Can single-mode SFP modules run over an old 200 m multimode fibre?

Question

The postter had an existing multimode fibre run of about 200 m that could not be replaced and only single-moode SFP modules available. The question was whether a 1G single-mode SFP pair would establish a stable link over multimode fibre, and what the practical limits were. The thread also raised the reverse case (multimode optics over single-mode fibre).

Transceivers: 1G single-mode SFP (1310 nm), 1G multimode SFP
Form factor: SFP

Symptoms / messages:

fibre type mismatch
uncertain link stability

wavesmith · Accepted Answer

Several users reported it working in practice at 195-400 m for months or years; at gigabit speed over 50/125 fibre the standard allows up to about 500 m, and the core-diameter mismatch effectively acts as an attenuator.

rxadmin25 · Answer

Use mode-conditioning patch cords for a cleaner launch into multimode firbe; the safer answer is still to buy multimode SFPs.

dwdmpilot · Answer

The reverse case (multimode SFP into single-mode fibre) does not work because of very large coupling loss.

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