Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Vector modulational instability induced by parametric resonance in
  periodically tapered highly-birefringent optical fibers   We study the modulational instability induced by periodic variations of
group-velocity dispersion and nonlinear coefficients in a highly birefringent
fiber. We observe, for each resonance order, the presence of two pairs of
genuine vector type sidebands, which are spectrally unbalanced between the
polarization components for nonzero group-index mismatch, and one pair of
balanced sidebands emerging and dominating at increasing group-index mismatch.
As the conventional modulational instability manifests itself, it is partially
suppressed by the proximity of these new unstable regions.

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The categories of this paper are: dg-ga
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The categories of this paper are: math-ph
2
The categories of this paper are: math
35
The categories of this paper are: mtrl-th
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The categories of this paper are: nucl-th
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The categories of this paper are: nucl-ex
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The categories of this paper are: stat
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The categories of this paper are: q-bio
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The categories of this paper are: hep-th
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The categories of this paper are: comp-gas
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The categories of this paper are: q-fin
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The categories of this paper are: funct-an
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The categories of this paper are: bayes-an
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The categories of this paper are: hep-lat
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The categories of this paper are: solv-int
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The categories of this paper are: gr-qc