China Telecom and ZTE Complete World’s First C+L Band Integrated 80×800G WDM Trial on Live Network

Amid the accelerating wave of global digital transformation, optical communication technology is driving the rapid evolution of the information society. As the core infrastructure for massive data transmission, the upgrade of optical networks has always been a focal point for the industry. In 2025, China Telecom and ZTE completed the world’s first 800G C+L integrated optical transponder unit (OTU) live network trial on the North China ROADM backbone network, marking a  major breakthrough in ultra-high-speed optical communications.

This trial validated the commercial viability of the full-band 800G solution and laid a solid foundation for China Telecom’s future 400G/800G all-optical ROADM networks. It also promotes industry standardization and ecosystem collaboration—representing a milestone in global optical communication development.

Industry Trend: From 200G/400G to 800G

With the explosive growth of big data, AI, and smart manufacturing, global network traffic continues to surge. Traditional single-wavelength 200G/400G optical transmission systems can no longer meet the demands for ultra-large bandwidth and ultra-long-distance transmission. Optical network technology is advancing toward 800G, while the occupied spectrum is expanding from the traditional C-band (1530–1565 nm) to the C+L band (1524–1626 nm) to improve spectrum utilization.

Against this backdrop, C+L integrated systems have become an industry trend. The extended C-band (1524–1572 nm) and extended L-band (1575–1626 nm) together expand spectral bandwidth from 6 THz (extended C-band) to 12 THz, significantly boosting transmission capacity. However, expanding to the C+L band imposes higher requirements on optical modules, devices, and network architecture. Seamless cross-band scheduling, reducing equipment complexity, improving system integration, and controlling costs have therefore become urgent challenges. The collaboration between China Telecom and ZTE aims to address these challenges.

C+L Integrated OTU Breakthrough

As early as 2023, China Telecom proposed that all-optical ROADM networks should be built on the extended C+L band with a 12 THz spectral width, while emphasizing the integrated design of key boards and devices. To meet this goal, China Telecom and ZTE conducted long-term technological research and development. In 2024, the two parties successfully completed laboratory verification of the 400 Gbps ultra-long-distance extended C+L band integrated optical modules, and in early 2025, they launched the world’s first 800G C+L integrated OTU live network trial on the ROADM backbone.

The core of this trial lies in the innovative design of the C+L integrated OTU. Traditional optical modules must separately support the C-band and L-band, resulting in high equipment complexity and cost. The integrated OTU module adopts a unified design that enables joint scheduling across C+L bands, greatly improving system flexibility and spectrum utilization. During testing, the team combined C+L integrated wavelength selective switch (WSS) devices to build a truly integrated C+L architecture, validating the following key capabilities:

• 80×800G system transmission capacity: Stable operation in complex live network environments, supporting 80×800 Gbps high-speed transmission to meet ultra-large bandwidth demands.
• C+L full-band optical-electrical seamless scheduling: Simultaneous support for C+L bands with arbitrary spectrum switching, significantly enhancing spectrum utilization.
• WASON protection and recovery capability: With WDM-based automatically switched optical network (WASON) technology, the system achieves rapid fault recovery, ensuring network reliability.

Test results show that the C+L integrated OTU module reduced spare-part types by 50% and doubled spectrum switching capability, effectively lowering both CAPEX and OPEX for operators. The module’s pluggable design also reduced its size by 60% compared to traditional fixed modules, cut per-gigabit power consumption by 68%, saved data-center space, and significantly reduced overall system energy consumption—providing a new solution for building green, low-carbon networks.

Live Network Validation: A Milestone  

The trial demonstrated the feasibility of C+L integration and its tremendous potential in real-world networks. As a key backbone node of China Telecom, the North China 400G ROADM network operates in complex environments with diverse service demands, requiring high levels of stability and scalability. During the trial,

the team conducted multidimensional testing to comprehensively evaluate the C+L integrated OTU module in scenarios such as long-haul transmission, multi-service bearing, and dynamic spectrum allocation. This achievement provides an important reference for future deployment of 400G/800G all-optical ROADM networks. C+L integration will serve as a key enabler for building intelligent, efficient, and green optical networks, driving a leap from single-wavelength expansion to full-band collaboration.

Industry Impact: Driving Standards and Ecosystem Collaboration

The cooperation between China Telecom and ZTE also has profound implications for industry standards and ecosystem collaboration. The mature application of C+L integration will accelerate standardization and provide unified technical specifications for global optical equipment vendors, while serving as a model for collaboration among universities, research institutions, and enterprises.

Together with ecosystem partners, the two companies validated full-spectrum optical-electrical scheduling capabilities and promoted the development of corporate and industry standards, laying the foundation for large-scale commercialization. Meanwhile, ZTE made breakthroughs in key technologies such as DSP, ITLA, and ICRM, achieving innovations in 130-GBd high-speed parallel ADC, new doping techniques, and optical component co-packaging, further enhancing device performance and reliability.

The success of this trial not only resolves core challenges in optical network evolution but also injects new momentum into the global communications industry through innovative technology.