Study of a figure-eight laser generating noise-like pulses with adjustable characteristics

In this work we study experimentally and numerically a passively mode-locked figure-eight fiber laser that includes a polarization-imbalanced Nonlinear Optical Loop Mirror (NOLM), whose switching power can be adjusted through a wave retarder plate. The laser emits broadband noise-like pulses with a bandwidth that can exceed 50 nm. The pulses are actually sub-nanosecond wave packets with an inner fine structure of sub-ps pulses with random amplitude and duration. The duration of the pulses as well as their spectral width can be adjusted through the variation of the NOLM switching power. Numerical simulations are in good agreement with experimental results, confirming in particular the strong dependence of the pulse properties on the value of the NOLM switching power, although NOLM switching alone does not explain the appearance of the noise-like pulsing mode. The properties of this kind of pulses, like their wide bandwidth and energy, make them attractive for applications like supercontinuum generation and metrology.