半导体微腔激光器瞬态响应及调制特性分析

针对半导体微腔激光器的结构特点,考虑到腔量子电动力学中自发辐射增强效应,采用传统速率方程的表示形式,建立了微腔激光器的速率方程,着重讨论了微腔激光器的瞬态响应及调制特性,给出了其动态特性的仿真结果,分析了自发辐射因子、注入电流和腔长对微腔激光器的激射阈值、延迟时间、驰豫振荡频率和光输出等参量的影响,从而为改善微腔激光器的高频调制特性和优化器件结构提供了理论依据。     

半导体微腔激光器瞬态响应及调制特性分析

针对半导体微腔激光器的结构特点,考虑到腔量子电动力学中自发辐射增强效应,采用传统速率方程的表示形式,建立了微腔激光器的速率方程,着重讨论了微腔激光器的瞬态响应及调制特性,给出了其动态特性的仿真结果,分析了自发辐射因子、注入电流和腔长对微腔激光器的激射阈值、延迟时间、驰豫振荡频率和光输出等参量的影响,从而为改善微腔激光器的高频调制特性和优化器件结构提供了理论依据.     

多量子阱半导体激光器的瞬态响应特性分析

根据光增益与载流子密度的对数关系,在受激发射速率中分别引入了增益饱和项和载流子复合项,通过适应于多量子阱激光器的速率方程,从理论上证明了短腔结构存在与阈值电流最小值对应的最佳阱数。给出了多量子阱激光器的瞬态呼应特性的直接仿真结果及相图,分析了注入电流、阱数和腔长对其激射阈值、开关延误时间、弛豫振荡频率和光输出等能量的影响。     

多量子阱VCSEL速率方程的数值模拟分析

采用光增益与载流子浓度的对数关系,考虑到非辐射复合的影响,从理论上推导出多量子阱垂直腔面发射半导体激光器(VCSEL) 的速率方程.讨论了阈值电流密度、最佳阱数与器件参数(腔长和端面反射率) 之间的关系,为改善VCSEL阈值特性和优化器件结构提供了理论依据.     

外腔面发射激光器自发辐射谱的热特性

热效应是限制外腔面发射激光器(VECSEL)输出功率和光束质量的主要原因。为了优化VECSEL增益芯片有源区量子阱的设计,降低激光器的热效应,提高斜效率和输出功率,采用光致荧光谱方法,对设计波长980nm VECSEL自发辐射谱的热特性进行了实验研究。取得了不同热沉温度下边发射和面发射谱随温度的变化数据。结果表明,反映有源区量子阱自身特性的边发射谱峰值波长随温度升高的红移速率是0.5nm/K,而受到增益芯片多层结构调制的面发射谱峰值波长随温度升高的红移速率只有0.1nm/K;由于受到VECSEL增益芯片中微腔的限制,面发射谱分离为多个模式,分别与微腔的腔模对应。可见对量子阱的发射波长及微腔腔长做预偏置优化处理,可以显著改善激光器的输出性能。     

基于对数关系的多量子阱VCSELs阈值特性研究

采用光增益与载流子浓度的对数关系,考虑到非辐射复合的影响,从理论上推导出多量子阱垂直腔面发射半导体激光器(VCSELs)的速率方程。讨论了阈值电流密度、最佳阱数等与器件参数(腔长和端面反射率)之间的依赖关系。为改善VCSELs阈值特性和优化器件结构提供了理论依据。     

基于对数关系的多量子阱VCSELs阈值特性研究

采用光增益与载流子浓度的对数关系，考虑到非辐射复合的影响，从理论上推导出多量子阱垂直腔面发射半导体激光器(VCSELs)的速率方程。讨论了阈值电流密度、最佳阱数等与器件参数(腔长和端面反射率)之间的依赖关系。为改善VCSELs阈值特性和优化器件结构提供了理论依据。     

平面工艺制作的定向输出微腔半导体激光器

光学微腔中偶极子自发辐射受到空间和频谱调制,能实现自发辐射增强或抑制效应,而且其有源区体积可以非常小,有利于极低阈值工作和极高的调制速率.在过去的二十多年来,垂直腔面发射激光器、回音壁模式(whispering-gallery mode)微腔激光器以及光子晶体微腔激光器三类光学微腔激光器的研究取得了很大的进展.回音擘模式微腔中,模式光线由于其在微腔界面的入射角大于全反射临界角而受到限制,是一种结构非常简单的光学微腔.微盘激光器作为典型的回音壁模式微腔激光器,可利用普通的边发射激光器外延片材料,采用半导体平面工艺制作,引起了人们很大的重视.但圆对称结构的微盘激光器易于实现回音壁模式的全反射限制,却难以得到定向的激光输出,限制了它的应用.人们往往采用局部破坏圆盘的对称性、整体变形以及消逝波耦合的输出波导实现微盘激光器的定向激光输出.在圆对称的微盘结构中,模式光线在微腔与空气界面上的入射角是恒定的,而在整体变形的圆盘中,如椭圆形微腔中,模式光线在界面的入射角则不断变化,并在某些位置上小于全反射临界角而折射出光学微腔,从而实现定向输出.这种变形微盘中模式光线往往具有混沌现象,因而吸引了人们的注意.     

