Demonstration of high-stable self-mode-locking pulses based on self-focusing in fiber lasers.

• Both the fundamental frequency operation, 3rd harmonic, and 81st harmonic are observed. • The self-mode-locking operation has excellent stability, since the SNR of the 81st harmonic is as high as 80 dB. • The 81st harmonic has a narrow 3-dB optical spectrum bandwidth of 0.29 nm. • The maximum output power in our work is 27.63 mW. • The self-focusing caused by the Kerr-lens effect of SMF is the major mechanism of self-mode-locking. Passive ultrafast photoelectric devices based on the self-focusing effect have been deeply studied in ultrashort pulse formation, and great progress has been made in solid-state oscillators known as Kerr-lens mode-locking (KLM). The intensity-dependent change of refractive index and the 1–2 fs electronic response time of materials are the basics of KLM. Recently, the advantages of fiber lasers such as compact structure, outstanding environmental stability, excellent heat dissipation potential, and low cost have stimulated great interest among researchers to explore stable and reliable fiber lasers. Based on the feasibility of KML in fiber lasers that have been reported, we demonstrate a high-stable self-mode-locking Er-doped fiber laser in this work. Diverse stable self-mode-locking pulses phenomena can be obtained through adjusting the polarization state of the cavity, including the output pulses with a fundamental frequency of 3.93 MHz, dark-bright soliton pulses, the 3rd harmonic operation, the 81st harmonic operation with the repetition rate of 318.4 MHz and the signal-to-noise ratio of 80 dB, and dual-wavelength output. [ABSTRACT FROM AUTHOR]