A bidirectional continuous-variable quantum key distribution method and system based on a single-transceiver ring network architecture and frequency division duplex technology

Abstract

This invention discloses a bidirectional continuous-variable quantum key distribution method and system based on frequency division duplexing in a single-transceiver ring network. The method is based on a monolithically integrated silicon photonics transceiver chip. By pre-setting optical carrier frequency offsets for the forward and reverse links, it isolates the quantum signal from Rayleigh backscattering noise in the fiber in the frequency domain. The transmitting end generates a broadband waveform containing quantum signals and pilot signals, which is transmitted bidirectionally through a single optical fiber. The receiving end uses a laser source from the same chip as the local oscillator for coherent heterodyne detection. A digital signal processing module performs orthogonalization correction, phase recovery, and matched filtering to suppress noise and extract the quantum signal to generate a secure key. This invention solves the problems of inflexible networking, low fiber utilization, and severe scattering noise interference in bidirectional transmission over a single fiber caused by the separation of the transmitting and receiving ends in integrated continuous-variable quantum key distribution systems. It provides a low-cost and highly flexible solution for metropolitan quantum ring networks.

Description

Technical Field

[0001] This invention relates to the field of quantum secure communication technology, and more particularly to integrated photonics and quantum communication network technology. Specifically, this invention provides a continuous variable quantum key distribution method and system implemented on a monolithic integrated silicon photonic chip, suitable for ring network topologies, and utilizing frequency division duplex technology to solve the Rayleigh scattering noise problem in bidirectional transmission over a single fiber. Background Technology

[0002] Quantum key distribution is one of the core technologies for building future information security systems, enabling the establishment of theoretically unconditionally secure shared keys between communicating parties. Among these, continuous-variable quantum key distribution (CVD) shows great application potential in metropolitan area access networks due to its good compatibility with classical optical communication infrastructure and relatively low cost. Integration technologies based on silicon photonics platforms further enable miniaturization, cost reduction, and large-scale production of equipment.

[0003] However, existing integrated continuous-variable quantum key distribution schemes mostly employ unidirectional link or discrete transceiver architectures, leading to problems such as high fiber resource consumption, high node costs, and inflexible deployment when constructing flexible network topologies (such as ring networks and mesh networks). More critically, if a single fiber is used for bidirectional transmission to save resources, Rayleigh backscattering noise from the strong light transmitted in the reverse direction will severely overwhelm the weak quantum signal transmitted in the forward direction, rendering the system malfunctioning. Furthermore, on-chip optical crosstalk between high-power local oscillator light and weak quantum signals on a monolithic integrated chip is also a technical challenge that urgently needs to be addressed.

[0004] Therefore, there is an urgent need in this field for a highly integrated continuous-variable quantum key distribution solution that can effectively suppress Rayleigh scattering and on-chip crosstalk, support bidirectional transmission over a single fiber, and is suitable for flexible networking (especially ring networks). Summary of the Invention

[0005] The purpose of this invention is to overcome the aforementioned deficiencies of the prior art and provide a bidirectional continuous-variable quantum key distribution method and system based on frequency division duplex in a single-transceiver ring network. This method and system, through an innovative frequency division duplex architecture and digital signal processing technology, achieves high-quality full-duplex quantum key distribution within a single optical fiber on a single integrated chip, making it particularly suitable for constructing metropolitan area quantum ring networks.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: According to one aspect of the present invention, a bidirectional continuous-variable quantum key distribution method based on frequency division duplexing is provided in a single transceiver ring network, comprising the following steps: Step S1: The transmitting end executes the frequency division duplex strategy to generate a baseband signal containing quantum signals and pilot signals, and generates an optical signal by modulation and transmission; Step S2: The receiver uses a laser source integrated on the same chip as the transmitter as a local oscillator to perform coherent heterodyne detection on the received optical signal to obtain an electrical signal containing beat frequency signal and noise. Step S3: Perform digital signal processing on the electrical signal to recover the quantum signal and calculate the security key rate, and finally generate a shared key.