基于半导体外腔激光器的光反馈研究﹡

以光栅外腔半导体激光器的理论知识为基础,对 Littrow 型的外腔半导体激光器的结构进行了说明。根据等效反射系数的概念,推导出外腔反馈作用下阈值增益的公式和线宽压窄公式,并详细地讨论了外腔半导体激光器的线宽压窄机制。同时,对影响 Littrow 型光栅外腔半导体激光器阈值增益和线宽压窄的各种因素进行了分析,发现外腔的反馈相当于增加了端面的反射率,阈值增益变小,在相同的输出功率下,增大受激辐射,抑制自发辐射,从而使线宽减小。     

微片激光器阈值附近的输出光谱特性研究

为了确定激光晶体在不同温度下的自发辐射光谱 (荧光谱),实验研究了阈值附近微片激光器的输出 光谱特性。当抽运功率略小于阈值时,微片激光器输出经干涉的自发辐射光;当抽运功率大 于阈值时,微 片激光器输出激光。测量了激光阈值与晶体温控的关系,结果表明激光阈值随晶体温度的升 高而增加,其 变化率为0.017W/℃。在不同温控条件下,对阈值以下的自发辐射光 谱包络进行了拟合测量,结果表明随 着晶体温度的升高自发辐射光谱包络峰值降低,下降率为0.681%/℃ ;光谱包络中心波长发生红移,漂移率为3.1pm/℃。     

Analysis Expression of Rate Equation for Vertical Cavity Lasers

An analysis solution of rate equation is derived for vertical cavity surface-emitting lasers.Based on the enhanced spontaneous emission caused by VCSELs and influence of nonradiative recombination, the relation between output properties and structural parametersof multi-quantum wells(MQWs) is obtanined.It was found that the characteristic curve of a “thresholdless“ laser is strongly nonradiative depopulation-dependent.When the nonradiative depopulation is no zero,the light-current characteristic is not linearly even for an ideal closed microcavity.The light output is increased by the enhanced well number and by the reduced width.In particular, a lower threshold current density for MQWs structure in the short cavity is realized by us, meanwhile the sharpness of the variation depends on spontaneous emission factor.     

Temperature dependence of the lasing characteristics of the 1.3 µm InGaAsP-InP and GaAs-Al0.36Ga0.64As DH lasers

We report here our experimental observations on the temperature dependence of threshold current, carrier lifetime at threshold, external differential quantum efficiency, and gain of both the 1.3 μm InGaAsP-InP and GaAs-AlGaAs double heterostructure (DH) lasers. We find that the gain decreases much faster with increasing temperature for a 1.3 μm InGaAsP DH laser than for a GaAs DH laser. Measurements of the spontaneous emission observed through the substrate shows that the emission is sublinear with injection current at high temperatures for the 1.3 μm InGaAsP DH laser. Such sublinearity is not observed for GaAs DH lasers in the entire temperature range 115-350 K. The experimental results are discussed with reference to the various mechanisms that have been proposed to explain the observed temperature dependence of threshold of InGaAsP DH lasers. We find that inclusion of a calculated nonradiative Auger recombination rate can explain the observed temperature dependence of threshold current, carder lifetime at threshold, gain, and also the sublinearity of the spontaneous emission with injection current of the 1.3 μm InGaAsP-InP DH laser. Measurement of the nonradiative component of the carrier lifetime (τA) as a function of injected carrier density (n) shows thattau_{A}^{-1} sim n^{2.1}which is characteristic of an Auger process.     

