Rapid Prototyping of Photonic Crystal
based THz Components towards
Integrated THz Micro-System
Ziran Wu
Department of Physics
Department of Electrical and Computer Engineering
wzr@email.arizona.edu
Outline
 Background / Motivations
 Photonic Crystal based Components
 Polymer-Jetting Rapid Prototyping
 Realizations of Various THz Components
 Components Systematic Integration
 Conclusions
1
THz Background
2
 Coverage in IR and
optical blind conditions
 Concealed object
screening
 Unallocated communication region
 Gigabit data capacity
 THz bio-medical image:
Identify tissue, tumor, DNA, etc.
 High bandwidth
 THz chemical signatures: Explosives
 Scattering loss < optical regime
* B. Ferguson, XC. Zhang, Nature Mater., 1, 26 (2002)
* Peter H. Siegel, IEEE Trans. Microwave Theory Tech., 50, 910 (2002)
* D. Arnone et. al., Physics World, 0953-8585, April 2000
* Optics.org, analysis article, Oct. 28, 2002
Motivations
3
We need THz components
Source, detector, filter, waveguides, antenna, quasi-optics, materials…
We need integration of components
Pre-alignments, packaging, systematic fabrication…
We need universality and customizability
Plug-and-play, easy customization…
We need THz rapid prototyping
Source
THz Micro-system
DUI
Detector
Results
Photonic Crystal based Components
Photonic Crystal (PhC)
 Periodic arrangement of dielectric/
metallic structures
 Bragg Diffraction among lattices
Band Gap
 Forbidden wave propagation in
certain frequency band
 Scalable dimensions with frequency
3-D Photonic Crystal
Radiation Core
Intensity
THz thermal radiation source
PBG fiber electron accelerator
Normal Planck
spectrum from
amorphous object
IR
PBG structure optimized
to generate strong
emission peak in the THz
band.
Intensity
l
Enhanced THz
emission
l
* H. Xin et al, IEEE Trans. Antennas Propag., 56, 2970 (2008)
* C. Sears et al, Proceedings PAC07, THPMS052, Albuquerque, NW, 2007
4
PBG Components Continued
Sub-wavelength effective-medium lens
Antenna with PhC substrate
* K. F. Brakora et. al., IEEE. Trans. Antenn. Propag., 55, 790 (2007)
* Peter de Maagt, et. al., IEEE Trans. Antennas Propag., 51, 2667 (2003)
Line-defect waveguide and bend
* K. Busch, Phys. Report 444, 101 (2007)
* Nielsen et.al.,OTST-2009, MB5, March 2009
Woodpile defect horn antenna
* A. Weily et. al., IEEE Trans. Antenn. Propag. 87, 151114 (2005)
5
THz 3-D Rapid Prototyping
 Objet (TM) polymer jetting prototyping
 Layer-by-layer printing of structures
 Printing resolution 42um (x) by 42um (y)
by 16um (z)
 UV curable model material
Support material removable by water flushing
(Matt mode)
 Non-support-material printing available
(Glossy mode)
 Possibility of mixing various printing materials
to achieve arbitrary spatial material properties
 Rapid prototyping of arbitrary shapes
 Alignment and assembly not necessary
 Mass production achievable with very low cost
6
Build Materials Characterization
THz Time Domain Spectrometer
Dispersion Compensation
Ultra-fast
Laser
Control Unit
THz Transmitter
THz Detector
Collimating Optics
 Photoconductive antennas as transmitter/receiver
 Ultra-fast gating enables time-domain measurement
 Covering 50GHz to 1.2THz with 10GHz resolution
 Transmission / Reflection setup available
* Ziran Wu, J. App. Phys., 50, 094324 (2008)
7
Build Materials THz Properties
8
2.85
VeroBlack
VeroGrey
VeroWhite
Real Permittivity
2.8
Vero Family
2.75
2.7
0.07
2.65
0.06
0.05
100
150
200
250
300
350
400
450
500
550
Frequency (GHz)
 Multiple-reflection excluded by using thick slabs
 Comparable EM properties in one family of polymers
Loss Tangent
2.6
0.04
0.03
0.02
VeroBlack
VeroGrey
VeroWhite
0.01
 Large enough refractive index contrast to open PBG
 Acceptable material loss
0
100
150
200
250
300
350
400
Frequency (GHz)
450
500
550
Filter: Woodpile Structure
9
Printed woodpile prototype
* S.Y. Lin et.al,, Nature 394, 251 (1998)
 Dielectric / metallic rods with
woodpile stacking formations
 Square rod width w= 352um
