The Influence of Structure Parameters on Terahertz Wave Filter
based on Photonic Crystal Ring Cavity
Xiaoying Wei, Heming Chen
*
and Wen Zhou
_________________________
*
corresponding author e-mail: chhm@njupt.edu.cn
Nanjing University of Posts and Telecommunications, Nanjing, Jiangsu, China
Keywords: THz Communication, Filter, the Finite Difference Time Domain Method, Photonic Crystal Ring Cavity,
WDM.
Abstract: Terahertz (THz) communication has important applications in high-speed and ultra-broadband wireless
access networks. THz filter is one of the key device of WDM communications. THz filter based on ring
cavity photonic crystal (TFRCPC) has many advantages such as simple structure, high integration and high
flexibility. According to the coupling characteristics of waveguide and ring cavity, a novel structure of
TFRCPC was proposed in this paper, the TFRCPC consists of 4×3 internal dielectric cylinder with four
scattering dielectric cylinder. The influence of structure parameters of TFRCPC is mainly studied. The
simulation results show that, on the basis of basal material of Si and lattice constant of 30μm, when the radius
of dielectric cylinder is 5.7368μm, the radius of 4×3 internal dielectric cylinder is 3.5μm, the radius of
scattering dielectric cylinder is 5μm, the wave at 83.535μm wavelength can go through the structure with the
transmittance of 0.97674.
1 INTRODUCTION
Terahertz (THz) wave refers to the electromagnetic
wave whose frequency is between 0.1~10THz
(30μm~3mm), which is located between millimeter
wave and infrared wave (Hu and Chen, 2008). It is
the transition area between electronics and photonics.
Terahertz communication devices have become the
study hotspot in recent years. Banmali S.Rawat* et
al. put forward 5G mobile communication should be
realized in THz wave band in 2013 (Banmali et al.,
2013). In 2014, G. Ducournau et al. (Ducournau,
Yoshimizu et al., 2014) put forward the high
performance of coherent THz wave in receiver data
rate and sensitivity, so that terahertz communication
could provide with high data rate services. The plane
coupling structure composed of waveguide and
resonant cavity has become a common THz filter
structure (Su and Chen, 2010). Ring cavity has many
advantages such as simple structure high integration
and strong flexibility. It can achieve many functions
such as filtering, splitting, WDM and so on (Guo,
Fang, Wu et al., 2010).In 2009, Yaw- Dong Wu et al.
has proposed a filter with high Q value which was
based on photonic crystal ring cavity (Wu, Shih et
al., 2009). The Q value was 3800, and the
transmittance was 92%, but the structure was
complex. It could filter the wave of 1550 nm.
This paper proposes a TFRCPC which consists
of 4×3 internal dielectric cylinder with four
scattering dielectric cylinder. By changing the radius
of internal dielectric cylinder and its refractive
index, the radius of scattering dielectric cylinder, the
coupling intensity of the light in the ring cavity can
change. Then it can filter the waves of different
wavelengths according to different structures.
Finally, the Q value of the filter is up to 3977.86, the
transmittance of 83.535μm is 0.97674.
2 STRUCTURE DESIGN
The parameters of the TFRCPC proposed in this
paper are set as follows: refractive index of silicon
dielectric cylinder material n=3.4, radius of
dielectric cylinder r=5.7368μm, lattice constant
a=30μm. Because tetragonal crystal lattice has high
symmetry, a ring cavity structure can get better
transmission performance. The bandgap of photonic
crystal structure can be acquired by the plane wave
73
Wei X., Chen H. and Zhou W..
The Influence of Structure Parameters on Terahertz Wave Filter based on Photonic Crystal Ring Cavity.
DOI: 10.5220/0005290600730076
In Proceedings of the 3rd International Conference on Photonics, Optics and Laser Technology (PHOTOPTICS-2015), pages 73-76
ISBN: 978-989-758-093-2
Copyright
c
2015 SCITEPRESS (Science and Technology Publications, Lda.)
expansion method (Yang, Xu, Ye et al., 2011). The
range of the normalized frequency a/λ is
0.29334~0.43124. The range of corresponding band
gap of photonic crystal is about 69.57μm
~102.27μm. Removing part of the dielectric cylinder
from the complete photonic crystal to form a straight
waveguide as an input waveguide, there are two
rows of columns between the photonic crystal
waveguide and a ring cavity. Output waveguide is
vertical to the input waveguide, as shown in Figure
1.
internal media
column
input waveguide
output
waveguide
scatter
i
ng me
di
a co
l
umn
Figure 1: The structure of TFRCPC.
