For the production of fibre waveguides mounted in a
metal hollow profile, a flat
metal strip is supplied to a deforming unit. The deforming unit is configured for continuously deforming the supplied flat
metal strip into a shape corresponding to the hollow profile. The hollow profile is continuously welded along a longitudinal seam by means of a
laser. A filler gel with a
viscosity which increases with decreasing temperature, and one or more fibre waveguides, are introduced into the welded hollow profile in a continuous process via a guide or protective tube. In order to introduce the one or more fibre waveguides with an excess length into the hollow profile, the welded hollow profile is elastically stretched, is cooled, and is relaxed again. The finished product is received in a receiving unit. The continuous closed-
loop control of the excess length of the fibre waveguides is performed inter alia through continuous open-
loop control of the gel temperature, of the
laser power and of the force exerted on the hollow profile for the elastic stretching.