Search

We study improvements of the Self-Injection Locked (SIL) distributed feedback (DFB) semiconductor laser phase noise as well as integral linewidth on the amount of the SIL feedback and show that SIL reduces the laser noise nearly equally in a broad frequency range, spanning from 1 Hz to 10 MHz. In our experiment SIL operation is supported by a tunable resonant reflector consisting of a high quality factor (high-Q) monolithic whispering gallery mode resonator (WGMR) supplied with a controllable attenuator. Using the experimental setup we validated theoretical formula describing the SIL spectral purity and identified practical parameters of the system allowing reaching the phase noise limit resulting from the fundamental thermodynamic noise of the resonator. We show that the linewidth improvement due to SIL effect is drastically impacted by the frequency spectral dependence of the phase noise of the laser and that it drops significantly in a flickering laser. We also confirmed that the thermorefractive coefficient as well as mode volume of the WGMR imposes the major limitations on the SIL performance. Low intracavity absorption is needed to suppress the attenuation-related thermal effects in the cavity. [ABSTRACT FROM AUTHOR]

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]

In this work the optical feedback generated by a tapered amplifier (TPA) emitting at 1120 nm is characterized at different operational conditions. The TPA is operated in a master oscillator power amplifier (MOPA) configuration, while the influence of pump current or seed power on the emitted feedback is investigated. Measurements are also performed with the TPA exposed to defined external optical feedback. For an estimation of the feedback from the TPA a simple formula is derived and the calculations are compared to the measurement results. With the experimental and theoretical results the required feedback resistance of the master oscillator seed source can be defined and the MOPA system optimized for certain applications with unwanted optical feedback. [ABSTRACT FROM AUTHOR]

A semiconductor laser with optical feedback and optical injection is an appealing scheme to construct the time-delay reservoir computing (TDRC) networks. Quantum dot (QD) lasers are compatible to the silicon platform, and hence is helpful to develop fully on-chip TDRCs. This work theoretically demonstrates a parallel TDRC based on a Fabry-Perot QD laser with multiple longitudinal modes. These modes act as connected physical neurons, which process the input signal in parallel. The interaction strength of the modes is characterized by the cross-gain saturation effect. We show that the neuron interaction strength affects the performance of various benchmark tasks, including the memory capacity, time series prediction, nonlinear channel equalization, and spoken digit recognition. In comparison with the one-channel TDRC with the same number of nodes, the parallel TDRC runs faster and its performance is improved on multiple benchmark tasks. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a chaos generation scheme that conceals the time-delay signature (TDS) by injecting the output of an external-cavity semiconductor laser (ECSL) into a two-element phased array (ECSL-TPA). We consider the case of the ECSL output with obvious TDS, and evaluate the performance of the ECSL-TPA with four waveguide structures in TDS suppression. The numerical results demonstrate that the ECSL-TPA allows for desired TDS suppression in wide parameter space regardless of the waveguide structures considered. However, different TDS behavior exists for these structures, which provides guidance for future design and optimization of the proposed ECSL-TPA. Additionally, the influence of some key parameters including the injection rate, frequency detuning, laser separation ratio, pump rate, linewidth enhancement factor, and frequency offset on TDS is systematically studied. Appropriate settings of these key parameters are beneficial for TDS suppression and thus optimizing optical chaos. The phased array can be extended to include a large number of elements and thus generates multiple independent chaotic signals with indistinguishable TDS in parallel, paying the way for chaos-based applications that require independent, high-quality chaos simultaneously. [ABSTRACT FROM AUTHOR]

Aiming at the problems of limited bandwidth and periodicity of chaotic laser, a monolithically integrated chaotic semiconductor laser subject to random feedback and mutual injection is proposed. The chaotic laser consists of two distributed feedback laser diodes (DFB-LD), two semiconductor optical amplifiers (SOA) and a passive optical waveguide. Optical injection of two coupled DFB-LDs achieves chaotic signal shaping and bandwidth enhancement. Random grating along the passive waveguide provides stochastic feedback to suppress the time delay signature (TDS). A theoretical model is established based on the Lang-Kobayashi model to explore the dynamics of the proposed chaotic laser. A chaotic signal with TDS of 0.06 and bandwidth of 13.12 GHz is obtained by simulation. Furthermore, the effects of parameters including feedback ratio, mutual injection ratio, and detuning frequency on the TDS and bandwidth of chaotic signal are investigated. The results show that the broadband chaotic laser signal with TDS suppression can be obtained by controlling parameters reasonably. [ABSTRACT FROM AUTHOR]

