We numerically study the synchronization of two chaotic semiconductor laser
s in a master-slave configuration. To synchronize the lasers, a small amoun
t of output power from the master laser is injected, after propagating thro
ugh an optical fiber, into the slave laser. We show that the output of the
master laser can be used as a chaotic carrier to encode a digital message w
hich can be recovered after propagating long distances. We also check the r
obustness of this scheme when the two lasers art slightly different.