requirements, the high-speed quantum key distribution becomes a trend, and for polarization encoding, light pulses in four polarization states need to be randomly generated at high speed. Conventionally, a scheme of multiple lasers, each of which generates one polarization state, is adopted, but due to the inconsistency of the multiple lasers, such as the central wavelength inconsistency, the security of key distribution is threatened. The realization of high-speed stable modulation of the polarization state of an optical pulse by a single laser is an important problem for polarization-encoded quantum key distribution application.
Disclosure of Invention
The invention mainly aims to provide a phase modulation polarization coding and decoding device and a quantum key distribution system based on the device, so as to solve the problem that a single laser is adopted in a polarization coding quantum key distribution system to realize high-speed stable modulation of the polarization state of an optical pulse.
The invention provides at least the following technical scheme:
1. a phase modulation polarization codec, comprising: an optical transmission device, a birefringent phase modulator, a polarization quadrature rotating reflective device, a first polarization maintaining transmission optical path optically coupled with the optical transmission device and the birefringent phase modulator, respectively, and a second polarization maintaining transmission optical path optically coupled with the birefringent phase modulator and the polarization quadrature rotating reflective device, respectively,
the optical transmission device comprises a first port, a second port and a third port, the first port of the optical transmission device is configured to receive an input optical pulse, the second port of the optical transmission device is configured to transmit the received input optical pulse to the birefringent phase modulator through the first polarization-preserving transmission optical path, the second port of the optical transmission device is further configured to receive an optical pulse transmitted back through the first polarization-preserving transmission optical path, and the optical transmission device transmits the optical pulse transmitted back to the second port of the optical transmission device to the third port of the optical transmission device for output;
the birefringent phase modulator has two ports, one of the two ports is optically coupled with the second port of the optical transmission device through the first polarization maintaining transmission optical path, and the other of the two ports is optically coupled with the polarization orthogonal rotation reflection device through the second polarization maintaining transmission optical path;
the polarization orthogonal rotation reflection device is used for performing polarization orthogonal rotation reflection on two orthogonal polarization states of the optical pulse output to the second polarization-maintaining transmission optical path from the birefringent phase modulator, so that after reflection of the polarization orthogonal rotation reflection device, the two orthogonal polarization states of the optical pulse are respectively converted into orthogonal polarization states; wherein,
the birefringent phase modulator is arranged to: the phase modulation is performed on one of the optical pulse transmitted through the first polarization maintaining transmission optical path and the optical pulse transmitted through the second polarization maintaining transmission optical path, or the phase modulation is performed differently on the optical pulse transmitted through the first polarization maintaining transmission optical path and the optical pulse transmitted through the second polarization maintaining transmission optical path.
2. The phase modulation polarization encoding and decoding device according to claim 1, wherein the polarization orthogonal rotation reflection device is a quarter-wave plate mirror, the quarter-wave plate mirror includes a mirror and a quarter-wave plate, and the mirror is integrally formed with the quarter-wave plate at a rear end of the quarter-wave plate.
3. The phase modulation polarization encoding and decoding device according to claim 1, wherein the optical transmission device is an optical circulator or an optical coupler.
4. The phase modulation polarization encoding and decoding device according to claim 1, wherein the first polarization maintaining transmission optical path is a first polarization maintaining fiber, and/or the second polarization maintaining transmission optical path is a second polarization maintaining fiber.
5. The phase modulation polarization encoding and decoding device according to scheme 1 or 3, wherein the optical transmission device is a polarization maintaining device, and a port of the optical transmission device is a free space port or a polarization maintaining optical fiber port.
6. The phase modulation polarization encoding and decoding device according to claim 4, wherein the amplitude components of the optical pulses output to the first polarization maintaining fiber via the second port of the optical transmission device projected along the slow axis and the fast axis of the first polarization maintaining fiber have the same magnitude and have arbitrary relative phases.
7. The phase modulation polarization encoding and decoding device according to claim 6, wherein the optical pulse output to the first polarization maintaining fiber via the second port of the optical transmission device is in a circular polarization state or in a linear polarization state having an angle of 45 degrees with the slow axis or the fast axis of the first polarization maintaining fiber.
8. The phase modulation polarization encoding and decoding device according to scheme 2 or 4, wherein an included angle between the slow axis of the second polarization maintaining fiber and the slow axis or the fast axis of the quarter-wave plate in the quarter-wave plate reflector is 45 degrees.
