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Based on the cascade relaxation model of the quantum dot (QD) lasers, the nonlinear dynamics of a two-state QD laser subject to optical injection is numerically studied. The simulation results show that, for a two-state QD laser operating at the ground-state (GS) and excited-state (ES) emission simultaneously, through adjusting the injection parameters, the two emission states can display the stable (S), injection locking (IL), suppression (SP), period-one (P1), period-two (P2), multi-period (MP), and chaotic pulse (CP) states when the frequency of the injection light is close to the GS lasing frequency. Further mapping of these dynamic states in the parameter space of frequency detuning and injection strength, it is found that the complex dynamic behaviors are mainly distributed in the negative frequency detuning region. In addition, the complexity of the chaotic signal is qualified by the permutation entropy (PE) calculating, and the high complexity signal with PE value over 0.95 is obtained. Moreover, within a certain frequency detuning range, the ES emission can be effectively suppressed by increasing the injection strength. [ABSTRACT FROM AUTHOR]

We theoretically and systematically study the dynamics of carrier density in optically injected VCSELs and correlate it to the observed frequency shift outside the locking region. We also show the dependence of carrier dynamics on all major parameters including frequency detuning, injection level and the linewidth enhancement factor (LEF). [ABSTRACT FROM AUTHOR]

Optical injection (OI) into VCSELs is a powerful tool to control VCSEL behavior and light emission. Previous studies by Doumbia et al. 2021 have shown that OI of a 3-line optical frequency comb (OFC) into a VCSEL allows tailoring the properties of the OFCs emitted in the VCSEL output light. Our efforts extend beyond the previous findings, as for the first time, we study the polarization-resolved nonlinear dynamics maps found in a VCSEL subject to two different types of orthogonal OI, namely continuous-wave (CW) injection and the injection of a 3-line gain-switched (GS) OFC. Our results reveal that, within a significant parameter region (encompassing frequency detuning and injected power), the VCSEL's nonlinear behaviors induced by the OI of a GS-OFC are mainly determined by two factors: (1) the frequencies of the nonlinear dynamics of the VCSEL under CW OI, and (2) the polarization switching curves obtained under both types of OI. Therefore, (1) and (2) provide guidelines to understand the OFCs obtained at the output of the VCSEL. When injecting a 3-line OFC with 2 GHz frequency comb spacing, we demonstrate OFCs with approximately 50 GHz width at the output of the VCSEL, similar to the experimental results of Doumbia et al. 2021. We also identify the nonlinear dynamics that underpin these results. • Revealing physics of VCSEL-generated frequency combs under continuous-wave and modulated injection. • First polarization-resolved nonlinear dynamics maps under both types of optical injection. • First observation of the modulated-Elliptically Polarized Injection Locked state. • Revealing impact of continuous-wave injection dynamics on modulated injection dynamics. • Identifying conditions for periodic, wide frequency combs at VCSEL output. [ABSTRACT FROM AUTHOR]

We numerically studied the chaotic dynamics of a laser diode (LD) system with optical injection, where a pseudorandom signal is applied to the drive current of the master LD, and compared two different methods of quantifying the orbital instability of the LD system, i.e., calculating the orbital expansion exponent (OEE) and the Lyapunov exponent. We found that both exponents are increased and the orbital instability is enhanced by applying a pseudorandom signal when the inherent system without the applied signal is a "window". On the other hand, when the inherent system is chaotic, the OEE is increased and the Lyapunov exponent is decreased with increasing standard deviation of the applied signal. Although the two exponents have a different tendency, it is suggested that the variation of the standard deviation of the applied signal can be identified using both exponents. We then investigated the response of the orbital instability to the frequency range of the applied signal and showed that the orbital instability is efficiently enhanced by using the inherent system is a window and by applying a broad signal that does not have a frequency near the spectral peak of the inherent system and has lower-frequency components than this frequency. [ABSTRACT FROM AUTHOR]

