Polarization Splitterwith Holey Fibers
using the Vector Finite Element MethodApplicationsOverview

 Passive optics

Elliptical-hole core circular-hole holey fibers (EC-CHFs) can beengineered to provide absolutely single polarization transmission [1].
Along with a more conventional circular-hole core circular-holey fiber(CC-CHF), a polarization splitter can be designed that will couple
light from an incident CC-CHF into either an EC-CHF that supports
an x-polarized mode or into another EC-CHF that supports a ypolarized mode, such as the structure presented below.

 Single-polarization transmission
 Polarization splitters Photonic crystal fibers
 Polarization division multiplexing
 Dispersion control

Scripted Layout GenerationBenefits TheVector Finite Element Method (VFEM) is
extraordinarily
accurateincalculating
allelectromagnetic field components and approximatinggeometry, which is of utmost importance in photoniccrystal fibers

 Uniaxial perfectly matched layers (UPML) can be used

to find leaky modes Triangularmesh size can be adapted to accurately
approximate electromagnetic field and waveguide geometry

 Exploiting the symmetry of the waveguide, the simulation

domain can be reduced and modes with certain symmetries
can be targetedSimulation Description
The goal of the reference [1] was to design a polarization
splitter with the layout given on the reverse side. The
splitter is made up of 3 separate holey fibers. The twoouter holey fibers each support a single polarization,
while the center structure supports both polarizations.
Incident light will selectively couple to either one of theouter holey fibers depending on its polarization.
The first step of the procedure is to phase match themodes of each structure to reduce any reflections [1].
The different structures must share some properties, likepitch and cladding atoms. Within the core of eachstructure, there is freedom in choosing the size andshape of the holes.

(a)

(b)

Figure 2: Magnetic field distribution of superstructure’s even mode y-polarization(c)Figure 1: Dominant magnetic field distribution for each type of core.
(a) yEC-CHF, (b) xEC-CHF, (c) CC-CHF

Using the properties given in [1], the modal indices of thethree different cores were calculated with OptiMode andrecorded in Table 1. These results provide excellent
agreement with the results demonstrated in [1], where all
three structures share the modal index of 1.31043.

Figure 3: Magnetic field distribution of superstructure’s even mode x-polarization

Putting the three cores together into a superstructure, results in a
waveguiding structure that supports both polarizations, with eachpolarization having even and odd modal solutions. The even modal
solutions are presented in Figure 2 and Figure 3. The coupling
length is then given by:

Table 1: Modal indices of single core structures

Structure
CC-CHF
xEC-CHF
yEC-CHF

Modal index by
OptiMODE
1.310431.310411.31043

Zhang et al. [1]1.310431.310431.31043

whereandare the modal indices of the even and odd
modes in Table 2. The coupling lengths calculated with OptiMODE
are compared to those of [1] in Table 3.
Table 3: Coupling length of polarization splitter

Polarization
x-pol
y-pol

Table 2: Modal indices of superstructures

ModeType
Even Mode(x-pol)
Odd Mode(x-pol)Even Mode(y-pol)
Odd Mode(y-pol)Modal index byOptiMODEZhang et al. [1]1.3109451

1.311040

1.3097384

1.309825

1.3109755

1.310982

1.3097233

1.309736(μm) byOptiMODE
642619(μm) Zhang et al. [1]638622

These results confirm that the VFEM mode solver in OptiMode canbe used to design and simulate holey fiber type structuresconfidently and accurately.

References[1]

Z. Zhang, Y. Tsuji, and M. Eguchi, “Design of Polarization Splitter
With Single-Polarized Elliptical-Hole Core Circular-Hole Holey Fibers,”
IEEE Photonics Technol. Lett., vol. 26, no. 6, pp. 541–543, Mar. 2014.