Controllable Preparation Of Saturable Absorber And Its Application In Erbium Doped Fiber Laser

Due to the advantages in high stability,low cost,compact structure,and system integration,ultrafast fiber lasers have gradually become the mainstream lasers used in industrial manufacturing,surgical medical treatment,military defense,optical fiber communications,and scientific research.Passively mode-locking is considered to be one of the most mature technologies currently used for the generation of short pulses,the main technical core of which is the introduction of saturable absorbers.With the further improvement of laser to higher power,shorter pulse and better stability,the requirements for saturable absorption devices have become more stringent.However,the traditional devices which are widely used at present show complex fabrication process and narrow working band,which hinders the further development of pulsed laser technology.Therefore,the exploration and application of new high-performance saturable absorber devices has become a frontier subject of extensive research in recent years.In order to overcome the shortcomings of the currently used saturable absorption devices,this article starts research from two aspects of new technology and new materials.Based on the controllable preparation of transition metal chalcogenides WSe2 and SnS2,the research of heterojunction MoS2-Sb2Te3-MoS2 and MoS2-WS2,and the nonlinear exploration of new materials AgNW and SnSSe,the light modulation ability of the corresponding saturable absorption devices are effectively enhanced.The new saturable absorbers with wider bandwidth,stronger nonlinear effect and faster relaxation time based on the above method have been successfully applied to erbium-doped fiber laser,and stable high-power femtosecond pulses have been obtained,which promotes the innovation of new optoelectronic devices and the development of ultrafast pulse technology.The main contents of this paper are as follows:(1)Nonlinear research of WSe2 saturable absorber with a tapered structure.In the experiment,by selecting the device structure and preparation method,the interaction between light and the material is enhanced,the crystallinity and uniformity of the material are also improved,so the nonlinearity of the material is further strengthened.The nonlinear refractive index coefficient and modulation depth of obtained WSe2 saturable absorber are-1.6×10-10 cm2/W and 21.89%.Based on the prepared highly nonlinear WSe2 saturable absorber,the mode-locked pulses as short as 163.5 fs are realized,which further proves that the choice of preparation method and structure can enhance the nonlinearity of the WSe2 saturable absorber.(2)The influence of SnS2 saturable absorber with different thickness on the output characteristics of lasers.For the first time,we have systematically explored the non-linear control of saturable absorber and the output characteristics of the corresponding laser by changing the thickness of the material.In the experiment,the nonlinear absorption parameters of three SnS2 saturable absorbers with thicknesses of 2.8,9.1 and 108.7 nm are measured,and the effect of concentration on nonlinear devices is obtained.By applying these three types of devices to lasers,the rule of the output characteristics in corresponding Q-switched and mode-locked lasers are revealed.This research promotes the process of engineering optical devices based on application requirements.(3)Theoretical and experimental optical nonlinearity studies of heterogeneous heterojunction MoS2-Sb2Te3-MoS2.By combining the excellent properties of MoS2 and Sb2Te3 through heterojunction,a MoS2-Sb2Te3-MoS2 saturable absorption mirror with a damage threshold of 14.13 J/cm2 and a modulation depth of 64.17%is obtained.In addition,the photoelectric properties of heterojunction materials,such as carrier mobility,carrier concentration,and band gap structure,are theoretically calculated,which provides a strong theoretical support for the experimental conclusions.Based on the MoS2-Sb2Te3-MoS2 saturable absorption mirror,a high output power of 20 mW is obtained in the mode-locked laser,which provides a new way for the development of saturable absorber with high damage threshold.(4)Nonlinear enhancement and comparative study of heterojunction MoS2-WS2.Through the comparative experiment of heterojunction material MoS2-WS2and pure WS2 and MoS2 devices,it is found that the heterostructure strengthened the absorption characteristics of materials,and the modulation depth increased by nearly 50%.The mode-locked laser based on the heterojunction MoS2-WS2 saturable absorber has a signal-to-noise ratio of up to 91.2 dB,an output power of 19.8 mW,and a pulse duration as short as 154 fs.Compared with similar lasers based on a separate material(MoS2 or WS2),the pulse duration of the laser based on heterojunction MoS2-WS2 has increased by nearly 40%,which proves the effectiveness of the homogeneous heterostructures in absorption enhancement.(5)The first application of new material AgNW in erbium-doped fiber laser.By adjusting the concentration of AgNW,three different saturable absorption devices with modulation depths of 13.79%,26.23%,and 46.19%are obtained.Based on AgNW with different concentration,the variation of threshold,SNR,output power and pulse duration of the laser with the saturation intensity,modulation depth and insertion loss of the saturable absorber are explored.In addition,the maximum output power of 25.9 mW and the shortest pulse duration of 149.3 fs are achieved.The experimental results proved the potential of the new material AgNW in realizing high-power ultrashort pulses.(6)High stability erbium-doped fiber laser based on ternary compound SnSSe.After measurement,the modulation depth of the saturable absorption device based on SnSSe is 56.7%,which is almost five to ten times higher than that of SnS2,SnSe2,Se,and SnS.Based on the SnSSe saturable absorber,a high-stability mode-locked laser with a signal-to-noise ratio greater than 94 dB is achieved.During 15 hours of output power monitoring,the standard deviation of the average output power is 0.157 mW,and the mode-locked pulse duration is 158.6 fs.Experimental results show that the ternary compound SnSSe has special advantages in achieving stable ultrashort pulses,and is expected to become a strong candidate material for the next generation of high-performance optoelectronic devices.