Residual-stress relaxation and densification in CO_2-laser-induced long-period fiber gratings

摘要

The first concurrent measurements of the three-dimensional refractive-index and residual-stress distributions in a CO_2-laser-irradiated fiber are presented. A Corning SMF-28 fiber was exposed from one side to focused pulses with durations of 100-500 ms. The cross-sectional form of the index modulation is asymmetric with changes concentrated on the side of the fiber facing the exposure. The longitudinal form is Gaussian-like with a wide top and extends approximately 100 μm from the center of the exposure. Relaxation of frozen-in viscoelasticity results in a maximum index modulation of 5 × 10~(-4) on the side of the fiber facing the exposure with mechanical stress relaxation contributing changes of less than 1 × 10~(-4).