CN104202157B - A synchronization method and device for a quantum key distribution system - Google Patents

Abstract

The invention provides a synchronization method of a quantum key distribution system, the quantum key distribution system is a duplex QKD system, Alice of QKD equipment at two ends of the duplex QKD system can respectively emit two kinds of synchronous light with different wavelengths, the transmitted synchronous light is transmitted in the same optical fiber link, so that when two QKD links run on the optical fiber link simultaneously, the synchronous light wavelengths on the two links are different, Bob of the QKD equipment at the two ends adopts 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

A synchronization method and device for a quantum key distribution system

technical field

The invention relates to the field of quantum secure communication, and in particular provides a synchronization method of a quantum key distribution system and a duplex QKD system based on the synchronization method.

Background technique

The fundamental difference between Quantum Key Distribution (QKD) and the classical key system is that it uses a single photon or entangled photon pair as the carrier of the key, and the basic principles of quantum mechanics guarantee that the process cannot be eavesdropped or Decipherability, thus providing a more secure key system. At present, the technology of using entangled photon pairs to realize quantum key distribution is not very mature, and there is still a considerable distance from practicality; while the technology of quantum key distribution based on single photon has been gradually matured.

Quantum key distribution technology based on single photon usually has two encoding methods: polarization encoding and phase encoding. Taking polarization encoding as an example, the basic process of quantum key distribution is:

1) The system sender (referred to as Alice by convention) selects two sets of base vectors and randomly sends a string of photons with different polarization states;

2) The receiver of the system (referred to as Bob) randomly selects the measurement base vector to receive. Due to the detection efficiency and path attenuation, Bob cannot detect all photons, and can only detect photons at some positions randomly;

3) Bob informs Alice which basis vector he used at the position where the photon was detected;

4) Alice compares the base vector used by herself when sending with the base vector used by Bob when measuring, and if the base vector used by the two is consistent at a certain position, that is, the base vector used by Bob is correct, then keep the information at this position , and tell Bob at which positions he uses the correct measurement base vector;

5) Bob leaves information on the correct position of the measurement vector;

6) In this way, Alice and Bob share a random key.

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, compare the basis vector used by Alice to send a photon at a certain position and the basis vector used by Bob to detect this position. Whether the measurement basis used for photons is consistent. In order to ensure that Alice and Bob perform base vector comparison at the same position, precise "position" synchronization is required between the sender and the receiver, otherwise, the keys at both ends of Alice and Bob will eventually be inconsistent. Therefore, the synchronization method of the system is particularly important.

The "position" mentioned above is vividly described as the number of pulses in a group of light pulses. At the sending end, the optical pulse of the signal light is continuously sent at a fixed frequency, and there is a fixed time slot between two adjacent optical pulses, while the optical pulse of the synchronous light is at a fixed frequency much lower than the sending frequency of the signal light sent continuously. When signal light and synchronous light are sent at the same time, the continuous signal light sent between 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 the pulse signal in a group of signal light pulses. Since there is a fixed time slot between two adjacent signal light pulses, the above "position" is also time information.

Figure 1 shows the synchronization method of the prior art solution. The synchronization method of the QKD system is that Alice of the QKD device sends the synchronization light, and Bob receives the synchronization light to complete the screening and generate a synchronization signal. The quantum channel in the system has only one optical fiber, that is, the signal light and the synchronous light are transmitted in the same optical fiber.

In the implementation of the QKD system, Alice may contain N signal light lasers (the specific number depends on the QKD encoding protocol adopted) and a synchronization light laser, the wavelength of the signal light is λ _signal , and the wavelength of the synchronization light is λ _sync , And λ _signal ≠ λ _sync , the two kinds of light are coupled into the same optical fiber, and transmitted to the Bob end through the optical fiber link. The Bob end contains an optical filter device, such as a Dense Wavelength Division Multiplexing (DWDM) device, whose central wavelength is λ _signal , which can separate the signal light from the synchronous light, and then perform corresponding subsequent processing on the separated signal light , sending the separated synchronous light to the synchronous light discriminator for discrimination. The signal discriminated by the discriminator is used as a synchronous signal for subsequent processing of the signal light.

The one-way, duplex QKD system based on the existing synchronization method is shown in Figure 2. Each device includes Alice at the sending end and Bob at the receiving end, and two QKD chains can be established between two QKD devices at the same time road. The two QKD links are: Alice of QKD device_L establishes a link with Bob of QKD device_R; Alice of QKD device_R establishes a link with Bob of QKD device_L. The synchronous light emitted by Alice's synchronous optical laser of QKD equipment_L is discriminated by Bob's synchronous optical discriminator of QKD equipment_R after being transmitted through the optical fiber link; The emitted synchronous light is discriminated by Bob's synchronous light discriminator of QKD equipment_L after being transmitted through the optical fiber link.