A systematic experimental study of the generation of Optical Frequency Combs (OFCs) by gain switching two types of edge emitting semiconductor lasers (Distributed Feedback and Discrete Mode) is presented. High resolution spectral measurements together with linewidth characterization and the analysis of the temporal profiles and the radio-frequency spectra are used to evaluate the evolution of the quality of the OFCs, as a function of the driving conditions. Different types of emission spectra are identified. The physical origin of the OFC properties is discussed. The results indicate that the driving conditions rather than the device properties determine the OFC quality. The optical injection is demonstrated to either improve or deteriorate the quality of the OFCs generated by gain switching, depending on the injection conditions. [ABSTRACT FROM AUTHOR]

We studied two methods that quantify the orbital instability of a laser diode (LD) in two typical chaotic systems. In one method, a coefficient named the orbital expansion exponent (OEE) is calculated from only the time series of the laser intensity. In the other method, the Lyapunov exponent is calculated from the rate equations. Then we compared the OEE and the Lyapunov exponent to discuss the appropriateness of the OEE. In an optical feedback LD system, the OEE cannot represent the dynamics of the chaotic LD satisfactorily for the large feedback ratio. However, when the LD has a larger drive current and the inherent parameters of the LD are dominant in the dynamics, the OEE represents the dynamics of the chaotic LD as well as the Lyapunov exponent. On the other hand, in an optical injection LD system, the correlation coefficient between the OEE and the Lyapunov exponent is large even if the injection ratio is large. To find the reason for this, we replaced the optical feedback system with a multistage optical injection system, and showed that the feedback terms prevent the OEE from accurately representing the orbital instability of a chaotic laser. [ABSTRACT FROM AUTHOR]

We have demonstrated optical frequency combs (OFCs) featuring low and continuously tunable line spacing in the kilohertz range. The OFCs are generated by pulsed gain-switching of optically injected commercial semiconductor lasers emitting at around 1.55 μ m. After generation, the OFCs are efficiently densified by pseudo-random-binary-sequence phase modulation. The case of an OFC generated by gain-switching at a repetition rate of 1 GHz has been numerically and experimentally analyzed and the conditions for optimal densification have been found. In this case, the comb has been densified by a factor of 2047 and exhibits a 90 GHz flat and broad spectrum consisting of more than 184,000 spectral lines, separated 488 kHz. Although this densification factor is not the largest that can be achieved with the method, it is more than 100 times larger than previously reported factors for gain-switching OFCs. These results open prospects for the use of potentially integrable gain-switching OFCs in applications requiring sub-megahertz line spacing. • Dense and broad-band OFCs in pulsed gain-switched optically injected semiconductor lasers. • Continuously tunable line spacing OFCs in the kilohertz range by PRBS phase modulation. • OFCs densified by 2047 with > 184,000 spectral lines separated 488 kHz were attained. • These results open prospects for the use of potentially integrable gain switching OFCs in applications requiring sub-megahertz line spacing. [ABSTRACT FROM AUTHOR]

In this paper, a novel scheme to generate ultra-wideband (UWB) signals based on cross-gain modulation (XGM) effect in a DFB laser is proposed and experimentally demonstrated, and the modulation and transmission of the UWB signals are also experimentally investigated. In the proposed system, a gain-switched laser (GSL) is used as master laser (ML) and the optical pulses from the ML are optically injected into a DFB laser, which is used as slave laser (SL). By proper system configuration, UWB monocycle, doublet or triplet UWB signals can be generated after the balanced photodiode (BPD) detection. Besides, other modulation formats can also be realized, such as on-off keying (OOK) and pulse amplitude modulation (PAM) by properly modulating the ML optical pulses. Finally, fiber transmission of the modulated UWB signals is experimentally investigated, and it is shown that the UWB signals can be well maintained after 40 km optical fiber transmission. [ABSTRACT FROM AUTHOR]

In this paper, a novel scheme to generate ultra-wideband (UWB) doublet signals based on the cross-gain modulation (XGM) effect in the DFB lasers is proposed and experimentally demonstrated, the modulation and transmission of the generated UWB doublet signals are also researched. In the proposed system, a gain-switched laser (GSL) is used as a master laser (ML) and the optical pulses from the ML are optically injected into two paralleled DFB lasers, which are used as slave lasers (SL). Then the outputs from the SLs are detected by a balanced photodiode (BPD) to generate the Bi-phased UWB signals. By properly setting the system parameters, UWB signals with various modulation formats such as on–off keying (OOK), pulse amplitude modulation (PAM) as well as the phase-shift keying (PSK) can be generated. In addition, fiber transmission of the modulated UWB signals is also experimentally investigated. [ABSTRACT FROM AUTHOR]

