Measurement Of Nonlinear Index Research Articles

Self-focusing collapse distance in ultrashort pulses and measurement of nonlinear index

We analyze the method of moving focus to determine the critical power for self-focusing by means of numerical simulation and a semianalytical model. It is shown that the original interpretation of a moving focus experiment does not hold in general and that inclusion of defocusing effects due to free electrons is necessary to relate the measured data to critical power.

Influence of the symmetry rules for Raman susceptibility on the accuracy of nonlinear index measurements in optical fibers

A general expression for a nonlinear polarization in fibers, in which the different symmetry rules for the electronic and Raman contributions to the susceptibility are taken into account, is derived. The contribution of the Raman effect to the total nonlinearity is calculated for different polarizations of a pump and the Stokes wave in polarization-maintaining fibers as well as in fibers with randomly varying birefringence. The error in the measurements of the n2 coefficient caused by the different symmetry rules for the Raman and electronic contributions is shown to depend on germanium concentration and a frequency shift varying from 3.3% in polarization-maintaining fibers to 10% in fibers with random birefringence. The ratio between cross-phase modulation and self-modulation strengths strongly depends on a frequency shift and the polarization state of the interacting waves and varies from 1.2 to 2 in fibers with germanium concentration from 0 to 18 mol.%.