Mode-switching in semiconductor lasers

In this paper, we experimentally analyze the modal dynamics of quantum-well semiconductor lasers. Modal switching is the dominant feature for semiconductor lasers that exhibit two or several active longitudinal modes in their time-averaged optical spectrum. In quantum-well lasers, these dynamics involve a periodic switching among several longitudinal modes, which follows a well-determined sequence from the bluest to the reddest mode in the optical spectrum. This feature is radically different from the well-known noise-driven mode-hopping occurring in bulk lasers which involves only two main modes. We analyze the differences in modal dynamics for these two kinds of laser by comparing the modal switching statistics and by studying the effects of noise and modulation in the pumping current.     

Dynamics of Broad-Area Semiconductor Lasers With Short Optical Feedback

The dynamics of filamentations in broad-area semiconductor lasers with short optical feedback were numerically studied. Regular pulse packages similar to those observed in narrow-stripe edge-emitting semiconductor lasers were found as the feedback reflectivity is increased. However, the regular pulse packages consisted of a periodic envelope of the external cavity frequency and fine pulse trains of periodic filaments, which is different from the regular pulse packages observed in narrow-stripe edge-emitting semiconductor lasers. From the analysis for spatio-temporal near-field patterns, we found periodic undulations of the spatial and temporal filament sizes as the external mirror reflectivity was changed. We also investigated filtered optical feedback, where a part of the emitted beam is fed back into the laser cavity. The time-averaged near-field pattern was found to have a strong dependence on the feedback level in the case of spatial filtered optical feedback.     

Dynamics of a multimode semiconductor laser with optical feedback

A new model of a multi-longitudinal-mode semiconductor laser with weak optical feedback is proposed. This model generalizes the well-known Tang-Statz-deMars equations, which are derived from the first principles and adequately describe solid-state lasers to a semiconductor active medium. Steady states of the model and the spectrum of relaxation oscillations are found, and the laser dynamics in the chaotic regime of low-frequency fluctuations of intensity is investigated. It is established that the dynamic properties of the proposed model depend mainly on the carrier diffusion, which controls mode-mode coupling in the active medium via spread of gratings of spatial inversion. The results obtained are compared with the predictions of previous semiphenomenological models and the scope of applicability of these models is determined.

     

Modeling multiple-longitudinal-mode dynamics in semiconductorlasers

We present a time-dependent coupled-wave equation analysis for simulating both single- and multilongitudinal-mode dynamics in semiconductor lasers, while incorporating frequency-dependent gain in a particularly simple way. In our first application, we analyze the response of Fabry-Perot semiconductor lasers to feedback levels ranging from -60 to -30 dB. This allows us to anchor, continuously, from single-mode phenomena at weak feedback levels to multimode behavior at stronger feedback levels. To our knowledge, this is the first simulation of multilongitudinal-mode dynamics that are induced in a laser at feedback levels exceeding -30 dB, Feedback-induced phenomena provide a significant test of both the single-mode and multimode capabilities of our coupled-wave model. In our second application, we analyze a modern, large-scale device for which multiple longitudinal modes, as well as compound cavity modes, are a significant possibility. Specifically, we consider facet-coating requirements for a new class of monolithic master-oscillator power-amplifier (MOPA) devices     

Modal noise and optical feedback in high-speed optical systems at 0.85 ?m

The most critical interferences in optical broadband communication systems at 0.85 ?m are the modal noise in a graded-index fibre and the feedback problems in d.h. semiconductor lasers. Experiments with these two phenomena in a high-speed digital transmission system are described.     

Turn-on jitter of external-cavity semiconductor lasers

Analytical expressions, validated by numerical simulations, are obtained for the turn-on delay jitter of semiconductor lasers subjected to weak optical feedback in short external cavities. The results show explicitly that displacement of the external reflector on optical wavelength scales causes significant changes in the switch-on dynamics of the laser. It is found that more than a 400% increase of jitter can occur under certain circumstances. The demonstrated sensitivity of laser switch-on dynamics to reflector location is considered to be particularly relevant to the performance of packaged laser diodes     

