Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Periodic thin-film interference filters as one-dimensional photonic
  crystals   We review photonic band gap related properties of a simple periodic system of
thin dielectric layers. Properties associated with forbidden and allowed bands
of such one-dimensional photonic crystals are presented. A revision of
forbidden bands properties leads to an omnidirectional Bragg mirror design. The
anisotropy of allowed bands suggests the formation of photon-focusing caustics
in one-dimensional photonic crystals.

11
The categories of this paper are: hep-lat
19
The categories of this paper are: eess
6
The categories of this paper are: astro-ph
18
The categories of this paper are: econ
23
The categories of this paper are: solv-int
14
The categories of this paper are: math-ph
12
The categories of this paper are: nucl-th
9
The categories of this paper are: nlin
35
The categories of this paper are: mtrl-th
25
The categories of this paper are: patt-sol
8
The categories of this paper are: hep-ex
30
The categories of this paper are: q-alg
3
The categories of this paper are: physics
20
The categories of this paper are: acc-phys
15
The categories of this paper are: nucl-ex
13
The categories of this paper are: quant-ph