Parallel quantum key distribution system and method based on integrated optical frequency comb on chip

Abstract

The present application relates to quantum key distribution, in particular to a parallel quantum key distribution system and method based on an on-chip integrated optical frequency comb, an on-chip integrated optical frequency comb light source module, a plurality of frequency-locked coherent light carriers are generated by using a single pump light; a parallel quantum transmitter module, comprising a plurality of parallel transmitting units, each transmitting unit performs phase randomization, quantum state encoding and decoy state modulation on a coherent light carrier; a multiplexing module, which combines a plurality of quantum signals output by the parallel quantum transmitter module, and transmits the multiplexed signal through a quantum channel; a demultiplexing module, which receives the multiplexed signal from the quantum channel and restores it to a plurality of independent quantum signals; a parallel quantum receiver module, comprising a plurality of parallel receiving units, each receiving unit demodulates and single-photon detects a quantum signal; the present application can effectively overcome the defect that it is difficult to generate a plurality of coherent light carriers with inherent frequency locking and controllable phase by using a single light source.

Description

Technical Field

[0001] This invention relates to quantum key distribution, specifically to a quantum key distribution system and its implementation method that utilizes an on-chip integrated optical frequency comb light source to achieve multi-wavelength, high-density parallel encoding and transmission. Background Technology

[0002] Quantum key distribution (QKD) enables information-theoretically secure key distribution between two parties in a remote communication. To improve the secure key rate (SKR) of the system, wavelength division multiplexing (WDM) technology is widely used in QKD systems, allowing multiple independent quantum channels to be transmitted in parallel over a single optical fiber.

[0003] The closest existing technology is to use multiple independent distributed feedback (DFB) lasers or external cavity laser arrays as the carrier light source of the WDM-QKD system. Each laser generates an optical carrier of a specific wavelength, which is then combined into a quantum channel after independent intensity and phase modulation.

[0004] The fundamental defects of the existing technology include:

[0005] 1) Complex frequency management and synchronization: Each laser is an independent oscillation source, and its output frequency is determined by the physical parameters of its own laser cavity (such as cavity length, refractive index, etc.). In order to accurately align and lock the frequencies of dozens or even hundreds of lasers onto the ITU-T standard wavelength grid (such as 100GHz or 50GHz interval), it is necessary to configure an independent temperature control and current feedback frequency locking circuit for each laser. This results in the system complexity, power consumption and cost increasing linearly with the number of channels, and debugging and maintenance are extremely difficult.

[0006] 2) Inherent relative frequency and phase noise: There is an unavoidable relative frequency drift and phase noise between multiple independent light sources, which will introduce inter-channel crosstalk, worsen the quantum bit error rate (QBER), and reduce the long-term stability of the system, posing a serious threat to the stable operation of the QKD system.

[0007] 3) Integration bottleneck: It is difficult to achieve high-density monolithic integration of multiple lasers and their supporting driving and temperature control circuits on the same photonic chip, which seriously limits the miniaturization, low power consumption and large-scale manufacturing of QKD terminal equipment.

[0008] Therefore, there is an urgent need in this field for a novel integrated light source solution that can provide multiple inherently frequency-locked and phase-controllable coherent optical carriers from a physical mechanism perspective, in order to completely transform the architecture of WDM-QKD systems. Summary of the Invention

[0009] (a) Technical problems to be solved

[0010] In view of the above-mentioned shortcomings of the existing technology, the present invention provides a parallel quantum key distribution system and method based on on-chip integrated optical frequency comb, which can effectively overcome the shortcomings of the existing technology that make it difficult to generate multiple inherently frequency-locked and phase-controllable coherent optical carriers using a single light source.

[0011] (II) Technical Solution

[0012] To achieve the above objectives, the present invention provides the following technical solution:

[0013] A parallel quantum key distribution system based on an on-chip integrated optical frequency comb includes a transmitter, a quantum channel, and a receiver. The transmitter includes an on-chip integrated optical frequency comb light source module, a parallel quantum transmitter module, and a multiplexing module. The receiver includes a demultiplexing module and a parallel quantum receiver module.

