Time-delay-signature-suppressed broadband chaos generated by scattering feedback and optical injection

Enhanced photonic reservoir computing using an optically injected VCSEL with random polarized optical feedback

We propose and numerically demonstrate a photonic time-delay reservoir computing (TDRC) system exhibiting enhanced parallel task processing performance, where an optically injected vertical-cavity surface-emitting laser (VCSEL) under random distributed optical feedback acts as the reservoir computer. To assess its effectiveness, we perform two benchmark tasks including chaotic time-series prediction and waveform recognition task, where the TDRC is associated with two different random feedback structures, i.e., orthogonally polarized optical feedback (OPOF) and parallelly polarized optical feedback (PPOF). Benefiting from the enhanced nonlinearity offered by the random distributed optical feedback, the proposed TDRC excels at parallel task processing with the PPOF structure, whereas the performance of the OPOF structure may be deteriorated. Additionally, we reveal the effect of the injection strength, feedback strength, pump current, and number of virtual nodes on the proposed TDRC. Our work paves the way for the performance enhancement of parallel task processing based on polarization multiplexing in a VCSEL-based TDRC.

Time-delay signature suppression in delayed-feedback semiconductor lasers as a paradigm for feedback control in complex physiological networks

Physiological networks, as observed in the human organism, involve multi-component systems with feedback loops that contribute to self-regulation. Physiological phenomena accompanied by time-delay effects may lead to oscillatory and even chaotic dynamics in their behaviors. Analogous dynamics are found in semiconductor lasers subjected to delayed optical feedback, where the dynamics typically include a time-delay signature. In many applications of semiconductor lasers, the suppression of the time-delay signature is essential, and hence several approaches have been adopted for that purpose. In this paper, experimental results are presented wherein photonic filters utilized in order to suppress time-delay signatures in semiconductor lasers subjected to delayed optical feedback effects. Two types of semiconductor lasers are used: discrete-mode semiconductor lasers and vertical-cavity surface-emitting lasers (VCSELs). It is shown that with the use of photonic filters, a complete suppression of the time-delay signature may be affected in discrete-mode semiconductor lasers, but a remnant of the signature persists in VCSELs. These results contribute to the broader understanding of time-delay effects in complex systems. The exploration of photonic filters as a means to suppress time-delay signatures opens avenues for potential applications in diverse fields, extending the interdisciplinary nature of this study.

Evolution of the time delay signature of chaos generated in three types of optical injection systems

The time delay signature (TDS) of chaos generated in three schemes of optical injection has been investigated, and the mechanism of TDS suppression (TDSS) is revealed. The first scheme is a continuous-wave (CW) laser unidirectionally injecting into a chaotic laser, and the TDS of the chaotic laser is suppressed below 0.08 in this structure. The second scheme is a chaotic laser unidirectionally injecting into a CW laser, where the parameter range of TDSS lower than 0.06 of this structure is the largest among the three schemes. The third scheme is two CW lasers coupling to each other, and two chaotic lasers with TDS (T D S<0.1) suppression can be obtained simultaneously. For the further analysis of the mechanism of TDSS, the quasi-linear relationship between the synchronization coefficient and TDS is revealed. This study will provide insight into the generation of chaotic lasers by optical injection and promote the application of chaotic lasers.

Wideband and high-dimensional chaos generation using optically pumped spin-VCSELs

We propose and numerically demonstrate wideband and high-dimensional chaos signal generation based on optically pumped spin-polarized vertical-cavity surface-emitting lasers (spin-VCSELs). Here, we focus on the chaotic characteristics of spin-VCSELs under two scenarios: one is a spin-VCSEL with optical feedback and the other is optical heterodyning the outputs of two free-running spin-VCSELs. Specifically, we systematically investigate the influence of some key parameters on the chaotic properties, i.e., bandwidth, spectral flatness (SF), time delay signature (TDS), correlation dimension (CD), and permutation entropy (PE), and reveal the route to enhance these properties simultaneously. Our simulation results demonstrate for the first time that spin-VCSELs with simple auxiliary configurations allow for chaos generation with desired properties, including effective bandwidth up to 30 GHz and above, no TDS of greater than 0.2, the flatness of 0.75 and above, and the high complexity/dimensionality over a wide range of parameters under both schemes. Therefore, our study may pave the way for potential applications requiring wideband and high-dimensional chaos.

