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The control of Fano resonances is of critical importance to opto-electronic and all-optical switching devices, light delay and storage, high sensitivity sensors, and quantum information processors. In this paper, we experimentally and theoretically demonstrate that controllable electromagnetically induced transparency (EIT)-like and Fano resonances can be achieved in a single quasi-cylindrical microresonator (QCMR). Robust and selective excitation of localized axial modes in a high quality QCMR is firstly demonstrated. Based on this stable platform, EIT-like lineshapes can be tuned and converted into Fano resonances by vertically moving the resonator. Moreover, by horizontally scanning the resonator, the transmission spectrum exhibits periodically changed Fano-like lineshapes. It is reported for the first time that the above two kinds of Fano resonances originated from different mechanisms can work on the same mode simultaneously. Our approach, demonstrated in this work, provides a robust photonic platform for accessing, controlling, and engineering the Fano resonances.

Microsphere resonators supporting whispering gallery modes (WGMs) have been extensively applied for considerable fields including narrow linewidth filters, high-sensitivity sensors, and nonlinear optics. We numerically demonstrate a coated microsphere resonator with three layers of high, low, high refractive-index (RI) from inside to outside. A phase matched waveguide is used to overlap the WGMs evanescent radiation field. Eigen-mode, relative intensity spectra, electromagnetic (EM) field distributions are observed to analyze resonant characteristics of WGMs by using the finite difference time domain method. As a result, two brilliant rings with strong EM fields distribute in two high-RI layers. By optimizing the gap distance between the microsphere and waveguide, the WGMs of two high-RI layer are efficiently excited. More energy is stored in such a structure rather than a single-layer-coated microsphere. Our approach provides the RI sensing application with such a triple-layer-coated structure.