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A high-speed neuromorphic reservoir computing system based on a semiconductor nanolaser with optical feedback (SNL-based RC) under electrical modulation is proposed for the first time and demonstrated numerically. A Santa-Fe chaotic time series prediction task is employed to quantify the prediction performance of the SNL-based RC system. The effects of the Purcell cavity-enhanced spontaneous emission factor F and the spontaneous emission coupling factor β on the proposed RC system are analyzed extensively. It is found that, in general, increased F and β extend the range of good prediction performance of the SNL-based RC system. Moreover, the influences of bias current and feedback phase are also considered. Due to the ultra-short photon lifetime in SNL, the information processing rate of the SNL-based RC system reaches 10Gpbs. The proposed high-speed SNL-based RC system in this paper provides theoretical guidelines for the design of RC-based integrated neuromorphic photonic systems. [ABSTRACT FROM AUTHOR]

We present a design of a tunable hybrid laser based on III-V Reflective Semiconductor Optical Amplifier (RSOA) and Silicon Photonics (SiPh) external mirror that represents a good trade off between high Wall-Plug Efficiency (WPE) and high tolerance to optical feedback caused by unwanted back reflections from the rest of the SiPh chip. The sensitivity to optical feedback of different configurations, an important issue in many SiPh applications, is evaluated through the calculation of the critical feedback level based on an effective Lang-Kobayashi model and the main results are validated through numerical simulations of laser dynamics. We conclude that hybrid lasers with long effective external cavities typically designed to reduce the laser linewidth can be also exploited to improve the tolerance to spurious optical feedback. [ABSTRACT FROM AUTHOR]

With the development of nanomanufacturing methods, the manipulation of photons down to the nanoscale in silicon integrated optical chips has become a feasible and promising solution for next-generation data processing as electronic chips reach their limit. As an essential active device that generates photons for all other working photonic components, silicon lasers are the last barrier to achieve silicon integrated optical chips. Although optical gain in silicon nanocrystals (Si–NCs) was observed in 2000, the progress in realizing all-Si lasers has been very limited due to the inferior optical gain compared to traditional gain materials. In this paper, highly luminescent thin films of Si–NCs with a photoluminescence quantum yield of 57% are developed. The broadband photoluminescence covers the wavelength range from 650 to 900 nm, and wide-range optical gains are identified, indicating the feasibility of a tunable laser. Distributed feedback (DFB) all-Si lasers are fabricated using these thin films and pumped by femtosecond pulses. Various characteristic lasing behaviors are observed. Additionally, three different DFB grating periods are selected, and the lasing peak can be tuned by over 100 nm. The lasing thresholds range from 8.3 to 53.3 MW/cm2. The linewidths of lasing peaks are less than 2 nm. [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]

We propose to realize the parallel tasks processing by reservoir computing (RC) using two polarization-resolved modes in a single vertical-cavity surface-emitting laser (VCSEL). Two feedback cases, parallelly-polarized optical feedback (PPOF) and orthogonally-polarized optical feedback, are considered in the VCSEL. A time series prediction task and a waveform recognition task are employed to examine the parallel tasks processing performance in two polarization-resolved modes of the VCSEL-based RC system. Through numerical simulations, the dependences of parallel tasks processing performance of the VCSEL-based RC system on the feedback strength, injection strength are analyzed carefully and compared for the two feedback cases. Besides, the effects of injection current, frequency detuning, spontaneous emission noise, and the number of virtual nodes are also examined. It is found that, for both feedback cases, good performance of parallel tasks processing in two polarization modes of the VCSEL-based RC system could be obtained in broad parameter regions, and in these regions a better performance is achieved for the PPOF case. This proposed polarization multiplexing RC based on VCSEL permits parallel tasks processing in two polarization modes in a single VCSEL, and hence is interesting and valuable for low power consumption neuromorphic photonics systems. [ABSTRACT FROM AUTHOR]

We propose a scheme for reservoir computing using multiple semiconductor lasers with optical feedback arranged in parallel on a photonic integrated circuit, and we investigate the performance of reservoir computing numerically. The virtual nodes are obtained from the temporal waveforms of the outputs of the parallel reservoir lasers. We test the chaotic time-series prediction task, memory capacity, and nonlinear channel equalization task to investigate the performance of reservoir computing. We found that our scheme using multiple lasers outperforms that using a single laser with multiple delay times. Large memory capacity can also be obtained for the multiple lasers. Finally, we investigate the effect of parameter mismatch of the multiple lasers on reservoir computing performance. [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]

