CN107947926B - Synchronization method and device of quantum key distribution system - Google Patents

Synchronization method and device of quantum key distribution system Download PDF

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CN107947926B
CN107947926B CN201711284142.5A CN201711284142A CN107947926B CN 107947926 B CN107947926 B CN 107947926B CN 201711284142 A CN201711284142 A CN 201711284142A CN 107947926 B CN107947926 B CN 107947926B
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qkd
synchronous
light
bob
alice
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CN107947926A (en
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唐世彪
姚海涛
贾云
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Quantumctek Co Ltd
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Quantumctek Co Ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
    • H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
    • H04L9/0852—Quantum cryptography
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2589—Bidirectional transmission
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0227—Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation
    • H04J14/0241—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths
    • H04J14/0242—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON

Abstract

The invention provides a synchronization method of a quantum key distribution system, the quantum key distribution system is a duplex QKD system, the sending ends Alice of a QKD device _ L and a QKD device _ R of the duplex QKD system can respectively send two kinds of synchronous light with different wavelengths, the sent synchronous light is transmitted in the same optical fiber link, when two QKD links run on the optical fiber link simultaneously, the synchronous light wavelengths on the two links are different, and the receiving ends Bob of the QKD device _ L and the QKD device _ R adopt optical filters to separate the synchronous light, and then corresponding discriminators are adopted to discriminate the synchronous light. The invention also provides a synchronizer of the quantum key distribution system. The invention has the advantages that: the two ends of the duplex QKD system respectively adopt the synchronous light with different wavelengths, so that the problem that the duplex QKD system cannot run in full duplex due to the reflection of the synchronous light is solved, and the equipment is simple and convenient to operate and is convenient for batch production.

Description

Synchronization method and device of quantum key distribution system
Technical Field
The invention relates to the field of quantum secret communication, and particularly provides a synchronization method of a quantum key distribution system and a duplex QKD system based on the synchronization method.
Background
Quantum Key Distribution (QKD) is fundamentally different from the classical Key system in that it uses a single photon or entangled photon pair as a carrier of the Key, and the basic principle of Quantum mechanics ensures that the process is not eavesdroppable and indecipherable, thereby providing a more secure Key system. At present, the technology for realizing quantum key distribution by utilizing entangled photons is not mature, and the distance from practical use is also a considerable distance; quantum key distribution technology based on single photon is becoming mature day by day.
The quantum key distribution technology based on single photon implementation generally has two coding modes: polarization encoding and phase encoding. Taking the polarization encoding mode as an example, the basic process of quantum key distribution is as follows:
1) a system sender (appointed to be called Alice) selects two groups of basis vectors and randomly sends a string of photons with different polarization states;
2) a system receiver (called Bob in agreement) randomly selects a measurement basis vector for receiving, and due to the problems of detection efficiency and path attenuation, Bob cannot detect all photons and can only randomly detect photons at some positions;
3) bob informs Alice which basis vector he uses at the location where the photon was detected;
4) alice compares the basis vector used by himself when sending with the basis vector used by Bob when measuring, if the basis vectors used by the two at a certain position are consistent, namely the basis vector used by Bob when measuring is correct, the information at the position is retained, and Bob is told which positions the measurement basis vector used by him is correct;
5) bob leaves information on the correct position of the basis vector;
6) so that Alice and Bob share a random series of keys.
It can be seen from the above process that in the process of quantum key distribution, Alice and Bob need to perform basis vector comparison, that is, whether a basis vector used by Alice to send a photon at a certain position is consistent with a measurement basis vector used by Bob to detect a photon at the certain position is compared. In order to ensure that Alice and Bob perform basis vector comparison at the same position, the sender and the receiver need to be precisely synchronized in position, otherwise, the keys at the two ends of Alice and Bob are inconsistent. Therefore, the synchronization method of the system is particularly important.
The "position" in the above description is visually described as the first pulse in a set of light pulses. At the transmitting end, the optical pulses of the signal light are transmitted continuously at a fixed frequency with a fixed time slot between two adjacent optical pulses, while the optical pulses of the synchronization light are transmitted continuously at a fixed frequency much lower than the signal light transmission frequency. When the signal light and the synchronous light are sent simultaneously, the continuous signal light sent between the two synchronous light pulses is a group of light pulses. When the receiving end receives continuous signal light, a group of light pulses can be determined by detecting the signal light pulse between two synchronous light pulses. The "position" information can be determined by the number of pulses in a set of signal light pulses. The "position" is also time information because of the fixed time slot between two adjacent signal light pulses.
Figure 1 shows a synchronization method of the prior art solution. The QKD system synchronization method is that Alice of the QKD equipment sends synchronous light, and Bob receives the synchronous light to complete discrimination and generate synchronous signals. The quantum channel in the system has only one optical fiber, i.e. the signal light and the synchronous light are transmitted in the same optical fiber.
In a QKD system implementation, Alice may include N signal light lasers (the specific number depending on the QKD encoding protocol employed) and one synchronous light laser, the signal light having a wavelength λsignalWavelength of the synchronizing light is lambdasyncAnd λsignal≠λsyncAnd the two kinds of light are coupled in the same optical fiber and transmitted to the Bob end through an optical fiber link. The Bob terminal includes an optical filter device, e.g. Dense Wavelength Division Multiplexing (DWDM) device, having a center wavelength λsignalThe signal light and the synchronous light can be separated, then the separated signal light is processed correspondingly, and the separated synchronous light is sent into a synchronous light discriminator for discrimination. And the signal screened by the discriminator is used as a synchronous signal for the subsequent processing process of the signal light.
