The future generations of the network are expected to have a transformative impact in our society, allowing heterogeneous network connectivity that can potentially facilitate various new applications extending from radio frequencies (RF), millimeter-waves (mmWave) to terahertz (THz) frequencies, forming the bedrock of wireless network spectrum, and are expected to exponentially expand to support future communication. While conventional research of electromagnetics (EM) has been segmented into isolated disciplines based upon their frequency and functionalities including mmWaves, terahertz, digital signal, power circuitry, we are observing a trend towards the highly integrated system with a re-unification of electromagnetics and an EM circuit-system co-design approach. This intersection of the spectrum, technology, and ideologies creates an exciting opportunity to realize a new class of sensing and communication, which harnesses the capability of programmable synthesis of electromagnetic fields with the integration of modern silicon IC processes.
Research Interests
Programmable mmWave Systems
5G network and beyond is expected to operate over multiple adjoining frequency bands across 28-100 GHz. The bandwidth empowers 5G with tremendous improvement in data capacity, throughput, and latency. However, it also makes beamforming more complicated when a classical phased array technique is used due to both frequency dispersion and the tradeoff between the generation of grating lobes in a sub-Nyquist sparse array and the mutual coupling in a dense array. We are interested in investigating not only new methodologies to improve individual circuitry blocks such as power amplifiers, phase-lock loops, and frequency multipliers, but also from a broader system perspective in array design tradeoffs, security in wireless communication, and wireless network topologies.
Integrated Metamaterial for Terahertz Systems
Terahertz (THz), especially frequencies ranging from 300 GHz to 600 GHz, is of our particular interest in its combination of penetration and resolution. Active and reconfigurable THz imaging is desired for imaging small yet dynamic systems, such as fluid flow rate in a microfluid channel. On the other hand, metamaterials, artificial materials that do not exist in nature, exhibit the ability to direct and alter the propagation of electromagnetic waves in the desired direction. We look into new opportunities and realizations of metamaterial on integrated platforms for smart sensing, hologram projection, and medical imaging. The electromagnetic properties of metamaterials can be explored further when integrated with silicon-based lithography. An active metasurface can be exploited as nanophotonic circuit components for its wave manipulation capabilities and frequency selective nature. Exotic physics and optics phenomenon can only be demonstrated at the nanometer scale, and silicon-based nano-lithography can be a powerful tool to make them happen.
Integrated Photonics and Smart Biosensing
In addition to EM-system co-design for communication and imaging, bio-medical related applications are of our particular interests, which is determined to have an unprecedented impact and market. Integrated THz and optics could drastically change the current medical screening standard, with the potential of making bio-label detection lightweight, ingestible, portable, and low-cost. Nanometer-level devices interact not only with EM waves but also with cells, protein, and bacteria with similar dimensions demonstrating cell trapping, filtering, and labeling for efficient miniaturized biomedical lab-on-chip.
Integrated Microwave Engineering
Integrated platforms offer new opportunities and challenges for microwave engineering. The advance in mmWave and Terahertz systems offers an opportunity for on-chip radiating surface designs where the antennas, high-frequency circuitry, and digital signal processing unit merge on a single die. It also introduces challenges since the system performances are limited to the dielectrics, size, and complexity of an integrated platform. We take innovative approaches, such as machine learning, to re-innovate chip-scale electromagnetic structures ranging from passive elements such as couplers and baluns, to computational metasurface for ultrafast optical/microwave computation.