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All 800G optics use eight 100G PAM4 lanes, but the media interface dictates deployment. Reach, fiber type, and connector style separate the four variants more than raw bandwidth. The «2x» prefix on DR4, FR4, and LR4 denotes a dual-400G structure that runs as one 800G port or breaks out into two independent 400G links.

The Four 800G Reach Classes at a Glance

MMF vs. SMF: The First Fork

The primary decision is whether the run stays in a rack row or spans a data hall.

• Choose MMF (SR8) for links under ~100 m (top-of-rack to leaf). It uses 850 nm VCSEL-based parallel optics and pairs naturally with MPO trunks. It is economical for short, dense links but limited by modal dispersion.

• Choose SMF (DR/FR/LR) for runs leaving the rack row, crossing halls, or connecting buildings. SMF uses 1310 nm-region lasers with no modal dispersion, supporting 500 m, 2 km, and 10 km by simply changing the optic. Standardizing on SMF future-proofs cabling for 400G, 800G, and 1.6T.

Cost Trade-off: Multimode optics are cheaper per module, but OM4 trunks cost more per meter/fiber. Parallel optics (SR8, 2xDR4) consume 16 fibers per 800G port, compounding fiber costs on longer runs. WDM optics (2xFR4, 2xLR4) collapse the fiber count to four, flipping the economics in favor of single-mode WDM as distance grows.

Variant Breakdown

800G-SR8: 100 m over Multimode
Carries eight 100G lanes over eight fiber pairs at 850 nm. Terminates on a 16-fiber MPO. Ideal for short, dense intra-pod links, breaking out cleanly into 2x400G-SR4 or 8x100G-SR.

800G-2xDR4/DR8: 500 m Parallel Single-Mode
Uses eight 1310 nm lanes as two DR4 groups of four, reaching 500 m on SMF. The workhorse for spine-leaf links inside a data hall where SMF is deployed but WDM isn’t required. Terminates on MPO (16-fiber for full 800G, or split to two 8-fiber groups) and breaks out to 2x400G-DR4, bridging 800G spines to 400G access layers.

800G-2xFR4: 2 km over Duplex Single-Mode
Replaces parallel fiber with WDM. Each 400G half is a CWDM4-style FR4 multiplexing four wavelengths onto a single fiber pair. It uses only four fibers total (two duplex LC pairs), lowering structured-cabling costs on longer runs. The right pick for cross-hall aggregation and campus links up to 2 km with existing FR4 infrastructure. Breaks out to 2x400G-FR4.

800G-2xLR4: 10 km over Duplex Single-Mode
Extends the duplex-LC, WDM approach to 10 km using higher-power lasers. Targets DCI within a metro campus, building-to-building links, and runs beyond FR4’s 2 km ceiling. Uses two duplex LC pairs and breaks out into 2x400G-LR4. For links beyond 10 km, coherent 800G ZR/ZR+ becomes relevant.

MPO vs. Duplex LC and Breakout Design

• Parallel optics (SR8, 2xDR4) spread lanes across many fibers using MPO connectors. More fibers mean higher trunk cost, but breakout to 400G or 100G is physically simple with MPO harnesses.

• WDM optics (2xFR4, 2xLR4) combine lanes onto one fiber pair per 400G, using standard duplex LC. Fewer fibers cut cabling costs over distance, but the WDM optics carry a mux/demux complexity premium.

Polarity and Polish: MPO plants must maintain consistent Method A/B/C polarity. Single-mode MPO uses APC polish; multimode MPO uses UPC. Mixing polish types or losing polarity causes dark links. For duplex LC WDM, use standard LC/UPC or LC/APC patch cords matched to the trunk and verify insertion-loss budgets near the 2 km and 10 km limits.

2x400G Breakout: The 2xDR4, 2xFR4, and 2xLR4 modules are built as two 400G engines, allowing one 800G port to serve two 400G leaf/NIC ports. The far-end partner must match reach and connector. Before committing, verify the switch ASIC and NOS support 2x400G channelized mode, and ensure cabling routes each 400G group correctly.

Quick Selection Summary

• Under 100 m, multimode plant, max density: 800G-SR8

• Up to 500 m, single-mode, no WDM, MPO cabling: 800G-2xDR4

• Up to 2 km, duplex LC, low fiber count: 800G-2xFR4

• Up to 10 km, campus/DCI reach: 800G-2xLR4