[0007] Preferably, in step S1, executing the frequency division duplex strategy includes: allocating different optical carrier frequencies to the forward and reverse transmission links, where the frequency offset Δf must satisfy: |Δf| > B signal + B RB + B guard B signal For the quantum signal bandwidth, B RB B is the bandwidth of Rayleigh scattering noise. guard The protection bandwidth is calculated based on the laser frequency drift and the filter transition band width. This strategy ensures effective isolation between the quantum signal and scattering noise in the frequency domain.

[0008] Preferably, the digital signal processing in step S3 includes: Gram-Schmidt orthogonalization correction is applied to the received signal to compensate for the non-ideal characteristics of the receiver's I / Q branches; A Kalman filter is used for high-precision phase recovery, and the signal is inversely rotated. A digital root-raised cosine matched filter is applied to further suppress out-of-band noise and residual scattering components; Based on the processed signal, parameter estimation is performed, the secure key rate is calculated according to the Holevo bound, and the final key is generated after error correction and security enhancement.

[0009] According to another aspect of the present invention, a system for implementing the above-described method is provided, comprising: Integrated emission module: Configured on a silicon photonic chip, it includes a tunable narrow linewidth laser, a high-speed IQ modulator, and an automatic bias control circuit, used to generate and emit frequency division duplex modulated optical signals.

[0010] Integrated receiver detection module: It is monolithically integrated with the transmitter module on the same chip substrate, including a 90-degree optical mixer, a balanced photodetector array and a polarization processing unit, used to realize coherent heterodyne detection and polarization diversity reception of the signal and the local oscillator light.

[0011] Digital processing and control module: Implemented based on FPGA or ASIC, used to perform signal digitization, the above-mentioned digital signal processing algorithms, and post-processing generation of security keys.

[0012] Furthermore, multiple nodes, each containing the integrated transmission module, receiving and detection module, and digital processing module, can be connected end-to-end via a single optical fiber to form a network with a ring physical layer that supports single-fiber bidirectional quantum key distribution.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. By using a single transceiver chip and frequency division duplex technology, full-duplex quantum communication within a single optical fiber is realized, supporting the construction of ring networks, greatly improving the utilization rate of optical fiber resources and the flexibility of network deployment, and reducing the cost of metropolitan area network nodes.

[0014] 2. The innovative frequency division duplex strategy combined with digital matched filtering suppresses Rayleigh backscatter noise to below the shot noise floor, fundamentally solving the core bottleneck of single-fiber bidirectional transmission. On-chip integration also reduces phase noise through thermal balance effects, improving the system's passive stability.

[0015] 3. The transmission and reception functions are integrated on a single photonic chip, which helps reduce costs, decrease size, and improve reliability. The receiver uses a local oscillator, avoiding the security risks and attenuation problems associated with long-distance transmission of local oscillator light. Attached Figure Description

[0016] Figure 1 This is a flowchart of a bidirectional continuous-variable quantum key distribution method based on a single transceiver ring network. Detailed Implementation

[0017] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0018] 1. Method Implementation This invention provides a bidirectional continuous-variable quantum key distribution method based on a single transceiver ring network architecture and frequency division duplex technology. Its core process is as follows: Figure 1 As shown. The method includes the following steps: Step S1: Signal Generation and Transmission The transmitting end (Alice or Bob) executes a frequency division duplex strategy at the physical layer, generating a quantum signal carrying key information and a classical pilot signal for synchronization, constructing a broadband signal and transmitting it. Specifically, this includes: Step S1.1: Two independent random number sequences are generated using a quantum random number generator to generate quantum signal components for either Gaussian modulation coherent state or discrete modulation coherent state protocols. The quantum signal and pilot signal are linearly superimposed to form the baseband signal, and pulse shaping is performed using a root-raised cosine filter. The baseband signal u(t) is expressed as: in, T is the complex amplitude of the k-th symbol. s For symbol period, Let be the root-raised cosine function of the roll-off factor β.

