Quantum-safe networking device and method based on independent optical frequency comb

Abstract

This application provides a quantum-safe networking device and method based on an independent optical frequency comb, belonging to the field of quantum information technology. This application generates an optical frequency comb by heating an optical microcavity with an auxiliary laser and controlling the pump laser parameters. Then, the pump frequency and the repetition frequency of the optical frequency comb are locked to achieve high-precision alignment of the optical frequency comb in different locations. After output detection and filtering to select qualified comb teeth, a decoy state protocol and phase shift are loaded through an encoding module, and a polarization control module processes the signal to a weakly coherent state level and completes interference beam combining. Finally, quantum key distribution is achieved based on single-photon detection and coincidence counting. This application possesses high stability, high security, and large-scale networking characteristics.

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 an independent optical frequency comb. Background Technology

[0002] Quantum secure communication, based on the fundamental principles of quantum mechanics, can achieve theoretically unconditionally secure transmission of information and is one of the core technologies for ensuring communication security in the information age. Quantum secure networking, as a large-scale application of quantum secure communication, enables secure key exchange between any two users by constructing a multi-user interconnected quantum network architecture. This has become a core security requirement in key sectors such as finance, government affairs, and energy. Quantum key distribution (QKD) is its core technological support, distributing secure keys between communicating parties to provide a theoretically unbreakable security foundation for subsequent data encryption.

[0003] Current technologies for quantum-secure networking mainly revolve around three core 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 single photons as the quantum information carrier, employing trusted repeaters or quantum repeater modes for networking. At the source end, key information is loaded via weakly coherent light to simulate a single-photon source or directly using a single-photon generator, transmitted through a quantum channel, and then received and decoded by a single-photon detector. The CVQKD route utilizes orthogonal component encoding of classical coherent light, is compatible with existing classical optical communication devices, and relies on existing optical communication networks to achieve multi-node interconnection. The optical frequency comb-assisted scheme leverages the multi-frequency line characteristics of the optical frequency comb to achieve parallel key transmission, attempting to improve the parallel processing capability and key distribution efficiency of the network.

[0004] Despite some progress in existing technologies, many technical bottlenecks remain insurmountable in large-scale applications. One core issue is the insufficient independence and scalability of multi-user networks. When single-photon QKD networks rely on trusted relays, relay security becomes a weak point, and shared channels by multiple users are prone to signal crosstalk, limiting the expansion of the number of users. In multi-user parallel communication in CVQKD networks, the issues of channel resource allocation and interference suppression have not been fully resolved. Furthermore, existing optical frequency comb-assisted schemes mostly adopt a shared optical frequency comb architecture, where key distribution among users is interconnected. A single user failure or attack can affect the security of the entire network, making independent key exchange between any user pair impossible.

[0005] The inadequate stability and frequency alignment accuracy of optical frequency combs also severely restrict the implementation of the technology. In existing solutions, the generation of optical frequency combs mostly relies on a single pump laser drive, which is easily affected by environmental factors such as temperature and vibration, causing the comb tooth frequency to drift. Moreover, remote optical frequency combs only lock a single degree of freedom such as the repetition frequency, lacking coordinated locking of key parameters such as the pump frequency, making it difficult to achieve high-precision frequency alignment and affecting the accuracy of multi-channel parallel coding and interferometric detection.

[0006] The problems of low compatibility of core components and low system integration are also prominent. The modulation rate and extinction ratio of the intensity modulator are difficult to meet the requirements of high-speed pulse coding and decoy state protocols. The adjustment range and accuracy of the adjustable delay line are limited, and it cannot effectively compensate for the signal delay difference in long-distance transmission. The single-photon detector has a high dark count rate and large time jitter, which affects the accuracy of photon detection and coincidence counting efficiency. At the same time, each functional module is designed independently and lacks a unified integrated architecture, resulting in a large system size, poor stability, and difficulty in adapting to actual network deployment requirements.

[0007] Furthermore, the limited key distribution efficiency and anti-interference capability cannot be ignored. The key rate of the single-photon QKD scheme is limited by the generation efficiency of the single-photon source and the detection efficiency of the detector, and it drops significantly during long-distance transmission. The CVQKD scheme is susceptible to background light noise and channel crosstalk in multi-user parallel transmission, and its anti-interference capability is insufficient. Moreover, the existing optical frequency comb-assisted scheme has not fully optimized the comb tooth selection and polarization state control process, resulting in a low effective signal ratio, which further limits the improvement of key distribution efficiency and makes it difficult to meet the high-speed communication requirements of large-scale networking. Summary of the Invention

[0008] In view of this, this application provides a quantum-secure networking device and method based on an independent optical frequency comb. The main purpose is to solve the problems of multi-user scalability, optical frequency comb stability and alignment accuracy, device adaptability and key distribution efficiency in the prior art, so as to realize multi-user full connectivity, high security and high efficiency independent key exchange.

[0009] According to one aspect of this application, a quantum-secure networking device based on independent optical frequency combs is provided. Each user is configured with an independent and frequency-aligned optical frequency comb and an independent encoder corresponding to each frequency line to achieve independent secure key exchange between any user pairs. The device includes an optical frequency comb generation and locking device and a HOM interference and quantum key distribution device, wherein: the optical frequency comb generation and locking device includes an optical frequency comb generation module, an optical frequency comb frequency locking module, an output detection module, a filtering module, and an encoding module connected in sequence; wherein the optical frequency comb generation module generates the optical frequency comb by auxiliary laser heating, and maintains intracavity thermal balance to stably generate the optical frequency comb by adjusting the coupling method and parameters of the pump laser and the auxiliary laser; the optical frequency comb frequency locking module locks the pump frequency and the optical frequency comb frequency... The complex frequency has two degrees of freedom, enabling frequency alignment of the optical frequency comb at different locations. The output detection module is used for spectral observation of the optical frequency comb, soliton mode-locking verification, pumping, auxiliary laser filtering, and optical frequency comb power measurement. The filtering module is used to screen the same-frequency comb teeth of the optical frequency comb at different locations and adjust the polarization state of the comb teeth. The encoding module is used to modulate the comb teeth into pulse wave packets, implement decoy state protocols, and apply phase shifts. The HOM interference and quantum key distribution device 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 a weakly coherent state level, compensate for optical signal delay differences, adjust photon polarization states, and achieve interference beam combining. The detection module is used to achieve phase, power, and photon number matching of the combined photons, detect photons, and complete two-photon coincidence counting.

[0010] In one implementation, the optical frequency comb is a frequency-aligned optical frequency comb; the optical frequency comb generation module includes a pump laser, an auxiliary laser, a polarization controller, a power amplifier, a fiber optic circulator, and an optical microcavity; the output signals of the pump laser and the auxiliary laser are polarized by the polarization controller, amplified by the power amplifier, and then sent into the optical microcavity through the fiber optic circulator; the pump laser is coupled into the optical microcavity and maintained in the red detuning region of the resonance peak, while the auxiliary laser is coupled into the optical microcavity from the opposite direction to maintain thermal equilibrium; by adjusting the frequency of the auxiliary laser, the pump laser is stabilized in the red detuning region of the resonance peak, thereby generating the optical frequency comb.

[0011] In one implementation, the optical microcavity is a silicon nitride microring cavity and is butterfly-shaped packaged to reduce the impact of the external environment on the stability of the optical frequency comb.

