Development of continuous-wave 1550 nm operated terahertz system


Demand for Terahertz (THz; 100 GHz-10 THz) devices and systems is on the rise globally. There is also a strong need for applications of the same in efficient practical systems at reduced costs. At present, several techniques can be employed to generate and detect the Terahertz radiation where the application defines the approach to be utilized. Continuous-wave photomixing is the technique of choice where large tunability, large bandwidth and good frequency resolution are required. Previously, such photomixers operated at 800nm but the advent of the 1550nm systems ousted the former. Unfortunately, 1550nm operated photoconductors have a detrimental drawback in that they are very difficult to design due to several partially conflicting requirements. Therefore, there is need to develop a device that can satisfy these requirements and allow for their concurrent maximization.

A.D.J. Fernandez Olvera and Professor Sascha Preu at TU Darmstadt in Germany in collaboration with Professor Hong Lu at Nanjing University in China and Professor Arthur C. Gossard at University of California, Santa Barbara, USA developed ErAs:InGaAs homodyne detectors and ErAs:InAlGaAs photoconductive Terahertz sources with excellent device parameters and Terahertz performance under continuous-wave operation. They employed  ErAs:In(Al)GaAs devices in a THz system with a peak dynamic range of 78 dB and a bandwidth of ∼3.65 THz at an integration time of 300ms and only 26 mW laser power on each device. Their work is published in the research journal Optics Express.

To begin with, the research team designed ErAs:In(Al)GaAs photoconductors comprising a superlattice layer structure designed to achieve the desired parameters, namely high resistivity, low carrier lifetime, high absorption of 1550 nm laser signals, and high carrier mobility. Next, the superlattice material was grown at the optimum growth temperature for InGaAs. The researchers then proceeded to demonstrate the superior capabilities of the material system by employing ErAs-based photoconductors as both source and receiver for the continuous wave 1550nm Terahertz system. Eventually, they characterized and qualified the ErAs:InGaAs receiver.

The research team observed excellent peak dynamic range of 78 dB and (extrapolated) bandwidth of 3.65 THz using a system with photoconductors for both emission and detection. They compared its performance to a state-of-the-art commercial system using a p-i-n diode as source and a photoconductive receiver. While the dynamic range of the state-of-the-art commercial system under the same predefined laser driving conditions was larger at 100 GHz, it was already smaller at 2 THz. The measured Terahertz photocurrent of the receiver increased linearly with source DC bias without any noticeable saturation within the examined biasing range of the photoconductive source, allowing for further increase of the dynamic range with even more powerful emitters in the future.

The study has reported the highest dynamic range ever to be achieved using a continuous wave system operating at 1550nm and employing only photoconductive elements. Additionally, the 3.65 Terahertz extrapolated bandwidth is on the level of the largest bandwidths reported to date with any 1550nm continuous-wave Terahertz system. Altogether, the ErAs:InAlGaAs-based photoconductive source is superior to the p-i-n diode based commercial device at high Terahertz frequencies, offering larger bandwidth at the expense of lower dynamic range at low frequencies.


The authors acknowledge funding by the Deutsche Forschungsgemeinschaft, Project PR1413/3-1 (REPHCON) and from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 675683 (CELTA).

Continuous-wave 1550 nm operated terahertz system using ErAs:In(Al)GaAs photoconductors with 52 dB dynamic range at 1 THz. Advances in Engineering

About the author

Anuar Fernandez Olvera received the B.S. degree in Electronic and Computer Engineering (summa cum laude) from Tecnologico de Monterrey, in 2010. He then received the M.S. degree in Electrical Engineering (cum laude) from TU Eindhoven in 2015. After that, he started his Ph.D. in Electrical and Computer Engineering at TU Darmstadt, in 2016, where he joined the Terahertz Systems Technology Group in the framework of the EU H2020 Project CELTA (Convergence of Electronics and Photonics Technologies for Enabling Terahertz Applications). As part of the CELTA project, he has conducted research stays at Universidad Carlos III de Madrid and at Toptica Photonics AG.

His main research topic is the development of broadband THz sources and detectors based on photomxing for different applications (a photonic vector analyzer, THz communication systems and non-destructive testing). His research interests also include new photoconductive materials for photomixing, micromachining techniques for THz waveguides, and electromagnetic simulations of THz antennas.

