Lab and Group Spotlights

Communications & Signal Processing


Signal Compression Lab (SCL)
Kenneth Rose, Professor

Fall 2013 Spotlight

SCL research covers a wide spectrum of topics in signal compression and related areas, and is a confluence of both theoretical foundations, and practical algorithms and applications.

multihop network 1

Theory and Methods for Source Coding and Networking: Research under this topic spans both information and estimation theories, with recent emphasis on joint source-channel coding and distributed source coding. Specific problems we are currently focused on include: Achievable rate-distortion region and communication cost minimization for a general multi-hop network with correlated sources and multiple sinks (as in the figure), via joint compression-routing scheme called dispersive information routing (DIR); Developing new communication schemes for emerging network applications with low delay and low energy constraints based on the general "analog networking” methods which achieve optimality at low delay and robustness to varying channel conditions.

multihop network 2

Image/Video Coding and Processing: Research under this topic spans image/video coding and transmission, bio-image informatics, and image/video tracking. Specific focus problems include: Jointly optimal spatial transform and intra-prediction (quality improvement depicted in the figure); Spatio-temporal prediction based on non-separable Markov models; Optimization frameworks, adaptive to time varying network conditions, for optimal scalability in video coders (covering bit-rate, encoding/decoding delay and spatial resolution scalability); Object tracking & 3D tracing in bio-image data via probabilistic graphical models.

multihop network 3

Audio Coding and Processing: Research under this topic spans audio coding and networking. Specific focus problems include: Unified coding paradigms for diverse types of aural signals; Cascaded long term prediction (illustrated in figure) for compression and frame loss concealment; Optimization algorithms for efficient coder design and resource allocation (bitrate, encoding/decoding delay and complexity); Common Information framework-based optimal coding for layered storage and transmission

Professor Rose's:

Advanced Graphics Lab (AGL)
Pradeep Sen, Associate Professor

Fall 2012 Spotlight

At the Advanced Graphics Lab, we work on problems in computer graphics and computational imaging. These include:

image synthesis image

Improved Algorithms for Image Synthesis: Image synthesis is the problem of generating an image from scene data that includes geometrical models, surface textures, and camera and light properties. In our lab, we work on new algorithms for image synthesis, from high-end algorithms that could be used to produce photorealistic images for feature films, to extremely fast algorithms that could be used to render scenes in videogames or other interactive applications. Our work combines ideas from signal processing, applied math, and computational methods to improve the speed and quality of rendered images.

high-dynamic range (HDR) images

Better Imaging Techniques: Digital photography is changing the way we communicate, socialize, and document events around us, but it still has several shortcomings. In our lab, we develop new technology and algorithms that improve photography or break its traditional paradigms. One example is our recent work to improve the acquisition of high-dynamic range (HDR) images with a conventional camera. Standard digital cameras have a small dynamic range and cannot capture the wide range of illumination of a scene in the way our eyes can (we can see the bright and dark parts of a scene simultaneously). Although researchers have developed techniques to compute HDR images from a set of sequential images at different exposures, these techniques usually only work robustly for static scenes. In our lab, we have developed a new optimization-based framework that reconstructs high-quality HDR images from a set of standard images of a dynamic scene. Algorithms like this could change the way people take pictures in the future.



interaction image

Novel modes of Interaction: As we develop new technologies for sensing, display, and interaction, we need to study new ways to use them to solve real-world problems. In this research thrust, we explore ways to leverage new technologies for applications in visualization, training, and entertainment. These new techniques are more immersive and more intuitive than traditional interaction.

Professor Sen's:

ViVoNets Lab
Jerry Gibson, Professor

Winter 2011 Spotlight

Research in the ViVoNets Lab is concerned with all aspects of the transmission and processing of voice, audio, still images, and video for communications over multihop, wireless, heterogeneous networks, with a particular emphasis on handheld devices and highly mobile broadband networks.

