[1] U. Keller. Recent developments in compact ultrafast lasers. Nature, 424, 831(2003).

[2] W. Shi, Q. Fang, X. Zhu, R. A. Norwood, N. Peyghambarian. Fiber lasers and their applications. Appl. Opt., 53, 6554(2014).

[3] C. Kerse, H. Kalaycıoğlu, P. Elahi, Ö. Akçaalan, F. Ö. Ilday. 3.5 GHz intra-burst repetition rate ultrafast Yb-doped fiber laser. Opt. Commun., 366, 404(2016).

[4] H. W. Chen, Z. Haider, J. K. Lim, S. Xu, Z. Yang, F. X. KäRtner, G. Chang. 3 GHz Yb-fiber laser-based, few-cycle ultrafast source at the Ti:sapphire laser wavelength. Opt. Lett., 38, 4927(2013).

[5] D. Panasenko, P. Polynkin, A. Polynkin, J. V. Moloney, M. Mansuripur, N. Peyghambarian. Er-Yb femtosecond ring fiber oscillator with 1.1-W average power and GHz repetition rates. IEEE Photon. Technol. Lett., 18, 853(2006).

[6] M. S. Kang, N. Y. Joly, P. ST.J. Russell. Passive mode-locking of fiber ring laser at the 337th harmonic using gigahertz acoustic core resonances. Opt. Lett., 38, 561(2013).

[7] G. Sobon, K. Krzempek, P. Kaczmarek, K. M. Abramski, M. Nikodem. 10 GHz passive harmonic mode-locking in Er-Yb double-clad fiber laser. Opt. Commun., 284, 4203(2011).

[8] J. Peng, L. Zhan, S. Luo, Q. Shen. Passive harmonic mode-locking of dissipative solitons in a normal-dispersion Er-doped fiber laser. J. Lightwave Technol., 31, 3009(2013).

[9] C. Lecaplain, P. Grelu. Multi-gigahertz repetition-rate-selectable passive harmonic mode locking of a fiber laser. Opt. Express, 21, 10897(2013).

[10] K. S. Abedin, J. T. Gopinath, L. A. Jiang, M. E. Grein, H. A. Haus, E. P. Ipeen. Self-stabilized passive, harmonically mode-locked stretched-pulse erbium fiber ring laser. Opt. Lett., 27, 1758(2002).

[11] D.-H. Yeh, W. He, M. Pang, X. Jiang, G. Wong, P. St.J. Russell. Pulse-repetition-rate tuning of a harmonically mode-locked fiber laser using a tapered photonic crystal fiber. Opt. Lett., 44, 1580(2019).

[12] Y. D. Ling, Q. Q. Huang, C. H. Zou, Z. J. Yan, C. B. Mo. Passively harmonic mode-locked fiber laser with switchable repetition rate based on a 45° tilted fiber grating. Inf. Laser Eng., 47, 803007(2018).

[13] Y.-Q. Huang, Z.-A. Hu, H. Cui, Z.-C. Luo, A.-P. Luo, W.-C. Xu. Coexistence of harmonic soliton molecules and rectangular noise-like pules in a figure-eight fiber laser. Opt. Lett., 41, 4056(2016).

[14] Q. Huang, T. Wang, C. Zou, M. Alaraimi, A. Rozhin, C. Mou. Passively harmonic mode-locked erbium-doped fiber laser at a 580 MHz repetition rate based on carbon nanotubes film. Chin. Opt. Lett., 16, 020019(2018).

[15] Z. C. Luo, M. Liu, H. Liu, X. W. Zheng, A. P. Luo, C. J. Zhao, H. Zang, S. C. Wen, W. C. Xu. 2 GHz passively harmonic mode locked fiber laser by a microfiber-band topological insulator saturable absorber. Opt. Lett., 38, 5212(2018).

[16] J. Koo, J. Park, J. Lee, Y. M. Jhon, J. H. Lee. Femtosecond harmonic mode-locking of a fiber laser at 3.27 GHz using a bulk-like, MoSe2-based saturable absorber. Opt. Express, 24, 10575(2016).

[17] A. R. Muhammad, R. Zakaria, M. T. Ahmad, P. Wang, S. W. Harun. Pure gold saturable absorber for generating Q-switching pulses at 2 µm in thulium-doped fiber laser cavity. Opt. Fiber Technol., 50, 23(2019).

[18] M. Han, S. Zhang, X. Li, H. Zhang, H. Yang, T. Yuan. Polarization dynamic patterns of vector solitons in a graphene mode-locked fiber laser. Opt. Express, 23, 2424(2015).

[19] S. V. Sergeyev, C. Mou, A. Rozhin, S. K. Turitsyn. Vector solitons with locked and precessing states of polarization. Opt. Express, 20, 27434(2012).

