The space-air-ground integrated network serves as the core infrastructure for 6G ubiquitous communication. Free-space optical (FSO) communication, with its inherent advantages of ultra-large bandwidth, low latency, electromagnetic interference resistance, and high confidentiality, has become the core transmission technology for space-air-ground three-dimensional networking. This network integrates space-based satellite optical links, air-based platform optical relays, and ground-based optical fiber and wireless optical access systems to build a three-dimensional, full-domain optical transmission architecture. It effectively breaks through the bottlenecks of limited coverage and insufficient bandwidth in traditional communication, supporting critical business scenarios such as remote area communication, ocean networking, disaster emergency response, and deep space exploration.
This paper systematically reviews the layered architecture, topological characteristics, and link types of the space-air-ground integrated optical network, summarizes typical research achievements and engineering trial progress at home and abroad, and focuses on analyzing key core technologies such as atmospheric turbulence suppression, high-precision APT (Acquisition, Pointing, and Tracking), dynamic intelligent networking, heterogeneous network convergence, and lightweight terminal integration.
Meanwhile, it focuses on current engineering bottlenecks such as weak link anti-interference, strong topological dynamics, high difficulty in heterogeneous collaboration, limited space-air payloads, lack of quality of service (QoS) guarantee, and imperfect industry standards. It looks forward to future development trends from six dimensions: intelligent anti-interference networking, full-domain all-optical interconnection, satellite-ground collaborative applications, lightweight integration, quantum secure transmission, and industrial standardization. This study provides a systematic theoretical reference for the technological iteration, engineering implementation, and industrialization development of the space-air-ground integrated optical network.
1 Research Overview
1.1 Research Background
Given the rapid growth of 6G ubiquitous communication, space-air IoT (Internet of Things), deep space exploration, and emergency disaster relief services, the shortcomings of traditional communication systems have become increasingly prominent. Ground-based optical fibers are constrained by terrain and infrastructure, making it impossible to achieve full-domain coverage in oceans, polar regions, and deserts. Wireless radio frequency (RF) communication suffers from tight spectrum, limited bandwidth, and weak anti-interference capabilities, making it difficult to meet the Tbit/s-level high-speed transmission requirements for space-air applications.
The space-air-ground integrated network integrates space-based satellites, air-based floating/unmanned aerial vehicle (UAV) platforms, and ground communication facilities to build a three-dimensional coverage architecture, which is the inevitable development form for achieving global ubiquitous connectivity. Free-space optical (FSO) communication, with advantages such as unconstrained bandwidth, low transmission latency, strong confidentiality, and no need for spectrum authorization, has become the optimal carrier for high-speed interconnection of space-air backbone networks. The space-air-ground integrated optical network integrates optical fiber and space optical communication technologies to form a "satellite-air-ground" collaborative transmission system. It is a critical component of the 6G space-ground integrated infrastructure and plays a key role in the technological iteration and engineering implementation of space-air communication technologies.
1.2 Research Significance
The space-air-ground integrated optical network possesses both theoretical and engineering value. Theoretically, this network integrates multidisciplinary technologies such as optical communication, satellite networking, and intelligent network optimization, which can refine theoretical systems like dynamic heterogeneous optical transmission and intelligent anti-interference networking. Engineering-wise, it breaks through traditional communication coverage blind spots, supports major projects such as satellite internet and deep space exploration, and enhances the guarantee capabilities for disaster emergency and national defense confidential communications, serving as a critical support for the national space-ground integrated information infrastructure.
Existing research mostly focuses on single satellite optical communication or ground FSO technology, lacking a global review of space-air-ground integrated networking. There is a scarcity of systematic summaries on dynamic topology evolution, heterogeneous collaborative scheduling, engineering construction bottlenecks, and intelligent trends. Based on this, from the perspective of integrated networking, this paper systematically reviews the network architecture, research status, core technologies, existing challenges, and development trends to make up for the shortcomings of existing research and provide a systematic reference for related technological research and development.
