Towards 640 Gbit/s wavelength conversion based on nonlinear polarization rotation in a semiconductor optical amplifier

Taking into account ultra-fast carrier dynamics, this paper models 640 Gbit/s wavelength conversion scheme based on nonlinear polarization rotation （NPR） in a single semiconductor optical amplifier （SOA） and investigates the performance of this kind of wavelength conversion scheme in detail. In this model, two carrier temperature equations are introduced to substitute two energy density equations, which reduce the complexity of calculation in comparison with the previous model. The temporary gain and phase shift dynamics induced by ultra-short optical pulses are numerically simulated and the simulated results are qualitatively in good agreement with reported experimental results. Simulated results show that non-inverted and inverted 640 Gbit/s wavelength conversions based on NPR are achieved with clear open eye diagrams. To further investigate the performance of the non-inverted wavelength conversion scheme, the dependence of output extinction ratio （ER） on some key parameters used in simulation is illustrated. Furthermore, simulated analyses show that high performance non-inverted wavelength conversion based on NPR can be achieved by using a red-shifted filtering scheme.

Polarization switching and synchronization of mutually coupled vertical-cavity surface-emitting semiconductor lasers

Polarization switching （PS） dynamics and synchronization performances of two mutually coupled vertical-cavity surface-emitting lasers （VCSELs） are studied theoretically in this paper. A group of dimensionless rate equations is derived to describe our model. While analysing the PS characteristics, we focus on the effects of coupling rate and frequency detuning regarding different mutual injection types. The results indicate that the x-mode injection defers the occurrence of PS, while the y-mode injection leads the PS to occur at a lower current. Strong enough polarization-selective injection can suppress the PS. Moreover, if frequency detuning is considered, the effects of polarization-selective mutual injection will be weakened. To evaluate the synchronization performance, the correlation coefficients and output dynamics of VCSELs with both pure mode and mixed mode polarizations are given. It is found that performance of complete synchronization is sensitive to the frequency mismatch but it is little affected by mixed mode polarizations, which is opposite to the case of injection-locking synchronization.

Spin-Polarized Carriers Injection from Ferromagnetic Metal into Organic Semiconductor

Charge carriers in organic semiconductor are different from that of traditional inorganic semiconductor.Based on three-current model, considering electrical field effect, we present a theoretical model to discuss spin-polarizedinjection from ferromagnetic electrode into organic semiconductor by analyzing electrochemical potential both in ferromagneticelectrode and organic semiconductors.The calculated result of this model shows effects of electrode's spinpolarization, equilibrium value of polarons ratio, interfacial conductance, bulk conductivity of materials and electricalfield.It is found that we could get decent spin polarization with common ferromagnetic electrode by increasing equilibriumvalue of polarons ratio.We also find that large and matched bulk conductivity of organic semiconductor andelectrode, small spin-dependent interfacial conductance, and enough large electrical field are critical factors for increasingspin polarization.

Cross-Polarized Single Photon Emission from Single Semiconductor Quantum Dots with V-Type Level Driven by Pulse Field

The statistic properties of photon emissions from single semiconductor quantum dots with V-type leveldriven by pulses are investigated theoretically.Based on quantum regression theorem and master equations,the dynamicequations of the second-order correlation function of the photon emissions are deduced.The calculated results reveal thatthe efficiency of single photon emissions from two orthogonal polarization eigenstates(|x〉and |y〉)reaches the maximumwhen the input pulses area is about π,and the probability of the cross-polarized single photon emission from |x〉and |y〉decreases with increasing of pulse width.

Influence of spin–orbit coupling on spin-polarized electronic transport in magnetic semiconductor nanowires with nanosized sharp domain walls

Influence of spin–orbit coupling on spin-polarized electronic transport in magnetic semiconductor nanowires with nanosized sharp domain walls is investigated theoretically.It is shown that the Rashba spin–orbit coupling can enhance significantly the spin-flip scattering of charge carriers from a nanosized sharp domain wall whose extension is much smaller than the carrier＇s Fermi wavelength.When there are more than one domain wall presented in a magnetic semiconductor nanowire,not only the spin-flip scattering of charge carriers from the domain walls but the quantum interference of charge carriers in the intermediate domain regions between neighboring domain walls may play important roles on spin-polarized electronic transport,and in such cases the influences of the Rashba spin–orbit coupling will depend sensitively both on the domain walls＇ width and the domain walls＇ separation.

