A TF-QKD system and a method for realizing phase synchronization

Abstract

The present invention provides a method for implementing a TF-QKD system and phase synchronization, including: a first device, a second device, and an interference device. The first quantum state modulation unit in the first device is respectively connected to a first light source and a first synchronization unit. The second quantum state modulation unit in the second device is respectively connected to a second light source and a second synchronization unit. The first quantum state modulation unit is further connected to an interference execution unit or a phase compensation unit, and the second quantum state modulation unit is further connected to the other one of them. The phase compensation unit is further connected to a third synchronization unit and the interference execution unit. The first synchronization unit, the second synchronization unit, and the third synchronization unit are connected by optical fibers. Based on the TF-QKD system architecture of the radio frequency synchronization system, the implementation cost and complexity of the TF-QKD system are significantly reduced. The complexity and cost of the synchronization system are effectively reduced, providing key technical support for large-scale industrial applications.

Description

Technical Field

[0001] The present invention relates to the field of quantum communication, and more particularly, to a TF-QKD system and a method for realizing phase synchronization. Background Art

[0002] Quantum key distribution (QKD) is based on the basic principles of quantum mechanics and provides a mechanism for secure key sharing at the information-theoretic level for both communication parties. Combined with the one-time pad information encryption method, unconditional secure communication can be achieved. In terms of signal transmission, both QKD and classical fiber optic communication face the problem that the signal strength decays exponentially with increasing distance. Classical optical communication can deploy optical amplifiers to enhance the transmitted signal and thus construct a long-distance fiber optic communication network. However, for QKD, due to the limitation of the quantum no-cloning theorem, it is impossible to extend the transmission distance of quantum signals through simple optical amplification, otherwise additional bit error rates will be generated, directly threatening the legitimacy and security of the communication services of authorized users. Channel loss has become the core factor restricting long-distance quantum key distribution.

[0003] Compared with the classical BB84 protocol, Twin-Field Quantum Key Distribution (TF-QKD) can improve the linear relationship between the key rate and the channel transmittance to a more efficient square root correlation, thus greatly increasing the secure transmission distance of QKD without relays. With the increasing maturity of TF-QKD technology, its application to existing networks can significantly reduce the number of trusted relay nodes required in long-distance quantum communication networks, thereby improving the overall security performance of long-haul QKD systems and effectively reducing the security cost. However, the implementation of TF-QKD technology faces strict conditional restrictions, including phase synchronization restrictions.

[0004] Therefore, how to achieve phase synchronization in a TF-QKD system has become a difficult problem that concerns those skilled in the art. Summary of the Invention

[0005] The purpose of the present invention is to provide a TF-QKD system and a method for realizing phase synchronization to improve the above problems.

[0006] To achieve the above purpose, the technical solutions adopted in the embodiments of the present invention are as follows:

[0007] In a first aspect, an embodiment of the present invention provides a TF-QKD system, which includes: a first device, a second device, and an interference device. The first device includes a first light source, a first quantum state modulation unit, and a first synchronization unit. The second device includes a second light source, a second quantum state modulation unit, and a second synchronization unit. The interference device includes an interference execution unit, a phase compensation unit, and a third synchronization unit;

[0008] The first quantum state modulation unit is respectively connected to the first light source and the first synchronization unit. The second quantum state modulation unit is respectively connected to the second light source and the second synchronization unit;

[0009] The first quantum state modulation unit is further connected to the interference execution unit or the phase compensation unit. The second quantum state modulation unit is further connected to the other one of them. The phase compensation unit is further connected to the third synchronization unit and the interference execution unit;

[0010] The first synchronization unit, the second synchronization unit, and the third synchronization unit are connected by optical fibers.

[0011] Optionally, the first quantum state modulation unit is configured to perform phase encoding on the first continuous light wave emitted by the first light source according to the first reference phase signal provided by the first synchronization unit, and transmit the obtained continuous light wave backward;

[0012] The second quantum state modulation unit is configured to perform phase encoding on the second continuous light wave emitted by the second light source according to the second reference phase signal provided by the second synchronization unit, and transmit the obtained continuous light wave backward;

[0013] The phase compensation unit is configured to perform phase compensation on the light wave passing through it according to the third reference phase signal provided by the third synchronization unit, and transmit the phase-compensated light wave to the interference execution unit;

[0014] The interference execution unit is configured to determine the interference result between the first device and the second device according to the received light wave;

[0015] The first reference phase signal, the second reference phase signal, and the third reference phase signal are the same.

[0016] Optionally, the first synchronization unit is configured to generate a first reference phase signal, and send a first synchronization optical signal corresponding to the first reference phase signal to the second synchronization unit and the third synchronization unit;

[0017] The second synchronization unit is configured to obtain a second reference phase signal according to the received first synchronization optical signal, and generate a second synchronization optical signal according to the second reference phase signal, and send the second synchronization optical signal to the first synchronization unit and the third synchronization unit;

[0018] The third synchronization unit is configured to obtain a third reference phase signal according to the received first synchronization optical signal and the second synchronization optical signal.

[0019] Optionally, the first synchronization unit includes a radio frequency signal generator, a first frequency divider, a downconverter, a first optoelectronic conversion unit, a first electro-optic converter, and a first wavelength division multiplexer;

[0020] The output end of the radio frequency signal generator is respectively connected to the input end of the first frequency divider and the first input end of the downconverter;

[0021] The output end of the first frequency divider is connected to the first quantum state modulation unit;

[0022] The second input end of the downconverter is connected to the output end of the first optoelectronic conversion unit; the output end of the downconverter is connected to the input end of the first electro-optic converter;

[0023] The output end of the first electro-optic converter and the input end of the first optoelectronic conversion unit are both connected to the first wavelength division multiplexer.

