Supercontinuum generation is usually the synergy of some fundamental sophisticated nonlinear processes. Although it is well known that self-phase modulation, stimulated Raman scattering and four-wave mixing etc., are the dominant contributors, the comparative importance of these effects is still blurry to some extent. Based on the extended nonlinear Schrödinger equation describing pulse propagation in the microstructured fiber, we have identified the role of higher-order effects in supercontinuum generation. It is shown that in the initial formation of the supercontinuum self-phase modulation plays a main role while all the higher-order effects play a minor role. After a certain propagation distance the spectral width saturates, suggesting that the supercontinuum in microstructured fiber has a maximum spectral width. During the saturation stage, the higher-order effects exert more important influence on supercontinuum, mainly changing its shape. The third-order dispersion leads to spectral asymmetry, while SRS leads to a red shift of the supercontinuum spectrum. Furthermore, based on our theoretical results, we have discussed the way to controlling supercontinuum generation by using the nonlinear processes of microstructured fiber.
The generic features of modulation instability (MI) in optical fibers are disclosed by application of an extended nonlinear Schroedinger equation. The role of arbitrary higher-order dispersions, stimulated Raman scattering (SRS) and self-steepening (SS) in MI is identified. It is shown that all odd-order dispersions contribute nothing to MI, whereas all even-order dispersions not only affect the conventional instability regions but may also lead to the appearance of new
MI regions. In the presence of SRS, the MI gain spectrum in optical fibers consists of two parts: the conventional MI gain spectrum and the Raman gain spectrum. In the case of normal dispersion, MI occurs due to SRS. In the case of anomalous dispersion, as the initial power increases, the SRS gain spectrum is gradually screened from the conventional MI gain spectrum. Self-steepening exerts little influence on MI in both normal and anomalous dispersion regimes.
Numerical simulation confirms the obtained analytical results.