可调谐半导体激光器研究及进展

可调谐半导体激光器是新一代密集波分复用系统以及全光网络中光子交换的关键光电子器件 ,它的运用使得光纤传输系统容量大大增加 ,灵活性和可扩展性大大增强 ,目前已经实现了宽波长范围的连续或准连续调谐 ,并有相应的产品投放市场 .文章介绍了各种基于不同谐振腔结构的可调谐激光器以及各自的调谐机理 ,对不同类型器件在制作以及实际应用中的优缺点进行了比较 .同时总结了国外可调谐半导体激光器的最新进展 ,并对我国可调谐半导体激光器的研制提出了相应的要求     

外光注入半导体激光器实现重复速率可调全光时钟分频

采用Fabry-Perot半导体激光器作为全光时钟分频器件,利用光注入半导体激光器产生的非线性动力学特性,实现了光脉冲的重复速率在9.0 GHz到19.8 GHz范围内连续可调的全光时钟分频. 同时利用半导体激光器速率方程,对脉冲光注入半导体激光器产生时钟分频进行了数值模拟. 实验和模拟结果表明半导体激光器在光注入的驱动下处于一周期振荡状态,当一周期振荡的二次谐波频率接近脉冲光的重复速率时,其二次谐波和基频被脉冲光同时锁定,此时将输出频率为脉冲光重复速率一半的时钟信号. 同时研究了波长失谐量和注入光功率对 关键词： 周期振荡 时钟分频 光注入 非线性动力学     

Instabilities in semiconductor lasers

One of the most relevant problems connected with optical fiber communication is that related to the presence of instabilities in the output of semiconductor lasers. These instabilities appear as nonlinearities in the optical power-current characteristic (kinks) or as dynamics instabilities (self-pulsing). These phenomena more frequently occur in devices without a refractive index profile introduced ad hoc in the junction plane (gain-guided lasers); self-pulsing, in particular, is present in aged lasers. Both of them, however, can appear also in nonaged lasers with lateral confinement of the e.m. field (index-guided lasers). In this paper the principal experimental results obtained studying instability phenomena and the physical mechanisms proposed for their explanation are reported and discussed.     

Square microcavity semiconductor lasers

Square microcavities, which support whispering-gallery modes with total internal reflections, can be employed as high-quality laser resonators for fabricating compact, low-threshold semiconductor lasers. In this paper, we review the recent progress of square microcavity semiconductor lasers. The characteristics of confined optical modes in the square microcavities are introduced briefly. Based on the mode properties of the square microcavities, dual-mode lasers with tunable wavelength intervals are realized for generating microwave signals. Furthermore, deformed square microcavity lasers with the sidewalls replaced by circular sides are proposed and experimentally demonstrated to enhance the mode confinement and increase the dual-mode interval to the THz range. In order to further reduce the device size, metal-confined wavelength-scale square cavity lasers are also demonstrated.     

Narrow spectral linewidth semiconductor lasers

Developments of narrow-linewidth distributed-Bragg-reflection (DBR) and distributed-feed-back (DFB) lasers are described. The design of a narrow-linewidth DBR laser is described in detail. Kl optimization from the viewpoint of narrow-linewidth operation and stable single mode operation is discussed. The linewidth dependences on cavity length, facet reflectivity and threshold current density are investigated. Some approaches to suppressing spatial hole burning in DFB lasers are described.     

Passively modelocked surface-emitting semiconductor lasers

This paper will review and discuss pico- and femtosecond pulse generation from passively modelocked vertical–external-cavity surface-emitting semiconductor lasers (VECSELs). We shall discuss the physical principles of ultrashort pulse generation in these lasers, considering in turn the role played by the semiconductor quantum well gain structure, and the saturable absorber. The paper will analyze the fundamental performance limits of these devices, and review the results that have been demonstrated to date. Different types of semiconductor saturable absorber mirror (SESAM) design, and their characteristic dynamics, are described in detail; exploring the ultimate goal of moving to a wafer integration approach, in which the SESAM is integrated into the VECSEL structure with tremendous gain in capability. In particular, the contrast between VECSELs and diode-pumped solid-state lasers and edge-emitting diode lasers will be discussed. Optically pumped VECSELs have led to an improvement by more than two orders of magnitude to date in the average output power achievable from a passively modelocked ultrafast semiconductor laser.     

