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Cluster Report Photonics in the Capital Region Berlin-Brandenburg

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58 Cluster Report Optics and Photonics – Optical Analytics The research conducted at Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute, HHI includes fast optoelectronic THz emitters and detectors. The use of mature technologies and components from indium-phosphide-based telecommunication enables the production of robust and powerful THz systems covering the frequency range from 0.1 to 6 THz. These glass-fibre-based systems have become the worldwide standard for optoelectronic THz systems in recent years, as many beam sources and components are available in high quality. The THz transmitters and receivers developed at Fraunhofer HHI are used both in THz spectroscopy and increasingly in the field of non-destructive testing and process control. One example is the non-contact measurement of the wall thickness of plastic pipes during the manufacturing process with an accuracy of less than 10 µm. Based on this technology, HHI launched an integrated fibre-coupled THz transceiver in 2016 that combines a THz transmitter and receiver on a single indium phosphide chip. This configuration enables THz reflection measurements under vertical beam incidence, resulting in very compact, robust, and powerful THz probes. This is one of the most important prerequisites for further applications for THz technology. These detectors are the first that allow the measurement of the THz output of the THz emitters developed at Fraunhofer HHI. The Federal Institute for Materials Research and Testing Bundesanstalt für Materialforschung und -prüfung (BAM) in Berlin is working on potential applications of commercially available time-resolved THz spectrometers (THz-TDS) for the spectroscopic investigation of dielectrics. Their initial THz activities in the field of spectral material characterisation of liquids, fires, and hazardous substances were supplemented by questions on contactless and non-destructive material testing for the detection of internal defects and structural structures of planar and spherical objects. For the characterisation of multiple layers in planar dielectric composite systems using the Thz TDS, a THz time-of-flight optical layer model was developed to measure the layer build-up in terms of material thickness and identify defects by scanning a dielectric object. The THz-TDS-SAFT tomography was developed for the non-destructive testing of three-dimensional dielectric components. It is used to reconstruct the internal structures of components after scanning with THz radiation. The focus is on the visual detection of material defects, such as pores or cracks in 2D and 3D images. BAM focuses its activities primarily on materials testing. Thz TDS is being prepared for use in industry applications such as the non-destructive testing of polymers, ceramics, and high-performance materials. The hope is that it will offer a viable alternative to existing test systems. THz module for mobile use from Fraunhofer HHI © Fraunhofer HHI Pyroelectric THz detectors not requiring cooling were developed in a partnership between the Physikalisch-Technische Bundesanstalt (PTB) in Berlin and SLT Sensor- und Lasertechnik GmbH based in Wildau. In 2017, the development team received the special “Young Company” award from the AMA Association for Sensor and Measurement Technology for this innovation. As a unique selling point, these detectors exhibit a constant spectral sensitivity in the entire THz spectral range and have been successfully sold with individual PTB calibration certificates by SLT worldwide. Calibration and standards The Physikalisch-Technische Bundesanstalt (PTB) in Berlin is the only place in the world where the spectral sensitivity of THz receivers can be traced back to the SI. This calibration service with a THz molecular gas laser not only serves the leading manufacturers of THz detectors in the frequency range from 700 GHz to 5 THz, but above all customers working in the research and development of THz systems and their users all over the world. In addition, a further measuring station with a state-of-the-art fibre-coupled THz TDS system from Fraunhofer HHI permits precise characterisation of ma-

Cluster Report Optics and Photonics – Optical Analytics 59 Pyroelectric measuring heads for THz radiation © SLT Sensor- und Lasertechnik GmbH terial properties (transmission, reflection, and absorption) in the THz spectral range. SLT’s pyroelectric THz detectors are the basis for the first calibrated THz reference material for use in precisely measuring transmission and reflection. In addition, the PTB in Berlin-Adlershof operates the Metrology Light Source electron storage ring, which can generate coherent THz radiation. PTB carries out spectroscopic work in the THz spectral range on a dedicated THz beam tube, partly as part of its several partnerships. Promoting collaboration Berlin is a popular place to go for international research in the field of THz waves. And collaboration within the region itself is helping to ensure success in national and international competition. One example is a partnership between Berlin-based eagleyard Photonics GmbH and the DLR, FBH, Humboldt University, and PDI to develop compact THz quantum cascade lasers for spectroscopic applications. This has resulted in the world’s most compact THz laser system. As part of the PolyPhotonics joint project, Fraunhofer HHI is developing a technology platform that can also be used in the THz range. The special feature here is the material: the core of the platform consists of a chip with optical waveguides made of polymer material, which can accommodate further passive elements such as glass fibres, thin-film filters, and micro-optics as well as active components such as photodiodes or laser chips (see chapter 2.3 “Photonics for Communication and Sensors”). Beyond THz ... is where the radar range begins. What is traditionally associated with large rotating antennas at airports or on ships can now be accommodated on a microchip. Such technology was developed at IHP in Frankfurt (Oder) and brought to market by Silicon Radar GmbH. Its high-frequency switching is used in radar solutions, phased array systems, and wireless communication applications. Silicon Radar is developing customer-specific ASICs and standard components in the frequency range from 10 GHz (X-band) to 200 GHz and beyond. These miniature radar systems, which can be used for precise distance measurements or as fill level sensors, were awarded with the Brandenburg Future Prize in 2016. Contact: Dr. Michael Kolbe Spokesperson Focus Area Optical Analytics Phone: +49 (0)30 34817131 E-mail: Contact: Prof. Dr. Stefan Kowarik THz calibration measuring station with THz camera (1), standard detector (2), and device under test (3) being hit by the THz laser beam (red line). When the gold-plated chopper (5) interrupts the beam, the monitor detector (4) measures the THz output. © PTB Spokesperson Focus Area Optical Analytics Phone: + 49 (0)30 8104-4817 E-mail:

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