| The 21st century is an era of light.The fiber laser technology is one of the most rapidly developing and promising technologies in lots of optical fields.And the application fields have covered industrial processing,medical cosmetology,optical communication,defense countermeasure and so on.Unique fine fiber core and double cladding structure of fiber lasers result in strong nonlinear effects in the cavity,such as the self-phase modulation,cross phase modulation,stimulated Raman scattering and stimulated Brillouin scattering and so on,making the pulse fiber lasers as an ideal platform to explore the pulse generation and dynamics process generated by different modulation way.Under the action of dispersion and nonlinear effects,fiber lasers have generated lots of interesting physical phenomena,such as optical solitons,bound solitons,strange force waves and square wave pulses.It is of great significance to study the formation mechanism of these physical phenomena for further understanding of ultrafast dynamics in fiber lasers.In 2004,monolayer graphene was prepared by mechanical stripping method,opening the door to explore the applications of two-dimensional(2D)materials.2D materials have attracted great attention due unique optical,electronic and mechanical characteristics that are different from their blocky structure,especially low dimensional characteristics and promising nonlinear optical properties.And 2D materials have been widely used to fabricate efficient,compact and broadband tunable optoelectronic and photonic devices,such as broadband optical modulator,optical frequency conversion,pulse laser and so on.In recent years,some novel 2D materials,such as three-element transition metal sulfides and transition metal carbides,which are easy to adjust the bandgap,have attracted great interest of researchers.In this paper,molybdenum sulfur selenium(MoSSe)and transition metal carbides(MXenes)are used as saturable absorber(SA)and near infrared fiber laser as carrier,the pulse output characteristics of different modulation techniques are studied.What's more,the mode-locked fiber lasers based on different types of MXenes are explored.The influence of SA with different saturation parameters on output pulse types are analyzed systematically.And the generation mechanism of optical solitons,bound state soliton and harmonic mode-locked and square wave pulse are studied,which is of great scientific value for further broadening the application of fiber lasers based on 2D materials.The specific content is as follows:1.A novel transition metal sulfide SA(MoSSe-SA)is fabricated by mechanical stripping method and inserted into Er-doped fiber laser to achieve stable dual wavelength passively Q-switched pulse output of 1532.2 nm and 1532.8 nm.When the pump power increases from 167 mW to 350 mW,the repetition rate increases from 50 kHz to 90 kHz and the pulse width decreases from 2.81 ?s to 1.78 ?s.The maximum single pulse energy is 257 nJ and the peak power is 145 mW.And the signal-to-noise ratio is 50 dB,indicating that the passively Q-switched Er-doped fiber laser based on MoSSe-SA has good long-term stability.The experimental results show that MoSSe-SA owns a higher damage threshold than traditional bimetallic transition metal sulfides,and can be used as a potential candidate for high energy pulsed fiber laser.In addition,a new type of acousto-optic crystal device-?-BTM is applied in Yb-doped fiber laser,and the Q-switched pulse output with repetition frequency of 10-50 kHz is obtained.When the repetition frequency is 10 kHz and the pump power is 410 mW,the narrowest pulse width is 167 ns,corresponding to the maximum peak power of 1.66 W.The research results provide an excellent acousto-optic device for fiber lasers.2.The V2CTX and Ta2CTx nanosheets are prepared by mechanical stripping method,and the V2CTX and Ta2CTx-SA are successfully prepared by method of photo deposition.The Z-scan system is constructed to characterize the V2CTx and Ta2CTx nanosheets,the large nonlinear coefficient is proved to be beneficial to the interaction between light and materials.The saturation parameters of SA at 1.0 ?m and 1.5 ?m are obtained by I-Scan technique.And the SA is applied to Yb-doped fiber laser and Er-doped fiber laser to realize dissipative soliton and traditional soliton mode-locked pulse output,respectively.At the same time,the formation mechanism of Kelly sideband and spectra along the steep edge of dissipative soliton are analyzed3.The W2C nanoplates and W2C-SA based on tapered fiber are prepared by magnetron sputtering deposition.The nonlinear absorption coefficient and nonlinear refractive index were measured by open and closed aperture Z-scan technique.The saturation parameters of W2C nanosheets are measured by I-Scan system,the modulation depth of W2C-SA is only 2.1%at 1.5 ?m.Moreover,the W2C-SA based on microfiber is successfully applied to Er-doped fiber laser,and multi-soliton pulses are successfully realized.In the process of increasing the pump power,the number of soliton pulses increase from 9 to 36.Because the adjacent pulse interval is not fixed,the loose bound soliton pulse is realized in the experiment.The results show that the peak power clamp effect plays a major role in the formation process of multi-soliton.The large nonlinear coefficient,small modulation depth of SA and long cavity length of fiber lasers are beneficial to the generation of multi-soliton pulses.In addition,the highest order harmonic mode-locking with the highest order of 6th is achieved in Er-doped fiber laser by using Ta2CTx-SA.The modulation depth of Ta2CTx-SA is 4.5%at 1.5 ?m.The harmonic mode-locked operation is realized under the effect of dispersion wave,gain loss and recovery.4.The Nb2C nanosheets and Nb2C-SA based on microfiber are prepared by magnetron sputtering deposition.The Z-scan and I-Scan systems are built to characterize nonlinear optical properties,the anti-saturation effect is observed at 1.0 ?m and 1.5 ?m,which is proved to be beneficial to the generation of square wave pulse.And the Nb2C-SA is inserted into the Yb-doped and Er-doped fiber lasers to realize square wave pulse output.The pulse width is adjustable from 0.652 ns to 1.616 ns and from 0.33 ns to 2.061 ns,respectively.In addition,the NPR and nonlinear amplifying loop mirror(NALM)mode-locked fiber lasers are constructed,and the square wave pulse is obtained except at 2.0 ?m.Through the experimental results comparison,it can be concluded that the anti-saturation absorption effect plays an important role in the process of shaping the hyperbolic secant pulse into flat top pulse or square wave pulse.The h-type pulse output is realized in Tm-doped NALM fiber laser.The characteristics and generation mechanism are similar to square wave pulse. |
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