Research On Few-cycle Pulse Generation And Frequency Conversion Within Fiber Laser

Ultrashort pulse fiber lasers are attractive in plenty of applications such as micro-processing,frequency metrology,optical frequency comb and so on.Compared with solid femtosecond lasers,femtosecond fiber lasers possess the advantage of compactness,stableness and cost efficiency.Moreover,fiber lasers have rich nonlinearity so they provide a good environment for nonlinear phenomena study.During the past decades,femtosecond fiber lasers have been devoloped fast and can compete with solid state femtosecond laser in pulse energy and pulse repetition frequency rate.However,limited to the gain bandwidth(~40 nm),few cycle pulses directly from the fiber oscillators are hard to achieve.Also,because of the limited doped elements,the center wavelength of main femtosecond fiber lasers is 1060 nm,1550 nm and 2000 nm.To compete with solid state femtosecond lasers in all aspects,great efforts should be made to shorten the pulse duration and extend the operating wavelength of the femtosecond fiber lasers.Our research focuses on the generation of the few-cycle pulse fiber lasers and the new band ultrashort pulse fiber lasers via fiber optic Cherenkov radiation.The main achievements are listed as follows:1.We have demonstrated all fiber generation of 1550 nm few cycle pulse source through outside cavity pulse amplification and compression technique.We have gotten 22.7 fs(four optical cycle pulse duration)pulse with the bandwidth of 137 nm through single stage pulse compression.To our knowledge,this is the shortest compared with the same type.2.Based on the fiber optic Cherenkov radiation(FOCR),we have converted the 1550 nm femtosecond pulse to be 1300 nm femtosecond pulse successfully with the conversion efficiency of 15%.Also,the center wavelength of the pulse source can be tuned between 1270 and 1315 nm and the pulse duration can be kept below 40 fs at the same time.The single pulse energy can be as high as 76 pJ,which can compete with the the Pr-doped and Bi-doped mode-locked fiber laser.Through entire dispersion management,the output pulse duration can be as short as 29 fs,which is the shortest among the same kind as far as we know.3.We have demonstrated all-fiber,widely tunable 920 nm femtosecond pulse source via fiber optic Cherenkov radiation.The center wavelength can be tuned between 905 and 960 nm.The spectrum width ranges from 30 to 50 nm.So the transform-limited duration can be 40 fs,which is shorter than the Nd-doped mode-locked fiber laser.4.We have investigated the possibility of backward Cherenkov radiation(BCR)generation in fiber.We find that the wavelength of the BCR depends on the value of group and phase refractive index.We have calculated the theory phase-matching wavelength of BCR.Also,we have designed the experiment scheme of BCR generation in fiber and analyzed the experimental condition to generate BCR in fiber.At last,we have compared BCR with the negative resonant radiation for the similarities and differences.In this thesis,we have researched the few-cycle pulse fiber laser and the new band ultrashort fiber laser based on fiber optic Cherenkov radiation,which promotes the development of the ultrafast fiber laser.