CN113162757A - Quantum key distribution system and feedback correction system thereof - Google Patents
Quantum key distribution system and feedback correction system thereof Download PDFInfo
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- CN113162757A CN113162757A CN202010076339.5A CN202010076339A CN113162757A CN 113162757 A CN113162757 A CN 113162757A CN 202010076339 A CN202010076339 A CN 202010076339A CN 113162757 A CN113162757 A CN 113162757A
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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
- H04L9/0858—Details about key distillation or coding, e.g. reconciliation, error correction, privacy amplification, polarisation coding or phase coding
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- H—ELECTRICITY
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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
- H04B10/50—Transmitters
- H04B10/501—Structural aspects
- H04B10/503—Laser transmitters
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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
- H04B10/50—Transmitters
- H04B10/516—Details of coding or modulation
- H04B10/548—Phase or frequency modulation
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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
- H04B10/50—Transmitters
- H04B10/572—Wavelength control
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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
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Abstract
The invention provides a quantum key distribution system and a feedback correction system thereof.A first beam splitter divides signal light emitted by a first laser into first signal light and second signal light with different light paths; the molecular absorption cell absorbs the first signal light; the first detector detects the actual transmission light power of the first signal light absorbed by the molecular absorption cell; the first control module compares the actual transmission light power ratio of the first signal light with the standard transmission light power ratio of the first signal light to obtain a first power drift amount, obtains a first correction value according to the first power drift amount and the corresponding relation between the transmission light power ratio obtained in advance and the wavelength correction parameter of the laser, and performs wavelength correction on the first laser according to the first correction value, so that the wavelength correction can be performed by adopting the first signal light, and the encoding and distribution of the quantum key are performed by adopting the second signal light, thereby solving the problem of higher cost of wavelength feedback equipment in the existing wavelength feedback loop.
Description
Technical Field
The invention relates to the technical field of quantum communication, in particular to a quantum key distribution system and a feedback correction system thereof.
Background
After the quantum key distribution protocol is combined with a decoy state quantum key distribution protocol, the measuring equipment based on time phase coding has no relation with a quantum key distribution system (MDIQKD), has the advantages of a time phase coding scheme, can close loopholes of a sending end and a measuring end, and has higher safety.
An unequal arm interferometer is generally adopted to generate two pulses with a fixed time difference, and the two pulses are subjected to intensity and phase modulation respectively to realize time phase encoding of the quantum key. The corresponding coincidence count is obtained by measuring the interference measurement results of two front and back pulses of two independent lasers of a sending end (Alice end and Bob end) in one period at a receiving end (Charlie end), that is, the measurement results for basis vector comparison can be obtained by carrying out Bell state measurement at the Charlie end.
Because the contrast of the front and back two corresponding pulse interferences of the Alice end and the Bob end directly affects the final bit error rate, in order to obtain a higher interference contrast, a wavelength feedback loop and a phase feedback loop need to be added to the quantum key distribution system, so as to ensure that the wavelengths of the independent lasers of the Alice end and the Bob end and the adopted phase reference systems are consistent. In the prior art, a spectrometer or a wavelength meter is adopted to measure the wavelengths input by an Alice end and a Bob end at a Charlie end to obtain the wavelength difference between the Alice end and the Bob end, and an unequal arm interferometer which is the same as the two sending ends is used at the Charlie end and extra phase correction light is needed to correct the phase difference between the optical pulses of the two sending ends. However, the arrangement of a spectrometer, a wavelength meter, a phase correction interferometer, a laser, and other devices at the receiving end leads to high application cost, which is not favorable for the practicality and convenient networking requirements of the quantum key distribution system.
Disclosure of Invention
In view of this, the present invention provides a quantum key distribution system and a feedback correction system thereof, so as to solve the problem of high cost of wavelength feedback equipment in the existing wavelength feedback loop, and simultaneously, phase consistency and stability between independent interferometers can be ensured through phase feedback.
In order to achieve the purpose, the invention provides the following technical scheme:
a feedback correction system comprises a first beam splitter, a molecular absorption cell, a first detector and a first control module;
the first beam splitter is used for splitting the signal light emitted by the first laser into first signal light and second signal light with different optical paths and transmitting the first signal light to the molecular absorption cell;
the molecular absorption cell is used for absorbing the first signal light;
the first detector is used for detecting the actual transmission light power of the first signal light absorbed by the molecular absorption cell;
the first control module is used for comparing the actual transmission light power of the first signal light with the actual transmission light power of a reference point to obtain an actual transmission light power ratio of the first signal light, comparing the actual transmission light power ratio of the first signal light with a standard transmission light power ratio of the first signal light to obtain a first power drift amount, obtaining a first correction amount according to the first power drift amount and a corresponding relation between the transmission light power ratio obtained in advance and a laser wavelength correction parameter, and performing wavelength correction on the first laser according to the first correction amount.