窄脊型波导半导体激光器偏振与横模关系研究

基于有效折射率法建立了窄脊型波导数值计算模型,通过实验研究了InGaAs量子阱窄脊型波导半导体激光器偏振特性与横模之间的关系。根据理论计算,脊型波导中类TM模式在慢轴方向的有效折射率差更大,类TM模式的限制因子比类TE模式的限制因子更大、更容易出现慢轴高阶模式;而随着脊型波导的高度增加,快轴高阶模式被截断,类TE00模式的限制因子逐渐增加至与类TM00模式相近,慢轴高阶模式因其大的散射损耗被抑制,理论上可实现高偏振度、高光束质量激光输出。在实验方面,利用量子阱材料的增益偏振特性,通过脊型高度与宽度的设计,制备了高偏振度、基横模的窄脊型波导半导体激光器。

基于二维半导体的图像传感器

图像传感器作为获取视觉信息的重要器件,可将感知到的光信号转换为电信号进行输出。目前,基于互补型金属氧化物半导体构建的图像传感器制造技术已相当成熟。然而,在某些特定的应用场景下,对微型化和多功能的图像传感器的需求仍待解决。面对此挑战,结合二维半导体丰富的材料体系及优异的光电特性,以及器件向微型化和多功能化发展的趋势,基于二维半导体的图像传感器在微型化和高集成度方面显示出巨大潜力,为图像传感器领域的发展带来了新机遇。本文首先介绍了二维半导体的带隙特性及其对应的光谱响应波段范围,展示了基于二维半导体的单像素成像技术;接着,阐述了如何利用二维半导体原子排布呈面内各向异性的特征,成功构筑了偏振敏感的图像传感器;最后,探讨了随着大面积二维半导体材料生长技术的不断成熟,如何进一步实现基于二维半导体像素阵列图像传感器的构筑。

Universal spin-dependent variable range hopping in wide-band-gap oxide ferromagnetic semiconductors

This paper proposes a universal spin-dependent variable range hopping theoretical model to describe various experimental transport phenomena observed in wide-band-gap oxide ferromagnetic semiconductors with high transition metal concentration. The contributions of the ＇hard gap＇ energy, Coulomb interaction, correlation energy, and exchange interaction to the electrical transport are considered in the universal variable range hopping theoretical model. By fitting the temperature and magnetic field dependence of the experimental sheet resistance to the theoretical model, the spin polarization ratio of electrical carriers near the Fermi level and interactions between electrical carriers can be obtained.

Spin Polarizations of Electron with Rashba Couplings in T-Shaped Devices:A Finite Element Approach

A generalized finite element formulation is proposed for the study of the spin-dependent ballistic transportof electron through the two-dimensional quantum structures with Rashba spin-orbit interactions (SOI).The transmissioncoefficient,conductance,the total and local polarization are numerically calculated and discussed as the Rashbacoefficient,the geometric sizes,and incident energy are changed in the T-shaped devices.Some interesting featuresare found in the proper parameter regime.The polarization has an enhancement as the Rashba coefficient becomesstronger.The polarization valley is rigid in the regime of the conductance plateaus since the local interference amongthe polarized multi-wave modes.The Rashba interactions coupling to geometry in sizes could form the structure-inducedFano-Rashba resonance.In the wider stub,the localized spin lattice of electron could be produced.The conductanceplateaus correspond to weak polarizations.Strong polarizations appear when the stub sizes,incident energy,and theRashba coupling coefficient are matched.The resonances are formed in a wide Fermi energy segment easily.

