Metropolitan area-access all-optical convergence network system based on digital subcarrier multiplexing technology

Abstract

The invention relates to the technical field of optical networks, and provides a metropolitan area-access all-optical convergence network system based on a digital subcarrier multiplexing technology. The system comprises a digital subcarrier-based continuous signal generation module in a metropolitan area node, a digital subcarrier-based burst signal generation module in an access network optical network unit, and a digital subcarrier beam splitting / combining module in a metropolitan area-access all-optical fusion node, the digital subcarrier-based west / east continuous signal receiving and processing module is arranged in the metropolitan area node; and the burst signal receiving and processing module is arranged in the access network optical network unit. All-optical fusion is achieved in a metropolitan area network and an access network system through the digital subcarrier multiplexing technology, delay and jitter caused by optical-electric-optical conversion can be effectively avoided, and precious wavelength resources are saved. In addition, different subcarriers are endowed with different functions, so that not only is bidirectional high-speed transmission realized, but also the flexibility of the network architecture is greatly improved.

Description

Technical Field

[0001] The present application relates to the field of communication network technology, and in particular to an optical network system supporting high-speed bidirectional transmission and all-optical fusion. Background Art

[0002] With the rapid development of optical fiber communication technology, the integration of metropolitan area networks and access networks has become an important trend in optical network construction. Traditional optical network systems mostly rely on optical-electrical-optical (OEO) conversion to achieve signal processing. Although it can meet the needs of network transmission to a certain extent, this architecture exposes a series of problems in large-scale, high-speed application scenarios.

[0003] First, the signal delay and jitter caused by optical-electrical-optical conversion have become a major bottleneck restricting system performance. Since optical signals need to be converted into electrical signals for processing, this process not only increases network latency, but may also introduce signal jitter, affecting transmission stability. For large-scale network systems that require real-time response, this delay and jitter inevitably lead to a decline in network performance.

[0004] Secondly, the shortage of wavelength resources is also one of the main problems facing the current optical network system. Existing optical networks mostly use wavelength routing for signal transmission and distribution. However, with the expansion of network scale and the increase of user bandwidth demand, the limited wavelength resources lead to low spectrum utilization, which further restricts the expansion and performance improvement of the network.

[0005] In addition, the lack of flexibility in network architecture is also a major challenge in existing technologies. Traditional optical network architectures often lack sufficient flexibility to cope with different application scenarios or business needs, and cannot quickly adjust the network according to actual conditions. This architecture is very rigid and difficult to adapt to the dynamic changes in the future network environment.

[0006] Finally, high operation and maintenance costs are also a major problem for traditional optical network systems. The widespread use of optical-electrical-optical conversion equipment not only increases the number of devices, leading to increased power consumption and floor space, but also increases the operation and maintenance costs of the network, limiting the economic feasibility of the optical network system.

[0007] In summary, the existing metropolitan area network and access network integration technology has obvious deficiencies in terms of latency, resource utilization, flexibility and cost, and an optical network architecture that can efficiently solve these problems is urgently needed. Summary of the invention

[0008] The purpose of the present application is to provide a metropolitan area-access all-optical fusion network system based on digital subcarrier multiplexing technology to solve the problems raised in the above background technology.

[0009] Specifically, the present application aims to provide a metropolitan area-access all-optical fusion network system based on digital subcarrier multiplexing technology to solve the problems in the above-mentioned background technology. Compared with the existing metropolitan area-access fusion network that relies on optical-electrical-optical conversion and the all-optical fusion network based on wavelength routing, the present application realizes the fine segmentation of spectrum resources through digital subcarrier multiplexing technology, and then constructs a flexible subcarrier-based all-optical routing system, ultimately realizing the efficient integration of metropolitan area network and access network, and supporting high-speed bidirectional transmission under this architecture.

[0010] In the solution of the present application, the metropolitan area network adopts a ring network topology, and the signal is transmitted bidirectionally in the east-west dual-channel optical fiber; multiple metropolitan nodes are distributed on the ring, and it also includes a core-metropolitan node connected to the core network and a metropolitan-access all-optical fusion node connected to the access network. The access network adopts a tree topology, and the uplink signal and the downlink signal are transmitted bidirectionally through a single optical fiber; the optical splitter, the optical network unit and the optical fiber connecting the two together constitute the passive optical network in the access network. The optical splitter splits the downlink signal from the fusion node to each optical network unit, and combines the uplink signal from each optical network unit.

[0011] The present application provides an optical network system that supports the full optical integration of metropolitan area networks and access networks through digital subcarrier multiplexing technology, specifically including downlinks and uplinks, which can improve the flexibility and resource utilization of network architecture while achieving efficient transmission.

[0012] The present application discloses a metropolitan area-access all-optical fusion network system based on digital subcarrier multiplexing technology, comprising:

[0013] The metropolitan area network part has a ring-shaped network topology, and the signal is transmitted bidirectionally in the east and west directions in two optical fibers. The metropolitan area network part includes multiple metropolitan area nodes, core-metropolitan area nodes, and metropolitan area-access all-optical fusion nodes;

[0014] The access network part has a tree-like network topology, and the uplink signal and the downlink signal are bidirectionally transmitted in a single optical fiber. The access network part includes an optical splitter and multiple optical network units;

[0015] The metropolitan area node includes: a westbound signal transmission module and an eastbound signal transmission module, both for transmitting continuous signals based on digital subcarrier multiplexing; a westbound signal receiving and processing module and an eastbound signal receiving and processing module, both for receiving and processing signals based on digital subcarrier multiplexing in corresponding directions; and,

[0016] The optical network unit includes: a downlink signal receiving and processing module, used to receive and process downlink signals based on digital subcarrier multiplexing from the access network; an uplink signal transmitting module, used to transmit uplink burst signals based on digital subcarrier multiplexing; and,

[0017] The metropolitan area-access all-optical fusion node includes: a westbound transmission module, which is used to split the westbound signal into two beams, one beam continues to be transmitted in the metropolitan area network, and the other beam is transmitted to the access network; an eastbound transmission module, which is used to perform all-optical beam combination of the eastbound signal in the metropolitan area network and the uplink signal in the access network, and continue to transmit them in the metropolitan area network;

[0018] Among them, through the digital subcarrier multiplexing technology, different digital subcarriers on the same carrier carry metropolitan area network signals and access network signals respectively, realizing the full optical integration of metropolitan area network and access network, avoiding optical-electrical-optical conversion;

[0019] The westbound signal receiving and processing module, the eastbound signal receiving and processing module and the downlink signal receiving and processing module all adopt coherent receiving technology to selectively detect specific digital subcarriers by adjusting the local oscillator light frequency.

[0020] In a preferred example, the westbound signal transmission module and the eastbound signal transmission module in the metropolitan area node specifically include:

[0021] A continuous subcarrier signal generating module, used for generating a continuous signal including a plurality of digital subcarriers;

[0022] A subcarrier dispersion precompensation module is used to precompensate the dispersion of each subcarrier according to its transmission distance to reduce the influence of dispersion on the signal;

[0023] A subcarrier power adjustment module, used to adjust the transmission power of each subcarrier signal to optimize its performance in the transmission channel;

[0024] The subcarrier up-conversion and coupling module is used to up-convert the generated subcarrier signals to different frequency bands and couple the subcarrier signals for transmission.

[0025] In a preferred example, the workflow of the continuous subcarrier signal generating module includes:

[0026] Generate random data for simulating actual communication information flow;

[0027] Performing quadrature amplitude modulation (QAM) constellation mapping on the random data to convert digital information into complex symbols;

[0028] Up-sampling the mapped signal to increase the sampling rate of the signal to meet the needs of subsequent digital signal processing;

[0029] The upsampled signal is subjected to shaping filtering to limit the signal bandwidth and improve the signal's spectral characteristics.

[0030] In a preferred example, the uplink signal transmission module in the optical network unit specifically includes:

[0031] A burst subcarrier signal generation module is used to generate a burst signal including multiple digital subcarriers to adapt to the burst transmission characteristics of the access network;

[0032] The subcarrier power adjustment module is used to adjust the transmission power of each subcarrier signal according to the uplink transmission requirements to optimize its performance in the uplink transmission channel;

[0033] The subcarrier up-conversion and coupling module is used to up-convert the generated subcarrier signals to a specified frequency band, and couple the subcarrier signals before sending them to the access network.

[0034] In a preferred example, the workflow of the burst subcarrier signal generating module includes:

[0035] Generate random data for simulating uplink information flow in access network;

[0036] Performing quadrature amplitude modulation (QAM) constellation mapping on the random data to convert digital information into complex symbols;

[0037] Inserting a preamble symbol into the signal frame, wherein the preamble symbol is used to assist the receiving end in digital signal processing, including signal synchronization, channel estimation, polarization state estimation and coarse frequency offset estimation;

[0038] Upsample the processed signal to increase the sampling rate to meet the subsequent digital signal processing requirements;

[0039] The upsampled signal is subjected to shaping filtering to limit the signal bandwidth and improve the signal's spectral characteristics.

[0040] In a preferred example, the leading symbol includes two training sequences:

[0041] The first training sequence is used to assist the digital signal processing (DSP) module at the receiving end to perform frame detection and clock recovery, wherein: frame detection is used to determine the starting position of the burst signal; clock recovery is used to synchronize the sampling clock of the receiving end with the signal clock of the transmitting end;

[0042] The second training sequence is used to assist the digital signal processing (DSP) module at the receiving end to perform the following operations:

[0043] 1) Frame synchronization, used to accurately locate the boundaries of data frames;

[0044] 2) Polarization state estimation, used to compensate for polarization mode dispersion generated during transmission;

[0045] 3) Coarse frequency offset estimation, used to correct the frequency offset between the transmitter and the receiver;

[0046] 4) Channel estimation, which is used to evaluate the characteristics of the transmission channel and provide a basis for subsequent equalization processing.

