Lag time and parameter mismatches in synchronization of unidirectionally   coupled chaotic external cavity semiconductor lasers
  We report an analysis of synchronization between two unidirectionally coupled chaotic external cavity master/slave semiconductor lasers with two characteristic delay times, where the delay time in the coupling is different from the delay time in the coupled systems themselves. We demonstrate for the first time that parameter mismatches in photon decay rates for the master and slave lasers can explain the experimental observation that the lag time is equal to the coupling delay time. 
E.M.Shahverdiev, S.Sivaprakasam and K.A.Shore