  We present a comprehensive review on the geometric-phase based metasurfaces
for orbital angular momentum(OAM) generation and detection. These metasurfaces
manipulate the electromagnetic (EM) wave by introducing abrupt phase change,
which is strongly dependent on the polarization state of incident EM wave and
can be interpreted by geometric phase. Hence, the conventional bulk devices
that based on the accumulated phase change along the optical path can be
avoided.
