光子晶体在半导体激光器中的应用

激光的发明，将人类带入光通信、光存储、光显示的高科技文明中，随着高科技的不断发展、进步和应用范围的不断扩大，对激光的要求更高，例如低阈值、高效率、高亮度、高速、小体积、好的模式特性等，这些要求在现有的传统激光器理论及技术中是难以达到的。但是当人们将光子晶体的理论与现有激光物理和技术相结合时，则有望突破传统激光器的性能瓶颈。例如，提高自发辐射速率，同时获得更高的自发辐射向受激辐射的耦合效率，实现激光器的无阈值工作；利用光子晶体对光子态的调制作用，可以获得比传统激光器大几个数量级的光学腔品质因子，大幅度提高激光的亮度、单色性；结合光子晶体微腔及其显著增加的光学腔品质因子，可以提高激光器的调制速率等，因此，人们预期光子晶体科学与技术将成为未来光电子领域发展的核心之一。文章介绍了光子晶体在半导体激光器中的应用，指出光子晶体科学技术引入发展了几十年的半导体激光器中，使半导体激光器展现出更加优异的性能。最后文章作者展望了光子晶体激光器的未来发展和应用的方向。     

一维光子晶体带边激光器的阈值特性分析

采用麦克斯韦方程和速率方程相结合的模型和时域有限差分法,利用引入的有效增益分布因子概念研究了光子晶体中本征模的阈值特性。增益介质的大小以及在光子晶体中的位置直接影响光子晶体带边激光器的输出特性;有效增益分布因子描述了光子晶体中增益介质的空间分布特性。结果显示,带边本征模的激射阈值依赖于有效增益分布因子。不同的本征模具有不同的有效增益分布因子,那些有效增益分布因子较大的模式具有较低的阈值。通过调整增益介质的位置和长度,可以提高有效增益分布因子的值,从而降低激光器的阈值,这对于实现激光器的低阈值运行有指导作用。     

蓝紫光氮化镓光子晶体面射型激光器

设计、制作了蓝紫光氮化镓光子晶体面射型激光器结构,并测量其光学性质,探讨了光子晶体的晶格常数、边界形状及晶格种类对激光器特性的影响。激光器结构采用有机金属化学气相沉积法配合电子束光刻及感应耦合等离子体干蚀刻等技术制作。由角度解析光致发光系统测得绕射图案、激光发射光谱及发散角等光学性质。同时,使用平面波展开法及多重散射法计算光子晶体的能带结构与阈值增益。由实验结果得出,可由改变光子晶体的晶格常数达到调变激光器操作模态的目的。此外,光子晶体的边界形状对激光器波长及半高宽并无显著的影响,但圆形边界的阈值激发能量密度比六角形边界低0.3 mJ/cm²。另一方面,将六角晶格、四角晶格与蜂巢晶格的晶格种类进行比较,蜂巢晶格具有较小的激发能量密度（1.6 mJ/cm²）及发散角（1.3°）,而四角晶格的激发能量密度（3.8 mJ/cm²）及发散角（2.2°）为三者之中最大。多重散射法求得的阈值增益与实验结果相吻合,可视为快速有效设计光子晶体激光器结构的工具。本文研究成果对今后发展高功率蓝紫光氮化镓光子晶体面射型激光器具有指导意义。     

平板型光子晶体谐振腔性能分析

介绍了一种平板型光子晶体微谐振腔的结构.利用三维时域有限差分法(FDTD)分析了平板型光子晶体的结构参量及其对谐振腔性能的影响.平板型光子晶体微腔具有较小的模式体积和较大的品质因子(Q),可以有效的使光子局域化.该谐振腔可以用来制造单频发光二极管和零阈值微腔激光发射器.     

双带型光子晶体中双V型四能级原子自发辐射谱中的黑线研究

研究了双带型光子晶体中双V型四能级原子自发辐射的辐射谱.双V型四能级原子同时与真空热库和双带型光子晶体热库耦合.研究发现双V型四能级原子自发辐射谱中有三种不同原因可能引起的黑线：第一种是由于量子干涉效应;第二种是由于各向同性光子晶体带边处态密度具有奇异性;第三种是真空场中的量子干涉和光子晶体禁带内态密度为零共同作用的结果.通过移动光子晶体的带边位置,在各向同性光子晶体带边引入光滑因子,以及在光子晶体中引入缺陷等对这三种黑线的影响,对上述结果进行了分析和讨论. 关键词： 双带型光子晶体 双V型四能级原子 黑线     

