CN112468298B - Pulse modulation device, transmitter, system and method for CV-QKD - Google Patents

Pulse modulation device, transmitter, system and method for CV-QKD Download PDF

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CN112468298B
CN112468298B CN202110106853.3A CN202110106853A CN112468298B CN 112468298 B CN112468298 B CN 112468298B CN 202110106853 A CN202110106853 A CN 202110106853A CN 112468298 B CN112468298 B CN 112468298B
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CN112468298A (en
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陈建
刘鹏
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Beijing Zhongchuangwei Nanjing Quantum Communication Technology Co ltd
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    • 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
    • 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
    • H04B10/50—Transmitters
    • H04B10/501—Structural aspects
    • H04B10/503—Laser transmitters
    • 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
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H04B10/5161—Combination of different modulation schemes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/70—Photonic quantum communication
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
    • 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
    • H04L9/0855—Quantum cryptography involving additional nodes, e.g. quantum relays, repeaters, intermediate nodes or remote nodes
    • 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

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  • Computer Security & Cryptography (AREA)
  • Optics & Photonics (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

The application provides a pulse modulation device, a transmitter, a system and a method for CV-QKD, wherein the pulse modulation device comprises a first pulse laser, a second pulse laser, a third pulse laser, an optical beam splitter, a first optical circulator, a second optical circulator, an optical modulation module and a polarization beam combiner, wherein the optical beam splitter is used for dividing pulse light output by the first pulse laser into a first optical pulse and a second optical pulse, the first optical pulse is injected into the second pulse laser, the second optical pulse is injected into the third pulse laser, so that the second pulse laser and the third pulse laser emit pulses with the same frequency, the manufactured reference light and signal light have good spectral quality, and a high extinction ratio pulse is not required to be obtained in a mode of cascading AM, thereby reducing the difficulty in obtaining pulse modulation, and saving at least more than two high-performance AMs of a chopping scheme, the cost of pulse modulation is greatly reduced.

Description

Pulse modulation device, transmitter, system and method for CV-QKD
Technical Field
The application relates to the technical field of quantum communication, in particular to a pulse modulation device, a transmitter, a system and a method for CV-QKD.
Background
Quantum Key Distribution (QKD) is the design of cryptographic schemes using the quantum properties of substances (e.g., photons), the security of which is based on the fundamental principles of quantum mechanics rather than the complexity of mathematical computations. The QKD discovers the existence of eavesdropping by utilizing a Heisenberg uncertainty principle and an unknown quantum state unclonable principle, and theoretically ensures the unconditional security of information.
The QKD can be divided into discrete variable quantum key distribution (DV-QKD) and continuous variable quantum key distribution (CV-QKD) according to the difference of modulation means and detection means. As shown in fig. 1, in a conventional pulse modulation device for CV-QKD, a laser outputs continuous light, the continuous light is chopped into pulse light after passing through at least two intensity modulators (AM), one path of the pulse light is input to a long arm of an unequal arm interferometer as reference light and the other path of the pulse light is input to a short arm of the unequal arm interferometer as signal light after passing through a 99:1 Beam Splitter (BS), and the signal light is modulated by the intensity modulator (AM), a Phase Modulator (PM), an optical attenuator (VOA) and the like so that the intensity and the phase of the signal light meet requirements, and then the pulse modulation is completed by combining the signal light with the reference light through a polarization beam combiner (PBS).
Usually only 10 because of the very weak intensity of the signal light0~1Intensity level, and reference lightIs very high, typically at 108The intensity level is high, so in order to meet the requirement of a continuous variable quantum key distribution system on the extinction ratio of 80dB to the pulsed light, at least two-stage intensity modulation cascade modulation (the extinction ratio of a common intensity modulator is not more than 30dB at present) is usually adopted in the continuous variable quantum key distribution system, and the optical pulse with weak extinction generated by the first AM is modulated for the second time, so that the part with light is stronger, and the part without light is weaker, thereby meeting the requirement of pulse production.
However, as shown in fig. 2, when the extinction ratio is near the highest extinction ratio, the extinction ratio changes greatly due to the small voltage fluctuation, and the existing device needs at least two AM cascades to complete the extinction ratio of 80dB, which requires extremely high stability of AM control, resulting in poor spectral quality of the pulsed light obtained by the pulse modulation device in the prior art.
Disclosure of Invention
The application provides a pulse modulation device, a transmitter, a system and a method for CV-QKD, which aim to solve the problem that the pulse modulation device in the prior art is poor in spectral quality of pulse light.