[20] E. Nazemosadat, A. Mafi. Nonlinear multimodal interference and saturable absorption using a short graded-index multimode optical fiber. J. Opt. Soc. Am. B, 30, 1357(2013).

[21] E. Nazemosadat, A. Mafi. Saturable absorption in multicore fiber couplers. J. Opt. Soc. Am. B, 30, 2787(2013).

[22] W. Zhao, G. Chen, W. Li, G. Wang. All-fiber saturable absorbers for ultrafast fiber lasers. IEEE Photon. J., 11, 7104019(2019).

[23] S. Fu, Q. Sheng, X. Zhu, W. Shi, J. Yao, G. Shi, R. A. Norwood, N. Peyghambarian. Passive Q switching of an all fiber laser induced by the Kerr effect of multimode interference. Opt. Express, 23, 17255(2015).

[24] Z. Wang, D. Wang, F. Yang, L. Li. Er doped mode locked fiber laser with a hybrid structure of a step index-graded index multimode fiber as the saturable absorber. J. Lightwave Technol., 35, 5280(2017).

[25] Y. Fan, D. N. Wang, Z. Wang, L. Li, C. L. Zhao, B. Xu, S. Jin, S. Y. Cao, Z. J. Fang. Saturable absorber based on a single mode fiber- graded index fiber-single mode fiber structure with inner microcavity. Opt. Express, 26, 927(2017).

[26] H. Zhang, L. Jin, H. Zhang, Y. Xu, X. Ma. All-fiber nonlinear optical switch based on polarization controller coiled SMF-GIMF-SMF for ultrashort pulse generation. Opt. Commun., 452, 7(2019).

[27] T. Wang, L. Jin, H. Zhang, W. Pan, H. Zhang, Y. Xu, L. Shi, Y. Li, Y. Zou, X. Ma. Gigahertz harmonic mode-locked fiber laser based on tunable SMS ultrafast optical switch. Annalen der Physik, 532, 2000018(2020).

[28] H. H. Li, Z. K. Wang, C. Li, J. J. Zhang, S. Q. Xu. Mode-locked Tm fiber laser using SMF-SIMF-GIMF-SMF fiber structure as a saturable absorber. Opt. Express, 25, 26546(2017).

[29] Z. Wang, D. N. Wang, Y. Fan, L. Li, C. L. Zhao, B. Xu, S. Jin, S. Y. Cao, Z. J. Fang. Stretched graded-index multimode optical fiber as a saturable absorber for erbium-doped fiber laser mode locking. Opt. Lett., 43, 2078(2018).

[30] Y. Fan, D. N. Wang, Z. Wang, L. Li, C. L. Zhao, B. Xu, S. Jin, S. Y. Cao, Z. J. Fang. Saturable absorber based on a single mode fiber-graded index fiber-single mode fiber structure with inner micro-cavity. Opt. Express, 26, 927(2018).

[31] A. Mafi, P. Hofmann, C. J. Salvin, A. Schülzgen. Low-loss coupling between two single-mode optical fibers with different mode-field diameters using a graded-index multimode optical fiber. Opt. Lett., 36, 3596(2011).

[32] F. Tan, J. Liu, R. Sun, P. Wang. All-normal-dispersion passively mode-locked Yb-doped fiber laser with multimode interference effect. Chin. J. Lasers, 40, 0402010(2013).

[33] L. Tong, J. Lou, E. Mazur. Single-mode guiding properties of subwavelength-diameter silica and silicon wire waveguides. Opt. Express, 12, 1025(2004).

[34] H. H. Liu, K. K. Chow. Enhanced stability of dispersion-managed mode-locked fiber lasers with near-zero net cavity dispersion by high-contrast saturable absorbers. Opt. Lett., 39, 150(2014).

[35] J. Wang, Z. Jiang, H. Chen, J. Li, J. Yin, J. Wang, T. He, P. Yan, S. Ruan. Magnetron-sputtering deposited WTe2 for an ultrafast thulium-doped fiber laser. Opt. Lett., 42, 5010(2017).

[36] J. Wang, Z. Jiang, H. Chen, J. Li, J. Yin, J. Wang, T. He, P. Yan, S. Ruan. High energy soliton pulse generation by a magnetron-sputtering-deposition-grown MoTe2 saturable absorber. Photon. Res., 6, 535(2018).

[37] H. F. Li, S. M. Zhang, J. Du, Y. C. Meng, X. L. Li. Passively harmonic mode-locked fiber laser with controllable repetition rate based on a carbon nanotube saturable absorber. Opt. Commun., 285, 1347(2012).

[38] R. Weill, A. Bekker, V. Smulakovsky, B. Fischer, O. Gat. Noise-mediated Casimir-like pulse interaction mechanism in lasers. Optica, 3, 189(2016).

[39] D. Y. Tang, B. Zhao, L. M. Zhao, H. Y. Tam. Soliton interaction in a fiber ring laser. Phys. Rev. E, 72, 016616(2005).