Quantum secure networking apparatus and method based on center-pumped frequency comb distribution

Abstract

The application discloses a quantum secure networking device and method based on center-pumped frequency comb distribution, relates to the technical field of quantum information, and simultaneously distributes pump laser to each user node through a center-pumped laser distribution unit, so that each user node can independently generate an electro-optical frequency comb; the electro-optical frequency comb generation unit is combined with a thin-film lithium niobate cascade modulator and a capacitively loaded slow-wave electrode structure, so that the half-wave voltage is effectively reduced and the modulation bandwidth is improved; polarization control and photon detection of the encoded comb teeth are performed through two-photon interference and a quantum key distribution unit, and quantum key distribution is realized based on the two-photon interference effect. The above functional modules work in sequence and in cooperation, so that pump light distribution, electro-optical comb generation, filtering and encoding, polarization control and two-photon interference detection form a complete closed loop, high security and high efficiency of quantum key distribution in a multi-user full-connection scene are realized, and the practical application requirements of large-scale quantum secure networking are met.

Description

Technical Field

[0001] This application relates to the field of quantum information technology, and in particular to a quantum-safe networking device and method based on a centrally pumped frequency distribution comb. Background Technology

[0002] Quantum secure communication, based on the fundamental principles of quantum mechanics, enables theoretically unconditionally secure transmission of information, making it one of the core technologies for ensuring communication security in the information age. Quantum key distribution (QKD), as the core technology supporting quantum secure communication, distributes secure keys between communicating parties, providing a theoretically unbreakable security foundation for subsequent data encryption.

[0003] Current technologies for quantum-secure networking mainly revolve around three routes: single-photon quantum key distribution (QKD), continuous variable quantum key distribution (CVQKD), and optical frequency comb-assisted QKD. The single-photon QKD route uses a single photon as the quantum information carrier. At the source end, a weakly coherent light source is used to simulate a single photon source, or a single-photon generator is used directly to load key information. After transmission through a quantum channel, it is received and decoded by a single-photon detector. The continuous variable CVQKD route utilizes the orthogonal component encoding of classical coherent light, is compatible with existing classical optical communication devices, and relies on existing optical communication networks to achieve key distribution. Optical frequency comb-assisted QKD, on the other hand, leverages the multi-frequency line characteristics of optical frequency combs to achieve parallel key transmission, attempting to improve key distribution efficiency.

[0004] Despite some progress in existing technologies, numerous technical bottlenecks remain insurmountable in large-scale applications. In single-photon QKD, the key rate is limited by the efficiency of the single-photon source and detector, significantly decreasing over long distances; crosstalk easily occurs when multiple users share a channel; and the performance of core components, such as intensity modulators and single-photon detectors, is insufficient to meet the requirements of high-speed coding and long-distance transmission. In continuous-variable CVQKD, the system is susceptible to background light noise and channel crosstalk during parallel transmission by multiple users, exhibiting weak anti-interference capabilities; channel resource allocation and interference suppression issues are not fully resolved; and the system is sensitive to environmental and phase noise, affecting system stability. In optical frequency comb-assisted QKD, the optical frequency comb exhibits poor stability; insufficient frequency alignment accuracy at different locations and comb tooth frequency offset affect interference visibility and bit error rate; and unoptimized comb tooth selection and polarization state control result in a low effective signal ratio.

[0005] In summary, existing technologies suffer from poor multi-user scalability, insufficient stability and frequency alignment accuracy of optical combs, low device adaptability, and low key distribution efficiency in quantum key distribution, making it difficult to achieve multi-user fully connected, highly secure, and highly efficient independent key exchange. Summary of the Invention

[0006] In view of this, this application provides a quantum-safe networking device and method based on a centrally pumped frequency distribution comb. The main purpose is to solve the problems of poor multi-user scalability, insufficient stability and frequency alignment accuracy of optical frequency combs, low device adaptability and low key distribution efficiency in the quantum key distribution process of existing technologies.

[0007] The first aspect provides a quantum-secure networking device based on a centrally pumped frequency comb, including multiple user nodes, each user node being configured with an independent electro-optic frequency comb and encoder to enable independent secure key exchange between any user pairs; the device also includes: a centrally pumped laser distribution unit, an electro-optic frequency comb generation unit, and a two-photon interference and quantum key distribution unit; The central pump laser distribution unit includes a pump laser module and a distribution link module connected in sequence; the pump laser module is used to generate a narrow linewidth frequency-stabilized pump laser; the distribution link module is a low-loss fiber optic network used to simultaneously distribute the pump laser to each user node; The electro-optic frequency comb generation unit includes an electro-optic modulation module, an output detection module, a filtering module, and an encoding module connected in sequence. The electro-optic modulation module receives the pump laser distributed by the central node and generates an electro-optic frequency comb based on a thin-film lithium niobate electro-optic modulator. It synchronizes the microwave signal generators of each user node based on satellite timing signals to achieve frequency alignment of the electro-optic frequency combs at different locations. The output detection module performs spectral observation, modulation effect verification, and power measurement on the electro-optic frequency comb, filters out residual pump laser components from the electro-optic frequency comb, and outputs the electro-optic frequency comb after pump laser filtering. The filtering module selects comb teeth with the same frequency from the electro-optic frequency comb after pump laser filtering and adjusts the polarization state of the comb teeth. The encoding module modulates the comb teeth with the same frequency into pulse packets, implements a decoy state protocol, and applies a phase shift. The two-photon interference and quantum key distribution unit includes a polarization control module and a detection module connected in sequence. The polarization control module is used to attenuate the encoded comb teeth to the single-photon level, compensate for the optical signal delay difference, adjust the photon polarization state, and achieve interference beam combining to output combined light. The detection module is used to perform phase, power, and photon number matching on the combined light, detect photons, and complete two-photon coincidence counting to achieve quantum key distribution based on the two-photon interference effect.

[0008] Secondly, a quantum-safe networking method based on a centrally pumped frequency distribution comb is provided, which includes: Narrow-linewidth frequency-stabilized pump lasers are generated by the pump laser module in the central pump laser distribution unit, and the pump lasers are simultaneously distributed to each user node via the distribution link module. At each user node, based on the electro-optic effect of thin-film lithium niobate, the distributed pump laser is received and an electro-optic frequency comb is generated through an electro-optic modulation module. The output detection module performs spectral observation, modulation effect verification and power measurement on the electro-optic frequency comb, and filters out the residual pump laser component in the electro-optic frequency comb, outputting the electro-optic frequency comb after filtering out the pump laser. The filtering module selects comb teeth of the same frequency from the electro-optic frequency comb after the pump laser has been filtered out and adjusts the polarization state of the comb teeth. The same-frequency comb teeth are modulated into pulse wave packets by the encoding module to realize the decoy state protocol and apply phase shift; The polarization control module attenuates the encoded comb teeth to the single-photon level, compensates for the optical signal delay difference, adjusts the photon polarization state, and achieves interference beam combining to output combined beam light. The combined beam is matched in phase, power and photon number by a detection module, the photons are detected and two-photon coincidence counting is completed, and quantum key distribution is realized based on the two-photon interference effect.

[0009] The core of the quantum-safe networking device based on the central pumped frequency comb that enables independent secure key exchange between any user pairs lies in the rational allocation and independent scheduling of frequency domain resources and user pair connections.

[0010] Specifically, each user node locally binds different teeth of the electro-optic frequency comb to other target users in the network. This connection relies on the network-wide comb tooth frequency alignment characteristics guaranteed by the centrally pumped laser distribution, ensuring that the comb teeth on different user nodes naturally form one-to-one frequency matching pairs. When a user pair performs key distribution, only the corresponding comb teeth of both parties need to be extracted from the frequency comb through a programmable optical filter. The remaining comb teeth can remain idle or be used for parallel communication of other user pairs, without reconfiguring any central switching equipment across the entire network. This frequency division multiple access mechanism, based on comb teeth as the basic unit, essentially transforms the connection between users into the selection of frequency comb teeth and the independent invocation of encoders. When the network scales up, only new comb tooth frequencies need to be added, avoiding the drawback of reconstructing the entire optical path due to the addition of new users in traditional shared light source architectures. Thus, it achieves user connection independence and strong scalability at the physical layer.