The application provides a pulse modulation device for CV-QKD in a first aspect, including first pulse laser, second pulse laser, third pulse laser, optical beam splitter, first optical circulator, second optical circulator, optical modulation module and polarization beam combiner: the optical beam splitter is used for splitting the pulse light output by the first pulse laser into a first light pulse and a second light pulse, wherein the first light pulse is injected into the second pulse laser through the first optical circulator and is used for generating reference light, and the second light pulse is injected into the third pulse laser through the second optical circulator and is used for generating signal light; the optical modulation module is used for adjusting the intensity and the phase of the signal light, so that each bit of information of the signal light comprises quantum light and feedback light, the quantum light is weak light and is used for quantum key distribution, and the feedback light is strong light and is used for phase feedback, and the optical modulation module specifically comprises the following components: the light modulation module comprises a first intensity modulator, a phase modulator and a second intensity modulator which are sequentially connected; the first intensity modulator and the phase modulator both adopt high-frequency modulators, and the second intensity modulator adopts a low-frequency modulator; the first intensity modulator is used for adjusting a section of continuous light pulse in each bit of information of the signal light to be within a first threshold range to obtain quantum light, adjusting the rest section of continuous light pulse to be within a second threshold range to obtain feedback light, and the intensity of each pulse of the quantum light is random; the phase modulator is used for adjusting the phase among the pulses of the quantum light to be random and adjusting the phase of each pulse of the feedback light to be one of 0, pi/2, pi and 3 pi/2; the second intensity modulator is used for adjusting quantum light to single photon intensity, and the polarization beam combiner is used for combining the reference light and the signal light to complete pulse modulation.
Preferably, the phase modulator is configured to adjust the phase between the pulses of the quantum light to be random, adjust the phase of the first pulse of the feedback light to be 0, adjust the phase of the second pulse of the feedback light to be pi/2, adjust the phase of the third pulse of the feedback light to be pi, adjust the phase of the fourth pulse of the feedback light to be 3 pi/2, adjust the phase of the fifth pulse of the feedback light to be 0, and so on, adjust the phases of the pulses in the feedback light in sequence according to the periods of 0, pi/2, pi, and 3 pi/2.
Preferably, the first intensity modulator is further configured to adjust a ratio of the quantum light and the feedback light according to the phase feedback result.
Preferably, the first and second intensity modulators are both non-modulating to the feedback light.
The second aspect of the present application provides a method for pulse modulation of CV-QKD, which is applied to any one of the pulse modulation devices for CV-QKD mentioned above, and includes the following specific steps: splitting the pulse light output by the first pulse laser to obtain a first light pulse and a second light pulse; injecting the first light pulse into the second pulse laser to generate reference light; injecting the second light pulse to the third pulse laser for generating signal light; adjusting the intensity and phase of the signal light to make each bit of information of the signal light contain quantum light and feedback light, and the method specifically comprises the following steps: adjusting a section of continuous light pulse in each bit of information of the signal light to be within a first threshold range to obtain quantum light, adjusting the rest section of continuous light pulse to be within a second threshold range to obtain feedback light, wherein the intensity of each pulse of the quantum light is random; adjusting the phase among the pulses of the quantum light to be random, adjusting the phase of the first pulse of the feedback light to be 0, adjusting the phase of the second pulse of the feedback light to be pi/2, adjusting the phase of the third pulse of the feedback light to be pi, adjusting the phase of the fourth pulse of the feedback light to be 3 pi/2, adjusting the phase of the fifth pulse of the feedback light to be 0, and adjusting the phases of the pulses in the feedback light according to the periods of 0, pi/2, pi and 3 pi/2 in sequence by the analogy; the quantum light is weak light and is used for quantum key distribution, and the feedback light is strong light and is used for phase feedback; and combining the reference light and the signal light to complete pulse modulation.
Preferably, the ratio of the quantum light to the feedback light in each bit of information of the signal light is adjusted according to the phase feedback result.
A third aspect of the present application provides a quantum key transmitter, characterized in that: including the pulse modulation arrangement for CV-QKD described above.
A fourth aspect of the present application provides a CV-QKD system comprising a transmitter and a receiver, wherein the receiver employs the quantum key transmitter described above.
