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We proposed a new reservoir computation (RC) structure using polarization dynamics of vertical cavity surface emitting lasers (VCSELs) with optoelectronic feedback. Santa-Fe time-series prediction and nonlinear channel equalization were used to evaluate its parallel processing capability. We numerically discussed the effects of feedback strength, injection strength, frequency detuning, injection current and scaling factors on the RC performance of the system. The results show that, the operation range of negative feedback is larger than that of positive feedback; under appropriate feedback and lager injection strengths, good RC performance can be achieved for a wider injection current; with continuous variation of feedback strength from negative to positive values, the optimized location for frequency detuning moves from positive to negative values. We also evaluated the processing rate of proposed RC structure. The related study is helpful for the design and optimization of VCSEL-based RC under optoelectronic feedback. [ABSTRACT FROM AUTHOR]

Analog photonic computing has been proposed and tested in recent years as an alternative approach for data recovery in fiber transmission systems. Photonic reservoir computing, performing nonlinear transformations of the transmitted signals and exhibiting internal fading memory, has been found advantageous for this kind of processing. In this work, we show that the effectiveness of the internal fading memory depends significantly on the properties of the signal to be processed. Specifically, we demonstrate two experimental photonic post-processing schemes for a 56 GBaud PAM-4 experimental transmission system, with 100 km uncompensated standard single-mode fiber and direct detection. We show that, for transmission systems with significant chromatic dispersion, the contribution of a photonic reservoir's fading memory to the computational performance is limited. In a comparison between the data recovery performances between a reservoir computing and an extreme learning machine fiber-based configuration, we find that both offer equivalent data recovery. The extreme learning machine approach eliminates the necessity of external recurrent connectivity, which simplifies the system and increases the computation speed. Above 31 dB OSNR, the photonics-based equalization exhibits a lower BER than the respective offline DSP-based KK receiver. [ABSTRACT FROM AUTHOR]

This work presents a design of a flip-flop controlled by the nonlinear optical response exhibited by a dynamic distribution of nanostructures in a liquid. Silver decorated carbon nanotubes suspended in ethanol were employed. The flip-flop proposed corresponds to a probabilistic NAND latch. The nonlinear nanofluids were studied by two-wave mixing experiments with nanosecond pulses at 532 nm wavelength. The behavior of the system is based on the Brownian motion with influence over the nonlinear transmittance of the nanostructures associated with a probabilistic optical bit. The optical response of the latch system output states was defined by the irradiance dependent on nonlinear optical absorption of the nanofluid. Specifically, the optical logical outputs depend on the state present at the optical inputs and the previous optical output states regulated by the feedback of the system. The nonlinear optical evolution of the effects in the nanofluids was explored as probabilistic phenomena governed by a concentration gradient of nanoparticles. The evaluation of the stability of a nanofluid defines the variables in the probabilistic system proposed. This work highlights the potential of nanohybrid materials for processing probabilistic functions, switching quantum effects, and for developing optical sensors. • An all-optical flip-flop based on probabilistic phenomena and nonlinear effects was designed. • Third-order optical nonlinearities were induced in concentration gradients of suspended nanoparticles. • Plasmonic carbon/metal-based nanofluids were explored by a nanosecond two-wave mixing. • Optical feedback was proposed for encryption and multi-criteria logic functions. [ABSTRACT FROM AUTHOR]

Practical aerial swarm applications are limited by the need to provide fast, robust feedback. To consider how biological agents incorporate visual feedback in multiagent environments, this study extends a well-developed model of bioinspired visual feedback for individual agent to feedback in multiagent dynamic environments. A multiagent visual model is developed and analyzed for an individual agent operating in a group of other agents. The theoretical model indicates a stable equilibrium trajectory within the neighboring agents. When a minority of agents conducting bioinspired visual feedback are introduced into a planar swarm simulation, results show robustness of agents to perturbations from reference condition. The bioinspired feedback rule is implemented experimentally using ground microbots for two cases identified by a theoretical observability condition. The experimental performance of the single agent in an established swarm is consistent with the theoretical stability and observability predictions. The results indicate insect visuomotor response can help participate in established swarms, and indicate the importance of optic flow input in maintaining group motion. [ABSTRACT FROM AUTHOR]

