报道一种由光纤环形激光器的拍频信号中提取高重复率正弦电信号，并以此信号调制腔内强度调制器，实现调制频率与腔长自适应的主动锁模方法。采用此方法获得重复率为２．５ＧＨｚ，脉宽为１１ｐｓ的变换极限超短光脉冲。 This paper reports a kind of active mode-locking method of extracting the high repetition rate sinusoidal signal from the beat signal of the fiber ring laser and modulating the cavity intensity modulator with this signal to realize the modulation frequency and cavity length adaptive. In this method, we get the transform ultrashort pulse with the repetition rate of 2.5GHz and the pulse width of 11ps.