and periodicity d= 1292um
 Printing took about 30 minutes;
Consumable cost of approximately $10
 Excellent agreements with simulations
on both gap positions and depths
Filter: Johnson Structure
Printed Johnson Structure prototype
* S. G. Johnson and J. D. Joannopoulos, Appl. Phys. Lett. 77, pp. 3490-3492, 2000
 Hole layer – air holes in dielectric
Rod layer – dielectric rods in air
Triangle lattice formation in each layer
 Practically difficult to fabricate
 Triangular lattice constant x= 1346um
Air hole radius r= 500um
Air hole height h= 1713um
Rod / hole layer height t= 1071um
 Fabrication well verified by characterization
* Ziran Wu, Opt. Express, 21, 16442-16451 (2008)
10
Waveguide: Hollow-core PCF Design
11
Frequency fa/c0
Cross-Section View
Energy Distribution
Only modes above the
light line can propagate




Wave vector kza/2Pi
Triangular-lattice array of air cylinders in a dielectric background
HE11 mode
Center core defect to form the wave tunnel
Defect modes within the band gap of the complete PhC*
90% energy concentration in the core  low radiation and material losses
* MIT Ab-Initio MPB package
Waveguide: Wave-port Simulation
12
0
S21
S11
-5
S-parameter (dB)
-10
Band
Gap 1
-15
-20
Power Loss Factor
Band
Gap 2
  ln(
-25
| S 21 |
1 | S11 |
-30
-35
-40
80
100
120
140
160
180
200
220
Frequency (GHz)




2
PEC circular waveguide, TE11 mode feeds
84mm long polymer PBG waveguide
Lattice pitch 3mm, air hole radius 1.3mm, center core radius 4.2mm
Transmission loss as low as 0.04 dB/mm in 1st pass-band; Low return loss
2
) /( l )
Waveguide: Gaussian Beam Excitation
13
0.5
Transmitted Power
Evaluation Plane
Powerr loss factor (dB/mm)
Gaussian Beam
Incidence
Beam waist 3mm ( 90% coupling to HE11 mode)
1.42
Log (Transmitted Power)
1.4
0.3
0.25
0.2
0.15
0.1
80
100
120
140
160
180
200
220
Frequency (GHz)
1.34
1.32
Semi-log plot
Slope = Power Loss Factor
1.28
1.26
100
0.35
0
60
1.36
1.3
0.4
0.05
112GHz
1.38
Waveport
Beam Incidence
0.45
105
110
115
120
Waveguide Length (mm)
125
130
 Identical coupling to free space at input
and output interfaces
 Transmitted power exponentially decays
as waveguide length increases
(Neglect multiple-reflections)
 Calculated loss matches well with
wave-port simulation
* GEMS conformal FDTD package
240
Waveguide: Modal Simulation / Coupling
Mode simulation based on effective index method
Modal E-field Profile
74% power coupled to HE11 mode
with a beam waist of 4.2mm
 Modal field overlapping with Gaussian beam  get coupling efficiency
 Optimum beam waist ~ 2.7mm, over 90% coupling to HE11 mode
 Plano-convex lens fabricated by rapid prototyping to reach optimal beam size
* Lumerical MODE Solution
14
Waveguide: Fabrication and Bench Setup
 Fabricated THz waveguide samples (Glossy modes)
 Quasi-optics to focus the beam waist to 2.7mm
15
0.8
0
0.6
-5
0.4
-10
Power Transmittance (dB)
Field magnitude (V)
Waveguide: Characterization Results
0.2
0
-0.2
-0.4
Reference
50mm
75mm
100mm
125mm
150mm
-0.6
-0.8
-1
-1.2
100
200
300
400
500
600
700
Time delay (ps)




800
900
16
-15
-20
-25
-30
50mm
75mm
100mm
125mm
150mm
-35
-40
-45
1000
-50
80
100
120
140
160
180
Frequency (GHz)
Waveguides of 50, 75, 100, 125, and 150 mm long characterized
Time-gating ensures no multiple reflection in the calculation
Guided mode resonance seen in all waveforms
Four pass bands clearly show up around 105, 123, 153, and 174 GHz
200
220
240
Waveguide: Power Loss Factor
17
Measure
Beam Inc
0.2
Linear fitting at 107GHz
0.15
52
51
Transmitted power (dB)
Power loss (dB/mm)
0.25
0.1
0.05
50
49
48
47
46
0
80
45
100
120
140
160
180
200
220
240
50
75
100
125
Waveguide length (mm)
Frequency (GHz)
 Linear fitting of power (dB) vs. waveguide length to get loss factor
 Extracted loss agrees pretty well with the beam incidence simulation
 Downshift of about 7 GHz probably due to fabrication error (need support material)
150
Antenna: Photonic Crystal Horn
18
-29
-30
S11 (dB)
-31
