AI Compute Clusters Are Rewriting the Optical Module Roadmap

Why AI clusters consume more optics than general-purpose data centers

A conventional data center rack might host 20–40 server ports. A rack of eight GPU compute trays in a training cluster can require several hundred high-speed optical links, because the fabric is not just server-to-switch — it is all-to-all communication between accelerators. When every GPU in a cluster needs to exchange gradient data with every other GPU, port count per unit of compute rises sharply, and the optics become the dominant cost element of the interconnect.

What speeds are actually being deployed

Three tiers dominate:

• 400G — Usually QSFP-DD or OSFP, with DR4 (500 m) and FR4 (2 km) being the mainstream reaches inside and between halls. This remains the highest-volume tier for new deployments.
• 800G — Built on 100G-per-lane electrical interfaces, mostly in OSFP and QSFP-DD800 form factors. SR8 for short multimode runs and DR8/2×FR4 for single-mode links.
• 1.6T — Emerging in OSFP-XD and similar larger form factors, primarily for the highest-radix switch fabrics.

For most buyers building out capacity today, 400G and 800G are the practical decision space. 1.6T should be planned for, but not built around yet.

The three selection criteria that actually matter

1. Reach and fiber plant. If your existing cable plant is multimode, SR-class optics keep the migration cost low. If it is single-mode, DR and FR classes give better scaling headroom.
2. Thermal budget. Higher speeds mean higher power per port. An 800G module can dissipate several times the power of a 400G module, which affects faceplate cooling and switch selection. This is why linear-drive pluggable optics (LPO) and co-packaged optics (CPO) are getting attention.
3. Density and breakout. Breakout cables that split one 800G port into two 400G or eight 100G links are often the cheapest way to match a fabric topology without buying new switches.

A practical starting point

If you are qualifying optics for an AI cluster build, start with the reach and fiber type you already have, confirm the thermal headroom on your switch line card, and only then choose speed tiers. Buying the fastest module your switch supports is not the same as buying the right module for your fabric.

Canjin Technology supplies 400G QSFP-DD and 100G QSFP28 modules with tested optical parameters, and supports OEM coding for accelerator fabric interoperability.