Time delay signature (TDS) of a semiconductor laser subject to dispersive optical feedback from a chirped fibre Bragg grating (CFBG) is investigated experimentally and numerically. Different from mirror, CFBG provides additional frequency-dependent delay caused by dispersion, and thus induces external-cavity modes with irregular mode separation rather than a fixed separation induced by mirror feedback. Compared with mirror feedback, the CFBG feedback can greatly depress and even eliminate the TDS, although it leads to a similar quasi-period route to chaos with increases of feedback. In experiments, by using a CFBG with dispersion of 2000ps/nm, the TDS is decreased by 90% to about 0.04 compared with mirror feedback. Furthermore, both numerical and experimental results show that the TDS evolution is quite different: the TDS decreases more quickly down to a lower plateau (even background noise level of autocorrelation function) and never rises again. This evolution tendency is also different from that of FBG feedback, of which the TDS first decreases to a minimal value and then increases again as feedback strength increases. In addition, the CFBG feedback has no filtering effects and does not require amplification for feedback light.

High-speed physical key distribution is diligently pursued for secure communication. In this paper, we propose and experimentally demonstrate a scheme of high-speed key distribution using mode-shift keying chaos synchronization between two multi-longitudinal-mode Fabry–Perot lasers commonly driven by a super-luminescent diode. Legitimate users dynamically select one of the longitudinal modes according to private control codes to achieve mode-shift keying chaos synchronization. The two remote chaotic light waveforms are quantized to generate two raw random bit streams, and then those bits corresponding to chaos synchronization are sifted as shared keys by comparing the control codes. In this method, the transition time, i.e., the chaos synchronization recovery time is determined by the rising time of the control codes rather than the laser transition response time, so the key distribution rate is improved greatly. Our experiment achieved a 0.75-Gbit/s key distribution rate with a bit error rate of 3.8 × 10−3 over 160-km fiber transmission with dispersion compensation. The entropy rate of the laser chaos is evaluated as 16 Gbit/s, which determines the ultimate final key rate together with the key generation ratio. It is therefore believed that the method pays a way for Gbit/s physical key distribution.

We experimentally demonstrate high-speed correlated random bit generation in real time using synchronized chaotic lasers commonly driven by a laser with dispersive feedback. The dispersive feedback from a chirped fiber Bragg grating induces frequency-dependent feedback delay and thus no longer causes time-delay signature, and resultantly ensures the signal randomness and security of chaotic laser. Driven by the time-delay signature-free chaotic signal, the two response lasers are routed into chaotic states and establish a synchronization with correlation beyond 0.97 while they maintain a low correlation level with the drive signal. Through quantizing the synchronized laser chaos with a one-bit differential comparator, real-time 2.5-Gb/s correlated random bits with verified randomness are experimentally obtained with a bit error ratio of 0.07. Combining with a robust sampling method, the BER could be further decreased to 1×10 −4 corresponding to an effective generation rate of 1.7 Gb/s. Bit error analysis indicates that the bit error ratio between the responses is lower than that between the drive and responses over a wide parameter region due to the synchronization superiority of the responses over the drive.

The chaotic characteristics of high-dimensional chaotic system are more complex, so the design of chaotic system with higher dimension has become a leading subject of chaos theory. In this paper, we constructed a nine-dimensional eight-order chaotic system. Matlab simulation of system is performed and Lyapunov exponents are figured out, which proved more complex dynamical behaviors. And the corresponding hardware circuit is designed. Multisim simulation results of the circuit coincide with Matlab simulation of the system completely, showing the same chaotic attractors. The consistent results verified the realizability of system. Therefore, the system can provide a more secure encryption source for information encryption.

High speed physical secure key distribution in a classical optical fiber channel is unprecedentedly desired for modern secure communication, but it still remains a worldwide technical challenge. In this paper, we propose and experimentally demonstrate a novel high-speed physical secure key distribution scheme based on chaotic optical signal processing and private hardware modules, which employs chaotic self-carrier phase modulation for chaotic bandwidth expansion and time-delayed shift keying of commonly driven synchronized optical chaos for physical layer security. In this scheme, the entropy source rate of synchronized chaos output from two remote response lasers is greatly expanded by chaotic self-carrier delayed nonlinear phase disturbance, which facilitates high speed key extraction from the entropy source with guaranteed randomness. Moreover, a synchronization recovery time of sub-nanosecond is achieved by dynamic keying of the chaotic delay time after chaos synchronization to accelerate the key distribution rate. Based on the proposed scheme, a high physical key distribution rate of 2.1 Gb/s over 40 km is successfully demonstrated in the experiment. The proposed solution provides a promising strategy for future high-speed key distribution based on chaotic optical signal processing and classical fiber channel.