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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 10 — May. 20, 2013
  • pp: 12728–12743
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Two-wire terahertz fibers with porous dielectric support

Andrey Markov and Maksim Skorobogatiy  »View Author Affiliations


Optics Express, Vol. 21, Issue 10, pp. 12728-12743 (2013)
http://dx.doi.org/10.1364/OE.21.012728


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Abstract

A novel plasmonic THz fiber is described that features two metallic wires that are held in place by the porous dielectric cladding functioning as a mechanical support. This design is more convenient for practical applications than a classic two metal wire THz waveguide as it allows direct manipulations of the fiber without the risk of perturbing its core-guided mode. Not surprisingly, optical properties of such fibers are inferior to those of a classic two-wire waveguide due to the presence of lossy dielectric near an inter-wire gap. At the same time, composite fibers outperform porous fibers of the same geometry both in bandwidth of operation and in lower dispersion. Finally, by increasing cladding porosity one can consistently improve optical properties of the composite fibers.

© 2013 OSA

1. Introduction

While having outstanding optical properties, a classic two-wire waveguide is inconvenient in practical applications. Thus, in a typical experiment the two wires have to be aligned and kept straight and parallel to each other with high precision. This requires bulky holders and cumbersome coupling setups. Moreover, the fiber core is not encapsulated into a protective cladding, thus leaving the core (space between wires) exposed to the environment.

Several experimental studies have been reported so far that studied propagation of THz pulses in composite metal-dielectric air-core fibers. Thus, in [18

18. A. Markov, S. Gorgutsa, H. Qu, and M. Skorobogatiy, “Practical Metal-Wire THz Waveguides,” arXiv:1206.2984 (2012); also presented at the Gordon Research Conference in Plasmonics, ME, USA (2012).

] we have reported a polyethylene fiber featuring three interconnected holes and two small copper wires of 250 μm diameter (see Fig. 4). The wires had a small 200 μm air gap between them, which served as a fiber core. Strong polarisation sensitivity of a three-hole composite fiber was confirmed. Moreover, we have clearly observed significant degradation of the composite fiber optical properties compared to those of a classic two-wire waveguide. Our preliminary experimental work has prompted this theoretical study where we quantify in a systematic manner the impact of porous plastic cladding on the properties of a two-wire composite waveguide.

In this paper we concentrate on the plasmonic guidance regime of a two-wire composite fiber. As a departure point, we detail outstanding optical properties of a classic two-wire waveguide. Then, we add porous plastic cladding in order to improve waveguide handling and investigate the impact of cladding on the properties of a resultant plasmonic waveguide. Finally, we show that one can mitigate the negative impact of the plastic cladding on the optical properties of a composite waveguide by increasing cladding porosity.

2. Classic two-wire waveguide

Before we present the study of composite fibers, we would like to address the issue of coupling efficiency into a classic two-wire waveguide. From our experiments, we observe that this coupling is a sensitive function of the excitation wavelength. As it is well known, the coupling efficiency into a classic two-wire waveguide achieves its maximal value at the wavelength that is comparable to the inter-wire separation, while the coupling efficiency stays relatively low for the wavelengths that are significantly smaller or larger than the optimal one. For a detailed discussion see for example [20

20. H. Pahlevaninezhad and T. E. Darcie, “Coupling of Terahertz Waves to a Two-Wire Waveguide,” Opt. Express 18(22), 22614–22624 (2010). [CrossRef] [PubMed]

], where the authors used the mode-matching technique and a full-wave FEM numerical simulations to study this issue. Ultimately, it is the frequency dependent coupling efficiency that limits practically usable bandwidth in such waveguides. Moreover, coupling efficiency into two-wire waveguides depends strongly on several geometric parameters such as position of the THz beam focal point, the width of the wires and the distance between them. For the completeness of presentation, we first study numerically the influence of each of these parameters on the waveguide excitation efficiency.