[0014] An on-chip integrated optical frequency comb light source module is used to generate multiple frequency-locked coherent optical carriers using a single pump light;

[0015] The parallel quantum transmitter module contains multiple parallel transmitter units, each of which performs phase randomization, quantum state encoding, and decoy state modulation on one coherent optical carrier.

[0016] The multiplexing module combines the multiple quantum signals output by the parallel quantum transmitter module and transmits the multiplexed signals through a quantum channel.

[0017] The demultiplexing module receives the multiplexed signal from the quantum channel and restores it to multiple independent quantum signals;

[0018] The parallel quantum receiver module contains multiple parallel receiving units. Each receiving unit demodulates and detects a single photon from one quantum signal to generate multiple parallel keys.

[0019] Preferably, the on-chip integrated optical frequency comb light source module includes a single pump laser, a pump laser frequency locking module, a high-quality on-chip optical microcavity resonator, and a thermal management unit;

[0020] Pump laser frequency locking module stabilizes the output frequency of the pump laser;

[0021] An on-chip optical microcavity resonator couples a pump laser into the microcavity. Under the condition that the phase matching condition is met and the pump power is sufficient, the third-order nonlinear Kerr effect in the cavity reaches a dynamic balance with the cavity loss and the pump energy injection, thereby generating a dissipative Kerr soliton state DKS.

[0022] Thermal management unit is used to stabilize the operating point of the microcavity.

[0023] Preferably, the dissipative Kerr soliton state DKS exhibits in the time domain as a stable ultrashort optical pulse circulating within the microcavity;

[0024] The dissipative Kerr soliton state DKS corresponds in the frequency domain to a series of coherent laser spectral lines with equal frequency spacing, i.e., an optical frequency comb, where the frequency f of the Nth comb tooth is... N Determined by the following formula:

[0025] ;

[0026] Among them, f pump The pump laser frequency is denoted by FSR, which represents the free frequency range of the microcavity and indicates the fixed frequency interval between two adjacent comb teeth. It is a core parameter of the optical frequency comb. The free spectrum range (FSR) of a microcavity is determined by the effective refractive index (n) of the microcavity. eff The cavity length L is uniquely determined, and c is the speed of light in a vacuum;

[0027] Therefore, the entire frequency system of the optical frequency comb is determined solely by the pump laser frequency f. pump It is locked together with the physical structure of the microcavity.

[0028] Preferably, each transmission unit in the parallel quantum transmitter module includes a phase randomization unit and a subsequent encoding unit;

[0029] The phase randomization unit applies a phase randomization function to each optical pulse. A random phase is uniformly distributed within the range to disrupt the initial phase correlation between coherent optical carriers of different comb teeth, ensuring the independence and security of quantum states within each parallel processing channel;

[0030] The subsequent encoding unit sends the phase-randomized light pulses into the encoder for phase encoding, and completes the decoy state intensity modulation and attenuation to the single-photon level.

[0031] Preferably, each receiving unit in the parallel quantum receiver module includes a decoder corresponding to the encoder and a single-photon detector to complete basis selection and single-photon detection.

[0032] The parallel quantum key distribution method based on on-chip integrated optical frequency comb includes the following steps:

[0033] S1. Multiple frequency-locked coherent optical carriers are generated using a single pump light and allocated to different parallel processing channels;

[0034] S2. Within each channel, the coherent optical carrier is subjected to independent phase randomization, quantum state encoding, and decoy state modulation;

[0035] S3. Combine multiple quantum signals and transmit the multiplexed signals through a quantum channel;

[0036] S4. Demultiplex the received multiplexed signal to each parallel processing channel and perform independent demodulation and single-photon detection to generate a multi-channel parallel key.