Optionally, the system further comprises a second laser, a second beam splitter, a first circulator, a second detector and a second control module, wherein the second laser is a continuous light laser;
the second beam splitter is used for splitting the reference light emitted by the second laser into first reference light and second reference light with different optical paths and transmitting the first reference light to the first circulator;
the first circulator is used for transmitting the first reference light to the molecular absorption cell so that the molecular absorption cell absorbs the first reference light; the first circulator is further used for transmitting the absorbed first signal light emitted by the molecular absorption cell to the first detector;
the second circulator is further used for transmitting the absorbed first reference light emitted by the molecular absorption cell to the second detector, and transmitting the first signal light emitted by the first beam splitter to the molecular absorption cell;
the second detector is used for detecting the actual transmission light power of the first reference light after being absorbed by the molecular absorption cell;
the second control module is configured to compare the actual transmitted light power of the first reference light with the actual transmitted light power of a reference point to obtain an actual transmitted light power ratio of the first reference light, compare the actual transmitted light power ratio of the first reference light with a standard transmitted light power ratio of the first reference light to obtain the second power drift amount, obtain a second correction amount according to the second power drift amount and a correspondence between a transmission light power ratio obtained in advance and a laser wavelength correction parameter, and perform wavelength correction on the second laser according to the second correction amount.
Optionally, an interferometer and a third detector are further included;
the second beam splitter is further configured to transmit the second reference light to the interferometer;
the interferometer is used for generating two continuous lights with phase difference according to the second reference light and obtaining a first interference light of the two continuous lights after interference;
the third detector is used for detecting the actual optical power of the first interference light;
the second control module is further configured to compare the actual optical power of the first interference light with a second standard optical power to obtain a third power drift amount, obtain a first voltage correction amount according to the third power drift amount and a correspondence between the optical power obtained in advance and an interferometer phase shifter driving voltage, and transmit the first voltage correction amount to the interferometer phase shifter, so that the interferometer corrects the phase difference according to the first voltage correction amount.
Optionally, the first beam splitter is further configured to transmit the second signal light to the interferometer;
the interferometer is also configured to generate two pulses having a fixed time difference from the second signal light to time phase encode the two pulses.
Optionally, the system further comprises an interferometer, a third circulator, a third detector and a fourth detector;
the interferometer is used for generating two beams of continuous light with phase difference according to the second reference light and obtaining first interference light and second interference light of the two beams of continuous light after interference;
the third detector is used for detecting the actual optical power of the first interference light;
the third circulator is used for transmitting the second interference light to the fourth detector;
the fourth detector is used for detecting the actual optical power of the second interference light;
the second control module is configured to compare an actual optical power output by the third detector with an actual optical power output by the fourth detector to obtain a first actual optical power ratio, compare the first actual optical power ratio with the first optical power ratio to obtain a first power ratio drift amount, obtain a second voltage correction amount according to a correspondence between the first power ratio drift amount and a previously obtained optical power ratio and an interferometer driving voltage, and transmit the second voltage correction amount to the interferometer, so that the interferometer corrects the phase difference according to the second voltage correction amount.
Optionally, the first beam splitter is further configured to transmit the second signal light to the third circulator;
the third circulator is also used for transmitting the second signal light to the interferometer;
the interferometer is also configured to generate two pulses having a fixed time difference from the second signal light to time phase encode the two pulses.
Optionally, a fourth circulator and a third laser are further included;
the fourth circulator is positioned on an optical path between the first beam splitter and the interferometer and is used for transmitting the second signal light emitted by the first beam splitter into the third laser so as to perform injection locking on the light emitted by the third laser;
the fourth circulator is further used for transmitting the light emitted by the third laser to the interferometer, so that the interferometer generates two pulses with a fixed time difference according to the light emitted by the third laser, and the two pulses are subjected to time phase coding.
Optionally, a third beam splitter and a fifth detector are further included;
the third beam splitter is located on an optical path between the first laser and the first beam splitter, and is configured to transmit a part of light rays in the signal light emitted by the first laser to the fifth detector, and transmit the other part of light rays in the signal light emitted by the first laser to the first beam splitter, so that the first beam splitter splits the other part of light rays into the first signal light and the second signal light;
the fifth detector is used for detecting the actual optical power of part of the light rays in the signal light;
the first control module is further configured to compare the actual transmitted light power output by the first detector with the actual light power output by the fifth detector to obtain a second actual light power ratio, compare the second actual light power ratio with the second light power ratio to obtain a second power ratio drift amount, obtain a third correction amount according to the second power ratio drift amount and a correspondence between the light power ratio obtained in advance and a laser wavelength correction parameter, and perform wavelength correction on the first laser according to the third correction amount.
Optionally, a fourth beam splitter and a sixth detector are further included;
the fourth beam splitter is located on a light path between the second laser and the second beam splitter, and is configured to transmit a part of light rays in the reference light emitted by the second laser to the sixth detector, and transmit the other part of light rays in the reference light emitted by the second laser to the second beam splitter, so that the second beam splitter splits the other part of light rays into the first reference light and the second reference light;
the sixth detector is used for detecting the actual optical power of part of the light rays in the signal light;
the second control module is further configured to compare the actual transmitted light power output by the second detector with the actual light power output by the sixth detector to obtain a third actual light power ratio, compare the third actual light power ratio with the third light power ratio to obtain a third power ratio drift amount, obtain a fourth correction amount according to the third power ratio drift amount and a correspondence between the light power ratio obtained in advance and a laser wavelength correction parameter, and perform wavelength correction on the second laser according to the fourth correction amount.
A quantum key distribution system, comprising:
at least two sending ends and one receiving end;
the transmitting end comprises a first laser and a feedback correction system;
the feedback correction system is as described in any one of the above.
