We propose what we believe to be a novel approach for generating wideband chaos via intensity-modulated chaotic optical injection, utilizing chaotic signals produced by a free-running vertical-cavity surface-emitting laser. Two injection configurations are considered: parallel injection and orthogonal injection. Specifically, we examine the effect of injection parameters, including injection strength and frequency detuning, on the chaos radio frequency spectrum bandwidth. The numerical simulation confirms that intensity modulation can destroy the injection-locking state which occurs in unidirectional injection and increase the chaos bandwidth by introducing additional frequency components. For this system, the chaotic region extends over the entire parameter space having, in some cases, chaos bandwidths more than double that of free-running chaos, with a maximum bandwidth of 47.9 GHz.

The response of semiconductor nano-lasers to frequency-modulated optical injection is studied theoretically. Such frequency modulation dynamically changes the detuning between the target slave laser and the injecting master laser. A comparison is also made of the behaviour of regular semiconductor lasers when subject to frequency-modulated optical injection. It is shown that both quantitatively and qualitatively different dynamical behaviours arise as the depth and frequency of the frequency modulation are changed. Such differences are revealed in the detail of the laser power spectra. A comparison is also made of the response of regular semiconductor lasers to frequency modulated optical injection where a range of behaviours is again made apparent via the power spectra. It is indicated that there is significant scope for further investigation of the phenomena revealed here.

An analysis is performed of the response of arrays of semiconductor nano-lasers to phase-conjugate optical feedback. A comparison is made of their response to conventional mirror feedback. It is shown that phase-conjugate feedback induces a quasi-periodic route to chaos. The impact of the Purcell-enhanced spontaneous emission, which is a salient feature of nano-lasers, is also delineated for both phase-conjugate and conventional mirror feedback.

We experimentally investigate the upper bound on the generation rate for nondeterministic random bits in a delayed feedback chaotic laser system. After obtaining the random bits in the context of 1-bit quantization of the chaotic intensity, we calculate the Shannon entropy and the recovery time (the time for the growth of Shannon entropy) as the bias current and the feedback strength change. Our results show that the recovery time first decreases and then converges to a stationary value with increase of the feedback strength when we fix the bias current at its optimal value. This means there exists a highest sampling rate for nondeterministic random bit generation in the chaotic laser system. Further investigation confirms that the maximum Lyapunov exponent determine the recovery time which depends on external parameters.

We numerically investigate the dynamics of an interband cascade laser (ICL) subjected to amplitude-modulated optical injection from a directly modulated master ICL. In comparison with steady-state optical injection, the proposed modulated optical injection significantly enlarges the chaos region. In excess of 10 GHz broadband mid-infrared chaos is obtained at large bias currents and with a high gain stage number for the appropriate choice of master-slave detuning, modulation frequency, and modulation depth.

Detailed simulations have been undertaken of the dynamical response of linear and triangular arrays of nano-lasers to external optical feedback from a common external mirror. Careful attention is given to forms of dynamics that arise in such devices when experimentally accessible parameters such as the optical feedback strength, laser bias current, and external cavity length are changed - including for the latter on wavelength scales. In addition, the role played by the strength of the coupling between the nano-lasers is indicated. A salient feature of nano-lasers is the possibility of enhanced spontaneous emission via the Purcell effect and its impact on obtainable dynamics is illustrated. In general, the elements of the arrays display a combination of stable, periodic, quasi-periodic, and chaotic behaviour. Prospects for significant generalizations of the analysis undertaken here are briefly addressed.

Semiconductor nano-lasers have been actively investigated both theoretically and experimentally with to the aim of providing a highly compact laser amenable to photonic integration. Such devices are naturally suited for assembly in close-packed one- and two-dimensional arrays. In such arrangements, optical coupling between elements of the array opens opportunities to generate a range of dynamical behaviours. In this paper, we present the first theoretical treatment of the dynamics of electrically pumped nano-laser arrays. Two specific forms of such arrays are analysed in detail: a three-element linear array, and triangular arrays. The former is the basis for extensive one-dimensional arrays, whilst the latter is a building block of many possible geometric configurations of two-dimensional nanolaser arrays. Using these prototypical configurations enables the identification of novel dynamical behaviours, which may be accessed using nano-laser arrays. A distinguishing physical feature of nano-lasers is the enhancement of the spontaneous emission rate via the so-called Purcell effect. Allowing for a range of Purcell enhancement factors, the analysis focusses on the effects of experimentally controllable parameters such as the laser drive current. It is shown that the Purcell enhancement factor is critical to the availability of a range of dynamical behaviours which arise simply due to inter-element optical coupling. Two-dimensional portraits of the regimes of differing dynamics offer a convenient means for determining the dynamics which may be accessed by varying the laser drive current.

