Study Unpredictability And Time-Delay Signature Concealment Of Semiconductor Ring Laser

With the development of modern information technology, the security of communication system has been threatened partly. On one hand, as the time series analysis has enhanced significantly, the time-delay signatures allow an eavesdropper to retrieve the time-delay of carrier signals; on the other hand, the system security has been affected by the unpredictability of carrier signals. Semiconductor ring laser (SRL), as a novel laser source, play an important role in chaotic communication system. Its resonator cavity supports the laser in clockwise (CW) and counterclockwise (CCW) directions which offers possibilities to enhance the security of chaotic communication system. In this paper, based on improving the security of system, it has been quantitatively presented the unpredictability degree and time-delay concealment of chaotic carrier signals in SRL.First, it is explored a chaos carrier signals scheme which based on parallel injection semiconductor ring lasers with chaotic cross-feedback. With tools of permutation entropy, the unpredictability degree of chaotic signals of SRLs is evaluated both in symmetric and asymmetric injections. Bandwidth properties of carrier signals are also studied both on symmetrical injection and asymmetrical injection. The results show that, this scheme produces better carrier signals than single SRL as the unpredictability of slave SRL’s output is higher than the master SRL’s. In high positive or negative frequency detuning, the unpredictability of carrier signals of the slave SRL are enhanced easily by choosing asymmetrical injection and the values of two modes’PE are increased to 0.8. With the increase of frequency detuning, the bandwidth of CW mode of slave SRL is enhanced. In high detuning frequency, by choosing appropriate asymmetric injection strength, we can simultaneously achieve two sets of higher unpredictability and bandwidth enhanced of chaotic carrier signals which are extremely useful in high speed random number generators as well as high capacity security-enhanced chaotic communication systems.Second, this paper has studied a chaos communication scheme that is parallel mutually injection semiconductor ring lasers subjected to self-feedback (SF-PMISRLs), which compares with an existing solution of parallel mutually injection semiconductor ring lasers (PMISRLs) mode. Time-delay signature of chaotic time series in intensity was quantitatively evaluated by the maximum of peak/trough of their autocorrelation function while unpredictability of chaotic time series was analyzed by using tools of permutation entropy, which were both solved by symmetric and asymmetric injections. The conclusions show that the region of time-delay concealment of SF-PMISRLs system will be widened as the detuning frequency increases while the PMISRLs system’s is narrow, which represents time-delay signature of SF-PMISRLs system can be well concealed. Specifically, in high detuning frequency, time-delay signature of SF-PMISRLs system was concealed better by choosing asymmetric injection than symmetric injection. The unpredictability degree of SRL’s output will be improved by choosing high frequency detuning and proper mutual injection strength because of the similar regions of desirable unpredictability degree of the two systems.