  An all-Si photonic structure emulating the quantum-valley-Hall effect is
proposed. We show that it acts as a photonic topological insulator (PTI), and
that an interface between two such PTIs can support edge states that are free
from scattering. The conservation of the valley degree of freedom enables
efficient in- and out-coupling of light between the free space and the photonic
structure. The topological protection of the edge waves can be utilized for
designing arrays of resonant time- delay photonic cavities that do not suffer
from reflections and cross-talk.
