Overview of THz waveguides and applications, updated Apr. 2007
Transcript of Overview of THz waveguides and applications, updated Apr. 2007
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THz waveguides : a reviewAlexandre Dupuis
École Polytechnique de Montréal
M. SkorobogatiyCanada Research Chair in photonic crystals
http://www.photonics.phys.polymtl.ca/
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Outline• Introduction • Applications in the THz regime• Early waveguide attempts
- Coplanar striplines, plastic ribbons, sapphire fibers, metal tubes• Recent breaktroughs
- Metal wire, microstructured fiber, plastic fiber, hollow plastic tubes with inner metal layer• Perspectives
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Bridges the gap between the microwave and optical regimes. = 0.1 THz - 10 THz= 3000 m - 30 m
Major applications sensing, imaging and spectroscopy.
IntroductionWhat is the THz regime ?
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Applications•Imaging of biological tissues (tissue recognition)
Löffler, Opt. Exp., 9, 12 (2001)
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Applications•Chemical recognition of gases
Jacobsen, Opt. Lett., 21, 24 (1996)
Time domain spectroscopy
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Applications• Tomography Pearce, Opt. Lett., 30, 13 (2005)
Mittleman, Opt. Lett., 22, 12 (1997)
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Applications• Non destructive sensing
Kawase, Opt. Exp., 11, 20 (2003)
Combining imaging and spectroscopy for the detection of organic compounds
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Applications• Non destructive sensing
Kawase, Opt. Exp., 11, 20 (2003)
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Applications•Inspecting electrical faults in integrated circuits
Kiwa, Opt. Lett., 28, 21 (2003)
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Technological challenges•Bulky free-space propagation of THz radiation
Goto, Jap. J. Appl. Phys. Lett., 43, 2B (2003)
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Technological challenges1. Virtually no low-loss waveguides
Conventionnal waveguides don’t work in the THz regime
Metals: high loss due to finite conductivityDielectrics: high absorption
2. Low dispersion waveguides necessary for spectroscopy
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Early waveguides•Coplanar striplines
Frankel, IEEE Transactions on microwave theory and techniques, 39, 6 (1991)
Metal electrodes on a semiconductor substrate = ~20 cm-1 at =1 THz ~3
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Early waveguides•Plastic ribbon waveguides
Mendis, J. Appl. Phys., 88, 7 (2000)
PE ribbon 150 mm thickDispersive single-mode propagationNo cut-off frequency = ~1 cm-1
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Early waveguides•Sapphire fiber
Jamison, Appl. Phys. Lett., 76, 15 (2000)
Single-crystal sapphire fiber
Diameter of 125, 250 and 325 m = ~1 cm-1
Dispersive propagation, mainly attributed to the waveguide and not the materialDominance of HE11 mode despite multimode fiber
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Early waveguides•Metal tubes
McGowan, Opt. Lett., 24, 20 (1999)
Stainless steel with an inside diameter of 280 m = 0.7 cm-1
Very dispersive multimode propagationLow frequency cut-off at 0.76 THz
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Recent waveguides•Parrallel metal plates
Mendis, IEEE Microwave and wireless components letters, 11, 11 (2001)
Two 100 m thick copper plates separated by a 90 m air gap = 0.1 cm-1 at 1 THzLow dispersionAbsorption still high and cross-section too large for medical application
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Recent waveguides•Hollow polymer waveguides with inner metallic layers
Harrington, Opt. Exp., 12, 21 (2004)
• Using liquid-phase chemistry methods, a metal or dielectric layer is deposited inside a silicon or polymer hollow waveguide.• It has been shown in the mid-IR region that hollow waveguides suffer a bending loss of 1/R, where R is the radius of curvature. It is possible to eliminate this effect with photonic bandgap structures.• The losses in Cu hollow waveguides can be significantly reduced if a dielectric coating of the correct optical thickness is deposited over the metallic layer.
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Recent waveguides•Hollow polymer waveguides with inner metallic layers
Hidaka, “Optical information, data processing and storage, and laser communication technologies”, Proc. SPIE, 5135, 11 (2003)
8 mm bore hollow waveguide with an inner wall of ferroelectric Polyvinylidene Fluoride (PVDF) = 0.015 cm-1 at 1 THz
With Cu inner layer, ~ 0.045 cm-1 at 1 THz
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Recent waveguides• Ferroelectric hollow core all-plastic Bragg fibers
Skorobogatiy, Appl. Phys. Lett., 90, 113514, (2007)
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Recent waveguides•Metal wire
Wang, Nature, 432, (2004)
Stainless steel wire with a diameter of 900 m < 0.03 cm-1
However, coupling efficiency is (very) lowNon polarization maintaning
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Recent waveguides•Metal wire
Cao, Opt. Exp., 13, 18 (2005)
Cu wire with a diameter of 450 m should have = 0.002 cm-1 at 1 THzTheoretical explanation of Wang’s results:Azimutely Polarized Surface Plasmon (APSP)
The polarization mismatch with the linearly polarized source leads to a very low coupling efficiency.
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Recent waveguides•Metal wire
Cao, Opt. Exp., 13, 18 (2005)
Outside the metal, air is very small, so the field decays very slowly in the radial direction and extends several 10 times R outside of the metal.
Inside the metal, m is very large, leaving a field penetration depth of less than 1 m.
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Recent waveguides•Metal wire with milled grooves
Cao, Opt. Exp., 13, 18 (2005)
Vain attempt to increase coupling
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Recent waveguides• Subwavelength plastic fibre
Sun, Opt. Lett., (Oct. 2005)
200 m diameter PE fiber ~ 0.01 cm-1 at 0.3 THzSingle-mode HE11 propagation
Fig.: Ponyting vector a) 0.3 THz b) 0.5 THzc) 0.7 THz d) 0.9 THz
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Recent waveguides• Plastic photonic crystal fibers (PPCF)
Han, Appl. Phys. Lett., 80, (2002)
500 m diameter HDPE tubesThe tubes were 2cm long, stacked in 2D triangular lattice and fused together at 135°C in a conventional furnace.
= 0.5 cm-1 at 1 THzMaterial absorption primary loss factorRelatively low dispersion, mainly due to waveguide dispersion
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Recent waveguides• Plastic photonic crystal fibers (PPCF)
Teflon tubes = 0.3 cm-1 at 1 THz
Goto, Jap. J. Appl. Phys. Lett., 43, 2B (2003)