The application provides a pulse modulation device, a transmitter, a system and a method for CV-QKD, which have the following advantages compared with the prior art:
1. the pulse modulation device for CV-QKD comprises a first pulse laser, a second pulse laser, a third pulse laser, an optical beam splitter, a first optical circulator, a second optical circulator, an optical modulation module and a polarization beam combiner, wherein the optical beam splitter is used for dividing pulse light output by the first pulse laser into first optical pulse and second optical pulse, the first optical pulse is injected into the second pulse laser through the first optical circulator and used for generating reference light, and the second optical pulse is injected into the third pulse laser through the second optical circulator and used for generating signal light; therefore, the pulse emitted by the first pulse laser is respectively injected into the second pulse laser and the third pulse laser, so that the second pulse laser and the third pulse laser emit pulses with the same frequency and the same phase, the manufactured reference light and signal light have good spectral quality, and the pulse with high extinction ratio is not required to be obtained in a cascaded AM mode, thereby reducing the difficulty of obtaining pulse modulation, saving more than two high-performance AMs of a chopping scheme, and greatly reducing the cost of pulse modulation.
2. According to the device characteristics of the laser, the laser can bring the polarization isolation degree of at least 25dB in an injection locking mode, and the PBS at least has the polarization isolation degree of 30dB, so that the polarization isolation degree of 55dB can be achieved by the laser, and the polarization isolation degree of only 30dB is achieved in the prior art, so that the polarization isolation degree of the laser is higher than that of the prior art.
3. In the prior art, a light source is additionally added to emit feedback light, and feedback voltage is generated by measuring the feedback light and is transmitted to a phase modulator on an intrinsic light path, so that phase compensation is realized. And this application passes through the intensity and the phase place of signal light are adjusted to the module of adjusting luminance for contain the quantum light that is used for quantum key distribution in every bit information of signal light and be used for the feedback light of phase place feedback, consequently this application need not add phase place feedback light source again, and the compensation precision is high.
4. In the prior art, a 99:1 BS is usually adopted after chopping, so that the intensity ratio of the obtained quantum light to the reference light is fixed. The intensity ratio of the quantum light to the reference light can be dynamically adjusted according to requirements through the light modulation module.
Drawings
In order to more clearly explain the technical solution of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious to those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic diagram of a pulse modulation apparatus in the prior art;
FIG. 2 is a graph of voltage versus intensity for an intensity modulator;
FIG. 3 is a schematic structural diagram of a pulse modulation apparatus according to the present application;
FIG. 4 is a schematic diagram of another pulse modulation apparatus according to the present application;
FIG. 5 is a schematic diagram of a pulse structure of a signal light according to the present application;
fig. 6 is a schematic structural diagram of a quantum key distribution system according to the present application.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present application more comprehensible, the present application is described in further detail with reference to the accompanying drawings and the detailed description. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.
A first aspect of the application provides a CV-QKD system comprising a transmitter and a receiver, wherein the receiver employs the quantum key transmitter of claim 9. A pulse modulation device for CV-QKD, the structure of which can refer to the schematic diagram shown in FIG. 3, comprises a first pulse laser 1, a second pulse laser 2, a third pulse laser 3, an optical beam splitter 4, a first optical circulator 5, a second optical circulator 6, an optical modulation module 7 and a polarization beam combiner 8: the optical beam splitter 4 is configured to split the pulse light output by the first pulse laser 1 into a first optical pulse and a second optical pulse, where the optical beam splitter 4 may employ a beam splitter BS or a polarization beam splitter PBS, and the optical beam splitter 4 herein may employ a conventional BS of 50:50 or a BS of 99:1, and may also be applicable to BSs of other specifications as long as the split optical pulses can excite the second pulse laser and the third pulse laser to emit pulses with the same frequency and phase.
The first optical pulse is injected into the second pulse laser 2 through the first optical circulator 5 to generate reference light, the first optical circulator 5 has at least three ports, a port i of the first optical circulator 5 is connected to one output end of the optical beam splitter 4, the first optical pulse input into the port i of the first optical circulator 5 can be output from a port ii of the first optical circulator 5, the port ii of the first optical circulator 5 is connected to the second optical pulse laser 2, so that the first optical pulse is injected into the second optical pulse laser 2 to excite the second optical pulse laser 2 to obtain reference light, the reference light emitted by the second optical pulse laser 2 is input to the port ii of the first optical circulator 5, and the reference light is output from a port iii of the first optical circulator 5.
