UV-Radiation induced losses in optical fibers and their control

Abstract Ultraviolet radiation used for crosslinking prepolymer liquid coatings applied to optical fibers has been found to induce wavelength-dependent optical losses in fibers of certain core compositions. Germanium and phosphorous-doped cores are especially sensitive to radiation exposure and high NA (=0.36) germanium-phosphosilicate core fibers are far more sensitive than moderate NA (=0.23) fibers. The damage is believed to be associated with the formation of color centers in the doped glass network. Uncoated fibers given ultraviolet radiation doses equivalent to those encountered during coating operations exhibit added losses of several hundred dB/km in the near infrared region. Coated fibers of high NA exhibit much smaller, but still significant, added losses. The coating thus acts as a filter for short UV wavelengths which cause the most significant damage. Techniques are discussed for controlling the degree of radiation damage in these fibers.