We propose and numerically demonstrate a scheme for physical-layer security based on chaotic phase encryption, where the transmitted carrier signal is used as the common injection for chaos synchronization, so there is no need for additional common driving. To ensure privacy, two identical optical scramblers consisting of a semiconductor laser and a dispersion component are used to observe the carrier signal. The results show that the responses of the optical scramblers are highly synchronized but are not synchronized with the injection. By properly setting the phase encryption index, the original message can be well encrypted and decrypted. Moreover, the legal decryption performance is sensitive to the parameter mismatch, since it can degrade the synchronization quality. A slight drop in synchronization induces an evident deterioration in decryption performance. Therefore, without perfectly reconstructing the optical scrambler, the original message cannot be decoded by an eavesdropper.

We study theoretically the Fano resonances (FRs) produced by the near-field coupling between the lowest-order (dipolar) sphere plasmon resonance and the dipolar cavity plasmon mode supported by an Ag nanoshell or the hybrid mode in a simple three-layered Ag nanomatryushka constructed by incorporating a solid Ag nanosphere into the center of Ag nanoshell. We find that the linewidth of dipolar cavity plasmon resonance or hybrid mode induced FR is as narrow as 6.8 nm (corresponding to a high Q-factor of ~160 and a long dephasing time of ~200 fs) due to the highly localized feature of the electric-fields. In addition, we attribute the formation mechanisms of typical asymmetrical Fano line profiles in the extinction spectra to the constructive (Fano peak) and the destructive interferences (Fano dip) arising from the symmetric and asymmetric charge distributions between the dipolar sphere and cavity plasmon or hybrid modes. Interestingly, by simply adjusting the structural parameters, the dielectric refractive index required for the strongest FR in the Ag nanomatryushka can be reduced to be as small as 1.4, which largely reduces the restriction on materials, and the positions of FR can also be easily tuned across a broad spectral range. The ultranarrow linewidth, highly tunability together with the huge enhancement of electric fields at the FR may find important applications in sensing, slow light, and plasmon rulers.

A high-security, high-speed stream cipher for physical-layer-secure optical communication, based on optical-carrier-induced private chaos synchronization and RC4 algorithm, is proposed and numerically demonstrated. The high security and speed are achieved by combining physical true random numbers generated from synchronized chaos, used as the key for random DNA coding, with the RC4 pseudo-random numbers. Moreover, no third-party signal is required as the optical carrier itself serves as the common drive for chaos synchronization in semiconductor lasers. To ensure privacy, phase encryption with confidential dispersion components is deployed at the communicating parties to encrypt the driving signals. A secure stream cipher exceeding 100 Gb/s, leveraging approximately 4 Gb/s physical random numbers to achieve a rate 32 times higher, has been numerically demonstrated. Additionally, it is also noted that pseudo-random numbers generated from different seeds can be encoded using the same physical true random numbers to create parallel stream ciphers, making this approach well-suited for wavelength-division-multiplexed and space-division-multiplexed high-speed optical communications.

This study presents a comprehensive numerical investigation on the generation of a microwave frequency comb (MFC) using a semiconductor laser subjected to periodic-modulated optical injection. To enhance performance, optoelectronic feedback is incorporated through a dual-drive Mach–Zehnder modulator. The results show that the first optoelectronic feedback loop, with a delay time inversely proportional to the modulation frequency, can optimize MFC generation through a mode-locking effect and the second optoelectronic feedback loop with a multiple delay time of the first one can further enhance the performance of the MFC. The comb linewidth appears to decrease with the increase in the second-loop delay time in the power function. These results are consistent with experimental observations reported in the literature. We also explore the impact of the feedback index on comb contrast, the statistical characteristics of the central 128 lines within the MFC, and side peak suppression. The simulation results demonstrate the presence of an optimal feedback index. The study also reveals that linewidth reduction, through increasing the feedback index and delay time, comes at the cost of declining side peak suppression. These findings collectively contribute to a deeper understanding of the factors influencing MFC generation and pave the way for the design and optimization of high-performance MFC systems for various applications.

Photonic generation of broadband linearly frequency modulated microwave waveforms based on ultra-short optical feedback in an optically injected semiconductor laser is proposed and numerically demonstrated. The optical injection is employed to induce period-one (P1) oscillation in the semiconductor laser for photonic microwave generation. An ultrashort feedback is introduced to further shift the laser’s cavity-resonance frequency, enhancing the generated microwave frequency. By properly modulating the feedback light, the cavity-resonance frequency can be continuously shifted with the variation of the feedback strength, giving rise to a linearly frequency-modulated microwave signal. Because the injection strength remains constant, the proposed approach bypasses the limitations imposed by injection-locking and achieves more than 60 GHz of linearly frequency modulated microwave bandwidth. In addition, the microwave-comb contrast can be further optimized using a weaker long feedback loop whose time delay is equal to the modulation period of the ultrashort feedback. This approach provides a compact and flexible route for high-bandwidth photonic linearly frequency-modulated microwave signal generation.

Chaos synchronization in closed-loop external cavity semiconductor lasers subject to phase-conjugate feedback is investigated theoretically and numerically. We theoretically analysed the injection-locking synchronization condition and numerically confirm it. The simulation results indicate that with introduction of feedback phase difference according to the theoretical synchronization condition, high quality chaos synchronization can be achieved as the conventional optical feedback scenario.