Heinrich Hertz Institute
Heinrich Hertz Institute
News Article | April 25, 2017
LUXEMBOURG--(BUSINESS WIRE)--SES (Euronext Paris:SESG) (LuxX:SESG), together with Fraunhofer Heinrich Hertz Institute HHI and Newtec, will demonstrate an immersive Virtual Reality (VR) experience with a live 360-degree Ultra HD VR satellite broadcast this week from the exhibit floor of the National Association of Broadcasters Convention in Las Vegas, Nevada. The live VR broadcast will originate from Fraunhofer HHI’s OmniCam-360 camera, which will capture the sights and sounds of the SES event b
News Article | August 30, 2016
Plastic foil substrates and chromium oxide interlayers are used in a novel technology that combines high efficiency, low weight, and extreme flexibility in a single platform. In the pursuit to solve the fossil fuel energy crisis, the use and development of photovoltaic technologies is thriving. In this technology, nature's most abundant source of energy—sunlight—is directly tapped. To achieve this, light-absorbing materials that are highly efficient, lightweight, low-cost, and stable during operation are required. Organolead halide perovskites1 are one such class of materials that show promise for photovoltaic applications, and they have recently become a strong focus of solar cell research. Indeed, their cell efficiency has been increased to about 20%2 within only a few years. Organolead halide perovskites are popular because their raw materials are plentiful and cheap, and because they can be fabricated in a simple manner (i.e., optimal prerequisites for cheap solar power). The limited stability of many perovskite absorbers under ambient conditions, however, may ultimately limit the widespread adoption of these materials in solar cells (especially if heavy and costly packaging is to be avoided). The main issue that gives rise to the poor stability of perovskites is water ingress3 and the subsequent liberation of highly corrosive species that rapidly damage metal contacts. In a previous attempt to overcome this problem,4 thick carbon electrodes were used to enable solar cell operation under ambient conditions. Nonetheless, if power output per solar cell weight (a critical metric for all mobile applications)—as well as power conversion efficiency—is to be optimized, alternative strategies are required. In such approaches, it is necessary to maintain the thin and light form factor of a direct band gap absorber material. In our approach,5 we thus demonstrate ultrathin (3μm), highly flexible perovskite solar cells that have stabilized 12% efficiency and a power-per-weight value as high as 23W/g. To realize these devices, we use 1μm-thick plastic foils as substrates and we process (from solution, at low temperature) pinhole-free perovskite films at high yield. We achieve perfect growth of tightly packed perovskite crystallites by treating the transparent polymer electrode with dimethyl sulfoxide. In addition, we introduce a chromium oxide–chromium interlayer, which effectively protects the metal top contacts from reacting with the perovskite, to facilitate air-stable operation. The detailed structure of our solar foils is depicted in Figure 1, together with a photograph of the freestanding ultrathin solar cell. The transparent conducting electrode and the absorber layer are processed from solution, and the electron-selective metal top contacts are thermally evaporated. Figure 1. (a) Schematic illustration of the cell stack. Polyethylene terephthalate (PET) foils (1.4μm thick) serve as the substrate and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is the transparent hole-selective electrode. Using dimethyl sulfoxide as an additive promotes the formation of pinhole-free perovskite layers. A one-step solution precursor deposition method is used to form the methylammonium lead iodide absorber. Perylene-3,4,9,10-tetracarboxylic-3,4,9,10-diimide (PTCDI) or [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) constitute the electron-transport layers. The chromium (Cr) oxide (Cr O ) stabilizes the metal top contact so that the device can be operated in ambient air. Low-resistivity metals, e.g., gold (Au), copper (Cu), and aluminum (Al), complete the device, and a 1μm-thick capping layer of polyurethane is used for mechanical protection. (b) Photograph of freestanding 3μm-thick solar cells (with copper top-metal contacts). (a) Schematic illustration of the cell stack. Polyethylene terephthalate (PET) foils (1.4μm thick) serve as the substrate and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is the transparent hole-selective electrode. Using dimethyl sulfoxide as an additive promotes the formation of pinhole-free perovskite layers. A one-step solution precursor deposition method is used to form the methylammonium lead iodide absorber. Perylene-3,4,9,10-tetracarboxylic-3,4,9,10-diimide (PTCDI) or [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) constitute the electron-transport layers. The chromium (Cr) oxide (Cr) stabilizes the metal top contact so that the device can be operated in ambient air. Low-resistivity metals, e.g., gold (Au), copper (Cu), and aluminum (Al), complete the device, and a 1μm-thick capping layer of polyurethane is used for mechanical protection. (b) Photograph of freestanding 3μm-thick solar cells (with copper top-metal contacts). 