Electro-optic tuning of split ring resonators embedded in a liquid crystal

Electrically Actuated Varifocal Lens Based on Liquid-Crystal-Embedded Dielectric Metasurfaces

Compact varifocal lenses are essential to various imaging and vision technologies. However, existing varifocal elements typically rely on mechanically actuated systems with limited tuning speeds and scalability. Here, an ultrathin electrically controlled varifocal lens based on a liquid crystal (LC) encapsulated dielectric metasurface is demonstrated. Enabled by the field-dependent LC anisotropy, applying a voltage bias across the LC cell modifies the local phase response of the silicon meta-atoms, in turn modifying the metalens focal length. In a numerical implementation, a voltage-actuated metalens with continuous zoom and up to 20% total focal shift is demonstrated. The LC-based metalens concept is experimentally verified through the design and fabrication of a bifocal metalens that facilitates high-contrast switching between two discrete focal lengths upon application of a 9.8 V_pp voltage bias. Owing to their ultrathin thickness and adaptable design, LC-driven dielectric metasurfaces open new opportunities for compact varifocal lensing in a diversity of modern imaging applications.

All-optical switching of a dye-doped liquid crystal plasmonic metasurface

A switchable metasurface composed of plasmonic split ring resonators and a dye-doped liquid crystal is developed. The transmission of the metasurface in the infrared spectral range can be changed by illuminating the dye-doped liquid crystal with light in the visible spectral range. The effect is particularly efficient in the case of hybrid alignment of the liquid crystal, i. e. alignment of the director perpendicular to the surface on one substrate and parallel alignment on the counter substrate. This all-optical switching effect can be attributed to the behavior described in earlier works as colossal optical nonlinearity or surface-induced nonlinear optical effect.

All-silicon reconfigurable metasurfaces for multifunction and tunable performance at optical frequencies based on glide symmetry

Dielectric metasurfaces have opened promising possibilities to enable a versatile platform in the miniaturization of optical elements at visible and infrared frequencies. Due to high efficiency and compatibility with CMOS fabrication technology, silicon-based metasurfaces have a remarkable potential for a wide variety of optical devices. Adding tunability mechanisms to metasurfaces could be beneficial for their application in areas such as communications, imaging and sensing. In this paper, we propose an all-silicon reconfigurable metasurface based on the concept of glide symmetry. The reconfigurability is achieved by a phase modulation of the transmitted wave activated by a lateral displacement of the layers. The misalignment between the layers creates a new inner periodicity which leads to the formation of a metamolecule with a new sort of near-field interaction. The proposed approach is highly versatile for developing multifunctional and tunable metadevices at optical frequencies. As a proof of concept, in this paper, we design a bifunctional metadevice, as well as a tunable lens and a controllable beam deflector operating at 1.55 μm.

Active tuning of all-dielectric metasurfaces

All-dielectric metasurfaces provide a powerful platform for highly efficient flat optical devices, owing to their strong electric and magnetic dipolar response accompanied by negligible losses at near-infrared frequencies. Here we experimentally demonstrate dynamic tuning of electric and magnetic resonances in all-dielectric silicon nanodisk metasurfaces in the telecom spectral range based on the temperature-dependent refractive-index change of a nematic liquid crystal. We achieve a maximum resonance tuning range of 40 nm and a pronounced change in the transmittance intensity up to a factor of 5. Strongly different tuning rates are observed for the electric and the magnetic response, which allows for dynamically adjusting the spectral mode separation. Furthermore, we experimentally investigate the influence of the anisotropic (temperature-dependent) dielectric environment provided by the liquid crystal on both the electric and magnetic resonances. We demonstrate that the phase transition of the liquid crystal from its nematic to its isotropic phase can be used to break the symmetry of the optical metasurface response. As such, our approach allows for spectral tuning of electric and magnetic resonances of all-dielectric metasurfaces as well as switching of the anisotropy of the optical response of the device.