Sensitivity of quantum-dot semiconductor lasers to optical feedback

The sensitivity of quantum-dot semiconductor lasers to optical feedback is analyzed with a Lang-Kobayashi approach applied to a standard quantum-dot laser model. The carriers are injected into a quantum well and are captured by, or escape from, the quantum dots through either carrier-carrier or phonon-carrier interaction. Because of Pauli blocking, the capture rate into the dots depends on the carrier occupancy level in the dots. Here we show that different carrier capture dynamics lead to a strong modification of the damping of the relaxation oscillations. Regions of increased damping display reduced sensitivity to optical feedback even for a relatively large alpha factor.     

Longitudinal mode competition in semiconductor lasers under optical feedback: Regime of short-external cavity

This paper introduces a theoretical study of longitudinal mode competition in semiconductor lasers subject to optical feedback. The study is based on a model of time-delay multimode rate equations taking into account both symmetric and asymmetric suppressions of modal gain. The model is numerically solved and applied to the case of a short-external cavity. Mode competition is characterized along the feedback-induced period-doubling route to chaos as well as under chaotic dynamics. Contributions of symmetric and asymmetric gain suppressions to both mode dynamics and modal operation under OFB are clarified. The results show that under chaotic dynamics, mode competition induces multimode hopping giving rise to asymmetric multimode output spectra. In regimes of continuous-wave operation, mode competition supports single-mode oscillation, and the side-mode suppression ratio improves with the increase of feedback. In the regime of strong feedback, the lasing mode moves to either long- or short-wavelength side in a seemingly random fashion, which is strongly related to asymmetric gain suppression.     

Rate equations for modelling of short-pulse rare-gas halide excimer lasers

In this work, on the basis of the analysis of data relating to relaxation processes and emission spectra of excimer molecules, the rate equations for modelling short-pulse rare-gas halide excimer lasers are formulated and discussed. The equations take into account relaxation processes important for short-pulse generation, such as decay of B-, C- and X-states, vibrational relaxation in these states, and B-C mixing. As a special case for these equations, simplified equations for KrF and XeCl lasers are introduced. The gain recovery curves and the dependences of saturation energy on pulse duration, computed both for KrF and XeCl, coincide well with the experimental data. Discussion of the factors influencing the gain dynamics and the saturation energy of these media, is also presented.     

Research progress of low-dimensional metal halide perovskites for lasing applications

Metal halide perovskites have been regarded as remarkable materials for next-generation light-harvesting and light emission devices. Due to their unique optical properties, such as high absorption coefficient, high optical gain, low trappingstate density, and ease of band gap engineering, perovskites promise to be used in lasing devices. In this article, the recent progresses of microlasers based on reduced-dimensional structures including nanoplatelets, nanowires, and quantum dots are reviewed from both fundamental photophysics and device applications. Furthermore, perovskite-based plasmonic nanolasers and polariton lasers are summarized. Perspectives on perovskite-based small lasers are also discussed. This review can serve as an overview and evaluation of state-of-the-art micro/nanolaser science.     

A theoretical analysis of the effects of erbium ion pair on the dynamics of an optical gain stabilized fiber amplifier

In this paper, the effects of ion-pair formation on the gain dynamics of multi cavity optical automatic gain control erbium doped fiber amplifier is modelled. The inhomogeneous Cabezas simple model is used to write the rate and propagation equations for the active medium. The solution of the governing equations shows that in high concentration of the erbium ions, depending on the pumping rate, the relaxation oscillations are converted to nT-Periodic or even to chaotic behavior. Although the high concentration erbium ion in the optical amplifiers decreases the conversion efficiency and increases the threshold pump power, amplitude of the transient effects is reduced in the multi feedback-loop WDM amplifiers relative to the low concentration erbium ions multi feedback-loop optical amplifiers and ion-pairs, which act as a saturable absorber to compensate the gain tilt caused by the OAGC laser spectral hole burning. The theoretical results are in complete agreement with the previous published experimental results.     

Low-frequency dynamics of lasers

An approach to nonlinear dynamics of multimode lasers is developed. It is based on the concept of two systems of eigenoscillations: optical modes and relaxation oscillations. The importance of a correct (not arbitrary) choice of a model is underlined. Characteristic features of two different rate equation models are formulated and compared. A method of selective perturbation on the system is described which makes it possible to study interrelations between optical modes and relaxation oscillations, and to control dynamical behavior of a laser. The possibility of using dynamical regularities for solving both applied and basic problems is illustrated in several examples. (c) 1996 American Institute of Physics.     