5 Solar cells that have aluminum or gold in direct contact with the perovskite degrade immediately upon exposure to ambient atmosphere. The ingress of water into the absorber layer causes this degradation of the perovskite crystal structure, i.e., by the formation of intermediate hydrated phases. The degradation culminates in the reforming of lead iodide, after enough water has permeated the film. In contrast, chromium oxide is resistant to aggressive oxidizing conditions (even nitric acid and aqua regia). It is for this reason (i.e., the excellent stability) that chromium plating is used to form corrosion-resistant coatings on various metals, and why we use a chromium oxide interlayer to provide an excellent buffer to shield the top-contact metal from chemical etching. We packaged our air-stable, thin, light solar cells (with a micrometer-thick spray-on polyurethane coating) so that they could be operated in field tests, where we used the solar panels to power various unmanned aerial vehicles. A snapshot of our model airplane, on a solar-powered flight, is shown in Figure 2. The same airplane is shown with our solar-powered blimp and a ‘solar leaf’ in a short video clip available online.6 For these tests, we powered the airplane and blimp with a 3μm-thick, 5.2g/cm2, light solar panel (with 64 individual cells). The high power-per-weight performance of our devices (i.e., up to 23W/g) is vital for such applications. Several other solar technologies for decentralized power generation and distribution (e.g., blimps, weather balloons, robotic insects, smart buildings, and aerospace applications), environmental and industrial monitoring, rescue and emergency response, as well as tactical security applications, all have a similar requirement. With our new technology we combine high power conversion efficiency, minimal weight, flexibility, mechanical resilience, operational stability, and low cost in a single platform and thus make the realization of these future concepts possible. Figure 2. Snapshot of the model airplane powered by the perovskite solar cell. This image was captured while the airplane was flying on a sunny winter afternoon (on the campus of the Johannes Kepler University). The airplane has a total weight of about 4.8g and is powered by air-stable, 3μm-thick solar arrays (with a power-per-weight value of 23W/g). The wingspan is 58cm. Through our tests we have also clearly demonstrated the high yield at which we fabricated the solar cells (even on thin, rough plastic foils). Our solar foils are extremely flexible and can endure severe mechanical deformation. In addition, they become stretchable (as shown in the video6) when they are laminated on a pre-stretched rubber band and they conform to arbitrary surfaces. Our foils are therefore ideal power sources for applications where conformability, stretchability, and light weight are required (e.g., portables, wearables, and robotics). In summary, we have presented a novel approach for achieving ultrathin, highly flexible perovskite solar cells. Our devices exhibit stable operation in air, 12% efficiency, and a power-per-weight value of up to 23W/g. The concepts we introduce (i.e., plastic foil substrates and chromium oxide interlayers) are readily applicable to the growing family of perovskite absorbers and could be used to increase the power-per-weight of such materials even further. By merging high efficiency, low weight, and extreme flexibility in our single photovoltaic platform, there seem to be few obstacles to keeping perovskite solar cells grounded. Indeed, our aeronautic models are still fully functional more than six months after their initial flights. In our future research we plan to focus on realizing perovskites with improved efficiency and moisture resistance (by exploring electrode transport materials, alternative metals, and superhydrophobic coatings). We will also investigate further ways to unify the high efficiency of perovskite cells with the low weight and flexibility of our technology. This work was supported by a European Research Council Advanced Investigators Grant (‘Soft-Map’) to Siegfied Bauer and the Austrian Science Fund's Wittgenstein Award (Solare Energie Umwandlung Z222-N19) to Niyazi Serdar Sariciftci. Department of Soft Matter Physics Johannes Kepler University Martin Kaltenbrunner received his PhD from the Johannes Kepler University Linz and then joined the Someya-Sekitani Laboratory for Organic Electronics at the University of Tokyo, Japan. He is now an assistant professor. His research interests include soft transducers, photovoltaics, as well as thin-film, flexible, and stretchable electronics. Siegfried Bauer received his PhD from the University of Karlsruhe, Germany. After stays at the Heinrich Hertz Institute in Berlin and the University of Potsdam (both Germany), he became a professor at the Johannes Kepler University Linz. He has has been head of the department since 2002. His research is devoted to functional soft matter. Institute for Physical Chemistry Johannes Kepler University Niyazi Serdar Sariciftci received his PhD from the University of Vienna, Austria. Following time at the University of Stuttgart, Germany, and the University of California at Santa Barbara, he became a professor at the Johannes Kepler University Linz in 1996. He has been a fellow of SPIE since 2009. His research is focused on organic photovoltaics and energy conversion. 