It can be seen from the prior art that in the conventional duplex QKD system based on synchronization, the synchronization light emitted by Alice of the QKD device_L and Alice of the QKD device_R have the same wavelength.

In this field, there is a definition of "two-way QKD system", which refers to the implementation of QKD, the signal light is sent from the first QKD end to the second QKD end, and then returns to the first QKD end along the original optical path. Generally speaking, the signal light sent from the first QKD end to the second QKD end is stronger, averaging hundreds or thousands of photons per pulse, and is attenuated at the second QKD end before returning to the first QKD end. On the order of single photons (on average one photon per pulse or less). There is only one QKD link on the optical fiber link of the system, which is a two-way, simplex process.

Comparative literature such as "Bidirectional QKD System with Backscattering Suppression" (Patent No. 200580025415.3) of MAGIQ Technology Company, its first QKD station has laser sources that emit light at different wavelengths, and multiple single-photon detectors (SPDs) unit. In a bi-directional QKD system, backscattered light is typically generated by the stronger output signal light in the fiber optic link connecting the first and second QKD stations. In order to reduce or avoid backscattered light from interfering with the detection of the signal light returning from the second QKD station to the first QKD station, this patent sequentially activates different light sources when each pair of SPDs in the SPD unit in the first QKD station is sequentially activated . What this patent aims to solve is the problem that the detection of signal light in a bidirectional QKD system is easily interfered by backscattered light, and it has high requirements for related control systems. It is necessary to calculate the expected arrival of signal light according to the length of the actual optical fiber link. Time, the activation control of different light sources and SPD units is performed at the expected arrival time, and the control accuracy is required to be high, and the process of sequential activation continues.

When the existing synchronization method is applied to a one-way (one-way), duplex system, as shown in Figure 2, the wavelength of the synchronization light sent by Alice of QKD equipment_L and Alice of QKD equipment_R is the same, and in transmitted in the same fiber. Due to the unsatisfactory environment of the actual optical fiber link, reflections at the end face of the optical fiber exist. For example, when the link between Alice in QKD device_L and Bob in QKD device_R is started, the synchronization light emitted by Alice in QKD device_L may reflect, and the reflected light enters Bob in QKD device_L, resulting in QKD The synchronization signal in the link between Alice of device_R and Bob of QKD device_L is misidentified; so when the link between Alice of QKD device_R and Bob of QKD device_L starts, the synchronization signal sent by Alice of QKD device_R The light will be disturbed, causing the system not to function properly.

Contents of the invention

The present invention provides a synchronization method and device for a quantum key distribution system, which is used to solve the synchronization light reflection caused by the same wavelength of synchronization light between Alice of QKD device_L and Alice of QKD device_R in a duplex QKD system It will lead to the problem that two QKD links cannot run at the same time.

The present invention adopts the following technical solutions to solve the above-mentioned technical problems: the synchronization method of the present invention is used in a duplex QKD system, and Alice of the QKD equipment at both ends of the duplex QKD system can send out two kinds of synchronous lights with different wavelengths respectively, and the synchronization of transmission The light is transmitted in the same optical fiber link, so that when two QKD links run on the optical fiber link at the same time, the wavelengths of the synchronous light on the two links are different, and the Bob of the QKD equipment at both ends uses the corresponding discriminator to pair the synchronization light for screening.

It should be noted that the concept of "duplex QKD system" used in the present invention is not the same concept as that of "two-way QKD system" in comparative literature.

The comparative literature "Two-way QKD System with Backscatter Suppression" proposes an implementation of QKD, not a system synchronization method. The definition of "two-way system" in this comparative literature is that the QKD device (Bob) at one end of the system emits a strong signal light, which is transmitted to the QKD device (Alice) at the other end of the system. After Alice attenuates the signal light to the single photon level, The signal light is returned to Bob according to the original optical path, and the optical path is a round-trip process. In the whole process, there is only one QKD working link on the optical fiber link between two QKD devices, which is a two-way, simplex process.

In the patent application of the present invention, "duplex system" is defined as a system that can work in "full duplex". Each end of the duplex system includes Alice and Bob, and two QKD links can be established at the same time. Weak signal light (single photon level) can be transmitted from Alice at the sending end of QKD device_L to Bob at the receiving end of QKD device_R, and can also be transmitted from Alice at QKD device_R to Bob at QKD_L (Figure 4). In this way, two QKD working links can be run simultaneously on the optical fiber link between the QKD devices at both ends of the duplex system, which is a one-way, full-duplex process. This is very different from the "two-way system" of the comparative literature in terms of structure and optical signal transmission.

