Razi Dehghannasiri and Sean Rodrigues, two recent graduates of the School of Electrical and Computer Engineering (ECE), have been chosen for Georgia Tech Sigma Xi Best Ph.D. Thesis Awards. They will be honored for their achievements at Tech’s Sigma Xi Awards Banquet on April 15. 

Razi Dehghannasiri’s thesis is entitled "Hypersonic phononic crystal structures for integrated nano-electromechanical/optomechanical devices.” Integrated phononic devices fabricated on silicon chips are of great interest for diverse scientific and industrial applications. Dehghannasiri’sdissertation presents the study of such integrated phononic devices in new CMOS-compatible platforms in the form of phononic crystal (PnC) structures (i.e., periodic structures supporting phononic bandgaps). These phononic structures have a higher efficiency and lower phononic/photonic losses. 

In particular, this dissertation presents the experimental study of the developed hypersonic pillar-based PnC platform with wideband surface phononic bandgaps on AlN-on-Si substrates for wireless communications. In addition, this dissertation includes the study of membrane PnC structures in silicon nitride for efficient stimulated Brillouin scattering in structures compatible with integrated optics platforms for on-chip RF-photonics. Advised by ECE Joseph M. Pettit Professor Ali Adibi, Dehghannasirigraduated last spring and is now a silicon photonics integration engineer with Intel Corporation in Albuquerque, New Mexico. 

Sean Rodrigues’ thesis is entitled "Instigating chiral-selective nonlinear optical phenomena in metamaterials.” Photonic metamaterials, engineered materials composed of building blocks smaller than the wavelength of light, provide a unique approach to create optical elements that are only 10’s of nanometers thick. 

In Rodrigues’ thesis, the Cai Lab introduces handed asymmetry into these nanostructures, in order to achieve strong polarization and nonlinear optical effects. The resulting research has impacts within the nanophotonics community that may result in photonic equipment for polarization and light management systems in augmented reality, LiDAR technologies, tamper proofing, and chiral sensing. Advised by ECE Associate Professor Wenshan Cai, Rodrigues graduated last summer and is now a senior scientist with Toyota Research Institute in Ann Arbor, Michigan.