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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 3 — Feb. 11, 2013
  • pp: 2903–2912
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Hybrid hollow core fibers with embedded wires as THz waveguides

Jessienta Anthony, Rainer Leonhardt, and Alexander Argyros  »View Author Affiliations


Optics Express, Vol. 21, Issue 3, pp. 2903-2912 (2013)
http://dx.doi.org/10.1364/OE.21.002903


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Abstract

Abstract: We experimentally demonstrate broadband terahertz (THz) pulse propagation through hollow core fibers with two or four embedded Indium wires in a THz time-domain spectroscopy (THz-TDS) setup. The hybrid mode is guided in the air core region with power attenuation coefficients of 0.3 cm−1 and 0.5 cm−1 for the two-wire and four-wire configurations, respectively.

© 2013 OSA

1. Introduction

Technology utilizing THz radiation has increased dramatically in recent times, with demonstrations such as the realization of metamaterials and negative index [1

1. H.-T. Chen, W. J. Padilla, J. M. O. Zide, A. C. Gossard, A. J. Taylor, and R. D. Averitt, “Active terahertz metamaterial devices,” Nature 444(7119), 597–600 (2006). [CrossRef] [PubMed]

] at these frequencies. From a more practical aspect, unguided free-space THz radiation utilized in non-destructive imaging or diagnostics is one example of an application that can potentially tap into a vast market. Beyond the in situ use of THz radiation for material characterization [2

2. K. Kawase, Y. Ogawa, Y. Watanabe, and H. Inoue, “Non-destructive terahertz imaging of illicit drugs using spectral fingerprints,” Opt. Express 11(20), 2549–2554 (2003). [CrossRef] [PubMed]

], there exists a demand for flexible THz transportation using waveguides and as such, a growing interest in the study of THz waveguides made of dielectrics and metals has been observed over the last decade. Dielectric waveguides such as polymer ribbons [3

3. R. Mendis and D. Grischkowsky, “Plastic ribbon THz waveguides,” J. Appl. Phys. 88(7), 4449–4451 (2000). [CrossRef]

] and wires [4

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]

], sapphire fibers [5

5. S. P. Jamison, R. W. McGowan, and D. Grischkowsky, “Single-mode waveguide propagation and reshaping of sub-ps terahertz pulses in sapphire fibers,” Appl. Phys. Lett. 76(15), 1987–1989 (2000). [CrossRef]

], photonic crystal slabs [6

6. C. Ponseca Jr, E. Estacio, R. Pobre, G. Diwa, G. de los Reyes, S. Ono, H. Murakami, N. Sarukura, K. Aosaki, Y. Sakane, H. Sato, A. Argyros, and M. C. J. Large, “Transmission characteristics of lens-duct and photonic crystal waveguides in the terahertz region,” J. Opt. Soc. Am. B 26(9), A95–A100 (2009). [CrossRef]

] and dielectric-core photonic crystal fibers (PCF) [7

7. K. Nielsen, H. K. Rasmussen, A. J. Adam, P. C. Planken, O. Bang, and P. U. Jepsen, “Bendable, low-loss Topas fibers for the terahertz frequency range,” Opt. Express 17(10), 8592–8601 (2009). [CrossRef] [PubMed]

,8

8. J. Anthony, R. Leonhardt, A. Argyros, and M. C. J. Large, “Characterization of a microstructured Zeonex terahertz fiber,” J. Opt. Soc. Am. B 28(5), 1013–1018 (2011). [CrossRef]

] have all been demonstrated, but are ultimately limited by the material absorption of the dielectric used. In the pursuit of an improvement beyond these, research has been directed towards waveguides that allow transmission unhindered by dielectric losses, with the THz radiation propagating essentially in air.

THz guidance in air can be achieved by using hollow metal waveguides, such as metallic tubes [9

9. R. W. McGowan, G. Gallot, and D. Grischkowsky, “Propagation of ultrawideband short pulses of terahertz radiation through submillimeter-diameter circular waveguides,” Opt. Lett. 24(20), 1431–1433 (1999). [CrossRef] [PubMed]

], dielectric-lined hollow metal waveguides [10

10. O. Mitrofanov and J. A. Harrington, “Dielectric-lined cylindrical metallic THz waveguides: mode structure and dispersion,” Opt. Express 18(3), 1898–1903 (2010). [CrossRef] [PubMed]

] and parallel plates [11

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

], but is not limited to this approach. Hollow-core dielectric PCF waveguides such as Bragg fibers [12

12. C. S. Ponseca Jr, R. Pobre, E. Estacio, N. Sarukura, A. Argyros, M. C. Large, and M. A. van Eijkelenborg, “Transmission of terahertz radiation using a microstructured polymer optical fiber,” Opt. Lett. 33(9), 902–904 (2008). [CrossRef] [PubMed]

,13

13. 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]