[0011] By employing the above technical solutions, this application provides a quantum-secure networking device and method based on a centrally pumped frequency comb. Compared with existing technologies, firstly, by using a centrally pumped laser distribution unit to simultaneously distribute pump lasers to each user node, each user node can independently generate an electro-optic frequency comb, overcoming the limitation of interconnected key distribution among users in traditional shared optical frequency comb architectures, and significantly improving the scalability and security of multi-user networking; secondly, by combining the electro-optic frequency comb generation unit with a thin-film lithium niobate cascade modulator and a capacitor-loaded slow-wave electrode structure, the half-wave voltage is effectively reduced and the modulation bandwidth is increased, achieving low-power, wide-bandwidth, and high-flatness electro-optic frequency comb output; furthermore, by using a two-photon interference and quantum key distribution unit to perform polarization control and photon detection on the encoded comb teeth, quantum key distribution is achieved based on the two-photon interference effect. The aforementioned functional modules are sequentially connected and work together to form a complete closed loop of pump light distribution, electro-optic comb generation, filtering and encoding, polarization control, and two-photon interferometry detection. The decoy state protocol and efficient signal processing flow enhance the anti-eavesdropping capability, ultimately achieving high-security and high-efficiency quantum key distribution in multi-user fully connected scenarios, fully meeting the practical application requirements of large-scale quantum secure networking.

[0012] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0013] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a schematic diagram of the network connection topology of a six-user quantum key distribution device based on an electro-optic frequency comb in one embodiment of this application; Figure 2 This is a schematic diagram of the optical path structure of a six-user quantum key distribution device based on an electro-optic frequency comb in one embodiment of this application; Figure 3 This is a schematic diagram of the structure of a two-user quantum key distribution device based on an electro-optic frequency comb according to one embodiment of this application; Figure 4 This is a schematic diagram of the device structure of a computer device provided in an embodiment of this application. Detailed Implementation

[0014] The present application will be described in detail below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present application can be combined with each other.

[0015] In related technologies, the current implementation of quantum secure networking mainly revolves around three routes: single-photon QKD, continuous-variable quantum key distribution (CVQKD), and optical frequency comb-assisted QKD. However, large-scale applications still face many insurmountable technical bottlenecks. In the single-photon QKD route, the key rate is limited by the efficiency of the single-photon source and detector during quantum key distribution, significantly decreasing over long distances; multi-user shared channels are prone to signal crosstalk; and the performance of core components, such as intensity modulators and single-photon detectors, is insufficient to meet the requirements of high-speed encoding and long-distance transmission. In the continuous-variable CVQKD route, multi-user parallel transmission is susceptible to background light noise and channel crosstalk, resulting in weak anti-interference capabilities; channel resource allocation and interference suppression issues are not fully resolved; and the system is sensitive to environmental and phase noise, affecting system stability. In the optical frequency comb-assisted QKD route, the optical frequency comb exhibits poor stability; insufficient frequency alignment accuracy at different locations, and comb tooth frequency offset affecting interference visibility and bit error rate; and unoptimized comb tooth selection and polarization state control result in a low effective signal ratio.

[0016] To address this issue, this embodiment provides a quantum-secure networking device based on a centrally pumped frequency comb, comprising multiple user nodes, each configured with an independent electro-optic frequency comb and encoder to enable independent secure key exchange between any user pairs; the device further comprises: a centrally pumped laser distribution unit, an electro-optic frequency comb generation unit, and a two-photon interference and quantum key distribution unit; The central pump laser distribution unit is used to generate pump laser and distribute the pump laser to each user node; The electro-optic frequency comb generating unit is set at each user node to receive the distributed pump laser and generate an electro-optic frequency comb containing multiple comb teeth, and to perform detection, filtering and encoding processing on the comb teeth of the electro-optic frequency comb. The two-photon interference and quantum key distribution unit is used to perform polarization control and photon detection on the encoded comb teeth, and realizes quantum key distribution based on the two-photon interference effect.

[0017] The quantum-secure networking device based on a centrally pumped frequency distribution comb provided in this invention, compared with existing technologies, firstly, distributes the pump laser simultaneously to each user node through a centrally pumped laser distribution unit, enabling each user node to independently generate an electro-optic frequency comb. This overcomes the limitation of interconnected key distribution among users in traditional shared optical frequency comb architectures, significantly improving the scalability and security of multi-user networking. Secondly, by combining the electro-optic frequency comb generation unit with a thin-film lithium niobate cascade modulator and a capacitor-loaded slow-wave electrode structure, the half-wave voltage is effectively reduced and the modulation bandwidth is increased, achieving low-power, wide-bandwidth, and high-flatness electro-optic frequency comb output. Furthermore, by using a two-photon interference and quantum key distribution unit to perform polarization control and photon detection on the encoded comb teeth, quantum key distribution is achieved based on the two-photon interference effect. The aforementioned functional modules are sequentially connected and work together to form a complete closed loop of pump light distribution, electro-optic comb generation, filtering and encoding, polarization control, and two-photon interferometry detection. The decoy state protocol and efficient signal processing flow enhance the anti-eavesdropping capability, ultimately achieving high-security and high-efficiency quantum key distribution in multi-user fully connected scenarios, fully meeting the practical application requirements of large-scale quantum secure networking.

[0018] In practical implementation, the quantum-safe networking device based on a centrally pumped frequency comb in this application, taking a device comprising six user nodes as an example, refers to... Figure 1 As shown in the diagram, the network topology of the six-user quantum key distribution device is clearly illustrated. The six user nodes are represented by circular human figures, labeled as User A to User F, and arranged in a hexagonal ring. Each user node receives a pump laser from the central node via a central laser distribution module and is equipped with an independent and perfectly aligned electro-optic frequency comb. This is illustrated by a frequency domain diagram of the electro-optic frequency comb to the right of each user node, consisting of seven equally spaced vertical lines numbered 1 to 7, representing comb teeth. The same code indicates that different users use the same comb tooth for quantum key distribution. Each frequency line for each user is equipped with an independent encoder to enable independent secure key exchange between any user pairs. Users are connected by multiple intersecting straight lines, with each line labeled with a partial value from 1 to 7, representing an independent quantum channel or key negotiation channel that can be established between different user pairs.

[0019] from Figure 1 It can be seen that each user only needs 5 comb teeth to achieve fully connected quantum key distribution among six users. Specifically, in this fully connected network structure, each user node is equipped with an independent electro-optic frequency comb that generates a set of comb teeth with uniform frequency spacing. By allocating different comb teeth to the communication links of different target users, isolation between users and channels is achieved in the frequency domain.

[0020] Taking user A as an example, the first tooth of its electro-optic frequency comb is assigned to the key exchange with user B, the second tooth to user C, and so on, until the fifth tooth is assigned to user F. Since the pump lasers of each user node originate from the same central node and the microwave signal generators are uniformly referenced to the satellite timing signal, the frequencies of the same numbered comb teeth generated by all nodes are perfectly aligned. Therefore, when user A uses the first comb tooth to send a quantum state and user B also uses the first comb tooth to perform the corresponding operation, the two can establish a secure key based on a measurement device-independent quantum key distribution protocol. Similarly, user A and user C use the second comb tooth, while user B and user C each use a pre-agreed other comb tooth. The key exchanges of different user pairs are orthogonal to each other in frequency, thus supporting multiple pairs of users to perform key distribution simultaneously without interference. When any pair of users needs to establish a connection, they first exchange connection request and confirmation information through a classical control channel. Each of them tunes its local programmable optical filter to the agreed comb frequency, and then performs encoding, two-photon interference and post-processing to complete an independent key exchange. After the key exchange is completed, the comb resource can be released and redistributed to other user pairs, thereby realizing dynamic, on-demand, fully connected quantum secure networking.

