Study of the influence of interaction of spectral filtering and slow saturable absorption on the formation of ultrashort pulses in fibre lasers

We study the formation of ultrashort pulses in a fibre laser cavity with a slow saturable absorber and a spectral filter. It is found that in a cavity with total normal chromatic dispersion, the finite relaxation time of a saturable absorber leads to a spectral shift of the generated pulses relative to the centre wavelength of the spectral filter. The numerical results are verified using two experimental laser sources: a ring fibre laser with a saturable semiconductor mirror and a fibre laser with a nonlinear amplifying loop mirror. The obtained results can be used to design ultrashort-pulse laser sources in applications for which the spectral properties of radiation are of key importance.