2019 Benjamin Franklin Medal in Electrical Engineering presented to Eli Yablonovitch, Ph.D

Periodic structures have been a cornerstone of filtering phenomena ever since size of periodic patterns of crystals were linked to wavelength of waves entering the periodic structure and then existing at limited angles, known as Bragg angles. The concept has been employed by various researchers in developing filters in acoustics, ultrasonic, and microwave domains, in addition to material characterizations using X-ray. Analogy between electronic waves propagating in crystallographic pattern of solids and electromagnetic waves traveling in ordered media has been exploited by Professor Eli Yablonovitch in the realization of efficient semiconductor lasers in 1987 and the experimental demonstration in the microwave domain in 1989. The concept of electromagnetic bandgap (EBG) in the microwave domain and its photonic bandgap (PBG) counterparts at optical wavelengths rapidly expanded the concept of artificial material with a variety of exciting behaviors. Particularly, in a "photonic crystal" (PhC)-a term first coined by Yablonovitch-light propagation characteristics differ from bulk behavior. The simplest form of PhC is a one-dimensional (1-D) stack of quarter-wavelength layers of low and high indices of refraction to filter out certain frequencies and effectively create a stopband in a fashion similar to forbidden energy states (bandgap) seen in semiconductor materials. A perfect 3-D translational symmetry of dielectric structure could be altered by adding extra dielectric (donor) or removing one of the unit cells (acceptor). In fact, the field of artificial dielectrics has rapidly grown by manipulating light propagation characteristics through slowness of wave by increasing effective index of refraction. In addition, high dispersive characteristics would lead to light slowness, which is used for greater optical energy confinement of guided waves. As result of the optical confinement, the field of Si-Photonics has evolved where simultaneous electronic and optical confinement is employed to establish integrated opto-electronics functions to catapult the next revolution in telecommunications beyond 5G. EBG engineering leads to the introduction of numerous engineered surfaces with various microwave and antenna applications. Particularly, concepts of high-impedance and EBG surfaces can enhance performance of antennas, reduce specific absorption rate (SAR) in mobile handsets, develop thin radar absorbers, and design microwave filters/phase-shifters.