Reversible optical switching of highly confined phonon–polaritons with an ultrathin phase-change material

Abstract

Surface phonon-polaritons (SPhPs), collective excitations of photons coupled with phonons in polar crystals, enable strong light-matter interaction and numerous infrared nanophotonic applications. However, as the lattice vibrations are determined by the crystal structure, the dynamical control of SPhPs remains challenging. Here, we realize the all-optical, non-volatile, and reversible switching of SPhPs by controlling the structural phase of a phase-change material (PCM) employed as a switchable dielectric environment. We experimentally demonstrate optical switching of an ultrathin PCM film (down to 7 nm, <λ/1,200) with single laser pulses and detect ultra-confined SPhPs (polariton wavevector kp > 70k0, k0 = 2π/λ) in quartz. Our proof of concept allows the preparation of all-dielectric, rewritable SPhP resonators without the need for complex fabrication methods. With optimized materials and parallelized optical addressing we foresee application potential for switchable infrared nanophotonic elements, for example, imaging elements such as superlenses and hyperlenses, as well as reconfigurable metasurfaces and sensors.

Nanoimaging of Electronic Heterogeneity in Bi2Se3 and Sb2Te3 Nanocrystals

“…However, for the case of a thin dielectric, the existence of these modes is confined only to the frequency range within the reststrahlen band of the substrate, when the dielectric function becomes negative, as was recently demonstrated for phase change materials on quartz (1070-1230 cm −1 ). [32] As seen in both monochromatic s-SNOM images taken at different illumination wavelengths ( Figure S2 Instead, our IR s-SNOM results can be well explained by a local variation of carrier concentration. The IR s-SNOM response of doped Bi 2 Se 3 nanocrystals on SiO 2 can be described qualitatively based on a simplified point dipole model, which is employed to approximate the AFM tip-sample interaction to first order.…”

Ultrafast all-optical tuning of direct-gap semiconductor metasurfaces

“…Such control would dramatically enhance the scope of optical metasurfaces, as their functionalities would no longer be permanently encoded during the fabrication process but could be tuned on demand. Numerous ways of actively modulating the optical properties of metasurfaces were reported, including phase-change materials 5, 6 , mechanical tuning 7, 8 , liquid-crystal-based tuning 9 , and all-optical modulation 10–13 . However, none of these approaches allows for fast and efficient modulation at the same time.…”

Nanoimaging of resonating hyperbolic polaritons in linear boron nitride antennas

“…Typically, propagating and localized surface plasmon–polaritons—collective oscillations of free electrons at metal or semiconductor surfaces coupled to electromagnetic fields678—have been employed. A promising alternative, which is by far less considered yet, are surface phonon–polaritons in polar crystals91011. These quasiparticles—resulting from the coupling of electromagnetic fields and crystal lattice vibrations—exist from mid-infrared to THz frequencies in the so-called reststrahlen band (defined as the region between the transversal and longitudinal optical phonon frequencies, TO and LO, respectively), where the real part of the crystals' dielectric permittivity is negative.…”

“…They offer significantly improved field enhancements and quality factors compared to plasmons910. At mid-infrared frequencies, they have been studied, for example, in SiC10 and quartz11, and could find applications in thermal emission control121314 and sensing1516.…”