3. A. M. A. Leguy, Y. Hu, M. Campoy-Quiles, M. I. Alonso, O. J. Weber, P. Azarhoosh, M. van Schilfgaarde, et al., Reversible hydration of CH NH PbI in films, single crystals, and solar cells, Chem. Mater. 27, p. 3397-3407, 2015. 5. M. Kaltenbrunner, G. Adam, E. D. Glowacki, M. Drack, R. Schwödiauer, L. Leonat, D. H. Apaydin, et al., Flexible high power-per-weight perovskite solar cells with chromium oxide–metal contacts for improved stability in air, Nat. Mater. 14, p. 1032-1039, 2015. 6. http://spie.org/documents/newsroom/videos/6223/Kaltenbrunner-solar_plane.mp4 a ‘solar leaf’ operated outdoors on sunny winter afternoons, with about 40 kilolux solar irradiation.
News Article | November 9, 2016
BERLIN, Germany, Nov. 09, 2016 (GLOBE NEWSWIRE) -- InterDigital (NASDAQ:IDCC), Fraunhofer Heinrich Hertz Institute HHI, and Core Network Dynamics (CND), three partners from the H2020 5GPPP 5G-Crosshaul consortium, today announced the successful result of an extended, real-world deployment of an integrated fronthaul/backhaul network delivering 5G throughput and latency. The test, a first of its kind, sets the stage for cost-effective, highly flexible 5G network architecture. The results of the integrated millimeter wave (mmW) fronthaul/backhaul 5G Berlin Testbed were announced at the November 2nd IEEE 5G Berlin Summit and will be further presented at the 5G-PPP Global 5G event, taking place today and tomorrow in Rome. The 5G-Crosshaul test was carried out over more than a month at the Fraunhofer Heinrich Hertz Institute in Berlin, and delivered higher than 1.2 Gbps throughput and less than millisecond latency. Beyond the speed, the test’s integrated fronthaul/backhaul provides a working model for future 5G networks that will combine 4G architecture with a 5G fronthaul-based network edge. With this deployment, 5G radio network solutions can be implemented using commodity servers or even in the cloud – a major innovation that throws open the doors for new operator models. The 5G Berlin Testbed is a 5G field trial of InterDigital’s EdgeLink™ 60GHz solution, multiplexing both backhaul and CND’s Cloud-RAN next generation fronthaul solution over an integrated mmW mesh transport network. The system is installed outdoors, executing under environmental conditions from the end of September through November. The trial has included both natural and induced link failure events, to test network resiliency. “Millimeter wave technology will be a decisive cornerstone to bring 5G forward to enhanced mobile broadband harvesting new spectrum opportunities well above 6GHz, ultra-dense deployments and energy-efficient multi-Gigabit transmission,” explains Dr. Thomas Haustein, Head of Department for Wireless Communication and Networks at Fraunhofer HHI. “The 5G Berlin Testbed will provide valuable information that can be used to help advance the evolving 5G standards and specifications. We are already adapting OpenEPC to support critical 5G requirements. These include a distributed core network, plus architectures to support C-RAN and the cloudification of the radio access network,” said Carsten Brinkschulte, CEO, Core Network Dynamics. “Many companies have demonstrated systems that they qualify as ‘5G’ because of speed or latency characteristics, but this extended outdoor trial is the first example of a network edge architecture, tested in real-world conditions, that will be a key in eventual 5G deployment,” said, Alan Carlton, Vice President, InterDigital Europe. “Crosshaul’s major innovation may set the stage for a world where our definitions of what constitutes a network operator or infrastructure equipment are radically changed.” 5G-Crosshaul is an international project with 21 members aimed at developing integrated fronthaul and backhaul system solutions to support flexibility and unified management for 5G network architectures. To learn more about the project, visit http://5g-crosshaul.eu/. InterDigital develops mobile technologies that are at the core of devices, networks, and services worldwide. We solve many of the industry's most critical and complex technical challenges, inventing solutions for more efficient broadband networks and a richer multimedia experience years ahead of market deployment. InterDigital has licenses and strategic relationships with many of the world's leading wireless companies. Founded in 1972, InterDigital is listed on NASDAQ and is included in the S&P MidCap 400® index. InterDigital is a registered trademark of InterDigital, Inc. EdgeLink is a trademark of InterDigital, Inc. Innovations