Abstract
Among various tunable optical devices, tunable metamaterials have exhibited their excellent ability to dynamically manipulate lights in an efficient manner. However, for unchangeable optical properties of metals, electromagnetic resonances of popular metallic metamaterials are usually tuned indirectly by varying the properties or structures of substrates around the resonant unit cells, and the tuning of metallic metamaterials has significantly low efficiency. In this paper, a direct-tuning method for semiconductor metamaterials is proposed. The resonance strength and resonance frequencies of the metamaterials can be significantly tuned by controlling free carriers’ distributions in unit cells under an applied voltage. This direct-tuning method has been verified in both two-dimensional and three-dimensional semiconductor metamaterials. In principle, the method allows for simplifying the structure of tunable metamaterials and opens the path to applications in ultrathin, linearly-tunable, and on-chip integrated optical components (e.g., tunable ultrathin lenses, nanoscale spatial light modulators and optical cavities with resonance modes switchable).
Highlights
Among various tunable optical devices, tunable metamaterials have exhibited their excellent ability to dynamically manipulate lights in an efficient manner
Electrons’ effective path length (EPL) determines the resonance wavelength, and the number of free electrons participating in resonance motions regulates the resonance strength[21]
A strip consists of two regions with different types of doping: an n-type region dominated by electrons, and a p-type region dominated by holes
Summary
Among various tunable optical devices, tunable metamaterials have exhibited their excellent ability to dynamically manipulate lights in an efficient manner. The resonance strength and resonance frequencies of the metamaterials can be significantly tuned by controlling free carriers’ distributions in unit cells under an applied voltage. This direct-tuning method has been verified in both two-dimensional and threedimensional semiconductor metamaterials. On the basis of the control of free electrons in unit cells of metamaterials, direct-tuning method can lead to a sufficiently large free electron distribution and density change in a material (e.g., heavily doped semiconductor or conducting oxide), resulting in a large variation for resonance frequency and resonance strength of metamaterials. Unit cells of SMs are made of n-doped and p-doped semiconductors to keep the depletion region from disappearing to achieve equilibrium, and substrates are intrinsic GaAs
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