] and kagome fibers [14

14. J. Anthony, R. Leonhardt, S. G. Leon-Saval, and A. Argyros, “THz propagation in kagome hollow-core microstructured fibers,” Opt. Express 19(19), 18470–18478 (2011). [CrossRef] [PubMed]

] offer an alternative, as does propagation on the surfaces of bare wires [15

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

] and metal sheets [16

16. T.-I. Jeon and D. Grischkowsky, “THz Zenneck surface wave (THz surface plasmon) propagation on a metal sheet,” Appl. Phys. Lett. 88(6), 061113 (2006). [CrossRef]

]. The transverse electromagnetic mode (TEM) and the Sommerfeld-wave mode have been demonstrated to propagate along the air-metal interface of the latter two examples, with minimal losses and low dispersion. The propagating TEM modes however do suffer to some extent from diffraction losses due to the incomplete confinement of the guide [17

17. R. Mendis and D. M. Mittleman, “Comparison of the lowest-order transverse-electric (TE1) and transverse-magnetic (TEM) modes of the parallel-plate waveguide for terahertz pulse applications,” Opt. Express 17(17), 14839–14850 (2009). [CrossRef] [PubMed]

], in comparison to the modes in the other enclosed metallic waveguides such as hollow tubes. Meanwhile the Sommerfeld-wave mode is inherently susceptible to bend losses, with the bare wires also being constantly exposed to perturbations and being difficult to handle [18

18. M. Wächter, M. Nagel, and H. Kurz, “Frequency-dependent characterization of THz Sommerfeld wave propagation on single-wires,” Opt. Express 13(26), 10815–10822 (2005). [CrossRef] [PubMed]

].

To improve the usefulness of wire-based waveguides, examples consisting of embedding wires in Styrofoam and using a plastic-coated cable have been reported [19

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

]. Also, a recently reported metallic-grating hollow waveguide [20

20. D. Tian, H. Zhang, Q. Wen, Z. Wang, S. Li, Z. Chen, and X. Guo, “Dual cylindrical metallic grating-cladding polymer hollow waveguide for terahertz transmission with low loss,” Appl. Phys. Lett. 97(13), 133502 (2010). [CrossRef]

] was fabricated from sheets of copper lines transferred onto a polymer substrate via photolithography techniques before being rolled on a cylindrical model and fused by thermal processing methods. However the fabrication techniques reported [19

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

,20

20. D. Tian, H. Zhang, Q. Wen, Z. Wang, S. Li, Z. Chen, and X. Guo, “Dual cylindrical metallic grating-cladding polymer hollow waveguide for terahertz transmission with low loss,” Appl. Phys. Lett. 97(13), 133502 (2010). [CrossRef]

] seem to limit the available options of wire dimensions and waveguide materials. In this paper we investigate the propagation of THz pulses in a hybrid metal-dielectric air-core fiber with embedded indium wires. The complexities of waveguide construction can be reduced by using PCF fabrication technology; we are able to create a hollow guiding region that is unhindered by the supporting material of the wires without the expense of constrained molds. The advantages of exploiting this fabrication method are that the spatial distance between the wires can be controlled with ease and precision, and the inclusion of thinner metal wires becomes possible since the drawn fibers are not prohibited by manual mounting and fragile supports. The use of a suitable dielectric host can also enhance the fiber flexibility. Indeed, this fabrication method of co-drawing polymers with indium has already been demonstrated to be a propitious option in manufacturing metamaterials alongside the more intricate methods of photolithography [21

21. A. Tuniz, B. T. Kuhlmey, R. Lwin, A. Wang, J. Anthony, R. Leonhardt, and S. C. Fleming, “Drawn metamaterials with plasmonic response at terahertz frequencies,” Appl. Phys. Lett. 96(19), 191101 (2010). [CrossRef]

].

In this work, we report on the fabrication of these hybrid fibers and their characterization using THz time domain spectroscopy (TDS). We investigate configurations with two and four metal wires surrounding the hollow core, and report on numerical studies of such designs for comparison. We demonstrate that THz pulses can be guided with low loss in such hollow-core fibers with metallic inclusions.

2. Method of experiments, fiber fabrication and numerical simulations

A standard free-space THz-TDS setup as in Fig. 1(a)
Fig. 1 (a) Schematic of THz-TDS setup using photoconductive antennas as a THz emitter and a THz detector to characterize the fibers. The THz emission is modulated with 40V amplitude at 28 kHz. The THz electric field direction is out of the page. (b) Micrograph of the fabricated two-wire fiber sample with core diameter of about 2 mm. The indium wires are located at the left- and right-hand side of the hollow core and are seen as optically silvertone in this micrograph. The four-wire fiber samples have all cladding holes filled with Indium.
was used to characterize the fibers, where both the THz generator and detector consisted of photoconductive antennas. The THz beam was collimated and focused using specially designed symmetric-pass (s-p) lenses [22