for the digital society of the future are the focus of research and development work at the Fraunhofer Heinrich Hertz Institute HHI. In this area, Fraunhofer HHI is a world leader in the development for mobile and optical communication networks and systems as well as processing and coding of video signals. Together with international partners from research and industry, Fraunhofer HHI works in the whole spectrum of digital infrastructure – from fundamental research to the development of prototypes and solutions. www.hhi.fraunhofer.de About Core Network Dynamics Headquartered in Berlin, Core Network Dynamics develops and markets OpenEPC, a complete mobile network infrastructure in software. Target markets include: carriers designing next-generation mobile networks using SDN/NFV; first responder/public safety organizations requiring a secure private LTE network compatible with off-the-shelf Smartphones; companies operating in remote areas where mobile coverage is patchy or non-existent; and operators evaluating advanced Mobile Edge Computing (MEC) concepts to implement distributed mobile networks for IoT applications. www.corenetdynamics.com
News Article | September 7, 2016
Scientists at the Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute, HHI in Berlin have developed a method by which the realistic image of a person can be transmitted in a virtual world; and just like in science fiction movies, the image appears full sized and three dimensional. The image can be viewed from different directions and the viewer can even walk around it – just like in the movie. Until now, this was not possible; even virtual reality (VR) still has its limits. People can be represented by artificial three-dimensional models (so-called avatars) that can be seen when the viewer puts on VR data goggles. Nevertheless, these artificial figures do not have a lifelike appearance or natural movement. Another option is to play the video image of a person in frontal view in the VR data goggles. However, the viewer cannot walk around the image. As a result, the whole scene looks artificial as one moves through the virtual world. The person always turns his two-dimensional front to the viewer. In contrast, the HHI researchers have perfected the three-dimensional impression. To do so, they have developed a camera system that films the person. The core of this system is a stereo camera: Just as people do with their two eyes, the camera records the person with two lenses. This stereoscopic vision results in distances being estimated well, because both eyes look at an object from a slightly different angle. The result is a three-dimensional impression. Recording a person in detail from all directions takes more than one camera. "We are currently using more than 20 stereo cameras to map a human," says Oliver Schreer, Head of the Research Group "Immersive Media & Communication" at HHI. Each camera only captures a part of the person. The challenge is to merge the individual camera images together so that a realistic overall picture is produced. The system includes more than just the camera technology. The researchers have developed algorithms that can quickly extract depth information from the stereoscopic camera images. This is necessary in order to calculate the 3-D form of a captured person. The computer calculates a virtual model of the human, which is then transferred into the virtual scene. The cameras perceive the surface shape with many details. In this way even small wrinkles, e.g. on the clothes of the person, can be shown. The model has a natural and realistic appearance. "In developing these algorithms, special care has been taken to ensure they work efficiently and fast, so the movements of dialogue partners can very quickly be converted into a dynamic model," Schreer says, since this is the only way that the movements will look natural. The images from a single camera pair can be processed in real time. The fusing of the 3-D information from the various camera images takes a few seconds. The illusion has already been perfected, though. The system transmits the three-dimensional dynamic model of a person rapidly in virtual reality. A person can move freely in a dedicated capture area. The virtual image portrays every gesture and movement realistically. "Our goal is that in the future a realistic image copy of a human is able to directly interact with the virtual world – for example, to let it grab virtual objects," says Schreer. In the future, the new camera system is planned to be used for other application fields too. For example, the researchers work on a virtual video conferencing application. It could as well be used for infotainment applications. Instead of a passive, frontal viewing experience, a television viewer could be directly involved in a movie scene by means of VR goggles. The viewer would not only see a three-dimensional image of the scene on the television, but could virtually walk around inside it, and, for example be a part of the adventures of his science fiction heroes. "We can also imagine installing the camera system at different