This paper investigates the intensity noise and pulse oscillation characteristics of an InAs/GaAs quantum dot laser epitaxially grown on germanium. We show that the relative intensity noise of the free-running laser generally decreases with increasing pump current, and the minimum value reaches down to about $-$ 126 dB/Hz. The intensity noise is hardly affected by the optical feedback, unless there is a resonance or pulse oscillation in the noise spectrum. The laser pumped at a high current is more sensitive to the optical feedback. Interestingly, it is found that the free-running Ge-based quantum dot laser generates self-sustained pulse oscillations with one period or two periods upon the pump current, without incorporating saturable absorbers. This behavior is valuable for both self-generation of photonic microwaves and for understanding nonlinear dynamics of semiconductor lasers. [ABSTRACT FROM AUTHOR]

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 present a route toward design and fabrication of a conceptually new type of optical feedback insensitive integrated semiconductor ring laser with a weak optical isolator included in the ring. Although the approach has not resulted in the clear advantages that were aimed at, this detailed account of the process we believe is valuable to readers active in the field. After a summary of optical-feedback sensitivity in semiconductor lasers, we review various attempts toward reducing this sensitivity and discuss the feasibility of the concept of weak intra-cavity isolation. The design, model and theory of the novel integrated ring laser device are presented. The observed 5 dB of isolation and 3 dB increase of tolerance for external optical feedback demonstrate the feasibility of the intra-cavity isolation concept. However, the observed output performance of the single-mode laser, both with and without activated intra-cavity isolation, suggests the presence of a spurious intra-cavity reflection, strongly coupling the directional modes. Due to this coupling, the sensitivity to external optical feedback is comparable to that of a Fabry–Pérot type laser. Therefore, an alternate route is indicated toward a less complex laser cavity with potentially less intra-cavity reflection and better tolerance for external optical feedback. [ABSTRACT FROM AUTHOR]

Consistency is a powerful concept to characterize and classify the behavior of driven dynamical systems, therefore playing an essential role for the understanding of information processing in and by complex photonic systems. Here, we discuss two different experimental configurations of semiconductor laser systems with delayed optical feedback allowing for a unifying view via the detailed characterization and comparison of consistency and synchronization properties. The first configuration comprises two unidirectionally coupled semiconductor lasers, which has found considerable interest for applications in encrypted communication. The second configuration consists of a single laser with two optical delay loops of significantly different lengths, designed such that only one loop is active at a time and that allows to study replays of injected optical signals. We show that, in terms of three characteristic correlation measures—consistency correlation, transformation correlation, and spurious correlation—the dynamical features of the two different experiments are very similar and how the two configurations are connected. Our approach shows that consistency allows to understand and relate various chaos synchronization and stability properties. We particularly discuss the experimental results in the context of a previously established analytical framework, providing a common dynamical interpretation of consistency and chaos synchronization in delay-driven laser systems. [ABSTRACT FROM AUTHOR]

Semiconductor lasers are notoriously sensitive to optical feedback, and their dynamics and coherence can be significantly modified through optical reinjection. We concentrate on the dynamical properties of a very small (i.e., microscale) Vertical Cavity Surface Emitting Laser (VCSEL) operated in the low coherence region between the emission of (partially) coherent pulses and ending below the accepted macroscopic lasing threshold, with the double objectives of: 1) studying the feedback influence in a regime of very low energy consumption and 2) using the micro-VCSEL as a surrogate for nanolasers, where measurements can only be based on photon statistics. The experimental investigation is based on time traces and radiofrequency spectra (common for macroscale devices) and correlation functions (required at the nanoscale). Comparison of these results confirms the ability of correlation functions to satisfactorily characterize the action of feedback on the laser dynamics. Numerical predictions obtained from a previously developed, fully stochastic modeling technique provide very close agreement with the experimental observations, thus, supporting the possible extension of our observations to the nanoscale. [ABSTRACT FROM AUTHOR]

We compare the timing jitter of a mode-locked InAs/InP quantum dash (QD) coherent comb laser (CCL) with and without an external cavity self-injection feedback locking (SIFL) system. The jitter is determined through a measurement of the first harmonic of the RF power spectrum of the laser output detected using a fast photodiode. A significant reduction in timing jitter is observed in the laser with the external cavity SIFL. A pulse to pulse root-mean-square time jitter of 1.56 fs is achieved for the laser with the external cavity SIFL. This low timing jitter is a promising light source for the next generation high-speed coherent networking systems and all-optical signal processing. We demonstrate results of a double polarization 16-QAM data format transmission system at a symbol rate of 25 GBd using more than 30 individual channels of the QD CCL. An error vector magnitude of 5.8% and bit error rate of 3.0 × 10–9 were obtained. And, 6.0 Tb/s (16QAM 30 × 25 Gbd PDM) coherent transmission is achieved. [ABSTRACT FROM AUTHOR]