Modes of the waveguides and fibers studied in this work were computed using COMSOL Multiphysics FEM mode solver. The frequency dependent relative permittivity and conductivity of metal in the THz spectral range is modeled using the Drude formula:
ε(ω)=1ωp2ω2+iωΓTHzωp2Γ2+iσωε0;σTHzε0ωp2Γ,
(1)
where ε0 is the free-space permittivity, ω is the angular frequency, ωp is the angular plasma frequency, and Γ is the electron scattering rate. In our simulations we assume copper as a metal, and we use the following values of the parameters: ωp=2π1.9691015Hz, Γ=2π4.7751012Hz(derived from [21

21. M. A. Ordal, R. J. Bell, R. W. Alexander Jr, L. L. Long, and M. R. Querry, “Optical properties of fourteen metals in the infrared and far infrared: Al, Co, Cu, Au, Fe, Pb, Mo, Ni, Pd, Pt, Ag, Ti, V, and W,” Appl. Opt. 24(24), 4493–4499 (1985). [CrossRef] [PubMed]

23

23. Y.-S. Lee, Principles of Terahertz Science and Technology (Springer, 2008).

]). In the THz frequency range the Drude model is especially simple as it predicts frequency independent real part of the relative permittivity εr=1.7105, and frequency independent conductivity σ=4.5107S/m.

In Fig. 3
Fig. 3 Excitation efficiency of the fundamental mode of a classic two-wire waveguide using Gaussian beam as an excitation source. Dependence of the excitation efficiency on various geometrical parameters, such as: a) displacement along the x axis from the core center; b) displacement along the y axis from the core center; c) inter-wire gap size; d) wire radius.
, we present excitation efficiency of the fundamental mode of a two-wire waveguide using Gaussian beam as a source. We consider effect of the various geometric parameters on the coupling efficiency, including misalignment of the THz beam relative to the position of the wires, as well as choice of the wire radius and size of the inter-wire gap.

First, we study excitation of the fundamental TEM mode of a two-wire waveguide using Gaussian beam with the focal point displaced from the mid-point between the two wires (the point of maximal coupling efficiency). From Fig. 3(a) we see that displacement of the beam focal point along the OX axis by 100 μm leads to 20% decrease in the TEM excitation efficiency in the whole THz range, while displacement by 200 μm leads to 50% drop in the TEM excitation efficiency. The effect of displacement of the Gaussian beam focal point along the OY axis is much less pronounced [see Fig. 3(b)]. Thus, displacement of the beam focal point by 100 μm from the waveguide center leads to only 5% decrease in the TEM excitation efficiency. Remembering that the inter-wire gap size is 200 μm, we conclude that coupling efficiency is only moderately sensitive to the errors in the positioning of the Gaussian beam.

We now examine excitation of the TEM mode using a perfectly centered Gaussian beam while varying distance between the two wires. From Fig. 3(c) we find that the TEM mode is excited most efficiently when the Gaussian beam waist is comparable to the size of the inter-wire gap. The excitation efficiency remains high 40 – 70% in the whole THz frequency range 0.5 – 1.5 THz when the inter-wire distance is 150 – 400 μm. Finally, for a fixed 200 μm gap between the two wires, in Fig. 3(d) we plot excitation efficiency as a function of the wire radii. For small values of the radius the excitation efficiency increases with the radius until reaching its maximal value at R = 200 μm. Further increase of the wire radius leads to a monotonous decrease of the coupling efficiency.

3. Composite fiber featuring two metal wires in a three-hole porous cladding

It is interesting to compare cladding modes of a composite fiber with the modes of a porous fiber of the same cross section, however, without the metallic wires. Optical properties of the modes of a porous fiber are presented in Fig. 6 in red color. We note that in the broad frequency range 0.13 – 1.0 THz, optical properties of the fundamental mode of a porous fiber are quite similar to those of the lowest order cladding mode of a composite fiber. At the same time, the corresponding field distributions are somewhat different at low frequencies. Thus, below 0.5 THz (see, for example, Fig. 9
Fig. 9 Longitudinal flux distribution of the fundamental mode of a porous fiber (same cross section as in Fig. 4, however, without metal wires).
, 0.17THz), field distribution of the fundamental mode of a porous fiber shows significant presence in the air cladding outside of the fiber, as well as in the air holes inside of a plastic cladding. In contrast, lowest order cladding mode of a composite fiber (see Fig. 8, 0.17THz), shows no field presence in the central air hole between the two metal wires, while having significant field concentration in the air region outside of the fiber. At higher frequencies (Figs. 8, 9, >0.5THz) field distributions of the two modes become very similar to each other and feature strong light localisation in the plastic fiber cladding. Consequently, optical properties of the two modes also become very similar at higher frequencies.

