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:

The THz range enables high-resolution imaging. The challenges to employ THz waves for imaging include sufficient amplification. To solve the fundamental problems for THz camera receivers, we have investigated super-regenerative oscillators (SRO) in TeraCaT, which allow a high gain due to the positive feedback. Novel signal distribution networks based on 3D printed dielectric waveguides allow low-loss and low-dispersion transmissions of THz signals with low complexity and high flexibility. 

In the continuation project TeraCaT II, we extend the 600 GHz receiver from TeraCaT I to a multi-channel capable 600 GHz camera transceiver. This involves gaining knowledge in the fields of circuits as well as system design. In order to achieve high gain for the transmitter at 600 GHz, we are also utilizing the advantages of SROs and a novel approach for integrating a large number of transmitter elements into the receiver array will be investigated. By power accumulation and the generation of large virtual apertures a high sensitivity and resolution will be realized. By means of variable phase shifts in the transmitted signals combined with different transmit-receive configurations, we can generate random illumination patterns despite of employing static arrays. Thanks to numerous receivers, this enables image reconstruction using compressed sensing algorithms, using only few individual measurements, and without any array movement or beam steering. 

Additively manufactured, dielectric mirror lines increase the scalability of the coherent local oscillator distribution network through laser structuring, so that a complicated placement of additional waveguide elements or machining post-processing is completely eliminated for the first time, even for large arrays. Novel, low-loss, tree-like branched antenna arrays made of monolithic 3D stereolithographically printed antennas replace the vertical dielectric waveguide antennas that previously had to be fitted individually. 

Overall, an efficient, scalable, complex 3D THz transceiver array concept at 600 GHz, which requires only a few technology building blocks, will be shown experimentally for the first time. To achieve this the SRO theory will be extended with regard to THz systems. In TeraCaT II the project partners continue to combine complementary competencies across the fields of radio-frequency systems, algorithms, antennas, and integrated circuit design.

TeraCaT Team:
Prof. Dr. Martin Vossiek, (Friedrich-Alexander-Universität Erlangen-Nürnberg), martin.vossiek@fau.de
Prof. Dr. Frank Ellinger, (Technische Universität Dresden), frank.ellinger@tu-dresden.de

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This project builds on the achievements of the first-phase INTEREST project ‘Micro-QCL’ which covered the development of a mechanically cooled micro-optical assembly consisting of an optimized terahertz (THz) quantum-cascade laser (QCL), optical components for optical isolation, outcoupling, as well as beam shaping, and an optical fiber. This second-phase project aims at extending this compact assembly towards a complete spectrometer transceiver, i.e., adding a quantum-cascade detector (QCD) and additional optical as well as electrical components on one compact breadboard. 

The QCD, which operates by detecting infrared light through intersubband transitions in quantum wells, offers high wavelength selectivity and low noise, making it particularly suited for precise THz detection. This architecture will enhance the sensitivity of the moderately cooled detector, circumvent the vibrations of a mechanical cooler as source of noise, and improve the frequency stability. The compact design also reduces the size and weight of the system, making it ideal for environments such as mobile platforms and space missions, where minimizing payload and power consumption is a critical requirement. Such an integrated THz transceiver will enable THz spectroscopy for astronomy, atmospheric science, biomedical studies and metrology. The miniaturized module will be developed for mobile measurements and space missions operating at frequencies of 3.5 and 4.7 THz which will enable monitoring of hydroxyl radicals and neutral atomic oxygen, respectively. 

iQCT Team:

Prof. Heinz-Wilhelm Hübers, (Deutsches Zentrum für Luft und Raumfahrt - Berlin), heinz-wilhelm.huebers@dlr.de
Dr. Martin Wienold, (Deutsches Zentrum für Luft und Raumfahrt - Berlin), martin.wienold@dlr.de
Robert Voigt, (Deutsches Zentrum für Luft und Raumfahrt - Berlin), robert.voigt@dlr.de

Dr. Katrin Paschke, (Ferdinand-Braun-Institut gGmbH - Berlin), katrin.paschke@fbh-berlin.de
Alexander Sahm, (Ferdinand-Braun-Institut gGmbH - Berlin), alexander.sahm@fbh-berlin.de

Dr. Klaus Biermann, (Paul-Drude-Institut für Festkörperelektronik - Berlin), biermann@pdi-berlin.de
Dr. Xiang Lü, (Paul-Drude-Institut für Festkörperelektronik - Berlin), lue@pdi-berlin.de
Dr. Valentino Pistore, (Paul-Drude-Institut für Festkörperelektronik - Berlin), pistore@pdi-berlin.de

Terahertz (THz) 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 “THz gap”, mainly due to the lack of cost-efficient, compact, high-power emitters at around 0.3-3 THz, has delayed the large-scale application of terahertz radiation. The main objective of this project is to help filling the “THz gap” by innovative coherent power-combing approaches for emitters based on resonant tunneling diodes (RTDs). This project is a continuation project in the second phase of the Priority Program INTEREST. In the first phase of the INTEREST project, we achieved coherent emission from line arrays of eleven RTD emitters reaching close to 1 mW of output power at about 750 GHz. This achievement was possible because we found a new way to reach in-phase coupling of neighboring oscillators. Before our study, it was believed that oscillators in a linear array always couple in the odd fundamental mode, with the oscillation in neighboring slots occurring with opposite phase, thus that the radiation destructively interferes in normal direction in the far field. We found, however, that asymmetrically-RTD-fed slot antennae coupled in a linear array can also exhibit even-mode operation if the mesa area of the RTDs is reduced: The odd mode prevails at large mesa areas, while the even mode dominates for small ones. The odd mode was found to run at lower frequencies than the even mode. Additionally, both odd and even modes exhibit constructive interference in the far field, but at different distinct radiation angles. For intermediate mesa areas, the RTD array could either run in even or odd mode, controlled by the bias current of the RTDs (the switching exhibiting a hysteresis). This finding opens the potential for current-controlled frequency and emission-direction switching. For the second phase of the project, we will now exploit these results, extend them to two dimensional oscillator arrays, and develop practically usable radiation sources with emission of narrow-band, single-mode radiation in normal direction at an output power of 5 mW or more. We aim for a beam profile closely approximating a radially symmetric power distribution. We target radiation frequencies in the 0.7-0.8 THz band and at or above 1.0 THz. We will then integrate such high-power RTD array emitters into THz imaging systems at Goethe-University and perform application tests of a) standard THz transmission imaging and b) heterodyne holographic imaging.


RTD Team:
Prof. Dr. Hartmut Roskos, (Goethe-University Frankfurt), roskos@physik.uni-frankfurt.de
Dr. Fanqi Meng, (Goethe-University Frankfurt), fmeng@physik.uni-frankfurt.de
Jahnabi Hazarika, (Goethe-University Frankfurt), jahnabi9814@gmail.com
Chunjiang He, (Goethe-University Frankfurt), chunjiang.he@foxmail.com