In the late 1990s, Telcordia Technologies studied the reliability of fiber optic enclosures in outside plant environment (field enclosures).
They assembled a report on the benefits of fiber connection cleaning in those fiber optic OSP enclosures. The statistics showed a significant improvement after connector and adapter cleaning.
Fiber optic adapters (mating sleeves) are used to mechanically connect two fiber connectors. A fiber adapter consists of two main parts: the connector alignment sleeve and the adapter housing.
Connector alignment sleeve is usually a split “C” and is made from a hard, low-wear material such as Zirconia (a type of ceramic ) and phosphor bronze.
The alignment sleeve is the most critical part since it provides the alignment of two connector ferrules. The most convenient way to clean it is with a fiber stick cleaner (pipe cleaner).
Highway dirt is typically 5 to 50 microns in diameter and tends to penetrate into the connector over time. In the Telcordia study, they experienced a big improvement in transmission through the connector after cleaning.
So whenever your insertion loss suddenly increases with an adapter or connector, your should clean them thoroughly before mating. This is always the best practice.