Analysis of frequency-doubling processes in optical fibers using Raman spectroscopy

We have experimentally found a correlation between the nonlinear characteristics of frequency-doubling optical fibers and a specific modification of their Raman spectra. We propose a tentative interpretation of the physical origin of these phenomena, based on the assumption of the existence of small Si-O rings inside the fiber material. These structures would explain the nonzero value of the second-order nonlinear susceptibility.