Quantum key distribution system and method supporting dynamic switching of quantum channels

Abstract

The application discloses a kind of quantum channel dynamic switching supporting quantum key distribution system and method, the system includes: at least one free space quantum key distribution node, at least one optical fiber quantum key distribution node and a shared quantum key receiving node;Free space quantum key distribution node is used to prepare and send beam combining light;Optical fiber quantum key distribution node is used to prepare and send QKD quantum channel optical signal;Shared quantum key receiving node is connected with free space quantum key distribution node by free space light quantum channel, and is connected with optical fiber quantum key distribution node by optical fiber quantum channel, for analyzing and processing beam combining light, and according to analysis result or preset period time, select to receive beam combining light or QKD quantum channel optical signal, generate shared key.The application supports intelligent dynamic switching based on real-time channel state, enables network to self-adaptingly avoid optical fiber fault, adverse atmospheric condition and the like influence, guarantees the continuity of key service.

Description

Technical Field

[0001] This invention relates to the field of quantum communication technology, and in particular to a quantum key distribution system and a quantum key distribution method that support dynamic switching of quantum channels. Background Technology

[0002] Quantum Key Distribution Network (QKD) technology is based on the principles of quantum mechanics and can provide secure key exchange between communicating parties. Currently, QKD networks mainly rely on two physical channels: fiber optic channels and free space channels.

[0003] Fiber optic QKD technology is relatively mature and can be based on standard telecommunications infrastructure, but its practical deployment is often limited by issues such as fiber reachability, deployment cost, and long-distance transmission loss. Free-space QKD technology, on the other hand, overcomes geographical limitations and is suitable for scenarios such as inter-building communications, cross-water communications, and emergency communications, and is an essential step towards achieving satellite-to-ground quantum communication. However, significant barriers have long existed between fiber optic QKD and free-space QKD technologies:

[0004] 1. Hardware and protocol incompatibility: Commercial fiber optic QKD equipment is usually optimized for single-mode fiber interfaces and operates in the 1550nm communication band; while free-space QKD relies on a dedicated terminal that includes a telescope and a precision tracking system. The two have very different hardware interfaces and optical designs, and cannot communicate directly.

[0005] 2. Network heterogeneity challenge: Most existing subnets are homogeneous networks (all-fiber or all-free space), lacking an effective solution for organically integrating and uniformly managing the two types of channels, which limits the network's flexibility and coverage.

[0006] 3. High system cost: Building a network that supports two channels simultaneously requires configuring independent and complete transceiver terminals for each channel, especially high-cost single-photon detector modules, which will lead to a doubling of the overall cost.

[0007] 4. Lack of dynamic adaptability: Systems in related technologies cannot dynamically select the optimal transmission medium based on real-time channel conditions (such as fiber optic failures, increased free-space turbulence), network strategies, or cost-effectiveness, resulting in low resource utilization efficiency.

[0008] Although existing research has explored "intermodal QKD" with the aim of connecting fiber optic QKD devices to free space links through adaptive optics technology, most of these works are limited to point-to-point static connections and have not been extended to multi-node network environments, nor do they have the ability to dynamically switch and manage channels. Summary of the Invention

[0009] In one embodiment of the present invention, the present invention is proposed to solve at least one of the above-mentioned problems. According to a first aspect of the present invention, a quantum key distribution system supporting dynamic switching of quantum channels is provided, comprising: at least one free-space quantum key distribution node, at least one fiber optic quantum key distribution node, and a shared quantum key receiving node; The free-space quantum key distribution node is used to prepare and transmit combined light; The fiber optic quantum key distribution node is used to prepare and transmit QKD quantum channel optical signals; The shared quantum key receiving node is connected to the free-space quantum key distribution node via a free-space optical quantum channel and to the fiber optic quantum key distribution node via a fiber optic quantum channel. It is used to analyze and process the combined light beam and, based on the analysis results or a preset period, select to receive the combined light beam or the QKD quantum channel optical signal to generate a shared key.

[0010] In one embodiment of the present invention, the shared quantum key receiving node includes: A beam receiving module is used to receive the combined beam; An adaptive optics interface module, connected to the beam receiving module, is used to correct and couple the combined beam and output a combined beam signal; The first wavelength division multiplexing module is connected to the adaptive optics interface module via a single-mode fiber. It is used to decompose the combined optical signal transmitted through the single-mode fiber to obtain the QKD quantum signal and the monitoring beacon optical signal. The monitoring module, connected to the first wavelength division multiplexing module, is used to receive the monitoring beacon optical signal, perform channel quality monitoring, and generate real-time quality assessment indicators. A control module, connected to the monitoring module, is used to generate control commands based on the real-time quality assessment indicators or the preset cycle time. An optical switch module, connected to the first wavelength division multiplexing module, the control module, and the fiber quantum key distribution node, is used to select to receive either the QKD quantum signal light or the QKD quantum channel light signal according to the control command. A shared QKD receiver, connected to the optical switch module, is used to generate the shared key based on the received QKD quantum signal light or the QKD quantum channel light signal.

