  The valleys of two-dimensional transition metal dichalcogenides (TMDCs) offer
a new degree of freedom for information processing. To take advantage of this
valley degree of freedom, on one hand, it is feasible to control valleys by
utilizing different external stimuli like optical and electric fields. On the
other hand, nanostructures are also used to separate the valleys by near field
coupling. However, for both above methods, either required low-temperature
environment or low degree of coherence properties limit their further
applications. Here, we demonstrate all-dielectric photonic crystal (PhC) slabs
without in-plane inversion symmetry (C2 symmetry) could separate and route
valley photons in a WS2 monolayer at room temperature. Coupling with circularly
polarized photonic Bloch modes of such PhC slabs, valley photons emitted by a
WS2 monolayer are routed directionally and efficiently separated in the far
field. In addition, the far-field emission is directionally enhanced and with
long-distance spatial coherence property.