2 Space-Air-Ground Integrated Optical Network Architecture
The space-air-ground integrated optical network adopts a three-dimensional three-layer architecture of "space-based backbone—air-based relay—ground-based access." Each layer has clear division of labor, complementary functions, and collaborative networking, forming a high-speed optical transmission system with full-domain coverage, dynamic adaptation, and heterogeneous convergence, which can adapt to multi-scenario and differentiated space-air communication needs.
2.1 Layered Spatial Architecture
2.1.1 Space-Based Backbone Layer
The space-based backbone layer consists of geostationary earth orbit (GEO), medium earth orbit (MEO), low earth orbit (LEO) satellites, and deep space explorers, undertaking full-domain coverage and cross-domain transmission tasks. GEO satellites have stable orbits and wide coverage, suitable for fixed satellite-ground relay transmission, but with relatively high latency. LEO satellites have the advantages of low latency and low loss, relying on large-scale constellations and inter-satellite optical links to build a space-based high-speed backbone. MEO satellites serve as transition nodes between high and low orbits, responsible for cross-orbit relay and topology balancing to ensure full-domain connectivity of the space-based network.
2.1.2 Air-Based Relay Layer
The air-based relay layer is composed of mobile platforms such as UAVs, stratospheric airships, and high-altitude balloons. With flexible deployment and dynamic reconfigurability, it serves as a key relay hub connecting space and ground. Stratospheric platforms can stay airborne for a long time to achieve continuous coverage over large areas. UAV swarms can quickly maneuver to form networks, adapting to scenarios such as disaster emergency response and local area blind spot filling. Air-based platforms achieve regional relay forwarding through "air-air" and "air-ground" optical links, effectively making up for the "last mile" shortcoming of satellite-ground link landing.
2.1.3 Ground-Based Access Layer
The ground-based access layer includes the ground optical fiber backbone network, ground FSO nodes, user terminals, and management and control centers, undertaking data aggregation, user access, and whole-network scheduling functions. The optical fiber network provides stable and large-capacity backbone transmission. Ground FSO nodes realize the landing and docking of space-ground optical links, adapting to high-speed access in scenarios without optical fibers. The whole-network management and control center is responsible for topology management, resource scheduling, and fault operation and maintenance to ensure stable network operation.
2.2 Network Topology Characteristics
The topology of the space-air-ground integrated optical network has three characteristics: static stability, dynamic time-varying, and heterogeneous convergence. GEO satellite-ground links and ground optical fibers constitute a static topology, adapting to fixed service transmission. The high-speed movement of LEO constellations and UAVs leads to second-level topology updates, forming a dynamic delay tolerant network (DTN). The network integrates multiple transmission systems such as optical fiber, FSO, and RF, with optical links as the main and RF as the backup, balancing transmission performance and network survivability.
2.3 Typical Link Types
The core links of the space-air-ground integrated optical network are divided into four categories: inter-satellite optical links operate in a vacuum environment with low loss and high rate, serving as the core of space-based networking; satellite-ground optical links traverse the atmosphere, most affected by turbulence and meteorological attenuation, serving as the focus of reliability research; "air-air" and "air-ground" optical links adapt to air-based dynamic relay and emergency networking; ground FSO links are used for short-distance high-speed blind spot filling access in cities and remote sites. The layered architecture of the space-air-ground integrated optical network is shown in Figure 1.
3 Research Status at Home and Abroad
3.1 Overseas Research Status
Developed countries and regions such as the United States, Japan, and Europe started early in the field of space-air optical communication and have a high degree of engineering. They have completed multiple generations of satellite-borne and airborne optical communication trials, forming a mature technological and engineering system.
The National Aeronautics and Space Administration (NASA) has conducted deep space laser communication trials such as LLCD (Lunar Laser Communication Demonstration) and LCRD (Laser Communications Relay Demonstration), verifying the feasibility of space-ground and deep space optical transmission. Space Exploration Technologies Corp. (SpaceX) has deployed inter-satellite laser links on a large scale in its Starlink project, achieving full-domain high-speed interconnection of low-orbit constellations. The Defense Advanced Research Projects Agency (DARPA) has been deeply engaged in UAV and stratospheric air-based optical networking technologies.
