In the case of a method and a device for transmitting data units by way of a transmission medium that comprises at least three adjacent transmission lines, first of all a plurality of codes is supplied. The suction recovery method firstly performs the first suction step for generating a negative pressure for sucking a filter section for separating bubbles from the filter section. The first LPG converts light, over a broad wavelength range, being transmitted in the fundamental, or LP01, mode of the optical fiber transmission line into light in a higher order mode of the optical fiber. The second sides are opposite the first sides. Vacuum pressure is substantially uniformly applied to the crystal, providing substantially uniform stresses on the surface of the final concave focusing optical lens.