Fiber optic cables (LWL — Lichtwellenleiter in German) transmit data as light signals. Compared to copper cables, they offer higher bandwidth, greater range, and a decisive security advantage: they do not emit electromagnetic signals that could be intercepted (TEMPEST protection). Physical tapping is technically demanding and leaves measurable signal losses. For your ISMS, fiber optics are relevant wherever high confidentiality requirements exist — for example, backbone connections between server rooms or links to particularly sensitive network segments. Document in your network plan which links use fiber optics and which still rely on copper.