In Europe, the European Space Agency (ESA) has promoted laser relay projects such as SILEX (Semiconductor Laser Inter-satellite Link Experiment) and EDRS (European Data Relay System), building a mature space-ground optical relay system widely serving businesses such as earth observation and meteorological remote sensing, with outstanding advantages in coherent optical communication and intelligent scheduling. In Japan, the Japan Aerospace Exploration Agency (JAXA) focuses on the research and development of lightweight optical terminals for microsatellites, adapting to small constellation networking. Overall, overseas single-point optical link technology is mature, but the three-layer integrated collaborative networking is still in the stage of theoretical exploration.
3.2 Domestic Research Status
Relying on the 6G special project and key research and development plans, China has achieved rapid technological catch-up. Aerospace institutes and key universities have completed a series of satellite-borne and airborne laser communication trials, and the technological level has gradually entered the international advanced ranks. The "Mozi" satellite completed satellite-ground quantum laser communication and key distribution, realizing the integrated verification of optical communication and quantum security. Domestic low-orbit satellite internet constellations continue to promote the deployment of inter-satellite laser links, gradually building an autonomous and controllable space-based optical backbone network.
At the air-based level, domestic universities and research institutions have broken through high-speed optical communication for UAVs and dynamic networking technology for multi-UAV swarms, completing multi-scenario "air-air" and "air-ground" optical link trials to support emergency dynamic networking applications. At the key algorithm level, China has achieved rich results in turbulence suppression, APT (Acquisition, Pointing and Tracking), and intelligent routing, entering the international advanced ranks as a whole. However, there are still shortcomings in the localization of high-end optoelectronic devices, long-term on-orbit reliability, and industry standardization.
4 Key Core Technologies
4.1 Atmospheric Interference Suppression Technology
Atmospheric turbulence, cloud, fog, rain, and snow attenuation, and background light noise are important factors causing the performance degradation of space-air FSO links. Atmospheric turbulence causes beam jitter, spot distortion, phase fluctuation, resulting in increased link bit error rate or even transmission interruption. Weather attenuation leads to a significant loss of optical power. Background light noise reduces the received signal-to-noise ratio.
Current mainstream suppression methods include: Adaptive Optics (AO) technology effectively corrects turbulence distortion through real-time phase detection and deformable mirror compensation, suitable for long-distance satellite-ground links. Spatial/time/wavelength diversity reception technology suppresses fast fading at low cost through multi-path signal combining. Multiple-input multiple-output (MIMO) optical communication utilizes multi-beam spatial multiplexing to improve anti-interference capability and transmission capacity. Optimal wavelength selection at 1550 nm, adaptive power control, and dynamic link switching can effectively mitigate the impact of weather attenuation. Narrowband filtering, coherent detection, and high-sensitivity optoelectronic detectors can significantly suppress background noise. Currently, single anti-interference technologies have their own advantages and disadvantages, and integrated anti-interference is the mainstream development direction.
4.2 High-Precision APT Technology
APT technology is the key to the stable establishment of space-air dynamic optical links, which can solve the problem of precise beam alignment between high-speed moving nodes. It adopts a three-level working mechanism of "coarse acquisition—fine pointing—high-precision tracking." "Coarse acquisition" completes the initial search of the target through large-range mechanical scanning. "Fine pointing" relies on micro-vibrating mirrors and high-precision angle sensors to achieve precise spot coupling. The tracking stage integrates Kalman filtering, trajectory prediction, and visual feedback mechanisms to provide real-time compensation for dynamic deviations caused by the high-speed movement of the platform.
Current technical bottlenecks are mainly reflected in insufficient tracking accuracy in high-dynamic scenarios, high difficulty in micro-vibration suppression, and the difficulty of balancing power consumption and volume of lightweight APT equipment. Intelligent tracking prediction algorithms based on deep learning and compound axis cooperative control are important research directions to improve dynamic adaptation capabilities.
