Industrial robot having a modular robot arm which has a plurality of arm modules, wherein at least one arm module has a housing with a first connection side and a second connection side, wherein the first connection side is designed to be controllably rotatable with respect to the second connection side about an axis of rotation, and wherein an optical rotation transmission device (501; 502) is arranged between the first connection side and the second connection side or a second connection side of a further arm module, which has an optomechanical rotation interface with a first interface side and a second interface side, which face each other and are each designed to complement each other and to be substantially rotationally symmetrical, wherein the first interface side has an optomechanical rotary plug-in device with a first optical device, and the second interface side has a mating optomechanical rotary plug-in device with a second optical device, which are set up so as to be rotatable relative to each other and are mounted mechanically so as to slide radially relative to each other by means of a radial plain bearing and a plain bearing shell complementary thereto, wherein the optomechanical rotary plug-in device and the mating optomechanical rotary plug-in device are formed as a cylindrical hollow system, wherein a gap, via which the optical signal transmission is carried out, is formed between the first optical device and the second optical device in the axial direction of the rotation transmission device, characterized in that the rotary plug-in device has a first ferrule and the mating rotary plug-in device has a second ferrule, wherein the first ferrule and the second ferrule are set up so as to be rotatable relative to each other, at least in some sections, within a radial bearing sleeve, wherein the radial bearing sleeve has an internal circumferential collar, on which the first ferrule and/or the second ferrule can be seated axially. which has an optomechanical rotation interface with a first interface side and a second interface side, which face each other and are each designed to complement each other and to be substantially rotationally symmetrical, wherein the first interface side has an optomechanical rotary plug-in device with a first optical device, and the second interface side has a mating optomechanical rotary plug-in device with a second optical device, which are set up so as to be rotatable relative to each other and are mounted mechanically so as to slide radially relative to each other by means of a radial plain bearing and a plain bearing shell complementary thereto, wherein the optomechanical rotary plug-in device and the mating optomechanical rotary plug-in device are formed as a cylindrical hollow system, wherein a gap, via which the optical signal transmission is carried out, is formed between the first optical device and the second optical device in the axial direction of the rotation transmission device, characterized in that the rotary plug-in device has a first ferrule and the mating rotary plug-in device has a second ferrule, wherein the first ferrule and the second ferrule are set up so as to be rotatable relative to each other, at least in some sections, within a radial bearing sleeve, wherein the radial bearing sleeve has an internal circumferential collar, on which the first ferrule and/or the second ferrule can be seated axially.