We have found a fine structure in the frequency dependence of modulation efficiency of a diode laser (DL) with a strong selective optical feedback. The FM response of an extended cavity diode laser (ECDL) to the microwave current modulation has two peaks whose frequencies are close to the intermode frequency of the laser longitudinal modes. The frequency splitting of the peaks depends on the power of laser radiation and on the difference between the frequency of operating ECDL mode and the frequency of the closest DL mode. We have observed similar splitting in AM noise spectra with the same type of dependencies on power and aforementioned frequency detuning. The peculiarity of the AM noise spectrum has been observed and explained previously by nonlinear interaction of fields in the active region of a DL that results in the frequency splitting of the modes. This dynamic splitting of the laser cavity modes explains the specific features of the modulation characteristics. [ABSTRACT FROM AUTHOR]

Dynamics of a multimode quantum dot laser with polarization-rotated optical feedback is investigated in a wide range of bias current. The results reveal that the laser is more sensitive to optical feedback when the polarization of feedback beam is rotated a large angle from the original polarization, which is different from the results in DFB lasers. Anticorrelated fluctuations between orthogonal polarizations are observed in a certain range of selected polarizations. Accordingly, dynamics in the total power can be weaker than that in a selected polarization. The anticorrelated polarization dynamics may be related to different polarizations of longitudinal modes. [ABSTRACT FROM AUTHOR]

In this work, we propose a new scheme of optical feedback using stimulated Brillouin scattering (SBS). A high-power laser diode emitting at 1450 nm stimulates Brillouin back-scattering in a 4km-long optical fibre and the back-scattered light is injected back into the laser diode for optical feedback. The experimental results with RF spectrum exhibit clearly the Brillouin frequency shift at 11.46 GHz. Although the frequency shift is very large, the laser diode subject to optical feedback using SBS shows abundant dynamics. RF spectrum maps are also established with respect to the laser drive current. The results are compared with the ones for conventional optical feedback and it is clearly shown that the dynamical behaviours for both the configurations are very different. The investigation with autocorrelation functions reveals that the time-delay signature vanishes completely using the SBS feedback scheme unlike the conventional feedback one. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate high-speed correlated random bit generation in real time using synchronized chaotic lasers commonly driven by a laser with dispersive feedback. The dispersive feedback from a chirped fiber Bragg grating induces frequency-dependent feedback delay and thus no longer causes time-delay signature, and resultantly ensures the signal randomness and security of chaotic laser. Driven by the time-delay signature-free chaotic signal, the two response lasers are routed into chaotic states and establish a synchronization with correlation beyond 0.97 while they maintain a low correlation level with the drive signal. Through quantizing the synchronized laser chaos with a one-bit differential comparator, real-time 2.5-Gb/s correlated random bits with verified randomness are experimentally obtained with a bit error ratio of 0.07. Combining with a robust sampling method, the BER could be further decreased to $1\times 10^{-4}$ corresponding to an effective generation rate of 1.7 Gb/s. Bit error analysis indicates that the bit error ratio between the responses is lower than that between the drive and responses over a wide parameter region due to the synchronization superiority of the responses over the drive. [ABSTRACT FROM AUTHOR]

In this paper we explain how to use rate equations to describe a laser that includes integrated optical feedback. We find a relation between the threshold current, the voltage drop at the gain section, output power, linewidth, and side mode suppression ratio, and show experimental results. [ABSTRACT FROM AUTHOR]

