Terahertz asymmetric metallic hole arrays with polarization-independent quasi-bound states in the continuum for membrane sensing

Resonances with both high-quality factor and polarization-independent characteristics are highly desirable for terahertz (THz) sensing. Here, THz sensors based on asymmetric metallic hole arrays (AMHAs) are experimentally demonstrated. Such sensors consisting of four-hole arrays support polarization-independent quasi-bound states in the continuum (BICs). The induced quasi-BIC presents a quality factor exceeding 2000, which enables enhanced sensing for thin membranes. Results show that the frequency shift is 97.5 GHz for the 25-& mu;m thick polyimide (PI), corresponding to a sensitivity of 147.7 GHz/RIU. The sensing performance strongly relates to the enhanced field originating from sharp quasi-BICs. A maximum field enhancement of 15.88 in contrast to the incident field is achieved. When the PI thickness is large than the decay length of enhanced fields, the interaction strength of field-PI becomes weak, resulting in a saturation effect for the shift of quasi-BICs. The proposed sensor possessing polarization-independent quasi-BICs has great potential for practical sensing applications in real-time chemical and biomolecular.

Automated summary

This experiment successfully demonstrates THz sensors based on asymmetric metallic hole arrays (AMHAs) that have both high-quality factor and polarization-independent characteristics. By introducing quasi-bound states in the continuum (BICs) with a quality factor exceeding 2000, the sensors exhibit enhanced sensitivity for thin membranes. The results show a frequency shift of 97.5 GHz for a 25-μm thick polyimide (PI), corresponding to a sensitivity of 147.7 GHz/RIU. The sensing performance is strongly related to the enhanced field generated by the sharp quasi-BICs. The proposed sensor has great potential for real-time chemical and biomolecular sensing applications.