Abstract
In this paper, a photo-excited switchable terahertz metamaterial (MM) polarization converter/absorber has been presented. The switchable structure comprises an orthogonal double split-ring resonator (ODSRR) and a metallic ground, separated by a dielectric spacer. The gaps of ODSRR are filled with semiconductor photoconductive silicon (Si), whose conductivity can be dynamically tuned by the incident pump beam with different power. From the simulated results, it can be observed that the proposed structure implements a wide polarization-conversion band in 2.01–2.56 THz with the conversion ratio of more than 90% and no pump beam power incident illuminating the structure, whereas two absorption peaks operate at 1.98 THz and 3.24 THz with the absorption rates of 70.5% and 94.2%, respectively, in the case of the maximum pump power. Equivalent circuit models are constructed for absorption states to provide physical insight into their operation. Meanwhile, the surface current distributions are also illustrated to explain the working principle. The simulated results show that this design has the advantage of the switchable performance afforded by semiconductor photoconductive Si, creating a path towards THz imaging, active switcher, etc.
Highlights
Metamaterials (MMs), a class of artificial materials comprised of sub-wavelength periodic or non-periodic structures, have received more and more interest in the past few decades [1] due to their extraordinary characteristics in manipulating electromagnetic (EM) waves unavailable in nature [2]
MM structures integrated with active media, such as MEMS [25,26], graphene [27,28,29], vanadium dioxide (VO2) [30,31], indium antimonide (InSb) [32,33] and semiconductors silicon (Si) [34,35], etc., have been presented and designed to realize the dynamic and active manipulation of THz wave under the control of external stimuli, such as electrical biasing, optical illumination and thermal excitation
The periodic boundary conditions (PBC) oriented along the x and y directions is used to model the periodic structure with a normal wave incident upon the unit cell with the E-field vector in the y axis, as described in detail in Figure 1c, behaving as the exciting source
Summary
Metamaterials (MMs), a class of artificial materials comprised of sub-wavelength periodic or non-periodic structures, have received more and more interest in the past few decades [1] due to their extraordinary characteristics in manipulating electromagnetic (EM) waves unavailable in nature [2]. Most THz devices usually can only work in static (reflection/transmission state), and have a single function making them difficult to change once fabricated, which severely hamper their practical applications To solve this challenge, MM structures integrated with active media (i.e., active THz devices), such as MEMS [25,26], graphene [27,28,29], vanadium dioxide (VO2) [30,31], indium antimonide (InSb) [32,33] and semiconductors silicon (Si) [34,35], etc., have been presented and designed to realize the dynamic and active manipulation of THz wave under the control of external stimuli, such as electrical biasing, optical illumination and thermal excitation
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