  The potential application of advanced digital communication schemes in a
future upgrade of the CMS Tracker readout optical links is currently being
investigated at CERN. We show experimentally that multi-Gbit/s data rates are
possible over the current 40 MSamples/s analog optical links by employing
techniques similar to those used in ADSL. The concept involves using one or
more digitally-modulated sinusoidal carriers in order to make efficient use of
the available bandwidth.
