High-Sensitive Refractive Index Sensing Enabled by Topological Charge Evolution

Abstract

A high-sensitive refractive index sensor is proposed and demonstrated by utilizing merging bound states in the continuum, namely a set of integer topological charges in the momentum space. Through varying cladding refractive index n c , the topological charges continuously depart from the merging state, and result in the robust and considerable high-Q factors (above 7 × 10 4) in a large detection range of 0.456. In such a range, sensing sensitivity of ∼36 nm/RIU and figureof-merit from ∼5990 (air) to 1607 (n c =1.456) are achieved. Meanwhile, the detection limit on the order of 10 −5 RIU is clearly distinguishable from the measured spectrum under tiny variation of cladding refractive index. Our work paves the way for promising integrated high-sensitive sensors in many biological and chemical applications.

High-Sensitivity Optical Sensors Empowered by Quasi-Bound States in the Continuum in a Hybrid Metal–Dielectric Metasurface

“…Second, the high- Q resonance is extremely sensitive to structural defects and light source conditions. For instance, extremely sharp resonances are usually measured in high-symmetry nanostructures with oblique incidence, , which is difficult to implement and observe in practice. Third, most of BIC-in-hybrid-system studies are only simulated or characterized without demonstrations on biosensing. − This creates uncertainty about the actualization of high-performance hybrid metasurface sensing platforms in practical use.…”

“…However, their quality factors ( Q factors) are restrained due to ohmic losses. Conversely, dielectric nanostructures enable extremely sharp resonances due to the decreased loss of material. − Nevertheless, the majority of their electromagnetic energy is confined within the structure, resulting in limited sensitivities compared to metallic nanostructures. To overcome these limitations, hybrid nanostructures combining features of metals and dielectrics (plasma and photon) have been proposed, which are able to integrate the high sensitivity of metals and the high Q factor of dielectrics, thereby endowing biosensors with high figures of merit (FOMs). − …”

Label-Free Bound-States-in-the-Continuum Biosensors

“…Some existing studies have provided solutions. The operation of Lv et al [ 85 ] of merging BICs can achieve higher Q values with better robustness and can ensure high Q -values above 10 4 both in air and in solution. Such robustness is particularly important in resisting manufacturing errors and obtaining a more stable biodetection environment.…”

“…All-dielectric structures that support BICs have been widely used in the design of high- Q biosensors based on their advantages of low loss and high functionality. In this section, some all-dielectric BICs biosensors are introduced, including BICs gratings [ 57 , 58 , 59 , 60 , 61 , 62 , 63 ], symmetry-broken [ 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 ] and topological-boundary-states-governed [ 78 ] BICs metasurfaces, and BICs PhCSs [ 56 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 ].…”

“…A high Q -value of 1.2 × 10 4 and a low- DL of 6 × 10 −5 was also realized experimentally. In addition, Lv et al [ 85 ] pinpointed the BIC property of a silicon PhCS from the perspective of the topological charge. BICs are essentially topological defects in the momentum space, namely nontrivial topological charge.…”