Abstract: A circular knitting machine having a main supporting frame which is stationary and a plurality of operating instrumentalities arranged to move about a central axis of the machine during the knitting operation. A first control device is provided on the stationary supporting frame. A second control device is provided on a machine part which is arranged to move about said axis. The first and second control devices each include a light signal source and a light signal receptor. A first optical fiber bundle is connected to the first control device and a second optical fiber bundle is connected to the second control device. The free ends of the first and second fiber bundles are provided in a mutually opposed configuration in radial planes and centered on the machine axis. The second fiber bundle is arranged for movement with the rotary machine part so as to be rotatable about the axis. Each fiber bundle comprises two sets of optical fibers.