Abstract: An optical fiber protected from degradation caused by corrosion from environmental fluids. The optical fiber includes a core-cladding assembly surrounded with a thin quasi metal oxide film (preferably .about.10 nm in depth). Over time, particularly under the influence of the elevated temperatures, the initially deposited reagents of the thin film oxidize or hydrolyze, removing the organic components, and bonding a quasi metal oxide film on the surface of the cladding. The resulting film significantly retards corrosion by blocking the environmental fluids from reacting with flaws in the cladding surface of the fiber, thus improving the mechanical performance and reliability of the optical fiber. In addition, the thin film protects the fiber against incidental abrasions.