  • Low-Delay Low-Complexity Multimode Tree Coder for Speech: Most voice codecs on handheld devices trade increased delay and complexity for acceptable voice communications quality. These techniques reduce battery life and cause "talkover" in mobile to mobile calls and calls through heterogeneous networks. Our current research is concerned with developing low delay/low complexity speech codecs and performance bounds on the best known codecs. These bounds are used to analyze the performance of existing codecs and to guide future improvements in voice codec design.
  • High Dynamic Range (HDR) Video for Handhelds: Our research on HDR video uses signal processing to compensate for the hardware limitations of handheld devices and harsh outdoor lighting conditions. Recent work includes using motion estimation and filtering to combine differently exposed frames, while mitigating ghosting and registration artifacts. The result is improved color and contrast in poorly lit environments.
  • Handheld 3D Video Communications: Stereoscopy enhances realism by presenting different views to each eye, producing an illusion of depth. New glasses-free, autostereoscopic displays have recently appeared on handheld devices. Our research is concerned with achieving 3D video communications by adding a front-facing stereo camera adjacent to the autostereoscopic screen. A key difficulty is finding a balance between "deep" 3D perception and viewing comfort. Ongoing work investigates optimal stereo camera placement and automatic disparity remapping to maintain viewing comfort.
  • Low-Complexity Video Encoding and High-Complexity Video Decoding: Most video compression methods have a high-complexity encoder and a low-complexity decoder. This structure is suitable for video streaming and entertainment broadcast applications, which have few expensive transmitters and many inexpensive receivers. In contrast, unmanned aerial vehicle (UAV) reconnaissance and video surveillance require low-complexity video encoders, but can allow highly complex decoders at central processing stations. Our recent work includes the development of a low-complexity video encoder suited for UAVs, as well as a high-complexity video decoding algorithm.

Professor Gibson's:

Center for Bioimage Informatics
B.S. Manjunath, Professor

Fall 2011 Spotlight

Brain Science has attracted the attention of many biology research groups around the world. With recent advances in imaging, it is possible to harvest large amounts of image data through in vitro and in vivo procedures at multiple scales. As a result the need to develop computational techniques that help biologists interpret the data is crucial.

The Center for Bio-Image Informatics is an interdisciplinary research effort between Biology, Neuroscience, Computer Science, Statistics, Multimedia and Engineering. The overarching goal of the center is the advancement of human knowledge of the complex biological processes which occur at various resolutions. To achieve this core objective, the center employs and develops cutting edge techniques in the fields of imaging, pattern recognition and data mining for analyzing data using different modalities.

  • Coarse Resolution: to analyze Magnetic Resonance Imaging (millimeter resolution) data to understand the morphology and functionality of the human brain better. Discriminative data analysis methods are employed for getting an understanding of regions that get affected due to a certain condition (e.g., psychopathy).
  • Intermediate Scale: techniques to understand the distribution of neuronal spines from confocal images (micrometer resolution) are presented. Statistical modeling of the spine distributions before and after treatment could yield valuable insights into alterations of spine behavior as a result of the treatment (with micro RNA in our case).
  • Finest Level: we develop methods to help biologists work with electron micrograph data (sub-nanometer resolution). Segmentation methods employing conditional random fields with learned topological priors helps trace neuronal processes over depth.

Professor Manjunath's:

Wireless Communications and Sensornets Lab
Upamanyu Madhow, Professor

Winter 2011 Spotlight

Our lab’s main focus is on new system concepts and architectures for wireless communication and sensor networks, with smaller efforts in areas such as multimedia security and neuroimaging. Some examples of recent and ongoing research efforts are as follows:

  • 60 GHz networking: The large amounts of unlicensed bandwidth available in the 60 GHz band enable a quantum leap in wireless communication, to multiGigabit speeds, but the small carrier wavelength (order of magnitude smaller than WiFi) and the high data rates (order of magnitude higher than WiFi) create unique design challenges. Examples of recent work include interference analysis and medium access control protocols for networks with highly directional links, signal processing with constraints on analog-to-digital conversion, space-time channel modeling, and prototypes demonstrating spatial multiplexing in line-of-sight environments.
  • Collaborative communication and signal processing: Examples of recent work include collaborative beamforming, where multiple transmitters form a distributed antenna array to increase range and power efficiency, and collaborative signal estimation, where multiple sensors pool observations to better reconstruct a common signal seen through different dispersive channels at different sensors.

Our research often involves interdisciplinary collaborations, since we tackle hard problems requiring diverse expertise. Current collaborators include faculty from computer science, controls, electronics, and psychology.

Professor Madhow's:

Systems Bioimaging Lab
Michael Liebling, Associate

Fall 2010 Spotlight

We pursue research on optical microscopy, image processing and image analysis to study biological systems.

Our group develops optical microscopy procedures to image live samples at high framerates and over extended periods of time. In particular, we study the development of dynamic organs, such as the heart in zebrafish embryos, with high temporal and spatial, single-cell, resolution.

