Towards three-dimensional optical metamaterials

Abstract

Metamaterials have opened up the possibility of unprecedented and fascinating concepts and applications in optics and photonics. Examples include negative refraction, perfect lenses, cloaking, perfect absorbers, and so on. Since these metamaterials are man-made materials composed of sub-wavelength structures, their development strongly depends on the advancement of micro- and nano-fabrication technologies. In particular, the realization of three-dimensional metamaterials is one of the big challenges in this research field. In this review, we describe recent progress in the fabrication technologies for three-dimensional metamaterials, as well as proposed applications.

Keywords: Metamaterials; Micro/nano-fabrication; Nanophotonics; Plasmonics.

Fig. 1

3D metamaterials vs. 3D functional metamaterials. a 2D structure but functionality of metamaterial is 1D. b 3D structure but 2D funtional metamaterials, and c 3D in both structure and functionality metamterial

Fig. 2

From stacked 2D to 3D metamaterials. a Magnetic metamaterial made of four-layer SRR structure [10]. b Negative-refractive-index metamaterial made of 21-layer fishnet structure [17]. c Chiral switching metamaterial made of 3D metallic structure [25], and d isotropic metamaterial made of 3D SRR structure [82]

Fig. 3

Fabrication techniques for 3D polymer structures. Two-photon polymerization technique for a 3D nano-structures [35] and b 3D photonic crystal [38]. c 3D carpet cloaking device fabricated by two-photon polymerization [39]

Fig. 4

Fabrication techniques for 3D metallic structures. a Silver chemical vapor deposition onto polymer template [50]. b Electroless plating in SU-8 3D template [51]. c Two-photon-induced photoreduction of metal ions [61], and d projection lithography technique [65]

Fig. 5

Metasurface structure for carpet cloaking of 3D objects [72]. a An AFM image of a 3D object with multiple bumps and dents. b SEM image of an object onto which a metasurface skin cloak has been fabricated. The inset shows an enlarged image of the entire object