[0024] Optionally, the radio frequency signal generator is configured to generate a radio frequency signal and transmit the radio frequency signal to the first frequency divider and the downconverter;

[0025] The first optoelectronic conversion unit is configured to detect the second synchronization optical signal collected by the first wavelength division multiplexer, and transmit the detected radio frequency signal to the downconverter;

[0026] The downconverter is configured to perform downconversion processing on the radio frequency signal using the radio frequency signal and transmit the obtained radio frequency signal to the first electro-optic converter;

[0027] The first electro-optic converter is configured to modulate the radio frequency signal onto the first auxiliary optical signal, and transmit the obtained first synchronization optical signal to the first wavelength division multiplexer, so as to transmit it to the second synchronization unit and the third synchronization unit;

[0028] The first frequency divider is configured to divide the radio frequency signal Perform frequency division by two and use the obtained first reference phase signal , and provide it to the first quantum state modulation unit.

[0029] Optionally, the second synchronization unit includes a power distribution unit, a second photoelectric conversion unit, a second electro-optic converter, and a second wavelength division multiplexer;

[0030] The input end of the second photoelectric conversion unit and the output end of the second electro-optic converter are both connected to the second wavelength division multiplexer;

[0031] The output end of the second photoelectric conversion unit is connected to the input end of the power distribution unit, the first output end of the power distribution unit is connected to the input end of the second electro-optic converter, and the second output end of the power distribution unit is connected to the second quantum state modulation unit.

[0032] Optionally, the second photoelectric conversion unit is used to detect the first synchronization optical signal collected by the second wavelength division multiplexer, and transmit the detected radio frequency signal to the power distribution unit;

[0033] The power distribution unit is used to perform power distribution on the radio frequency signal , and send the radio frequency signal to the second electro-optic converter according to the power distribution result;

[0034] The second electro-optic converter is used to modulate the radio frequency signal onto the second auxiliary optical signal, and transmit the obtained second synchronization optical signal to the second wavelength division multiplexer, so as to transmit it to the first synchronization unit and the third synchronization unit;

[0035] The power distribution unit is also used to send the radio frequency signal to the second quantum state modulation unit according to the power distribution result, as the second reference phase signal .

[0036] Optionally, the third synchronization unit includes an optical coupler, a third photoelectric conversion unit, a fourth photoelectric conversion unit, a second mixer, a second frequency divider by two, and a sixth band-pass filter;

[0037] The input end of the third photoelectric conversion unit and the input end of the fourth photoelectric conversion unit are both connected to the optical coupler, and the output end of the third photoelectric conversion unit and the output end of the fourth photoelectric conversion unit are both connected to the input end of the second mixer;

[0038] The output end of the second mixer is connected to the input end of the second frequency divider, the output end of the second frequency divider is connected to the input end of the sixth band-pass filter, and the output end of the sixth band-pass filter is connected to the phase compensation unit.

[0039] Optionally, the third optoelectronic conversion unit is used to detect the first synchronous optical signal collected by the optical coupler and transmit the detected radio frequency signal to the second mixer;

[0040] The fourth optoelectronic conversion unit is used to detect the second synchronous optical signal collected by the optical coupler and transmit the detected radio frequency signal to the second mixer;

[0041] The second mixer is used to perform mixing processing on the radio frequency signal and the radio frequency signal and transmit the obtained mixed signal to the second frequency divider;

[0042] The second frequency divider is used to perform frequency division by two on the mixed signal and transmit the obtained third reference phase signal to the sixth band-pass filter;

[0043] The sixth band-pass filter is used to perform band-pass filtering on the third reference phase signal and provide the filtered third reference phase signal to the phase compensation unit.

[0044] In a second aspect, an embodiment of the present invention provides a method for realizing phase synchronization, which is applied to the above-mentioned TF-QKD system. When the first light source and the second light source achieve frequency synchronization, the method includes:

[0045] The first quantum state modulation unit performs phase encoding on the first continuous light wave emitted by the first light source according to the first reference phase signal provided by the first synchronization unit, and transmits the obtained continuous light wave backward;

[0046] The second quantum state modulation unit is used to perform phase encoding on the second continuous light wave emitted by the second light source according to the second reference phase signal provided by the second synchronization unit, and transmit the obtained continuous light wave backward;

[0047] The phase compensation unit is used to perform phase compensation on the light wave passing through it according to the third reference phase signal provided by the third synchronization unit, and transmit the phase-compensated light wave to the interference execution unit;

[0048] The interference execution unit is used to determine the interference result between the first device and the second device according to the received optical wave;

[0049] Wherein, the first reference phase signal, the second reference phase signal, and the third reference phase signal are the same.

[0050] Compared with the prior art, a TF-QKD system and a phase synchronization implementation method provided by an embodiment of the present invention include: a first device, a second device, and an interference device. The first quantum state modulation unit in the first device is respectively connected to a first light source and a first synchronization unit, and the second quantum state modulation unit in the second device is respectively connected to a second light source and a second synchronization unit; the first quantum state modulation unit is further connected to an interference execution unit or a phase compensation unit, the second quantum state modulation unit is further connected to the other one of them, and the phase compensation unit is further connected to a third synchronization unit and the interference execution unit; the first synchronization unit, the second synchronization unit, and the third synchronization unit are fiber-connected. Based on the TF-QKD system architecture of the radio frequency synchronization system, the implementation cost and complexity of the TF-QKD system are significantly reduced. The complexity and cost of the synchronization system are effectively reduced, providing key technical support for the large-scale industrial application of TF-QKD devices.

