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ISSN 2394-3777 (Print)
ISSN 2394-3785 (Online)
Available online at www.ijartet.com
International Journal of Advanced Research Trends in Engineering and Technology (IJARTET)
Vol. II, Special Issue XXIII, March 2015 in association with
FRANCIS XAVIER ENGINEERING COLLEGE, TIRUNELVELI
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
INTERNATIONAL CONFERENCE ON RECENT ADVANCES IN COMMUNICATION SYSTEMS AND
TECHNOLOGIES
(ICRACST’15)
TH
25 MARCH 2015
Modeling of Twin Core Liquid Filled Photonic
Crystal Fiber Coupler with Elliptical Air Holes
1
K.Rohini Priya, 2A.Sivanantha Raja, 3D.Shanmuga sundar,
1
PG Scholar, 2Associate Professor, 3Research Scholar,
1, 2,3
Alagappa Chettiar College of Engineering and Technology,
Karaikudi,

Abstract— Twin core photonic crystal fiber (PCF) couplers are
generally used for dispersion compensation and relatively short
coupling length. In this paper, we have theoretically investigated
the dispersion and the coupling characteristics of twin-core
photonic crystal fiber coupler (PCFC), based on hexagonal-lattice
with the elliptical air-holes of uniform dimension and the effective
core size are modified with a packing of circular air-holes with
liquids. The dependence of the PCFC structural parameters
namely air-hole diameter (d) and hole-to-hole distance () along
with the liquid packing has been investigated in details. By proper
adjustment of the available parameters, a high negative
dispersion value of −10,000 ps/nm/km and short coupling length
(Lc) of 0.0015m has been achieved with different liquid filling
materials. Our proposed fiber will be an excellent device for
wavelength division multiplexing, Dispersion compensation
applications.
Index Terms— Coupling Length (Lc), Dispersion,
Effective Refractive Index (neff), Photonic Crystal Fiber
Coupler (PCFC), Wavelength Division Multiplexing (WDM).
P
I. INTRODUCTION
hotonic crystal fibers are a new class of optical fibers.
They can guide light not only through a well-known
modified total internal reflection (MTIR) mechanism, but
also using a photonic band gap (PBG) effect [1].Conventional
photonic crystal fibers are fibers with an internal periodic
structure made of capillaries, which are filled with air, and laid
to form a hexagonal lattice. Light can propagate along the fiber
in defects of its crystal structure, which are realized by
removing one or more central capillaries. Combining the
properties of optical fibers and photonic crystals they possess a
series of unique properties impossible to achieve in classical
step index fibers [2], [3].
Index-guiding PCFs possess the attractive property of great
controllability in chromatic dispersion by varying the hole
diameter (d) and hole-to-hole spacing (). Control of
dispersion in PCFs is very important problem for realistic
applications of optical fiber communications. Several designs
for the PCF have been proposed to achieve the ultra negative
dispersion properties. So far, various PCFs with remarkable
dispersion properties such as, zero dispersion wavelengths
shifted to the visible and near infrared wavelengths [4], [5],
ultra-flattened chromatic dispersion [6], [7] have been
reported.
A PCF with two adjacent defect areas (serving as two cores)
can be used as an optical coupler [8], [9]. These PCF couplers
can be realized as a multiplexer-demultiplexer (MUXDEMUX). Only coupling lengths of dual-core PCF couplers
were evaluated by using a finite element method [10], [11].
Such photonic crystal fiber couplers (PCFC) favors many of
the exciting light guiding features, when compared to that of
the fiber namely endless single mode operation over a wide
wavelength range, enhanced nonlinearity and desired zero
dispersion wavelength, required coupling length and high
design flexibility for the desired applications. They present an
excellent opportunity to achieve such desired optical
characteristics for required applications by suitable adjustment
of the PCF structure parameters namely air hole diameter, air
hole separation, inter-core separation and core radius.
[12],[13].
