Regulation of cluster synchronization in multilayer networks of delay coupled semiconductor lasers with the use of disjoint layer symmetry.

In real-world complex systems, heterogeneous components often interact in complex connection patterns and could be schematized by a formalism of multilayer network. In this work, the synchronization characteristics of multilayer network composed of semiconductor lasers (SLs) are investigated systematically. It is demonstrated that the interplay between different layers plays an important role on the synchronization patterns.

Wideband chaos synchronization using discrete-mode semiconductor lasers.

Optical chaos communication encounters difficulty in high-speed transmission due to the challenge of realizing wideband chaos synchronization. Here, we experimentally demonstrate a wideband chaos synchronization using discrete-mode semiconductor lasers (DMLs) in a master-slave open-loop configuration. The DML can generate wideband chaos with a 10-dB bandwidth of 30 GHz under simple external mirror feedback.

Photonic reservoir computing using a self-injection locked semiconductor laser under narrowband optical feedback.

Photonic time-delay reservoir computing (TDRC) using a self-injection locked semiconductor laser under optical feedback from a narrowband apodized fiber Bragg grating (AFBG) is proposed and numerically demonstrated. The narrowband AFBG suppresses the laser's relaxation oscillation and provides self-injection locking in both the weak and strong feedback regimes. By contrast, conventional optical feedback provides locking only in the weak feedback regime.

Performance improvement of coherent optical chaos communication using probabilistic shaping.

We numerically investigate the effects of probabilistic shaping on the performance improvement of coherent optical chaos communication. Results show that the decryption bit-error ratio (BER) of the 16-ary quadrature amplitude modulation (QAM) signal decreases upon increasing the probabilistic shaping factor. It is predicted that the BER of 10-GBd 16QAM can be decreased by one order of magnitude.

Modeling of a multi-parameter chaotic optoelectronic oscillator based on the Fourier neural operator.

A model construction scheme of chaotic optoelectronic oscillator (OEO) based on the Fourier neural operator (FNO) is proposed. Different from the conventional methods, we learn the nonlinear dynamics of OEO (actual components) in a data-driven way, expecting to obtain a multi-parameter OEO model for generating chaotic carrier with high-efficiency and low-cost. FNO is a deep learning architecture which utilizes neural network as a parameter structure to learn the trajectory of the family of equations from training data.

Hierarchical-dependent cluster synchronization in directed networks with semiconductor lasers.

Cluster synchronization in complex networks with mutually coupled semiconductor lasers (SLs) has recently been extensively studied. However, most of the previous works on cluster synchronization patterns have concentrated on undirected networks. Here, we numerically study the complete cluster synchronization patterns in directed networks composed of SLs, and demonstrate that the values of the SLs parameter and network parameter play a prominent role on the formation and stability of cluster synchronization patterns.

Chaotic optical communications at 56 Gbit/s over 100-km fiber transmission based on a chaos generation model driven by long short-term memory networks.

Chaotic optical communication technology is considered as an effective secure communication technology, which can protect information from a physical layer and is compatible with the existing optical networks. At present, to realize long-distance chaos synchronization is still a very difficult problem, mainly because well-matched hardware cannot always be guaranteed between the transmitter and receiver. In this Letter, we introduce long short-term memory (LSTM) networks to learn a nonlinear dynamics model of an opto-electronic feedback loop, and then apply the trained deep learning model to generate a chaotic waveform for encryption and decryption at the transmitter and receiver.

Instability of optical phase synchronization between chaotic semiconductor lasers.

The instability of optical phase chaos synchronization between semiconductor lasers under master-slave open-loop configuration is investigated. The phase difference between the master and slave lasers is obtained and analyzed in experiment by heterodyne detection and Hilbert transform, and in simulation by solving the rate equations. The results show that the phase difference only maintains in a short duration time and then jumps to another value.

Scheme of coherent optical chaos communication.

We propose and numerically demonstrate a scheme of coherent optical chaos communication using semiconductor lasers for secure transmission of optical quadrature amplitude modulation (QAM) signals. In this scheme, a laser intensity chaos and its delayed duplicate are used to amplitude-quadrature modulate a continuous-wave light to generate a chaotic carrier. High-quality chaotic carrier synchronization between the transmitter and receiver is guaranteed by laser intensity chaos synchronization, avoiding laser phase fluctuation.

