Beam switching and bifocal zoom lensing using active plasmonic metasurfaces

TLDR

Compact nanophotonic elements with adaptable properties are essential for miniaturizing adaptive optics and spatial light modulators, but conventional mechanical actuation is impractical at microscopic scales due to space constraints. The authors propose a highly integrated active optical component that combines resonant plasmonic metasurfaces with the phase‑change material Ge3Sb2Te6. They fabricated gold‑patterned nanostructures on a GeSbTe layer, using the material’s distinct amorphous and crystalline dielectric constants to thermally trigger phase changes that steer a 3.1 µm beam and create a cylindrical bifocal lens with different focal lengths. The resulting device demonstrates beam switching and bifocal lensing, offering a compact platform for active optical elements applicable to scanning, imaging, and holography.

Abstract

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.