  Perhaps the most significant progress to the field of infrared optics and
nanophotonics has been made through the real space realisation of polaritons in
two-dimensional materials that provide maximum light confinement
functionalities. The recent breakthrough discovery of in-plane hyperbolicity in
the natural van der Waals material has revealed a most exciting optical
property which enable an in-plane anisotropic dispersion. Yet, the most
intriguing feature of in-plane anisotropic dispersion is the manipulation of
polaritons at the nano scale. This development has opened a new window of
opportunity in order to develop unique nanophotonic devices with unprecedented
controls. This chapter will cover these developments with focus on fundamental
understandings and progress of real space visualisation of in-plane anisotropic
polaritons in the near-field range. The last section will conclude with the
future prospects of this rapidly emerging area.