9. A quantum key distribution system comprising a transmitting end and a receiving end, wherein:
the phase modulation polarization coding and decoding device according to any one of the schemes 1-8 is arranged at the transmitting end for polarization coding; and/or
The phase modulation polarization encoding and decoding device according to any one of the schemes 1 to 8 is arranged at the receiving end for polarization decoding or polarization decoding selection base.
10. The quantum key distribution system of claim 9, wherein:
when the quantum key distribution system is used for polarization decoding, the receiving end of the quantum key distribution system also comprises a polarizer optically coupled with the phase modulation polarization coding and decoding device and a single photon detector optically coupled with the polarizer; or,
when the quantum key distribution system is used for polarization decoding and base selection, the receiving end of the quantum key distribution system further comprises a polarization beam splitter optically coupled with the phase modulation polarization encoding and decoding device and two single photon detectors optically coupled with the polarization beam splitter.
The present invention, by an inventive configuration, phase-modulates one of the optical pulses transmitted through the first polarization maintaining transmission optical path and the optical pulses transmitted through the second polarization maintaining transmission optical path using a birefringent phase modulator, or differently phase-modulates the optical pulses transmitted through the first polarization maintaining transmission optical path and the optical pulses transmitted through the second polarization maintaining transmission optical path, so that high-speed modulation of the polarization state of the optical pulses can be achieved by phase modulation, and polarization state modulation is achieved by employing a polarization orthogonal rotation reflecting device independently of interference of the first polarization maintaining transmission optical path and the second polarization maintaining transmission optical path. The phase modulation polarization coding and decoding device and the corresponding quantum key distribution system can easily realize the technical effect of stably modulating the polarization state of the optical pulse at high speed by modulating the phase, and solve the technical problem that the polarization state of the optical pulse is difficult to stably modulate at high speed by adopting a single laser. The invention provides a scheme of a phase modulation polarization coding and decoding device and a corresponding quantum key distribution system, which are easy to realize and apply.
Drawings
Fig. 1 is a schematic structural diagram of a phase modulation polarization encoding and decoding device according to a preferred embodiment of the present invention;
fig. 2 is a schematic diagram of the composition structure of a quantum key distribution system according to a preferred embodiment of the present invention;
fig. 3 is a schematic structural diagram of a quantum key distribution system according to another preferred embodiment of the present invention.
Detailed Description
Embodiments of the present invention will now be described with reference to the accompanying drawings, which form a part hereof, and which together with the embodiments of the invention serve to explain the principles of the invention. For the purpose of clarity and simplicity, a detailed description of known functions and configurations of devices described herein will be omitted when it may obscure the subject matter of the present invention.
According to an aspect of the present invention, there is provided a phase modulation polarization codec device including: the polarization maintaining device comprises an optical transmission device, a birefringence phase modulator, a polarization orthogonal rotation reflection device, a first polarization maintaining transmission optical path respectively optically coupled with the optical transmission device and the birefringence phase modulator, and a second polarization maintaining transmission optical path respectively optically coupled with the birefringence phase modulator and the polarization orthogonal rotation reflection device.
Specifically, the optical transmission apparatus includes a first port, a second port, and a third port, where the first port of the optical transmission apparatus is configured to receive an input optical pulse, the second port of the optical transmission apparatus is configured to transmit the received input optical pulse to the birefringent phase modulator through the first polarization maintaining transmission optical path, the second port of the optical transmission apparatus is further configured to receive an optical pulse transmitted back through the first polarization maintaining transmission optical path, and the optical transmission apparatus transmits the optical pulse transmitted back to the second port of the optical transmission apparatus to the third port of the optical transmission apparatus for output.
Preferably, the optical transmission device is an optical circulator or an optical coupler. In addition, preferably, the optical transmission device is a polarization maintaining device, and the first port, the second port and the third port of the optical transmission device may be free space ports or polarization maintaining fiber ports.
The birefringent phase modulator has two ports, one of the two ports is optically coupled to the second port of the optical transmission device via the first polarization maintaining transmission optical path, and the other of the two ports is optically coupled to the polarization quadrature rotating reflective device via the second polarization maintaining transmission optical path.