• A photonic microwave signal generator was theoretically proposed and demonstrated. • The scheme is based on sustained oscillation dynamics produced in spin-VCSELs under right circularly polarized optical injection. • A very broad tunability range from below 2.5 GHz to around 100 GHz is demonstrated. • The generated microwave frequencies can be tuned by detuning the frequency of the optical injection signal. • The microwave linewidth is reduced from 58 MHz to a medium linewidth of about 14 MHz under optical injection technique. • This configuration paves the way for potential uses of spin-VCSELs in Radio-over-Fiber applications and future technologies. We theoretically propose and demonstrate photonic microwave signal generation with a very broad tunability range from below 2.5 GHz to around 100 GHz. The proposed scheme is based on sustained oscillation dynamics produced in spin-VCSELs under right circularly polarized optical injection. The generated microwave frequencies can be tuned by detuning the frequency of the optical injection signal. The system also takes the advantage of polarization switching phenomena to generate broader microwave frequencies where the generated frequencies are equal to the sum of the absolute detuning frequency and the birefringence split between the spin-VCSEL modes which is 47.7 GHz. Sustained oscillation dynamics provokes tunable periodical oscillations through the adjustment of the frequency detuning and injection strength which can be used as a microwave signal generator. Enhancement of the RF power of the oscillations can be achieved by increasing the injection strength towards the locking regions. The microwave linewidth is reduced from 58 MHz to a medium linewidth of about 14 MHz under optical injection technique. This simple configuration paves the way for potential uses of spin-VCSELs in Radio-over-Fiber (RoF) applications and future technologies. [ABSTRACT FROM AUTHOR]

In this paper, we propose the selective adhesion and rapid injection of a fluorescent sensor into a target cell via the optical control of zeta potential and local vibration stimulus using optical tweezers. A multi-fluorescent sensor, which can respond to both temperature and pH, was encapsulated in anionic lipid layers containing a photochromic material (spiropyran) via the layer-by-layer method. The zeta potential of the lipid layers containing spiropyran was adjusted from negative to positive by photo-isomerization of spiropyran using UV illumination. A single sensor was manipulated by optical tweezers and transferred to a cell surface, thereafter adhering selectively to the cell surface under UV illumination without excess sensor adhesion. We then drove the focal point of the optical tweezers to move up and down circularly near the sensor, mimicking a vibration on the sensor or rapid injection. The surface zeta potential of the liposome layers was measured using a zeta potential analyzer. The fluorescence resonance energy transfer (FRET) method was used to observe the changes in contact area between the adhered sensor and cell membrane before and after vibration. Holographic optical tweezers (HOT) and laser confocal microscopy were used to manipulate the single sensor and to capture fluorescent images. The results showed that the vibration applied on the sensor could push down the sensor, inducing a downward displacement. This displacement caused a corresponding deformation of the cell membrane, which increased the contact area between the sensor and the cell membrane. Without vibration, the sensor was injected into the cytoplasm in 5 h at an injection rate of 40%. By applying the vibration stimulus, we succeeded in the rapid injection of the sensor in 30 min at an injection rate of 80%. [ABSTRACT FROM AUTHOR]

Wide bandwidth chaotic signal generation in a three-section monolithically integrated semiconductor laser (MISL) under external optical injection is investigated experimentally. Through evaluating the effective bandwidth of chaotic signals, the influences of the optical injection on the bandwidth of chaotic signal from the MISL are analyzed. The experimental results indicate that, for the currents of the DFB section (I DFB ) and the phase section (I P ) are fixed at 70.00 mA and 34.00 mA, respectively, the effective bandwidth of chaos signal generated by the solitary MISL reaches its maximum value of 14.36 GHz when the current of the amplification section ( I A ) takes 23.22 mA. After an external optical injection is introduced into the MISL, the effective bandwidth of the generated chaotic signal can be beyond 2.5 times of the maximum value. Furthermore, the effects of the injection strength and the frequency detuning on the effective bandwidth of the generated chaotic signal are also discussed. [ABSTRACT FROM AUTHOR]

