The comb like filter characteristic of a Fabry Perot etalon in frequency domain was deployed to filter out the discrete spectral lines of injected 10GHz optical pulse train. By changing the free spectral range and obtaining the spectral components spaced to 4 and 6 times of the repetition rate, the pulse trains with 40 GHz and 60 GHz were successfully obtained. The comb like filter characteristic of a Fabry Perot etalon in frequency domain was deployed to filter out the discrete spectral lines of injected 10 GHz optical pulse train. By changing the free spectral range and obtaining the spectral components spaced to 4 and 6 times of the repetition rate , the pulse trains with 40 GHz and 60 GHz were successfully obtained.