A whispering gallery mode resonator (WGMR) with a high‐quality factor and large coupling spectrum width can enhance the interaction of matter and lightwave by several orders of magnitude in a large bandwidth range. The performance of the resonator determines the accuracy and range of terahertz (THz) sensing. However, the quality factors of the reported THz WGMRs are highly limited by the high absorption loss of materials within THz spectral range. The coupling spectrum width is usually limited by the coupling structure. In this paper, an on‐chip THz whispering gallery mode resonator based on multislot waveguide and gradual coupling structure is proposed. By increasing the evanescent field of guided wave mode, the absorption loss in the resonator is significantly reduced. Through gradual coupling structure, resonance curves are more uniform within a wide spectrum. The simulation results show that the structure can improve the instinct quality factor of the THz resonator to the order of 104 when the bending radius is as small as 2mm. At the same time, sensitivity is increased by more than six times and uniform resonance curves are achieved from 0.45 ~ 0.55THz.

C.G. Xin et al.,Microw Opt Technol Lett. 65, 2177-2182(2023).