[0051] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following specifically enumerates preferred embodiments and, in conjunction with the accompanying drawings, makes a detailed description as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0053] Figure 1 It is a schematic structural diagram of the TF-QKD system provided by an embodiment of the present invention.

[0054] Figure 2 It is a schematic structural diagram of the first synchronization unit provided by an embodiment of the present invention.

[0055] Figure 3 It is a schematic structural diagram of the second synchronization unit provided by an embodiment of the present invention.

[0056] Figure 4 It is a schematic structural diagram of the third synchronization unit provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0057] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and illustrated herein generally may be arranged and designed in a variety of different configurations.

[0058] Therefore, the detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of the present invention.

[0059] It should be noted that like reference numerals and letters denote like items in the following drawings. Therefore, once an item is defined in one drawing, it does not require further definition and explanation in subsequent drawings. At the same time, in the description of the present invention, the terms "first", "second", etc. are only used for descriptive distinction and cannot be construed as indicating or implying relative importance.

[0060] It should be noted that in this document, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variation thereof is intended to cover a non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the phrase "comprising a..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0061] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings or the orientation or positional relationship in which the inventive product is customarily placed during use. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present invention.

[0062] In the description of the present invention, it should also be noted that, unless otherwise clearly defined and limited, the terms "arrangement" and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0063] The following will, with reference to the accompanying drawings, describe in detail some embodiments of the present invention. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0064] In performing quantum key negotiation, it is necessary to precisely control the frequencies of two lasers to ensure that the photons they emit can achieve high-quality interference at the interference device end. Secondly, the phase encoding of the two lasers needs to be highly accurate, and at the same time, the phase measurement at the interference device end must also be precise and error-free, which is the key to ensuring the safe and efficient generation of keys. For this reason, the two lasers must achieve phase synchronization when performing phase encoding through a phase modulator. In addition, due to the inevitable phase jitter in the optical fiber link, the interference device end also needs to perform real-time or post-data processing compensation on the phase, and this step also depends on the realization of phase synchronization.

[0065] In order to solve various problems existing in the synchronization module in the current TF-QKD system, one of which is that the optical path of the polarization consistency coupling scheme is complex, the cost is high, it is difficult to implement, and the stability is poor and requires manual calibration. The embodiment of the present invention provides a TF-QKD system and a method for realizing phase synchronization, and proposes a TF-QKD system architecture based on a radio frequency synchronization system, which significantly reduces the implementation cost and complexity of the TF-QKD system. And the synchronization system uses an optical carrier radio frequency structure to realize the synchronization function, transmits by modulating the radio frequency signal onto the optical carrier, and performs feedback compensation accordingly, successfully realizing phase synchronization. It effectively reduces the complexity and cost of the synchronization system, provides key technical support for the large-scale industrial application of TF-QKD devices. Thereby enhancing the feasibility of its commercial application and laying a solid foundation for realizing future ultra-long-distance quantum key distribution technology.

[0066] Please refer to Figure 1 , Figure 1 which is a schematic structural diagram of the TF-QKD system provided by the embodiment of the present invention.

[0067] The TF-QKD system includes a first device, a second device, and an interference device. The first device includes a first light source (laser light source), a first quantum state modulation unit, and a first synchronization unit. The second device includes a second light source (laser light source), a second quantum state modulation unit, and a second synchronization unit. The interference device includes an interference execution unit, a phase compensation unit, and a third synchronization unit.

[0068] The first quantum state modulation unit is respectively connected to the first light source and the first synchronization unit, and the second quantum state modulation unit is respectively connected to the second light source and the second synchronization unit.

[0069] The first quantum state modulation unit is also connected to the interference execution unit or the phase compensation unit, the second quantum state modulation unit is also connected to the other one of them, and the phase compensation unit is also connected to the third synchronization unit and the interference execution unit.

[0070] Figure 1 As shown in the figure, the first quantum state modulation unit is connected to the interference execution unit, and the second quantum state modulation unit is connected to the phase compensation unit. Of course, it can also be that the first quantum state modulation unit is connected to the phase compensation unit and the second quantum state modulation unit is connected to the interference execution unit, which is not shown in the figure.

[0071] The first synchronization unit, the second synchronization unit, and the third synchronization unit are connected by optical fibers.

[0072] Optionally, the first wavelength division multiplexer in the first synchronization unit, the second wavelength division multiplexer in the second synchronization unit, and the optical coupler in the third synchronization unit are connected by optical fibers.

[0073] Please continue to refer to Figure 1 , in an optional implementation manner, the interference device further includes a frequency-locked reference light unit, and the frequency-locked reference light unit is respectively connected to the first light source in the first device and the second light source in the second device. Optionally, a polarization monitoring and compensation device (PB shown in the figure) is provided between the frequency-locked reference light unit and the first light source, and a polarization monitoring and compensation device (PB shown in the figure) is also provided between the frequency-locked reference light unit and the second light source.

[0074] During the process of light source synchronization, the frequency-locked reference light unit in the interference device generates a frequency-locked reference light, and then sends it to the first light source and the second light source. After polarization detection and compensation, this reference light is used to lock the frequencies of the two light sources at both ends to ensure that their frequencies are the same.

