[1] D. Y. Tang, L. M. Zhao, B. Zhao, A. Q. Liu. Mechanism of multisoliton formation and soliton energy quantization in passively mode-locked fiber lasers. Phys. Rev. A, 2009, 72: 1-38.

[2] M. Olivier, M. Piché. Origin of the bound states of pulses in the stretched-pulse fiber laser. Opt. Express, 2009, 17: 405-418.

[3] P. Wang, K. Zhao, L. Gui, X. Xiao, C. Yang. Self-organized structures of soliton molecules in 2-μm fiber laser based on MoS₂ saturable absorber. IEEE Photon. Technol. Lett., 2018, 30: 1210-1213.

[4] MalomedB. A., “Bound solitons in the nonlinear Schrödinger/Ginzburg-Landau equation,” in Large Scale Structures in Nonlinear Physics, Lecture Notes in Physics (Springer, 1991).

[5] N. Akhmediev, A. Ankiewicz, J. Soto-Crespo. Multisoliton solutions of the complex Ginzburg-Landau equation. Phys. Rev. Lett., 1997, 79: 4047-4051.

[6] N. N. Akhmediev, A. Ankiewicz, J. M. Soto-Crespo. Stable soliton pairs in optical transmission lines and fiber lasers. J. Opt. Soc. Am. B, 1998, 15: 515-523.

[7] TangD. Y.DrummondP. D.ManW. S.TamH. Y.DemokanM. S., “Observation of bound solitons in a passively mode-locked fiber laser,” in Quantum Electronics and Laser Science Conference (2000), paper QWG4.

[8] L. Gui, P. Wang, Y. Ding, K. Zhao, C. Bao, X. Xiao, C. Yang. Soliton molecules and multisoliton states in ultrafast fibre lasers: intrinsic complexes in dissipative systems. Appl. Sci., 2018, 8: 201.

[9] P. Grelu, J. M. Soto-Crespo. Multisoliton states and pulse fragmentation in a passively mode-locked fibre laser. J. Opt. B Quantum Semiclass. Opt., 2004, 6: S271-S278.

[10] D. Y. Tang, B. Zhao, L. M. Zhao, H. Y. Tam. Soliton interaction in a fiber ring laser. Phys. Rev. E, 2005, 72: 1-51.

[11] A. Komarov, F. Amrani, A. Dmitriev, K. Komarov, D. Meshcheriakov, F. Sanchez. Multiple-pulse operation and bound states of solitons in passive mode-locked fiber lasers. Int. J. Opt., 2012, 2012: 418469.

[12] A. Hideur, B. Ortaç, T. Chartier, M. Brunel, H. Leblond, F. Sanchez. Ultra-short bound states generation with a passively mode-locked high-power Yb-doped double-clad fiber laser. Opt. Commun., 2003, 225: 71-78.

[13] B. Ortac, A. Hideur, M. Brunel, C. Chedot, J. Limpert, A. Tunnermann, F. O. Ilday. Generation of parabolic bound pulses from a Yb-fiber laser. Opt. Express, 2006, 14: 6075-6083.

[14] H. P. Li, H. D. Xia, Z. Jing, J. K. Liao, X. G. Tang, Y. Liu, Y. Z. Liu. Dark pulse generation in a dispersion-managed fiber laser. Laser Phys., 2012, 22: 261-264.

[15] W. C. Chen, Z. C. Luo, W. C. Xu, D. A. Han, H. Cao. Effect of gain media characteristics on the formation of soliton molecules in fiber laser. Laser Phys., 2011, 21: 1919-1924.

[16] P. Wang, X. Xiao, C. Yang. Quantized pulse separations of phase-locked soliton molecules in a dispersion-managed mode-locked Tm fiber laser at 2 μm. Opt. Lett., 2017, 42: 29-32.

