1. Department of Electrical and Computer Engineering
Rapid Prototyping of Photonic Crystal based THz Components towards Integrated THz Micro-System
Ziran Wu
Department of Physics
Department of Electrical and Computer Engineering

2. Background / Motivations Photonic Crystal based Components
Outline 1
Background / Motivations
Photonic Crystal based Components
Polymer-Jetting Rapid Prototyping
Realizations of Various THz Components
Components Systematic Integration
Conclusions

3. THz Background 2 Coverage in IR and optical blind conditions
Concealed object screening
Unallocated communication region
Gigabit data capacity
High bandwidth
Scattering loss < optical regime
THz bio-medical image: Identify tissue, tumor, DNA, etc.
THz chemical signatures: Explosives
* 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, , April 2000 * Optics.org, analysis article, Oct. 28, 2002

4. 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
Results
THz Micro-system
Source
Detector
DUI

5. Photonic Crystal based Components4
Photonic Crystal (PhC)
Periodic arrangement of dielectric/ metallic structures
Bragg Diffraction among lattices
Forbidden wave propagation in certain frequency band
Scalable dimensions with frequency
Band Gap
THz thermal radiation source
PBG fiber electron accelerator l
Normal Planck
spectrum from
amorphous object IR
Intensity
Enhanced THz
emission 3 -
D Photonic Crystal
Radiation Core
PBG structure optimized
to generate strong
emission peak in the THz
band.
* H. Xin et al, IEEE Trans. Antennas Propag., 56, 2970 (2008)
* C. Sears et al, Proceedings PAC07, THPMS052, Albuquerque, NW, 2007

6. PBG Components Continued5
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
Woodpile defect horn antenna
* K. Busch, Phys. Report 444, 101 (2007)
* Nielsen et.al.,OTST-2009, MB5, March 2009
* A. Weily et. al., IEEE Trans. Antenn. Propag. 87, (2005)

7. THz 3-D Rapid Prototyping6
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

8. Build Materials Characterization7
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, (2008)

9. Build Materials THz Properties8
Vero Family
Multiple-reflection excluded by using thick slabs
Comparable EM properties in one family of polymers
Large enough refractive index contrast to open PBG
Acceptable material loss

10. Filter: Woodpile Structure9
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

11. Filter: Johnson Structure10
Printed Johnson Structure prototype
* S. G. Johnson and J. D. Joannopoulos, Appl. Phys. Lett. 77, pp , 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, (2008)

12. Waveguide: Hollow-core PCF Design11
Cross-Section View
Band Gap 1
Band Gap 2
Only modes above the light line can propagate
Wave vector kza/2Pi
Frequency fa/c0
Energy Distribution
Triangular-lattice array of air cylinders in a dielectric background
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
HE11 mode
* MIT Ab-Initio MPB package

13. Waveguide: Wave-port Simulation12
Band Gap 1
Band Gap 2
Power Loss Factor
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

14. Waveguide: Gaussian Beam Excitation13
Transmitted Power Evaluation Plane
Gaussian Beam
Incidence
Beam waist 3mm ( 90% coupling to HE11 mode)
112GHz
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
Semi-log plot
Slope = Power Loss Factor
* GEMS conformal FDTD package

15. Waveguide: Modal Simulation / Coupling14
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

16. Waveguide: Fabrication and Bench Setup15
Fabricated THz waveguide samples (Glossy modes)
Quasi-optics to focus the beam waist to 2.7mm

17. Waveguide: Characterization Results16
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

18. Waveguide: Power Loss Factor17
Linear fitting at 107GHz
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)

19. Antenna: Photonic Crystal Horn18
Circular waveguide TE11 feeding Polymer loss: constant conductivity 0.23
Not bad considering
1.5dB material loss
4.2mm flared to 8mm aperture radii (12.4 degree) 35mm optimized horn length along axis

20. Antenna: Radiation Patterns19
Far-Field Radiation Pattern of Phi= 0º Cut (x-z plane)
114GHz
164GHz
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

21. Transition: Waveguide-to-Planar Circuit20
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 um substrate thick)
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

22. Transition: Waveguide-to-Planar Circuit21
-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

23. Sub-wavelength Effective Medium22
* K. F. Brakora et. al., IEEE. Trans. Antenn. Propag., 55, 790 (2007)
Capacitive Estimation of the Permittivity Tensor
Effective medium with artificially designed anisotropy

24. Source: Photonic Cavity Array23
Array of cubes with ~ 200um sides
Printed by polymer-jetting and metalized via sputtering
Electroplating or electro-less deposition for D metallization
Complete band gaps between THz resonance frequencies
Strong and sharp thermal emission at THz
500um

25. Source: PBG e-Accelerator at THz?24
Very cheap prototyping
Arbitrary fiber / coupler design
Need a THz power source to drive it
* R. England et al., Bob Siemann Symposium and ICFA Workshop, July 8th, 2009

26. Integrated THz Micro-System25
Waveguide
Antenna
Filter
THz Micro-System
Source
Metamaterial
THz Chip THz Sample
Transition to planar-circuits

27. Conclusions 26 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

28. Graduate Student Faculty
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 3
Prof. Michael Gehm 2
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

29. Thanks for your attention!

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“Lab-on-chip” transmission-line characterization circuits