[0075] It should be noted that the first light source and the second light source can also achieve frequency synchronization through other means, which are not limited herein.

[0076] Optionally, a polarization monitoring and compensation device (PB shown in the figure) is also provided between the interference execution unit and the corresponding quantum state modulation unit, and a polarization monitoring and compensation device (PB shown in the figure) is also provided between the phase compensation unit and the corresponding quantum state modulation unit. The polarization monitoring and compensation device is used for polarization detection and compensation.

[0077] Optionally, when the first light source and the second light source achieve frequency synchronization, the first quantum state modulation unit is used to perform phase encoding on the first continuous light wave emitted by the first light source according to the first reference phase signal provided by the first synchronization unit, and transmit the obtained continuous light wave backward (transmit it to the interference execution unit or the phase compensation unit in the interference device).

[0078] The second quantum state modulation unit is used to perform phase encoding on the second continuous light wave emitted by the second light source according to the second reference phase signal provided by the second synchronization unit, and transmit the obtained continuous light wave backward (transmit it to the interference execution unit or the phase compensation unit in the interference device).

[0079] The phase compensation unit is used to perform phase compensation on the light wave passing through it according to the third reference phase signal provided by the third synchronization unit, and transmit the phase-compensated light wave to the interference execution unit.

[0080] The interference execution unit is used to determine the interference result between the first device and the second device according to the received light wave.

[0081] When the interference result is correct, it indicates that the first device and the second device have completed quantum entanglement, and quantum key negotiation can be performed.

[0082] Among them, the first reference phase signal, the second reference phase signal, and the third reference phase signal are the same.

[0083] Optionally, please continue to refer to Figure 1 , in an optional implementation manner, both the first quantum state modulation unit and the second quantum state modulation unit include a phase modulator, an amplitude modulator, and an optical attenuator connected in sequence. The optical signal entering the quantum state modulation unit (including the first quantum state modulation unit and the second quantum state modulation unit) sequentially undergoes phase modulation and amplitude modulation to complete the decoy state phase encoding, and the optical intensity is reduced to the weak coherence level through the optical attenuator for quantum state transmission.

[0084] It should be noted that during the phase post - processing, since the interference result of the optical pulses sent by the first device and the second device in the TF - QKD system reaching the interference device depends on their global phase difference, that is, the encoding phase and the transmission phase. The encoding phase carries information and is realized during the phase encoding process; the transmission phase is the total phase that reaches the interference point after the initial phase generated from the light source passes through the link transmission and is superimposed with the link phase. In order to accurately obtain the information of the encoding phase, the relative phase difference of the channels of the two pulses on both sides needs to be completely compensated. Therefore, a phase compensation module is added to one of the interference arms in the interference device to adjust the arrival time of the two optical signals and eliminate the transmission phase of the two pulses.

[0085] Optionally, the first synchronization unit is used to generate a first reference phase signal (and send it to the first quantum state modulation unit), and send the first synchronization optical signal corresponding to the first reference phase signal to the second synchronization unit and the third synchronization unit;

[0086] The second synchronization unit is used to obtain a second reference phase signal according to the received first synchronization optical signal (and send it to the second quantum state modulation unit), and send the second synchronization optical signal generated according to the second reference phase signal to the first synchronization unit and the third synchronization unit;

[0087] The third synchronization unit is used to obtain a third reference phase signal according to the received first synchronization optical signal and the second synchronization optical signal (and send it to the phase compensation unit).

[0088] Based on the above, regarding the structure of the first synchronization unit, an optional implementation manner is further provided in the embodiments of the present invention. Please refer to Figure 2 , Figure 2 which is the schematic structural diagram of the first synchronization unit provided by the embodiments of the present invention.

[0089] The first synchronization unit includes a radio frequency signal generator, a first frequency divider, a down - converter, a first optoelectronic conversion unit, a first electro - optic converter, and a first wavelength - division multiplexer. The wavelength - division multiplexer in the embodiments of the present invention is also called WDM.

[0090] The output end of the radio frequency signal generator is respectively connected to the input end of the first frequency divider and the first input end of the down - converter.

[0091] The output end of the first frequency divider is connected to the first quantum state modulation unit (for providing the first reference phase signal , radio frequency signal).

[0092] The second input end of the down - converter is connected to the output end of the first optoelectronic conversion unit; the output end of the down - converter is connected to the input end of the first electro - optic converter.

[0093] The output end of the first electro-optical converter and the input end of the first opto-electronic conversion unit are both connected to the first wavelength division multiplexer.

[0094] The radio frequency signal generator is used to generate a radio frequency signal and transmit the radio frequency signal to the first frequency divider and the down-converter.

[0095] Optionally, the radio frequency signal is represented as follows:

[0096]

[0097] Wherein, represents the frequency of the radio frequency signal and represents the phase of the radio frequency signal

[0098] The first opto-electronic conversion unit is used to detect the second synchronous optical signal (with a wavelength of ) collected by the first wavelength division multiplexer, and transmit the detected radio frequency signal to the down-converter, wherein the second synchronous optical signal comes from the second device.

[0099] Optionally, the radio frequency signal is represented as follows:

[0100]

[0101] Wherein, represents the frequency of the radio frequency signal and represents the phase of the radio frequency signal

[0102] The down-converter is used to perform down-conversion processing on the radio frequency signal using the radio frequency signal and transmit the obtained radio frequency signal to the first electro-optical converter.

