Abstract
Controlling of the lineshape of Fano resonance attracts much attention recently due to its wide capabilities for lasing, biosensing, slow-light applications and so on. However, the controllable Fano resonance always requires stringent alignment of complex symmetry-breaking structures and thus the manipulation could only be performed with limited degrees of freedom and narrow tuning range. Furthermore, there is no report so far on independent controlling of both the bright and dark modes in a single structure. Here, we semi-analytically show that the spectral position and linewidth of both the bright and dark modes can be tuned independently and/or simultaneously in a simple and symmetric metal-slit superlattice, and thus allowing for a free and continuous controlling of the lineshape of both the single and multiple Fano resonances. The independent controlling scheme is applicable for an extremely large electromagnetic spectrum range from optical to microwave frequencies, which is demonstrated by the numerical simulations with real metal and a microwave experiment. Our findings may provide convenient and flexible strategies for future tunable electromagnetic devices.
Highlights
Controlling of the lineshape of Fano resonance attracts much attention recently due to its wide capabilities for lasing, biosensing, slow-light applications and so on
Optical Fano resonance has been a focus in nanophotonics field owing to its ultra-narrow linewidth which is available for switching[1,2], lasing[3,4,5,6], biosensing[7,8,9,10], nonlinear optics, slow light application[11,12,13] and so on
Fano resonance with an unusual asymmetric lineshape arises from the interference between a subradiant dark mode and a superradiant bright mode[14,15]
Summary
Controlling of the lineshape of Fano resonance attracts much attention recently due to its wide capabilities for lasing, biosensing, slow-light applications and so on. We semi-analytically show that the spectral position and linewidth of both the bright and dark modes can be tuned independently and/or simultaneously in a simple and symmetric metal-slit superlattice, and allowing for a free and continuous controlling of the lineshape of both the single and multiple Fano resonances. The system that supports Fano or EIT-like response usually requires complex unit cell geometry with symmetry-breaking structures such as the dipole quadrupole coupled metamaterials or metasurfaces[17,18,20,21,22], asymmetric split ring resonators[23,24,25,26], detuned resonator-pair[27,28,29], waveguide-plasmon coupled systems[30,31,32] and so on Those structures rely on the near-field coupling and they require stringent alignment precision between nanostructure elements. The general variation regularity of the spectral position as well as the linewidth of either the dark or bright mode is still unclear due to the lack of systematic study on the coupling mechanism between the slit cavity modes
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