Optionally, the receiving end is further configured to adjust a static difference of the molecular absorption spectrum line frequencies of the molecular absorption cells of the two transmitting ends according to an interference result of the second signal light transmitted by the two transmitting ends.
Compared with the prior art, the technical scheme provided by the invention has the following advantages:
according to the quantum key distribution system and the feedback correction system thereof provided by the invention, the signal light emitted by the first laser is divided into the first signal light and the second signal light with different light paths through the first beam splitter, the wavelength of the first laser is corrected through the molecular absorption pool, the first detector and the first control module according to the first power drift amount of the first signal light, the corresponding relation between the transmission light power ratio and the wavelength correction parameter of the laser, and the like, and meanwhile, the quantum key can be coded and distributed by adopting the second signal light, so that the problem of higher cost of wavelength feedback equipment in the existing wavelength feedback loop is solved, and meanwhile, the phase consistency and stability among independent interferometers can be ensured through phase feedback.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a feedback correction system according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a first reference curve provided by an embodiment of the present invention;
FIG. 3 is a schematic structural diagram of another feedback correction system according to an embodiment of the present invention;
FIG. 4 is a schematic structural diagram of another feedback correction system according to an embodiment of the present invention;
FIG. 5 is a schematic structural diagram of another feedback correction system according to an embodiment of the present invention;
FIG. 6 is a schematic structural diagram of another feedback correction system according to an embodiment of the present invention;
FIG. 7 is a schematic structural diagram of another feedback correction system according to an embodiment of the present invention;
fig. 8 is a schematic structural diagram of a quantum key distribution system according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment of the invention provides a feedback correction system, which is applied to a measuring equipment irrelevant quantum key distribution system based on time phase coding, and more particularly, is applied to wavelength and phase correction of the measuring equipment irrelevant quantum key distribution system based on time phase coding.
As shown in fig. 1, the feedback correction system includes a first beam splitter 11, a molecular absorption cell 12, a first detector 13, and a first control module (not shown), which is a control module of the first laser 10.
The first beam splitter 11 is configured to split the signal light emitted from the first laser 10 into first signal light and second signal light with different optical paths, and transmit the first signal light to the molecular absorption cell 12. The molecular absorption cell 12 is configured to absorb the first signal light. The first detector 13 is used for detecting the actual transmitted light power of the first signal light absorbed by the molecular absorption cell 12. The first control module is configured to compare the actual transmission light power of the first signal light with the actual transmission light power of the reference point to obtain a ratio, where the ratio is the actual transmission light power ratio of the first signal light, compare the actual transmission light power ratio of the first signal light with the standard transmission light power ratio of the first signal light to obtain a first power drift amount, obtain a first correction amount according to the first power drift amount and a correspondence between the transmission light power ratio obtained in advance and a laser wavelength correction parameter, and perform wavelength correction on the first laser 10 according to the first correction amount.
Wherein, as shown in fig. 2, the actual transmitted light power of the reference point may be the first maximum actual transmitted light power in the wavelength increasing direction of the central wavelength of the molecular absorption line of the desired molecular absorption cell 12. The laser wavelength correction parameters include the driving temperature, the driving current, and the like of the laser, that is, in the embodiment of the present invention, after the first power drift amount is obtained, a first temperature correction amount may be obtained according to the first power drift amount and a correspondence between a transmission light power ratio obtained in advance and the laser driving temperature, and the wavelength of the first laser 10 may be corrected according to the first temperature correction amount. In the embodiments of the present invention, the laser wavelength calibration parameter is only used as an example of the laser driving temperature, and the present invention is not limited thereto.
Based on the above, the feedback correction system of the invention can perform feedback correction of wavelength through the first signal light, and perform coding and distribution of quantum key through the second signal light, thereby solving the problem of high cost of wavelength feedback equipment in the existing wavelength feedback loop.
Alternatively, the molecular absorption cell 12 is a hydrocyanic acid (HCN) molecular absorption cell, that is, an absorption cell of hydrocyanic acid molecules with a certain pressure. Since hydrocyanic acid molecules have a plurality of stable absorption spectral lines for the laser with 1550nm wave band, the laser light power at the specific frequency of 1550nm wave band after being absorbed by the molecular absorption cell 12 is attenuated. If the wavelength of the laser is 1550.5154nm, the optical power absorbed by the molecular absorption cell 12, i.e., the transmitted optical power, is attenuated, and the ratio of the attenuated optical power is G1; when the wavelength of the laser drifts and becomes 1550.5156nm, the molecular absorption cell 12 absorbs light with a wavelength of 1550.5156nm, that is, the optical power absorbed by the molecular absorption cell 12 is attenuated less, the ratio of the attenuated optical power is G2, and G2 is greater than G1, based on which, the driving temperature T2 corresponding to G2 is obtained according to the corresponding relationship between the transmission optical power and the driving temperature of the laser, then the driving temperature T1 corresponding to T2 and G1 is obtained, or the temperature adjustment quantity or temperature correction quantity δ T is T2-T1, and after the driving temperature of the first laser 10 is adjusted according to the temperature adjustment quantity δ T, the wavelength of the first laser 10 is corrected, that is, the wavelength of the first laser 10 is locked at the position of 1550.5154 nm.