[0011] In one embodiment of the present invention, the adaptive optics interface module includes: A fast-turning mirror is used to perform high-speed, real-time correction of the angular arrival fluctuations of the combined light received by the beam receiving module. A single-mode fiber coupled lens assembly, connected to the fast-turning mirror and the single-mode fiber end face, is used to focus the corrected beam onto the single-mode fiber end face. The single-mode fiber end face is used to couple the light beam to the fiber and output the combined optical signal.

[0012] In one embodiment of the present invention, the adaptive optics interface module further includes: A beam reducer is disposed between the beam receiving module and the fast-turning mirror, and is used to reduce the beam of the combined beam received by the beam receiving module. A position-sensitive detector, connected to the fast-turning mirror, is used to detect the position of the light spot in real time and provide a closed-loop feedback signal for the fast-turning mirror.

[0013] In one embodiment of the present invention, the real-time quality assessment metric includes at least one of single-mode fiber coupling efficiency and quantum bit error rate; When generating control commands based on the real-time quality assessment indicators, the control module is specifically used for: When the single-mode fiber coupling efficiency is lower than a first threshold or the qubit error rate is higher than a second threshold, the generated control command is to receive the QKD quantum channel optical signal.

[0014] In one embodiment of the present invention, the shared QKD receiver further includes an automatic polarization controller; The control module is also connected to the shared QKD receiver and includes an automatic polarization calibration program. When the channel is switched, the automatic polarization calibration program performs feedback adjustment on the automatic polarization controller based on the known polarization state sequence sent by the distribution node after the switch.

[0015] In one embodiment of the present invention, the free-space quantum key distribution node includes: Free-space link QKD transmitter, used to prepare and output quantum signal light; Control the laser module to emit multi-wavelength beacon light; The second wavelength division multiplexing module is connected to the free space link QKD transmitter and the control laser module, and is used to combine the quantum signal light and the multi-wavelength beacon light to obtain the combined beam light; A beam emission module, connected to the second wavelength division multiplexing module, is used to transmit the combined beam to the free-space optical quantum channel.

[0016] In one embodiment of the present invention, the fiber optic quantum key distribution node includes: A fiber optic link QKD transmitter is used to prepare and transmit the QKD quantum channel optical signal.

[0017] In one embodiment of the present invention, the shared quantum key receiving node is also connected to the free space quantum key distribution node via a free space radio classical channel, for carrying classical information interaction with the free space quantum key distribution node; The shared quantum key receiving node is also connected to the fiber optic quantum key distribution node via a parallel fiber optic classical channel to carry classical data transmission with the fiber optic quantum key distribution node.

[0018] According to a second aspect of the present invention, a quantum key distribution method supporting dynamic switching of quantum channels is provided. This method is applied to the aforementioned quantum key distribution system supporting dynamic switching of quantum channels, wherein the quantum key distribution system supporting dynamic switching of quantum channels comprises: at least one free-space quantum key distribution node, at least one fiber optic quantum key distribution node, and a shared quantum key receiving node. The method comprises: The free-space quantum key distribution node generates a beam of combined light and transmits it to the shared quantum key receiving node through a free-space optical quantum channel. The fiber optic quantum key distribution node prepares a QKD quantum channel optical signal and sends it to the shared quantum key receiving node through the fiber optic quantum channel; The shared quantum key receiving node analyzes and processes the combined light beam, and selects to receive either the combined light beam or the QKD quantum channel optical signal based on the analysis results or a preset period of time, thereby generating a shared key.

[0019] The quantum key distribution system and method supporting dynamic switching of quantum channels provided by embodiments of the present invention, through the design of a shared receiving terminal, enables the reuse of quantum key receiving nodes, significantly reducing the hardware threshold and overall construction cost of building multi-channel, multi-node quantum networks. Furthermore, it supports intelligent dynamic switching based on real-time channel states, enabling the network to adaptively avoid the impact of fiber optic failures, severe atmospheric conditions, etc., ensuring the continuity of key services and providing greater flexibility for network topology planning. Specifically, it allows for the optimal hybrid use of two channels based on geographical environment and economic considerations. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the structure of a quantum key distribution system supporting dynamic switching of quantum channels according to an embodiment of the present invention; Figure 2 A schematic diagram of a quantum key distribution system supporting dynamic switching of quantum channels provided in another embodiment of the present invention; Figure 3 This is a flowchart illustrating a quantum key distribution method supporting dynamic switching of quantum channels, provided in an embodiment of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the present invention more apparent, exemplary embodiments according to the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are merely a part of the embodiments of the present invention, and not all of the embodiments of the present invention. It should be understood that the present invention is not limited to the exemplary embodiments described herein. Based on the embodiments of the present invention described herein, all other embodiments obtained by those skilled in the art without inventive effort should fall within the protection scope of the present invention.

[0023] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without one or more of these details. In other instances, certain technical features well-known in the art have not been described in order to avoid obscuring the invention.

[0024] It should be understood that the invention can be embodied in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0025] To fully understand this invention, a detailed structure will be presented in the following description to illustrate the technical solution proposed by this invention. Optional embodiments of the invention are described in detail below; however, in addition to these detailed descriptions, the invention may have other embodiments.

[0026] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0027] To improve the flexibility of quantum key distribution, the first aspect of this invention provides a quantum key distribution system that supports dynamic switching of quantum channels, such as... Figure 1 As shown, the quantum key distribution system supporting dynamic switching of quantum channels includes: at least one free-space quantum key distribution node 10, at least one fiber optic quantum key distribution node 20, and a shared quantum key receiving node 30.

