Tunable van der Waals-based metasurfaces for perfect absorption, sensing, radiative heat transfer, beam splitting and 5G/beyond applications

Abstract

Metasurfaces are thin, subwavelength structures that have extraordinary properties that cannot be found naturally. Tunable metasurfaces drew attention not only for their lightweight designs but also with the tunning option, having multiple responses without complex fabrication steps for each desired response. Besides tuning the structures by their intrinsic properties, the addition of van der Waals materials which are a specific type of 2D materials, can expand their tuning flexibilities and offer a wide range of applications. Here, we propose and investigate tunable metasurfaces in the following areas: Perfect Absorption, Sensing, Radiative Heat Transfer, Beam Splitting and 5G/Beyond Applications as: 1. All-Dielectric Metamirror for thermally tunable spectrally selective absorber, 2. Metasurface Design for Phonon-Induced Transparency and Nearly Perfect Resonant Absorption, 3. Near-Field Radiative Heat Transfer in Parallel-Plate Structures, 4. Gradient Metasurfaces for Beam Splitting and Light Absorption, 5. 5G and Beyond applications of mentioned works and future outlook. In the first work, we numerically propose a temperature-tunable, ultranarrowband one-way perfect near-infrared radiation absorber with high transmission in the longer wavelength neighboring spectral range. We obtained this functionality by using a guided-mode resonance-based grating-waveguide metamirror that is comprised of silicon, a spacer dielectric, an absorbing semiconductor, and germanium. Within the ultra-narrow bandwidth of the guided-mode resonance excited at 1.16 µm with a full width at half-maximum of 3.3 nm, we confirmed perfect absorption when light is incident from one of the two opposite directions. Excitation from the opposite direction resulted in perfect reflection. The thickness of the entire structure is limited to about one third the operating wavelength. Furthermore, due to the temperature tunability of silicon and germanium the thermo-optical sensitivity was found to be approximately 0.068 nm/K. In addition to this spectral tunability, our proposed device supports transparency windows with 80% transmission in the higher wavelength ranges. Our device is highly promising in the applications of thermo-tunable modulators and obtaining single frequency near-infrared signals from broadband sources. In the second work, A bi-tunable hexagonal boron nitride (hBN)-based metasurface with bi-functional phonon-induced transparency (PIT) and nearly perfect resonant absorption features in the mid-infrared (MIR) range is proposed. The metasurface, that is composed of axially symmetric hBN rings, is separated from a uniform thin vanadium dioxide (V O2) film with a SiO2 spacing layer and is integrated with a top graphene sheet. For the insulating phase of V O2 (i-V O2), PIT with an 80% transmission contrast ratio is observed inside the reststrahlen (RS) band of hBN due to the support of hyperbolic phonon polaritons. A considerably large group delay of 9.5 ps and up to 1.8 THz RIU −1 frequency shift per refractive index unit is also achieved for the i-V O2 case. On the other hand, it is found that for the metallic phase of V O2 (m-V O2), light transmission is prohibited and nearly perfect resonant absorption peaks are appeared inside the RS band of hBN. Finally, by integrating the hBN-based metasurface into the graphene sheet on the top, a tunable PIT-like effect and nearly perfect light absorption is achieved duo to the hybridization of graphene plasmons and hBN phonons. This leads to a modulation depth as high as 87% in the transmission (i-V O2) and 62% in the absorption (m-V O2) responses. Our findings offer a tunable and bi-functional device that is practical for MIR slow-light, sensing, and thermal emission applications. In the third work, we comprehensively analyze the near-field radiative heat transfer (NFRHT) between a pair of parallel non-rotated BP flakes that occurs due to the tunneling of the coupled anisotropic surface plasmon polaritons (SPPs) supported by the flakes. It is demonstrated that the covering of the BP flakes with (hBN) films leads to the hybridization of the BP’s SPPs with the hBN’s hyperbolic phonon polaritons and to the significant enhancement of the NFRHT at the hBN’s epsilon-near-zero frequencies. It is also shown that the NFRHT in the BP/hBN parallel-plate structure can be actively switched between the ON and OFF states by changing the chemical potential of the BPs and that the NFRHT can be modified by altering the number of the BP layers. Finally, we replace hBN with α − MoO3 and explore how the NFRHT is spectrally and strongly modified in the BP/α − MoO3 parallel-plate structure. We believe that the proposed BP/polar-vdW-material parallel-plate structures can prove useful in the thermal management of optoelectronic devices. In the fourth work, we propose multifunctional gradient metasurfaces that are composed of a periodic array of binary Si microcylinders integrated with V O2 and graphene. The metasurfaces act as transmittive (reflective) beamsplitters for the dielectric (metallic) phase of V O2 with a switchable characteristic. Moreover, by integrating the metasurfaces with graphene and modifying its chemical potential, one can tune the intensity of the split beam as well as obtain nearly perfect resonant absorptions. Consequently, the proposed metasurfaces can find potential applications in THz interferometers, multiplexers, and light absorbers. Finally, the works mentioned above, as well as diverse works in the literature will be explained and discussed upon emerging technologies in the area of communication and applications for 5G and mostly beyond and future outlook.