Equivalent circuit of semiconductor lasers with weak coherentoptical feedback

The equivalent circuit modelling of semiconductor lasers makes simulation of direct modulation of semiconductor lasers extremely simple through the use of circuit simulators such as SPICE. The authors extend the circuit model to incorporate the effect of weak coherent optical feedback into the laser cavity. Results from circuit simulation of the model are compared with results reported earlier as well as results obtained from direct numerical analysis of rate equations     

Analysis and characterization of the hyperchaos generated by a semiconductor laser subject to a delayed feedback loop

We characterize the chaotic dynamics of semiconductor lasers subject to either optical or electrooptical feedback modeled by Lang-Kobayashi and Ikeda equations, respectively. This characterization is relevant for secure optical communications based on chaos encryption. In particular, for each system we compute as a function of tunable parameters the Lyapunov spectrum, Kaplan-Yorke dimension and Kolmogorov-Sinai entropy.     

外部光注入分布反馈激光器的非线性动力学特性

实验研究了外部光注入分布反馈(DFB)激光器的非线性动力学行为,并给出了其输出特性随注入光强度和频率失谐量变化的动力学特征图.实验结果表明,激光器的动力学行为对外部的微扰十分敏感;在不同外部光注入条件下,激光器可以呈现出单周期、倍周期、多周期以及混沌等多种非线性动力学特征;在注入光强度和频率失谐量变化空间存在三个复杂动力学区域;激光器表现出的复杂动力学行为总是与周期行为有关;当激光器处于复杂动力学区域时,其频谱为连续谱,在连续谱上存在多个明显的峰,所对应的频率定义为特征频率,特征频率的大小不随注入光的强弱以及频率变化.     

Nonlinear injection locking dynamics and the onset of coherencecollapse in external cavity lasers

A theoretical analysis is presented of the experimentally observed collapse of coherence in semiconductor lasers exposed to moderate optical feedback. A main point in the analysis is, that coherence collapse in the delayed-feedback (DFB) system shows up as bistability in a much simpler model which corresponds to an injection locking system. Based on this, the authors derive a simple analytical expression, valid for DFB as well as Fabry-Perot lasers, for the critical feedback level at which coherence collapse sets in. Simulations of the nonlinear injection locking model reveal the presence of complicated nonlinear dynamics with period-doubling bifurcations and coexisting attractors even inside what is normally denoted the stable locking range     

Relative intensity noise for laser diodes with arbitrary amounts ofoptical feedback

A unified study of the noise characteristics of semiconductor lasers with optical feedback and short external cavity length is presented. A new set of nonlinear rate equations that can describe a laser diode with any amount of optical feedback is proposed. The relative intensity noise (RIN) is calculated by using a numerical solution of these equations. This paper concentrates mainly on the moderate and strong feedback regimes. The spectral phenomena observed during the transition from the weak feedback to the “coherence collapse” regime and then to the strong feedback regime are studied and explained. The effect of the variation of some of the laser diode parameters on the RIN characteristics is also investigated     

耦合半导体激光器的多调制延时混沌同步

为了研究多调制延时混沌系统的动力学,用数值计算法研究了非相干光反馈与非相干光注入半导体激光器的多常数延时与多调制延时混沌同步,由于该系统是基于非相干注入的,所以不需要接收激光器与发送激光器频率完全匹配。另外,研究了非相干光反馈半导体激光器输出自相关函数。结果表明,多常数延时和多调制延时两种情况下都能获得高质量的同步,但在多调制延时系统中自相关函数的延时标识可以被隐藏,这一特性大大提高了系统的安全性,非常适用于混沌保密通信系统。     

A two-port bilateral model for semiconductor lasers

A bilateral two-port model of a semiconductor laser that includes bidirectional electronic and photonic interfaces is developed by combining an equivalent circuit laser model and a transmission-line laser model (TLLM). The new model includes chip and package parasitics, gain nonlinearities, and a detailed optical cavity model based on optical traveling waves. This model can be applied to a variety of device structures to simulate optical spectra, optical and electrical waveforms, intensity spectra, and noise characteristics. Three examples demonstrate the flexibility of the model: (1) transient response simulation of semiconductor lasers, (2) characteristics of lasers used as detectors, and (3) coherence collapse in lasers with optical feedback. In all cases, the results are in good agreement with experimental measurements     

Numerical Study of Doppler Dynamics in Self-Mixing Semiconductor Lasers

We present a new approach for performing numerical simulations of optical feedback semiconductor lasers for moving targets. The derived rate equation for the complex electric field is suitable for the numerical analysis of the dynamics in a self-mixing semiconductor laser with a Doppler frequency shift. We present numerical examples calculated using the rate equations.      

