Quantum-classical fusion access optical network based on qubit frame synchronization

Abstract

The present invention relates to a quantum-classical fusion access optical network based on quantum bit frame synchronization. It comprises: multiple users inserting a synchronization sequence with characteristic autocorrelation into a random data sequence, constructing a synchronization frame, and sending an uplink quantum signal through time division multiplexing. The quantum receiver uses the received quantum signal to obtain a precise clock, constructs a receiving frame in different user time slots, and performs screening and preprocessing; and then uses the cross-correlation characteristics of each user's synchronization sequence to determine the position of the user and synchronization signal corresponding to the time slot. The uplink quantum signal and the classical signal are coupled into the distribution optical fiber through a first wavelength division multiplexer and transmitted to a second wavelength division multiplexer, and coupled into the feeder optical fiber with the signals of other users. The present invention combines the classical access network with the quantum access network based on quantum bit frame synchronization, reducing the need for additional synchronization equipment in the fusion access network to adapt to the existing network communication infrastructure, while making network maintenance simpler.

Description

Technical Field

[0001] The present invention relates to the field of combining classical communication systems with quantum information technology, and in particular to a quantum-classical fusion access optical network based on quantum bit frame synchronization. Background Art

[0002] With the advent of the information age, internet technology has permeated every aspect of life, transforming how we live and work. Consequently, information security issues have become a focal point of social concern. To address this, quantum key distribution (QKD), a technology that combines quantum mechanics with cryptography, has emerged. Based on the fundamental principles of quantum mechanics, quantum communication technology can guarantee unconditional security during communication.

[0003] In recent decades, the field of quantum key distribution has developed rapidly and is moving towards practical application and networking. The quantum access network provides quantum secure communication for the optical network units of the classical passive access network (PON), and serves as a bridge between multiple terminal units and the quantum backbone network. However, the quantum-classical fusion access network is inevitably limited by optical fiber resources and hardware equipment. In particular, the normal operation of the QKD system is inseparable from the clock synchronization of the communication users. When QKD technology is integrated into the PON, the synchronization of the quantum access network is even more critical to the stable operation of the network. Existing quantum access network synchronization solutions include the use of additional synchronization light for synchronization, or using external clocks as a reference, such as the use of global navigation satellite systems, etc. These synchronization solutions usually require additional optical fiber resources and hardware equipment, which not only increases the complexity and cost of the network, but also affects the network stability and increases the difficulty of maintenance.

[0004] Therefore, building a low-cost and efficient quantum access network on top of a classical access network will significantly promote the development of quantum networks. We propose a quantum-classical fusion access optical network and system based on qubit-frame synchronization, ensuring that optical network units can perform quantum key distribution tasks even under conditions of limited fiber resources and low signal-to-noise ratio.

[0005] The information disclosed in the background technology section is only intended to enhance understanding of the overall background of the invention and should not be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the Invention

[0006] In response to the shortcomings of the existing technology, the present invention combines quantum communication technology with classical communication networks to provide a quantum-classical fusion access optical network based on quantum bit frame synchronization.

[0007] To achieve the above objectives, the present invention provides the following implementation scheme: the quantum transmission module of the optical network unit (ONU) is constructed with a distributed periodic insertion synchronization frame with autocorrelation characteristics, the classical transmission module sends an uplink signal, and the quantum signal of the ONU and the classical uplink signal are merged into the distribution optical fiber through the first wavelength division multiplexer and sent upstream; the signals of different ONUs arrive at the second wavelength division multiplexer for distribution, and are concentrated in the feeder optical fiber for common fiber transmission; they arrive at the quantum receiver and classical signal processor of the optical line terminal (OLT) in a time-sharing manner; the quantum receiver establishes synchronization between the ONUs and the OLT based on the received quantum signal

[0008] Furthermore, the quantum-classical fusion access network includes optical network units (ONUs), optical distribution networks (ODNs) and optical line terminals (OLTs). The ONUs include PON network classical signal modules and quantum transmission modules. The OLT includes PON network classical signal modules and quantum receiving modules. The ODN includes optical fibers and wavelength division multiplexers.

[0009] Furthermore, the ONUs quantum transmission modules each construct a synchronization frame, which consists of a synchronization sequence and a random sequence, wherein the synchronization sequence with characteristic autocorrelation marks different ONUs, and transmits quantum signals through time division multiplexing.

[0010] Furthermore, the quantum signal and classical uplink signal of the ONU are coupled into the distribution optical fiber through the first wavelength division multiplexer for common fiber transmission. The signals of different ONUs pass through the second wavelength division multiplexer and are coupled into the feeder optical fiber for common fiber transmission, and reach the quantum receiver and classical signal processor of the OLT in time division.

[0011] Furthermore, the quantum receiver in the quantum access network based on quantum bit frame synchronization establishes synchronization with the ONUs only through the received quantum signals.

[0012] Furthermore, the quantum receiver establishes synchronization between the ONUs and the OLT based on the received quantum signal, including the following steps:

[0013] Steps for obtaining a synchronized clock: Using the quantum signal received in the time domain, the synchronized clock is estimated by Fourier transform, and the accurate synchronized clock is obtained by repeatedly performing least squares fitting.