4.3 Dynamic Topology Networking and Intelligent Routing Technology
The space-air-ground integrated optical network is a typical time-varying DTN with dynamic topology updates and frequent link interruptions, making traditional static routing inapplicable. Existing technologies use the DTN store-and-forward mechanism to solve the transmission problem of intermittent links, combined with intelligent routing algorithms such as deep learning and reinforcement learning to perceive topology and link status in real time and dynamically optimize forwarding paths. Meanwhile, satellite-ground collaborative routing and cross-layer optimization technologies can realize unified scheduling of full-domain resources, significantly improving networking stability and resource utilization.
4.4 Heterogeneous Network Convergence Technology
The space-air-ground optical network is characterized by the heterogeneous coexistence of multiple transmission systems such as optical fiber, FSO, and RF. Various links have significant differences in latency, bandwidth, and reliability, with unified protocol systems and high difficulty in collaborative scheduling. Heterogeneous convergence technology mainly includes three parts: unified interface adaptation, whole-network resource collaborative scheduling, and intelligent seamless link switching. Multi-system signal compatibility and interoperability are realized through standardized heterogeneous interfaces. Dynamic allocation of bandwidth, power, and time slots is realized relying on network slicing and intelligent resource scheduling. Seamless switching of optical/RF links is realized using link status prediction to ensure continuous and stable services.
4.5 Lightweight All-Optical Switching and Virtualization Technology
Space-air platforms have limited payloads. Traditional electrical switching has high latency and low integration, making it difficult to adapt to high-speed transmission needs. Lightweight all-optical switching directly completes data forwarding in the optical domain without optoelectronic conversion, possessing the advantages of low latency, large bandwidth, and small size, adapting to satellite and airborne deployment. Optical network virtualization and slicing technologies can realize the abstract reconstruction of physical resources, providing dedicated logical channels for differentiated services to meet the layered service needs of high-speed remote sensing, low-latency measurement and control, and emergency communication.
4.6 Physical Layer Security and Quantum Encrypted Transmission Technology
Optical communication is naturally resistant to electromagnetic interference, but there are still security risks such as beam interception, polarization deception, and link interference. Physical layer security realizes low-interception transmission of signals through beam forming, polarization encryption, and phase coding. Quantum key distribution technology relies on the unclonable characteristics of quantum mechanics to realize theoretically unconditionally secure key distribution, which can significantly improve the confidentiality level of space-ground optical transmission and has important application value in national defense communication and deep space classified transmission scenarios.
4.7 Lightweight and Low-Power Integration Technology
Based on silicon photonics integration and Micro-Electro-Mechanical Systems (MEMS) technology, the miniaturization and low-power integration of optical communication terminals and APT modules can be realized. Coupled with intelligent sleep and dynamic power management mechanisms, it can adapt to the long-term airborne and on-orbit working needs of satellites and UAVs, serving as an important foundation for the engineering implementation of technology. The key components and technologies of the transceiver are shown in Figure 2.
5 Existing Technical Bottlenecks and Engineering Challenges
Currently, the single-point link communication technology of the space-air-ground integrated optical network is basically mature, but there are still many bottlenecks in large-scale integrated networking, all-weather reliable transmission, and engineering implementation. The core challenges can be summarized into the following six categories.
5.1 Insufficient All-Weather Anti-Interference Reliability of Links
Atmospheric environmental disturbance and space transmission loss are the fundamental reasons for the insufficient reliability of space-air optical links. Satellite-ground and air-ground optical links need to traverse complex atmospheric environments such as the troposphere and stratosphere. Beam drift, spot expansion, phase distortion, and light intensity flicker caused by atmospheric turbulence directly cause random fluctuations in the received optical power, significantly increasing the system bit error rate, and even causing instantaneous link interruption in severe cases. Existing anti-interference technologies such as adaptive optics and diversity reception can effectively compensate for link loss in conventional weak turbulence scenarios, but there are still obvious shortcomings in compensation accuracy and response speed in complex airspace environments such as strong turbulence and wind shear. Meanwhile, severe weather such as rain, snow, fog, and haze will produce strong scattering and absorption effects on laser signals, causing a significant attenuation of optical power. Existing technologies such as adaptive power adjustment and optimal wavelength selection are difficult to achieve all-weather stable transmission in severe weather. In addition, the high-speed movement of low-orbit satellites and UAVs will introduce significant Doppler frequency shifts, causing optical signal carrier offset and demodulation distortion, further degrading transmission performance. The inherent transmission loss of long-distance space links also puts forward extremely high requirements for terminal transmission power and receiving sensitivity. The performance of existing commercial devices is difficult to balance the comprehensive transmission needs of long distance, high rate, and high reliability.