Alice of the QKD devices at both ends of the duplex QKD system can send out two synchronous lights with different wavelengths, and the screening process can be realized by any of the following methods:

1. Alice of the QKD equipment at both ends of the QKD system is equipped with two synchronous optical lasers of different wavelengths, and a control module needs to be configured in the duplex QKD system. The control module controls which Alice of the QKD equipment at both ends of the QKD system sends A wavelength of synchronous light, the transmitted synchronous light is sent to Bob corresponding to the QKD device in the same optical fiber link, and Bob of the QKD device at both ends of the QKD system is equipped with an optical filter device, which separates the synchronized The light is sent to the corresponding discriminator for discrimination, and the control module also controls which signal detected by the discriminator is used by Bob of the QKD device at both ends as the synchronization signal.

Due to the unsatisfactory environment of the actual optical fiber link and the phenomenon of fiber end reflection, there may be two channels of synchronous light with different wavelengths on a QKD working link. The synchronous light of one wavelength and the reflected synchronous light of the other wavelength are After the optical filtering device, it will be sent to the corresponding discriminator respectively. For example, the center frequency of the optical filter device is λ ₁ (this center frequency is generally a fixed value), when using synchronous light with a wavelength of λ ₁ , after the optical filter device, it is sent to the discriminator 1 for discrimination; When using the synchronous light with a wavelength of _λ2 , after the optical filtering device, all other optical signals except λ1 are sent to the discriminator ₂ for discrimination, and interference such as noise in the optical fiber link has little influence on the discrimination of the synchronous light , can be ignored, so the synchronous light with a wavelength of _λ2 can be correctly identified. (The process of "sending the separated synchronous light into the corresponding discriminator for discrimination" mentioned in the following content refers to this process)

2. Alice of the QKD equipment at both ends of the QKD system is equipped with two synchronous optical lasers of different wavelengths, and the transmitted synchronous light is sent to Bob of the corresponding QKD equipment in the same optical fiber link, and the QKD equipment at both ends of the QKD system Bob is equipped with an optical filter device, which sends the separated synchronous light to the corresponding discriminator for discrimination. After the initial configuration of the system, one of the QKD devices uses one of the synchronous optical lasers to send the laser with a wavelength of λ ₁ Synchronize light sync1, and use the signal detected by a corresponding discriminator as a synchronous signal, another QKD device uses a synchronous optical laser to send a synchronous light _sync2 with a wavelength of λ2, and use a signal detected by a corresponding discriminator as a synchronization signal.

3. Alice of the QKD equipment at both ends of the QKD system is equipped with a wavelength-tunable synchronous optical laser. The wavelength-tunable synchronous optical laser can emit two types of synchronous light with different wavelengths. Which wavelength of synchronous light to send is scheduled by the control module, and the sent synchronous light is sent to Bob of the corresponding QKD device in the same optical fiber link, and Bob of the QKD device at both ends of the QKD system is equipped with an optical filter device, and the optical filter The device sends the separated synchronous light to the corresponding discriminator for discrimination, and the control module also controls which signal detected by the discriminator is used by Bob of the QKD device at both ends as the synchronous signal.

4. Alice of the QKD equipment at both ends of the QKD system is equipped with a wavelength-tunable synchronous optical laser. The wavelength-tunable synchronous optical laser can emit two types of synchronous light with different wavelengths. The synchronous light sent is in the same optical fiber chain In the middle of the road, it is sent to Bob of the corresponding QKD device. Bob of the QKD device at both ends of the QKD system is equipped with an optical filter device. The optical filter device sends the separated synchronous light to the corresponding discriminator for discrimination. After the initial configuration of the system , the synchronous optical laser of one of the QKD devices sends the synchronous optical sync1 with a wavelength of λ ₁ , and uses the signal detected by a corresponding discriminator as a synchronous signal, and the synchronous optical laser of the other QKD device sends a synchronous optical with a wavelength of λ ₂ sync2, and use the signal detected by a corresponding discriminator as the synchronization signal.

5. Alice of the QKD equipment at both ends of the QKD system is equipped with a fixed-wavelength synchronous optical laser. The wavelengths sent by the synchronous optical lasers at both ends are different, and the transmitted synchronous light is sent to Bob of the corresponding QKD equipment in the same optical fiber link. , Bob of the QKD device at both ends of the QKD system uses the corresponding discriminator to discriminate the synchronous light.

The present invention also provides a synchronization device for a quantum key distribution system. The quantum key distribution system is a duplex QKD system, including Alice's synchronous optical lasers respectively configured on the QKD devices at both ends of the QKD system, and the QKD devices at both ends of the QKD system. The synchronous light laser of the equipment can emit synchronous light of two different wavelengths respectively, and the Bob of the QKD equipment at both ends of the QKD system is equipped with a discriminator, and the corresponding discriminator is used to discriminate the synchronous light.