A central aspect of our lab is the tight integration of image processing (3D-reconstruction, noise reduction, alignment) and image analysis (tracking, flow estimation) algorithms into our image acquisition system, so as to increase the amount of information extracted from images while limiting the invasiveness of the imaging procedure.

Professor Liebling's:

Computer Engineering


Learning-Based Multimedia (LBMM) Lab
Kwang-Ting (Tim) Cheng, Professor

Winter 2013 Spotlight

youtube video demo

The Learning-Based Multimedia Lab focuses on research projects for a wide range of multimedia applications. Our current research directions include:

  • Mobile Computer Vision: There is an explosive demand of running computer vision (CV) algorithms on low power mobile devices, such as smartphones. However, most existing CV algorithms are either too computational expensive for mobile devices or lack sufficient robustness. Thus they cannot provide a satisfactory user experience. We focus on: 1) designing new light-weight and robust algorithms, and 2) adapting existing algorithms to mobile CPU and/or GPU, for fundamental computer vision components, such as feature extraction, recognition and tracking, etc.
  • Heterogeneous Mobile Computing: Mainstream mobile application processors (AP) are accelerator-rich, heterogeneous multi-core SoCs. It provides high computing capability with ultra-low power consumption, yet mapping algorithms to such platforms is a challenge task due to a huge and complex design space. We are developing a method to guide the app developers to explore smart utilization of platform's computing resource and to adapt algorithms for energy minimization.
  • Mobile Medical Image Viewing: High-quality, augmented bio-sensor and the increasing computing power enables medical imaging systems, which only available in clinic workstations in the past, a viable application on mobile devices. We investigate approaches to deliver an optimized user experience per energy unit, from both computing and displaying aspects, for such emerging applications.

Professor Cheng's:

image of VeSFET

VLSI CAD Lab
Margaret Marek-Sadowska, Professor

Fall 2012 Spotlight

Since its inception in 1990, many researchers including graduate students, scholars, faculty, and industry associates have actively participated in the lab's activities. Members of the VLSI CAD Lab exhibit diverse research interests in the field of Electronic Design Automation ranging from logic synthesis to manufacturing and more.

Recent research activities include:

  • Electromigration (EM): has become a serious problem for integrated circuits due to feature size shrinking. Our target is to detect hotspot wires/vias that are prone to EM failure, and provide EM design guidelines and intelligent method to fix hotspot wires/vias.
  • Heterogeneous 3D Chip: recently, CPU and GPU have been integrated in one chip. No exploration tool exists for studying a CPU+GPU, cache, and NoC together on 3D architectures. We are developing a tool for 3D heterogeneous structures that allows designers to quantify various architectural solutions from a physical design standpoint.
  • VeSFET Physical Design: Vertical Slit Field Effect Transistor (VeSFET) is a novel twin-gate 3D device. VeSFET-based designs have many advantages such as low power, regular layout, small footprint area and easy 3D integration. Our research includes VeSFET physical design (placement & routing), testing strategies and low power applications.
  • Testing Analog Components in SoCs: Analog components in SoC designs are difficult to test within the digital design verification flow. Components are simulated and verified using SPICE, which is time consuming for complex components. We are working on a machine learning method that automatically creates behavioral System Verilog macromodels that remove the need for SPICE simulation and can be tested using EDA digital design tools.

Professor Marek-Sadowska's:

Computer Networks and Distributed Systems Laboratory
Louise Moser, Professor
Michael Melliar-Smith, Professor

Spring 2012 Spotlight

The Computer Networks and Distributed Systems Group focuses on a wide range of distributed networking applications, ranging from e-healthcare to supply chain applications.

One current project, funded by NSF, addresses the problem that many Internet applications depend on central servers, which are vulnerable to information filtering and censorship, both by commercial providers and by government agencies.

We are developing the iTrust information distribution, search and retrieval system. The iTrust system contains no centralized search engines and no centralized control. Thus, it is much less vulnerable to information filtering and censorship. The iTrust system can be used in social networks, in particular social networks oriented towards social change.

The iTrust system is completely decentralized and distributed, and works as follows (select each figure for zoom view): iTrust figure figure 3figure 2 figure 1

  • A source node that has a document to share distributes metadata for the document to randomly selected nodes in the network.
  • A requesting (searching) node that desires information distributes keywords for that information to randomly selected nodes in the network. One of the nodes receives both the metadata and the keywords, and an encounter (match) occurs.
  • The matching node reports the match to the requesting node, along with the address of the source node. The requesting node then retrieves the document from the source node using that address.