[0047] In a preferred example, the workflow of the westbound transmission module of the metro-access all-optical fusion node includes the following steps:

[0048] 1) Receive westbound transmission signals from a node on the metropolitan area network;

[0049] 2) Use erbium-doped fiber amplifiers to amplify the received signal to compensate for the transmission loss between nodes;

[0050] 3) Separate the wavelength used for metro-access convergence that carries metropolitan area network and access network signals from other wavelengths through a wavelength selective switch;

[0051] 4) using another erbium-doped fiber amplifier to amplify the separated signal to compensate for the device insertion loss;

[0052] 5) The signal is split into two beams through a 3-dB optical beam splitter: one beam continues to be transmitted westward in the metropolitan area network; the other beam is transmitted to the access network;

[0053] 6) The signal that continues to be transmitted in the metropolitan area network is processed as follows: the signal is recombined with other wavelengths through a wavelength selective switch; the signal is pre-amplified using an erbium-doped fiber amplifier;

[0054] 7) The signal transmitted to the access network is processed as follows:

[0055] An optical circulator is used to direct the signal into the access network transmission path.

[0056] In a preferred example, the workflow of the eastbound transmission module of the metro-access all-optical fusion node includes the following steps:

[0057] 1) Receive eastbound transmission signals from a node on the metropolitan area network;

[0058] 2) Use erbium-doped fiber amplifiers to amplify the received metropolitan area network signals to compensate for the transmission loss between nodes;

[0059] 3) Separate the wavelength carrying the metropolitan area network signal from other wavelengths through a wavelength selective switch;

[0060] 4) Input the separated metropolitan area network signal into one input end of a 3-dB optical coupler;

[0061] 5) receiving an uplink signal from the access network, the specific steps comprising: receiving the uplink signal of the access network through an optical circulator; amplifying the access network signal using an erbium-doped fiber amplifier; inputting the amplified access network signal into another input end of the 3-dB optical coupler;

[0062] 6) Fully optically combine the metropolitan area network signal and the access network signal through a 3-dB optical coupler;

[0063] 7) Processing the combined signal as follows: Recombining the combined signal with other wavelengths through a wavelength selective switch; Pre-amplifying the signal using an erbium-doped fiber amplifier;

[0064] 8) The processed signal continues to be transmitted eastward in the metropolitan area network.

[0065] In a preferred example, the workflow of the signal receiving and processing module in the metropolitan area node includes the following steps:

[0066] 1) Use coherent receiving technology to receive the transmitted signal: by adjusting the central wavelength of the local oscillator light, selective detection of specific digital subcarriers is achieved;

[0067] 2) An integrated coherent receiver converts the received optical signal into an electrical signal;

[0068] 3) Convert the analog signal to a digital signal using an analog-to-digital converter.

[0069] 4) Perform digital signal processing (DSP) on digital signals: down-convert each subcarrier signal and convert the signal to baseband; perform clock recovery to ensure that the sampling clock at the receiving end is synchronized with the transmitting end; perform dispersion compensation to eliminate the dispersion effect during transmission; use cascaded multimode algorithms to perform channel equalization to compensate for polarization mode dispersion and other polarization-related damage; first perform frequency offset estimation and compensation, and then perform carrier phase recovery to eliminate the influence of phase noise;

[0070] 5) Demodulate and decode the processed signal: make symbol decisions based on the modulation format (such as QAM); perform forward error correction (FEC) decoding to correct errors that occur during transmission;

[0071] 6) Output the recovered data stream and calculate the bit error rate.

[0072] In a preferred embodiment, the system further includes a mechanism for dispersion compensation, specifically including:

[0073] Dispersion pre-compensation at the transmitting end: In the westbound and eastbound signal transmission modules of the metropolitan area node, dispersion pre-compensation is performed on each digital subcarrier signal; the corresponding pre-compensation amount is calculated and applied based on the estimated transmission distance and the dispersion parameters of the optical fiber;

[0074] Post-dispersion compensation at the receiving end: Post-dispersion compensation is performed on the received signals in the westbound signal receiving and processing module, eastbound signal receiving and processing module of the metropolitan area node, and the downlink signal receiving and processing module of the optical network unit;

[0075] Flexible configuration of dispersion compensation: The system can flexibly choose to perform pre-compensation at the transmitting end, post-compensation at the receiving end, or both at the same time according to the network deployment and transmission performance requirements; for the metropolitan area network, post-compensation is mainly performed at the receiving end; for the access network, the uplink signal is mainly post-compensated at the receiving end, and the downlink signal is mainly pre-compensated at the transmitting end;

[0076] Subcarrier-level dispersion compensation: Dispersion compensation is performed on subcarriers of different frequencies to adapt to the differences in dispersion characteristics of subcarriers in different frequency bands.

[0077] The implementation methods of this application have the following technical effects:

[0078] Avoid the delay and jitter caused by optical-electrical-optical conversion: Traditional optical network systems often rely on optical-electrical-optical conversion for signal processing, which is prone to large signal delay and jitter. The present invention eliminates this conversion link through all-optical transmission, significantly reduces system delay, and improves the stability and real-time performance of transmission.

[0079] Saving wavelength resources: The present invention uses digital subcarrier multiplexing technology to achieve efficient utilization of frequency domain resources by dividing the subcarrier spectrum, avoiding the waste of wavelength resources in traditional systems and greatly improving the spectrum utilization of the network system.

[0080] Improve the flexibility of network architecture: By assigning different functions to different subcarriers, the present invention can flexibly respond to changes in network structure and different business requirements while achieving two-way high-speed transmission, greatly enhancing the scalability and adaptability of the network.

[0081] Support large-scale data transmission: After adopting subcarrier multiplexing technology, the system can support bidirectional parallel transmission of large-scale data, meeting the requirements of the next generation of high-speed optical fiber communication networks for high bandwidth and high speed, and effectively improving the transmission capacity and efficiency of the network.

[0082] Reduced operating and maintenance costs: Since the present invention avoids the use of optical-electrical-optical equipment in traditional networks, the number of devices is reduced, power consumption is reduced, and network operating and maintenance costs are reduced, thereby improving the economy and environmental protection of the system.

[0083] A large number of technical features are recorded in the specification of this application, which are distributed in various technical solutions. If all possible combinations of technical features of this application (i.e., technical solutions) are to be listed, the specification will be too long. In order to avoid this problem, the various technical features disclosed in the above-mentioned invention content of this application, the various technical features disclosed in the various embodiments and examples below, and the various technical features disclosed in the accompanying drawings can be freely combined with each other to form various new technical solutions (these technical solutions are all deemed to have been recorded in this specification), unless the combination of such technical features is technically infeasible. For example, in one example, feature A+B+C is disclosed, and in another example, feature A+B+D+E is disclosed, and features C and D are equivalent technical means that play the same role. Technically, only one can be used, and it is impossible to use them at the same time. Feature E can be combined with feature C technically. Then, the solution of A+B+C+D should not be deemed to have been recorded because it is technically infeasible, and the solution of A+B+C+E should be deemed to have been recorded. BRIEF DESCRIPTION OF THE DRAWINGS

[0084] Figure 1 It is a schematic diagram of a network topology structure of a metropolitan area network and an access network integrated in a metropolitan area-access all-optical integrated network system based on digital subcarrier multiplexing technology according to the first embodiment of the present application.

[0085] Figure 2 It is a schematic diagram of the internal structure of a metropolitan area node provided by a metropolitan area-access all-optical fusion network system based on digital subcarrier multiplexing technology according to the first implementation mode of the present application.

[0086] Figure 3 It is a schematic diagram of the internal structure of an optical network unit provided by a metropolitan area-access all-optical fusion network system based on digital subcarrier multiplexing technology according to the first embodiment of the present application.

[0087] Figure 4 It is a schematic diagram of the internal structure of a metropolitan area-access all-optical fusion node provided by a metropolitan area-access all-optical fusion network system based on digital subcarrier multiplexing technology according to the first implementation mode of the present application.

[0088] Figure 5 It is a system block diagram of a metropolitan area-access all-optical fusion network system based on digital subcarrier multiplexing technology according to the first embodiment of the present application, which supports all-optical fusion of a metropolitan area network and an access network through digital subcarrier multiplexing technology, and is divided into a downlink and an uplink.

[0089] Figure 6It is a diagram of experimental results (a) of exploring the dispersion compensation problem and detection method problem in the downlink in the metropolitan area-access all-optical fusion network system based on digital subcarrier multiplexing technology according to the first embodiment of the present application; and a diagram of experimental results (b) of the change of the optical signal-to-noise ratio-bit error rate curve at different transmission distances and the comparison with the theoretical curve.

[0090] Figure 7 It is a diagram of experimental results (a) that explores the influence of semiconductor optical amplifiers in access network-side transmitters on sensitivity curves in the uplink in a metropolitan-access all-optical fusion network system based on digital subcarrier multiplexing technology according to the first embodiment of the present application; and a diagram of experimental results (b) that explores the influence of different combinations of optical power when entering the photosynthetic combiner and after amplification by the erbium-doped fiber amplifier on the dynamic range.

