  The incorporation of multiplexing techniques used in Microwave Photonics to
Quantum Key Distribution (QKD) systems bring important advantages enabling the
simultaneous and parallel delivery of multiple keys between a central station
and different end-users in the context of multipoint access and metropolitan
networks, or by providing higher key distribution rates in point to point links
by suitably linking the parallel distributed keys. It also allows the
coexistence of classical information and quantum key distribution channels over
a single optical fibre infrastructure. Here we show, for the first time to our
knowledge, the successful operation of a two domain (subcarrier and wavelength
division) multiplexed strong reference BB84 quantum key distribution system. A
four independent channel QKD system featuring 10 kb/s/channel over an 11 km
link with Quantum Bit Error Rate (QBER) < 2 % is reported. These results open
the way for multi-quantum key distribution over optical fiber networks.