[0028] It should be noted that, Figure 1 The example given shows only one free-space quantum key distribution node 10 and one fiber optic quantum key distribution node 20. This is just an example, and the actual number of free-space quantum key distribution nodes 10 and fiber optic quantum key distribution nodes 20 can be determined according to the actual application.

[0029] Free-space quantum key distribution node 10 is used to prepare and transmit combined light.

[0030] Specifically, the free-space quantum key distribution node 10 is adaptable to atmospheric free-space transmission scenarios and can be deployed in scenarios where fiber optic links cannot cover, such as ground fixed stations, mobile carriers, and low-altitude platforms.

[0031] The fiber optic quantum key distribution node 20 is used to prepare and transmit QKD quantum channel optical signals.

[0032] Specifically, the fiber optic quantum key distribution node 20 is adaptable to fixed fiber optic communication network scenarios and can be deployed at fixed sites accessible by fiber optic links.

[0033] The shared quantum key receiving node 30 is connected to the free space quantum key distribution node 10 through a free space optical quantum channel and to the fiber optic quantum key distribution node 20 through a fiber optic quantum channel. It is used to analyze and process the combined light and, based on the analysis results or a preset period, select to receive the combined light or the QKD quantum channel optical signal to generate a shared key.

[0034] It is worth mentioning that the system of the present invention, through a shared quantum key receiving node 30, can realize dynamic access and key generation services for multiple QKD transmitting terminals from different physical media (optical fiber / free space) and different geographical locations.

[0035] The quantum key distribution system supporting dynamic switching of quantum channels in this invention, through the design of a shared receiving terminal, enables the reuse of quantum key receiving nodes, significantly reducing the hardware threshold and overall construction cost of building multi-channel, multi-node quantum networks. Furthermore, it supports intelligent dynamic switching based on real-time channel status, allowing the network to adaptively avoid the impact of fiber optic failures, severe atmospheric conditions, etc., ensuring the continuity of key services and providing greater flexibility for network topology planning. Specifically, it allows for the optimal use of two channels in combination based on geographical environment and economic considerations.

[0036] In some embodiments, such as Figure 2As shown, the shared quantum key receiving node 30 includes: a beam receiving module 301, an adaptive optics interface module 302, a first wavelength division multiplexing module 303, a monitoring module 304, a control module 305, an optical switch module 306, and a shared QKD receiver 307.

[0037] It should be noted that, Figure 2 In this context, k1 represents the shared quantum key generated by free-space quantum key distribution node 10 and shared quantum key receiving node 30 through a free-space QKD link; k2 represents the shared quantum key generated by fiber optic quantum key distribution node 20 and shared quantum key receiving node 30 through a fiber optic QKD link.

[0038] The beam receiving module 301 is used to receive combined beam light.

[0039] As an example, the beam receiving module 301 may be a receiving optical antenna and / or a receiving telescope.

[0040] Specifically, the beam receiving module 301 is used to collect the combined beam transmitted from the 620m free space quantum light channel, complete the reception and preliminary collimation of the spatial light, and couple the combined beam into the subsequent optical processing optical path.

[0041] The adaptive optics interface module 302 is connected to the beam receiving module 301 and is used to correct and couple the combined beam and output the combined beam signal.

[0042] Specifically, the adaptive optics interface module 302 is designed for free-space links and is located between the free-space receiving telescope and the first wavelength division multiplexing module 303. Its core task is to efficiently couple the far-field light spot, which is affected by turbulence after transmission in the atmosphere, into the single-mode optical fiber.

[0043] The first wavelength division multiplexing module 303 is connected to the adaptive optics interface module 302 via a single-mode fiber. It is used to decompose the combined optical signal transmitted through the single-mode fiber to obtain the QKD quantum signal and the monitoring beacon optical signal.

[0044] The monitoring module 304 is connected to the first wavelength division multiplexing module 303 and is used to receive the monitoring beacon optical signal, perform channel quality monitoring, and generate real-time quality assessment indicators.

[0045] Specifically, real-time quality assessment metrics include at least one of single-mode fiber coupling efficiency and quantum bit error rate (QBER).

[0046] The control module 305 is connected to the monitoring module 304 and is used to generate control commands based on real-time quality assessment indicators or preset cycle times.

[0047] As an example, the control module 305 contains QKD master control software, which can abstract and shield the underlying physical channel differences from the upper layer applications, so that the standard QKD protocol processing flow does not need to be aware of the specific channel type.

[0048] Specifically, the handover control logic of control module 305 supports manual commands, automatic handover triggering based on fixed time periods (e.g., every 15 minutes), or based on real-time channel quality indicators (e.g., 1545 nm beacon coupling efficiency below a threshold, QBER above a threshold). Simultaneously, control module 305 can also perform channel monitoring and management, collecting performance parameters (coupling efficiency, QBER, raw count rate) of each channel in real time to provide data support for intelligent handover decisions, and can interact with upper-layer applications through a standard-compliant key manager. Furthermore, in addition to fixed time periods and triggering based on coupling efficiency or QBER, handover decisions can also be based on more complex indicators or strategies such as key generation rate, network scheduling instructions, or predictive models (e.g., weather forecasts), which will not be elaborated upon here.