We study experimentally the behavior of a multistable vertical cavity surface-emitting laser under influence of isotropic optical feedback (OF). Without feedback, this laser displays spatial multistability which shows up in the laser power and polarized-resolved measurements of the laser intensity. We show that OF shifts the existence boundaries of multistability and can suppress multistability for a strong enough strength of optical feedback transforming it into bistability. This effect is demonstrated with the help of hysteretic dependencies of the laser intensity on the injection current and by the method of vibrational resonance. The latter method allows one to reveal “hidden” states which cannot be observed in the hysteretic behavior. Besides, we study also how optical feedback changes statistical properties of polarization fluctuations. We show that a strong enough OF leads to symmetrization of the distribution function of polarization noise. [ABSTRACT FROM AUTHOR]

We show numerically that dual-mode continues wave optical injection into a Fabry–Pérot laser diode subject to optical feedback generates a chaos bandwidth, which is four to six times that without optical injection. As a comparison, it is shown that single-mode optical injection can increase the chaos bandwidth threefold with careful choice of detuning. Furthermore, any combination of dual-mode injection will enhance the chaos bandwidth and especially for strong injection and over relatively large positive detuning ranges. Even, when the bias current of the Fabry–Pérot laser diode is relatively low, the bandwidth of chaos can reach 35 GHz after dual-mode optical injection, which is six times than that of without optical injection. The enhanced bandwidth with dual-beam optical injection is in accordance with our previous experiments. The present simulations provide detailed guidance on the choice of experimentally accessible parameters to generate chaotic signals with enhanced bandwidth by using single or dual-beam optical injection into a Fabry–Pérot laser diode with optical feedback. [ABSTRACT FROM AUTHOR]

The time delay signature (TDS) concealment properties of a novel semiconductor nanolaser subject to double chaotic optical injections are investigated numerically. The TDS concealment is evaluated by the peak size of the autocorrelation function (ACF). The effects of feedback rate, injection rate, frequency detuning, Purcell cavity-enhanced spontaneous emission factor, and spontaneous emission coupling factor on the TDS concealment are carefully examined. It is found that, with the double chaotic optical injections, the TDS can be concealed in wide ranges of feedback rate, injection rate, and frequency detuning. Moreover, better TDS concealment can be achieved for a smaller frequency detuning and a larger injection rate. The 2-D maps of peak size of ACF further show that the range of parameter space contributing to better TDS concealment is wider for a moderate Purcell cavity-enhanced spontaneous emission factor and a smaller spontaneous emission coupling factor. These results may be interesting for the enhanced chaotic sources on-a-chip based on novel semiconductor nanolasers. [ABSTRACT FROM AUTHOR]

The phase synchronization of two semiconductor DFB lasers submitted to both frequency-shifted cross-injection and self-feedback is investigated, both numerically and experimentally. A dedicated setup based on monolithic DFB lasers permits to effectively lock the frequency difference of the two lasers on an external reference over a broad range of parameters. In agreement with a delayed rate equation model, it is shown that the sensitivity of the locking to the optical feedback phases is mitigated by using strong cross-injection thus paving the way to applications for microwave photonics. Other synchronization dynamics can also be observed, such as bounded-phase oscillations. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of the temporal behavior of a bistable vertical cavity surface emitting laser (VCSEL) under the effect of optical feedback coming from vibrating diffusely reflecting surface. We demonstrate that a VCSEL operating in the regime of polarization switchings caused by self-mixing effects can greatly enhance a responsivity of the detection of microvibrations. For small amplitudes of microvibrations (less than $\lambda $ /2, where $\lambda $ is the operating wavelength of the laser), which cause only harmonic (or close to harmonic) oscillations in the laser output outside of the bistability region, the use of polarization switching can increase the responsivity up to 45 times. For the amplitudes larger than $\lambda $ /2, the response of a bistable VCSEL well reproduces a fine temporal structure of the self-mixing signal. A procedure of the data processing in the switching regime for the correct determination of the direction of the displacement and for the reconstruction of the waveform of surface vibrations with a basic resolution of $\lambda $ /2 is also shown. [ABSTRACT FROM AUTHOR]

Catastrophic failure of diode pumps in laser systems exhibiting back-irradiance is a common occurrence yet poorly understood. Prior paper has established boundaries for time-zero failures, but these results cannot be used to deduce safe back-irradiance levels for long-term reliable operation. In this paper, a framework to describe the impact of back-irradiance on the reliability of diode pumps is established. The root-cause of back-irradiance induced failure is identified as thermal in nature. The approach follows conventional reliability methodologies by treating the parameters of back-irradiance as stressors, which accelerate failures. [ABSTRACT FROM AUTHOR]

