Tuesday, April 24, 2018

Mittleman Wins Humboldt Award




https://www.brown.edu/academics/engineering/news/2018-04/mittleman-wins-humboldt-award

Daniel Mittleman, professor of engineering who studies frequencies in the terahertz range, has received an Alexander von Humboldt Foundation Research Award for 2018.
Brown Professor of Engineering Daniel Mittleman is a 2018 recipient of the Alexander von Humboldt Foundation Research Award. The foundation grants up to 100 such awards each year to researchers from around the world to support collaborative projects with scientists and researchers in Germany. The awards are granted to researchers “whose fundamental discoveries, new theories, or insights have had a significant impact on their own discipline and who are expected to continue producing cutting-edge achievements in the future.”
Mittleman was recognized for his work on the science and technology of terahertz radiation. The award will support ongoing research and enable new partnerships involving devices for terahertz wireless communications and non-linear terahertz spectroscopy of materials. He will collaborate with Professor Martin Koch at the University of Marburg, a collaboration that began many years ago.
“I am honored to receive this prestigious award from the Humboldt Foundation,” Mittleman said. It will provide me with the opportunity to extend my long-standing research collaboration with Professor Koch, as well as to build new collaborations with other groups in Germany who are doing cutting-edge research in terahertz science and technology. Many of my current research interests overlap strongly with ongoing work in Germany, including not only my group’s work in terahertz wireless systems, but also terahertz high-field science and terahertz nano-spectroscopy.”
Mittleman received his B.S. in physics from the Massachusetts Institute of Technology in 1988, and his M.S. in 1990 and Ph.D. in 1994, both from the University of California, Berkeley, under the direction of Dr. Charles Shank. He then joined AT&T Bell Laboratories as a post-doctoral member of the technical staff, working first for Dr. Richard Freeman on a terawatt laser system, and then for Dr. Martin Nuss on terahertz spectroscopy and imaging.
Mittleman joined the Electrical and Computer Engineering Department at Rice University in September 1996, before moving to the School of Engineering at Brown University in 2015. He is a Fellow of the Optical Society of America, the American Physical Society, and the Institute of Electrical and Electronics Engineers, and is currently serving a three-year term as Chair of the International Society for Infrared Millimeter and Terahertz Waves.
Brown Professor of Engineering Sharvan Kumar was a 2015 recipient of the award.

Abstract-Broadband terahertz generation via the interface inverse Rashba-Edelstein effect




Novel mechanisms for electromagnetic wave emission in the terahertz (THz) frequency regime emerging at the nanometer scale have recently attracted intense attention for the purpose of searching next-generation broadband THz emitters. Here, we report a new mechanism for broadband THz emission, utilizing the interface inverse Rashba-Edelstein effect. By engineering the symmetry of the Ag/Bi Rashba interface, we demonstrate a controllable THz radiation (~0.1-5 THz) waveform emitted from metallic Fe/Ag/Bi heterostructures following photo-excitation. We further reveal that this type of THz radiation can be selectively superimposed on the emission discovered recently due to the inverse Spin Hall effect, yielding a unique film thickness dependent emission pattern. Our results thus offer new opportunities for versatile broadband THz radiation using the interface quantum effects.

Abstract-A quantum rings based on multiple quantum wells for 1.2–2.8 THz detection



Alireza Mobini, M. Solaiman,

https://www.sciencedirect.com/science/article/pii/S1386947717320027

In this paper optical properties of a new QR based on MQWs have been investigated for detection in the THz range. The QR composed of a periodic effective quantum sites that each one considered as QW in theta direction. Using Tight binding method, eigen value problem for a QR with circumstance of 100 nm number with different number of wells i.e. 2, 4, 6 and 8 are solved and the absorption spectrum have been calculated. The results show that absorption has maximum value in range of (1.2–2.88 THz) that can be used for THz detection. Finally, it is realized that by increasing the number of wells, the numbers of absorption line also increase.

Abstract-Eight-Capillary Cladding THz Waveguide With Low Propagation Losses and Dispersion



Maxim M. Nazarov,  Artur V. Shilov,  Kazbek A. Bzheumikhov,  Zaur Ch. Margushev,  Viktor I. Sokolov, Alexander B. Sotsky,  Alexander P. Shkurinov,

https://ieeexplore.ieee.org/document/8281070

We investigated the perspectives of a hollow core fiber with a cladding of eight polypropylene capillaries that provides flexibility, low propagation losses, and a single-mode regime in the terahertz frequency range. Optimization procedure is developed. The 7-dB/m propagation loss for 1.3-mm core size and 20-cm waveguide length is experimentally demonstrated at 2-2.2 THz frequency band. The measured group velocity dispersion do not exceed 1 ps/(THz·cm). The theoretical calculations based on the method of Green's functions confirm the experimental data, demonstrate the influence of capillary radius and wall thickness and predict 1.7-dB/m propagation losses for optimized geometry.

