| A tremendous group of two-dimensional layered materials(2DMs),as a representative of graphene,featured with diverse and complete system,simple and unique structures,are enriched with various and special physics properties,which are not only superior in the research of physical mechanisms,but also own great potential applications in many aspects including optoelectronics,information and energy.Very recently,increasing research efforts on 2DMs are projected toward their nonlinear optical properties,which are not only fascinating from the fundamental science point of view but also intriguing for various potential applications.Here,we start with the second-,third-order optical nonlinearity of several 2DMs,then explore the potential physics and applications such as all-optical modulators,laser techniques.The main context and results are illustrated as follows:(1)Exciton dominant second harmonic generation(SHG)modulation on monolayer Mo S2.Firstly,the SHG spectroscopy of monolayer Mo S2 is experimentally characterized,where the exciton resonance are able to enhance the SHG signal.For example,1s Cexciton possesses with 40 times enhancements.Secondly,the pump-prope system is built to excite dark excitons such as 2p B,3p B or bleach bright excitons,such as 1s A,1s B,1s C,which offers a new method to control the SHG intensity.Furthermore,it is found that the SHG intensities are highly dependent on the behaviors of exciton formation,transition,and recombination.Finally,the exciton controlled nonlinear all-optical modulation is demonstrated with modulation depth of 62%,rise time of 80 fs and drop time of 900 fs,which enriches advantages of ultrafast response and high extinction ratio.(2)Frequency mixing effect on monolayer Mo S2.The nonlinear optical processes including SHG,sum frequency generation,third harmonic generation,four-wave mixing,are experimentally demonstrated on monolayer Mo S2.Different from bulk crystals,the phase-matching free enables the monolayer Mo S2 with wide-bandwidth of?300 nm,high conversion efficiency operation for nonlinear optical processes.Besides the energy up-conversion process,the difference frequency generation,as one of the typical energy down-conversion nonlinear optical processes,is experimentally achieved and studied.The basic characterizations including broadband spectrum,power dependency,polarization dependency are collected.Further,the role of exciton resonance in difference frequency generation is discussed.(3)Study on saturable absorption effect with WS2/Mo S2 nanosheets and enabled mode-locked lasers.Firstly,D-shaped fibers are fabricated by the home-made fiber-polishing stage,and WS2/Mo S2 nanosheets are prepared by the liquid exfoliation method;then saturable absorbers are made by integrating D-shaped fiber with nanosheets.To achieve the mode locking,the Er-doped fiber laser system is built with the saturable absorber.Finally,the mode-locked lasers are achieved with two types:one is high power mode-locked laser with WS2-D-shaped fiber,the other is bound state mode-locked laser with Mo S2-D-shaped fiber.At last,the broadbandwith operation of saturable absorption in nanosheets is analyzed and discussed.(4)Study on graphene's photothermal effect and the enabled active all-in-fiber devices.The photothermal effect of graphene is firstly characterized by integrating hybrid structure of graphene and microfiber(GMF)into into the Mach–Zehnder interferometer.Then the all-optical phase shifter and switching is achieved by the GMF.Secondly,the microfiber resonator(MFR)is fabricated and integrated with graphene which has enhanced the light-graphene integration by 8 folds.The low threshold bistability is observed and all-optical switching is achieved with time response of 0.2 ms.Thirdly,the optically controlled phase-shifted fiber Bragg grating(FBG)and chirped FBG are achieved by integrating graphene with micro-FBG,which enables nonlinear optical multi-stabilities.Finally,the optically controlled slow and fast light is achieved by integrating graphene with tilted FBG. |
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