The statistical properties of chaotic signals generated from semiconductor lasers are important in different applications such as secure communications and random bit generation. While the laser dynamics determines the intrinsic statistics of the emission, the process of detection can significantly affect the statistics of the output signals. Using the rate-equation model, the role of detection on the statistical properties of the output signal is systematically investigated for a chaotic laser subject to optical injection. The chaotic emission is converted into electrical outputs using different detection schemes. The statistics of the output signals are evaluated through the probability density functions (PDFs). By low-passed direct detection, the PDF becomes nearly Gaussian when the cutoff frequency of the filter is lower than the relaxation resonance frequency of the laser. Alternatively, the PDF becomes nearly Gaussian when strong frequency components are avoided in band-passed direct detection, optical heterodyne detection, or electrical heterodyne detection. Additionally, through reconstructing the detected state space, the divergence of neighboring states is quantified by the time-dependent exponent (TDE). Gaussian PDFs are yielded using the abovementioned detection schemes without much affecting the TDE slopes. The results indicate the importance of detection on the statistics associated with chaotic lasers in random signal generation. [ABSTRACT FROM AUTHOR]

Gain-coupled 4 × 25 Gb/s electroabsorption modulated laser (EML) array is implemented by an identical epitaxial layer integration scheme. Gain-coupling is incorporated via absorptive gratings to improve the single mode yield of the device. The EML array exhibits excellent single-mode performance, high extinction ratio, and a modulation bandwidth over 28 GHz. Clear eye opening under 28-Gb/s nonreturn-to-zero modulation has been demonstrated for all four channels. Transmission performance of the EML array over 20- and 40-km single-mode fiber is tested, confirming its potential for 100 GbE applications. [ABSTRACT FROM AUTHOR]

This paper presents numerical investigations into the effect of feedback phase on the stability of semiconductor nanolasers (SNLs) in the presence of the external optical feedback. For this purpose, numerical solutions are obtained from rate equations where the effects of Purcell cavity-enhanced spontaneous emission factor F and an enhanced spontaneous emission coupling factor β are included. In this way, a phase-insensitive stable SNL is identified when the feedback coupling fraction is below a critical threshold ηc. Furthermore, the relationship between ηc and two other important system parameters, namely the injection current (Idc) and the initial external cavity length (L0), is studied. The results show that ηc has a bi-exponential relationship with either Idc or L0. Moreover, the influence of F on the ηc is evaluated, and it is found that ηc increases with the increase of F. The results presented in this paper provide practical guidelines for the design of phase-insensitive stable SNLs, which are useful for densely integrated photonic circuits based applications, such as optical communications and sensing. [ABSTRACT FROM AUTHOR]

Mode-locked laser sources with high repetition rates in the range of 10–1000 GHz are of considerable interest in modern communications, optical metrology, and photonic applications. Currently, developed laser systems generally suffer from the hardware complexity and energy loss. Here, we demonstrate a compact robust scheme based on a self-mode-locked monolithic Yb:KGW laser with external feedback coupling to achieve numerous repetition rate multiplications in the range of 25–330 GHz. The output pulse train consists of two orthogonally polarized components to form a vector state that is beneficial to practical applications. More intriguing, the pulse train measured as a function of the distance of the coupling feedback reveals a feature of the fractional recurrence that is like the Talbot carpet. An analytic formula is derived to manifest the formation of the temporal carpets. The developed experiment and formula not only pave a useful way for generating ultrahigh-repetition-rate femtosecond lasers but also provide new perspectives in the fractional recurrences of coherent waves. [ABSTRACT FROM AUTHOR]

We propose a method to generate physical random numbers based on intermittent optical chaos. Intermittent chaotic output is produced in a semiconductor laser subjected to optical feedback embedded in a photonic integrated circuit. This dynamics is characterized by a temporal waveform organized in a succession of laminar regions of low amplitude and bursts of high amplitude. The temporal randomness ruling the alternation of successive laminar regions and bursts is used as an entropy source to generate sequences of random bits. We compare the performances of the exclusive OR and reverse methods implemented in the bit generation process and evaluate the quality of the random bits with the Rabbit test of TestU01 for different bit sequences lengths. [ABSTRACT FROM PUBLISHER]

