The fibres, either of single-more or multimode type, are positioned in a loose tube made of a high modulus plastic. The tube is filled with a water- resistant filling compound. The tube is wrapped with a layer of PSP longitudinally. Between the PSP and the loose tube water-blocking material is applied to keep the cable compact and watertight. Two parallel steel wires are placed at the two sides of the steel tape. The cable is completed with a polyethylene(PE) sheath.