In this are evaluated potential realizations of combined WDM systems. In systems’ channels with 10 and / or 40 Gbit/s per channel bit rate are transmitted differently modulated optical signals. Our issues of the combined system solutions are offered as a possible transition stage from traditional NRZ – OOK WDM communication systems to high-density WDM (HDWDM) systems with a higher information transmission capacity and spectral efficiency. Such modernization strategy is necessary because currently a number of internet users is increasing rapidly, as well as data capacity required per one user are growing continuously.