Abstract We study the effects of the semiconductor laser noise on the generated beat signal, in Coherent Optical Domain Reflectometry device. By using a general laser noise analytical model, based on Volterra non-linear treatment of laser rate equations, we find a novel general expression of the beat photocurrent. We show that the coherence and the incoherence cases are observed for a different delay time intervals than the ones known in literature. We show that the coherence domain corresponds to a delay time lower than the half of the laser coherence time τ 0 1 / 2 τ c , and the incoherence domain corresponds for τ 0 > 2 τ c . An original shape of the beat signal autocorrelation function affected by the laser noises is obtained.