The Precise Dispersion Compensation Of The Ultrashort Pulse Based On The Stress Characteristic Of Chirped Fiber Bragg Grating

Femtosecond laser processing is a new material processing technology.Due to its high machining accuracy and no thermal effect,the technology has been widely used in the fields of precision machining and biological medicine.Femtosecond laser processing technology has high requirements for femtosecond laser pulse quality,and the excellent femtosecond laser has become one of the core components of femtosecond laser processing technology.Fiber laser due to the flexible character of the optical fiber and optical fiber surface area per unit volume greater than the rod or disc shaped crystal laser,shrink sharply relative to traditional solid laser for amplification module and do not need to install the cooling unit.Single-mode fiber output light is close to ideal point light source and optical fiber laser of the various optical components by electric arc welding,thus can fiber laser output is close to the ideal high quality beam at the same time ensure its stability and reliability of the running state.The femtosecond fiber laser is very suitable for micro machining because the focusing beam is easy to reach the focus limit of the lens.Therefore,the research of high power femtosecond laser is of great significance to the development of ultra-fast laser precision machining technology.At present,the high-power femtosecond fiber laser is usually used to amplify(CPA)system.Reasonable compensation in the CPA system dispersion mismatch between the stretcher and compressor to become in the CPA system access to quality the key to the ultrafast laser pulse output,in order to solve the problem of tuning in the CPA system dispersion,people put forward many solutions,such as using dispersion compensation fibers,using chirp fiber grating compensation and intermediate frequency spectrum inversion technology,etc.Because of the chirp fiber grating light efficiency should be the existence of the thermal effect of light,so can apply on chirp fiber grating by stress or temperature field to precision by adjusting the parameters of the chirp fiber grating dispersion.The advantage of the stress tuning of the chirped fiber Bragg grating relative to the temperature tuning is that the regulation range is large,the response speed is fast and it is not affected by the ambient temperature.Therefore,the chirped fiber Bragg grating can adjust the dispersion in the CPA system.Chirp fiber grating dispersion compensation with low insertion loss,has nothing to do with the polarization,is not affected by fiber nonlinear and the advantages of small volume is considered one of the most practical value of the dispersion compensation scheme at present.In this paper,based on stress of the chirp fiber grating tunable effect,through the system as a stretcher chirp pulse amplification fiber grating applied stress adjustment,so as to realize the precise tuning of the amount of dispersion effect,achieve in a chirp fiber grating as the stretcher and body grating as ultrafast laser system of compressor continuous precision adjustment of the output pulse width.Firstly,it is theoretically calculated that when the stress field is applied to the chirped fiber Bragg grating,its dispersion changes,and then verified by experiment.The experimental results show that the second order dispersion of the system is compensated,and the pulse width is shortened by 1.977 ps.The third order dispersion of the system can be compensated by the local tension of the chirped fiber Bragg grating,and the high quality pulse output of 544 fs is obtained.The dispersion mismatch between the stretcher and the compressor can be compensated by adjusting the stress of the chirp fiber Bragg grating,avoiding the complicated pulse width optimization step.The dispersion management technology based on the stress regulation effect of chirped fiber Bragg grating has a broad application prospect in the development of high power femtosecond laser.