In this letter, a novel scheme to generate optical frequency combs (OFCs) using gain switched (GS) semiconductor nanolasers (SNLs) is proposed. Numerical calculations have been performed using rate equations, which include the Purcell cavity-enhanced spontaneous emission factor F and the spontaneous emission coupling factor $\beta $ . The results demonstrate that broadband OFCs (10 dB frequency span, $f_{10} >1 THz $ ) can be generated over a wide range of parameter space due to the intrinsic dynamics of the SNLs. Moreover, it is observed that f10 is associated with the effective reduction of the carrier lifetime and increases with increase of the bias current. The broadband OFCs generated in GS SNLs offers opportunities for their practical applications and notably in photonic integrated circuits.

We theoretically explore Gb/s message encryption in free space communications exploiting synchronized mid-infrared chaos from unidirectionally coupled interband cascade lasers (ICLs) with optical feedback. The achievable message encryption rate depends on the chaos bandwidth and relaxation frequency oscillation of the ICL which in turn, are determined by the bias current and the number of stages of the ICL. It is shown that message encryption rates up to 4 Gb/s may be obtained with bit error rate (BER) compatible with regular telecommunication systems requirements.

Random bit generators are critical for information security, cryptography, stochastic modeling, and simulations. Speed and scalability are key challenges faced by current physical random bit generation. Herein, we propose a massively parallel scheme for ultrafast random bit generation towards rates of order 100 terabit per second based on a single micro-ring resonator. A modulation-instability-driven chaotic comb in a micro-ring resonator enables the simultaneous generation of hundreds of independent and unbiased random bit streams. A proof-of-concept experiment demonstrates that using our method, random bit streams beyond 2 terabit per second can be successfully generated with only 7 comb lines. This bit rate can be easily enhanced by further increasing the number of comb lines used. Our approach provides a chip-scale solution to random bit generation for secure communication and high-performance computation, and offers superhigh speed and large scalability.

It is shown that a significant reduction in the threshold gain of electrically pumped semiconductor nano-lasers may be achieved in bridge-connected tandem semiconductor nano-lasers. Optimization of the design is achieved by exploring the impact of bridge length and width on the threshold gain. In addition, a detailed examination is also made of the emission patterns of the structure. It is found that a trade-off emerges between threshold gain and beam quality where multi-lobed far field emission may be associated with the lowest threshold gains.

A monolithically integrated two-section laser is presented for wideband and frequency-tunable photonic microwave generation. The laser consists of two back-to-back DFB sections forming a mutually coupled structure. By properly adjusting the bias currents of two sections, the laser can stably work at the state of period-one oscillation over a wide range of frequency detuning. Based on this, continuous and linear tuning of photonic microwave signals can be achieved. Experimental results confirm that a large tunable range from 12.45 to 80.30 GHz can be realized using this laser.

The time delay signature is a crucial secure key for chaos communication using optical feedback semiconductor lasers. Herein, we propose a single node-based photonic reservoir computing method for extracting the time delay signature of optical-feedback-induced chaos. Through drawing the phase diagram of the chaotic time series and its delayed copies, we transform the time delay signature into the shape feature of the obtained two-dimensional image. After training the optimized photonic reservoir with these two-dimensional images, we numerically demonstrate that our method can achieve an overall extraction accuracy rate of 97.3% for different optical feedback semiconductor lasers. Considering its good performance and simple configuration, we believe that this single node-based photonic reservoir computing offers a hardware-friendly solution for time delay signature extraction.