22. Y. H. Lo and R. Leonhardt, “Aspheric lenses for terahertz imaging,” Opt. Express 16(20), 15991–15998 (2008). [CrossRef] [PubMed]

] made of ultrahigh molecular weight polyethylene (UHMWPE), one of the low-loss polymers widely used for THz radiation, instead of the commonly used off-axis parabolic mirrors. A pair of s-p lenses with a focal length f = 75 mm (NA is 0.33) was used for coupling the THz pulses to and from the fibers. The fibers themselves were made by drilling a preform made of Zeonex [8

8. J. Anthony, R. Leonhardt, A. Argyros, and M. C. J. Large, “Characterization of a microstructured Zeonex terahertz fiber,” J. Opt. Soc. Am. B 28(5), 1013–1018 (2011). [CrossRef]

], another polymer with low loss in the THz region, and drawing it to the desired dimensions. Molten indium was inserted via suction into the selected (two or four) holes to form the conducting wires. Indium was chosen because of its low melting temperature (156.6 °C). The fibers investigated had a core diameter of approximately 2 mm measured as the distance between the edges of the parallel wires. The wires had an average diameter of 1.0 mm along the semi-minor axis and 1.8 mm along the semi-major axis. An image of the fiber endface with two wires is shown in Fig. 1(b).

The lengths of fiber used were 5 to 10 cm for the two-wire configuration, and 5 to 8 cm for the four-wire configuration. The Fourier transform of the recorded electric field of the reference (without the fiber sample) and that through the fibers were used to collate the spectral information for the fibers in each case. The power attenuation constant was determined from the ratio of the absolute square of the complex modulus of the transformed data for different fiber lengths. The coupling to fibers for samples of different length was assumed to be constant, as the average of tens of scans was used for each of the fiber measurements. The phase of the radiation transmitted through the fibers was compared to the reference scan to determine the mode effective phase indices.

The numerical investigation of the fiber properties was conducted using the finite-difference-frequency-domain solver employed by MODE [23

23. MODE Solutions, www.lumerical.com.

]. The simulations used an image of the transverse cross-section of the fiber, with the appropriate material data, i.e. the refractive index and attenuation constant of Zeonex [8

8. J. Anthony, R. Leonhardt, A. Argyros, and M. C. J. Large, “Characterization of a microstructured Zeonex terahertz fiber,” J. Opt. Soc. Am. B 28(5), 1013–1018 (2011). [CrossRef]

], and the complex permittivity of indium [24

24. R. Y. Koyama, N. V. Smith, and W. E. Spicer, “Optical properties of indium,” Phys. Rev. B 8(6), 2426–2432 (1973). [CrossRef]

]. Alternatively, indium was treated as a perfect conductor.

3. Fiber characteristics

3.1 Mode propagation in two-wire and four-wire configurations

The measured temporal signals of the reference and through the two-wire and four- wire fibers are plotted in Figs. 2(a)
Fig. 2 Measured temporal signals through several lengths of (a) two-wire and (b) four wire fibers. Inset in (a) is the input reference pulse. Vertical dashed cyan lines indicate the position of the amplitude peak, to highlight time delays from 1 to 2 ps for the different fiber lengths. All temporal signals through the fibers are on the same scale. (c) The calculated group index for the fibers shows a group index is close to that of air (n = 1.0).
and 2(b). For the two-wire configuration, the electric-field polarization was oriented in the plane of the wires. It is seen that the centers of the pulses from the different fibers are only displaced by a few ps relative to the reference. This delay is expected as the group index of the propagating modes will be greater than 1, and indeed was calculated to range between ~1.01 at higher frequencies, and 1.06 at lower frequencies in the range of interest (0.6 to 1.1 THz), as shown in Fig. 2(c). The chirping observed in the fiber output pulses in Figs. 2(a) and 2(b) is also in qualitative agreement with this decrease in group index at higher frequencies.

The mode guided through the fibers in the frequency range investigated is the HE11-like mode. The scanned mode profiles are shown in Figs. 3(a)
Fig. 3 Experimentally observed mode field intensity (normalized, linear plot) at 0.8 THz from a 5 cm length of (a) two-wire and (b) four-wire fiber. In the two-wire fiber in (a) the metal wires are aligned in the x-direction. The white vectors show the simulation results of magnitude and direction of the mode electric-field components obtained from MODE. The mode simulation plots at 1.2 THz for (c) Hz and (d) Ez components for the two-wire fiber show the hybrid mode characteristics, having non-zero longitudinal components. The simulated mode at (e) 0.65 THz and (f) 1.2 THz for the two-wire fiber shows some energy leaked into the cladding holes for the lower frequency, compared to the near-round shape at higher frequency. In all (c-f) plots, the color map is linear and the metal is in the left and right side of the hollow core. (g) The full-width-half-maximum (FWHM) of the modes as calculated from the simulations for the two-wire (blue) and four-wire (red-filled triangle) fibers. The FWHM experimental data are obtained from the mode scan of the two-wire (black-hollow square and black-filled circle) and the four-wire (black-hollow triangle) configurations. The FWHM for the four-wire configuration has one-standard deviation (black vertical line). The average FWHM for the two-wire configuration is calculated separately along the axes with and without wires.
and 3(b) for each fiber, in agreement with the simulation results, and furthermore the simulated mode fields show non-zero Ez and Hz components (Figs. 3(c) and 3(d)), confirming the HE11-like behavior. The measured mode profile is taken from raster scanning the output end of the fiber with a metal pinhole with a diameter of 0.8 mm in the focal plane of the s-p lens. Our numerical simulations indicate that higher order modes show markedly higher loss. The high losses of the other higher order modes and the better mode-matching efficiency with the Gaussian-profile input beam contribute to the fundamental mode being the only mode observed. We also note that the annular TE01 mode, the lowest loss mode found in circular hollow metallic waveguides [25

