Research On Ultrafast Optical Properties Based On Nanomaterials

Ultrashort pulse fiber laser has many applications in different fields such as industrial processing,optical fiber communication,optical microscopy,laser guided weapons,space ranging,biomedicine and many other fields.Compared with solid laser,dye laser and other lasers,due to ultrashort pulse laser in all-fiber system has the unique advantages,such as small size,low thermal effect,low cost,easily to fabrication integration and transportation,it is a hot research direction to obtain ultrashort pulse fiber laser in all-fiber system.We can use active and passive mode-locking to obtain ultrashort pulse and passive mode-locking has the advantages of simple structure and flexible design.Common passive mode-locking technology include nonlinear polarization evolution(NPR),nonlinear amplification loop mirror(NALM),nonlinear optical loop mirror(NOLM),semiconductor saturable absorption mirror(SESAM).In addition,nanomaterial can also be widely applied to passively mode-locked fiber laser as a saturable absorber(SA)depending on its nonlinear optical absorption property.These nanomaterials have many excellent properties,such as easy preparation,interaction between materials and light in various ways,nonlinear optical transmittance varying with injecting light,stable mechanical properties,ultrafast recovery time and so on.In this paper,the saturable absorption properties of three nanomaterials,bismuthene,graphdiyne(GDY)and gold nanorods(GNRs),are introduced and their saturable absorbers are prepared.Then we apply the saturable absorbers based on nanomaterials to near infrared passively mode-locked ultrashort pulse fiber lasers with wavelength of 1.5 μm,and obtain the pulse output whose pulse width is vary from picosecond to 100 femtosecond magnitude.Bismuthenne is a two-dimensional form of bismuth.It is a two-dimensional material with tunable narrow band gap and no magnetism.Its micro-atomic arrangement structure is buckled honeycomb-like and back-phosphorus-like structures.It has properties of high carrier mobility,topological phase transition,high temperature quantum spin Hall effect,room temperature stability and ultrafast photon response.It can be used to the design of optical devices,spin Hall devices and so on.graphdiyne(GDY)is the first allotrope of carbon formed by sp and sp2 hybridization.It has a two-dimensional planar grid structure and excellent electronic and mechanical properties.GDY has been applied in many fields such as gas separation,energy storage and lithium ion batteries.But it is rarely reported in the field of nonlinear optics.Gold nanorods(GNRs)are rod-like gold particles with nano-scale.They have physical stability,tunable light absorption with variation of aspect ratio and other properties.Especially,it has stronger absorbance for light with wavelength of 1.5μm than light with other wavelengths.Therefore,they can be considered as broadband absorption laterials and used in optoelectronic devices.The mainly studied contents and structure arrangement of this paper are as follows:The first chapter introduces the passively mode-locked ultrashort pulse fiber laser and its development history.Then it expounds the pulse formation mechanism in the passively mode-locked fiber laser from the theoretical aspect,and then describes the saturable absorber based on the new special nano material.The research progress of obtaining passive mode-locked fiber laser and its significance for studying ultrafast photonics and nonlinear optics.In Chapter Z,we first apply scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),transmission electron microscopy(TEM),Raman spectroscopy,and X-ray diffraction(XRD)to measure the characteristics of the few-layer bismuthene.Subsequently,a method for preparing a tapered micro-fiber is introduced,and a saturable absorber is prepared by coupling it with a fewolayers bismuthene depending on optical induced deposition effect.We measure nonlinear optical properties of bismuthene saturable absorber and apply it to a passively mode-locked fiber laser and obtain a high.splitting threshold conventional soliton and harmonic dual-wavelength mode-locking with the pulse width of picoseconds.In Chapters 3 and 4,we study the saturable absorption property of graphdyine and gold nanorods in a similar way.We apply it to near-infirared ultrashort pulse fiber lasers and obtain pulse output with hundred femtosecond pulse pulse width.The 5 th chapter summarizes the research content of the whole article.It summarizes the main research results and issues,and describes the issues that need to be further studied in the future.