Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Coupling silica waveguides to photonic crystal waveguides through
  multilayered Luneburg lens   We present a detailed analysis of a coupler based on the Luneburg lens to
couple a silica waveguide to a photonic crystal waveguide. The dependence of
coupling efficiency on the lens's truncation, cut position of the photonic
crystal structure, coupler tip width, and misalignment are investigated with
two-dimensional finite element method. We implement the lens with a concentric
ring-based multilayer structure. We also present a method to replace layers
with very narrow widths by layers of predetermined minimum widths in the
structure of the lens. The coupling loss of the designed 2.7 $\mu m$-long
coupler, connecting a 2.79 $\mu m$-wide silica waveguide to a photonic crystal
structure with a rod-type square lattice, is lower than 0.49 dB in the C-band.
The average coupling loss in the entire S, C, L, and U bands of optical
communications is 0.70 dB.

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The categories of this paper are: quant-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: hep-th
29
The categories of this paper are: funct-an
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The categories of this paper are: dg-ga
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The categories of this paper are: nlin
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The categories of this paper are: nucl-ex
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The categories of this paper are: hep-ex
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The categories of this paper are: supr-con
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The categories of this paper are: acc-phys
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The categories of this paper are: bayes-an
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The categories of this paper are: alg-geom
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The categories of this paper are: cmp-lg
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The categories of this paper are: chem-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: atom-ph