The effect of diffusion rates in optical fiber polymer coatings on aging

Optical fibers have been found to exhibit an accelerated rate of strength reduction during static fatigue and zero stress aging for long times in aggressive environments. This phenomenon has been commonly referred to as the fatigue and aging "knee". The onset of the knee has been found to be highly variable and is sensitive to the polymer buffer coating. In past work we have shown that moisture vapor penetrates most polymer coatings on the time scale of minutes, which implies that the diffusion rate of small molecules is not the rate-determining step for aging. On the other hand, the diffusion of large molecules through the polymer coatings can take anywhere from weeks to years to reach the polymer/glass interface. The implication of this result is that large molecule diffusion might be the rate-determining step in aging. In the work presented here the diffusion of moisture and pH buffer solutions through various optical fiber coatings will be discussed. These results are correlated with the zero stress aging behavior of the same fibers.