Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Effective Second Order Susceptibility in Photonic Crystals Composed from
  Centro-Symmetric Materials   A technique for obtaining efficient bulk second order susceptibility in non
centro-symmetric Photonic Crystals (PC) made from centro-symmetric materials is
discussed. The effect is based on the electric quadrupole effect, strong
electromagnetic mode deformation and non homogeneous contribution to volume
polarization from different parts of the PC. The required symmetry breaking is
introduced on the macroscale of the PC unit cell. The obtained structural
chi_str^(2) is comparable with the second order susceptibility of ordinary
non-linear materials. Phase matching can be achieved by introducing symmetry
modulation (Quasi Phase Matching) during fabrication of the PC.

23
The categories of this paper are: solv-int
14
The categories of this paper are: math-ph
7
The categories of this paper are: hep-th
30
The categories of this paper are: q-alg
32
The categories of this paper are: atom-ph
26
The categories of this paper are: bayes-an
11
The categories of this paper are: hep-lat
1
The categories of this paper are: cs
21
The categories of this paper are: adap-org
2
The categories of this paper are: math
24
The categories of this paper are: dg-ga
27
The categories of this paper are: comp-gas
12
The categories of this paper are: nucl-th
6
The categories of this paper are: astro-ph
0
The categories of this paper are: hep-ph
10
The categories of this paper are: q-bio