5.2 Poor Stability of High-Dynamic Topology Networking
Different from traditional static optical fiber networks, the space-air-ground integrated optical network is a typical high-dynamic time-varying DTN. The high-speed earth-orbiting operation of LEO satellite constellations and the mobile deployment of air-based UAV swarms make the whole-network topology present the characteristic of second-level rapid updates. The link connection time is short, and the on-off status is random, making it difficult to form a stable end-to-end transmission path. Traditional fixed network routing protocols and networking architectures are designed based on static topologies and cannot adapt to working scenarios with frequent link interruptions and real-time topology reconstruction. Problems such as routing failure, data packet loss, and severe end-to-end latency jitter are extremely easy to occur. At this stage, although the store-and-forward mechanism based on DTN and intelligent reinforcement learning routing algorithms can adapt to dynamic topologies to a certain extent, there are still problems such as poor whole-network collaboration, slow convergence speed for large-scale networking, large redundant overhead, and insufficient fault tolerance in extreme scenarios. Meanwhile, the movement laws of the three-layer nodes in space, air, and ground are significantly different. Satellite orbital movement is predictable, while UAV mobile movement is random. The superposition of dual-layer dynamic characteristics further increases the difficulty of whole-network topology prediction and stable networking. The network self-healing and dynamic reconstruction capabilities need to be further strengthened.
5.3 Complexity of Cross-Domain Collaborative Scheduling in Heterogeneous Networks
The space-air-ground integrated optical network is a typical multi-system heterogeneous convergence network, integrating three differentiated transmission systems: ground optical fiber, free-space optical communication, and RF wireless communication. Different links have huge differences in transmission bandwidth, latency characteristics, anti-interference capability, coverage range, and link survival time. Optical fiber links have high stability, low latency, and sufficient bandwidth, but the coverage range is fixed. FSO links are high-speed and unconstrained by spectrum, but are easily interfered with by the environment. RF links are resistant to occlusion and have good continuity, but bandwidth is limited. The interface protocols, frame structures, and resource scheduling mechanisms of the three transmission systems are not unified, lacking general adaptation standards, which leads to barriers in cross-system and cross-layer data interoperability. Meanwhile, existing resource scheduling strategies are mostly designed for single-layer networks and cannot realize the unified scheduling of full-domain resources in space, air, and ground. The problem of coexistence of resource idleness and resource congestion is prominent. At the link switching level, the seamless switching mechanism between optical links and RF backup links is immature. The switching prediction accuracy is insufficient, and the switching latency is high. High-speed services and real-time measurement and control services are prone to data interruption, making it difficult to meet the service transmission needs of high continuity and high reliability. The deep convergence and unified management of heterogeneous networks remain a key technical difficulty in the current industry.
5.4 Strict Payload Constraints on Space-Air Platforms
Space-air platforms such as satellites, UAVs, and stratospheric airships have strict constraints on the Size, Weight, and Power (SWaP) of the equipped devices, which is one of the main bottlenecks for the engineering implementation of space-air optical communication. Core devices such as high-precision APT components, high-speed optical modulation and demodulation modules, adaptive optical compensation equipment, and all-optical switching units have large volumes, high power consumption, and complex structures, making it difficult to adapt to the payload limits of small LEO satellites and light UAVs. At this stage, although silicon photonics integration and MEMS technologies have realized equipment lightweight upgrades, there are still technical shortcomings in core chips and devices such as high-end low-noise optical amplifiers, high-sensitivity detectors, and high-precision micro-vibrating mirrors. Some key devices rely on imports, and the degree of domestic substitution is insufficient. Meanwhile, lightweight transformation is often accompanied by performance loss. The tracking accuracy and dynamic response speed of miniaturized APT equipment, as well as the transmission rate and anti-interference capability of lightweight optical modules, are weaker than those of large ground equipment. It is difficult to achieve a perfect balance of "miniaturization, low power consumption, and high performance," which severely restricts the large-scale deployment and long-term on-orbit stable operation of space-air-ground integrated optical network terminals.