Two prototype versions of iTrust have been developed:

  • iTrust over HTTP for the Internet
  • iTrust over SMS for Android mobile phones.

A third version of iTrust is being designed for ad-hoc networks of mobile phones or other devices that can communicate via Bluetooth or Wi-Fi Direct. That version of iTrust will allow continued operation even if the base stations are disabled.

Professor Moser and Melliar-Smith's:

Nanoelectronics Research Lab
Kaustav Banerjee, Professor

Fall 2011 Spotlight

The Banerjee group focuses on various aspects of nanoelectronics research, including fundamental physics, electrical and thermal modeling, robust circuit/architecture design, as well as nanomaterial synthesis and nanostructure/device fabrication. Work in the Nanoelectronics Research Lab (NRL) falls into one of the following areas:

  • Carbon Nanoelectronics: Physics, technology, and applications of graphene and carbon nanotubes in electronics, energy harvesting /storage and bio/medicine
  • Green Electronics: Sub-kT/q devices such as tunneling-FETs and NEMS; ultra low-voltage circuit and system design
  • Nano-Devices & 3-D ICs: Emerging CMOS technologies such as FinFET and Nanowire-FET; innovative digital and memory devices; 3-D heterogeneous ICs; device-circuit interactions
  • Nanoscale Interconnects: Ultra high-frequency modeling/extraction for VLSI interconnects and passive elements; exploration of emerging interconnect/passive structures and technologies

Professor Banerjee's:

Novel Electronic Devices and Computing Systems Laboratory
Dmitri Strukov, Assistant

Winter 2011 Spotlight

Research Focus:

  • Novel electronic devices with a particular focus on resistive switching effects
  • Circuit design for novel electronic devices
  • Emerging architectures for computing and design automation

Particular Focus - CMOL Technology:

The basic idea of CMOL circuits (standing for Cmos + MOLecular-scale devices) is to combine the advantages of the CMOS technology including its flexibility and high fabrication yield with those of ultra dense stackable crosspoint devices, e.g. those based on resistive switching phenomena. The nanoscale devices are naturally incorporated into the crossbar fabric enabling very high functional density at acceptable fabrication cost. In particular, CMOL circuits are especially suitable for digital memories, reconfigurable computing and bio-inspired signal processing.

Professor Strukov's:

Wireless Networking Lab
Volkan Rodoplu, Associate

Fall 2010 Spotlight

Research Interests: Wireless Communications and Networking with a research focus in:

  • Protocol Design and Optimization for Wireless Networks
  • Quality of Service in Mobile Networks
  • Energy-Efficient Wireless Sensor and Ad Hoc Networks

Professor Rodoplu works on design and optimization of wireless systems and networks. He is interested in working with undergraduate and M.S. students with strong backgrounds in either 1) Mathematical modeling or 2) Programming.

Professor Rodoplu's:

Control Systems


Sensor and Robotic Network Lab
Yasamin Mostofi, Associate Professor

Fall 2013 Spotlight

illustration of autonomous mobile robotic networks

Autonomous mobile robotic networks can have a tremendous impact in many different areas such as disaster relief, emergency response, and national security.  In such networks, a group of unmanned vehicles with limited local sensing, processing, communications, and actuation capabilities are given a task to perform jointly. Each node needs to constantly plan and adapt its trajectory, in order to sense and gather as much information from the environment as possible while maintaining the needed connectivity for cooperation. Its given resources such as energy, time or bandwidth are further very limited, while the operation environment presents uncertainty for sensing, communications and navigation.

Thus, in order to realize the full potentials of a robotic network, we need a foundational understanding of the interplay between sensing, communications and navigation in these systems, which is the main motivation for the ongoing work in our lab.  More specifically, we work on developing a new multi-disciplinary paradigm for the optimum design, task assignment and use of limited resources in robotic networks.  Our current research thrusts include communication-aware navigation and decision making, compressive sensing and control, obstacle mapping, robotic routers, and cooperative information processing. By utilizing tools from control, robotics, communications, and signal processing, and co-optimizing the sensing, communications and navigation aspects of these problems, we have shown that considerable performance improvement can be achieved.