[0019] The pilot signal p(t) is designed with a frequency offset of f. pilot Single-frequency continuous wave: Preferably, the roll-off factor β is set to 0.3, and the symbol period T s The corresponding sampling rate was set to 5 GSa / s to optimize spectral efficiency.

[0020] Step S1.2: To physically isolate the forward signal from backscattered noise, a preset frequency offset is introduced between the optical carriers of the forward and reverse links. The optical carrier is modulated by an IQ modulator to output an optical field, E. out (t) is represented as: Where P LO γu(t) represents the amplitude of the laser field, and γu(t) represents the driving voltage signal.

[0021] Frequency offset Δf = |f A -f B | Must satisfy strict inequality conditions: Among them B signal For the quantum signal bandwidth (e.g., 500 MHz), B RB The effective bandwidth for Rayleigh scattering noise. Guard bandwidth B guard Calculated based on system hardware characteristics: Here, δ drift B represents the maximum frequency drift of the laser within its operating temperature range (e.g., the drift of a 0.1 kHz linewidth laser). trans The transition band width of the digital root-raised cosine filter is calculated using the following formula: η is a correction factor related to the filter sidelobe suppression ratio (usually taken as 1.0-1.2).

[0022] In this embodiment, the frequency offset Δf is set to 0.5 GHz and the guard bandwidth Bguard is 10 MHz to ensure robustness.

[0023] Step S2: Coherent heterodyne detection The receiver employs a local oscillator coherent heterodyne detection method, utilizing a laser source on the same transceiver chip as the local oscillator light, which interferes with and detects the incident signal transmitted via optical fiber. The photocurrent signal output by the balanced photodetector is expressed as: in, For intermediate frequency (e.g., 0.5 GHz), i RB (t) represents Rayleigh backscattering noise, i shot θ(t) represents shot noise, and θ(t) represents the phase difference between the signal and the local oscillator.

[0024] Preferably, the local oscillator power is set to 14.5 dBm, the system detection efficiency is 0.37, and the electronic noise normalized to shot noise units (SNU) is 0.35. The photocurrent is digitally acquired by a high-bandwidth oscilloscope at a sampling rate of 5 GSa / s.

[0025] Step S3: Digital Signal Processing and Key Generation The receiving end performs digital signal processing on the acquired electrical signal to extract the quantum signal from the strong noise background and generate a secure key. Specific sub-steps include: Step S3.1: To address the IQ gain imbalance and phase non-orthogonality errors in the receiver, the Gram-Schmidt algorithm is used to construct an orthogonalization matrix to correct the original received vector. The correction matrix R... GS for: Where ϕ err denoted as phase error, and g is the gain imbalance factor.

[0026] Step S3.2: Phase recovery is performed using a Kalman filter, and the state equation and observation equation are established: Obtain the optimal phase estimate θ opt Then, the quantum signal is reverse-rotated: Subsequently, a digital root-raised cosine matched filter is applied to suppress noise, and its frequency domain response H RRC (f) Designed as follows: Preferably, the roll-off factor β = 0.3 to balance bandwidth and noise immunity.

[0027] Step S3.3: Calculate the channel transmittance and excess noise, and calculate the asymptotic security key rate based on the Holevo bound. K secure = β eff I(A:B)−χ(E), where the Holevo bound χ(E) is calculated from the symplectic eigenvalues ​​of the covariance matrix. Finally, the key K is applied. final Generated using the HKDF function: In this embodiment, the proportion of parameter estimation data is set to 50%, and the reverse negotiation efficiency β is... recon =0.96, frame error rate FER=0.2, to ensure efficient key generation.

[0028] 2. System Implementation This invention also provides a bidirectional continuous-variable quantum key distribution system based on a single transceiver ring network architecture and frequency division duplex technology, the system comprising the following modules: Integrated Transmitter Module (M1) This module is manufactured based on silicon-on-insulator (SiI) photonics integration technology and is equipped with a tunable narrow-linewidth laser source, a high-speed IQ modulator, and an automatic bias control circuit. Specifically: Light source unit: Employs an external or hybrid integrated narrow linewidth continuous wave laser with wavelength tuning accuracy better than 100 MHz and linewidth less than 10 kHz (e.g., a center wavelength of 1550.12 nm).