[0021] Accordingly, a schematic diagram of the optical path structure of a six-user electro-optic frequency comb quantum key distribution device is shown below. Figure 2 As shown, Figure 2 A central rectangular module containing a glowing symbol represents the central pump laser source distribution module. Six straight lines radiate outwards from this module, connecting to six user nodes. Each link features a double-elliptical ring, symbolizing the fiber optic transmission path or optical isolation / modulation components. Figure 1 Similarly, each user node is represented by a human-shaped icon and labeled as user A through user F. Each user is equipped with an independent, frequency-aligned electro-optic frequency comb, consisting of seven equally spaced vertical lines numbered 1 through 7. This indicates that after receiving the central pump light, each user generates its own independent, frequency-aligned electro-optic frequency comb locally. The diagram clearly shows that the central node simultaneously distributes the pump laser to each user node via a low-loss fiber optic link through the central pump laser distribution unit. Each user node is equipped with an independent electro-optic frequency comb generator, providing a separate electro-optic frequency comb for each user.

[0022] In the above embodiments, the central pumped laser distribution unit includes a pumped laser module and a distribution link module connected in sequence; The pump laser module is used to generate a narrow linewidth frequency-stabilized pump laser; the pump laser module includes a laser and an ultra-stable Fabry-Perot cavity, and the laser is locked to the ultra-stable Fabry-Perot cavity by frequency-stabilization locking technology to generate a narrow linewidth frequency-stabilized pump laser; The distribution link module is an optical fiber network used to simultaneously distribute the pump laser to each user node. The distribution link module includes a multi-channel optical fiber splitter and a transmission optical fiber. The input end of the multi-channel optical fiber splitter is connected to the pump laser module, and the output end of the multi-channel optical fiber splitter is connected to each user node through the transmission optical fiber.

[0023] In the above embodiments, the electro-optic frequency comb generating unit includes an electro-optic modulation module, an output detection module, a filtering module, and an encoding module connected in sequence; the input terminal of the electro-optic modulation module receives the pump laser distributed by the central node, the output terminal of the electro-optic modulation module is connected to the input terminal of the output detection module; the output terminal of the output detection module is connected to the input terminal of the filtering module; and the output terminal of the filtering module is connected to the input terminal of the encoding module. The electro-optic modulation module is used to receive the pump laser distributed by the central node, generate an electro-optic frequency comb based on a thin-film lithium niobate electro-optic modulator, and also to synchronize the microwave signal generators of each user node based on the satellite timing signal to achieve frequency alignment of the electro-optic frequency comb in different locations. The output detection module is used to perform spectral observation, modulation effect verification and power measurement on the electro-optic frequency comb, and to filter out the residual pump laser component in the electro-optic frequency comb, and output the electro-optic frequency comb after filtering out the pump laser. The filtering module is used to select comb teeth of the same frequency from the electro-optic frequency comb after filtering out the pump laser and adjust the polarization state of the comb teeth. The encoding module is used to modulate the same-frequency comb teeth into pulse wave packets, implement the decoy state protocol, and apply phase offset.

[0024] In one possible implementation, the electro-optic frequency comb is a frequency-aligned electro-optic frequency comb; the electro-optic modulation module includes an optical power amplifier, a circulator, a Bragg grating, a polarization controller, a cascaded modulator structure integrated on a thin-film lithium niobate material, and a microwave driving circuit; the cascaded modulator structure includes an intensity modulator and two phase modulators. The input terminal of the optical power amplifier receives the pump laser, and the output terminal of the optical power amplifier is connected to the first port of the circulator; the second port of the circulator is connected to the Bragg grating, and the third port of the circulator is connected to the input terminal of the polarization controller; the output terminal of the polarization controller is connected to the input terminal of the cascaded modulator structure; the output terminal of the microwave driving circuit is connected to the driving terminals of the intensity modulator and the two phase modulators respectively. The optical power amplifier is used to amplify the received pump laser; the amplified pump laser enters the Bragg grating through the circulator, and the bounced pump light after filtering out out-of-band noise is output to the polarization controller through the circulator; the polarization controller is used to adjust the polarization state of the pump laser to maximize the modulation efficiency; both the intensity modulator and the phase modulator adopt a capacitor-loaded slow-wave electrode structure to reduce the half-wave voltage and increase the modulation bandwidth; the microwave driving circuit drives the cascaded intensity modulator and phase modulator simultaneously through the microwave signal generated by the microwave signal generator, generating sidebands with equal frequency intervals on both sides of the pump laser through the electro-optic effect, forming the electro-optic frequency comb.

[0025] For example, the electro-optic frequency comb is a frequency-aligned electro-optic frequency comb with repetition frequency alignment accuracy controlled within ±1Hz. Locking via satellite timing signals ensures a one-to-one correspondence between the comb teeth frequencies of different user nodes, providing a unified frequency reference for quantum key exchange among multiple users. The electro-optic modulation module operates as follows: First, each user node receives a 1550.12 nm pump laser from the central node. The pump laser is first amplified to approximately 500 mW by an optical power amplifier. The amplified pump laser then passes through a fiber optic circulator into a Bragg grating with a central wavelength of 1550.12 nm and a bandwidth of 0.5 nm. After filtering out spontaneous emission noise generated during amplification, the light is reflected back to the circulator. The reflected light is output through the circulator to a polarization controller, which adjusts the polarization state to match the transverse electric mode of the thin-film lithium niobate waveguide. Subsequently, the polarized pump laser enters a cascaded modulator, including one intensity modulator and two phase modulators. A 12.5 GHz microwave signal generated by the microwave drive circuit simultaneously drives the intensity modulator and the two phase modulators. Through the electro-optic effect, sidebands with equal frequency intervals are generated on both sides of the pump laser, forming an electro-optic frequency comb. By employing a capacitively loaded slow-wave electrode structure, the half-wave voltage of the intensity modulator is reduced to 1.1V, and the half-wave voltage of the phase modulator is 1.5 to 2.5V in the range of 5 to 25 GHz, with a modulation bandwidth greater than 26 GHz. At a repetition frequency of 12.5 GHz, 121 comb teeth can be generated, with comb tooth power fluctuations of less than ±1 dB within a 10 dB bandwidth, exhibiting excellent spectral flatness.

[0026] In one possible implementation, the microwave signal generator references the satellite time signal and synchronizes the microwave drive source of each user node based on the satellite time signal, thereby locking the repetition frequency of the electro-optic frequency comb of each user node and achieving precise frequency alignment of the electro-optic frequency comb in different locations.

[0027] For example, at each user node, the reference input of the microwave signal generator is connected to the satellite timing signal receiving module, and the frequency stability of the received BeiDou or GPS signal is better than 1×10⁻⁶. -12A 10MHz reference signal is used. A microwave signal generator uses this signal to produce a continuously adjustable microwave drive signal to drive the electro-optic modulation module. Closed-loop control ensures that the repetition frequency of the electro-optic frequency comb is strictly synchronized with the satellite timing reference, with frequency fluctuations less than 0.1Hz within 24 hours. The repetition frequency deviation between different user nodes is less than ±1Hz, achieving comb-level frequency alignment without additional calibration. Therefore, the satellite timing signal ensures long-term stable synchronization of the electro-optic frequency comb across different locations, providing a reliable frequency reference for multi-user two-photon interferometry.

[0028] In one possible implementation, the output detection module includes a first fiber coupler, a dense wavelength division multiplexer (DWDM), a second fiber coupler, a power meter, and a spectrometer; the input terminal of the first fiber coupler is connected to the output terminal of the electro-optic modulation module, the first output terminal of the first fiber coupler is connected to the input terminal of the spectrometer, and the second output terminal of the first fiber coupler is connected to the input terminal of the DWDM; the output terminal of the DWDM is connected to the input terminal of the second fiber coupler, the first output terminal of the second fiber coupler is connected to the input terminal of the power meter, and the second output terminal of the second fiber coupler is used for comb selection; The electro-optic frequency comb of the electro-optic modulation module is split by the first fiber coupler. One path is transmitted to the spectrometer for spectral observation, and the other path is transmitted to the dense wavelength division multiplexer to filter out the pump laser. Then, it is split by the second fiber coupler. One path is transmitted to the power meter for electro-optic frequency comb power measurement, and the other path is transmitted to the filtering module for comb tooth selection. The filtering module includes a programmable optical filter and a polarization controller; the input of the programmable optical filter is connected to the output of the output detection module, and the output of the programmable optical filter is connected to the input of the polarization controller; the output of the polarization controller is connected to the input of the encoding module. The electro-optic frequency comb of the output detection module filters out comb teeth of the same frequency through the programmable optical filter. After the polarization state of the comb teeth is adjusted by the polarization controller, the comb teeth are transmitted to the encoding module.

