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The emergence of π-magnetism in low-dimensional carbon-based nanostructures, such as nanographenes (NGs), has captured significant attention due to their unique properties and potential applications in spintronics and quantum technologies. Recent advancements in on-surface synthesis under ultra-high vacuum conditions have enabled the atomically precise engineering of these nanostructures, effectively overcoming the challenges posed by their inherent strong chemical reactivity. This review highlights the essential concepts and synthesis methodologies used in studying NGs. It also outlines the remarkable progress made in understanding and controlling their magnetic properties. Advanced characterization techniques, such as scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM), have been instrumental in visualizing and manipulating these nanostructures, which highlighting their critical role in the field. The review underscores the versatility of carbon-based π-magnetic materials and their potential for integration into next-generation electronic devices. It also outlines future research directions aimed at optimizing their synthesis and exploring applications in cutting-edge technologies., (© 2024 Wiley‐VCH GmbH.)

Enhancing physical layer encryption in fiber-optic networks remains a challenging yet vital task. In this Letter, we propose a simplified coherent chaotic secure optical communication scheme based on the Kramers-Kronig (KK) receiver. This scheme incorporates a semiconductor laser with a phase-conjugated optical feedback serving as a common chaotic source, and its chaotic output is directly injected into the two slave lasers arranged separately at the transmitter and receiver end to achieve high-quality synchronization of chaotic signals, with a corresponding chaotic bandwidth of 30.6 GHz. By virtue of the common-signal-induced broad chaotic synchronization, a proof-of-principle demonstration is successfully conducted. It involves the secure transmission of a 20 Gbaud 16-level quadrature amplitude modulation (16QAM) signal over a 50 km standard single-mode fiber (SSMF) link. At the receiver end, we deploy a KK receiver to reconstruct the field of the optical signal and hence enable signal compensation and recovery with offline digital signal processing (DSP). This method simplifies device requirements in the current chaotic coherent optical secure communication, offering a cost-effective mode and promising path for advancing physical layer encryption in inter-data center communications.

Time-delay reservoir computing (TDRC) represents a simplified variant of recurrent neural networks, employing a nonlinear node with a feedback mechanism to construct virtual nodes. The capabilities of TDRC can be enhanced by transitioning to a deep architecture. In this work, we propose a novel photonic deep residual TDRC (DR-TDRC) with augmented capabilities. The additional time delay added to the residual structure enables DR-TDRC superior to traditional deep structures across various benchmark tasks, especially in memory capability and almost an order of magnitude improvement in nonlinear channel equalization. Additionally, a specifically designed clipping algorithm is utilized to counteract the damage of redundant layers in deep structures, enabling the extension of the deep TDRC to dozens rather than just a few layers, with higher performance. We experimentally demonstrate the proof-of-concept with a 4-layer DR-TDRC containing 960 interrelated neurons (240 neurons per layer), based on four injection-locked distributed feedback lasers. We confirm the potential for scalable deep RC with elevated performance. Our results provide a feasible approach for expanding deep photonic computing to satisfy the boosting demand for artificial intelligence., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

The rapid advancement of photonic technologies has facilitated the development of photonic neurons that emulate neuronal functionalities akin to those observed in the human brain. Neuronal bursts frequently occur in behaviors where information is encoded and transmitted. Here, we present the demonstration of the bursting response activated by an artificial photonic neuron. This neuron utilizes a single vertical-cavity surface-emitting laser (VCSEL) and encodes multiple stimuli effectively by varying the spike count during a burst based on the polarization competition in the VCSEL. By virtue of the modulated optical injection in the VCSEL employed to trigger the spiking response, we activate bursts output in the VCSEL with a feedback structure in this scheme. The bursting response activated by the VCSEL-neuron exhibits neural signal characteristics, promising an excitation threshold and the refractory period. Significantly, this marks the inaugural implementation of a controllable integrated encoding scheme predicated on bursts within photonic neurons. There are two remarkable merits; on the one hand, the interspike interval of bursts is distinctly diminished, amounting to merely one twenty-fourth compared to that observed in optoelectronic oscillators. Moreover, the interspike period of bursts is about 70.8% shorter than the period of spikes activated by a VCSEL neuron without optical feedback. Our results may shed light on the analogy between optical and biological neurons and open the door to fast burst encoding-based optical systems with a speed several orders of magnitude faster than their biological counterparts.

Extreme events (EEs) are rare and unpredictable, as have been observed in nature. Up to now, manipulating EEs has remained a challenge. Here, we experimentally observe the enhancement of EEs in a three cascade-coupled semiconductor laser system. Specifically, a continuous-wave optical injection semiconductor laser acts as the chaotic source with rare EEs, which is subsequently injected into a second laser for increasing the number of EEs. Interestingly, we find that the number and region size of EEs can be further enhanced by sequentially injecting into a third laser, i.e., a cascade-injection structure. Our experimental observations are in good agreement with the numerical results, which indicate that EEs can be significantly enhanced in wide injection parameter space due to the cascade-injection effect. Furthermore, our simulations show that the evoluation of the regions with enhanced EEs may be associated with the noise considered.