In this paper, a novel self-mixing grating interferometer (SMGI) with dual laser diodes (LDs) is proposed for 2-D dynamic displacement measurement. The light beams emitted from the LDs are incident onto a reflection grating with ±1st order auto-collimation diffraction angles and then diffracted back into the lasers, respectively, which can cause self-mixing interference effect in each LD. Theoretical analysis on the SMGI signals corresponding to 2-D displacement is presented and verified with the experimental observations. Measurement results of 2-D dynamic displacement demonstrate that the proposed system can achieve the measurement resolution better than 10 nm. The proposed SMGI sensing system has the advantages of high stability, compact mechanical structure, and relatively straightforward operation. [ABSTRACT FROM AUTHOR]

Improper back-coupling of optical feedback is a known cause for accelerated gradual degradation as well as catastrophic optical mirror damage of GaAs-based high-power semiconductor lasers. For those material systems emitting below the GaAs bandgap (870 nm at room temperature), such damage is induced by feedback-light absorption in the non-transparent cap layers and substrate, which intensifies the heating of the area close to the emission facet. For InGaAs/AlGaAs-based diode lasers in the spectral range from 880 to 1060 nm, however, all passive layers as well as the substrate are, with respect to interband absorption, transparent for the lasing wavelength so that, in this case, the degrading mechanism of misaligned optical feedback could not be explained entirely. By use of an experimental multi-device study of 950-nm broad-area lasers, we demonstrate that the threshold of catastrophic optical damage is decreased the most by positioning the feedback return spot such that it covers the p-side solder and the highly p-doped semiconductor layers. By means of thermoreflectance microscopy in conjunction with numerical simulations we find that such low damage thresholds are caused by a strong localization of the absorption of feedback light close to the laser front facet. [ABSTRACT FROM AUTHOR]

In a self-mixing interferometer based on a diode laser, the measurement of the external reflector displacement $s(t)$ is carried out by looking at the optical-phase signal $\cos 2ks(t)$ , a signal readily detected as an amplitude modulation (AM) of emitted power. In contrast, the other available signal, sin $2ks(t)$ , a frequency modulation (FM) of the emitted field at optical frequency, is never used because difficult to recover. Recently, Contreras et al. used a narrow-band acetylene cell to convert the FM into an amplitude signal, finding it is larger and has a better SNR than the AM. In this paper, we analyze the advantages of the new CFM (converted-FM) signal, calculating both amplitude and SNR, and compare theoretical results to published experimental evidence, finding good agreement. We then present options for realizing the selective filter in different configurations and technology. Finally, we evaluate the improvement offered by CFM in a number of measurements, like sub-wavelength vibrations, digital readout displacement, and diode laser alpha factor. [ABSTRACT FROM PUBLISHER]

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]

In this paper, the influence of variable-angle polarization-rotated optical feedback on the polarization switching properties of vertical-cavity surface-emitting lasers (VCSELs) is investigated theoretically and experimentally. The optical feedback (OF) level and the rotated polarization angle \theta p of OF are considered. Two configurations of OF are used to re-injected parallel and orthogonal polarization modes back into the VCSEL. For the parallel OF, it is shown that polarization switching (PS) of VCSELs’ modes can occur at a fixed feedback level and bias current with variable \theta p . However, in case of orthogonal optical feedback, PS occurs only at certain values of \theta p , particularly when the intensities of two polarization modes become comparable with each other. In the theoretical model for both OF conditions, there is good agreement between the experimental measurements and recent theoretical results reported in the literature. [ABSTRACT FROM AUTHOR]

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]

An analysis of the turn-ON time for a thyristor-based photoreceiver is presented. Using an equivalent circuit that incorporates internal bipolar current gain, the time to trigger and switch the detector on is quantified analytically. For typical device parameters and applying values of photocurrent gain obtained from experimental data, turn-ON times on the order of 25 ps are predicted for a 10~\mu \textm device diameter. [ABSTRACT FROM AUTHOR]