The polarization orthogonal rotation reflection device is configured to perform polarization orthogonal rotation reflection on two orthogonal polarization states of the optical pulse output from the birefringent phase modulator to the second polarization-maintaining transmission optical path, so that after reflection by the polarization orthogonal rotation reflection device, the two orthogonal polarization states of the optical pulse in the path are respectively converted into polarization states orthogonal to the two orthogonal polarization states.
Preferably, the polarization orthogonal rotation reflecting device is a quarter wave plate mirror, the quarter wave plate mirror includes a mirror and a quarter wave plate, and the mirror is integrally formed with the quarter wave plate at a rear end of the quarter wave plate. The birefringent phase modulator is arranged to: the phase modulation is performed on one of the optical pulse transmitted through the first polarization maintaining transmission optical path and the optical pulse transmitted through the second polarization maintaining transmission optical path, or the phase modulation is performed differently on the optical pulse transmitted through the first polarization maintaining transmission optical path and the optical pulse transmitted through the second polarization maintaining transmission optical path.
Preferably, the first polarization-maintaining transmission optical path is a first polarization-maintaining optical fiber, and/or the second polarization-maintaining transmission optical path is a second polarization-maintaining optical fiber.
Fig. 1 shows a phase modulation polarization encoding and decoding apparatus according to a preferred embodiment of the present invention. As shown in fig. 1, the phase modulation polarization encoding and decoding device includes the following components: an optical transmission device 102, a birefringent phase modulator 104, a first polarization maintaining fiber 103 optically coupled to the optical transmission device and the birefringent phase modulator, respectively, a second polarization maintaining fiber 105 optically coupled to the birefringent phase modulator and the polarization orthogonal rotating reflective device, respectively, and a polarization orthogonal rotating reflective device 106 (hereinafter referred to as "reflective device" 106).
The optical transmission device 102 includes three ports, namely a first port a, a second port B and a third port C. The first port a (i.e., the port 101) of the optical transmission device 102 is an input port of the phase modulation polarization encoding and decoding device, and is configured to receive a path of input optical pulses. The third port C (i.e., the port 107) of the optical transmission device 102 is an output port of the phase modulation polarization codec device. The second port B of the optical transmission apparatus is configured to transmit the received input optical pulse to the birefringent phase modulator 104 through the first polarization maintaining fiber 103, and the second port B of the optical transmission apparatus is further configured to receive the optical pulse transmitted back through the first polarization maintaining fiber 103 and then transmit the transmitted optical pulse to the third port C of the optical transmission apparatus for output. Specifically, the optical pulse input to the first port a of the optical transmission device 102 is output from the second port B of the optical transmission device 102 to the first polarization maintaining fiber 103, transmitted to the polarization orthogonal rotation reflection device 106 via the second polarization maintaining fiber 105 after passing through the birefringent phase modulator 104, and the polarization orthogonal rotation reflection device 106 reflects the optical pulse subjected to the phase modulation by polarization orthogonal rotation, reaches the second port B of the optical transmission device 102 via the second polarization maintaining fiber 105 and returns to the first polarization maintaining fiber 103, and is output from the third port C of the optical transmission device 102.
Preferably, the optical transmission device 102 may be a three-port optical circulator or a 1 × 2 optical coupler. Preferably, the optical transmission device 102 is a polarization maintaining device, and its port is a free space port or a polarization maintaining fiber port.
The birefringent phase modulator 104 has two ports, one of the two ports (e.g., the left port in fig. 1) is optically coupled to the second port B of the optical transmission device through the first polarization maintaining fiber 103, and the other of the two ports (e.g., the right port in fig. 1) is optically coupled to the polarization quadrature rotating reflective device 106 through the second polarization maintaining fiber 105.
The polarization orthogonal rotation reflection device 106 is configured to perform polarization orthogonal rotation reflection on two orthogonal polarization states of the optical pulse output from the birefringent phase modulator to the second polarization maintaining fiber, so that after reflection by the polarization orthogonal rotation reflection device, the two orthogonal polarization states of the optical pulse are respectively transformed into polarization states orthogonal to the two orthogonal polarization states, and a phase between the two orthogonal polarization states after reflection is the same as a phase between the two orthogonal polarization states before reflection.