5.5 Imperfect Multi-Service QoS Guarantee Mechanism
The service types carried by the space-air-ground integrated optical network are highly differentiated, covering multiple services such as high-speed remote sensing big data transmission, low-latency satellite measurement and control, emergency command communication, full-domain IoT (Internet of Things) access, and civil broadband coverage. Different services have huge differences in requirements for bandwidth, latency, bit error rate, and transmission reliability. Remote sensing services require ultra-large bandwidth to support massive data return. Measurement and control services have extremely high requirements for latency and stability. Emergency services prioritize link availability. The access of massive heterogeneous users and the concurrency of differentiated services are extremely easy to cause network congestion and resource allocation imbalance. Current network resource scheduling mostly adopts static or semi-dynamic allocation strategies, which cannot adapt to service traffic fluctuations and link status changes in real time. There is a lack of refined and intelligent quality of service (QoS) hierarchical guarantee mechanisms. Meanwhile, congestion control and traffic balancing technologies for high-dynamic topology scenarios are not yet mature. It is difficult to realize the optimal configuration of whole-network resources in multi-service concurrent scenarios and cannot meet the service quality needs of various services.
5.6 Imperfect Standard and Engineering Verification System
Currently, the development of space-air-ground integrated optical networks at home and abroad is still in the stage of technological iteration and experimental verification, and a unified and perfect industry standard system has not yet been formed. At the technical level, the interface protocols, frame formats, synchronization mechanisms, and networking interaction standards for inter-satellite, satellite-ground, and air-ground optical links are not unified. The compatibility of optical terminal equipment from different manufacturers and different models is poor, making it difficult to realize cross-platform and cross-constellation interconnection. At the test and verification level, there is a lack of unified performance test indicators, environmental adaptability test specifications, and reliability evaluation systems. The experimental data of various research institutions lack universality and comparability. Meanwhile, existing engineering verifications are mostly short-cycle, single-point scenario trials. There is a serious lack of verification data for complex real scenarios such as long-term on-orbit operation, extreme meteorological environments, high-intensity dynamic interference, and large-scale networking. This cannot fully support technological iteration and system optimization, greatly restricting the standardization, industrialization, and large-scale implementation of space-air-ground integrated optical networks. Figure 3 shows the G.641 international standard led by China Unicom in ITU-T.
6 Future Development Trends
Aiming at current network technology shortcomings and combining with the iteration trends of cutting-edge technologies, the future space-air-ground integrated optical network will evolve in six major directions: intelligent self-adaptation, full-domain all-optical interconnection, device localization and lightweight, satellite-ground collaborative applications, quantum security convergence, and industrial standardization, realizing the leap from single-point verification to large-scale commercial use.
6.1 AI (Artificial Intelligence) Will Empower Intelligent Self-Adaptive Optical Networks
Traditional space-air-ground integrated optical networks rely on fixed algorithms and passive compensation mechanisms, with limited adaptability to complex environments and dynamic topologies. The integration of AI (Artificial Intelligence) and deep learning technologies will completely reconstruct the operation mode of space-air-ground integrated optical networks. In the future, based on algorithms such as machine learning, deep learning, and reinforcement learning, the intelligent upgrade of the whole network and full process will be realized. At the link anti-interference level, neural networks can be used to learn the dynamic characteristics of atmospheric turbulence and weather attenuation in real time, accurately predict link quality changes, and combine with adaptive optics and diversity reception to realize intelligent joint compensation, significantly improving link stability in complex environments. At the APT level, relying on intelligent trajectory prediction algorithms, the alignment deviation caused by high-speed node movement and micro-vibration is compensated to realize high-precision stable tracking in high-dynamic scenarios. At the networking scheduling level, intelligent algorithms can perceive whole-network topology changes, link loads, and service traffic distribution in real time, dynamically optimize routing paths and bandwidth resource allocation, and realize network self-healing, traffic balancing, and intelligent congestion avoidance. AI will effectively solve the pain points of traditional networks, such as poor dynamic adaptability, weak anti-interference capability, and low resource utilization, building a new generation of intelligent space-air optical transmission system with high robustness, self-perception, self-decision, and self-repair.