We propose and experimentally demonstrate a photonic time-delay reservoir computing (TDRC) system with random distributed optical feedback under optical injection. To evaluate the performance, we calculate the memory ability and perform two benchmark tasks, i.e., chaotic time series prediction and nonlinear channel equalization task. Our numerical results show that the proposed TDRC has a superior performance compared with the case with conventional single optical feedback. This is attributed to the fact that the random distributed optical feedback offers multiple external cavity modes, which enhance the nonlinearity of the reservoir laser. Additionally, the experimental result also shows that our proposed TDRC scheme outperforms the computer with single optical feedback in the chaotic time series prediction task. To the best of our knowledge, our work offers a novel path to improve the performance of TDRC by introducing random distributed optical feedback.

We report on the global dynamics of a free-running vertical-cavity surface-emitting laser (VCSEL) with misalignment between the linear phase and amplitude anisotropies due to the fact that this case might occur in practice caused unintentionally by minor manufacturing variations or design, in virtue of high-resolution phase stability diagrams, where two kinds of self-similar structures are revealed. Of interest is that the Arnold tongue cascades covered by multiple distinct periodicities are discovered for the first time in several scenarios specified in the free-running VCSEL, to the best of our knowledge. Additionally, we also uncover the existence of multistability through the basin of the attraction, as well as the eyes of anti-chaos and periodicity characterized by fractal. The findings may shed new light on interesting polarization dynamics of VCSELs, and also open the possibility to detect the above-mentioned structures experimentally and develop some potential applications.

Chimera states are rich and fascinating phenomena existing in many networks, where the identical oscillators self-organize into spatially separated coexisting domains of coherent and incoherent oscillations. Here, we report these states in the large laterally coupled laser array with four different waveguiding structures, with which a variety of chimera patterns can be revealed. We present the bifurcation diagrams giving birth to them and find that the chimeras exist in the boundary of the steady state and multi-period oscillation solutions, which applies to all the prevalent waveguiding structures considered. We also find that the waveguiding structures play an important role in the chimera states, e.g., the array composed of the index antiguiding with gain-guiding has a wider chimera region compared to other waveguides considered. Additionally, the effects of the crucial parameters including the laser separation ratio, pump rate, frequency detuning, and linewidth enhancement factor on the observed phenomena are discussed. Our analysis shows that the frequency detuning between lasers and the linewidth enhancement factor affects the lifetime and pattern of chimeras. The results could guide the design of laser arrays or introduce more insight into a new understanding of the dynamical behaviors of networks., (© 2023 Author(s). Published under an exclusive license by AIP Publishing.)

We report on the occurrence of a non-quantum chiral structure in a free-running vertical-cavity surface-emitting laser (VCSEL) with a small misalignment between birefringence and dichroism. Through high-resolution phase diagrams, we show how oscillations evolve in parameter space for different values of the misalignment. Unlike a previously reported non-quantum chiral dynamic system involving closed rings in parameter space, this work manifests another case, i.e., the chiral structure exists in some open parameter spaces. Furthermore, the possible underlying physical mechanism of the emergence of the structures is offered through bifurcation analysis.

We report on the manipulation of extreme events (EEs) in a slave spin-polarized vertical-cavity surface-emitting laser (spin-VCSEL) subject to chaotic optical injection from a master spin-VCSEL. The master laser is free-running but yielding a chaotic regime with obvious EEs, while the slave laser originally (i.e., without external injection) operates in either continuous-wave (CW), period-one (P1), period-two (P2), or a chaotic state. We systematically investigate the influence of injection parameters, i.e., injection strength and frequency detuning, on the characteristics of EEs. We find that injection parameters can regularly trigger, enhance, or suppress the relative number of EEs in the slave spin-VCSEL, where the large ranges of enhanced vectorial EEs and average intensity of both vectorial and scalar EEs can be achieved with suitable parameter conditions. Moreover, with the help of two-dimensional correlation maps, we confirm that the probability of occurrence of EEs in the slave spin-VCSEL is associated with the injection locking regions, outside which enhanced relative number of EEs regions can be obtained and expanded with augmenting the complexity of the initial dynamic state of the slave spin-VCSEL.

Photonic microwave generation based on period-one (P1) dynamics of an optically pumped spin-polarized vertical-cavity surface-emitting laser (spin-VCSEL) is investigated numerically. Here, the frequency tunability of the photonic microwave generated from a free-running spin-VCSEL is demonstrated. The results show that the frequency of the photonic microwave signals can be widely tuned (from several gigahertz to hundreds of gigahertz) by changing the birefringence. Furthermore, the frequency of the photonic microwave can be modestly adjusted by introducing an axial magnetic field, although it degrades the microwave linewidth in the edge of Hopf bifurcation. To improve the quality of the photonic microwave, an optical feedback technique is employed in a spin-VCSEL. Under the scenario of single-loop feedback, the microwave linewidth is decreased by enhancing the feedback strength and/or delay time, whereas the phase noise oscillation increases with the increase of the feedback delay time. By adding the dual-loop feedback, the Vernier effect can effectively suppress the side peaks around the central frequency of P1, and simultaneously supports P1 linewidth narrowing and phase noise minimization at long times.

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.

