Tuesday, September 8th, 10 am (PDT) via Zoom
Meeting ID: 978 3569 2970 Passcode: 468555
Infectious diseases and water are some of the greatest, most urgent challenges of the 21st century. III-nitride ultraviolet (UV) light sources, including light emitting diodes (LEDs) and lasers, are the only alternative technology to replace conventional power-hungry, hazardous mercury lamps for disinfection and water purification. Recent studies showed that AlGaN-based UV-C LEDs can readily shred genetic material of viruses and bacterial and achieve 99.9% sterilization of SARS-COV-2. In this talk, I will present the recent advances of AlGaN and BN nanostructures and heterostructures and their applications in UV optoelectronics, including the first demonstration of mid and deep UV laser diodes and tunnel junction UV-C LEDs with significantly improved performance. The recent development of far-UV-C LEDs, in the wavelength range of 207-222 nm, will also be presented, which has shown to be faster and far more effective than traditional UV-C light (~265 nm) in preventing the transmission of microbial diseases, while causing virtually no harm to mammalian skin or eye.
Friday, February 7th from 12:00 - 1:00 pm in ESB 2001
The electrical power consumed in data transmission systems is now hampering efforts to further increase speed and capacity at various scales, ranging from data centers to microprocessors. Optical interconnects employing ultra-low-energy directly-modulated lasers will play a key role in reducing the power consumption. Since a laser's operating energy is proportional to the size of its active volume, developing high-performance laser with a small cavity is important. For this purpose, we have developed DFB and photonic crystal (PhC) lasers, in which active regions are buried with an InP layer. Thanks to the reduction of cavity size and the increase in optical confinement factor, we have achieved an extremely small operating energy of 4.4 fJ/bit by employing a wavelength-scale PhC cavity. Cost reduction is also an important issue because a larger number of transmitters are required for short-distance optical links. For this purpose, Si photonics technology is expected to be a potential solution because it can provide large-scale photonic integrated circuits (PICs). Therefore, heterogeneous integration of III-V compound semiconductors and Si has attracted much attention. To fabricate these devices, we have developed wafer-scale fabrication that employs regrowth of III-V compound semiconductors on directly-bonded thin InP templates on an SiO2/Si substrate.
Thursday, January 30th, 11 am, Elings 1605
NASA’s trend toward less costly missions has created a need for smaller and more capable instruments for in situ planetary applications, space weather, and Earth Observations. The rise of cubesats has created a new powerful platform that if enabled with powerful sensing technology can be an instrument of discovery. At the same time, large aperture UV/visible/Near Infrared space telescope are being planned for cosmology and astrophysics studies that will need high performance yet affordable detectors to populate their very large focal plane arrays. In nearly all these facets of space exploration, there is a strong need for high signal to noise ultraviolet detection technology. This is due to the fact that the ultraviolet part of the spectrum is rich in spectral information that are key to study exo-solar planets, protoplanets, intergalactic medium, supernovae, electromagnetic counterpart of gravitational wave, star formation, galaxy evolution, and more. Semiconductor detectors offer a rich spectral range, tailorable spectral response, high resolution, and sensitivity; however, these capabilities are not available in a single material or class of material. For example, while silicon imagers have reached high performance levels in format, pixel size, and signal to noise, they are naturally insensitive to ultraviolet light. Using non-equilibrium processes, we can manipulate materials at nanometer scale, form unusual and quantum structures, and alter bandstructures. Through nanoscale surface and interface engineering of 2D doping (superlattice doping and delta doping) high performance silicon-based imagers are produced with record high quantum efficiency in the ultraviolet. Furthermore, the response of silicon imagers can be tailored for out of band rejection through nano-scale interface engineering. In this talk we will discuss the underlying physics of the ultraviolet silicon detectors, their performance, their integration in systems, and their application in cubesats and space flagship missions. We will also discuss the synergy between the requirements for instruments in NASA space applications and medical applications and show how space technologies can and have been used for medical applications.
Friday April 26th | 12:00 pm | Elings 1605
Two-dimensional Van der Waals materials have emerged as a very attractive class of optoelectronic material due to the unprecedented strength in its interaction with light. In this talk I will discuss approaches to realize quantum photonic devices by integrating these 2D materials with microcavities, and metamaterials. I will first discuss the formation of strongly coupled half-light half-matter quasiparticles (microcavity polaritons) and their optical and electrical control in the 2D transition metal dichacogenide (TMD) systems. Prospects of realizing condensation and few photon nonlinear switches using Rydberg states in TMDs will also be discussed. Following this, I will discuss the broadband enhancement of light-matter interaction in these 2D materials using photonic hypercrystals and chiral metasurfaces. Finally, I will talk about room temperature single photon emission from hexagonal boron nitride and the prospects of developing deterministic quantum emitters using them through strain engineering. The realization of room temperature single photon emitters and few photon
nonlinear switches using 2D materials presents an attractive direction for robust next generation quantum photonic technologies.
