To provide directionally dependent attenuation for an optical information transmission link using simple means without the use of an active component, it is proposed to couple two optical waveguides (1, 2) having different core diameters to one another, the core diameter of the second fiber (2) being at least six times greater than the core diameter of the first fiber (1). In this manner, it is achieved that the conduction of light signals in a predefined direction is attenuated by at least the factor 30, while, on the other hand, the light propagating in the reverse direction, is attenuated very slightly.