A tunable distributed feedback (DFB) laser array integrated with a silica-based external optical feedback planar lightwave circuit is proposed and developed. The laser does not have high-resolution optical filters, and we can tune the wavelength over the entire C-band simply via laser selection and temperature control. The spectral linewidth is successfully reduced thanks to the optical feedback effect. Narrow linewidths of less than 10 kHz are obtained over the entire C-band. [ABSTRACT FROM PUBLISHER]

The effect of bias current on the complexity and time-delay signature of chaotic signals in semiconductor lasers with polarization preserved optical feedback has been studied experimentally and theoretically. The peak value of the autocorrelation coefficient and the normalized permutation entropy at the feedback round trip time are used to quantify the time delay signature and complexity, respectively. The results show that the time-delay signature is approximately in an inverse relationship with the complexity of chaos when the semiconductor laser is subject to low or strong optical feedback. However, the inverse relationship disappears when the laser operates at higher bias currents with intermediate feedback strength. The simulation results are qualitatively agreed with the experimental results. [ABSTRACT FROM PUBLISHER]

The dynamics of hybrid III-V/Si lasers are studied for the first time under a combination of two optical feedbacks. A cleaved fiber placed about 20 μm away from the laser creates a short feedback cavity. The effect of this short feedback is studied on a Fabry–Perot laser and reveals the sensitivity of the device to such perturbation, as well as the presence of sub-cavities in the Si waveguides. The dynamics of the laser subjected to additional feedback from a 70-m fiber cavity show that the long-feedback dynamics are governed by the sub-cavities. This behavior is confirmed using a complex tunable III-V/Si laser. [ABSTRACT FROM PUBLISHER]

Self-mixing interferometry is a noncontact method well suited for measuring a variety of biological signals, like blood pressure wave at wrist and thorax (the optical stethoscope), blood velocity in vein and in external circulation, THz echoes from skin, ear drum vibration, and oculomotor reflex measurements. In this review, after presenting the underlying theory and the main developments of self-mixing, we analyze the applications to biosignal measurement reported so far, and illustrate potentialities and perspectives of the technique. [ABSTRACT FROM PUBLISHER]

We introduce a novel scheme for the simultaneous reduction of time-bandwidth product (TBP) and RF linewidth of quantum-dash two-section mode-locked lasers using optical injection-locking and filtered optical feedback. The optical injection-locked laser, double-locked with optical feedback showed 2\!\!\times TBP reduction and RF linewidth reduction by two orders of magnitude. This stabilization technique is implemented in an all-optical arrangement without optical/electrical conversion which is ideal for high-repetition-rate devices and photonic integration. [ABSTRACT FROM PUBLISHER]

Time-delay (TD) signature concealment in a chaotic vertical-cavity surface-emitting laser (VCSEL) is studied experimentally. The VCSEL is subject to variable optical polarization angle of feedback along with variable optical feedback strength and bias current. The TD signature concealment is determined through the use of autocorrelation and information theory-based permutation entropy functions. It is found that the TD signature is concealed at low feedback of strength of order –18 dB. At moderate feedback strength, the TD signature is sensitive to the rotation of optical polarization angle of feedback with TD concealment being observed for polarization angles in the range from 45° to 90°. [ABSTRACT FROM PUBLISHER]

This paper investigates the modulation properties of self-injected quantum-dot semiconductor lasers. Using a semianalytical approach, the modulation characteristic of a quantum-dot nanostructure laser operating under the influence of optical feedback is successfully modeled. This novel approach derives a feedback-induced modulation response model based on the incorporation of the specific quantum nanostructure carrier dynamics as well as the effects of nonlinear gain. This study investigates the impacts of the carrier capture and relaxation time as well as other material parameters such as linewidth enhancement factor, differential gain, and gain compression factor for different feedback configurations. It is also shown that, under the short external cavity configuration, the dynamic properties such as the relaxation frequency as well as the laser's bandwidth can be improved through controlled optical feedback. On the other hand, numerical results show that under the long external cavity configuration, any small back-reflection from the laser's facets combined with the large variations of linewidth enhancement factor would significantly alter the laser's modulation response. [ABSTRACT FROM PUBLISHER]

