Abstract
Manipulating the speed of light has never been more exciting since electromagnetic induced transparency and its classical analogs led to slow light. Here, we report the manipulation of light group velocity in a terahertz metamaterial without needing a dark resonator, but utilizing instead two concentric split-ring bright resonators (meta-atoms) exhibiting a bright Fano resonance in close vicinity of a bright Lorentzian resonance to create a narrowband transmittance. Unlike earlier reports, the bright Fano resonance does not stem from an asymmetry of meta-atoms or an interaction between them. Additionally, we develop a method to determine the metamaterial “effective thickness”, which quantifies the influence of the substrate on the metamaterial response and has remained challenging to estimate so far. By doing so, very good agreement between simulated and measured group delays and velocities is accomplished. The proposed structure and method will be useful in designing optical buffers, delay lines, and ultra-sensitive sensors.
Highlights
Manipulating the speed of light has been the focus of growing fundamental scientific interest, along with a high potential technological impact
We report the observation of slow light phenomena in a terahertz metamaterial structure consisting of two concentric SRRs as bright resonators but without the need for a dark resonator
A sharp Fano resonance associated with the small SRR resides in spectral proximity of a Lorentzian resonance originating from the large SRR, which essentially results in a transparency window between the two resonances where the velocity of light is diminished
Summary
Manipulating the speed of light has been the focus of growing fundamental scientific interest, along with a high potential technological impact. The vast majority of EIT metamaterials to date most closely mimic quantum destructive interference In this type, dark meta-atoms are used to create a narrowband dark state that opens a transparency window within a broadband bright state arising from bright meta-atoms coupling directly to the electric field of www.nature.com/scientificreports/. There have been few reports of achieving EIT-like characteristics without using dark meta-atoms[40,41] In this case, two bright meta-atoms directly couple to the incident electric field, leading to two resonances, (one of which being a Fano resonance) which are spectrally close to each other and where a narrowband transmission window emerges in between. We demonstrate that the sharp Fano resonance observed in our structure arises from excitation of the second order mode in a symmetric SRR without interaction with adjacent SRRs, unlike previously reported Fano metamaterials where breaking the symmetry of meta-atoms or interaction between adjacent symmetric meta-atoms were reportedly essential conditions to achieve Fano resonance
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