Extreme events are observed in the spatiotemporal chaos dynamics of a three-element laterally coupled laser array. With the help of statistical and dynamical analyses, we confirm that spatiotemporal chaos induces extreme pulses that are high enough to be identified as extreme events and cannot be found in synchronization chaos. Interestingly, our results show that extreme events always preferentially appear in the middle laser as the laser separation ratio is decreased (i.e., upon increasing the coupling strength), and then in the two outer lasers. This thus reveals the importance of the middle laser in the transition between synchronization chaos and spatiotemporal chaos states. Additionally, we show the evolution of extreme events in the plane of the pump level and laser separation ratio by calculating the corresponding proportion. Our results build a relation between extreme events and the spatiotemporal dynamics, which makes it easy to understand the formation mechanism of extreme events.

Rogue waves (RWs) are extreme and rare waves that emerge unexpectedly in many natural systems and their formation mechanism and prediction have been extensively studied. Here, we numerically demonstrate the appearance of extreme events (EEs) for the first time, to the best of our knowledge, in the chaotic regimes of a two-element coupled semiconductor laser array. Based on coupled-mode theory, we characterize the occurrence of EEs by calculating the probability distribution, which confirms the RW-type feature of the intensity pulses, i.e., non-Gaussian distribution. Combining with the results of the 0-1 test for chaos, we confirm that EEs originate from deterministic nonlinearities in coupled semiconductor laser systems. We show that EEs can be predicted with a long anticipation time. Furthermore, simulation results manifest that the occurrence probability of EEs can be flexibly tuned by tailoring the coupling parameter space. With the help of two-dimension maps, the effects of key parameters, i.e., the waveguide structure and the pump level, on the formation of EEs are discussed systematically. This work provides a new platform for the research of EEs in a highly integrated structure and opens up a novel investigation field for coupled semiconductor laser arrays.

A bandwidth-enhanced linear frequency-modulated (LFM) waveform generation scheme is proposed and demonstrated based on dynamic control of an optically injected semiconductor laser (OISL). The OISL operates at the period-one (P1) oscillation state under proper injection conditions. After photodetection, a tunable microwave signal is obtained with its frequency determined by the optical injection strength and the detuning frequency between the master and slave lasers. For a fixed detuning frequency, an LFM waveform can be generated by introducing an electrical control signal S(t) with a quasi-sawtooth profile to dynamically manipulate the injection strength of the OISL. Then, to overcome the bandwidth limitation by the achievable P1 frequency range under a given detuning frequency, both the injection strength and the detuning frequency are dynamically controlled to achieve a synthesized P1 frequency range, thus generating LFM waveforms with enhanced bandwidths. In our demonstration, LFM waveforms with a synthesized bandwidth of 8 GHz (12-20 GHz) and 24.8 GHz (12.6-37.4 GHz) are generated in the experiment and simulation, respectively.

We numerically study the synchronized chaos (SC) and spatiotemporal chaos (STC) in a three-element laterally-coupled laser array in the case of four waveguiding structures. The coupled rate equations are used to analyze the dynamics of the laser array, where spatiotemporal dynamic maps are generated to identify regions of SC, STC, and non-chaos in the parameter space of interest. First, we show that the key parameters of the laser array, i.e., the laser separation ratio, pump rate, linewidth enhancement factor, and frequency detuning play important roles in the array dynamics and synchronization properties. Then we show that the laser array composed of the purely real index guiding exhibits more obvious boundaries between SC and STC in wider parameter space with respect to these composed of either the positive index guiding with gain-indexing, the pure gain guiding, or the index antiguiding with gain-guiding. Finally, we show that the proposed laser array allows for two scenarios of parallel random bit generation (PRBG) by applying the same post-processing on chaos sources based on SC and STC dynamic states. Hence, our results provide a comprehensive study on the collective dynamics in the three-element laterally-coupled laser array and pave the way for PRBG based on laser arrays.

Extreme events (EEs) are predicted for the first time, to the best of our knowledge, in the chaotic dynamics of a free-running spin-polarized vertical-cavity surface-emitting laser (spin-VCSEL). Here, we not only show two types of EEs, i.e., vectorial and scalar EEs separately corresponding to the emission of a high-power pulse in both linear polarizations (LPs) simultaneously and in single LP, but we also observe a new EE type that only occurs in total intensity. We also confirm that the observed EEs follow similar statistical distributions to conventional rogue waves. Moreover, the effects of pump power and pump ellipticity on the generation of EEs are analyzed. Finally, we compare free-running and optical feedback spin-VCSELs, which provides more insights into the study of EEs. More importantly, this work offers a novel platform for the study of EEs with a simple structure and opens up new research fields into spin-VCSELs.

We propose and numerically demonstrate a high-speed photonic reservoir computing (RC) system using a compact Fano laser (FL) with optical feedback under electrical modulation. Benefiting from its insensitivity to external feedback, an FL has a wider dynamic steady-state region compared with a conventional Fabry-Perot laser, which significantly extends the ranges of desirable RC implementation. Interestingly, we observe two separate regions of good RC performances corresponding to two scenarios of the dynamic steady state of the FL, respectively. Moreover, the robust RC performance versus the feedback phase can be achieved in one of the steady-state regions, where the laser is not destabilized for lower external reflectivity. Owing to the ultra-short photon lifetime in the FL, the information processing rate of our proposed RC system may reach 10 Gbps. More importantly, as a specific type of microscopic laser, the FL offers potential applications to RC-based integrated neuromorphic photonic systems.

