May 6,2025, In the short course session of this year's OFC, the topic of SC444 is "Emerging Optical Network Technologies towards 2030", and the lecturer is Dr. Liu Xiang from Huawei. I was fortunate enough to obtain his course materials and would like to summarize for readers which new technologies he deems worthy of attention.
F5G Advanced and F6G
As we all know, Huawei previously proposed the concept of Fixed Network 5G, namely F5G. Similar to the evolution of wireless communication, Dr. Liu Xiang's materials mention the concepts of F5G Advanced and F6G for the year 2030. If F5G means Gigabit connectivity to everywhere and everything, then F5G Advanced means 10 Gigabit connectivity to everything and everywhere. As for F6G, it places more emphasis on environmental protection and green initiatives. Just like in wireless communication, F5G Advanced also emphasizes the concept of slicing, especially end-to-end slicing. To achieve F5G Advanced, the key technologies include Fiber to the Terminal , latency control, 800G+ in the core network, 50G PON in the access network. Meanwhile, it is necessary to introduce Optical Cross Connect (OXC) and fiber optic sensing, address the low energy efficiency at the entire network and equipment levels, and possess the capability of providing distributed computing power.
Currently, the mobile communication network is evolving from the 5G era to the 6G era. In November 2024, the ITU also held a meeting to discuss the optical network standards for 6G. Generally speaking, it includes an access network with a speed of 10Gbps, a backbone line with a speed of 1.6Tbps, a latency of less than 1 millisecond for metro data center (DC) connections, a sub-1G Optical Service Unit (OSU), support for automatic path protection against fiber cuts, the introduction of reconfigurable optical routing for greater flexibility, the introduction of a resource-efficient network architecture for higher energy efficiency, support for more precise time synchronization, and meeting the requirements of AI networks simultaneously.
Better OXC and Optical Cross-Connect System (OCS) for Data Centers
The so-called better OXC requires the introduction of super channels to address the issue of insufficient channels per node. The new Add/Drop Wavelength Selective Switch (A/D WSS) supports lower loss and is independent of channel power, eliminating the need for Erbium-Doped Fiber Amplifiers (EDFA). The upgrade is achieved through the C+L band, and by introducing 64D/128D technology, spatial switching is added in addition to wavelength switching. In the era of OXC 3.0, not only should an optical backplane be introduced, but also the integration of optical and electrical switching.
800Gbps per Wavelength and 100Tbps per Fiber
Technologies for achieving larger fiber transmission capacity include shaping (constellation shaping, spectrum shaping, dynamic distortion shaping, etc.) and spectrum expansion technologies (Super C + Super L, achieving a bandwidth of 12THz), etc. Dr. Liu Xiang also mentioned here that according to the current growth rate of network traffic, which doubles every two years, considering that the transmission capacity of a single fiber increases by approximately 12% per year, and the data from 1997 to 2017 shows that the deployment volume of fibers increases by 14% per year, this fundamentally explains the source of demand in the fiber market.
Technical Considerations for 1.6T ZR+
Compared with the PDM-QAM modulation used in 400G ZR/ZR+, many concepts of 1.6T ZR/ZR+ exceed the comprehension ability of the editor. Dr. Liu Xiang mentioned some new concepts in his materials, such as the binary tree encoder in the PCS design, the Equalization-Enhanced Phase Noise (EEPN), and the Transmit Constellation Closure (TCC). In particular, digital sub-carrier modulation will be the key to implementing the 1.6T ZR module.
FWM Suppression for 800G-LR4
The nonlinear phenomenon of Four-Wave Mixing (FWM) poses a problem for 800G-LR4 optical modules. The solution is to introduce polarization control in the XYYX mode, and for this purpose, a 90-degree polarization rotation needs to be introduced in the Silicon Photonics Integrated Circuit (PIC).
Next-Generation OTN: fgOTN
During the first Huawei Global Optical Summit held in Bangkok on April 30, 2024, Huawei released the "fine-grain Optical Transport Network (fgOTN) Technology White Paper". fgOTN is clearly defined as the next-generation technology of Synchronous Digital Hierarchy (SDH). It is the only technology in the industry, other than SDH, that has international standard support for carrying Constant Bit Rate (CBR) services. At the same time, it can efficiently carry Ethernet services, support fast and lossless bandwidth adjustment, and can be widely applied in private networks of industries such as power and transportation, as well as in scenarios such as enterprise and government dedicated lines, meeting the requirements of intelligent service development for communication networks.
In simple terms, fgOTN adds the capability to carry Sub 1G small-granule Packet (PKT) and CBR (Constant Bit Rate) services in the OTN. It is mainly positioned for carrying small-granule high-quality services below 1G and can be widely applied in enterprise and government networks, such as dedicated network lines for industries like power and healthcare.