Harmonic mode-locking of a directly modulated weak-resonant-cavity Fabry–Perot laser diode (WRC-FPLD) at 10 GHz via the self-feedback of a fiber ring is demonstrated. The WRC-FPLD directly modulated at 10 GHz simultaneously functions as the gain medium and the active mode-locker in the self-feedback ring. The competition between the gain-switched lasing mechanism inside the WRC-FPLD and the harmonic mode-locking mechanism of the incorporated self-feedback fiber ring is monitored. The enhanced mode-locking force can be achieved at self-feedback ratio of 90% and modulation power of 28 dBm. The evolution of pulsating dynamics is dependent with modulation frequency, which enhances the mode-locking and shortens the pulsewidth at the longitudinal mode spacing. A mode-locking theory is used to simulate the coupled-cavity self-injected WRC-FPLD fiber ring. When the lasing mechanism transfers from intracavity gain-switching to intercavity harmonic mode-locking, the longitudinal mode of the WRC-FPLD is broadened with the mode extinction reduced from maximum to minimum. Due to the transformation from the gain-switching to harmonic mode-locking, the coupled-cavity self-feedback WRC-FPLD fiber ring delivers a pulsewidth of 22 ps, a timing jitter of 153 fs, a pulse extinction ratio of 13.65 dB, and a spectral linewidth of 7.6 nm, by setting the WRC-FPLD bias at three times above threshold (∼60 mA) and the intracavity feedback ratio of 90%. [ABSTRACT FROM PUBLISHER]

The increasing amount of data being generated in different areas of science and technology require novel and efficient techniques of processing, going beyond traditional concepts. In this paper, we numerically study the information processing capabilities of semiconductor lasers subject to delayed optical feedback. Based on the recent concept of reservoir computing, we show that certain tasks, which are inherently hard for traditional computers, can be efficiently tackled by such systems. Major advantages of this approach comprise the possibility of simple and low-cost hardware implementation of the reservoir and ultrafast processing speed. Experimental results corroborate the numerical predictions. [ABSTRACT FROM PUBLISHER]

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]

We revisit the well-known Tkach and Chraplyvy (T–C) diagram of feedback regimes in semiconductor lasers. Our aim is twofold: first, extending the classification of feedback effects in the T–C diagram to short and long external cavities, and to coherent and incoherent interactions; second and more important, identifying in the diagram feedback phenomena that have been meanwhile studied and developed to noteworthy applications, namely, self-mixing, period-1 and multiperiodicity, intermittency and chaos. We complement the feedback diagram with application regions, so as to describe not only feedback effects detrimental to a laser used as the transmitter of an optical link, but also feedback effects in the weak and strong regime of interaction, developed into applications for instrumentation and communications in recent years. [ABSTRACT FROM PUBLISHER]

Vertical-cavity surface-emitting lasers (VCSELs) are as sensitive to optical feedback (OF) as edge-emitting lasers as their much higher mirror reflectivity is compensated by the much smaller intracavity round-trip time resulting in a similar OF rate. VCSELs may emit light in multiple transverse modes and may exhibit polarization bistability which adds new features to their behavior when subject to OF. We present a survey on experimental and modeling results for three regimes of OF in VCSELs: long, short, and extremely short external cavities (ECs). We show that for long and short ECs, the Lang–Kobayashi model is in good agreement with experiments on OF-induced polarization switching, mode hopping, and antiphase oscillatory dynamics at the delay time. These last dynamics modify polarization residence-time distribution making it oscillatory. We demonstrate numerically and experimentally coherence resonance in such bistable, time-delayed optical system. We present results on low-frequency fluctuation and pulse-package dynamics in VCSELs and discuss the role of light polarization. We discuss polarization rotating OF for generating high-frequency pulses as a result of EC mode beating. Finally, we demonstrate how OF from extremely short EC can strongly modify VCSEL characteristics and can be used to effectively control their polarization properties by subwavelength changes of the EC length. [ABSTRACT FROM PUBLISHER]

The polarization switching (PS) properties of mutually coupled vertical-cavity surface-emitting lasers (VCSELs) subject to variable-polarization optical feedback (VPOF) are investigated numerically. Two injection schemes, parallel-polarization optical injection (PPOI), and orthogonal-polarization optical injection (OPOI) are considered. The effects of VPOF on PS properties are focused on, and the roles of feedback strength, injection strength, and frequency detuning are also discussed. The outputs in the time domain and the polarization evolution through the representation on the Poincaré sphere are further presented to explain the dynamics during the PS process. For PPOI, both VCSELs exhibit similar PS properties, abrupt PS can be observed with the variation of polarizer angle, and are hardly affected by frequency detuning. For OPOI, both VCSELs exhibit mixed polarization for all polarizer angles when without frequency detuning. In particular, frequency detuning induced PS can also be observed for a given polarizer angle, and are affected by the leader-lagged relationship in terms of injection locking effect in mutually coupled VCSELs. These results provide an effective tool to obtain controllable PS in mutually coupled VCSELs, and give more insight into the polarization dynamics. [ABSTRACT FROM PUBLISHER]