光子晶体晶粒尺寸和排列结构对随机激光辐射特性的影响

研究了光子晶体对随机激光器的输出特性的调控,并分析了光子晶体的晶粒尺寸和排列结构等对调控作用的影响.对于同一随机介质而言,上下表面用同种材料不同晶粒尺寸的光子晶体覆盖,结果显示:晶粒尺寸合适的光子晶体会使光在系统中来回振荡从而得到很好的放大,使系统中的光与随机增益介质的相互作用加强,激光阈值降低;同时还对激光模式有较强的调制能力,能在一定程度上抑制自发辐射,使之向所需要的频率内辐射.但如果光子晶体的晶粒尺寸与随机增益介质结构匹配不当,则光子晶体对激光模式调制能力较弱,光场能量不能有效地被局域在系统中,系统 关键词： 有限时域差分法 光子晶体 随机激光 辐射特性     

具有复介电常量二维光子晶体的特性研究

采用平面波展开法,通过数值模拟研究了具有复介电常量的二维光子晶体的能带结构和光传输特性,重点讨论介电常量的虚部为负值情形时对传输特性的影响。研究表明由于光子带隙的存在有效地抑制了频率位于带隙内光的自发辐射。当在介质中掺入具有增益特性的杂质时,即使两种介质的介电常量相差很小,在靠近光子带隙边缘,出现了较强的受激辐射放大。通常在带隙的边缘处,光子晶体的群速度较小,而激光阈值正比于群速度的平方,当群速度很小时,激光阈值将大大减小。这为实现零阈值激光器提供了基础,也为制作光放大微器件提供了一个有益的理论参考。     

固体激光器与光纤激光器对光子晶体光纤棒耦合的分析与对比

耦合效率的高低与耦合后光斑的好坏直接影响着光子晶体光纤棒的放大效果,因此需要对种子光的耦合效果进行研究,选择合适的激光器作为种子源。本文对光子晶体光纤棒在固体激光器与光纤激光器两种情况下的耦合效率进行了理论分析;模拟计算了两种激光器情况下耦合效率的变化规律以及对准误差对耦合效率的影响;选择合适的透镜或透镜组,使用两种激光器对光子晶体光纤棒进行了耦合实验;对比两种激光器的耦合效果可知:固体激光器的耦合效率最高只能达到62.4%,而光纤激光器的耦合效率可以达到80%以上;在光纤激光器耦合情况下,对不同功率注入时耦合效率,以及耦合后光斑进行了实验分析。得到的实验结果对后续光纤棒的放大实验具有指导作用。     

电抽运有机准晶光子晶体激光器及其特性研究

利用有机共轭聚合物MEH-PPV优良的发光特性和光子晶体对光的调制特性,设计制备了有机半导体二维平板的准晶光子晶体激光器。该激光器是以MEH-PPV为增益介质,利用二维平板准晶光子晶体点缺陷和上下电极表面作为反射膜共同构建激光器的微腔,获得了具有激射效应的电抽运8重准晶垂直腔面发射激光器。该激光器的阈值电流为8 m A,激射波长为606 nm,谱线半峰全宽为0.5 nm,接近光纤光谱仪的分辨率极限。     

光子晶体对非晶纳米团簇辐射特性的影响

用有限时域差分法研究了非晶ZnO纳米团簇的辐射频谱,结果显示频谱呈自发辐射的特性. 为了对非晶纳米团簇的辐射输出进行有效的控制和利用,提出了利用光子晶体来控制纳米团簇的自发辐射,使之向所需要的频率内辐射的理论设计;并构想了一种制备简单、成本较低的实现方法,依据这种设想构建了一个二维系统,对其辐射特性进行数值模拟,结果显示光被有效地控制. 为制备可嵌入到集成光路中的、具有良好可加工性能的低阈值微型激光器提供了一条新途径. 关键词： 有限时域差分法 光子晶体 非晶纳米团簇 辐射特性     

Enhanced spontaneous emission factor for microcavity lasers

The microcavity and the influence of nonradiative recombination can control spontaneous emission. An analytic resolution of rate equation is studied for microcavity lasers. The relationship between output prop- erties and structural parameters of multi-quantum wells (MQWs) is obtained. One of the most important consequences of the incrcased spontaneous emission factor is the reduction of laser threshold. It is found that the characteristic curve of a "thresholdless" laser is strongly nonradiative depopulation-dependent. The light output is increased by the enhanced well number and the reduced width. In particular, there is an optimal well number corresponding to the lowest threshold current density for MQW structure in the microcavity lasers.     

