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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 18, Iss. 25 — Dec. 6, 2010
  • pp: 26332–26338
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Bending loss of terahertz pipe waveguides

Jen-Tang Lu, Yu-Chun Hsueh, Yu-Ru Huang, Yuh-Jing Hwang, and Chi-Kuang Sun  »View Author Affiliations


Optics Express, Vol. 18, Issue 25, pp. 26332-26338 (2010)
http://dx.doi.org/10.1364/OE.18.026332


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Abstract

We present an experimental study on the bending loss of terahertz (THz) pipe waveguide. Bending loss of pipe waveguides is investigated for various frequencies, polarizations, core diameters, cladding thicknesses, and cladding materials. Our results indicate that the pipe waveguides with lower guiding loss suffer lower bending loss due to stronger mode confinement. The unexpected low bending loss in the investigated simple leaky waveguide structure promises variety of flexible applications.

© 2010 OSA

1. Introduction

The study of terahertz (THz) waveguides has attracted growing research interests in the past decade [1

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

19

19. H.-W. Chen, C.-M. Chiu, J.-L. Kuo, P.-J. Chiang, H.-C. Chang, and C.-K. Sun, “Subwavelength dielectric-fiber-based terahertz coupler,” J. Lightwave Technol. 27(11), 1489–1495 (2009). [CrossRef]

] and it is a common trend to guide THz waves in dry air for low-loss THz delivery. We recently proposed and demonstrated a low-loss THz air-core pipe waveguide [20

20. C.-H. Lai, Y.-C. Hsueh, H.-W. Chen, Y.-J. Huang, H.-C. Chang, and C.-K. Sun, “Low-index terahertz pipe waveguides,” Opt. Lett. 34(21), 3457–3459 (2009). [CrossRef] [PubMed]

,21

21. 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), http://www.opticsinfobase.org/abstract.cfm?uri=oe-18-1-309. [CrossRef] [PubMed]

] for THz waveguiding. The pipe waveguide is the simplest pipe with a large air core region surrounded by thin and low-index dielectric cladding. The structure of the pipe waveguide is shown in Fig. 1
Fig. 1 (a) Structure of the pipe waveguide. (b) Cross section of the pipe waveguide (n1 = 1).
. The THz guiding mechanism in the air-core was found to be the anti-resonant reflection with a leaky mode nature [20

20. C.-H. Lai, Y.-C. Hsueh, H.-W. Chen, Y.-J. Huang, H.-C. Chang, and C.-K. Sun, “Low-index terahertz pipe waveguides,” Opt. Lett. 34(21), 3457–3459 (2009). [CrossRef] [PubMed]

22

22. N. M. Litchinitser, A. K. Abeeluck, C. Headley, and B. J. Eggleton, “Antiresonant reflecting photonic crystal optical waveguides,” Opt. Lett. 27(18), 1592–1594 (2002). [CrossRef]

], while a low attenuation constant on the order of or lower than 0.005cm−1 was successfully achieved. Without complicated metallic coating or multi-layer structures, the pipe waveguides, just like common water pipes and air pipes, are commercially available. The easy availability significantly enhances the practicability of the pipe waveguide. With commercial Teflon pipes, we previously demonstrated that THz waves can be guided in the air-core region up to a distance of 3 meter [20

20. C.-H. Lai, Y.-C. Hsueh, H.-W. Chen, Y.-J. Huang, H.-C. Chang, and C.-K. Sun, “Low-index terahertz pipe waveguides,” Opt. Lett. 34(21), 3457–3459 (2009). [CrossRef] [PubMed]

].

In this paper, we focus on the experimental aspect of the bending loss of the pipe waveguides. The bending loss is investigated for various frequencies, polarizations, core diameters, cladding thicknesses, and cladding materials. Our result indicates that the pipe waveguides with lower guiding loss also suffer lower bending loss. The unexpected low bending loss in the investigated simple leaky-waveguide-structure promises variety of flexible applications .

