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title: China Telecom and ZTE claim C+L band WDM first - Developing Telecoms
description: Tech giant ZTE Corporation announced at MWC25 that it had successfully completed the world’s first extended C+L band integrated 80×800 Gbps wavelength division multiplexing (WDM) trial in collaboration with China Telecom. This trial achieved flexible adjustment of wavelengths within a 12 THz ultra-wide spectrum.
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Tech giant ZTE has announced at MWC25 that it has successfully completed the world’s first extended C+L band integrated 80×800 Gbps wavelength division multiplexing (WDM) trial in collaboration with China Telecom. This trial achieved flexible adjustment of wavelengths within a 12THz ultra-wide spectrum.

ZTE says this breakthrough provides an important reference for future network deployment and optimisation and promotes the development of optical transport networks toward a more efficient and flexible direction.

In the digital era, network traffic is experiencing explosive growth. The single-wavelength transmission rate of optical networks has gradually increased to 400 Gbps and is now advancing towards 800 Gbps. ZTE says the evolution towards extended C+L band transmission has become the mainstream technology direction in the industry.

As early as 2023, China Telecom proposed that all-optical ROADM networks should be built using the extended C+L bandband and has continuously promoted the implementation of key boards and components. In 2024, China Telecom successfully completed the laboratory verification of the 400 Gbps ultra-long-haul (ULH) extended C+L integrated optical module.

The trial was conducted on China Telecom’s ongoing ROADM all-optical switching backbone network. Based on the extended C+L integrated optical layer platform, the trial comprehensively verified the service transport capability of extended C+L integrated 800 Gbps OTU module; the optical-electrical scheduling capability within the 12 THz ultra-wide spectrum; and the wavelength recovery capability of the wavelength switched optical network (WSON).

In the live network environment, the trial successfully completed two service rerouting operations, demonstrating flexible switching of any wavelength within the extended C+L ultra-wide spectrum, with each wavelength switch completed in approximately 30 seconds.

This, say the partners, marks a key step towards the commercialisation of the extended C+L integrated all-optical switching system.

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