A modulator-less scheme of pulse position modulation (PPM) which converts a digital FM signal applied directly on the laser source to a PPM signal with a natural synchronization pulse is proposed. The laser source is directly modulated at a center frequency of 2.33 GHz. The reflected pulses provide a synchronization signal at the output of the fiber coupler, while the transmitted ones represent time-shifted replicas. The key point of this loop device is that the small variation in the period of the 2.33 GHz carrier when it is frequency-shifted by few kHz is multiplied by the number of pulsed inside the loop, producing a long decay (50-200 ps) between synchronization and replicated pulses.19119
