High-Q Fano Resonance in Subwavelength Stub-Wall-Coupled MDM Waveguide Structure and Its Terahertz Sensing Application

Meiping Li,Jinmei Song,Xiaoyu Liu,Yanpeng Shi,Yifei Zhang,Fuhua Yang,Xiaodong Wang

doi:10.1109/access.2021.3110512

Meiping Li, Jinmei Song + Show 5 more

Open Access

https://doi.org/10.1109/access.2021.3110512

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Abstract

Waveguide structures effectively controlling and guiding terahertz (THz) waves can achieve interesting resonance effects when combined with resonators. At present, achieving high quality factor (Q-factor) resonance in THz resonator-coupled waveguide structure is still a critical consideration to expand its practical application. Here, a high Q-factor Fano resonance based on a metal-dielectric-metal (MDM) waveguide consisting of a stub resonator and a metal wall with an aperture in the center is investigated theoretically and numerically in the THz region. The results show that the sharp and asymmetric Fano resonance peak is induced by the destructive interference between the stub resonator and metal wall which act as a Fabry-Perot cavity. Q-factor is obviously improved about 60 times (3.72 to ~225) by introducing the metal wall into the stub-coupled MDM waveguide. Moreover, Fano resonance can be effectively tuned by varying different structure parameters. Owing to the high sensitivity of Fano resonance peak to dielectric surroundings, a large-range refractive index (RI) sensor based on the proposed structure with a high sensitivity of 96480 nm/RIU is obtained. The figure of merit (FOM) of 195 is greatly improved compared to other THz Fano-based RI sensors. These results provide possibilities for subwavelength MDM waveguide structure to apply for THz bio/chemical sensing, bandpass filters, and on-chip highly integrated plasmonic device.

Highlights

Fano resonance was firstly discovered in the autoionizing states of atoms by Ugo Fano, caused by the constructive and destructive interference between a discrete excited state and a broad continuum resonant scattering process [1], [2]
Comparing Hz field distributions at three points, it can be seen that the high Q-factor of Fano resonance are attributed to the strong destructive interference between the stub resonator and metal wall, and the weak coupling between the stub resonator and MDM waveguide
The numerical results simulated by finitedifferent time-domain (FDTD) are in good agreement with the theoretical results analyzed by scattering matrix theory (SMT)

Summary

INTRODUCTION

Fano resonance was firstly discovered in the autoionizing states of atoms by Ugo Fano, caused by the constructive and destructive interference between a discrete excited state and a broad continuum resonant scattering process [1], [2]. Considering figure of merit (FOM) is an important indicator of sensor, Zhang et al proposed a Fano-based RI sensor with sensitivity of 923nm/RIU and FOM of 710 in MDM waveguide coupled with an equilateral triangle-shaped cavity, which significantly improved FOM [33] These studies show that the sensing performance of RI sensor realized by Fano-based MDM waveguide structure has been improved in visible and infrared band. MDM waveguide, due to its deep subwavelength confinement of light, easy fabrication, low propagation loss and long propagation distance [40]-[42], can be used to solve these problems It holds compact size and great promise for THz subwavelength plasmonic device and highly integrated optical circuits. The structure provides new routes for THz sensing application and subwavelength plasmonic device

STRUCTURE DESIGN AND THEORICAL ANALYSIS

RESULTS AND DISCUSSION

CONCLUSION