Lattice Collective Interaction Engineered Optical Activity in Metamaterials

The metamaterials with chiral metamolecular structure designs would show optical activity. In the past, researchers devoted themselves to proper designs of the individual metamolecules to improve the optical activity performance, however the roles of the lattice collective modes in the metamaterial array to the final optical activity have received much less attention. Here, how collective resonances can be utilized to engineer the optical activity of the metamaterials is systematically studied. Metamaterial arrays consisting of various numbers of L-shaped chiral metamolecules are fabricated. It is illustrated that the intermolecule collective interactions are capable to dramatically improve the quality factor of the resonances of metamolecule ensembles. Also, it is shown that with the aid of lattice collective resonances, the spectral linewidth of the optical rotation and ellipticity angle modification to the light collapse efficiently and the magnitudes of the optical activity effects can be dramatically boosted. Both the spectral line collapses and the optical activity magnitude becomes saturated as the size of metamaterial array becomes larger than certain sizes, which implies the maximum coupling length between the metamolecules. The results provide a new freedom in optimizing the optical activity of the chiral metamaterials.