Dual core PCFC, where light guided through any one of the
input cores with inter-core separation is of the order of
wavelength, transferred to the neighboring core by the
excitation of the evanescent mode as it propagates [14].
In this paper, we have proposed the dispersion along with
the coupling length of the twin core liquid filled photonic
crystal fiber coupler in which the diameter of air holes is
changed by keeping the d/Λ as fixed facilitates the use of
PCF coupler for wavelength-selective applications.
186
All Rights Reserved © 2015 IJARTET
ISSN 2394-3777 (Print)
ISSN 2394-3785 (Online)
Available online at www.ijartet.com
International Journal of Advanced Research Trends in Engineering and Technology (IJARTET)
Vol. II, Special Issue XXIII, March 2015 in association with
FRANCIS XAVIER ENGINEERING COLLEGE, TIRUNELVELI
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
INTERNATIONAL CONFERENCE ON RECENT ADVANCES IN COMMUNICATION SYSTEMS AND
TECHNOLOGIES
(ICRACST’15)
TH
25 MARCH 2015
II. DESIGN METHODOLOGY
A design of high tunable coupler based on silica PCF with
elliptical air holes and dual liquid crystal core is presented and
analyzed. The suggested design depends on using silica and
liquid crystal (LC) of types chloro benzene and benzene
respectively and the refractive index of the chloro benzene and
benzene is 1.525 and 1.501. In addition, the propagation
through the LC-PCF coupler has taken place by the modified
total internal reflection mechanism due to the index variation
between the core and cladding region.
refractive indexes, Dispersion, Coupling length are calculated
by using finite element method (FEM) with perfectly matched
boundary layers (PML) [15]. The FEM directly solves the
Maxwell equations to get an approximate value of the effective
refractive index. Once the effective refractive index, neff of the
model is obtained by solving Maxwell equations using the
software, dispersion and coupling length of PCFCs can be
calculated easily.
A. Coupling length
The coupling length is defined as the minimum longitudinal
distance at which maximum power is transferred from the left
core to the right core. The coupling length LC can be obtained
using the operating wavelength λ, and effective indices of the
even and odd modes are neven and nodd as follows. The coupling
length is given by
Lc 

2 n even  n odd
Fig.1. Schematic diagram of twin core liquid filled PCFC
Fig 1 shows cross section of the suggested hexagonal lattice
twin core liquid filled PCF coupler. The two identical cores of
diameter have been packed with chloro benzene and benzene.
All the cladding elliptical air holes have the same diameter d
and are arranged with a hole pitch . The separation between
the two identical cores is equal to(c= 2) were optimized to
obtain the desired values of coupling length and dispersion.
The precise coupling length LC of the even and odd stability
biased modes and the dispersion value for the proposed model
is measured.
III. SIMULATION RESULTS AND DISCUSSIONS
We have used COMSOL MULTIPHYSICS software to
investigate the guiding properties of this PCFC. Effective
Fig. 2: Simulation model of twin core liquid filled PCFC
The coupling length of the coupler mainly depends upon the
inter core separation, core radius and transmitting wavelength.
Also the coupling length increases with the increase in the
effective core area because of increase in the inner core
separation. Thus, for increase in the Λ the coupling length also
increases [16]. Increase in coupling length also possesses
higher nonlinearity due to its larger effective core area.
187
All Rights Reserved © 2015 IJARTET
ISSN 2394-3777 (Print)
ISSN 2394-3785 (Online)
Available online at www.ijartet.com
International Journal of Advanced Research Trends in Engineering and Technology (IJARTET)
Vol. II, Special Issue XXIII, March 2015 in association with
FRANCIS XAVIER ENGINEERING COLLEGE, TIRUNELVELI
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
INTERNATIONAL CONFERENCE ON RECENT ADVANCES IN COMMUNICATION SYSTEMS AND
TECHNOLOGIES
(ICRACST’15)
TH
25 MARCH 2015
Fig.3a. Variation of coupling length for different wavelengths of twin core
chlorobenzene filled PCFC
Fig. 3a and 3b shows that the coupling length for different
wavelengths for both chlorobenzene and benzene filled PCFC
and is found to be the maximum for shorter wavelength, due to
the decrease in difference between the even and odd modes
and minimum for longer wavelengths.
