基于WTe_(2)可饱和吸收体的超快掺铒光纤激光器

Ultrafast Erbium-Doped Fiber Laser Based on WTe_(2)Saturable Absorber

采用磁控溅射沉积的WTe_(2)作为可饱和吸收体,在掺铒光纤激光器中实现了超快脉冲的产生。在1559.31 nm波长处,实验测得的3 d B光谱带宽为11.54 nm,脉冲宽度为231 fs。在26.6 MHz基频处获得了最大平均输出功率为58 m W、脉冲能量为2.18 n J的超短脉冲。研究结果表明,WTe_(2)可饱和吸收体可作为一种性能优异的光子器件,在1.5μm波段实现超短脉冲的产生。

Objective In recent years,1.5μm ultrafast fiber lasers have attracted wide attention due to their critical roles in many fields.Fiber modelocked lasers mainly include active and passive modelocked fiber lasers.The passive modelocked fiber laser is a simple and economical method to realize ultrafast pulse generation.Saturable absorbers play an important role in passive modelocked fiber lasers.In recent years,different kinds of saturable absorbers(e.g.,carbon nanotubes,graphene,topological insulators,transition metal chalcogenides,and black phosphorus)have been used to generate ultrafast pulses.In this paper,we use the magnetron sputtering deposited WTe2 as a saturable absorber to achieve ultrafast pulse generation in an erbiumdoped fiber laser.With the wavelength of 1559.31 nm,the measured 3 dB spectral bandwidth is 11.54 nm and the pulse duration is 231 fs.The ultrashort pulse with the maximum average output power of 58 mW and the pulse energy of 2.18 nJ is obtained at the fundamental frequency of 26.6 MHz.The results indicate that the WTe2 saturable absorber can be used as an excellent photonic device to generate ultrashort pulses at 1.5μm band.Methods To study the nonlinear properties of the WTe2 saturable absorber based on micronanofiber,we apply the device in an erbiumdoped fiber laser to generate ultrafast pulses at a 1.5μm band.The pump source is a commercial 980 nm laser diode(LD)with a maximum output power of 400 mW.A 1.5 m long erbiumdoped fiber is used as the gain medium.The optical coupler has a spectral ratio of 50∶50.The length of the entire resonant cavity is about 9.3 m.A polarization controller is utilized to adjust the polarization state of the oscillating beam in the cavity,while a polarizationindependent optical isolator is used to ensure unidirectional operation.In addition to the erbiumdoped fiber,the other fibers including the pigtails of each component are SMF28e fibers.In fiber laser systems,all components are polarizationindependent,which avoids selfstarting modelocking operation caused by nonlinear polarization evolution.It is worth noting that in erbiumdoped fiber laser systems,the direction of the laser is opposite to that of the pumping laser,avoiding the output of residual pump power.The output characteristics of the laser are measured by spectrometers(Yokogawa AQ63700),oscilloscopes(ROHDE&SCHWARZ RTO2024),and photodetectors(EOT ET3500F).We use an emission spectrum analyzer(ROHDE&SCHWARZ FSV13)to record the emission spectrum during modelocked operation,and a commercial autocorrelator(APE Pulsecheck)to measure the pulse width.Results and Discussions With the increase in pump power,the cavity is initially in continuous operation.When the pump power reaches 40 mW,we observe a selfstarting stable modelocking.When the pump power reaches a maximum of 400 mW,it still maintains a stable modelocked operation state,with the maximum average output power of 58 mW and the corresponding pulse energy of 2.18 nJ.The measurement results of the spectrum of the output pulse ranging from 900 to 1700 nm show no pump signal at 980 nm,indicating no residual pump power.When the pump power reaches the maximum,the output power basically still maintains a linear increase,with a slope of 15.3%.The modelocking performance is characterized at the maximum pump power.The modelocking spectrum centered at 1559.31 nm is obtained with a 3 dB spectral bandwidth of 11.54 nm.The Kelly sideband on the spectrum confirms that the modelocked laser operates in the soliton region.The autocorrelation curve of the modelocked pulse with a full width at half maximum of 356 fs is obtained,and can be well fitted by the sech^(2)(·)curve.With a decorrelation factor of 0.648,the actual pulse width is calculated to be 231 fs.In addition to the excellent nonlinear properties of WTe_(2)materials,erbiumdoped fibers feature large dispersion compensation,with a dispersion parameter of 36 ps^(2)/km at 1560 nm,which also helps realize ultrashort pulses.Since the dispersion parameter of the singlemode fiber at 1560 nm is-22 ps^(2)/km,the total group velocity dispersion is about-0.12 ps^(2).In addition,the timebandwidth product is 0.33,indicating slight pulse chirps.Further compression with certain methods is possible.Conclusions The saturable absorber of WTe_(2)based on micronanofiber is prepared by magnetron sputtering technology,and its nonlinear optical properties are studied.The micronanofiber WTe_(2)saturable absorber is embedded in an erbiumdoped fiber laser system with a ring cavity structure.At 1559.31 nm,the measured 3 dB spectral bandwidth is 11.54 nm and the pulse width is 231 fs.The modelocked laser output with the highest average output power of 58 mW and the pulse energy of 2.18 nJ is obtained at the fundamental frequency of 26.6 MHz.The results show that WTe_(2)saturable absorber can be used as an excellent photonic device to generate ultrafast pulses at 1.5μm band.In addition,magnetron sputtering deposition technology is expected to prepare highperformance saturable absorbers with large modulation depth,low nonsaturable loss,and low saturable intensity,which is conducive to the generation of ultrafast pulses with high stability and high power.