[0029] In specific application scenarios, the electro-optic frequency comb from the electro-optic modulation module is first split into two paths by a 1:1 fiber coupler. One path is sent to a spectrometer, where the modulation effect is judged by observing the morphology of the electro-optic frequency comb spectrum. When the spectrum exhibits a flat, equally spaced sideband structure, the electro-optic frequency comb is considered to be generating normally, at which point the comb power uniformity is <±1 dB. The other path passes through a dense wavelength division multiplexer to filter out the pump laser, retaining only the electro-optic frequency comb signal. After filtering out stray light, the electro-optic frequency comb is then split by a 1:9 fiber coupler. 90% of the optical power is sent to a power meter for electro-optic frequency comb power measurement, and 10% of the optical power is sent to a filtering module for comb selection. Thus, the output detection module can verify the modulation status of the electro-optic frequency comb in real time, ensuring that the electro-optic frequency comb quality meets the standards. The high isolation design of the dense wavelength division multiplexer effectively filters out the pump laser, avoiding pump light interference with subsequent key exchange.

[0030] In specific application scenarios, the filtering module includes a programmable optical filter and a polarization controller. Two electro-optic frequency combs, originating from two user nodes respectively, are precisely filtered by the programmable optical filter to select comb teeth with consistent frequencies, controlling the frequency deviation within ±1 MHz. The polarization controller then adjusts the polarization state of the comb teeth to be consistent, ensuring polarization matching of the comb tooth signals sent to the encoding module. Thus, the high-precision comb tooth selection and polarization adjustment of the filtering module control the frequency deviation of comb teeth with the same frequency within a certain range and ensure polarization matching, providing the encoding module with high-quality electro-optic frequency comb signals.

[0031] In one possible implementation, the encoding module includes a first intensity modulator, a second intensity modulator, a phase modulator, and an arbitrary waveform generator; the input terminal of the first intensity modulator is connected to the output terminal of the filtering module, and the output terminal of the first intensity modulator is connected to the input terminal of the second intensity modulator; the output terminal of the second intensity modulator is connected to the input terminal of the phase modulator; the arbitrary waveform generator is connected to the first intensity modulator, the second intensity modulator, and the phase modulator respectively. The first intensity modulator and the second intensity modulator have high modulation rate, wide pulse width adjustment range, fixed repetition frequency and high extinction ratio characteristics; the same frequency comb from the filter module is modulated into a pulse wave packet by the first intensity modulator, and then the decoy state protocol is realized by the second intensity modulator; the phase modulator is used to apply phase offset.

[0032] The specific encoding module implements the quantum encoding process of the comb signal in three steps: First, the filtered comb teeth of the same frequency are transmitted to the first intensity modulator. The arbitrary waveform generator outputs a custom pulse sequence including non-return-to-zero code and return-to-zero code. The output pulse width is set to 500 ps and the repetition frequency is 1 GHz, which modulates the comb teeth of the same frequency into discrete pulse packets. Second, the discrete pulse packets are input to the second intensity modulator. This modulator is loaded with a decoy state protocol. By switching the modulation voltage (e.g., 0V and 5V), the pulse packets are divided into a signal state (high power, accounting for 80%), a decoy state (medium power, accounting for 15%), and a vacuum state (zero power, accounting for 5%). The decoy state protocol can effectively resist photon number separation attacks and improve the security of quantum key distribution. Third, the phase modulator applies a phase offset of 0 or π to the pulse packets according to the key sequence to realize the encoding of qubits. Here, 0 phase represents "0" and π phase represents "1". Thus, the high modulation rate intensity modulator meets the requirements of high-speed quantum key distribution; the wide pulse width adjustment range adapts to key exchange at different transmission distances (narrow pulses for short distances and wide pulses for long distances); the combination of decoy state protocol and phase offset coding enhances the anti-attack capability of quantum keys to the highest commercial security level, which can resist common attack methods such as photon number splitting and phase eavesdropping.

[0033] In the above embodiment, the two-photon interference and quantum key distribution unit includes a polarization control module and a detection module connected in sequence; the input end of the polarization control module receives the encoded comb teeth, and the output end of the polarization control module outputs a combined beam and is connected to the input end of the detection module; The polarization control module is used to attenuate the encoded comb teeth to the single-photon level, compensate for the optical signal delay difference, adjust the photon polarization state, and achieve interference beam combining to output combined beam light. The detection module is used to match the phase, power, and number of photons of the combined beam, detect the photons, and complete the two-photon coincidence counting, thereby realizing quantum key distribution based on the two-photon interference effect.

[0034] In one possible implementation, the polarization control module includes an adjustable optical attenuator, an electrically adjustable delay line, a polarization beam splitter, and a polarization-maintaining beam splitter; the input terminal of the adjustable optical attenuator is connected to the output terminal of the encoding module, the output terminal of the adjustable optical attenuator is connected to the input terminal of the electrically adjustable delay line, the output terminal of the electrically adjustable delay line is connected to the input terminal of the polarization beam splitter, and the output terminal of the polarization beam splitter is connected to the input terminal of the polarization-maintaining beam splitter. The electrically controlled adjustable delay line has a wide delay adjustment range and high adjustment accuracy; the coding comb from the coding module is attenuated to the single-photon level by the adjustable optical attenuator, the delay difference is compensated by the electrically controlled adjustable delay line, the polarization state is adjusted by the polarization beam splitter, and then input to the polarization-maintaining beam splitter to achieve interference beam combining.

[0035] In practical applications, the encoded comb signal can be converted into a single-photon signal that meets the interference requirements through four steps: attenuation, delay, polarization, and beam combining. The first step involves attenuating the encoded comb signal to the single-photon level using an adjustable optical attenuator, reducing the photon count of each comb tooth to 300±20k to avoid key leakage due to multiphoton effects. The second step compensates for the optical signal delay difference between the two user nodes using an adjustable delay line, with a delay adjustment range of 0 to 10nm and an accuracy of 1ps, ensuring that both photons arrive at the interference beam combining device simultaneously. The third step uses a polarization beam splitter to decompose the polarization states of the two photons into orthogonal polarizations and adjust them to a preset polarization direction. The fourth step inputs the two photons into a polarization-maintaining beam splitter, utilizing polarization-maintaining characteristics to maintain polarization stability and achieve high-precision interference beam combining.

[0036] In one possible implementation, the detection module includes a polarization controller, a superconducting nanowire single-photon detector, and a time-to-digital converter; the input terminal of the polarization controller is connected to the output terminal of the polarization control module, and the output terminal of the polarization controller is connected to the input terminal of the superconducting nanowire single-photon detector; the output terminal of the superconducting nanowire single-photon detector is connected to the input terminal of the time-to-digital converter. The superconducting nanowire single-photon detector has high detection efficiency, low dark count rate, and low time jitter characteristics. The time-to-digital converter has high time resolution and high coincidence count upper limit. The combined photons from the polarization control module are transmitted to the superconducting nanowire single-photon detector for single-photon detection after the polarization parameters are matched by the polarization controller. The electrical signal output by the superconducting nanowire single-photon detector is used for two-photon coincidence counting by the time-to-digital converter.

[0037] In practical applications, quantum key extraction can be achieved through three steps: parameter matching, photon detection, and coincidence counting. First, after photon beam combining, the phase, power, and photon number parameters are readjusted by a polarization controller to ensure matching with the detection parameters of the superconducting nanowire single-photon detector. Second, the matched photon signal is fed into the superconducting nanowire single-photon detector, which has a detection efficiency greater than 70%, a dark count rate less than 100Hz, and a time jitter less than 50ps. The superconducting nanowire single-photon detector converts the photon signal into an electrical pulse signal. High detection efficiency ensures no photon signal loss, and a low dark count rate reduces false triggering. Third, a time-to-digital converter (with a time resolution better than 10ps and a coincidence count rate upper limit greater than 100MHz) performs time correlation analysis on the electrical pulse signal output by the superconducting nanowire single-photon detector, filtering out coincidence count events. The coincidence count result is the original data for the quantum key.