As shown in fig. 2, each device includes a sending end Alice and a receiving end Bob, and two QKD links can be established between the two QKD devices at the same time. The two QKD links are: establishing a link between Alice of the QKD device _ L and Bob of the QKD device _ R; alice of QKD device _ R establishes a chain with Bob of QKD device _ L. After the synchronous light emitted by the Alice synchronous light laser of the QKD device _ L is transmitted by the optical fiber link, the synchronous light is discriminated by the Bob synchronous light discriminator of the QKD device _ R; after the synchronous light emitted by Alice's synchronous light laser of QKD device _ R is transmitted through the optical fiber link, it is discriminated by Bob's synchronous light discriminator of QKD device _ L.
As can be seen from the prior art, in the conventional duplex QKD system based on synchronization, the wavelengths of the synchronization light emitted by Alice of the QKD device _ L and Alice of the QKD device _ R are the same.
In the art, there is a definition of a "two-way QKD system," which refers to a QKD implementation in which signal light is sent from a first QKD terminal to a second QKD terminal, and then back along the original optical path. Generally, the signal light transmitted from the first QKD terminal to the second QKD terminal is strong, averaging hundreds or thousands of photons per pulse, and attenuated to single photon magnitude (averaging one photon per pulse or less) at the second QKD terminal before returning to the first QKD terminal. The optical fiber link of the system has only one QKD link, and is a two-way (two-way) simplex process.
In contrast, such as the two-way QKD system with backscattering suppression by MAGIQ technology corporation (patent No. 200580025415.3), the first QKD station has a laser source emitting light at different wavelengths and a plurality of single-photon detector (SPD) units. In a two-way QKD system, backscattered light is generally generated by the stronger output signal light in the fiber link connecting the first and second QKD stations. To reduce or avoid back-scattered light interfering with the detection of signal light returning from the second QKD station to the first QKD station, the patent sequentially activates different light sources when pairs of SPDs in SPD units in the first QKD station are sequentially activated. The patent aims to solve the problem that the detection of signal light in a two-way QKD system is easily interfered by back scattering light, the requirement on a related control system is high, the expected arrival time of the signal light needs to be calculated according to the length of an actual optical fiber link, the activation control of different light sources and SPD units is carried out at the expected arrival time, the control precision requirement is high, and the sequential activation process is continuously carried out.
When the existing synchronization method is applied to a one-way (one-way) duplex system, as shown in fig. 2, the wavelengths of the synchronization light emitted by Alice of the QKD device _ L and Alice of the QKD device _ R are the same and are transmitted in the same optical fiber. Due to the fact that the actual optical fiber link environment is not ideal, the phenomenon of optical fiber end face reflection exists. For example, after the chain between Alice of the QKD device _ L and Bob of the QKD device _ R is started, there may be a reflection phenomenon of the synchronization light emitted by Alice of the QKD device _ L, and the reflected light enters Bob of the QKD device _ L, so that the synchronization signals in the chain between Alice of the QKD device _ R and Bob of the QKD device _ L are mistakenly discriminated; thus, when the link between Alice of the QKD device _ R and Bob of the QKD device _ L is started, the synchronous light emitted by Alice of the QKD device _ R may be interfered, resulting in the system not operating normally.
Disclosure of Invention
The invention provides a synchronization method and a synchronization device of a quantum key distribution system, which are used for solving the problem that two QKD links cannot run simultaneously due to synchronous light reflection caused by the fact that the wavelengths of Alice of a QKD device _ L and Alice of a QKD device _ R in a duplex QKD system are the same.
The invention adopts the following technical scheme to solve the technical problems: the synchronization method is used in a duplex QKD system, the sending ends Alice of a QKD device _ L and a QKD device _ R of the duplex QKD system can respectively send two kinds of synchronization light with different wavelengths, the sent synchronization light is transmitted in the same optical fiber link, when the two QKD links run on the optical fiber link simultaneously, the synchronization light wavelengths on the two links are different, and the receiving ends Bob of the QKD device _ L and the QKD device _ R adopt corresponding discriminators to discriminate the synchronization light.
It is noted that the "duplex QKD system" concept used in the present invention is not the same concept as the "two-way QKD system" in the reference.
One implementation of QKD is proposed in the reference "two-way QKD system with backscatter suppression", and is not a method of synchronization of the system. The definition of the "two-way system" in this reference is that a QKD device (Bob) at one end of the system emits a strong signal light, which is transmitted to a QKD device (Alice) at the other end of the system, Alice attenuates the signal light to a single-photon magnitude, and then returns the signal light to Bob according to the original optical path, where the optical path is a back-and-forth process. In the whole process, only one QKD working link is arranged on the optical fiber link between the two QKD devices, and the process is a two-way (two-way) and simplex process.
The duplex system in the patent application of the invention is defined as a system capable of working in full duplex, each end of the duplex system comprises Alice and Bob, and two QKD links can be established simultaneously. Weak signal light (single photon magnitude) may be transmitted from a transmitting end Alice of the QKD device _ L to a receiving end Bob of the QKD device _ R, and may also be transmitted from Alice of the QKD device _ R to Bob of the QKD device _ L (fig. 4). Thus, two QKD working links can be simultaneously operated on the optical fiber link between the QKD devices at two ends of the duplex system, and the process is one-way and full-duplex. This is very different from the "bidirectional system" of the reference in terms of structure and optical signal transmission.
The sending ends Alice of the QKD device _ L and the QKD device _ R of the duplex QKD system can respectively send two kinds of synchronous light with different wavelengths, and the discrimination process can be realized by any one of the following methods:
1. two synchronous optical lasers with different wavelengths are respectively arranged at the sending ends Alice of the QKD system QKD device _ L and the QKD device _ R, a control module is required to be arranged in the duplex QKD system, the sending ends Alice of the QKD system QKD device _ L and the QKD device _ R are controlled by the control module to respectively send synchronous light with which wavelength, the sent synchronous light is sent to Bob corresponding to the QKD device in the same optical fiber link, the receiving ends Bob of the QKD system QKD device _ L and the QKD device _ R are respectively provided with an optical filter, the optical filter sends the separated synchronous light into corresponding discriminators for discrimination, and the control module also controls the receiving ends Bob of the QKD device _ L and the QKD device _ R to respectively use signals detected by which discriminators as synchronous signals.
