THz Waveguides: The Evolution

Rajind MendisUniversity of Wollongong, Australia

“Chronological” series of experimental investigations into

the guided-wave propagation andthe associated coupling of

THz pulses

Approach……

f

λ

Microwaves OpticsTHz

Ideas

IdeasTechniques

Techniques

Outline

• THz-TDS System

• Incorporating the Waveguide

• Important Considerations

• Waveguides…………….….

• Guided-Wave THz-TDS

Parabolic Mirror

Mirror

Lens

LIA

THz Beam

Chopper

Manual Delay

Aperture

Pump Laser

Ti:Sapphire Laser

Scanning Delay

Attenuator

Spectrometer

Periscope

Polarizer

InAs (Tx)

ZnTe (Rx)

λ/4 Plate

Si Plate

Wollaston Prism

Balanced Photo Detector

Beam Splitter

Pump

Probe

University of Wollongong

Schematic Diagram

THz-TDS System

THz-TDS System

Purge Chamber

Sample Position

Ti:SapphireLaserInAs

(Tx)

Pump Laser

ZnTe(Rx)

BalancedPhoto Detector

SpectrometerManual Delay

λ/4Plate

WollastonPrism

Quasi-Optic Coupling

Sample ≡ Lens-Waveguide-Lens

Waveguide

High Resistivity Si Lens(Hyper-Hemispherical or Plano-Cylindrical)

THzBeam

Sample

THz Beam

Incorporating the Waveguide

• Attenuation• Dispersion – Group-Velocity (vg)

• Input/Output Coupling – Mode-Matching

• Single-Mode Propagation

LLjrefout ee ozTCEE αββωω −−−= )()()( 2

AttenuationConstant

PropagationLength

PhaseConstant

2π /λ0CouplingCoefficient

TransmissionCoefficient

OutputField

ReferenceField

Important Considerations

Waveguides……

Hollow Metallic Circular WaveguideStainless Steel240 µm diameter

24 mm long

Negative Chirp 1ps 70 ps !

R. W. McGowan, G. Gallot, D. GrischkowskyOpt. Lett. 24, 1431 (1999)

Multi-Mode

0 10 20 30 40 50 60 70−30

−20

−10

0

10

20

30

Time (ps)

Ave

rage

Cur

rent

(pA

)

0 5 10−500

0

500

Ave

rage

Cur

rent

(pA

)

Time (ps)0 0.5 1 1.5 2 2.5 3 3.5 4

0

200

400

600

800

1000

1200

1400

Frequency (THz)

Rel

ativ

e A

mpl

itude

(0.76)TE11

TM11

TE12

Rel

ativ

e Am

plitu

de

Frequency (THz)

Fiel

d A

bsor

ptio

n (c

m-1

)

Frequency (THz)

AttenuationTE11

TM11

TE12

G. Gallot, S. P. Jamison, R. W. McGowan, D. GrischkowskyJ. Opt. Soc. Am. B 17, 851 (2000)

Hollow Metallic Circular WaveguideStainless Steel240 µm diameter

24 mm long

Vel

ocity

/c

Frequency (THz)

Dispersion

TE11

TM11

TE12 vp

vg

Hollow Metallic Rectangular Waveguide

0 5 10 15 20 25 30-30

-20

-10

0

10

20

30

Ave

rage

Cur

rent

(pA

)

Time (ps)

0 5-400

0

400

Brass250 µm × 125 µm

25 mm long

G. Gallot, S. P. Jamison, R. W. McGowan, D. GrischkowskyJ. Opt. Soc. Am. B 17, 851 (2000)

Negative Chirp 1ps 25 ps

“Effectively”Single-Mode (TE10)

0 1 2 3 4 50

100

200

300

400

Rel

ativ

e A

mpl

itude

Frequency (THz)

(0.6)TE10

G. Gallot, S. P. Jamison, R. W. McGowan, D. GrischkowskyJ. Opt. Soc. Am. B 17, 851 (2000)

Fiel

d A

bsor

ptio

n (c

m-1

)

Frequency (THz)

AttenuationTE10

TE30

TM12

Hollow Metallic Rectangular WaveguideBrass

250 µm × 125 µm25 mm long

Vel

ocity

/c

Frequency (THz)

TE10

TM12TE30

Dispersion

vp

vg

Single Crystal Sapphire325 µm diameter

7.3 mm long

S. P. Jamison, R. W. McGowan, D. GrischkowskyAppl. Phys. Lett. 76, 1987 (2000)

Negative Chirp 1ps 15 ps

Single-Mode (HE11)

Dielectric Fiber

0 1 2 3 40

100

200

300

400

500

Frequency (THz)A

mpl

itude

50 55 60 65

−20

−15

−10

−5

0

5

10

15

20

25

Time (ps)

pA

(a) 325µm diameter

−1 0 1 2−100

0

100

Reference

Dashed Lines – 150 µm dia.

