Hydroxyl ion absorption

Hydroxyl ion absorption: In optical fibers, the absorption of electromagnetic waves, including the near-infrared, due to the presence of trapped hydroxyl ions remaining from water as a contaminant.

Note: The hydroxyl (OH^-) ion can penetrate glass during or after product fabrication, resulting in significant attenuation of discrete optical wavelengths, e.g. , approximately 1.3 μm, used for communications via optical fibers.

Source: from Federal Standard 1037C