Various resonance lineshapes available in a single microring resonator

To accommodate different application requirements, resonances of microring resonator (MRR)-based devices have been developed into various lineshapes, such as electromagnetically induced transparency, electromagnetically induced absorption, and Fano lineshapes. However, these lineshapes are mainly achieved in large-footprint structures demanding precise control. Under such context, this work investigates the formation of various resonance lineshapes in a single MRR with two partially reflecting elements incorporated into the bus waveguide. The transfer matrix model of the compact structure is established with the reflective wave in the MRR included. It is revealed that the abundant resonance lineshapes originate from the mode-coupling between the Fabry–Perot cavity and the MRR. Based on this model, the formation of each resonance lineshape is analyzed. The conditions under which each resonance lineshape can occur are identified and the characteristics of these resonance lineshapes are studied. In addition, the significant role of the reflective wave in the formation of these lineshapes is emphasized. Under the theoretical guidance of the presented work, various resonance lineshapes can be achieved and designed flexibly in a single MRR. Thus, the lineshapes required for a range of applications can be realized in a simple and reproducible MRR. (paper)