ABSTRACT
In this chapter, we will show that a photonic crystal comprising
an array of subwavelength metallic helices has a unique photonic
dispersion that allows for the realization of negative refraction
for frequencies both above and below the polarization gap for
electromagnetic waves propagating along the helical axis. The
helical photonic crystal can also serve as a broadband wave plate for
waves propagating perpendicular to the helical axis of the metallic
photonic crystal. In addition, we show that robust transport of light
can be achieved using chiral photonic guided modes in a channel of
a dielectric photonic crystal. The light transport is immune to the
scattering of isotropic homogenous impurities and the phenomenon
bears some phenomenological similarity to robust transport of
electrons in topological insulators, although the mechanism is not
the same. In particular, the system is time-reversal invariant and the
robust one-way transport does not require an external field, which
is distinct from the previous strategies employing two-dimensional
magnetic photonic crystals with explicit time reversal breaking by
an external field.