2. Experiment

In this paper, we are interested in the bending loss of the fundamental guiding mode (HE11). Even though the pipe waveguide is a multi-mode one, higher-order modes suffer much stronger propagation attenuation [21

21. 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), http://www.opticsinfobase.org/abstract.cfm?uri=oe-18-1-309. [CrossRef] [PubMed]

]. That is to say, after propagation in a long-enough pipe waveguide, the fundamental mode will dominate the output power. Figure 2
Fig. 2 Experimental setup for measuring the bending losses of THz pipe waveguides.
shows the experimental setup for the measurement of a 100-cm long waveguide. We conducted our experiments with a CW Gunn oscillator module tunable between 320 GHz and 420 GHz. The emitted CW THz waves were directly coupled into the input end of the measured pipe waveguide. We used commercial Teflon pipes (Fluo-Tech Industrial Co., Tao Yuan, Taiwan [29]) as THz pipe waveguides, and the pipe-output waves were detected by a Golay cell (Microtech Instruments). First, we measured the output power (Ps) of a straight pipe, and then kept the first 30 cm and the last 20 cm of the pipe straight but bent the middle part of the pipe. The position of the Gunn oscillator module was fixed, and we varied the radius of curvature (R) and the location of the Golay cell. After bending, we measured the output power (Pb) again. The bending loss αR is defined as:
Pb=Ps×eαRL
(1)
L is the length (50 cm in this experiment) of the bent part of the pipe. Since the bending loss was obtained by comparing the output power of straight pipes and that of the bent pipes, the coupling efficiency between Gunn module and the input end of the pipe waveguides did not affect the bending loss calculation.

3. Results and discussion

First, we investigated the dependence of bending loss on frequencies. The core diameter (D) and cladding thickness (t) of the Teflon pipe waveguide in this experiment were 9 mm and 0.5 mm, respectively. Before measuring the bending loss, we checked the attenuation spectra of the pipe waveguide at first (Fig. 3(a)
Fig. 3 (a) Attenuation spectrum of straight Teflon pipe waveguides for D = 9 mm and t = 0.5 mm. (b) Bending loss spectra of the pipe waveguide (D = 9 mm, t = 0.5 mm) for R = 75 cm (solid black squares) and R = 60 cm (solid red circles). Polarization of the input THz waves was perpendicular to the bending plane.
). At or near anti-resonant frequencies (about 420 GHz in this case), the pipe waveguide suffers the lowest attenuation and have excellent mode confinement. In contrast, near resonant frequencies (about 336 GHz in this case), the pipe waveguide suffers high guiding loss, since THz waves are hardly confined in the air-core region. We also measured the THz waves by removing the pipe waveguides in the system, and found that the measured power from free space propagating THz waves is lower than 1% of the output power of the pipe waveguides at anti-resonant frequencies. Thus, the THz stray beams hardly affect our experiments. After measuring the guiding loss, we measured the bending loss of the pipe waveguide, and let the polarization of THz waves perpendicular to the bending plane. Figure 3(b) shows the bending loss spectra of the pipe waveguide. It can be found that when operating frequencies are close to the resonant frequencies, the bending loss increases. On the other hand, near the anti-resonant frequencies, bending loss decreases significantly. The plausible argument is that lower guiding loss indicates better mode confinement, thus leads to lower bending loss. Even though the pipe waveguide is with a leaky mode nature, the measured bending loss at the anti-resonant frequencies is unexpected low. When the R = 60 cm, the measured bending loss is about 0.006 cm−1, which is comparable to the bending loss of a strongly confined THz mode in a dielectric pipe with inner metallic coating [27

27. 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), http://www.opticsinfobase.org/oe/abstract.cfm?URI = OPEX-12–21–5263.

].

We then investigated the relation between bending loss and the polarization of input THz waves. Since the THz waves generated by Gunn oscillator are linearly polarized and the Gunn module is in a compact size (10 × 5 × 15 cm3), we changed the polarization of the input THz waves simply by rotating the Gunn module. In the experiment, the core diameter and cladding thickness of the Teflon pipe waveguide were 9 mm and 0.5 mm, respectively, and the measurement frequency was 420 GHz. At first, we made the polarization perpendicular to the bending plane, and measured the bending loss for different radii of curvatures. After that, we rotated the Gunn module by 90 degrees to make the polarization parallel to the bending plane, and measured the bending loss again. Figure 4
Fig. 4 Bending loss of the Teflon pipe waveguides for polarization perpendicular (solid black squares) and parallel (solid red circles) to the bending plane. Measurement frequency was 420GHz. The core diameter and cladding thickness of the Teflon pipe waveguide in this experiment were 9 mm and 0.5 mm, respectively.
shows the measured bending loss as a function of the bending radius for two different linear polarizations: perpendicular and parallel to the bending plane. Result shown in Fig. 4 indicates that the bending loss of the pipe waveguide is independent on the polarization of the input THz waves. We also checked the polarization of the output waves before and after bending the pipe waveguides. It was observed that the bent pipe waveguides do not change the polarization of the input THz waves (within the noise level).