Finally, we consider the second order cladding mode of a composite fiber, which is presented in Fig. 6 in magenta color in the frequency range of 0.54 – 1.0 THz. From the corresponding field distributions showed in Fig. 10
Fig. 10 Longitudinal flux distribution of the second plasmonic mode of a composite fiber.
it follows that the second order cladding mode is, in fact, a hybrid mode that has a significant plasmon contribution. Moreover, at lower frequencies (0.5 – 0.7 THz) the plasmon is propagating at the air/metal interface with a significant amount of energy concentrated in the central air hole between the two wires. In what follows we call this mode the second plasmonic mode as it can be used for low loss guidance of THz light within the central air hole of a composite fiber.

It is now timely to highlight the main differences in the optical properties of the modes of a two-wire composite fiber and the modes of a corresponding porous fiber without metal wires. Firstly, from Fig. 6 we note that the fundamental plasmonic mode of a composite fiber extends into very low frequencies (<0.1THz), while being well confined within the fiber (see Fig. 7). This can be of advantage when compared to the fundamental mode of a porous fiber, which at low frequencies is highly delocalised in the air cladding outside of the fiber (see Fig. 9). In practical terms it means that at very low frequencies, the fundamental plasmonic mode of a composite fiber is still suitable for guiding THz light due to its strong confinement in the core and, consequently, low sensitivity to bending, imperfections on the fiber surface, as well as perturbations in the environment. At the same time, at very low frequencies, fundamental mode of a porous fiber is largely found outside of the fiber core, which makes it highly sensitive to perturbations in the environment, as well as bending and fiber surface quality.

4. The influence of porosity on the fiber optical properties

5. Composite fiber featuring two metal wires in a seven-hole porous cladding

In order to decrease the number of cladding modes, thickness of the outer cladding has to be minimized. This thickness is defined as the smallest distance between the fiber outer surface and the boundary of the internal air holes. From our experience with plastic porous fibers and capillaries [11

11. A. Mazhorova, A. Markov, B. Ung, M. Rozé, S. Gorgutsa, and M. Skorobogatiy, “Thin chalcogenide capillaries as efficient waveguides from mid-infrared to terahertz,” J. Opt. Soc. Am. B 29(8), 2116 (2012). [CrossRef]

, 24

24. A. Hassani, A. Dupuis, and M. Skorobogatiy, “Low loss porous terahertz fibers containing multiple subwavelength holes,” Appl. Phys. Lett. 92(7), 071101 (2008). [CrossRef]

], outer cladding thickness larger than 50 µm is sufficient to mechanically protect the inner structure of the fiber. In our calculations, the smallest bridge size between any two air holes is taken to be 10 µm, which can be readily realised in practice as demonstrated in our prior experiments with suspended core fibers [3

3. M. Rozé, B. Ung, A. Mazhorova, M. Walther, and M. Skorobogatiy, “Suspended core subwavelength fibers: towards practical designs for low-loss terahertz guidance,” Opt. Express 19(10), 9127–9138 (2011). [CrossRef] [PubMed]

]. The outer diameter of the seven-hole fiber is 870 μm, the wire diameter is the same as before and equal to 250 μm, and the air hole diameter is equal to the wire diameter.

Conclusion

A novel type of practical THz fibers is proposed that combines low-loss, low-dispersion and efficient excitation properties of the classic two-wire waveguides together with mechanical robustness, and ease of manipulation of the porous dielectric fibers. We then show that while optical properties of composite fibers are inferior to those of a classic two-wire waveguide, at the same time, composite fibers outperform porous fibers of the same geometry both in bandwidth of operation and in lower dispersion. Finally, we demonstrated that by increasing porosity of the fiber dielectric cladding its optical properties could be consistently improved.

Particularly, using the finite element method we first ascertained that a classic two-wire waveguide features very low loss (<0.01 cm−1) and very low group velocity dispersion (<0.1 ps/(THz·cm)) in the whole THz spectral range. We then studied coupling efficiency into such a waveguide as a function of various geometrical parameters and concluded that for an optimised waveguide, excitation efficiency of the fundamental mode can be relatively high (>50%) in the broad frequency range ~1 THz. Moreover, we confirmed that this excitation efficiency has a weak dependence on the misalignment in the position of a Gaussian excitation beam that was considered as the excitation source.

