▎ 摘　　要

A strong chiral near-field is crucial for the detection of chiral molecules. Active tuning of the chiral near-field can shorten the detection process. In this study, a graphene-based achiral nanoring (GAN) that can actively control chiral near-fields is presented. The GAN is composed of three identical graphene pieces. The handedness and strength of the chiral near-fields can be actively controlled by adjusting the Fermi levels of these three graphene pieces. The optical chirality of the GAN near-field is 500 times that of circularly polarized light. In addition, the GAN enhances the chiral response of the chiral material by a factor of 250. This work provides opportunities for the ultrasensitive detection and location of molecules through the active control of chiral near-fields. (C) 2017 Optical Society of America