25. E. A. J. Marcatili and R. A. Schmeltzer, “Hollow core and dielectric waveguides for long distance optical transmission and lasers,” Bell Syst. Tech. J. 43, 1783–1809 (1964).

] and also present in dielectric-lined hollow metallic waveguides [10

10. O. Mitrofanov and J. A. Harrington, “Dielectric-lined cylindrical metallic THz waveguides: mode structure and dispersion,” Opt. Express 18(3), 1898–1903 (2010). [CrossRef] [PubMed]

], did not emerge in the simulation results of either the two-wire or four-wire fibers, nor was any evidence of it observed experimentally. The discontinuity of the fiber boundary conditions in the azimuthal direction is thought to prohibit the manifestation of such azimuthally polarized modes. We confirmed in simulations that in an ideal, thin dielectric-lined hollow metal tube with the same parameters used in this work, the TE01 mode is indeed supported in the core. However, introducing an azimuthal discontinuity in the metal akin to the fibers presented in this work caused this mode to no longer be supported.

At low frequencies the spatial distribution of the modes become increasingly distinct as differences develop in the two-wire fiber along the axes that have/lack the wires as shown by the simulated mode in Figs. 3(e) and 3(f). The two-wire and four-wire fibers do not differ much in the shape of the mode at high frequencies, clearly seen in Fig. 3(f). In Fig. 3(g), the full-width-half-maximum (FWHM) of the Poynting vector in the direction of propagation (Pz) is plotted for each fiber. The simulated mode areas from both fibers were fitted with an elliptical function to approximate the mode widths – for circular shaped modes, a single width was returned. The directions of the axes of the ellipses were found to coincide with the positions of the wires, as expected. With the four-wire fiber, the mode size was almost identical along both axes, and this was averaged and plotted as red-filled triangles in Fig. 3(g). In the two-wire configuration, the mode is elliptical (plotted as blue-empty circles and filled squares in Fig. 3(g)), most pronounced at low frequencies. At these lower frequencies/longer wavelengths there is some leakage into the air holes adjacent to the core, as well as the mode re-shaping (contracting) in the plane of the two wires. The former does not greatly influence the mode shape as observed in Fig. 3(g) (blue-empty circles), where the mode FWHM is seen to remain approximately constant. The latter effect is more prominent, also seen in Fig. 3(g) (filled squares). Figure 3(e) shows that as the central lobe of the mode reshaped in the plane of the wires, two additional lobes emerge concentrated on the thin dielectric layer on the metal surface. The wire separation in Fig. 3(e) is approximately 4λ(at 0.65 THz), and this weak additional concentration of field near the metal surface is reminiscent of surface plasmon modes. Such modes are prone to some radiation losses at randomly uneven surfaces [26

26. D. L. Mills, “Attenuation of surface polaritons by surface roughness,” Phys. Rev. B 12(10), 4036–4046 (1975). [CrossRef]

] along the fiber axis. From the scanned mode profiles, we calculated the mode widths with respect to the axis that have/lack metal wires, and the measurement give similar curves to the calculated FWHMs from the simulation. The discrepancies of the values from the measured and simulated FWHMs are attributed to the variance in the measured fiber core diameters. We note that the asymmetry in the mode shape is not extreme, with the mode size differing by up to only 20% along the two axes. However, this will cause the mode-matching to the input Gaussian beam to be slightly reduced in the two-wire fiber compared to the four-wire configuration.