The specific device structure can be any of the following:

1. There are two synchronous optical lasers of Alice’s QKD equipment at both ends of the QKD system, and the two synchronous optical lasers can emit different wavelengths, and Bob of the QKD equipment at both ends of the QKD system is equipped with optical filter devices and two types of lasers that can respectively A discriminator for discriminating two different wavelengths emitted by the synchronous light laser, and the optical filter device sends the separated synchronous light to the corresponding discriminator for discrimination.

In this structure, a control module is also configured in the duplex QKD system, and the control module controls which wavelength of synchronous light is sent by the synchronous optical lasers of the QKD equipment at both ends of the QKD system, and the control module also controls the synchronization of the QKD equipment at both ends. Bob respectively uses the signal detected by which discriminator as a synchronization signal.

Or, which wavelength of synchronous light is sent by the synchronous optical lasers of the QKD equipment at both ends of the QKD system and which signal detected by the discriminators respectively used by Bob of the QKD equipment at both ends of the QKD system is determined by the initial configuration of the system.

2. Alice of the QKD equipment at both ends of the QKD system is equipped with a wavelength-tunable synchronous optical laser. It is equipped with an optical filter device and two kinds of discriminators capable of distinguishing two different wavelengths emitted by the synchronous optical laser, and the optical filter device sends the separated synchronous light into the corresponding discriminator for discrimination.

In this structure, a control module is also configured in the duplex QKD system, and which wavelength of synchronous light is sent by Alice’s adjustable-wavelength synchronous optical lasers at both ends of the QKD device is scheduled by the control module, and the control module also controls Bob of the QKD device at both ends uses the signal detected by which discriminator as a synchronization signal.

Or, which wavelength of synchronous light is sent by the wavelength-tunable synchronous optical laser of the QKD equipment at both ends of the QKD system and which signal detected by the discriminator is used by Bob of the QKD equipment at both ends of the QKD system as a synchronous signal, which is determined by the initial configuration of the system .

3. Alice of the QKD equipment at both ends of the QKD system is equipped with a synchronous optical laser with a fixed wavelength. The wavelengths sent by the synchronous optical lasers at both ends are different. Bob of the QKD equipment at both ends of the QKD system is equipped with Discriminator for fixed discrimination of received wavelengths.

The advantages of the present invention are:

1. Both ends of the duplex QKD system use synchronous light of different wavelengths, which solves the problem that the duplex QKD system cannot run in full duplex due to the reflection of synchronous light;

2. According to Embodiment 1 and Embodiment 2, compared with the original QKD system, its QKD equipment only needs to add one more synchronous optical laser at the Alice end, or Alice uses a wavelength-tunable synchronous optical laser to achieve two different The function of the wavelength; only one more optical filtering device and a synchronous optical discriminator need to be added at the Bob end. The cost of additional devices required by the system equipment is low, and the structure can realize the same characteristics of QKD equipment_L and QKD equipment_R, so that any two QKD equipment can realize the function of point-to-point connection and communication, and the equipment is easy to operate Convenient for mass production;

3. According to Embodiment 3, compared with the original QKD system, Alice and Bob of the QKD device do not need to add any new hardware, and only need to be configured separately for Alice of QKD device_L and QKD device_R when the system is factory configured For synchronous light of different wavelengths, correspondingly, different discriminators can be configured for Bob of QKD equipment _L and QKD equipment _R, and QKD equipment _L and QKD equipment _R are produced in pairs, and the operation of the equipment is simple and convenient. Facilitate mass production;

4. The Bob end at both ends of the duplex QKD system uses an optical filter device and two discriminators, which is convenient for identifying link quality, system debugging, and problem location. For example, Alice on QKD_L and Bob on QKD_R have established a link and started running. If it is found that the discriminator corresponding to the wavelength of the synchronization light sent by Bob on QKD_L and Alice on the local end has an output, it means that there is synchronization light reflection on the optical fiber link. .

Description of 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, duplex QKD system based on an existing synchronization method.

FIG. 3 is a schematic diagram of a synchronization method scenario 1 of a synchronization method of a quantum key distribution system according to the present invention.

Figure 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 Alice's duplex QKD system using two synchronous optical lasers with different wavelengths.

FIG. 7 is a schematic diagram of Alice's duplex QKD system using a synchronous optical laser with variable wavelength.

FIG. 8 is a schematic diagram of a duplex QKD system in which Alice and Bob respectively use synchronous optical lasers of different wavelengths.

FIG. 9 is a schematic diagram of a synchronization method scenario 2 of a synchronization method of a quantum key distribution system according to the present invention.

detailed description

The present invention will be described in detail below in conjunction with the accompanying drawings.

