Metamaterials for Enhanced Optical Responses and their Application to Active Control of Terahertz Waves

Abstract

Metamaterials, artificially constructed structures that mimic lattices in natural materials, have made numerous contributions to the development of unconventional optical devices. With an increasing demand for more diverse functionalities, terahertz (THz) metamaterials are also expanding their domain, from the realm of mere passive devices to the broader area where functionalized active THz devices are particularly required. A brief review on THz metamaterials is given with a focus on research conducted in the authors' group. The first part is centered on enhanced THz optical responses from tightly coupled meta‐atom structures, such as high refractive index, enhanced optical activity, anomalous wavelength scaling, large phase retardation, and nondispersive polarization rotation. Next, electrically gated graphene metamaterials are reviewed with an emphasis on the functionalization of enhanced THz optical responses. Finally, the linear frequency conversion of THz waves in a rapidly time‐variant THz metamaterial is briefly discussed in the more general context of spatiotemporal control of light.

Retrieving the Effective Parameters of an Electromagnetic Metamaterial Using the Nicolson-Ross-Weir Method: An Analytic Continuation Problem Along the Path Determined by Scattering Parameters

“…In this study, we rigorously demonstrated that the NWR branch ambiguity issue can be avoided by computing the proper right-inverse of the relationship (5) through the analytic continuation of a suitable analytic logarithm along the path determined in the complex plane by the scattering parameters of the MM under analysis. This prolongation has to be realized according to the formulation provided by Theorem 1, which states the conditions so that we can determine a unique solution for this problem.…”

“…This clearly indicates that its preimage,γ(t), does not lie exclusively inside the strip (−π, π]. Thus, on the contrary of the previous case L(•) = log(•), and the analytic continuation has to be employed to solve (5). Since the point γ(a) (green diamond marker) lies on R + (as it must), the principal logarithm log(•) can and must be used as…”

“…Effective refractive index Electromagnetic metamaterials (MMs) are composites that exhibit unusual physical characteristics when exposed to the action of an external electromagnetic field [1], [2]. This can potentially make the development of cutting-edge innovative microwave, millimetre wave, and optical frequency devices a real possibility, see for example [3]- [5] and references within for a detailed overview of this argument. An MM is usually created by arranging suitable identical scattering elements, the meta-atoms, in an appropriate lattice configuration [1].…”

“…Now, we return to (5). To obtain the unique meaningful solution of this relation, the constraint Im(L(γ(a))) = θ 0 must specialize as follows:…”

Recent advances in optical dynamic meta-holography

“…Recently, several groups reported their research progress in electrically tunable metasurface-based SLMs 68,72,137 . Although these works were based on different materials and methods, all of these designs were onedimensional (1D) metasurface-based SLMs.…”