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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 23 — Nov. 18, 2013
  • pp: 27802–27803
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A complementary study to “Hybrid hollow core fibers with embedded wires as THz waveguides” and “Two-wire terahertz fibers with porous dielectric support:” comment

Andrey Markov, Hichem Guerboukha, Alexander Argyros, and Maksim Skorobogatiy  »View Author Affiliations


Optics Express, Vol. 21, Issue 23, pp. 27802-27803 (2013)
http://dx.doi.org/10.1364/OE.21.027802


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Abstract

In a recent paper, Anthony et al. [Opt. Express 21, 2903 (2013)] demonstrated broadband terahertz pulse propagation through the hollow core fibers with two embedded Indium wires. In another paper by A. Markov et al. [Opt. Express 21, 12728 (2013)], we proposed a plasmonic THz fiber featuring two metallic wires held in place by the porous dielectric cladding functioning as a mechanical support. Although the cross sections of the two waveguides look very similar, we were surprised to find that the guidance mechanisms for these two waveguides are quite different. In fact, waveguide considered by A. Markov et al. was guiding a plasmonic mode, while the waveguide presented by Anthony et al. was guiding a dielectric waveguide-like mode. Finally, we have realized that by reducing the waveguide dimensions by a factor of ~10-20 one can transition from the dielectric waveguide guidance as it is demonstrated by Anthony et al. to plasmonic guidance as reported in A. Markov et al. Therefore, we conclude that both waveguide are essentially identical, while their guidance mechanism changes as a function of the waveguide overall size.

© 2013 Optical Society of America

In a recent paper, Anthony et al. [1

1. 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]

] demonstrated broadband terahertz pulse propagation through hollow core fibers with two embedded Indium wires. In another paper [2

2. A. Markov and M. Skorobogatiy, “Two-wire terahertz fibers with porous dielectric support,” Opt. Express 21(10), 12728–12743 (2013). [CrossRef] [PubMed]

], Markov et al. proposed a plasmonic THz fiber featuring two metallic wires held in place by the porous dielectric cladding functioning as a mechanical support. Although the two waveguides appear very similar, as they both contain a plastic cladding and two metal inclusions, their guiding mechanisms are surprisingly quite different. Particularly, the waveguide in [1

1. 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]

] guides a hollow waveguide mode of a plastic capillary, a HE11-like mode concentrated in the centre of the hollow core and with longitudinal field components, while the waveguide in [2

2. A. Markov and M. Skorobogatiy, “Two-wire terahertz fibers with porous dielectric support,” Opt. Express 21(10), 12728–12743 (2013). [CrossRef] [PubMed]

] guides the plasmonic mode bound to the surface of metallic wires. As we have discovered, the main reason for this difference is that the core size of the waveguide in [1

1. 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]

] is 10-20 times bigger than the core size of the waveguide studied in [2

2. A. Markov and M. Skorobogatiy, “Two-wire terahertz fibers with porous dielectric support,” Opt. Express 21(10), 12728–12743 (2013). [CrossRef] [PubMed]

].

Particularly, in [1

1. 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]

] Anthony et al. start with a large hollow tube that is known to support hollow waveguide modes, and then add metallic inclusions. In this case, the large plastic tube is essential for guidance. As a result, the guided mode has an effective refractive index smaller than 1 as expected. In [2

2. A. Markov and M. Skorobogatiy, “Two-wire terahertz fibers with porous dielectric support,” Opt. Express 21(10), 12728–12743 (2013). [CrossRef] [PubMed]

], A. Markov et al. use a different approach. They start with a two-wire waveguide whose size is comparable to the guided wavelength, and then add plastic web for mechanical support. In that case, the plastic cladding is not essential for guidance as the guided mode is a plasmonic one supported by the wires and not by the cladding. Also, the effective refractive index of this mode is higher than 1, which indicates plasmonic guidance.

The loss of the hollow waveguide mode increases as the core size is reduced, and this mode finally disappears when the distance between the two wires becomes smaller than 0.4 mm. In this regime, the guiding mechanism switches to TIR guidance that features much higher absorption losses. By shrinking the fiber dimensions further we observe plasmonic modes localized in the hollow core that are described in paper [2

2. A. Markov and M. Skorobogatiy, “Two-wire terahertz fibers with porous dielectric support,” Opt. Express 21(10), 12728–12743 (2013). [CrossRef] [PubMed]

] [see Fig. 1(b)]. The modes in Fig. 1(b) have refractive indices of 1.15 - 1.35 which clearly demonstrates the different guiding mechanism compared to the modes described in [1

1. 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]

]. Thus, we have confirmed that by shrinking the structure of [1

1. 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]

] by a factor of ~20 one can change the dominant guidance mechanism in a hybrid hollow-core waveguide from that of a dielectric waveguide to a plasmonic waveguide.

References and links

1.

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]

2.

A. Markov and M. Skorobogatiy, “Two-wire terahertz fibers with porous dielectric support,” Opt. Express 21(10), 12728–12743 (2013). [CrossRef] [PubMed]

OCIS Codes
(060.2280) Fiber optics and optical communications : Fiber design and fabrication
(040.2235) Detectors : Far infrared or terahertz
(250.5403) Optoelectronics : Plasmonics
(300.6495) Spectroscopy : Spectroscopy, teraherz

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: September 12, 2013
Manuscript Accepted: October 2, 2013
Published: November 5, 2013

Citation
Andrey Markov, Hichem Guerboukha, Alexander Argyros, and Maksim Skorobogatiy, "A complementary study to “Hybrid hollow core fibers with embedded wires as THz waveguides” and “Two-wire terahertz fibers with porous dielectric support:” comment," Opt. Express 21, 27802-27803 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-23-27802


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