Liyue Zhang

Photonic Generation of Wideband Time-Delay-Signature-Eliminated Chaotic Signals Utilizing an Optically Injected Semiconductor Laser

Photonic generation of wideband chaotic signals with time delay signature elimination is investigated experimentally and numerically based on a semiconductor laser (slave laser) with chaotic optical injection from a master laser. The master laser is subject to moderate optical feedback where the feedback strength and external-cavity length are fixed, while the slave laser stands alone. The experimental results show that wideband chaotic signals with successful time delay concealment can be generated in the slave laser by simply adjusting the coupling strength and frequency detuning between the two lasers. Furthermore, the numerical results are in accordance with the experimental observations. Finally, we propose a simple method for simultaneously generating multiple streams of high-quality chaotic signals using multichaotic lasers, where the time delay is effectively concealed in the autocorrelation function and delayed mutual information calculated from the chaotic time series.

Randomness-Enhanced Chaotic Source With Dual-Path Injection From a Single Master Laser

The randomness and bandwidth enhancement of chaotic signals in optically injected semiconductor lasers (SLs) with dual-path injection from a single master laser are investigated experimentally and numerically. It is shown that both the randomness and bandwidth of chaotic signals generated in a slave SL (SSL) can be enhanced significantly, especially for positive frequency detuning, by simply adding an additional injection path in the conventional master-slave configuration. The region of injection parameter space leading to wideband randomness-enhanced chaos in SSL can be greatly broadened compared to the SSL with single-path injection. This low-cost and simple configuration for wideband randomness-enhanced chaotic source is highly desirable for high-speed random number generators based on chaotic SLs.

Conceal Time-Delay Signature of Mutually Coupled Vertical-Cavity Surface-Emitting Lasers by Variable Polarization Optical Injection

In this letter, we quantitatively investigate the time-delay (TD) signature of chaotic outputs generated by mutually coupled vertical-cavity surface-emitting lasers (VCSELs) with variable polarization optical injection (VPOI). The research is performed using a novel estimator, which calculates the peak-to-mean ratio on the basis of the autocorrelation function (ACF). It is shown that the TD signature of mutually coupled VCSELs with VPOI at intermediate polarizer angles can be better concealed than that of mutually coupled VCSELs with conventional polarization-selected optical injection. The effects of bias current and injection delay are also taken into account. The system is further discussed by applying a recent approach that computes the ACF from a phase of chaotic outputs.

Simulation of Multi-bit Extraction for Fast Random Bit Generation Using a Chaotic Laser

Multi-bit extraction schemes for fast random bit generation using a semiconductor laser subject to delayed optical feedback are numerically investigated. The simulation shows that the statistical properties of the chaotic signal significantly influence the generation of random bit sequences. More importantly, bit sequences with verified randomness at hundreds of gigabit per second, even up to the order of terabit per second could be numerically generated utilizing some effective postprocessing techniques even though the original statistical distribution substantially differs from a symmetric distribution. Such numerical results frequently required for developing ultrafast random bit generators as the first stage help to evaluate the experimental implementations of the corresponding schemes.

Quantifying the Complexity of the Chaotic Intensity of an External-Cavity Semiconductor Laser via Sample Entropy

This paper presents detailed numerical investigations of quantifying the complexity of the chaotic intensity obtained from the well-known Lang-Kobayashi model for an external-cavity semiconductor laser (ECSL) using sample entropy (SampEn). We demonstrate that the modified SampEn could be an alternative to quantify the underlying dynamics of an ECSL under the condition that the dimension, radius, and time delay of the delayed vectors are properly selected. The numerical results are supported by the earlier numerical studies using the permutation entropy and Kolmogorov-Sinai entropy. Furthermore, we also confirm that the SampEn shows certain robustness to the additive observational noise.

The Role of Master Laser with Feedback in Time-Delay Signature Suppression of Semiconductor Laser Subject to Chaotic Optical Injection

The important role of parameters in master laser with optical feedback for the elimination of time-delay (TD) signature in semiconductor laser subject to chaotic optical injection is investigated systemically. The experimental results show that TD signature suppressed chaotic signals can be credibly generated by increasing the feedback strength of the master laser, which is quite different from the trends observed in semiconductor laser (SL) with optical feedback. Systematically numerical analysis is also carried out as a validation, and it is shown that with low bias current and strong feedback strength, parameter regions contributing to successful TD suppression are much wider. Furthermore, it is shown that the influence of frequency detuning in TD concealment will change with the increase of feedback strength. All the numerical results are in perfect accordance with experimental observation.

Duplex chaotic message tranmission using polarization mode carriers in small networks of three chaotic vertical-cavity surface-emitting lasers

Duplex chaotic message transmission based on polarization mode carriers is investigated numerically in a small network consisting of three chaotic vertical-cavity surface-emitting lasers. The results show that, under proper conditions, two messages at the speed of a few GHz can be encoded/decoded separately and successfully. The performance of the communication is evaluated by using the well-known eye diagram and Q-factor.