There are two typical scenarios for sending signal light and synchronous light in a duplex QKD system. Scenario 1 (Figure 3) is that the signal light and synchronous light at Alice’s end of the QKD equipment at both ends of the system can be coupled in the same optical fiber for transmission. A discriminator, the first-stage optical filter device separates the signal light and the synchronous light, and the second-stage optical filter device sends the separated synchronous light to the corresponding discriminator for discrimination. Scenario 2 (Figure 9) is that the signal light and synchronous light of Alice’s end of the QKD equipment at both ends of the system are transmitted in two optical fibers respectively. a discriminator, and the optical filtering device sends the separated synchronous light to the corresponding discriminator for discrimination.

The following embodiments are all introduced by taking Scenario 1 as an example.

Fig. 3 is a schematic diagram of the synchronization method scenario 1 of the present invention. The system using the method shown in the figure is only a typical case, not the only situation. This schematic diagram is only for explaining the QKD devices at both ends of the duplex QKD system in detail. One of the processes in which Alice emits two kinds of synchronous light with different wavelengths respectively, and Bob in the QKD device at both ends separates the signal light from the synchronous light with an optical filter device, and then uses the corresponding discriminator to discriminate the synchronous light , which is mainly used to illustrate the process of separating signal light and synchronous light by optical filter devices and the selection of optical filter devices.

Figure 3 omits the Bob end of the QKD device_L and the Alice end of the QKD device_R, and only reflects the process of the unidirectional synchronous light sent from the Alice end of the QKD device_L to the Bob end of the QKD device_R; QKD The process of sending sync light from Alice in device_R to Bob in QKD device_L is the same.

Alice of the QKD device_L contains multiple signal light lasers and two synchronous light lasers, and the synchronous light lasers 1 and 2 can respectively send two kinds of synchronous light λ ₁ and λ ₂ with different wavelengths. Alice in QKD device_L chooses to use one of the wavelengths (λ ₁ or λ ₂ ) of the synchronous light, for example, selects the synchronous light with the wavelength of λ ₁ , that is, the central wavelength λ _sync = λ ₁ of the synchronous light, and the central wavelength of the N channels The signal optical coupling of λ _signal is sent to Bob of the QKD device_R in the same optical fiber link. Correspondingly, Alice (not shown in FIG. ₃ ) of the QKD device_R chooses to use the synchronization light with a wavelength of λ2.

Bob of QKD equipment_R uses the first-stage optical filter to separate the signal light, and then uses the second-stage optical filter to separate the synchronous light. Preferably, the first-stage optical filter device may be a dense wavelength division multiplexing (Dense Wavelength Division Multiplexing, DWDM) device, and its center wavelength is λ _signal . After the signal light and synchronous light pass through the DWDM device, the signal light is separated according to the central wavelength, and the subsequent processing of the signal light is performed; the synchronous optical signals except the signal light are uniformly sent to the second-level optical filter device. Preferably, the second-stage optical filter device can be selected as a DWDM device, and its center wavelength is λ ₁ or λ ₂ , which can separate two kinds of synchronous light with different wavelengths, and send the synchronous light with a wavelength of λ ₁ into the discriminator 1, The synchronous light with a wavelength of λ2 is sent into the discriminator ₂ to discriminate the synchronous light. The signal discriminated from the discriminator 1 or the discriminator 2 is used as a synchronous signal (in this example, _a synchronous signal corresponding to λ1), which is used in the subsequent processing of the signal light.

In the duplex QKD system structure based on the synchronization method described in Figure 3, each QKD device includes Alice at the sending end and Bob at the receiving end, and can perform full-duplex work, and two channels of synchronous light can be transmitted in the optical fiber link, as shown in the figure 4. The Alice of the QKD equipment at both ends of the duplex system contains lasers that can send two different wavelengths of synchronized light, and the Bob of the QKD equipment at both ends contains two-stage optical filter devices. The first-stage optical filter device can separate signal light and synchronization light. , the second-stage optical filtering device sends the separated synchronous light to the corresponding discriminator for discrimination.

The duplex QKD system based on the synchronization method may also include an upper layer control module, as shown in FIG. 5 , the main function of the control module is to control which wavelength of synchronization light is used on the QKD link. When one link selects the synchronous optical sync1 with a wavelength of λ1, the other link uses the synchronous optical _sync2 with a wavelength of _λ2 . The control module can be implemented by software, or by hardware such as single-chip microcomputer, FPGA, and DSP.

