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

This paper investigated the fiber-end surface modulation by atomic force mi croscopy (AFM) and optical profilometry after a careful cross cleavage with a diamond. The image of the surface allows to see the different parts of t he fiber. The cladding appears above the mean level whereas the core appear s depressed. This profile is tightly connected to the stress profile, itsel f 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 wi th some of approximate to 80 nm, This method seems to be suitable to study fiber defects but is still difficult to perform due to the small size of th e sample (phi = 125 mu m) and the dependence of the surface profile with th e care to cleave the fiber, However, due to the better spatial resolution o f the AFM measurements compared to the optical profilometry, itself larger than the one of photoelasticity measurements, it was possible to conclude t hat the axial stress exhibits a discontinuity at the core-cladding interfac e and not a peak at the center of the core.