Delay signature concealment in chaotic semiconductor ring lasers

We investigate different scenarios leading to simultaneous time-delay concealment both in the intensity and the phase dynamics generated from semiconductor ring lasers (SRLs) subject to delayed feedback. Under appropriate conditions, we found that the delay signature can be eliminated both in the intensity and the phase dynamics of SRLs with cross-feedback even when subject to long delayed feedback. For SRLs with self-feedback configuration, we also found that the concealment of short delay time is possible. The fact that such delay signatures can be eliminated in SRLs subject to short feedback opens the possibility of implementing secure communication schemes and random number generators on chip.