The birefringent phase modulator 104 is arranged to: one of the optical pulses transmitted through the first polarization maintaining fiber 103 and the optical pulses transmitted through the second polarization maintaining fiber 105 is phase-modulated, or the optical pulses transmitted through the first polarization maintaining fiber 103 and the optical pulses transmitted through the second polarization maintaining fiber 105 are differently phase-modulated. In other words, the birefringent phase modulator 104 phase-modulates only the optical pulses input via one of the two ports of the birefringent phase modulator, or differently phase-modulates the optical pulses input from the two ports. The birefringent phase modulator 104 is adapted to apply different adjustable phase modulations to the two orthogonal polarization states of the light pulses passing therethrough. For example, the birefringent phase modulator may be a lithium niobate birefringent phase modulator, and by controlling the voltage applied to the lithium niobate crystal, the phase modulation experienced by each of the two orthogonal polarization states passing through the lithium niobate birefringent phase modulator may be controlled and adjusted.
In this context, the polarization orthogonal rotation reflection device can perform polarization orthogonal rotation reflection on two orthogonal polarization states of one path of input light pulse, so that after reflection by the polarization orthogonal rotation reflection device, the two orthogonal polarization states of the path of light pulse are transformed into polarization states orthogonal to the two orthogonal polarization states, respectively, and a phase between the two orthogonal polarization states after reflection is the same as a phase between the two orthogonal polarization states before reflection. For example, it is assumed that the two orthogonal polarization states of the input light pulse are an x polarization state and a y polarization state, respectively, the x polarization state of the light pulse transmitted along the optical path to one polarization orthogonal rotation reflection device is converted into a polarization state orthogonal thereto, i.e., a y polarization state, after polarization orthogonal rotation reflection at the reflection device, the y polarization state of the light pulse transmitted along the optical path to the reflection device is converted into a polarization state orthogonal thereto, i.e., an x polarization state, after polarization orthogonal rotation reflection at the polarization orthogonal rotation reflection device, and a phase between the y polarization state and the x polarization state after reflection is the same as a phase between the x polarization state and the y polarization state before reflection.
Specifically, the polarization orthogonal rotation reflection device 106 can convert the orthogonal polarization states corresponding to the slow axis and the fast axis of the second polarization maintaining fiber 105 into the orthogonal polarization states after reflection. For example, the polarization orthogonal rotation reflection device 106 reflects the light pulse input by the slow axis of the second polarization maintaining fiber 105 and outputs the light pulse by the fast axis of the second polarization maintaining fiber 105; the polarization orthogonal rotation reflection device 106 reflects the optical pulse input by the fast axis of the second polarization maintaining fiber 105 and outputs the optical pulse by the slow axis of the second polarization maintaining fiber 105.
According to one possible configuration, the polarization orthogonal rotation reflecting means 106 is a quarter-wave plate mirror comprising a mirror and a quarter-wave plate, the mirror being integrally formed with the quarter-wave plate at the rear end of the quarter-wave plate. Preferably, the included angle between the slow axis of the second polarization maintaining optical fiber and the slow axis or the fast axis of the quarter-wave plate in the quarter-wave plate reflector is 45 degrees.
In one embodiment, the amplitude components of the optical pulses output via the second port B of the optical transmission device 102 projected along the slow axis and the fast axis of the first polarization maintaining fiber have the same magnitude and are in an arbitrary phase with respect to each other. The following description will exemplify optical pulses having the same amplitude component and an arbitrary relative phase as those projected along the slow axis and the fast axis of the first polarization maintaining fiber. Assuming that the polarized light transmitted along the slow axis and the fast axis of the polarization maintaining fiber are respectively in the x-polarization state and the y-polarization state
And (4) showing. The amplitude of the light pulse may be expressed as
Wherein A, B represents the amplitude of the x-polarization and the y-polarization respectively and A is B, relative phase
Is an arbitrary phase. So that the amplitude component projected to the slow axis of the polarization maintaining fiber is A and the amplitude component projected to the fast axis of the polarization maintaining fiber is A
The two amplitude components have the same magnitude and the relative phase is an arbitrary phase. Preferably, the optical pulse output through the second port B of the optical transmission device 102 is in a circular polarization state or in a slow axis or fast axis clamp with the first polarization maintaining fiberLinear polarization state with an angle of 45 degrees.
If the optical circulator 102 is replaced with a 1 x 2 optical coupler, the results are not affected.
The operation of the phase modulation polarization encoding and decoding device of the present invention will be described with reference to a specific embodiment.
