Versatile and reconfigurable integrated silicon nitride photonic microresonator

Unlocking the full potential of integrated photonics requires versatile, multi-functional devices that can adapt to diverse application demands. However, confronting this challenge with conventional single-function resonators often results in cumbersome system designs. We present an elegant solution: a versatile and reconfigurable dual-polarization Si3N4 microresonator that represents a new perspective in on-chip photonic designs. Our device can be dynamically reconfigured into three distinct topologies: a Möbius-like microcavity, a Fabry–Pérot resonator, and a microring resonator. This unprecedented functionality is enabled by a tunable balanced Mach-Zehnder interferometer that facilitates controllable mutual mode coupling of counterpropagating light using a single control knob. We experimentally demonstrate that the device not only supports polarization-diverse operation on a compact footprint but also gives rise to a wide variety of physical phenomena, including a standing wave cavity, a traveling wave cavity, free spectral range multiplication, and the photonic pinning effect. These behaviors are accurately modeled using the transfer matrix method and intuitively explained by the temporal coupled-mode theory. Our results underscore the potential for a chip-scale platform to realize reconfigurable reconstructive spectrometers and on-chip synthetic dimensions for topological physics.