Residual stresses in optical fiber preforms

Abstract

AbstractThe optical fiber consisting mainly of quartz glass comprises a number of different kinds of glass having different constituents. Therefore, as is widely known, there are residual stresses left in the optical fiber preforms and the fiber itself which are caused by the difference of thermal expansion coefficients. To clarify the effect of the residual stress on the optical performances of the optical fiber, a measurement was carried out on the residual stresses of the optical fiber preforms and the fiber in a vertical plane normal to the longitudinal axis by means of optoelastic effect. Then the variation due to different thermal hysteresis and dimensions, influence of GeO2 addition concentration in the core and the effect of different refractive index were studied. As a result, it was revealed that the thermal hysteresis during drawing almost did not influence the residual stress distribution. The residual stress increased depending on the increase of additive concentration and its tendency agreed well qualitatively with a theoretical forecast. The residual stresses had such an influence on the refraction index decrease that with respect to the quadratic distribution of 1% relative refractive index difference between core and clad, the refractive index decreased by approximately 3.9 × 10‐4, Also, it was made obvious that the effect of residual stresses could not be disregarded for more precise refractive index control.