Spatial photoluminescence and lifetime mappings of quasi-2D perovskites coupled with a dielectric metasurface.

Light-matter interaction between quantum emitters and optical cavities plays a vital role in fundamental quantum photonics and the development of optoelectronics. Resonant metasurfaces are proven to be an efficient platform for tailoring the spontaneous emission (SE) of the emitters. In this work, we study the interplay between quasi-2D perovskites and dielectric TiO2 metasurfaces. The metasurface, functioning as an open cavity, enhances electric fields near its plane, thereby influencing the emissions of the perovskite. This is verified through angle-resolved photoluminescence (PL) studies. We also conducted reflectivity measurements and numerical simulations to validate the coupling between the quasi-2D perovskites and photonic modes. Notably, our work introduces a spatial mapping approach to study Purcell enhancement. Using fluorescence lifetime imaging microscopy (FLIM), we directly link the PL and lifetimes of the quasi-2D perovskites in spatial distribution when positioned on the metasurface. This correlation provides unprecedented insights into emitter distribution and emitter-resonator interactions. The methodology opens a new (to the best of our knowledge) approach for studies in quantum optics, optoelectronics, and medical imaging by enabling spatial mapping of both PL intensity and lifetime, differentiating between uncoupled quantum emitters and those coupled with different types of resonators.

Rotary bi-layer ring-shaped metamaterials for reconfiguration absorbers: publisher's note.

This publisher's note corrects errors in Appl. Opt.61, 9078 (2022)APOPAI0003-693510.1364/AO.471949.

Rotary bi-layer ring-shaped metamaterials for reconfiguration absorbers.

A reconfigurable metamaterial absorber (MA) in the microwave region is numerically and experimentally demonstrated based on a multi-layered metamaterial. The proposed structure can be mechanically switched between two different configurations to obtain designated absorption behaviors. By rotating the upper ring layer by multiples of 90 deg, two separated absorption modes of the MA are created. The first configuration acts as a single-band absorber, while the second configuration performs multi-band perfect absorption. In addition, the proposed structure can be easily switched into two different configurations to obtain a designated absorption feature. Our work is expected to provide an effective approach to obtaining reconfigurable MAs, which are useful for various applications.

Flexible Magnetic Metasurface with Defect Cavity for Wireless Power Transfer System.

In this paper, we present a flexible magnetic metamaterial structure for enhancing the efficiency of wireless power transfer (WPT) systems operating at 13.56 MHz. The metasurface between transmitter (Tx) and receiver (Rx) coils of the WPT system is constructed of a 3 × 5 metamaterial unit cell array with a total size of 150 × 300 mm2. Most metamaterial structures integrated into WPT systems are in planar configurations with a rigid substrate, which limits practical applications. The proposed metasurface is fabricated on an FR-4 substrate with a thin thickness of 0.2 mm; therefore, it can be bent with radii greater than 80 mm. A defect cavity is formed in the non-homogeneous metasurface by controlling the resonant frequency of the unit cell with an external capacitor. Simulation and measurement results show that the efficiency of the WPT system is significantly enhanced with metasurfaces. The performance of the WPT system can also be optimized with suitable bend profiles of metasurfaces. This proposed flexible metasurface could be widely applied to WPT systems, especially asymmetric, bendable, or wearable WPT systems.

Optimal frequency for magnetic resonant wireless power transfer in conducting medium.

In this article, we investigated the efficiency of a magnetic resonant wireless power transfer (MR-WPT) in conducting medium and found out an optimal frequency for designing the system. In conducting environment, the eddy current loss is generated by the high-frequency alternating currents in the coils. It is manifested by increased radiation resistance of resonator coil leads to decrease the quality factor (Q-factor), which reduces the wireless power transfer (WPT) efficiency in conducting medium. The Q-factor of the resonator coil strongly depending on the conductivity, frequency, and thickness of conducting block. Two MR-WPT systems operating at 10.0 MHz and 20.0 MHz are implemented to study the effect of conducting medium on efficiency. The achieved results indicated that the 20.0 MHz system has higher efficiency at a conductivity smaller than 6.0 S/m. However, at the larger conductivity, the 10.0 MHz system is more efficient. The results provide a method to determine the optimal frequency of a WPT system operating in the conducting medium with various conductivities and thickness blocks. This method can be used to design MR-WPT systems in numerous situations, such as autonomous underwater vehicles and medical implants.

Ultra-subwavelength thickness for dual/triple-band metamaterial absorber at very low frequency.

An integrated model utilizing external parasitic capacitors for a dual-band metamaterial perfect absorber (DMPA) is proposed and demonstrated in the UHF radio band. By adjusting the lumped capacitors on a simple meta-surface, the thickness of absorber is reduced to be only 1/378 and 1/320 with respect to the operating wavelength at 305 and 360.5 MHz, respectively. The simulations and the experiments confirm that the DMPA can maintain an absorption over 91% in a wide range of incident angle (up to 55°) and independent of the polarization of incident radiation. Additionally, we examine the integrated model for smaller dual-band absorber and absorption performance at higher frequencies (LTE band). Finally, we consolidate our approach by fabricating an ultrathin triple-band perfect absorber miniaturized to be only 1/591 of the longest operating wavelength. Our work is expected to contribute to the actualization of metamaterial-based devices working at radio frequency.

Polarization-independent, wide-incident-angle and dual-band perfect absorption, based on near-field coupling in a symmetric metamaterial.

We numerically and experimentally investigated a dual-band metamaterial perfect absorber (MPA), utilizing the near-field coupling of double split-ring resonators (DSRRs). Owing to the near-field coupling between resonators, two arms in each DSRR resonate in different phases, leading to a dual-band perfect absorption. The proposed MPA also exhibits polarization-insensitive behavior and maintains the high absorption above 90% up to a wide range of incident angle more than 45°. Finally, to further consolidate our approach, a multi-band absorption is also studied by exploiting the near-field coupling among a larger number of DSRRs. Our work is expected to be applied to future broadband devices using MPA.

Miniaturization for ultrathin metamaterial perfect absorber in the VHF band.

An efficient resolution for ultrathin metamaterial perfect absorber (MPA) is proposed and demonstrated in the VHF radio band (30-300 MHz). By adjusting the lumped capacitors and the through vertical interconnects, the absorber is miniaturized to be only λ/816 and λ/84 for its thickness and periodicity with respect to the operating wavelength (at 102 MHz), respectively. The detailed simulation and calculation show that the MPA can maintain an absorption rate over 90% in a certain range of incident angle and with a wide variation of capacitance. Additionally, we utilized the advantages of the initial single-band structure to realize a nearly perfect dual-band absorber in the same range. The results were confirmed by both simulation and experiment at oblique incidence angles up to 50°. Our work is expected to contribute to the actualization of future metamaterial-based devices working at radio frequency.