Recently reported miniature configurations with semiconductor distributed feedback lasers under resonant feedback are considered theoretically. Limiting instabilities and bifurcations are systematically explored by combining the theory of chirp reduction and a bifurcation analysis. It is shown that the regime of optimal chirp reduction also exhibits the best local stability. It suffers only from undamping of relaxation oscillations in a finite interval of feedback strength. The existence of a separate strong-feedback regime with high stability is consistent with the two experiments available so far. We regard this feature as a generic specificum of miniature configurations not known from large-scale setups. This regime can open new prospects for applications of compact frequency-stabilized semiconductor lasers with extremely low noise and small line width. [ABSTRACT FROM AUTHOR]

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]

Optoelectronic oscillators (OEOs) are microwave photonic systems intended to generate ultra-pure radio-frequency signals for aerospace and communication engineering applications. Typically, a long optical fiber delay line is inserted in the feedback loop as an energy storage element intended to improve the phase noise performance. An ultra-high $Q$ whispering-gallery mode resonator can be inserted as well in order to filter-out the spurious ring-cavity peaks arising in the radio-frequency spectrum. However, dynamical instabilities induced by a relatively large delay have never been analyzed for these OEOs. In this paper, we systematically investigate the stability of the generated microwaves as a function of the effective OEO loop gain and delay. We find that close enough to the oscillation threshold, the generated microwaves are unconditionally stable, but as the gain is increased, their stability becomes dependent on the ratio between the time delay and the overall photon lifetime of the resonator. Our results allow an optimal design for these OEOs, leading to both enhanced spectral stability and phase noise performance. [ABSTRACT FROM PUBLISHER]

Based on the spin-flip model, the polarization switching (PS) characteristics of two polarization outputs in a 1550-nm vertical-cavity surface-emitting laser (1550-nm VCSEL) subject to double polarization pulsed injection (DPPI) are investigated theoretically, and the obtained results are compared with the case, in which the 1550-nm VCSEL is simultaneously injected by the pulses of orthogonal polarized light and a continuous wave (CW) parallel polarized light, which is called double optical injection with pulsed orthogonal polarization (DIPOP). The simulated results show that, compared with the DIPOP, the DPPI method is beneficial to improving the PS performance under suitable parameters. The influences of the timing difference ( \Delta t ) in the switching of two injection pulses on the PS performance of 1550-nm VCSEL subject to DPPI are analyzed, and the optimized values of \Delta \text{t} under different bias currents are determined. Furthermore, for optimized \Delta \text{t}$ , the dependences of the switching times on the amplitudes of two polarization pulses and the frequency detuning are given. [ABSTRACT FROM AUTHOR]

The time-delay signature and the chaos bandwidth in three-cascaded vertical-cavity surface-emitting lasers have been investigated experimentally. A peak value of autocorrelation coefficient at the feedback round trip time and the ratio between this peak value and its background are used to quantitatively identify the time-delay (TD) signature of chaos. A new concept—peak to side-peak ratio is introduced for better quantification of the TD signature concealment. The peak to side-peak ratio is defined as the ratio between the peak value of autocorrelation coefficient at the TD and the peak value at a delay time other than the TD and zero delay time. Three injection cases, namely, small bandwidth, intermediate bandwidth, and wide bandwidth of the injecting chaos signals, have been used to study the effect of the bandwidth of the injecting chaos on the TD concealment. The experimental results show that the time-delay signature can be totally concealed in the slave laser subject to the intermediate bandwidth of chaotic optical injection over a wide frequency detuning range. [ABSTRACT FROM AUTHOR]

Modulation bandwidth enhancement of an optically controlled single-mode semiconductor laser is achieved by introducing an external cavity into the laser. A calculation based on a rate equation model shows that the 3-dB bandwidth of the optically controlled external cavity laser (OC-ECL) can be substantially enhanced by controlling the feedback light intensity and phase properly. A broad 3-dB bandwidth of 59 GHz is experimentally confirmed by using the fabricated OC-ECL. The results suggest that a combination of cross-gain modulation and photon–photon resonance is suitable to enhance the modulation bandwidth of semiconductor lasers. [ABSTRACT FROM AUTHOR]