Linearly polarized light pulses are input to the phase modulation polarization encoding and decoding device via the port 101 (i.e., the first port a of the optical transmission device 102), and then output to the first polarization maintaining fiber 103 via the second port B of the optical transmission device 102, the polarization state of the light pulses input to the first polarization maintaining fiber 103 is at an angle of 45 degrees with the slow axis of the first polarization maintaining fiber 103, the light pulses input to the first polarization maintaining fiber 103 may be divided into first and second component light pulses (e.g., horizontal and vertical components), which may be transmitted to the birefringent phase modulator 104, for example, along the slow axis and the fast axis of the first polarization maintaining fiber 103, respectively. Suppose that the first component optical pulse is transmitted along the slow axis of the birefringent phase modulator 104 and output to the slow axis of the second polarization maintaining fiber 105 for transmission, and then the first component optical pulse is continuously transmitted along the slow axis of the second polarization maintaining fiber 105 to the polarization orthogonal rotating reflecting device 106, and is reflected by the polarization orthogonal rotating reflecting device 106, and then sequentially transmitted back along the fast axis of the second polarization maintaining fiber 105, the fast axis of the phase modulator 104, and the fast axis of the first polarization maintaining fiber 103, and output to the second port B of the optical transmission device 102, and then output from the third port C of the optical transmission device 102. Suppose that the second component optical pulse is transmitted along the fast axis of the birefringent phase modulator 104 and output to the fast axis of the second polarization maintaining fiber 105 for transmission, and then the second component optical pulse is continuously transmitted along the fast axis of the second polarization maintaining fiber 105 to the polarization orthogonal rotating reflecting device 106, and is reflected by the polarization orthogonal rotating reflecting device 106, and then sequentially transmitted back along the slow axis of the second polarization maintaining fiber 105, the slow axis of the phase modulator 104, and the slow axis of the first polarization maintaining fiber 103, and output to the second port B of the optical transmission device 102, and then output from the third port C of the optical transmission device 102.
The birefringent phase modulator 104 is phase-modulated only when an optical pulse is input to the birefringent phase modulator 104 for transmission by the first polarization maintaining fiber 103 or only when an optical pulse is input to the birefringent phase modulator 104 for transmission by the second polarization maintaining fiber 105. In other words, the birefringent phase modulator modulates the light pulses that traverse the birefringent phase modulator only once. Thus, the function of modulating the polarization state of the optical pulse can be achieved by modulating the phase difference between the two components (two orthogonal polarization state components) of the optical pulse. Or, in an alternative embodiment, when the optical pulse is input to the birefringent phase modulator 104 from the first polarization maintaining fiber 103 for transmission, and when the optical pulse is input to the birefringent phase modulator 104 from the second polarization maintaining fiber 105 for transmission, the birefringent phase modulator 104 performs different phase modulation on the optical pulse and the optical pulse, respectively, so as to achieve the function of modulating the polarization state of the optical pulse.
Since the orthogonal polarization rotation reflection device 106 is a device capable of orthogonal polarization rotation reflection of each of the two polarization states of the input optical pulse, it is possible to automatically compensate for the phase difference (inherent to the phase difference when not modulated) and the insertion loss mismatch between the two components of the optical pulse due to the slow axis and the fast axis of the birefringent phase modulator 104, the first polarization maintaining fiber 103, and the second polarization maintaining fiber 105. Thus, the polarization modulation of the optical pulse is correlated only with the phase difference generated by the birefringent phase modulator 104 phase-modulating the two components (two orthogonal polarization state components) of the optical pulse, and stable polarization state modulation can be realized. By phase-modulating one of the optical pulses transmitted through the first polarization maintaining fiber 103 and the optical pulses transmitted through the second polarization maintaining fiber 105 using the birefringent phase modulator 104, or by differently phase-modulating the optical pulses transmitted through the first polarization maintaining fiber 103 and the optical pulses transmitted through the second polarization maintaining fiber 105, it is possible to modulate the phase difference between the two orthogonal polarization states of the optical pulses at a high speed using the birefringent phase modulator 104, and further realize high-speed polarization state modulation.
In another aspect of the present invention, a quantum key distribution system is provided, which includes a transmitting end and a receiving end, wherein: the phase modulation polarization encoding and decoding device is arranged at the transmitting end and used for polarization encoding; and/or the receiving end is provided with the phase modulation polarization encoding and decoding device for polarization decoding or polarization decoding selection base.