locations in small studios," says Schreer. "Film producers could use it to transfer the movement of actors into scenes more easily than ever before." That has been very costly so far. In general, the actor's movements are recorded using the motion tracking method. As part of this process, the face and body of the actor are marked with small dots. The computer tracks the movement of the points and transfers it to the computer-generated artificial image of the actor – for example, an action star jumping from skyscraper to skyscraper. However, with individual marker points, motion tracking methods can only detect movements and, especially, fine facial expressions very inaccurately or with very high technical effort. That means a lot of post processing for the computer-graphic artists until the scene looks more realistic. "With our camera system, however, our goal is to break down and represent a person and it's movement in the future with much more details," says Schreer. The researchers are currently improving their camera system and the accompanying analysis software. Whether they will make both of these available as a service or license them out to production companies is not yet known. Explore further: New technology for animation film experts: Movie heroes to be transferred to virtual worlds more easily, realistically
News Article | February 27, 2017
BARCELONA, Spain, Feb. 27, 2017 (GLOBE NEWSWIRE) -- MOBILE WORLD CONGRESS 2017 -- The biggest trade event in the mobile industry is abuzz with 5G news, and InterDigital, Inc. (NASDAQ:IDCC) has been invited to present its technology at Mobile World Congress’ headline demo event, a mainstage feature of live, interactive demonstrations by industry R&D leaders. ‘5G Impact’ will showcase network technology, innovative services, and life-changing applications through live and interactive demonstrations followed by a panel discussion surrounding the impact of 5G plus enhanced senses. InterDigital will demonstrate demanding low-latency traffic within a remote surgery game application via 5G-Crosshaul technology with EdgeLink™60 Ghz platform, a transport technology that aims to solve architecture challenges of 5G. The demo by InterDigital and others will be followed by a panel discussion led by Jennifer Pigg Clark, Vice President, Network Research, 451 Research, and featuring the following speakers: 5G-Crosshaul is an international project with 21 members aimed at developing integrated fronthaul and backhaul system solutions to support flexibility and unified management for 5G network architectures. In November 2016, InterDigital, Fraunhofer Heinrich Hertz Institute HHI, and Core Network Dynamics (CND), three partners from the H2020 5GPPP 5G-Crosshaul consortium, announced the successful result of an extended, real-world deployment of the system, a first of its kind. To learn more about the project, visit http://5g-crosshaul.eu/. The conference session will take place on Thursday, March 2 from 11:30 a.m. – 1:00 p.m. CET in Hall 4 Auditorium 5. To learn more about the panel, please click here. For more information on the Mobile World Congress conference agenda, please visit https://www.mobileworldcongress.com/start-here/agenda. Attendees of Mobile World Congress can see the Crosshaul demo, and other 5G and IoT demos, at InterDigital’s pavilion in Hall 7, Stand 7C61. InterDigital develops mobile technologies that are at the core of devices, networks, and services worldwide. We solve many of the industry's most critical and complex technical challenges, inventing solutions for more efficient broadband networks and a richer multimedia experience years ahead of market deployment. InterDigital has licenses and strategic relationships with many of the world's leading wireless companies. Founded in 1972, InterDigital is listed on NASDAQ and is included in the S&P MidCap 400® index. InterDigital is a registered trademark of InterDigital, Inc. EdgeLink is a trademark of InterDigital.
Boche H.,Heinrich Hertz Institute |
Schubert M.,MCI Communications
IEEE Transactions on Signal Processing | Year: 2010
The paper addresses the problem of interference modeling for wireless networks. Two axiomatic approaches are known from the literature: 1) "standard interference functions" proposed by Yates in 1995, and 2) general interference functions proposed by the authors in their previous work. In this paper, both frameworks are thoroughly analyzed and compared. It is shown that every function from framework 1) can be expressed in terms of framework 2). This means that recent structure results for convex interference functions, which were derived for 2), can also be applied to 1). The results provide a bridge between the frameworks 1) and 2), which were studied separately in the literature. Also, new structure results are shown in this paper. For the example of QoS balancing, it is shown that analyzing the structure of interference functions can lead to interesting algorithmic opportunities. The results are potentially useful for the development of physical-layer aware resource allocation algorithms. © 2010 IEEE.