Because the actual optical fiber link environment is not ideal, the phenomenon of optical fiber end face reflection exists, two paths of synchronous light with different wavelengths may exist on one QKD working link, wherein the synchronous light with one wavelength and the reflected synchronous light with the other wavelength are respectively sent to corresponding discriminators after passing through optical filters. For example, the center frequency of the optical filter device is λ1(this center frequency is generally a fixed value), when the wavelength used is λ1When the synchronous light is emitted, the synchronous light passes through the optical filterThen, the obtained product is sent into a discriminator 1 for discrimination; when the wavelength used is lambda2When the synchronous light passes through the optical filter, the lambda is removed1All other optical signals are sent into the discriminator 2 for discrimination, interference such as noise in the optical fiber link has little influence on the discrimination of the synchronous light and can be ignored, therefore, the wavelength lambda can be correctly discriminated2The synchronizing light of (1). (the process of "discriminating by sending the separated synchronization light to the corresponding discriminator" mentioned in the following is referred to as the process)
2. Two synchronous optical lasers with different wavelengths are respectively arranged at the sending ends Alice of the QKD system QKD device _ L and the QKD device _ R, the sent synchronous light is sent to the Bob corresponding to the QKD device in the same optical fiber link, the receiving ends Bob of the QKD system QKD device _ L and the QKD device _ R are respectively provided with an optical filter, the optical filter sends the separated synchronous light into the corresponding discriminator for discrimination, after the system is initially configured, one of the QKD devices adopts one of the synchronous optical lasers to send light with the wavelength of lambda1The synchronous light sync1, and the signal detected by a corresponding discriminator is taken as the synchronous signal, and the other QKD device adopts a synchronous light laser to send the signal with the wavelength of lambda2And sync light sync2, and takes the signal detected by the corresponding one of the discriminators as the sync signal.
3. The sending ends Alice of the QKD system QKD device _ L and the QKD device _ R are respectively provided with a wavelength-adjustable synchronous light laser which can send out two kinds of synchronous light with different wavelengths, the sending ends Alice of the QKD system QKD device _ L and the QKD device _ R respectively send which kind of wavelength of synchronous light to be dispatched by a control module, the sent synchronous light is sent to Bob corresponding to the QKD device in the same optical fiber link, the receiving ends Bob of the QKD system QKD device _ L and the QKD device _ R are respectively provided with an optical filter, the optical filter sends the separated synchronous light into corresponding discriminators for discrimination, and the control module further controls the receiving ends Bob of the QKD device _ L and the QKD device _ R to respectively use which kind of discriminator detected signal as a synchronous signal.
4. A wave is configured at the sending ends Alice of the QKD device _ L and the QKD device _ R of the QKD systemThe wavelength-adjustable synchronous optical laser can emit two kinds of synchronous light with different wavelengths, the transmitted synchronous light is transmitted to Bob corresponding to QKD equipment in the same optical fiber link, optical filters are arranged at receiving ends Bob of QKD system QKD equipment _ L and QKD equipment _ R, the optical filters transmit the separated synchronous light into corresponding discriminators for discrimination, and after the system is initially configured, the synchronous optical laser of one QKD equipment transmits the synchronous light with the wavelength of lambda1And the synchronous light sync1, and the signal detected by a corresponding discriminator is taken as the synchronous signal, and the synchronous light laser of the other QKD device sends out the signal with the wavelength of lambda2And sync light sync2, and takes the signal detected by the corresponding one of the discriminators as the sync signal.
5. The sending ends Alice of the QKD system QKD device _ L and the QKD device _ R are respectively provided with a synchronous optical laser with fixed wavelength, the wavelengths sent by the synchronous optical lasers at the two ends are different, the sent synchronous light is sent to Bob of the corresponding QKD device in the same optical fiber link, and the receiving ends Bob of the QKD system QKD device _ L and the QKD device _ R adopt corresponding discriminators to discriminate the synchronous light.
The invention also provides a synchronizer of the quantum key distribution system, the quantum key distribution system is a duplex QKD system, the synchronizer comprises synchronous optical lasers respectively arranged at the sending ends Alice of the QKD system QKD device _ L and the QKD device _ R, the synchronous optical lasers of the QKD devices at the two ends of the QKD system can respectively send out two kinds of synchronous light with different wavelengths, and the receiving ends Bob of the QKD system QKD device _ L and the QKD device _ R are both provided with discriminators which are used for discriminating the synchronous light.
The specific device structure may be any of the following:
1. the sending end Alice's of QKD system QKD equipment _ L and QKD equipment _ R synchronous optical laser instrument all has two, and two synchronous optical laser instruments can send different wavelength to QKD system QKD equipment _ L and QKD equipment _ R's receiving end Bob all disposes optical filter and two kinds of discriminator that can discriminate two kinds of different wavelengths that synchronous optical laser instrument sent respectively, and optical filter sends the synchronous light that separates into in the corresponding discriminator and discriminates.
In this structure, the duplex QKD system is further configured with a control module, the control module controls which wavelength of the synchronous light is respectively sent by the synchronous light lasers of the QKD devices at the two ends of the QKD system, and the control module also controls which discriminator the signal detected by the receiving ends Bob of the QKD device _ L and the QKD device _ R is respectively used as the synchronous signal.
Or, the synchronous light lasers of the QKD devices at two ends of the QKD system send synchronous light of which wavelength and the receiving ends Bob of the QKD device _ L and the QKD device _ R respectively use signals detected by which discriminator as synchronous signals, and the signals are determined by system initial configuration.
