Researches On All-fiber Er/Yb Co-doped Chirped Pulse Amplifier Based On TOD Compensation

Ultrafast fiber laser has widely used in many fields such as optics communication,biomedical imaging,precisive material processing and so on,for the distinguishing features of compact structure,free of alignment,good environmental stability and excellent beam quality.1.5-?m band is in the low-loss optics communication window,and also in the human-eye-safety band.So high-power femtosecond laser in 1.5?m band has been paid much attention to many important applications,such as optics communication transmission,Si waveguide writing,cornea surgery and so on.The thesis mainly discusses the high-power Er/Yb co-doped chirped pulse amplification(CPA)system in 1.5?m band with the following aspects:1.The development of ultrafast pulse amplification technology and the researches background of the 1.5?m fiber CPA system have been reviewed,followed by the researches progress on third-order dispersion(TOD)and self-phase modulation(SPM)compensation in high-power CPA system to improve compressed pulse quality.2.The basic principle of mode locking and three common methods in passive mode-locked fiber laser have been introduced at first,and the formation mechanisms and characteristics of soliton,stretched pulse,self-similar pulse,dissipative soliton and giant-chirp pulse in mode-locked fiber laser have been also discussed.Then the principle of CPA technique and main factors limiting the pulse transmission in fiber CPA system have been introduced,with an emphasis on the compensation mechanism between TOD and SPM.Finally,the hollow core photonics bandgap fiber(HC-PBF)compressor has been reviewed.3.The basic principle and methods of dispersion measurement with fibers have been introduced.Based on white-light interferometry technique,a dispersion measurement system has been set up,which consists of a Mach-Zehnder interferometer and a broadband light source.The fiber dispersion parameters are calculated by retrieving phase information from the interferogram.And the dispersion parameters and of different fibers have been measured finally,such as dispersion compensation fiber(DCF),single mode fiber(SMF),HC-PBF,and so on.4.An all-fiber Er/Yb co-doped chirped pulse amplification system,based on DCF stretcher and HC-PBF compressor,has been constructed.The seed oscillator is an all-fiber carbon nanotube(CNT)mode-locked soliton fiber laser with spectrum bandwidth of 11.4 nm,pulse width of 227.3 fs,average power of 4.67 m W.The influence of different net TOD in CPA system to compressed pulse is studied,and it is proposed for the first time that larger negative TOD helps to improve the compressed pulse quality by compensating SPM when amplified in 1.5-?m CPA system.Then by optimizing the TOD in the CPA system,the shortest pulse of 344 fs with average power of?1.02 W is obtained at the net TOD value of-0.041 ps~3 in CPA system.The corresponding pulse energy is 25.1 n J.This is the shortest pulse in the 1.5?m band generating from a truly all-fiber high-power Er/Yb co-doped CPA system with Watt-level average power to date.5.Mode locking by nonlinear amplified loop mirror,an all-polarization-maintaining self-similar pulse fiber laser with wider spectrum has been set up.The self-similar pulse's spectrum bandwidth is 40.82 nm with transform limited pulse of 88 fs,and the average power is 54.4m W.Seeded with the self-similar fiber laser,stretched by DCF and compressed by HC-PBF,the CPA system has been constructed.By studying the effect of different net TOD on compressed pulse in Er-doped CPA system,the shortest pulse with 233-fs width is obtained at the net TOD of-0.036 ps~3 in CPA system.The average output power is 1.14 W,corresponding with the pulse energy of 22.8 n J.The pulse from high-power Er/Yb co-doped CPA system based on the self-similar pulse fiber laser becomes shorter apparently.