3.2 Attenuation constants

Figures 4(a)
Fig. 4 Loss coefficients as measured (grey) and as simulated (red line) for (a) two-wire and (b) four-wire fibers. The plotted vertical thin (grey) lines represent one standard deviation of measurement values. The green regions in both plots indicate the frequencies where the simulations gave no solutions to the eigenvalue problem formulation employed by MODE.
and 4(b) shows the power absorption coefficient determined from the experiments, along with the simulated values for the two-wire and four-wire fibers. The experimentally measured average power attenuation coefficients were 0.3 cm−1 for the two-wire and 0.5 cm−1 for the four-wire configurations averaged over several lengths of fiber. Overall, the experimentally determined data show good agreement with the values obtained from the simulations. The simulated attenuation was not affected when the indium was replaced with a perfect electric conductor, indicating that metallic losses were not significant. However, scattering loss due to the metal is not computed in this simulation procedure. Discrepancies between the measured loss values and the simulated values originate from defects in the fiber samples used in the experiments such as non-uniformities along the core walls and irregularities of the indium surfaces.

3.3 Effective phase index and dispersion parameter

For the two-wire configuration, the experimentally determined data give on average a dispersion magnitude of the order of 5 psTHz−1cm−1 within the frequency range of 0.65 to 1.0 THz; the four-wire configuration has less than 5 psTHz−1cm−1 between 0.7 to 0.95 THz. For comparison, an explicit β2 value of 8 psTHz−1cm−1 is reported in [10

10. O. Mitrofanov and J. A. Harrington, “Dielectric-lined cylindrical metallic THz waveguides: mode structure and dispersion,” Opt. Express 18(3), 1898–1903 (2010). [CrossRef] [PubMed]

] for dielectric waveguides with metallic inclusions, and the data obtained here strongly indicate comparable low dispersion propagation achieved with the two-wire and four-wire configurations. We note that qualitative comparison with the data obtained from other works on metallic inclusion waveguides (e.g [9

9. R. W. McGowan, G. Gallot, and D. Grischkowsky, “Propagation of ultrawideband short pulses of terahertz radiation through submillimeter-diameter circular waveguides,” Opt. Lett. 24(20), 1431–1433 (1999). [CrossRef] [PubMed]

,11

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

]. among others) shows similar trend of dispersion behavior: steeper rise near the cut-off frequencies and flatter curves towards higher frequencies. Simulation data for these fibers suggest that the two-wire configuration is a better candidate than the four-wire configuration in managing lower dispersion pulse propagation, as it is seen in Fig. 7 where an average of zero dispersion is feasible from 0.6 to 1.05 THz. Nonetheless, both fibers exhibit calculated β2 values of less than 10 psTHz−1cm−1 in the frequency range of 0.6 to 1.05 THz. From the perspective of guided modes in a hollow core fiber, we note that this is a marked improvement in comparison to that obtained from some all-dielectric PCFs [14

14. J. Anthony, R. Leonhardt, S. G. Leon-Saval, and A. Argyros, “THz propagation in kagome hollow-core microstructured fibers,” Opt. Express 19(19), 18470–18478 (2011). [CrossRef] [PubMed]

].

4. Conclusions and outlook

We demonstrated THz guidance in an air core fiber with two or four embedded indium wires. The average measured power loss was 0.3 cm−1 for the two-wire fiber, and 0.5 cm−1 for the four-wire fiber. The measured data are in good agreement with simulations. The dominant guided mode is a HE11-like mode. We observed experimentally that both polarizations; parallel and perpendicular to the wire plane in the two-wire case, are guided and with similar low-frequency cut-offs, albeit a reduced transmission amplitude was observed in the latter. It is also noted that the TE01 mode was not observed either in experiments or simulations. Also, no higher order modes were observed experimentally.

In the context of the performance of our metallic inclusion fibers, these fibers offer an approximate two-fold reduction in the loss compared to hollow multimode metallic tubes [30

30. G. Gallot, S. P. Jamison, R. W. McGowan, and D. Grischkowsky, “Terahertz waveguides,” J. Opt. Soc. Am. B 17(5), 851–863 (2000). [CrossRef]

] and have comparable loss to manually mounted parallel-plate configurations [11

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

]. For waveguides with approximate dimensions as the fibers presented here, they offer at least three times reduction in loss compared to broadband air-core kagome fibers [14

14. J. Anthony, R. Leonhardt, S. G. Leon-Saval, and A. Argyros, “THz propagation in kagome hollow-core microstructured fibers,” Opt. Express 19(19), 18470–18478 (2011). [CrossRef] [PubMed]

] within the same frequency range. Improvement of the metallic inclusion fiber designs and fabrication is anticipated to enable low loss HE11 mode guidance as demonstrated in [7

7. K. Nielsen, H. K. Rasmussen, A. J. Adam, P. C. Planken, O. Bang, and P. U. Jepsen, “Bendable, low-loss Topas fibers for the terahertz frequency range,” Opt. Express 17(10), 8592–8601 (2009). [CrossRef] [PubMed]

,8

8. J. Anthony, R. Leonhardt, A. Argyros, and M. C. J. Large, “Characterization of a microstructured Zeonex terahertz fiber,” J. Opt. Soc. Am. B 28(5), 1013–1018 (2011). [CrossRef]

,20

20. D. Tian, H. Zhang, Q. Wen, Z. Wang, S. Li, Z. Chen, and X. Guo, “Dual cylindrical metallic grating-cladding polymer hollow waveguide for terahertz transmission with low loss,” Appl. Phys. Lett. 97(13), 133502 (2010). [CrossRef]

].

