Dark pulses are characterized by being formed from a localized reduction of intensity compared to a more intense continuous wave background. Scalar dark solitons (linearly polarized dark solitons) can be formed in all normal dispersion fiber lasers mode-locked by the nonlinear polarizaiton rotation method and can be rather stable. Vector dark solitons are much less stable due to the cross-interaction between the two polarization components. Therefore it is interesting to investigate how the polarization state of these two polarization components evolves.
In 2008, the first dark pulse laser was reported in a quantum dot diode laser with a saturable absorber.
In 2009, the dark pulse fiber laser was successfully achieved in an all-normal dispersion erbium-doped ﬁber laser with a polarizer in cavity. Experimentation has revealed that apart from the bright pulse emission, under appropriate conditions the ﬁber laser could also emit single or multiple dark pulses. Based on numerical simulations, the dark pulse formation in the laser is a result of dark soliton shaping.
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