Abstract
We investigate a hybrid re-configurable three dimensional metamaterial based on liquid crystal as tuning element in order to build novel devices operating in the terahertz range. The proposed metadevice is an array of meta-atoms consisting of split ring resonators having suspended conducting cantilevers in the gap region. Adding a “third dimension” to a standard planar device plays a dual role: (i) enhance the tunability of the overall structure, exploiting the birefringence of the liquid crystal at its best, and (ii) improve the field confinement and therefore the ability of the metadevice to efficiently steer the THz signal. We describe the design, electromagnetic simulation, fabrication and experimental characterization of this new class of tunable metamaterials under an externally applied small voltage. By infiltrating tiny quantities of a nematic liquid crystal in the structure, we induce a frequency shift in the resonant response of the order of 7–8% in terms of bandwidth and about two orders of magnitude change in the signal absorption. We discuss how such a hybrid structure can be exploited for the development of a THz spatial light modulator.
Highlights
The enormous progress in the field of metamaterials paved the way in recent years to a new era for novel devices able to realise exotic electromagnetic responses, some of them impossible to achieve with natural materials, ranging from negative refraction[1] and superlensing[2] to enhanced transmission[3], perfect absorption[4], cloaking[5,6] and, more generally, to those properties based on coordinate transformation design[7]
The initial approach towards our hybrid device was the design and analysis of a simple tuning system operating at around 1 THz and composed of arrays of split-ring resonator (SRR) unit cells covered with liquid crystal
We have designed, fabricated and experimentally demonstrated the capability of a hybrid metadevice having three-dimensional features and functionalised using a high birefringence liquid crystals (LC) to act as a spatial light modulator for THz waves
Summary
The enormous progress in the field of metamaterials paved the way in recent years to a new era for novel devices able to realise exotic electromagnetic responses, some of them impossible to achieve with natural materials, ranging from negative refraction[1] and superlensing[2] to enhanced transmission[3], perfect absorption[4], cloaking[5,6] and, more generally, to those properties based on coordinate transformation design[7]. The electric and magnetic responses achieved by metamaterials derive microscopically from the geometry of their unit cells and are preserved in the macroscopic medium This is analogous to the overall properties of a conventional material, which are determined by the nature of the constituent atoms (its chemical composition) and by a strong dependence on the lattice structure. The mechanism relies mostly on the transformation induced in the constituent materials or in the surrounding media by an external excitation like optical pumping[14], magnetostatic field[15], bias voltage[16], electrical or thermal effects[17] Many materials, such as liquid crystals (LC)[18], phase change materials[19], III–V semiconductors[20] etc, have been shown to be effective in developing prototypal devices, and some of them are possible candidates for wide use of tunable metamaterials
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