ALPS9-2(invited)
The 5th Advanced Lasers and Photon Sources (ALPS’16), Yokohama, Japan, May. 17 - May. 20, 2016

Terahertz Component Platforms Inspired by Metamaterials
Takehito Suzuki11) Department of Electrical and Electronic Engineering, College of Engineering,

Ibaraki University, 4-12-1 Nakanarusawa, Hitachi, Ibaraki 316-8511, Japan
Abstract: Terahertz metamaterials make unprecedented refractive indices possible and open up the potential of terahertz components
with on-demand electromagnetic properties. We demonstrate a wide range of refractive indices from 11.3 to −5.1 in the terahertz
waveband, including a refractive index near zero. We have also produced extreme-sensitivity terahertz polarizers and a terahertz
quarter-wave plate. These metamaterials can provide a variety of path-breaking applications and develop terahertz component
platforms for terahertz science and technology.

1. Introduction
The recent rapid advances in terahertz science andtechnology puts stress on demands for high-performanceand convenient optical elements with properties
exceeding those of conventionally possible naturallyavailable compounds. However, naturally occurring
materials are extremely limited in the terahertz
waveband when considering the performance losses theygive rise to, and it is not straightforward to simply
produce materials with arbitrary refractive indices. Here,inspired by the possibilities of metamaterials, wedemonstrate unprecedented refractive indices in theterahertz waveband and the first steps in thedevelopment of terahertz component platforms for awide range of potential applications, such as imaging
and wireless communication.
2. Terahertz Metamaterials
Figures 1 and 2 [1] show terahertz metamaterials withextremely high refractive indices and low reflections bypaired cut metal wires on the front and back surfaces in asymmetric alignment. These properties can be achievedby simultaneous control of permittivity and permeability.
Figures 3 [2], 4 [3], 5, and 6 [4] show artificial dielectric
terahertz lenses with the control of only permittivity
which have been utilized in the microwave band insteadof bulk dielectric lenses. Figure 6 shows a terahertz
epsilon-near-zero (ENZ) structure controlled by holes on
the metal slits, here the dimensions of the holes canarbitrarily generate designs of an effective refractiveindex between 0 and 1. Figure 7 shows a structure with arefractive index near zero and with nearly perfecttransmission achieved by the simultaneous control ofpermittivity and permeability. Figures 8 [5] and 9 showterahertz metamaterials with negative refractive indices,and Fig. 9 achieves a negative refractive index above 1.0THz.

n≈3.3(0.48 THz)

Fig. 3. Artificial dielectric multilayer terahertz lens withrectangular metal chips.

n=1.32(0.52 THz)

Fig. 4. Terahertz path-length lens consisting of anoblique metal slit array

n=0.51(0.5 THz)

Fig. 5. Terahertz ENZ array antenna with concave cutthrough metal slits.
Metal plate

n=11.3+j0.91(0.31 THz)
R=2.1% T=75%

Fig. 1. Extremely high refractive index and low
reflection by symmetrically aligned paired cut metalwires.

n=6.7+j0.12(0.31 THz)
R=1.2% T=92%

Fig. 2. High refractive index and low reflection bysymmetrically aligned paired cut metal wires.

Hole array

Hole0<n<1(0.5 THz)

Fig. 6. Terahertz ENZ array antenna with holes.

n=0.11+j0.26(0.5 THz)
T≈100%

Fig. 7. Refractive index near zero and nearly perfecttransmission by symmetrically aligned paired cut metalwires.

