Switchable supermode emission in a doubly-coupled-ring system for multifunctional integrated photonic devices.

Effective integration of optical modes within chip-scale devices is critical to realize functional light emission, as it offers abundant physics and a versatile ability to control the mode evolution. Here, we present an efficient approach to achieve switchable emission by flexibly controlling supermode states in a doubly-coupled-ring system with four guided modes. The lasing conditions, which rely on the system's Hamiltonian, are revealed to yield multiple supermode states, including an exceptional-point state, a (quasi-)dark state, and a bright state. By freely engineering the coupling rate via phase-change material, the proposed system allows the generation of any desired states, enabling switchable and multifunctional emissions in fixed on-chip structures. Beyond the manipulation of various supermode emission states, our work presents a promising path toward the development of multifunctional integrated photonic devices, which may have applications in light storage, optical isolation, sensing, and so on.