In one embodiment, when used for polarization decoding, the receiving end of the quantum key distribution system further comprises a polarizer optically coupled with the phase modulation polarization encoding and decoding device and a single photon detector optically coupled with the polarizer; or, when the quantum key distribution system is used for polarization decoding and basis selection, the receiving end of the quantum key distribution system further comprises a polarization beam splitter optically coupled with the phase modulation polarization encoding and decoding device and two single photon detectors optically coupled with the polarization beam splitter.
Fig. 2 is a schematic diagram showing the composition structure of a quantum key distribution system according to a preferred embodiment of the present invention. The quantum key distribution system shown in fig. 2 includes the following components: a laser 201, an intensity modulator 202, a polarization encoder 203, an attenuator 204, a quantum channel 205, a polarization controller 206, a polarization decoding and selecting device 207, a polarization beam splitter 208, and single photon detectors 209 and 210.
Specifically, a laser 201, an intensity modulator 202, a polarization encoder 203, and an attenuator 204 are provided at the transmitting end of the quantum key distribution system, wherein: the laser 201 is used for generating optical pulses; the intensity modulator 202 is used for randomly modulating the intensity of the light pulse generated by the laser 201 to generate a decoy state; the polarization encoder 203 is the phase modulation polarization encoding and decoding device, which can be used for polarization encoding of the light pulse; the attenuator 204 is used to attenuate the optical pulses to a single photon state output.
A quantum channel 205 is disposed between the transmitting end and the receiving end of the quantum key distribution system for transmitting single photon optical pulses. The quantum channel 205 may be an optical waveguide, an optical fiber, free space, a discrete optical element, a planar waveguide optical element, a fiber optical element, or a light propagation channel combining any two or more of the above.
The polarization controller 206, the polarization decoding and base selecting device 207, the polarization beam splitter 208 and the single photon detectors 209 and 210 are arranged at the receiving end of the quantum key distribution system, wherein: the polarization controller 206 is used for regulating and controlling the polarization state of the single-photon light pulse; the polarization decoding and base selecting device 207 is the phase modulation polarization encoding and decoding device, and can be used for performing polarization decoding and base selecting on the single-photon optical pulse; the polarization beam splitter 208 is used for polarizing and splitting the single photon light pulse and outputting the single photon light pulse to the single photon detector, and forms a polarization decoding device together with the polarization decoding base selection device 207; the single- photon detectors 209 and 210 are configured to detect the single-photon optical pulse output by the polarization beam splitter 208, and perform quantum key distribution according to the detection result and a quantum key distribution protocol.
In operation, at the transmitting end, the laser 201 transmits light pulses into the intensity modulator 202, and the intensity modulator 202 randomly intensity modulates the light pulses to generate a signal state and a decoy state, which are output to the polarization encoder 203. The polarization encoder 203 encodes the light pulse at random into four polarization states (e.g., into ± 45-degree linear polarization state and left/right-hand circular polarization state), and outputs the encoded light pulse to the attenuator 204. The attenuator 204 attenuates the encoded optical pulses into single photon optical pulses (e.g., to an average of 0.1 photons per pulse) and outputs the single photon optical pulses to the quantum channel 205. The quantum channel 205 may be a single mode fiber or a free space, and the single photon optical pulse is transmitted to the receiving end through the quantum channel 205 for polarization decoding.
At the receiving end, the single photon optical pulse is input into a polarization controller 206, and the polarization controller 206 is used for compensating the polarization state change caused by the influence of the birefringence of the quantum channel, the optical paths of the transmitting end and the receiving end before the single photon optical pulse polarization decoding. The single-photon optical pulse output from the polarization controller 206 is input to a polarization decoding selection device 207 for performing polarization decoding selection (for example, a diagonal basis corresponding to a ± 45-degree linear polarization state code and a circular polarization basis corresponding to a left/right circular polarization state are selected). The single-photon optical pulse output from the polarization decoding and base selection device 207 is input into the polarization beam splitter 208 for polarization beam splitting, and the optical pulse polarized and split by the polarization beam splitter 208 is input into the single- photon detector 209 or 210 for result detection. The polarization encoder 203 and the polarization decoding base selection device 207 can be implemented by the phase modulation offset encoding and decoding device described above with reference to fig. 1, and perform polarization encoding and polarization decoding base selection on the optical pulse according to the quantum key distribution protocol, so as to perform key distribution according to the quantum key distribution protocol.