In one line of work, for instance, we have developed the mathematical foundations of communication-aware motion planning, a term we use to refer to a navigation strategy in which each robot considers not only the impact of motion decisions on its sensing, but also considers realistic probabilistic communication prediction metrics when planning its trajectory. In order for each node to do so, it needs to have an assessment of the link quality at the locations that it has not yet visited. Thus, we have further brought an understanding to the fundamentals of wireless channel predictability, which is key to communication-aware navigation.

In another line of work, we have shown how a robotic network can build an understanding of its environment with minimal sensing and in non-conventional ways, by exploiting the sparse representation of the information in another domain. For instance, we have shown that through proper motion design and by exploiting the sparse representation of the environment, it is indeed possible for the robotic network to see through the walls and build a spatial map of occluded obstacles, using only a small number of wireless measurements.

Overall, our work allows the agents to better understand their environment with minimal sensing, optimize the flow of information between them, and successfully operate under uncertainty and resource constraints.

Professor Mostofi's:

Research Center Spotlight — Control, Dynamical Systems & Computation (CCDC)

Fall 2012 Spotlight

The Center: The Center for Control, Dynamical Systems and Computation (CCDC) was founded in 1991 to facilitate interdepartmental research in control engineering, dynamical systems, and computation and to provide a forum for the exchange of ideas through lectures, seminars, conferences, scholarly meetings, and publications. Currently, the center brings together faculty, students, and visitors from the Departments of Electrical, Mechanical, and Chemical Engineering, Mathematics, Statistics and Applied Probability, and Computer Science.

Activities: The Center focuses on initiating and coordinating research projects with cross-disciplinary investigations and applications to industrial, environmental, transportation, and defense systems. To that end, the Center organizes a weekly seminar series that brings in domain experts, workshops, short courses, publishes a technical report series, and sponsors several fellowships and awards. The Center has a comprehensive graduate program in which students can pursue their studies across several engineering departments. The Center also offers post-doctoral positions and regularly hosts visiting faculty to facilitate inter-institutional and international cooperation.

Cooperation: The Center strives to enable cross-disciplinary teamwork in which theoretical concepts, computational methods, and engineering design are organically merged. Interactions among faculty create an environment in which members benefit from the expertise across several engineering disciplines, applied mathematics and scientific computation. The Center’s collaborative nature is evidenced in the frequent cross listing of courses, as well as joint projects and publications.

Areas of expertise within the center include: nonlinear control, robust control, optimal control, process control, hybrid systems, system identification, stochastic control, distributed control, systems biology, dynamical systems, multi-agent systems, power networks, autonomous vehicles, robotics, and scientific computing.

image of 1D 5PT FMM Matrix

Scientific Computing Group
Shiv Chandrasekaran, Professor

Fall 2011 Spotlight

Historically computers were first used for the numerical solution of partial differential equations (PDEs) that arise in engineering design work. Today the desire to create "virtual labs" where engineers can quickly design, test and tune complex designs on a computer, is a major motivator for designing extremely fast, memory efficient algorithms for physical simulations. This is the aim of the Scientific Computing Group.

To design fast algorithms for PDEs we have to exploit special patterns that arise in these problems. The patterns are complicated and their description requires tools from functional analysis, harmonic analysis, approximation theory, elliptic PDE theory, linear algebra and computer science.

We have attacked the problem on several fronts. At the numerical linear algebra end, we have worked on exploiting low-rank micro-structure in matrices to speed-up the solution of large linear systems of equations.

At the functional analysis end, we have worked on developing new breakthrough ideas on high-order linear polynomial approximators, and used these to develop new classes of highly efficient high-order schemes for PDEs.

However, we are still far from delivering a virtual lab-on-a-computer to engineers. There are many examples of PDEs where the current state-of-the-art can be dramatically improved. To achieve this involves the clever synthesis of many existing ideas, and more importantly, new ones that take better advantage of the patterns present. This is an exciting field at the junction of mathematics, computing and physics, and we expect many more breakthroughs ahead.

Networked Control Laboratory
João Hespanha, Professor

Winter 2011 Spotlight

As computers, digital networks, and embedded systems become ubiquitous and increasingly complex, one needs to understand the coupling between logic-based components and continuous physical systems. This prompted a shift in the standard control paradigm — in which dynamical systems were typically described by differential or difference equations — to allow the modeling, analysis, and design of systems that combine continuous dynamics with discrete logic. This new paradigm is often called hybrid, impulsive, or switched control.

