On-chip generation of dual-Fano resonances with tunable lineshape diversity in a single whispering-gallery mode microcavity

Multiple Fano resonances provide advantages such as multi-band operation and enhanced light–matter interaction, enabling applications in optical sensing, filtering, and related photonic functionalities. However, many existing approaches for generating multiple Fano resonances rely on cascaded microcavity structures, which impose significant challenges for device integration and fabrication. Here, we propose and experimentally demonstrate a single multimode microring resonator with a pulley coupler based on multimode waveguide to support dual Fano resonances. By simultaneously exciting two propagating modes in the bus waveguide and controlling their relative phase, dual Fano resonances are realized through interference between the waveguide modes and distinct cavity modes. This configuration introduces an explicit and continuously tunable phase degree of freedom, enabling deterministic modulation of the Fano lineshape and yielding diverse dual-Fano lineshape combinations. Benefiting from a low-loss multimode microring design, an ultrahigh slope rate of up to 667.3 dB/nm is experimentally achieved. The proposed approach provides a compact and simplified platform for phase-controlled multi-Fano generation in a single microcavity and demonstrates strong potential for multi-channel, reconfigurable, and multifunctional integrated photonic devices.