About the author

Hong Lu received the B.S. degree in chemistry from the University of Science and Technology of China, Hefei, China, and the Ph.D. degree in chemistry from the City University of New York, New York, NY, USA, in 2007, where she focused on inter-subband transitions of wide-bandgap II-VI semiconductors grown by molecular beam epitaxy (MBE). After working as a project scientist at the Materials Department, University of California, Santa Barbara, CA, USA for 8 years, Hong joined Nanjing University and she is currently a Professor with the Department of Materials Science and Engineering, College of Engineering and Applied Sciences at Nanjing University.

She has co-authored more than 100 papers in refereed journals. Her current research interests include using and developing MBE growth techniques for synthesis of novel materials and material structures, and characterization and processing for fundamental understanding and device applications, especially hetero-structures formed by semiconductors, metals and semimetals, and their applications in optoelectronics, thermal management and terahertz-based technology.

About the author

Arthur C. Gossard received his bachelor’s degree in physics from Harvard University and his Ph.D. in physics from University of California, Berkeley.  In his Ph.D. research at Berkeley, he observed the first nuclear magnetic resonance in a ferromagnetic material and discovered the enhancement of rf magnetic field at the nucleus caused by domain rotation and domain wall motion. He is professor of Materials and Electrical and Computer Engineering at University of California, Santa Barbara.

His research involves the creation and study of nanoscale artificially structured materials.  His special interests are molecular beam epitaxy, the growth of quantum wells, nanostructures and superlattices and their applications to high performance electrical and optical devices and the physics of low-dimensional structures.  In work at AT&T Bell Laboratories, he created the first alternate monolayer superlattices, the first selectively doped high-mobility heterostructures, and was the co-discoverer of the Nobel prize-winning fractional quantum Hall effect.  He was also co-discoverer of the quantum-confined Stark effect and optical modulator.  At UCSB, he pioneered the growth of epitaxial composites of metallic erbium arsenide and related rare-earth compound nanoparticles in semiconductor hosts.  He developed improved thermoelectric materials for direct creation of electrical power from waste heat.  And he produced semiconductor devices with increased electron-hole tunneling for creation of multicolor solar cells.

His work most recently produced high performance quantum dot lasers grown epitaxially on on-axis silicon substrates.  This work has the potential to replace wires in computer chips with light beams.  He is a fellow of the American Physical Society and the IEEE, a member of the National Academy of Engineering, a member of the National Academy of Sciences, a recipient of the 1983 Oliver Buckley Condensed Matter Physics prize and recipient of the 2001 James McGroddy New Materials prize of the American Physical Society and the 2009 Al Cho International Molecular Beam Epitaxy Award.  In 2017, he was awarded the U.S. National Medal of Technology and Innovation.

About the author

Sascha Preu received the Diploma degree (2005) and the Ph.D. degree in physics (summa cum laude) from the Friedrich-Alexander Universität Erlangen-Nürnberg, in 2009. From 2004-2010 he was working at the Max Planck Institute for the Science of Light, Erlangen, Germany, on THz photomixer technology. 2010-2011 he was with the Materials and Physics Department, University of Santa Barbara, California within the framework of a Feodor Lynen Stipend of the Humboldt Foundation where he worked on field effect transistor rectifiers and rare-earth:III-V materials. From 2011-2014 he was at the Chair of Applied Physics, Universität Erlangen-Nürnberg, continuing research on field effect transistors, ErAs:In(Al)GaAs photoconductors and graphene-based THz devices. Currently, he is Professor at the Department of Electrical Engineering and Information Technology, Technische Universität Darmstadt, Germany, leading the Terahertz Systems Technology group. He authored and coauthored more than 70 journal articles or conference contributions.

His research interests focus on the development of semiconductor-based THz sources and detectors, including photomixers, photoconductors and field effect transistor rectifiers as well as high performance systems constructed thereof. He also works on applications of THz radiation, in particular characterization of novel THz components and materials, including graphene, and THz spectroscopy.


A.D.J. Fernandez Olvera, H. Lu, A. C. Gossard, S. Preu. Continuous-wave 1550 nm operated terahertz system using ErAs:In(Al)GaAs photoconductors with 52 dB dynamic range at 1 THz. Volume 25, Number 23 | 13 Nov 2017 | Optics Express 29492


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