While some of our work on hybrid systems is of a theoretical nature, it is motivated by several high-impact application areas:

  • Network Control Systems (NCSs) are spatially distributed systems in which the communication between sensors, actuators and controllers occurs through a shared band-limited digital communication network. NCSs have been finding application in a broad range of areas such as the automotive and aerospace industries, mobile sensor networks, remote surgery, automated highway systems, and unmanned aerial vehicles.
  • Cooperative control of autonomous agents refers to the control of ground, aerial or aquatic robots so as to perform tasks that require a significant amount of information gathering, data processing, and decision making, without explicit human control. These tasks include environmental monitoring, search and rescue operations for disaster response, law enforcement activities, crop monitoring and spraying, etc.
  • Systems biology seeks to understand living organisms by modeling and analyzing the complex interactions of genes, proteins, and other cell elements. A key goal of systems biology is to transform the methodology used for drug discovery by guiding the search for effective treatments for diseases.

Professor Hespanha's:

Robotics Lab
Katie Byl, Assistant Professor

Fall 2010 Spotlight

Research Interests: Robotics, Dynamics, Locomotion, Control, Autonomous Systems, Learning

In our lab group, we study the interplay between passive dynamics and active control in achieving two of the most fundamental challenges in autonomous robotics: locomotion & manipulation.

The three central applications on which we are currently focused are: rough-terrain legged locomotion; maneuverable flapping-wing and rotary flight; and variable-compliance manipulation.

Our overall approach in all work involves developing simplified dynamic models, deriving control laws for achieving particular motions and limit cycle behaviors, and predicting and optimizing reliability. This last aspect is both critical and challenging, because robots in real-world environments are typically subject to significant underactuation and stochasticity. By contrast, the classic study of robotics is founded on having well-characterized and deterministic ("robotic") behaviors from our machines.

Within robotics, our work essentially focuses on the mid-level control problem of getting a desired dynamic response for a body's overall motion through exploitation of both physical impedance (i.e., stiffness, mass and damping) and active control. We invite academic and industry collaboration on both higher-level tasks, such as vision or motion planning, and on low-level problems, such as variable-impedance actuation, real-time control platforms, or novel sensing solutions.

Professor Byl's:

Electronics & Photonics


Palmstrøm Research Group
Chris Palmstrøm, Professor

Fall 2013 Spotlight

The general research interests of the group are on the heteroepitaxial growth of novel materials and structures to form the basis for making new electronic, optoelectronic, magnetic and micromechanical devices. Critical to the advancement of materials and structures is the fundamental understanding of growth. A key to developing structures with novel properties is the ability to control, at the atomic level, the interface structure and chemistry.

The program has a strong emphasis on heteroepitaxial growth of dissimilar materials. These include materials with different crystal structure, bonding, electronic, optical and magnetic properties.

Palmstrøm Group — Areas of Research

  • OTDM research imageLow Dimensional Semiconductors: their application in the study of mesoscopic phenomena and in quantum information processing has cemented low-dimensional semiconductors at the forefront condensed matter and materials physics research.
  • OTDM research imageHeusler Alloys: focuses on the growth of Heusler compounds by molecular beam epitaxy and characterization of their atomic, electronic, and magnetic properties. Examples include the half metal Co2MnSi, the semiconductors NiTiSn and CoTiSb, and the shape memory alloy Ni2MnGa.
  • OTDM research imageSpintronics: studies the fundametals of spin transport, including spin injection into semiconductors, spin transport in semiconductors, and spin valve and spin torque related effects in magnetoresistive device
  • OTDM research imageThermoelectrics and Self Assembled Nanostructures: research is in two promising classes of thermoelectric materials for increasing the efficiency of thermoelectric devices: (i) Epitaxial III-V based nanocomposites and (ii) Semiconducting half-Heusler alloys.
  • OTDM research imageOxides: the ability to grow thin film heterostructures of Oxide materials, with techniques such as MBE, has resulted in a wealth of new material properties not seen in the bulk state.

Professor Palmstrøm's:

Optical Communications and Photonic Networks Group
Dan Blumenthal

Winter Spotlight 2013

The Blumenthal Group’s research includes systems level photonic networks, photonic integrated circuits, and low loss waveguides.