In conclusion, we demonstrated THz guidance through a hollow-core dielectric fiber with metallic wire inclusions. We found that the mode diffraction losses and radiation losses in open boundary waveguides such as parallel-plates and dual wires configurations can be eliminated in the proposed hollow-core fibers with embedded metallic wires. Work towards reducing the current loss values of these fibers should include improving the fabrication techniques to ensure smoother metal surface contact to the dielectric film by the core region as well as maintaining uniformity of the shape of the metal wires. Future work will also concentrate on the birefringence of the two-wire configuration.

Acknowledgments

J.A. acknowledges the financial support of Industrial Research Limited (IRL) New Zealand. A.A. is supported by an Australian Research Council Australian Research Fellowship. This work was performed in part at the OptoFab node of the Australian National Fabrication Facility, a company established under the National Collaborative Research Infrastructure Strategy to provide nanofabrication and microfabrication facilities for Australian researchers.

References and links

1.

H.-T. Chen, W. J. Padilla, J. M. O. Zide, A. C. Gossard, A. J. Taylor, and R. D. Averitt, “Active terahertz metamaterial devices,” Nature 444(7119), 597–600 (2006). [CrossRef] [PubMed]

2.

K. Kawase, Y. Ogawa, Y. Watanabe, and H. Inoue, “Non-destructive terahertz imaging of illicit drugs using spectral fingerprints,” Opt. Express 11(20), 2549–2554 (2003). [CrossRef] [PubMed]

3.

R. Mendis and D. Grischkowsky, “Plastic ribbon THz waveguides,” J. Appl. Phys. 88(7), 4449–4451 (2000). [CrossRef]

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.

S. P. Jamison, R. W. McGowan, and D. Grischkowsky, “Single-mode waveguide propagation and reshaping of sub-ps terahertz pulses in sapphire fibers,” Appl. Phys. Lett. 76(15), 1987–1989 (2000). [CrossRef]

6.

C. Ponseca Jr, E. Estacio, R. Pobre, G. Diwa, G. de los Reyes, S. Ono, H. Murakami, N. Sarukura, K. Aosaki, Y. Sakane, H. Sato, A. Argyros, and M. C. J. Large, “Transmission characteristics of lens-duct and photonic crystal waveguides in the terahertz region,” J. Opt. Soc. Am. B 26(9), A95–A100 (2009). [CrossRef]

7.

K. Nielsen, H. K. Rasmussen, A. J. Adam, P. C. Planken, O. Bang, and P. U. Jepsen, “Bendable, low-loss Topas fibers for the terahertz frequency range,” Opt. Express 17(10), 8592–8601 (2009). [CrossRef] [PubMed]

8.

J. Anthony, R. Leonhardt, A. Argyros, and M. C. J. Large, “Characterization of a microstructured Zeonex terahertz fiber,” J. Opt. Soc. Am. B 28(5), 1013–1018 (2011). [CrossRef]

9.

R. W. McGowan, G. Gallot, and D. Grischkowsky, “Propagation of ultrawideband short pulses of terahertz radiation through submillimeter-diameter circular waveguides,” Opt. Lett. 24(20), 1431–1433 (1999). [CrossRef] [PubMed]

10.

O. Mitrofanov and J. A. Harrington, “Dielectric-lined cylindrical metallic THz waveguides: mode structure and dispersion,” Opt. Express 18(3), 1898–1903 (2010). [CrossRef] [PubMed]

11.

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

12.

C. S. Ponseca Jr, R. Pobre, E. Estacio, N. Sarukura, A. Argyros, M. C. Large, and M. A. van Eijkelenborg, “Transmission of terahertz radiation using a microstructured polymer optical fiber,” Opt. Lett. 33(9), 902–904 (2008). [CrossRef] [PubMed]

13.

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]

14.

J. Anthony, R. Leonhardt, S. G. Leon-Saval, and A. Argyros, “THz propagation in kagome hollow-core microstructured fibers,” Opt. Express 19(19), 18470–18478 (2011). [CrossRef] [PubMed]

15.

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

16.

T.-I. Jeon and D. Grischkowsky, “THz Zenneck surface wave (THz surface plasmon) propagation on a metal sheet,” Appl. Phys. Lett. 88(6), 061113 (2006). [CrossRef]

17.

R. Mendis and D. M. Mittleman, “Comparison of the lowest-order transverse-electric (TE1) and transverse-magnetic (TEM) modes of the parallel-plate waveguide for terahertz pulse applications,” Opt. Express 17(17), 14839–14850 (2009). [CrossRef] [PubMed]

18.