2. The sending ends Alice of the QKD system QKD device _ L and the QKD device _ R are both provided with a wavelength-adjustable synchronous optical laser which can send out synchronous light with two different wavelengths, and the receiving ends Bob of the QKD system QKD device _ L and the QKD device _ R are both provided with an optical filter and two discriminators which can discriminate the two different wavelengths sent out by the synchronous optical laser respectively, and the optical filter sends the separated synchronous light into the corresponding discriminators for discrimination.
In the structure, a control module is further configured in the duplex QKD system, which wavelength of the synchronous light is respectively sent by the synchronous light lasers with adjustable wavelengths at the sending ends Alice of the QKD device _ L and the QKD device _ R is scheduled by the control module, and the control module further controls which discriminator detected signal is respectively used as the synchronous signal by the receiving ends Bob of the QKD device _ L and the QKD device _ R.
Or, the wavelength-adjustable synchronous light lasers of the QKD devices at the two ends of the QKD system send synchronous light of which wavelength and the receiving ends Bob of the QKD device _ L and the QKD device _ R respectively use signals detected by which discriminator as synchronous signals, and the determination is made through system initial configuration.
3. The sending ends Alice of the QKD system QKD device _ L and the QKD device _ R are provided with synchronous optical lasers with fixed wavelengths, the wavelengths sent by the synchronous optical lasers at the two ends are different, and the receiving ends Bob of the QKD system QKD device _ L and the QKD device _ R are provided with discriminators capable of fixedly discriminating the received wavelengths.
The invention has the advantages that:
1. the two ends of the duplex QKD system respectively adopt the synchronous light with different wavelengths, so that the problem that the duplex QKD system cannot run in full duplex due to the reflection of the synchronous light is solved;
2. according to the first embodiment and the second embodiment, compared with the original QKD system, the QKD equipment only needs to add one more synchronous optical laser at the Alice end, or the Alice uses the synchronous optical laser with adjustable wavelength to achieve the function of transmitting two different wavelengths; only one optical filter and one synchronous optical discriminator are added at the Bob end. The cost of the added devices of the system equipment is lower, the characteristics that the QKD equipment _ L and the QKD equipment _ R are completely the same can be realized in the structure, the functions of point-to-point connection and communication can be realized by any two pieces of QKD equipment, the equipment operation is simple and convenient, and the batch production is convenient;
3. according to the third embodiment, compared with the original QKD system, Alice and Bob of the QKD device do not need to add any new hardware, and only synchronous lights with different wavelengths are respectively configured for Alice of the QKD device _ L and the QKD device _ R when the system is factory configured, and correspondingly, different discriminators are respectively configured for Bob of the QKD device _ L and the QKD device _ R, so that the QKD device _ L and the QKD device _ R are produced in pairs, the device is simple and convenient to operate, and batch production is facilitated;
4. bob ends at two ends of the duplex QKD system use an optical filter and two discriminators, so that the link quality, system debugging and problem location can be conveniently identified. For example, Alice on the QKD device _ L and Bob on the QKD _ R have established a link and started to operate, and if it is found that a discriminator corresponding to the synchronous optical wavelength sent by the Bob end and the Alice at the home end on the QKD device _ L has an output, it is indicated that synchronous optical reflection exists on the optical fiber link.
Drawings
Fig. 1 is a schematic diagram of a synchronization method in a prior art solution.
Fig. 2 is a schematic diagram of a one-way (one-way), duplex QKD system based on existing synchronization approaches.
Fig. 3 is a schematic diagram of a synchronization method scenario of the synchronization method of the quantum key distribution system according to the present invention.
Fig. 4 is a schematic diagram of a duplex system.
Fig. 5 is a schematic diagram of a duplex QKD system based on the synchronization method of the present invention.
FIG. 6 is a schematic diagram of a duplex QKD system in which Alice uses two synchronized optical lasers at different wavelengths.
FIG. 7 is a schematic diagram of a duplex QKD system using a variable wavelength synchronous optical laser by Alice.
FIG. 8 is a schematic diagram of a duplex QKD system using synchronized optical lasers of different wavelengths for Alice and Bob, respectively.
Fig. 9 is a schematic diagram of a synchronization method scenario two of the synchronization method of the quantum key distribution system according to the present invention.
Detailed Description
The present invention is described in detail below with reference to the attached drawings.
There are two typical scenarios for the transmission of signal light and synchronization light in a duplex QKD system. Scene one (fig. 3) is that the sending end Alice end signal light and the synchronous light of the system QKD device _ L and the QKD device _ R can be coupled and transmitted in the same optical fiber, under the condition, the receiving ends Bob of the system QKD device _ L and the QKD device _ R need two stages of optical filters and two discriminators, the first stage of optical filter separates the signal light and the synchronous light, and the second stage of optical filter sends the separated synchronous light into the corresponding discriminators for discrimination. In a second scenario (fig. 9), the signal light and the synchronous light at the Alice end of the sending end of the QKD device _ L and the QKD device _ R of the system are transmitted in two optical fibers, in this case, the receiving end Bob of the QKD device _ L and the QKD device _ R of the system only needs a first-order optical filter and two discriminators, and the optical filter sends the separated synchronous light into the corresponding discriminators for discrimination.
The following embodiments are described by taking the scenario one as an example.
Fig. 3 is a schematic diagram of a first scenario of the synchronization method according to the present invention, where the system using the method shown in the diagram is only a typical case and is not the only case, and the schematic diagram is only to describe in detail one of processes of sending out two kinds of synchronization light with different wavelengths respectively by sending terminals Alice of a QKD device _ L and a QKD device _ R of a duplex QKD system, and a specific process of separating signal light from synchronization light by using an optical filter and then screening the synchronization light by using a corresponding discriminator by using a receiving terminal Bob of the QKD device _ L and the QKD device _ R, and is mainly used to describe a process of separating the signal light from the synchronization light by using the optical filter and a selection of the optical filter.
