  We experimentally study the synchronization of chaos generated by
semiconductor lasers in a cascade injection configuration, i.e., a tunable
master laser is used to generate chaos by optical injection in a transmitter
laser that injects light into a receiver laser. Chaos synchronization between
the transmitter and the receiver lasers is achieved with a correlation
coefficient of 90 % for a measurement bandwidth up to 35 GHz. Two parameter
regions of good synchronization are found, corresponding to the alignment of
the oscillation frequencies of the receiver laser with either the transmitter
laser or the master laser.
