Impedance-matched metadevices with a single matrix material
摘要
Artificial periodic structures including photonic crystals (PCs) and metamaterials have been widely employed to construct metadevices, whereas their effective refractive indices ne and relative impedances Zr are usually coupled together and hard to design separately. Here, we present a method for flexibly tuning the indices ne and impedances Zr of PCs. The unit cell of PC consists of a dielectric matrix with multiple air holes symmetrically distributed around the center of the unit cell. We find that the index ne of the PC mainly depends on the filling ratio of the dielectric, while its impedance Zr relies on the position of the holes. When the holes have an appropriate distance from the center of the unit cell, matched impedances (Zr = 1) can be achieved for PCs with different indices ne. As a result, impedance-matched metadevices, such as generalized Mikaelian lenses with high efficiency (> 96%), can be constructed even with high refractive indices in their matrices.