Fig.4a. Variation of coupling length with respect to different pitch constants
for twin core chlorobenzene filled PCFC
Fig. 4a and 4b shows that the coupling length for different
pitch constant for both chlorobenzene and benzene filled
PCFC. For smaller pitch values the coupling length increases
due to larger core area whereas the increase in pitch results in
decreased coupling length
B. Dispersion
To design negative dispersion PCFC for wideband
wavelength, we need variable air-hole diameter in the
cladding. The same can be achieved with uniform air-hole
diameter by filling the cores with liquid of certain refractive
indices. Depending on the refractive index of the different
liquids such as chlorobenzene and benzene, the effective size
of the air-hole diameter can be modified. First the effective
indexes neff are solved, and then the dispersion parameter D
can be obtained [17]
D
Fig.3b. Variation of coupling length for different wavelengths of twin core
benzene filled PCFC
2
 d n eff
C  .d
Where c is the velocity of the light in a vacuum and λ is the
operating wavelength [18].
The waveguide dispersion is strongly related to the design
parameters of the PCFs and therefore can be optimized to
achieve desired dispersion properties.
188
All Rights Reserved © 2015 IJARTET
ISSN 2394-3777 (Print)
ISSN 2394-3785 (Online)
Available online at www.ijartet.com
International Journal of Advanced Research Trends in Engineering and Technology (IJARTET)
Vol. II, Special Issue XXIII, March 2015 in association with
FRANCIS XAVIER ENGINEERING COLLEGE, TIRUNELVELI
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
INTERNATIONAL CONFERENCE ON RECENT ADVANCES IN COMMUNICATION SYSTEMS AND
TECHNOLOGIES
(ICRACST’15)
TH
25 MARCH 2015
Fig.4b. Variation of coupling length with respect to different pitch constants
for twin core benzene filled PCFC
Fig.5b. Variation of dispersion with respect to different wavelengths of twin
core benzene filled PCFC
Fig 5a and 5b shows dispersion curves. From the figure
negative dispersion in the range of -10,000 ps/nm.km to-5000
ps/nm.km for wavelength range of 1000 nm to 1800nm is
observed. It is seen that with the structure designed we could
achieve a high negative dispersion. For high values of d/, the
core becomes small and the dispersion becomes more negative
for wavelength between range of 1000nm to 1800nm.
IV. CONCLUSION
In this paper, a three ring hexagonal lattice PCFC with
elliptical air holes having same diameter and the core is filled
with chlorobenzene and benzene is proposed. The designed
dual core PCFC offers ultra negative dispersion in wide range
of wavelength from 1000nm to 1800nm and relatively short
coupling length. The proposed PCFC is easy to fabricate due
to the same size of air holes. This structure design is more
effective and easier because lesser geometrical parameters need to
be optimized. Proposed PCF can be suitable for dispersion
compensation, coupler and non linear applications.
Fig.5a. Variation of dispersion with respect to different wavelengths of twin
core chlorobenzene filled PCFC
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189
All Rights Reserved © 2015 IJARTET
ISSN 2394-3777 (Print)
ISSN 2394-3785 (Online)
Available online at www.ijartet.com
International Journal of Advanced Research Trends in Engineering and Technology (IJARTET)
Vol. II, Special Issue XXIII, March 2015 in association with
FRANCIS XAVIER ENGINEERING COLLEGE, TIRUNELVELI
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
INTERNATIONAL CONFERENCE ON RECENT ADVANCES IN COMMUNICATION SYSTEMS AND
TECHNOLOGIES
(ICRACST’15)
TH
25 MARCH 2015
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