We propose and experimentally demonstrate a parallel physical random number generator (Ph-RNG) based on a single quarter-wavelength-shifted distributed feedback laser (QWS-DFB LD). Though simply connecting the two output ports of the QWS-DFB LD to form a cross-coupled perturbation, we simultaneously produce two paths of complex optical chaotic signals with a bandwidth above 10 GHz. Furthermore, a dual-channel Ph-RNG with a bit rate of order terabit per second (Tbps) is implemented by combining a multi-bit extraction method. Final results show that our generated physical random numbers can successfully pass standard benchmark tests for randomness.

"Fundamental properties of semiconductor nanowires." Contemporary Physics, ahead-of-print(ahead-of-print), pp. 1–2

We propose an image recognition approach using a single physical node based optical reservoir computing. Specifically, an optically injected semiconductor laser with self-delayed feedback is used as the reservoir. We perform a handwritten-digit recognition task by greatly increasing the number of virtual nodes in delayed feedback using outputs from multiple delay times. Final simulation results confirm that the recognition accuracy can reach 99% after systematically optimizing the reservoir hyperparameters. Due to its simple architecture, this scheme may provide a resource-efficient alternative approach to image recognition.

. Optical chaos generated by perturbing semiconductor lasers has been viewed, over recent decades, as an excellent entropy source for fast physical random bit generation (RBG) owing to its high bandwidth and large random fluctuations. However, most optical-chaos-based random bit generators perform their quantization process in the electrical domain using electrical analog-to-digital converters, so their real-time rates in a single channel are severely limited at the level of Gb/s due to the electronic bottleneck. Here, we propose and experimentally demonstrate an all-optical method for RBG where chaotic pulses are quantized into a physical random bit stream in the all-optical domain by means of a length of highly nonlinear fiber. In our proof-of-concept experiment, a 10-Gb/s random bit stream is successfully generated on-line using our method. Note that the single-channel real-time rate is limited only by the chaos bandwidth. Considering that the Kerr nonlinearity of silica fiber with an ultrafast response of few femtoseconds is exploited for composing the key part of quantizing laser chaos, this scheme thus may operate potentially at much higher real-time rates than 100 Gb/s provided that a chaotic entropy source of sufficient bandwidth is available.

We present a theoretical study of the nonlinear dynamics of a long external cavity delayed optical feedback-induced interband cascade laser (ICL). Using the modified Lang–Kobayashi equations, we numerically investigate the effects of some key parameters on the first Hopf bifurcation point of ICL with optical feedback, such as the delay time (τf), pump current (I), linewidth enhancement factor (LEF), stage number (m) and feedback strength (fext). It is found that compared with τf, I, LEF and m have a significant effect on the stability of the ICL. Additionally, our results show that an ICL with few stage numbers subjected to external cavity optical feedback is more susceptible to exhibiting chaos. The chaos bandwidth dependences on m, I and fext are investigated, and 8 GHz bandwidth mid-infrared chaos is observed.

All-optical analog-to-digital conversion is a paramount issue in modern science. How to implement real-time and ultrafast quantization to optical pulses with different intensities in an all-optical domain is a central problem. Here, we report a realtime demonstration of an all-optical quantization scheme based on slicing the supercontinuum in a nonlinear fiber. In comparison with previous schemes through off-line analysis of the power of different optical spectral components in the super continuum, this, to the best of our knowledge, is the first demonstration of such functionality online in the time domain. Moreover, the extinction ratio among the quantized outputs can exceed 10 dB, which further confirms the feasibility of the proposed quantization scheme. The current 3 bit resolution in the proof-of-principle experiment is limited by the current experimental condition, but it can be expected to be greatly enhanced through improving both the spectral width of the generated supercontinuum and the number of filtering channels used.

We present a photonic approach for fast quantum random number generation based on optically sampled amplified spontaneous emission (ASE). This approach utilizes a terahertz optical asymmetric demultiplexer to sample the ASE and then digitize the sampled optical pulses into random bits using a multi-bit parallel comparator. A proof-of-concept experiment demonstrates that 40 Gb/s random bits with verified randomness can be obtained using our method. The current generation rate is mainly limited by the bandwidth of the available ASE source.