[0091] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0092] 101: Metropolitan Area Network

[0093] 102: Access network part

[0094] 201: Westbound signal transmission module

[0095] 202: Westbound signal receiving and processing module

[0096] 203: Eastbound signal transmission module

[0097] 204: Eastbound signal receiving and processing module

[0098] 301: Downlink signal receiving and processing module

[0099] 302: Uplink signal transmission module

[0100] 401: Westbound transmission module

[0101] 402: Eastbound transmission module

[0102] 501: Continuous subcarrier signal generation module

[0103] 502: Subcarrier dispersion pre-compensation module

[0104] 503: Power adjustment module between subcarriers

[0105] 504: Subcarrier up-conversion and coupling module

[0106] 505: Signal generation module in metropolitan area network

[0107] 506: Metropolitan Area: Digital Subcarrier Splitting Module in Access All-Optical Fusion Node

[0108] 507: Signal receiving and processing module in metropolitan area node

[0109] 508: Signal receiving and processing module in optical network unit

[0110] 509: Burst subcarrier signal generation module

[0111] 510: Uplink signal generation module in access network optical network unit

[0112] 511: Metro: Digital subcarrier beam combining module in access all-optical fusion node DETAILED DESCRIPTION

[0113] In the following description, many technical details are provided to help readers better understand the present application. However, those skilled in the art can understand that the technical solution claimed in the present application can be implemented even without these technical details and various changes and modifications based on the following embodiments.

[0114] Description of some concepts:

[0115] Digital subcarrier multiplexing technology: Digital subcarrier multiplexing technology is a signal processing technology that modulates multiple digital subcarriers and transmits them simultaneously on a single carrier. This technology can flexibly divide spectrum resources, thereby achieving fine control at the subcarrier level and more efficient spectrum utilization.

[0116] All-optical convergence: All-optical convergence refers to the direct fusion of different optical networks (such as metropolitan area networks and access networks) into a unified optical network system without optical-electrical-optical conversion. This technology can reduce signal delay, reduce power consumption and improve network transmission efficiency.

[0117] Metropolitan Area Network: A metropolitan area network (MAN) is a communication network built in a city or a large area. It is used to realize data exchange between multiple local area networks and is usually connected to a wide area network or the Internet.

[0118] Access Network: Access Network is the part of the network that connects user terminals to the service provider network and is responsible for connecting user equipment to a larger communication network, such as a metropolitan area network or a core network.

[0119] Passive Optical Network (PON): Passive optical network is a fiber optic communication system that does not require any active electronic equipment or intermediate signal amplifiers. It uses optical splitters to distribute signals to multiple user terminals to achieve point-to-multipoint communication.

[0120] Coherent reception: Coherent reception is an optical signal reception technology that achieves high-precision recovery and demodulation of optical signals by coherent detection with the local oscillator optical signal at the receiving end. Compared with traditional direct detection technology, it has higher sensitivity and signal processing capabilities.

[0121] 3-dB optical beam splitter: A 3-dB optical beam splitter is an optical device that can split an input optical signal into two optical signals of equal power. It is usually used for signal distribution and multipath transmission.

[0122] Dual-polarization IQ modulator: A dual-polarization IQ modulator is a device that can modulate optical signals in two polarization directions simultaneously, enabling higher optical signal transmission rates and bandwidth utilization.

[0123] Erbium-doped fiber amplifier (EDFA): An erbium-doped fiber amplifier is an optical signal amplifier commonly used in optical fiber communication systems. It amplifies optical signals within a specific wavelength range through erbium-doped optical fibers, thereby improving the transmission distance and quality of the signal.

[0124] Wavelength Selective Switch (WSS): A wavelength selective switch is an optical network device that can selectively separate or merge multiple wavelength signals according to network requirements to achieve independent transmission or fusion of different wavelength signals.

[0125] Westbound signal and eastbound signal: In this application, westbound signal and eastbound signal refer to signals transmitted in opposite directions in the ring topology of the metropolitan area network, which are used to realize two-way communication of the network. Specifically, in the metropolitan area-access all-optical fusion network system of this application, the westbound signal is sent from a certain metropolitan area node, and after passing through the metropolitan area-access all-optical fusion node, a part of it continues to be transmitted westward to the next metropolitan area node, and the other part is transmitted to the access network and transmitted to the optical network unit in the downstream direction. The eastbound signal is also sent from a certain metropolitan area node, and after passing through the metropolitan area-access all-optical fusion node, it is combined with the uplink signal from the access network optical network unit, and then continues to be transmitted eastward to the next metropolitan area node.

[0126] The following is a brief description of some of the innovative features of this application:

[0127] In general, the present application provides a novel metropolitan area-access fusion optical network, which supports the full optical fusion of the metropolitan area network and the access network, and can realize bidirectional transmission, and the network includes a metropolitan area network part and an access network part. The metropolitan area network part adopts a ring network topology structure, and the signal is bidirectionally transmitted in two optical fibers in the east and west directions respectively. A plurality of metropolitan area nodes are set on the ring, and include a core-metropolitan area node connected to the core network and a metropolitan area-access full optical fusion node connected to the access network.

[0128] The network topology of the access network is tree-like. Uplink and downlink signals are transmitted bidirectionally through a single optical fiber. The optical splitter, optical network unit, and the optical fiber connecting the two together constitute the passive optical network in the access network. The optical splitter splits the downlink signal from the fusion node, connects it to each optical network unit, and combines the uplink signals from each optical network unit.

[0129] In the downlink, the westward-transmitted metropolitan area network signal is transmitted through the metropolitan area-access all-optical fusion node. Part of the signal enters the access network and is transmitted to each optical network unit through the optical splitter of the passive optical network system. The other part of the signal continues to be transmitted in the metropolitan area network to the next metropolitan area node.

[0130] In the uplink, the metropolitan area network signal transmitted eastward passes through the metro-access all-optical fusion node, is integrated with the optical network units of the uplink signal from the access network, and then continues to be transmitted in the metropolitan area network to the next metropolitan area node.

[0131] In the downlink of the network system, it specifically includes: the westbound signal transmission module in the metropolitan area node, the digital subcarrier beam splitting module in the metropolitan area-access all-optical fusion node, and the downlink signal receiving and processing module in the access network optical network unit. The westbound signal transmission module in the metropolitan area node transmits a westbound continuous signal based on digital subcarrier multiplexing according to the application scenario requirements; the digital subcarrier beam splitting module divides the digital subcarrier multiplexing signal transmitted westward into two beams, one beam continues to be transmitted in the metropolitan area network to the next metropolitan area node, and the other beam enters the access network and is transmitted to each optical network unit; the downlink signal receiving and processing module in the access network optical network unit selectively detects the digital subcarrier carrying the access network signal through the selection of the central wavelength of the local oscillator light of the coherent receiver, converts the analog signal into a digital signal, and decodes the signal through the DSP algorithm.

[0132] In the uplink, the eastbound signal transmission module includes: the eastbound signal transmission module in the metropolitan area node and the uplink signal transmission module in the access network optical network unit. The eastbound signal transmission module in the metropolitan area node transmits the eastbound continuous signal based on digital subcarrier multiplexing according to the application scenario requirements, while the uplink signal transmission module in the access network optical network unit transmits the uplink burst signal based on digital subcarrier multiplexing. The digital subcarrier beam combining module combines the continuous signal carrying the eastbound transmission of the metropolitan area network with the digital subcarrier of the uplink burst signal of the access network. The eastbound signal receiving and processing module of the metropolitan area node selects the appropriate wavelength for coherent detection and decodes the signal.

[0133] The metro-access all-optical fusion node in this system includes a westbound transmission module and an eastbound transmission module. The westbound transmission module divides the westbound signal from the previous metro node into two beams, one of which continues to be transmitted to the next metro node, and the other enters the access network for downlink transmission. The eastbound transmission module combines the eastbound signal from the previous metro node with the uplink signal in the access network and transmits it to the next metro node.

[0134] The westbound signal transmission module of the metropolitan area node specifically includes a westbound signal generation module and a westbound signal production module. The westbound signal generation module generates a continuous signal of multiple digital subcarriers according to the application scenario requirements. Some subcarriers carry metropolitan area network signals, and the other part carries access network signals. The westbound signal generation module converts the digital signal into an analog signal, completes the signal modulation through a dual-polarization IQ modulator, and amplifies the optical signal through an erbium-doped fiber amplifier.

[0135] The eastbound signal transmission module of the metropolitan area node also includes an eastbound signal generation module and an eastbound signal production module. The eastbound signal generation module generates a continuous signal of multiple digital subcarriers and carries the metropolitan area network signal. The production module converts the digital signal into an analog signal, modulates the signal through a dual-polarization IQ modulator, and amplifies the signal through an erbium-doped fiber amplifier.

[0136] The uplink signal transmission module in the access network optical network unit includes an uplink signal generation module and an uplink signal production module. The uplink signal generation module generates burst signals of multiple digital subcarriers according to the application scenario requirements and carries the access network signal. The uplink signal generation module converts the digital signal into an analog signal, modulates it through a dual-polarization IQ modulator, and then amplifies the signal through a semiconductor optical amplifier.

[0137] Optionally, the metro-access all-optical fusion node also includes a wavelength selection switch to separate or merge the wavelength for metro-access network fusion from other wavelengths. The optical circulator is used to connect the access network and the metropolitan area network, supporting the fusion of the access network with single-fiber bidirectional transmission and the metropolitan area network system with dual-fiber bidirectional transmission.

[0138] The specially designed preamble sequence includes two sections. The first section is used to assist the receiving end DSP in frame detection and clock recovery, and the second section is used to assist the receiving end DSP in frame synchronization, polarization state estimation, coarse frequency offset estimation and channel estimation.

[0139] It should be noted that the signals from the metropolitan area network and the access network are combined at the metropolitan area-access all-optical fusion node and transmitted to the eastbound signal receiving module. This module selectively detects the subcarriers carrying the metropolitan area network signal and the access network signal through a coherent receiver. After the signal is converted into digital form, it is decoded by the DSP algorithm to complete high-speed two-way transmission.

