Excitation and Tuning of Fano-like Resonances in Whispering Gallery Microcavity and Microfiber Modal Interferometer Coupled System

We propose a method for the excitation and controllable tuning of Fano-like resonance based on whispering gallery mode (WGM) microcavities and microfiber modal interferometers (MMIs). By the interaction of the discrete comb-like resonant modes excited by the WGM microcavity and the continuous interference spectrum generated by the MMI, the excitation of Lorentzian, Fano-like resonance, and electromagnetically induced transparency (EIT) lineshapes is achieved. In this system, the resonant modes of thin-walled WGM can interact with the liquid inside the cavity; thus, the Fano-like lineshape can be tuned via intracavity refractive index modulation. By adjusting the diameter and transition region length of the MMI, the Fano-like lineshape generated by the WGM-MMI coupled structure can be tuned. More importantly, as the refractive index of the liquid inside the cavity increases from 1.33 to 1.351, the Fano-like resonance lineshape evolves and the corresponding Fano parameter q shifts from 0.19 to 1.24. The proposed system enables stable excitation and controllable tuning of Fano-like resonances, demonstrating potential for applications in microfluidic sensing and optical switching.