Fig. 3 is a schematic diagram showing the composition structure of a quantum key distribution system according to a preferred embodiment of the present invention. The quantum key distribution system shown in fig. 3 includes the following components: a laser 301, an intensity modulator 302, a polarization encoder 303, an attenuator 304, a quantum channel 305, a polarization controller 306, a polarization decoder 307, a polarizer 308, and a single photon detector 309.
Specifically, similar to the transmitting end in fig. 2, in fig. 3, a laser 301, an intensity modulator 302, a polarization encoder 303, and an attenuator 304 are provided at the transmitting end of the quantum key distribution system, where the laser 301 is used to generate optical pulses; the intensity modulator 302 is used for randomly modulating the intensity of the light pulse generated by the laser 301 to generate a decoy state; the polarization encoder 303 is the phase modulation polarization encoding and decoding device, and is configured to perform polarization encoding on the optical pulse; the attenuator 304 is used to attenuate the optical pulses to a single photon state output.
Similar to the quantum channel in fig. 2, a quantum channel 305 is disposed between the transmitting end and the receiving end of the quantum key distribution system for transmitting single photon optical pulses. The quantum channel 305 may also be an optical waveguide, an optical fiber, free space, a discrete optical element, a planar waveguide optical element, a fiber optical element, or a light propagation channel combining any two or more of the above.
The polarization controller 306, the polarization decoder 307, the polarizer 308, and the single-photon detector 309 are disposed at a receiving end of the quantum key distribution system, wherein: the polarization controller 306 is used for regulating and controlling the polarization state of the single photon light pulse; the polarization decoder 307 is the phase modulation polarization encoding and decoding device, and is configured to perform polarization decoding on the single photon optical pulse; the polarizer 308 is used for polarizing and outputting the single photon light pulse; the single-photon detector 309 is configured to detect the single-photon optical pulse output by the polarizer 308, and perform quantum key distribution according to the detection result and a quantum key distribution protocol.
In operation, similar to the transmit side of fig. 2, at the transmit side of fig. 3, a laser 301 transmits light pulses into an intensity modulator 302, and the intensity modulator 302 randomly intensity modulates the light pulses to generate a signal state and a spoof state and outputs the signal state and the spoof state to a polarization encoder 303. The polarization encoder 303 randomly encodes the optical pulse in four polarization states (e.g., into a ± 45-degree linear polarization state and a left/right circular polarization state), and outputs the encoded optical pulse to the attenuator 304. The attenuator 304 attenuates the encoded optical pulses into single photon optical pulses (e.g., to an average of 0.1 photons per pulse) and outputs the single photon optical pulses to the quantum channel 305. The quantum channel 305 may be a single mode fiber or a free space, and the single photon light pulse is transmitted to the receiving end through the quantum channel 305 for polarization decoding.
At the receiving end, the single photon optical pulse is input to a polarization controller 306, and the polarization controller 306 is used for compensating the polarization state change caused by the influence of the birefringence of the quantum channel, the optical paths of the transmitting end and the receiving end before the single photon optical pulse polarization decoding. The single photon optical pulses output from the polarization controller 306 are input to the polarization decoder 307 for polarization decoding (e.g., decoding of ± 45-degree linear polarization states and corresponding left/right-hand circular polarization states). The single-photon optical pulse output from the polarization decoder 307 is input to the polarizer 308 for polarization, and the optical pulse polarized by the polarizer 308 is input to the single-photon detector 309 for detection. The polarization encoder 303 and the polarization decoder 307 respectively perform polarization encoding and polarization decoding on the optical pulses according to a quantum key distribution protocol, and perform key distribution according to the quantum key distribution protocol.
Herein, the transmission optical path formed by the polarization maintaining fiber refers to an optical path for transmitting light pulses by using the polarization maintaining fiber or an optical path formed by connecting the polarization maintaining fibers.
While the invention has been described in connection with specific embodiments thereof, it is to be understood that it is intended by the appended drawings that all such modifications as fall within the true spirit and scope of the invention are intended to be included within the scope of the invention.