In the embodiment of the present invention, the wavelength of the first laser 10 is first set near the specific molecular absorption lines of the molecular absorption cell 12, and if the central wavelength of one of the molecular absorption lines is 1550.5154nm, the wavelength of the first laser 10 can be set to 1550.515 nm. The wavelength of the first laser 10 can be adjusted by adjusting parameters such as the driving temperature and the driving current of the first laser 10.
Then, the driving temperature of the first laser 10 is set to T0, T1, T2 … Tn, the ratio of the transmitted light power of the laser light absorbed by the molecular absorption cell 12 detected by the first detector 13 to the transmitted light power of the reference point is set to G0, G1, G2 … Gn, n is an integer greater than 1, and a curve of the transmitted light power ratio with the change of the driving temperature of the laser is obtained from T0, T1, T2 … Tn, G0, G1, G2 … Gn. Wherein, the transmitted light power G0 is the optical power ratio of the laser absorbed by the molecular absorption cell 12 at the driving temperature T0, the transmitted light power G1 is the optical power ratio of the laser absorbed by the molecular absorption cell 12 at the driving temperature T1, and so on, the transmitted light power Gn is the optical power ratio of the laser absorbed by the molecular absorption cell 12 at the driving temperature Tn.
And after repeating the steps for a plurality of times, taking the average value of the obtained curves as a first reference curve. And obtaining the corresponding relation between the transmission light power ratio and the laser driving temperature according to the first reference curve.
And then, selecting a point on the first reference curve as a feedback target point, and carrying out feedback and wavelength correction according to the power monitoring characteristics of the point. The two coordinate values of the feedback target point are the ratio of the first standard temperature to the standard transmitted light power of the first signal light, and the power drift amount of the first laser 10 in the detection period, that is, the first power drift amount, can be obtained according to the difference or quotient between the actual transmitted light power ratio detected in real time and the standard transmitted light power ratio of the first signal light, and the first power drift amount represents the wavelength drift amount of the first laser 10.
Then, a first temperature correction value is obtained according to the first power drift amount and the corresponding relationship between the transmission light power ratio obtained in advance and the laser driving temperature, and the first laser 10 is feedback-adjusted according to the first temperature correction value, so that the wavelength of the first laser 10 can be corrected.
In one embodiment, as shown in FIG. 2, a driving temperature value at half height of a molecular absorption peak of a first reference curve is selected as a feedback target point for wavelength feedback. Let the coordinates of the feedback target point be (T1, G1), where the wavelength corresponding to the driving temperature value T1 is the wavelength λ at which the first laser 10 is to be stabilized. Assuming that the ratio of the actual transmitted light power detected by the first detector 13 in real time to the actual transmitted light power of the reference point is G2, after difference is made between G2 and G1, a first power drift amount δ G is obtained, then a first temperature correction amount δ T is obtained as T2-T1 according to a first reference curve, that is, the corresponding relationship between the transmitted light power ratio and the laser driving temperature, then the driving temperature of the first laser 10 is adjusted according to the first temperature correction amount δ T, and the driving temperature of the first laser 10 is locked at the driving temperature T1, so that the wavelength of the first laser 10 can be locked at λ.
Of course, in this embodiment, only one driving temperature value at the half height of one molecular absorption peak of the first reference curve is taken as an example for description, but the present invention is not limited thereto, and in other embodiments, a point (T3, G3) at the peak of one molecular absorption peak may be used as the feedback target point. It should be noted that, when a point (T3, G3) at the peak is selected as the feedback target point, after a wavelength feedback cycle begins, driving temperature values of a plurality of points may be selected respectively at the left and right of the feedback target point, the transmission light power value ratio corresponding to each driving temperature value is obtained according to the transmission light power ratio detected by the first detector 13 in real time, a curve is formed again according to the driving temperature values and the transmission light power value ratios, and then the newly formed point at the peak of the absorption peak is used as the feedback target point.
In another embodiment of the present invention, as shown in fig. 3, based on the structure shown in fig. 1, the feedback correction system further includes a second laser 14, a second beam splitter 15, a first circulator 16, a second circulator 17, a second detector 18, a second control module (not shown), an interferometer 19, and a third detector 20. In the embodiment of the present invention, the interferometer 19 is an unequal arm interferometer, the second laser 14 is a continuous light laser, and the first laser 10 is a pulsed light laser. Of course, the invention is not limited thereto.
The second beam splitter 15 is configured to split the reference light emitted by the second laser 14 into first reference light and second reference light with different optical paths, and transmit the first reference light to the first circulator 16;
the first circulator 16 is used for transmitting the first reference light to the molecular absorption cell 12, so that the molecular absorption cell 12 absorbs the first reference light; the first circulator 16 is further configured to transmit the absorbed first signal light emitted from the molecular absorption cell 12 to the first detector 13; in the drawings, P1, P2, and P3 are ports of a circulator, and light is input from port P1 and output from port P2, and light is input from port P2 and output from port P3.