Frequency (THz)

Pow

er A

bsor

ptio

n (c

m-1

)

Cou

plin

g C

oeffi

cien

t

Attenuation

Coupling

HE11

Frequency (THz)

Velo

city

/c

vp

vg

Dispersion

HE11

Dielectric FiberSingle Crystal Sapphire

325 µm diameter7.3 mm long

S. P. Jamison, R. W. McGowan, D. GrischkowskyAppl. Phys. Lett. 76, 1987 (2000)

Dielectric Slab (Plastic Ribbon)

-500

0

500

0 10 20 30 40 50-150

-100

-50

0

50

100

150

Aver

age

Cur

rent

(pA)

Time (ps)

High Density Polythene120 µm thick20 mm long20 mm wide

R. Mendis, D. GrischkowskyJ. Appl. Phys. 88, 4449 (2000)

Positive Chirp 1ps 45 ps

THz Beam

Dielectric Slab

Si Lens

Single-Mode (TM0)

0 1 2 30.0

0.2

0.4

0.6

0.8

1.0

Frequency (THz)R

elat

ive

Ampl

itude

Dielectric Slab (Plastic Ribbon)

R. Mendis, D. GrischkowskyJ. Appl. Phys. 88, 4449 (2000)

Dashed Line – High Resistivity Si (αBulk = 0.05 cm-1)

0 1 2 30.0

0.1

0.2

0.3

0.4

0.5

0.6

Fiel

d Ab

sorp

tion

(cm

-1)

Frequency (THz)

αBulk = 1 cm-1

TM0

Slab

Attenuation

0 1 2 30.6

0.7

0.8

0.9

1.0

vg

vp

Vel

ocity

/c

Frequency (THz)

TM0

Dispersion

THz Beam

Dielectric Slab

Si Lens

High Density Polythene120 µm thick20 mm long20 mm wide

Parallel-Plate Waveguide

0 5 10 15 20

-200

0

200

-200

0

200

400-200

0

200

400

A

vera

ge C

urre

nt (p

A)

Time (ps)

THz BeamE

E

E Parallel Plate Waveguide

Reference

12.6 mm long

24.4 mm long

Copper108 µm separation

20 mm wide

Single-Mode (TEM)

Undistorted propagation!!

R. Mendis, D. GrischkowskyOpt. Lett. 26, 846 (2001)

0.0

0.2

0.4

0.6

α

TM2

TM1

TEM

TM2

TM1

TEM

(cm

-1)

0

1

2

vg

vp

Velo

city

/ c

0 1 2 3 40.998

1.000

Frequency (THz)

0 1 2 3 40.0

0.2

0.4

0.6

0.8

1.0

5 6 7 8

-200

0

200

400

Rel

ativ

e Am

plitu

de

Frequency (THz)

Time (ps)

Aver

age

Cur

rent

(pA

)

Reference

12.6 mm

24.4 mm

Atte

nuat

ion

Dis

pers

ion

Parallel-Plate Waveguide

< 0.1 % change in velocity

R. Mendis, D. GrischkowskyOpt. Lett. 26, 846 (2001)

Copper Shims90 µm separation

15 mm wide

R. Mendis, D. GrischkowskyIEEE Microwave Wireless Comp. Lett. 11, 444 (2001)

x

r’

r

Waveguide

Si Lens

r = 11.5 mmr’ = 27.5 mm

250 mm longFlexible

Adhesive Tape

Parallel-Plate Waveguide

741 746 751 756 761

-15

0

15

30

Ave

rage

Cur

rent

(pA

)

Time (ps)

Photonic Crystal Fiber

H. Han, H.Park, M. Cho, J. KimApp. Phys. Lett. 80, 2634 (2002)

High Density Polythene500 µm diameter Tubes

20 mm long

Tubes

Filament

High-IndexCore

Time (ps)

Cur

rent

(pA

)

Frequency (THz)