Characteristics of chaos synchronization in semiconductor lasers subject to polarization-rotated optical feedback

We numerically investigate the detailed characteristics of chaos synchronization in semiconductor lasers subject to polarization-rotated optical feedback. The emission of the dominant TE mode of a drive laser is rotated 90 deg and fed back to the laser with time delay. The polarization-rotated TE mode is also injected with time delay into the TM mode of a second laser. Two types of synchronization with different time-lags are found, as in the case for synchronization in semiconductor lasers with nonrotated optical feedback. However, a significant difference to the nonrotated optical feedback case is that neither of the two types of synchronization requires matching of optical carrier frequency between the two lasers.     

Feedback effects in tapered broad-area semiconductor lasers andamplifiers

A detailed experimental investigation of the effect of optical feedback upon the operation of high-power broad area InGaAs strained quantum well semiconductor lasers is presented. In particular, we examine the effect optical feedback has upon the beam quality of high-brightness lasers employing a tapered electrical contact. The far-field of such lasers is shown to degrade rapidly with power feedback ratios exceeding -30 dB, leading to a significantly reduced power in the central diffraction-limited far-field lobe. Far-field degradation is accompanied by dynamic instability and spectral broadening. Good beam quality and low intensity noise can be recovered, however, by rotating the feedback polarization     

相位共轭反馈下垂直腔面发射激光器动态分岔特性的理论研究

在传统半导体激光器动力学方程的基础上，突出了垂直腔面发射激光器(VCSELs)的微腔结构特点以及相位共轭反馈(PCF)的时间反演特性，建立起相位共轭反馈条件下的复合腔仿真模型。仿真结果表明：在外部反射率小于0．05的弱反馈条件下，垂直腔面发射激光器的微腔结构导致了它的动态特性与边发射器件有较大的区别，给出两者在混沌带的出现次数、存在范围以及分岔点的出现条件等方面的比较。相对于常规光反馈(COF)而言，相位共轭反馈的累积相位为零，这使得该机制下垂直腔面发射激光器表现出更为丰富的非线性特性。仿真中观察到常规光反馈经历了三个混沌带，相位共轭反馈经历了两个混沌带且稳定区域较宽；并发现在混沌吸引子产生的过程中常规光反馈光场的实虚部相空间轨迹保持对称，而相位共轭反馈的相空间轨迹则表现为对称的‘建立→破坏→再建立’这样的循环过程。     

Effects of current modulation on timing jitter of single-modesemiconductor lasers in short external cavities

Turn-on jitter of single-mode semiconductor lasers with modulated injection current and weak optical feedback exhibits periodic oscillations as a function of the length of the external cavity, under configurations appropriate for packaged laser diodes. Numerical results for both periodic and pseudorandom word modulation show that the oscillations persist even when increasing the external cavity length to a few millimeters. It is found that under particular positions of the external reflector a large increase of jitter occurs as compared with the jitter without optical feedback     

Waveform distortion due to near-end reflections in direct detectionlightwave systems using single-mode semiconductor lasers

Deterministic rate equations describing the nonlinear modulation dynamics of single-mode semiconductor lasers are used to assess the performance implications of external optical feedback for multigigabit-per-second lightwave systems. The rapid increase in the eye closure penalty resulting in a return loss of about 20 dB, is consistent with published experimental data     

Time-domain large-signal investigation on nonlinear interactionsbetween an optical pulse and semiconductor waveguides

A time-domain large-signal model is developed to investigate nonlinear interactions between picosecond optical pulses and semiconductor active waveguide devices, including distributed-feedback and Fabry-Perot lasers, as well as optical amplifiers. The model predicts interesting phenomena such as transform-limited superluminal transmission and directional DFB amplification. The influence of electrical carrier dynamics and feedback from a Bragg grating and/or reflecting facets on output pulses are demonstrated. Moreover, it is found that the time delay of the reflected and transmitted pulses is strongly related to the Bragg grating parameters, as well as to carrier dynamics. As a consequence, careful attention should be paid when the notions of group refractive index and group velocity are to be used in device modeling