The second circulator 17 is further configured to transmit the absorbed first reference light emitted from the molecular absorption cell 12 to the second detector 18, and transmit the first signal light emitted from the first beam splitter 11 to the molecular absorption cell 12; the second detector 18 is used for detecting the actual transmission light power of the first reference light after being absorbed by the molecular absorption cell 12;
the second control module is configured to compare the actual transmitted light power of the first reference light with the actual transmitted light power of the reference point to obtain an actual transmitted light power ratio of the first reference light, compare the actual transmitted light power ratio of the first reference light with the standard transmitted light power ratio of the first reference light to obtain a second power drift amount, obtain a second correction amount according to the second power drift amount and a correspondence between the transmitted light power ratio obtained in advance and the laser wavelength correction parameter, and perform wavelength correction on the second laser 14 according to the second correction amount.
It should be noted that, in the embodiment of the present invention, the wavelength correction may be performed on the second laser 14 in the same manner as the wavelength correction of the first laser 10, and the feedback target point of the wavelength correction of the first laser 10 is the same as the feedback target point of the wavelength correction of the second laser 14, that is, the relative positions of the spectral lines corresponding to the standard transmitted light power ratio of the first signal light corrected by the wavelength correction of the first laser 10 and the standard transmitted light power ratio of the first reference light corrected by the wavelength correction of the second laser 14 are the same, so that the wavelength consistency of the first laser 10 and the second laser 14 can be ensured.
On this basis, the second beam splitter 15 is also used to transmit the second reference light to the unequal arm interferometer 19;
the unequal arm interferometer 19 is configured to generate two continuous lights having a phase difference from the second reference light and obtain a first interference light of the two continuous lights after the interference;
the third detector 20 is used for detecting the actual optical power of the first interference light;
the second control module is further configured to compare the actual optical power of the first interference light with the second standard optical power to obtain a third power drift amount, obtain a first voltage correction amount according to the third power drift amount and a correspondence between the optical power obtained in advance and the interferometer phase shifter driving voltage, and transmit the first voltage correction amount to the unequal arm interferometer 19, so that the unequal arm interferometer 19 corrects the phase difference according to the first voltage correction amount.
In this embodiment, the second reference light enters the unequal arm interferometer 19 from the output end of the unequal arm interferometer 19, the beam splitter at the output end of the unequal arm interferometer 19 splits the second reference light into two beams of light, that is, the two beams of continuous light are transmitted through the two arms of the unequal arm interferometer 19, and then two continuous lights with phase difference are formed and interfered at the beam splitter at the input end of the unequal arm interferometer 19, so as to form the first interference light. The intensity of the first interference light is determined by the phase difference between the two arms of the interferometer 19. Further, the correction of the first voltage correction amount can be performed based on the detection of the optical power by adjusting the phase shifter output in the unequal arm interferometer 19 so that the optical power of the first interference light becomes the interference maximum value or the interference minimum value (i.e., the second standard optical power).
After the third detector 20 disposed at the idle input end of the unequal arm interferometer 19 detects the actual optical power of the first interference light, the second control module compares the actual optical power of the first interference light with the second standard optical power to obtain a third power drift amount, obtains a first voltage correction amount according to the third power drift amount and the corresponding relationship between the optical power obtained in advance and the interferometer driving voltage, and transmits the first voltage correction amount to the unequal arm interferometer 19, so that the phase shifter driving voltage source in the unequal arm interferometer 19 corrects the phase difference between the two arms of the unequal arm interferometer 19 according to the first voltage correction amount.
In this case, the phase difference between the long arm and the short arm of the interferometer 19 can be changed by changing the driving voltage of the phase shifter. Based on this, the driving voltage can take a plurality of different values, and then the third detector 20 obtains the optical power value corresponding to each driving voltage value, and then the corresponding relationship between the optical power and the interferometer driving voltage can be obtained.
In the embodiment of the present invention, the first beam splitter 11 is further configured to transmit the second signal light to the unequal arm interferometer 19; the unequal arm interferometer 19 is also configured to generate two pulses having a fixed time difference from the second signal light to time-phase encode the two pulses. That is, it is possible to perform a process such as time-phase encoding of the quantum key distribution system while performing wavelength and phase correction.
It should be noted that the first laser 10 and the feedback correction system of the present invention may be located at any one of the sending ends of the quantum key distribution system, that is, both the Alice end and the Bob end have the first laser 10 and the feedback correction system, and based on this, after the wavelength of the first laser 10 and the second laser 14 at the Alice end and the Bob end is corrected by the feedback correction system, it may be ensured that the wavelengths of the first laser 10 and the second laser 14 at the Alice end are equal or approximately equal to the wavelengths of the first laser 10 and the second laser 14 at the Bob end, that is, the wavelength consistency of the lasers at the Alice end and the Bob end is ensured.
Since the wavelength of the second laser 14 at the Alice end is equal to the wavelength of the second laser 14 at the Bob end, after the phase correction of the unequal-arm interferometer 19 is performed by using the reference light of the second laser 14 as the feedback light, the phase difference δ Φ between the unequal-arm interferometer 19 at the Alice end and the unequal-arm interferometer 19 at the Bob end can be kept highly consistent, that is, the phase modulation of the signal light at the Alice end and the Bob end in the same phase reference system is ensured.
In another embodiment of the present invention, as shown in fig. 4, based on the structure shown in fig. 2, the feedback correction system further includes a second laser 14, a second beam splitter 15, a first circulator 16, a second circulator 17, a second detector 18, a second control module (not shown), an unequal arm interferometer 19, a third detector 20, a third circulator 21, and a fourth detector 22.
