Understanding Fiber Optic Link Budgets

Did you know that ignoring fiber optic link budgets could result in damaging that very expensive pair of SFPs you just purchased? Link budgets are important for several reasons, one of which may surprise you.

Primarily, the link budget retrieved or calculated from an SFP/transceiver datasheet gives you the maximum allowable loss (dB) across installed fiber, connectors, patch panels, etc., between two fiber transceivers.

An Optical Loss Test (OLT) with a Fluke or similar tester provides the measured link margin across all these components for a single pair of fiber. If the measured margin is under the budget, the link will operate. 

A little known fact is the budget also provides insight into situations where there might be TOO MUCH power. Most short haul SFPs have a link budget lower limit of zero such as the example below.

This means you can link the transceivers in an extremely short distance lab scenario, as is commonly done for system testing, using standard patch cables with no concern.

If, however, you have long haul SFPs designed to communicate longer distances, you'll find the datasheets reference a non-zero lower limit in the link budget such as the 5 dB below.

Linking these SFPs in the lab without at least 5 dB attenuation could result in permanently damaging the SFPs. In this scenario, you should contact us to purchase an attenuating patch cord to protect those precious SFPs.