[0012] In one implementation, the optical frequency comb frequency locking module includes an acousto-optic modulator, an optical fiber coupler, a high-stability Fabry-Perot cavity, a narrow-linewidth acetylene gas chamber, a photodetector, a voltage-controlled oscillator, a servo, a phase modulator, and a microwave signal generator. The continuous light output from the tunable laser is frequency-shifted by the acousto-optic modulator and then split into two paths by the optical fiber coupler. One path is used for pump laser locking, and the other path is used for optical frequency comb generation. Pump laser locking is achieved by forming a closed loop with the Fabry-Perot cavity, the acetylene gas chamber, the photodetector, the servo, the voltage-controlled oscillator, and the acousto-optic modulator. The optical frequency comb repetition frequency locking is achieved by modulation by the phase modulator, and the microwave drive signal of the phase modulator is set with reference to a high-stability clock source of satellite communication signal.

[0013] In one implementation, the frequency stability of the high-stability clock source meets the accuracy requirements of quantum key distribution, and the frequency stability of the Fabry-Perot cavity and the linewidth characteristics of the acetylene gas chamber are adapted to the locking requirements of the pump laser.

[0014] In one implementation, the output detection module includes an optical fiber coupler, a dense wavelength division multiplexer, a power meter, and a spectrometer. The pump laser and optical frequency comb from the optical microcavity are split by the optical fiber coupler. One path is sent to the spectrometer for soliton mode-locking verification, and the other path is filtered by the dense wavelength division multiplexer to remove the pump and auxiliary laser, and then split by the optical fiber coupler again for optical frequency comb power measurement and comb tooth selection, respectively. The filtering module includes a programmable optical filter and a polarization controller. The two optical frequency combs are filtered to produce comb teeth of the same frequency by the programmable optical filter, and after the polarization state of the comb teeth is adjusted by the polarization controller, they are sent to the encoding module.

[0015] In one implementation, the encoding module includes two high-intensity modulators, one phase modulator, and an arbitrary waveform generator; the intensity modulator has high modulation rate, wide pulse width adjustment range, fixed repetition frequency, and high extinction ratio characteristics; the comb teeth are modulated into pulse wave packets by the first intensity modulator, and then the decoy state protocol is implemented by the second intensity modulator; the phase modulator is used to apply phase offset.

[0016] In one 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 adjustable delay line has a wide delay adjustment range and high adjustment accuracy. The encoded comb teeth are attenuated to a weakly coherent state level by the adjustable optical attenuator, the delay difference is compensated by the 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.

[0017] In one implementation, the detection module includes a polarization controller, a superconducting nanowire single-photon detector, and a time-to-digital converter. The superconducting nanowire single-photon detector has high detection efficiency, low dark count rate, and low time jitter characteristics, while the time-to-digital converter has high time resolution and a high upper limit for the coincidence count rate. After the combined photons are matched with parameters by the polarization controller, they are sent to the superconducting nanowire single-photon detector for detection, and two-photon coincidence counting is performed by the time-to-digital converter.

[0018] According to one aspect of this application, a quantum-safe networking method based on an independent optical frequency comb is provided. The method employs the aforementioned quantum-safe networking device based on an independent optical frequency comb to achieve quantum-safe networking. The method includes: using an auxiliary laser heating method, adjusting the coupling parameters and polarization state of the pump laser and the auxiliary laser through an optical frequency comb generation module to stabilize the pump laser in the red detuning region of the optical microcavity resonant peak, maintaining intracavity thermal balance to generate the optical frequency comb; locking the pump frequency and the optical frequency comb repetition frequency (two degrees of freedom) through an optical frequency comb frequency locking module, and forming a closed-loop control by combining a high-stability clock source, a Fabry-Perot cavity, and an acetylene gas chamber to achieve precise frequency alignment of the optical frequency comb in a different location. The output detection module performs spectral observation, soliton mode-locking verification, pumping, auxiliary laser filtering, and power measurement of the optical frequency comb. The filtering module then filters the same-frequency comb teeth from different locations and adjusts their polarization states. The encoding module modulates the comb teeth into pulse wave packets, implements the decoy state protocol, and applies a phase shift to complete time-slice quantum bit encoding. The polarization control module attenuates the encoded comb teeth to a weakly coherent state level to compensate for the optical signal delay difference and adjusts the photon polarization state to achieve interference beam combining. The detection module performs parameter matching, photon detection, and two-photon coincidence counting of the combined photons. Based on a measurement device-independent quantum key distribution protocol, it enables independent and secure key exchange between any user pairs.

[0019] By employing the above technical solutions, the quantum-secure networking device and method based on independent optical frequency combs provided in this application, firstly, by configuring each user with an independent and frequency-aligned optical frequency comb and an independent encoder corresponding to each frequency line, overcomes the limitations of traditional shared optical frequency combs or relay-dependent networking. This allows any user pair to achieve independent secure key exchange through a dedicated channel, effectively avoiding the impact of signal crosstalk between users and single-node failures on the overall network, and significantly improving the scalability and security of multi-user networking. Secondly, the auxiliary laser heating method adopted by the optical frequency comb generation module maintains intracavity thermal balance by precisely controlling the coupling parameters of the pump laser and the auxiliary laser, which can significantly suppress the frequency drift of the comb teeth caused by environmental disturbances. Combined with the dual-degree-of-freedom locking of the pump frequency and repetition frequency by the optical frequency comb frequency locking module, high-precision frequency alignment of the remote optical frequency comb is achieved, providing a high-precision frequency alignment for multi-user networks. Parallel channel coding and HOM interferometry provide a stable and reliable optical signal foundation. Furthermore, the structured design of sequentially connected and collaboratively working functional modules enables the optical frequency comb to form a closed loop from generation, locking, detection, filtering, coding to polarization control and detection. The output detection module efficiently filters redundant lasers and verifies the mode-locking effect, the filtering module accurately selects comb teeth of the same frequency and optimizes the polarization state, the coding module completes pulse modulation and decoy state protocol deployment, and the polarization control module and detection module ensure interference beam combining and high-precision detection of weakly coherent horizontal signals. This not only improves the system integration and operational stability, but also enhances anti-eavesdropping capabilities and the effective signal ratio through the application of decoy state protocols and efficient signal processing. Ultimately, it achieves 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.

[0020] 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

[0021] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0022] Figure 1 This is a schematic diagram illustrating a quantum-safe networking example based on an independent optical frequency comb, as described in this application.

[0023] Figure 2 This is a schematic diagram of the quantum-safe networking device based on an independent optical frequency comb, as described in this application.

[0024] Figure 3This is a schematic diagram of a specific implementation of a quantum-safe networking device based on independent optical frequency combs, using two users as an example.

[0025] Figure 4 This is the off-site optical frequency comb spectrum of this application;

[0026] Figure 5 This is the HOM interference fringe pattern of the fourth comb tooth in this application;

[0027] Figure 6 These are the experimental results of the multichannel HOM interference of this application: (a) and (b) comb-like spectral lines of two independent soliton microcombs; (c) visibility of HOM interference fringes of ten pairs of comb teeth. Detailed Implementation

[0028] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, and not all of them. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present application. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present application can be combined with each other.

[0029] As analyzed above, existing quantum secure networking technologies generally adopt a shared optical frequency comb architecture, locking the optical frequency comb parameters with only a single degree of freedom. They rely on relay networking and multi-user key exchanges are interconnected, resulting in poor network independence and scalability, insufficient optical frequency comb stability and frequency alignment accuracy, and low key distribution efficiency and anti-interference capabilities. In response, this application's embodiment configures each user with an independent and precisely frequency-aligned optical frequency comb and an independent encoder corresponding to each frequency line. It abandons the traditional shared architecture and relay-dependent mode, using an auxiliary laser heating method to stably generate the optical frequency comb. High-precision alignment of the optical frequency comb is achieved remotely through dual-degree-of-freedom locking of the pump frequency and the optical frequency comb repetition frequency. An optical frequency comb generation and locking device, along with a HOM interference and quantum key distribution device, are constructed. Each functional module is sequentially connected and works in synergy to complete the entire process of optical frequency comb processing, quantum encoding, and interference detection, ultimately achieving independent secure key exchange between any user pairs without any association. Compared with existing technologies, this application completely solves the problem of insufficient network independence at the architectural level, significantly improves the working stability and frequency alignment accuracy of optical frequency combs, and simultaneously enhances the security and transmission efficiency of quantum key distribution, meeting the practical application needs of large-scale quantum secure networking.