[0029] Modulation unit: Employs a silicon-based carrier depletion-type IQ modulator, supporting traveling wave electrode design to modulate high-frequency frequency division duplex signals.

[0030] Bias control unit: Locks the modulator operating point in real time by superimposing low-frequency jitter signals to ensure modulation stability.

[0031] This module strictly implements the frequency division duplex strategy, isolates noise through frequency offset, and optimizes the signal waveform using a root-raised cosine filter.

[0032] Integrated receiver detection module (M2) This module is integrated with the transmitting module on the same photonic chip substrate and includes a 90-degree optical mixer, a balanced photodetector array, and a polarization beam rotator. Specifically: Polarization processing unit: integrates a polarization beam splitter rotator to achieve polarization diversity reception, decomposing the input light into orthogonal TE modes.

[0033] Optical mixing unit: A 90-degree optical mixer based on a multimode interferometer structure is used to ensure I / Q phase accuracy.

[0034] Balanced detection unit: Integrated germanium-silicon high-speed waveguide photodetector with a responsivity greater than 0.8 A / W and a common-mode rejection ratio greater than 30 dB, effectively suppressing local oscillator intensity noise.

[0035] This module is connected to the fiber optic link via an optical path coupling component and supports coherent heterodyne detection.

[0036] Digital processing module (M3) This module, implemented using an FPGA or ASIC, is configured to perform signal digitization, equalization processing, and secure key generation. It includes: Preprocessing logic unit: includes a high-speed ADC interface, a deserializer, and a time-domain equalizer to compensate for inter-symbol interference caused by bandwidth limitations.

[0037] Core algorithm logic unit: Hardware implementation of Gram-Schmidt orthogonalization, RRC filtering and Kalman filtering algorithms (RRC filter adopts polyphase decomposition architecture).

[0038] Secure post-processing logic unit: integrates an LDPC decoder (using the belief propagation algorithm) for error correction, a Toeplitz hash engine for security enhancement, and an HKDF accelerator for key derivation.

[0039] This module calculates the progressive security key rate and ultimately outputs the application key.

[0040] 3. Implementation Details Example 1: Experimental Validation of the Method In an experimental system with a center wavelength of 1550.12 nm, perform the above method steps: The transmitter uses a laser with a linewidth of less than 0.1 kHz, the arbitrary waveform generator has a sampling rate of 5 GSa / s, and a roll-off factor β=0.3.

[0041] Frequency division duplex configuration: frequency offset Δf = 0.5 GHz, signal bandwidth 500 MHz, guard band 10 MHz.

[0042] The receiver local oscillator power is 14.5 dBm, the system detection efficiency is 0.37, and the electronic noise is 0.35 SNU.

[0043] Digital processing employs Kalman filtering and RRC matched filtering, with key generation parameters such as β. recon =0.96, FER=0.2.

[0044] Experimental results show that scattering noise suppression of more than 20 dB is achieved, verifying the feasibility of the method.

[0045] Example 2: System Deployment Scheme The system is deployed in a metropolitan area ring network, with multiple nodes connected end-to-end via a single optical fiber to form a ring network. Each node integrates the aforementioned modules and supports full-duplex communication. The passive thermal stability of the silicon photonics chip reduces phase drift by an order of magnitude, reducing the burden of active compensation. The network topology is reconfigurable, making it suitable for high-density metropolitan area access scenarios.

[0046] 4. Summary of Beneficial Effects This invention combines a single transceiver chip with frequency division duplex technology to improve fiber optic resource utilization, reduce costs, and enhance crosstalk resistance. Specifically: The innovative architecture supports ring network topologies, eliminating the need for dual fiber optic connections.

[0047] Frequency division duplexing and digital filtering techniques suppress Rayleigh scattering noise to 20 dB below the shot noise floor.

[0048] High integration improves phase stability and reduces power consumption.