[0140] The metropolitan area-access all-optical fusion optical network system provided in this application can support 400G high-speed bidirectional transmission through digital subcarrier multiplexing technology. In the system, the metropolitan area network and the access network share the same carrier, the transmitting end adopts digital subcarrier multiplexing technology, and the receiving end uses the corresponding digital subcarrier demultiplexing technology. By dividing the spectrum resources of the same carrier in the digital domain, different subcarriers can carry different signals: some subcarriers are used to carry metropolitan area network signals, and the other subcarriers carry access network signals. Based on this, in the uplink, the signals of the metropolitan area network and the access network can be fully optically integrated through the 3-dB optical combiner in the metropolitan area-access all-optical fusion node, avoiding the optical-electrical-optical conversion in the traditional architecture; in the downlink, the metropolitan area-access all-optical fusion node divides the signal into two beams of equal power through a 3-dB optical splitter. Although both signals contain all subcarriers, the receiver uses coherent detection technology to flexibly select the subcarriers to be detected by adjusting the local oscillator frequency: in the receiver of the metropolitan area node, the subcarrier is coherently detected to obtain the metropolitan area network signal; in the access network optical network unit, the coherent detection subcarrier is used for the access network signal. In addition, digital subcarrier multiplexing technology further releases the multiplexing potential of the spectrum. By further dividing the subcarriers, the access network side can flexibly realize time-frequency division multiplexing, thereby enhancing the flexibility of the network.

[0141] The metropolitan area network and access network integration solution proposed in this application effectively responds to the demand for closer network integration in the next generation of high-speed fiber-optic communication networks. This system realizes the all-optical integration of the metropolitan area network and the access network, avoids the delay and power consumption caused by optical-electrical-optical conversion, eliminates the receiver and transmitter at the metropolitan area-access all-optical integration node, and greatly saves operation and maintenance costs. At the same time, this system saves scarce wavelength resources by realizing integration within the same carrier. After applying digital subcarrier multiplexing technology, the utilization rate of frequency domain resources and system flexibility are greatly improved, and it can cope with more complex application scenarios. In addition, this system realizes 400G high-speed bidirectional transmission, meets the next generation of high-speed fiber-optic communication networks' expectations for speed, and has the potential to support larger capacity and higher-speed optical networks.

[0142] The metropolitan area-access all-optical converged optical network system based on digital subcarrier multiplexing technology proposed in this application has the following advantages:

[0143] 1. Compared with the optical network architecture based on direct modulation and direct detection system, the coherent optical communication system has higher sensitivity and can support a larger splitting ratio;

[0144] 2. Compared with the traditional metro-access network converged optical network architecture that relies on optical-electrical-optical conversion, the all-optical converged network effectively avoids the use of a pair of receivers and transmitters at the metro-access all-optical converged node, reducing operation and maintenance costs. At the same time, it reduces the delay and jitter caused by optical-electrical-optical conversion, supporting application scenarios that require ultra-low latency;

[0145] 3. Compared with the all-optical converged optical network architecture based on wavelength routing, digital subcarrier multiplexing technology saves scarce wavelength resources.

[0146] This application belongs to the field of optical network technology, and can effectively respond to the demand for further close integration of metropolitan area networks and access networks in the next generation of high-speed optical fiber communication networks and their expectations for high-speed and large-capacity transmission. By avoiding the delay and power consumption caused by optical-electrical-optical conversion, this system greatly reduces the operation and maintenance costs of the network, significantly improves resource utilization and system flexibility, has the potential to upgrade the existing high-speed optical fiber communication network architecture, and can flexibly respond to more complex application scenarios in the future.

[0147] In order to make the objectives, technical solutions and advantages of the present application clearer, the implementation methods of the present application will be further described in detail below in conjunction with the accompanying drawings.

[0148] The first embodiment of the present application relates to a metropolitan area-access all-optical fusion network system based on digital subcarrier multiplexing technology, including:

[0149] The metropolitan area network part has a ring-shaped network topology, and the signal is transmitted bidirectionally in the east and west directions in two optical fibers. The metropolitan area network part includes multiple metropolitan area nodes, core-metropolitan area nodes, and metropolitan area-access all-optical fusion nodes;

[0150] The access network part has a tree-like network topology, and the uplink signal and the downlink signal are bidirectionally transmitted in a single optical fiber. The access network part includes an optical splitter and multiple optical network units;

[0151] The metropolitan area node includes: a westbound signal transmission module and an eastbound signal transmission module, both for transmitting continuous signals based on digital subcarrier multiplexing; a westbound signal receiving and processing module and an eastbound signal receiving and processing module, both for receiving and processing signals based on digital subcarrier multiplexing in corresponding directions; and,

[0152] The optical network unit includes: a downlink signal receiving and processing module, used to receive and process downlink signals based on digital subcarrier multiplexing from the access network; an uplink signal transmitting module, used to transmit uplink burst signals based on digital subcarrier multiplexing; and,

[0153] The metropolitan area-access all-optical fusion node includes: a westbound transmission module, which is used to split the westbound signal into two beams, one beam continues to be transmitted in the metropolitan area network, and the other beam is transmitted to the access network; an eastbound transmission module, which is used to perform all-optical beam combination of the eastbound signal in the metropolitan area network and the uplink signal in the access network, and continue to transmit them in the metropolitan area network;

[0154] Among them, through the digital subcarrier multiplexing technology, different digital subcarriers on the same carrier carry metropolitan area network signals and access network signals respectively, realizing the full optical integration of metropolitan area network and access network, avoiding optical-electrical-optical conversion;

[0155] The westbound signal receiving and processing module, the eastbound signal receiving and processing module and the downlink signal receiving and processing module all adopt coherent receiving technology to selectively detect specific digital subcarriers by adjusting the local oscillator light frequency.

[0156] Specifically, the first embodiment of the present application proposes a metropolitan area network-access all-optical fusion network system based on digital subcarrier multiplexing technology. The system includes a metropolitan area network part and an access network part, and can realize the all-optical fusion of the metropolitan area network and the access network through bidirectional transmission, avoiding optical-electrical-optical conversion and improving network transmission efficiency.

[0157] In the metropolitan area network, the network topology adopts a ring design, and the signal is transmitted bidirectionally in two optical fibers in the east and west directions. The metropolitan area network consists of multiple metropolitan nodes, including core-metropolitan nodes connected to the core network and metropolitan-access all-optical fusion nodes connected to the access network. Each metropolitan area node is equipped with a westbound signal transmission module and an eastbound signal transmission module, which are used to transmit continuous signals based on digital subcarrier multiplexing technology. In addition, the westbound signal receiving and processing module and the eastbound signal receiving and processing module are responsible for receiving and processing the digital subcarrier multiplexing signals in the corresponding directions.

[0158] The network topology of the access network is tree-like, and the signal is transmitted bidirectionally in a single optical fiber. The access network consists of an optical splitter and multiple optical network units. Each optical network unit is equipped with a downlink signal receiving and processing module, which can receive and process downlink signals based on digital subcarrier multiplexing from the access network. In addition, the uplink signal transmission module is used to transmit uplink burst signals based on digital subcarrier multiplexing, thereby completing uplink data transmission.

[0159] The metro-access all-optical fusion node is one of the key components in the network system. It includes a westbound transmission module and an eastbound transmission module. The function of the westbound transmission module is to split the westbound signal from the metropolitan area network into two beams, one of which continues to be transmitted in the metropolitan area network, and the other is transmitted to the access network. The eastbound transmission module is responsible for all-optical beam combination of the eastbound signal in the metropolitan area network and the uplink signal in the access network, and continues to transmit it to the next node in the metropolitan area network.

[0160] The core technology of the system lies in the digital subcarrier multiplexing technology. Through this technology, different digital subcarriers on the same carrier can carry metropolitan area network signals and access network signals respectively, realizing the full optical integration of metropolitan area network and access network, and avoiding the need for optical-electrical-optical conversion in traditional optical networks. In addition, the westbound signal receiving and processing module, the eastbound signal receiving and processing module, and the downlink signal receiving and processing module all adopt coherent reception technology. By adjusting the local oscillator optical frequency, specific digital subcarriers can be selectively detected, further improving the accuracy of signal reception and system performance.

[0161] This implementation method effectively improves the integration efficiency of the metropolitan area network and the access network by combining digital subcarrier multiplexing technology and coherent reception technology, reduces the delay and power consumption problems caused by optical-electrical-optical conversion, significantly enhances the network's flexibility and resource utilization, supports high-speed two-way transmission, and meets the needs of future high-speed fiber-optic communication networks.

[0162] Optionally, the westbound signal transmission module and the eastbound signal transmission module in the metropolitan area node specifically include:

[0163] A continuous subcarrier signal generating module, used for generating a continuous signal including a plurality of digital subcarriers;

[0164] A subcarrier dispersion precompensation module is used to precompensate the dispersion of each subcarrier according to its transmission distance to reduce the influence of dispersion on the signal;

[0165] A subcarrier power adjustment module, used to adjust the transmission power of each subcarrier signal to optimize its performance in the transmission channel;

[0166] The subcarrier up-conversion and coupling module is used to up-convert the generated subcarrier signals to different frequency bands and couple the subcarrier signals for transmission.

[0167] Optionally, the workflow of the continuous subcarrier signal generating module includes:

[0168] Generate random data for simulating actual communication information flow;

[0169] Performing quadrature amplitude modulation (QAM) constellation mapping on the random data to convert digital information into complex symbols;

[0170] Up-sampling the mapped signal to increase the sampling rate of the signal to meet the needs of subsequent digital signal processing;

[0171] The upsampled signal is subjected to shaping filtering to limit the signal bandwidth and improve the signal's spectral characteristics.

[0172] Optionally, the uplink signal transmission module in the optical network unit specifically includes:

[0173] A burst subcarrier signal generation module is used to generate a burst signal including multiple digital subcarriers to adapt to the burst transmission characteristics of the access network;

[0174] The subcarrier power adjustment module is used to adjust the transmission power of each subcarrier signal according to the uplink transmission requirements to optimize its performance in the uplink transmission channel;

[0175] The subcarrier up-conversion and coupling module is used to up-convert the generated subcarrier signals to a specified frequency band, and couple the subcarrier signals before sending them to the access network.

