Low Dimension Materials Q-switched Er-doped Fiber Laser Based On All-optical Modulation

Passively Q-switched fiber laser can deliver different wavelength and stable pulses output based on different saturable absorbers.However,with the passively Q-switched fiber laser set up,the output characteristics have been fixed.How to alter the output parameters with more degrees of freedom in Q-switched fiber laser is still an important issue to optical communities.In this thesis,the passively Q-switched fiber lasers based on topological insulators and gold nanorods with pulse output parameters tuned by an external modulated beam have been designed and investigated experimentally.Specific research results are summarized as follows:First,the bismuth telluride nanosheet was prepared by polyol method.And then,we researched the nonlinear optical properties of topological insulator,bismuth telluride nanosheet,by using the balanced twin detector method.Then,we introduced an external continuous light,whose wavelength is 980 nm,to modulate the nonlinear absorption of bismuth telluride nanosheets.Obviously,the modulation depth of bismuth telluride nanosheet is successfully changed by this modulation light.Finally,the prepared bismuth telluride saturable absorber is inserted into the fiber laser and we can obtain the Q-switched pulse output successfully.Then we could modulate the frequency and the pulse width of pluse output by varying the external modulation light power.Without the effect of modulated light,the Q-switched fiber laser can deliver pulsed laser with pulse duration down to 2.91 ?s with a pump power of 170 mW.With the modulating laser,the pulse duration and repetition rate tunable Q-switched f-iber laser can be realized by modulating the saturable absorber via a continuous wave laser.Second,gold nanorods have been successfully prepared by seed growth method,and then we use the method of optical deposition method to prepare a gold nanorods saturable absorber(GNRs-SA).The excellent saturable absorption of GNRs-SA is verified by the balanced twin detector method.Through an external continuous light with wavelength of 980 nm,we successfully change the modulation depth of GNRs-SA,and then we attribute this phenomenon to the photothermal effect of gold nanoparticles.Finally,by introducing the prepared GNRs-SA into the Er-doped fiber laser,the Q-switched fiber laser can deliver pulsed laser with pulse duration down to 3.35 ?s and the output power of 300 ?W with 150 mW pump power.While introducing the modulation light with wavelength centered at 980 nm,the pulse duration and repetition rate can be successfully tuned by varying the power of modulation light.