Nonvolatile light modulation in optoelectronic nanodevices

A Pitt ECE Seminar

Abstract: The active control of phase and amplitude of light enables programmable nanophotonic devices, enabling optical technologies such as switching networks, beam steering, sensing, computing, and quantum processing with photons. Phase modulation is often achieved with carrier injection or depletion in semiconductors, thermo-optic effect, and mechanical actuators, while the amplitude is modulated using electro-absorption in semiconductors. In both types of modulators, the state and information they carry are lost once the power is turned off. This volatile response means a constant power supply that becomes prominently large in applications where reprogramming occurs sporadically or in slow intervals. Nonvolatile control of light is thus desirable. In addition to energy considerations, this type of modulation enables emerging applications such as in-memory computing, data storage, and optical trimming. Although nonvolatile light modulation has been achieved with charge-trapping effects, mechanically latched micro-electromechanical systems, and ferroelectric domain switching, these methods have suffered from high losses, long-term drift, large footprints, or CMOS incompatibility. Chalcogenide-based phase change materials (PCMs) have emerged as an alternative versatile and ultra-compact platform thanks to their giant, bistable, and reversible change in refractive index. Either simultaneously controlling phase and amplitude with traditional lossy alloys such as Ge2Sb2Te5 or achieving phase-only modulation with zero or low-loss alloys such as Ge2Sb2Se4Te1, Sb2Se3, and Sb2S3, PCMs have demonstrated tremendous potential to revolutionize photonics. This talk will present the state-of-the-art PCM-based devices for optoelectronics, their challenges, opportunities, and underlying physics and engineering.

Bio: Carlos A. Ríos Ocampo is a Colombian scientist working at the intersection of Photonics and Materials Science at the nanoscale. Carlos joined the University of Maryland, College Park, in August 2021 as an Assistant Professor with a joint appointment between the Institute for Research in Electronics and Applied Physics (IREAP) and the Department of Materials Science and Engineering. Before this, Carlos was a Postdoctoral Associate at MIT, received a DPhil (PhD) degree in 2017 from the University of Oxford (UK); an MSc degree in Optics and Photonics in 2013 from the KIT (Germany); and a BSc in Physics in 2010 from the University of Antioquia (Colombia). Carlos’s scientific interests focus on studying and developing new on-chip technologies driven by nanomaterials and photonics. Carlos has extensively studied Chalcogenide Phase-Change materials for nanophotonics – some of his results represent the pioneering work and IP for this emerging, fast-growing field. Carlos was named one of the ten Rising Stars of Light in 2021 by the Journal of Light: Science & Applications.