Manipulating The Electromagnetic Wave With Metamaterials

Metamaterials (MMs), artificial electromagnetic (EM) media that are structured on the subwavelength scale, can realize unusual EM material parameters beyond the limitation of natural materials, such as negative index, zero index, and hyperbolic anisotropy, resulting in many exotic phenomena and peculiar applications including EM cloaking, wavefront control and anomalous light bending. Owing to the rapid development of MMs, people are pursuing the dream of manipulating the EM wave at will gradually. In this thesis, we demonstrate our research work on manipulating the EM wave with MMs focused on three aspects, including thin-film broadband absorbers, polarization conversion and unidirectional surface plasmon polaritons (SPPs) couplers.First, in the research area of absorbers, we propose a thin-film optical broadband MM absorber on the basis of slow-wave effect. Additionally, we assemble multi-sized slow-wave structures with appropriate geometrical parameters in a co-planar to increase the absorption bandwidth through the superposition of multiple slow-wave modes. Furthermore, an unprecedentedly broadband strong light absorber is experimentally demonstrated, which consists of periodic taper arrays constructed by a multilayered MM. This MM can change from a hyperbolic material to an anisotropic dielectric material at different frequency ranges and the special material features are the fundamental origins of the broadband absorption. The measured absorption is over 90% over almost the entire solar spectrum, reaching an average level of 96%, and remains high (above 85%) even in the longer-wavelength range till 4 μm. As the proposal is scalable, we finally apply the slow-wave effect at microwave and terahertz frequencies and fabricate the corresponding samples with polarization-insensitive, omnidirectional, and broadband absorption.Second, we design, fabricate and experimentally demonstrate an ultrathin, broadband half-wave plate in the near-infrared range using a plasmonic metasurface. The simulated results show that the linear polarization conversion efficiency is over 97% with over 90% reflectance across an 800-nm bandwidth. Moreover, simulated and experimental results indicate that such broadband and high-efficiency performance is also sustained over a wide range of incident angles. To further obtain a background-free half-wave plate, we arrange such a plate as a periodic array of integrated supercells made of several plasmonic antennas with high linear polarization conversion efficiency, consequently achieving reflection-phase gradient for the cross-polarized beam. In this design, the anomalous (cross-polarized) and the normal (co-polarized) reflected beams become spatially separated, hence enabling highly efficient and robust, background-free polarization conversion along with broadband operation.Third, we investigate the phase gradient metasurfaces which can link the propagating wave and SPPs together. After that, we design a unidirectional SPPs coupler working in visible (λ=690 nm) with a coupling efficiency of about 45%. Then we move our attention to the polarization-controlled phase gradient in reflection. We present two proposals in designing polarization-switchable SPPs couplers. One is the polarization-sensitive SPPs router in which orthogonal polarized light is converted into SPPs propagating along the specific orthogonal direction. The other is bi-functional metasurface whose functionality can be switched from unidirectional SPPs launcher to anomalously light reflector for different polarizations.In the end, we conclude the thesis and give perspectives about the MMs.