Fig. 3 omits the Bob end of the QKD device _ L and the Alice end of the QKD device _ R, and only embodies the process of unidirectional synchronous light sent from the Alice end of the QKD device _ L to the Bob end of the QKD device _ R; the process by which Alice of QKD device _ R sends a sync light to Bob of QKD device _ L is the same.
Alice of the QKD device _ L comprises a plurality of signal light lasers and two synchronous light lasers, wherein the synchronous light lasers 1 and 2 can respectively send two kinds of synchronous light lambda with different wavelengths1And λ2. Alice of the QKD device _ L chooses to use one of the wavelengths (lambda)1Or λ2) Of synchronous light, e.g. of selected wavelength λ1Of the synchronous light, i.e. the central wavelength λ of the synchronous lightsync＝λ1And the center wavelength of the N path is lambdasignalIs optically coupled to Bob, which is sent to QKD device _ R in the same optical fiber link. Accordingly, Alice (not shown in fig. 3) of QKD device _ R chooses to use a wavelength λ2The synchronizing light of (1).
Bob of the QKD device _ R separates out the signal light using the first-stage optical filter and then separates out the synchronization light using the second-stage optical filter. Preferably, the first stage optical filter device may be a Dense Wavelength Division Multiplexing (DWDM) device with a central Wavelength λsignal. After the signal light and the synchronous light pass through the DWDM device, the signal light is separated according to the central wavelength and is subjected to subsequent processing; the synchronous optical signals except the signal light are uniformly sent to the second stage optical filter. Preferably, the second stage optical filter device is a DWDM device with a center wavelength of λ1Or λ2Two kinds of synchronous light with different wavelengths can be separated, and the wavelength is lambda1Is sent into the discriminator 1, the wavelength is lambda2Is sent into the discriminator 2 to discriminateThe light is synchronized. The signal selected by the discriminator 1 or the discriminator 2 is the synchronization signal (in this case, λ and λ)1Corresponding synchronization signals) for subsequent processing of the signal light.
In the duplex QKD system structure based on the synchronization method described in fig. 3, each QKD device includes a sending end Alice and a receiving end Bob, and can perform full-duplex operation, and two paths of synchronization light can be transmitted in an optical fiber link, as shown in fig. 4. The sending ends Alice of the QKD equipment _ L and the QKD equipment _ R of the duplex system both comprise lasers capable of sending two kinds of synchronous light with different wavelengths, the receiving ends Bob of the QKD equipment _ L and the QKD equipment _ R both comprise two stages of optical filters, the first stage of optical filters can separate signal light and synchronous light, and the second stage of optical filters can send the separated synchronous light into corresponding discriminators for discrimination.
The duplex QKD system based on this synchronous approach may also include an upper control module, as shown in fig. 5, whose main function is to control which wavelength of synchronous light is used on the QKD link. When a link is selected with a wavelength of lambda1When the synchronous light is sync1, the other link uses the wavelength of lambda2Synchronous light sync 2. The control module can be realized by software, or can be realized by hardware such as a single chip microcomputer, an FPGA, a DSP and the like.
The duplex QKD system described in the present invention has a structure shown in fig. 5, where each of the QKD device _ L and the QKD device _ R includes Alice and Bob, and two QKD links, i.e., a link between Alice of the QKD device _ L and Bob of the QKD device _ R and a link between Alice of the QKD device _ R and Bob of the QKD device _ L, can be established between the two devices at the same time. The entire duplex QKD system operates using full duplex mode. The duplex QKD system is characterized in that the two QKD links use the synchronous light with different wavelengths, so that the problem that the reflected light of the synchronous light of one link interferes with the normal discrimination of the synchronous light of the other link when the wavelengths of the synchronous light used by the two links are the same is solved, the problem that the two QKD links cannot run simultaneously is solved, and the full duplex function of the QKD system is realized.
The Alice of the QKD device _ L and the QKD device _ R may be a laser including a synchronous light capable of transmitting two different wavelengths, or the Alice of the QKD device _ L and the Alice of the QKD device _ R may use a laser including a synchronous light with different wavelengths. If Alice of the QKD device _ L and the QKD device _ R is the first condition, Bob of the QKD device _ L and the QKD device _ R both comprise two stages of optical filters, and can separate signal light and two kinds of synchronous light with different wavelengths; if Alice of the QKD device _ L and QKD device _ R is the second case, Bob of the QKD device _ L and QKD device _ R only has a primary optical filter device, and the signal light and the synchronization light can be separated.
The synchronous optical lasers for Alice of the QKD device _ L and the QKD device _ R in the duplex QKD system may include, but are not limited to, the following forms:
EXAMPLE one (Simultaneous light laser using two different wavelengths)
Option1 (wavelength of synchronous light sent by Alice is determined by control module):
as shown in FIG. 6, Alice of each of the QKD devices _ L and _ R is configured with two synchronous optical lasers-a synchronous optical laser 1 and a synchronous optical laser 2, wherein the synchronous optical laser 1 fixedly transmits synchronous light sync1 with a wavelength λ1The synchronous optical laser 2 constantly transmits synchronous light sync2 with a wavelength λ2And λ1≠λ2. Bob of each of the QKD devices _ L and QKD device _ R is configured with two stages of optical filters, the first stage of optical filter can separate signal light and synchronization light, and the second stage of optical filter can separate two paths of synchronization light with different wavelengths, as shown in fig. 3. The second-stage optical filter device respectively transmits the two paths of separated synchronous light into corresponding discriminators, and the discriminator 1 fixedly discriminates the central wavelength of lambda1The discriminator 2 fixedly discriminates the central wavelength as lambda2Synchronous light sync 2.
The duplex QKD system is provided with a control module for controlling the QKD equipment _ L and the QKD equipment _ R to respectively send synchronous light sync1 and sync2 with different wavelengths; meanwhile, the control module also controls Bob of the QKD device _ L and the QKD device _ R to respectively use the signal detected by which discriminator as the synchronous signal corresponding to the synchronous light sent by Alice.