[0014] Extracting and identifying data from different ONUs: Based on the acquired synchronization clock, the quantum signal is divided into different time slots to extract the data from different ONUs. The quantum signal in the time slot is taken out to construct a receiving frame. The quantum signal in the frame is sequentially cross-correlated with the synchronization sequence of different ONU synchronization frames, and the data from different ONUs is identified through the correlation peak.

[0015] Determine the delay between different ONUs: By identifying different ONU data and determining the position and delay of the synchronization signal in the received frame, the synchronization between ONUs and OLT is established.

[0016] Beneficial effects of the present invention:

[0017] (1) The quantum access network based on quantum bit frame synchronization provided by the present invention does not require additional synchronization light and hardware equipment in the optical network unit, which saves optical fiber resources and reduces network costs. At the same time, there is no need to consider the impact of noise crosstalk caused by synchronization light on the stability of network operation.

[0018] (2) The ONUs in the quantum access network provided by the present invention each construct a synchronization frame. The synchronization sequence in the synchronization frame marks different ONUs. The quantum receiver receives the ONU quantum signals arriving at different time slots and identifies different ONUs through the synchronization sequence, thereby flexibly constructing the quantum access network and simplifying network maintenance.

[0019] (3) The present invention combines the quantum access network based on quantum bit frame synchronization with the classical optical network, which can expand the QKD technology at low cost based on the existing classical communication network and effectively promote the development of quantum networks. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the present invention together with the specification. Other features, purposes, and advantages of the present invention will become more apparent from the following detailed description of exemplary embodiments with reference to the accompanying drawings.

[0021] Figure 1 A schematic diagram of a quantum-classical fusion access optical network provided by the present invention is shown.

[0022] Figure 2 A schematic diagram showing the steps of a quantum access network based on quantum bit frame synchronization provided by the present invention is shown.

[0023] Figure 3 A schematic diagram showing the synchronization frame structure provided by the present invention, identifying different ONUs and completing synchronization steps. DETAILED DESCRIPTION

[0024] To more clearly describe the technical solutions and beneficial effects of the present invention, specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, but it should be understood that the scope of protection of the present invention is not limited by the specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can be made without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0025] Reference Figure 1 , Figure 2 and Figure 3 The embodiment of the quantum-classical fusion access optical network provided by the present invention includes optical network units (ONUs), an optical distribution network (ODN), and an optical line terminal (OLT). The ONUs include a PON network classical signal module and a quantum transmission module, the OLT includes a PON network classical signal module and a quantum receiving module, and the ODN includes an optical fiber and a wavelength division multiplexer. The ONUs are connected to the OLT via the ODN. In this embodiment, the process of establishing synchronization between the quantum access network OLT and the ONUs based on quantum bit frame synchronization includes the following steps:

[0026] ONU constructs synchronization frame steps:

[0027] a1: The ONUs quantum transmission module constructs a synchronization sequence with autocorrelation characteristics, including 1 and -1, in the form of a step function, with adjustable maximum correlation peak and small peak contrast.

[0028] a2: The ONUs quantum random number generator constructs a quantum random data sequence.

[0029] a3: The ONUq quantum sending module inserts the synchronization sequence into the random sequence in a dispersed manner, constructing a structure such as [s q,1 ,s q,d(1) ,...,s q,d(i) ,s q,2 ,s q,d(i+1) ,...,s q,L ,s q,d((L-1)i+1) ,...,s q,d(Li) ] synchronization frame, where s q,n ,n∈[1,2,3,...,L] represents the synchronization sequence, s q,d(*) represents a random sequence, ONUq represents user q, q∈[1,2,3,...,n], and n is the total number of network users.

[0030] a4: The classic signal module constructs the uplink signal.

[0031] a5: The ONUs transmit quantum signals containing a synchronous frame structure and PON classical signals at different wavelengths. The quantum signals are transmitted in the C-band, the upstream signals in the O-band, and the downstream signals in the S-band. The first wavelength division multiplexer couples the ONU quantum signals and classical upstream signals into the distribution fiber, where they are transmitted upstream using time-division multiplexing (TDM) over the shared fiber.

[0032] ODN signal transmission steps:

[0033] b1: Different ONU signals and OLT downstream signals reach the optical distribution node. The second wavelength division multiplexer is used to distribute the downstream signal from the OLT to each user's distribution fiber. The quantum signals and upstream signals of the ONUs are concentrated and transmitted on the feeder fiber for co-fiber transmission. They reach the quantum receiver and classical signal processor of the OLT in a time-sharing manner.

[0034] The OLT processes the signal to complete the synchronization steps:

[0035] c1: The third wavelength division multiplexer at the end of the feeder separates the quantum and classical signals. The OLT quantum receiving module and classical signal module process the received quantum and classical signals respectively.

