A team of researchers at Penn State has integrated metasurfaces onto a photonic integrated circuit (PIC) chip. The design maintains high light controllability, allowing guided waves inside the PIC to drive the metasurfaces, enabling routing light among different metasurfaces. The architecture supports the performance of multiple complex functions on a single chip. Led by Xingjie Ni, assistant professor of electrical engineering, the team combined two technologies in its effort to establish more complete light control for use in various optical devices. The approach included taking the benefits in portability of a PIC, which researchers can physically incorporate onto a small chip, and a thin, artificially engineered layer (metasurface) that enables light manipulation at a subwavelength scale that researchers cannot integrate on a chip. The design eliminates researchers’ reliance on large materials and structures that are often difficult to integrate into existing systems to achieve high levels of light control. The chip could enhance applications in optical remote sensing, VR, lidar, and additional optical technologies. “The developed technology will pave exciting ways for building multifunctional PIC devices with flexible access to free space, as well as guided, wave-driven metasurfaces with full on-chip integration capability,” Ni said. Xingjie Ni, assistant professor of electrical engineering at the Penn State School of Electrical Engineering and Computer Science. Courtesy of Penn State College of Engineering. Traditional PICs are limited in their ability to control free-space light that propagates in air, outer space, and a vacuum. By increasing phase (light) control, the new technology bridges a gap between wave propagation in free space and controlled waveguides. “I think the most exciting part of the research is that we married two powerful technologies with complementary capabilities — integrated photonics and metasurfaces. Our hybrid system has the advantages from both the metasurfaces and the PICs,” Ni said. Metasurfaces allow a dual transformation to occur between a wavefront in free space and single-mode transmission. The use of photons in a circuit increases power efficiency; photons, as compared to electrons, do not generate a significant amount of heat the system does not need and must expel. Ni was part of a Penn State research team that last year discovered a new type of optical metasurface that makes light reflect in a single direction only. Optical devices supporting unidirectional light flow, such as isolators and circulators, are almost exclusively based on the magneto-optic effect. Unlike an optical metasurface, those devices are often bulky and difficult to integrate into existing systems. Another benefit of the new design involves its durability. “Our design is highly flexible and modular,” Ni said. “A library of the building blocks can be established for reusing and creating consistent functional components across various devices or systems.” Funding for the research came from the Gordon and Betty Moore Foundation, the NASA Early Career Faculty Award, the Office of Naval Research, and the Penn State Materials and Research Science Engineering Center. The research was published in Science Advances (www.doi.org/10.1126/sciadv.abb4142).