An approach of continuously tunable unidirectional emission through bending a notched-elliptical polymer microdisk is proposed. The characteristics of the bending-dependent action are carefully analyzed, and the resonance wavelength for unidirectional emission can be tuned continuously through bending the device. Such a whispering-gallery-mode microresonator enables unidirectional emission with ultra-low divergence, of which the emission efficiency and Q factor are stabilized, demonstrating the whole structure is robust and relatively insensitive within a certain bending angle range. A maximum resonance wavelength shift of ∼100 nm and Q factor of 1500 can be achieved with the total size of the microdisk less than 10 μm. This kind of microresonator is promising for applications in multilevel integrated photonics circuits and may open the door to new functionalities of resonator devices, from sensing to optical amplification.

An approach to generating microwave frequency combs (MFCs) with superior performance is proposed and experimentally demonstrated based on an optically injected semiconductor laser (OISL). The OISL operates at the period-one (P1) oscillation state under proper injection conditions. A sinusoidal voltage signal is used to modulate the P1 state for the initial MFC generation, and then two optoelectronic feedback loops are introduced to enhance the performance of the MFC: a short-delay feedback loop is firstly applied to improve comb contrast based on Fourier domain mode locking (FDML), and a long-delay feedback loop is added to reduce the comb linewidth based on the self-injection-locking technique. In the proof-of-concept experiment, a K-band MFC (18-26 GHz) with a line spacing of 8.45 MHz is obtained, where a comb linewidth of approximately 500 Hz and a comb contrast over 45 dB are simultaneously achieved. Additionally, each comb component exhibits superior performance in terms of phase noise, all below -90 d B c / H z at 10 kHz offset, demonstrating an excellent coherence among these combs.

We numerically report on an optical chaos signal generation scheme based on a semiconductor laser subject to intensity-modulated (IM) optical injection. In this scheme, the characteristics of the chaos signal obtained by destabilizing period-one nonlinear dynamics are numerically investigated. With the aid of bifurcation diagrams and the 0-1 tests for chaos, the chaotic dynamics excited by continuous-wave and IM optical injection are located, and the effects of injection and modulation parameters on chaotic regions are illustrated. Moreover, effective bandwidths and auto-correlation characteristics of chaos signals from the IM optical injection system are systematically investigated. The results show that although chaotic signals under the IM optical injection scenario have a limitation in unambiguous range detection in most parameter regions, wideband chaotic dynamics in large injection and modulation parameter regions can be easily achieved. This study paves the way for potential applications requiring no time-delay signature and broad bandwidth chaos, such as high-speed chaos communications and random bit generation.

We propose and numerically demonstrate a photonic microwave generation scheme based on the dynamic period-one oscillation of a solitary spin-polarized vertical-cavity surface-emitting laser (spin-VCSEL). The evolution of the oscillation amplitude, frequency, power, and linewidth of the generated microwave is systematically investigated by using two-dimensional maps. The results show that the generated microwave signals with a dominant linewidth of about 3 MHz have a broad tunable frequency (from several gigahertz to hundreds of gigahertz), which benefits from the birefringence-induced oscillation in spin-VCSELs. Moreover, with the help of optical feedback, the microwave linewidth can be effectively minimized (∼51 k H z ) by increasing the feedback strength and feedback delay time. Importantly, this Letter offers prospects for applications requiring a feasible and resource-efficient microwave source in microwave photonic fields.

We propose and numerically demonstrate a high-speed secure key distribution (SKD) based on polarization-keying chaos synchronization in two quantum dot (QD) spin-polarized vertical-cavity surface-emitting lasers (VCSELs) without any external feedback. In this scheme, high-quality chaos synchronization can be obtained when the response lasers have the same polarization ellipticity. The proposed SKD scheme is benefited from the feasible tunability of the pump polarization ellipticity, and no other complex components are necessary. Moreover, the open-loop configuration is constructed in the commonly driven lasers and results in a short synchronization recovery time of hundreds of picoseconds, which is much shorter than that in most previous reports. Combined with these merits, a 1.34 Gb/s SKD with a bit error ratio lower than 3.8 × 10 -3 can be achieved. The current study provides a new way to realize high-speed physical key distribution.

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.

We propose an approach to generating nonlinear frequency-modulated (NLFM) microwave waveforms, which is based on controlled period-one (P1) dynamics of an optically injected semiconductor laser (OISL). When the optical injection is modulated, the OISL, which originally operates at a P1 oscillation state, acts as a microwave voltage-controlled oscillator (VCO). In the proposed system, the microwave frequency output depends closely on the optical injection strength controlled by the modulation voltage input, while the electrical modulation signal required to generate a desired NLFM microwave waveform can be calculated on the basis of the "voltage-to-frequency" transfer function of the established VCO system. Our simulations and experiments demonstrate that both single-chirp and dual-chirp NLFM microwave waveforms can be readily generated with a bandwidth up to 9 GHz. Considering peak-to-sidelobe ratio (PSLR) of the compressed pulses, the NLFM signals generated by the VCO exhibit a practical improvement of ∼13 dB when compared with LFM signals with the same bandwidth, and the tunability of the generated NLFM signals is also experimentally demonstrated.

