Research On Tunable High Repetition Rate Fiber Laser Based On Graphene Optical Modulator

With the rapid development of laser technology,laser with high repetition rate has been widely used in the fields of optical communication,optical frequency comb,nonlinear microscope and laser processing.It has become another important research direction besides high power,multi wavelength,ultra short pulse and ultra wide spectrum.Especially in the field of optical communication,it has gradually become a pillar technology,Therefore,the repetition rate of laser is required to be higher and higher.How to design a compact,low-cost and high repetition rate laser has become one of the current research hotspots.In order to meet this demand,two kinds of compact fiber lasers are studied in this paper to obtain ultra-high repetition rate and ultra short pulse laser with adjustable repetition rate,At the same time,the repetition rate of the laser pulse is further increased by combining the fiber micro ring resonator or Mach Zehnder interferometer,and the ultra-high repetition rate laser pulse sequence with adjustable repetition rate of the output laser is obtained.The main research contents and innovative achievements of this paper are as follows:1.On the basis of summarizing the research background and application prospect of high repetition rate fiber lasers,the filtering mechanism and transmission theory of fiber micro ring resonator(MRR)and Mach Zehnder interferometer(MZI)as optical comb filters are analyzed,and the filtering characteristics of MRR and MZI are analyzed,The influence of different parameters on the filtering results is further explained;2.A tunable high repetition rate fiber laser with graphene modulation and fiber micro ring filter is built.By designing a mode-locked erbium-doped fiber laser with graphene and fusing a fiber micro ring resonator into it as a comb filter,a pulse train with a repetition rate of 106.04 GHz is obtained.After that,the repetition rate of the output pulse is changed by adjusting the micro ring radius,and the pulse with the highest repetition rate of 292.4 GHz is obtained;3.A high repetition rate tunable fiber laser with graphene modulation and MZI is built to reduce the graphene oxide film as a saturable absorber.An MZI interferometer is added into the erbium-doped ring fiber laser cavity.By continuously adjusting the fiber delay line or polarization controller,the output power of the laser is reduced,High repetition rate pulse trains with repetition rates varying from 101.21 GHz to 11.11 THz are obtained.The repetition rate can be changed continuously by adjusting the optical path difference between the two arms of MZI.The repetition rate can also be increased by an integral multiple by adjusting the polarization controller and changing the pump power.This result makes it possible to produce laser with repetition rate higher than 10 THz,and the all fiber structure greatly reduces the manufacturing cost;4.Based on the Ginzburg-Landau equation,the evolution of experimental results of tunable repetition rate fiber laser with graphene modulation and MZI filtering is analyzed.Each device in the experiment is simplified as a computable model to calculate the influence of different devices on the optical field.At the same time,the effects of gain,loss,group velocity dispersion and self phase modulation of the fiber are considered to study the evolution process of the optical field in the cavity.The Ginzburg-Landau equation is solved by using the split step Fourier algorithm,and the accurate numerical solution is obtained.The evolution results are basically consistent with the experimental results,and the repetition rate of the pulse train can be adjusted by changing the optical path difference of MZI.In addition,when the polarization controller is adjusted,graphene as a saturable absorber can change the repetition rate by an integral multiple under the combined action of dissipative four wave mixing,fiber birefringence filtering and pulse splitting.It is proposed for the first time that the pulse with higher repetition rate can be generated when a variety of mechanisms work together,which provides a new idea for the study of the generation method of high repetition rate laser.