Direct electrostriction measurement in optical fibers

Summary form only given. We report the direct measurement of the electrostrictive contribution to the nonlinear refractive index n/sub 2/ in standard optical fibers for telecommunications. The fiber under test (FUT) is inserted between two flat electrodes to induce a quasi-static intense electric field in the fiber core. The FUT is kept in a straight line to preserve the polarization, controlled by a polarizer. Because of the Kerr effect and the electrostriction, the refractive index slightly changed, and the phase shift induced on the probe light is measured by means of an interferometric technique. To minimize acoustical and mechanical noises, the whole interferometer was kept in a vacuum, and a feedback control was added to the reference arm of the interferometer. This technique has several advantages, leading to a reliable measurement of n/sub 2/: the applied electric field is uniform over the fiber cross section, its intensity can be accurately calculated from the applied voltage, and the field direction is exactly known. Moreover, by controlling the polarization state of the light propagating in the FUT, the electrostriction effect can be discriminated from the Kerr effect.