Chaos is a fascinating phenomenon of nonlinear dynamical systems, and optical chaos communication has been one of potential frontier techniques to implement secure transmission of information. In this paper a novel high-speed bidirectional dual-channel chaos secure communication system is proposed based on semiconductor ring lasers (SRLs). In this system, the time delay signatures in chaotic output of clockwise (CW) and counterclockwise (CCW) patterns from a driving SRL (D-SRL) are firstly suppressed by using the double optical cross-feedback frame. Then, the chaotic output of D-SRL is injected into two response SRLs (R-SRLs) to drive the corresponding CW and CCW patterns of R-SRLs that are synchronized and bandwidth enhanced simultaneously. Thus, a bidirectional dual-channel chaos communication could be built based on chaotic synchronization of the two R-SRLs. We theoretically investigated the chaotic characteristics of a D-SRL under double optical cross-feedback and the chaotic synchronization features between R-SRL1 and R-SRL2 under different driving conditions. Results show that the time delay signatures of CW and CCW patterns of D-SRL could be effectively hidden under proper feedback conditions. The bandwidths of CW and CCW patterns of the D-SRL could be enhanced significantly. Furthermore, high-quality isochronous synchronization between R-SRL1 and R-SRL2 can be realized by choosing appropriate injection strength and detuning frequency in D-SRL and R-SRLs. Finally, the communication performances of bidirectional dual-channel chaos secure communication based on this proposed system are preliminarily examined and discussed, and the simulated results demonstrate that for 10 Gbit/s message, the Q factor of decoded message could be maintained above 6 after 10 kilometers distance transmission.

Photonic microwave generation has attracted much attention in recent years due to its potential applications in various fields such as radio-over-fiber communication, signal processing and radar systems. So far, different photonic microwave generation schemes have been proposed and investigated, such as the optical heterodyne method based on the beat of two independent lasers with a certain wavelength difference, the external modulation method based on electro-optical modulator, the dual-mode beat method based on the monolithic dual-mode semiconductor lasers, and the optoelectronic microwave oscillator method based on optoelectronic feedback loops. These schemes have their own advantages and deficiencies. Unlike the above schemes, in this paper we propose an all optical scheme for generating high-quality microwave based on a 1550 nm vertical-cavity surface-emitting laser (1550 nm-VCSEL). For such a scheme, high frequency microwave can be obtained based on a 1550 nm-VCSEL subjected to external optical injection, where the polarization of the injected light is the same as that of the dominant mode of the free-running 1550 nm-VCSEL (named parallel-polarized optical injection) and its wavelength is adjusted to being close to the wavelength of the suppressed polarization mode of the free-running 1550 nm-VCSEL. With the aid of double optical feedback, the linewidth of the obtained microwave can be narrowed. In this work, firstly, the feasibility of microwave generation based on parallel-polarized optically injected 1550 nm-VCSEL is analyzed theoretically by using the spin-flip model. Next, a corresponding experimental system is constructed, and the performance of microwave generation is preliminarily investigated experimentally. The experimental results show that 30 GHz microwave signals could be obtained based on a parallel-polarized, optically injected 1550 nm-VCSEL under suitable injection parameters, but the linewidth of microwave signal is relatively wide (hundreds of MHz). Finally, after introducing double optical feedback, the linewidth of microwave signal can be reduced by more than two orders of magnitude and narrowed to less than 1 MHz, meanwhile the signal-noise ratio is larger than 40 dB. This work is helpful to develop relevant techniques to acquire high-performance narrow linewidth photonic microwave.

Through employing permutation entropy and the self-correlation function, the time-delay signature (TDS) of a vertical-cavity surface-emitting laser (VCSEL) with variable-polarization filtered optical feedback (VPFOF) is evaluated theoretically. The work shows that the feedback rate η, polarizer angle θ p , and filter bandwidth Λ have an obvious influence on the TDS. The evolution maps of the TDS in parameter space ðη; ΛÞ and ðη; θ p Þ are simulated for searching the chaos with weak TDS. Furthermore, compared with a VCSEL with polarization-preserved filtered optical feedback and a VCSEL with variable-polarization mirror optical feedback, this VPFOF-VCSEL shows superiority in TDS suppression.