Abstract-Tunable high-quality Fano resonance in coupled terahertz whispering-gallery-mode resonators

Applied Physics Letters

Shixing Yuan, Liao Chen, Ziwei Wang, Ruolan Wang,  Xiaojun Wu,  Xinliang Zhang

Schematic of the proposed coupled-WGMR system, which consists of a waveguide and two coupled WGMRs. The inset illustrates the photograph of two WGMRs utilized in the experiment. (b) Calculated transmission spectra of the coupled-WGMR system in different situations according to Eq. (3). Parameters (Δ/2π, γ1i /2π, γ2i /2π, γc /2π, and μ2 /2π) utilized in the figure are: line 1: 300 MHz, 820 MHz, 240 MHz, 470 MHz, 0 MHz; line 2: 300 MHz, 820 MHz, 240 MHz, 470 MHz, 150 MHz; line 3: 150 MHz, 820 MHz, 240 MHz, 470 MHz, 150 MHz; line 4: 150 MHz, 820 MHz, 240 MHz, 470 MHz, 150 MHz.

https://aip.scitation.org/doi/10.1063/1.5129073

Fano resonance is widely discussed in designing functional terahertz components, such as sensors, filters, modulators, and group delay modules. Usually, a high quality (Q) factor and flexible tunability of Fano resonance are key requirements for these applications. Here, we present tunable terahertz Fano resonance with a Q factor of 2095 at 0.439 THz in coupled terahertz whispering-gallery-mode resonators (WGMRs). Coupling between a relatively low Q (578) quartz ring and a high Q (2095) silicon ring is employed to generate high Q Fano resonance. The resonant frequency of the Fano resonance can be actively manipulated by tuning the resonant frequency of the high Q WGMR, which is achieved through utilizing an electrical thermo-optic tuning method; meanwhile, the resonance intensity of the Fano resonance can be engineered by adjusting the coupling strength between two WGMRs. This coupled-WGMR scheme delivers tunable high Q Fano resonance and may contribute to the design of high-performance configurable terahertz devices.

This research was supported by the National Natural Science Foundation of China (NSFC) (Nos. 61735006 and 61905007) and Laboratory Research Fund from Wuhan National Laboratory for Optoelectronics (Grant No. 2018WNLOKF001). The authors thank the 41st research institute of China Electronics Technology Group Corporation for providing the test equipment.