Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Frenet-Serret analysis of helical Bloch modes in N-fold rotationally
  symmetric rings of coupled spiralling optical waveguides   The behavior of electromagnetic waves in chirally twisted structures is a
topic of enduring interest, dating back at least to the invention in the 1940s
of the microwave travelling wave tube amplifier and culminating in contemporary
studies of chiral metamaterials, metasurfaces, and photonic crystal fibers
(PCFs). Optical fibers with chiral microstructures, drawn from a spinning
preform, have many useful properties, exhibiting for example circular
birefringence and circular dichroism. It has recently been shown that chiral
fibers with N fold rotationally symmetric (symmetry group CN) transverse
microstructures support families of helical Bloch modes (HBMs), each of which
consists of a superposition of azimuthal Bloch harmonics (or optical vortices).
An example is a fiber with N coupled cores arranged in a ring around its
central axis (N core single ring fiber). Although this type of fiber can be
readily modelled using scalar coupled mode theory, a full description of its
optical properties requires a vectorial analysis that takes account of the
polarization state of the light particularly important in studies of circular
and vortical birefringence. In this paper we develop, using an orthogonal two
dimensional helicoidal coordinate system embedded in a cylindrical surface at
constant radius, a rigorous vector coupled mode description of the fields using
local Frenet Serret frames that rotate and twist with each of the N cores. The
analysis places on a firm theoretical footing a previous HBM theory in which a
heuristic approach was taken, based on physical intuition of the properties of
Bloch waves. We believe this study provides clarity in what can sometimes be a
rather difficult field, and will facilitate further exploration of real-world
applications of these fascinating waveguiding systems.

0
The categories of this paper are: hep-ph
37
The categories of this paper are: supr-con
8
The categories of this paper are: hep-ex
27
The categories of this paper are: comp-gas
21
The categories of this paper are: adap-org
9
The categories of this paper are: nlin
17
The categories of this paper are: q-fin
34
The categories of this paper are: chem-ph
2
The categories of this paper are: math
4
The categories of this paper are: cond-mat
19
The categories of this paper are: eess
14
The categories of this paper are: math-ph
1
The categories of this paper are: cs
5
The categories of this paper are: gr-qc
31
The categories of this paper are: ao-sci
32
The categories of this paper are: atom-ph