Abstract-In order to both experimentally and numerically investigate nonlinear femtosecond ultrabroadband-pulse propagation in a silica fiber, we have extended the finite-difference time-domain (FDTD) calculation of Maxwell's equations with nonlinear terms to that including all exact Sellmeier-fitting values. We have compared results of this extended FDTD method with experimental results, as well as with the solution of the generalized nonlinear Schrödinger equation by the split-step Fourier method with a slowly varying-envelope approximation. To the best of our knowledge, this is the first comparison between FDTD calculation and experimental results for nonlinear propagation of a very short (12 fs) laser pulse in a silica fiber.Index Terms-FDTD, femtosecond, GNLSE, monocycle optical pulse, nonlinear chirp, nonlinear fiber optics, nonlinear propagation, Raman, self-phase modulation, self-steepening, Sellmeier, silica fiber, SVEA, ultrabroad-band spectrum.T HERE WAS RECENTLY significant interest in the generation of single-cycle optical pulses by optical pulse compression of ultrabroad-band light produced in fibers. We reported some experiments on the ultrabroad-band pulse generation using a silica fiber [1], [2] and an Ar-gas filled hollow fiber [3], and the optical pulse compression by nonlinear chirp compensation [1], [3]. For these experiments on generating few-optical-cycle pulses, characterizing the spectral phase of ultrabroad-band pulses analytically as well as experimentally is highly significant. We performed an experiment of 12-fs optical pulse propagation [1] [2]. In order to compare an FDTD calculation results with the experimentally measured ultrabroad spectra of such an ultrashort laser pulse, we extend the GJTH algorithm to that considering all exact Sellmeier's fitting values for ultrabroad spectra. Owing to broad spectrum of pulse propagating in a fiber, it becomes much more important to take accurate linear dispersion into account. It is well known that at least two resonant frequencies must be required for the linear dispersion to fit accurately to a refractive index data. Recent report by Kalosha and his coworker considers the linear dispersion with two resonant frequencies and the nonlinear terms without Raman effect [6]. For the single-cycle pulse generation experiment, we must use at least sub-5 fs [3], [7] or commercially available 12-fs pulses. Such a time regime is comparable to the Raman characteristic time of 5 fs [4] in a silica fiber. Therefore, it is very important to consider not only the accurate linear dispersion of silica but also the Raman effect in a silica fiber in the few-optical-cycles regime. In addition, owing to the high repetition rate and pulse intensity stability, in particular, ultrabroad-band supercontinuum light generation and few-optical-cycles pulse generation by nonlinear pulse propagation in photonic crystal fibers and tapered fibers [8], [9], which both are made of silica, have attracted much attention. In this work, we have extended the FDTD method with nonl...