Two-photon absorption coefficient dichroism in Ⅱ-Ⅵ semiconductor crystals

Considering two beams propagate in semiconductor crystal, this paper discusses the polarization dependence of pump beam-induced intensity attenuation of probe beam due to two-photon absorption （TPA）. Numerical calculation and experimental measurement demonstrate that TPA coefficient is polarization dependent. For homogeneous materials, probe beam attenuation arises from the imaginary part of diagonal and off-diagonal components of third-order nonlinear susceptibilities.

光场辐照下稀磁半导体/半导体超晶格中自旋电子输运特性研究

基于单电子有效质量近似理论和传递矩阵方法,理论研究了稀磁半导体/半导体超晶格结构中电子的自旋极化输运特性.主要讨论了光场和磁场联合调制对自旋极化输运的影响,以及不同自旋电子在该超晶格结构中的隧穿时间.理论和数值计算结果表明,由于导带电子与掺杂Mn离子之间的sp-d电子相互作用引起巨塞曼劈裂,因此在磁场调制下,不同自旋电子在该结构中感受到的势函数不同而呈现出自旋过滤效应,不同自旋电子的共振透射能带的位置和宽度可以通过磁场进行调制.同时在该结构中考虑光场时,自旋依赖的透射谱会因为吸收和发射光子而呈现出对光场的强度和频率响应;最后,通过不同自旋电子的高斯波包在该结构中随时间的演化给出了不同自旋电子的隧穿时间.本文研究结果对研究和设计基于稀磁半导体/半导体超晶格结构的高速量子器件具有一定的指导意义.

基于偏振动力学的全光储备池计算系统

在半导体光放大器光纤环形激光器的基础上,提出一种基于偏振动力学的全光储备池计算系统.实验分析了该激光器的偏振动力学状态响应的影响因素,且结合储备池基本属性确定了系统参数的选取范围.通过处理Santa Fe时间序列预测任务和多波形识别任务来评估该储备池计算系统的网络性能.在合适的系统参数下,仅用30个虚节点,时间序列预测任务的归一化均方误差可低至0.0058,识别任务的识别率可高达100%.实验结果表明,该偏振动力学储备池计算系统具有良好的预测性能和分类能力,且与已有的基于该环形激光器的强度动力学储备池计算系统的性能相当.该工作为光储备池计算神经网络的研究提供了新的思路.当其偏振动力学和强度动力学一起使用时,该系统有望实现两个任务的并行处理.

贵金属/半导体异质结中的光致自旋电流效应研究

自旋电子材料因能同时对电子的自旋和电荷两个自由度实施操控,在构筑以低功耗、超高速、大容量和超宽带为特征的新一代信息处理技术中展现出巨大的应用潜力.然而,通过掺杂过渡金属元素和稀土离子而形成的传统稀磁半导体和钙钛矿锰氧化物往往因结构缺陷导致的居里温度不高、自旋磁矩和自旋极化率偏低等不足,阻碍了自旋电子材料的商业化应用.近年来,在高纯半导体上沉积贵金属薄膜所形成的贵金属/半导体异质结中,通过使用偏振光激发该类异质结可产生纯自旋电流.这种基于逆自旋霍尔效应(ISHE)、可在室温下运行的、非接触和非破坏型的自旋极化激励方法理论上可获得高于50%自旋极化率,引起了人们的广泛关注.文章主要介绍光致自旋电流形成机制和测试方法,以及入射光圆偏振度、光强、入射角度等参数对光致自旋注入效率的调控机理,介绍杂质介导和声子介导对光致自旋输运的贡献,最后提出增强光致自旋电子极化率的可行方案,可为揭示自旋载流子产生、注入和输运相关的自旋动力学核心科学问题以及研制高性能自旋电子器件提供有益的参考.