The structure of the duplex QKD system according to the present invention is shown in Figure 5. Both QKD device_L and QKD device_R include Alice and Bob, and two QKD links can be established between the two devices at the same time, that is, the QKD device The link between Alice in _L and Bob in QKD device_R, and the link between Alice in QKD device_R and Bob in QKD device_L. The entire duplex QKD system works in full-duplex mode. The feature of the duplex QKD system is that the two QKD links use synchronous light of different wavelengths, which avoids that when the wavelengths of the synchronous light used by the two links are the same, the reflected light of the synchronous light of one link will interfere with the other chain. It solves the problem that two QKD links cannot run at the same time, and realizes the full-duplex function of the QKD system.

Alice in QKD device_L and QKD device_R may have synchronous optical lasers that can transmit two different wavelengths, or Alice in QKD device_L and QKD device_R may use synchronous optical lasers with different wavelengths respectively. If Alice in QKD device_L and QKD device_R is the first case, then Bob in QKD device_L and QKD device_R both contain two-stage optical filter devices, which can separate signal light and two kinds of synchronous light with different wavelengths ; If Alice in QKD device_L and QKD device_R is the second case, then Bob in QKD device_L and QKD device_R only contains one-stage optical filtering device, which can separate signal light and synchronous light.

The synchronous optical lasers of Alice in the QKD device_L and QKD device_R in the duplex QKD system can include, but are not limited to the following forms:

Embodiment one (using synchronous optical lasers of two different wavelengths)

Option1 (the wavelength of the synchronization light sent by Alice is determined by the control module):

As shown in Figure 6, Alice in QKD device_L and QKD device_R are equipped with two synchronous optical lasers—synchronous optical laser 1 and synchronous optical laser 2, wherein synchronous optical laser 1 fixedly sends synchronous optical sync1, the wavelength is λ ₁ , the synchronous optical laser 2 fixedly transmits the synchronous optical sync2, the wavelength is λ ₂ , and λ ₁ ≠λ ₂ . Both QKD equipment_L and QKD equipment_R’s Bob are equipped with two-stage optical filter devices. The first-stage optical filter device can separate signal light and synchronous light, and the second-stage optical filter device can separate two channels of synchronous light with different wavelengths. light, as shown in Figure 3. The second-stage optical filter device sends the separated two-way synchronous light into the corresponding discriminator respectively, discriminator ₁ fixedly discriminates the synchronous light sync1 whose center wavelength is λ1, and discriminator 2 fixedly discriminates the center wavelength as λ ₂ sync light sync2.

The duplex QKD system is equipped with a control module to control the QKD device_L and QKD device_R to send synchronous light sync1 and sync2 with different wavelengths respectively; at the same time, corresponding to the synchronous light sent by Alice, the control module also controls Bob of QKD device_L and QKD device_R uses the signal detected by which discriminator as the synchronization signal respectively.

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 Alice of the QKD device_L to use the synchronous optical laser ₁ and send the synchronous optical sync1 with a wavelength of λ1; Then, at the Bob end of the 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. After scheduling by the control module, the signal detected by the discriminator 1 is used as a synchronization 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 send a synchronous optical sync2 with a wavelength of λ2; Then, at the Bob end of the QKD device_L, the signal light is separated by the first-stage optical filter device, and then the synchronization light sync2 is separated by the second-stage optical filter device. After scheduling by the control module, the signal detected by the discriminator 2 is used as a synchronization signal.

The advantage of using the control module is that when there is a problem with the synchronization of a certain QKD link, for example, the synchronous optical laser or the discriminator used for the QKD link is abnormal, the control module can be used to conveniently monitor the QKD devices at both ends. Synchronous optical lasers and discriminators are scheduled to switch, so that the full-duplex QKD system can still work normally. For example, if the synchronous optical laser 1 used by Alice in QKD equipment_L is working abnormally, the control module schedules Alice in QKD equipment_L to use synchronous optical laser 2, and schedules Bob in QKD equipment_R to use the signal detected by discriminator 2 as Synchronization signal; at the same time, the control module dispatches Alice of QKD device_R to use the synchronous optical laser 1, and dispatches Bob of QKD device_L to use the signal detected by discriminator 1 as a synchronization signal.

Option2 (the wavelength of the sync light sent by Alice is configured initially):

Alice in both QKD device_L and QKD device_R is configured with two synchronous optical lasers—synchronous optical laser 1 and synchronous optical laser 2 . Synchronous optical laser 1 fixedly sends synchronous light sync1 with wavelength λ ₁ ; synchronous optical laser 2 fixedly sends synchronous light sync2 with wavelength λ ₂ , and λ ₁ ≠λ ₂ .

Both QKD equipment_L and QKD equipment_R’s Bob are equipped with two-stage optical filter devices. The first-stage optical filter device can separate signal light, and the second-stage optical filter device can separate two kinds of synchronous light with different wavelengths, such as Figure 3 shows. The second-stage optical filter device sends the separated two-way synchronous light into the corresponding discriminator respectively, discriminator ₁ fixedly discriminates the synchronous light sync1 whose center wavelength is λ1, and discriminator 2 fixedly discriminates the center wavelength as λ ₂ sync light sync2.