[0037] (III) Beneficial Effects

[0038] Compared with the prior art, the parallel quantum key distribution system and method based on on-chip integrated optical frequency comb provided by the present invention has the following advantages:

[0039] 1) Fundamental simplification and cost reduction in system architecture: The entire laser array and its bulky frequency locking control circuit are replaced by a single "pump laser + integrated microcavity", which greatly reduces the hardware complexity, power consumption and manufacturing cost of the system;

[0040] 2) Excellent frequency stability: based on The optical frequency comb physical principle ensures that the frequencies of all coherent optical carriers are inherently locked, eliminating the relative drift between multiple independent light sources, greatly improving the long-term stability and reliability of the system, and significantly reducing channel crosstalk.

[0041] 3) Enables high integration: The light source itself is an on-chip device, compatible with mature AWG (multiplexing / demultiplexing), modulator, detector and other processes on silicon photonics and other platforms, making it possible to achieve fully integrated "QKD-on-a-chip" and accelerating the miniaturization and large-scale manufacturing of terminal devices.

[0042] 4) Supports ultra-high key generation rate: One optical frequency comb can provide hundreds of available coherent optical carriers covering the C+L band, providing a physical layer basis for achieving a total key generation rate of Tbps through large-scale wavelength parallelism, which is a key path to break through the current bottleneck of key generation rate.

[0043] 5) Solved new problems introduced by the new light source: The innovative "phase randomization" processing scheme specifically eliminates the quantum state correlation risk brought about by the integrated optical frequency comb when used for multi-channel QKD, ensuring the security of the parallel system. It is a necessary link for the safe implementation of this invention. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 This is a schematic diagram illustrating the working principle of the present invention;

[0046] Figure 2 The spectrum of the optical frequency comb generated by the on-chip integrated optical frequency comb light source module in this invention;

[0047] Figure 3 This is a system performance diagram of a single transmit-receive combination TR1 operating independently on channel 1 in this invention;

[0048] Figure 4 This is a system performance diagram of a single pair of transmit / receive combinations TR2 operating independently on channel 5 in this invention;

[0049] Figure 5 This is a system performance diagram of the two pairs of transmit-receive combinations TR1 and TR2 operating simultaneously on channels 1 and 2, respectively, in this invention;

[0050] Figure 6 This is a system performance diagram of the two pairs of transmit-receive combinations TR1 and TR2 operating simultaneously on channels 1 and 3, respectively, in this invention;

[0051] Figure 7 This is a system performance diagram of the two pairs of transmit / receive combinations TR1 and TR2 operating simultaneously on channels 1 and 4, respectively, in this invention. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0053] The core of this invention lies in the fact that the on-chip integrated optical frequency comb is used as a multi-carrier generator and is systematically applied to the QKD system for the first time. In view of the characteristics of the multi-coherent optical carriers generated by it, necessary phase randomization processing is introduced to construct a complete and high-density parallel QKD physical layer solution.

[0054] The following describes the specific functional modules and technical effects of the parallel quantum key distribution system based on an on-chip integrated optical frequency comb provided by this invention, using concrete examples. The system functional modules include: a transmitter, a quantum channel, and a receiver. The transmitter includes an on-chip integrated optical frequency comb light source module, a parallel quantum transmitter module, and a multiplexing module. The receiver includes a demultiplexing module and a parallel quantum receiver module.

[0055] An on-chip integrated optical frequency comb light source module is used to generate multiple frequency-locked coherent optical carriers using a single pump light;

[0056] The parallel quantum transmitter module contains multiple parallel transmitter units, each of which performs phase randomization, quantum state encoding, and decoy state modulation on one coherent optical carrier.

[0057] The multiplexing module combines the multiple quantum signals output from the parallel quantum transmitter module and transmits the multiplexed signals through a quantum channel (standard single-mode fiber).

[0058] The demultiplexing module receives the multiplexed signal from the quantum channel and restores it to multiple independent quantum signals;

[0059] The parallel quantum receiver module contains multiple parallel receiving units. Each receiving unit demodulates and detects a single photon from one quantum signal to generate multiple parallel keys.

[0060] I. On-chip integrated optical frequency comb light source module

[0061] The on-chip integrated optical frequency comb light source module includes a single pump laser, a pump laser frequency locking module, a high-quality on-chip optical microcavity resonator (such as a microring, microdisk, etc.) and a thermal management unit (such as a thermoelectric cooler TEC, etc.).