Frequency stabilization in semiconductor lasers

Three promising methods of improving temporal coherence in semiconductor lasers are reviewed. They are the development of novel laser devices, a technique of optical feedback and a technique of electrical feedback. The main discussion in this paper is focused on the technique of electrical feedback. The theoretical limit of frequency stability and recent experimental results are presented with respect to the following five subjects which are indispensable in the realization of highly coherent lasers: (a) frequency stabilization; (b) improvements in frequency reproducibility; (c) linewidth reduction; (d) frequency tracking; and (e) stable, accurate and wideband frequency sweep.     

Optical bistability in semiconductor lasers

Optical and Quantum Electronics -     

Modulation behavior of semiconductor injection lasers

GaAs double heterostructure semiconductor injection lasers which now exhibit more than 25000 h cw room temperature lifetime are of great interest for future use as directly modulated transmitters for high bit-rate fiber optical communications. The effects limiting this application are modulation distortions, spectral width and additional spectral broadening in the case of modulation and spontaneous fluctuations of the output power. The dynamic and spectral behavior of injection lasers, the methods of high bit-rate modulation and the improvement of the high bit-rate modulation capability by coupling two lasers are discussed.     

Switching mechanism in polarization-bistable semiconductor lasers

The steady-state and transient properties of polarization-bistable semiconductor lasers are investigated, both experimentally and theoretically. An analysis based on coupled rate equations for a two-mode system with unequal gain/current characteristics is presented. The simple rate-equation model explains the general features of the observed bistable-switching behaviour. The condition for the existence of polarization bistability is determined using laser parameters.     

Photon statistics of semiconductor microcavity lasers

We present measurements of first- and second-order coherence of quantum-dot micropillar lasers together with a semiconductor laser theory. Our results show a broad threshold region for the observed high-beta microcavities. The intensity jump is accompanied by both pronounced photon intensity fluctuations and strong coherence length changes. The investigations clearly visualize a smooth transition from spontaneous to predominantly stimulated emission which becomes harder to determine for high beta. In our theory, a microscopic approach is used to incorporate the semiconductor nature of quantum dots. The results are in agreement with the experimental intensity traces and the photon statistics measurements.     

Gain and saturation in semiconductor lasers

Several approaches have been developed for modelling the gain and saturation behaviour of semiconductor lasers, and this study includes a historical review of these various approaches. Special attention is given to rate equation models and to the possibility of so-called gain nonlinearities that might affect the CW and modulation performance of semiconductor lasers. Discussions are mainly limited to the GaAs/GaAIAs and InGaAsP/InP systems, for which the gain and gain nonlinearities have been most extensively studied.     

Alternate oscillations in semiconductor ring lasers

We report on fabrication and characterization of single-longitudinal- and transverse-mode semiconductor ring lasers. A bifurcation from bidirectional stable operation to a regime with alternate oscillations of the counterpropagating modes was observed experimentally and is theoretically explained through a two-mode model. Analytical expressions for the onset and the frequency of the oscillations are derived, and L-I curves numerically evaluated. Good quantitative agreement between theory and measurements made over a large number of tested devices is obtained.     

High-frequency modulation of segmented-contact semiconductor lasers

Simulations of the high-frequency modulation characteristics of semiconductor lasers with segmented contacts predict a pronounced resonance-like modulation response that is beyond five times the original cut-off modulation frequency. Based on an effective multi-mode Maxwell–Bloch model, the simulations reveal the underlying phenomena. They show that the high-frequency response is a direct consequence of the particular spatio-temporal and multi-mode dynamics induced by the segmented-contact laser geometry.     

Ultrashort pulses from semiconductor diode lasers

Careful design of mounting structures and drive-circuit parameters is essential to obtain very short pulse-lengths with high peak powers from semiconductor diode lasers. We have developed a diode laser model using a coupled rate equation approach to predict operating regimes producing ultrashort output pulses. The model has been refined through comparison with experiment, and a 10 ps source, designed on the basis of this model, has been implemented.     

Coupling of concentric semiconductor microring lasers

Coupling between whispering-gallery modes of concentric microcavity lasers was analyzed, and a closed-form three-dimensional vectorial solution for the coupled fields was obtained. Experiments performed with concentric gain-guided vertical cavity ring lasers resulted in regimes of resonant coupling in good agreement with the theory.