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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
DESIGN AND OPTIMIZATION OF TWO
CHANNEL DROP FILTER BASED ON TWO
DIMENSIONAL PHOTONIC CRYSTAL
1
G.Rajalakshmi, 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— In this paper, the channel drop filter based on
two dimensional photonic crystal is proposed. The shape of
the structure is made of silicon rods with refractive index
n1 =3.46 which are perforated in air with refractive index
n2=1. The simulation results are obtained from Two
Dimensional Finite Difference Time Domain method.
Resonant mode of the ring resonator and the filter
transmission spectrum is calculated using 2D FDTD
method. Two different wavelengths are dropped through
dropping port with the resonance of the ring resonator and
other wavelengths are transmitted through bus waveguide.
Full Width Half Maximum (FWHM) bandwidth of the
filter at the output transmission spectrum of the first ring
from 1.487µm to 1.483µm is 4nm and second ring from
1.502 µm to 1.498µm is also 4nm. The quality factor of the
filter is 269 and 267. The proposed filter design is around
21×15µm which is suitable for photonic integrated circuits.
Index Terms— Photonic crystal ring resonator, FDTD
method, Channel drop filter,
Photonic bandgap, PWE
Solver.
P
I. INTRODUCTION
HOTONIC CRYSTALS are periodic structures composed
of low and high index dielectric materials arranged
respectively. Such optical media have some optical
properties which gives an opportunity for a number of
applications to be implemented on their basis. The most
important one is the band of photons, which is a useful theory
for the understanding of light behavior in a complex photonic
crystal structure. As a result of this periodicity, Photonic
Crystals exhibit an unique optical property, namely photonic
bandgap (PBG) where the electromagnetic modes propagation
is absolutely zero due to reflection. Hence, the density of
states becomes negligible. By introducing a defect (point or
line or both) in these structures, the periodicity and
completeness of the bandgap are broken and the propagation
of light can be localized in the Photonic Band Gap region. The
PBG region in 2D Photonic Crystals depends on the refractive
index of the dielectric materials, the shape and radius of the
rods, the crystal structure and the lattice constant of the
structure.
The optical channel add drop filter is one of the fundamental
building blocks for optical add drop multiplexers (OADMs),
reconfigurable OADMs and optical switches needed for
silicon photonics, photonic integrated circuits (PICs), and
wavelength
division
multiplexed
(WDM)
optical
communication systems. One of the most promising designs
for wave guided drop filters is the strip-based (or rib-based)
micro-ring resonator wherein a circulating mode in the ring is
excited by the coupling of the forward propagating wave in a
nearby bus waveguide. Very high spectral selectivity can be
achieved due to the high resonator quality factor Q and the
ring’s intrinsic single mode nature. The backward or forward
dropping of the resonant modes in the ring cavity can be
realized by the bus/ring coupling scheme and by choosing the
number of rings within the channel drop filter. Here the silicon
based ring resonator, the radiation loss increases while
decreasing the ring radius. In addition, the performance of
stripe waveguide micro-ring resonators is highly sensitive to
the surface roughness and the nanoscale gap between the ring
resonator and the bus waveguide, which produces another
challenge in manufacturing. Photonic crystal (PC) structures,
can overcome these challenges because they have the potential
to achieve high Quality factor, low-loss resonators in ultracompact cavities. The Photonic Crystal structure offers very
high spectral selectivity, efficient wavelength selection,
195
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
scalability, narrow line width and flexible mode design.
Wavelength selective active and passive PC devices have been
proposed based on various point and line defect photonic
crystal linear and ring waveguide cavities. One is a low
refractive index waveguide with low contrast between core
and clad. This type of waveguides has advantages such as low
propagation loss, low coupling loss and low dispersion. A
multichannel-drop filter using photonic crystal ring resonator
is the most recent work, two different structures have been
proposed for designing optical channel-drop filters using
photonic crystal ring resonators.
In this paper, two different shape of photonic crystal ring
resonator based channel drop filter is proposed and designed.
Two different rings are used for dropping the different
wavelengths through dropping waveguide. It is efficient for
dropping the multiple wavelengths. To design the proposed
channel drop filter, the silicon rods are arranged by 0.3µm
major and minor radius. The photonic band gap region is
calculated using plane wave expansion solver method. The
two dimensional Finite difference time domain methods have
been employed to obtain the wavelength response of the filter.
II.STRUCTURE DESIGN
The design in this paper is based on two dimensional
hexagonal lattice of silicon rods (refractive index n=3.46) in
an air background (n=1). The distance between two adjacent
rods is 0.9µm, which is termed as lattice constant. It is denoted
by “a”. The number of rods in the x and y directions are 17
and 19 respectively. The Photonic crystal structure has a PBG
for Transverse Electric (TE) mode. The band diagram of the
filter shows the frequency range 0.22a/λ to 0.32a/λ which
defines the wavelength, the wavelength corresponding to the
bandgap is 1.33µm to 1.9µm. Second PBG span expands
from 0.4a/λ to 0.5a/λ, the wavelength corresponding to the
span is 2.4µm to 3.0µm.