Coherent Ising machine: a photonic Ising model solver based on degenerate optical parametric oscillator network
Friday, Jan 18, 12 – 1 pm, Elings 1605
As various systems and networks in our society grow larger and more complex, analysis and
optimization of such systems are becoming increasingly important. Such tasks are classified as combinatorial optimization problems, which are generally difficult to solve with current digital computers. It is well known that combinatorial optimization problems can be converted to ground-state-search problems of the Ising model, a theoretical model for the interacting spins. Recently, several approaches to find solutions to the Ising model using artificial spin systems have been studied intensively. A coherent Ising machine (CIM) is one of such systems in which degenerate optical parametric oscillators (DOPO) pulses are used as artificial spins. By using a long-distance (typically 1 km) fiber cavity that contains a phase sensitive amplifier based on a periodically poled lithium niobate waveguide, we can generate thousands of DOPO pulses multiplexed in time domain. Since a DOPO phase only takes either 0 or p at above threshold, we can stably express an Ising spin with a DOPO by allocating phase 0 (p) as spin up (down). The “spin-spin interaction” can be implemented by using a measurement-feedback scheme, with which we can effectively realize mutual injection of lights among thousands of DOPO pulses. The networked DOPOs are most likely to oscillate at a phase configuration that best stabilize the whole network, which gives the solution to the given Ising problem. Based on this scheme, we realized a CIM with all-to-all-coupled 2000 DOPO pulses, by which we could find good solutions to 2000-node combinatorial optimization problems in less than 100 microseconds. In the talk, I will describe the basic principle and the experimental details of the CIM, as well as our effort for finding its applications.
Dr. Ken-Tye Yong
Director of the Bio Devices and Signal Analysis (VALENS)
School of Electrical and Electronic Engineering
Nanyang Technological University (NTU)
Tuesday, Nov. 20th, 3 - 4 pm, ESB 2001
Nanomaterials have been applied in healthcare applications such as cancer imaging, lymph node mapping and brain diseases therapy. These nanomaterials can be engineered to serve as a platform for challenges in highly sensitive optical diagnostic tools, biosensors, and guided imaging and therapy. The versatility of nanomaterials may provide the keys to improve diagnostics and therapy of human diseases. In this talk, we will highlight the use of nanomaterials with different sizes, compositions, and shapes for nanomedicine applications. This talk is intended to promote the awareness of past and present developments of nanomaterials in biomedical fields, the potential toxicity of nanomaterials, and the approaches to engineer new types of safe nanomaterials, whereby encouraging researchers to think about exciting and promising biophotonic and nanomedicine applications with nanomaterials in the future.
Friday Nov 9th, 1pm, Elings 1605
The past decade has seen accelerated progress in III-V semiconductor infrared photodetector technology. The advent of the unipolar barrier infrared detector device architecture has in many instances greatly alleviated generation-recombination (G-R) and surface-leakage dark current issues that had been problematic for many III-V photodiodes. Meanwhile advances in a variety type-II superlattices (T2SLs) such as InGaAs/GaAsSb, InAs/GaSb, and InAs/InAsSb, as well as in bulk III-V material such as InGaAsSb and metamorphic InAsSb, have provided continuously adjustable detector cutoff wavelength coverage from the short wavelength infrared (SWIR) to the very long wavelength infrared (VLWIR). The confluence of these developments has led to a new generation of versatile, cost-effective, high-performance infrared detectors and focal plane arrays based on robust III-V semiconductors, providing a viable alternative to HgCdTe (MCT).
Department of Electrical and Computer Engineering,
Department of Bioengineering
University of Illinois at Urbana-Champaign
Tuesday, Oct 16th, 11am, ESB 1001
Circulating exosomal miRNA represents a potentially useful class of bloodborne biomarkers for cancer. We present the initial proof-of-concept of an approach in which gold nanoparticle tags are prepared with thermodynamically optimized nucleic acid toehold probes that displace a oligonucleotide and reveal a capture sequence that is used to selectively pull down the target-probe-nanoparticle complex to a photonic crystal (PC) biosensor surface. By matching the surface plasmon resonant wavelength of the nanoparticle tag to the resonant wavelength of the PC nanostructure, the reflected light intensity from the PC is dramatically and locally quenched by the presence of each nanoparticle.
The talk described the optical operating principles of Photonic Resonator Absorption Microscopy (PRAM), the thermodynamic design of DNA toehold probes, and our first results demonstrating the detection limits, selectivity, and dynamic range of the assay.
Friday, Jun. 8th, 4:30 - 5:30 pm, ESB 2001
Communications networks and systems are seeing extreme increases in network traffic which is growing at the tremendous rate of 30% per year. It is estimated that the energy and cost requirements will increase tenfold in coming year. But this progress is not sustainable from an ecological and economic point of view. However, this information explosion can be dealt with, using the integration of very small photonic components on very high density Photonic Integrated Circuits (PICs). The technolgoical advancements in PICs have made them a popular choice for components of next generation networks. Silicon being the evident choice due to its high availability, mature fabrication technology, and low cost has attracted components on a chip. At the same time, the unique, material properties and direct bandgap of group III-V materials have huge potential in applications like laser amplifiers, modulators, and detectors. Due to robustness, flexibility, reliability, and performance of PICs, many commercial solutions are now available for a variety of applications.
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