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In this talk, we provide an overview of our recent efforts on deriving and elucidating bandwidth limits for two important classes of metamaterial devices: (i) metalenses and (ii) invisibility cloaks. (i) Recent works have demonstrated broadband metalenses with minimized chromatic aberrations, potentially paving the way for ultrathin achromatic optics. Within this context, here we derive fundamental bandwidth limits to achromatic metalenses, regardless of their implementation, and we show that all metalenses designed thus far obey these bounds. (ii) In the second part of the talk, we focus on the problem of broadband invisibility and address some relevant issues that have been the subject of debate in the recent literature. Specifically, we clarify that “active” invisibility cloaks suffer from fundamental bandwidth and size limitations that arise due to causality and stability.
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