6.2 "Satellite-Air-Ground" Full-Domain All-Optical Networking Evolution
Currently, the space-air-ground integrated optical network still has some optoelectronic conversion links and heterogeneous transmission barriers, limiting the whole-network transmission latency, capacity, and interoperability. In the future, the network will gradually upgrade to a full-domain all-optical networking architecture, completely breaking through the three-layer transmission boundaries of space, air, and ground. At the space-based level, GEO, MEO, and LEO satellites will fully deploy high-speed inter-satellite all-optical links to build a seamless space-based all-optical backbone network, realizing full-domain high-speed interconnection between constellations and getting rid of excessive reliance on ground gateway stations. At the air-based level, mobile platforms such as UAVs and stratospheric airships will be equipped with lightweight all-optical switching terminals to form a dynamically reconfigurable air-based all-optical relay network, accurately making up for ground coverage blind spots and the shortcoming of satellite-ground link landing. At the ground-based level, the all-optical convergence of the ground optical fiber backbone network and ground FSO nodes will be realized to build a full-domain ground all-optical access system. Full-domain all-optical networking can save the process of frequent optoelectronic conversion, significantly reduce whole-network transmission latency, and improve Tbit/s-level ultra-large bandwidth transmission capability, realizing end-to-end high-speed, efficient, and transparent data transmission, and fully adapting to future business needs such as high-definition remote sensing and deep space exploration.
6.3 Lightweight and Localized Integration Upgrade of Core Devices
Aiming at the core pain point of limited payloads on space-air platforms, future space-air optical communication terminals will take silicon photonics integration, micro-nano optics, and MEMS technology as the core to realize the comprehensive upgrade of device chipization, equipment miniaturization, and system low power consumption. At the core device level, high-speed optical modulation chips, high-sensitivity detection chips, and micro optical amplification chips will realize localized integration substitution, solving the "choke point" problem of high-end devices while significantly reducing device volume and power consumption. At the terminal equipment level, traditional large APT systems and adaptive optical compensation equipment will be iterated into micro-integrated modules. Under the premise of ensuring tracking accuracy and anti-interference performance, they will adapt to the payload constraints of light UAVs and small LEO satellites. At the power consumption optimization level, through intelligent power regulation, dynamic sleep mechanisms, and low-power modulation algorithms, combined with the solar power supply system of space-air platforms, long-term stable and low-power operation of equipment will be realized. The integrated upgrade of core technologies will completely solve the contradiction between performance and payload, providing hardware support for large-scale networking of space-air optical networks.
6.4 Large-Scale Application of Deep Satellite-Ground Collaborative Scenarios
In the future, the space-air-ground integrated optical network will break through the single-layer independent working mode, realize the deep collaborative linkage of space-based wide-area coverage, air-based mobile blind spot filling, and ground-based precise access, and build a full-domain integrated resource scheduling and application service system. Space-based satellites are responsible for cross-domain massive data return and wide-area networking scheduling. Air-based platforms realize rapid mobile networking for scenarios such as disaster emergency response, local monitoring, and remote area blind spot filling. Ground-based networks are responsible for user access, data aggregation, and whole-network management. The collaboration of the three can realize the global optimal allocation of resources and adapt to large-scale applications in multiple fields. In the aerospace field, it supports deep space exploration, lunar bases, and high-speed return of satellite remote sensing big data. In the livelihood field, it solves broadband coverage in areas without infrastructure such as oceans, deserts, and polar regions, narrowing the "digital divide." In the emergency field, it realizes rapid networking in disaster scenarios such as earthquakes and floods, ensuring smooth emergency command and rescue communication.