The concealment of time delay signature of chaotic signals, which are generated by a slave laser (SL) with dual-chaotic optical injections (DCOI) from two external-cavity master lasers (MLs), is investigated numerically. Under certain circumstances, the SL can generate complex and wideband chaotic signals by adopting DCOI. Two scenarios of time delay concealment are identified by adjusting the injection strength and frequency detuning. Both the time delays of MLs can be masked simultaneously or only one of them can be eliminated. It is shown that enhanced two-channel optical chaotic communication using isochronous synchronization is successfully achieved, when twin semiconductor lasers are driven by the time delay eliminated chaotic signal. Moreover, this two-channel approach can be extended to any communication systems using complex chaotic signals generated by a small network of coupled semiconductor lasers. Our results are also valuable for understanding the characteristics of time delay signatures in laser networks and chaos-based multiplexing systems. [ABSTRACT FROM PUBLISHER]

All-optical digital circuits based on loop memories are demonstrated. These circuits are a variable optical buffer, an optical random access memory, an optical shift register, and an optical linear feedback shift register. Buffers are employed in network nodes to solve the contentions without loosing information. Shift registers are used for error detection and correction techniques. Linear feedback shift registers are employed for generation of pseudo-random bit sequences, data scrambling, and encryption/decryption of information in secure communication systems. Since the role of optical processing is gradually increasing within the communication systems, the possibility to store information directly in the optical domain can lead to a systems simplification and to a performance improvement. In order to make the schemes suitable for practical applications, optical integration is necessary. The use of semiconductor optical amplifier as gain element into the memory loop allows all the proposed schemes to be integrated. [ABSTRACT FROM PUBLISHER]

A synthesizer-free self-starting optoelectronic oscillating-pulsator based return-to-zero (RZ) carrier, clock, and data generator is demonstrated by using an integrated distributed feedback laser diode and electroabsorption modulator (DFBLD-EAM) link. The theoretical model of the self-pulsating EAM is numerically analyzed to optimize optical RZ carrier, providing the relatively short pulsewidth, highest ON/OFF extinction ratio, timing jitter, and frequency variation of 16.5 ps, 10.1 dB, 0.6 ps, and <220 kHz, respectively. Such a self-pulsating EAM pulsed carrier exhibits a chirp of –13.5 GHz with corresponding chirp parameter of –0.48, which reveals lower frequency chirp accompanied with higher chirp parameter at lower EAM bias. To trigger the pseudorandom binary-sequence (PRBS) data generator, the DFBLD-EAM based self-starting pulsator also delivers an OC-192 microwave clock with a carrier-to-noise ratio of 51.1 dB, a second-harmonics suppression ratio of 55 dB, and a single-side-band phase noise of −110 dBc/Hz at 10 kHz offset. The proposed system provides a synthesizer-free OC-192 RZ data generation with bit-error rate of 10^-9 under receiving power of −19.8 and −17.2 dBm at back-to-back and 25-km propagation. The receiving sensitivity is improved by 2 and 1.6 dB when comparing with that of a commercial synthesizer triggered RZ data generator. The reduced power penalty is attributed to the signal broadening induced by higher frequency chirp of the self-pulsating EAM. The signal-to-noise ratio of the generated RZ data plays more important role than the extinction ratio on obtaining a better Q-factor up to 6.6. [ABSTRACT FROM PUBLISHER]

The pulse-to-pulse rms timing jitter of a 5.25-GHz quantum-dot (QD) two-section passively mode-locked laser is characterized through an all-microwave technique. The experimental phase noise spectra at different harmonics are in good agreement with previous diffusion-based theory. This theory is validated for a QD mode-locked laser device for the first time. This measurement technique provides a simple way to characterize the noise performance of a passively mode-locked laser. Furthermore, the average pulse-to-pulse rms timing jitter reduces from 295 to 32 fs/cycle via external optical feedback. [ABSTRACT FROM PUBLISHER]