In recent years, various methods, architectures, and implementations have been proposed to realize hardware-based reservoir computing (RC) for a range of classification and prediction tasks. Here we compare two photonic platforms that owe their computational nonlinearity to an optically injected semiconductor laser and to the optical transmission function of a Mach-Zehnder modulator, respectively. We numerically compare these platforms in a delay-based reservoir computing framework, in particular exploring their ability to perform equalization tasks on nonlinearly distorted signals at the output of a fiber-optic transmission line. Although the non-linear processing provided by the two systems is different, both produce a substantial reduction of the bit-error-rate (BER) for such signals of up to several orders of magnitude. We show that the obtained equalization performance depends significantly on the operating conditions of the physical systems, the size of the reservoir and the output layer training method. [ABSTRACT FROM AUTHOR]

Reservoir computing is a neuromorphic computing scheme inspired by the human brain. It has found great success as a versatile hardware-compatible application of machine learning concepts. In this paper, we highlight the fundamental working principles and important characteristics of reservoir computing with a particular focus on photonic systems and networks. These systems can further be enhanced by the inclusion of delayed variables to produce complex spatiotemporally mixed “time-multiplexed” networks. We use a simple nonlinear oscillator model, that is not only applicable to lasers, but can also describe a variety of other oscillating systems. [ABSTRACT FROM AUTHOR]

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This study investigates chaotic and spiking dynamics of mid-infrared quantum cascade lasers operating under external optical feedback and emitting at 5.5 $\mu {\text{m}}$ and 9 $\mu {\text{m}}$. In order to deepen the understanding, the route to chaos is experimentally studied in the case of continuous-wave and current modulation operation. The non-linear dynamics are analyzed with bifurcation diagrams. While for quasi-continuous wave operation, chaos is found to be more complex, pure continuous wave pumping always leads to the generation of a regular spiking induced low-frequency fluctuations dynamics. In the latter, results show that by combining external optical feedback with periodic forcing and further induced current modulation allows a better control of the chaotic dropouts. This work provides a novel insight into the development of future secure free-space communications based on quantum cascade lasers or unpredictable optical countermeasure systems operating within the two transparency atmospheric windows hence between 3 $\mu {\text{m}}$ –5 $\mu {\text{m}}$ and 8.5  $\mu {\text{m}}$ –11 $\mu {\text{m}}$. [ABSTRACT FROM AUTHOR]

We have demonstrated that the bifurcation patterns can generate by the double Panda‐ring resonator system, where the first system is configured as the input source, while the second system is the feedback control systems. The key concept of the proposal is the two nonlinear side ring resonators that can induce the nonlinear Kerr effect into the center ring. The feedback signals generated from the second ring will induce into the first Panda‐ring, from which the required bifurcation behaviors are obtained. By adjusting the suitable parameters, the simulation results obtained have shown that there are the various exciting bifurcation behaviors in both systems that can be used for the applications such as textile pattern design, information security, and biosensors. [ABSTRACT FROM AUTHOR]

We present the design and numerical study of a nonlinear equalizer for optical communications based on silicon photonics and reservoir computing. The proposed equalizer leverages the optical information processing capabilities of integrated photonic reservoirs to combat distortions both in metro links of a few hundred kilometers and in high-speed short-reach intensity-modulation-direct-detection links. We show nonlinear compensation in unrepeated metro links of up to 200 km that outperform electrical feedforward equalizers based equalizers, and ultimately any linear compensation device. For a high-speed short-reach 40-Gb/s link based on a distributed feedback laser and an electroabsorptive modulator, and considering a hard decision forward error correction limit of $0.2 \times 10^{-2}$ , we can increase the reach by almost 10 km. Our equalizer is compact (only 16 nodes) and operates in the optical domain without the need for complex electronic DSP, meaning its performance is not bandwidth constrained. The approach is, therefore, a viable candidate even for equalization techniques far beyond 100G optical communication links. [ABSTRACT FROM AUTHOR]