The second optical pulse is injected into the third pulse laser 3 through the second optical circulator 6 to generate signal light, the second optical circulator 6 has at least three ports, a port i of the second optical circulator 6 is connected to another output end of the optical beam splitter 4, the second optical pulse input into the port i of the second optical circulator 6 can be output from a port ii of the second optical circulator 6, a port ii of the second optical circulator 6 is connected to the third optical pulse laser 3, so that the second optical pulse is injected into the third optical pulse laser 3 to excite the third optical pulse laser 3 to obtain signal light, the signal light emitted by the third optical pulse laser 3 is input to the port ii of the second optical circulator 6, and the reference light is output from a port iii of the second optical circulator 6.
Therefore, the pulses emitted by the first pulse laser 1 are respectively injected into the second pulse laser 2 and the third pulse laser 3, so that the second pulse laser 2 and the third pulse laser 3 emit pulses with the same frequency and phase, the manufactured reference light and signal light have good spectral quality, and the pulses with high extinction ratio are not required to be obtained in a cascaded AM mode, so that the difficulty in obtaining pulse modulation is reduced, at least more than two high-performance AMs of a chopping scheme are saved, and the cost of pulse modulation is greatly reduced.
The light modulation module 7 is configured to adjust intensity and phase of the signal light, so that each bit of information of the signal light includes a quantum light and a feedback light in a certain ratio. In the field of communication, information is generally transmitted in units of bits, each bit of information comprises a certain number of information frames, so that the light modulation module 7 modulates each bit of information into information frames with two intensities, each frame intensity of a first section of information frame in each bit of information is adjusted to be within a first threshold range, each frame intensity of a second section of information frame in each bit of information is adjusted to be within a second threshold range, the intensity of the first section of information frame is weaker than that of the second section of information frame, the first section of information frame is called quantum light, and the second section of information frame is called feedback light. Besides, if the quantum light is 101Intensity level/pulse, feedback light is at least 104The feedback light is strong light and the quantum light is weak light compared with the quantum light. In addition, the optical modulation module 7 is controlled to modulate the phase of the first segment of information frame according to the requirement of quantum key distribution, so that quantum light energy is used for quantum key distribution, and the optical modulation module 7 is controlled to modulate the phase of the first segment of information frame according to the requirement of quantum key distribution, so that feedback light energy is used for phase feedback. Therefore this application passes through the intensity and the phase place of signal light are adjusted to the module of adjusting luminance for contain the quantum light that is used for quantum key distribution in every bit information of signal light and be used for the feedback light of phase place feedback, consequently this application need not add phase place feedback light source again, and the compensation precision is high.
And the polarization beam combiner 8 is used for combining the reference light and the signal light to complete pulse modulation. According to the device characteristics of the laser, the laser can bring the polarization isolation degree of at least 25dB in an injection locking mode, and the PBS at least has the polarization isolation degree of 30dB, so that the polarization isolation degree of 55dB can be achieved by the laser, and the polarization isolation degree of only 30dB is achieved in the prior art, so that the polarization isolation degree of the laser is higher than that of the prior art.
A specific structure of the light modulation module 7 can be seen from the schematic diagram shown in fig. 4, where the light modulation module 7 includes a first intensity modulator 701 and a phase modulator connected in sequenceA controller 702 and a second intensity modulator 703; the first intensity modulator 701 and the phase modulator 702 both use high-frequency modulators, and the second intensity modulator 703 uses low-frequency modulators; the first intensity modulator 701 is configured to adjust a segment of continuous optical pulses in each bit of information of the signal light to be within a first threshold range to obtain quantum light, adjust the remaining segment of continuous optical pulses to be within a second threshold range to obtain feedback light, and the intensity of each pulse of the quantum light is random, as shown in a schematic diagram shown in fig. 5, if the quantum light is 10, the quantum light is emitted from the light source1Intensity level/pulse, feedback light is at least 104Above the intensity level/pulse, even the first and second intensity modulators 701, 703 are not tuned to the feedback light, so that the feedback light has at least 10 relative to the quantum light8The feedback light is strong light and the quantum light is weak light, besides, the proportion of the quantum light and the feedback light can be adjusted in real time according to a phase feedback result, and the change of the phase of the light is caused by the change of the phase of the light along with the change of the external environment, such as the change of temperature, vibration, the refractive index of an optical fiber and the like, so that the proportion of the quantum light and the feedback light can be dynamically adjusted according to the phase feedback result, for example, when the phase fluctuates greatly, the proportion of the quantum light is controlled to be smaller and the proportion of the feedback light is larger; if the phase change is stable, the proportion of the control quantum light is larger and the proportion of the feedback light is smaller, so that a better code forming effect or a feedback effect is obtained, and the system has good applicability.
