Square-Wave Pulse Passively Mode-Locked Thulium-Doped Fiber Laser With Adjustable Pulse Duration and Amplitude

A passively mode-locked thulium-doped fiber laser with square-wave pulse generation has been demonstrated using a figure-of-eight configuration with two gain mediums respectively located in the left and right loops. In this laser, mode-locking is achieved based on equivalent saturation absorption of a nonlinear amplifying loop mirror (NALM). The pulse amplitude and width of the square-wave pulse can be continuously extended through controlling pump power of gain mediums in the left and right loops. Moreover, the pulse dynamics and autocorrelation trace reveal the obtained square-wave pulse is a new kind of noise-like pulse, i.e., noise-like square-wave pulse, with capability of supporting higher pulse energy. This find enriches laser pulse dynamics and has important potential applications in laser detection, sensing and other fields.