[0176] Optionally, the workflow of the burst subcarrier signal generating module includes:

[0177] Generate random data for simulating uplink information flow in access network;

[0178] Performing quadrature amplitude modulation (QAM) constellation mapping on the random data to convert digital information into complex symbols;

[0179] Inserting a preamble symbol into the signal frame, wherein the preamble symbol is used to assist the receiving end in digital signal processing, including signal synchronization, channel estimation, polarization state estimation and coarse frequency offset estimation;

[0180] Upsample the processed signal to increase the sampling rate to meet the subsequent digital signal processing requirements;

[0181] The upsampled signal is subjected to shaping filtering to limit the signal bandwidth and improve the signal's spectral characteristics.

[0182] Optionally, the leading symbol includes two training sequences:

[0183] The first training sequence is used to assist the digital signal processing (DSP) module at the receiving end to perform frame detection and clock recovery, wherein: frame detection is used to determine the starting position of the burst signal; clock recovery is used to synchronize the sampling clock of the receiving end with the signal clock of the transmitting end;

[0184] The second training sequence is used to assist the digital signal processing (DSP) module at the receiving end to perform the following operations:

[0185] 1) Frame synchronization, used to accurately locate the boundaries of data frames;

[0186] 2) Polarization state estimation, used to compensate for polarization mode dispersion generated during transmission;

[0187] 3) Coarse frequency offset estimation, used to correct the frequency offset between the transmitter and the receiver;

[0188] 4) Channel estimation, which is used to evaluate the characteristics of the transmission channel and provide a basis for subsequent equalization processing.

[0189] Optionally, the workflow of the westbound transmission module of the metro-access all-optical fusion node includes the following steps:

[0190] 1) Receive westbound transmission signals from a node on the metropolitan area network;

[0191] 2) Use erbium-doped fiber amplifiers to amplify the received signal to compensate for the transmission loss between nodes;

[0192] 3) Separate the wavelength used for metro-access convergence that carries metropolitan area network and access network signals from other wavelengths through a wavelength selective switch;

[0193] 4) using another erbium-doped fiber amplifier to amplify the separated signal to compensate for the device insertion loss;

[0194] 5) The signal is split into two beams through a 3-dB optical beam splitter: one beam continues to be transmitted westward in the metropolitan area network; the other beam is transmitted to the access network;

[0195] 6) The signal that continues to be transmitted in the metropolitan area network is processed as follows: the signal is recombined with other wavelengths through a wavelength selective switch; the signal is pre-amplified using an erbium-doped fiber amplifier;

[0196] 7) The signal transmitted to the access network is processed as follows:

[0197] An optical circulator is used to direct the signal into the access network transmission path.

[0198] Optionally, the workflow of the eastbound transmission module of the metro-access all-optical fusion node includes the following steps:

[0199] 1) Receive eastbound transmission signals from a node on the metropolitan area network;

[0200] 2) Use erbium-doped fiber amplifiers to amplify the received metropolitan area network signals to compensate for the transmission loss between nodes;

[0201] 3) Separate the wavelength carrying the metropolitan area network signal from other wavelengths through a wavelength selective switch;

[0202] 4) Input the separated metropolitan area network signal into one input end of a 3-dB optical coupler;

[0203] 5) receiving an uplink signal from the access network, the specific steps comprising: receiving the uplink signal of the access network through an optical circulator; amplifying the access network signal using an erbium-doped fiber amplifier; inputting the amplified access network signal into another input end of the 3-dB optical coupler;

[0204] 6) Fully optically combine the metropolitan area network signal and the access network signal through a 3-dB optical coupler;

[0205] 7) Processing the combined signal as follows: Recombining the combined signal with other wavelengths through a wavelength selective switch; Pre-amplifying the signal using an erbium-doped fiber amplifier;

[0206] 8) The processed signal continues to be transmitted eastward in the metropolitan area network.

[0207] Optionally, the workflow of the signal receiving and processing module in the metropolitan area node includes the following steps:

[0208] 1) Use coherent receiving technology to receive the transmitted signal: by adjusting the central wavelength of the local oscillator light, selective detection of specific digital subcarriers is achieved;

[0209] 2) An integrated coherent receiver converts the received optical signal into an electrical signal;

[0210] 3) Convert the analog signal to a digital signal using an analog-to-digital converter.

[0211] 4) Perform digital signal processing (DSP) on digital signals: down-convert each subcarrier signal and convert the signal to baseband; perform clock recovery to ensure that the sampling clock at the receiving end is synchronized with the transmitting end; perform dispersion compensation to eliminate the dispersion effect during transmission; use cascaded multimode algorithms to perform channel equalization to compensate for polarization mode dispersion and other polarization-related damage; first perform frequency offset estimation and compensation, and then perform carrier phase recovery to eliminate the influence of phase noise;

[0212] 5) Demodulate and decode the processed signal: make symbol decisions based on the modulation format (such as QAM); perform forward error correction (FEC) decoding to correct errors that occur during transmission;

[0213] 6) Output the recovered data stream and calculate the bit error rate.

[0214] Optionally, the system further includes a mechanism for dispersion compensation, specifically including:

[0215] Dispersion pre-compensation at the transmitting end: In the westbound and eastbound signal transmission modules of the metropolitan area node, dispersion pre-compensation is performed on each digital subcarrier signal; the corresponding pre-compensation amount is calculated and applied based on the estimated transmission distance and the dispersion parameters of the optical fiber;

[0216] Post-dispersion compensation at the receiving end: Post-dispersion compensation is performed on the received signals in the westbound signal receiving and processing module, eastbound signal receiving and processing module of the metropolitan area node, and the downlink signal receiving and processing module of the optical network unit;

[0217] Flexible configuration of dispersion compensation: The system can flexibly choose to perform pre-compensation at the transmitting end, post-compensation at the receiving end, or both at the same time according to the network deployment and transmission performance requirements; for the metropolitan area network, post-compensation is mainly performed at the receiving end; for the access network, the uplink signal is mainly post-compensated at the receiving end, and the downlink signal is mainly pre-compensated at the transmitting end;

[0218] Subcarrier-level dispersion compensation: Dispersion compensation is performed on subcarriers of different frequencies to adapt to the differences in dispersion characteristics of subcarriers in different frequency bands.

[0219] In order to better understand the technical solution of this example, a specific example is used for illustration below. The details listed in this example are mainly for ease of understanding and are not intended to limit the scope of protection of this example.

[0220] In this example, an optical network system is provided that supports all-optical integration of metropolitan area network and access network and can realize high-speed bidirectional transmission. Compared with the traditional metropolitan area-access integrated network using optical-electrical-optical conversion and the all-optical integrated network based on wavelength routing, the purpose of this example is to divide spectrum resources through digital subcarrier multiplexing technology and realize flexible all-optical routing based on subcarriers, thereby further improving the integration of metropolitan area network and access network and supporting high-speed bidirectional transmission.

[0221] In the solution proposed in this example, the metropolitan area network adopts a ring network topology, and the signal is transmitted bidirectionally in two-way optical fibers in the east and west directions. The ring contains multiple metropolitan nodes, as well as core-metropolitan nodes connected to the core network and metropolitan-access all-optical fusion nodes connected to the access network. The network topology of the access network part is tree-like, supporting bidirectional transmission of uplink and downlink signals in a single optical fiber. The passive optical network in the access network consists of an optical splitter, an optical network unit, and an optical fiber connecting the two. The optical splitter splits the downlink signal from the fusion node, connects each optical network unit, and combines the uplink signal emitted by each optical network unit.

[0222] In this system, all-optical fusion is achieved through digital subcarrier multiplexing technology. The system consists of two parts: downlink and uplink.

[0223] In the downlink, after the westbound metropolitan area network signal is transmitted to the metropolitan area-access all-optical fusion node, part of the signal enters the access network and is transmitted to each optical network unit through the optical splitter in the passive optical network system, and the other part of the signal continues to be transmitted in the metropolitan area network to the next metropolitan area node. The westbound signal transmission module in the metropolitan area node transmits a westbound continuous signal based on digital subcarrier multiplexing according to demand. This process includes steps such as signal generation, modulation and amplification: the signal generation module generates a continuous signal of multiple digital subcarriers, some of which carry metropolitan area network signals, and other subcarriers carry access network signals; the generated digital signal is transmitted after modulation and amplification.

[0224] In the specific implementation, the signal generation module of the metropolitan area node also includes a subcarrier dispersion pre-compensation module, which performs dispersion pre-compensation on the digital subcarrier according to the transmission distance. The subcarrier power adjustment module adjusts the signal power of each subcarrier to optimize the channel transmission effect. The generated subcarrier signal is up-converted to different frequency bands through the up-conversion and coupling module and then coupled and transmitted.

[0225] After the westbound signal is transmitted to the metropolitan area network-access all-optical fusion node, the system divides the signal into two beams: one beam continues to be transmitted in the metropolitan area network, and the other beam enters the access network and is transmitted downstream to the optical network unit. In the specific implementation, the signal first passes through the optical fiber amplifier to compensate for the transmission loss between nodes, and then separates the wavelength through the wavelength selection switch, and then further divides it into two signals through the optical beam splitter. One signal continues to be transmitted in the metropolitan area network, and the other signal enters the access network through the optical circulator.

[0226] In the access network optical network unit, the received downlink signal is selectively detected by the coherent receiver, and the analog signal is converted into a digital signal and decoded by the DSP algorithm. The westbound signal receiving module in the metropolitan area node selectively detects the subcarrier carrying the metropolitan area network signal through the same coherent receiver to complete the signal reception and decoding.

