Optical pulses with a repetition frequency of 1GHz and pulse width of 17 ps at 1.3μm are obtained by using a comb generator and direct modulation of DCPBH lasers. Experiments on SHG correlation measurement system are also described. The depencence of pulse width and the peak power on the variation of biased current are shown, which indicates when the laser diode is biased near the threshold, the shortest pulse width and the highest peak can be obtained.