Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: InP femtosecond mode-locked laser in a compound feedback cavity with a
  switchable repetition rate   A monolithically integrated mode-locked semiconductor laser is proposed. The
compound ring cavity is composed of a colliding pulse mode-locking (ML)
subcavity and a passive Fabry-Perot feedback subcavity. These two 1.6 mm long
subcavities are coupled by using on-chip reflectors at both ends, enabling
harmonic mode locking. By changing DC-bias conditions, optical mode spacing
from 50 to 450 GHz is experimentally demonstrated. Ultrafast pulses shorter
than 0.3 ps emitted from this laser diode are shown in autocorrelation traces.

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The categories of this paper are: gr-qc
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The categories of this paper are: nlin
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The categories of this paper are: hep-th
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The categories of this paper are: q-bio
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The categories of this paper are: chao-dyn
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The categories of this paper are: quant-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: cond-mat
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The categories of this paper are: dg-ga
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The categories of this paper are: stat
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The categories of this paper are: adap-org
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The categories of this paper are: hep-lat
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The categories of this paper are: alg-geom
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The categories of this paper are: bayes-an
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The categories of this paper are: cs
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The categories of this paper are: comp-gas