[0036] c2: Obtaining the synchronous clock: The OLT quantum receiving module uses the quantum signal received in the time domain to perform a fast Fourier transform to estimate the synchronous clock, and then repeatedly performs the least squares fitting to obtain the accurate synchronous clock.

[0037] c3: The OLT quantum receiving module performs overall noise filtering on the received signal. Based on the accurately synchronized clock, it divides the quantum signal into different time slots according to the arrival time. The data is then fitted. The fitting results indicate that the independent, near-linear data lines near the fitting line belong to different users, and the data for each user is extracted.

[0038] c4: The OLT quantum receiving module constructs a receiving frame with each extracted quantum signal belonging to a different user. It then performs cross-correlation operations on the quantum signal within the frame with the synchronization sequences of different ONU synchronization frames, and identifies the data of different ONUs through correlation peaks.

[0039] c7: The OLT quantum receiving module determines the position and delay of the synchronization signal within the received frame by identifying the data of different ONUs until the maximum correlation peak is observed, thereby establishing the synchronization between the ONUs and the OLT.

[0040] The quantum-classical fusion access network proposed in this paper combines a PON network with a quantum access network. Building on existing communication components, it places lasers in optical network units (ONUs) and quantum receivers in optical line terminals (OLTs). Wavelength division multiplexing (WDMs) are then used to integrate and distribute signals from different users. This system can adapt to existing network communication infrastructure, significantly expand the number of users of quantum key distribution systems, improve the system's practicality, and accelerate the construction of a global quantum information network.

[0041] The present invention provides a quantum-classical fusion access optical network system based on a qubit-frame synchronization method. By constructing synchronization frames with characteristic autocorrelation and utilizing algorithms such as fast Fourier transforms and optimized cross-correlation, user data can be extracted, user identification can be achieved, and system synchronization can be rapidly achieved. This method eliminates the need for additional hardware in the network, conserving device resources and simplifying the network. Furthermore, it eliminates the need for synchronization light and eliminates concerns about crosstalk caused by strong synchronization light, thus conserving fiber resources.

[0042] Those skilled in the art will appreciate that, in addition to implementing the system and its various devices, modules, and units provided by the present invention in purely computer-readable program code, it is entirely possible to implement the same functions of the system and its various devices, modules, and units provided by the present invention in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered structures within the hardware component; the devices, modules, and units used to implement various functions can also be considered as both software modules implementing the method and structures within the hardware component.

[0043] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

Claims

1. A quantum-classical fusion access optical network based on qubit frame synchronization, characterized in that: The quantum transmission module of the optical network unit (ONU) constructs a distributed, periodically inserted synchronization frame with autocorrelation characteristics. The classical transmission module sends an upstream signal. The ONU's quantum signal and the classical upstream signal are merged into the distribution fiber through the first wavelength division multiplexer and sent upstream. The signals from different ONUs arrive at the second wavelength division multiplexer for distribution, concentrated on the common fiber transmission in the feeder fiber, and reach the quantum receiver and classical signal processor of the optical line terminal (OLT) in a time-sharing manner. The quantum receiver establishes synchronization between the ONUs and the OLT based on the received quantum signal, including the following steps: using Fourier transform to estimate the synchronization clock of the quantum signal received in the time domain, and repeatedly performing least squares fitting to obtain an accurate synchronization clock; based on the obtained synchronization clock, the quantum signal is divided and transmitted to different time slots, and the quantum signals of different ONUs are extracted to construct a receive frame. The quantum signal in the frame is sequentially cross-correlated with the synchronization sequence of the synchronization frames of different ONUs, and the data of different ONUs is identified by correlation peaks; and the position and delay of the synchronization signal within the receive frame of different ONUs are determined.

2. The quantum-classical fusion access optical network based on qubit frame synchronization according to claim 1, characterized in that: The ONUs quantum transmission modules each construct a synchronization frame, which consists of a synchronization sequence and a random sequence. The synchronization sequence with characteristic autocorrelation marks different ONUs and sends quantum signals through time division multiplexing.

3. The quantum-classical fusion access optical network based on qubit frame synchronization according to claim 1, characterized in that: The quantum signal and classical uplink signal of the ONU are coupled into the distribution optical fiber through the first wavelength division multiplexer for common fiber transmission. The signals of different ONUs pass through the second wavelength division multiplexer, are coupled into the feeder optical fiber for common fiber transmission, and reach the quantum receiver and classical signal processor of the OLT in a time-sharing manner.

4. The quantum-classical fusion access optical network based on qubit frame synchronization according to claim 1, characterized in that: The quantum receiver in the quantum access network based on quantum bit frame synchronization establishes synchronization with the ONUs only through the received quantum signals.

5. The quantum-classical fusion access optical network based on qubit frame synchronization according to claim 1, characterized in that: The quantum receiver establishes synchronization between the ONUs and the OLT based on the received quantum signal, which also includes the following steps: Determine the delay of different ONUs: By identifying the data of different ONUs, the position and delay of the synchronization signal in the received frame are determined; the quantum receiver establishes synchronization between the ONUs and the OLT based on the received quantum signal.

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