Distinguished Lecturer Program

The continuing growth in demand for bandwidth (from residential and business users), necessitates significant research into new advanced technologies that will be employed in future broadband communication systems. Two specific technologies which are becoming increasingly important for future photonic systems are wavelength tunable lasers and optical frequency combs. Although these topics have been studied for over two decades their significance for the development of future ultra-high capacity photonic systems has only recently been fully understood. Wavelength tunable lasers are currently becoming the norm in optical communication systems because of their flexibility and ability to work on any wavelength. However, as their operating principles are different to standard single mode lasers they can effect how future systems will operate. For example as optical transmission systems move towards more coherent transmission (where the data is carried using both the intensity and phase of the optical carrier), the phase noise in these tunable lasers will become increasingly important. Optical frequency combs also have many applications for future photonics systems, and for telecommunications they can be used to obtain the highest spectral efficiency in optical transmission systems by employing the technology of optical frequency division multiplexing (OFDM) that has been widely employed to increase spectral efficiency in wireless systems. Wavelength tunable lasers and optical frequency combs are thus topics at the leading edge of current photonics systems research, and their detailed understanding promises new applications in all-optical signal processing, optical sensing and metrology, and specifically telecommunications. This talk will focus on the development and characterization of various wavelength tunable lasers and optical frequency combs, and then outline how these sources can be employed for developing optical transmission systems and networks which make the best use of available optical spectrum.

The most demanding challenges in diagnostics require detection of low concentrations of virus, proteins, or nucleic acids within test samples comprised of only a few droplets of test sample.  The idea of a “liquid biopsy” in which biomarkers for disease can be detected in a single droplet of blood from a fingerstick will enable diagnostic tests to be performed with much less pain, inconvenience, and invasiveness compared to tissue biopsy or a blood draw performed by a phlebotomist.   The potential to perform routine (daily) ultrasensitive diagnostic tests using simple assay protocols and inexpensive detection instruments is the driving force behind “personalized” cancer treatment that is directed towards specific mutations as they evolve, the ability to adjust antiviral therapy in response to viral load, and the ability to detect/identify deadly pathogens.
This presentation will summarize recent efforts in the Cunningham group to develop point-of-care, digital-resolution technologies for sensing pathogens and molecular disease biomarkers in bodily fluids.  Utilizing the unique properties of photonic crystal nanostructured surfaces, we have developed approaches for enhancing the output of photon emitters, such as semiconductor quantum dots (QD), by >100x, enabling individual emitters to be detected with high contrast.  We are applying photonic crystal enhanced fluorescence (PCEF) of QD tags towards detection of circulating mRNA and miRNA that are correlated with specific mutations involved in prostate cancer.  In parallel, we have developed a new form of biosensor microscopy, called NanoParticle Photonic Resonator Absorption Microscopy (NP-PRAM) in which plasmonic gold nanoparticles serve as resonant-matched nanoantennas that, when attached to a photonic crystal surface, enabling single nanoparticles to be visualized with high contrast.  We are developing novel assay methods and detection instruments that enable NP-PRAM to quantify femtomolar concentrations of miRNA biomarkers, with a simple, rapid test that does not require chemical amplification.  We are also applying NP-PRAM to detection intact HIV particles as a direct approach to viral load monitoring.  While PCEF and NP-PRAM detection systems are intended for the laboratory bench, we are also developing mobile sensing platforms that utilize a smartphone’s internal camera as the detection instrument, in conjunction with a handheld special-purpose cradle.  We are developing microfluidic chips that perform nucleic acid amplification assays, in which the amplification process can be dynamically imaged to enable counting of pathogenic DNA.

The electrical power consumed in data transmission systems is now hampering efforts to further increase the speed and capacity at various scales, ranging from data centers to microprocessors. Optical interconnects employing an ultralow 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 lasers with a small cavity is important. For this purpose, we have developed membrane DFB and photonic crystal (PhC) lasers, in which active regions are buried with InP layer. Thanks to the reduction of cavity size and the increase in optical confinement factor, we have achieved extremely small operating energy and demonstrated 4.4-fJ/bit operating energy by employing wavelength-scale PhC cavity. Reduction of the cost is also important issue because huge 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 phonic integrated circuits (PICs), which can reduce the assembly cost compared with transmitters constructed by discrete devices. Therefore, heterogeneous integration of III-V compound semiconductors and Si has attracted much attention. For fabricating these devices, we have developed wafer-scale fabrication procedure that employs regrowth of III-V compound semiconductors on directly bonded thin InP template on SiO2/Si substrate. A key to realize high-quality epitaxial layer is total thickness, which must be below the critical thickness, typically 430 nm. Thus, membrane structure is quite suitable for heterogeneous integration.  I will talk about our recent progress, focusing on ultralow-power-consumption directly modulated lasers and their photonic integrated circuit.  I will also describe progress in heterogeneous integration of these lasers and Si photonics devices.

Two-dimensional (2D) 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) [1] and their spin-optic control [2] 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 [3, 4] and chiral metasurfaces. Finally, I will talk about room temperature single photon emission from hexagonal boron nitride [5] and the prospects of developing deterministic quantum emitters using them through strain engineering [6]. 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.

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.

Microwave measurement refers to the acquisition of parameters of a microwave signal, device, and subsystem, or the identification of properties of an object via microwave-based approaches. Thanks to the broad bandwidth and high-speed analog signal processing provided by modern photonics, microwave measurement in the optical domain can provide better performance in terms of bandwidth, resolution, and speed which may not be achievable using traditional, even state-of-the-art electronics. This talk performs an overview of recent photonics-based microwave measurement techniques developed for broadband microwave measurements such as electric field, phase noise, instantaneous frequency, and spectrum. Photonics-based radars for high-resolution imaging and fiber-connected distributed antenna systems for precise position localization are also introduced. Based on the broadband spectrum measurement and radar detection, microwave photonics based cognitive radio for future green wireless communication is described and discussed. Emerging technologies in this area and possible future research directions are also discussed.