| The early use of the induced grating autocorrelation (IGA) method to measure the nonlinear refractive index of single mode fibers utilized 50-70 ps pulses at 1064-nm and required only 15-20 m lengths of fiber. Exotic fibers, such as photonic crystal fibers (PCFs), are extremely expensive and limit many applications to a few meters. Therefore, a practical measurement of the nonlinear coefficient for such exotic fibers requires a technique sensitive to shorter fiber lengths (< 5 m). To reduce the fiber length requirements, the IGA technique must use shorter pulses.;In this work, a new mathematical description was developed for the IGA technique that is applicable to pulses as short as 100 fs. This model includes effects such as dispersion, self-phase modulation, stimulated Raman scattering, intra-pulse Raman scattering and self-steepening. The model was used to investigate pulse propagation at three pulsewidths: 50 ps, 2 ps, and 120 fs. The model predicted the sensitivity of IGA measurements to dispersive and nonlinear effects at these pulsewidths.;The numerical model led to the successful experimental determination of both the dispersion and nonlinear coefficients of a 15m long single-mode fiber using a 2 ps Ti: sapphire laser at 800 nm. The nonlinear coefficient for several PCFs (a 30 cm long highly nonlinear PCF and two large mode area PCFs of 4.5 m and 4.9 m long) were also successfully measured with excellent numerical fits using this new IGA model. |
