纳米尺度高斯模式金属半导体激光器研究

In recent years, metallic semiconductor lasers are proposed and investigated widely, and have been shrunk into subwavelength and even nano-scale sizes successfully. However, the cost of the miniaturization of such lasers is that the huge optical loss, such as the plasmonic loss, of the metallic semiconductor cavity increases the lasing threshold and energy consumption dramatically, and thus cannot meet the increasing demands for low energy consumption and ultra-small laser size, which impede the progress of ultra-large photonic integrated circuits and integrated optical communication technology. Those difficulties are needed to be overcome. In this project, we propose a novel topology for metallic semiconductor cavity, which is named “Gaussian mode-like” cavity. This new cavity structure introduces cylindrical reflective facets and curved sidewalls, and thus generate Gaussian resonant mode, which allows concentration of optical energy in the center of the cavity and reduction of the overlap of optical field distribution and metallic sidewalls. Thus the metallic loss, especially the plasmonic loss, can be reduced effectively, and both the cavity quality factor and the performance of the proposed laser can be improved. Besides, by asymmetrically designing the curvature of both reflective facets, the optical energy inside the cavity can be directionally coupled from the cavity substrate into a waveguide. This project aims at designing a novel type of metallic semiconductor laser with dimension smaller than half wavelength and low threshold (lower than 50-μA current or 100-μW optical pumping power), and then does both numerical and experimental demonstration. This project will introduce new schemes and methods to the academic research and industrial applications of nanolasers.

近年来，金属半导体激光器被发明和广泛研究，并成功将尺寸缩小到亚波长乃至纳米尺度。然而，金属半导体腔的巨大光学损耗如表面等离激元损耗等，使得激光器尺寸小型化的同时，阈值和功耗大为提高，从而不能满足不断增加的低功率和小型化需求，严重阻碍极大规模光子集成电路和集成化光通信技术的进步。这一问题亟待解决。本项目提出一种新型的金属半导体谐振腔结构——高斯型谐振腔。该结构引入圆柱形的反射端面和曲线形的侧壁，产生高斯谐振模式，可使光场能量集中在腔中心，减少光场在腔壁金属层的分布，从而有效降低金属损耗，特别是表面等离激元损耗，提高谐振腔的品质因子和激光器性能。通过两个反射端面曲率半径的非对称设计，实现光场能量从腔底部的定向波导耦合输出。本项目拟设计出尺寸小于半波长、低阈值（低于50微安电流或100微瓦泵浦光）的新型金属半导体激光器，并作数值模拟和实验验证，为纳米激光器的学术研究和工业应用提供新机制和新方法。

近年来，纳米尺度的金属半导体激光器被发明和广泛研究。然而，金属半导体腔的巨大光学损耗，使得激光器尺寸小型化的同时，阈值和功耗大为提高，严重阻碍极大规模光子集成电路和集成化光通信技术的进步。本项目提出并研究了一种高斯型金属半导体谐振腔结构，通过优化谐振模式的电磁场分布特性减小金属损耗，提升纳米激光器性能。主要研究内容包括：.（1）理论分析了高斯模式的金属半导体纳米激光器的物理特性，如谐振腔品质因子、谐振模式的电磁场分布、限制因子、阈值增益与阈值电流等，揭示了其物理性质随谐振腔结构变化的一般规律。证明了高斯型谐振腔对纳米激光器性能提升的有效性。.（2）通过电子束曝光与离子束刻蚀的微加工实验，制备出符合本项目设计要求的高斯型金属半导体谐振腔结构，并进行了扫描电子显微镜表征，验证了高斯模式的金属半导体纳米激光器的制备可行性。.（3）研究并优化了金属和介质结构的混合等离激元波导，实现了亚波长模式限制和低损耗特性。在此基础上研究了金属半导体谐振腔的波导耦合机制，并通过谐振腔反射端面曲率半径的非对称设计，实现光场能量的定向波导耦合输出。.（4）研究了纳米激光器相关的微纳尺度光场调控问题，通过设计金属或介质的人工微结构，在微纳尺度范围对入射光场进行传播、光束整形和聚焦等调控，拓宽了金属半导体纳米激光器的应用领域。.项目的研究结果阐明了具有高斯模式的新型金属半导体激光器的物理特性，为纳米激光器的学术研究及其在集成光子学中的应用提供新机制和新方法。