[17] P. Wang, C. Bao, B. Fu, X. Xiao, P. Grelu, C. Yang. Generation of wavelength-tunable soliton molecules in a 2-μm ultrafast all-fiber laser based on nonlinear polarization evolution. Opt. Lett., 2016, 41: 2254-2257.

[18] J. Wang, M. Yao, C. Hu, A. Ping Zhang, Y. Shen, H. Tam, P. K. A. Wai. Optofluidic tunable mode-locked fiber laser using a long-period grating integrated microfluidic chip. Opt. Lett., 2017, 42: 1117-1120.

[19] Y. Xiang, Y. Luo, B. Liu, Z. Yan, Q. Sun, D. Liu. Observation of wavelength tuning and bound states in fiber lasers. Sci. Rep., 2018, 8: 6049.

[20] L. Gui, C. Yang. Soliton molecules with ±π/2, 0, and π phase differences in a graphene-based mode locked erbium-doped fiber laser. IEEE Photon. J., 2018, 10: 1502609.

[21] K. Li, Y. Song, J. Tian, H. Guoyu, R. Xu. Analysis of bound-soliton states in a dual-wavelength mode-locked fiber laser based on Bi2Se3. IEEE Photon. J., 2017, 9: 1400209.

[22] X. Li, K. Xia, D. Wu, Q. Nie, S. Dai. Bound states of solitons in a fiber laser with a microfiber-based WS₂ saturable absorber. IEEE Photon. Technol. Lett., 2017, 29: 2071-2074.

[23] Y. Chen, S. Chen, J. Liu, Y. Gao, W. Zhang. Sub-300 femtosecond soliton tunable fiber laser with all-anomalous dispersion passively mode locked by black phosphorus. Opt. Express, 2016, 24: 13316-13324.

[24] Z. Wang, D. N. Wang, F. Yang, L. Li, C. Zhao, B. Xu, S. Jin, S. Cao, Z. Fang. 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., 2017, 35: 5280-5285.

[25] Z. Wang, D. N. Wang, F. Yang, L. Li, C. Zhao, B. Xu, S. Jin, S. Cao, Z. Fang. Stretched graded-index multimode optical fiber as a saturable absorber for erbium-doped fiber laser mode locking. Opt. Lett., 2018, 43: 2078-2081.

[26] Z. T. Wang, Y. Chen, C. J. Zhao, H. Zhang, S. C. Wen. Switchable dual-wavelength synchronously Q-switched erbium-doped fiber laser based on graphene saturable absorber. IEEE Photon. J., 2012, 4: 869-876.

[27] P. Grelu, N. Akhmediev. Dissipative solitons for mode-locked lasers. Nat. Photonics, 2012, 6: 84-92.

[28] J. Peng, L. Zhan, S. Luo, Q. S. Shen. Generation of soliton molecules in a normal-dispersion fiber laser. IEEE Photon. Technol. Lett., 2013, 25: 948-951.

[29] A. Mafi, P. Hofmann, C. J. Salvin, A. Schulzgen. Low-loss coupling between two single-mode optical fibers with different mode-field diameters using a graded-index multimode optical fiber. Opt. Lett., 2011, 36: 3596-3598.

[30] P. Hofmann, A. Mafi, C. Jollivet, T. Tiess, N. Peyghambarian, A. Schulzgen. Detailed investigation of mode-field adapters utilizing multimode-interference in graded index fibers. J. Lightwave Technol., 2012, 30: 2289-2298.

[31] D. Y. Tang, L. M. Zhao, B. Zhao. Multipulse bound solitons with fixed pulse separations formed by direct soliton interaction. Appl. Phys. B, 2005, 80: 239-242.

[32] L. M. Zhao, D. Y. Tang, X. Wu, H. Zhang. Dissipative soliton generation in Yb-fiber laser with an invisible intracavity bandpass filter. Opt. Lett., 2010, 35: 2756-2758.

[33] L. Socci, M. Romagnoli. Long-range soliton interactions in periodically amplified fiber links. J. Opt. Soc. Am. B, 1999, 16: 12-17.