An optical device, in particular for a motor vehicle, such as a lighting or signaling device, this device comprising at least one light guide which is designed to guide at least part of the light which is emitted by a source of light, the light guide comprising at least one output surface and at least one main reflection surface, which is designed to reflect towards the output surface light which is propagated in the guide, the light guide comprising a portion for coupling with the source of light, this coupling portion having a transverse axis (Y), wherein the coupling portion is arranged such that the light which is emitted from this coupling portion is propagated in the light guide, around the transverse axis, according to a total angular opening, measured around this transverse axis, which is strictly less than 360°, and in particular is less than 320° or 300°.