[0103] The first electro-optical converter is used to modulate the radio frequency signal onto the first auxiliary optical signal (with a wavelength of ) and transmit the obtained first synchronous optical signal to the first wavelength division multiplexer, so as to transmit it to the second synchronous unit and the third synchronous unit.

[0104] The first frequency divider is used to perform frequency division by two on the radio frequency signal and provide the obtained first reference phase signal (radio frequency signal) to the first quantum state modulation unit. ​​

[0105] Optionally, the radio frequency signal is frequency-divided by two to obtain a radio frequency signal , and its expression is:

[0106]

[0107] wherein, represents the frequency of the radio frequency signal , represents the radio frequency signal phase of.

[0108] Please continue to refer to Figure 2 , in an alternative embodiment, the first optoelectronic conversion unit includes a first optoelectronic converter, a first radio frequency amplifier, and a first band-pass filter connected in sequence. The input end of the first optoelectronic converter is connected to the first wavelength division multiplexer, and the output end of the first band-pass filter is connected to the down-converter (first mixer).

[0109] The first optoelectronic converter is used to detect the second synchronous optical signal (wavelength is ) collected by the first wavelength division multiplexer, and transmit the detection signal to the first radio frequency amplifier.

[0110] The first radio frequency amplifier is used to perform radio frequency amplification on the received detection signal and transmit the amplified signal to the first band-pass filter.

[0111] The first band-pass filter is used to perform band-pass filtering (filter out noise) on the received amplified signal, so as to obtain the radio frequency signal , and the radio frequency signal is transmitted to the down-converter (the second synchronous optical signal comes from the second device).

[0112] Please continue to refer to Figure 2 , in an alternative embodiment, the down-converter includes a first mixer and a second band-pass filter.

[0113] The first input end of the first mixer is connected to the output end of the radio frequency signal generator, and the second input end of the first mixer is connected to the output end of the first optoelectronic conversion unit (the output end of the first band-pass filter).

[0114] The output end of the first mixer is connected to the input end of the second band-pass filter, and the output end of the second band-pass filter is connected to the input end of the first electro-optical converter.

[0115] The first mixer is used to mix the radio frequency signal and the radio frequency signal , and transmit the mixed signal to the second band-pass filter.

[0116] Set , the mixed-frequency signal is expressed as:

[0117]

[0118] wherein, represents the frequency of the radio frequency signal , represents the phase of the radio frequency signal . represents the frequency of the radio frequency signal , represents the phase of the radio frequency signal .

[0119] The second band-pass filter is used to perform lower sideband filtering on the mixed-frequency signal (filter out the upper sideband signal therein) to obtain and output the radio frequency signal .

[0120] Optionally, the radio frequency signal is expressed as:

[0121]

[0122] Furthermore, the radio frequency signal is modulated on the continuous optical signal with a wavelength of through optoelectronic conversion. The modulated optical signal is transmitted to the second synchronization unit and the third synchronization unit through WDM.

[0123] On the basis of the foregoing, regarding the structure of the second synchronization unit, an optional implementation manner is further provided in an embodiment of the present invention. Please refer to Figure 3 , Figure 3 which is a schematic structural diagram of the second synchronization unit provided in an embodiment of the present invention.

[0124] The second synchronization unit includes a power distribution unit, a second optoelectronic conversion unit, a second electro-optic converter, and a second wavelength division multiplexer.

[0125] The input end of the second optoelectronic conversion unit and the output end of the second electro-optic converter are both connected to the second wavelength division multiplexer.

[0126] The output end of the second optoelectronic conversion unit is connected to the input end of the power distribution unit. The first output end of the power distribution unit is connected to the input end of the second electro-optic converter, and the second output end of the power distribution unit is connected to the second quantum state modulation unit (for providing the second reference phase signal , radio frequency signal).

[0127] The second optoelectronic conversion unit is used to detect the first synchronization optical signal (wavelength of ), and transmits the detected radio frequency signal to the power distribution unit, where the first synchronous optical signal comes from the first device.

[0128] Optionally, the second optoelectronic conversion unit converts an optical signal with a central wavelength of to obtain a radio frequency signal , and its expression is:

[0129]

[0130] where represents the frequency of the radio frequency signal , represents the phase of the radio frequency signal , represents the frequency of the radio frequency signal , represents the phase of the radio frequency signal , represents the phase error accumulated during the transmission of the radio frequency signal from the first device to the second device, which is related to the transmission time , and there is .

[0131] The power distribution unit is used to distribute the power of the radio frequency signal , and sends the radio frequency signal to the second electro-optic converter according to the power distribution result.

[0132] Optionally, the power distribution unit includes a regenerative phase-locked loop and a power distributor. The input end of the regenerative phase-locked loop is connected to the output end of the second optoelectronic conversion unit (the third band-pass filter), the output end of the regenerative phase-locked loop is connected to the input end of the power distributor, the first output end of the power distributor is connected to the input end of the second electro-optic converter, and the second output end of the power distributor is connected to the second quantum state modulation unit.

[0133] After the radio frequency signal is optimized by the regenerative phase-locked loop, the signal-to-noise ratio can be improved. After power distribution, part of the signal is led out and transmitted to the second electro-optic converter and the second quantum state modulation unit respectively.

