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Sustainability conversations in data centers focus on server power and cooling — PUE, renewable energy, liquid cooling. The optical network is rarely part of the discussion. But at 800G densities, optics consume 15–25% of total switch power in a leaf-spine fabric. For a 50 MW data center, that is 7.5–12.5 MW of power that optics directly control. The choices network architects make — which transceiver type, which reach, which form factor — directly determine the facility's carbon footprint. Here is how to make those choices count.
Where Optics Power Goes
A 32-port 800G switch populated with DR8 transceivers draws roughly 600 W in optics alone. In a fabric with 128 leaf switches and 16 spine switches, that is 86.4 kW — before counting a single watt of switch ASIC or server power. At $0.10/kWh, optics in this fabric cost roughly $75,000 per year in electricity alone.
| Transceiver Type | Power per Port | 32-Port Switch | Power per Tbps | Best For |
|---|---|---|---|---|
| DAC (800G, 3m) | ~0.5–1 W | 16–32 W | ~1.2 W | Intra-rack |
| AOC (800G, 30m) | ~2–3 W | 64–96 W | ~3.8 W | Same-row |
| 800G SR8 (MMF) | ~10–14 W | 320–448 W | ~16.3 W | Intra-rack MMF |
| 800G DR8 (SMF) | ~14–18 W | 448–576 W | ~20 W | Spine-to-leaf SMF |
| 800G FR4 (SMF) | ~14–18 W | 448–576 W | ~20 W | Campus SMF |
| 800G ZR+ (coherent) | ~20–24 W | 640–768 W | ~27.5 W | Metro/regional DCI |
Where the Real Carbon Savings Live
DAC instead of SR8 for intra-rack. A DAC draws 0.5–1 W. An SR8 transceiver draws 10–14 W. For a rack with 16 server-to-leaf connections, that is 8–16 W with DACs vs 160–224 W with SR8 optics. Over three years, the DAC approach saves roughly 4,000–5,500 kWh per rack — about 2–3 tons of CO₂ equivalent. Multiplied across a data center with 500 racks, this single decision saves 1,000–1,500 tons of CO₂.
800G instead of 2 × 400G for spine. An 800G port draws 14–18 W. Two 400G ports draw 20–28 W combined. Consolidating to 800G saves 6–10 W per spine link while doubling capacity. The switch count reduction saves more power in switch ASICs than the optics alone.
Coherent only where necessary. A coherent ZR+ module draws 20–24 W. A PAM4 FR4 draws 14–18 W for the same 800G capacity at campus distances. Using coherent for a 2 km campus link wastes 6–10 W per port with no functional benefit.
The Sustainability Framework for Optical Procurement
Three decisions that directly reduce the carbon footprint:
- Match the interconnect type to the distance. DAC < 3 m, AOC 3–30 m, PAM4 optics 30 m–2 km, coherent 2 km+. Every category jump roughly doubles power consumption.
- Consolidate to higher speeds. One 800G port uses less power than two 400G ports. 1.6T will use less per Gbps than 800G.
- Consider LPO for high-density spine. Linear-drive pluggable optics remove the DSP, cutting module power by 30–50%.
- Practical takeaway: A single decision — using DACs instead of SR8 optics for all intra-rack connections in a 500-rack data center — saves roughly 200,000 kWh over three years, equivalent to 100 tons of CO₂. The optical layer is not visible in the PUE number, but it is directly measurable on the power bill. Treat optics power density as a procurement criterion, not an afterthought.
APEX Group supplies the full interconnect range — from sub-1W DACs and AOCs to power-optimized 800G PAM4 and coherent transceivers — enabling network architects to match optics to distance and power budget at every tier.
APEX GROUP — www.apexallinone.com