In this paper, a novel electro-optic feedback phase chaotic system based on nonlinear coupling of two delayed interfering branches is proposed and analyzed by numerical simulation. The feedback loop of the proposed system contains two delay branches and a Mach–Zehnder modulator. The chaotic voltages generated from two branches are nonlinearly converted in order to reduce their temporal correlations. The dynamic characteristics and the complexity of the generated chaotic signal are evaluated by the bifurcation diagram and permutation entropy, respectively. Besides, the simulated results show that the time-delay signature can be concealed effectively with a lower feedback gain, meanwhile the key space is extended considerably since more tunable parameters are nonlinearly coupled, thus the security can be improved greatly. Furthermore, the communication system based on the proposed scheme is discussed, and the results demonstrate that this system can be applied in secure communication. [ABSTRACT FROM AUTHOR]

The behavior of a sampling optical phase-locked loop (OPLL) is analyzed. An equivalent time invariant system model for the sampling OPLL was derived. With the help of the model, the stability of a sampling OPLL was found to depend not only on the sampling frequency but also on the duty cycle of the sampling pulse. In addition, the closed-form solutions for the sampling OPLL output noise and nonlinear distortions were also derived. The theoretical results were validated by numeric simulations. [ABSTRACT FROM AUTHOR]

In this paper, we describe a generalized visible light communication (VLC) channel, which consists of the frequency responses of the light emitting diode (LED), the wireless optical channel, and the photo detector (PD). Based on the theoretical analysis of the generalized VLC channel, we found the response mask invariant characteristic (RMIC) under the condition of strong line of sight components, which means the shape of frequency response of generalized VLC channel is time-independent and invariant at different distances of the transceivers, different emitting angles of the LED and different incident angles of the PD. Depending on the RMIC, the shapes of received spectrum and signal-to-noise rate are also invariant. The experimental platform was set up to verify the proposed RMIC. Furthermore, a predefined VLC system with a new channel feedback method is described, both the complexity and time cost of feedback can greatly reduce through the proposed channel feedback method. [ABSTRACT FROM AUTHOR]

Optical feedback originating from the interfaces of the periodically poled domains of a nonlinear crystal is usually blocked by a bulky optical isolator to avoid an influence on the pump source. Here, a nonlinear bulk crystal with a slanted design of the periodic poling is used to suppress the optical feedback toward the laser source. This crystal is compared with a conventionally poled crystal, in which the incident radiation propagates perpendicular to the domains. Both crystals are made of magnesium oxide doped congruent lithium niobate (PPMgO:CLN). A distributed Bragg reflector tapered diode lasers with a maximum optical power of 7.0 W at a wavelength of 1122 nm and each nonlinear crystal are employed in a single-pass setup. In comparison with the conventional crystal, the optical feedback of the crystal with slanted domains is reduced by 13.4 dB enabling a stable narrow-band operation of the pump laser source without an optical isolator. The impact of the optical feedback on the diode laser with respect to the optical output power and the spectral behavior is investigated. For the crystal with slanted domains, a frequency doubled output power up to 0.39 W at 561 nm is generated without reaching the coherence collapse regime, as observed in case of the conventional crystal. These results are promising for miniaturization of the setup without a need for a bulky optical isolator. [ABSTRACT FROM PUBLISHER]

