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:

Principal Investigators:
Prof. Martin Vossiek, martin.vossiek@fau.de
Prof. Frank Ellinger, frank.ellinger@tu-dresden.de

Members:
Dr. Christian Carlowitz, christian.carlowitz@fau.de
Tilo Meister, tilo.meister@tu-dresden.de
Yu Zhu, yu.zhu2@tu-dresden.de
Lea Borngraber, lea.borngraeber@tu-dresden.de
Leonhard Hahn, leonhard.hahn@fau.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:

Principal Investigators:
Prof. Heinz-Wilhelm Hübers, (Deutsches Zentrum für Luft und Raumfahrt - Berlin), heinz-wilhelm.huebers@dlr.de
Dr. Klaus Biermann, (Paul-Drude-Institut für Festkörperelektronik - Berlin), biermann@pdi-berlin.de
Dr. Katrin Paschke, (Ferdinand-Braun-Institut gGmbH - Berlin), katrin.paschke@fbh-berlin.de

Members:
Alexander Sahm, (Ferdinand-Braun-Institut gGmbH - Berlin), alexander.sahm@fbh-berlin.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. 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
Dr. I. La Penna, irene.lapenna@dlr.de
Dr. S. Henn, henn@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:

Principal Investigators:
Prof. Dr. Hartmut Roskos, roskos@physik.uni-frankfurt.de
Dr. Fanqi Meng, fmeng@physik.uni-frankfurt.de

Members:
Jahnabi Hazarika, jahnabi9814@gmail.com 
Chunjiang He, chunjiang.he@foxmail.com 

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A high-resolution, accurate atmospheric and astronomical molecule of gas spectroscopy in the range of 2 to 5 THz requires the use of stable-running local oscillators which must have a signal with the lowest possible line width. The most promising local oscillators (LO) in this spectral range are THz quantum cascade lasers (QCL) which have an intrinsic line width of typically a few hundred Hz. However, thermal, electrical and mechanical instabilities lead to free-running LO frequencies and thus to line widths of the QCL signal of a few MHz. Common techniques for stabilizing the LO frequency of QCLs are all based on an electrical control loop to match the frequency of the QCL to a reference signal. A major disadvantage of the electrical control loop is the limitations of the flange-band width. The aim of the project is to develop a THz control loop for quantum cascade lasers with the aid of modified uni-traveling carrier THz photodiodes (MUTC-PDs). In the ramen of the project, the use of room temperature as well as cryogenic MUTC-PDs are investigated.

UTC4QCL Team:

Principal Investigators:
Dr. Johanna Böhm, johanna.boehm@uni-due.de
Dr. Heinz-Wilhelm Hübers, heinz-wilhelm.huebers@dlr.de
Dr. Xiang Lü, lue@pdi-berlin.de
Dr. Andreas Stöhr, andreas.stoehr@uni-due.de

Members:
Dr. Klaus Biermann, biermann@pdi-berlin.de 
Dr. Valentino Pistore, biermann@pdi-berlin.de 
Walid Anders, anders@pdi-berlin.de 
Nicole Volkmer, volkmer@pdi-berlin.de 
Dr. Martin Wienold, martin.wienold@dlr.de 

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The proposed project will pioneer the use of chip-integrated THz sources, which were previously used exclusively for chip-integrated electron paramagnet resonance (EPRoC) measurements in the first funding phase of the center of gravity program, in battery research by increasing the sensitivity of nuclear magnetic resonance (NMR) to dendritic microstructures on lithium metal surfaces during charging/discharging cycles by dynamic nuclear polarization (DNP). The use of lithium-metal anodes is an important current goal in battery development, as they offer significant benefits in terms of energy density and voltage. However, the reactive surface shortens the service life and can cause short circuits, since lithium dendrites and other microstructures can form on the metal anode surface, the development of which is not yet sufficiently understood due to the lack of spectroscopic methods that would enable in-operando measurements, as well as the low intrinsic sensitivity of nuclear magnetic resonance. By using intact batteries and DNP through THz magnetic fields generated by EPRoC technology, this project aims to understand the processes that lead to dendrite formation, and provides insights that are critical to the stability and performance of batteries. In addition, the project envisages extending the application of EPRoC to post-lithium technologies such as sodium metal, opening up opportunities for broader applications in battery research. To achieve these objectives, significant improvements are needed that go beyond the current state of the art of EPRoC technology. The proposed project aims in particular to enable pulsed DNP methods and to extend the operating frequencies beyond 263 GHz through novel circuit topologies. These performance improvements will be accompanied by an increase in the performance efficiency of the integrated system to allow operation at low temperatures down to low temperatures. In addition, we will study the use of higher harmonic frequencies of the oscillator circuits used, including amplification of the higher harmonic frequencies, with the aim of reaching frequencies of up to 1.2 THz. In order for the THz magnetic fields to penetrate the metal electrode of the battery, we will study both conventional metal grid electrodes and novel plasmonic meta-surfaces that could locally reinforce the required magnetic component of the THz field.

TeraLiNaBat Team:

Principal Investigators:
Anders, Jens, jens.anders@iis.uni-stuttgart.de 
Lips, Klaus, lips@helmholtz-berlin.de

Members:
Dr. Pedro B. Groszewicz, pedro.groszewicz@helmholtz-berlin.de 
Dr. Michal Kern, michal.kern@iis.uni-stuttgart.de 
Matan Perez,  matan.perez@helmholtz-berlin.de 
Golsa Nezami, golsa.nezami@iis.uni-stuttgart.de 

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