| Attributing to the small size,stable performance and high conversion efficiency,fiber lasers have been widely used in optical communication,nonlinear optics,laser processing,biomedicine and other fields.Among all kinds of fiber lasers,passive Q-switched and passive mode-locked fiber lasers based on saturable absorbers can effectively generate pulses with narrower pulse width and higher peak power,and have attracting plenty of attentions.Saturable absorber plays a key role in laser pulse generation.With the development of material technology,two-dimensional materials as broadband saturable absorbers have been successfully used in the preparation of saturable absorbers.The saturable absorbers of two-dimensional materials show excellent performance in fiber lasers,it have been greatly developed in the basic and application research of photonic device structure.In order to further expand the range and diversity of ultrafast laser and advanced photonics,more new two-dimensional materials with excellent nonlinear absorption characteristics need to be explored and developed.In this thesis,the nonlinear absorption characteristics of three two-dimensional ferromagnetic insulators used as saturable absorbers and their pulse output characteristics in Erbium-doped fiber lasers were studied systematically.The main research contents of this paper are summarized as follows:1.An erbium-doped fiber laser based on Cr2Si2Te6 saturable absorber was developed.Cr2Si2Te6 nanosheets were prepared by liquid phase stripping method.The nanosheet suspensions were deposited on the surface of pre-prepared tapered fiber by optical deposition method,and the saturable absorber was prepared.The nonlinear absorption characteristics of Cr2Si2Te6 nanosheets were studied.The saturation strength and modulation depth of Cr2Si2Te6 nanosheets were 5.16 MW/cm2 and 5.69%,respectively.The saturable absorber was placed in the ring cavity of an Erbium-doped fiber laser.Two kinds of stable modelocked pulse output were obtained,namely,dark-bright soliton and bright-dark-bright soliton.The maximum energy of single pulse is 1.35 nJ,and the maximum output power is 9.795 mW.It was proved that Cr2Si2Te6 saturable absorber has good unsaturated absorption characteristics and can be used in fiber lasers to produce stable mode-locked pulse output.2.A mode-locked Erbium-doped fiber laser based on Cr2Sn2Te6 saturable absorber was constructed to produce stable output of bright and dark soliton pulses.The nanosheet dispersion of Cr2Sn2Te6 was successfully prepared by liquid-phase stripping method,and it was systematically characterized.The nonlinearity was tested and analyzed,its saturation strength and modulation depth were 6.11 MW/cm2 and 3.7%,respectively.The nanosheet suspension was deposited on the surface of the tapered fiber by optical deposition method to form a saturable absorber,and it was applied to erbium-doped fiber lasers.Stable output of light-dark soliton mode-locking pulses was obtained successfully.The basic repetition rate is 7.16 MHz,the maximum output power is 11.71 mW,and the maximum single pulse energy is 1.64 nJ.This is the first time that Cr2Sn2Te6 saturable absorber was used to obtain the bright-dark soliton mode-locked pulse output.The experimental results show that Cr2Sn2Te6 saturable absorber has a good value in ultrafast photonics application.3.Q-switched fiber laser based on Cr2Ge2Te6 saturable absorber was studied.The Cr2Ge2Te6 nanosheets were prepared by liquid phase stripping method,and then the saturable absorber of Cr2Ge2Te6 was prepared by PVA membrane forming method.The saturable absorber was connected to the constructed fiber laser cavity to achieve stable Qswitched pulse output.The central wavelength is 1563.73 nm.When the pump power varies from 45 mW to 130 mW,the repetition frequency increases from 2.928 kHz to 15.7 kHz,and the pulse width is the narrowest at 13.45 μs.It was proved that Cr2Ge2Te6 saturable absorber can be used to stabilize Q-switched pulse output. |