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.

An approach to generating dual-chirp microwave waveforms (DCMWs) is proposed and experimentally demonstrated. The proposed scheme consists of a typical semiconductor slave laser (SL), which is subject to a dual-beam optical injection from two master lasers with one being positively detuned (${\rm ML}_1$ML 1 ) and the other negatively detuned (${\rm ML}_2$ML 2 ) from the SL. Under proper injection conditions, the SL operates in the so-called Scenario B of dual-beam injection. After optical-to-electrical conversion, a dual-frequency microwave signal can be generated with one of its two frequencies increasing linearly and the other decreasing linearly as the ${\rm ML}_1$ML 1 injection strength is increased. By incorporating a fast injection strength controller (formed by an intensity modulator and an electrical control signal), a DCMW with a large time-bandwidth product can be generated. In the experimental demonstration, a DCMW with a temporal period of 1 µs has been obtained. This simultaneously offers an up-chirp (13.4-20.2 GHz) and a down-chirp (27.3-20.5 GHz), and its frequency tunability has been achieved by simply adjusting the injection parameters. Furthermore, the auto-ambiguity function of the generated DCMW has also been investigated, which proves that the proposed scheme has the ability to improve the range-velocity resolution and, thus, could be promising for use in radar systems.

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.

Photonic microwave harmonic down-conversion is demonstrated using an optically injected semiconductor laser operating at period-one (P1) nonlinear dynamics. In this method, the P1 oscillation is stabilized through low-frequency local oscillator signal modulation, thus generating high-order harmonics in the optical domain. Meanwhile, a radio-frequency (RF) signal is received by an intensity modulator. After the subsequent optical heterodyning, photonic microwave harmonic down-conversion can be realized. In the proof-of-concept experiment, the 4th, 6th, 9th, and 12th harmonic down-conversions are demonstrated; i.e., an RF signal with a frequency of 39 GHz is down-converted to frequency-tunable intermediate frequency (IF) signals within 2 GHz. The resultant IF signal mainly holds the microwave linewidth and phase noise comparable to those of the original high-frequency one.

We propose and experimentally demonstrate a bidirectional radio-over-fiber (RoF) link based on a Sagnac loop incorporating a polarization modulator (PolM) to generate simultaneously a polarization-modulated optical signal and an unmodulated optical signal for wavelength reuse and for increasing the dynamic range. Thanks to the traveling-wave nature of the PolM, a polarization-modulated optical signal and an unmodulated optical signal are generated at the output of the Sagnac loop, which are combined at a polarizer and detected at a photodetector. By controlling the powers of the two optical signals, the third-order intermodulation distortion terms can be fully suppressed to increase the dynamic range for downstream transmission. The unmodulated optical signal is reused for upstream transmission. A bidirectional RoF link to transmit 2.5 Gb/s 16QAM downstream and upstream signals, and a 7.1 Gb/s 128 subcarrier orthogonal frequency division multiplexing 16QAM downstream and upstream signals using a single wavelength over a 10.5 km single-mode fiber are experimentally demonstrated. The transmission performance versus the dynamic range is also studied.

We report on the dynamics of free-running and optically injected VCSELs. In particular, the powerful measures including the 0-1 test for chaos and permutation entropy are used for locating the chaotic dynamics in a free-running VCSEL, which illustrates the effects of some key parameters on the chaotic region. In order to enhance chaotic dynamics, the output of the free-running VCSEL (master) is injected to another free-running VCSEL (slave). Our results show that the chaotic dynamics of the slave VCSEL can be greatly enhanced, i.e., both the bandwidth and complexity, while this occurs only outside of the injection locking region where the correlation between the mater and slave lasers is low. To take advantage of these enhanced chaotic dynamics exhibiting extremely high complexity and broadband bandwidth, a three-laser synchronization scheme is proposed and demonstrated. These findings pave the way to the generation of high-quality chaos (no time-delay signature, high bandwidth and complexity) and notably chaos-based applications based on free-running and optically injected VCSELs.

We consider a modified version of the spin-flip model (SFM) that describes optically pumped quantum dot (QD) spin-polarized vertical-cavity surface-emitting lasers (VCSELs). Maps showing different dynamical regions and those consisting of various key bifurcations are constructed by direct numerical simulations and a numerical path continuation technique, respectively. A comparison between them clarifies the physical mechanism that governs the underlying dynamics as well as routes to chaos in QD spin-VCSELs. Detailed numerical simulations illustrate the role played by the capture rate from wetting layer (WL) to QD ground state, the gain parameter, and the amplitude-phase coupling. By tuning the aforementioned key parameters in turn we show how the dynamical regions evolve as a function of the intensity and polarization of the optical pump, as well as in the plane of the spin relaxation rate and linear birefringence rate, which is of importance in the design of spin lasers promising potential applications. By increasing the capture rate from WL to QD our simulation accurately describes the transition from the QD spin-VCSEL to the quantum well case, in agreement with a previous mathematical derivation, and thus validates the modified SFM equations.