[0062] The pump laser frequency locking module locks the output frequency of the pump laser to the microcavity resonant frequency or an external reference frequency.

[0063] An on-chip optical microcavity resonator couples a pump laser into the microcavity. Under the condition that the phase matching condition is met (usually requiring the microcavity to have anomalous dispersion at the pump wavelength) and the pump power is sufficient, the third-order nonlinear Kerr effect in the cavity reaches a dynamic balance with the cavity loss and the pump energy injection, thereby generating a dissipative Kerr soliton state DKS.

[0064] Thermal management unit is used to stabilize the operating point of the microcavity.

[0065] Specifically, the dissipative Kerr soliton state DKS behaves in the time domain as a stable ultrashort optical pulse circulating within the microcavity;

[0066] Dissipative Kerr soliton states (DKS) correspond in the frequency domain to a series of coherent laser spectral lines with equal frequency spacing, i.e., an optical frequency comb (such as...). Figure 2 As shown in the figure, the generated optical frequency comb has a spectrum as wide as 3.2 THz and uniform frequency spacing, with the frequency f of its Nth comb tooth. N Determined by the following formula:

[0067] ;

[0068] Among them, f pump The pump laser frequency is denoted by FSR, which represents the free frequency range of the microcavity and indicates the fixed frequency interval between two adjacent comb teeth. It is a core parameter of the optical frequency comb. The free spectrum range (FSR) of a microcavity is determined by the effective refractive index (n) of the microcavity. eff The cavity length L is uniquely determined, and c is the speed of light in a vacuum;

[0069] Therefore, the entire frequency system of the optical frequency comb is determined solely by the pump laser frequency f. pump Locked together with the physical structure of the microcavity, this means that by simply stabilizing the pump laser and the microcavity environment (such as through a thermoelectric cooler TEC), hundreds or thousands of carrier frequencies can be stabilized simultaneously, completely solving the frequency synchronization problem of multiple laser arrays.

[0070] II. Parallel Quantum Transmitter Module

[0071] Each transmitter unit in the parallel quantum transmitter module includes a phase randomization unit and a subsequent encoding unit;

[0072] The phase randomization unit is used to destroy the initial phase correlation between coherent optical carriers of different comb teeth. In this embodiment, the phase randomization unit adopts an electro-optic phase modulator (such as a lithium niobate phase modulator). Its driving signal is generated by a high-speed arbitrary waveform generator or an FPGA with a digital-to-analog converter. The driving signal provides a random phase value uniformly distributed in the range [0, 2π) for each optical pulse. The random number sequence can be a pseudo-random sequence generated by the linear feedback shift register (LFSR) in the FPGA, or generated by a true random number generator (such as a quantum random number generator or a thermal noise source). The bandwidth of the electro-optic phase modulator is not less than the optical pulse repetition frequency, and the driving signal is synchronized with the optical pulse to ensure that each optical pulse is independently loaded with a random phase. In this way, the inherent phase correlation between the comb teeth of the optical frequency comb caused by the nonlinear process is completely eliminated, and the quantum states of each parallel processing channel are independent of each other in terms of security.

[0073] The subsequent encoding unit sends the phase-randomized light pulses into the encoder (using an encoder based on a Faraday-Sagnak-Michelson interferometer FSMI structure) to perform phase encoding and complete the decoy state intensity modulation and attenuation to the single-photon level.

[0074] In the above technical solution, phase randomization is a key step designed by this invention to solve the new problems introduced by the characteristics of optical frequency combs. Since all the comb teeth of an optical frequency comb originate from the same nonlinear process, there is an inherent phase correlation between them. If this correlation is not processed, it may introduce undesirable correlations between the quantum states of different channels, affecting security or increasing bit errors.

[0075] III. Reuse Module / De-reuse Module

[0076] It is achieved using integrated optical devices such as arrayed waveguide gratings (AWG) or cascaded microring resonators.