Self-optimization of optical confinement in an ultraviolet photonic crystal slab laser

We studied numerically and experimentally the effects of structural disorder on the performance of ultraviolet photonic crystal slab lasers. Optical gain selectively amplifies the high-quality modes of the passive system. For these modes, the in-plane and out-of-plane leakage rates may be automatically balanced in the presence of disorder. The spontaneous optimization of in-plane and out-of-plane confinement of light in a photonic crystal slab may lead to a reduction of the lasing threshold.     

Threshold characteristics of microcavity semiconductor lasers

The influence of spontaneous emission coupling on the threshold characteristics of microcavity semiconductor lasers is studied using explicit algebraic expressions for the pump rate dependence of photon and carrier numbers. It is shown that fractional spontaneous emission coupling in practical microcavity laser structures imposes limitations on thresholdless lasing operation.     

Controlling spontaneous emission with the local density of states of honeycomb photonic crystals

We calculated the local density of state for various positions in a photonic crystal of honeycomb lattice to study how the spontaneous emission rate of a radiating dipole is altered in the presence of the photonic crystal. The local density of states is found to be position-sensitive and its value can be enhanced or depressed relative to the density of states, depending on the location of the dipole. Our study shows that the density of states tends to underestimate the effect of a photonic crystal on the prohibition of light propagation, while on the contrary tends to overestimate the effect on the enhancement of light emission. The calculations also indicate that it is possible to tailor the spontaneous emission of an active medium by careful selecting its location in the photonic crystal. The results are helpful in determining the insertion location of the active medium and in evaluating the efficiency of active photonic crystal devices such as light-emitting diodes or lasers.     

Quasiparity‐Time Symmetric Microdisk Laser

Recent developments in parity‐time (PT) symmetric systems have ushered in unique photonic devices with enhanced functionalities. While single‐mode laser emission has been demonstrated in such systems, the current designs face severe challenges in applications, either due to their stringent requirement on fabrication precision or nonscalability to larger devices. Here, we demonstrate a general mechanism to achieve single‐mode lasing in coupled cavities, which relies on external mode coupling and overcomes these drawbacks. We find significant gain enhancement for selected modes by external coupling, and our experiments have confirmed the resulting single‐mode laser emission in size‐mismatched photonic molecules (PMs), when only one constituent cavity is pumped. This behavior persists for a wide range of pump power, from transparent threshold to gain saturation, and it is highly tolerant of fabrication imprecisions. In addition, the output intensity of such single‐mode lasers also displays enhancement when compared with the same PMs under uniformly pumping. We believe our results will both advance the understanding of different coupling scenarios in coupled cavities and improve the characteristics of onchip laser sources for practical applications.     

λ／4相移分布反馈半导体激光器在高输出功率时的特性分析

从光场限制因子周期性主烨这一概念出发，指出在纯折射率耦合分布反馈激光器中存在着增益耦合作用，这种作用在阈值附近较小，但在输出功率增加时迅速大，并因此使λ／４相移分布反馈激光器的单模特性主。量子效应对这种增益耦合作用影响不大。在λ／４相移量子阱分布反馈激光器中，量子效应对空间烧孔效应有很强的抑制作用，因此在其高力功率值出特性出中，增益耦合的影响将变得比较明显。     

Dynamics of spontaneous emission from SiN with two-dimensional photonic crystals

We investigated the dynamics of spontaneous emission from a photonic crystal etched into a SiN slab. After fitting the decay curves of the emission to double exponential functions, we divided the dynamic process of the spontaneous emission into a fast process and a slow process. It was observed that the presence of the photonic crystal increased the proportion of the fast decay component, and consequently, the emission rate and time-integrated emission intensity were also enhanced. These enhancements were a result of the coupling of the guide modes to the leaky modes of the photonic crystal slab waveguide.     

Wavelength switching by mode interference of coupled cavities with photonic crystal reflectors

We report the development of current-controlled widely tunable laser diodes based on InP with photonic crystal reflectors. The lasers consist of two longitudinally coupled and individually contacted segments that are coupled through photonic crystal sections. Two designs are presented, one based on a gain-coupled distributed feedback mechanism, the second based on contra-directional coupling of two photonic crystal waveguides. The emission wavelength can be switched quasi-continuously over a range around 53 nm for the first design. PACS 42.55.Px; 42.60.Da; 42.60.Fc; 42.25.Hz; 42.70.Qs