A pulsewidth tunable 10GHz flat-top pulse train was generated based on the combined action of active mode locking and nonlinear-polarization-rotation pulse shaping.The laser cavity consisted of two parts:one was a commonly used active-mode-locking fiber laser;the other was for NPR based pulse shaping,which was composed of two PCs between which a high nonlinear fiber was inserted,and an inline polarizer,was inserted into the cavity to control the pulse shape.The setup has previously been used for pulse compr...