An industrial robot comprises a modular robot arm having a plurality of arm modules, where a rotation transfer device for optical signal transmission is provided in an arm module or between a first and a second arm module. The rotation transfer device comprises an optomechanical rotation interface having a first interface side and a second interface side, which face each other and are substantially rotationally symmetrical and complementary. The first and second interface sides are configured to rotate relative to each other. The first and second interface sides are mechanically mounted with respect to each other, with a radial plain bearing on one interface side and a slide bearing shell complementary thereto on the other interface side. A gap is formed between the first and second interface sides, in the axial direction of the rotation transfer device, across which the optical signal transmission takes place.