ALPS9-2(invited)
The 5th Advanced Lasers and Photon Sources (ALPS’16), Yokohama, Japan, May. 17 - May. 20, 2016

n=-4.4+j0.25(0.42 THz)

Fig. 8. Negative refractive index by asymmetricallyaligned paired cut metal wires.

n=-5.1+j0.61(1.05 THz)

Fig. 9. Negative refractive index above 1.0 THz bysymmetrically aligned paired cut metal wires.
3. Terahertz componentsFigures 10 [6] and 11 [7] show terahertz polarizers GoISⓇ
consisting of laminated dielectric films with copperlayers and a hollow cut-through metal slit array withgold layers. The terahertz polarizers consisting of therobust structures compared with fragile conventionalpolarizers can achieve both high extinction ratios below
approximately −50 dB and transmission power withapproximately 80%. Figure 12 shows a terahertz quarterwave plate with symmetrically aligned paired cut metal
wires which has been utilized in a microwave banddevice. This structure can simply convert a linearlypolarized wave generated from various CW terahertz
sources to circular one.
10014 mm

E⊥E//

30 mm
Base10-10-10TM mode Approximately 76%-20(Amplitude ofElectrical field is 87%)
-30-40
-50

10-2
0.2

εr<0(～1.9 THz)<-50 dB

Extinction ratio

0.5

1.0
1.5
Frequency (THz)

Extinction ratio (dB)

Transmission power

Terahertz polarizer
1.0 mm-60
1.95

Fig. 10. Terahertz polarizer with a dielectric structure.
100

13.2mm

E⊥E//

12 mm

Base

<-50 dB-10-20-30-40-50

10-2
0.3 0.5

εr<0(～2.9 THz)

0TM mode
Approximately 81%(Amplitude ofElectrical field is 90%)
10-1
Extinction ratio

1.0
1.5
Frequency (THz)

Extinction ratio (dB)

Transmission power

Terahertz polarizer-60
2.0 2.3

Fig. 11. Terahertz polarizer with a hollow structure.
4.0 cm

k4.0 cm

EFig. 12. Terahertz quarter-wave plate with symmetricallyaligned paired cut metal wires.

4. Conclusions and future potential
We have demonstrated various terahertz metamaterials
with refractive indices from extremely high to negativerefractive indices including a refractive index near zeroand have produced terahertz components utilizing theconcept of metamaterials, such as extreme-sensitivity
polarizers and a quarter-wave plate. Metamaterials overa range from 11.3 to −5.1 can offer numerous practicaland industrial applications, such as the extremely thinterahertz components in Fig. 13 (a) instead of
conventional bulk components as in Fig. 13 (b). Further,a metamaterial with an extremely high refractive index
as well as a negative index offers the potential to achieveterahertz imaging with resolutions better than one
wavelength.
Collimating Lens
with Distributed Refractive Indices
CW Terahertz Source
Quarter-Wave Plate

EHxk

SilliconLenszy(a)Conventional Collimating Lens
Conventional
CW Terahertz Source
Quarter-Wave Plate

EHyxkzSilliconLens(b)Fig. 13. Terahertz CW application consisting of (a)terahertz components inspired by metamaterials and (b)conventional terahertz components.
Acknowledgement
This research has been supported by a Grant-in-Aid forYoung Scientists (A) (No. 26706017) from the Japan Societyfor the Promotion of Science (JSPS) and a grant-in-Aid for
Challenging Exploratory Research (No. 26600108) from Japan
Society for the Promotion of Science (JSPS). The authorwishes to thank students and graduates of my laboratory, Prof.
Masanori Hangyo, Dr. Keisuke Takano, Dr. Hideaki Kitahara,
and Dr. Masaya Nagai.
References[1] K. Ishihara et al., presented at the 40th Int. Conf. on
Infrared, Millimeter, and Terahertz Waves, Hong Kong,
23-28 August 2015.
[2] Y. Takebayash et al., Applied Physics A 115, 501 (2013).
[3] T. Togashi et al., Applied Physics A 118, 397 (2015).
[4] T. Sato et al., presented at the 40th Int. Conf. on Infrared,Millimeter, and Terahertz Waves, Hong Kong, 23-28
August 2015.
[5] Y. Takebayashi et al., presented at Optical Terahertz
Science & Technology Conference 2015, San Diego, 8-13
March 2015.
[6] Y. Kishi et al., Appl. Phys. Express 8, 032201 (2015).
[7] T. Suzuki et al., Opt. Lett. 41, 325 (2016).