Investigations On The Time-delay Signature And Bandwidth Of Chaotic Signals In 1550Nm VCSELs With Variable-polarization FBG Feedback

In recent years, optical chaos has been studied extensively for its potential applications in secure communications, chaotic radar and ultra-fast random bit sequences etc. Chaotic signals generated by lasers with external optical feedback are usually used as the source of secure communication but the time delay signature (TDS) is raised accordingly. So far, few methods have been proposed to solve this problem while most of them are designed for traditional edge-emiting-lasers (EELs).1550nm VCSELs are divided as long wavelength lasers and have great prospects in metro area access networks and high speed optical interconnects beyond the superiorities than EELs. With the development of the chaotic secure communication, the chaos synchronization networks which can realize multi-directional chaos communications have been proposed in succession based on EELs. In these chaos synchronization networks, the bandwidths of chaotic carrier are usually limited to a few GHz mainly due to the low relaxation oscillation frequency of EELs. Therefore, the communication capacities reported in these chaos networks are not beyond lOGHz. In order to meet the needs of modern communications for high-capacity, the chaos synchronization networks which can realize larger capacity secret communications are always highly expected.We have proposed a new method to suppress the TDS of 1550nm VCSEL by optical feedback from variable-polarization fiber Bragg grating (FBG) and investigated the chaotic bandwidths of the network composed of few VCSELs with polarization rotated feedback. We adopted self-correlation function (SF) and the permutation entropy (PE) function to estimate the TDS of chaotic output from the time series derived by the spin-flip model. To overestimate the effective bandwidths of the chaotic signals, a new calculation for effective bandwidth is employed. The synchronizations of interactive VCSELs are assessed by cross-correlation function (CF). Results show that:TDS can be restrained successfully in variable polarization FBG feedback VCSEL (VPFBGF-VCSEL) system under suitable feedback parameters. Furthermore, the value of TDS is much smaller than that generated by traditional feedback ways. On the other hand, the TDS of D-VSEL is suppressed in 1550nm VCSEL chaotic synchronization network by polarization rotated FBG feedback. Effective bandwidths of polarization-resolved components have been enhanced significantly as both of two orthogonality liner components of R-VCSEL can be about 20GHz at some domains. Completely synchronization is also achieved for the cross-correlation coefficient of corresponding direction are almost 1. The results give some theoretically advises for implementing fiber communication network which owns higher security and larger capacity.