Double-Peak Electromagnetically Induced Transparency (EIT) via Resonator Coupling

In this study, we conducted separate investigations into the properties of RR and SR. Our findings indicate the presence of two BICs and a broad dip in the RR, as well as one BIC in the SR. We observed an EIT and two BICs in RSR resulting from the coupling between two modes originating from the same resonator. These results demonstrate the existence of multiple BICs arising from the coupling effect between the two resonators. This mechanism of EIT differs from previous research where the bright mode and dark mode were derived from different resonators. In our study, two modes contribute to the formation of EIT within the same resonator, while the SR facilitates the coupling between the two modes through optical field coupling. To validate this hypothesis, we replaced the original SR structure with a simplified resonator structure and obtained consistent results with the original SR. During the coupling process, both the bright mode and dark mode frequencies from the RR experience significant redshift, with the dark mode moving faster than the bright mode. It is the superposition of the bright and dark modes that leads to the formation of EIT. We also observed that by increasing the distance 'd' between RR and SR through the movement of the SR, another dark mode BIC2 generated by RR can rapidly move to the original broad dip, resulting in the formation of a double-peak EIT. All the bright and dark modes contributing to the double-peak EIT originate from the same resonator RR. In this study, we found that changing the incident angle parameter and the parameter 'd' cannot achieve the double-peak EIT effect. This is because during the process of varying the angle, the movement of BIC2 towards the reverse direction of the dip increases the distance between the dip and BIC2, preventing the coupling required for the formation of a double-peak EIT. With the variation of parameter 'd', BIC2 also continuously moves towards the direction of the broad dip, but the movement speed is too slow to couple with the dip. Additionally, BIC1 is influenced by 'd' and continuously shifts to the left, resulting in a weakening of the original EIT effect.