The Research On Fiber Laser Based On Two-dimensional Nanomaterials

Fiber lasers generate pules through Q-switching and mode-locking technology.For the passively Q-switching and mode-locking fiber lasers,the saturable absorbor is the most critical component,which as a nonlinear optical material requires wide optical bandwidth,fast response and low loss.Additionally,in order to get a high energy pulse,modulation depth and damage threshold of the saturable absorbor should be considered.Semiconductor saturable absorber mirrors(SESAMs)were considered as one kind of the most successful passive Q-switching and mode-locking elements.However,SESAMs have prodigious limitations in terms of broad-band tunable pulse generation due to its relatively narrow operation bandwidth,which is typically a few tens of nanometers.The fabrication process is complex and costly,which delimited its applications.Another two novel saturable absorbor materials including carbon nanotube(CNT)and graphene were also under investigation.However,the response spectral range of CNT sensitively depends on the diameter and chirality,restricting its practical applications in lasers at specific wavelengths or with broadband tunability.Graphene SA had relatively low damage threshold and low saturating intensity.Additionally,graphene SA could be easily bleached at low energy level as a result of its relatively low saturating intensity,also limiting the maximum available pulse energy.The researchers try to find better saturable absorbor with broadband absorption,fast response,low loss,harge modulation depth,high damage threshold.Topological insulators(TIs)are novel quantum electronic materials that have a bulk band gap like an ordinary insulator but a protected conducting state on their edges or surface.These unique properties,originating from the combined effects of spin-orbit interactions and time-reversal symmetry,render TIs with ultra-broadband nonlinear optical response ranging from the visible to the microwave frequency.In addition to carbon-based two-dimensional materials,atomic layered transition-metal dichalcogenides(TMDs)are now under continuously rising attentions due to their exceptional optical properties that may even over-come the disadvantages of graphene.Based on two-dimensional nanomaterials,topological insulator and Mo S2,this thesis systematically studies the preparation,transfer and the application in Q-switching and mode-locking fiber lasers of topological insulator and Mo S2.(1)Through employing a cost-effective solvothermal method,ultrathin topological insulator Bi2Te3 nanosheets with uniformly hexagonal morphology have been successfully synthesized.These Bi2Te3 nanosheets are 500-800 nm in edge width and 10-20 nm in thickness.(2)The as-grown and washed Bi2Te3 powders were dispersed in an ethanol solution.Then,we drop casted the Bi2Te3 dispersion directly onto the fiber ferrule.Once the ethanol was volatilized,the nanosheets would form a uniform volatile film on the fiber ferrule contributed to the high uniformity of the TI dispersion.By deliberately controlling the thickness of the TI sample,which corresponds to change the saturable absorption parameters of the as-fabricated SA device,two different types of pulsed laser operation states had been successfully demonstrated: one is high quality Q-switching with large per-pulse energy of 278.8 n J if the SA film is thicker,and the other is femo-second mode-locking(with pulse duration down to 448 fs)if we peel off the Bi2Te3 film on the fiber ending using scotch tape and shorten the cavity length.Our work provides a simple and effective method to manufacture fibered SA device for researchers.(3)We have fabricated a new kind of PMMA-TI-PMMA sandwiched construction saturable absorbor by using high quality topological insulator Bi2Te3 covered by the upper and down PMMA polymer layers.The dispersion of Bi2Te3 nanosheets was gently placed on top of the DI water surface and generated the self-assembled layers.We then placed the Bi2Te3 self-assembled layer on the copper foil coated with PMMA so that the original morphology and dispersion of the Bi2Te3 self-assembled layers were still kept on the surface of PMMA.Then another protection layer of PMMA was spin-coated onto the self-assembly layer,which was under the second rounds of drying.After being placed in the ferric chloride solution,the copper layer was completely etched and the PMMA-TI-PMMA structure was finally fabricated after washed several times in DI water.The saturable absorber device based on PMMA-TI-PMMA structure was finally fabricated.The self-assembly layer spontaneously generated at the interface between the DI water and the air can remain very uniform.Additionally,the self-assembled layer can be effectively protected by double PMMA layers,and the original morphology will be automatically kept while being transferred and installed.The SA device can be effectively protected from oxidation,since it is isolated from air due to the double PMMA sandwich structure.(4)Based on the new PMMA-TI-PMMA saturable absorber,we experimentally achieve the dissipative soliton output in an erdium-doped fiber laser.A typical single-pulse mode-locking state can maintain at a pump power of 150 m W.The pulse-to-pulse interval is about 93.37 ns,which corresponds to a repetition rate of 10.71 MHz and matches with the cavity round-trip time.The optical spectrum of the mode-locked pulses has an extremely steep spectral edge,and a central wavelength of 1571 nm and a 3 d B spectral bandwidth of 39.95 nm.The time-bandwidth product(TBP)of the pulses is calculated to be 22.9,indicating that the obtained dissipative solitons are strongly chirped.The average output power is about 11 m W,corresponding to single pulse energy of 1.03 n J.(5)By coupling few-layer molybdenum disulfide with fiber-taper,a new type of Mo S2 based nonlinear optical modulating element had been successfully fabricated as a two-dimensional layered saturable absorber.This Mo S2-taper-fiber device is capable of passively mode-locking an all-normal-dispersion ytterbium-doped fiber laser and enduring high power laser excitation.Thanks to the combined advantages from the strong nonlinear optical response in Mo S2 together with the sufficiently-long-range interaction between light and Mo S2,this device allows for the generation of high power stable dissipative solitons at 1042.6 nm with pulse duration of 656 ps.