Engineering Strongly Chiral Plasmonic Lattices with Achiral Unit Cells for Sensing and Photodetection

Although the concept of chirality has its origin in chemistry, the field of photonics is actively exploring and utilizing it. A new family of 2D chiral lattices constructed from fully achiral unit cells is introduced here. This type of chiral structure differs fundamentally from previously reported arrays made of chiral unit cells. In this system, circular dichroism (CD) appears due to the electromagnetic interaction between unit cells and the formation of lattice plasmons (LP). Importantly, the CD is strongly enhanced for anisotropic rectangular lattices, whereas the chiral signal in square lattices is found to be relatively weak. The results cover two configurations. The first has an index-matched environment, and the second includes an asymmetric arrangement of refractive indices. The index-matched model is preferable and supports ultrasharp LP resonances. Overall, excellent control of the spectral position and broadening of the CD peaks is also demonstrated by tuning the geometry and matrix refractive indices. These results can be useful for engineering polarization filters and chiral biosensors.