[0049] The optical switch module 306 is connected to the first wavelength division multiplexing module 303, the control module 305 and the fiber quantum key distribution node 20, and is used to select to receive QKD quantum signal light or QKD quantum channel light signal according to the control command.

[0050] Preferably, the optical switch module 306 is a 2×2 mechanical fiber optic switch with low insertion loss (e.g., -1 dB) that supports remote network control (e.g., via TCP / IP protocol). Its function is to physically switch the input port of the shared QKD receiver 307 to either a fiber optic link from a free-space interface or a direct fiber optic link, according to control commands.

[0051] More preferably, the 2×2 mechanical fiber optic switch can be replaced with a microelectromechanical system optical switch, a thermo-optic switch, or a larger-scale N×M optical switch matrix to accommodate the access needs of more network nodes.

[0052] The shared QKD receiver 307 is connected to the optical switch module 306 and is used to generate a shared key based on the received QKD quantum signal light or QKD quantum channel light signal.

[0053] Specifically, the shared QKD receiver 307 typically includes core components such as a single-photon detector and a polarization analysis module, and can be time-division multiplexed by multiple transmitters.

[0054] In this embodiment, the shared quantum key receiver 30 achieves compatible access, intelligent switching, and time-division multiplexing of free space and fiber optic dual heterogeneous quantum channels through a single shared QKD receiver 307, significantly reducing the hardware deployment cost of multi-node QKD networks. At the same time, through adaptive optics interfaces and a unified control framework, standard, unmodified commercial fiber optic QKD equipment can be directly used in free space links, breaking down long-standing technical barriers and promoting the standardization and large-scale application of quantum network equipment.

[0055] In some embodiments, such as Figure 2 As shown, the adaptive optics interface module 302 includes: a fast-steering mirror 3021, a single-mode fiber coupling lens group 3022, and a single-mode fiber end face 3023.

[0056] The fast-turning mirror 3021 is used to perform high-speed, real-time correction of the angular arrival fluctuations of the combined beam received by the beam receiving module 301.

[0057] Specifically, the fast-steering mirror 3021 performs high-speed, real-time correction of beam arrival angle fluctuations caused by atmospheric turbulence, compensates for turbulence disturbances, and improves the coupling efficiency of subsequent single-mode optical fibers.

[0058] It should be noted that, for stronger turbulence conditions, higher-order wavefront aberration corrections can be performed by adding deformable mirrors on top of tilt correction, in order to maintain higher single-mode fiber coupling efficiency.

[0059] The single-mode fiber coupled lens group 3022 is connected to the fast-turning mirror 3021 and the single-mode fiber end face 3023 to focus the corrected beam onto the single-mode fiber end face 3023.

[0060] As an example, the single-mode fiber-coupled lens group 3022 includes a dichroic mirror that can split the combined light based on wavelength.

[0061] Specifically, the single-mode fiber coupling lens group 3022 compresses and focuses the combined beam (including 1550.12nm QKD quantum signal light and 1545nm monitoring beacon light) after being corrected by the fast-turning mirror 3021 into an extremely small converged beam whose spot size perfectly matches the core diameter of the single-mode fiber through the converging effect of the lens. Finally, the beam spot is precisely projected onto the core center of the single-mode fiber end face 3023.

[0062] The single-mode fiber end facet 3023 is used to couple the beam to the fiber and output a combined optical signal.

[0063] In this embodiment, the adaptive optics interface module 302 performs high-speed real-time correction of the beam arrival angle fluctuations caused by atmospheric turbulence through the fast-turning mirror 3021, and achieves efficient and stable coupling of spatial light to single-mode fiber with the coupling lens group and the single-mode fiber end face 3023.

[0064] In some embodiments, such as Figure 2 As shown, the adaptive optics interface module 302 also includes a beam reducer 3024 and a position-sensitive detector 3025.

[0065] The beam reducer 3024 is disposed between the beam receiving module 301 and the fast steering mirror 3021, and is used to reduce the beam of the combined beam received by the beam receiving module 301.

[0066] As an example, the beam reducer 3024 can be a 6× beam-shrinking system that reduces the large-aperture beam (e.g., 50.8 mm) of the receiving telescope to accommodate subsequent optical elements.

[0067] The position-sensitive detector 3025 is connected to the fast-steering mirror 3021 to detect the position of the light spot in real time and provide a closed-loop feedback signal for the fast-steering mirror 3021.

[0068] As an example, the position-sensitive detector 3025 receives beacon light (e.g., 980 nm), detects the position of the light spot, and provides a closed-loop feedback signal for the fast-steering mirror 3021.

[0069] In this embodiment, the beam reducer 3024 reduces the size of the received large-aperture combined beam to fit subsequent small-aperture optical elements, effectively reducing device size, lowering hardware costs, and improving beam correction accuracy. Simultaneously, the position-sensitive detector 3025 detects the spot position in real time, providing a closed-loop feedback signal to the fast-steering mirror 3021, thus improving the response speed and accuracy of beam arrival angle fluctuation correction.

