  The photonic spin Hall effect (SHE), featured by a spin-dependent transverse
shift of an impinging optical beam driven by its polarization handedness, has
many applications including precise metrology and spin-based nanophotonic
devices. It is highly desirable to control and enhance the photonic SHE.
However, such a goal remains elusive, due to the weak spin-orbit interaction of
light, especially for systems with optical loss. Here we reveal a flexible way
to modulate the photonic SHE via exceptional points, by exploiting the
transverse shift in a parity-time (PT) symmetric system with balanced gain and
loss. The underlying physics is associated with the near-zero value and abrupt
phase jump of the reflection coefficients at exceptional points. We find that
the transverse shift is zero at exceptional points, but it is largely enhanced
in their vicinity. In addition, the transverse shift switches its sign across
the exceptional point, resulting from spontaneous PT-symmetry breaking. Due to
the sensitivity of transverse shift at exceptional points, our work also
indicates that the photonic SHE can enable a precise way to probe the location
of exceptional point in photonic systems.

Optics