Theory of carrier gain dynamics in InGaAs/AlGaAs strained-layer single-quantum-well diode lasers

Calculations of the femtosecond gain dynamics in InGaAs/AlGaAs strained-layer single-quantum-well diode lasers are presented and compared to experiments which use a novel multiple-wavelength pump probe technique. We develop a detailed theoretical model for the gain dynamics in a quantum well laser diode structure to aid in the interpretation of gain dynamics induced by both interband absorption and stimulated emission of photons. In the model, transient gain and differential transmission are computed in a multiband effective mass model including biaxial strain, valence subband mixing, and scattering both within and between subbands. The transient photogeneration of electron-hole pairs by the pump pulse and subsequent relaxation of carriers by both polar optical phonon scattering and carrier-carrier scattering are calculated within a Boltzmann equation framework. A relaxation approximation for the carrier-carrier scattering is made making the coupled Boltzmann equations an effective one dimensional model which are then solved using an adaptive Runge-Kutta technique rather than a more computationally intensive Monte Carlo approach.     

用直接模拟法分析量子阱半导体激光器瞬态响应

根据光增益与载流子密度的对数关系 ,通过适应于多量子阱激光器的速率方程的直接模拟分析 ,得到了注入电流、阱数和腔长对多量子阱激光器的激射阈值、开关延迟时间、弛豫振荡频率和光输出等参量之间的依赖关系 .运用相图确立了在瞬态过程中 ,载流子数密度和光子数密度之间的转化过程 .从而为改善量子阱激光器的高频调制特性以及优化设计器件结构参数提供了理论依据     

用直接模拟法分析量子阱半导体激光器瞬态响应

根据光增益与载流子密度的对数关系,通过适应于多量子阱激光器的速率方程的直接模拟分析,得到了注入电流、阱数和腔长对多量子阱激光器的激射阈值、开关延迟时间、弛豫振荡频率和光输出等参量之间的依赖关系.运用相图确立了在瞬态过程中,载流子数密度和光子数密度之间的转化过程.从而为改善量子阱激光器的高频调制特性以及优化设计器件结构参数提供了理论依据.     

Multi-state optical flip-flop memory based on ring lasers coupled through the same gain medium

We investigate a system consisting of multiple ring lasers coupled by a single gain medium. All the ring lasers share a common feedback arm. The output power of an individual laser shows periodic oscillations as a function of time. The periodicity of the oscillation is determined by the ratio of the roundtrip times of the feedback arm and the ring cavity. In the case that two of such ring lasers are coupled, either their oscillation periodicities are synchronized, or the system is bi-stable. In the latter operation regime, the system can act as an optical flip-flop memory whose state be switched by injection of external light. The concept can be extended to multi-state operations; an eight-state optical flip-flop memory is experimentally demonstrated.     

Noninvasive optical control of complex semiconductor laser dynamics

Time-delayed feedback control (TDFC) is transferred to the optical domain and applied to complex multisection semiconductor lasers as used in optical communication. Pyragas-type control is provided by purely optical feedback from an external Fabry-Pérot interferometer. This all-optical setup needs no time-consuming signal processing and, thus, has practically no speed limit. Proof-of-principle experiments demonstrate noninvasive stabilization of unstable steady states, chaos control, and suppression of noise-induced oscillations on picosecond time scales. A Lang-Kobayashi type model with optical TDFC is investigated taking into account the dynamic details of the device as well as all-optical time-delayed feedback. The parameter regimes that allow for stabilization of stationary emission are mapped out in good agreement with the experiments. Including noise, an analytical expression for the power spectral density is derived, which is confirmed by the experimental all-optical suppression of noise-induced relaxation oscillations.     

Low frequency fluctuation with two external cavity reflectors

The dynamics of a semiconductor laser with two optical feedbacks is studied in this paper. A new set of nonlinear rate equations that can describe external cavity semiconductor lasers with any amount of two optical feedbacks is proposed. It is found that when the laser is biased above the threshold and subjected to one feedback, the other feedback can induce low-frequency fluctuations.     

新型双波长激光增益控制掺铒光纤放大器

掺铒光纤非均匀展宽引起的空间烧孔现象导致单波长激光并不能完全控制放大器增益。提出了一种新颖简单的结构，利用自由光谱范围为26．7nm的法布里－珀罗可调谐滤波器和由长周期光纤光栅制成的波长选择性可调谐的衰减器，有效地调整不同波长处的腔内损耗，可以实现不同强度的双波长激射。由两个不同波长的激光共同承担增益控制的任务，降低了控制激光引起的空间烧孔，同时双波长激射有效地抑制了信号光的弛豫振荡。     

Nonstationary chaotic oscillations in lasers with frequency-shifted feedback

The nonlinear dynamics of lasers with frequency-shifted delayed feedback are investigated. Resonant excitation of sustained relaxation oscillations by harmonic resonance is demonstrated. Self-induced switching between sustained relaxation oscillation and spiking oscillation is observed as the feedback coefficient is increased. Observed instabilities are well reproduced by numerical simulations of proposed model equations. A statistical analysis of this switching phenomenon is carried out numerically, and the results indicate that an inverse-power relation with the feedback coefficient determines the periods over which the system dwells in its relaxation-oscillation state.     

