Dielectric super-absorbing ( > 50 % ) metasurfaces, born of necessity to break the 50% absorption limit of an ultrathin film, offer an efficient way to manipulate light. However, in previous works, super absorption in dielectric systems was predominately realized via making two modes reach the degenerate critical coupling condition, which restricted the two modes to be orthogonal. Here, we demonstrate that in nonorthogonal-mode systems, which represent a broader range of metasurfaces, super absorption can be achieved by breaking parity-time (PT) symmetry. As a proof of concept, super absorption (100% in simulation and 71% in experiment) at near-infrared frequencies is achieved in a Si-Ge-Si metasurface with two nonorthogonal modes. Engineering PT symmetry enriches the field of non-Hermitian flat photonics, opening-up new possibilities in optical sensing, thermal emission, photovoltaic, and photodetecting devices.

Sensing Microcystin-LR (MC-LR) is an important issue for environmental monitoring, as the MC-LR is a common toxic pollutant found in freshwater bodies. The demand for sensitive detection method of MC-LR at low concentrations can be addressed by metasurface-based sensors, which are feasible and highly efficient. Here, we demonstrate an all-dielectric metasurface for sensing MC-LR. Its working principle is based on quasi-bound states in the continuum mode (QBIC), and it manifests a high-quality factor and high sensitivity. The dielectric metasurface can detect a small change in the refractive index of the surrounding environment with a quality factor of ~170 and a sensitivity of ~788 nm/RIU. MC-LR can be specifically identified in mixed water with a concentration limit of as low as 0.002 μg/L by a specific recognition technique for combined antigen and antibody. Furthermore, the demonstrated detection of MC-LR can be extended to the identification and monitoring of other analytes, such as viruses, and the designed dielectric metasurface can serve as a monitor platform with high sensitivity and high specific recognition capability.

The ability to trap light in an ultrathin photoactive layer has been of great significance for applications ranging from optoelectronics, energy to spectroscopy. However, the current broadband light trapping suffers from undesirable direct Joule heat output with plasmonics or bulkiness with photonics. Here, we report a light-trapping photonic structure using an ultrathin all-dielectric super-absorbing metasurface. This presented photonic structure features asymmetrically coupled magnetic resonances, which eliminate reflection and transmission simultaneously by introducing destructive interference between the backscattered field of the resonance and the direct reflected field of the highly reflective Fabry–Pérot background. In particular, this photonic structure enables broadband light trapping by placing nanostructures of different sizes in a supercell. As a proof of concept, we experimentally demonstrate broadband (550–1280 nm) super absorption (>50%) within an ultrathin (∼200 nm) all-dielectric germanium metasurface. This work provides a design paradigm for harvesting light through flat photonic structures at the nanoscale and paves the way for cost-effective light management.

High sensitivity detection of acetylcholinesterase (Ache) concentration is an important method for water pollution control and treatment. Compared with commonly used detection methods, the dielectric nanoantenna detection method is more direct, efficient, and safer. In this paper, we first studied a silicon disk dielectric antenna for the detection of Ache. We made the structure by electron beam lithography technology and set up the optical system of spectrum measurement. We used the electrical resonance position of its transmission spectrum to calibrate the refractive index of the surface environment, and the sensitivity reaches 222nm/RIU. We introduced the chemical bond coupling method to monitor the Ache concentration changing process, and there is no need to mark the detection substance by modifying the surface of the antenna structure and fixing the antibodies of the substance to be monitored. We achieved the specific monitoring process of Ache concentration, and the minimum detectable concentration is 0.01mg/ml.

No abstract