  Chirality is a concept that one object is not superimposable on its mirror
image by translation and rotation. In particular, chiral plasmonics have been
widely investigated due to their excellent optical chiral properties, and have
led to numerous applications such as optical polarizing element etc. In this
study, we develop a model based on the concept of the interaction between
harmonic oscillators to investigate and explain the optical chiral mechanisms
of strongly coupled metal nanoparticles (MNPs). The chirality of the
scattering, absorption, and photoluminescence spectra are carefully discussed
in detail. The results show that the chirality of the system originates not
only from the orientations of the MNPs, but also from the different eigen
parameters between them. Specifically, the derived three factors contribute to
the chirality: the symmetry, the coupling strength, and the coherent
superposition of the emitted electric field. This work provides a deeper
understanding on the chiral plasmonics and may guide relevant applications in
theory.