[0134] The second electro-optic converter is used to modulate the radio frequency signal onto the second auxiliary optical signal (with a wavelength of ), and transmits the obtained second synchronous optical signal to the second wavelength division multiplexer, so as to transmit it to the first synchronous unit and the third synchronous unit.

[0135] The power distribution unit is also used to send the radio frequency signal Sent to the second quantum state modulation unit as the second reference phase signal .

[0136] Please continue to refer to Figure 3 , in an alternative embodiment, the second optoelectronic conversion unit includes a second optoelectronic converter, a second radio frequency amplifier, and a third band-pass filter connected in sequence. The input end of the second optoelectronic converter is connected to the second wavelength division multiplexer, and the output end of the third band-pass filter is connected to the power distribution unit (the input end of the regenerative phase-locked loop).

[0137] The second optoelectronic converter is used to detect the first synchronous optical signal (wavelength is ) collected by the second wavelength division multiplexer and transmit the detection signal to the second radio frequency amplifier.

[0138] The second radio frequency amplifier is used to perform radio frequency amplification on the received detection signal and transmit the amplified signal to the third band-pass filter.

[0139] The third band-pass filter is used to perform band-pass filtering (filter out noise) on the received amplified signal to obtain a radio frequency signal , and transmit the radio frequency signal to the power distribution unit (the input end of the regenerative phase-locked loop).

[0140] It should be noted that the second synchronous optical signal modulated by the second electro-optical converter will be returned to the first device. The second synchronous optical signal is converted into a radio frequency signal after optoelectronic conversion . At this time, the signal will be added with the phase error accumulated during the transmission process from the second device to the first device. Therefore, the expression form of the radio frequency signal is:

[0141]

[0142] Among them, the radio frequency signal and the radio frequency signal are different expression forms of the same signal. Therefore, the two are equivalent and have the following relationship:

[0143]

[0144] The above relationship can be expressed as:

[0145]

[0146] Substituting it into the expression of the radio frequency signal , the simplified expression of the radio frequency signal can be obtained:

[0147]

[0148] Among them, the radio frequency signal has the same simplified expression as the radio frequency signal .

[0149] It can be seen from this that the radio frequency signal and are of the same frequency and in phase. Therefore, phase synchronization between the first device and the second device can be achieved by this method.

[0150] On the basis of the foregoing, with regard to the structure of the third synchronization unit, an optional implementation manner is further provided in an embodiment of the present invention. Please refer to Figure 4 , Figure 4 , which is a schematic structural diagram of the third synchronization unit provided in an embodiment of the present invention.

[0151] The third synchronization unit includes an optical coupler, a third optoelectronic conversion unit, a fourth optoelectronic conversion unit, a second mixer, a second frequency divider, and a sixth band-pass filter.

[0152] The input ends of the third optoelectronic conversion unit and the fourth optoelectronic conversion unit are both connected to the optical coupler, and the output ends of the third optoelectronic conversion unit and the fourth optoelectronic conversion unit are both connected to the input end of the second mixer.

[0153] The output end of the second mixer is connected to the input end of the second frequency divider, the output end of the second frequency divider is connected to the input end of the sixth band-pass filter, and the output end of the sixth band-pass filter is connected to a phase compensation unit (for providing a third reference phase signal ).

[0154] The third optoelectronic conversion unit is configured to detect the first synchronous optical signal (with a wavelength of ) collected by the optical coupler, and transmit the detected radio frequency signal to the second mixer (the first synchronous optical signal comes from the first device).

[0155] The fourth optoelectronic conversion unit is configured to detect the second synchronous optical signal (with a wavelength of ) collected by the optical coupler, and transmit the detected radio frequency signal to the second mixer (the second synchronous optical signal comes from the second device).

[0156] The second mixer is configured to perform mixing processing on the radio frequency signal and the radio frequency signal , and transmit the obtained mixed signal to the second frequency divider.

[0157] The second frequency divider is configured to perform frequency division by two on the mixed signal , and transmit the obtained third reference phase signal (RF signal) is sent to the sixth bandpass filter.

[0158] The sixth bandpass filter is used to filter the third reference phase signal Perform bandpass filtering and convert the filtered third reference phase signal Provided to the phase compensation unit.

[0159] The wavelength is The radio frequency signal obtained by the first synchronous optical signal It is expressed as:

[0160]

[0161] in, represents the transmission time between the first device and the interfering device;

[0162] The wavelength is The second synchronous optical signal is converted into a radio frequency signal It is expressed as:

[0163]

[0164] in, represents the transmission time between the second device and the interfering device;

[0165] RF Signal and RF signals Perform mixing processing to obtain the mixed signal It is expressed as:

[0166]

[0167] in, , Represents the transmission time between the first device and the second device, simplified as:

[0168]

[0169] in, Indicates RF signal The frequency, Indicates RF signal The phase of

[0170] Mixing signal After the frequency is divided by two, the third reference phase signal is obtained (RF signal), which is expressed as:

[0171]

[0172] The third reference phase signal - RF signal and the simplified expression of the second reference phase signal - radio frequency signal is the same as that of the first reference phase signal - radio frequency signal .

[0173] Please continue to refer to Figure 4 . Optionally, the third photoelectric conversion unit includes a third photoelectric converter, a third radio frequency amplifier, and a fourth band - pass filter connected in sequence. The input end of the third photoelectric converter is connected to the optical coupler, and the output end of the fourth band - pass filter is connected to the second mixer.

[0174] The third photoelectric converter is used to detect the first synchronous optical signal (with a wavelength of ) collected by the optical coupler, and transmit the detection signal to the third radio frequency amplifier.