[0038] The following section describes the specific implementation process in four stages: laser distribution at the pump center, electro-optic frequency comb generation, signal processing, and quantum detection.

[0039] First, pumped laser distribution is achieved based on a central pumped laser distribution unit. This unit consists of a pumped laser module and a distribution link module. The pumped laser module includes a narrow-linewidth frequency-stabilized laser; the distribution link module includes a 1×N fiber splitter and low-loss transmission fiber. The specific operation steps are as follows: determine the output wavelength and output power of the narrow-linewidth frequency-stabilized laser, set the splitting ratio of the 1×N fiber splitter (e.g., 1×6), and calculate the required transmission fiber length for each branch; then, directly feed the continuous pumped laser output from the narrow-linewidth frequency-stabilized laser into the 1×N fiber splitter, splitting it into multiple paths (e.g., 6 paths), each transmitted to a user node via a long-distance low-loss transmission fiber. After parameter and link adjustments, pumped laser distribution is implemented step-by-step: first, the pumped laser is split into multiple paths via the fiber splitter; then, each branch is extended to user nodes in different geographical locations via low-loss fiber. Each user node receiver does not need to be configured with a local pump source to obtain highly coherent pumped laser light, thus ensuring high consistency of pump light across multiple nodes.

[0040] Second, an electro-optic frequency comb is generated based on the electro-optic modulation module. The electro-optic modulation module includes an optical power amplifier, a circulator, a Bragg grating, a polarization controller, a cascaded modulator structure integrated on a thin-film lithium niobate material, and a microwave driving circuit. The cascaded modulator structure includes one intensity modulator and two phase modulators. After receiving the pump laser from the central node, each user node first amplifies the pump laser power to the required level through the optical power amplifier. The amplified pump laser then enters the Bragg grating through the fiber optic circulator, filters out spontaneous emission noise generated during amplification, and is reflected back to the circulator. The reflected light is output through the circulator to the polarization controller, which adjusts the polarization state to match the transverse electric mode of the thin-film lithium niobate waveguide, maximizing the modulation efficiency. Subsequently, the polarization-matched pump laser is fed into the cascaded intensity modulator and the two phase modulators. The microwave driving circuit simultaneously drives the intensity modulator and the two phase modulators through a microwave signal generated by a microwave signal generator. The intensity modulator operates at an orthogonal bias point, while the two phase modulators operate at a high modulation index. Through the electro-optic effect, they generate equally spaced sidebands on both sides of the pump laser, thus forming an electro-optic frequency comb. Both the intensity and phase modulators employ a capacitively loaded slow-wave electrode structure to reduce the half-wave voltage and increase the modulation bandwidth. Simultaneously, the microwave signal generators at each user node are referenced to the satellite timing signal, ensuring that the repetition frequency of the electro-optic frequency comb is strictly synchronized with the satellite timing reference. The repetition frequency deviation between different user nodes is controlled within a very small range, thereby achieving automatic alignment of the comb teeth across different locations.

[0041] Third, the electro-optic frequency comb output detection and filtering process. The output detection module and the filtering module are connected to the electro-optic modulation module to complete the performance verification and comb tooth selection of the electro-optic frequency comb, providing qualified comb tooth signals for subsequent encoding. The output detection module includes an optical fiber coupler, a dense wavelength division multiplexer, a power meter, and a spectrometer: First, the electro-optic frequency comb output from the electro-optic modulation module is extracted and split into two paths by the optical fiber coupler. One path is sent to the spectrometer to observe the spectrum of the electro-optic frequency comb. When the spectrum shows a flat, equally spaced sideband structure, the electro-optic frequency comb is considered to be generating normally. The other path is filtered by the dense wavelength division multiplexer to remove the pump laser, and after obtaining a clean electro-optic frequency comb, it is split again. One path is sent to the power meter (to complete the power measurement), and the other path is sent to the filtering module. The filtering module consists of a programmable optical filter and a polarization controller: The electro-optic frequency comb from the output detection module is screened for comb teeth of the same frequency by the programmable optical filter, and then the polarization state of the comb teeth is adjusted by the polarization controller to maximize the subsequent modulation efficiency.

[0042] Fourth, key distribution via encoding, polarization control, and quantum detection. The filtered comb signal sequentially passes through the encoding module, polarization control module, and detection module to complete the core process of quantum key distribution. The encoding module contains two intensity modulators, one phase modulator, and an arbitrary waveform generator: the filtered comb teeth are first fed into the first intensity modulator, where the arbitrary waveform generator sets the pulse width and repetition frequency, modulating the continuous comb teeth into pulse packets; the modulated pulse packets are then input into the second intensity modulator to load the decoy state protocol; the phase modulator applies a 0 or π phase shift to the signal, completing the quantum encoding. The polarization control module consists of an adjustable optical attenuator, an adjustable delay line, a polarization beam splitter, and a polarization-maintaining beam splitter: the encoded comb teeth are attenuated to the single-photon level by the adjustable optical attenuator, the optical signal delay difference is compensated by the adjustable delay line, the polarization beam splitter adjusts the polarization states of the two photons, and finally, interference beam combining is achieved by the polarization-maintaining beam splitter. The detection module includes a superconducting nanowire single-photon detector and a time-to-digital converter: the combined photons first pass through a polarization controller to match the phase, power, and number of photons, and then are sent to the superconducting nanowire single-photon detector for photon detection. At the same time, the time-to-digital converter is used to complete the two-photon coincidence counting, and finally realize the extraction and verification of quantum keys.

[0043] In practical implementation, the quantum-safe networking device based on a centrally pumped frequency comb in this application, taking a device including two user nodes as an example, refers to... Figure 3 As shown in the figure, the schematic diagram of the two-user quantum key distribution device is clearly displayed. It includes the complete optical path architecture of the device from light source generation, frequency comb generation and modulation, signal encoding, polarization control, filtering and beam combining to detection and key extraction. Specifically, it includes: pump laser module 1, distribution link module 2, first electro-optic modulation module 3 and second electro-optic modulation module 5, first output detection module 4 and second output detection module 6, filtering module 7, encoding module 8, polarization control module 9 and detection module 10.

[0044] The pump laser module 1 includes a pump laser 101 and an ultra-stable Fabry-Perot cavity 102; the distribution link module 2 includes a 1×2 fiber splitter 201, a first low-loss transmission fiber 202, and a second low-loss transmission fiber 203.

[0045] In practical applications, the pump laser 101 can select a specific laser and lock it to the ultra-stable Fabry-Perot cavity 102 using frequency stabilization technology to obtain a narrow-linewidth frequency-stabilized pump laser. Its output continuous laser wavelength is 1550.12 nm and its power is 16 dBm. After passing through a 1×2 fiber splitter 201, it is split into two paths, which are then simultaneously distributed to two user nodes via a first low-loss transmission fiber 202 and a second low-loss transmission fiber 203.

[0046] The first electro-optic modulation module 3 includes a first optical power amplifier 301, a first fiber optic circulator 302, a first Bragg grating 303, a first polarization controller 304, a cascaded modulator structure integrated on a thin-film lithium niobate material, and a first microwave signal generator 308. The cascaded modulator structure includes a first intensity modulator 305, a first phase modulator 306, and a second phase modulator 307. Similarly, the second electro-optic modulation module 5 has the same structure and working principle as the first electro-optic modulation module 3, and will not be described in detail here.

[0047] In practical applications, the electro-optic frequency comb is generated in two cascaded modulators of thin-film lithium niobate with identical design parameters. All three cascaded modulators utilize X-cut thin-film lithium niobate material. The first intensity modulator 305, the second intensity modulator 505, the first phase modulator 306, the second phase modulator 307, the third phase modulator 506, and the fourth phase modulator 507 all employ a capacitively loaded slow-wave electrode structure, achieving a half-wave voltage Vπ as low as 1.1 V and a modulation bandwidth greater than 26 GHz. The first microwave signal generator 308 and the second microwave signal generator 508 reference satellite timing signals and output continuously adjustable microwave drive signals.