Abstract-Terahertz emission from metal nanoparticle array



Daniil A. Fadeev, Ivan V. Oladyshkin, and Vyacheslav A. Mironov

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-43-8-1939

We demonstrate theoretically that ultrafast heating of metal nanoparticles by the laser pulse should lead to the generation of coherent terahertz (THz) radiation during the heat redistribution process. It is shown that after the femtosecond laser pulse action, the time-dependent gradient of the electronic temperature induces low-frequency particle polarization with the characteristic timescale of about fractions of a picosecond. In the case of the directed metallic pattern, the THz pulse waveform can be controlled by changing the geometry of the particle. The proposed THz generation mechanism can be the basis for interpretation of recent experiments with metallic nanoparticles and nanostructures.
© 2018 Optical Society of America

Monday, April 23, 2018

3D Nanoprinting facilitates communication with light

https://www.nanowerk.com/nanotechnology-news/newsid=49995.php


(Nanowerk News) At Karlsruhe Institute of Technology (KIT), researchers have developed a flexible and efficient concept to combine optical components in compact systems. They use a high-resolution 3D printing process to produce tiny beam-shaping elements directly on optical microchips or fibers and, hence, enable low-loss coupling. This approach replaces complicated positioning processes that represent a high obstacle to many applications today. The scientists present their concept in the Nature Photonics journal ("In situ 3D nanoprinting of free-form coupling elements for hybrid photonic integration").
In view of constantly growing data traffic, communication with light is gaining importance. For many years now, computing centers and worldwide telecommunication networks have been using optical connections for the quick and energy-efficient transmission of large amounts of data. The present challenge in photonics is to miniaturize components and to assemble them in compact and high-performance integrated systems suited for a variety of applications, from information and communication technologies to measurement and sensor technologies, to medical engineering.

Microlenses and micromirrors can be produced on optical fibers and microchips by 3D nanoprinting. This considerably facilitates assembly of photonic systems. (Image: Philipp-Immanuel Dietrich/Florian Rupp/Paul Abaffy, Karlsruhe Institute of Technology) (click on image to enlarge)
In this respect, hybrid systems are of very high interest. They combine a number of optical components with different functions. Hybrid systems offer superior performance and design freedom compared to monolithic integration concepts, for which all components are realized on a chip. Hybrid integration, for instance, allows individual optimization and testing of all components before they are assembled to a more complex system. Setup of optical hybrid systems, however, requires complex and expensive methods for the highly precise alignment of components and low-loss coupling of optical interfaces.
Researchers of KIT have how developed a new solution for the coupling of optical microchips to each other or to optical fibers. They use tiny beam-shaping elements that are printed directly onto the facets of optical components by a high-precision 3D printing process. These elements can be produced with nearly any three-dimensional shape and enable low-loss coupling of various optical components with a high positioning tolerance.
The researchers validated their concept in several experiments. They produced micrometer-sized beam-shaping elements of various designs and tested them on a variety of chip and fiber facets. As reported by the scientists in the journal Nature Photonics, they reached coupling efficiencies of up to 88% between an indium phosphide laser and an optical fiber. The experiments were carried out at the Institute of Microstructure Technology (IMT), the Institute of Photonics and Quantum Electronics (IPQ), and the Institute for Automation and Applied Informatics (IAI) of KIT, in cooperation with the Fraunhofer Institute for Telecommunications (Heinrich Hertz Institute, HHI) in Berlin and IBM Research in Zurich. The technology is presently being transferred to industrial application by Vanguard Photonics, a spinoff of KIT, under the PRIMA project funded by the Federal Ministry of Education and Research.
For the production of the three-dimensional elements, the researchers used multi-photon lithography: Layer by layer, a laser with an ultrashort pulse length writes the given structures into a photoresist that hardens simultaneously. In this way, 3D structures as small as a few hundred nanometers can be printed. Apart from microlenses, the process is also suited for producing other free-form elements, such as micromirrors, for the simultaneous adaptation of beam shape and propagation direction. In addition, complete multi-lens systems for beam expansion can be fabricated. With them, positioning tolerance during assembly of the components is enhanced.
“Our concept paves the way to automated and, hence, cost-efficient manufacture of high-performance and versatile optical hybrid systems,” says Professor Christian Koos, Head of IPQ and member of the Board of Directors of IMT as well as co-founder of Vanguard Photonics. “Hence, it essentially contributes to using the vast potential of integrated optics in industrial applications.”