This paper presents a novel collision-less optical burst transmission scheme, namely, look-ahead optical burst transmission (LAOBT) for WDM ring networks. In the LAOBT, bursts are generated and inserted into burst streams by utilizing the void intervals of incoming bursts (IBs) in advance. The void size is estimated by splitting optical power into two paths, delaying one of the signals at the fiber delay line (FDL) and calculating IBs' residual time from the splitter to the optical cross-connect (OXC). The performance evaluation results show that our proposed scheme increases link utilization without significant increment of end-to-end delay and signaling overhead.