[0048] Specifically, the first electro-optic modulation module 3 and the second optical modulation module 5 adopt thin-film lithium niobate electro-optic modulation. The working process is as follows: At the user node, the received pump laser first enters the first optical power amplifier 301 and the second optical power amplifier 501 for amplification, and the output power of the optical power amplifier is set to 500 mW; the amplified pump laser enters the first Bragg grating 303 and the second Bragg grating 503 with a center wavelength of 1550.12 nm and a bandwidth of 0.5 nm through the first fiber circulator 302 and the second fiber circulator 502. After filtering out out-of-band noise, the reflected light is output to the first polarization controller 304 and the second polarization controller 504 through the first fiber circulator 302 and the second fiber circulator 502, and the polarization state is adjusted to be consistent with the transverse electric mode of the thin-film lithium niobate waveguide; then the pump laser is sent to the cascaded first intensity modulator 305, second intensity modulator 505 and first phase modulator 306, second phase modulator 307, third phase modulator 506 and fourth phase modulator 507.

[0049] In this embodiment, the use of a capacitor-loaded slow-wave electrode structure enables the modulator to have low half-wave voltage and high bandwidth characteristics. At the same time, the first microwave signal generator 308 and the second microwave signal generator 508 of each node are synchronized through satellite timing signals, which suppresses the repetition frequency change caused by microwave frequency drift.

[0050] In practical applications, the microwave signal frequency is set to 12.5 GHz. Through modulation, sidebands with equal frequency intervals are generated on both sides of the pump laser, and the repetition frequency of the electro-optic frequency comb is 12.5 GHz. By carefully adjusting the microwave power and bias point, the number of comb teeth can exceed 70, and the power fluctuation of the comb teeth within a 10 dB bandwidth is less than ±1 dB.

[0051] The aforementioned first output detection module 4 includes a first fiber coupler 401, a second fiber coupler 404, a first spectrometer 402, a first dense wavelength division multiplexer 403, and a first power meter 405. The electro-optic frequency comb from the electro-optic modulation module is split into two paths by the first fiber coupler 401. One path is sent to the first spectrometer 402, and the spectrum of the output electro-optic frequency comb is observed by the spectrometer. When the spectrum shows a flat and equally spaced sideband structure, it is determined that the electro-optic frequency comb is generating normally. The other path is sent to the first dense wavelength division multiplexer 403 to filter out the pump laser. The resulting electro-optic frequency comb is split into two paths by the second fiber coupler 404. One path is sent to the first power meter 405 for power measurement, and the other path is distributed to the filtering module 7. Similarly, the second output detection module 6 has the same structure as the first output detection module 4. The second output detection module 6 includes a third fiber coupler 601, a fourth fiber coupler 604, a second spectrometer 602, a second dense wavelength division multiplexer 603, and a second power meter 605. Accordingly, the working principle of the second output detection module 6 is exactly the same as that of the first output detection module 4, and will not be described in detail here.

[0052] The aforementioned filtering module 7 includes a first programmable optical filter 701, a second programmable optical filter 702, a third polarization controller 703, and a fourth polarization controller 704. The two electro-optic frequency combs output by the output detection module are filtered out by the first programmable optical filter 701 and the second programmable optical filter 702 to produce corresponding comb teeth of the same frequency; the polarization state of the comb teeth is adjusted by the third polarization controller 703 and the fourth polarization controller 704 to maximize their subsequent modulation efficiency; and then input to the encoding module 8.

[0053] The aforementioned encoding module 8 includes a third intensity modulator 801, a fourth intensity modulator 802, a fifth intensity modulator 805, a sixth intensity modulator 806, a fifth phase modulator 803, a sixth phase modulator 807, a first arbitrary waveform generator 804, and a second arbitrary waveform generator 808. The comb teeth filtered out in the filtering module are fed into the third intensity modulator 801 and the fifth intensity modulator 805, respectively. The first arbitrary waveform generator 804 and the second arbitrary waveform generator 808 are used to set the output pulse width to 500 ps and the repetition frequency to 1 GHz, modulating the continuous comb teeth into pulse packets. The modulated pulse packets are input into the fourth intensity modulator 802 and the sixth intensity modulator 806 for decoy state encoding (signal state accounting for 80%, decoy state accounting for 15%, and vacuum state accounting for 5%). A phase shift of 0 or π is applied using the fifth phase modulator 803 and the sixth phase modulator 807 to complete the quantum bit encoding.

[0054] The aforementioned polarization control module 9 includes an adjustable delay line 903, a first adjustable optical attenuator 901, a second adjustable optical attenuator 904, a first polarization beamsplitter 902, a second polarization beamsplitter 905, and a polarization-maintaining beamsplitter 906. The optical signal is attenuated to a single-photon level by the first and second adjustable optical attenuators 901 and 904, with the photon count per comb tooth attenuated to 300 ± 20 k. The adjustable delay line 903 compensates for the optical signal delay difference (adjustment range 0–10 ns, accuracy 1 ps). The first and second polarization beamsplitters 902 and 905 adjust the polarization states of the two photons. Finally, the two photons are input to the polarization-maintaining beamsplitter 906 to achieve interference beam combining.

[0055] The aforementioned detection module 10 includes a fifth polarization controller 1001, a sixth polarization controller 1002, a first superconducting nanowire single-photon detector 1003, a second superconducting nanowire single-photon detector 1004, and a time-to-digital converter 1005. The combined photons are matched for phase, power, and photon count by the fifth polarization controller 1001 and the sixth polarization controller 1002; then, they are fed into the first superconducting nanowire single-photon detector 1003 and the second superconducting nanowire single-photon detector 1004 for detection (detection efficiency > 90%, dark count rate < 100 Hz, time jitter < 50 ps), and the time-to-digital converter 1005 performs two-photon coincidence counting, with a time resolution better than 10 ps and a coincidence count rate upper limit greater than 100 MHz.

[0056] In summary, the quantum-secure networking device based on a centrally pumped frequency comb utilizes the multi-wavelength characteristics of the electro-optic frequency comb and combines it with a measurement-device-independent quantum key distribution protocol to achieve multi-user, fully connected quantum-secure networking. The device first distributes highly coherent pump lasers simultaneously to each user node via a centrally pumped laser distribution unit. Each user node generates an electro-optic frequency comb based on the thin-film lithium niobate electro-optic effect and achieves precise alignment of the repetition frequencies of the electro-optic frequency combs at different locations via satellite timing signals. Then, the generated electro-optic frequency combs are filtered to remove the pump laser using a dense wavelength division multiplexer, and programmable optical filters are used to filter out the same-frequency comb teeth of the electro-optic frequency combs at different locations. Time-slice qubit encoding is performed using intensity modulators and phase modulators, and the qubits are attenuated to the single-photon level by an adjustable optical attenuator before being input to a polarization-maintaining beam splitter to achieve two-path photon interference and beam combining. Finally, the combined photons are sent to a superconducting nanowire single-photon detector for detection, and a time-to-digital converter is used for two-photon coincidence counting.

[0057] Compared with existing technologies, the quantum-safe networking device based on a centrally pumped frequency comb in this application has at least the following advantages: 1. This application adopts a central node central laser distribution scheme, which distributes highly coherent and highly consistent pump lasers to each user node simultaneously through a low-loss optical fiber network, enabling each user node to independently generate an electro-optic frequency comb. This eliminates the limitation of inter-user key distribution being interconnected in the traditional shared optical frequency comb architecture, and significantly improves the scalability and security of multi-user networking.

[0058] 2. The thin-film lithium niobate cascade modulator used in this application adopts a capacitor-loaded slow-wave electrode structure, which significantly reduces the half-wave voltage and increases the modulation bandwidth, realizing low power consumption, wide bandwidth, and high flatness electro-optic frequency comb output, solving the technical problems of high power consumption, limited bandwidth, and mode aliasing caused by birefringence in traditional electro-optic frequency combs.

[0059] 3. This application uses satellite timing signals as a frequency reference to synchronize the microwave signal generators of each user node, achieving high-precision alignment of the repetition frequency of the electro-optic frequency comb in different locations. This provides a stable frequency reference for multi-channel two-photon interferometry and overcomes the problem of insufficient frequency alignment accuracy caused by controlling only a single degree of freedom in existing schemes.

[0060] 4. The Bragg grating in the electro-optic modulation module used in this application filters out out-of-band noise and effectively suppresses the influence of amplified spontaneous emission on the quality of the comb teeth; at the same time, the thin-film lithium niobate waveguide, after dispersion engineering and birefringence suppression treatment, realizes the output of an electro-optic frequency comb with continuously adjustable comb tooth spacing.