We study the nonlinear dynamics of solitary and optically injected two-element laser arrays with a range of waveguide structures. The analysis is performed with a detailed direct numerical simulation, where high-resolution dynamic maps are generated to identify regions of dynamic instability in the parameter space of interest. Our combined one- and two-parameter bifurcation analysis uncovers globally diverse dynamical regimes (steady-state, oscillation, and chaos) in the solitary laser arrays, which are greatly influenced by static design waveguiding structures, the amplitude-phase coupling factor of the electric field, i.e. the linewidth-enhancement factor, as well as the control parameter, e.g. the pump rate. When external optical injection is introduced to one element of the arrays, we show that the whole system can be either injection-locked simultaneously or display rich, different dynamics outside the locking region. The effect of optical injection is to significantly modify the nature and the regions of nonlinear dynamics from those found in the solitary case. We also show similarities and differences (asymmetry) between the oscillation amplitude of the two elements of the array in specific well-defined regions, which hold for all the waveguiding structures considered. Our findings pave the way to a better understanding of dynamic instability in large arrays of lasers.

We report here for the first time (to our knowledge), a new and universal mechanism by which a two-element laser array is locked to external optical injection and admits stably injection-locked states within a nontrivial trapezoidal region. The rate equations for the system are studied both analytically and numerically. We derive a simple mathematical expression for the locking conditions, which reveals that two parallel saddle-node bifurcation branches, not reported for conventional single lasers subject to optical injection, delimit the injection locking range and its width. Important parameters are the linewidth enhancement factor, the laser separation, and the frequency offset between the two laterally-coupled lasers; the influence of these parameters on locking conditions is explored comprehensively. Our analytic approximations are validated numerically by using a path continuation technique as well as direct numerical integration of the rate equations. More importantly, our results are not restricted by waveguiding structures and uncover a generic locking behavior in the lateral arrays in the presence of injection.

We report on a master and slave configuration consisting of two optically pumped spin-vertical-cavity surface-emitting lasers for chaos synchronization and secure communication. Under appropriate conditions, high-quality chaos synchronization is achieved. We propose two encryption schemes, where either the pump magnitude or polarization is modulated. The results show that these allow for Gb/s transmission of secure data, but exhibit different features: one indicates that the message can be recovered by the total intensity, but not the polarization components, whereas the other shows that the message can be better or exclusively retrieved from the polarization components at high bit rates.

Sustained, large amplitude and tunable birefringence-induced oscillations are obtained in a spin-vertical cavity surface-emitting laser (spin-VCSEL). Experimental evidence is provided using a spin-VCSEL operating at 1300 nm, under continuous-wave optical pumping and at room temperature. Numerical and stability analyses are performed to interpret the experiments and to identify the combined effects of pump ellipticity, spin relaxation rate, and cavity birefringence. Importantly, the frequency of the induced oscillations is determined by the device's birefringence rate, which can be tuned to very large values. This opens the path for ultrafast spin-lasers operating at record frequencies exceeding those possible in traditional semiconductor lasers and with ample expected impact in disparate disciplines (e.g., datacomms, spectroscopy).

The concealment of the time-delay signature (TDS) of chaotic external-cavity lasers is necessary to ensure the security of optical chaos-based cryptosystems. We show that this signature can be removed simply by optically injecting an external-cavity laser with a large linewidth-enhancement factor into a second, noninjection-locked, semiconductor laser. Concealment is ensured both in the amplitude and in the phase of the optical field, satisfying a sought-after property of optical chaos-based communications. Meanwhile, enhancement of the dynamical complexity, characterized by permutation entropy, coincides with strong TDS suppression over a wide range of parameters, the area for which depends sensitively on the linewidth-enhancement factor.

The output characteristics of a fiber optic parametric oscillator (FOPO) based on multiple four-wave mixing (multi-FWM) processes are investigated numerically and demonstrated experimentally. The theoretical model of a FOPO based on multi-FWM processes is presented. It is proved that the output signal starts to saturate when the high-order parametric products are generated in the multi-FWM processes of FOPOs. Moreover, a higher output power of the idler (i.e., the first-order parametric product) is achieved. On the other hand, the pump power is proved to be a key factor that significantly influences the output of the FOPO.

Optical chaos generated by chaotic lasers has been widely used in several important applications, such as chaos-based communications and high-speed random-number generators. However, these applications are susceptible to degradation by the presence of time-delay (TD) signature identified from the chaotic output. Here we propose to achieve the concealment of TD signature, along with the enhancement of chaos bandwidth, in three-cascaded vertical-cavity surface-emitting lasers (VCSELs). The cascaded system is composed of an external-cavity master VCSEL, a solitary intermediate VCSEL, and a solitary slave VCSEL. Through mapping the evolutions of TD signature and chaos bandwidth in the parameter space of the injection strength and frequency detuning, photonic generation of polarization-resolved wideband chaos with TD concealment is numerically demonstrated for wide regions of the injection parameters.

