What Is the Next Generation of Multimode Fiber?

As enterprise data centers have made the shift from the traditional owner-operated model to off-premise colocation and cloud facilities, the tech industry has experienced one of the greatest growth engines ever seen. Customer adoption of off-premise solutions coupled with the explosion of devices connecting to the network has changed the way data center network infrastructure is architected. While data transmission speed still dominates, low latency has also proven to be critical to designing a data center for high performance, flexibility and scalability.

Video: Next-Generation Multimode Fiber Technology

Single-mode fiber—with its longer physical reach and supported data rates—is usually the optimal cabling solution for hyperscale and cloud data centers. Especially since the IEEE standardized on 200 Gb/s and 400 Gb/s optical interconnects that can operate up to 10 km in distance over single-mode fiber (IEEE 802.3bs). However, there may be situations where cost-effective shorter reach optics based on multimode fiber technology would be a better fit. This inspired the IEEE to develop a 400 Gb/s standard for multimode fiber (802.3cm).

The development of the 802.3cm standard was driven by three key motivators:

  • Deployment of cost-optimized lower fiber count solutions over installed base, as well as greenfield multimode fiber cabling, for 200 and 400 Gb/s by leveraging technologies currently under development
  • Global web-scale data centers and cloud-based services—as well as the largest enterprise datacenters—are presented as leading applications
  • Synergy with broader enterprise networking extends the application space and potential market adoption.

A primary use of multimode fiber is in the switch-to-switch connections of a leaf-spine network architecture, which is favored in many hyperscale data centers due to its very high-data-rate, low-latency connection between servers. In this two-layer architecture, the leaf switches located in top-of-rack, middle-of-row or end-of-row physical configurations can be connected to the spine switches using short reach optical modules operating over multimode fiber.   

Switch-to-Switch Connection Diagram

The IEEE 802.3cm standard has technical objectives for 400 Gb/s operation over eight pairs (BASE-16) and four pairs (BASE-8) of multimode fiber, each with an installed length of up to at least 100 m. The parallel solutions proposed in the IEEE 802.3cm will look to minimize the implementation costs by leveraging the lower cost VCSEL sources used with multimode fiber when compared to the longer wavelength single-mode optics. Another benefit of the parallel fiber configuration is that it significantly improves the flexibility of the multimode fiber installation by supporting individual duplex breakouts of the 400 Gb/s circuit.

As multimode fiber technology continues to develop, education becomes even more pertinent in order to determine the right solution based on the application environment. 

Learn more about fiber optic cabling infrastructure.