Information obtained from the surface profile of a cut single-mode fiber

This paper investigated the fiber-end surface modulation by atomic force microscopy (AFM) and optical profilometry after a careful cross cleavage with a diamond. The image of the surface allows to see the different parts of the fiber. The cladding appears above the mean level whereas the core appears depressed. This profile is tightly connected to the stress profile, itself induced by the doping field and the drawing conditions. Magnification of the core shows fluctuations of the glass structure at the scale of 25 nm with some of ≈80 nm. This method seems to be suitable to study fiber defects but is still difficult to perform due to the small size of the sample (φ=125 μm) and the dependence of the surface profile with the care to cleave the fiber. However, due to the better spatial resolution of the AFM measurements compared to the optical profilometry, itself larger than the one of photoelasticity measurements, it was possible to conclude that the axial stress exhibits a discontinuity at the core cladding interface and not a peak at the center of the core