Rapid Prototyping of Photonic Rapid Prototyping of Photonic Crystal based THz Components Crystal based THz Components towards Integrated THz Micro- towards Integrated THz Micro- System System Ziran Wu Ziran Wu Department of Department of Physics Physics Department of Electrical and Computer Engineering Department of Electrical and Computer Engineering [email protected][email protected]
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Rapid Prototyping of Photonic Crystal based THz Components towards Integrated THz Micro-System Ziran Wu Department ofPhysics Department of Physics Department.
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Rapid Prototyping of Photonic Crystal Rapid Prototyping of Photonic Crystal based THz Components towards based THz Components towards
Comparable EM properties in one family of polymers
Large enough refractive index contrast to open PBG Acceptable material loss
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Printed woodpile prototype
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 StructureFilter: Johnson Structure 10
* 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)
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
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
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
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
74% power coupled to HE11 modewith a beam waist of 4.2mm
* Lumerical MODE Solution
Waveguide: Fabrication and Bench SetupWaveguide: Fabrication and Bench Setup 15
Fabricated THz waveguide samples (Glossy modes)
Quasi-optics to focus the beam waist to 2.7mm
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
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)
Waveguide: Power Loss FactorWaveguide: Power Loss Factor 17
4.2mm flared to 8mm aperture radii (12.4 degree)35mm optimized horn length along axis
Not bad considering1.5dB material loss
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
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
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)
-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
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Sub-wavelength Effective MediumSub-wavelength Effective Medium 22
2 2
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(1 ( 1) )(1 ( 1)( ))
1 ( 1)( 2 )
y z y y zzr r
xxeff
y x y y z x y zx zzr
a a a a aa
L L L La a a a a a a aa aa
L L L L L L
Capacitive Estimation of the Permittivity Tensor
Effective medium with artificially designed anisotropy
* K. F. Brakora et. al., IEEE. Trans. Antenn. Propag., 55, 790 (2007)
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 500um
Source: PBG e-Accelerator at THz?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