[0227] In the uplink, the metropolitan area network signal transmitted eastward is transmitted to the metropolitan area-access all-optical fusion node, merged with the uplink signal from the access network, and then continued to be transmitted in the metropolitan area network to the next metropolitan area node. The eastward signal transmission module of the metropolitan area node generates and transmits the eastward continuous signal based on digital subcarrier multiplexing. The uplink signal transmission module of the access network optical network unit transmits the uplink burst signal, and the signal generation module generates multiple subcarrier signals, which are transmitted after modulation and amplification.

[0228] In the specific implementation, a specially designed preamble sequence is inserted before the signal is transmitted to assist the DSP algorithm at the receiving end to converge quickly. The preamble sequence consists of two sections. The first section is used for frame detection and clock recovery, and the second section is used for frame synchronization, polarization state estimation, coarse frequency offset estimation, and channel estimation. Finally, the combined multi-subcarrier signal is transmitted to the next metropolitan area node in the fusion node.

[0229] Refer to the following Figures 1 to 7 , further explain this example.

[0230] like Figure 1 As shown, the metropolitan area-access all-optical fusion network system based on digital subcarrier multiplexing technology in this example specifically includes: 101-metropolitan area network part, 102-access network part. Among them, the metropolitan area network part 101 has a ring-shaped network topology, and the signal is transmitted bidirectionally in two optical fibers in the east and west directions; the ring includes multiple metropolitan area nodes, in addition to core-metropolitan area nodes connected to the core network and metropolitan area-access all-optical fusion nodes connected to the access network. The access network part 102 has a tree-shaped network topology, and the uplink signal and the downlink signal are transmitted bidirectionally in a single optical fiber; the optical splitter, each optical network unit and the optical fiber connecting the two together constitute the passive optical network in the access network: the optical splitter splits the downlink signal from the metropolitan area-access all-optical fusion node, connects to each optical network unit, and combines the uplink signal sent by each optical network unit.

[0231] The following further describes the internal structure of each network node involved in this example.

[0232] Figure 2 This is a schematic diagram of the internal structure of a metropolitan area node. Since there are both westbound and eastbound signals in the bidirectional transmission architecture of the metropolitan area network, the interior of the metropolitan area node is divided into a westbound part and an eastbound part.

[0233] The westbound part includes a westbound signal transmission module 201 and a westbound signal receiving and processing module 202. The westbound signal transmission module transmits a westbound continuous signal based on digital subcarrier multiplexing according to the application scenario requirements. The westbound signal receiving and processing module selectively detects the digital subcarrier carrying the metropolitan area network signal by selecting the central wavelength of the local oscillator light of the coherent receiver according to the application scenario requirements. The analog-to-digital converter converts the analog signal into a digital signal, and each subcarrier is down-converted to the baseband and then the signal is decoded using the DSP algorithm.

[0234] The eastbound part includes an eastbound signal transmission module 203 and an eastbound signal receiving and processing module 204. The eastbound signal transmission module transmits westbound continuous signals based on digital subcarrier multiplexing according to the application scenario requirements. The eastbound signal receiving and processing module selectively detects the digital subcarriers carrying metropolitan area network signals and access network signals respectively by selecting the central wavelength of the local oscillator light of the coherent receiver according to the application scenario requirements. The analog-to-digital converter converts the analog signal into a digital signal, and each subcarrier is down-converted to the baseband for dispersion compensation, and finally the DSP algorithm is used for signal decoding.

[0235] Figure 3 The figure is a schematic diagram of the internal structure of the optical network unit. In the access network, the signal is transmitted in two lines in the same optical fiber, which is divided into an upstream part and a downstream part.

[0236] The downlink part includes a downlink signal receiving and processing module 301. According to the application scenario requirements, this module selectively detects the digital subcarrier carrying the access network signal by selecting the central wavelength of the local oscillator light of the coherent receiver; the analog-to-digital converter converts the analog signal into a digital signal, and uses the DSP algorithm to decode the signal after down-converting the subcarriers to the baseband. The uplink part includes an uplink signal transmitting module 302. According to the application scenario requirements, this module transmits an uplink burst signal based on digital subcarrier multiplexing.

[0237] Figure 4 The figure is a schematic diagram of the internal structure of the metropolitan area-access all-optical fusion node. Specifically, it includes: a westbound transmission module 401 and an eastbound transmission module 402. Among them, the westbound transmission module divides the westbound signal of the previous metropolitan area node in the metropolitan area network into two beams according to the application scenario requirements, one beam is transmitted to the next metropolitan area node in the metropolitan area network, and the other part enters the access network for downlink transmission. The eastbound transmission module combines the eastbound signal of the previous metropolitan area node in the metropolitan area network with the uplink signal in the access network according to the application scenario requirements, and transmits them together to the next metropolitan area node in the metropolitan area network.

[0238] Specifically, in the westbound transmission module, the signal transmitted westward from the previous node in the metropolitan area network first passes through an erbium-doped fiber amplifier to compensate for the transmission loss between nodes, and then is separated from other wavelengths by a wavelength selective switch. Then it passes through an erbium-doped fiber amplifier to compensate for the device insertion loss, and finally is divided into two beams by a 3-dB optical splitter. The part that continues to be transmitted in the metropolitan area network passes through another wavelength selective switch and is combined with other wavelengths, and is pre-amplified by an erbium-doped fiber amplifier together; the other part passes through an optical circulator and enters the access network.

[0239] In the eastbound transmission module, the signal transmitted from the previous node in the metropolitan area network to the east first passes through an erbium-doped fiber amplifier to compensate for the transmission loss between nodes, and then passes through a wavelength selective switch and inputs one end of the 3-dB optical coupler. The signal transmitted from the access network through an optical circulator passes through an erbium-doped fiber amplifier and inputs the other end of the 3-dB optical coupler. After passing through the 3-dB optical coupler, the subcarriers are combined. The combined multi-subcarrier signal passes through another wavelength selective switch and is combined with other wavelengths, and is pre-amplified through an erbium-doped fiber amplifier.

[0240] It should be noted that the wavelength selection switch in the metro-access all-optical fusion node allows the wavelength for metro-access network fusion to be separated or merged with other wavelengths. One end of the optical circulator in the structure is connected to the access network, and the other two ends are respectively connected to the west transmission module and the east transmission module of the metro-access all-optical fusion node; so that the signal in the access network is transmitted bidirectionally with a single fiber, and can be integrated with the dual-fiber bidirectional metropolitan area network system. In addition, the erbium-doped fiber amplifier involved in the structure in this example is used to compensate for transmission and insertion losses or perform signal pre-amplification. In the actual implementation process, the position and amplification degree of the erbium-doped fiber amplifier should be adjusted accordingly according to the needs in the actual situation.

[0241] The system architecture of this example is described below.

[0242] like Figure 5 As shown, it includes: a westbound continuous signal generation module based on digital subcarriers in a metropolitan area node (including a continuous subcarrier signal generation module 501, a subcarrier dispersion pre-compensation module 502, a power adjustment module 503 between subcarriers, and a subcarrier up-conversion and coupling module 504), a westbound / eastbound signal generation module 505 in a metropolitan area node, a digital subcarrier beam splitting module 506 in a metropolitan area-access all-optical fusion node, a westbound signal receiving and processing module 507 in a metropolitan area node, a signal receiving and processing module 508 in an optical network unit, and an eastbound continuous signal based on digital subcarriers in a metropolitan area node. A generation module (including a continuous subcarrier signal generation module 501, a power adjustment module 503 between subcarriers, and a subcarrier up-conversion and coupling module 504), an uplink burst signal generation module based on digital subcarriers in an access network optical network unit (including a burst subcarrier signal generation module 509, a power adjustment module 503 between subcarriers, and a subcarrier up-conversion and coupling module 504), an uplink signal generation module 510 in an access network optical network unit, a digital subcarrier beam combining module 511 in a metropolitan-access all-optical fusion node, and a eastbound signal receiving and processing module 512 in a metropolitan node.

[0243] In general, modules 501-505 constitute the westbound signal transmission module in the metropolitan area node. Modules 507 and 508 are respectively the westbound signal receiving and processing module in the metropolitan area node and the downlink signal receiving and processing module in the access network optical network unit. Modules 501, 503, 504 and 505 constitute the eastbound signal transmission module in the metropolitan area node. Modules 509, 503, 504 and 510 constitute the uplink signal transmission module in the access network optical network unit. Module 512 is the eastbound signal receiving and processing module in the metropolitan area node. Modules 506 and 511 are respectively the westbound transmission module and the eastbound transmission module in the metropolitan area-access all-optical fusion node.

[0244] The following is a more detailed description of the detailed workflow of each module involved in the system architecture of this example.

[0245] The continuous subcarrier signal generation module 501 generates a continuous signal with multiple digital subcarriers according to the application scenario requirements. Its working process is as follows: firstly, random data is generated and QAM constellation point mapping is completed, and then the signal is upsampled and shaped and filtered.

[0246] The subcarrier dispersion pre-compensation module 502 performs dispersion pre-compensation for each digital subcarrier at a corresponding transmission distance according to application scenario requirements.

[0247] The power adjustment module 503 between subcarriers multiplies the multiple digital subcarrier signals generated by the digital multicarrier signal generation module by the power ratio, and adjusts the performance level of each subcarrier signal when it is received after being transmitted through the channel according to the application scenario requirements.

[0248] The subcarrier up-conversion and coupling module 504 up-converts the generated subcarrier signals to different frequency bands and couples them.

[0249] The west / east signal generating module 505 in the metropolitan area node converts the digital signal into an analog signal, performs signal modulation through a dual polarization IQ modulator, and amplifies the optical signal through an erbium-doped fiber amplifier.

