60 Gbps bidirectional dual-channel chaotic secure communication based on two 1550 nm synchronized VCSELs

Based on chaos synchronization between two 1550 nm response vertical-cavity surface-emitting lasers (R-VCSELs), we propose and numerically investigate a bidirectional dual-channel chaotic secure communication system. Under delayed dual-path chaotic signal injections from the injection VCSEL (I-VCSEL) with polarization-preserved optical feedback, a driving VCSEL (D-VCSEL) can generate an optimized chaotic signal, which can drive two R-VCSELs to output polarization-resolved chaotic signals with wide bandwidth about 35 GHz and low TDS below 0.1 in a relatively large parameter range. Moreover, high-quality isochronal chaos synchronization between the corresponding linear polarization components of two R-VCSELs can be achieved. In contrast, the synchronization quality between D-VCSEL and arbitrary one R-VCSEL is inferior. On this basis, through the polarization-division-multiplexing technique in conjunction with the chaos modulation (CM) method, this proposed system can realize security-enhanced bidirectional dual-channel message transmission of 30 Gbps bipolar non-return-to-zero signals over a 140 km fiber link with Q-factors above six. After adopting four-level pulse amplitude modulation, 60 Gbps signals can be successfully transmitted over a 60 km fiber link with Bit-Error-Rates (BERs) below the hard-decision forward error correction (HD-FEC) threshold of 3.8×10^-3.