Nonlinear optical interactions in optical fibers

We report on our research program aimed at clarifying the physical processes leading to the nonlinear optical response of silica optical fibers and at studying the implications of optical nonlinearities on optical pulse propagation and optical switching devices. The dominant physical processes leading to the nonlinear optical response of an optical fiber are nonresonant electronic polarization, with essentially instantaneous response, the Raman interaction, with sub-picosecond response, and electrostriction, with nanosecond response. We present experimental results that show the consequence of each of these processes on the propagation of a light pulse through an optical fiber. We have also performed one of the first direct measurements of the electrostrictive contribution to the nonlinear refractive index of optical fibers. We measure values ranging from 1.5 x 10(-16) to 5.8 x 10(-16)cm(2)/W, depending on fiber type. These values are comparable to that of the fast, Kerr nonlinearity (i.e., sum of electronic and Raman contributions) of 2.5 x 10(-16)cm(2)/W. The measured electrostrictive nonlinearities are significantly larger than those predicted by simple models, and the possible explanations of this difference are discussed.