Nonlinear dynamical characteristics of a slave semiconductor laser (S-SL) subject to optical injection from a master SL (M-SL) and optical feedback from a fiber Bragg grating (FBG) are investigated experimentally. First, we investigate the nonlinear dynamics of the S-SL subject to only optical injection. Through varying the injection coefficient and fixing the frequency detuning between the M-SL and S-SL, some dynamical states with typical characteristics are recorded and identified. Next, the variations of these dynamical states are further investigated with the introduction of a FBG feedback, and the according results show that these dynamical states may be changed after a FBG feedback is introduced into the S-SL. Finally, after collecting the mappings of the dynamical states of S-SL in the parameter space of injection coefficient and frequency detuning under different FBG feedback coefficients, the influences of FBG feedback on the nonlinear dynamics of the S-SL are analyzed. [ABSTRACT FROM AUTHOR]

In this paper the transmission of OFDM based wired/wireless services for hybrid PONs using direct laser modulation is studied. To overcome the limitations imposed by direct modulation of cost effective low bandwidth laser transmitters, we make use of novel monolithically integrated Discrete Mode lasers and optical injection. The system includes a wired OFDM signal, operating at 12.5 Gb/s and three wireless signals delivering Long Term Evolution (LTE) services encoded with 16 QAM. The system's performance is evaluated for various relative power ratios of the wired/wireless signals. Additionally, the impact of Relative Intensity Noise (RIN) on such a hybrid system is studied through computer simulations. [ABSTRACT FROM AUTHOR]

Abstract: A chaotic ultra-wideband (UWB) over fiber link is proposed and numerically demonstrated. The UWB signals with steerable and flatted power spectrum are generated in the optical domain based on the chaotic dynamics of an optically injected semiconductor laser with optical feedback. The 2.5Gb/s on-off keying encoded chaotic UWB signals are error-free transmitted through a 25km signal-mode (SMF) while the signal to noise ratio (SNR) of the wireless channel was fixed on 20dB. Without utilizing any dispersion compensation module, the RF spectral of the chaotic UWB signals received by antenna fully comply with the spectral mask specified by the U.S. Federal Communications Commission (FCC), and the eye opening penalty (EOP) of the demodulated message are smaller than 3dB. Moreover, we investigate the dependency of the decoded data EOP on the data bit rate, the fiber transmission distance, and SNR of the wireless channel. [Copyright &y& Elsevier]

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

Abstract: A model for optical injection locking in quantum dot (QD) lasers is stated where the electron and hole dynamics are treated separately and their scenarios in the ground state (GS), excited state (ES) in the QDs and in the wetting layer (WL) are examined. A decline in the GS electron occupation probability, and then, a left returned spiral behavior is shown in their phase space projections at high injection ratio. The GS occupation probabilities for electrons and holes are reduced drastically with increasing injection ratio. The injection map is also plotted. [Copyright &y& Elsevier]

Abstract: We experimentally study the intensity dynamics and the optical spectra of two similar mutually delay-coupled semiconductor lasers. While changing two relevant parameters of the coupled system, namely the bias currents and the coupling strength of the lasers, we observe significant modifications in the laser emission characterized via optical spectra, laser intensity dynamics, and cross-correlation functions. We find distinct synchronization scenarios for two bias currents: 1.02 and 1.25 times the threshold bias current of the solitary laser. Optical spectra in both cases strongly depend on the coupling strength between the lasers. For the low bias current and strong coupling, the lasers exhibit dynamical bistability, i.e. the coexistence of low-frequency fluctuations and stable continuous-wave emission. [Copyright &y& Elsevier]

Abstract: An experimental analysis of the influence of optical injection at 1.4μm wavelength into two different commercial 1.55μm DFB lasers is reported. The results demonstrate the strong dependence of the DFB behaviour on the injection parameters. Complete mode suppression or signal amplification can be obtained by varying the excitation wavelength and/or intensity, suggesting that these devices could be operated as logic ports or signal amplifiers, according to the injected signal. [Copyright &y& Elsevier]