[0175] The third radio frequency amplifier is used to perform radio frequency amplification on the received detection signal and transmit the amplified signal to the fourth band - pass filter.

[0176] The tenth band - pass filter is used to perform band - pass filtering (removing noise) on the received amplified signal to obtain a radio frequency signal , and transmit the radio frequency signal to the second mixer.

[0177] The fourth photoelectric conversion unit includes a fourth photoelectric converter, a fourth radio frequency amplifier, and a fifth band - pass filter connected in sequence. The input end of the fourth photoelectric converter is connected to the optical coupler, and the output end of the fifth band - pass filter is connected to the second mixer.

[0178] The fourth photoelectric converter is used to detect the second synchronous optical signal (with a wavelength of ) collected by the optical coupler, and transmit the detection signal to the fourth radio frequency amplifier.

[0179] The fourth radio frequency amplifier is used to perform radio frequency amplification on the received detection signal and transmit the amplified signal to the fifth band - pass filter.

[0180] The fifth band - pass filter is used to perform band - pass filtering (removing noise) on the received amplified signal to obtain a radio frequency signal , and transmit the radio frequency signal to the second mixer.

[0181] An embodiment of the present invention also provides a method for realizing phase synchronization, which is applied to the above - mentioned TF - QKD system. When the first light source and the second light source achieve frequency synchronization, the method for realizing phase synchronization includes: S101, S102, S103, and S104, which are specifically described as follows.

[0182] S101. The first quantum state modulation unit performs phase encoding on the first continuous light wave emitted by the first light source according to the first reference phase signal provided by the first synchronization unit, and forwards the obtained continuous light wave backward.

[0183] S102. The second quantum state modulation unit is used to perform phase encoding on the second continuous light wave emitted by the second light source according to the second reference phase signal provided by the second synchronization unit, and forwards the obtained continuous light wave backward.

[0184] S103. The phase compensation unit is used to perform phase compensation on the light wave passing through it according to the third reference phase signal provided by the third synchronization unit, and forwards the phase-compensated light wave to the interference execution unit.

[0185] S104. The interference execution unit is used to determine the interference result between the first device and the second device according to the received light wave.

[0186] Wherein, the first reference phase signal, the second reference phase signal, and the third reference phase signal are the same.

[0187] It should be noted that the phase synchronization implementation method provided in this embodiment can perform the functions and uses shown in the above TF-QKD system embodiment to achieve the corresponding technical effects. For the sake of brief description, for the parts not mentioned in this embodiment, reference can be made to the corresponding content in the above embodiment.

[0188] In summary, a TF-QKD system and a phase synchronization implementation method provided by an embodiment of the present invention include: a first device, a second device, and an interference device. The first quantum state modulation unit in the first device is respectively connected to the first light source and the first synchronization unit. The second quantum state modulation unit in the second device is respectively connected to the second light source and the second synchronization unit. The first quantum state modulation unit is also connected to the interference execution unit or the phase compensation unit, and the second quantum state modulation unit is also connected to the other one of them. The phase compensation unit is also connected to the third synchronization unit and the interference execution unit. The first synchronization unit, the second synchronization unit, and the third synchronization unit are connected by optical fibers. Based on the TF-QKD system architecture of the radio frequency synchronization system, the implementation cost and complexity of the TF-QKD system are significantly reduced. The complexity and cost of the synchronization system are effectively reduced, providing key technical support for the large-scale industrial application of TF-QKD devices.

[0189] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0190] It is obvious to those skilled in the art that the present invention is not limited to the details of the above-described exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, in all respects, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes that fall within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention. Any reference signs in the claims should not be construed as limiting the claims concerned.

Claims

1. A TF-QKD system, characterized in that, The TF-QKD system includes: a first device, a second device, and an interference device. The first device includes a first light source, a first quantum state modulation unit, and a first synchronization unit. The second device includes a second light source, a second quantum state modulation unit, and a second synchronization unit. The interference device includes an interference execution unit, a phase compensation unit, and a third synchronization unit; The first quantum state modulation unit is respectively connected to the first light source and the first synchronization unit. The second quantum state modulation unit is respectively connected to the second light source and the second synchronization unit; The first quantum state modulation unit is further connected to the interference execution unit or the phase compensation unit. The second quantum state modulation unit is further connected to the other one of them. The phase compensation unit is further connected to the third synchronization unit and the interference execution unit; The first synchronization unit, the second synchronization unit, and the third synchronization unit are connected by optical fibers; The first quantum state modulation unit is configured to perform phase encoding on the first continuous light wave emitted by the first light source according to the first reference phase signal provided by the first synchronization unit, and transmit the obtained continuous light wave backward; The second quantum state modulation unit is configured to perform phase encoding on the second continuous light wave emitted by the second light source according to the second reference phase signal provided by the second synchronization unit, and transmit the obtained continuous light wave backward; The phase compensation unit is configured to perform phase compensation on the light wave passing through it according to the third reference phase signal provided by the third synchronization unit, and transmit the phase-compensated light wave to the interference execution unit; The interference execution unit is configured to determine the interference result between the first device and the second device according to the received light wave; The first reference phase signal, the second reference phase signal, and the third reference phase signal are the same; The first synchronization unit is configured to generate a first reference phase signal, and send a first synchronization optical signal corresponding to the first reference phase signal to the second synchronization unit and the third synchronization unit; The second synchronization unit is configured to obtain a second reference phase signal according to the received first synchronization optical signal, and send a second synchronization optical signal generated according to the second reference phase signal to the first synchronization unit and the third synchronization unit; The third synchronization unit is configured to obtain a third reference phase signal according to the received first synchronization optical signal and the second synchronization optical signal.

