New low noise, photonic two-tone terahertz spectroscopy and imaging system
Sebastian Dülme wins Best Student Paper Award
Microwave photonics is an interdisciplinary field dealing with the interaction of microwaves and light waves in the generation, processing, control and distribution of signals in the terahertz, microwaves and millimeter wave range. Microwave photonics can be found in many applications, such as wireless high-speed networks, spectroscopy and imaging, radar, sensors and modern metrology.
The "IEEE International Topical Meeting on Microwave Photonics" (MWP) is the most important international meeting for microwave photonics and offers a platform for the presentation of new developments in this multidisciplinary field of research, from new devices to field trials. The venue of the MWP changes every three years between Europe, America and the Asia-Pacific region and this year was Ottawa, Canada, from October 7 to 10. The University of Duisburg-Essen was represented in Ottawa by three employees of the Center for Semiconductor Technology and Optoelectronics: Sebastian Dülme, Matthias Steeg and Prof. Dr. Andreas Stöhr travelled to Ottawa to present system and technology developments from the field of optoelectronics in recent months. Work from the fields of millimeter wave radar and millimeter wave beam deflection for 5G applications using photonic leak wave antennas as well as photonic terahertz spectroscopy and imaging systems was presented.
Sebastian Dülme was awarded the "Best Student Paper Award (2nd Place)" for his work "300 GHz Photonic Self-Mixing Imaging System with vertical illuminated Triple-Transit-Region Photodiode Terahertz Emitters".
Sebastian Dülme, currently in the Collaborative Research Center Mobile Material Characterization and Localization by Electromagnetic Sensing (SFB/TRR 196 - MARIE), funded by the German Research Foundation (DFG), PhD student in the field of optoelectronics at the University of Duisburg-Essen, presented novel photonic two-tone terahertz spectroscopy and imaging system, enables extremely low noise amplitude and phase measurements. Due to the low phase noise of the presented system, smallest changes e.g. of the complex permittivity or the thickness of the objects to be examined can be determined. The system is based on the detection of two terahertz signals by means of an envelope detector, which mixes the terahertz signals down to a low-frequency signal in which the phase information of the terahertz signals is still contained. In contrast to conventional coherent systems, a space-consuming optical delay line can thus be dispensed with and a significant reduction in phase noise can be achieved.
High-performance, ultrafast terahertz photodiodes developed at the Center for Semiconductor Technology and Optoelectronics were used to generate the necessary terahertz radiation. Photodiodes are key elements in many photonic terahertz systems for e.g. communication, radar, spectroscopy and imaging applications, where they are used to generate terahertz waves by optoelectrical conversion. The characterization of the indium phosphide-based terahertz photodiodes was partly carried out in cooperation with the Chair Optoelectronic Device Group of Prof. Dr. Andreas Beling at the University of Virginia in Charlottesville, USA, which Sebastian Dülme visited during a Short Term Scientific Mission in December 2018. The flat frequency response of the photodiodes in the J frequency band (225 GHz to 330 GHz) made it possible to use the two-tone terahertz system at 300 GHz. In addition to the experimentally determined results, numerical simulations of the semiconductor physics of the component were also presented at the conference.
Future work in this field will include further performance optimization of terahertz photodiodes, their integration with other material systems, the production of fiber-bound photodiode modules, the development of photodiode arrays and the realization of electromagnetic terahertz beam guidance.
Contact: Andreas Stöhr