Weber H.G.,Heinrich Hertz Institute
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2015
We show that light-induced coherence between a state |〉 of the electronic ground state X2 A1 and a state |b〉 of the excited electronic state A2 B2 of a laser-induced transition in NO2 affects the evolution of the molecule in the excited state. The optical coherence couples |b〉 strongly with |〉. This optical coupling works against a radiationless process, which is driving the molecule away from the metastable state |b〉 to a final state |c〉. The optical field stabilizes the molecule in the state |b〉 by the coupling to the ground state |〉. This causes the inversion effect in NO2. © 2015 Elsevier B.V. All rights reserved.
News Article | September 20, 2016
Fujitsu Laboratories and the Fraunhofer Heinrich Hertz Institute HHI today announced the development of a new method to simultaneously convert the wavelengths of wavelength-division-multiplexed signals necessary for optical communication relay nodes in future wavelength-division-multiplexed optical networks, and have successfully tested the method using high-bandwidth signal transmission in the range of 1 Tbps.
News Article | September 9, 2016
Since the first radio transmission, the size of the radio spectrum has doubled every 30 months, following an exponential increase in data transfer rates in wireless communications. Over the past two decades, it has become clear that photonics can be combined with radio-frequency (RF) engineering to enable the generation of carrier wave signals with very high frequencies of up to the millimeter-wave (30–300GHz) and terahertz (300–3000GHz) frequency ranges. These frequency bands are essential for enabling an increase in wireless data transfer rates to above 100Gb/s. The combination of photonics and high-frequency electronics has evolved into microwave photonics (MWP), owing to the availability of cost-effective telecom-based components such as lasers, modulators, and photodiodes. The ability to use optical fibers to transmit RF signals over long distances to remote antenna units has been critical in the growth of MWP. Recently, there has been interest in the potential of MWP to enable the seamless convergence of wired (fiber optic) and wireless communication networks in terms of data transfer rates and modulation formats.1 In particular, the growth of fifth-generation (5G) networks—which aim to increase the number of connected devices tenfold, as well as the data transfer rates for the end user—requires such a combination of wired and wireless networks. We have now succeeded in combining photonics and high-frequency electronics at the chip level, by developing so-called radio frequency light engines. These provide a cost-effective method of achieving the increased bandwidth required for 5G networks. As part of the iPHOS research project funded by the European Commission, in collaboration with III-V Lab and University College, London, we integrated a complete photonic transmitter system in a single chip: see Figure 1. This chip received an electrical input and generated a modulated millimeter-wave electronic signal in a coplanar microstrip line ready for transmission to an antenna.2 The development of integrated photonic components has been facilitated by the establishment of new facilities in Europe. In particular, collaboration between academia and industry with the support of the European Commission has resulted in multi-project wafer production runs that are commercially available to circuit designers.3 These production runs, which use fabrication foundries, have the advantage that circuit designers can share the costs of the design tools, fabrication processes, and maintenance of the facilities. Each foundry uses a specific material substrate, such as indium phosphide or silicon, has a specific set of components that master onto that substrate, and provides designers with a standardized set of photonic components that are optimized to enable high performance. Using a library of components, we designed a chip that was fabricated at the SMART Photonics foundry: see Figure 2. This chip contains different laser structures that produce optical signals which generate high-frequency electronic signals when used to illuminate a high-speed photodiode. A patent held by NTT for a uni-traveling carrier photodiode is close to expiry,4 which might increase the availability of high-speed photodiodes. Unfortunately, the integration of broadband antennas onto the substrate materials is hampered by the high dielectric constant of the substrates, which does not allow RF signals to be radiated efficiently. This indicates a need for new integration techniques, as different components require specific sets of material parameters that cannot be achieved using a single substrate. Instead of monolithic integration of all the circuit elements in a single chip, the focus has shifted to heterogeneous or hybrid integration. Heterogeneous integration comprises combining multiple material substrates on a chip-scale form factor to ‘mix and match’ a variety of devices and materials to provide the best substrate for each function. Hybrid integration, on the other hand, involves combining multiple preprocessed chips. The current focus of hybrid and heterogeneous integration is predominantly on silicon components. However, polymer-based hybrid components have also attracted attention, owing to their potentially low cost and the possibility of integrating in one chip broadly tunable lasers and phase shifters for phased-array transmitters. Also, the low permittivity of polymer materials allows the integration of broadband antennas. Recently, in collaboration with the Fraunhofer Heinrich Hertz Institute (HHI) and Osaka University, we demonstrated the advantages of dual polymer-based distributed Bragg reflector lasers based on the HHI PolyBoard integration structure for generating high frequencies.5 Current pressure to increase data transfer rates in wireless communications is bringing new challenges to photonic integration. We believe that this will result in a diversification of the materials used in integrated devices, instead of the current dominance of silicon-based devices. In addition to the contribution that our chips have made to facilitating the increase in data transfer rates, our future work will focus on the development of high-speed wireless links, which will improve the cost-effectiveness of small cells in 5G networks.