[0070] In some embodiments, when the control module 305 generates control instructions based on real-time quality assessment indicators, it is specifically used to: when the single-mode fiber coupling efficiency is lower than a first threshold or the quantum bit error rate is higher than a second threshold, generate control instructions to receive QKD quantum channel optical signals.

[0071] As an example, the first threshold can be set between 20% and 30%, and the second threshold can be set between 4% and 6%.

[0072] In this embodiment, when the free space link single-mode fiber coupling efficiency is lower than a preset first threshold or the qubit error rate is higher than a preset second threshold, the system automatically switches to a stable fiber quantum key distribution link to receive QKD quantum channel optical signals, thereby avoiding key service interruptions caused by atmospheric disturbances, severe weather, etc.

[0073] In some embodiments, the shared QKD receiver 307 also includes an automatic polarization controller.

[0074] The control module 305 is also connected to the shared QKD receiver 307 and includes an automatic polarization calibration program. When the channel is switched, the automatic polarization calibration program performs feedback adjustment on the automatic polarization controller based on the known polarization state sequence sent by the distribution node after the switch.

[0075] After channel switching, initialize the receive parameter calibration process for the selected channel.

[0076] As an example, the automatic polarization calibration procedure is automatically initiated after channel switching. By controlling the automatic polarization controller of the shared QKD receiver 307, it performs feedback adjustment based on the known test states sent by the transmitting node until the measurement basis vectors are aligned and the bit error rate of the qubits is reduced to an acceptable level (e.g., < 4%).

[0077] In this embodiment, the automatic polarization calibration program can quickly achieve precise alignment of the measurement basis vectors at both ends of the transmitter and receiver by controlling the automatic polarization controller, reducing the bit error rate of the qubit to within the safe key generation threshold, thereby ensuring that the QKD system can quickly resume stable and secure shared key generation after switching heterogeneous channels.

[0078] It should be noted that the beacon system within the quantum key distribution system supporting dynamic switching of quantum channels of this invention includes lasers with two wavelengths: 980 nm and 1545 nm. The 980 nm beacon is used for closed-loop tracking of the fast steering mirror 3021; ​​the 1545 nm beacon, with a wavelength close to that of the QKD signal (1550.12 nm), is transmitted via a shared optical path and is used for real-time, lossless monitoring of the single-mode fiber coupling efficiency of the free-space channel, serving as a key indicator for channel quality assessment.

[0079] In some embodiments, the free-space quantum key distribution node 10 includes: a free-space link QKD transmitter 101, a control laser module 102, a second wavelength division multiplexing module 103, and a beam emission module 104.

[0080] The free-space link QKD transmitter 101 is used to prepare and output quantum signal light.

[0081] Specifically, the free-space link QKD transmitter 101 is used to complete the generation and transmission of quantum states of the distribution node.

[0082] The laser control module 102 is used to emit multi-wavelength beacon light.

[0083] Specifically, the control laser module 102 is the transmitting unit of the beacon system, which can output beacon light with two wavelengths: 980nm and 1545nm.

[0084] The second wavelength division multiplexing module 103 is connected to the free space link QKD transmitter 101 and the control laser module 102, and is used to combine quantum signal light and multi-wavelength beacon light to obtain combined light.

[0085] As an example, the second wavelength division multiplexing module 103 combines the quantum signal light and the multi-wavelength beacon light into the same optical path, realizing the transmission of the quantum signal light and the beacon light through the same optical path, and then transmits them to the free space channel through the beam emission module 104.

[0086] The beam emission module 104 is connected to the second wavelength division multiplexing module 103 and is used to send the combined beam to the free space optical quantum channel.

[0087] As an example, the beam transmitting module 104 includes a radio transmitting antenna.

[0088] In this embodiment, the free-space quantum key distribution node 10 ensures that the beacon light and the quantum signal light experience a completely identical atmospheric transmission environment.

[0089] In some embodiments, such as Figure 2 As shown, the fiber optic quantum key distribution node 20 includes a fiber-link QKD transmitter 201. The fiber-link QKD transmitter 201 is used to prepare and transmit QKD quantum channel optical signals.

[0090] As an example, the fiber optic link QKD transmitter 201 can send quantum states to the shared QKD receiver 307 via a 17km fiber optic quantum channel, thus fulfilling the function of the QKD transmitter and cooperating with the shared QKD receiver 307 to complete quantum key distribution.

[0091] It should be noted that the fiber optic link QKD transmitter 201 and the free space link QKD transmitter 101 can be standard commercial or customized polarization-coded QKD transmitters, and they can be located in different geographical locations.

[0092] Furthermore, although the system of this invention uses polarization encoding, it can also be replaced by time-phase encoding or other schemes. However, it should be noted that the automatic calibration of polarization encoding is relatively quick (e.g., 20-30 seconds), while time encoding may require a more complex interferometer stabilization process. The switching overhead must be weighed when choosing between the two.

[0093] In some embodiments, such as Figure 2 As shown, the shared quantum key receiving node 30 is also connected to the free space quantum key distribution node 10 via a free space radio classical channel, which is used to carry classical information interaction with the free space quantum key distribution node 10.