2. The TF-QKD system according to claim 1, wherein, The first synchronization unit includes a radio frequency signal generator, a first frequency divider, a down converter, a first optoelectronic conversion unit, a first electro-optic converter, and a first wavelength division multiplexer; The output end of the radio frequency signal generator is respectively connected to the input end of the first frequency divider and the first input end of the down converter; The output end of the first frequency divider is connected to the first quantum state modulation unit; The second input end of the down converter is connected to the output end of the first optoelectronic conversion unit. The output end of the down converter is connected to the input end of the first electro-optic converter; The output end of the first electro-optical converter and the input end of the first opto-electronic conversion unit are both connected to the first wavelength division multiplexer.

3. The TF-QKD system according to claim 2, wherein The radio frequency signal generator is used to generate a radio frequency signal and transmit the radio frequency signal to the first frequency divider and the downconverter; The first optoelectronic conversion unit is used to detect the second synchronous optical signal collected by the first wavelength division multiplexer and transmit the detected radio frequency signal to the downconverter; The downconverter is used to utilize a radio frequency signal for the radio frequency signal to perform downconversion processing, and transmit the obtained radio frequency signal to the first electro-optical converter; The first electro-optical converter is used to modulate a radio frequency signal onto a first auxiliary optical signal, and transmit the obtained first synchronous optical signal to the first wavelength division multiplexer, so as to transmit it to the second synchronization unit and the third synchronization unit; The first frequency divider is used to perform a frequency division process on the radio frequency signal and provide the obtained first reference phase signal to the first quantum state modulation unit.

4. The TF-QKD system according to claim 1, characterized in that, the second synchronization unit includes a power distribution unit, a second opto-electronic conversion unit, a second electro-optical converter, and a second wavelength division multiplexer; the input end of the second opto-electronic conversion unit and the output end of the second electro-optical converter are both connected to the second wavelength division multiplexer; the output end of the second opto-electronic conversion unit is connected to the input end of the power distribution unit, the first output end of the power distribution unit is connected to the input end of the second electro-optical converter, and the second output end of the power distribution unit is connected to the second quantum state modulation unit.

5. The TF-QKD system according to claim 4, wherein The second photoelectric conversion unit is used to detect the first synchronous optical signal collected by the second wavelength division multiplexer and transmit the detected radio frequency signal to the power distribution unit; The power distribution unit is used to distribute the power of the radio frequency signal and distribute the radio frequency signal according to the power distribution result and send it to the second electro-optic converter; The second electro-optical converter is used to modulate the radio frequency signal onto the second auxiliary optical signal, and transmit the obtained second synchronous optical signal to the second wavelength division multiplexer, so as to transmit it to the first synchronous unit and the third synchronous unit; The power distribution unit is further configured to send the radio frequency signal according to the power distribution result to the second quantum state modulation unit as a second reference phase signal .

6. The TF-QKD system according to claim 1, wherein the third synchronization unit includes an optical coupler, a third opto-electronic conversion unit, a fourth opto-electronic conversion unit, a second mixer, a second frequency divider, and a sixth band-pass filter; the input ends of the third opto-electronic conversion unit and the fourth opto-electronic conversion unit are both connected to the optical coupler, and the output ends of the third opto-electronic conversion unit and the fourth opto-electronic conversion unit are both connected to the input end of the second mixer; the output end of the second mixer is connected to the input end of the second frequency divider, the output end of the second frequency divider is connected to the input end of the sixth band-pass filter, and the output end of the sixth band-pass filter is connected to the phase compensation unit.

7. The TF-QKD system according to claim 6, wherein The third photoelectric conversion unit is configured to detect the first synchronous optical signal collected by the optical coupler and transmit the detected radio frequency signal to the second mixer; The fourth photoelectric conversion unit is used to detect the second synchronous optical signal collected by the optical coupler and transmit the detected radio frequency signal to the second mixer; The second mixer is used to mix the radio frequency signal and the radio frequency signal and perform mixing processing on them, and transmit the obtained mixed signal to the second frequency divider; The second frequency divider is used for performing a frequency division process on the mixed signal and sending the obtained third reference phase signal to the sixth band-pass filter; The sixth band-pass filter is used to perform band-pass filtering on the third reference phase signal and provide the filtered third reference phase signal to the phase compensation unit.

8. A method for realizing phase synchronization, characterized in that, applied to the TF-QKD system according to any one of claims 1-7, when the first light source and the second light source achieve frequency synchronization, the method includes: The first quantum state modulation unit performs phase encoding on the first continuous light wave emitted by the first light source according to the first reference phase signal provided by the first synchronization unit, and transmits the obtained continuous light wave backward; The second quantum state modulation unit is used to perform phase encoding on the second continuous light wave emitted by the second light source according to the second reference phase signal provided by the second synchronization unit, and transmit the obtained continuous light wave backward; The phase compensation unit is used to perform phase compensation on the light wave passing through it according to the third reference phase signal provided by the third synchronization unit, and transmit the phase-compensated light wave to the interference execution unit; The interference execution unit is used to determine the interference result between the first device and the second device according to the received light wave; wherein, the first reference phase signal, the second reference phase signal, and the third reference phase signal are the same.

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