Abstract: We show experimentally and by simulation a performance enhancement of a directly modulated 10Gb/s optical Orthogonal Frequency Division Multiplexing (OFDM) system due to external optical injection. The experiment is performed back to back and over 12km of single mode fiber. The injection extends the range of linear operation of the laser and therefore extends the usable bandwidth for direct modulation formats which are susceptible to nonlinearity, such as OFDM. Nonlinearity in the system and its reduction due to injection are estimated by means of a two tone test. Additionally the performance enhancement on OFDM systems was verified in both simulation and experimentally by the comparisons of the average Bit Error Rate (BER) and Error Vector Magnitude (EVM). [Copyright &y& Elsevier]

Abstract: In this paper, the spectral relation between the master and the frequency-locked slave laser (FLSL) is investigated by the conventional technique of optical intensity modulation and optical heterodyne. Experimentally, we demonstrate that under complete and stable locking condition, the lightwave of the FLSL and the sidebands of the master laser produced by the optical intensity modulation are perfectly coherent (frequency coherence). Referring to our recent studies, the lightwave of the master laser and its corresponding sidebands are also perfectly coherent. Additionally, the spectral structures of two perfectly coherent lightwaves are identical in the level of wave train. Therefore, we indirectly verify that the spectral structures of the FLSL and the master laser are identical in the level of wave train. [Copyright &y& Elsevier]

Abstract: We experimentally investigate the dynamical injection-locking map of distributed feedback (DFB) semiconductor laser under strong optical injection (>0dB) with comparison to the weak injection regime and a discussion of associated phenomena. [Copyright &y& Elsevier]

- In recent years, special attention has been paid to the injection lock of quantum cascade lasers, which leads to the improvement of their small signal properties and output power. In this paper, the operation of an injection-locked quantum cascade laser including the output characteristics and modulation response has been investigated. By using one external cavity for optical lock, the resulted structure has complexities may cause instability of a laser that limit the use of this system. In this paper, for the first time, to solve this problem, an optical self-locking system was proposed and the properties of laser under these conditions were investigated. By adding a second external cavity to a single external cavity laser, output power will reach a constant value. The output power of the single cavity laser in free-running mode was about 400 mw while the output power of the laser with two external cavities has been increased to 700 mw. In addition to stabilizing the output power, we also see an increase in bandwidth. We found that for different lengths and reflectivity, the output power of the proposed one external cavity laser in free-running mode does not reach a fixed value and even in some cases, it becomes unstable. But by adding a second cavity to the laser in the free-running mode, it will be able to produce a stable laser with constant output power. Adding external cavities can be used as an effective tool to improve frequency stability or increase bandwidth. [ABSTRACT FROM AUTHOR]

Abstract: We present a comprehensive analytical theoretical model for the relative intensity noise (RIN) spectrum of integrated semiconductor quantum-well (QW) lasers under injection-locking. We use a novel setup by employing an integrated electroabsorption modulator-laser (EML) to measure the RIN of the injection-locked distributed feedback (DFB) laser, where the modulator section is used as a photodetector. The EML has an anti-reflection coating on the laser side, so that an injection light from an external master laser can be coupled effectively into the laser section. This scheme simplifies the setup and reduces the alignment loss between discrete optical components. Experimental data indicates that the injection-locking technique can reduce the RIN noise floor and increase the relaxation frequency of the laser. We also compare the RIN spectra of the free-running laser with the injection-locked laser and show an increase of the relaxation frequency from 3.7GHz (free-running) to 11.3GHz (injection-locked). By fitting the experimental data using our model, we show very good agreement between our data and theory. Our model considers the optical confinement factor of photons and carriers for quantum-well structure lasers. We also improve the injection-locking RIN model by including the gain saturation from the master laser noise. [Copyright &y& Elsevier]

Abstract: In this paper, based on a system composed of a multimode emitted laser diode and a single-mode received laser, chaos synchronization performance has been investigated numerically under different optical injection patterns. The results show that, for single mode injection (SMI) which means the received laser is injected by a selective longitudinal mode of the multimode emitted laser whose wavelength corresponds to that of the single-mode received laser, the system synchronization performance is better than that with multi mode injection (MMI); depending on the optical spectrum of the received laser, the physical mechanism of chaos synchronization deterioration for MMI is given. Additionally, after taking into account the parameter mismatches, the chaos synchronization performance of the system with different injection pattern have also been discussed. For either SMI or MMI, the synchronization performance with negative parameter mismatches is better than that with positive parameter mismatches. [Copyright &y& Elsevier]