[0094] It should be noted that the free-space radio classical channel is a classical communication link that runs parallel to the free-space optical quantum channel. It carries all classical information exchanges between the free-space link QKD transmitter 101 and the shared QKD receiver 307, providing classical communication support for the operation of the QKD protocol and link control.

[0095] The shared quantum key receiving node 30 is also connected to the fiber optic quantum key distribution node 20 via a parallel fiber optic classical channel to carry classical data transmission with the fiber optic quantum key distribution node 20.

[0096] It should be noted that the parallel fiber classical channel is a classical communication link that runs parallel to the fiber quantum channel. It carries bidirectional classical data transmission, such as classical interaction information and channel switching, required by the QKD protocol between the fiber link QKD transmitter 201 and the shared QKD receiver 307.

[0097] Next, we will use a field experiment of a heterogeneous quantum network in a city as an example. In this experiment, the free space link QKD transmitter 101 is named Alice1, the fiber optic link QKD transmitter 201 is named Alice2, and the shared QKD receiver 307 is named Bob.

[0098] Scene and configuration:

[0099] A 3-node network is deployed in City X. Alice1 is located at node A and connected to Bob via a 620-meter free-space link; Alice2 is located at node B, 17 kilometers away, and connected to Bob via an existing fiber optic link; Bob is located at node C.

[0100] QKD Equipment: Alice1 and Bob use commercially available polarization-encoded QKD equipment, while Alice2 uses a self-developed similar equipment. All use the efficient 3-state + 1 decoy state BB84 protocol, with a laser wavelength of 1550.12 nm and a repetition frequency of 50 MHz.

[0101] Optical switch module 306: It adopts a custom-developed network-controlled 2×2 fiber optic mechanical switch with an insertion loss of approximately -1dB and a switching time in the millisecond range.

[0102] Free-space terminal: Transmitter beam waist radius 25 mm. Receiver telescope aperture 50.8 mm, adaptive optics interface design optimized for moderate turbulence conditions D_Rx / r0 ≈ 4 (r0 is 13 mm), primarily correcting tilt aberrations.

[0103] Workflow and Data:

[0104] 1. Initialization: Power on each node and establish a classic communication link. The free-space terminal uses an auxiliary telescope and a CMOS camera to complete coarse alignment, and then activates the 980 nm beacon to complete fine alignment.

[0105] 2. Dynamic switching operation: The control software is set to rotate channels every 15 minutes (for demonstration purposes). When switching is triggered:

[0106] The control module 305 sends instructions to the optical switch module 306.

[0107] The optical switch module 306 completes port switching in less than 1 second.

[0108] The system initiates automatic polarization calibration: Alice sends a fixed polarization state sequence, and Bob adjusts his polarization controller, reducing the QBER from the initial ~4% to a stable operating level within an average of 20-30 seconds.

[0109] 3. Key generation performance:

[0110] Free-space channel: Under sunlight and moderate turbulence conditions (measured D_Rx / r0 = 3.0 ± 0.2), the average key generation rate is approximately 1.5 kbps, and the average QBER is 2.5%. Monitoring with a 1545 nm beacon confirms that the system can maintain positive key generation even under turbulence conditions with D_Rx / r0 ≤ 7.

[0111] Fiber optic channel: With 17 km fiber (loss ~-11 dB), the average key generation rate is approximately 1.6 kbps and the average QBER is 1.4%.

[0112] Cost-benefit analysis: Compared to traditional solutions requiring two separate Bob units, this shared architecture halves the number of single-photon detectors needed. It is estimated that hardware costs can be reduced by approximately 40%, and long-term maintenance costs by approximately 30%.

[0113] Next, the intelligent switching strategy of the present invention will be described.

[0114] This embodiment illustrates that the switching strategy is not limited to a fixed period. Based on the aforementioned urban heterogeneous quantum network, the following adaptive strategies can be configured:

[0115] Monitoring metrics: Real-time reading of the 1545 nm beacon coupling efficiency (reflecting turbulence intensity) and real-time QBER of the free space channel.

[0116] Switching threshold: Sets the threshold T when the coupling efficiency continuously falls below a certain threshold. η (e.g., corresponding to D_Rx / r0 > 6), or QBER continuously exceeding a certain threshold T. Q When the free space channel quality is degraded (e.g., 5%), it is determined that the free space channel quality has deteriorated.

[0117] Switching action: Control module 305 automatically triggers a switch to the fiber optic channel (if available). Simultaneously, the system continues to monitor the free-space channel. Once its quality recovers (coupling efficiency increases, QBER decreases) and stabilizes for a period, it can automatically or upon confirmation switch back to the free-space channel, achieving dynamic optimization of network resources and link redundancy backup.

[0118] Furthermore, this invention also provides a quantum key distribution method supporting dynamic switching of quantum channels, applied to the aforementioned quantum key distribution system supporting dynamic switching of quantum channels. The quantum key distribution system supporting dynamic switching of quantum channels includes: at least one free-space quantum key distribution node 10, at least one fiber optic quantum key distribution node 20, and a shared quantum key receiving node 30, such as... Figure 3 As shown, quantum key distribution methods that support dynamic switching of quantum channels include:

[0119] S1, the free-space quantum key distribution node prepares a beam of light and sends it to the shared quantum key receiving node through the free-space optical quantum channel.

