The invention concerns a valve arrangement for controlling a hydraulic drive, the supply to and the outflow from the hydraulic drive being separately controllable. Such symbols can be polysemous in nature and thus be associated with a plurality of different meanings depending upon other symbols sequenced therewith. The server also stores the identification data transmitted by it. A thermal oxide layer is formed to fill the opening, such that the indented sidewalls are completely sealed. The optical fiber thus formed can serve as a photoelectric optical fiber for transmission of current signals.