News Article | February 23, 2017
Sorting photos on the computer used to be a tedious job. Today, you simply click on face recognition and instantly get a selection of photos of your daughter or son. Computers have gotten very good at analyzing large volumes of data and searching for certain structures, such as faces in images. This is made possible by neural networks, which have developed into an established and sophisticated IT analysis method (see box, “How neural networks function”). The problem is that it isn’t just researchers who currently don’t know exactly how neural networks function step by step, or why they reach one result or another. Neural networks are, in a sense, black boxes – computer programs that people feed values into and that reliably return results. If you want to teach a neural network, for instance, to recognize cats, then you instruct the system by feeding it thousands of cat pictures. Just like a small child that slowly learns to distinguish cats from dogs, the neural network, too, learns automatically. “In many cases, though, researchers are less interested in the result and far more interested in what the neural network actually does – how it reaches decisions,” says Dr. Wojciech Samek, head of the Machine Learning Group at Fraunhofer Heinrich Hertz Institute HHI in Berlin. So Samek and his team, in collaboration with colleagues from TU Berlin, developed a method that makes it possible to watch a neural network think. This is important, for instance, in detecting diseases. We already have the capability today to feed patients’ genetic data into computers – or neural networks – which then analyze the probability of a patient having a certain genetic disorder. “But it would be much more interesting to know precisely which characteristics the program bases its decisions on,” says Samek. It could be certain genetic defects the patient has – and these, in turn, could be a possible target for a cancer treatment that is tailored to individual patients. The researchers’ method allows them to watch the work of the neural networks in reverse: they work through the program backwards, starting from the result. “We can see exactly where a certain group of neurons made a certain decision, and how strongly this decision impacted the result,” says Samek. The researchers have already impressively demonstrated – multiple times – that the method works. For instance, they compared two programs that are publicly available on the Internet and that are both capable of recognizing horses in images. The result was surprising. The first program actually recognized the horses’ bodies. The second one, however, focused on the copyright symbols on the photos, which pointed to forums for horse lovers, or riding and breeding associations, enabling the program to achieve a high success rate even though it had never learned what horses look like. “So you can see how important it is to understand exactly how such a network functions,” says Samek. This knowledge is also of particular interest to industry. “It is conceivable, for instance, that the operating data of a complex production plant could be analyzed to deduce which parameters impact product quality or cause it to fluctuate,” he says. The invention is also interesting for many other applications that involve the neural analysis of large or complex data volumes. “In another experiment, we were able to show which parameters a network uses to decide whether a face appears young or old.” According to Samek, for a long time banks have even been using neural networks to analyze bank customers’ creditworthiness. To do this, large volumes of customer data are collected and evaluated by a neural network. “If we knew how the network reaches its decision, we could reduce the data volume right from the start by selecting the relevant parameters,” he says. This would certainly be in the customers’ interests, too. At the CeBIT trade fair in Hannover from March 20 to 24, 2017, Samek’s team of researchers will demonstrate how they use their software to analyze the black boxes of neural networks – and how these networks can deduce a person’s age or sex from their face, or recognize animals.