The phase modulator 702 is configured to adjust the phase between the pulses of the quantum light to be random, and adjust the phase of each pulse of the feedback light to be one of 0, pi/2, pi, and 3 pi/2; preferably, the phase modulator 702 is configured to adjust the phase between the pulses of the quantum light to be random, that is, the phase of the first pulse of the feedback light is adjusted to be 0, the phase of the second pulse of the feedback light is adjusted to be pi/2, the phase of the third pulse of the feedback light is adjusted to be pi, the phase of the fourth pulse of the feedback light is adjusted to be 3 pi/2, the phase of the fifth pulse of the feedback light is adjusted to be 0, and so on, the mode of periodically adjusting the pulse phase of the feedback light is simple and easy to operate, the phase compensation precision is high, and the phase compensation effect is good.
The second intensity modulator 703 is configured to adjust the quantum light to the single photon intensity. Because each bit of information of the signal light comprises a section of quantum light and a section of feedback light, compared with the prior art that the signal light only comprises the quantum light, the quantum light which is contained in each bit of information of the signal light plus the feedback light is the same as the quantum light which is contained in each bit of information in the prior art, and therefore the quantum light or the feedback light contains a small amount of information in each bit compared with the prior art, the modulation frequency is low, and the requirement on the device is low. In addition, since quantum light is usually single photon intensity, this means that most quantum light cannot be detected, and only one of one thousand pulses can be detected, so that the feedback light is incorporated into a part of the feedback light, and the detection efficiency of the quantum light is not greatly affected, and the ratio of the quantum light to the feedback light is about 9:1, so that the feedback light can be incorporated into the signal light on the premise of hardly reducing the detection efficiency of the quantum light.
A method for pulse modulation of CV-QKD, which is applied to any one of the above pulse modulation devices for CV-QKD, comprises the following steps: splitting the pulse light output by the first pulse laser to obtain a first light pulse and a second light pulse; injecting the first light pulse into the second pulse laser to generate reference light; injecting the second light pulse to the third pulse laser for generating signal light; adjusting the intensity and the phase of the signal light to enable each bit of information of the signal light to contain quantum light and feedback light in a certain proportion, wherein the quantum light is weak light and is used for quantum key distribution, and the feedback light is strong light and is used for phase feedback; and combining the reference light and the signal light to complete pulse modulation.
Preferably, the adjusting the intensity and the phase of the signal light so that each bit of information of the signal light includes a quantum light and a feedback light in a certain ratio, the quantum light is weak light and is used for quantum key distribution, and the feedback light is strong light and is used for phase feedback includes:
adjusting a section of continuous light pulse in each bit of information of the signal light to be within a first threshold range to obtain quantum light, adjusting the rest section of continuous light pulse to be within a second threshold range to obtain feedback light, wherein the intensity of each pulse of the quantum light is random;
adjusting the phase among the pulses of the quantum light to be random, adjusting the phase of the first pulse of the feedback light to be 0, adjusting the phase of the second pulse of the feedback light to be pi/2, adjusting the phase of the third pulse of the feedback light to be pi, adjusting the phase of the fourth pulse of the feedback light to be 3 pi/2, adjusting the phase of the fifth pulse of the feedback light to be 0, and adjusting the phases of the pulses in the feedback light according to the periods of 0, pi/2, pi and 3 pi/2 in sequence by the analogy; the quantum light is weak light and is used for quantum key distribution, and the feedback light is strong light and is used for phase feedback.
Preferably, the ratio of the quantum light to the feedback light in each bit of information of the signal light is adjusted according to the phase feedback result.
A quantum key transmitter comprising the pulse modulation device for CV-QKD of any of the above.
A CV-QKD system includes a transmitter and a receiver, and the specific structure of the receiver is shown in fig. 6, the receiver in the CV-QKD system adopts the above-mentioned quantum key transmitter, the receiver generates a feedback signal by measuring the feedback light and transmits the feedback signal to the transmitter, and the transmitter controls an optical modulation module 7 according to the feedback signal, so as to achieve the purpose of adjusting the intensity and phase of the signal light according to the feedback signal.
The present application has been described in detail with reference to specific embodiments and illustrative examples, but the description is not intended to limit the application. Those skilled in the art will appreciate that various equivalent substitutions, modifications or improvements may be made to the presently disclosed embodiments and implementations thereof without departing from the spirit and scope of the present disclosure, and these fall within the scope of the present disclosure. The protection scope of this application is subject to the appended claims.

