The invention relates to a method for detecting collisions in an out-of-band communication channel, implemented by a master device of an optical communications network enabling in-band communications and further comprising slave devices. The out-of-band communication channel enables transmissions of signalling information with respect to the in-band communications in the form of modulation symbols over successive symbol periods. Collisions occur when plural slave devices access the out-of-band communication channel by using carrier wavelengths matching each other. The master device: receives a signal via the out-of-band communication channel; oversamples the received signal, so as to obtain samples thereof, by using a frequency used for sampling the in-band communications or a submultiple derived therefrom; checks variations of magnitude of at least one parameter of the samples on a per symbol period basis; and detects a collision when the variations of each said parameter are greater than a predefined threshold.