Tomographic measurement of femtosecond-laser induced stress changes in optical fibers

The tomographic measurement of the residual stress profile in femtosecond-laser irradiated standard SMF-28 germanium-doped telecommunication fiber is demonstrated. The fiber is irradiated with weakly focused pulses to realize long-period fiber gratings. In the irradiated grating regions, an asymmetrical increase in axial core stress up to 6.2 kg/mm(2) is found. The increase in stress is attributed to a densification of the irradiated glass matrix. The stress-induced anisotropic index distribution is calculated and related to the absolute index change in the irradiated regions. (C) 2004 American Institute of Physics.