The time evolution of the output of a semiconductor laser subject to delayed optical feedback can exhibit high-dimensional chaotic fluctuations. In this contribution, our aim is to quantify the degree of unpredictability of this hyperchaotic time evolution. To that end, we estimate permutation entropy, a novel information-theory-derived quantifier particularly robust in a noisy environment. The permutation entropy is defined as a functional of a symbolic probability distribution, evaluated using the Bandt–Pompe recipe to assign a probability distribution function to the time series generated by the chaotic system. This measure quantifies the diversity of orderings present in the associated time series. In order to evaluate the performance of this novel quantifier, we compare with the results obtained by using a more standard chaos quantifier, namely the Kolmogorov–Sinai entropy. Here, we present numerical results showing that the permutation entropy, evaluated at specific time-scales involved in the chaotic regime of the semiconductor laser subject to optical feedback, give valuable information about the degree of unpredictability of the chaotic laser dynamics. The influence of additive observational noise on the proposed tool is also investigated. [ABSTRACT FROM PUBLISHER]

We introduce and demonstrate experimentally that 2-D photonic crystals (PhC) allow the integration of single-mode distributed-feedback (DFB) lasers with both a precise control of the emission wavelength and a high robustness toward optical feedback. This work is based on double deformation , a novel approach, offering theoretical Q-factors above 6\times 10^5 for high volume guided mode. Experimentally, DFB lasers on a GaAs membrane, lasing around 1 \,\mum, show stable single-mode emission with unaltered performances under high optical feedback of around 15% in energy. [ABSTRACT FROM PUBLISHER]

To quantify the unpredictability of chaotic signals generated by vertical-cavity surface-emitting lasers (VCSELs) subject to polarized optical feedback, we numerically investigate the properties of recently introduced quantifier based on information theory, i.e., permutation entropy (PE) H. VCSEL1 subject to polarization-preserved optical feedback and VCSEL2 subject to polarization-rotated optical feedback are considered. The H for X-polarization (XP) mode, Y-polarization (YP) mode, and total output for both VCSELs are discussed and compared in detail. The influences of feedback strengths, feedback delays, and injection currents are focused on. For lower injection current, the 2-D maps illustrate that the trends of H for the XP mode, YP mode, and total output are different for both VCSELs. While for higher injection current, the values of H for both VCSELs increase with the feedback strengths, are not sensitive to feedback delays, and are higher than the counterparts for lower injection current. Moreover, the H increases with injection current for both VCSELs with a decreasing slope. These results show that the PE is an effective tool for quantifying the degree of unpredictability of chaotic signals of VCSELs, and provides valuable information for choosing the proper chaotic carrier. [ABSTRACT FROM PUBLISHER]

This paper presents our recent progress with the integration of silicon (Si) photonic devices for optical telecommunications. To integrate Si wire waveguides, germanium (Ge) photodetectors (PDs) and silica waveguides, we have developed processes for the selective epitaxial growth of Ge on a Si waveguide core and for the low-temperature deposition of silica waveguide film and introduced spot size converters (SSCs) for coupling Si-wire and silica waveguide with low loss. Using these processes and SSCs, we have managed to monolithically integrate Si variable optical attenuators (VOAs) and Ge PDs, and Si VOAs and a silica arrayed waveguide grating (AWG). In the integrated VOA-PD, the Ge PD accurately detects the attenuation of light power in the Si VOA. The 3-dB cutoff frequency in VOA-PD synchronous operation is around 100 MHz, which is limited by the VOA. The integrated VOA-AWG provides high-speed power-level adjustment independently in every channel of the AWG with a response time of 15 ns. These integrated Si photonics devices exhibit sufficient performance for application to future telecommunications systems that combine WDM and burst-mode packets. [ABSTRACT FROM PUBLISHER]

Optical signal processing, including clock recovery, nonreturn-to-zero (NRZ) to return-to-zero (RZ) or to carrier-suppressed return-to-zero (CSRZ) format conversions, serial-to-parallel conversion, and optical regeneration in NRZ systems using a frequency-doubling optoelectronic oscillator (OEO) is investigated. The key device in the OEO is a dual-output intensity modulator (IM), which is implemented using a polarization modulator (PolM). If a continuous-wave (CW) probe along with a multichannel NRZ signal is injected into the OEO, an electrical clock at half the data rate of the NRZ signal will be generated. When the electrical clock is fed back into the PolM-based IM, it will modulate the later injected CW probe and the NRZ signal, thus carving the NRZ signal to be an RZ/CSRZ signal at the same data rate or an RZ signal at half the data rate of the NRZ signal. Meanwhile, the CW probe is also carved to be an optical pulse train with a frequency equal to the data rate or half the data rate of the NRZ signal. Multichannel line-rate and prescaled clock recovery, NRZ-to-RZ/CSRZ conversion, 1:2 serial-to-parallel conversion, and synchronous-modulation-based regeneration are thus realized. An experiment is performed with all the aforementioned signal processing functions verified. [ABSTRACT FROM PUBLISHER]

