  We introduce and theoretically analyze the concept of manipulating optical
chirality via strong coupling of the optical modes of chiral nanostructures
with excitonic transitions in molecular layers or semiconductors. With
chirality being omnipresent in chemistry and biomedicine, and highly desirable
for technological applications related to efficient light manipulation, the
design of nanophotonic architectures that sense the handedness of molecules or
generate the desired light polarization in an externally controllable manner is
of major interdisciplinary importance. Here we propose that such capabilities
can be provided by the mode splitting resulting from polaritonic hybridization.
Starting with an object with well-known chiroptical response -- here, for a
proof of concept, a chiral sphere -- we show that strong coupling with a nearby
excitonic material generates two distinct frequency regions that retain the
object's chirality density and handedness, which manifest most clearly through
anticrossings in circular-dichroism or differential-scattering dispersion
diagrams. These windows can be controlled by the intrinsic properties of the
excitonic layer and the strength of the interaction, enabling thus the
post-fabrication manipulation of optical chirality. Our findings are further
verified via simulations of the circular dichroism of a realistic chiral
architecture, namely a helical assembly of plasmonic nanospheres embedded in a
resonant matrix.