Laser diodes with optical feedback can exhibit periodic intensity oscillations at or near the relaxation-oscillation frequency. We demonstrate optoelectronic oscillators based on external-cavity semiconductor lasers in a periodic dynamical regime tunable over the entire $X$ -band. Moreover, unlike standard optoelectronic oscillators, we need not employ the time-dependent optical intensity incident on a photodiode to generate the microwave signal, but rather have the option of generating the electrical microwave signal directly as a voltage V(t)$ at the laser-diode injection terminals under constant current operation; no photodiode need be involved, thus circumventing optical-to-electrical conversion. We achieve a timing jitter of \lesssim 10$ ps and a quality factor of across the entire $X$ -band, that ranges from 6.79 to 11.48 GHz. Tuning is achieved by varying the injection current $J$ . [ABSTRACT FROM AUTHOR]

It has been an important research subject to find new nonlinear optical phenomena. In this paper, we report the experimental observation of stochastic, periodic, and localized light structures in a super long single-mode standard fiber with external optical feedback provided by the fiber end. The end facet reflection provides an analogous Fabry-Perot stimulated Brillouin resonator cavity. By increasing the pump power to exceed stimulated Brillouin scattering threshold, we observed light structures exhibiting extremely rich temporal-pulse characteristics that had never been reported in literature before, including supercontinuum background generation, the localization of periodic optical structure formation, fission, and compression. These optical structures are of period-doubling distribution and have different recurrence rates. What is more interesting is that we have observed sets of low frequency bipolar cycle-pulse trains that is often seen in the electrical field and hardly seen in pure optical system. Real-time specification of dynamical temporal regimes of laser operation may bring new insight into rich underlying nonlinear physics of practical fiber cavity systems. Therefore, some new nonlinear optical phenomena have been observed. [ABSTRACT FROM AUTHOR]

We present a single stack active region design for terahertz emission by difference frequency generation in quantum cascade lasers. The active region contains a single design, which is based on multiple optical transitions within one period. This results in both a giant nonlinearity and an ultra-broad optical gain. The provided optical gain spectrum is broad enough to support two distinct mid-infrared modes with a significant spectral separation. For dual-emission, the waveguide contains a buried, index-coupled distributed feedback grating. This grating is based on a sampled approach to provide selective feedback for two mid-infrared modes at λ1=8.39  μm and $\lambda _{{\text{2 }}}= {\text{9.38}}\, \mu {\text{m}} . Simultaneously, the manifold of possible transitions within the active region is designed to provide a peak nonlinear susceptibility of \vert \chi ^(2)\rm\vert \, \,= \,\, \text29 nm \textV^- 1 at the conversion to 3.8 THz. The device emits up to 210-μW THz power at room temperature with a nonlinear conversion efficiency of \eta =\text 2.05 mW \textW^- 2. [ABSTRACT FROM PUBLISHER]

We present an optically coupled chaotic system involving three-phase modulated electro-optic nonlinear loops and an optical coupler. The dynamical properties and the time delay signature (TDS) suppressing performance of the system is analyzed in detail. Numerical results show that the TDS can be suppressed not only under statistical analysis of a single output, but also under mutual statistical analysis of the multiple outputs. Compared with the intensity modulated electrically coupled scheme, the presented system has less interior noise due to the simpler construction. [ABSTRACT FROM PUBLISHER]

A novel microwave photonic filter (MPF) based on carrier-suppressed single sideband (CS-SSB) injected distributed feedback (DFB) laser is proposed. The proposed MPF system exploits the frequency selective gain feature of optical injected DFB lasers, which can be tuned by adjusting the optical injection parameters or the working conditions of the laser. Therefore, the proposed MPF system can be tunable. The proposed system is verified by a proof-of-concept experiment, and the results show that the passband of the proposed MPF can be tuned by tuning the injection ratio and bias current of the slave laser, where the tuning range of 9–39 GHz is realized. At the same time, the out-of-band rejection of the proposed MPF can reach to 32 dB. Moreover, a dual-passband MPF response is also realized by the proposed system with a couple of master lasers, and the two passbands can be tuned independently from 10 to 39 GHz. [ABSTRACT FROM PUBLISHER]

