Research On Fiber Mode-locked Laser Based On Graphene Oxide Electro-optic Modulato

In fiber lasers,the saturated absorption effect of nonlinear optical materials has been used to achieve stable output of ultrashort pulses with narrow pulse width and high peak,and such fiber lasers are widely used in laser medical treatment,fiber communication and other fields.The saturation absorption capacity of graphene oxide(GO)materials is relatively fixed,and it is difficult to achieve variable switching of laser system operation mode at lower pump power without the intervention of an external active modulator.Therefore,a new type of on-chip integrated optical fiber capacitive optical modulator is proposed,and two structural devices are designed by polyvinyl alcohol(PVA)and polystyrene(PS)nanospheres,which respectively use the nonlinear absorption characteristics of the external driving voltage to adjust the GO,and realize the flexible regulation of the output characteristics of fiber lasers at low pump power.The specific research content of this paper is as follows:(1)The improved Hummers method was used to prepare GO saturable absorption solution,and the drop-coated thin film materials were characterized by X-ray photoelectron spectroscopy,Raman spectroscopy and scanning electron microscopy,and the characterization results showed that the prepared film was GO with a few-layer two-dimensional nanostructure.With the help of Comsol Multiphysics software simulation,the local field enhancement effect of PS nanospheres was verified.Vertical capacitive optical modulation devices based on GO-PVA composites and GO/PS nanospheres were prepared by microelectronic printing process.At the same time,the photoelectric characteristic curve of GO/PS nanosphere electro-optical modulator is determined,and the results show that the optical fiber electro-optical modulator has high optical transmission efficiency and good electrical modulation characteristics under the action of external driving voltage.(2)A 1550 nm fiber ring laser system was built,and the GO-PVA film and GO-PVA electro-optical modulator were used to realize passive mode locking and electro-optical modulation mode locking,respectively.The experimental results show that the passive modelocked fiber laser system based on GO-PVA film can stably output a continuous wave modelocked signal with a pulse width of 28 ps when the pump power is 100.11 m W.When the pump power is 44.05 m W and the drive voltage is 30 V,the GO-PVA electro-optical modulator switches the operating mode of the CW signal to a CW mode-locked signal with a pulse width of 25 ps.(3)In order to improve the output performance of the fiber laser system,the electro-optical modulator was optimized by PS nanospheres,and the passive mode locking of the output of the system was successfully realized without relying on the external active modulator,and the variable switching of the operation mode of the fiber laser system was realized by using the external driving voltage.When the pump power is 88.56 m W,the passive mode-locked fiber laser based on GO/PS nanospheres outputs a continuous wave mode-locked pulse signal with a pulse width of 25 ps and an output power of 3.41 m W.For the electro-optical modulator of GO/PS nanospheres,when the pump power is 34.3 m W,the system realizes the variable switching of three operating modes: continuous wave,Q-switched mode locking,and continuous wave mode locking in the driving voltage range of 0 V～20 V.Finally,by comparing the output performance of fiber mode-locked lasers,the application advantages of GO/PS nanosphere-based electro-optical modulators in fiber lasers are analyzed.