Electrically Reconfigurable Mode Chirality in Integrated Microring Resonators

Chirality, one of the universal phenomena in physics, forms the playground for fascinating phenomena in modern electromagnetism and industrial applications. Within the rapidly advancing technologies of integrated optoelectronic and all-optical devices, controlling the light flow on a chip using optical chiral modes emerges as a crucial topic, which implies numerous counterintuitive chiroptical effects such as unidirectional emission, magnetic-free non-reciprocity, chiral switching, and enhanced sensitivity. Here strong yet reconfigurable mode chirality is demonstrated in integrated silicon-based spiral microring resonators. Leveraging the adjustable azimuthal positions of two spiral edges as asymmetric local scatterers, the inter-modal coupling can be manipulated, which bypasses the requirement of external off-chip components in conventional schemes. Besides, an integrated phase shifter enables electrical reconfiguration of the non-Hermiticity toward or away from exceptional points. Experimental results reveal post-fabrication reconfiguration with a sign-reversible chirality and chirality-induced suppression of backscattering down to −24 dB. By virtue of demonstrations using standard silicon photonics foundry services, the findings provide a new design framework of microresonators as a building block for integrated chiral photonics in both classical and quantum regimes.