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

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

 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

internal media

column

input waveguide

output

waveguide

scatter

ng me

a co

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 4×3 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

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

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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PHOTOPTICS2015-InternationalConferenceonPhotonics,OpticsandLaserTechnology