Next, we proposed using porous polyethylene cladding as a mechanical support for the two metal wires in order to provide a practical packaging solution for the classical two-wire waveguide. In their simplest implementation, resultant composite fibers feature three adjacent air holes placed in a plastic cladding. Two peripheral holes are occupied by the metal wires, while the central one is used to guide the THz light. We then concluded that in a three-hole fiber the lowest order modes could be classified as either plasmonic modes or the modes of a porous cladding. This identification is possible when comparing field distributions and dispersion relations of the composite fiber modes with those of a corresponding porous fiber without metal wires, as well as with those of a classic two-wire waveguide.

Notably, the fundamental plasmonic mode of a composite fiber extends into very low frequencies (<0.1 THz), while being well confined within the fiber. Both the fundamental and second plasmonic modes have reasonable excitation efficiencies of >10% in the broad frequency range 0.25 – 1.25 THz, while having relatively low group velocity dispersion of 1-3 ps/(THz·cm) and absorption losses that are, generally, 1.5–3 times smaller than the bulk absorption loss of a polyethylene cladding in the broad THz range 0.1 – 0.6 THz.

Similarly, the lowest order cladding mode of a composite fiber has, generally, lower absorption losses compared to those of the fundamental mode of the corresponding porous fiber without wires. At the same time, group velocity dispersion of this mode at low frequencies <0.3THz can be as high as 10 ps/(THz·cm), which is typical for porous fibers. Finally, coupling into the lowest order cladding mode of a composite fiber is quite efficient at lower frequencies < 1.0 THz and could be consistently above 50%.

We, therefore, conclude that composite three-hole fiber can somewhat outperform the corresponding porous fiber without wires, in terms of the bandwidth, absorption losses and lower group velocity dispersion if a restricted launch condition is used in order to preferentially excite the fiber plasmonic modes.

Finally, we demonstrated that the optical properties of a composite fiber could be consistently improved by further increasing the porosity of the fiber cladding. As an example, we considered a seven-hole composite fiber and demonstrated that such a fiber can have absorption losses that are at least ~3–5 times smaller than those of the bulk polyethylene in the broad THz frequency range 0.1 – 1.2 THz. Moreover, coupling efficiency into some plasmonic modes of such fibers was significantly improved (above 50% in the 0.75-1.25 THz range), thus enabling low-loss light transmission with low group velocity dispersion of <3 ps/(THz·cm). In this case of higher cladding porosity, the seven-hole composite fiber can clearly outperform the corresponding porous fiber both in the overall bandwidth and in the lower group velocity dispersion.

In order to consistently improve the optical properties of a composite two-wire fiber one has to further increase porosity of its plastic cladding. The composite fibers presented in this work have simple geometries, which are easy to fabricate. At the same time, it appears that more complex structures offering higher porosities have to investigated in order to approach the outstanding low-loss, low-dispersion performance of the classic two-wire waveguides.

References and links

1.

Y.-S. Jin, G.-J. Kim, and S.-G. Jeon, “Terahertz Dielectric Properties of Polymers,” J. Korean Phys. Soc. 49, 513–517 (2006).

2.

B. Ung, A. Mazhorova, A. Dupuis, M. Rozé, and M. Skorobogatiy, “Polymer microstructured optical fibers for terahertz wave guiding,” Opt. Express 19(26), B848–B861 (2011). [CrossRef] [PubMed]

3.

M. Rozé, B. Ung, A. Mazhorova, M. Walther, and M. Skorobogatiy, “Suspended core subwavelength fibers: towards practical designs for low-loss terahertz guidance,” Opt. Express 19(10), 9127–9138 (2011). [CrossRef] [PubMed]

4.

L.-J. Chen, H.-W. Chen, T.-F. Kao, J.-Y. Lu, and C.-K. Sun, “Low-loss subwavelength plastic fiber for terahertz waveguiding,” Opt. Lett. 31(3), 308–310 (2006). [CrossRef] [PubMed]

5.