[0250] The digital subcarrier splitting module 506 in the metropolitan area network-access all-optical fusion node splits the westbound signal in the metropolitan area network. A part of the signal enters the access network and reaches each optical network unit after passing through the passive optical network system; the other part of the signal continues to be transmitted in the metropolitan area network. Its working process is as follows: the signal transmitted from the previous node in the metropolitan area network to the west first passes through an erbium-doped fiber amplifier to compensate for the transmission loss between nodes, and then is separated from other wavelengths through a wavelength selection switch, and then passes through an erbium-doped fiber amplifier to compensate for the device insertion loss, and finally passes through a 3-dB optical splitter to be divided into two beams: the part that continues to be transmitted in the metropolitan area network passes through another wavelength selection switch and is combined with other wavelengths, and is pre-amplified by an erbium-doped fiber amplifier together; the other part passes through an optical circulator and enters the access network.

[0251] The westbound signal receiving and processing module 507 in the metropolitan area node selectively detects the digital subcarriers carrying the metropolitan area network signal by selecting the central wavelength of the local oscillator light of the coherent receiver according to the application scenario requirements. Then, the analog-to-digital converter converts the analog signal into a digital signal, and each subcarrier is down-converted to the baseband and then the signal is decoded using the DSP algorithm.

[0252] The signal receiving and processing module 508 in the optical network unit selectively detects the digital subcarrier carrying the access network signal by selecting the central wavelength of the local oscillator light of the coherent receiver according to the application scenario requirements. Then, the analog-to-digital converter converts the analog signal into a digital signal, down-converts the subcarriers to the baseband, and uses the DSP algorithm to decode the signal.

[0253] The burst subcarrier signal generation module 509 has the following working process: firstly, random data is generated and QAM constellation point mapping is completed; then, a specially designed preamble is inserted into the signal frame to assist the receiving end DSP algorithm to converge quickly; finally, the signal is upsampled and shaped and filtered. Among them, the training sequence in the specially designed preamble includes two sections: the first section sequence is used to assist the receiving end DSP to perform frame detection and clock recovery; the second section sequence is used to assist the receiving end DSP to perform frame synchronization, SOP estimation, coarse frequency offset estimation and channel estimation.

[0254] The uplink signal generating module 510 in the access network optical network unit converts the digital signal into an analog signal, performs signal modulation through a dual-polarization IQ modulator, and amplifies the optical signal through a semiconductor optical amplifier.

[0255] The digital subcarrier beam combining module 511 in the metropolitan area-access all-optical fusion node combines the metropolitan area network signal transmitted eastward with the access network uplink signal from each optical network unit, and continues to transmit them together in the metropolitan area network. Its working process is as follows: the signal transmitted eastward from the previous node in the metropolitan area network first passes through an erbium-doped fiber amplifier to compensate for the transmission loss between nodes, and then passes through a wavelength selection switch and inputs one end of the 3-dB optical coupler. The signal transmitted from the access network through an optical circulator passes through an erbium-doped fiber amplifier and then inputs the other end of the 3-dB optical coupler. After passing through the 3-dB optical coupler, the subcarriers are combined. The combined multi-subcarrier signal passes through another wavelength selection switch and is combined with other wavelengths, and is pre-amplified together through an erbium-doped fiber amplifier.

[0256] The eastbound signal receiving and processing module 512 in the metropolitan area node selectively detects the digital subcarriers carrying the metropolitan area network signal and the access network signal by selecting the central wavelength of the local oscillator light of the coherent receiver according to the application scenario requirements; the analog-to-digital converter converts the analog signal into a digital signal, and each subcarrier is down-converted to the baseband for dispersion compensation, and finally the DSP algorithm is used to decode the signal.

[0257] The verification and results of this example system in a coherent communication experimental system are further given below.

[0258] In this specific embodiment, a single carrier signal with a baud rate of 50Gbaud is divided into four digital subcarriers through DSCM technology. Subcarrier 1 (SC1) and subcarrier 2 (SC2) carry the signal on the access network side, and subcarrier 3 (SC3) and subcarrier 4 (SC4) carry the signal on the metropolitan area network side. The modulation format of the signal is dual polarization 16-order orthogonal amplitude modulation (DP-16QAM). 80km standard single-mode optical fiber is used to simulate the spacing between metropolitan nodes in the metropolitan area network, and 20km standard single-mode optical fiber is used to simulate the spacing between the metropolitan-access all-optical fusion node and the optical network unit of the access network.

[0259] Figure 6 The experimental result diagram (a) shows the discussion of the dispersion compensation problem and detection method problem in the downlink of this example, and the experimental result diagram (b) shows the change of the optical signal-to-noise ratio-bit error rate curve at different transmission distances and the comparison with the theoretical curve.

[0260] (a) The figure explores the impact of dispersion compensation on system performance in the 80km+20km transmission link. At the same time, in order to better combine with TFDM technology, we assume that the optical network unit side of the access network of this downlink does not necessarily adopt the fixed method of inserting the local oscillator (LO) between SC1 and SC2 to detect two subcarriers at the same time. That is, in the same time slot, there may be multiple optical network units, some of which only need the information carried on SC1, and some only need the information carried on SC2. Then, LO can be inserted in the middle of a certain subcarrier spectrum for coherent detection, so that a subcarrier can be detected separately. In the figure, we adjust the power in the DSP on the transmitter side during the experiment so that each subcarrier has consistent performance when detected separately, and compare it with the performance when detected together. Since the detection of two waves together will be affected by the detector bandwidth and IQ skew, compared with separate detection, the transmission quality will be degraded by 1.1dB at the error threshold of 2e-2. In addition, it can be seen from the experimental results that there is almost no difference in performance between the dispersion compensation steps of pre-compensation at the transmitter end of the metropolitan area network and post-compensation at the receiver end of the optical network unit on the access network side. Therefore, in the downlink, in order to save power and cost, it is possible to choose to perform dispersion pre-compensation in the transmitter DSP in the metropolitan area node.

[0261] Figure (b) focuses on another issue that needs to be considered in long-distance transmission, that is, the erbium-doped fiber amplifier (EDFA) will not only amplify the signal power, but also the noise power during the amplification process, which will lead to the degradation of the system OSNR. Therefore, even if EDFA can be used to compensate for various losses during long-distance transmission, the system OSNR will continue to degrade with the use of EDFA at each level. For DP-16QAM signals, the degradation caused by 80km transmission is not obvious, and the two curves are almost overlapping. However, when it reaches the next node after another 80km of optical fiber, the OSNR degradation becomes obvious. In general, there is a gap of about 3.5dB between the error threshold of 2e-2 and the theoretical value.

[0262] Figure 7 The figure (a) shows the experimental results of exploring the influence of the semiconductor optical amplifier (SOA) in the access network side transmitter on the sensitivity curve in the uplink of this example; and the figure (b) shows the experimental results of exploring the influence of different combinations of optical power entering the photosynthetic combiner and after amplification by the erbium-doped fiber amplifier on the dynamic range.

[0263] Since the output power of the transmitter is relatively small, in order to meet the power budget requirements, optical amplification will be performed in advance at the output of the transmitter. In the metropolitan area node, optical amplification is achieved through EDFA, but in the optical network unit on the access network side, EDFA is not conducive to integration, so SOA is used for amplification. However, the experimental results in Figure (a) show that as the output optical power of the SOA increases, the nonlinear effect will become more significant, resulting in a decrease in sensitivity. Therefore, unrestrained increase in the amplification degree of the SOA will not lead to an unlimited increase in the power budget. When the output optical power of the SOA increases to about 4dBm, the power budget reaches the maximum value (about 35.4dB), and further increase in the output optical power of the SOA will reduce the power budget.

[0264] In actual links, the distances of each ONU from the metro-access all-optical fusion node are different, which means that in the traditional time division multiplexing (TDM) scheme, the system architecture with fixed parameters will face large or small optical signals in different time slots. Therefore, under the premise of ensuring that the access network signal farthest from the metro-access all-optical fusion node can reach the bit error threshold and does not affect the normal reception of the metropolitan area network signal, we further explored how large the dynamic range of the ONU side signal can be tolerated in the proposed metro-access all-optical fusion architecture without adjusting various parameters. (b) Figure reflects the influence of the optical power entering the two ends of the coupler and the output optical power of the EDFA of the metro-access all-optical fusion node on the proposed metro-access all-optical fusion architecture under a large dynamic range when the SOA output optical power is also 0dBm. In general, as the distance between the ONU and the metro-access all-optical fusion node gets closer, that is, the optical power of the access network side signal entering the metro-access all-optical fusion node gets larger and larger, the bit error rate of the access network side signal represented by the solid line gets smaller. Correspondingly, as the image interference caused by the subcarrier IQ skew of the access network side signal increases, the bit error rate of the metropolitan area network side signal represented by the dotted line increases. However, when the ROP on the access network side reaches above -20dBm, this change will tend to be gentle, which is caused by the nonlinearity introduced by SOA. When the optical power of the access network side signal entering the metro-access all-optical fusion node is too large, it will cause the input fiber optical power to be too large when transmitted in the metropolitan area network after passing through the metro-access all-optical fusion node, thereby causing the nonlinearity of the optical fiber to affect the signal quality, resulting in an increase in the bit error rate at a large receiving optical power.

[0265] The experimental results show that the optical network system of metropolitan area-access network all-optical integration supported by digital subcarrier multiplexing technology proposed in this application can effectively respond to the urgent needs of the next generation of high-speed optical fiber communication networks for further close network integration and the expectation of high speed and large capacity. By applying digital subcarrier multiplexing technology, the delay and power consumption caused by optical-electrical-optical conversion can be effectively avoided, which greatly saves the operation and maintenance costs of the network, greatly improves the resource utilization and flexibility of the system, and is expected to support the upgrade of high-speed optical fiber communication network architecture to flexibly respond to more complex application scenarios in the future.

[0266] In the embodiments provided in the present application, it should be understood that the disclosed system architecture, device and method can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the module is only a logical function division. There may be other division methods in actual implementation, such as multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or modules, or it can be an electrical, mechanical or other form of connection.

