In this work, several normally dispersive highly nonlinear chalcogenide optical fibers (NDHNCFs) with a step-index profile have been designed and optimized in view of efficient parabolic pulse (PP) generation. A typical NDHNCF is selected such that the group velocity dispersion is highest among them and the corresponding nonlinearity is also very high. The input pulse parameters are optimized to find the lowest possible optimum length (L) of the fiber where the linearly chirped PP is obtained. Further, it is found that for a shorter input pulse width, PP can be generated at a sufficiently smaller length of the NDHNCF with a slight compromise for its misfit parameter. A detailed analysis of the effect of pre-chirping helps to identify the suitable amount of initial chirp for different chalcogenide fibers with a choice of input pulse parameters. Although no improvement in PP generation is found for normal and initially chirped hyperbolic secant pulses, a highly efficient triangular pulse is achieved for a particular value of input pulse energy and the initial chirp parameter. Finally, the comparative study substantiates that our optimized NDHNCF is capable enough to generate quality PP at a length almost 70% shorter than a standard silica-based fiber.

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A highly nonlinear single-mode anomalous dispersion silicon-core fiber (SMADSF) is designed and optimized at the operating wavelength of 2.2 µm for the purpose of generating stable temporal pulse doublets. To designate the output pulse pair as a perfect Gaussian doublet, two new parameters, dissimilarity factor (ρ_g) and co-similarity index (μ_cs) are introduced. Different input pulse parameters such as power, pulse width and chirp are optimized to obtain Gaussian temporal doublets at the shortest optimum length (~ few cm) which is sufficiently smaller in comparison to silica fibers reported earlier. The output pulse pairs remain as a doublet for quite a good stability length. In view of serving practical purposes, the possibilities of fluctuations of input power and pulse width are included to investigate the changes in stability length and effective repetition rate (ERR). The change in ERR along the fiber length produces a remarkable change in free carrier concentration in core, which has also been taken into account for the first time as per our knowledge to obtain the temporal pulse doublet in the so designed Si-core fiber.

The objective of this work is to investigate the effect of nonlinearity-induced virtual gain in parabolic pulse (PP) formation by dispersion varying fibers and utilizing this gain over that of dispersion. As chalcogenides show high values of nonlinear coefficient, a dispersion decreasing fiber, named as nonlinearly tapered chalcogenide fiber (NLTCF), is designed here by optimizing different combinations of chalcogenide materials and core radius profiles such that efficient PP can be generated at considerably shorter optimum lengths with respect to the corresponding constant dispersion fiber. With suitable manoeuvring of the nonlinearity-induced virtual gain, a fiber combination consisting of a dispersion increasing fiber and the NLTCF shows enough efficiency to reduce the optimum length significantly. Although the virtual gain due to dispersion dominates over that due to nonlinearity in silica fibers, the situation is completely reversed in the case of specially designed highly nonlinear fibers. When compared to silica-based fibers, these types of fibers perform remarkably better in PP formation at shorter values of optimum fiber length with a higher amount percentage reduction of length making the higher order dispersive terms ineffective as well.

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