Mode-locked Fiber Laser

Ultra-short optical pulse finds lots of application, and mode-locking of laser is the most important technology to achieve coherent optical pulse, where the actively mode-locking draws so much attention due to its simple configuration, controllable repetition-rate and producing nearly transform-limited high-quality pulse. Now fiber itself combines the dispersion, the nonlinearity with the gain, all of which play a subtle impact on the parameters of optical pulse. Therefore, researches on the actively mode-locking fiber laser (AMLFL) have significant meaning in both theory and practice.In the dissertation, we theoretically and experimentally investigate the characteristics of output pulse from the AMLFL. Firstly, a path-averaged mode-locking equation (PAE) is derived from the Maxwell Equations, the term describing the effect of mode-locking is included into PAE, and meanwhile the model of EDFA is discussed here to avoid a common mistake when calculating the emission and absorption cross section of Erbium-doped fiber. By replacing the mode-locking term, the PAE can be extended to describe other mechanism of mode-locked lasers.Two numerical approaches for the PAE are developed here: the self-consistent field and the moment method. The first one deals with the amplitude of the optical filed, and the latter concentrates on the parameter of pulse such as energy, width and chirp. Both of them are used to study the transient states of AMLFL, and how the features of pulse vary as the dispersion and nonlinearity. And different position of output from the ring is studied by the first method. The results reveal that with the abnormal dispersion and effect of proper nonlinearity, a soliton pulse can be produced and in our short cavity, the position of output makes no differences.In the experiment, an ultra-wide bandwidth sine-wave signal source is designed, manufactured all by myself based on the DDFS (direct digital frequency syntheses). With a MCU-based control system, frequency-resolution as high as 1Hz from nearly dc to 200MHz is obtained, and user-friendly interface is achieved. Finally, a high-repetition optical pulse is obtained on the oscilloscope.