Effect of Zero Stress Aging on the Strength of Optical Fibers

Abstract

The effect of moisture under zero stress on the subsequent fracture strength of optical fibers is of considerable importance because optical fibers in service are likely to encounter water and high humidity environments. The effects of zero-stress aging on the strength of a uvcured epoxy acrylate coated optical fiber were determined for different aging environments and temperatures. Aging at high humidities and up to 60°C causes a strength decrease which can be recovered on drying. The recoverability of the strength shows that the strength decrease is not due to flaw growth. The aging effect can be explained in terms of an enhancement of dynamic fatigue by the establishment of a higher humidity crack tip environment. It is speculated that the latter is caused by absorption of water molecules at the polymer-glass interface and the existing flaw surfaces. A much larger strength decrease that is not fully recoverable occurs upon aging above 60°C in high humidity. It is speculated that a further chemical change in the crack tip environment related to the coating chemistry (the thermal and hydrolytic stabilities) occurs at the higher aging temperatures. Although the decrease in strength caused by aging in high humidities up to 60°C is recoverable in laboratory drying experiments, it is a factor to contend with in service and should be considered in the design of optical cables.