How Alibaba Cloud Extended VCSEL Reach to 500 m: Breakthroughs from ECOC 2025

On September 28, 2025, the 51st European Conference on Optical Communication (ECOC 2025) was held in Copenhagen, Denmark, gathering top research institutions and technology companies to present cutting‑edge results in photonic devices, transmission systems, and network architectures. The event featured 15 workshops and 79 technical sessions, with over 300 companies exhibiting the latest technologies. AI‑related topics, such as AI‑driven optical networks, CPO co‑packaging, hollow‑core fiber, and pluggable colorless optical modules, were highlighted. Alibaba Cloud’s infrastructure network team had two papers accepted, covering high‑speed VCSEL transmission distance extension and hollow‑core fiber applications.

Vertical‑cavity surface‑emitting lasers (VCSELs) are attractive for short‑reach interconnects in AI‑driven data‑center networks due to low power consumption, low cost, and high reliability. When combined with 50 µm multimode fiber, VCSEL‑based modules offer generous alignment tolerance, improved packaging efficiency, and robustness against dust and contamination, enhancing long‑term stability of AI clusters. However, multimode dispersion typically limits VCSEL transmission distance to about 50 m, restricting its use in larger data‑center scenarios.

In a recent breakthrough, Alibaba Cloud demonstrated a 500‑meter transmission over standard multimode fiber using 106 Gb/s 850 nm single‑mode VCSELs, as reported in the paper “500‑Meter Multimode Fiber Transmission with 106 Gb/s 850 nm Single‑Mode VCSELs.” This ten‑fold increase in reach expands deployment possibilities for VCSELs in AI networks and provides a practical path toward low‑cost, low‑power, high‑speed, high‑density optical interconnects.

Hollow‑core fiber (HCF) is a transformative technology that breaks the latency ceiling of solid‑core single‑mode fiber, offering competitive low‑latency services for latency‑sensitive users and data‑center site selection. Significant academic and industrial investment has accelerated product maturity and field deployment. In the workshop “What type of optical fibre will be deployed, When and Where?” Alibaba Cloud presented optimal deployment scenarios for HCF and identified future research directions. Their paper “Characteristics and Impacts of CO₂ Absorption Effects in Core Fiber (HCF) Transmission Systems” revealed that CO₂ absorption is a key obstacle to large‑scale HCF deployment. By precisely characterizing absorption spectra and comparing C/L bands, the study showed that the L‑band suffers significantly more performance loss than the C‑band, and current commercial equipment exhibits notable degradation in the affected spectrum. Overcoming this will require coordinated advances in fiber manufacturing, absorption‑aware coherent DSP algorithms, and system spectrum planning.

To simplify data‑center interconnect (DCI) construction, Alibaba Cloud continues to promote the deployment of 800ZR pluggable optical modules across vendors, reducing operational complexity of coherent modules. The Optical Internetworking Forum (OIF) released a whitepaper at ECOC on 800ZR module interoperability in protection switching scenarios, marking a major step toward real‑world ecosystem adoption.

With ECOC 2025 concluded, the pace of AI‑driven transformation of infrastructure, software, and applications will accelerate, ushering in a new wave of intelligent revolution. Alibaba Group will keep investing alongside partners and customers to embed AI deeper into industry and co‑create the future.