  With the advance of on-chip nanophotonics, there is a high demand for high
refractive index, low-loss materials. Currently, this technology is dominated
by silicon, but van der Waals (vdW) materials with high refractive index can
offer a very advanced alternative. Still, up to now it was not clear if the
optical anisotropy perpendicular to the layers might be a hindering factor for
the development of vdW nanophotonics. Here, we studied WS2-based waveguides in
terms of their optical properties and, particularly, in terms of possible
crosstalk distance. Surprisingly, we discovered that the low refractive index
in the direction perpendicular to the atomic layers improves the
characteristics of such devices, mainly due to expanding the range of
parameters at which single-mode propagation can be achieved. Thus, using
anisotropic materials offers new opportunities and novel control knobs when
designing the nanophotonic devices.