[0077] IV. Parallel Quantum Receiver Module

[0078] Each receiving unit in the parallel quantum receiver module includes a decoder corresponding to the encoder, as well as a single-photon detector, to complete basis selection and single-photon detection.

[0079] Based on the aforementioned parallel quantum key distribution system based on an on-chip integrated optical frequency comb, this invention also discloses a parallel quantum key distribution method based on an on-chip integrated optical frequency comb, such as... Figure 1 As shown, it includes the following steps:

[0080] S1. Multiple frequency-locked coherent optical carriers are generated using a single pump light and allocated to different parallel processing channels;

[0081] S2. Within each channel, the coherent optical carrier is subjected to independent phase randomization, quantum state encoding, and decoy state modulation;

[0082] S3. Combine multiple quantum signals and transmit the multiplexed signals through a quantum channel;

[0083] S4. Demultiplex the received multiplexed signal to each parallel processing channel and perform independent demodulation and single-photon detection to generate a multi-channel parallel key.

[0084] To better illustrate the technical solution of this application, a detailed explanation is provided below in conjunction with an experiment.

[0085] Experiment 1: Performance Verification of a Dual-Channel QKD System Based on a Doped Silica Glass Microring DKS Light Source

[0086] • Experimental objective:

[0087] This experiment aims to illustrate how to implement the present invention and to verify its core advantages.

[0088] •System Construction:

[0089] On-chip optical microcavity resonator: A microring resonator made of high-refractive-index doped silicon dioxide glass, with a microring radius of 592.1 μm, corresponding to a free spectrum range (FSR) of approximately 49 GHz and a quality factor (Q) of approximately 1.7 × 10⁻⁶. 6 The dissipative Kerr soliton state DKS is excited and maintained by an auxiliary laser thermal tuning method;

[0090] Carrier selection: Select two comb teeth spaced 100 GHz apart (conforming to standard DWDM grid) from the generated optical frequency comb and use them as the carriers of channel 1 (CH1) and channel 2 (CH2) respectively;

[0091] Transmit and receive modules: Both channels use the BB84 decoy protocol with a 1GHz clock. Each transmit unit contains a phase modulator (for phase randomization processing) and an FSMI encoder. Each receive unit uses a symmetrical FSMI decoder and a single-photon detector.

[0092] Quantum channel: 25km long standard single-mode fiber with a loss of 0.2dB / km.

[0093] •Experimental data and conclusions:

[0094] Frequency stability and crosstalk: During continuous operation of the system, the center wavelength drift of CH1 and CH2 was observed to be less than 0.01nm, which verified the "frequency locking" characteristic of the optical frequency comb. The crosstalk between adjacent channels (CH1 and CH2) was measured to be less than -20dB, proving that the present invention can effectively achieve channel isolation and meet the requirements of parallel QKD.

[0095] System performance: The two channels are independent (e.g., Figure 3 and Figure 4 As shown), parallel operation (such as...) Figures 5 to 7 As shown in the figure: RKR is the original key rate; SiKR is the key rate after screening; SKR is the secure key rate), the average quantum bit error rate (QBER) of the signal state (μ) is consistently below 3%, and the SKR of CH2 reaches 195.36 kbps.

[0096] •Key verification points:

[0097] The QBER and SKR of dual-channel parallel operation are not significantly different from those of single-channel independent operation (e.g.) Figures 3 to 7 As shown in the figure, this directly proves the effectiveness of "phase randomization", that is, it successfully eliminates the potential impact of the inherent phase correlation between the comb teeth of the optical frequency comb on the performance of the parallel QKD system.

[0098] The invention supports the operation of two complete QKD links using a single pump laser and a microring resonator, demonstrating its significant advantages in simplifying system architecture and reducing frequency management complexity.