Claims (6)

1. The pulse modulation device for CV-QKD is characterized by comprising a first pulse laser (1), a second pulse laser (2), a third pulse laser (3), an optical beam splitter (4), a first optical circulator (5), a second optical circulator (6), an optical modulation module (7) and a polarization beam combiner (8):
the optical beam splitter (4) is used for splitting the pulse light output by the first pulse laser (1) into a first light pulse and a second light pulse, wherein the first light pulse is injected to the second pulse laser (2) through the first optical circulator (5) and is used for generating reference light, and the second light pulse is injected to the third pulse laser (3) through the second optical circulator (6) and is used for generating signal light;
the optical modulation module (7) is configured to adjust intensity and phase of signal light, so that each bit of information of the signal light includes quantum light and feedback light, the quantum light is weak light and is used for quantum key distribution, and the feedback light is strong light and is used for phase feedback, specifically as follows:
the light modulation module (7) comprises a first intensity modulator (701), a phase modulator (702) and a second intensity modulator (703) which are connected in sequence;
the first intensity modulator (701) and the phase modulator (702) both adopt high-frequency modulators, and the second intensity modulator (703) adopts a low-frequency modulator;
the first intensity modulator (701) is used for adjusting a section of continuous light pulses in each bit of information of the signal light to be within a first threshold range to obtain quantum light, adjusting the rest section of continuous light pulses to be within a second threshold range to obtain feedback light, and the intensity of each pulse of the quantum light is random;
the phase modulator (702) is used for adjusting the phase among the pulses of the quantum light to be random and adjusting the phase of each pulse of the feedback light to be one of 0, pi/2, pi and 3 pi/2;
the second intensity modulator (703) is used for adjusting the quantum light to single-photon intensity;
and the polarization beam combiner (8) is used for combining the reference light and the signal light to complete pulse modulation.
2. The pulse modulation device for CV-QKD of claim 1, wherein said phase modulator (702) is configured to adjust the phase between the pulses of the quantum light to be random, to adjust the phase of the first pulse of the feedback light to be 0, to adjust the phase of the second pulse of the feedback light to be pi/2, to adjust the phase of the third pulse of the feedback light to be pi, to adjust the phase of the fourth pulse of the feedback light to be 3 pi/2, to adjust the phase of the fifth pulse of the feedback light to be 0, and so on to adjust the phases of the pulses in the feedback light in sequence by 0, pi/2, pi, 3 pi/2 periods.
3. The pulse modulation device for CV-QKD according to any of claims 1-2, characterized in that the first intensity modulator (701) is further configured to adjust the ratio of quantum light and feedback light according to the phase feedback result.
4. The pulse modulation device according to claim 3, wherein the first intensity modulator (701) and the second intensity modulator (703) are both unregulated for feedback light.
5. A method for pulse modulation of CV-QKD, the method being applied to the pulse modulation apparatus for CV-QKD as claimed in any one of claims 1 to 4, and comprising the steps of:
splitting the pulse light output by the first pulse laser to obtain a first light pulse and a second light pulse;
injecting the first light pulse into the second pulse laser to generate reference light;
injecting the second light pulse to the third pulse laser for generating signal light;
the method comprises the following steps of adjusting the intensity and the phase of signal light to enable each bit of information of the signal light to contain quantum light and feedback light in a certain proportion, and specifically comprises the following steps:
adjusting a section of continuous light pulse in each bit of information of the signal light to be within a first threshold range to obtain quantum light, adjusting the rest section of continuous light pulse to be within a second threshold range to obtain feedback light, wherein the intensity of each pulse of the quantum light is random;
adjusting the phase among the pulses of the quantum light to be random, adjusting the phase of the first pulse of the feedback light to be 0, adjusting the phase of the second pulse of the feedback light to be pi/2, adjusting the phase of the third pulse of the feedback light to be pi, adjusting the phase of the fourth pulse of the feedback light to be 3 pi/2, adjusting the phase of the fifth pulse of the feedback light to be 0, and adjusting the phases of the pulses in the feedback light according to the periods of 0, pi/2, pi and 3 pi/2 in sequence by the analogy;
the quantum light is weak light and is used for quantum key distribution, and the feedback light is strong light and is used for phase feedback;
and combining the reference light and the signal light to complete pulse modulation.
6. The method for pulse modulation of CV-QKD as defined in claim 5, characterized in that the ratio of quantum light and feedback light in each bit of information of the signal light is adjusted according to the phase feedback result.
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