6.5 Deep Convergence of Quantum Security and Optical Networks
Space-air optical communication naturally has the advantages of anti-electromagnetic interference and difficulty in interception, but security risks such as link eavesdropping, signal deception, and link interference in high-speed dynamic networking scenarios cannot be ignored. In the future, the deep convergence of quantum encryption technology and optical transmission networks will be realized to build a comprehensive and multi-level full-domain secure transmission system. Relying on satellite-ground and inter-satellite quantum key distribution technology, utilizing the unclonable and uncertainty principles of quantum mechanics, theoretically unconditionally secure key encrypted transmission is realized, completely eliminating the risk of traditional encryption algorithms being cracked. Meanwhile, combined with physical layer security technologies such as beam forming, polarization encryption, and phase coding, the beam diffusion range is compressed, signal interception is avoided, and link deception and interference attacks are suppressed. Through the dual security mechanism of "physical layer anti-interference + quantum encryption," the transmission confidentiality, anti-attack capability, and information security level of the space-air-ground integrated optical network will be comprehensively improved to meet the high-security business needs of classified communication, deep space exploration, and national defense communication.
6.6 Standardization Improvement and Industrial Ecosystem Construction
As technology gradually matures, standardization and industrialization will become the development direction of the future space-air-ground integrated optical network. At home and abroad, efforts will be accelerated to unify space-air optical communication interface protocols, link synchronization standards, networking interaction specifications, performance testing, and reliability evaluation systems, solving the industry pain points of poor equipment compatibility and weak system interoperability, and forming a complete technical standard system. At the industrial level, relying on the collaborative mechanism of industry, university, and research, the whole industrial chain of core device research and development, terminal equipment manufacturing, system integration, and scenario application will be opened up. Breakthroughs will be made in the localization technology of core products such as high-end optoelectronic devices, integrated terminals, and intelligent scheduling systems, building an autonomous and controllable space-air optical communication industrial ecosystem. Meanwhile, through multi-scenario engineering trials and long-term on-orbit verification, technical solutions will be continuously iterated and optimized, promoting the space-air-ground integrated optical network from the experimental verification stage to comprehensive commercialization and large-scale implementation, making it an important support for the 6G space-ground integrated information infrastructure.
7 Conclusion
The space-air-ground integrated optical network is a key infrastructure for 6G ubiquitous communication, effectively breaking through the bottlenecks of traditional communication coverage and bandwidth. This paper systematically expounds the three-dimensional architecture, topology, and link characteristics of the network, reviews the research progress at home and abroad, analyzes seven key core technologies, focuses on six major challenges including weak link reliability, unstable dynamic networking, complex heterogeneous collaboration, limited payloads, insufficient QoS guarantee, and lack of standards, and predicts six major development trends of network intelligence, full-domain all-optical, device localization, large-scale application, security integration, and industrial standardization.
Currently, single-point optical link technology has tended to be mature, but core capabilities such as three-layer collaborative networking, intelligent scheduling, and all-weather reliable transmission still need to be broken through. In the future, efforts should focus on tackling key technologies such as localized core devices, intelligent anti-interference networking, and cross-domain collaborative management and control, making up for technological and standard shortcomings, and continuously promoting the evolution of the space-air-ground integrated optical network towards intelligence, high reliability, and industrialization, providing solid technical support for China's 6G construction, deep space exploration, national defense communication, and other fields.
This article is published in Issue 7, 2026 of "Communications World"; Original title: "Review of Space-Air-Ground Integrated Optical Network for 6G Ubiquitous Communication."
Authors: Tang Yingqi, China United Network Communications Group Co., Ltd. Zhejiang Branch; Wei Buzheng, Zhang He, China United Network Communications Group Co., Ltd. Research Institute; Zhi Chunlong, China United Network Communications Group Co., Ltd. Network Operation Division; Song Mei, China United Network Communications Group Co., Ltd. Jiangsu Branch; Liu Xiaocun, China Unicom International Limited Hong Kong.
Managing Editor/Layout: Sun Tian
Reviewed by: Mei Yaxin
Supervised by: Liu Qicheng