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The interaction and compression of the similariton beam generated in a mode-locked similariton laser system and compressed in a DDF (dispersion-decreasing fiber) with negative dispersion is investigated in this paper. First, a quality factor R is established to evaluate the quality of compressed similariton beams to design optimum tapered DDF. The result shows that the hyperbolically tapered DDF can achieve a best R compared to the linearly tapered DDF, exponentially tapered DDF, Gaussian tapered DDF, cosinoidally tapered DDF and logarithmically tapered DDF. Then, a pedestal energy ratio PE and a compression quality parameter Q are further established to evaluate the quality of compressed output beams considering the pulses with and without interaction by adjusting the time-delay q0 between the pulse pairs in a hyperbolically tapered DDF. Finally, we obtain the optimum compressed pulse pair both considering q0 = 4ps and q0 = 2.6ps, the pedestal energy ratios are 3.0048% and 13.4306%, maximum compression quality parameters are 454.3059 and 293.1326, the corresponding FWHM and peak power are 177.3fs and 302.2695W, 189.7fs and 249.4017W, respectively, demonstrating efficient and high-quality similariton beam compression.

The generation of effective ultra-short laser pulses in the picosecond pulse range is very important for modern communication. This paper firstly investigates a combined dispersion-decreasing fiber (DDF) loop mirror consisting of a fourth-order super-Gaussian DDF and a Gaussian DDF. First, the transmission principle of the designed fiber loop mirror is analyzed theoretically. Secondly, the influence of the total fiber length on pulse compression is studied to obtain an optimal total fiber length. Then the length ratio of the two optical fibers in the loop mirror is analyzed and optimized to achieve a high-quality ultra-short output pulse. The results show that the optimal output pulse with no pedestal and a high compression factor of F=49.6 can be obtained at the total fiber length L=4.3km and the combined fiber length ratio of the fourth-order super-Gaussian DDF and the Gaussian DDF is equal to 0.102. Compared with the traditional DDF loop mirror, the compression factor is increased by 18.5 times, achieving a high-quality compressed pulse with higher compression factor.