The specific implementation is as follows: on the link between Alice of the QKD device _ L and Bob of the QKD device _ R, the control module schedules the Alice of the QKD device _ L to use the synchronous optical laser 1 to transmit light with the wavelength of lambda1Synchronous light sync 1; then at the Bob end of QKD device _ R, the signal light is separated by the first stage optical filter device, and then the synchronization light sync1 is separated by the second stage optical filter device. And (4) scheduling by a control module, and taking the signal detected by the discriminator 1 as a synchronous signal.
Correspondingly, on the link between Alice of the QKD device _ R and Bob of the QKD device _ L, the control module schedules Alice of the QKD device _ R to use the synchronous optical laser 2 to transmit light with the wavelength λ2Synchronous light sync 2; then at the Bob end of QKD device _ L, the first stage optical filter device separates out the signal light, and the second stage optical filter device separates out the synchronization light sync 2. And the signals detected by the discriminator 2 are taken as synchronous signals through the scheduling of the control module.
The control module has the advantage that when synchronization of a certain QKD link is in a problem, for example, a synchronous optical laser or a discriminator used for the QKD link is abnormal, the synchronous optical laser and the discriminator in the QKD devices at two ends can be conveniently scheduled and switched through the control module, so that the full-duplex QKD system can still normally work. For example, if the synchronous optical laser 1 used by Alice of the QKD device _ L works abnormally, the control module schedules Alice of the QKD device _ L to use the synchronous optical laser 2, and schedules Bob of the QKD device _ R to use a signal detected by the discriminator 2 as a synchronous signal; meanwhile, the control module schedules Alice of the QKD device _ R to use the synchronous optical laser 1, and schedules Bob of the QKD device _ L to use the signal detected by the discriminator 1 as a synchronous signal.
Option2 (wavelength of synchronous light sent by Alice is initially configured):
alice of the QKD device _ L and the QKD device _ R is provided with two synchronous light lasers, namely a synchronous light laser 1 and a synchronous light laser 2. The synchronous optical laser 1 constantly emits synchronous light sync1 with a wavelength λ1(ii) a The synchronous optical laser 2 constantly emits synchronous light sync2 with a wavelength λ2And λ1≠λ2。
QKD device _ LBob of the QKD device _ R and the QKD device _ R are both configured with two stages of optical filters, the first stage of optical filter can separate out signal light, and the second stage of optical filter can separate out two kinds of synchronous light with different wavelengths, as shown in fig. 3. The second-stage optical filter device respectively transmits the two paths of separated synchronous light into corresponding discriminators, and the discriminator 1 fixedly discriminates the central wavelength of lambda1The discriminator 2 fixedly discriminates the central wavelength as lambda2Synchronous light sync 2.
After the initial configuration of the system, the QKD device _ L adopts a synchronous light laser 1 to send synchronous light sync1, and takes the signal detected by the discriminator 2 as a synchronous signal; the QKD device _ R sends synchronous light sync2 using a synchronous light laser 2, and takes the signal detected by the discriminator 1 as a synchronous signal.
When a problem occurs in synchronization of a certain QKD link, for example, a synchronous optical laser or a discriminator used for the QKD link is abnormal, the synchronous optical laser and the discriminator in the QKD devices at two ends can be scheduled and switched through modes such as system reinitialization, so that the full-duplex QKD system can still work normally. For example, if the synchronous optical laser 1 used by Alice of the QKD device _ L works abnormally, the duplex QKD system is initialized again, and during initial configuration, Alice configuring the QKD device _ L uses the synchronous optical laser 2, and Bob configuring the QKD device _ R takes a signal detected by the discriminator 2 as a synchronous signal; meanwhile, Alice configuring the QKD device _ R uses the synchronous optical laser 1, and Bob configuring the QKD device _ L takes the signal detected by the discriminator 1 as a synchronous signal.
EXAMPLE two (use of a variable wavelength synchronous laser)
Option1 (wavelength of synchronous light sent by Alice is determined by control module):
as shown in FIG. 7, Alice of both QKD device _ L and QKD device _ R uses a wavelength-tunable synchronous optical laser that transmits synchronous light sync1 at a wavelength λ1Synchronous light sync2 can also be sent with wavelength lambda2And λ1≠λ2The wavelength at which it transmits the synchronization light is scheduled by the control module. QKD device _ L andbob of the QKD device _ R is configured with two stages of optical filters, the first stage of optical filter can separate out signal light and synchronization light, and the second stage of optical filter can separate out synchronization light with different wavelengths, as shown in fig. 3. The two separated paths of synchronous light are respectively sent into corresponding discriminators, and the discriminator 1 discriminates the wavelength of lambda fixedly1The discriminator 2 fixedly discriminates the wavelength λ of the synchronous light sync12Synchronous light sync 2.
The duplex QKD system is provided with a control module which is used for controlling Alice of the QKD device _ L and Alice of the QKD device _ R to respectively send synchronous light sync1 and sync2 with different wavelengths. Meanwhile, the control module also controls Bob of the QKD device _ L and the QKD device _ R to respectively use the signal detected by which discriminator as the synchronous signal corresponding to the synchronous light sent by Alice.
The specific implementation is as follows: on a link between Alice of the QKD device _ L and Bob of the QKD device _ R, the control module schedules the Alice of the QKD device _ L to use a wavelength-adjustable synchronous optical laser to send a synchronous optical laser with a wavelength of lambda1Synchronous light sync 1; then at the Bob end of QKD device _ R, the signal light is separated by the first stage optical filter device, and then the synchronization light sync1 is separated by the second stage optical filter device. And (4) scheduling by a control module, and taking the signal detected by the discriminator 1 as a synchronous signal.