A novel electrochemical lab-on-paper cyto-device (ELPCD) was fabricated to demonstrate sensitive and specific cancer cell detection as well as in-situ monitoring of multi-glycans on living cancer cells. In this ELPCD, aptamers modified three-dimensional macroporous Au-paper electrode (Au-PE) was employed as the working electrode for specific and efficient cancer cell capture. Using a sandwich format, sensitive and reproducible cell detection was achieved in this ELPCD on the basis of the electrochemical signal amplification of the Au-PE and the horseradish peroxidase-lectin electrochemical probe. The ELPCD displayed excellent analytical performance for the detection of four K562 cells with a wide linear calibration range from 550 to 2.0×10(7) cells mL(-1). Then, this ELPCD was successfully applied to determine cell-surface multi-glycans in parallel and in-situ monitor multi-glycans expression on living cells in response to drug treatment through in-electrode 3D cell culture. The proposed method provides promising application in decipherment of the glycomic codes as well as clinical diagnosis and treatment in early process of cancer., (Copyright © 2014 Elsevier B.V. All rights reserved.)

In this work, using human acute promyelocytic leukemia cells (HL-60) as a model, a novel microfluidic paper-based electrochemical cyto-device (μ-PECD) was fabricated to demonstrate a facile, portable, and disposable approach for cancer cell detection and in situ screening of anticancer drugs in a high-throughput manner. In this μ-PECD, aptamers modified three-dimensional macroporous Au-paper electrode (Au-PE) was fabricated and employed as the working electrode for specific and efficient cancer cell capture as well as for sequential in-electrode 3D cell culture. This Au-PE showed enhanced capture capacity for cancer cells and good biocompatibility for preserving the activity of captured living cells. Sensitive cancer cell detection was achieved in this μ-PECD, which could respond down to four HL-60 cells in 10 μL volume with a wide linear calibration range from 5.0×10(2) to 7.5×10(7) cells mL(-1) and exhibited good stability and reproducibility. Then, in situ anticancer drug screening was successfully implemented in this μ-PECD through monitoring of the apoptotic cancer cells after the in-electrode 3D cell culture with drug-containing culture medium, demonstrating its wide range of potential applications to facilitate effective clinical cancer diagnosis and treatment., (Copyright © 2014 Elsevier B.V. All rights reserved.)

We study experimentally and theoretically the first- and second-order statistics of the optical intensity of a chaotic external-cavity semiconductor DFB laser in fully developed coherence-collapse. The second-order statistic is characterized by the autocorrelation, where we achieve consistent experimental and theoretical results over the entire parameter range considered. For the first-order statistic, we find that the experimental probability-density function is significantly more concentrated around the mean optical power and robust to parameter changes than theory predicts.

In this work, a microfluidic paper-based analytical device was further exploited by coupling with an electrophoretic separation technique for the first time. A low-cost, simple, portable, and disposable microfluidic paper-based electrophoretic device with an on-column wireless electro-generated chemiluminescence detector was demonstrated.

This paper reports the experimental investigation of two different approaches to random bit generation based on the chaotic dynamics of a semiconductor laser with optical feedback. By computing high-order finite differences of the chaotic laser intensity time series, we obtain time series with symmetric statistical distributions that are more conducive to ultrafast random bit generation. The first approach is guided by information-theoretic considerations and could potentially reach random bit generation rates as high as 160 Gb/s by extracting 4 bits per sample. The second approach is based on pragmatic considerations and could lead to rates of 2.2 Tb/s by extracting 55 bits per sample. The randomness of the bit sequences obtained from the two approaches is tested against three standard randomness tests (ENT, Diehard, and NIST tests), as well as by calculating the statistical bias and the serial correlation coefficients on longer sequences of random bits than those used in the standard tests.

This Letter is the first to report experimental bifurcation diagrams of an external-cavity semiconductor laser (ECSL) in the low-to-moderate current injection regime and long-cavity case. Based on the bifurcation cascade behavior which was unveiled by Hohl and Gavrielides [Phys. Rev. Lett. 82, 1148-1151 (1999)], we present a detailed experimental investigation of the nonlinear dynamics of ECSLs and of the robustness of the cascade to changes in the current and cavity length. Also, we report for the first time a well resolved experimental Hopf bifurcation in an ECSL. Based on the Lang and Kobayashi model, we identify the dynamical regimes and the instabilities involved in the cascade, as well as the influence of the current and cavity length on the cascade.

The sequence-specific detection of DNA hybridization has attracted considerable interest in numerous fields. Although traditional DNA biosensors have been widely explored due to their high sensitivity, it is still challenging to develop a low-cost, portable, disposable, fast, and easy-to-use DNA detection method for public use at home or in the field. To address these challenges, herein, we report a novel microfluidic photoelectrochemical (PEC) paper-based analytical platform, integrated with an internal chemiluminescent light source, a novel paper supercapacitor (PS) amplifier, and a terminal digital multi-meter (DMM) detector, for sensitive DNA detection using a graphene-modified porous Au-paper electrode as the working electrode to obtain enhanced PEC responses. The quantification mechanism of this strategy is based on the charging of this PS, which was constructed on a paper-based analytical platform through a simple "drawing and soaking" method, by the generated photocurrent. After a fixed period, the PS was automatically shorted under the control of a novel built-in fluidic delay-switch to output an instantaneously amplified current, which could be sensitively detected by the DMM. At optimal conditions, this paper-based analytical platform can detect DNA at concentrations at femtomolar level. This approach also shows excellent specificity toward single nucleotide mismatches.

