It has been investigated of nonlinear propagation of femosecond pulse and supercontinuum generation (SCG) in three
photonic crystal fibers (PCFs) with different dispersion profile in the 1550nm window by numerical stimulation. The
influence of higher-order effects on supercontinuum, including higher-order dispersion (HOD), self-steepening (SS), and
stimulated Raman scattering (SRS), are discussed in detail as well. The results of numerical simulations show that group
velocity dispersion and self-phase modulation take main effect in the initial stage. In the PCF with anomalous dispersion,
SRS plays main role when the propagation distance increases, which induces a red-shift of the central wavelength,
suggesting the appearance of soliton self-frequency shift. In the PCF with near-zero anomalous dispersion, HOD plays
main role. This results in the fission of higher-order solitons and remarkable broadening of the pulse spectrum. In the
PCF with normal dispersion, higher-order effects have almost no effect on the pulse. The Gaussian pulse wave broadens
to rectangular symmetrically, and the pulse spectrum broadens symmetrically, too. However, the broadening is smaller
than the former two cases.
We study the performance of all-optical switching in long period fiber grating based on the coupled nonlinear Schrodinger equations. The switching rate of long period fiber grating in the on-resonance and off-resonance case is obtained, respectively. It is found that in both cases, the on-off ratio of all-optical switching in long period fiber grating can be improved remarkably, and the phenomenon of pulse breakup can be avoided effectively, by using the higher order
We study modulation instability (MI) in the fiber Bragg grating with nonlinearity management based on the coupled-mode theory. The role of both average Kerr nonlinearity and variance of Kerr nonlinearity between the layers of fiber grating in MI is identified. It is found that the variance of Kerr nonlinearity affect MI gain spectrum remarkably in both anomalous dispersion and normal dispersion regimes. In the anomalous dispersion regime, when the variance of Kerr nonlinearity is much smaller than the average Kerr nonlinearity, the MI gain spectrum is similar to that without the variance of Kerr nonlinearity, but the range of wave number for MI to occur is narrowed, and the amplitude of gain decreased. When the variance of Kerr nonlinearity is enhanced to be equivalent to the average Kerr nonlinearity, the role of variance of Kerr nonlinearity in MI becomes important: At low intensity, the range of wave number for MI to occur shrinks notably, and the gain gets only a single peak compared with the original one which has two symmetrical side-bands. At high intensity, there appear three MI ranges. In the normal dispersion regime, near the lower edge of photonic band gap, the amplitude of MI gain is slowed down due to the influence of variance of Kerr nonlinearity, and only two small symmetrical MI range appear, in sharp contrast to the original case without the influence of variance of Kerr nonlinearity, in which MI occurs for all wave numbers. Whereas in the case that far away from the edge of photonic band gap, we find that the range of wave number for MI to occur and the amplitude of MI gain increase as the value of variance of Kerr nonlinearity increases.
We investigate modulation instability (MI) in the distributed fiber amplifier based on a modified Ginzburg-Landau equation. The role of gain dispersion and stimulated Raman scattering (SRS) in MI is identified. It is found that, due to SRS, the MI gain spectrum consists of two parts: the conventional MI gain spectrum and the Raman gain spectrum. Gain dispersion exerts little influence on the conventional MI spectrum, yet it deforms the Raman gain spectrum seriously, mainly by reducing its growth rate. Moreover, as the signal power increases, the bandwidths of the conventional MI and the Raman gain spectrum are simultaneously extended, with the latter spectrum being extended more quickly.
We use the standard linear stability analysis to study the role of stimulated Raman scattering in spatiotemporal instability in dispersive Kerr medium based on an extended (3+1)-dimensional nonlinear Schrodinger equation. We show that the spatiotemporal instability gain spectrum consists of two parts: the conventional spatiotemporal instability gain spectrum and the Raman gain spectrum. Stimulated Raman scattering doesn't affect the conventional spatiotemporal instability gain spectrum; yet it provides additional sidebands which have almost the same gain spectrum in all combinations of the signs of group velocity dispersion and nonlinear refractive index. It is interesting that spatiotemporal instability gain can appear for any spatial frequencies in the presence of stimulated Raman scattering, in sharp contrast to conventional spatiotemporal instability whose gain is located in a limited spatial frequency range.
We apply the variational approach to solve the nonparaxial nonlinear Schrodinger equation to disclose the nonparaxial propagation properties of a Gaussian beam. A system of differential equations for the evolution of the parameters of Gaussian beam is obtained. The obtained analytical results clearly show the nonparaxial propagation process of periodic focusing-defocusing. This process is significantly influenced by the initial power and chirp of the beam. A positive chirp retards the first self-focus, while a negative chirp brings forward the first self-focus. Both positive and negative chirps increase the subsequent focusing-defocusing cycles.