Dual-frequency Characterization of Bending Loss in Hollow Flexible Terahertz Waveguides

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1 Dual-frequency Characterization of Bending Loss in Hollow Flexible Terahertz Waveguides Pallavi Doradla a,b, and Robert H. Giles a,b a Submillimeter Wave Technology Laboratory, University of Massachusetts Lowell b Department of Physics & Applied Physics, University of Massachusetts Lowell, USA Feb

2 Outline Introduction Fabrication Theory Selection of Material Optimal Thickness Liquid Flow Coating (LFC) Process Dynamic Liquid Phase Coating Process Experimental Method Experimental Setup Mode Cleaning Experimental Method Summary Propagation Loss Measurement Bending Loss Measurement Modal Characteristics

3 Introduction - Security screening - Remote sensing - Bio-Medical Imaging 1 Wai Lam Chan, Jason Daibel, and Daniel M. Mittleman, Imaging with terahertz radiation, Rep.Prog. Phys. 70, (2007) 2 Figure copied from: Coherent Infrared Center Advance Light Source:

4 Basic Design Schematic cross section of metal and dielectric coated Hollow-core THz waveguide

Wavelength for lower order TE & TM modes 3 T. Ito, M. Miyagi, H. Minamide, H. Ito and Y.

5 Theory α tot = α propagation + α bending α TM pq = 10 1 r n n 2 + k 2 & α TE pq = 10 u 4 u 2 p 2 n n 2 + k 2 1 p2 k r3 u 4 r Lines of current flow Magnetic Lines Theoretical Loss as a function of Wavelength for lower order TE & TM modes 3 T. 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, (2007).

6 Selection of Metal When λ = 215μm F Ag = 0.684, F Au = 0.878, F Al = F Cu = 1.159, F W = 1.965, F Pb = Skin Depth: 2 f 2 R 0 ρ - Resistivity (Ωm) f - Frequency = 1.4THz µ 0-4πx10-7 (Henries/meter) δ Ag =0.05µm at 1.4 THz and 0.08 µm at 584 GHz; δ Au =0.07µm at 1.4 THz and 0.1 µm at 584 GHz. 4 Ordal, 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), (1983)

7 Selection of Dielectric Attenuation coefficient of as a function of bore diameter for lower order HE modes, for TE 11 and HE 11 modes of Silver coated waveguide 5 M. Miyagi and S. Kawakami, Design Theory of Dielectric-Coated Circular Metallic Waveguides for Infrared Transmission, J. Light. Wave Technol. 2(2), (1984).

Process Fabrication: dynamic liquid phase coating process 6 P. Doradla, C. S. Joseph, J. Kumar, and R. H.

8 Fabrication Peristaltic Pump Channel 1 Channel 2 Silver Solution Y Connector Reducing Agent Polycarbonate or Glass tube Waste Collector Base Material: Polycarbonate Metal: Silver, Gold Dielectric Material: Polystyrene Fabrication: Liquid Flow Coating Process Fabrication: dynamic liquid phase coating process 6 P. 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, 82601P P10 (2012).

9 Experimental Setup Experimental setup for the measurement of attenuation coefficient for metal, metal/dielectric coated Terahertz waveguides

Mode Cleaning The attenuation constant for EH nm modes in db/m is given by, nm 2 2 u 2 nm 3 8.

7 db for EH11, EH12, and EH13 modes Two-dimensional mode profiles of the propagated terahertz beam acquired using silicon bolometer a) 20 cm after OAP,

10 Mode Cleaning The attenuation constant for EH nm modes in db/m is given by, nm 2 2 u 2 nm Re n r & ν n N N 1 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, db, 48.7 db for EH11, EH12, and EH13 modes 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. 7 P. Doradla, C. S. Joseph, J. Kumar, and R. H. Giles, Characterization of bending loss in hollow flexible terahertz waveguides, Opt. Express 20 (17), (2012).

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.

11 Propagation Loss 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 mm mm 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.

Bending Loss 3 3 C r / / / 3 L tot pq R r3 R r6 3 1 1 r L L r L C R r C C Total attenuation coefficient per bore diameter cube

12 Bending Loss 3 3 C r / / / 3 L tot pq R r3 R r r L L r L C R r C C 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.

13 Modal Characteristics According to Beer-Lambert s Law, 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) 0 0, (2) 60 0, (3)

14 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 TE 11 mode. The 2 mm ID metal coated waveguide showed least variation in transmission loss (<1 db/m) with 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.

15 THANK YOU

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