T. Ito, Y. Matsuura, M. Miyagi, H. Minamide, and H. Ito, “Flexible terahertz fiber optics with low bend-induced losses,” J. Opt. Soc. Am. B 24(5), 1230–1235 (2007). [CrossRef]

6.

J. A. Harrington, R. George, P. Pedersen, and E. Mueller, “Hollow polycarbonate waveguides with inner Cu coatings for delivery of terahertz radiation,” Opt. Express 12(21), 5263–5268 (2004). [CrossRef] [PubMed]

7.

B. Bowden, J. A. Harrington, and O. Mitrofanov, “Silver/polystyrene-coated hollow glass waveguides for the transmission of terahertz radiation,” Opt. Lett. 32(20), 2945–2947 (2007). [CrossRef] [PubMed]

8.

A. Dupuis, K. Stoeffler, B. Ung, C. Dubois, and M. Skorobogatiy, “Transmission measurements of hollow-core THz Bragg fibers,” J. Opt. Soc. Am. B 28(4), 896–907 (2011). [CrossRef]

9.

C.-H. Lai, B. You, J.-Y. Lu, T.-A. Liu, J.-L. Peng, C.-K. Sun, and H. C. Chang, “Modal characteristics of antiresonant reflecting pipe waveguides for terahertz waveguiding,” Opt. Express 18(1), 309–322 (2010). [CrossRef] [PubMed]

10.

S. Sato, T. Katagiri, and Y. Matsuura, “Fabrication method of small-diameter hollow waveguides for terahertz waves,” J. Opt. Soc. Am. B 29(11), 3006–3009 (2012). [CrossRef]

11.

A. Mazhorova, A. Markov, B. Ung, M. Rozé, S. Gorgutsa, and M. Skorobogatiy, “Thin chalcogenide capillaries as efficient waveguides from mid-infrared to terahertz,” J. Opt. Soc. Am. B 29(8), 2116 (2012). [CrossRef]

12.

R. Mendis and D. Grischkowsky, “Undistorted guided-wave propagation of subpicosecond terahertz pulses,” Opt. Lett. 26(11), 846–848 (2001). [CrossRef] [PubMed]

13.

M. Nagel, A. Marchewka, and H. Kurz, “Low-index discontinuity terahertz waveguides,” Opt. Express 14(21), 9944–9954 (2006). [CrossRef] [PubMed]

14.

K. Wang and D. M. Mittleman, “Metal wires for terahertz wave guiding,” Nature 432(7015), 376–379 (2004). [CrossRef] [PubMed]

15.

K. Wang and D. Mittleman, “Guided propagation of terahertz pulses on metal wires,” J. Opt. Soc. Am. B 22(9), 2001–2008 (2005). [CrossRef]

16.

M. Mbonye, R. Mendis, and D. Mittleman, “A terahertz two-wire waveguide with low bending loss,” Appl. Phys. Lett. 95(23), 233506 (2009). [CrossRef]

17.

A. Mazhorova, A. Markov, A. Ng, R. Chinnappan, O. Skorobogata, M. Zourob, and M. Skorobogatiy, “Label-free bacteria detection using evanescent mode of a suspended core terahertz fiber,” Opt. Express 20(5), 5344–5355 (2012). [CrossRef] [PubMed]

18.

A. Markov, S. Gorgutsa, H. Qu, and M. Skorobogatiy, “Practical Metal-Wire THz Waveguides,” arXiv:1206.2984 (2012); also presented at the Gordon Research Conference in Plasmonics, ME, USA (2012).

19.

J. Anthony, R. Leonhardt, and A. Argyros, “Hybrid hollow core fibers with embedded wires as THz waveguides,” Opt. Express 21(3), 2903–2912 (2013). [CrossRef] [PubMed]

20.

H. Pahlevaninezhad and T. E. Darcie, “Coupling of Terahertz Waves to a Two-Wire Waveguide,” Opt. Express 18(22), 22614–22624 (2010). [CrossRef] [PubMed]

21.

M. A. Ordal, R. J. Bell, R. W. Alexander Jr, L. L. Long, and M. R. Querry, “Optical properties of fourteen metals in the infrared and far infrared: Al, Co, Cu, Au, Fe, Pb, Mo, Ni, Pd, Pt, Ag, Ti, V, and W,” Appl. Opt. 24(24), 4493–4499 (1985). [CrossRef] [PubMed]

22.

