Coherent THz emission from an array of resonant tunneling diodes (RTDs) mediated by a strong-coupling Fabry-Perot cavity

太赫兹辐射的频率介于红外辐射和微波辐射之间，在无损检测、医学成像、安全检查以及高比特率无线通信等方面有着广泛的应用。然而，由于缺乏具有成本效益的、紧凑的、高功率的0.3-3太赫兹左右的发射器，臭名昭著的“太赫兹差距”阻碍了太赫兹辐射的大规模应用。随着技术的不断进步，该项目的主要目标是通过一种创新的跨学科的辐射源功率梳理方法来帮助填补“太赫兹缺口”，该方法基于两项迄今尚未连接起来的先进技术。该项目涉及两个太赫兹研究小组：日本东京理工学院浅田雅弘教授的研究小组和德国美因河畔歌德大学的哈特穆特·G·罗斯科斯教授的研究小组。浅田教授的团队开发和优化了作为紧凑型芯片电子太赫兹发射器的共振隧道二极管(RTD)，他们已经成为此类太赫兹辐射源的世界领先实验室。他们的RTD现在可以从几十GHz到1.94太赫兹工作，因此覆盖了很大一部分“太赫兹间隙”。但RTD的输出功率仍然限制在几十微瓦，这不足以满足大多数设想的太赫兹应用，而且还没有看到大幅增加输出功率的好策略。我们来自太赫兹光子学的另一个研究领域，现在我们提出了一种新的协同方法来解决这个问题。在过去的几年里，我们已经建立和研究了太赫兹频率范围内的高品质因数一维光子晶体腔，并通过腔内光子与超材料等离子体的耦合展示了强烈的光-物质相互作用。我们想到，通过将太赫兹腔与RTD阵列相结合，应该能够通过强耦合导致RTD阵列的相干超辐射发射来显著增加RTD的输出功率。在DFG的资助下，我们开始了一项国际合作，通过成功的数值模拟和在日本的联合实验工作，我们能够为这一雄心勃勃的努力奠定基础。在此基础上，我们现在进入一个完整的项目，将强耦合腔与最先进的RTD阵列相结合的想法，形成一个强大而紧凑的光子太赫兹发射器。

Terahertz radiation, whose frequency lies between those of infrared radiation and microwave radiation, has a broad range of applications, e.g. in non-destructive testing, medical imaging, security screening, as well as high-bit-rate wireless communications. However, the notorious “terahertz gap”, mainly due to the lack of cost-efficient, compact, high-power emitters at around 0.3-3 THz, has prevented the large-scale application of terahertz radiation. As the technology continues to advance, the main objective of this project is to help to fill the “terahertz gap” by an innovative interdisciplinary power-combing approach for emitters, which is based on two hitherto unconnected advanced technologies. This project involves two terahertz research groups: That of Prof. Masahiro Asada at the Tokyo Institute of Technology in Japan and that of Prof. Hartmut G. Roskos at Goethe-University Frankfurt am Main in Germany. Prof. Asada’s group develop and optimize resonant tunneling diodes (RTDs) as compact, chip-based electronic terahertz emitters, and they have become a world-leading laboratory for this type of terahertz radiation source. Their RTDs can now operate from tens of GHz up to 1.94 THz, and thus cover a large part of the “terahertz gap”. But the output power of the RTDs remains limited to tens of microwatt, which is not sufficient for most of the envisaged terahertz applications, and no good strategy has been visible to substantially increase the output power. Coming from a different area of research of terahertz photonics, we now suggest a novel synergistic approach to this problem. During the last few years, we have built and studied one-dimensional photonic crystal cavities with high quality factor in the terahertz frequency range, and demonstrated strong light-matter interaction by coupling the cavity photons with metamaterial plasmons within the cavity. It occurred to us that by combining a terahertz cavity with an array of RTDs, one should be able to substantially increase the output power of the RTDs via strong coupling leading to coherent superradiant emission from the RTD arrays. Funded by a grant of DFG to start an international collaboration, we were able to build the foundation for this ambitious endeavor by successful numerical simulations and joint experimental work in Japan. On this basis, we now enter into a full project to put into practice the idea of the combination of a strong-coupling cavity with state-of-the-art RTD arrays to form a powerful and compact photonic terahertz emitter.