[0030] See Figure 1This diagram illustrates a quantum-secure network example based on independent optical frequency combs, using six users as an example. Each user is equipped with an independent, fully frequency-aligned optical frequency comb and an independent encoder for each frequency line of each user, enabling independent secure key exchange between any two users. The codes 1, 2, 3, ... represent comb teeth; the same code indicates that different users use the same comb tooth for quantum key distribution. Figure 1 It can be seen that each user only needs to use 5 comb teeth to achieve fully connected quantum key distribution among six users.

[0031] Figure 1 In this architecture, each user node (A, B, C, D, E, F) is configured with an independent optical frequency comb, labeled "OFC" and accompanied by the numbers "1234567". This indicates that each user has an independent optical frequency comb, with numbers 1-7 corresponding to multiple independent frequency lines of the optical frequency comb. Each frequency line is paired with a dedicated encoder, which solves the crosstalk problem caused by traditional shared optical frequency combs. A fully connected network architecture is adopted, where any two user nodes are directly connected via numerically labeled lines (without repeater nodes), enabling direct communication between any two user pairs. The link numerical labels, such as "1" between AB, "2" between AC, and "3" between BC, represent the frequency line numbers of the optical frequency comb used by different user pairs for communication. Different user pairs reuse different frequency lines to avoid crosstalk. Furthermore, each frequency line is independently encoded, and key exchange between user pairs is independent, enabling independent secure key exchange between any two user pairs, thus improving network scalability and communication independence.

[0032] See Figure 2 This is a schematic diagram of the quantum-secure networking device based on an independent optical frequency comb, as described in this application. The overall structure is divided into four functional layers: the top layer consists of multiple user terminals (users 1-n), each equipped with an independent optical frequency comb and an independent encoder for each frequency line; below this is an optical frequency comb generation and locking device, in which an optical frequency comb generation module, an optical frequency comb frequency locking module, an output detection module, a filtering module, and an encoding module are connected in series; the next layer is a HOM interference and quantum key distribution device, containing a polarization control module and a detection module connected in series; the bottom layer is a key negotiation and storage module, which enables arbitrary users to exchange independent secure keys based on the MDI-QKD protocol.

[0033] The quantum-secure networking device based on independent optical frequency combs provided in this application configures each user with an independent and frequency-aligned optical frequency comb and an independent encoder corresponding to each frequency line to achieve independent secure key exchange between any user pairs. The device includes an optical frequency comb generation and locking device and a HOM interference and quantum key distribution device. The optical frequency comb generation and locking device includes an optical frequency comb generation module, an optical frequency comb frequency locking module, an output detection module, a filtering module, and an encoding module connected in sequence. The optical frequency comb generation module generates the optical frequency comb by auxiliary laser heating. By adjusting the coupling method and parameters of the pump laser and the auxiliary laser, the intracavity thermal balance is maintained to stably generate the optical frequency comb. The optical frequency comb frequency locking module locks the pump frequency and the optical frequency comb repetition frequency. The device features two degrees of freedom for frequency alignment of a remote optical frequency comb; an output detection module for spectral observation, soliton mode-locking verification, pumping, auxiliary laser filtering, and power measurement of the optical frequency comb; a filtering module for screening co-frequency comb teeth and adjusting their polarization states; an encoding module for modulating the comb teeth into pulse packets, implementing decoy state protocols, and applying phase shifts; and a HOM interferometer and quantum key distribution device comprising a polarization control module and a detection module connected in sequence. The polarization control module attenuates the encoded comb teeth to a weakly coherent state level, compensates for optical signal delay differences, adjusts photon polarization states, and achieves interference beam combining. The detection module matches the phase, power, and number of photons in the combined beam, detects photons, and performs two-photon coincidence counting.

[0034] In one implementation, the optical frequency comb is a frequency-aligned optical frequency comb; the optical frequency comb generation module includes a pump laser, an auxiliary laser, a polarization controller, a power amplifier, a fiber optic circulator, and an optical microcavity; the output signals of the pump laser and the auxiliary laser are polarized by the polarization controller, amplified by the power amplifier, and then sent into the optical microcavity through the fiber optic circulator; the pump laser is coupled into the optical microcavity and maintained in the red detuning region of the resonance peak, while the auxiliary laser is coupled into the optical microcavity from the opposite direction to maintain thermal equilibrium; by adjusting the frequency of the auxiliary laser, the pump laser is stabilized in the red detuning region of the resonance peak, thereby generating the optical frequency comb.

[0035] For example, the optical frequency comb is a frequency-aligned optical frequency comb with a frequency alignment accuracy controlled within ±10MHz, ensuring that the comb tooth frequencies of different user nodes correspond one-to-one, providing a unified frequency reference for quantum key exchange among multiple users; the optical frequency comb generation module includes a pump laser, an auxiliary laser, a polarization controller, a power amplifier, a fiber optic circulator, and an optical microcavity; its working process is as follows: the pump laser is the core excitation source for the generation of the optical frequency comb, while the auxiliary laser modulates the temperature field of the optical microcavity through thermal effects. The two work together to achieve stable generation of the optical frequency comb: the output signals of the pump laser and the auxiliary laser are first precisely adjusted by the polarization controller to match the TE mode (transverse electric mode) of the optical microcavity, avoiding light energy loss caused by polarization mismatch. Then, the laser power is amplified to the threshold coupling power of the optical microcavity by the power amplifier, for example, the pump laser is amplified to 200mW and the auxiliary laser is amplified to 250mW, and then sent unidirectionally into the optical microcavity through the fiber optic circulator. The fiber optic circulator can effectively avoid the reverse interference of microcavity reflected light to the laser. For example, the pump laser is first coupled into the optical microcavity, and its output wavelength is adjusted by a wavelength tuner to stabilize the pump laser in the red detuning region of the optical microcavity's resonance peak, such as controlling the red detuning amount to 0.1-0.5 nm, while keeping the pump laser wavelength and output power constant. Next, an auxiliary laser is coupled into the optical microcavity from the opposite direction to the pump laser. When the auxiliary laser propagates within the microcavity, it generates a local thermal effect through photon absorption, which counteracts the temperature drift of the microcavity during the pump laser's excitation of the optical frequency comb, maintaining thermal balance within the cavity. Subsequently, the frequency of the auxiliary laser is slowly decreased to the blue detuning region of the resonance peak, and then gradually increased until the pump laser is always stable in the red detuning region of the resonance peak, ultimately producing an optical frequency comb with a flat spectrum and uniform comb tooth spacing. Thus, by controlling the thermal balance of the auxiliary laser, the frequency drift of the optical frequency comb can be controlled within ±5 MHz per hour, significantly improving the long-term stability of the optical frequency comb. The fully frequency-aligned optical frequency comb design ensures that key exchange can be performed directly between multiple user nodes without additional frequency calibration, reducing network complexity and effectively shortening the key exchange response time.

[0036] In one implementation, the optical microcavity is a silicon nitride microring cavity, which is then processed through a butterfly-shaped package to reduce the impact of the external environment on the stability of the optical frequency comb. The butterfly package adopts a double-layer protective structure of a metal shell and a ceramic substrate. The metal shell has electromagnetic shielding function, which can resist the influence of external electromagnetic interference on the optical properties of the microcavity, while the ceramic substrate provides high rigidity support for the microcavity, reducing the deformation of the microcavity caused by mechanical vibration.