The effects of gain nonlinearity on the time delay signature (TDS) of both intensity and phase chaos in semiconductor lasers (SLs) with optical feedback are investigated numerically. The SLs subject to single-path feedback are mainly considered, and SLs with dual-path feedback are also discussed for the sake of generality. The TDS is evaluated via both auto-correlation function (ACF) and permutation entropy function. It is found that the TDS is more sensitive to nonlinear gain factor (NGF) for large injection current and low feedback strength. For given feedback strength, the peak heights of ACF for both intensity and phase chaos around TDS can be decreased by using SL with low NGF, especially when the injection current is relative high. Furthermore, with low NGF, successful TDS concealment can be achieved in wider region in the parameter planes of feedback strength and injection current. Hence, careful selection of an internal parameter is an effective candidate for TDS concealment in wider parameter region, which is complementary to the existing techniques by controlling the external parameters, and thus is highly desirable for expanding the key space for chaos-based secure communication. [ABSTRACT FROM AUTHOR]

The response of the nanolasers subject to the phase conjugate feedback (PCF) 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 feedback rate. It is observed that, in general, the onset of chaos occurs at a higher feedback rate for PCF than for conventional mirror feedback (CMF), where PCF has lower intensity noise in comparison with the CMF. [ABSTRACT FROM AUTHOR]

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 show that a self-mixing interferometer can supply not only to the usual optical-phase signal cos 2ks( $t$ ) of the external reflector displacement $s(t)$ , but also the attitude signal $P(a$ ) because of the dependence of power from the angle a between wavevector k and normal n to the target reflective surface. By proper interrogation of $P(a$ ) along two orthogonal components of tilt and yaw, the two angles can be measured simultaneously, together with the displacement, in a single self-mixing interferometer channel implemented by a single-laser diode and monitor photodiode combination. [ABSTRACT FROM AUTHOR]

Optoelectronic oscillators based on whispering-gallery mode resonators (WGMRs) are efficient oscillators for ultra-stable microwave generation, in which the energy can be stored in an ultra-high $Q$ -factor resonator instead of the usual long delay line. In this paper, we derive a stochastic model for the calculation of the phase noise performance in these systems considering three different configurations, namely, the case where the energy is stored in high- $Q$ disk-shaped WGMR, the case where energy is stored in an optical delay-line only, and the case for which the energy is stored simultaneously by the resonator and the delay line. Our investigations explain how the WGMR can be optimally used for spurious peak rejection in optoelectronic oscillators. Our experimental measurements are found to be in excellent agreement with analytical and simulation results. [ABSTRACT FROM PUBLISHER]

We theoretically analyze the use of fully integrated high- $Q$ ring cavities (intrinsic $Q \sim 1$ million) with widely tunable semiconductor lasers to realize narrow linewidth lasers. Different configurations are studied, including cases where the high- $Q$ cavity is external to the laser cavity and provides filtered optical feedback to the laser cavity and cases where the high- $Q$ cavity is an integral part of the laser cavity. We show that the current heterogeneous silicon platform should allow subkilohertz instantaneous linewidths, and we outline the advantages and disadvantages of different high- $Q$ cavity placements. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a novel dual-channel optical chaos system with a time-delay (TD) feature simultaneously suppressed in all observables, i.e., in both intensity and phase. A hybrid optical and electro-optic feedback for a single vertical-cavity surface-emitting laser (VCSEL) is verified to induce simultaneous TD suppression for the polarization-resolved components of the chaotic output. A comprehensive mathematical model is developed to incorporate the optical and electro-optic time delays into the rate equations of the VCSEL. The suppression of TD signature is then examined by means of autocorrelation function and delayed mutual information. The results show that the output chaotic signal has the TD feature well eliminated in both the intensity and phase over certain regions of parameter space identified using the peak signal to mean ratio technique. The independent evolution of the two orthogonal VCSEL modes renders the polarization-resolved output modes appropriate for the enhanced dual-channel chaos applications. To the best of our knowledge, this is the first time that a dual-channel chaos communication system is reported with simultaneous suppression of the TD feature in all the transmitted observables. [ABSTRACT FROM PUBLISHER]