[0049] The above embodiments illustrate specific implementations of the present invention, but those skilled in the art can make modifications without departing from the inventive concept. For example, laser parameters or filter coefficients can be adjusted according to actual applications. These variations all fall within the protection scope of the present invention.

Claims

1. A bidirectional continuous-variable quantum key distribution method based on frequency division duplex in a single-transceiver ring network, characterized in that, The method includes: Step S1: The transmitting end executes the frequency division duplex strategy to generate a baseband signal containing quantum signals and pilot signals, and generates an optical signal by modulation and transmission; Step S2: The receiver uses a laser source integrated on the same chip as the transmitter as a local oscillator to perform coherent heterodyne detection on the received optical signal to obtain an electrical signal containing beat frequency signal and noise. Step S3: Perform digital signal processing on the electrical signal to recover the quantum signal and calculate the security key rate, and finally generate a shared key.

2. The method according to claim 1, characterized in that, In step S1, generating the baseband signal includes: A random number sequence for modulating quantum signals is generated using a quantum random number generator; The quantum signal is linearly superimposed with a single-frequency continuous waveguide signal; A root-raised cosine filter is used to pulse shape the superimposed signals.

3. The method according to claim 1 or 2, characterized in that, In step S1, executing the frequency division duplex strategy includes: Different optical carrier frequencies are assigned to the forward and reverse transmission links, and the frequency offset Δf between them satisfies: Among them, B signal For the quantum signal bandwidth, B RB B is the effective bandwidth of Rayleigh backscattered noise. guard To protect bandwidth.

4. The method according to claim 3, characterized in that, The protection bandwidth B guard Based on the system hardware parameters, the calculation formula is as follows: B guard = 2·d drift + B trans Where, δ drift B represents the maximum frequency shift of the laser within its operating temperature range. trans This represents the transition band width of the digital root-raised cosine filter.

5. The method according to claim 1, characterized in that, In step S2, the photocurrent signal i(t) output by the coherent heterodyne detector is expressed as: Among them, f IF For intermediate frequency, i RB (t) represents Rayleigh backscattering noise, i shot θ(t) represents shot noise, and θ(t) represents the phase difference between the signal and the local oscillator.

6. The method according to claim 1, characterized in that, Step S3 includes: Step S3.1: Perform orthogonalization correction on the received signal to compensate for the gain imbalance and phase non-orthogonality error of the receiver I / Q branch; Step S3.2: Perform phase recovery and matched filtering to suppress noise and optimize the signal-to-noise ratio; Step S3.3: Based on the processed signal, perform parameter estimation and secure key rate calculation, and generate the final key through error correction and confidentiality enhancement.

7. The method according to claim 6, characterized in that, In step S3.1, the Gram-Schmidt orthogonalization algorithm is used to construct the correction matrix R. GS The received vector is corrected, and the matrix is: Where, φ err denoted as phase non-orthogonality error, and g is the gain imbalance factor.

8. The method according to claim 6, characterized in that, In step S3.2, a Kalman filter is used for phase estimation and recovery, and a digital root-raised cosine filter is applied as a matched filter, whose frequency domain response H RRC (f) is: Where β is the roll-off factor, T s The symbol period.

9. A bidirectional continuous-variable quantum key distribution system based on frequency division duplex in a single transceiver ring network, used to implement the method of any one of claims 1 to 8, characterized in that, The system includes: An integrated transmission module, which is equipped with a laser, an IQ modulator and an automatic bias control circuit, is used to generate and transmit optical signals modulated by frequency division duplex; An integrated receiving and detection module is integrated on the same photonic chip as the integrated transmitting module. It is equipped with an optical mixer and a balanced photodetector for coherent heterodyne detection of the received signal. The digital processing and control module is used to digitize the detected electrical signals, perform digital signal processing, and generate security keys.

10. The system according to claim 9, characterized in that, The integrated transmitter module and the integrated receiver and detector module are monolithically integrated on a silicon-on-insulator substrate to form a single transceiver chip; multiple nodes containing the single transceiver chip are connected end to end through a single optical fiber to form a ring quantum key distribution network.

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