[0099] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A parallel quantum key distribution system based on an on-chip integrated optical frequency comb, characterized in that: It includes a transmitter, a quantum channel, and a receiver. The transmitter includes an on-chip integrated optical frequency comb light source module, a parallel quantum transmitter module, and a multiplexing module. The receiver includes a demultiplexing module and a parallel quantum receiver module. An on-chip integrated optical frequency comb light source module is used to generate multiple frequency-locked coherent optical carriers using a single pump light; The parallel quantum transmitter module contains multiple parallel transmitter units, each of which performs phase randomization, quantum state encoding, and decoy state modulation on one coherent optical carrier. The multiplexing module combines the multiple quantum signals output by the parallel quantum transmitter module and transmits the multiplexed signals through a quantum channel. The demultiplexing module receives the multiplexed signal from the quantum channel and restores it to multiple independent quantum signals; The parallel quantum receiver module contains multiple parallel receiving units. Each receiving unit demodulates and detects a single photon from one quantum signal to generate multiple parallel keys.

2. The parallel quantum key distribution system based on on-chip integrated optical frequency comb according to claim 1, characterized in that: The on-chip integrated optical frequency comb light source module includes a single pump laser, a pump laser frequency locking module, a high-quality on-chip optical microcavity resonator, and a thermal management unit. Pump laser frequency locking module stabilizes the output frequency of the pump laser; An on-chip optical microcavity resonator couples a pump laser into the microcavity. Under the condition that the phase matching condition is met and the pump power is sufficient, the third-order nonlinear Kerr effect in the cavity reaches a dynamic balance with the cavity loss and the pump energy injection, thereby generating a dissipative Kerr soliton state DKS. Thermal management unit is used to stabilize the operating point of the microcavity.

3. The parallel quantum key distribution system based on on-chip integrated optical frequency comb according to claim 2, characterized in that: The dissipative Kerr soliton state DKS is characterized in the time domain as a stable ultrashort optical pulse circulating within the microcavity; The dissipative Kerr soliton state DKS corresponds in the frequency domain to a series of coherent laser spectral lines with equal frequency spacing, i.e., an optical frequency comb, where the frequency f of the Nth comb tooth is... N Determined by the following formula: ； Among them, f pump The pump laser frequency is denoted by FSR, which represents the free frequency range of the microcavity and indicates the fixed frequency interval between two adjacent comb teeth. It is a core parameter of the optical frequency comb. The free spectrum range (FSR) of a microcavity is determined by the effective refractive index (n) of the microcavity. eff The cavity length L is uniquely determined, and c is the speed of light in a vacuum; Therefore, the entire frequency system of the optical frequency comb is determined solely by the pump laser frequency f. pump It is locked together with the physical structure of the microcavity.

4. The parallel quantum key distribution system based on on-chip integrated optical frequency comb according to claim 3, characterized in that: Each transmitter unit in the parallel quantum transmitter module includes a phase randomization unit and a subsequent encoding unit; The phase randomization unit applies a phase randomization function to each optical pulse. A random phase is uniformly distributed within the range to disrupt the initial phase correlation between coherent optical carriers of different comb teeth, ensuring the independence and security of quantum states within each parallel processing channel; The subsequent encoding unit sends the phase-randomized light pulses into the encoder for phase encoding, and completes the decoy state intensity modulation and attenuation to the single-photon level.

5. The parallel quantum key distribution system based on on-chip integrated optical frequency comb according to claim 4, characterized in that: Each receiving unit in the parallel quantum receiver module includes a decoder corresponding to the encoder and a single-photon detector to complete basis selection and single-photon detection.

6. A parallel quantum key distribution method based on an on-chip integrated optical frequency comb, applicable to the parallel quantum key distribution system based on an on-chip integrated optical frequency comb as described in claim 1, characterized in that: Includes the following steps: S1. Multiple frequency-locked coherent optical carriers are generated using a single pump light and allocated to different parallel processing channels; S2. Within each channel, the coherent optical carrier is subjected to independent phase randomization, quantum state encoding, and decoy state modulation; S3. Combine multiple quantum signals and transmit the multiplexed signals through a quantum channel; S4. Demultiplex the received multiplexed signal to each parallel processing channel and perform independent demodulation and single-photon detection to generate a multi-channel parallel key.

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