In this paper, we compare the performances of the well-known two-laser and three-laser chaos communications schemes, in terms of privacy. It is found by numerical analysis that in optimized conditions both methods are well suited for private transmission. However, while the three-laser scheme gives its optimum performance with the twin laser pair, the two-laser scheme reaches its best performance using two slightly different lasers (the optimum pair). This results in an easier device selection and in a slightly higher privacy level of the three-laser scheme. Using a twin pair with the two-laser scheme still offers a good level of privacy in most cases; however, in principle the eavesdropper has a chance to extract the message, by selecting a suitable laser. [ABSTRACT FROM AUTHOR]

Low-cost vertical-cavity surface-emitting laser (VCSEL) and semiconductor optical amplifier (SOA) have been explored experimentally in a setup with a fiber ring resonator to generate flat broadband chaos. The effect of the frequency detuning between the fiber grating frequency and the freerunning VCSEL's frequency, and the bias current of the SOA on the bandwidth of chaos has been studied. The results show that the bandwidth of the chaos is strongly dependent on the frequency detuning and the bias current of the SOA. Using the conventional definition of chaos bandwidth, the bandwidth of chaos with the fiber ring resonator can be about three times greater than that with a conventional mirror. In order to consider the flatness of the chaos spectra, the flat bandwidth of chaos is redefined as the frequency range between dc and the frequency where the power fluctuation is within ±3 dB. With this definition, the flat bandwidth of chaos with the fiber ring resonator is >10 times higher than that with conventional mirror feedback. [ABSTRACT FROM AUTHOR]

We report detailed experimental bifurcation diagrams of an external-cavity semiconductor laser. We have focused on the case of a DFB laser biased up to 1.6 times the threshold current and subjected to feedback from a distant reflector. We observe bifurcation cascades resulting from the destabilization of external-cavity modes that appear successively when the feedback is increased, and explain, in light of the Lang and Kobayashi (LK) model, how the cascading is influenced by various laser operating parameters (current, delay, and feedback phase) and experimental conditions. The semiquantitative agreement between experiments and simulations validates over a large range of operating parameters, the LK model as a tool for reproducing the salient aspects of the dynamics of a DFB laser subjected to external optical feedback. [ABSTRACT FROM AUTHOR]

A detailed experiment was conducted to characterize the stable fundamental-mode operation of a commercial Laguerre-Gaussian (LG)-mode vertical-cavity surface-emitting laser when single-mode-fiber optical feedback was applied. Two steady-state beam profiles of laser output were established and four radial-intensity profiles obtained through simulation were compared with experimental results. The steady high-order mode can be applied in technology featuring a unitary wavelength and multiple connections. An oscillating competition state of the coupled patterns was analyzed; in this state, the laser output between an LG beam and a Gaussian beam was established after optical feedback. [ABSTRACT FROM AUTHOR]

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

This paper on observers of chaotic systems is comparatively poor. There are no systematic design methods and current methods are difficult to deal with uncertainties. To solve these problems, a robust observer based on radial basis function neural network (RBF NN) is proposed. This design divides the system into linear and nonlinear parts and describes them as the addition of nominal part and uncertain part. The RBF NN estimates the uncertainties, and the choice of observer gain is required to satisfy the Lyapunov equation, which avoids the strictly positive real condition. The proposed method improves the robust performance of observer by robust control method at the same time. Finally, to solve the problem that the laser synchronization control only depends on the photon number at present, an observer is designed to estimate the electron-hole pair number, and the integration design method of the observer and controller is put forward for the first time. The asymptotical convergence of synchronization errors is proved by Taylor expansion. The simulations verify the superiority of the proposed scheme. [ABSTRACT FROM AUTHOR]

Both the time-delay signature and the bandwidth of chaos have been investigated in four schemes of chaos generation in vertical-cavity surface-emitting lasers (VCSELs). The results show that suppression of the TD signature and the enhanced bandwidth of chaos can be obtained simultaneously in two schemes - a chaotic beam unidirectionally injected into a CW VCSEL and a CW VCSEL mutually coupled to a chaotic VCSEL. However, suppression of the TD signature and the enhanced chaos bandwidth cannot be achieved simultaneously in two other schemes - a CW optical beam unidirectionally injected into a chaotic VCSEL and two mutually coupled CW VCSELs. [ABSTRACT FROM PUBLISHER]