Abstract: In an optically injected semiconductor laser, we theoretically investigate the effect of strong double optical injection on the dynamics of electron density within the secondary locking area and the conventional locking region. [Copyright &y& Elsevier]

Abstract: Semiconductor laser with optical feedback emitting chaotic optical signal can be treated as chaotic carrier transmitter. Based on laser rate equations, we numerically study the effect of external injection light on the bandwidth of chaotic carrier transmitter. Our numerical simulation shows that the bandwidth of the chaotic carrier transmitter can be enhanced significantly by external photons injection. Compared with the 2GHz relaxation oscillation frequency of a solitary laser diode without optical injection, the bandwidth of a chaotic carrier transmitter is expanded to 14.5GHz with injection parameter at k inj =0.39. Simulation results also demonstrate that the enhanced bandwidth depends obviously on the frequency detuning between the external injection laser diode and the chaotic carrier transmitter. The maximum bandwidth of the chaotic transmitter can be obtained when the frequency of the injected light is higher than the central frequency of the carrier transmitter between 2GHz and 4GHz. [Copyright &y& Elsevier]

Abstract: An analysis of optical injection on a gain-switched distributed feedback (DFB) laser and its impact on pulse parameters that influence the performance of the pulse source in high-speed optical communication systems is presented in this paper. A range of 10GHz in detuning and 5dB in injected power has been experimentally identified to attain pulses, from an optically injected gain-switched DFB laser, with durations below 10ps and pedestal suppression higher than 35dB. These pulse features are associated with a side mode suppression ratio of about 30dB and a timing jitter of less than 1ps. This demonstrates the feasibility of using optical injection in conjunction with appropriate pulse compression schemes for developing an optimized and cost-efficient pulse source, based on a gain-switched DFB laser, for high-speed photonic systems. [Copyright &y& Elsevier]

Abstract: A method is presented for the automatic construction of an experimental bifurcation diagram of an optically injected solid state laser. From measured time series of laser output intensity, different identifiers of aspects of the dynamics are derived. Combinations of these identifiers are then used to characterize different possible bifurcations. The resulting experimental bifurcation diagram in the plane of injection strength versus detuning includes saddle-node, Hopf, period-doubling and torus bifurcations. It is shown to agree well with a theoretical bifurcation analysis of a corresponding rate equation model. [Copyright &y& Elsevier]

Abstract: We demonstrate theoretically and experimentally that the injection of two optical signals into a semiconductor laser can be a feasible and practical method of enhancing chaos, influencing the stability map and generating various nonlinear dynamics. [Copyright &y& Elsevier]

Abstract: Theory and experiment for dc and small-signal electrical modulation of an injection-locked quantum-well (QW) Fabry-Perot laser are presented. Our experiment is realized by performing side-mode injection locking of a multiple-quantum-well (MQW) InGaAsP Fabry-Perot (FP) laser, which has the advantage of optical wavelength conversion. We first measure the dc characteristics and optical spectra of an injection-locked laser to define its locking range and linewidth enhancement factor. We then show experimentally that the bandwidth of an injection-locked semiconductor laser is 10.5GHz, which is around twice the free-running electrical modulation bandwidth (5.3GHz). The relaxation frequency of the injection-locked laser can be 3.5 times greater than the free-running value. Our theoretical model includes mode competition, gain saturation, low frequency roll-off, and optical confinement factor of the QW structure. The theory shows good agreement with our experimental results. We point out that the small-signal modulation of injection-locked lasers still suffers severely from low frequency roll-off, which comes from the carrier transport effect and parasitic effect of the bias circuit. If we can reduce those effects, the modulation bandwidth can be further increased to 15GHz, which is around 3 times of the free-running value. [Copyright &y& Elsevier]