[0037] In one implementation, the optical frequency comb frequency locking module includes an acousto-optic modulator, an optical fiber coupler, a high-stability Fabry-Perot cavity, a narrow-linewidth acetylene gas chamber, a photodetector, a voltage-controlled oscillator, a servo motor, a phase modulator, and a microwave signal generator. The continuous light output from the tunable laser is frequency-shifted by the acousto-optic modulator and then split into two paths by the optical fiber coupler: one path is used for pump laser locking, and the other is used for optical frequency comb generation. Pump laser locking is achieved by forming a closed loop with the Fabry-Perot cavity, acetylene gas chamber, photodetector, servo motor, voltage-controlled oscillator, and acousto-optic modulator. Optical frequency comb repetition frequency locking is achieved through modulation by the phase modulator, with the microwave drive signal of the phase modulator set to reference a high-stability clock source from satellite communication signals. (Optical frequency comb frequency locking module)

[0038] Precise locking of the pump frequency and optical frequency comb repetition frequency is achieved through dual closed-loop locking: The continuous light output from the tunable laser is frequency-shifted by an acousto-optic modulator and then split into two equal paths by an optical fiber coupler. One path is used for pump laser locking, and the other path serves as a seed light input to the optical frequency comb generation module to assist in optical frequency comb generation. The pump laser locking closed loop is as follows: the pump laser is sequentially transmitted to a high-stability FP cavity and a narrow-linewidth acetylene gas chamber. The FP cavity performs coarse screening of the pump laser, while the acetylene gas chamber uses its molecular absorption spectrum to perform precise calibration of the pump laser. The transmitted light is converted into an electrical signal by a photodetector. The servo analyzes the error of this electrical signal and outputs a control voltage to drive a voltage-controlled oscillator to generate an RF signal that is fed back to the acousto-optic modulator. The frequency shift of the acousto-optic modulator is adjusted in real time to achieve closed-loop locking of the pump laser frequency. The optical frequency comb repetition frequency locking closed loop is as follows: another pump laser path is input to a phase modulator. The microwave drive signal of the phase modulator is set by a high-stability clock source of a reference satellite communication signal. By modulating the phase, the optical frequency comb repetition frequency is precisely synchronized with the clock source frequency.

[0039] In one implementation, the frequency stability of the high-stability clock source meets the accuracy requirements of quantum key distribution, and the frequency stability of the Fabry-Perot cavity and the linewidth characteristics of the acetylene gas chamber are adapted to the locking requirements of the pump laser.

[0040] In practical network applications, a high-stability clock source is connected to the BeiDou-3 satellite timing system to calibrate the clock source frequency in real time. The 10GHz reference signal output by the clock source is transmitted to the phase modulator via a microwave cable. The frequency fluctuation of the microwave drive signal of the phase modulator is <0.1Hz within 24 hours. The Fabry-Perot cavity is placed in a constant temperature chamber with a temperature control accuracy of ±0.01℃. The acetylene gas chamber and the FP cavity are connected through a polarization-maintaining fiber. After two-stage locking, the pump laser frequency fluctuation is <±1MHz, meeting the frequency synchronization requirements of quantum key distribution. Thus, the high-stability clock source ensures the long-term stability of the optical frequency comb repetition frequency, avoiding key exchange interruptions caused by frequency drift. The adaptively designed FP cavity and acetylene gas chamber achieve coarse and fine two-stage locking of the pump laser, ensuring locking speed (e.g., locking response time <10 ms) while improving locking accuracy and increasing the success rate of pump laser locking.

[0041] In one implementation, the output detection module includes an optical fiber coupler, a dense wavelength division multiplexer, a power meter, and a spectrometer. The pump laser and optical frequency comb from the optical microcavity are split by the optical fiber coupler. One path is sent to the spectrometer for soliton mode-locking verification, and the other path is filtered by the dense wavelength division multiplexer to remove the pump and auxiliary laser, and then split by the optical fiber coupler again for optical frequency comb power measurement and comb tooth selection, respectively. The filtering module includes a programmable optical filter and a polarization controller. The two optical frequency combs are filtered to produce comb teeth of the same frequency by the programmable optical filter, and after the polarization state of the comb teeth is adjusted by the polarization controller, they are sent to the encoding module.

[0042] For example, performance verification and signal screening of the optical frequency comb can be achieved through split detection and hierarchical processing. The pump laser from the optical microcavity and the optical frequency comb are first split into two paths by a 1:1 fiber coupler. One path is sent to a spectrometer, and the soliton mode-locking state is determined by observing the envelope morphology of the optical frequency comb spectrum. When the spectrum shows a smooth Gaussian envelope without stray peaks, the soliton mode-locking is determined to be complete. At this time, the power uniformity of the optical frequency comb teeth is <±1dB. The other path is filtered by a dense wavelength division multiplexer to remove the pump laser and auxiliary laser, retaining only the optical frequency comb signal. After filtering out stray light, The optical frequency comb is then split by a 1:9 fiber coupler. 10% of the optical power is sent to a power meter for power measurement, for example, within a range of -30dBm to 10dBm, while the remaining 90% is sent to a filtering module for comb tooth selection. The filtering module includes a programmable optical filter and a polarization controller. Two optical frequency combs from two user nodes are precisely filtered out with the same frequency by the programmable optical filter, and then the polarization state of the comb teeth is adjusted to be consistent by the polarization controller, ensuring polarization matching of the optical frequency comb signal sent to the encoding module. Thus, the output detection module can verify the soliton mode-locking state of the optical frequency comb in real time, ensuring that the optical frequency comb quality meets the standards. The high isolation design of the dense wavelength division multiplexer effectively filters out stray light, avoiding pump / auxiliary laser interference with subsequent key exchange. The high-precision comb tooth selection and polarization adjustment of the filtering module control the frequency deviation of the comb teeth with the same frequency within a certain range and ensure polarization matching, providing a high-quality optical frequency comb signal for the encoding module.

[0043] In one implementation, the encoding module includes two high-intensity modulators, one phase modulator, and an arbitrary waveform generator; the intensity modulators have high modulation rate, wide pulse width adjustment range, fixed repetition frequency, and high extinction ratio characteristics; the comb teeth are modulated into pulse wave packets by the first intensity modulator, and then the decoy state protocol is implemented by the second intensity modulator; the phase modulator is used to apply phase offset.

[0044] For example, the quantum encoding of the comb signal consists of three steps: First, the filtered continuous comb teeth are fed into the first intensity modulator. An arbitrary waveform generator outputs a custom pulse sequence, such as NRZ code or RZ code, with the output pulse width set to 500ps and the repetition frequency to 1GHz, modulating the continuous comb teeth into discrete pulse packets. Second, the modulated pulse packets are input into the second intensity modulator, which is loaded with a decoy state protocol. By switching the modulation voltage, such as 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 encode the qubits, where 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, with 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.

[0045] In one 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 adjustable delay line has a wide delay adjustment range and high adjustment accuracy. The encoded comb teeth are attenuated to a weakly coherent state level by the adjustable optical attenuator, the delay difference is compensated by the 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.

[0046] For example, through four steps of attenuation, delay, polarization, and beam combining, the encoded comb signal is converted into a single-photon signal that meets the interference requirements: First, the encoded comb signal is attenuated to a weakly coherent state level by an adjustable optical attenuator to avoid key leakage caused by multiphoton effects; Second, the optical signal delay difference between the two user nodes is compensated by an adjustable delay line, so that the two photons arrive at the interference beam combining device simultaneously; Third, the polarization state of the two photons is decomposed into orthogonal polarization by a polarization beam splitter and adjusted to a preset polarization direction; Fourth, the two photons are input into a polarization-maintaining beam splitter, and the polarization-maintaining characteristic is used to maintain the stability of the polarization state, thereby achieving high-precision interference beam combining.