[0267] In addition, each module in the embodiment of the present application can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module. The above integrated modules can be implemented in the form of hardware or software modules.

[0268] In this application, the terms "first", "second", etc. are used to distinguish between identical or similar items with substantially the same effects and functions. It should be understood that there is no logical or temporal dependency between "first" and "second", nor is there a limit on the quantity and execution order. It should also be understood that although the following description uses the terms first, second, etc. to describe various elements, these elements should not be limited by the terms. These terms are only used to distinguish one element from another element.

Claims

1. A metropolitan area-access all-optical fusion network system based on digital subcarrier multiplexing technology, characterized in that: include: The metropolitan area network part has a ring-shaped network topology, and the signal is transmitted bidirectionally in the east and west directions in two optical fibers. The metropolitan area network part includes multiple metropolitan area nodes, core-metropolitan area nodes, and metropolitan area-access all-optical fusion nodes; The access network part has a tree-like network topology, and the uplink signal and the downlink signal are bidirectionally transmitted in a single optical fiber. The access network part includes an optical splitter and multiple optical network units; The metropolitan area node includes: a westbound signal transmission module and an eastbound signal transmission module, both for transmitting continuous signals based on digital subcarrier multiplexing; a westbound signal receiving and processing module and an eastbound signal receiving and processing module, both for receiving and processing signals based on digital subcarrier multiplexing in corresponding directions; and, The optical network unit includes: a downlink signal receiving and processing module, used to receive and process downlink signals based on digital subcarrier multiplexing from the access network; an uplink signal transmitting module, used to transmit uplink burst signals based on digital subcarrier multiplexing; and, The metropolitan area-access all-optical fusion node includes: a westbound transmission module, which is used to split the westbound signal into two beams, one beam continues to be transmitted in the metropolitan area network, and the other beam is transmitted to the access network; an eastbound transmission module, which is used to perform all-optical beam combination of the eastbound signal in the metropolitan area network and the uplink signal in the access network, and continue to transmit them in the metropolitan area network; Among them, through the digital subcarrier multiplexing technology, different digital subcarriers on the same carrier carry metropolitan area network signals and access network signals respectively, realizing the full optical integration of metropolitan area network and access network, avoiding optical-electrical-optical conversion; The westbound signal receiving and processing module, the eastbound signal receiving and processing module and the downlink signal receiving and processing module all adopt coherent receiving technology to selectively detect specific digital subcarriers by adjusting the local oscillator light frequency.

2. The system according to claim 1, characterized in that The westbound signal transmission module and the eastbound signal transmission module in the metropolitan area node specifically include: A continuous subcarrier signal generating module, used for generating a continuous signal including a plurality of digital subcarriers; A subcarrier dispersion precompensation module is used to precompensate the dispersion of each subcarrier according to its transmission distance to reduce the influence of dispersion on the signal; A subcarrier power adjustment module, used to adjust the transmission power of each subcarrier signal to optimize its performance in the transmission channel; The subcarrier up-conversion and coupling module is used to up-convert the generated subcarrier signals to different frequency bands and couple the subcarrier signals for transmission.

3. The system according to claim 2, characterized in that The working process of the continuous subcarrier signal generating module includes: Generate random data for simulating actual communication information flow; Performing quadrature amplitude modulation (QAM) constellation mapping on the random data to convert digital information into complex symbols; Up-sampling the mapped signal to increase the sampling rate of the signal to meet the needs of subsequent digital signal processing; The upsampled signal is subjected to shaping filtering to limit the signal bandwidth and improve the signal's spectral characteristics.

4. The system according to claim 1, characterized in that The uplink signal transmission module in the optical network unit specifically includes: A burst subcarrier signal generation module is used to generate a burst signal including multiple digital subcarriers to adapt to the burst transmission characteristics of the access network; The subcarrier power adjustment module is used to adjust the transmission power of each subcarrier signal according to the uplink transmission requirements to optimize its performance in the uplink transmission channel; The subcarrier up-conversion and coupling module is used to up-convert the generated subcarrier signals to a specified frequency band, and couple the subcarrier signals before sending them to the access network.

5. The system according to claim 4, characterized in that The workflow of the burst subcarrier signal generation module includes: Generate random data for simulating uplink information flow in access network; Performing quadrature amplitude modulation (QAM) constellation mapping on the random data to convert digital information into complex symbols; Inserting a preamble symbol into the signal frame, wherein the preamble symbol is used to assist the receiving end in digital signal processing, including signal synchronization, channel estimation, polarization state estimation and coarse frequency offset estimation; Upsample the processed signal to increase the sampling rate to meet the subsequent digital signal processing requirements; The upsampled signal is subjected to shaping filtering to limit the signal bandwidth and improve the signal's spectral characteristics.

6. The system according to claim 5, characterized in that The leading symbol includes two training sequences: The first training sequence is used to assist the digital signal processing (DSP) module at the receiving end to perform frame detection and clock recovery, wherein: frame detection is used to determine the starting position of the burst signal; clock recovery is used to synchronize the sampling clock of the receiving end with the signal clock of the transmitting end; The second training sequence is used to assist the digital signal processing (DSP) module at the receiving end to perform the following operations: 1) Frame synchronization, used to accurately locate the boundaries of data frames; 2) Polarization state estimation, used to compensate for polarization mode dispersion generated during transmission; 3) Coarse frequency offset estimation, used to correct the frequency offset between the transmitter and the receiver; 4) Channel estimation, which is used to evaluate the characteristics of the transmission channel and provide a basis for subsequent equalization processing.

7. The system according to claim 1, characterized in that The working process of the westbound transmission module of the metro-access all-optical fusion node includes the following steps: 1) Receive westbound transmission signals from a node on the metropolitan area network; 2) Use erbium-doped fiber amplifiers to amplify the received signal to compensate for the transmission loss between nodes; 3) Separate the wavelength used for metro-access convergence that carries metropolitan area network and access network signals from other wavelengths through a wavelength selective switch; 4) using another erbium-doped fiber amplifier to amplify the separated signal to compensate for the device insertion loss; 5) The signal is split into two beams through a 3-dB optical beam splitter: one beam continues to be transmitted westward in the metropolitan area network; the other beam is transmitted to the access network; 6) The signal that continues to be transmitted in the metropolitan area network is processed as follows: the signal is recombined with other wavelengths through a wavelength selective switch; the signal is pre-amplified using an erbium-doped fiber amplifier; 7) The signal transmitted to the access network is processed as follows: An optical circulator is used to direct the signal into the access network transmission path.

8. The system according to claim 1, characterized in that The working process of the eastbound transmission module of the metro-access all-optical fusion node includes the following steps: 1) Receive the eastbound transmission signal from a node on the metropolitan area network; 2) Use erbium-doped fiber amplifiers to amplify the received metropolitan area network signals to compensate for the transmission loss between nodes; 3) Separate the wavelength carrying the metropolitan area network signal from other wavelengths through a wavelength selective switch; 4) Input the separated metropolitan area network signal into one input end of a 3-dB optical coupler; 5) receiving an uplink signal from the access network, the specific steps comprising: receiving the uplink signal of the access network through an optical circulator; amplifying the access network signal using an erbium-doped fiber amplifier; inputting the amplified access network signal into another input end of the 3-dB optical coupler; 6) Fully optically combine the metropolitan area network signal and the access network signal through a 3-dB optical coupler; 7) Processing the combined signal as follows: Recombining the combined signal with other wavelengths through a wavelength selective switch; Pre-amplifying the signal using an erbium-doped fiber amplifier; 8) The processed signal continues to be transmitted eastward in the metropolitan area network.

9. The system according to claim 1, characterized in that The workflow of the signal receiving and processing module in the metropolitan area node includes the following steps: 1) Use coherent receiving technology to receive the transmitted signal: by adjusting the central wavelength of the local oscillator light, selective detection of specific digital subcarriers is achieved; 2) An integrated coherent receiver converts the received optical signal into an electrical signal; 3) Convert the analog signal to a digital signal using an analog-to-digital converter. 4) Perform digital signal processing (DSP) on digital signals: down-convert each subcarrier signal and convert the signal to baseband; perform clock recovery to ensure that the sampling clock at the receiving end is synchronized with the transmitting end; perform dispersion compensation to eliminate the dispersion effect during transmission; use cascaded multimode algorithms to perform channel equalization to compensate for polarization mode dispersion and other polarization-related damage; first perform frequency offset estimation and compensation, and then perform carrier phase recovery to eliminate the influence of phase noise; 5) Demodulate and decode the processed signal: make symbol decisions based on the modulation format (such as QAM); perform forward error correction (FEC) decoding to correct errors that occur during transmission; 6) Output the recovered data stream and calculate the bit error rate.

10. The system according to claim 1, characterized in that The system also includes a mechanism for dispersion compensation, specifically including: Dispersion pre-compensation at the transmitting end: In the westbound and eastbound signal transmission modules of the metropolitan area node, dispersion pre-compensation is performed on each digital subcarrier signal; the corresponding pre-compensation amount is calculated and applied based on the estimated transmission distance and the dispersion parameters of the optical fiber; Post-dispersion compensation at the receiving end: Post-dispersion compensation is performed on the received signals in the westbound signal receiving and processing module, eastbound signal receiving and processing module of the metropolitan area node, and the downlink signal receiving and processing module of the optical network unit; Flexible configuration of dispersion compensation: The system can flexibly choose to perform pre-compensation at the transmitting end, post-compensation at the receiving end, or both at the same time according to the network deployment and transmission performance requirements; for the metropolitan area network, post-compensation is mainly performed at the receiving end; for the access network, the uplink signal is mainly post-compensated at the receiving end, and the downlink signal is mainly pre-compensated at the transmitting end; Subcarrier-level dispersion compensation: Dispersion compensation is performed on subcarriers of different frequencies to adapt to the differences in dispersion characteristics of subcarriers in different frequency bands.

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