Numerical study of converting beat-note signals of dual-frequency lasers to optical frequency combs by optical injection locking of semiconductor lasers

The optical injection locking of semiconductor lasers to dual-frequency lasers is studied by numerical simulations. The beat-note signals can be effectively transformed to optical frequency combs due to the effective four wave-mixing in the active semiconductor gain medium. The low-noise Gaussian-like pulse can be obtained by locking the relaxation oscillation and compensating the gain asymmetry. The simulations suggest that pulse trains of width below 30 ps and repetition rate in GHz frequency can be generated simply by the optical injection locking of semiconductor lasers. Since the optical injection locking can broaden the spectrum and amplify the optical power simultaneously, it can be a good initial stage for generating optical frequency combs from dual-frequency lasers by multi-stage of spectral broadening in nonlinear waveguides.     

Theoretical modeling of the dynamics of a semiconductor laser subject to double-reflector optical feedback

We theoretically model the dynamics of semiconductor lasers subject to the double-reflector feedback. The proposed model is a new modification of the time-delay rate equations of semiconductor lasers under the optical feedback to account for this type of the double-reflector feedback. We examine the influence of adding the second reflector to dynamical states induced by the single-reflector feedback: periodic oscillations, period doubling, and chaos. Regimes of both short and long external cavities are considered. The present analyses are done using the bifurcation diagram, temporal trajectory, phase portrait, and fast Fourier transform of the laser intensity. We show that adding the second reflector attracts the periodic and perioddoubling oscillations, and chaos induced by the first reflector to a route-to-continuous-wave operation. During this operation, the periodic-oscillation frequency increases with strengthening the optical feedback. We show that the chaos induced by the double-reflector feedback is more irregular than that induced by the single-reflector feedback. The power spectrum of this chaos state does not reflect information on the geometry of the optical system, which then has potential for use in chaotic (secure) optical data encryption.     

强流电子束泵浦XeCl准分子激光动力学模型

强流电子束泵浦XeCl准分子激光动力学模型由三部分组成,即电子束能量沉积的计算;电子温度、电子反应速率的计算和化学/激光动力学。这个模型可以准确地预报小信号增益、吸收等激光特征量的时间变化规律。 该模型是在文献[1]、[2]、[3]报导的动力学模型的基础上提出的。采用四阶龙格_库塔法在VAX—11/780机器上进行数值求解。 计算给出XeCl准分子激光反应过程中各种粒子浓度、小信号增益、吸收、输出光强、激发速率以及平均电子能量随时间的变化规律。计算结果表明本征效率是激发速率,电流密度和工作气体(Ne/Xe/HCl)的各分压比的函数。 该模型可为高功率准分子激光器的研制提供设计参数和最佳实验条件。     

Current self-distribution effects in oxide-confined vertical-cavity surface-emitting lasers

We develop a self-consistent electro-optical model for oxide-confined Vertical-Cavity Surface-Emitting Lasers, including optical polarization and spin-flip dynamics. When subject to large signal modulation, current self-distribution effects reduce the amount of spatial-hole burning in the device, leading to a reduced overshoot during transients and an increased damping of the relaxation oscillations.     

脉冲CO2激光器注入锁定特性的数值模拟

扩展了脉冲CO2激光器的多频动力学理论。将多频动力学模型中的光强方程用光场方程代替,建立了脉冲CO2激光器注入锁定的理论计算模型。采用四阶经典龙格库塔(Runge-Kutta)算法,计算了不同注入信号强度和失谐频率下的激光输出功率、瞬时频率和增益系数。研究了注入锁定宽调谐横向激励大气压(TEA)CO2激光器模式锁定的稳定性问题。研究结果表明,当频率偏离谱线中心600 MHz时,为了实现稳定的模式锁定所需要的注入信号强度应比在谱线中心处高出两个数量级。理论结果和已发表的实验数据符合得很好。研究进一步预示:当激光器气压增大至10倍大气压时,对于同样调谐范围所需的注入信号强度仅比在谱线中心处高出10%左右。