[0047] In one implementation, the detection module includes a polarization controller, a superconducting nanowire single-photon detector, and a time-to-digital converter. The superconducting nanowire single-photon detector has high detection efficiency, low dark count rate, and low time jitter characteristics, while the time-to-digital converter has high time resolution and a high upper limit for the coincidence count rate. After the combined photons are matched with parameters by the polarization controller, they are sent to the superconducting nanowire single-photon detector for detection, and two-photon coincidence counting is performed by the time-to-digital converter.

[0048] For example, quantum key extraction is achieved through three steps: parameter matching, photon detection, and coincidence counting. First, the combined photons are re-adjusted in phase, power, and photon number parameters by a polarization controller to ensure they match the detection parameters of the superconducting nanowire single-photon detector. Second, the matched photons are fed into the superconducting nanowire single-photon detector, which 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 performs time correlation analysis on the electrical pulse signals from both detectors, filtering out coincidence count events. The coincidence count result is the original data for the quantum key.

[0049] The following section describes the specific implementation process in four stages: precise generation of optical frequency comb, frequency locking, signal processing, and quantum detection.

[0050] First, an optical frequency comb is generated based on auxiliary laser heating. The optical frequency comb generation module consists of a pump laser, an auxiliary laser, a polarization controller (PC), a power amplifier (EDFA), a fiber optic circulator (CIR), and an optical microcavity. The auxiliary laser heating maintains thermal equilibrium within the cavity, achieving stable generation of the optical frequency comb. The specific operation steps are as follows: First, the core parameters are preset: the output frequency of the auxiliary laser and the output power of the auxiliary laser power amplifier are determined, the output frequency of the pump laser is set and kept fixed, and the output power of the pump laser power amplifier is configured. Then, the laser signal is preprocessed. The output signals of the pump laser and the auxiliary laser are adjusted in polarization state by the polarization controller (PC) to match the TE mode of the optical microcavity. After amplification by the power amplifier (EDFA), the signals are fed into the optical microcavity through the fiber optic circulator (CIR). After parameter and polarization adjustments are completed, the optical frequency comb is generated in steps: First, the pump laser is coupled into the optical microcavity, and its output wavelength is adjusted to the red detuned region of the resonance peak while maintaining wavelength and output power stability; then, the auxiliary laser is coupled into the optical microcavity from the opposite direction of the pump laser, and the frequency of the auxiliary laser is slowly reduced to allow it to enter the blue detuned region of the resonance peak. Subsequently, the frequency of the auxiliary laser is increased in the opposite direction until the pump laser is stable in the red detuned region of the resonance peak, thus completing the generation of the optical frequency comb.

[0051] Second, dual-degree-of-freedom locked optical frequency comb frequency alignment. To achieve high-precision frequency alignment of the optical frequency comb in different locations, the optical frequency comb frequency locking module completes the calibration by locking the pump frequency and the optical frequency comb repetition frequency, two degrees of freedom. This module includes an acousto-optic modulator (AOM), a fiber coupler, a Fabry-Perot cavity (FP cavity), an acetylene gas chamber (C2H2), a photodetector (PD), a voltage-controlled oscillator (VCO), a servo, a phase modulator (PM), and a microwave signal generator (RF). The specific locking logic is as follows: the continuous light output from the tunable laser is frequency-shifted by an acousto-optic modulator (AOM) and then split into two paths by a fiber coupler. One path is used for pump laser locking, and the other path is used for optical frequency comb generation. The pump laser is transmitted to a Fabry-Perot cavity (FP) and an acetylene gas chamber (C2H2). The transmitted light is converted into an electrical signal by a photodetector (PD). The servo outputs a control voltage based on this electrical signal, which drives a voltage-controlled oscillator (VCO) to generate an radio frequency signal and feeds it back to the acousto-optic modulator (AOM) to achieve frequency locking of the pump laser. The other pump laser is modulated by a phase modulator (PM). Combined with a high-stability clock source of a reference satellite signal, the microwave drive signal of the phase modulator (PM) is set to complete the locking of the optical frequency comb repetition frequency.

[0052] Third, optical frequency comb output detection and filtering. The output detection module connects to the optical frequency comb generation stage with the filtering module, completing the performance verification and comb tooth selection of the optical frequency comb, providing a qualified optical frequency comb signal for the subsequent encoding stage. The output detection module includes a fiber coupler, a dense wavelength division multiplexer (DWDM), a power meter, and an OSA: First, the pump laser and optical frequency comb output from the optical microcavity are extracted and split into two paths by the fiber coupler. One path is sent to the OSA to observe the optical frequency comb spectrum. When the spectrum shows a smooth envelope, soliton mode locking is determined to be complete. The other path is filtered by the DWDM to remove the pump laser and auxiliary laser. After obtaining a clean optical frequency comb, it is split again. One path is sent to the power meter for power measurement, and the other path is sent to the filtering module. The filtering module consists of a programmable optical filter (WSS) and a polarization controller (PC): the programmable optical filter (WSS) filters out comb teeth of the same frequency from the two optical frequency combs, and then the polarization state of the comb teeth is adjusted by the polarization controller (PC) to ensure the consistency of the comb tooth signals.

[0053] 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 (IM), one phase modulator (PM), and an arbitrary waveform generator (AWG): The filtered comb is first fed into the first intensity modulator (IM), where the arbitrary waveform generator (AWG) sets the pulse width and repetition frequency to modulate the continuous comb into pulse packets; the modulated pulse packets are then input into the second intensity modulator (IM) to load the decoy state protocol; the phase modulator (PM) applies a phase shift of 0 or π to the signal to complete quantum encoding. The polarization control module consists of a tunable optical attenuator (VOA), a tunable delay line (Delay), a polarization beam splitter (PBS), and a polarization-maintaining beam splitter (PMBS). The encoded comb teeth are attenuated to a weakly coherent state by the VOA, the delay line (Delay) compensates for the optical signal delay difference, the PBS adjusts the polarization state of the two photons, and finally, the PMBS achieves interference beam combining. The detection module includes a superconducting nanowire single-photon detector (SNSPD) and a time-to-digital converter (TDC). The combined photons are first matched for phase, power, and photon count by the polarization controller (PC), then sent to the SNSPD for photon detection. Simultaneously, the TDC performs two-photon coincidence counting, ultimately enabling the extraction and verification of the quantum key.

[0054] In one implementation, the optical frequency comb is a frequency-aligned optical frequency comb; the optical frequency comb generation module includes a pump laser, an auxiliary laser, a polarization controller, a power amplifier, a fiber optic circulator, and an optical microcavity; the output signals of the pump laser and the auxiliary laser are polarized by the polarization controller, amplified by the power amplifier, and then sent into the optical microcavity through the fiber optic circulator; the pump laser is coupled into the optical microcavity and maintained in the red detuning region of the resonance peak, while the auxiliary laser is coupled into the optical microcavity from the opposite direction to maintain thermal equilibrium. By adjusting the frequency of the auxiliary laser, the pump laser is stabilized in the red detuning region of the resonance peak, thereby generating the optical frequency comb.

[0055] Figure 3 This is a schematic diagram of a specific implementation of a quantum-safe networking device based on independent optical frequency combs, using two users as an example. It illustrates the generation and alignment of the optical frequency comb at each user's location, and how QKD is implemented between different users. Figure 3 As shown. The device includes: optical frequency comb generation modules 11 and 44, optical frequency comb frequency locking modules 22 and 55, output detection modules 33 and 66, filtering module 77, encoding module 88, polarization control module 99, and detection module 10.

