Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spectral singularities of a potential created by two coupled microring
  resonators   Two microring resonators, one with gain and one with loss, coupled to each
other and to a bus waveguide, create an effective non-Hermitian potential for
light propagating in the waveguide. Due to geometry, coupling for each
microring resonator yields two counter-propagating modes with equal
frequencies. We show that such a system enables implementation of many types of
scattering peculiarities, which are either the second or fourth order. The
spectral singularities separate parameter regions where the spectrum is either
pure real or else comprises complex eigenvalues; hence, they represent the
points of the phase transition. By modifying the gain-loss relation for the
resonators such an optical scatterer can act as a laser, as a coherent perfect
absorber, be unidirectionally reflectionless or transparent, and support bound
states either growing or decaying in time. These characteristics are observed
for a discrete series of the incident-radiation wavelengths.

17
The categories of this paper are: q-fin
24
The categories of this paper are: dg-ga
22
The categories of this paper are: chao-dyn
20
The categories of this paper are: acc-phys
33
The categories of this paper are: plasm-ph
4
The categories of this paper are: cond-mat
31
The categories of this paper are: ao-sci
26
The categories of this paper are: bayes-an
8
The categories of this paper are: hep-ex
29
The categories of this paper are: funct-an
25
The categories of this paper are: patt-sol
10
The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
19
The categories of this paper are: eess
16
The categories of this paper are: stat
28
The categories of this paper are: alg-geom