Abstract
We observed generation of stable picoseconds pulse train and double-scale optical lumps with picosecond envelope and femtosecond noise-like oscillations in the same Yb-doped fiber laser with all-positive-dispersion cavity mode-locked due to the effect of non-linear polarization evolution. In the noise-like pulse generation regime the auto-correlation function has a non-usual double (femto- and picosecond) scale shape. We discuss mechanisms of laser switching between two operation regimes and demonstrate a good qualitative agreement between experimental results and numerical modeling based on modified nonlinear Schrödinger equations.
Highlights
Nonlinear polarisation evolution (NPE) [1,2,3,4] is a commonly employed mechanism used to achieve stable mode-locking and ultra-short pulse generation in an all-positive dispersion cavity
In [11], similar noise-like pulse operation was demonstrated in erbium-doped fiber laser with weak birefringence. It was conjectured in [11] that the formation of the noise-like oscillations is caused by the pulse collapse effect [13] and that such dynamics is a generic feature of a range of the passively mode-locking systems
The collapse effect dynamics is more sensitive to initial conditions and as a result the forming field structures tend to be more random and complex compared to non-collapse pulse generation regimes
Summary
Nonlinear polarisation evolution (NPE) [1,2,3,4] is a commonly employed mechanism used to achieve stable mode-locking and ultra-short pulse generation in an all-positive dispersion cavity. In [11], similar noise-like pulse operation was demonstrated in erbium-doped fiber laser with weak birefringence It was conjectured in [11] that the formation of the noise-like oscillations is caused by the pulse collapse effect [13] and that such dynamics is a generic feature of a range of the passively mode-locking systems. The collapse effect dynamics is more sensitive to initial conditions and as a result the forming field structures tend to be more random and complex compared to non-collapse pulse generation regimes Though, such fast growth of the field amplitude is saturated at some level by the higher terms in the expansion and other high-order effects, the resulting noisy and random asymptotic state could be quite different from more smooth regimes of the radiation intensity growth. We present experimental and numerical studies of the double-scale femto-pico-second optical lumps generation in Yb fiber laser and discuss in detail physical mechanisms behind the generation of mode switching in mode-locked all-positive-dispersion fiber lasers
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