Claims (10)
1. A phase modulation polarization codec, comprising: an optical transmission device, a birefringent phase modulator, a polarization quadrature rotating reflective device, a first polarization maintaining transmission optical path optically coupled with the optical transmission device and the birefringent phase modulator, respectively, and a second polarization maintaining transmission optical path optically coupled with the birefringent phase modulator and the polarization quadrature rotating reflective device, respectively,
the optical transmission device comprises a first port, a second port and a third port, the first port of the optical transmission device is configured to receive an input optical pulse, the second port of the optical transmission device is configured to transmit the received input optical pulse to the birefringent phase modulator through the first polarization-preserving transmission optical path, the second port of the optical transmission device is further configured to receive an optical pulse transmitted back through the first polarization-preserving transmission optical path, and the optical transmission device transmits the optical pulse transmitted back to the second port of the optical transmission device to the third port of the optical transmission device for output;
the birefringent phase modulator has two ports, one of the two ports is optically coupled with the second port of the optical transmission device through the first polarization maintaining transmission optical path, and the other of the two ports is optically coupled with the polarization orthogonal rotation reflection device through the second polarization maintaining transmission optical path;
the polarization orthogonal rotation reflection device is used for performing polarization orthogonal rotation reflection on two orthogonal polarization states of the optical pulse output to the second polarization-maintaining transmission optical path from the birefringent phase modulator, so that after reflection of the polarization orthogonal rotation reflection device, the two orthogonal polarization states of the optical pulse are respectively converted into orthogonal polarization states; wherein,
the birefringent phase modulator is arranged to: the phase modulation is performed on one of the optical pulse transmitted through the first polarization maintaining transmission optical path and the optical pulse transmitted through the second polarization maintaining transmission optical path, or the phase modulation is performed differently on the optical pulse transmitted through the first polarization maintaining transmission optical path and the optical pulse transmitted through the second polarization maintaining transmission optical path.
2. The phase modulation polarization encoding and decoding device according to claim 1, wherein the polarization orthogonal rotation reflection means is a quarter wave plate mirror including a mirror and a quarter wave plate, the mirror being integrally formed with the quarter wave plate at a rear end of the quarter wave plate.
3. The phase modulation polarization codec of claim 1, wherein the optical transmission device is an optical circulator or an optical coupler.
4. The phase modulation polarization encoding and decoding device according to claim 1, wherein the first polarization maintaining transmission optical path is a first polarization maintaining fiber, and/or the second polarization maintaining transmission optical path is a second polarization maintaining fiber.
5. The phase modulation polarization encoding and decoding device according to claim 1 or 3, wherein the optical transmission device is a polarization maintaining device, and the port of the optical transmission device is a free space port or a polarization maintaining optical fiber port.
6. The phase modulation polarization encoding and decoding device according to claim 4, wherein the amplitude components of the optical pulses output to the first polarization maintaining fiber via the second port of the optical transmission device projected along the slow axis and the fast axis of the first polarization maintaining fiber have the same magnitude and the relative phase is an arbitrary phase.
7. The phase modulation polarization encoding and decoding device according to claim 6, wherein the optical pulse output to the first polarization maintaining fiber via the second port of the optical transmission device is in a circular polarization state or in a linear polarization state having an angle of 45 degrees with the slow axis or the fast axis of the first polarization maintaining fiber.
8. The phase modulation polarization encoding and decoding device of claim 2 or 4, wherein the slow axis of the second polarization maintaining fiber forms an angle of 45 degrees with the slow axis or the fast axis of the quarter-wave plate in the quarter-wave plate reflector.
9. A quantum key distribution system comprising a transmitting end and a receiving end, wherein:
the phase modulation polarization coding and decoding device according to any one of claims 1 to 8 is arranged at the transmitting end for polarization coding; and/or
The phase modulation polarization encoding and decoding device according to any one of claims 1 to 8 is arranged at the receiving end for polarization decoding or polarization decoding selection base.
10. The quantum key distribution system of claim 9, wherein:
when the quantum key distribution system is used for polarization decoding, the receiving end of the quantum key distribution system also comprises a polarizer optically coupled with the phase modulation polarization coding and decoding device and a single photon detector optically coupled with the polarizer; or,
when the quantum key distribution system is used for polarization decoding and base selection, the receiving end of the quantum key distribution system further comprises a polarization beam splitter optically coupled with the phase modulation polarization encoding and decoding device and two single photon detectors optically coupled with the polarization beam splitter.
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