In this work, a photoelectrochemical (PEC) method was introduced into a microfluidic paper-based analytical device (μ-PAD), and thus, a truly low-cost, simple, portable, and disposable microfluidic PEC origami device (μ-PECOD) with an internal chemiluminescence light source and external digital multimeter (DMM) was demonstrated. The PEC responses of this μ-PECOD were investigated, and the enhancements of photocurrents in μ-PECOD were observed under both external and internal light sources compared with that on a traditional flat electrode counterpart. As a further amplification of the generated photocurrents, an all-solid-state paper supercapacitor was constructed and integrated into the μ-PECOD to collect and store the generated photocurrents. The stored electrical energy could be released instantaneously through the DMM to obtain an amplified (∼13-fold) and DMM-detectable current as well as a higher sensitivity than the direct photocurrent measurement, allowing the expensive and sophisticated electrochemical workstation or lock-in amplifier to be abandoned. As a model, sandwich adenosine triphosphate (ATP)-binding aptamers were taken as molecular reorganization elements on this μ-PECOD for the sensitive determination of ATP in human serum samples in the linear range from 1.0 pM to 1.0 nM with a detection limit of 0.2 pM. The specificity, reproducibility, and stability of this μ-PECOD were also investigated.

Convenient sensor array for simultaneous multi-analyte testing was increasingly needed in clinical diagnosis. A novel electrochemiluminescence (ECL) immunosensor array for the sequential detection of multiple tumor markers was developed by site-selectively immobilizing multiple antigens on different electrodes. Disposable indium tin oxide (ITO) glass array was employed as detection platform. With a sandwich-type immunoassay format, the amount of carbon dots coated silica (SiO(2)@C-dots) labeled antibodies increased with the increment of antigens in the samples. The ECL signal from different immunosensors was collected in turn by a photomultiplier (PMT) with the aid of a home-made potential transformer equiped with a home-made multiplexed-switch. Using carcino embryonic antigen (CEA), prostate specific antigen (PSA) and α-fetoprotein (α-AFP) as model analytes, the proposed immunoassay exhibited excellent precision and sensitivity. For all three analytes, the relative standard deviations (RSDs) for six times detection were lower than 7.1% and the detection limits were in the range of 0.003-0.006 ng mL(-1). The results for real sample analysis demonstrated that the newly constructed immunosensor array provided a rapid, simple, simultaneous multi-analyte immunoassay with high throughput, cost-effective and sufficiently low detection limits for clinical applications. Importantly, the novel individually addressable immunosensor array for multi-analyte immunoassay by introducing the ECL readout mechanism with the aid of the home-made potential transformer and multiplexed-switch could be a useful supplement to commercial assay methods in clinical chemistry., (Copyright © 2012. Published by Elsevier B.V.)

We report on the realization of a hybrid chaos-based communication scheme using three chaotic semiconductor ring lasers (SRLs). In this scheme, two slave SRLs (S-SRLs) are identically driven by a master SRL (M-SRL) subject to delayed optical feedback. Under proper conditions, the S-SRLs are completely synchronized with each other due to the symmetric operation, and they are also synchronized with the M-SRL through the injection-locking effect. The results also show that a message encrypted through chaos shift keying at the M-SRL end can be successfully decrypted by the two S-SRLs, while the two uncoupled S-SRLs allow for dual-channel chaos communication when both counterpropagating modes of one S-SRL are encoded with a message.

A potential-resolution strategy for multiplex electrochemiluminescence (ECL) immunoassay on a microfluidic paper-based analytical device (μ-PAD) was demonstrated for the first time, using tris-(bipyridine)-ruthenium(ii) (Ru(bpy)(3)(2+)) and carbon nanodots (CNDs) as the ECL labels for high-throughput ECL immunoassay on μ-PAD. Based on this strategy, simultaneous detection of four tumor markers using only two screen-printed carbon working electrodes (one electrode for two analytes) on an immunodevice consisting of a piece of patterned paper (denoted as μ-PECLI in this work) was realized, which is a simplification of the configuration of traditional μ-PADs. As a further development of μ-PECLI in low-cost and disposable applications, battery-triggered (constant-potential) ECL detection on μ-PECLI was developed, allowing the traditional electrochemical workstation to be abandoned. In addition, to exactly control the output voltage of the battery, a low-cost and simple voltage-controller was designed and fabricated for the first time. The battery-triggered ECL immunoassay principle on μ-PECLI is explained. We found that the simultaneous determination of two analytes in one paper working zone could be achieved by controlling the operational constant-potential (+1.2 V for Ru(bpy)(3)(2+) labels and -1.2 V for CNDs labels (vs. Ag/AgCl auxiliary electrode)) by simply reversing the connection mode. Finally, four tumor markers in human serum samples from the Tumor Hospital were assayed and the results obtained were in acceptable agreement with the reference values from parallel single-analyte test. This battery-triggered μ-PECLI provides a new strategy for high-throughput, low-cost, sensitive, automated and simultaneous multiplex immunoassay and point-of-care diagnosis.