The strong confinement and enhancement of light when coupled to surface waves or nanoparticles is key for various applications in nanophotonics such as sensing, imaging or other devices that enable the manipulation of light fields. In the mid-infrared spectral range, metallic nanoantennas and materials supporting surface phonon polaritons (SPhPs) can be used as building blocks of such devices. In both cases, the optical functionality is usually only obtained at a fixed wavelength, determined by the geometric design and the material properties.
In the first part of this talk, I will present our latest results on active mid-infrared plasmonics, i.e. the tuning of nanoantennas resonances via variation of the refractive index n of an embedding medium based on phase-change materials (PCMs) [1,2]. PCMs offer a huge contrast in the refractive index n due to a phase transition from amorphous to crystalline state, which can be thermally, optically or electrically triggered. I will show thermal and optical large-area switching of IR antenna resonances as well as individually addressable switching of single structures. Application potential for switchable chirality [3] and switchable detectors [4] will also be presented.
In the second part, I will introduce Phonon-Polariton-based IR antennas made from polar dielectrics which exhibit lower losses and larger Q-values compared to metallic nanoantennas. Specifically, we employ a PCM as a switchable dielectric environment for loading the SPhPs [5]. This allows us to realize all-optical, non-volatile, and reversible switching of the SPhPs by controlling the structural phase of the PCM. We experimentally demonstrate that single nanosecond (ns) laser pulses can locally switch an ultra-thin PCM (down to 7 nm, < λ/1200) for exciting ultra-confined SPhPs (polariton wavevector k_p > 70k₀, k₀ = 2π/λ) in quartz. This offers a new, elegant way to prepare all- dielectric, optically rewritable SPhP resonators without the need of complex fabrication methods.
Our approach of combining PCMs and SPhPs opens up new possibilities for non-volatile, rewritable and active nanophotonics, in particular for re-configurable, digital and memory metamaterials, flat optics and metasurfaces.
[1] A. U. Michel, T. Taubner, et al. Nano Letters 13, 3470 (2013).
[2] A. U. Michel, P. Zalden, T. Taubner et al. ACS Photonics, 1, 833−839 (2014). [3] Yin, X. et al. Nano Letters 15, 4255-4260 (2015).
[4] Tittl, A. et al., Advanced Materials 27, 4597-4603 (2015)
[5] P. Li et al, Nature Materials 15, 870-875 (2016).