We observed residual stress relaxation by CO<sub>2</sub> laser irradiation in the cores of optical fibers by direct stress measurement. It was demonstrated that the mechanical stress was fully relaxed by CO<sub>2</sub> laser irradiation and that the remaining stress in the core was thermal stress that was due to a mismatch of the thermal expansion coefficients of the fiber core and cladding. The net core stresses after relaxation were 17, 68, and 203 MPa in Ge–B-codoped fibers drawn at 0.53, 1.38, and 3.48 N, respectively. Changes in the refractive indices of the cores as a result of residual stress relaxation were also estimated.
© 2001 Optical Society of America
B. H. Kim, Y. Park, T.-J. Ahn, D. Y. Kim, B. H. Lee, Y. Chung, U. C. Paek, and W.-T. Han, "Residual stress relaxation in the core of optical fiber by CO2 laser irradiation," Opt. Lett. 26, 1657-1659 (2001)