In this paper, we numerically demonstrate that the performances of private transmission using chaotic lasers can be substantially improved by double masking the message by a suitable scheme. In addition to standard optical chaos, our method makes use of the chaotic voltage waveform available across the transmitter laser junction. With respect to the standard setup, the new one requires only one more electrical amplifier and a passive adder at the transmitter, while the receiver remains unchanged. It has been found that with this new scheme, synchronization quality is significantly improved for the twin lasers, while this is not the case for an unmatched laser pair. This results in an increased bit error rate differential between the authorized user and an eavesdropper, thus enhancing privacy. Simulations have been performed with the Lang–Kobayashi model. [ABSTRACT FROM AUTHOR]

We design and implement a chaotic-based system, enabling ultra-fast random bit sequence generation. The potential of this system to realize bit rates of 160 Gb/s for 8-bit digitization and 480 Gb/s for 16-bit digitization is demonstrated. In addition, we provide detailed insight into the interplay of dynamical properties, acquisition conditions, and post-processing, using simple and robust procedures. We employ the chaotic output of a semiconductor laser subjected to polarization-rotated feedback. We show that not only dynamics affect the randomness of the bits, but also the digitization conditions and postprocessing must be considered for successful random bit generation. Applying these general guidelines, extensible to other chaos-based systems, we can define the optimal conditions for random bit generation. We experimentally demonstrate the relevance of these criteria by extending the bit rate of our random bit generator by about two orders of magnitude. Finally, we discuss the information theoretic limits, showing that following our approach we reach the maximum possible generation rate. [ABSTRACT FROM AUTHOR]

In this paper, we experimentally and numerically study the dynamics of semiconductor ring lasers that are subjected to long delay and moderate self-feedback. Through varying the pump current or the feedback strength or both, we study the appearance and parameter dependence of low frequency fluctuations in these systems. In particular, we observe different routes to the building up of the initial power amplitude. [ABSTRACT FROM AUTHOR]

The randomness enhancement of physical chaos generated by slave vertical-cavity surface-emitting lasers (S-VCSEL) subject to dual-path polarization-preserved optical injection (DP-PPOI) from single master VCSEL (M-VCSEL) with variable-polarization optical feedback (VPOF) is investigated numerically. The randomness of chaotic signals is evaluated quantitatively by an information-theory-based quantifier, the permutation entropy. The randomness properties for S-VCSEL with DP-PPOI and S-VCSEL with single-path PPOI are compared, as well as the effects of injection strength, frequency detuning, and VPOF are considered. It is shown that, the PE values for S-VCSELs with two different injection schemes are both much higher than those for M-VCSEL, and increase initially and then decrease until they saturate at a constant level. The region of injection parameter space contributing to randomness-enhanced chaos in S-VCSEL can be greatly broadened by adopting DP-PPOI. The generation of randomness-enhanced chaos via photonic approach is highly desirable for high-speed random number generators based on chaotic VCSELs. [ABSTRACT FROM AUTHOR]

A set of nonlinear rate equations that can describe an external cavity laser with any arbitrary external optical feedback (OFB) level are derived. A comprehensive study on the relative intensity noise (RIN) characteristics of a fiber grating Fabry–Perot is performed numerically. In this paper, fiber Bragg grating (FBG) is used as a wavelength lasing selective element to control the external OFB level, thereby control the RIN. In addition to the external OFB level, the effect of other external cavity parameters such as temperature, injection current, cavity volume, gain compression factor, and FBG parameters on RIN characteristics is investigated. The temperature dependence (TD) of RIN is calculated according to TD of laser parameters instead of well-known Parkove relationship. Results show that by optimization, the peak value of the RIN can be reduced down to around -150∼dB/Hz. The optimum and the shortest external cavity length that provides the minimum RIN is found to be around 3.1 cm. In addition, by optimization, the relaxation oscillation frequency of RIN spectra is shifted toward around 5.6 GHz. [ABSTRACT FROM AUTHOR]