Optical feedback due to mutual relation between local field effect and intersubband transition in quantum dots is investigated for the first time. In this regard, dielectric function of quantum dots is considered up to the third order of nonlinearity. It is found that near the resonance, the intensity inside the dot is a function of frequency, which is determined by the optical feedback. This effect changes the magnitude of optical nonlinearity and its symmetry around the transition energy. The results indicate that the magnitude of the dielectric function decreases at frequencies below the transition frequency because of concentration of electric field inside the dot and vice versa. It is also shown that this effect is enhanced by increasing the intensity and resonance contribution in the dielectric function. [ABSTRACT FROM AUTHOR]

An optoelectronic feedback reservoir computing (RC) system that can identify optical packet headers for an optical packet switching (OPS) network is proposed and implemented by the numerical simulation and the experiment in this paper. First, a simulation system of optical packet header recognition based on the optoelectronic feedback RC is established through optimizing its parameters. It is shown that the optoelectronic feedback RC system can correctly identify optical packet headers with lengths from 3 bits to 32 bits and that the recognition word-error rate (WER) is 0. Then, an experiment system consistent with the optimal simulation system is set up, whose WER for the 3-bit header recognition is only 1.25%. The experimental results also indicate that the bias voltage of the Mach–Zehnder modulator (MZM) has a significant impact on recognition results. When the RC system is in the critical state between the multiple-period oscillation and the chaos, the maximal Lyapunov exponent is slightly larger than 0, and the recognition normalized root-mean-square error (NRMSE) reaches its minimal value. [ABSTRACT FROM PUBLISHER]

We report the optical bistability in two core oppositely directed coupler with negative index material channel. Using Langrangian variational method and Jacobi elliptic functions, we construct the solutions of the coupled nonlinear Schrödinger equations. The bistability arises due to the effective feedback mechanism as a result of opposite directionality of the phase velocity and energy flow in the negative index material channel. We report the various ways to control and manipulate the bistability threshold and hysteresis loop, which could be useful in the design and development of fast and low-threshold optical switches. [ABSTRACT FROM PUBLISHER]

The response of nanolasers subject to optical injection has been analyzed. Calculations have been performed using rate equations, which include the Purcell cavity-enhanced spontaneous emission factor $F$ and the spontaneous emission coupling factor $\beta $ . In the analysis, the influence of $F$ and $\beta $ is evaluated for varying the injection strength and frequency detuning between the master and slave laser. It is observed that, in general, increased $F$ and $\beta $ increases the stable locking region and have only a few regions of dynamic instability as compared with conventional semiconductor lasers over a large frequency detuning. It is also found that for larger $F$ , the modulation bandwidths of 90 GHz can be achieved. [ABSTRACT FROM AUTHOR]

We present a theoretical and experimental study of the most simple autonomous optoelectronic oscillator (OEO) with a delayed feedback loop. Contrarily to the overwhelming majority of OEOs, our OEO does not use an external intensity- or phase-modulator to translate the electrical radio-frequency signal into the optical domain. Instead, we show that the electric signal can simply be used as a driving pump current of the laser that is seeding the oscillator. With this architecture, the intensity modulation is performed through the piecewise-linear (that is, nonlinear) power-intensity transfer function of the laser-diode, instead of the sinusoidal transfer function of the usual Mach–Zehnder modulators. We provide a model to investigate the dynamics of this simple architecture of OEO. This model is an integro-differential delay equation which is characterized by three timescales as in the conventional OEO, namely the low/high-cutoff frequencies of the wideband filter and the time delay. The stability analysis of our OEO reveals a complex bifurcation behavior which critically depends on the gain of the feedback loop. In particular, we show that a sequence of Hopf bifurcations may lead to fast-scale oscillations with a period which is the double of the time-delay, or to slow-scale oscillations with a period which depends on the three aforementioned timescales. Our theoretical results are shown to be in excellent agreement with numerical simulations and the experimental measurements. [ABSTRACT FROM PUBLISHER]