M. Wächter, M. Nagel, and H. Kurz, “Frequency-dependent characterization of THz Sommerfeld wave propagation on single-wires,” Opt. Express 13(26), 10815–10822 (2005). [CrossRef] [PubMed]

19.

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

20.

D. Tian, H. Zhang, Q. Wen, Z. Wang, S. Li, Z. Chen, and X. Guo, “Dual cylindrical metallic grating-cladding polymer hollow waveguide for terahertz transmission with low loss,” Appl. Phys. Lett. 97(13), 133502 (2010). [CrossRef]

21.

A. Tuniz, B. T. Kuhlmey, R. Lwin, A. Wang, J. Anthony, R. Leonhardt, and S. C. Fleming, “Drawn metamaterials with plasmonic response at terahertz frequencies,” Appl. Phys. Lett. 96(19), 191101 (2010). [CrossRef]

22.

Y. H. Lo and R. Leonhardt, “Aspheric lenses for terahertz imaging,” Opt. Express 16(20), 15991–15998 (2008). [CrossRef] [PubMed]

23.

MODE Solutions, www.lumerical.com.

24.

R. Y. Koyama, N. V. Smith, and W. E. Spicer, “Optical properties of indium,” Phys. Rev. B 8(6), 2426–2432 (1973). [CrossRef]

25.

E. A. J. Marcatili and R. A. Schmeltzer, “Hollow core and dielectric waveguides for long distance optical transmission and lasers,” Bell Syst. Tech. J. 43, 1783–1809 (1964).

26.

D. L. Mills, “Attenuation of surface polaritons by surface roughness,” Phys. Rev. B 12(10), 4036–4046 (1975). [CrossRef]

27.

R. Mendis and D. M. Mittleman, “An investigation of the lowest-order transverse-electric (TE1) mode of the parallel-plate waveguide for THz pulse propagation,” J. Opt. Soc. Am. B 26(9), A6–A13 (2009). [CrossRef]

28.

J. R. Carson, S. P. Mead, and S. A. Schelkunoff, “Hyper-frequency wave guides: mathematical theory,” Bell Syst. Tech. J. 15, 310–333 (1936).

29.

L. J. Chu and W. L. Barrow, “Electromagnetic waves in hollow metal tubes or rectangular cross section,” Proc. I.R.E. 26, 1520–1555 (1938).

30.

G. Gallot, S. P. Jamison, R. W. McGowan, and D. Grischkowsky, “Terahertz waveguides,” J. Opt. Soc. Am. B 17(5), 851–863 (2000). [CrossRef]

OCIS Codes
(060.2280) Fiber optics and optical communications : Fiber design and fabrication
(060.2430) Fiber optics and optical communications : Fibers, single-mode
(300.6495) Spectroscopy : Spectroscopy, teraherz

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: November 15, 2012
Revised Manuscript: January 21, 2013
Manuscript Accepted: January 21, 2013
Published: January 30, 2013

Citation
Jessienta Anthony, Rainer Leonhardt, and Alexander Argyros, "Hybrid hollow core fibers with embedded wires as THz waveguides," Opt. Express 21, 2903-2912 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-3-2903