The proposed channel drop filter is composed of three parts:
one line defect as the bus waveguide (the upper one), the drop
waveguide (the lower one) is placed at the end of the ring and
the resonant ring located between the waveguides. Also it has
four ports, among them ports A and B input and output
transmission terminals whereas ports C and D are dropping
terminals respectively. For creating the resonant ring, we first
removed the 25 silicon rods in the middle of layout. The
radius of the rod is 0.3µm which is r=0.3a. The refractive
index of these dielectric rods is the same as the refractive
index of the initial structure, which is n= 3.46. The schematic
diagram of the ring resonator is shown in figure1.
Fig 1. Schematic layout of ring resonator based CDF
Photonic band gap’ (PBG) is a term applicable to dielectric
media which possess alternate regions of low and high
refractive index such that transmission of ‘photons’ or light
energy of certain frequencies is forbidden. The band gap
analysis of the filter which is done by plane wave expansion
method Using PWE Band Solver of FDTD tool. Here
vertical input plane must be considered for the band gap
analysis.
FDTD method allows for the effective and powerful
simulation and analysis of sub-micron devices with very fine
structural details. Finite difference time domain (FDTD) is
another numerical method used for studying the optical
properties of Photonic crystals. FDTD can be used for
obtaining the distribution patterns of optical waves and the
transmission properties of Photonic crystal based devices.
Obtaining accurate results from FDTD simulations requires
choosing proper values for mesh sizes and the time step of the
FDTD calculations. FDTD method is used to simulate the PC
structure and the Perfect Matched Layer (PML) is placed as
absorbing boundary condition. The PWE method is used to
calculate the PBG of the PC structure with and without
introducing the defects.
II. SIMULATION RESULTS
The structure used in this paper is 2D hexagonal lattice
photonic crystal of Si rods in air host. Refractive index of Si is
196
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
3.46, the radius of the 0.3µm and lattice constant of the
structure is 0.9µm. The polarization of the signal in our
simulation is TE. The spectrum of the power transmission is
obtained with finite difference time domain (FDTD) method.
Perfect matched layers (PMLs) are used around the CDF
structure. The power transmission spectra are computed by
taking the FFT of the fields that calculated by FDTD
incorporating with integrating the pointing vector over the
cells of the output ports.
One of the most important features of any filter is tunability.
Here we investigate parameters which affect resonant
frequency in photonic crystal CDFs. If we change the radius of
the rods more wavelengths will be dropped through the
dropping waveguide. A Gaussian input signal is launched into
the input port. The normalized transmission spectra of port ‘B’
is obtained by conducting Fast Fourier Transform (FFT) of the
fields that are calculated by FDTD method. In this design, the
first ring will resonant at λ=1.485µm and the second ring will
resonant at λ=1.5µm after that the signals are dropped by the
corresponding waveguides. Using finite difference time
domain (FDTD), we simulated the proposed structure and
obtain the output transmission of the filter. Three dimensional
structure of the filter design is required to achieve accurate
results, but it is very time consuming and needs very powerful
computer systems. The effective refractive index method is
used to reduce the 3D calculation to 2D with minimum errors.
Fig 2. Electric field intensity of the filter at λ=1.5µm
The output spectra, which is suitable for obtaining the
bandwidth and crosstalk values of the channels. The proposed
design of the filter resonance at 1.485µm and 1.50µm dropped
out through the port C and port D. Transmission spectra of the
resonator are calculated using PWE solver. Quality factor of
the filter is calculated using the expression
Q=λ0/∆λ
→ (1)
Fig 3. Electric field intensity of the filter at λ=1.486µm
For PWE band solver, we had considered PC of two
dimensional structures with TE polarization. The PWE band
solver simulation is done for our proposed design and band
gaps are observed. The PWE band solver has taken 2D
structure and TE polarization. The mesh delta size is 0.1µm
µm in horizontal and vertical direction and the mesh delta
cells in the x and z direction are 150 and 210. As a result two
band gaps are obtained and it is represented in fig.5
197
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
Figure 6 which indicates that optical signals in all the
wavelengths will go toward port B except the wavelength
λ=1.5µm in which optical signals will get dropped at the
drop waveguide of port C and no output signal at port D.
Fig 4. Band structure of the filter for 0.1 tolerance value
Fig 7. Transmission spectra of PCRR channel drop filter.
Figure 7 which indicates that optical signals in all the
wavelengths will go toward port B except the wavelength
λ=1.5µm in which optical signals will get dropped at the
drop waveguide of port D and no output signal at port C.
III. CONCLUSION
Fig 5. Band structure of the filter for 0.01 tolerance value
In this paper, we have designed two different shape of
photonic crystal ring resonator based channel drop filter.
Resonant modes of the ring resonator and their corresponding
photonic band gaps are calculated using PWE band solver.
Also, the filter transmission spectrum of the system is
calculated using 2D FDTD numerical method. Full width half
maximum (FWHM) bandwidth of the filter for two rings is
4nm. The quality factor of the filter is 267and 269. The
proposed filter design is around 21×15µm which is suggested
for photonic integrated circuits.
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[1] Steven G. Johnson, Joshua N.winn, John D. Joannopoulus“Modeling
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and
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[3] M. Djavid, A.Ghaffari, and F.monifi“T-shaped channel drop filters using
photonic crystal ring resonator” journal of Physica E 40 (2008) 3151– 3154.
Fig 6. Transrmission spectra of PCRR channel drop filter.
198
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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