Stable period-one oscillations in a semiconductor laser under optical feedback from a narrowband fiber Bragg grating.

Period-one (P1) oscillations in a semiconductor laser under optical feedback from a narrowband fiber Bragg grating (FBG) are numerically investigated. FBG feedback enhances the stability of P1 oscillations compared to the conventional mirror feedback in the form of P1 microwave linewidth and phase noise reduction and residual noise peaks suppression. In the proposed scheme, the FBG has a narrow bandwidth smaller than the laser relaxation oscillation frequency.

Chaotic time-delay signature suppression with bandwidth broadening by fiber propagation.

Chaotic emission of a semiconductor laser is investigated through propagation over a fiber for achieving broadening of the bandwidth and suppression of the time-delay signature (TDS). Subject to delayed optical feedback, the laser first generates chaos with a limited bandwidth and an undesirable TDS. The laser emission is then delivered over a standard single-mode fiber for experiencing self-phase modulation, together with anomalous group-velocity dispersion, which leads to the broadening of the optical bandwidth and suppression of the TDS in the intensity signal.

Experimental investigation on feedback insensitivity in semiconductor ring lasers.

The insensitivity to optical feedback is experimentally measured for a semiconductor ring laser (SRL) and compared to that of a Fabry-Perot laser (FPL) fabricated with the same technology and on the same material. An analysis of the optical spectra reveals that the SRL remains nearly unaffected for values of optical feedback as strong as -23  dB. Furthermore, through both optical linewidth and self-mixing measurements, we show that the tolerance to feedback in SRLs is 25-30 dB stronger than in FPLs.

Frequency-modulated microwave generation with feedback stabilization using an optically injected semiconductor laser.

Generation of frequency-modulated continuous-wave (FMCW) microwave signals is investigated using the period-one (P1) dynamics of a semiconductor laser. A modulated optical injection drives the laser into P1 oscillation with a modulated microwave frequency, while adding feedback to the injection reduces the microwave phase noise. Using simply a single-mode laser, the tunability of P1 dynamics allows for wide tuning of the central frequency of the FMCW signal.

Randomness evaluation for an optically injected chaotic semiconductor laser by attractor reconstruction.

State-space reconstruction is investigated for evaluating the randomness generated by an optically injected semiconductor laser in chaos. The reconstruction of the attractor requires only the emission intensity time series, allowing both experimental and numerical evaluations with good qualitative agreement. The randomness generation is evaluated by the divergence of neighboring states, which is quantified by the time-dependent exponents (TDEs) as well as the associated entropies.

Square-wave oscillations in a semiconductor ring laser subject to counter-directional delayed mutual feedback.

Square-wave (SW) switching of the lasing direction in a semiconductor ring laser (SRL) is investigated using counter-directional mutual feedback. The SRL is electrically biased to a regime that supports lasing in either counter-clockwise (CCW) or clockwise (CW) direction. The CCW and CW modes are then counter-directionally coupled by optical feedback, where the CCW-to-CW and CW-to-CCW feedback are delayed by τ and τ, respectively.

Random bit generation at tunable rates using a chaotic semiconductor laser under distributed feedback.

A semiconductor laser with distributed feedback from a fiber Bragg grating (FBG) is investigated for random bit generation (RBG). The feedback perturbs the laser to emit chaotically with the intensity being sampled periodically. The samples are then converted into random bits by a simple postprocessing of self-differencing and selecting bits.

Polarization-resolved time-delay signatures of chaos induced by FBG-feedback in VCSEL.

Polarization-resolved chaotic emission intensities from a vertical-cavity surface-emitting laser (VCSEL) subject to feedback from a fiber Bragg grating (FBG) are numerically investigated. Time-delay (TD) signatures of the feedback are examined through various means including self-correlations of intensity time-series of individual polarizations, cross-correlation of intensities time-series between both polarizations, and permutation entropies calculated for the individual polarizations. The results show that the TD signatures can be clearly suppressed by selecting suitable operation parameters such as the feedback strength, FBG bandwidth, and Bragg frequency.