Ein THz-System besteht aus einer oder mehreren der folgenden Komponenten: einem Sender, einer Übertragungsstrecke und einem Empfänger. Fortschrittliche Integrationstechnologie für alle diskreten Komponenten eines Terahertz-Messsystems in einem kombinierten Ansatz. Beispiele für Themen für das Forschungsgebiet 2:
In TeraCaT, compact and extremely power-efficient super-regenerative integrated receiver circuits will be investigated, which enable efficient beyond-fmax operation with high amplification gain and high sensitivity. This ambitious goal is achieved with a novel 3rd-harmonic downconversion concept that enables downconversion of a 0.6 THz signal to a 0.2 THz IF using a power-efficient non-linear super-regenerative oscillator. Instead of traditional chip-packaging and interconnect techniques, the complete system will be built upon a joint technology stack. It consists of 3-dimensional structures and dielectric components, which are analyzed, simulated, designed and 3D printed together with embedded integrated circuits. TeraCaT plan to set up and demonstrate a fully-functional THz imaging system and the associated tailored assembly, connection and integration technology.
Quantum-cascade lasers (QCLs) are promising radiation sources for high-resolution spectroscopy with sub-MHz or even kHz spectral resolution for the terahertz (THz) spectral region. However, micro-optical integration becomes crucial when it comes to space applications. Besides the small mass and volume, micro-optical integration is important for the optical performance in such a harsh environment. The reasons are the vibrations of the required cryocooler and other non-stationary mechanical and microphonic disturbances, which act back on the laser by the residual external optical feedback from direct and indirect reflections. Without measures, the result is a linewidth enhancement of typically several MHz and a reduced output power stability, which is both problematic for demanding applications such as heterodyne radiometry. Eliminating the underlying effects requires a micro-optical platform with integrated optical isolator.
The key objective of this project is the development of integrated THz QCLs for high-resolution spectroscopy and future space applications at 3.5 THz and 4.7 THz. These two frequencies are very important for the detection of the OH radical and neutral atomic oxygen, respectively, in atmospheric research as well as in astronomy. The overarching goal is to integrate the QCL chip with the most important optical components in a micro-optical assembly, not larger than a matchbox. This includes the QCL chip, the optics for optical isolation, outcoupling, and beam shaping as well as an optical fiber.
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 filling 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 develops and optimizes 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. An example of strong coupling between complementary metamaterials and the cavity photons is shown in the following Figure 1, where Rabi splitting is clearly visible.
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.