Advanced Optical Programming of Individual Meta‐Atoms Beyond the Effective Medium Approach

Abstract

Nanometer‐thick active metasurfaces (MSs) based on phase‐change materials (PCMs) enable compact photonic components, offering adjustable functionalities for the manipulation of light, such as polarization filtering, lensing, and beam steering. Commonly, they feature multiple operation states by switching the whole PCM fully between two states of drastically different optical properties. Intermediate states of the PCM are also exploited to obtain gradual resonance shifts, which are usually uniform over the whole MS and described by effective medium response. For programmable MSs, however, the ability to selectively address and switch the PCM in individual meta‐atoms is required. Here, simultaneous control of size, position, and crystallization depth of the switched phase‐change material (PCM) volume within each meta‐atom in a proof‐of‐principle MS consisting of a PCM‐covered Al–nanorod antenna array is demonstrated. By modifying optical properties locally, amplitude and light phase can be programmed at the meta‐atom scale. As this goes beyond previous effective medium concepts, it will enable small adaptive corrections to external aberrations and fabrication errors or multiple complex functionalities programmable on the same MS.

All‐Dielectric Programmable Huygens' Metasurfaces

“…However, for more accurate description of the crystallization profile during optical switching, multiphysics simulations should be taken into account. [ 48 ]…”

“…Optical switching of the phase change material GST was realized by a custom‐made laser setup. [ 43,48 ] The light from a red, pulsed laser diode (λ = 660 nm) was focused through a 10× objective with a numerical aperture of 0.5 onto the sample surface. The sample was placed on a Thorlabs NanoMax‐TS (Max311/M) stage, which is movable in x , y , and z direction and connected to a Thorlabs closed‐loop piezo controller (BPC303).…”

“…In addition, intermediate crystallization states enable the encoding of different values of the light phase in the whole accessible phase range while maintaining high average transmittance at the operating wavelength (grey region in Figure 1c,d). Crucially, by optically switching individual meta‐units of the metasurface, it is possible to write an arbitrary optical phase profile onto the surface, which enables the realization of versatile optical devices like tunable lenses, and spatial light modulators [ 48 ] (Figure 1e).…”

Tunable nanophotonics enabled by chalcogenide phase-change materials

“…Recently, Michel et al demonstrated that phase switching of the PCM with localized laser spots can arbitrarily tune the resonance of an individual hybrid metaatom up to one FWHM [167]. The investigated MS is composed of a 2D arrangement of Al nanorods deposited on a Si substrate and covered by a 75-nm-thick Ge 3 Sb 2 Te 6 layer which is protected by a thin capping film of ZnS-SiO 2 (see Figure 7A).…”

Multistate Switching of Photonic Angular Momentum Coupling in Phase‐Change Metadevices

“…[ 22–26 ] However, the tunability of PSOIs has been demonstrated with only “ON” and “OFF” states, although a couple of demonstrations of multilevel (even up to 11 states) and fully reversible tuning of metasurfaces have been reported. [ 27–31 ] Since the information can be coded in merely “ON” state, it is unavoidable to employ interleaved subarrays to achieve multiple functions with each one contributing to only a single function, resulting in the fundamental limitations of pixel loss, information infidelity, and low energy efficiency. [ 17 ] Additionally, interlacing different subarrays also increase the period of unit cells, resulting in a dramatic loss of light to spurious diffraction orders, which may further deteriorate the information fidelity and energy efficiency.…”