Optical codes with large cardinality and tree structure of multiple levels of subsets of codewords for adjustable performance and cardinality have recently been studied. These codes support contemporary applications, such as a scalable, multihop, multilevel network architecture with rapid code-switching/dropping and multicode-keying encryption for improving physical-layer confidentiality in optical code-division multiple-access systems and networks. In this paper, to further enlarge such code collection, two new families of optical codes are constructed from the rich families of cyclic maximal-distance-separable (MDS) codes. The code performances are algebraically analyzed using both the distance and weight distributions of the MDS codes and validated with computer simulation. [ABSTRACT FROM PUBLISHER]

In a long-haul optical fiber communication system, fiber attenuation, dispersion, and nonlinearity combined with nondeterministic noise from optical amplifiers used for periodic regeneration cause adverse effects on system performance. Several optical and electrical signal processing techniques have been proposed, and implemented to extract the transmitted data; some provide better performance than others, but at a cost of higher computational complexity. We present a modified nonlinear decision feedback equalizer designed for use in a legacy optical communication system with periodic dispersion compensation. The effects of noise and nonlinearity on the equalizer coefficients are investigated, and a suboptimal convergence algorithm to reduce such effects is proposed and verified. Our equalizer provides performance comparable to that obtained using digital backpropagation, while being computationally simpler, compensating linear and nonlinear physical impairment effects effectively even at high power levels where fiber nonlinearity is significant. Performance prediction of the designed DFE is also discussed, using a numerical method, with and without error propagation. [ABSTRACT FROM PUBLISHER]

A scheme to enhance the efficiency and number of the cascaded four-wave mixing (FWM) products in chalcogenide planar waveguide is proposed and investigated numerically. Through introducing the optical feedback cavity and Mach-Zehnder interferometer, the modulated broadband cascaded FWM products can be obtained based on the high nonlinear chalcogenide planar waveguide. The numerical results show that the bandwidth of the modulated cascaded FWM is increased and the number of cascaded FWM products is improved compared with the single pass way of generating cascaded FWM products. Moreover, the feedback ratio plays an important role in the modulated cascaded FWM. This research can find important potential applications in nonlinear optics and integrated optics. [ABSTRACT FROM AUTHOR]

A wideband frequency-tunable optoelectronic oscillator using four-wave mixing nonlinear dynamics of an optical-injected distributed feedback (DFB) semiconductor laser is proposed and experimentally demonstrated. Utilizing the wavelength-selective optical gain of the DFB laser under optical injection, a frequency-tunable microwave photonic filter is realized, which is used as the desired oscillation frequency selector. Therefore, the electrical bandpass filter is not required in the proposed scheme. An optoelectronic oscillating signal with a frequency tuned from 9.63 to 19.11 GHz is obtained by changing the injection parameters. The single sideband phase noise of the generated 13.74-GHz microwave signal is measured to be −103.19 dBc/Hz at 10-kHz offset. [ABSTRACT FROM PUBLISHER]

We propose a technique to generate broadband chaotic and breather signals employing an optoelectronic oscillator (OEO) comprising a phase modulator (PM) and a linearly chirped fiber Bragg grating (LCFBG). The joint operation of the PM and the LCFBG forms a broadband microwave photonic filter (MPF), which allows the OEO to generate chaotic signals and breathers taking advantage of the interplay between the broadband MPF and the time-delayed feedback loop provided by a long optical fiber delay line. The breather excitations are characterized by nanosecond chaotic oscillations breathing periodically at a significantly lower time-scale determined by the OEO large delay time. A theoretical analysis based on a modified Ikeda time-delayed model to include the effect of the broadband filtering process is provided. The analysis is verified by an experiment. The proposed LCFBG-based OEO and the possibility to control in the optical domain its broadband bandpass characteristics considering the flexibility, accuracy, and precision in FBG fabrication can find applications in chaos-based communications and in fast optical processing systems, such as random number generation, or optical processing in reservoir computing taking advantage of the intrinsic multiple time scales of the LCFBG-based OEO. [ABSTRACT FROM PUBLISHER]