Correspondingly, on a link between Alice of the QKD device _ R and Bob of the QKD device _ L, the control module schedules the Alice of the QKD device _ R to use a synchronous optical laser with adjustable wavelength to send the synchronous optical laser with the wavelength of lambda2Synchronous light sync 2; then at the Bob end of QKD device _ L, the first stage optical filter device separates out the signal light, and the second stage optical filter device separates out the synchronization light sync 2. And the signals detected by the discriminator 2 are taken as synchronous signals through the scheduling of the control module.
Option2 (wavelength of synchronous light sent by Alice is initially configured):
the Alice of the QKD device _ L and the Alice of the QKD device _ R both use a wavelength-adjustable synchronous light laser which can send synchronous light sync1 with the wavelength of lambda1Synchronous light sync2 can also be sent with wavelength lambda2And is andλ1≠λ2。
bob of each of the QKD devices _ L and QKD device _ R is configured with two stages of optical filters, the first stage of optical filter can separate out signal light and synchronization light, and the second stage of optical filter can separate out two types of synchronization light with different wavelengths, as shown in fig. 3. The two separated paths of synchronous light are respectively sent into corresponding discriminators, and the discriminator 1 fixedly discriminates that the central wavelength is lambda1The discriminator 2 fixedly discriminates the central wavelength as lambda2Synchronous light sync 2.
At system initial configuration, the configurable QKD device _ L transmits a wavelength λ1The synchronous light sync1, and the signal detected by the discriminator 2 is taken as a synchronous signal; configuring QKD device _ R to transmit at a wavelength of λ2And sync light sync2, and takes the signal detected by the discriminator 1 as a sync signal.
EXAMPLE three (two synchronous lasers with different wavelengths are used at the two ends of the system)
As shown in fig. 8, the QKD device _ L and the QKD device _ R each use a synchronous optical laser of a different wavelength, and the synchronous optical laser 1 fixedly transmits light of wavelength λ1Synchronous light sync1, synchronous light laser 2 constantly transmitting light of wavelength λ2Synchronous light sync2, and λ1≠λ2. The Bob of each of the QKD device _ L and the QKD device _ R employs a primary optical filter device for separating the signal light and the synchronization light. The separated synchronous light is sent into a discriminator, and the discriminator 1 discriminates the central wavelength of lambda fixedly1The discriminator 2 fixedly discriminates the central wavelength as lambda2Synchronous light sync 2.
The specific implementation is as follows: on the link between Alice of the QKD device _ L and Bob of the QKD device _ R, Alice of the QKD device _ L fixedly transmits light with a wavelength λ using a synchronous optical laser 11The synchronous light sync1 is obtained by separating the synchronous light from the Bob end of the QKD device _ R through a first-order optical filter, and then using a discriminator 1 to discriminate the central wavelength λ1Synchronous light sync 1. Correspondingly, on the link between Alice of the QKD device _ R and Bob of the QKD device _ L, Alice of the QKD device _ R uses the synchronous optical laser 2, fixedGround transmission wavelength is lambda2The synchronous light sync2 is obtained by separating the synchronous light from the Bob end of the QKD device _ L through a first-order optical filter, and then using a discriminator 2 to discriminate the central wavelength λ2Synchronous light sync 2.
Fig. 9 is a schematic diagram of a second scenario in the synchronization method of the present invention. The system shown in fig. 9 using this method is only a typical case and not the only case. Fig. 9 omits the Bob end of the QKD device _ L and the Alice end of the QKD device _ R, and only embodies the process of unidirectional synchronous light sent from the Alice end of the QKD device _ L to the Bob end of the QKD device _ R; the process by which Alice of QKD device _ R sends a sync light to Bob of QKD device _ L is the same.
The signal light and the synchronous light shown in the scene two are transmitted by using two optical fiber links respectively, and the method is also applicable to the situations described in the first, second and third embodiments of the present invention.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and should not be taken as limiting the invention, so that any modifications, equivalents, improvements, etc. made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (11)

1. A quantum key distribution system synchronization method, the quantum key distribution system is a duplex QKD system, each end includes Alice and Bob, can establish two QKD links at the same time, the signal light is transmitted from the sending end Alice of QKD equipment _ L to the receiving end Bob of QKD equipment _ R, also can be transmitted from Alice of QKD equipment _ R to Bob of QKD equipment _ L, can run two QKD working links on the optical fiber link between the QKD equipment of both ends of the duplex QKD system, it is a unidirectional, full-duplex process, characterized by: the sending ends Alice of the QKD device _ L and the QKD device _ R of the duplex QKD system can respectively send two kinds of synchronous light with different wavelengths, the sent synchronous light is transmitted in the same optical fiber link, so that when the two QKD links run on the optical fiber link at the same time, the synchronous light wavelengths on the two links are different, and the receiving ends Bob of the QKD device _ L and the QKD device _ R adopt corresponding discriminators to discriminate the synchronous light.
2. The synchronization method of a quantum key distribution system according to claim 1, characterized in that: the synchronization method specifically comprises the following steps: two synchronous optical lasers with different wavelengths are respectively arranged at the sending ends Alice of the QKD system QKD device _ L and the QKD device _ R, a control module is arranged in the duplex QKD system, the sending ends Alice of the QKD system QKD device _ L and the QKD device _ R are controlled by the control module to respectively send synchronous light with which wavelength, the sent synchronous light is sent to Bob corresponding to the QKD device in the same optical fiber link, the receiving ends Bob of the QKD system QKD device _ L and the QKD device _ R are respectively provided with an optical filter, the optical filter sends the separated synchronous light into corresponding discriminators for discrimination, and the control module also controls the receiving ends Bob of the QKD device _ L and the QKD device _ R to respectively use signals detected by which discriminators as synchronous signals.