[0056] The optical frequency comb generation modules 11 and 14 have the same structure and working principle, and respectively include tunable lasers 101 and 401, polarization controllers (PC) 102, 106, 402 and 406, power amplifiers (EDFA) 103, 107, 403 and 407, fiber optic circulators (CIR) 104, 108, 404 and 408, and optical microcavities 105 and 405.

[0057] In this embodiment, an auxiliary laser heating scheme is selected to generate the optical frequency comb. Pump lasers 201 and 501 are NKT lasers with a wavelength of 1550 nm and a linewidth of less than 10 Hz, which can enhance the stability of the generated optical frequency comb. Auxiliary lasers 101 and 401 are PPCL lasers used to keep the microcavity self-heated and locked.

[0058] In this embodiment, the optical frequency comb is generated in two independent microring resonators (MRRs) with identical design parameters. Both MRRs are silicon nitride microring cavities with free spectral widths FSR1 = 49.949 GHz and FSR2 = 49.958 GHz, and quality factors Q1 = 5.9 × 10⁶ and Q2 = 5.4 × 10⁶, respectively.

[0059] When using auxiliary laser heating, first set the output wavelength and output power of the pump and auxiliary lasers, as well as the power amplifier power: First, configure the auxiliary laser link. Adjust the output wavelength of auxiliary lasers 101 and 401 to 1535.82nm; adjust the polarization to match the TE mode of optical microcavities 105 and 405 using polarization controllers (PC) 102 and 402; then, amplify the laser signal by inputting it to power amplifiers (EDFA) 103 and 403, and set the output power of EDFA 103 and 403 to 700mW; finally, send the signal into the optical microcavity through fiber optic circulators (CIR) 104 and 404; then configure the pump laser link. The output wavelength of the pump lasers 210 and 501 is adjusted to 1550.12 nm and kept constant. The polarization is adjusted to match the TE mode of the optical microcavities 105 and 405 by the polarization controllers (PC) 106 and 406. Then the laser signal is input to the power amplifiers (EDFA) 107 and 407 for amplification, and the output power of EDFA 107 and 407 is set to 500mW. Finally, the signal is sent to the optical microcavity module through the fiber optic circulators (CIR) 108 and 408.

[0060] In this embodiment, even when the pump laser enters a red detuned state after entering a soliton state, the auxiliary laser heating method keeps the microcavity self-heated and locked. This effectively stabilizes the pump detuning and suppresses the soliton pulse width variation caused by random pump laser frequency drift. In fact, in this setup, the pump laser is locked to the ultrastable cavity and acetylene chamber using PDH locking technology, and their frequencies are very stable. This configuration further suppresses pump frequency jitter.

[0061] The frequency locking modules 22 and 25 include tunable lasers 201 and 501, acousto-optic modulators (AOM) 202 and 502, fiber optic couplers (Coupler) 203 and 503, Fabry-Perot cavities (FP cavities) 204 and 504, acetylene gas chambers (C2H2) 205 and 405, photodetectors (PD) 206 and 506, servos (Servo) 207 and 507, voltage-controlled oscillators (VCO) 208 and 508, phase modulators (PM) 209 and 509, and microwave signal generators (RF) 210 and 510.

[0062] The continuous light output from tunable lasers 201 and 501 is frequency-shifted by acousto-optic modulators (AOMs) 202 and 502. The frequency shift amount is set according to the frequency supported by voltage-controlled oscillators (VCOs) 208 and 508. In this embodiment, the frequency shift amount is set to 185MHz. Then, it is split into two paths by fiber couplers 203 and 503. One path is transmitted to Fabry-Perot cavities (FPs) 204 and 504. The reflected light after resonance in the cavity is input to acetylene gas chambers (C2H2) 205 and 405. The transmitted light from the acetylene gas chamber is output to photodetectors (PDs) 206 and 506 and converted into an electrical signal. Servos 207 and 507 output a control voltage according to the electrical signal to drive VCOs 208 and 508 to generate radio frequency signals, which are then fed back to the acousto-optic modulators (AOMs) 202 and 502 for frequency modulation. The other path split by fiber couplers 203 and 503 is transmitted through a polarization controller PC. After the polarization states of 106 and 406 are adjusted, they are input to phase modulators (PM) 209 and 509 for modulation. The microwave drive signals of phase modulators (PM) 209 and 509 are set by high-stability clock sources (RF) 210 and 510 referenced to the satellite communication signal. The frequency of the microwave signal is set to 12.5 GHz. Through modulation, the frequency difference between the fourth-order sideband and the pump laser is approximately 50 GHz, which is consistent with the repetition frequency of the optical frequency comb. By carefully adjusting the microwave frequency and power, the soliton repetition frequency can be automatically locked to the microwave frequency.

[0063] After the above setup, the pump laser is first coupled into optical microcavities 105 and 405. Then, the output wavelengths of tunable lasers 201 and 501 are adjusted to keep the pump laser in the red detuned region of the resonance peak, maintaining the pump laser wavelength at 1550.12 nm and the output power at 500 mW. Next, the auxiliary laser is coupled into optical microcavities 105 and 405 from the opposite direction to the pump laser, thereby maintaining the thermal balance within the cavity during the generation of the Kerr soliton. The frequency of tunable lasers 101 and 401 in the auxiliary module is slowly decreased, causing the auxiliary laser to enter the blue detuned region of the resonance peak. Then, the frequency of tunable lasers 101 and 401 is increased until the pump laser stabilizes in the red detuned region of the resonance peak, thereby generating a dissipative Kerr soliton optical comb.

[0064] In this embodiment, the frequency of the auxiliary laser is reduced by 5 MHz / s, and the output light spectrum of the microcavity in the spectrometer is observed. Figure 4 As shown, after a smooth envelope appears, the frequency scan is stopped, at which point mode-locking of the dissipative Kerr soliton optical comb is achieved. Figure 4 This is a spectrum of remote optical frequency combs, used to verify the generation stability and frequency alignment basis of two independent remote optical frequency combs (comb1, comb2). The horizontal axis represents wavelength, covering the commonly used communication band for quantum key distribution (1500-1600nm), and the vertical axis represents the relative light intensity of the optical frequency combs. The two comb-shaped spectral lines in the figure correspond to the optical frequency combs generated by the two user nodes, respectively. The spectral lines exhibit a smooth Gaussian envelope without obvious clutter peaks, indicating successful soliton mode locking. Furthermore, the high consistency of the comb tooth frequency distributions on the two spectral lines provides stable optical signal support for subsequent precise alignment of the remote optical frequency combs and quantum key exchange.

[0065] The output detection modules 33 and 66 have the same structure and working principle, including fiber optic couplers 301, 305, 601, 605, optical spectrum analyzers (OSA) 302, 602, dense wavelength division multiplexers (DWDM) 303, 304, 603, 604, and power meters 306, 606.

[0066] The auxiliary laser generated by the auxiliary module passes through the fiber optic circulator (CIR) 304 to the optical microcavity module. Simultaneously, the pump laser and optical frequency comb from the optical microcavity are extracted. Then, fiber couplers 301 and 601 split the laser into two paths. One path is sent to the optical spectrum analyzer (OSA) 302 and 602, where the spectrum of the output optical frequency comb is observed. When the optical frequency comb spectrum has a smooth envelope, soliton mode locking is completed. The other path is sent to the dense wavelength division multiplexer (DWDM) 303, 304, 603, and 604 to filter out the pump laser and auxiliary laser. The resulting optical frequency comb is split into two paths by fiber couplers 305 and 605. One path is sent to the power meter 306 and 606 for power measurement of the optical frequency comb, and the other path is distributed to each user for quantum key distribution.

