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Darmstadt, Germany

Semenov A.,German Aerospace Center | Cojocari O.,ACST GmbH | Hubers H.-W.,German Aerospace Center | Hubers H.-W.,TU Berlin | And 4 more authors.
IEEE Electron Device Letters | Year: 2010

Schottky diodes are well-known nonlinear elements allowing for effective detection and mixing of electromagnetic radiation in the range through microwave to terahertz. Although less sensitive than their superconducting counterparts, they generally do not require cooling that makes them the devices of choice for applications where the ultimate sensitivity is not needed. In the emerging field of terahertz technology, there is a long-time quest for cheap and handy detectors for laboratory use, as well as for serial compact and midsize instruments. We describe the use of a quasi-optically coupled zero-bias planar Schottky-diode detector for monitoring picosecond pulses of synchrotron terahertz radiation and weak continuous-wave emission from an array of Josephson junctions. © 2010 IEEE. Source


Rettich F.,TOPTICA Photonics AG | Vieweg N.,TOPTICA Photonics AG | Cojocari O.,ACST GmbH | Deninger A.,TOPTICA Photonics AG
Journal of Infrared, Millimeter, and Terahertz Waves | Year: 2015

We present a new approach to detect the intensity of individual terahertz pulses at repetition rates as high as 80 MHz. Our setup comprises a femtosecond fiber laser, an InGaAs-based terahertz emitter, a zero-bias Schottky detector, and a high-speed data acquisition unit. The detected pulses consist of two lobes with half-widths of 1–2 ns, which is much shorter than the inverse repetition rate of the laser. The system lends itself for high-speed terahertz transmission measurements, e.g., to study wetting dynamics in real time. © 2015, The Author(s). Source


Preu S.,TU Darmstadt | Mittendorff M.,Helmholtz Center Dresden | Mittendorff M.,University of Maryland University College | Winnerl S.,Helmholtz Center Dresden | And 3 more authors.
IEEE Transactions on Terahertz Science and Technology | Year: 2015

When operating Schottky diodes and rectifying field-effect transistors in the saturation regime, where they show a sublinear response to incident THz power, they can be used as fast autorcorrelators yielding information on the pulse envelope. We report on autocorrelation measurements at 3.41 THz of high-power THz pulses for determination of the pulse duration and pulse structure. By fringe-resolved measurements, the THz frequency of the pulse is also obtained. We develop a theoretical model for the rectification process and compare the performance of an antenna-coupled Schottky diode to a large-Area field-effect transistor rectifier. While the Schottky diode saturates earlier and can therefore be used for autocorrelation measurements at lower input power, antenna-less large-Area field-effect transistors can be used for highest power levels-even at free electron lasers-and turn out to be very robust. © 2011-2012 IEEE. Source


Montero-De-Paz J.,Charles III University of Madrid | Oprea I.,ACST GmbH | Rymanov V.,University of Duisburg - Essen | Babiel S.,University of Duisburg - Essen | And 10 more authors.
Journal of Infrared, Millimeter, and Terahertz Waves | Year: 2013

The millimeter-wave spectrum above 70 GHz provides a cost-effective solution to increase the wireless communications data rates by increasing the carrier wave frequencies. We report on the development of two key components of a wireless transmission system, a high-speed photodiode (HS-PD) and a Schottky Barrier Diode (SBD). Both components operate uncooled, a key issue in the development of compact modules. On the transmitter side, an improved design of the HS-PD allows it to deliver an output RF power exceeding 0 dBm (1 mW). On the receiver side, we present the design process and achieved results on the development of a compact direct envelope detection receiver based on a quasi-optical SDB module. Different resonant (meander dipole) and broadband (Log-Spiral and Log-Periodic) planar antenna solutions are designed, matching the antenna and Schottky diode impedances at high frequency. Impedance matching at baseband is also provided by means of an impedance transition to a 50 Ohm output. From this comparison, we demonstrate the excellent performance of the broadband antennas over the entire E-band by setting up a short-range wireless link transmitting a 1 Gbps data signal. © 2013 Springer Science+Business Media New York. Source


Hoefle M.,TU Darmstadt | Hoefle M.,ACST GmbH | Penirschke A.,TU Darmstadt | Cojocari O.,ACST GmbH | And 5 more authors.
Electronics Letters | Year: 2014

An 89 GHz waveguide coupled direct detector based on a low-barrier Schottky diode is presented. The main focus is to reduce white and 1/f noise to achieve high signal-to-noise ratio values above 35 dB. The design also addresses the Schottky barrier height deviation over temperature and its compensation within the RF circuit. The fabricated detector is characterised and compared with simulation results, proving a high accuracy level of the design and fabrication process, as well as good knowledge of the applied Schottky diode. The results prove the suitability of the detector to be considered for the second European meteorological operational satellite programme (MetOp-SG). © The Institution of Engineering and Technology 2014. Source

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