[0120] S2, the fiber optic quantum key distribution node prepares the QKD quantum channel optical signal and sends it to the shared quantum key receiving node through the fiber optic quantum channel.

[0121] S3, the shared quantum key receiving node analyzes and processes the combined light beam, and selects to receive the combined light beam or the QKD quantum channel optical signal according to the analysis results or a preset period time to generate a shared key.

[0122] Specifically, the method of the present invention may include the following steps:

[0123] Channel quality monitoring steps: Monitor the performance parameters of at least one free space channel and one fiber optic channel.

[0124] Switching decision steps: Based on preset strategies or performance parameters, decide to perform channel switching.

[0125] Switching execution steps: Control the optical switch to switch the input of the shared receiving terminal from the current channel to the target channel.

[0126] Automatic calibration steps: After the handover is completed, the parameters of the shared receiving terminal are calibrated for the target channel until its performance meets the key distribution requirements.

[0127] More specifically, the switching decision steps include: when the coupling efficiency is lower than a first threshold or the qubit error rate is higher than a second threshold, deciding to switch from the free space channel to the optical fiber channel.

[0128] The automatic calibration step is specifically a polarization automatic calibration step, which includes: controlling the target transmitting terminal to send a known polarization state sequence, and adjusting its polarization controller according to the detection results of the shared receiving terminal.

[0129] It should be noted that other specific embodiments of the quantum key distribution method supporting dynamic switching of quantum channels in the embodiments of the present invention can be found in the specific embodiments of the quantum key distribution system supporting dynamic switching of quantum channels in the above embodiments of the present invention.

[0130] The quantum key distribution method supporting dynamic switching of quantum channels in this invention supports intelligent dynamic switching based on real-time channel status, enabling the network to adaptively avoid the impact of fiber optic failures, severe atmospheric conditions, etc., ensuring the continuity of key services, and providing greater flexibility for network topology planning. Specifically, it can optimally mix and use two channels according to geographical environment and economic efficiency.

[0131] Although exemplary embodiments have been described herein with reference to the accompanying drawings, it should be understood that the above exemplary embodiments are merely illustrative and are not intended to limit the scope of this application. Various changes and modifications can be made therein by those skilled in the art without departing from the scope and spirit of this application. All such changes and modifications are intended to be included within the scope of this application as claimed in the appended claims.

[0132] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0133] In the several embodiments provided in this application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another device, or some features may be ignored or not executed.

[0134] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of this application may be practiced without these specific details. In some instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0135] Similarly, it should be understood that, in order to streamline this application and aid in understanding one or more of the various inventive aspects, features of this application may sometimes be grouped together in a single embodiment, figure, or description thereof in the description of exemplary embodiments of this application. However, this approach should not be construed as reflecting an intention that the claimed application requires more features than are expressly recited in each claim. Rather, as reflected in the corresponding claims, its inventive point lies in solving the corresponding technical problem with features fewer than all features of a single disclosed embodiment. Therefore, the claims following the detailed description are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of this application.

[0136] Those skilled in the art will understand that, apart from the mutual exclusion of features, all features disclosed in this specification (including the accompanying claims, abstract, and drawings) and all processes or elements of any method or apparatus so disclosed may be combined in any combination. Unless otherwise expressly stated, each feature disclosed in this specification (including the accompanying claims, abstract, and drawings) may be replaced by an alternative feature that serves the same, equivalent, or similar purpose.

[0137] Furthermore, those skilled in the art will understand that although some embodiments described herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, in the claims, any one of the claimed embodiments can be used in any combination.

[0138] The various component embodiments of this application can be implemented in hardware, or as software modules running on one or more processors, or a combination thereof. Those skilled in the art will understand that microprocessors or digital signal processors (DSPs) can be used in practice to implement some or all of the functions of some modules according to the embodiments of this application. This application can also be implemented as an apparatus program (e.g., a computer program and computer program product) for performing part or all of the methods described herein. Such an implementation of this application can be stored on a computer-readable medium, or can be in the form of one or more signals. Such signals can be downloaded from an Internet website, provided on a carrier signal, or provided in any other form.

[0139] It should be noted that the above embodiments are illustrative of this application and not restrictive, and that those skilled in the art can devise alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses should not be construed as limiting the claims. The word "comprising" does not exclude the presence of elements or steps not listed in the claims. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. This application can be implemented by means of hardware comprising several different elements and by means of a suitably programmed computer. In the unit claims enumerating several means, several of these means may be embodied by the same item of hardware. The use of the words first, second, and third, etc., does not indicate any order. These words can be interpreted as names.

[0140] The above description is merely a specific embodiment or illustration of the embodiments of this application. The scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. The scope of protection of this application shall be determined by the scope of the claims.

Claims

1. A quantum key distribution system supporting dynamic switching of quantum channels, characterized in that, The system includes: at least one free-space quantum key distribution node, at least one fiber optic quantum key distribution node, and a shared quantum key receiving node; The free-space quantum key distribution node is used to prepare and transmit combined light; The fiber optic quantum key distribution node is used to prepare and transmit QKD quantum channel optical signals; The shared quantum key receiving node is connected to the free-space quantum key distribution node via a free-space optical quantum channel and to the fiber optic quantum key distribution node via a fiber optic quantum channel. It is used to analyze and process the combined light beam and, based on the analysis results or a preset period, select to receive the combined light beam or the QKD quantum channel optical signal to generate a shared key.

