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Every IEEE and MSA optical standard fixes a wavelength plan, a fibre type, a connector and a maximum channel loss. This is the reference table, with a link straight to the matching FOT module. Loss budgets are planning figures — confirm against the datasheet for the exact part you buy.
What the standard actually fixes. An optical Ethernet standard pins down the wavelength plan, the fibre type, the connector, the lane structure and the maximum channel insertion loss. Anything that claims compliance has to interoperate with anything else that does — which is why a compliant third-party module works with an OEM module at the far end.
Reach is a channel-loss limit, not a distance. The distance in the name assumes a channel built to the standard's loss budget. A 10 km LR link through six patch panels may fail well short of 10 km, and a clean 12 km span with two connectors may work fine. Always work from the measured channel loss, not the map. The link budget calculator does the arithmetic.
Parallel versus WDM. SR4, PSM4, DR4 and SR8 are parallel: one fibre per lane, MPO connector, cheapest optics. LR4, FR4, CWDM4 and ER4 put every lane on its own wavelength down one fibre pair with LC. Parallel is cheaper per module but needs four or eight times the fibre — which is exactly the trade-off that decides whether you buy MPO trunks or duplex patch cords.
They are the standard planning figures and they are right for design work, but the authoritative number for the part you actually buy is on its datasheet — vendors sometimes specify better than the standard requires. Use these to size the plant, then confirm before you commit.
No. SR-class optics use 850 nm VCSELs, which single-mode fibre will not guide properly. The reverse — single-mode optics over multimode fibre — also does not work reliably. Match the module to the fibre that is installed.
SR4 and PSM4 are parallel: four lanes on four fibre pairs, so they need an eight-fibre MPO. LR4, ER4 and CWDM4 multiplex four wavelengths onto one pair, so a duplex LC is enough. If your plant is duplex LC, you want the WDM variants; if you have MPO trunks, parallel is cheaper.
Total channel loss, power budget and pass/fail margin for single-mode and multimode links
Open tool →Turn a switch port count into the trunks, cassettes and harnesses you actually have to buy
Open tool →Pulse spread from Δt = D · L · Δλ, and the distance at which dispersion — not loss — ends the link
Open tool →Transceivers, MPO assemblies, WDM and patch cords — built and tested to the figures you just calculated.