The pulse repetition frequency of an optical pulse generator built with a fiber laser (LAS) is synchronized to a fixed clock frequency (fc). The synchronization is accomplished via means (M) for changing the optical path length of the resonator (RES), which is controlled by a signal from a control device (RE). The criterion for the synchronization is the effective value of an interference signal superimposed on the signal light, which increases with increasing deviation of the pulse repetition frequency from the clock frequency. A portion of the output signal (A) of fiber laser (LAS) is optically/electrically converted by the control device (RE), and the effective value of the interference signal is determined by filtering and rectifying the electrical signal obtained in this manner. After subsequent amplification and regulation, the control signal for the means (M) to change the optical wavelength is obtained. The control signal is additionally modulated with a wobble signal, so that the pulse repetition frequency always varies around the optimum value and is synchronized in this way.