  Topological photonics provides an ideal platform for demonstrating novel band
topology concepts, which are also promising for robust waveguiding,
communication and computation applications. However, many challenges such as
extremely large device footprint and functionality at short wavelengths remain
to be solved which are required to make practical and useful devices that can
also couple to electronic excitations in many important organic and inorganic
semiconductors. In this letter, we report an experimental realization of Z_2
photonic topological insulators with their topological edge state energies
spanning across the visible wavelength range including in the sub-500 nm
regime. The photonic structures are based on deformed hexagonal lattices with
preserved six-fold rotational symmetry patterned on suspended SiNx membranes.
The experimentally measured energy-momentum dispersion of the topological
lattices directly show topological band inversion by the swapping of the
brightness of the bulk energy bands, and also the helical edge states when the
measurement is taken near the topological interface. The robust topological
transport of the helical edge modes in real space is demonstrated by
successfully guiding circularly polarized light beams unidirectionally through
sharp kinks without major signal loss. This work paves the way for small
footprint photonic topological devices working in the short wavelength range
that can also be utilized to couple to excitons for unconventional light-matter
interactions at the nanoscale.