  • Label Switched Optical Router (LASOR)
    The current bottleneck in high-speed optical communications is the high speed electronics required to process 40 Gb/s signals. This is due to the current OEO conversion - converting the optics into high-speed electronics, performing all the routing and buffering decisions, then converting back into the optical domain by modulating a fiber-coupled laser. An integral concept of the LASOR project is that we only convert a much lower bit rate "label" into the electrical domain, allowing the 40 Gbps "payload" to remain in the optical domain. The 10 Gbps header information contains routing information for the physical layer optical network, and is deserialized and processed using 156.25 MHz FPGA boards to provide appropriate electrical signals for the PFCs (Packet Forwarding Chips) and Buffer chips, which then physically route and synchronize the data.
  • Terabit/s Coherent OTDM Transmission SystemOTDM research image
    In fiber-optic communications, optical time-division multiplexing (OTDM) technique aggregates large capacity on a single optical wavelength. Traditional OTDM system encodes data with a simple binary power level scheme, namely on-off keying (OOK). This research explores ways of incorporating OTDM with coherent optical communication technique, which encodes data with multi-level amplitude and phase of optical wave, therefore increases the single wavelength capacity beyond Terabit/s without expanding the optical bandwidth.
  • InP Photonic Integrated Circuits (PICs):
    A wide variety of PICs have been developed on InP, including wavelength converters, packet forwarding chips for optical packet switched networks, mode-locked lasers for clock recovery and retiming applications, lasers with sub-wavelength metal gratings, coherent receivers, all-optical regenerators.
  • Ultra-Low-Loss Waveguides and Applicationsultra-low-loss waveguides and applications research image
    We design and fabricate ultra low loss waveguides on a Si3N4/SiO2 platform. Record low loss has been achieved, which allows for the integration of optical delay lines with lengths not previously feasible on a chip scale. With this new platform developed, many applications are now being studied where long delay line can be of great impact. Some of the applications currently under study are: true time delays for phased array antennas in microwave photonics, optical gyroscopes, narrow linewidth lasers, and optical buffering.

Professor Blumenthal's:

molecular antenna

Nanophotonics Research Group
Jon Schuller, Assistant Professor

Fall 2012 Spotlight

At a fundamental level, our research concerns novel physical phenomena that occur when light interacts with objects of subwavelength dimensions. As engineers, we exploit these discoveries to make smaller, faster, and more efficient photonics technologies. The essential constituents of these investigations are individual subwavelength elements we refer to as “optical antennas”.

We are particularly interested in antenna-like effects arising from oriented multipolar resonances in dielectric and molecular constituents. We study how these effects lead to novel optical properties in engineered metamaterials and organic semiconductors respectively. We use engineered nanoantennas as model systems for understanding and influencing electromagnetic phenomena in atoms and molecules. Ultimately, we hope this research will lead to a future where optical properties are controlled and engineered at the atomic or molecular level.

Our research comprises investigations in the following areas:

  • Plasmonics
  • Metamaterials
  • Thermal Emitters
  • Optical Forces
  • Optical Properties of Organics
  • Nanophotonic Solar Cell Architectures

Professor Schuller's:

otc research illustration

Optoelectronics Technology Center
Larry Coldren, Professor

Winter 2012 Spotlight

It is widely recognized that technologies that can intelligently manipulate light (photons) is the key to addressing current and future challenges in communications. Our research group is poised to meet these challenges by developing highly-functional photonic integrated circuits (PICs) and efficient high-speed vertical cavity surface emitting lasers (VCSELs) for advanced fiber optic communications and sensor networks as well as for use in optical interconnects.

Our PICs have demonstrated mode and phase locking, programmability in amplitude, phase and wavelength as well as electro-optic beam steering -- all in a monolithically integrated platform. Our recent work on VCSELs have led to devices that operate >35 Gb/s while using only 286 fJ/bit, and more recently, the first demonstration of gain modulation in a VCSEL using carrier separation as well as high extinction polarization-switching VCSELs.

We focus on all aspects of the design process from simulation and epitaxial design to fabrication and system testing. In addition, our capability of growing high quality GaAs, and InP based material in-house gives us a unique perspective in our research.

