Chaos-based communication schemes using semiconductor lasers subject to filtered optical feedback

We study numerically the synchronization properties of two unidirectionally
coupled semiconductor lasers subject to filtered optical feedback. Due to the
filter, the induced delay dynamics is modified with respect to the dynamics of
the conventional optical feedback case. We find substantially higher degree of
correlation between the lasers when the receiver has similar feedback to the
emitter (closed loop scheme) than when the receiver operates without feedback
(open loop scheme). Furthermore, filtered feedback schemes require less
coupling strength than their conventional optical feedback counterparts. We
show that this chaos-based communication scheme allows for the transmission
and recovery of encrypted messages. The performance of the system is optimal
when similar filters are used in transmitter and receiver.