High‐Performance Terahertz Sensing at Exceptional Points in a Bilayer Structure

Abstract

Many intra-and inter-molecular vibrations lying at terahertz (THz) frequencies in bulk, powder, and thin film, which could provide rich structure information, can be accessed by conventional Raman and Fourier transform infrared spectroscopies. However, due to the lack of high-quality THz sources and detectors, the sensitivity that has been demonstrated with THz sensors is far from the level needed to detect small amounts of sample, like monolayer biomolecules. This puts forward an urgent requirement for a THz biosensor with ultra-high sensitivity. Here, a theoretical design is proposed using a bilayer metasurface to construct a two-resonator coupled system that obeys passive parity time symmetry and that possesses an exceptional point. By designing the coupled resonators to have orthogonal excitation orientations and retrieving the eigenfrequencies in polarization space, eigenfrequency splitting even smaller than the resonance linewidth can be distinguished, and thus attain ultra-high THz sensitivity. Electromagnetic simulations show that the sensitivity, defined as the frequency change per micrometer in thickness and per refractive index unit (RIU) of the analyte, can reach 800 GHz RIU −1 µm −1 , an order of magnitude higher than the values reported in previous work. This proposed high-sensitivity approach could open a path toward the detection of monolayer molecules at THz frequencies.

Non-Hermitian Electromagnetic Metasurfaces at Exceptional Points (Invited Review)

“…EP-enhanced sensitivity has been theoretically illustrated in a non-Hermitian metasurface composed of passive PT-symmetric resonators [80]. The resonators are split-ring bilayer structures with orthogonally orientated gaps.…”

A Review of THz Technologies for Rapid Sensing and Detection of Viruses including SARS-CoV-2

“…Until now, THz biosensors primarily used spectrum or intensity modulation methods to estimate analyte concentration, despite the fact that phase and polarization states can provide additional information. An ultrasensitive THz biosensor has been theoretically shown in [84] using a passive bilayer metasurface to construct a two-resonator linked system that obeys passive parity time symmetry. By creating coupled resonators with orthogonal excitation orientations and retrieving the eigenfrequencies in polarization space, ultra-high THz sensitivity can be achieved by distinguishing eigenfrequency splitting even smaller than the resonance linewidth.…”

Photoinduced Tunable and Reconfigurable Electronic and Photonic Devices Using a Silk‐Based Diffractive Optics Platform

“…To further explore the applications of silk-DOEs in digitally programmable coding metamaterials, we combined photosensitive materials with the sub-wavelength metamaterial elements of SRRs. [28,29] THz spectroscopy is used to detect small changes in the conductivity of the coating on the SRRs for photoinduced programmable and reconfigurable binary coding metamaterials. [30] Incorporation of such photosensitive materials into the resonator system can alter the capacitance (C) and/or inductance (L) of the system, thus modifying its resonance frequency, = 1/LC.…”