E. J. Zeman and G. C. Schatz, “An accurate electromagnetic theory study of surface enhancement factors for silver, gold, copper, lithium, sodium, aluminum, gallium, indium, zinc, and cadmium,” J. Phys. Chem. 91(3), 634–643 (1987). [CrossRef]

23.

Y.-S. Lee, Principles of Terahertz Science and Technology (Springer, 2008).

24.

A. Hassani, A. Dupuis, and M. Skorobogatiy, “Low loss porous terahertz fibers containing multiple subwavelength holes,” Appl. Phys. Lett. 92(7), 071101 (2008). [CrossRef]

25.

A. Hassani, A. Dupuis, and M. Skorobogatiy, “Porous polymer fibers for low-loss Terahertz guiding,” Opt. Express 16(9), 6340–6351 (2008). [CrossRef] [PubMed]

26.

A. Dupuis, J. F. Allard, D. Morris, K. Stoeffler, C. Dubois, and M. Skorobogatiy, “Fabrication and THz loss measurements of porous subwavelength fibers using a directional coupler method,” Opt. Express 17(10), 8012–8028 (2009). [CrossRef] [PubMed]

27.

M. Skorobogatiy, Nanostructured and Subwavelength Waveguides (Wiley, 2012).

OCIS Codes
(060.2310) Fiber optics and optical communications : Fiber optics
(040.2235) Detectors : Far infrared or terahertz
(250.5403) Optoelectronics : Plasmonics

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: February 21, 2013
Revised Manuscript: April 15, 2013
Manuscript Accepted: May 14, 2013
Published: May 16, 2013

Citation
Andrey Markov and Maksim Skorobogatiy, "Two-wire terahertz fibers with porous dielectric support," Opt. Express 21, 12728-12743 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-10-12728


