| Summary: | 碩士 === 國立臺灣大學 === 應用物理所 === 100 === Plasmonic metamaterials are artificial composites made by sub-wavelength local resonance structures of electric and/or magnetic type(s) exhibiting novel electromagnetic properties, such as negative refraction, perfect imaging, etc. In last several years, various graded metamaterial systems have brought us new fascinating phenomena such as invisibility cloaking [1], trapped rainbow [2], etc. Recently, N. Yu et. al. showed that a graded optical antenna array could realize anomalous reflection and refraction for light at infra-red (8 micrometer), following a generalized Snell’s law [3], and X. Ni et. al. soon pushed the idea to 2-micrometer wavelength with a relative broad operation bandwidth [4]. Sun et. al. further proved that a particular gradient-index meta-surface can convert a propagating wave to a surface wave with nearly 100% efficiency [5], and demonstrated the idea in microwave frequency regime. The key idea behind this set of works is to utilize the local reflection/refraction phase properties of a gradient metamaterial, so that coherent beams can be formed by constructive interference.
In this work, we push the idea to visible frequencies. We designed and fabricated a graded meta-surface working around 850 nm, and demonstrated that an incident beam can be redirected to a non-specular channel after reflection by our system. The measured conversion efficiency from the incident beam to the anomalous reflection one is quite high (up to 78%), and the working bandwidth is very broad (about 200 nm). We believe that our systems can have broad applications including beam splitter, SPP coupler, light absorber, etc.
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