[0061] 5. The intensity modulator used in this application has a modulation rate of no less than 20 GHz, which can accurately modulate the target comb teeth of the electro-optic frequency comb into pulse wave packets that meet the requirements and complete the time-slice quantum bit encoding. Combined with the decoy state protocol and phase encoding, it can effectively resist photon number separation attacks and phase eavesdropping. The encoding process is stable and controllable, providing a high-quality and high-security optical signal carrier for quantum information transmission.

[0062] Furthermore, as a specific implementation of the above-mentioned device, this embodiment provides a quantum-safe networking method based on a centrally pumped frequency distribution comb, including the following steps: Step 1: A narrow-linewidth frequency-stabilized pump laser is generated by the pump laser module in the central pump laser distribution unit, and the pump laser is simultaneously distributed to each user node via the distribution link module. Step 2: At each user node, based on the thin-film lithium niobate electro-optic effect, the distributed pump laser is received through the electro-optic modulation module and an electro-optic frequency comb is generated. Step 3: Perform spectral observation, modulation effect verification and power measurement on the electro-optic frequency comb through the output detection module, filter out the residual pump laser component in the electro-optic frequency comb, and output the electro-optic frequency comb after filtering out the pump laser. Step 4: Select comb teeth of the same frequency from the electro-optic frequency comb after the pump laser has been filtered out using the filtering module and adjust the polarization state of the comb teeth; Step 5: Modulate the same-frequency comb teeth into pulse wave packets through the encoding module to realize the decoy state protocol and apply phase shift; Step 6: The polarization control module attenuates the encoded comb teeth to the single-photon level, compensates for the optical signal delay difference, adjusts the photon polarization state, and achieves interference beam combining to output combined beam light; Step 7: Match the phase, power and photon number of the combined beam using the detection module, detect the photons and complete the two-photon coincidence counting, and realize quantum key distribution based on the two-photon interference effect.

[0063] Based on the above-described quantum-safe networking method based on a central pump distribution frequency comb, this application embodiment also provides a storage medium storing a computer program that, when executed by a processor, implements the above-described quantum-safe networking method based on a central pump distribution frequency comb.

[0064] Based on this understanding, the technical solution of this application can be embodied in the form of a software product. The software product can be stored in a non-volatile storage medium (such as a CD-ROM, USB flash drive, or portable hard drive), and includes several instructions to cause a computer device (such as a personal computer, server, or network device) to execute the methods described in the various implementation scenarios of this application.

[0065] Based on the above-described quantum-safe networking device and method based on a central pump frequency distribution comb, in order to achieve the above objectives, this application embodiment also provides a physical device for quantum-safe networking based on a central pump frequency distribution comb, which can be a computer, smartphone, tablet computer, smartwatch, server, or network device, etc. The physical device includes a storage medium and a processor; the storage medium is used to store computer programs; the processor is used to execute the computer programs to implement the above-described quantum-safe networking method based on a central pump frequency distribution comb.

[0066] Optionally, the physical device may also include a user interface, a network interface, a camera, radio frequency (RF) circuitry, sensors, audio circuitry, a Wi-Fi module, etc. The user interface may include a display screen, an input module such as a keyboard, etc., and optional user interfaces may also include USB interfaces, card reader interfaces, etc. The network interface may optionally include standard wired interfaces, wireless interfaces (such as Wi-Fi interfaces), etc.

[0067] In an exemplary embodiment, see Figure 4 The aforementioned physical device includes a communication bus, a processor, a memory, and a communication interface. It may also include an input / output interface and a display device. The various functional modules can communicate with each other via the bus. The memory stores a computer program, and the processor executes the program stored in the memory to perform the quantum-safe networking method based on a central pump distribution frequency comb as described in the above embodiments.

[0068] Those skilled in the art will understand that the physical device structure of a quantum-safe network based on a central pump distribution frequency comb provided in this embodiment does not constitute a limitation on the physical device, and may include more or fewer components, or combine certain components, or have different component arrangements.

[0069] The storage medium may also include an operating system and a network communication module. The operating system is the program that manages the hardware and software resources of the physical device in the aforementioned quantum-safe network based on a centrally pumped frequency distribution comb, supporting the operation of information processing programs and other software and / or programs. The network communication module is used to enable communication between the various components within the storage medium, as well as communication with other hardware and software in the information processing physical device.

[0070] Through the above description of the embodiments, those skilled in the art can clearly understand that this application can be implemented by means of software plus necessary general-purpose hardware platforms, or it can be implemented by hardware. By applying the technical solution of this application, compared with the existing methods, firstly, by using a central pump laser distribution unit to simultaneously distribute the pump laser to each user node, each user node can independently generate an electro-optic frequency comb, thus overcoming the limitation of inter-user key distribution interconnection in the traditional shared optical frequency comb architecture, and significantly improving the scalability and security of multi-user networking; secondly, by combining the electro-optic frequency comb generation unit with a thin-film lithium niobate cascade modulator and a capacitor-loaded slow-wave electrode structure, the half-wave voltage is effectively reduced and the modulation bandwidth is increased, realizing low-power, wide-bandwidth, and high-flatness electro-optic frequency comb output; furthermore, by using a two-photon interference and quantum key distribution unit to perform polarization control and photon detection on the encoded comb teeth, quantum key distribution is realized based on the two-photon interference effect. The aforementioned functional modules are sequentially connected and work together to form a complete closed loop of pump light distribution, electro-optic comb generation, filtering and encoding, polarization control, and two-photon interferometry detection. The decoy state protocol and efficient signal processing flow enhance the anti-eavesdropping capability, ultimately achieving high-security and high-efficiency quantum key distribution in multi-user fully connected scenarios, fully meeting the practical application requirements of large-scale quantum secure networking.

[0071] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of a preferred embodiment, and the modules or processes shown in the drawings are not necessarily essential for implementing this application. Those skilled in the art will understand that the modules in the apparatus of the embodiment can be distributed within the apparatus of the embodiment as described, or they can be located in one or more apparatuses different from this embodiment, with corresponding changes. The modules of the above-described embodiment can be combined into one module, or further divided into multiple modules.

[0072] The serial numbers in this application are for descriptive purposes only and do not represent the superiority or inferiority of any particular implementation scenario. The above disclosures are merely a few specific implementation scenarios of this application; however, this application is not limited thereto, and any variations conceived by those skilled in the art should fall within the protection scope of this application.

Claims

1. A quantum-safe networking device based on a centrally pumped frequency distribution comb, characterized in that, The device includes multiple user nodes, each configured with an independent electro-optic frequency comb and encoder to enable independent secure key exchange between any user pairs; the device also includes: a central pumped laser distribution unit, an electro-optic frequency comb generation unit, and a two-photon interference and quantum key distribution unit; The central pump laser distribution unit includes a pump laser module and a distribution link module connected in sequence; the pump laser module is used to generate a narrow linewidth frequency-stabilized pump laser; the distribution link module is a low-loss fiber optic network used to simultaneously distribute the pump laser to each user node; The electro-optic frequency comb generation unit includes an electro-optic modulation module, an output detection module, a filtering module, and an encoding module connected in sequence. The electro-optic modulation module receives the pump laser distributed by the central node and generates an electro-optic frequency comb based on a thin-film lithium niobate electro-optic modulator. The output detection module performs spectral observation, modulation effect verification, and power measurement on the electro-optic frequency comb, filters out residual pump laser components from the electro-optic frequency comb, and outputs the electro-optic frequency comb after pump laser filtering. The filtering module selects comb teeth of the same frequency from the electro-optic frequency comb after pump laser filtering and adjusts the polarization state of the comb teeth. The encoding module modulates the comb teeth of the same frequency into pulse wave packets, implements decoy state protocols, and applies phase shifts. The two-photon interference and quantum key distribution unit includes a polarization control module and a detection module connected in sequence. The polarization control module is used to attenuate the encoded comb teeth to the single-photon level, compensate for the optical signal delay difference, adjust the photon polarization state, and achieve interference beam combining to output combined light. The detection module is used to perform phase, power, and photon number matching on the combined light, detect photons, and complete two-photon coincidence counting to achieve quantum key distribution based on the two-photon interference effect.