Light saturation of InGaAsP-InP LED's

The saturation behavior of the spontaneous light-current characteristic of InGaAsP (lambda = 1.3 mum) lasers and light emitting diodes are investigated as a function of injection level and temperature. For carrier injection levels below that at which optical gain is observed, it is shown that a nonradiative Auger recombination mechanism is consistent with the observed saturation behavior of the spontaneous emission intensity of lasers. Further evidence of the importance of Auger recombination at these low injection levels is provided by the dependence of the nonradiative component of the measured carrier lifetime (τA) on injection level (n) where it is found thattau_{A}^{-1} propto n^{2.1}. For injection levels above that required to achieve optical gain we report the direct observation of superlinear emission due to single pass gain in edge emitting LED's. The onset of this superluminescence at low temperatures (T < 200K) is found to correspond with the onset of saturation of the spontaneous emission from the sides. These results show that both Auger recombination and superluminescence should be taken into account when the electrooptical characteristics of InGaAsP LED's are calculated.     

半导体激光器的微腔结构调制及其脉码在光纤中的传输

采用腔量子电动力学(QED)方法,定量讨论了平面结构微腔半导体激光器的自发发射特征物理量随腔结构的变化规律.在微腔半导体激光器自发发射因子调制、自发发射寿命调制以及一些实验依据的基础上,提出了微腔结构调制方法.数值模拟了其脉码在光纤中的传输图形.结果表明,微腔结构调制方法在提高脉码比特率方面优于同参数下的电流调制方法.     

半导体微腔中电偶极子的自发发射

由于反射电场的影响，电偶极子在微腔中的自发发射速度不同于自由空间中的自发发射速度。本文采用镜像法计算了理想平面微腔、金属平面镜组成的半导体微腔和由分布布喇格反射镜（DBR）作为谐振腔的垂直发射激光器（VCSEL）中电偶极子的自发发射速率。计算结果表明：由于微腔的调制作用，在某些情况下电偶极子自发发射速率增加，在一定腔长下电偶极子自发发射速度被抑制。     

Spontaneous emission factor in post microcavity lasers

The first measurements of the spontaneous emission coupling efficiency (/spl beta/) for electrically pumped microcavity lasers with transverse photon confinement are reported. The influence of scattering losses and carrier diffusion on microcavity lasers is investigated, A /spl beta/ of 0.01 is measured at 126 K in a 3-/spl mu/m diameter device with optimal gain-cavity detuning.     

Characteristics of a photonic bandgap single defect microcavityelectroluminescent device

A microcavity surface-emitting coherent electroluminescent device operating at room temperature under pulsed current injection is described. The microcavity is formed by a single defect in the center of a 2-D photonic crystal consisting of a GaAs-based heterostructure. The gain region consists of two 70-Å compressively strained In_0.15Ga_0.85As quantum wells, which exhibit a spontaneous emission peak at 940 nm. The maximum measured output power from a single device is 14.4 μW. The near-field image of the output resembles the calculated TE mode distribution in a single defect microcavity. The measured far-field pattern indicates the predicted directionality of a microcavity light source. The light-current characteristics of the device exhibit a gradual turn-on, or a soft threshold, typical of single- or few-mode microcavity devices. Analysis of the characteristics with the carrier and photon rate equations yields a spontaneous emission factor β≈0.06     

Variation of intensity noise and frequency noise with thespontaneous emission factor in semiconductor lasers

The intensity noise level and the spectral line-width of semiconductor injection lasers are theoretically analyzed. Approximated but simple forms representing these characteristics are found to give criteria for various types and sizes of cavity, including microcavity lasers. The noise and the line-width are reduced by operation with high injection current or high optical power in general. For operation at a low-power level in the microcavity laser, increase of the spontaneous emission factor as well as reduction of the threshold current level and the threshold gain level are important to get a low noise level and narrow line-width     

Spontaneous emission and threshold characteristics of 1.3-μmInGaAs-GaAs quantum-dot GaAs-based lasers

The spontaneous emission spectra and lasing characteristics of long-wavelength (1.3-μm) quantum-dot lasers are studied. It is found experimentally that nonradiative recombination can dominate the room-temperature efficiency and limit threshold, By describing the quantum-dot spectral emission as due to energy levels of a two-dimensional harmonic oscillator, rate equations are developed to account for the temperature-dependent spontaneous and lasing characteristics     

微腔激光器数码调制及其光纤传输的研究

从微腔半导体激光器速率方程出发，分析讨论了微腔激光器的脉码调制特性，发现微腔具有较规则的脉冲响应，可以减少误码率；自发发射因子为０．１的微腔，具有脉码率高达５０Ｇｂｉｔ／ｓ良好的调制眼图，微腔激光器在光互联中将有广泛的应用前景。模拟了以微腔激光器为光源的光纤通信系统，给出脉码率为１０Ｇｂｉｔ／ｓ传输不同距离的接收眼图，证明能够实现６０ｋｍ的传输。