According to CNII news, China Telecom has successfully trialed and achieved a maximum transmission capacity of 64Tbps per fiber pair over a distance of more than 1,200 kilometers, using the existing in-service G.652 optical fiber cable, and extended C+L technology.

The China Telecom Research Institute, together with partners including Huawei, ZTE, FiberHome and Shanghai Nokia Bell, successfully completed a single-wavelength 800G/400G mixed-rate transmission system on the Nanjing-Shanghai existing in-service G.652 optical fiber. The test achieved a maximum transmission capacity of 64Tbps and a maximum transmission distance of more than 1,200 kilometers without electric relay, confirming the technical feasibility of 800G/400G hybrid transmission.

According to reports, this live network transmission test is based on China Telecom’s optical cable backbone network and backbone hub in the Yangtze River Delta region. The new generation 800G and 400G hybrid DWDM transmission system was deployed on the in-service G.652 optical fiber cable, with loop configuration on its Nanjing-Shanghai-Nanjing backbone routes.

The equipment, combined with the industry's advanced extended C+L bands broadband transmission technology, only uses EDFA optical amplification to achieve a maximum capacity of 64Tbps and a long-distance powerless relay transmission of more than 1,200 kilometers.

This trial with mixed 800G and 400G DWDM on the in-service G.652 optical fiber cable fully confirmed the technical feasibility to deploy 800Gbps channels on in-service backbone network which was previously deployed with 400Gbps QPSK technology.

Prior to the trial on its backbone between Shanghai and Nanjing, China Telecom had deployed 800G 16QAM pluggable module for data center interconnection (DCI) on its metro-network in Beijing, and hybrid 800G/400G transmission on its backbone network between Beijing and Tianjin which spans approximately 200 kilometers.

In March 2024, ZTE, a leading Optical Transport Network (OTN) supplier, released a white paper, 800G C+L System —— Ultra-large Capacity Optical Transmission Technology, demonstrating the commercial solutions to deploy 800Gbps DWDM system using C+L technology.