The structures and functions of the second laser 14, the second beam splitter 15, the first circulator 16, the second circulator 17, the second detector 18, and the unequal arm interferometer 19 are the same as those of the second laser 14, the second beam splitter 15, the first circulator 16, the second circulator 17, the second detector 18, and the unequal arm interferometer 19 shown in fig. 3, and are not described herein again. Fig. 4 is different from the structure shown in fig. 3 in that fig. 4 employs two detectors to detect the optical powers of the first interference light and the second interference light, respectively, and determines the correction amount of the driving voltage according to the ratio of the two optical powers. The intensities of the first and second interference lights are determined by the phase difference between the two arms of the interferometer 19, and the two interference lights change in an opposite manner following the phase difference, and if the first interference light is maximum, the second interference light is minimum. The output of the phase shifter in the unequal arm interferometer 19 can be adjusted to make the optical power ratio of the first interference light and the second interference light maximum or minimum (i.e. the first optical power ratio).
As shown in fig. 4, a third detector 20 and a fourth detector 22 are respectively located at two input ends of the unequal arm interferometer 19, and the third detector 20 is used for detecting the actual optical power of the first interference light; the third circulator 21 is configured to transmit the second interference light to the fourth detector 22; the fourth detector 22 is used for detecting the actual optical power of the second interference light;
the second control module is configured to compare the actual optical power output by the third detector 20 with the actual optical power output by the fourth detector 22 to obtain a first actual optical power ratio, compare the first actual optical power ratio with the first optical power ratio to obtain a first power ratio drift amount, obtain a second voltage correction amount according to the first power ratio drift amount and a correspondence between the optical power ratio obtained in advance and the interferometer driving voltage, and transmit the second voltage correction amount to the unequal arm interferometer 19, so that the unequal arm interferometer 19 corrects the phase difference according to the second voltage correction amount.
Note that, the first beam splitter 11 is also configured to transmit the second signal light to the third circulator 21; the third circulator 21 is also configured to transmit the second signal light to the unequal arm interferometer 19; the unequal arm interferometer 19 is also configured to generate two pulses having a fixed time difference from the second signal light and time-phase encode the two pulses. That is, while wavelength and phase correction is performed, a time-phase encoding process of the quantum key distribution system may also be performed.
As shown in fig. 5, based on the structure shown in fig. 3, the feedback correction system further includes a fourth circulator 23 and a third laser 24, wherein the first laser 10 is a master laser and the third laser 24 is a slave laser. Namely, the light source of the quantum key distribution system in the embodiment of the invention is a master-slave laser injection locking light source.
The fourth circulator 23 is located on the optical path between the first beam splitter 11 and the unequal arm interferometer 19, and is configured to transmit the second signal light emitted from the first beam splitter 11 to the third laser 24, so as to perform injection locking on the light emitted from the third laser 24; the fourth circulator 23 is further configured to transmit the light emitted from the third laser 24 to the unequal arm interferometer 19, so that the unequal arm interferometer 19 generates two pulses with a fixed time difference according to the light emitted from the third laser 24, and performs time phase encoding on the two pulses.
The structure shown in fig. 5 can realize wavelength feedback of the master laser, and perform phase feedback on the unequal arm interferometer 19 on the basis of wavelength feedback of the continuous laser, thereby ensuring that the phase of the injection-locked slave laser between two pulses generated by the unequal arm interferometer 19 is stable.
As shown in fig. 6, based on the structure shown in fig. 5, the feedback correction system further includes a third beam splitter 25 and a fifth detector 26 to ensure the stability of the wavelength feedback of the signal light laser, i.e., the first laser 10.
The third beam splitter 25 is located on the optical path between the first laser 10 and the first beam splitter 11, and is configured to transmit a part of light rays of the signal light emitted from the first laser 10 to the fifth detector 26, and transmit the other part of light rays of the signal light emitted from the first laser 10 to the first beam splitter 11, so that the first beam splitter 11 splits the other part of light rays into the first signal light and the second signal light;
the fifth detector 26 is used for detecting the actual optical power of part of the light rays in the signal light;
the first control module is further configured to compare the actual transmitted light power output by the first detector 13 with the actual light power output by the fifth detector 26 to obtain a second actual light power ratio, compare the second actual light power ratio with the second light power ratio (which is the same as the standard transmitted light power ratio of the first signal light) to obtain a second power ratio drift amount, obtain a third correction amount according to the second power ratio drift amount and a correspondence between the light power ratio obtained in advance and the laser wavelength correction parameter, and perform wavelength correction on the first laser 10 according to the third correction amount.
As shown in fig. 7, the feedback correction system further includes a fourth beam splitter 27 and a sixth detector 28 based on the structure shown in fig. 6 to ensure the stability of the wavelength feedback of the continuous light laser, i.e. the second laser 14.
The fourth beam splitter 27 is located on the optical path between the second laser 14 and the second beam splitter 15, and is configured to transmit a part of the reference light emitted by the second laser 14 to the sixth detector 28, and transmit the other part of the reference light emitted by the second laser 14 to the second beam splitter 15, so that the second beam splitter 15 splits the other part of the reference light into the first reference light and the second reference light;
the sixth detector 28 is used for detecting the actual optical power of a part of the light rays in the signal light;
the second control module is further configured to compare the actual transmitted light power output by the second detector 18 with the actual light power output by the sixth detector 28 to obtain a third actual light power ratio, compare the third actual light power ratio with the third light power ratio (which is the same as the standard transmitted light power ratio of the first reference light) to obtain a third power ratio drift amount, obtain a fourth temperature correction amount according to the third power ratio drift amount and a correspondence between the light power ratio obtained in advance and the laser wavelength correction parameter, and perform wavelength correction on the second laser 14 according to the fourth temperature correction amount.
