A device for transmitting modulated optical signals between units comprises a first unit and a second unit, the first unit being supported to be rotatable with respect to the second unit, a light guide along a circular track on the first unit, a first and a second light coupler for coupling light signals into or out of the light guide, the second light coupler being disposed on the second unit and movable with respect to the light guide. For an achievement of a high transmission bandwidth, a controllable absorber is provided in the light guide to prevent a propagation of light along a plurality of paths between the two units. In a method for operating the device, the absorber is controlled so that modulated light signals from the first and the second directions have a same amplitude at a point at which the modulated light signals have the same phase.