An optical device comprising at least one first light guide having an exit face. The first guide is configured to propagate the light rays emitted by a first light source toward its exit face. The exit face is placed facing a coupling zone that forms part of the lateral surface of a generally tubular second light guide of the optical device. The optical device allows the transmission of the light emitted via the exit face of the first guide through the second guide to be improved. The optical device especially proposes the implementation of a luminous device for an automotive vehicle integrating two luminous functions.