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References

  1. H.-T. Chen, W. J. Padilla, J. M. O. Zide, A. C. Gossard, A. J. Taylor, and R. D. Averitt, “Active terahertz metamaterial devices,” Nature444(7119), 597–600 (2006). [CrossRef] [PubMed]
  2. K. Kawase, Y. Ogawa, Y. Watanabe, and H. Inoue, “Non-destructive terahertz imaging of illicit drugs using spectral fingerprints,” Opt. Express11(20), 2549–2554 (2003). [CrossRef] [PubMed]
  3. R. Mendis and D. Grischkowsky, “Plastic ribbon THz waveguides,” J. Appl. Phys.88(7), 4449–4451 (2000). [CrossRef]
  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. S. P. Jamison, R. W. McGowan, and D. Grischkowsky, “Single-mode waveguide propagation and reshaping of sub-ps terahertz pulses in sapphire fibers,” Appl. Phys. Lett.76(15), 1987–1989 (2000). [CrossRef]
  6. C. Ponseca, E. Estacio, R. Pobre, G. Diwa, G. de los Reyes, S. Ono, H. Murakami, N. Sarukura, K. Aosaki, Y. Sakane, H. Sato, A. Argyros, and M. C. J. Large, “Transmission characteristics of lens-duct and photonic crystal waveguides in the terahertz region,” J. Opt. Soc. Am. B26(9), A95–A100 (2009). [CrossRef]
  7. K. Nielsen, H. K. Rasmussen, A. J. Adam, P. C. Planken, O. Bang, and P. U. Jepsen, “Bendable, low-loss Topas fibers for the terahertz frequency range,” Opt. Express17(10), 8592–8601 (2009). [CrossRef] [PubMed]
  8. J. Anthony, R. Leonhardt, A. Argyros, and M. C. J. Large, “Characterization of a microstructured Zeonex terahertz fiber,” J. Opt. Soc. Am. B28(5), 1013–1018 (2011). [CrossRef]
  9. R. W. McGowan, G. Gallot, and D. Grischkowsky, “Propagation of ultrawideband short pulses of terahertz radiation through submillimeter-diameter circular waveguides,” Opt. Lett.24(20), 1431–1433 (1999). [CrossRef] [PubMed]
  10. O. Mitrofanov and J. A. Harrington, “Dielectric-lined cylindrical metallic THz waveguides: mode structure and dispersion,” Opt. Express18(3), 1898–1903 (2010). [CrossRef] [PubMed]
  11. R. Mendis and D. Grischkowsky, “Undistorted guided-wave propagation of subpicosecond terahertz pulses,” Opt. Lett.26(11), 846–848 (2001). [CrossRef] [PubMed]
  12. C. S. Ponseca, R. Pobre, E. Estacio, N. Sarukura, A. Argyros, M. C. Large, and M. A. van Eijkelenborg, “Transmission of terahertz radiation using a microstructured polymer optical fiber,” Opt. Lett.33(9), 902–904 (2008). [CrossRef] [PubMed]
  13. 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]
  14. J. Anthony, R. Leonhardt, S. G. Leon-Saval, and A. Argyros, “THz propagation in kagome hollow-core microstructured fibers,” Opt. Express19(19), 18470–18478 (2011). [CrossRef] [PubMed]
  15. K. Wang and D. M. Mittleman, “Metal wires for terahertz wave guiding,” Nature432(7015), 376–379 (2004). [CrossRef] [PubMed]
  16. T.-I. Jeon and D. Grischkowsky, “THz Zenneck surface wave (THz surface plasmon) propagation on a metal sheet,” Appl. Phys. Lett.88(6), 061113 (2006). [CrossRef]
  17. R. Mendis and D. M. Mittleman, “Comparison of the lowest-order transverse-electric (TE1) and transverse-magnetic (TEM) modes of the parallel-plate waveguide for terahertz pulse applications,” Opt. Express17(17), 14839–14850 (2009). [CrossRef] [PubMed]
  18. M. Wächter, M. Nagel, and H. Kurz, “Frequency-dependent characterization of THz Sommerfeld wave propagation on single-wires,” Opt. Express13(26), 10815–10822 (2005). [CrossRef] [PubMed]
  19. M. Mbonye, R. Mendis, and D. M. Mittleman, “A terahertz two-wire waveguide with low bending loss,” Appl. Phys. Lett.95(23), 233506 (2009). [CrossRef]
  20. D. Tian, H. Zhang, Q. Wen, Z. Wang, S. Li, Z. Chen, and X. Guo, “Dual cylindrical metallic grating-cladding polymer hollow waveguide for terahertz transmission with low loss,” Appl. Phys. Lett.97(13), 133502 (2010). [CrossRef]
  21. A. Tuniz, B. T. Kuhlmey, R. Lwin, A. Wang, J. Anthony, R. Leonhardt, and S. C. Fleming, “Drawn metamaterials with plasmonic response at terahertz frequencies,” Appl. Phys. Lett.96(19), 191101 (2010). [CrossRef]
  22. Y. H. Lo and R. Leonhardt, “Aspheric lenses for terahertz imaging,” Opt. Express16(20), 15991–15998 (2008). [CrossRef] [PubMed]
  23. MODE Solutions, www.lumerical.com .
  24. R. Y. Koyama, N. V. Smith, and W. E. Spicer, “Optical properties of indium,” Phys. Rev. B8(6), 2426–2432 (1973). [CrossRef]
  25. E. A. J. Marcatili and R. A. Schmeltzer, “Hollow core and dielectric waveguides for long distance optical transmission and lasers,” Bell Syst. Tech. J.43, 1783–1809 (1964).
  26. D. L. Mills, “Attenuation of surface polaritons by surface roughness,” Phys. Rev. B12(10), 4036–4046 (1975). [CrossRef]
  27. R. Mendis and D. M. Mittleman, “An investigation of the lowest-order transverse-electric (TE1) mode of the parallel-plate waveguide for THz pulse propagation,” J. Opt. Soc. Am. B26(9), A6–A13 (2009). [CrossRef]
  28. J. R. Carson, S. P. Mead, and S. A. Schelkunoff, “Hyper-frequency wave guides: mathematical theory,” Bell Syst. Tech. J.15, 310–333 (1936).
  29. L. J. Chu and W. L. Barrow, “Electromagnetic waves in hollow metal tubes or rectangular cross section,” Proc. I.R.E. 26, 1520–1555 (1938).
  30. G. Gallot, S. P. Jamison, R. W. McGowan, and D. Grischkowsky, “Terahertz waveguides,” J. Opt. Soc. Am. B17(5), 851–863 (2000). [CrossRef]

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