After the initial configuration of the system, QKD equipment_L uses synchronous optical laser 1 to send synchronous optical sync1, and uses the signal detected by discriminator 2 as a synchronous signal; QKD equipment_R uses synchronous optical laser 2 to transmit synchronous optical sync2, and discriminates The signal detected by device 1 is used as the synchronization signal.

When there is a problem with the synchronization of a certain QKD link, for example, the synchronous optical laser or discriminator used for the QKD link is abnormal, the synchronous optical laser and discriminator in the QKD equipment at both ends can be reinitialized by the system, etc. The switch is scheduled and switched so that the full-duplex QKD system can still work normally. For example, if the synchronous optical laser 1 used by Alice in QKD device_L is working abnormally, re-initialize the duplex QKD system. During the initial configuration, Alice in QKD device_L uses synchronous optical laser 2, and configures QKD device_L Bob in R uses the signal detected by discriminator 2 as a synchronization signal; at the same time, Alice with QKD device_R uses synchronization optical laser 1, and Bob with QKD device_L uses the signal detected by discriminator 1 as a synchronization signal.

Embodiment two (using a synchronous optical laser with variable wavelength)

Option1 (the wavelength of the synchronization light sent by Alice is determined by the control module):

As shown in Figure 7, Alice in QKD equipment_L and QKD equipment_R both use a wavelength-tunable synchronous optical laser, which can transmit synchronous optical sync1 with a wavelength of λ ₁ , and can also transmit The wavelength of the synchronous light sync2 is λ ₂ , and λ ₁ ≠ λ ₂ , and the wavelength for sending the synchronous light is scheduled by the control module. Both QKD equipment_L and QKD equipment_R’s Bob are equipped with two-stage optical filter devices. The first-stage optical filter device can separate signal light and synchronous light, and the second-stage optical filter device can separate synchronous light of different wavelengths. As shown in Figure 3. The separated two synchronous lights are respectively sent into the corresponding discriminators, the discriminator ₁ fixedly discriminates the synchronous light sync1 whose wavelength is λ1, and the discriminator ₂ fixedly discriminates the synchronous light sync2 whose wavelength is λ2.

The duplex QKD system is equipped with a control module, which is used to control Alice of the QKD device_L and Alice of the QKD device_R to send synchronous light sync1 and sync2 with different wavelengths respectively. At the same time, corresponding to the synchronization light sent by Alice, the control module also controls which signals detected by the discriminators are used by Bob of the QKD device_L and QKD device_R respectively as the synchronization signal.

The specific implementation is as follows: on the link between Alice in QKD device_L and Bob in QKD device_R, the control module schedules Alice in QKD device_L to use a synchronous optical laser with adjustable wavelength to send _a synchronous light sync1; at the Bob end of the QKD device_R, the signal light is separated by the first-stage optical filtering device, and then the synchronous light sync1 is separated by the second-stage optical filtering device. After scheduling by the control module, the signal detected by the discriminator 1 is used as a synchronization signal.

Correspondingly, on the link between Alice in QKD device_R and Bob in QKD device_L, the control module schedules Alice in QKD device_R to use a wavelength _- tunable synchronous optical laser to send a synchronous Optical sync2; at the Bob end of the QKD device_L, the signal light is separated by the first-stage optical filter device, and then the synchronous light sync2 is separated by the second-stage optical filter device. After scheduling by the control module, the signal detected by the discriminator 2 is used as a synchronization signal.

Option2 (the wavelength of the sync light sent by Alice is configured initially):

Alice in QKD equipment_L and QKD equipment_R both use a wavelength-tunable synchronous optical laser. The wavelength-tunable synchronous optical laser can send synchronous light sync1 with a wavelength of λ ₁ , and can also send a synchronous light sync2 with a wavelength of λ ₂ , and λ ₁ ≠λ ₂ .

The Bob of QKD equipment_L and QKD equipment_R are equipped with two-stage optical filter devices. The first-stage optical filter device can separate signal light and synchronous light, and the second-stage optical filter device can separate two different wavelengths of synchronous light. light, as shown in Figure 3. The separated two synchronous lights are respectively sent into the corresponding discriminators, the discriminator ₁ fixedly discriminates the synchronous light sync1 whose center wavelength is λ1, and the discriminator ₂ fixedly discriminates the synchronous light sync2 whose center wavelength is λ2.