2. The quantum-safe networking device based on a centrally pumped frequency distribution comb according to claim 1, characterized in that, The pump laser module includes a laser and an ultra-stable Fabry-Perot cavity. The laser is locked to the ultra-stable Fabry-Perot cavity through frequency stabilization locking technology to generate a narrow linewidth frequency-stabilized pump laser. The distribution link module is an optical fiber network, including a multi-channel optical fiber splitter and a transmission optical fiber. The input end of the multi-channel optical fiber splitter is connected to the pump laser module, and the output end of the multi-channel optical fiber splitter is connected to each user node through the transmission optical fiber.

3. The quantum-safe networking device based on a centrally pumped frequency distribution comb according to claim 1, characterized in that, The electro-optic frequency comb is a frequency-aligned electro-optic frequency comb; the electro-optic modulation module includes an optical power amplifier, a circulator, a Bragg grating, a polarization controller, a cascaded modulator structure integrated on a thin-film lithium niobate material, and a microwave driving circuit. The cascaded modulator structure includes one intensity modulator and two phase modulators; The input terminal of the optical power amplifier receives the pump laser, and the output terminal of the optical power amplifier is connected to the first port of the circulator; the second port of the circulator is connected to the Bragg grating, and the third port of the circulator is connected to the input terminal of the polarization controller; the output terminal of the polarization controller is connected to the input terminal of the cascaded modulator structure; the output terminal of the microwave driving circuit is connected to the driving terminals of the intensity modulator and the two phase modulators respectively. The optical power amplifier is used to amplify the received pump laser; the amplified pump laser enters the Bragg grating through the circulator, and the bounced pump light after filtering out out-of-band noise is output to the polarization controller through the circulator; the polarization controller is used to adjust the polarization state of the pump laser to maximize the modulation efficiency; both the intensity modulator and the phase modulator adopt a capacitor-loaded slow-wave electrode structure to reduce the half-wave voltage and increase the modulation bandwidth; the microwave driving circuit drives the cascaded intensity modulator and phase modulator simultaneously through the microwave signal generated by the microwave signal generator, generating sidebands with equal frequency intervals on both sides of the pump laser through the electro-optic effect, forming the electro-optic frequency comb.

4. The quantum-safe networking device based on a centrally pumped frequency distribution comb according to claim 3, characterized in that, The microwave signal generator references the satellite time signal and synchronizes the microwave drive source of each user node based on the satellite time signal, locking the repetition frequency of the electro-optic frequency comb of each user node, thereby achieving precise frequency alignment of the electro-optic frequency comb in different locations.

5. The quantum-safe networking device based on a centrally pumped frequency distribution comb according to claim 1, characterized in that, The output detection module includes a first fiber coupler, a dense wavelength division multiplexer (DWDM), a second fiber coupler, a power meter, and a spectrometer. The input of the first fiber coupler is connected to the output of the electro-optic modulation module, the first output of the first fiber coupler is connected to the input of the spectrometer, and the second output of the first fiber coupler is connected to the input of the DWDM. The output of the DWDM is connected to the input of the second fiber coupler, the first output of the second fiber coupler is connected to the input of the power meter, and the second output of the second fiber coupler is connected to the filtering module. The electro-optic frequency comb of the electro-optic modulation module is split by the first fiber coupler. One path is transmitted to the spectrometer for spectral observation, and the other path is transmitted to the dense wavelength division multiplexer to filter out the pump laser. Then, it is split by the second fiber coupler. One path is transmitted to the power meter for electro-optic frequency comb power measurement, and the other path is transmitted to the filtering module for comb tooth selection.

6. The quantum-safe networking device based on a centrally pumped frequency distribution comb according to claim 1, characterized in that, The filtering module includes a programmable optical filter and a polarization controller; the input of the programmable optical filter is connected to the output of the output detection module, and the output of the programmable optical filter is connected to the input of the polarization controller; the output of the polarization controller is connected to the input of the encoding module. The electro-optic frequency comb of the output detection module filters out comb teeth of the same frequency through the programmable optical filter. After the polarization state of the comb teeth is adjusted by the polarization controller, the comb teeth are transmitted to the encoding module.

7. The quantum-safe networking device based on a centrally pumped frequency distribution comb according to claim 1, characterized in that, The encoding module includes a first intensity modulator, a second intensity modulator, a phase modulator, and an arbitrary waveform generator; the input of the first intensity modulator is connected to the output of the filtering module, and the output of the first intensity modulator is connected to the input of the second intensity modulator; the output of the second intensity modulator is connected to the input of the phase modulator; the arbitrary waveform generator is connected to the first intensity modulator, the second intensity modulator, and the phase modulator respectively. The first intensity modulator and the second intensity modulator have high modulation rate, wide pulse width adjustment range, fixed repetition frequency and high extinction ratio characteristics; The same-frequency comb teeth from the filtering module are modulated into pulse wave packets by the first intensity modulator, and then the decoy state protocol is realized by the second intensity modulator. The phase modulator is used to apply phase offset.

8. The quantum-safe networking device based on a centrally pumped frequency distribution comb according to claim 1, characterized in that, The polarization control module includes an adjustable optical attenuator, an electrically adjustable delay line, a polarization beam splitter, and a polarization-maintaining beam splitter. The input of the adjustable optical attenuator is connected to the output of the encoding module, and the output of the adjustable optical attenuator is connected to the input of the electrically adjustable delay line. The output of the electrically adjustable delay line is connected to the input of the polarization beam splitter, and the output of the polarization beam splitter is connected to the input of the polarization-maintaining beam splitter. The electronically controlled adjustable delay line has a wide delay adjustment range and high adjustment accuracy; The coding comb from the coding module is attenuated to the single-photon level by the adjustable optical attenuator, the delay difference is compensated by the electronically controlled adjustable delay line, the polarization state is adjusted by the polarization beam splitter, and then input to the polarization-maintaining beam splitter to achieve interference beam combining.

9. The quantum-safe networking device based on a centrally pumped frequency distribution comb according to claim 1, characterized in that, The detection module includes a polarization controller, a superconducting nanowire single-photon detector, and a time-to-digital converter; the input terminal of the polarization controller is connected to the output terminal of the polarization control module, and the output terminal of the polarization controller is connected to the input terminal of the superconducting nanowire single-photon detector; the output terminal of the superconducting nanowire single-photon detector is connected to the input terminal of the time-to-digital converter. The superconducting nanowire single-photon detector has high detection efficiency, low dark count rate and low time jitter characteristics, and the time-to-digital converter has high time resolution and high coincidence count upper limit. The combined photons from the polarization control module are transmitted to the superconducting nanowire single-photon detector for single-photon detection after the polarization parameters are matched by the polarization controller. The electrical signal output by the superconducting nanowire single-photon detector is used for two-photon coincidence counting by the time-to-digital converter.

10. A quantum-safe networking method based on a centrally pumped frequency distribution comb, characterized in that, include: Narrow-linewidth frequency-stabilized pump lasers are generated by the pump laser module in the central pump laser distribution unit, and the pump lasers are simultaneously distributed to each user node via the distribution link module. At each user node, based on the electro-optic effect of thin-film lithium niobate, the distributed pump laser is received and an electro-optic frequency comb is generated through an electro-optic modulation module. The output detection module performs spectral observation, modulation effect verification and power measurement on the electro-optic frequency comb, and filters out the residual pump laser component in the electro-optic frequency comb, outputting the electro-optic frequency comb after filtering out the pump laser. The filtering module selects comb teeth of the same frequency from the electro-optic frequency comb after the pump laser has been filtered out and adjusts the polarization state of the comb teeth. The same-frequency comb teeth are modulated into pulse wave packets by the encoding module to realize the decoy state protocol and apply phase shift; The polarization control module attenuates the encoded comb teeth to the single-photon level, compensates for the optical signal delay difference, adjusts the photon polarization state, and achieves interference beam combining to output combined beam light. The combined beam is matched in phase, power and photon number by a detection module, the photons are detected and two-photon coincidence counting is completed, and quantum key distribution is realized based on the two-photon interference effect.

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