Ultrashort pulse formation from a thulium-doped fiber laser: Self-characterization and mapping

We have performed an automatic characterization of a mode-locked thulium-doped fiber laser in soliton regime based on a versatile scheme of nonlinear polarization rotation (NPR) mode-locking. The cavity includes three fiber loop waveplates for adjusting the oscillation states of the cavity. The polarization controllers are equipped with servo motors that allow for automated stepping through a large number of polarization controller settings. The optical spectra and the radio frequency spectra of the cavity output are recorded at each polarization controller setting to extract key laser parameters from the data, automatically. Analyzing the large data sets, not only provides maps of the laser operation in various modes, but also it identifies the polarization controller settings leading to optimal mode-locking, consequently. Such method allows a detailed self-characterization of the fiber laser cavity which paves the way to achieve smart fiber lasers. This approach facilitates applications of fiber lasers and improves their reliability for practical purposes, where environmental instabilities might limit their performances.