Abstract: The dynamics of an optically injected solid state Nd:YVO4 laser is studied using intensity time series analysis. Experimental time series are demonstrated to be in good agreement with the rate equation model of an injected class B laser if α ≃0.35 is chosen for the linewidth enhancement factor in the model. Asymmetry in the dynamics is observed; the route to locking is via a Hopf bifurcation above and via a saddle-node bifurcation below the symmetric locking region. [Copyright &y& Elsevier]

Abstract: A numerical study of using external optical injection to suppress the nonlinear dynamics introduced by external optical feedback in vertical-cavity surface-emitting lasers (VCSELs) has been undertaken. The model under consideration is a master–slave configuration where the master VCSEL provides the continuous wave to control the nonlinear behaviors arising in the slave VCSEL. Simulation results indicate that the feedback-induced nonlinear dynamics (e.g. chaotic, single-periodic, and multi-periodic oscillations), relative intensity noise (RIN) as well as the coherence collapse can be suppressed effectively as long as the injection is strong enough to overcome the nonlinear effects of the feedback. [Copyright &y& Elsevier]

Nonlinear dynamical characteristics of an optically injected semiconductor laser subject to optoelectronic feedback is studied numerically. The dynamic states including stable locking, periodic oscillation, chaotic oscillation, regular pulsing, quasiperiodic pulsing, and chaotic pulsing seen in a semiconductor laser subject to either optical injection or delayed optoelectronic feedback alone, can all be found in this hybrid system where the laser is subject to both optical injection and optoelectronic feedback. While this system can follow either the period-doubling or the quasiperiodic route to chaos, transition states bridging chaotic oscillation states and chaotic pulsing states are identified and shown. Mappings of dynamic states in the parameter space are plotted, where a large expansion and shifting of the chaos region is observed and is compared with an optically injected laser without optoelectronic feedback. As the injection strength increases, the bandwidths of the chaotic states in the broadened area of this hybrid system are significantly enhanced. The advantages and potential applications of this hybrid system are discussed. [Copyright &y& Elsevier]

We demonstrate an all-optical scheme for coding high frequency mode-locked semiconductor laser pulse trains. The scheme is experimentally demonstrated by optically modulating a high frequency pulse train at 38 GHz generated by a subharmonic synchronous mode-locked semiconductor laser with binary information contained in multiple low bit rate optical data signals (3.8 Gb/s). Synchronization between the two signals is achieved through optical injection into the mode-locked laser while high speed modulation is achieved via a nonlinear optical loop mirror made of dispersion shifted fiber. The coding scheme has advantages over existing passive multiplexing schemes in generating high data rate optical signals due to its regeneration and wavelength conversion functionality. [Copyright &y& Elsevier]

An experimental study of the dynamical properties of a semiconductor laser subjected to external optical injection is presented. The effect of the laser current on the dynamical regions as found in an experiment is reported on for the first time. The nonlinear dynamical regions are mapped in the parameter plane consisting of the detuning between lasers and the injection strength, by utilizing a method of condensing the information in output spectra to two-dimensional images. Corresponding maps for different values of the slave laser current are recorded. The recordings present conclusive experimental evidence that the overall locations of the dynamical regions scale with respect to the relaxation–oscillation frequency and the injection strength relative to the free running laser power. The results further support the theoretical prediction that the linewidth-enhancement factor is the parameter which most strongly affects the dynamics. Locally, specific chaotic regions are found to grow for higher operating points of the slave laser. A complete characterization of the parameters that enter the rate-equations for the visible output AlGaInP laser used in this experiment is performed. [Copyright &y& Elsevier]

We investigate semiconductor quantum dots by optically injecting a well controlled unequal number of electrons and holes into an isolated single dot. The injected carriers form charged complexes of many carriers in the dot. Radiative electron–hole pair recombination takes place after the charged complex relaxes to its ground state. We spectrally and temporally resolve the emission and show that it can be used to unambiguously determine the discrete charge states of the emitting quantum dot. In particular, we identify the emission from both negative and positive charge states of the same dot. We show that while negative charging results in red shifted emission energy, compared with a neutral dot, positive charging results in blue shifted emission energy. We explain this observation in terms of the better confined wave functions of the holes. Due to their smaller volume, the energy associated with hole–hole repulsion is larger than the combined energy associated with electron–hole attraction and electron–electron repulsion. [Copyright &y& Elsevier]

