The easiest way to determine the type of your SFP module is by checking the label or the product's specifications. Typically, single mode SFP modules are labeled as "SM" or "single mode," while multimode modules may be labeled as "MM" or "multimode. For example, during network maintenance, you may remove an old SFP. So, to cut right to the chase, you can generally tell if fiber is multimode or singlemode by examining the cable's jacket color, looking for printed markings on the jacket, checking the connector type, and if all else fails, by measuring the core diameter or using an optical time-domain. Single fiber modules—often called bidirectional (BIDI) transceivers—transmit and receive signals over a single optical fiber by using two different wavelengths.
[PDF Version]