Investigation On Time-delay Signature Of Chaotic Outputs In VCSELs With Variable-polarization Filtered Optical Feedback

With the fast development of information technology, the information security problems have attracted more and more attention in daily life. Nowadays, optical fiber communication is one of the mainstream transmission methods, apparently, secure research based on optical fiber communication is particularly important. Because of the output chaotic signals from semiconductor lasers(SLs) are well applied to optical fiber secure communication, chaotic radar, optical logic gates etc, the SLs are concerned by many scientific research workers. In general, the primary methods of chaos generated by SLs are optoelectronic feedback, optical injection, optical feedback etc. Chaotic signals of high dimensional complex can be easily generated by optical feedback, so it has been one of the preferred options for producing chaotic signals of SLs. Usually, the obvious time delay signature(TDS) could be observed in the chaotic signals of SLs with optical feedback. Through introducing appropriate mathematical algorithm, the chaotic delay time of secure communication system can be detected by the espionage, which brings major threats to the security of the secure communication system. Compared with the conventional edge-emitting semiconductor lasers(EELs), Vertical cavity surface emitting lasers(VCSELs) have many natural advantages, and the VCSELs can output two mutually vertical polarization components simultaneously, which is benefit to achieve the dual channels chaotic secure communication. Now, it is very necessary to find a system solution that the TDS of chaotic output in VCSELs is suppressed.This paper puts forward a system solution to suppress chaotic TDS, a variable polarization filtered optical feedback(VPFOF) is introduced to suppress chaotic TDS in the VCSEL system. By using the spin flip model(SFM), autocorrelation function(SF) and permutation entropy algorithm(PE), the TDS of chaotic output in VPFOF-VCSEL system is calculated. The results show that, fixed other feedback parameters, through changing the feedback intensity(η) and variable polarization angle(θp) of VPFOF-VCSEL system respectively, the η and θp of VPFOF-VCSEL have great influences on the TDS of chaotic signals, and under the proper η, θp and half-width at half-maximum of the filter(Λ), the TDS of X polarized component(X-PC) and Y polarized component(Y-PC) can be suppressed simultaneously in the VPFOF-VCSEL system. Next, through calculating the evolution maps of the TDS in the parameter space(η, θp) and(η, Λ) respectively, the regions of simultaneously suppressed TDS for the X-PC and Y-PC are acquired. Last, compared with polarization-preserved filtered optical feedback(PPFOF) and variable-polarization mirror optical feedback(VPMOF) respectively, under an optimized value, the chaotic TDS of X-PC and Y-PC output of VPFOF-VCSEL system can be more easily suppressed simultaneously.