3. The synchronization method of a quantum key distribution system according to claim 1, characterized in that: the synchronization method specifically comprises the following steps: the sending ends Alice of the QKD system QKD device _ L and the QKD device _ R are respectively provided with a wavelength-adjustable synchronous optical laser which can send out two kinds of synchronous light with different wavelengths, the sending ends Alice of the QKD system QKD device _ L and the QKD device _ R respectively send which kind of wavelength of synchronous light to be dispatched by a control module, the sent synchronous light is sent to Bob corresponding to the QKD device in the same optical fiber link, the receiving ends Bob of the QKD system QKD device _ L and the QKD device _ R are respectively provided with an optical filter, the optical filter sends the separated synchronous light to a corresponding discriminator for discrimination, and the control module further controls the receiving ends Bob of the QKD device _ L and the QKD device _ R to respectively use which kind of discriminator detected signal as a synchronous signal.
4. The synchronization method of a quantum key distribution system according to claim 1, characterized in that: the synchronization method specifically comprises the following steps: the sending ends Alice of the QKD system QKD device _ L and the QKD device _ R are both provided with a wavelength-adjustable synchronous light laser which is provided with a wavelength-adjustable synchronous lightThe laser can emit two kinds of synchronous light with different wavelengths, the transmitted synchronous light is transmitted to the Bob corresponding to the QKD equipment in the same optical fiber link, the receiving ends Bob of the QKD system QKD equipment _ L and the QKD equipment _ R are both provided with optical filters, the optical filters transmit the separated synchronous light into corresponding discriminators for discrimination, and after the initial configuration of the system, the synchronous light laser of one of the QKD equipment transmits light with the wavelength of lambda1And the synchronous light sync1, and the signal detected by a corresponding discriminator is taken as the synchronous signal, and the synchronous light laser of the other QKD device sends out the signal with the wavelength of lambda2And sync light sync2, and takes the signal detected by the corresponding one of the discriminators as the sync signal.
5. The synchronization method of a quantum key distribution system according to claim 1, characterized in that: the synchronization method specifically comprises the following steps: the sending ends Alice of the QKD system QKD device _ L and the QKD device _ R are respectively provided with a synchronous optical laser with fixed wavelength, the wavelengths sent by the synchronous optical lasers at the two ends are different, the sent synchronous light is sent to Bob of the corresponding QKD device in the same optical fiber link, and the receiving ends Bob of the QKD system QKD device _ L and the QKD device _ R adopt corresponding discriminators to discriminate the synchronous light.
6. A synchronizer of the quantum key distribution system, the quantum key distribution system is a duplex QKD system, each end includes Alice and Bob, can set up two QKD links at the same time, the signal light transmits from Alice of QKD apparatus _ L to Bob of QKD apparatus _ R's receiving end, can also transmit from Alice of QKD apparatus _ R to Bob of QKD apparatus _ L at the same time, can run two QKD work links on the optical fiber link at the same time between QKD apparatuses of both ends of the duplex QKD system, it is a unidirectional, full-duplex process, characterized by that: the system comprises synchronous optical lasers of Alice arranged at the sending ends of a QKD device _ L and a QKD device _ R of a QKD system respectively, the synchronous optical lasers of the QKD devices at the two ends of the QKD system can respectively send out two kinds of synchronous light with different wavelengths, and the receiving ends Bob of the QKD device _ L and the QKD device _ R of the QKD system are both provided with discriminators which are used for discriminating the synchronous light.
7. The synchronization apparatus of a quantum key distribution system according to claim 6, wherein: two synchronous optical lasers of a sending end Alice of the QKD system QKD device _ L and a sending end of the QKD device _ R can emit different wavelengths, and receiving ends Bob of the QKD system QKD device _ L and the QKD device _ R are respectively provided with an optical filter and two discriminators which can discriminate the two different wavelengths emitted by the synchronous optical lasers, and the optical filter sends the separated synchronous light into the corresponding discriminators for discrimination; the duplex QKD system is also provided with a control module, the control module controls the synchronous light lasers of the QKD devices at the two ends of the QKD system to respectively send synchronous light with which wavelength, and the control module also controls the receiving ends Bob of the QKD device _ L and the QKD device _ R to respectively use the signal detected by which discriminator as a synchronous signal.
8. The synchronization apparatus of a quantum key distribution system according to claim 6, wherein: the sending ends Alice of the QKD system QKD device _ L and the QKD device _ R are both provided with a wavelength-adjustable synchronous optical laser which can send out synchronous light with two different wavelengths, and the receiving ends Bob of the QKD system QKD device _ L and the QKD device _ R are both provided with an optical filter and two discriminators which can discriminate the two different wavelengths sent out by the synchronous optical laser respectively, and the optical filter sends the separated synchronous light into the corresponding discriminators for discrimination.
9. The synchronization apparatus of a quantum key distribution system according to claim 8, wherein: the duplex QKD system is also provided with a control module, the sending ends Alice of the QKD equipment _ L and the QKD equipment _ R respectively send synchronous light with which wavelength is scheduled by the control module, and the control module also controls the receiving ends Bob of the QKD equipment _ L and the QKD equipment _ R to respectively use the signal detected by which discriminator is used as a synchronous signal.
10. The synchronization apparatus of a quantum key distribution system according to claim 8, wherein: the wavelength-adjustable synchronous light lasers of the QKD devices at two ends of the QKD system send synchronous light with which wavelength and the receiving ends Bob of the QKD device _ L and the QKD device _ R respectively use signals detected by which discriminator as synchronous signals, and the signals are determined by system initial configuration.
11. The synchronization apparatus of a quantum key distribution system according to claim 6, wherein: the sending ends Alice of the QKD system QKD device _ L and the QKD device _ R are provided with synchronous optical lasers with fixed wavelengths, the wavelengths sent by the synchronous optical lasers at the two ends are different, and the receiving ends Bob of the QKD system QKD device _ L and the QKD device _ R are provided with discriminators capable of fixedly discriminating the received wavelengths.
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