3 THE INFLUENCE OF
STRUCTURE PARAMETERS
ON THZ FILTER
PERFORMANCE
3.1 The Influence of Internal Dielectric
Cylinder Radius
By changing the radius of internal dielectric
cylinder, the resonance wavelength can be changed.
Then different wavelengths of THz waves can go
through the output waveguide. On the basis of 4×3
internal dielectric cylinder, we study the influence of
transmission spectrum when the radius of internal
dielectric cylinder changes from 3.49μm to 3.52μm,
as shown in Figure 2. The radius of internal
dielectric cylinder from left to right is 3.49μm,
3.5μm, 3.51μm, 3.52μm respectively.
As can be seen from Figure 2, when the radius of
dielectric cylinder increases, the transmission
spectrum moves to long wavelength direction. When
the radius of internal dielectric cylinder is 3.5μm,
Figure 2: The influence of internal dielectric cylinder
radius on the transmission spectrum.
the transmission spectrum peak of the THz wave at
83.535μm wavelength is the highest.
3.2 The Influence of Scattering
Dielectric Cylinder Radius
By changing the radius of the scattering dielectric
cylinder in the ring cavity, the output wavelength
will change. On the basis of 3 internal dielectric
cylinder, by introducing four scattering dielectric
cylinder, we study when the radius of internal
dielectric cylinder is 3.5μm, the impact on the
transmission spectrum when the radius of scattering
dielectric cylinder changes from 4.5μm to 6μm, as
Figure 3: The influence of internal scattering dielectric
cylinder radius on the transmission spectrum.
PHOTOPTICS2015-InternationalConferenceonPhotonics,OpticsandLaserTechnology
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shown in Figure 3. The radius of scattering dielectric
cylinder from high to low is 5μm, 5.5μm, 4.5μm,
6μm respectively.
Figure 3 shows that when the radius of internal
dielectric cylinder is 3.5μm, transmission spectrum
moves to long wavelength direction when the radius
of scattering dielectric cylinder increases; when the
radius of scattering dielectric cylinder is 5μm, the
transmission spectrum peak of the THz wave which
wavelength is 83.535μm is the highest.
3.3 The Influence of Internal Dielectric
Cylinder Material
By changing the internal dielectric cylinder material
in the ring cavity, the output wavelength will also
change. When the radius of internal dielectric
cylinder is 3.5μm, internal dielectric cylinder uses
GaAs whose refractive index is 3.55. When the
radius of scattering dielectric cylinder is 5μm, the
wave which can go through the structure is different
from the one whose internal dielectric cylinder is
made of Si, as shown in Figure 4.
Figure 4: The influence of internal dielectric cylinder
material on the transmission spectrum.
Figure 4 shows that when the radius of internal
dielectric cylinder is 3.5μm, the radius of scattering
dielectric cylinder is 5μm, internal dielectric
cylinder uses GaAs whose refractive index is 3.55,
the THz wave which wavelength is 82.866μm can
penetrate. If internal dielectric cylinder uses Si, the
wavelength of 83.535μm can penetrate.
4 THE TRANSMITTANCE OF
FILTER
Based on FDTD of Rsoft software simulation, the
results show that the basal material adopts silicon,
lattice constant is 30μm, the radius of dielectric
cylinder is 5.7368μm, the radius of internal column
is 3.5μm, the radius of scattering dielectric cylinder
is 5μm, the wave which wavelength is 83.535μm can
penetrate. The Q value is as high as 3977.86, the
transmittance is as high as 0.97674, the time domain
steady state response and corresponding steady state
mode field distribution are shown in Figure 5 and
Figure 6.
Figure 5: The figure of time domain steady state response
when the incident wavelength is 83.535μm.
Figure 6: The steady mode field distribution when the
incident wavelength is 83.535μm.
5 CONCLUSIONS
A novel TFRCPC which has 4×3 internal dielectric
cylinder and four scattering dielectric cylinder is
TheInfluenceofStructureParametersonTerahertzWaveFilterbasedonPhotonicCrystalRingCavity
75
proposed in this paper. By changing the radius and
refractive index of internal dielectric cylinder, the
waves of different wavelengths can go through the
filter. The radius of the scattering dielectric cylinder
has an impact on the transmittance of the
wavelength (Yang, Xu, 2010). The Q value of the
final filter is as high as 3977.86, the transmittance of
the wave which wavelength is 83.535μm is 0.97674.
Compared with the TFRCPC in the literature (Wu,
Shih et al., 2009), this filter’s transmittance is
higher. This terahertz wave filter with ring cavity
has important significance for the future THz wave
division multiplexing communication system (Chen
and Wei, 2013).
ACKNOWLEDGEMENTS
This work was supported by the National Natural
Science Foundation of China (project No.
61077084).
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