Beam switching and bifocal zoom lensing using active plasmonic metasurfaces

Compact nanophotonic elements exhibiting adaptable properties are essential components for the miniaturization of powerful optical technologies such as adaptive optics and spatial light modulators. While the larger counterparts typically rely on mechanical actuation, this can be undesirable in some cases on a microscopic scale due to inherent space restrictions. Here, we present a novel design concept for highly integrated active optical components that employs a combination of resonant plasmonic metasurfaces and the phase-change material Ge3Sb2Te6. In particular, we demonstrate beam switching and bifocal lensing, thus, paving the way for a plethora of active optical elements employing plasmonic metasurfaces, which follow the same design principles. Plasmonic metasurfaces employing a phase-change material have yielded highly compact devices for switching and focusing light beams. Such devices are promising for realizing nanophotonic components for applications in scanning, imaging and holography. Xinghui Yin at the University of Stuttgart, Germany, and co-workers fabricated gold patterned nanostructures on a layer of the phase-change material germanium−antimony−tellurium (GeSbTe; GST). Since the amorphous and crystalline phases of the GST layer have very different optical dielectric constants, thermally triggering a phase change in the layer allowed a 3.1 μm wavelength light beam to be steered in different directions. A different design of the gold nanopattern realized a cylindrical bifocal lens that had different focal lengths for the amorphous and crystalline GST phases. This demonstration opens the way for a wide range of active optical elements based on plasmonic metasurfaces.