COL 9(10), 100609(2011) CHINESE OPTICS LETTERS Octob er 10, 2011
Highly birefringent octagonal photonic crystal fibers with
two zero-dispersion wavelengths
Changming Xia (夏夏夏长长长明明明)
1∗
, Guiyao Zhou (周周周桂桂桂耀耀耀)
1,2
, Ying Han (韩韩韩 颖颖颖)
1
, and Lantian Hou (侯侯侯蓝蓝蓝田田田)
1
1
State Key Laboratory of Metastable Materials Science and Technology, Yanshan University,
Qinhuangdao 066004, China
2
Scho ol of Information and Optoelectronic Science and Engineering, South China Normal University,
Guangzhou 510006, China
∗
Corresp onding author: xiacmm@126.com
Received March 14, 2011; accepted May 9, 2011; posted online August 5, 2011
A new highly birefringent octagonal photonic crystal fiber (Hi-Bi OPCF) with a rectangular array of four
elliptical airholes in the fiber core region is proposed and analyzed using the full-vector finite element
metho d with anisotropic perfect match layer absorbing boundaries. Numerical results show that the
phase birefringence of the photonic crystal fiber (PCF) reaches 3.43×10
−2
at the wavelength of 1 550 nm.
Moreover, two zero-dispersion wavelengths are achieved in the visible and near infrared wavelength regions
for one polarization state but not in the other.
OCIS codes: 060.2400, 060.2280.
doi: 10.3788/COL201109.100609.
Photonic crystal fibers (PCFs)
[1−3]
have a wavelength-
scale periodic silica-air microstructure around the core
along their length, providing much more degrees of free-
dom for tailoring the properties of PCF, such as chro-
matic dispersion
[4,5]
, confinement loss
[6]
, nonlinear
[7]
,
and birefringence. As a result, it is also possible to
fabricate a highly birefringent PCF by introducing suit-
able airholes in cladding
[8,9]
. Recently, great attention
has been devoted to the enhancement of birefringence of
PCF
[10−13]
, because the highly birefringent polarization
maintaining PCFs have been widely used in the fiber
communication systems and sensing applications
[14,15]
.
Some highly birefringent hexagonal PCFs have been pro-
posed by introducing an asymmetric structure
[12,13,16]
.
An et al.
[17]
reported an ultrahigh birefringent hexagonal
PCF with ultralow confinement loss using four airholes in
the core, An ultrahigh mode birefringence is realized with
a mode birefringence of up to 10
−2
. Moreover, hexagonal
photonic bandgap fibers (PBGFs) with asymmetric air
cores have also been suggested in high birefringence
[18]
.
However, there are few reports for highly birefringent oc-
tagonal PCFs (OPCFs). OPCFs have isosceles triangu-
lar unit lattices with a vertex angle of 45
◦
; for the same
numbers of air-hole rings in cladding, OPCFs have more
airholes than the conventional hexagonal PCF, resulting
in an increase in the air-filling ratios
[19,20]
. Due to these
properties, the birefringence of OPCF is very sensitive to
the structure.
In this letter, we numerically explore the possibility of
designing a highly phase birefringent OPCF. Simulation
results show that the phase birefringence of the OPCF is
3.43×10
−2
at the wavelength of 1 550 nm. To the best of
our knowledge, this is the first theoretical demonstration
of such high level of phase birefringence for microstruc-
tured optical fibers. Due to the abovementioned proper-
ties, the proposed OPCFs in this letter have many optical
applications in future.
The cross-section of the proposed OPCF is shown in
Fig. 1. The cladding consists of an octagonal lattice
with circular airholes in fused silica. The diameters of
the first-ring airholes and the outer-ring airholes are d
1
and d
2
, respectively. In order to obtain high birefrin-
gence, a rectangular array of four elliptical airholes was
introduced in the core region. These holes were identical,
with their diameters along the x- and y-axis denoted as
a and b, respectively. The pitched between the holes in
the vertical and horizontal directions were labeled as Λ
1
and Λ
2
, respectively.
Due to the high refractive index contrast and complex
structure, it is very difficult to obtain the simulation re-
sults for PCFs. Many modeling techniques have been
applied in their characterization, including the finite
element methods (FEMs)
[21,22]
, plane-wave expansion
method
[23,24]
, finite difference time domain method
[25]
,
and multipole method
[26]
. In this letter, FEM with
anisotropic perfectly matched layer (PML)
[27]
boundaries
were used to calculate the modal complex effective refrac-
tive index n
eff
by solving an eigenvalue drawn from the
following Maxwell equation with a magnetic field:
∇ × (ε
−1
γ
∇ × h) − k
2
0
µ
γ
h = 0, (1)
where h is the magnetic field; ε
γ
and µ
γ
are the relative
Fig. 1. Cross-section geometry of the proposed high birefrin-
gence OPCF.
1671-7694/2011/100609(4) 100609-1
c
° 2011 Chinese Optics Letters