2. The quantum key distribution system supporting dynamic switching of quantum channels according to claim 1, characterized in that, The shared quantum key receiving node includes: A beam receiving module is used to receive the combined beam; An adaptive optics interface module, connected to the beam receiving module, is used to correct and couple the combined beam and output a combined beam signal; The first wavelength division multiplexing module is connected to the adaptive optics interface module via a single-mode fiber. It is used to decompose the combined optical signal transmitted through the single-mode fiber to obtain the QKD quantum signal and the monitoring beacon optical signal. The monitoring module, connected to the first wavelength division multiplexing module, is used to receive the monitoring beacon optical signal, perform channel quality monitoring, and generate real-time quality assessment indicators. A control module, connected to the monitoring module, is used to generate control commands based on the real-time quality assessment indicators or the preset cycle time. An optical switch module, connected to the first wavelength division multiplexing module, the control module, and the fiber quantum key distribution node, is used to select to receive either the QKD quantum signal light or the QKD quantum channel light signal according to the control command. A shared QKD receiver, connected to the optical switch module, is used to generate the shared key based on the received QKD quantum signal light or the QKD quantum channel light signal.

3. The quantum key distribution system supporting dynamic switching of quantum channels according to claim 2, characterized in that, The adaptive optics interface module includes: A fast-turning mirror is used to perform high-speed, real-time correction of the angular arrival fluctuations of the combined light received by the beam receiving module. A single-mode fiber coupled lens assembly, connected to the fast-turning mirror and the single-mode fiber end face, is used to focus the corrected beam onto the single-mode fiber end face. The single-mode fiber end face is used to couple the light beam to the fiber and output the combined optical signal.

4. The quantum key distribution system supporting dynamic switching of quantum channels according to claim 3, characterized in that, The adaptive optics interface module further includes: A beam reducer is disposed between the beam receiving module and the fast-turning mirror, and is used to reduce the beam of the combined beam received by the beam receiving module. A position-sensitive detector, connected to the fast-turning mirror, is used to detect the position of the light spot in real time and provide a closed-loop feedback signal for the fast-turning mirror.

5. The quantum key distribution system supporting dynamic switching of quantum channels according to claim 2, characterized in that, The real-time quality assessment metrics include at least one of single-mode fiber coupling efficiency and quantum bit error rate. When generating control commands based on the real-time quality assessment indicators, the control module is specifically used for: When the single-mode fiber coupling efficiency is lower than a first threshold or the qubit error rate is higher than a second threshold, the generated control command is to receive the QKD quantum channel optical signal.

6. The quantum key distribution system supporting dynamic switching of quantum channels according to claim 2, characterized in that, The shared QKD receiver also includes an automatic polarization controller; The control module is also connected to the shared QKD receiver and includes an automatic polarization calibration program. When the channel is switched, the automatic polarization calibration program performs feedback adjustment on the automatic polarization controller based on the known polarization state sequence sent by the distribution node after the switch.

7. The quantum key distribution system supporting dynamic switching of quantum channels according to claim 1, characterized in that, The free-space quantum key distribution node includes: Free-space link QKD transmitter, used to prepare and output quantum signal light; Control the laser module to emit multi-wavelength beacon light; The second wavelength division multiplexing module is connected to the free space link QKD transmitter and the control laser module, and is used to combine the quantum signal light and the multi-wavelength beacon light to obtain the combined beam light; A beam emission module, connected to the second wavelength division multiplexing module, is used to transmit the combined beam to the free-space optical quantum channel.

8. The quantum key distribution system supporting dynamic switching of quantum channels according to claim 1, characterized in that, The fiber optic quantum key distribution node includes: A fiber optic link QKD transmitter is used to prepare and transmit the QKD quantum channel optical signal.

9. The quantum key distribution system supporting dynamic switching of quantum channels according to claim 1, characterized in that, The shared quantum key receiving node is also connected to the free space quantum key distribution node via a free space radio classical channel, which is used to carry classical information interaction with the free space quantum key distribution node; The shared quantum key receiving node is also connected to the fiber optic quantum key distribution node via a parallel fiber optic classical channel to carry classical data transmission with the fiber optic quantum key distribution node.

10. A quantum key distribution method supporting dynamic switching of quantum channels, characterized in that, This method is applied to a quantum key distribution system supporting dynamic switching of quantum channels according to any one of claims 1-9, wherein the quantum key distribution system supporting dynamic switching of quantum channels comprises: at least one free-space quantum key distribution node, at least one fiber optic quantum key distribution node, and a shared quantum key receiving node, and the method comprises: The free-space quantum key distribution node generates a beam of combined light and transmits it to the shared quantum key receiving node through a free-space optical quantum channel. The fiber optic quantum key distribution node prepares a QKD quantum channel optical signal and sends it to the shared quantum key receiving node through the fiber optic quantum channel; The shared quantum key receiving node analyzes and processes the combined light beam, and selects to receive either the combined light beam or the QKD quantum channel optical signal based on the analysis results or a preset period of time, thereby generating a shared key.

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