Rel

ativ

e Am

plitu

de

Positive Chirp 1ps 35 ps Single-Mode

Field Attenuation < 0.25 cm-1

Coaxial Waveguide

T.-I. Jeon, D. GrischkowskyApp. Phys. Lett. 85, 6092 (2004)

260 µm (inner) diameter Cu Tube80 µm diameter Al-W Core

Teflon105 mm long

0 0.2 0.4 0.6 0.8 1.0 1.20

0.05

0.1

0.15

Rel

ativ

e A

mpl

itude

Frequency (THz)

(c)

Rel

ativ

e Am

plitu

de

Frequency (THz)

“Effectively”Single-Mode (TEM)

Direct Generation & Detection

Undistorted Propagation

Conduction Loss+

Dielectric Loss

0 20 40 60 80 100−40

−20

0

20

40

60

80

100

Time (ps)

Ave

rage

Cur

rent

(pA

) (c)

1.56ps

Time (ps)

Ave

rage

Cur

rent

(pA

)

1.56 ps

Al - W

TE11

Metal Wire Waveguide

THz Pulse

Cu Wire Teflon Support

Laser Excitation Beam

Laser Detection Beam

SOS Chip SOS Chip

T.-I. Jeon, J. Zhang, D. GrischkowskyApp. Phys. Lett. 86, 161904 (2005)

K. Wang, D. MittlemanNature 432, 376 (2004)

THz Endoscope

Copper0.52 mm diameter

Time (ps)

Ave

rage

Cur

rent

(pA

)

20 cm long

64 cm long104 cm long

Undistorted Propagation Single-Mode (Sommerfeld)

Metal Wire Waveguide

T.-I. Jeon, J. Zhang, D. GrischkowskyApp. Phys. Lett. 86, 161904 (2005)

Frequency (THz)

Fiel

d A

bsor

ptio

n (c

m-1

)R

elat

ive

Am

plitu

de 20 cm64 cm104 cm

Time (ps)

Ave

rage

Cur

rent

(pA

)

∆h =

17 cm

∆h

Atte

nuat

ion

Bending Loss

Copper0.52 mm diameter

Dashed Line – Air-Filled Coaxial (TEM)

Metal Sheet Waveguide

T.-I. Jeon, D. GrischkowskyApp. Phys. Lett. 88, 061113 (2006)

Al Sheet

Al Plate

PPWGTx Rx

LEB LDB THz Pulse L1

L2

L3

Aluminium51 µm thick10 cm wide14 cm long

Frequency (THz)

Am

plitu

de (a

.u.)

Time (ps)

Cur

rent

(pA

) Plate Out

Plate In

Undistorted Propagation Single-Mode (Zenneck)

Parallel-Plate Variations

A. Bingham, Y. Zhao, D. GrischkowskyApp. Phys. Lett. 87, 051101 (2005)

Parallel-Plate Photonic Waveguide

30 4020100Time (ps)

Frequency (THz)

Tran

smis

sion

(dB

)A

mpl

itude

(a.u

.)C

urre

nt (n

A)

Dielectric-FilledParallel-Plate Waveguide

R. MendisOpt. Lett. 31, 2643 (2006)

-50

0

50

100

-50

0

50

0 2 4 6 8

-50

0

50

100

Time (ps)

Elec

tric

Fiel

d (a

.u.)

THz

THz70 µm

Positive Chirp

Guided-Wave THz-TDS

4 6 8 10

-50

0

50

-150

0

150

300

Time (ps)

Aver

age

Cur

rent

(pA

)

0.0

0.2

0.4

0.6

0.8

1.0

Rel

ativ

e A

mpl

itude

R. MendisElectron. Lett. 42, 26 (2006)

0 1 2 3 3.520

40

60

80

100

Frequency (THz)

Con

duct

ivity

(S/c

m)

Parallel-Plate Waveguide

N = 1.6×1018 cm-3

µ = 398 cm2V-1s-1

5.75 mm long130 µm separation

• Highly-Doped Semiconductors• Conducting Polymers• Superconductors• Metals

Metal

Highly-Doped Si

Air

Reference

Sample

Reference

Sample

CollaboratorsOklahoma State University, USA

Dan Grischkowsky

Roger McGowan

Alan Cheville

Tae-In Jeon

Guilhem Gallot

Weili Zhang

John O’Hara

Jianquang Zhang

Steve Jamison

Abul Azad

University of Wollongong, AustraliaChao Zhang

Roger Lewis

Rodney Vickers

Michael Smith