During the initial configuration of the system, the QKD device_L can be configured to send the synchronous light sync1 with _a wavelength of λ1, and the signal detected by the discriminator 2 can be used as a synchronous signal; the QKD device_R can be configured to send the synchronous light _sync2 with a wavelength of λ2, And the signal detected by the discriminator 1 is used as a synchronous signal.

Embodiment 3 (a synchronous optical laser with a different wavelength is used at both ends of the system respectively)

As shown in Figure 8, QKD equipment_L and QKD equipment_R respectively use a synchronous optical laser of different wavelengths, synchronous optical laser 1 fixedly transmits the synchronous optical sync1 of wavelength λ ₁ , and synchronous optical laser 2 fixedly transmits the wavelength of The synchronous light sync2 of λ ₂ , and λ ₁ ≠λ ₂ . The Bob of QKD equipment_L and QKD equipment_R both use a first-stage optical filter device to separate signal light and synchronous light. The separated synchronous light is sent into the discriminator, and the discriminator ₁ fixedly discriminates the synchronous light sync1 whose center wavelength is λ1, and the discriminator ₂ fixedly discriminates the synchronous light sync2 whose center wavelength is λ2.

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 uses the synchronous optical laser ₁ to fixedly send the synchronous optical sync1 with a wavelength of λ1, then At the Bob end of the QKD device_R, after the synchronous light is separated by a primary optical filter, the discriminator ₁ is used to discriminate the synchronous light sync1 with a center wavelength of λ1. 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 to fixedly send the synchronous optical sync2 with a wavelength of λ2, then At the Bob end of the QKD device_L, after the synchronous light is separated by the primary optical filter, the discriminator ₂ is used to discriminate the synchronous light sync2 whose center wavelength is λ2.

FIG. 9 is a schematic diagram of scenario 2 in the synchronization method of the present invention. The system using this method shown in Figure 9 is just a typical case, not the only one. Figure 9 omits the Bob end of the QKD device_L and the Alice end of the QKD device_R, and only reflects the process of the unidirectional synchronous light sent from the Alice end of the QKD device_L to the Bob end of the QKD device_R; QKD The process of sending sync light from Alice in device_R to Bob in QKD device_L is the same.

The signal light and synchronous light shown in the second scene are respectively transmitted using two optical fiber links, which is also applicable to the situations described in the first, second and third embodiments of the present invention.

The above descriptions are only preferred embodiments of the invention, and are not intended to limit the invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the invention shall be included in this invention. within the protection scope of inventions and creations.

Claims (2)

1. a kind of synchronous method of quantum key distribution system, the quantum key distribution system is duplexing QKD system, and its feature exists In：The Alice of duplexing QKD system both ends QKD equipment can send two kinds of different synchronizable opticals of wavelength, the synchronizable optical of transmission respectively Transmitted in same fiber link, when making in fiber link while running two QKD links, the synchronous light wave in both links Long different, the Bob of both ends QKD equipment is screened using corresponding discriminator to synchronizable optical；

The synchronous method specifically includes：The same of two different wave lengths is provided with the Alice of the QKD equipment at QKD system both ends Light laser is walked, the synchronizable optical of transmission is sent to the Bob of corresponding QKD equipment, and QKD system two in same fiber link The Bob of the QKD equipment at end is each equipped with optical filter part, optical filter part by the synchronizable optical isolated be sent into corresponding to discriminator Among screened, after system initial configuration, one of QKD equipment is using one of them synchronous light laser send wave length For λ₁Synchronizable optical sync1, and using the signal that a corresponding discriminator detects as synchronizing signal, another QKD equipment Using a synchronous a length of λ of light laser send wave₂Synchronizable optical sync2, and the letter that a corresponding discriminator is detected Number it is used as synchronizing signal.

2. a kind of sychronisation of quantum key distribution system, the quantum key distribution system is duplexing QKD system, and its feature exists In：The synchronous light laser of Alice including the QKD equipment that is arranged respectively at QKD system both ends, the QKD at QKD system both ends are set Standby synchronous light laser can send the synchronizable optical of two kinds of different wave lengths respectively, and the QKD equipment at QKD system both ends Bob is each equipped with discriminator, and synchronizable optical is screened using corresponding discriminator；The QKD equipment at QKD system both ends Alice synchronous light laser has two, and two synchronous light lasers can send different wavelength, and QKD system two The Bob of the QKD equipment at end be each equipped with optical filter part and two kinds be able to screen synchronous light laser is sent two kinds not The discriminator of co-wavelength, optical filter part will be screened among discriminator corresponding to the synchronizable optical isolated feeding；

The synchronous light laser of the QKD equipment at QKD system both ends sends the synchronizable optical of any wavelength and the QKD equipment at both ends Bob respectively using the signal which kind of discriminator detects as synchronizing signal, determined through system initial configuration.