With the presented calculation and optimization procedure for digital multi-level optical waveguide transmission systems it is possible to give answers to special problems such as the achievable repeater spacing, the necessary radiation energy per signal pulse, or the system sensitivity to the variation of different system parameters. In particular, we consider a problem which has not been discussed so far, namely the deterioration of the signal-to-noise ratio to be expected, if the equidistant level spacings well known from conventional transmission systems are retained. The result for a theoretically investigated 140 MBaud-system working at 1.3 μιη is that the deterioration increases with growing number of levels, but this tendency is dependent on the signal duration at the far end of the optical waveguide. Furthermore, the influence of splices on the achievable repeater spacing is calculated for the same system example.