Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Coherent WDM Systems Using in-Line Semiconductor Optical Amplifiers   A theory of nonlinear signal propagation in multi-span wavelength division
multiplexed coherent transmission systems that employ the semiconductor optical
amplifier as in-line amplifiers is presented for the first time. The rigorous
derivation, based on time-domain first-order perturbation theory, is developed
in detail. The end result is the expressions for the signal-to-noise ratio of
the received sampled photocurrent, including contributions from noise,
fiber-induced nonlinear distortions, and amplified-induced nonlinear
distortions.

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The categories of this paper are: hep-ex
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The categories of this paper are: cs
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The categories of this paper are: gr-qc
34
The categories of this paper are: chem-ph
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The categories of this paper are: nlin
25
The categories of this paper are: patt-sol
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The categories of this paper are: acc-phys
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The categories of this paper are: atom-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: solv-int
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The categories of this paper are: astro-ph
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The categories of this paper are: math
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The categories of this paper are: hep-lat
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The categories of this paper are: quant-ph
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The categories of this paper are: eess
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The categories of this paper are: dg-ga