Study On Pulse Shortening In Dispersion-managed Soliton Laser Based On Erbium-doped Fiber

Fiber lasers have always been of fundamental interest in the past few decades forits feature of compact size, flexible cavity, abundant dispersion and nonlinear effects,low cost, and high stability. Generation of ultra-short pulses through fiber lasers hasappealed considerable attention to the field of consumer electronics, mechanicalmanufacture, bio-imaging, medicine, telecommunications, and the military anddefense industry.In this paper, we mainly focused on the dispersion-managed soliton laser basedon Erbium-doped fiber. Here, Er-doped fiber had normal dispersion. We utilizedsingle mode fibers to induce abnormal dispersion so that the laser cavity was builtwith dispersion map. In this way, we can achieve short pulses through optimizing thecavity design. The main subjects were summarized in the following outline:1、 Exploring the effect of cavity length on pulse shortening.We experimentally built up a compact-sized ring-cavity fiber laser with passivelymode-locking mechanism of nonlinear polarization rotation. By stepwise alteringthe length of active fibers and single mode fibers, and properly adjusting thepolarization of wave plates, mode-locking operation with three differentdispersion regimes were achieved. Then, comparing two kinds of Er-doped fiberswith drastically different doping concentrations, we obtained the advantages ofhighly Er-doped fiber lasers working in the vicinity of zero dispersion.2、 Gaining pulse shortening via increasing nonlinear effects within cavity.We investigated the effects of a piece of zero dispersion fiber on the pulsedynamics in a passively mode-locked fiber laser operating in stretched-pulseregime. Numerical simulation suggests that proper location and length of the zerodispersion fiber facilitates spectrum broadening and pulse shortening in fiberlasers while keeping a constant of net cavity dispersion. A nonlinear polarizationevolution mode-locked Er-doped fiber laser with dispersion map is built based onthe simulation. Larger optical spectrum broadening can be obtained by insertionof a longer zero dispersion fiber after the active fiber in single pulse operation,which agrees with the simulation very well. 3、 Directly obtaining ultra-short pulses with output port position optimized.By the means of varying the position of output port, the ultra-short pulses can beachieved directly without any dispersion compensation. As a result, weexperimentally adjust the length of the two segments of single mode fibers beforeand behind output port respectively, and got the output position optimized.Ultimately,55-fs,141-nm pulse train was gained directly from the output port.