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Dual-frequency Characterization of Bending Loss in Hollow Flexible Terahertz Waveguides
Pallavi Doradlaa,b, and Robert H. Gilesa,b
aSubmillimeter Wave Technology Laboratory, University of Massachusetts Lowell
bDepartment of Physics & Applied Physics, University of Massachusetts Lowell, USA
Feb-06-2014
Outline
Introduction
Theory
Selection of Material
Optimal Thickness
Fabrication
Liquid Flow Coating (LFC) Process
Dynamic Liquid Phase Coating Process
Experimental Method
Experimental Setup
Mode Cleaning
Experimental Method
Propagation Loss Measurement
Bending Loss Measurement
Modal Characteristics
Summary
Introduction
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1Wai Lam Chan, Jason Daibel, and Daniel M. Mittleman, “Imaging with terahertz radiation,” Rep.Prog. Phys. 70, 1325-1379 (2007)2Figure copied from: Coherent Infrared Center Advance Light Source: http://circe.lbl.gov/THzGap.html
Basic Design
Schematic cross section of metal and dielectric coated
Hollow-core THz waveguide
Theory
Theoretical Loss as a function of Wavelength for lower order TE & TM modes
𝛂 𝐓𝐌𝐩𝐪 = 𝟏𝟎 ∗𝟏
𝐫
𝐧
𝐧𝟐 + 𝐤𝟐& 𝛂 𝐓𝐄𝐩𝐪 = 𝟏𝟎 ∗
𝐮𝟒
𝐮𝟐 − 𝐩𝟐𝐧
𝐧𝟐 + 𝐤𝟐𝟏
𝐤𝟎𝟐𝐫𝟑
+𝐩𝟐
𝐮𝟒𝐫
𝛂𝐭𝐨𝐭 = 𝛂𝐩𝐫𝐨𝐩𝐚𝐠𝐚𝐭𝐢𝐨𝐧 + 𝛂𝐛𝐞𝐧𝐝𝐢𝐧𝐠
Lines of current flow Magnetic Lines
3T. Ito, M. Miyagi, H. Minamide, H. Ito and Y. Matsuura, "Flexible terahertz fiber optics with low bend-induced
losses," J. Opt. Soc. Am. B 24, 1230–1235 (2007).
Skin Depth:
ρ - Resistivity (Ωm)
f - Frequency = 1.4THz
µ0 - 4πx10-7 (Henries/meter)
δAg=0.05µm at 1.4 THz and 0.08 µm at 584 GHz;
δAu=0.07µm at 1.4 THz and 0.1 µm at 584 GHz.
When λ = 215μm
FAg = 0.684 , FAu = 0.878, FAl = 0.994
FCu = 1.159, FW = 1.965, FPb = 2.945
Selection of Metal
4Ordal, M., A., et. al., “Optical properties of the metals Al, Co, Au, Fe, Pb, Ni, Pd, Pt, Ag, Ti, and W in IR & FIR”,
Applied Optics, 22(7), 1099-1119 (1983)
0
22
Rf
Selection of Dielectric
Attenuation coefficient of as a function of bore diameter for lower order HE
modes, for TE11 and HE11 modes of Silver coated waveguide
5M. Miyagi and S. Kawakami, “Design Theory of Dielectric-Coated Circular Metallic Waveguides for Infrared
Transmission,” J. Light. Wave Technol. 2(2), 116–126 (1984).
Base Material: Polycarbonate Metal: Silver, Gold Dielectric Material: Polystyrene
Fabrication: Liquid Flow Coating Process
Fabrication: dynamic liquid phase coating process ………
Fabrication
Y Connector
Waste Collector
Peristaltic Pump
Silver
Solution
Reducing
Agent
Channel 1 Channel 2
Polycarbonate
or Glass tube
6P. Doradla, C. S. Joseph, J. Kumar, and R. H. Giles, “Propagation Loss Optimization in Metal/Dielectric Coated
Hollow Flexible Terahertz Waveguides,” Proc. of SPIE 8261, 82601P1–82610P10 (2012).
Experimental Setup
Experimental setup for the measurement of attenuation coefficient for
metal, metal/dielectric coated Terahertz waveguides
The attenuation constant for EHnm modes in dB/m is given by ,
Mode Cleaning
Two-dimensional mode profiles of the propagated terahertz beam acquired using silicon
bolometer a) 20 cm after OAP, b) after 5 cm, and c) 15 cm Polycarbonate tube.
2 2
38.686 Re
2nm
nm nu
r
2
n2
1 ν
2 1&
N
N
A polycarbonate tube with CIR 1.64 – ix0.05, 5 cm length: 1.25 dB, 6.6 dB, 16.2 dB and
15 cm length: 3.76 dB, 19.79 dB, 48.7 dB for EH11, EH12, and EH13 modes
7P. Doradla, C. S. Joseph, J. Kumar, and R. H. Giles, “Characterization of bending loss in hollow flexible
terahertz waveguides,” Opt. Express 20 (17), 19176 – 19184 (2012).
Propagation Loss
Theoretical and Experimental attenuation coefficients as a function of inner bore diameter
for silver and gold coated waveguides at 1.4 THz and 584 GHz freq.
Bore
Diamete
r
1.4 THz 584 GHz
Loss (dB/m) in Ag Loss (dB/m) in Au Loss (dB/m) in Ag Loss (dB/m) in Au
Theo. Exp. Theo. Exp. Theo. Exp. Theo. Exp.
4mm 1.44 1.77 1.85 1.98 1.03 1.62 1.29 1.89
3mm 1.8 2.64 2.31 2.93 1.4 2.3 1.63 2.6
2mm 2.9 3.5 3.73 4.02 2.19 3.0 2.73 3.65
Bending Loss
Total attenuation coefficient per bore diameter cube as a function of
bending angle and bore diameters for Ag coated waveguides at 584 GHz
(inset: 1.4 THz) with 6.5 cm bend radius.
3
3 3 3113 6
/ / /tot pq R
C r Lr L L r L C R r C C
Rr r
According to Beer-Lambert’s Law,
Modal Characteristics
Spatial output profile from Ag coated waveguides at (I) 1.4 THz, (II) 584 GHz as a function of bore diameter (rows) (2) 2 mm, (3) 3 mm, (4) 4mm; and
bending angle (columns) (1) 00, (2) 600, (3) 1200.
Summary
Attenuation Characteristics of flexible Terahertz waveguides were studied
at both 1.4 THz and 584 GHz frequencies .
Propagation loss as small as 1.7 dB/m was achieved in silver coated
waveguides by coupling the lowest loss TE11 mode.
The 2 mm ID metal coated waveguide showed least variation in
transmission loss (<1 dB/m) with 00 – 1500 bending angle.
The 1 µm thick silver coated 2 mm inner diameter waveguides can be used
at both the frequencies, to obtain low transmission losses and mode
preservation.
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