  The physics of exceptional point (EP) singularities, has been a key to a wide
range of unique physical applications in open systems. In this context, the
mutual interactions among four coupled states around a fourth-order EP (EP4) in
a physical system is yet to be explored. Here, we investigate the unique
features of an EP4 in a fabrication feasible planar optical waveguide with a
multilayer gain-loss profile based on only two tunable parameters. A unique
`fourth-order $\beta$-switching' phenomenon due to quasi-static gain-loss
variation around EP4 has been explored. An exclusive chiral light dynamics
following the dynamical variation of the gain-loss profile has been reported
for the first time, which enables a special type of asymmetric higher-order
mode conversion scheme. Here, all the coupled modes associated with an EP4 are
fully converted into different specific higher-order modes based on the choice
of encirclement directions. The proposed scheme would present EP4 as a new
light manipulation tool for integrated photonic devices.