Areas of Interest:

  • High-performance photonic integrated circuits (PICs): PICs incorporate active gain regions together with other waveguide elements, such as splitters, reflectors, modulators and detectors, in a compatible guided wave technology to produce highly versatile optical circuits on-chip. Some devices, such as optical phase-locked loops, require such short feedback delays require integration. Others devices, such as tunable lasers, wavelength converters, and tunable filters, benefit from the stability and great tolerance to noise, achieved by integration. Recently, we have demonstrated fully integrated optical phase-locked loops, homodyne coherent receivers, programmable active optical-filters, broadband mode-locked lasers, and electro-optical beam steering.
  • Vertical Cavity Surface Emitting Lasers: Compact, efficient and capable of direct high-speed modulation, VCSELs are great sources for active cables and highly-efficient optical interconnects. Our group has developed VCSELs that can support data rates > 35Gbps with the highest energy efficiency value of 286 fJ/bit for a 980 nm wavelength. Methods for enhancing the active region through precise doping and highly-strained quantum wells are currently being explored. A novel three-terminal VCSEL was also developed in our group that demonstrated for the first time in a VCSEL structure gain-modulation through carrier separation. In another unique design, we demonstrated the ability to switch output polarization of a VCSEL through asymmetric current injection.

Professor Coldren's:

Optoelectronics Research Group
John Bowers, Professor

Fall 2011 Spotlight

The Bowers group develops new optoelectronic components and photonic integrated circuits (PICs) for advanced fiber optic communications networks and optical interconnects. Our focus is on integrating optimum waveguiding materials, which do not interact strongly with light, with materials better-suited for active components. Most of this research falls into one of the following two areas:

  • Silicon photonics: the hybrid silicon photonic platform combines the optical properties of III-V materials and germanium with the low material loss and low cost of silicon. Our group has demonstrated high-performance components such as continuous-wave and mode-locked lasers, 40Gb/s Mach-Zehnder and 50Gb/s electroabsorption modulators, and high-speed photodetectors, as well as more complex photonic integrated circuits: optical buffers, tunable microwave filters, a laser-modulator array, and a triplexer
  • Silica-based platform: ultra-low loss waveguides have applications in PICs that require long delay lines, such as optical gyroscopes on a chip, optical buffers, true-time delays, and stable and narrow-linewidth microwave and optical sources. The group uses high aspect ratio Si3N4 waveguides to achieve record low loss

Our group also explores ways to efficiently convert heat and light into energy:

  • Thermoelectrics: our lab is developing and characterizing novel III-V compound and Si-based nanostructured thermoelectric materials. We work both on optimizing the material power conversion efficiency and characterizing thermal and electrical properties of thin-films and challenging structures
  • Photovoltaics: our research focuses on combining various materials to further enhance multi-junction solar cell efficiency

Professor Bowers':

High Frequency Electronics Group
Mark Rodwell, Professor

Winter 2011 Spotlight

In the Rodwell group, we explore the boundaries of high-frequency transistor fabrication and integrated circuit design. Unlike the microelectronics industry, which uses silicon for their transistors, we use elements such as gallium, indium, arsenic, and phosphorus. By using elements from column III and column V of the periodic table, we can create high performance heterojunction bipolar transistors (HBT) and field effect transistors (FET) using InP and InGaAs.

High performance HBTs are required for high speed digital logic and mixed signal circuits enabling sub-mm wave and THz ICs for imaging, sensing, radio astronomy and spectroscopy applications. HBTs designed and fabricated in the group have demonstrated power gain cut-off and current gain cut-off frequencies in excess of 800 and 650 GHz respectively.

Moore’s Law has kept the pace in personal computing for close to 40 years using silicon metal-oxide-semiconductor field effect transistors (MOSFETs). We leverage thirty years of experience in the III-V Arsenide/Phosphide materials system to build MOSFETs using InGaAs. Using technology such as atomic layer deposition (ALD) for gate dielectrics and molecular beam epitaxy (MBE) growth for low resistance self-aligned ohmic contacts, we can create transistors w/ unprecedented performance characteristics.

The group is actively researching devices at all levels: fundamental semiconductor physics and material design; fabrication techniques in our state-of-the-art cleanroom; cutting edge circuit design; and fully integrated system designs. This level of vertical integration allows the students to intelligently guide research for the world’s future technological demands.

Professor Rodwell's:

Photonic Devices and Integrated Circuits Laboratory
Professor Nadir Dagli

Fall 2010 Spotlight

Research Focus

  • Design, fabrication and modeling of guided-wave components for photonic integrated circuits
  • Ultra fast, ultra low drive voltage electro-optic compound semiconductor optical modulators
  • WDM components
  • Advanced novel processing techniques
  • Photonic nanostructures

Professor Dagli's: