Graphene-based Passively Q-switched Erbium-doped Fiber Lasers Based On A Lyot Filter

Q-switched fiber laser with good beam quality, high efficiency, small size, hasimportant applications in optical fiber communication systems, industrial processing,laser medicine, military and some other fields. Graphene is a novel two-dimensionalstructure of carbonaceous materials with high mechanical strength, excellent thermalconductivity, unique electrical properties and unique optical properties, which can beused to generate short laser pulse. Based on the excellent optical properties ofgraphene, the graphene saturable absorber was prepared by optical deposition method,and output characteristics of the passively Q erbium-doped fiber laser based on theLyot filter were studied experimentally. The main results of the thesis can besummarized as follows:1.Based on matrix optics theory, the transmission characteristics of single-stageand cascaded Lyot filter have been studied by numerical simulation. The main resultsare as follows: wavelength tuning can be achieved by adjusting the polarizationcontroller, and the tuning range is related to the birefringence coefficient and lengthof the polarization maintaining fiber; fixing one polarization controller, the extinctionratio decreases for the phase shift introduced by adjusting another polarizationcontroller; the filter wavelength interval is inversely proportional to the length ofpolarization maintaining fiber, and decreases with length increasing of thepolarization maintaining fiber; adjusting the orientation of two polarizationmaintaining fiber of the two cascaded Lyot filter, the effective length of the twopolarization maintaining fiber can be changed and the filtering wavelength spacingtunable can be achieved.2.Based on optical deposition method, the optimum deposition parameters havebeen obtained and the graphene saturable absorber has been prepared. By mixing3mg graphene and10mL dimethylformamide (DMF) solution, the graphene dispersionwas then ultrasonic vibrated and centrifuged. Then the optical fiber connector wasimmersed into the graphene for10minutes with pump power40mW. Finaly, the fiberferrule was dried and connected to another fiber optic connectors for laterapplications.3. Graphene-based passively Q-switched erbium-doped fiber laser has been setup and stable Q-switched output has been obtained. When the pump power was61 mW, the fiber laser is self-starting. With the increasing pump power, the laserrepetition rate varies from5.1kHz to14.2kHz, and the average output powerincreased from111.2μW162.3μW. The obtained narrowest pulse width is8μs, andthe maximum single pulse energy is11.5nJ. By adjusting the polarization controller,the single wavelength of the laser output can be tuned int the range1556nm~1558nm. For the dual-wavelength case, the tuning range is about3nm.