Fiber optical parametric oscillators (FOPOs) contain multiple longitudinal modes arising from the hundreds of meters to a kilometer scale length of their cavity. To obtain better understanding of the longitudinal modes and to find out how to suppress them, a model for the operation of FOPOs is introduced. This model utilizes the sinusoidal-input describing function (SIDF) as a quasi-linear approximation of the nonlinear dynamics of parametric amplification. Applying this model, the SIDF of the FOPO is derived, which predicts that the origin of the longitudinal modes is the presence of the cavity round-trip delay term in the characteristic equation (the denominator) of the transfer function. To eliminate the effect of the delay term, a modified Smith predictor control scheme has been applied to the FOPO cavity, and a control algorithm is developed. This algorithm has been numerically analyzed and experimentally implemented, where the results indicate drastic suppression of the longitudinal modes. [ABSTRACT FROM PUBLISHER]

A new scheme for a flexible modulation and bit rate independent, polarization-insensitive optical wavelength converter (WC) based on four-wave mixing in a highly nonlinear fiber is demonstrated and characterized for different modulation formats and data rates. Its robustness is demonstrated in a data transmission experiment in which the WC is incorporated at the mid-point of a transmission line based on installed fiber. In addition, an optical feedback system designed to prevent slow polarization drift of the pumps, and consequently, to ensure the long-term stability of the system is implemented and characterized. The WC is tested with the feedback system in place enabling turn-key operation. [ABSTRACT FROM PUBLISHER]

Abstract: Chaotic stimulated Brillouin scattering (SBS) in optical fibers with weak external optical feedback has been investigated experimentally and theoretically. However, only the bifurcation route to chaos through period-one and quasi-periodic emission was discovered in the former work because the chaotic domain is very short in the general nonlinear system. In order to control the chaos process and observe finer periodic-orbit structures, a novel experiment was designed to extend the chaotic domain by using long optical fibers in the SBS system. In this experiment, the period-one, period-doubling, period-four and period-eight cycle routes to the chaos laser process as well as the more details of chaos, have been observed. [Copyright &y& Elsevier]

Abstract: This works presents an efficient technique for generating multi-wavelength sources, which consist of an expanded optical frequency comb based on the nonlinear process of multiple four-wave mixing. The nonlinear efficiency is significantly enhanced by the use of the proposed scheme based on optical feedback, highly nonlinear and erbium-doped fibers. Numerical and experimental results illustrate its efficiency and applicability by expanding a comb from 20 to over 200 coherent lines spaced by only 12.5GHz. [Copyright &y& Elsevier]

A dual-loop nonlinear optoelectronic oscillator with an inbuilt ultra-wideband (UWB) band pass filter is proposed to generate chaotic-UWB signals for the first time. To avoid the spectrum-overlay-induced interference between UWB signals and the other existing narrow band signals, a microwave photonics filter is built up in the loops to filter out the corresponding frequency components. In the experiment, the chaotic-UWB signals with a frequency notch response located at 7.5 GHz, 5 GHz, or simultaneous 7.5 and 5 GHz are generated as the time delay difference between the two loops is set at 133, 200, or 400 ps, respectively. The peak sidelobe levels of the autocorrelation traces are as low as -33.7~dB at least, which implies that the generated UWB signals could be applied in random UWB radar directly. [ABSTRACT FROM PUBLISHER]

