Abstract

Despite several calculations¹,² discussing the possibility that self-phase modulation (SPM) and cross-phase modulation (CPM) are the main factors for saturation with length of second-harmonic (SH) light in optical fibers, we believe that we have experimentally proven³ that SPM and CPM have a very limited influence on the variation of saturation with length for the SH light in an optical fiber. Instead, we propose that absorption plays a major role, both for saturation as a function of length and for overall saturation as a funciton of time. Assuming the absorption has two contributions, one from a resonant two-photon transition of fundamental and harmonic photons in the germanium oxide molecules of the glass and the second from photo-induced absorption based upon free-carriers, we can explain most of the experimentally found anomalies³ of saturated SH light with length and time. We will also discuss various possibilities for photo-inducing free carriers in doped fused silica.

© 1990 Optical Society of America