SFP Reach and Wavelength Guide: From 100 m to 120 km

Attenuation in glass is not uniform: at 850 nm a single-mode or multimode span loses several dB per kilometer, at 1310 nm roughly 0.35 dB/km, and at 1550 nm about 0.2 dB/km — the lowest-loss window, which is why every long-reach standard lives there. Shorter wavelengths also scatter more, and multimode's larger core adds modal dispersion that caps its reach regardless of wavelength. Reach classes exist because each standard pairs a wavelength, a light source and a receiver budget that together define how far the signal can go.

This table covers every module family in the Fibertrixa catalog. "Typical reach" is the standard's rating over the listed fiber; our catalog may include longer or shorter variants of the same standard.

Most part numbers encode the whole spec. Take SFP-10G-LR-SM1310-10KM: form factor SFP+, 10G Ethernet, LR reach class, single-mode fiber, 1310 nm, 10 km. A BiDi example, SFP-T1310/R1550-LC-3KM: transmits at 1310 nm, receives at 1550 nm, simplex LC connector, 3 km. The two numbers after T/R are the pairing clue for BiDi modules — the R value of one end must equal the T value of the other.

Catalog reach assumes clean fiber. Every mated pair of connectors costs 0.3–0.75 dB, each fusion splice adds only about 0.1 dB, and older plant can be worse. A 120 km ZX link with eight patch panels can exhaust its budget before the fiber ends. Two practical rules: keep patch panels out of long spans where you can, and if a long-reach module lands on a short link, check the RX power with DOM — receivers can be overloaded at under 10 km on 1550 nm modules, and a fixed attenuator is a cheap fix.

The catalog is organized by reach class and interface, so matching this table to a part is a two-click job. If your link distance sits between two standards — say 15 km on a 10 km/40 km boundary — send us the route and the switch model; we check the optical budget and confirm coding before quoting.