-32
-33
-34
-35
90
100
110
120
130
140
150
160
170
Frequency (GHz)
1
Circular waveguide TE11 feeding
Polymer loss: constant conductivity 0.23
0.9
Radiation Efficiency
0.8
0.7
Not bad considering
1.5dB material loss
Copper Horn
PCF Horn
0.6
0.5
0.4
0.3
4.2mm flared to 8mm aperture radii (12.4 degree)
35mm optimized horn length along axis
0.2
100
110
120
130
140
Frequency (GHz)
150
160
170
Antenna: Radiation Patterns
19
Far-Field Radiation Pattern of Phi= 0º Cut (x-z plane)
30
30
Copper Horn
PCF Horn
Copper Horn
PCF Horn
20
20
164GHz
10
10
0
0
Directivity (dB)
Directivity (dB)
114GHz
-10
-20
-10
-20
-30
-30
-40
-40
-50
0
50
100
150
200
Theta Angle (Degree)
250
300
350
-50
0
50
100
150
200
Theta Angle (Degree)
 Directional beam obtained at two working frequencies
 Comparable main beam angle with copper horn; Side-lobe level not as low
 Works much better than copper horn (over-moded) at high frequency
250
300
350
Transition: Waveguide-to-Planar Circuit
 Tapered cone helps impedance
matching
 Power directed into the dielectric
rod waveguide (TIR guiding)
 Circular-to-square cross section
transition
 Smooth surface generated by
HFSS
20
 Tapered wedge transit to
microstrip substrate
 PEC flares on top and
bottom shrink the field
spread
 Mstrip single-mode
operation up to 120GHz
(400um trace width
127um substrate thick)
Transition: Waveguide-to-Planar Circuit
21
0
-10
-30
-10
-15
-20
-40
-25
S11 (dB)
S21 (dB)
-20
-50
-30
-35
-60
70
-40
Mstrip connected
Mstrip disconnected
80
90
100
110
120
130
140
150
160
170
-45
180
-50
70
80
90
100
110
120
130
140
Frequency (GHz)
Frequency (GHz)
 -6.75dB insertion loss best at 108GHz; low return loss
 Excluding 2.1dB waveguide loss  2.3dB loss at each transition section
 About 4dB more loss if polymer material loss included
150
160
170
180
Sub-wavelength Effective Medium
* K. F. Brakora et. al., IEEE. Trans. Antenn. Propag., 55, 790 (2007)
Capacitive Estimation of the Permittivity Tensor
a y az
a y az a y az
(1  ( r  1) 2 )(1  ( r  1)(   2 ))
xx
L
L L
L
 eff 
a y az ax a y ax az a y a z
ax a y az
1  ( r  1)(   2  2  2  2
)
3
L L
L
L
L
L
Effective medium with artificially designed anisotropy
22
Source: Photonic Cavity Array
 Array of cubes with ~ 200um sides
 Printed by polymer-jetting and metalized
via sputtering
 Electroplating or electro-less deposition for
3-D metallization
 Complete band gaps between THz resonance
frequencies
 Strong and sharp thermal emission at THz
23
500um
Source: PBG e-Accelerator at THz?
Very cheap prototyping
24
Arbitrary fiber / coupler design
Need a THz power source to drive it
* R. England et al., Bob Siemann Symposium and ICFA Workshop, July 8 th, 2009
Integrated THz Micro-System
Filter
Waveguide
25
Antenna
Source
Metamaterial
THz Micro-System
Transition to planar-circuits
THz Chip
THz
Sample
Conclusions
 THz rapid prototyping technique demonstrated
 THz filter, waveguide, and antenna fabricated by prototyping
 Characterizations of these components show good agreements
with the designs
 Prototype-able transition-to-planar circuit, effective medium,
and source proposed and under study
 Systematic integration of the aforementioned building blocks
leads to THz micro-system
26
Acknowledgement
Graduate Student
Ian Zimmerman 1
For metal sputtering on cavity array
Wei Ren Ng
2
For sample fabrication and post-process
Faculty
Prof. Hao Xin 1
Prof. Richard Ziolkowski
Prof. Michael Gehm 2
3
For help on both EM modeling and sample fabrications
1
Millimeter Wave Circuits and Antennas Lab
2 Non-Traditional Sensors Lab
3 Computational Electromagnetics Lab
Thanks for your
attention!
Other PhD Work
 Thermal radiation from THz photonic crystals
 THz characterization of carbon nanotube ensemble and
on-substrate thin films
 De-metallization of single-walled carbon nanotube thin film
with microwave irradiation
 Frequency-tunable THz photonic crystals using liquid crystal
 “Lab-on-chip” transmission-line characterization circuits