Rashba自旋-轨道耦合调制的单层半导体纳米结构中电子的自旋极化效应

利用现代材料生长技术纳米厚的半导体可以沿着良好的方向有序生长,形成层状半导体纳米结构.在这种半导体纳米结构中由于结构反演对称性破缺出现较强的自旋-轨道耦合,能有效消除半导体中电子的自旋简并,导致电子自旋极化效应,在自旋电子学领域中具有重要的应用.本文从理论上研究了单层半导体纳米结构中由Rashba型自旋-轨道耦合引起的电子自旋极化效应.由于Rashba型自旋-轨道耦合,相当强的电子自旋极化效应出现在该单层半导体纳米结构中.自旋极化率与电子的能量和平面内波矢有关,尤其是其可通过外加电场或半导体层厚度进行调控.因此,该单层半导体纳米结构可作为半导体自旋电子器件应用中的可控电子自旋过滤器.

半导体激光芯片封装后的偏振特性测量与分析

激光器的偏振特性在一定程度上反映了激光器的性能优劣,激光器的出射光束的偏振状态对材料加工的效率与质量均有重大影响。材料对激光束的光谱吸收不仅由材料本身的光学性质决定,还与激光束的偏振状态有直接关系。本文主要通过依据激光准直透镜的光学原理、偏振分光棱镜的双折射分光特性、1/2波片能够改变激光光束偏振态的特性等几个要素,对COS(Chip on sub-mount)封装形式的半导体激光芯片的偏振特性进行检测与分析,文章先阐述了测试半导体激光芯片偏振特性的目的,从而引出了以COS封装形式的880nm半导体激光芯片为例的激光偏振特性的测试方法、相应的检测装置以及影响封装型半导体激光芯片偏振特性的因素。

1.55μm偏振无关半导体光放大器腔面减反膜的研制

设计并制作了1.55 μm偏振无关半导体光放大器腔面TiO2/SiO2多层减反膜,工艺过程中设计并使用了反射率实时监控装置,得到了低于5×10-4的腔面剩余反射率.器件测试结果表明,管芯在250 mA电流下仍处于未激射状态,表明减反膜有效抑制了芯片的激射.半导体光放大器的自发辐射(ASE)谱波动在0.4 dB以下,3 dB带宽大于52 nm,半导体光放大器小信号增益近27 dB,在1520～1580 nm波长范围内偏振灵敏度小于0.5 dB.

介电常数的概念研究

在设计电路、天线、电容器等过程中经常会涉及所用材料的介电常数,所以深入了解介电常数的相关概念对实际工作有重要意义。首先介绍了介质和导体、半导体的区别,然后解释了介电常数的基本概念,并给出相对介电常数的另一种导出定义。介质极化的微观模型这一部分讲清楚了4种不同的极化。最后介绍介电常数的一些宏观特性,得出电介质介电常数将会影响电介质中电场强度的结论。

1.55μm波段低偏振灵敏度半导体光放大器

研制了１．５５μｍ 波段低偏振灵敏度的半导体光放大器（ＳＯＡ）．其有源区材料采用张应变和压应变交替排列的混合应变量子阱结构，由ＭＯＣＶＤ生长．张应变量子阱加强了ＴＭ 模式的增益，改善了ＳＯＡ 的偏振灵敏度．腔长为４００μｍ 的单端耦合ＳＯＡ，在１６０ｍ Ａ 偏置下，增益大于１６ｄＢ，偏振灵敏度约为１．８ｄＢ．

温度对AACVD法制备AZO透明导电薄膜的影响

低成本、大面积、沉积速率高、均匀性好、光电性能优良的Al掺杂ZnO薄膜(AZO)制备技术依然是透明导电薄膜领域研究的重点之一。本文采用冷壁式气溶胶辅助化学气相沉积(AACVD)技术在玻璃衬底上制备了AZO透明导电薄膜,研究了衬底温度对薄膜结构和光、电性能的影响。利用X射线衍射、原子力显微镜、紫外-可见光谱和光致发光光谱等对样品进行了表征。结果表明:在AACVD法生长AZO薄膜的过程中,衬底温度对AZO薄膜晶面的择优取向生长影响呈起伏式变化。明显的电学性能的转变温度发生在约400℃,光学性能和晶面的择优取向生长变化出现在约450℃。讨论了温度对AACVD法制备AZO透明导电薄膜结构和光、电性能影响的微观机制。400℃时沉积的AZO薄膜方阻190Ω/□,平均透过率为80%。