Abstract: Two chaos generation schemes are demonstrated numerically based on a semiconductor ring laser (SRL) with either a constant or a chaotic optical injection from an external distributed feedback (DFB) laser. Under a certain bias current, the chaotic output can be generated by the SRL with appropriate injection parameters. Parameter map is achieved numerically to show types of oscillation in the SRL. Bifurcation diagrams and Lyapunov exponent spectra roughly describe the routes to chaos for the SRL with disturbance. A bandwidth-enhanced chaos generation can be describes based on the chaotic optical injection scheme. The bandwidth of the bandwidth-enhanced chaos generated is about 12GHz, which achieves approximately a two-fold increase compared with the constant injection scheme. [Copyright &y& Elsevier]

We report an experimental investigation on the nonlinear dynamics of a 1550-nm vertical-cavity surface emitting laser subject to positive optoelectronic feedback. A bifurcation diagram of the extrema of output peak series versus the feedback strength is plotted. Various nonlinear dynamical behaviors including regular pulsing, quasiperiodic pulsing, chaotic pulsing, and mode locking (ML) have been experimentally observed. A mapping of dynamical states is presented in the parameter space of bias current and feedback strength, where different states are identified and shown. [ABSTRACT FROM PUBLISHER]

Abstract: An efficient multiwavelength Brillouin–Erbium fiber laser (BEFL) was developed by improving the feedback mechanism of Brillouin Stokes lines. The BEFL performance in terms of threshold power and wavelengths count was improved by using a new structure of double pass amplification cavity. The new structure utilized the variable optical coupler (VOA) not only as the input and output ports but also to form a fiber loop mirror that reduces the number of optical components, thus, only three optical components were needed. By optimizing the Brillouin and 1480nm pump power, up to 41 channels and 26 channels were obtained using 0.6km and 0.3km long of standard single mode fiber (SSMF), respectively. [Copyright &y& Elsevier]

Combining optical injection and polarization-rotated optical feedback in a semiconductor laser can induce self-referenced periodic output that is widely tunable by simply varying the dc-bias points of the system’s master and slave lasers. We observed a feedback-induced reduction of the fundamental period-one oscillation linewidth by more than two orders of magnitude relative to the injection-only case. Performance was found to be negatively affected by the interference between the external injection signal and the residual feedback in the same polarization. The nonlinear dynamics of the optically injected semiconductor laser can be used to minimize sensitivity to fluctuations in the operating points. However, the use of the nonlinear dynamics at high oscillation frequencies is limited by the decreasing strength of the interaction between the circulating intracavity optical field and the carrier density. [ABSTRACT FROM PUBLISHER]

A comb generator based on feeding a single dual drive Mach–Zehnder modulator with a sinusoidal radio frequency (RF) at one arm and its double frequency at the other arm is demonstrated. Our comb generator benefits from the superposition of optical subcarriers generated by the fundamental and its second harmonic. We demonstrate flexibility in center wavelength tunability, subcarrier spacing, and subcarrier count. For a fundamental frequency at, e.g., 6.25 GHz, our comb generator can produce 9, 5, 4, or 3 optical subcarriers with a spectral flatness of <1.2~dB. We successfully demonstrate to the best of our knowledge, the generation of the largest number of comblines requiring the lowest drive signal with the least components within the field of RF-generated combs. [ABSTRACT FROM PUBLISHER]

Recent studies demonstrated that chaotic spike sequences appearing in the context of incomplete homoclinic scenarios can be understood in terms of excitability of chaotic attractors. So far, this particular dynamic has been found in a semiconductor laser with optoelectronic feedback. Here, we show that the same phenomenology occurs also in light-emitting diodes, which are ideal candidates for the implementation of a complex network on a chip. In particular, we study the appearance of both stochastic incoherence (SI) and stochastic coherence (SC) in a single unit, as well as in two coupled units. We demonstrate experimentally and explore numerically the enhancement of SC and worsening of SI induced by coupling systems in array. [ABSTRACT FROM PUBLISHER]