[0067] The filtering module 77 includes programmable optical filters (WSS) 701 and 702 and polarization controllers (PC) 703 and 704.

[0068] The two optical frequency combs are filtered out by programmable optical filters (WSS) 701 and 702 to produce corresponding comb teeth of the same frequency; the polarization state of the comb teeth is adjusted by polarization controllers PC703 and 704; and then input into the encoding module.

[0069] The encoding module 88 includes intensity modulators (IM) 801, 802, 803, 804, phase modulators PM 805, 806, and arbitrary waveform generators (AWG) 807, 808.

[0070] The comb teeth filtered out in the filtering module are fed into intensity modulators (IM) 801 and 802 respectively. The output pulse width is set to 150ps and the repetition frequency is set to 10MHz by arbitrary waveform generators (AWG) 807 and 808, and the continuous comb teeth are modulated into pulse packets. The modulated pulse packets are input into intensity modulators (IM) 803 and 804 for decoy state encoding. A phase shift of 0 or π is applied by phase modulators (PM) 805 and 806.

[0071] The polarization control module 99 includes an adjustable delay line (Delay) 901, adjustable optical attenuators (VOA) 902 and 903, a polarization beam splitter (PBS) 904 and 905, and a polarization-maintaining beam splitter (PMBS) 906.

[0072] The photons are attenuated to a weakly coherent state level by adjustable optical attenuators (VOA) 902 and 903, and the photon count of each comb tooth is attenuated to 300±20 k. The delay difference of the optical signal is compensated by an adjustable delay line (Delay) 901. The polarization state of the two photons is then adjusted by polarization beam splitters (PBS) 904 and 905. Finally, the two photons are input to a polarization-maintaining beam splitter (PMBS) 906 to achieve interference beam combining.

[0073] The detection module 10 includes polarization controllers (PC) 1001 and 1002, superconducting nanowire single-photon detectors (SNSPD) 1003 and 1004, and time-to-digital converter (TDC) 1005.

[0074] The combined photons are matched for phase, power, and photon number by polarization controllers (PC) 1001 and 1002; then they are detected by superconducting nanowire single-photon detectors (SNSPD) 1003 and 1004, and two-photon coincidence counting is performed using a time-to-digital converter (TDC) 1005. The average dark count of the SNSPD is approximately 60 times / second, which is negligible when measuring the visibility of HOM interference fringes.

[0075] Figure 5 The image shows the HOM interference fringe pattern of the fourth comb tooth, a key experimental diagram for verifying the interference quality of the same-frequency comb teeth in a remote optical frequency comb and ensuring the accuracy of quantum key distribution. The horizontal axis represents the delay (usually in picoseconds per second) of the two photons arriving at the interference combining device, used to control the time synchronization condition of the two-photon interference. The vertical axis represents the two-photon coincidence count rate; the periodic fluctuations in the count rate form the interference fringes. The fringe visibility is estimated at 42.4 ± 0.21%. High visibility (>40%) indicates a high degree of matching in parameters such as frequency and polarization state between the same-frequency comb teeth in the remote optical frequency comb, meeting the requirements of two-photon interference and supporting subsequent quantum key extraction based on the HOM effect, ensuring the security and reliability of key distribution.

[0076] To demonstrate multi-channel HOM interference, two programmable optical filters (WSS) 701 and 702 were used to separate the comb teeth numbered 3 to 12. Figure 6 Figures (a) and (b) show the comb lines numbered 3 to 12. For HOM interference coincidence counting, the cumulative time was set to 15 minutes, which is significantly longer than the mutual coherence time of independently phase-randomized photons. Experimental results are as follows... Figure 6 As shown in (c), the visibility of the HOM interference fringes is distributed between 40% and 45%. To evaluate stability, the HOM interference of each pair of comb teeth was measured three times. The fitted fringe visibility is shown in (c), with a maximum deviation of ±0.35%.

[0077] In summary, the quantum-secure networking device based on independent optical frequency combs in this application utilizes the multi-wavelength characteristics of optical frequency combs and combines them with the measurement-device-independent quantum key distribution (MDI-QKD) protocol to achieve multi-user, fully connected quantum-secure networking. The device first generates geographically isolated independent optical frequency combs and achieves precise frequency alignment between them. Then, the generated Kerr combs are filtered by a dense wavelength division multiplexer (DWDM) to remove the pump laser and auxiliary laser. A programmable optical filter (WSS) is used to filter out the same-frequency comb teeth from the geographically isolated optical frequency combs. Time-slice qubit encoding is performed using an intensity modulator (IM) and a phase modulator (PM). After attenuation to a weakly coherent state level by a tunable optical attenuator (VOA), the signal is input to a polarization-maintaining beam splitter (PMBS) to achieve two-path photon interference beam combining. Finally, the combined photons are sent to a superconducting nanowire single-photon detector (SNSPD) for detection, and a time-to-digital converter (TDC) is used for two-photon coincidence counting.

[0078] This application presents a quantum-safe networking device based on an independent optical frequency comb, which offers at least the following advantages: 1. The application employs an auxiliary laser heating scheme, which keeps the microcavity self-heated and locked, stabilizing pump detuning and suppressing soliton pulse width variations caused by random pump laser frequency drift. 2. The two silicon nitride micro-ring cavities used in this application have a free spectral range of FSR~50GHz. Similar free spectral ranges allow for the generation of optical frequency combs with similar repetition frequencies. 3. The silicon nitride micro-ring cavities used in this application are butterfly-shaped encapsulated, preventing external environmental influences on the stable existence of the optical frequency comb. 4. This application uses a satellite communication signal as a high-stability clock source reference, combined with a three-level collaborative mechanism of acetylene gas chamber frequency locking, PDH frequency stabilization, and microwave injection locking in the pump locking module, to accurately calibrate the optical frequency comb frequency, significantly improving its long-term stability. 5. The modulator used in this application has a modulation rate of not less than 20 GHz, which can accurately modulate the target comb teeth of the optical comb into pulse wave packets that meet the requirements and complete the time-slice quantum bit encoding. The encoding process is stable and controllable, providing a high-quality and highly compatible optical signal carrier for quantum information transmission.

[0079] Corresponding to the above-mentioned device, this application also provides a quantum-safe networking method based on independent optical frequency combs. Using the aforementioned quantum-safe networking device based on independent optical frequency combs, a quantum-safe networking based on independent optical frequency combs is realized. The method includes:

[0080] Step 1: Using an auxiliary laser heating method, the coupling parameters and polarization state of the pump laser and the auxiliary laser are adjusted through the optical frequency comb generation module to stabilize the pump laser in the red detuning region of the optical microcavity resonance peak and maintain the thermal balance inside the cavity to generate the optical frequency comb.

[0081] Step 2: Lock the pump frequency and optical frequency comb repetition frequency, two degrees of freedom, through the optical frequency comb frequency locking module. Combine with a high-stability clock source, Fabry-Perot cavity and acetylene gas chamber to form a closed-loop control, and achieve precise frequency alignment of the optical frequency comb in a remote location.

[0082] Step 3: Complete the spectral observation, soliton mode-locking verification, pump and auxiliary laser filtering and power measurement of the optical frequency comb through the output detection module, and then use the filtering module to screen the same frequency comb teeth of the optical frequency comb from different locations and adjust the polarization state.

