Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Periodically poled thin film lithium niobate microring resonators with a
  second-harmonic generation efficiency of 250,000%/W   Lithium niobate (LN), dubbed by many as the silicon of photonics, has
recently risen to the forefront of chip-scale nonlinear optics research since
its demonstration as an ultralow-loss integrated photonics platform. Due to its
significant quadratic nonlinearity ($\chi^{(2)}$), LN inspires many important
applications such as second-harmonic generation (SHG), spontaneous parametric
down-conversion, and optical parametric oscillation. Here, we demonstrate
high-efficiency SHG in dual-resonant, periodically poled z-cut LN microrings,
where quasi-phase matching is realized by field-assisted domain engineering.
Meanwhile, dual-band operation is accessed by optimizing the coupling
conditions in fundamental and second-harmonic bands via a single pulley
waveguide. As a result, when pumping a periodically poled LN microring in the
low power regime at around 1617nm, an on-chip SHG efficiency of 250,000%/W is
achieved, a state-of-the-art value reported among current integrated photonics
platforms. An absolute conversion efficiency of 15% is recorded with a low pump
power of 115$\mu$W in the waveguide. Such periodically poled LN microrings also
present a versatile platform for other cavity-enhanced quasi-phase matched
$\chi^{(2)}$ nonlinear optical processes.

15
The categories of this paper are: nucl-ex
2
The categories of this paper are: math
34
The categories of this paper are: chem-ph
12
The categories of this paper are: nucl-th
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The categories of this paper are: bayes-an
28
The categories of this paper are: alg-geom
32
The categories of this paper are: atom-ph
8
The categories of this paper are: hep-ex
6
The categories of this paper are: astro-ph
33
The categories of this paper are: plasm-ph
1
The categories of this paper are: cs
23
The categories of this paper are: solv-int
9
The categories of this paper are: nlin
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The categories of this paper are: funct-an
14
The categories of this paper are: math-ph
25
The categories of this paper are: patt-sol