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References

  1. Y.-S. Jin, G.-J. Kim, and S.-G. Jeon, “Terahertz Dielectric Properties of Polymers,” J. Korean Phys. Soc.49, 513–517 (2006).
  2. B. Ung, A. Mazhorova, A. Dupuis, M. Rozé, and M. Skorobogatiy, “Polymer microstructured optical fibers for terahertz wave guiding,” Opt. Express19(26), B848–B861 (2011). [CrossRef] [PubMed]
  3. M. Rozé, B. Ung, A. Mazhorova, M. Walther, and M. Skorobogatiy, “Suspended core subwavelength fibers: towards practical designs for low-loss terahertz guidance,” Opt. Express19(10), 9127–9138 (2011). [CrossRef] [PubMed]
  4. L.-J. Chen, H.-W. Chen, T.-F. Kao, J.-Y. Lu, and C.-K. Sun, “Low-loss subwavelength plastic fiber for terahertz waveguiding,” Opt. Lett.31(3), 308–310 (2006). [CrossRef] [PubMed]
  5. T. Ito, Y. Matsuura, M. Miyagi, H. Minamide, and H. Ito, “Flexible terahertz fiber optics with low bend-induced losses,” J. Opt. Soc. Am. B24(5), 1230–1235 (2007). [CrossRef]
  6. J. A. Harrington, R. George, P. Pedersen, and E. Mueller, “Hollow polycarbonate waveguides with inner Cu coatings for delivery of terahertz radiation,” Opt. Express12(21), 5263–5268 (2004). [CrossRef] [PubMed]
  7. B. Bowden, J. A. Harrington, and O. Mitrofanov, “Silver/polystyrene-coated hollow glass waveguides for the transmission of terahertz radiation,” Opt. Lett.32(20), 2945–2947 (2007). [CrossRef] [PubMed]
  8. A. Dupuis, K. Stoeffler, B. Ung, C. Dubois, and M. Skorobogatiy, “Transmission measurements of hollow-core THz Bragg fibers,” J. Opt. Soc. Am. B28(4), 896–907 (2011). [CrossRef]
  9. C.-H. Lai, B. You, J.-Y. Lu, T.-A. Liu, J.-L. Peng, C.-K. Sun, and H. C. Chang, “Modal characteristics of antiresonant reflecting pipe waveguides for terahertz waveguiding,” Opt. Express18(1), 309–322 (2010). [CrossRef] [PubMed]
  10. S. Sato, T. Katagiri, and Y. Matsuura, “Fabrication method of small-diameter hollow waveguides for terahertz waves,” J. Opt. Soc. Am. B29(11), 3006–3009 (2012). [CrossRef]
  11. A. Mazhorova, A. Markov, B. Ung, M. Rozé, S. Gorgutsa, and M. Skorobogatiy, “Thin chalcogenide capillaries as efficient waveguides from mid-infrared to terahertz,” J. Opt. Soc. Am. B29(8), 2116 (2012). [CrossRef]
  12. R. Mendis and D. Grischkowsky, “Undistorted guided-wave propagation of subpicosecond terahertz pulses,” Opt. Lett.26(11), 846–848 (2001). [CrossRef] [PubMed]
  13. M. Nagel, A. Marchewka, and H. Kurz, “Low-index discontinuity terahertz waveguides,” Opt. Express14(21), 9944–9954 (2006). [CrossRef] [PubMed]
  14. K. Wang and D. M. Mittleman, “Metal wires for terahertz wave guiding,” Nature432(7015), 376–379 (2004). [CrossRef] [PubMed]
  15. K. Wang and D. Mittleman, “Guided propagation of terahertz pulses on metal wires,” J. Opt. Soc. Am. B22(9), 2001–2008 (2005). [CrossRef]
  16. M. Mbonye, R. Mendis, and D. Mittleman, “A terahertz two-wire waveguide with low bending loss,” Appl. Phys. Lett.95(23), 233506 (2009). [CrossRef]
  17. A. Mazhorova, A. Markov, A. Ng, R. Chinnappan, O. Skorobogata, M. Zourob, and M. Skorobogatiy, “Label-free bacteria detection using evanescent mode of a suspended core terahertz fiber,” Opt. Express20(5), 5344–5355 (2012). [CrossRef] [PubMed]
  18. A. Markov, S. Gorgutsa, H. Qu, and M. Skorobogatiy, “Practical Metal-Wire THz Waveguides,” arXiv:1206.2984 (2012); also presented at the Gordon Research Conference in Plasmonics, ME, USA (2012).
  19. J. Anthony, R. Leonhardt, and A. Argyros, “Hybrid hollow core fibers with embedded wires as THz waveguides,” Opt. Express21(3), 2903–2912 (2013). [CrossRef] [PubMed]
  20. H. Pahlevaninezhad and T. E. Darcie, “Coupling of Terahertz Waves to a Two-Wire Waveguide,” Opt. Express18(22), 22614–22624 (2010). [CrossRef] [PubMed]
  21. M. A. Ordal, R. J. Bell, R. W. Alexander, L. L. Long, and M. R. Querry, “Optical properties of fourteen metals in the infrared and far infrared: Al, Co, Cu, Au, Fe, Pb, Mo, Ni, Pd, Pt, Ag, Ti, V, and W,” Appl. Opt.24(24), 4493–4499 (1985). [CrossRef] [PubMed]
  22. E. J. Zeman and G. C. Schatz, “An accurate electromagnetic theory study of surface enhancement factors for silver, gold, copper, lithium, sodium, aluminum, gallium, indium, zinc, and cadmium,” J. Phys. Chem.91(3), 634–643 (1987). [CrossRef]
  23. Y.-S. Lee, Principles of Terahertz Science and Technology (Springer, 2008).
  24. A. Hassani, A. Dupuis, and M. Skorobogatiy, “Low loss porous terahertz fibers containing multiple subwavelength holes,” Appl. Phys. Lett.92(7), 071101 (2008). [CrossRef]
  25. A. Hassani, A. Dupuis, and M. Skorobogatiy, “Porous polymer fibers for low-loss Terahertz guiding,” Opt. Express16(9), 6340–6351 (2008). [CrossRef] [PubMed]
  26. A. Dupuis, J. F. Allard, D. Morris, K. Stoeffler, C. Dubois, and M. Skorobogatiy, “Fabrication and THz loss measurements of porous subwavelength fibers using a directional coupler method,” Opt. Express17(10), 8012–8028 (2009). [CrossRef] [PubMed]
  27. M. Skorobogatiy, Nanostructured and Subwavelength Waveguides (Wiley, 2012).

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