Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Orbital Angular Momentum Generation and Detection by Geometric-Phase
  Based Metasurfaces   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.

10
The categories of this paper are: q-bio
6
The categories of this paper are: astro-ph
15
The categories of this paper are: nucl-ex
34
The categories of this paper are: chem-ph
29
The categories of this paper are: funct-an
28
The categories of this paper are: alg-geom
12
The categories of this paper are: nucl-th
22
The categories of this paper are: chao-dyn
26
The categories of this paper are: bayes-an
18
The categories of this paper are: econ
27
The categories of this paper are: comp-gas
35
The categories of this paper are: mtrl-th
37
The categories of this paper are: supr-con
11
The categories of this paper are: hep-lat
4
The categories of this paper are: cond-mat
9
The categories of this paper are: nlin