The optimized design of microstructured optical fibers (MOFs) for supercontinuum generation is investigated. The dependence of the group velocity dispersion and effective mode area on wavelength is analyzed. We consider first the case of a conventional MOF with a hexagonal pattern of air holes. In addition, we propose a new design, corresponding to a layered spiral microstructured optical fiber (LS-MOF). By changing appropriately its three parameters, it is possible to shift the zero dispersion wavelength to visible and near-infrared regions, as well as to achieve a very high nonlinearity near this wavelength. Supercontinuum generation is simulated in a LS-MOF with optimized design .
We investigate numerically the temporal and spectral characteristics of fixed-shape pulses, resulting from pulsating,
erupting and creeping soliton solutions of a generalized complex Ginzburg-Landau equation (CGLE), which includes the
third-order dispersion, intrapulse Raman scattering, and self-steepening effects. In general, the resulting fixed-shape
solutions are asymmetric and chirped pulses. The interaction between such fixed-shape pulses is also investigated, and
we show that a stable propagation is achieved, except when the pulses have an oscillating tail.
We perform an accurate numerical modelling of both tapered and microstructured fibers using a finite element numerical
approach. We compute the propagation modes, i.e., distribution of the electric field over the cross section, effective
modal area and dispersion characteristics. The dependence of the dispersion properties on wavelength are calculated by
solving the eigenvalue equation for fiber modes and using Sellmeier equation. The optical properties of tapered fibers are
shown to be very sensitive to the core size. The zero dispersion wavelength can be shifted to the visible range and, in
some cases, two zero dispersion wavelengths are observed. The dependence of the dispersion properties and of the
effective mode area of a microstructured fiber with hexagonal symmetry on the air-hole diameter and the hole-to-hole
spacing is also investigated.
In this paper we investigate the interaction between solitary-plain pulses (SP) of the quintic CGLE modified,
which describes the soliton behaviour in the presence of spectral filtering, linear and nonlinear gains, and selffrequency
shift (intrapulse Raman scattering). In particular, we look for a clear understanding of fundamental
properties of the bound sates, especially as concerns their stability. We use the interaction plane (distancephase
difference) to analyze the dynamics of the two soliton system. We have found stable BS's of plain
pulses when the phase difference between them is π / 2 + ▵, and ▵ is a quantity that depends on a selffrequency
shift coefficient.
We investigate numerically the dynamics of pulsating, erupting and creeping soliton solutions of a generalized complex
Ginzburg-Landau equation (CGLE), including the third-order dispersion (TOD), intrapulse Raman scattering (IRS) and
self-steepening (SST) effects. We show that these higher-order effects (HOEs) can have a dramatic impact on the
dynamics of the above mentioned CGLE solitons. For small values of the HOEs, the periodic behavior of some of these
pulses is eliminated and they are transformed into fixed-shape solitons. However, a rather different behaviour is observed
by increasing the magnitude of the HOEs. Some particular interesting cases are discussed concerning the combined
action of the three HOEs.
We consider the formation and stability characteristics of bound states in the complex Ginzburg-Landau equation. Using the perturbation theory, we derive a dynamical system describing the interaction between two weakly overlapping pulses. Two types of bound states were found, which correposnd to fixed points of this system. One of them is unstable, while the other corresponds to practically stable stationary points of the dynamical system governing the interaction. Our numerical results indeed confirm the existence of stable bound sttes of two solitons when thephase difference between them is plus or minus π/2. This happens when we consider the interaction of both two standard plain pulses and of two composite pulses. We find that two-composite pulses bound states have zero velocity, which is contrast with the behavior of the bound states formed by plain pulses. The existence of stable bound states with zero velocity formed by multiple composite pulses is also demonstrated.
The soliton propagation and interaction characteristics in the presence of spectral filtering, linear and nonlinear gain are investigated. Using a perturbation approach, it is shown that the nonlinear gain has a significant impact on the soliton interaction when the adjacent solitons have different phases or amplitudes. In a system with purely nonlinear gain, for which arbitrary amplitude solitons can propagate, we find that the phase difference varies continuously and the solitons oscillate only slightly around their initial time separation. Concerning the quintic Ginzburg-Laudau equation and taking into account the soliton chirping, we find the existence of two types of bound states. One of them is unstable, while the other corresponds to practically stable stationary points of the dynamical system governing the interaction. These findings are in accordance with the numerical results obtained by ourselves as well as by other authors.
We investigate, both analytically and numerically, the effectiveness of the nonlinear gain to suppress the background instability in bandwidth-limited soliton transmission. Different types of analytical solutions of the complex Ginzburg-Landau equation (CGLE), namely solutions with fixed amplitude and solutions with arbitrary amplitude, are discussed. The conditions for the stable pulse propagation are defined within the domain of validity of the soliton perturbation theory. The CGLE is solved numerically assuming various input waveforms with different phase profiles, amplitudes and durations. Relatively stable pulse propagation can be achieved over long distances by the use of suitable combination of linear and nonlinear gains. For the cubic CGLE, truly stable propagation of arbitrary amplitude solitons can be achieved in a system with purely nonlinear gain. A new soliton compression effect is demonstrated both for fixed- amplitude and for arbitrary-amplitude solitons. This compression can be particularly significant when the system parameters are chosen near the singularity of the fixed- amplitude solution.
We examine the influence of the third-order filter contribution on soliton propagation in a system with sliding-frequency guiding filters. The soliton loss in a system with up-sliding than it is in a system with down- sliding. We derive also an analytical expression for the variance of the timing jitter of a soliton transmission system using sliding-frequency guiding filters, taking into account the third-order filter term. The variance of timing jitter is significantly increased by the sliding action. As a consequence of the third-order filter contribution, the timing jitter is lower in a system with down-sliding than it is in a system with up-sliding at the same sliding rate.
The stability of soliton propagation in a system with spectral filtering, linear and nonlinear gain is numerically investigated. Different types of analytical solutions of the cubic complex Ginzburg-Landau equation, namely solutions with fixed amplitude and solutions with arbitrary amplitude, are presented. Then, the evolution equation is solved numerically assuming various input waveforms. Our results show that it will be possible to achieve relatively stable pulse propagation over long distances by the use of suitable combination of linear and nonlinear gains. However, truly stable propagation of arbitrary amplitude solitons can be achieved only in a system with purely nonlinear gain. A new soliton compression effect is demonstrated both for fixed- amplitude and arbitrary-amplitude solitons.
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