Impact of FBG feedback phase on laser dynamics

Fiber Bragg gratings (FBGs) have been advantageously used to improve the chaotic properties of semiconductor lasers. Though these components are known to be highly sensitive to environmental conditions, feedback phase fluctuations are often neglected. In this work, we experimentally demonstrate that the small variations of the propagation time induced by a simple thermal tuning of the FBG are sufficient to induce significant changes of the laser behavior. We report periodic stability enhancements linked with phase variations and highlight that both phase variation and phase offsets play an important role. Last, we show a good qualitative agreement with simulations based on an expanded version of the Lang-Kobayashi model.

Characterizing the chaotic dynamics of a semiconductor nanolaser subjected to FBG feedback

Nonlinear dynamics of semiconductor nanolasers subjected to distributed feedbacks from fiber Bragg grating (FBG) are investigated through modified rate equations, which include the unique Purcell cavity-enhanced spontaneous emission factor F and spontaneous emission coupling factor β. In the analysis, the effects of F, β, frequency detuning, feedback strength, feedback delay, FBG bandwidth and length on chaotic performance are evaluated. It is observed that the approach of FBG feedback outperforms mirror feedback in terms of concealing time-delay signature and increasing effective bandwidth by choosing intermediate feedback strength and frequency detuning. Additionally, chaotic regions and the corresponding chaotic characteristics are revealed by dynamical mappings of nanolasers subjected to FBG feedback. The results show that decreased F, β and increased FBG bandwidth can extend the parameter range of chaos. However, the variation of feedback delay and FBG length has no obvious effect on TDS suppression and effective bandwidth enhancement. Most importantly, high quality optical chaos with low TDS and high effective bandwidth induced by increased dispersion is obtained within broad parameter regions considered, which is beneficial to achieving chaos-based applications.

Optically injected nanolasers for time-delay signature suppression and communications

A large number of studies have been carried out to understand the nonlinear dynamics of nanolasers, yet there is a lack of comprehensive consideration on the optimization of chaotic output and its application to chaos secure communications. In this paper, we used an optically injected nanolaser structure to generate broadband chaos without a time-delay signature (TDS), which acts as the chaotic carrier in the proposed communication scheme. Due to the combination of desired TDS suppression enabled by the nanolasers and a two-channel transmission technique, the proposed scheme offers enhanced security for message encryption and decryption. We also considered the influence of some key parameters on the TDS suppression and that of parameter mismatch on chaos synchronization and message recovery. The detailed studies indicate that the proposed nanolaser-based scheme offers satisfactory TDS suppression performance over a wide range of parameters considered and is robust to resist fabrication imperfections-induced mismatch under proper injection conditions.

Unveil the time delay signature of optical chaos systems with a convolutional neural network

We propose a time delay signature extraction method for optical chaos systems based on a convolutional neural network. Through transforming the time delay signature of a one-dimensional time series into two-dimensional image features, the excellent ability of convolutional neural networks for image feature recognition is fully utilized. The effectiveness of the method is verified on chaos systems with opto-electronic feedback and all optical feedback. The recognition accuracy of the method is 100% under normal conditions. For the system with extremely strong nonlinearity, the accuracy can be 93.25%, and the amount of data required is less than traditional methods. Moreover, it is verified that the proposed method possesses a strong ability to withstand the effects of noise.

Enhancing time-delay suppression in a semiconductor laser with chaotic optical injection via parameter mismatch

Time-delay signature (TDS) suppression of an external-cavity semiconductor laser (ECSL) is important for chaos-based applications and has been widely studied in the literature. In this paper, the chaotic output of an ECSL is injected into a semiconductor laser and TDS suppression in the regenerated time series is revisited. The focus of the current work is the influence of parameter mismatch on the TDS evolution, which is investigated experimentally and compared systematically to simulations. The experimental results demonstrate that it is much easier to achieve desired TDS suppression in the configuration composed of mismatched laser pairs. Numerical simulations confirm the validity of the experimental results. In the experiments and simulations, the influence of the injection parameters on TDS suppression is also studied and good agreement is obtained.