[0083] Step 4: Modulate the comb teeth into pulse wave packets through the encoding module to realize the decoy state protocol and apply a phase shift to complete the time-slice qubit encoding;

[0084] Step 5: Attenuate the encoded comb teeth to a weakly coherent state level through the polarization control module, compensate for the optical signal delay difference, and achieve interference beam combining after adjusting the photon polarization state;

[0085] Step 6: Complete parameter matching, photon detection, and two-photon coincidence counting of the combined photons through the detection module. Based on the measurement device-independent quantum key distribution protocol, realize independent secure key exchange between any user pairs.

[0086] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A quantum-safe networking device based on an independent optical frequency comb, characterized in that, Each user is configured with an independent and frequency-aligned optical frequency comb and an independent encoder corresponding to each frequency line to enable independent secure key exchange between any user pairs; the device includes an optical frequency comb generation and locking device and a HOM interference and quantum key distribution device, wherein: The optical frequency comb generation and locking device includes an optical frequency comb generation module, an optical frequency comb frequency locking module, an output detection module, a filtering module, and an encoding module connected in sequence. The optical frequency comb generation module generates the optical frequency comb using an auxiliary laser heating method. By adjusting the coupling method and parameters of the pump laser and the auxiliary laser, intracavity thermal balance is maintained to stably generate the optical frequency comb. The optical frequency comb frequency locking module achieves frequency alignment of the optical frequency comb in different locations by locking two degrees of freedom: the pump frequency and the optical frequency comb repetition frequency. The output detection module is used for spectral observation of the optical frequency comb, soliton mode-locking verification, pump and auxiliary laser filtering, and optical frequency comb power measurement. The filtering module is used to screen for co-frequency comb teeth in different locations and adjust the polarization state of the comb teeth. The encoding module is used to modulate the comb teeth into pulse wave packets, implement decoy state protocols, and apply phase shifts. The HOM interference and quantum key distribution device 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 a weakly coherent state level, compensate for the optical signal delay difference, adjust the photon polarization state, and realize interference beam combining. The detection module is used to achieve phase, power, and photon number matching of the combined photons, detect the photons, and complete two-photon coincidence counting.

2. The quantum-safe networking device based on an independent optical frequency comb according to claim 1, characterized in that, The optical frequency comb is a frequency-aligned optical frequency comb; the optical frequency comb generation module includes a pump laser, an auxiliary laser, a polarization controller, a power amplifier, a fiber optic circulator, and an optical microcavity; the output signals of the pump laser and the auxiliary laser are polarized by the polarization controller, amplified by the power amplifier, and then sent into the optical microcavity through the fiber optic circulator; the pump laser is coupled into the optical microcavity and maintained in the red detuning region of the resonance peak, while the auxiliary laser is coupled into the optical microcavity from the opposite direction to maintain thermal balance. By adjusting the frequency of the auxiliary laser, the pump laser is stabilized in the red detuning region of the resonance peak, thereby generating the optical frequency comb.

3. The quantum-safe networking device based on an independent optical frequency comb according to claim 2, characterized in that, The optical microcavity is a silicon nitride microring cavity and is butterfly-shaped packaged to reduce the impact of the external environment on the stability of the optical frequency comb.

4. The quantum-safe networking device based on an independent optical frequency comb according to claim 1, characterized in that, The optical frequency comb frequency locking module includes an acousto-optic modulator, an optical fiber coupler, a high-stability Fabry-Perot cavity, a narrow-linewidth acetylene gas chamber, a photodetector, a voltage-controlled oscillator, a servo, a phase modulator, and a microwave signal generator. The continuous light output from the tunable laser is frequency-shifted by the acousto-optic modulator and then split into two paths by the optical fiber coupler. One path is used for pump laser locking, and the other path is used for optical frequency comb generation. Pump laser locking is achieved by forming a closed loop with the Fabry-Perot cavity, the acetylene gas chamber, the photodetector, the servo, the voltage-controlled oscillator, and the acousto-optic modulator. The optical frequency comb repetition frequency locking is achieved by modulation by the phase modulator, and the microwave drive signal of the phase modulator is set with reference to a high-stability clock source of satellite communication signal.

5. The quantum-safe networking device based on an independent optical frequency comb according to claim 4, characterized in that, The frequency stability of the high-stability clock source meets the accuracy requirements of quantum key distribution, and the frequency stability of the Fabry-Perot cavity and the linewidth characteristics of the acetylene gas chamber are adapted to the locking requirements of the pump laser.

6. The quantum-safe networking device based on an independent optical frequency comb according to any one of claims 1-5, characterized in that, The output detection module includes an optical fiber coupler, a dense wavelength division multiplexer, a power meter, and a spectrometer. The pump laser and optical frequency comb from the optical microcavity are split by the optical fiber coupler. One path is sent to the spectrometer for soliton mode-locking verification, and the other path is filtered by the dense wavelength division multiplexer to remove the pump and auxiliary laser, and then split by the optical fiber coupler again for optical frequency comb power measurement and comb tooth selection, respectively. The filtering module includes a programmable optical filter and a polarization controller. The two optical frequency combs are filtered to produce comb teeth of the same frequency by the programmable optical filter, and after the polarization state of the comb teeth is adjusted by the polarization controller, they are sent to the encoding module.

7. The quantum-safe networking device based on an independent optical frequency comb according to any one of claims 1-5, characterized in that, The encoding module includes two high-intensity modulators, one phase modulator, and an arbitrary waveform generator. The intensity modulator has high modulation rate, wide pulse width adjustment range, fixed repetition frequency, and high extinction ratio. The comb teeth are modulated into pulse packets by the first intensity modulator and then decoy state protocol by the second intensity modulator. The phase modulator is used to apply phase offset.

8. The quantum-safe networking device based on an independent optical frequency comb according to any one of claims 1-5, 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 adjustable delay line has a wide delay adjustment range and high adjustment accuracy. The encoded comb teeth are attenuated to a weakly coherent state level by the adjustable optical attenuator, the delay difference is compensated by the 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 an independent optical frequency comb according to any one of claims 1-5, characterized in that, The detection module includes a polarization controller, a superconducting nanowire single-photon detector, and a 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 upper limit of coincidence count rate. After the combined photons are matched with the parameters by the polarization controller, they are sent to the superconducting nanowire single-photon detector for detection, and two-photon coincidence counting is performed by the time-to-digital converter.

10. A quantum-safe networking method based on independent optical frequency combs, characterized in that, Using the quantum-secure networking device based on independent optical frequency combs as described in any one of claims 1-9, a quantum-secure networking based on independent optical frequency combs is realized, the method comprising: An auxiliary laser heating method is adopted. The coupling parameters and polarization state of the pump laser and the auxiliary laser are adjusted by the optical frequency comb generation module to stabilize the pump laser in the red detuning region of the optical microcavity resonance peak and maintain the thermal balance in the cavity to generate the optical frequency comb. By locking the pump frequency and the optical frequency comb repetition frequency using an optical frequency comb frequency locking module, and combining a high-stability clock source, a Fabry-Perot cavity, and an acetylene gas chamber to form a closed-loop control, precise frequency alignment of the optical frequency comb in a remote location can be achieved. The output detection module completes the spectral observation, soliton mode-locking verification, pumping and auxiliary laser filtering and power measurement of the optical frequency comb. Then, the filtering module screens the same frequency comb teeth of the optical frequency comb from different locations and adjusts the polarization state. The comb teeth are modulated into pulse wave packets by the encoding module to realize the decoy state protocol and apply a phase shift, thus completing the time-slice qubit encoding; The polarization control module attenuates the encoded comb teeth to a weakly coherent state level to compensate for the optical signal delay difference and achieves interference beam combining after adjusting the photon polarization state. The detection module completes parameter matching, photon detection, and two-photon coincidence counting of the combined photons. Based on the measurement device-independent quantum key distribution protocol, it enables independent secure key exchange between any user pairs.

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