The optical pulse trains with multiplied repetition frequency is generated by fractional Talbot effect in optical fiber. The principles of Talbot and fractional Talbot effects in fiber are analyzed. The 20,40 and 50 GHz optical pulse trains are obtained from the original pulse with 2.8 ps width at 10 GHz repetition frequency. An optical pulse at 40 GHz repetition frequency is also produced by upshifting the repetition frequency of 5 GHz pulse. The degradation of 40 GHz and 50 GHz pulse trains is discussed by spectrum analysis of pulse and some improvement methods are proposed.