We propose a microcavity-to-waveguide side coupling system with a reflector at one end of the waveguide for the feedback. Using this system, one can get a unidirectional output from a microcavity-based light emitter, where the output coupling efficiency and the cavity loss can be enhanced or suppressed through tuning optical phase of the feedback. Theoretical calculations are confirmed by finite-difference time domain (FDTD) simulation of the coupling between a photonic crystal cavity and a microfiber with a perfect mirror attached. Unidirectional coupling from the photonic crystal cavity to the fiber with efficiency of 90% is demonstrated in the simulation [ABSTRACT FROM PUBLISHER]

This paper introduces our self-recognition type of the computer-controlled spectral phase compensator (SRCSC), which consists of a greatly accurate phase manipulator with a spatial light modulator (SLM), a highly sensitive phase characterizer using a modified spectral phase interferometry for direct electric field reconstruction (M-SPIDER), and a computer for phase analysis and SLM control operating in the immediate feedback (FB) mode. The application of the SRCSC to adaptive compensation of various kinds of complicated spectral phases such as nonlinear chirped pulses with a weak intensity, induced-phase modulated pulses, photonic-crystal-fiber (PCF) output pulses, and nonlinear chirped pulses exceeding a 500-rad phase variation over-one-octave bandwidth demonstrated that the SRCSC is significantly useful for compensation of arbitrary nonlinear chirp and hence enables us to generate quasi-monocycle transform-limited (TL) pulses with a 2.8-fs duration. To the best of our knowledge, this 1.5-cycle pulse is the shortest single pulse with a clean temporal profile in the visible to near-infrared region. [ABSTRACT FROM PUBLISHER]

Wavelength stabilization of high-power pump lasers for fiber amplifier applications involves complex interactions between the laser chip and the fiber Bragg grating (FBG). We present a comprehensive theoretical model for the window of operation in the coherence collapse (CC) regime while maintaining wavelength locking in 980-nm FBG-stabilized pumps. Experimental data from the development of a 500-mW grating stabilized pump verifies the theory. We also provide the first evidence that the critical feedback distance for CC operation of longer laser diode chips is sensitive to detuning. [ABSTRACT FROM PUBLISHER]

The behavior of relative intensity noise of GaInNAsSb 1300-nm-range vertical-cavity surface-emitting lasers (VCSELs) is presented for the first time. The relative intensity noise drastically increases beyond a critical optical feedback. It was theoretically and experimentally found that the increase of relaxation oscillation frequencies was effective for the sensitivity of the optical feedback in the single-mode long-wavelength VCSELs. In our experiment, the critical feedback levels were -32 and -29 dB when frequencies were 4.0 and 5.8 GHz. This result is in good agreement with a theory. [ABSTRACT FROM PUBLISHER]

The effect of optical feedback from various reflected points on the spectral-linewidth was analyzed for a wavelength selectable laser consisting of a 12 distributed feedback (DFB) laser array, multimode interference coupler, and semiconductor optical amplifiers (SOA). For all 12 DFB lasers, a narrow linewidth of less than 2 MHz was achieved with over 50 mW by reducing facet reflectivity. [ABSTRACT FROM PUBLISHER]

We present the amplifier- and modulator-integrated laser diode designed for 10-Gb/s transmission over 80-km distance. An antireflection window structure is implemented at the tilt facet of the amplifier to reduce optical feedback by 40 dB. A monitor photodiode is monolithically integrated in the antireflection window region for accurate power regulation. To better control the amplifier input power and to reduce the feedback of amplified spontaneous emission, an attenuation inner-window is incorporated by removing a section of the waveguide. The reproducibility of the chip fabrication process is tested to confirm the design margin. Through amplifying the modulated signals and reducing modulator chirp by amplifier saturation, high-power optical transmission is demonstrated. [ABSTRACT FROM PUBLISHER]

We present a novel optical flip-flop configuration that consists of two unidirectional ring lasers with separate cavities but sharing the same active element unidirectionally. We show that in such a configuration light in the lasing cavity can suppress lasing in the other cavity so that this system forms an optical bistable element. Essential for obtaining the bistability is the presence of an additional feedback circuit that is shared by both lasers. We show experimentally that the flip-flop can be optically set and reset, has a contrast ratio of 40 dB and allows low optical power operation. We also present a model based on roundtrip equations. Good agreement between theory and experiments is obtained. [ABSTRACT FROM PUBLISHER]