A microwave frequency comb (MFC) consists of equally spaced discrete microwave frequency components that have small magnitude variations across its bandwidth. In this work, a scheme comprising of a slave laser that is optically injected by a strongly intensity-modulated master laser is proposed and numerically investigated to generate MFCs. Based on the double-locking characteristics of the periodic oscillations induced by strong intensity-modulated optical injection, locked comb structures are invoked when the modulation frequency is at a submultiple frequency of the period-one oscillation frequency. Furthermore, broad microwave frequency comb bandwidths are achieved through the bandwidth enhancement effect of optically injected lasers at appropriate operating conditions. The demonstrated MFC source has a continuously tunable comb-line spacing between 1–10 GHz reaching bandwidths that are six times the relaxation resonance frequency of the free-running semiconductor laser. [ABSTRACT FROM AUTHOR]

• Generation of high-quality OFCs in optically injected laser diodes by pulsed gain-switching. • Cost-effective SRDs used as electrical generators produce OFCs with 900 tones spaced by 100 MHz. • The optical injection does not affect evenly all the tones, leading to a relatively non-uniform OFC. • Timing jitter of the electrical source has been demonstrated to impact the quality of the OFCs. • The use of SRDs reduces the cost, size and footprint of the low repetition rate OFC generators. We report on the experimental generation of high-quality Optical Frequency Combs (OFCs) at low repetition rates in an externally-injected gain-switched semiconductor laser using a Step-Recovery Diode (SRD) as the pulsing source. The use of an SRD as the electrical pulse generator allows us to produce high-quality OFCs with over 900 comb tones spaced by 100 MHz. Through experimental measurements, supported by simulations, the timing jitter of the electrical source has been demonstrated to impact the quality of the generated OFCs giving rise to a non-uniform Carrier-to-Noise Ratio which is higher around the injection and reduces with decreasing frequency. Nevertheless, comparing the OFC quality obtained using an SRD with those obtained with a costly pulse pattern generator, we conclude, that despite the slightly degraded OFC quality, the use of SRDs could reduce the cost, size and footprint of the equipment required for low repetition rate OFC generation. [ABSTRACT FROM AUTHOR]

• An ultra-wideband tunable chaotic laser is obtained based on electro-optic modulation. • This system is can be applied in high-speed broadband communication and sensing. • A controllable chaotic laser signal production method is demonstrated. A tunable self-mixing chaotic laser based on high frequency electro-optical modulation is proposed. A laser dynamics system is designed and tested for tunable chaotic laser generation and provides optical feedback and electro-optic modulation with two degrees of freedom. The chaotic laser is generated by optical feedback, and it becomes tunable by high frequency electro-optic modulation. The frequency is modulated from 10 MHz to 10 GHz to test this system, and an ultra-wide band chaotic laser from 0.8 GHz to 24 GHz is measured by an electrical spectrum analyzer (ESA). The experimental results show the generation of a tunable chaotic laser via electro-optic modulation. At the same time, this tunable chaotic laser has a highly sensitive dynamic response near the 2.0 GHz range of frequency modulation. The system is proved to be suitable for applications in high-speed broadband communication and sensing. [ABSTRACT FROM AUTHOR]

This paper shows a complex nonlinear dynamics of an optically injected laser diode (LD) directly modulated by electrical current from a resonant tunneling diode (RTD) circuit. The LD model evolves a new control parameter called effective gain coefficient (EGC) and can switch between a free-running laser and a perturbed laser. A bifurcation diagram analysis sustained Lyapunov exponents' spectra reveals chaotic and quasi-periodic dynamics for restricted ranges of the frequency f i n and by EGC variations, including the generation of the hyperchaotic regime and multiscroll chaotic attractors through a cascade of periodic oscillations to the chaos. Moreover, an implementation of this new coupled system also shows that when an AC signal V a c sin ⁡ 2 π f i n t is added to the DC voltage bias, the LD outputs show several optical signals such as periodic, coherence collapse and chaotic regimes with different strange complex attractors which are devoted to more improve secure optical telecommunications. [ABSTRACT FROM AUTHOR]