The feedback correction system provided by the embodiment of the invention solves the problems of wavelength consistency and time phase coding phase reference consistency between two sending end pulse light lasers and continuous light lasers which are far away from each other. Compared with the MDIQKD system which adopts the mode of collecting the HOM interference signal at the receiving end for a long time, the feedback correction system provided by the embodiment of the invention has the advantages of high reliability of wavelength feedback and phase feedback, short feedback time, capability of flexibly adjusting a wavelength feedback target point, convenience for large-scale networking application and the like.
The feedback correction system provided by the embodiment of the invention does not need to establish an additional optical fiber channel between different sending ends or between the sending end and the receiving end, does not need to use nearly identical unequal arm interferometers 19 at the receiving end, adopts the continuous optical laser subjected to wavelength feedback to ensure the wavelength of continuous light and signal light to be consistent, ensures the phase reference consistency of the unequal arm interferometers 19 with different sending end values, does not influence the working process of the quantum key distribution system during phase feedback, and improves the efficiency and the stability of the quantum key distribution system.
The embodiment of the invention also provides a quantum key distribution system, optionally, the quantum key distribution system is a measurement device-independent quantum key distribution system based on time phase coding, and comprises at least two sending ends 1 (an Alice end and a Bob end) and a receiving end 2 (a Charlie end); each transmitting end 1 includes a first laser 10 and a feedback correction system, wherein the feedback correction system is the feedback correction system provided in any of the embodiments described above.
It should be noted that, as shown in fig. 8, the receiving end 2 may adjust the static difference of the molecular absorption spectrum line frequencies of the molecular absorption cells 12 of the two transmitting ends 1 according to the interference result of the second signal light transmitted by the two transmitting ends 1, so as to ensure that the locked wavelengths of the two transmitting ends 1 are the same, and further ensure the consistency between the wavelength of the lasers of the two transmitting ends 1 and the phase difference of the unequal-arm interferometer 19.
Specifically, the static difference of the molecular absorption spectrum line frequency of the molecular absorption cells 12 of the two transmitting ends 1 can be adjusted by adjusting the position of the wavelength locking feedback target point of one of the transmitting ends, that is, adjusting the value of the first standard optical power according to the interference result of the second signal light of the two transmitting ends 1, so as to ensure the wavelength consistency of the two transmitting ends 1.
According to the quantum key distribution system provided by the embodiment of the invention, an additional optical fiber channel is not required to be established between different sending ends or between the sending end and the receiving end, the nearly same unequal arm interferometer 19 is not required to be used at the receiving end, the wavelength of continuous light is ensured to be consistent with that of signal light by adopting a continuous light laser fed back by wavelength, the consistency of phase reference of the unequal arm interferometer 19 with different sending end values is ensured, the working process of the quantum key distribution system is not influenced while phase feedback is carried out, and the efficiency and the stability of the quantum key distribution system are improved.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (11)
1. A feedback correction system is characterized by comprising a first beam splitter, a molecular absorption cell, a first detector and a first control module;
the first beam splitter is used for splitting the signal light emitted by the first laser into first signal light and second signal light with different optical paths and transmitting the first signal light to the molecular absorption cell;
the molecular absorption cell is used for absorbing the first signal light;
the first detector is used for detecting the actual transmission light power of the first signal light absorbed by the molecular absorption cell;
the first control module is used for comparing the actual transmission light power of the first signal light with the actual transmission light power of a reference point to obtain an actual transmission light power ratio of the first signal light, comparing the actual transmission light power ratio of the first signal light with a standard transmission light power ratio of the first signal light to obtain a first power drift amount, obtaining a first correction amount according to the first power drift amount and a corresponding relation between the transmission light power ratio obtained in advance and a laser wavelength correction parameter, and performing wavelength correction on the first laser according to the first correction amount.
2. The correction system of claim 1, further comprising a second laser, a second beam splitter, a first circulator, a second detector, and a second control module, the second laser being a continuous light laser;
the second beam splitter is used for splitting the reference light emitted by the second laser into first reference light and second reference light with different optical paths and transmitting the first reference light to the first circulator;
the first circulator is used for transmitting the first reference light to the molecular absorption cell so that the molecular absorption cell absorbs the first reference light; the first circulator is further used for transmitting the absorbed first signal light emitted by the molecular absorption cell to the first detector;
the second circulator is further used for transmitting the absorbed first reference light emitted by the molecular absorption cell to the second detector, and transmitting the first signal light emitted by the first beam splitter to the molecular absorption cell;
the second detector is used for detecting the actual transmission light power of the first reference light after being absorbed by the molecular absorption cell;
the second control module is configured to compare the actual transmitted light power of the first reference light with the actual transmitted light power of the reference point to obtain an actual transmitted light power ratio of the first reference light, compare the actual transmitted light power ratio of the first reference light with a standard transmitted light power ratio of the first reference light to obtain the second power drift amount, obtain a second correction amount according to the second power drift amount and a correspondence between a transmission light power ratio obtained in advance and a laser wavelength correction parameter, and perform wavelength correction on the second laser according to the second correction amount.
3. The calibration system of claim 2, further comprising an interferometer and a third detector;
the second beam splitter is further configured to transmit the second reference light to the interferometer;
the interferometer is used for generating two continuous lights with phase difference according to the second reference light and obtaining a first interference light of the two continuous lights after interference;
the third detector is used for detecting the actual optical power of the first interference light;
the second control module is further configured to compare the actual optical power of the first interference light with a second standard optical power to obtain a third power drift amount, obtain a first voltage correction amount according to the third power drift amount and a correspondence between the optical power obtained in advance and an interferometer phase shifter driving voltage, and transmit the first voltage correction amount to the interferometer phase shifter, so that the interferometer corrects the phase difference according to the first voltage correction amount.
4. The correction system of claim 3, wherein the first beam splitter is further configured to transmit the second signal light to the interferometer;
the interferometer is also configured to generate two pulses having a fixed time difference from the second signal light to time phase encode the two pulses.
5. The calibration system of claim 2, further comprising an interferometer, a third circulator, a third detector, and a fourth detector;
the interferometer is used for generating two beams of continuous light with phase difference according to the second reference light and obtaining first interference light and second interference light of the two beams of continuous light after interference;
the third detector is used for detecting the actual optical power of the first interference light;
the third circulator is used for transmitting the second interference light to the fourth detector;
the fourth detector is used for detecting the actual optical power of the second interference light;
the second control module is configured to compare an actual optical power output by the third detector with an actual optical power output by the fourth detector to obtain a first actual optical power ratio, compare the first actual optical power ratio with the first optical power ratio to obtain a first power ratio drift amount, obtain a second voltage correction amount according to a correspondence between the first power ratio drift amount and a previously obtained optical power ratio and an interferometer driving voltage, and transmit the second voltage correction amount to the interferometer, so that the interferometer corrects the phase difference according to the second voltage correction amount.
6. The correction system of claim 5, wherein the first beam splitter is further configured to transmit the second signal light to the third circulator;
the third circulator is also used for transmitting the second signal light to the interferometer;
the interferometer is also configured to generate two pulses having a fixed time difference from the second signal light to time phase encode the two pulses.
7. The correction system of claim 3, further comprising a fourth circulator and a third laser;
the fourth circulator is positioned on an optical path between the first beam splitter and the interferometer and is used for transmitting the second signal light emitted by the first beam splitter into the third laser so as to perform injection locking on the light emitted by the third laser;
the fourth circulator is further used for transmitting the light emitted by the third laser to the interferometer, so that the interferometer generates two pulses with a fixed time difference according to the light emitted by the third laser, and the two pulses are subjected to time phase coding.
8. The correction system of any one of claims 1 to 7, further comprising a third beam splitter and a fifth detector;
the third beam splitter is located on an optical path between the first laser and the first beam splitter, and is configured to transmit a part of light rays in the signal light emitted by the first laser to the fifth detector, and transmit the other part of light rays in the signal light emitted by the first laser to the first beam splitter, so that the first beam splitter splits the other part of light rays into the first signal light and the second signal light;
the fifth detector is used for detecting the actual optical power of part of the light rays in the signal light;
the first control module is further configured to compare the actual transmitted light power output by the first detector with the actual light power output by the fifth detector to obtain a second actual light power ratio, compare the second actual light power ratio with the second light power ratio to obtain a second power ratio drift amount, obtain a third correction amount according to the second power ratio drift amount and a correspondence between the light power ratio obtained in advance and a laser wavelength correction parameter, and perform wavelength correction on the first laser according to the third correction amount.
9. The correction system of claim 8, further comprising a fourth beam splitter and a sixth detector;
the fourth beam splitter is located on a light path between the second laser and the second beam splitter, and is configured to transmit a part of light rays in the reference light emitted by the second laser to the sixth detector, and transmit the other part of light rays in the reference light emitted by the second laser to the second beam splitter, so that the second beam splitter splits the other part of light rays into the first reference light and the second reference light;
the sixth detector is used for detecting the actual optical power of part of the light rays in the signal light;
the second control module is further configured to compare the actual transmitted light power output by the second detector with the actual light power output by the sixth detector to obtain a third actual light power ratio, compare the third actual light power ratio with the third light power ratio to obtain a third power ratio drift amount, obtain a fourth correction amount according to the third power ratio drift amount and a correspondence between the light power ratio obtained in advance and a laser wavelength correction parameter, and perform wavelength correction on the second laser according to the fourth correction amount.
10. A quantum key distribution system, comprising:
at least two sending ends and one receiving end;
the transmitting end comprises a first laser and a feedback correction system;
the feedback correction system is the feedback correction system as claimed in any one of claims 1 to 9.
11. The distribution system according to claim 10, wherein the receiving end is further configured to adjust a static difference of the molecular absorption spectrum line frequencies of the molecular absorption cells of the two transmitting ends according to the interference result of the second signal light transmitted by the two transmitting ends.
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| CN116633541A (en) * | 2023-07-19 | 2023-08-22 | 济南量子技术研究院 | Double-field light source frequency locking method and system based on air chamber frequency reference |
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