Finally, we compared the bending loss of glass pipes with that of Teflon pipes. Since glass pipes are hard ones, it is hard to bend glass pipes and measure bending loss directly. Thus, we used statistical methods to estimate the bending loss of glass pipe waveguides: at first, we measured the output power of five straight glass pipe waveguides, and Ps is the average value of the output power. We also had two bent glass pipes with R = 60 cm and one bent glass pipe with R = 75 cm, and measured Pb from them. Figure 7(a)
Fig. 7 (a) Attenuation spectra of Teflon (black solid squares) and glass (red solid circles) pipe waveguides. The core diameter (9mm) and the cladding thickness (1mm) were the same. (b) The corresponding bending loss of the pipe waveguides measured at the anti-resonant frequencies for Teflon (black solid squares) and glass (red solid circles) pipe waveguides. THz polarization was perpendicular to the bending plane.
shows the measured attenuation spectra of Teflon and glass pipe waveguides. At the anti-resonant frequencies (364-368GHz), the attenuation constant of straight glass pipes is about 0.01 cm−1, and that of the straight Teflon pipes is slightly lower than 0.01 cm−1. That is to say, Teflon pipes provide better mode confinement of THz waves. Figure 7(b) shows the bending loss measurement for two different pipes. The measurement results indicate that glass pipe waveguides suffer greater bending loss than Teflon pipe waveguides. Once again, we found that the pipe waveguides with lower guiding loss encounter lower bending loss.

4. Conclusion

In conclusion, bending loss of leaky-mode pipe waveguides is investigated for different frequencies, polarizations, core diameters, cladding thicknesses, and cladding materials. It is observed that bending loss is independent on the polarization of THz waves. Experiment results indicate that, to have a low bending loss, pipe waveguides with a large core diameter and a thin cladding thickness are desired. At or near anti-resonant frequencies, the pipe waveguide also suffers lower bending loss. All different experiments support that those pipe waveguides which possess lower guiding attenuation also possess lower bending loss, attributed to stronger mode confinement. Our investigation indicates that even though it is with a leaky mode nature, the dielectric pipe waveguide holds not only magnificent flexibility but also possess unexpected low bending loss. It is expected that these easily available, low loss, and low bending loss THz pipe waveguides would have a high potential for THz sensing, communication, and imaging applications [30

30. J.-Y. Lu, C.-C. Kuo, C.-M. Chiu, H.-W. Chen, Y.-J. Hwang, C.-L. Pan, and C.-K. Sun, “THz interferometric imaging using subwavelength plastic fiber based THz endoscopes,” Opt. Express 16(4), 2494–2501 (2008), http://www.opticsinfobase.org/abstract.cfm?uri=oe-16-4-2494. [CrossRef] [PubMed]

32

32. Y.-W. Huang, T.-F. Tseng, C.-C. Kuo, Y.-J. Hwang, and C.-K. Sun, “Fiber-based swept-source terahertz radar,” Opt. Lett. 35(9), 1344–1346 (2010). [CrossRef] [PubMed]

].

Acknowledgments

References and links

1.

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

2.

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

3.

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

4.

H. Han, H. Park, M. Cho, and J. Kim, “THz pulse propagation in plastic photonic crystal fiber,” Appl. Phys. Lett. 80(15), 2634–2636 (2002). [CrossRef]

5.

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

6.

M. Goto, A. Quema, H. Takahashi, S. Ono, and N. Sarukura, “Teflon photonic crystal fiber as terahertz waveguide,” Jpn. J. Appl. Lett. 43(No. 2B), L317–L319 (2004). [CrossRef]

7.

T. Hidaka, H. Minamide, H. Ito, J.-I. Nishizawa, K. Tamura, and S. Ichikawa, “Ferroelectric PVDF cladding terahertz waveguide,” J. Lightwave Technol. 23(8), 2469–2473 (2005). [CrossRef]

8.

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]

9.

M. Nagel, A. Marchewka, and H. Kurz, “Low-index discontinuity terahertz waveguides,” Opt. Express 14(21), 9944–9954 (2006), http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-14-21-9944. [CrossRef] [PubMed]

10.

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]

11.

H.-W. Chen, Y.-T. Li, C. L. Pan, J. L. Kuo, J. Y. Lu, L. J. Chen, and C.-K. Sun, “Investigation on spectral loss characteristics of subwavelength terahertz fibers,” Opt. Lett. 32(9), 1017–1019 (2007). [CrossRef] [PubMed]

12.

M. Skorobogatiy and A. Dupuis, “Ferroelectric all-polymer hollow Bragg fibers for terahertz guidance,” Appl. Phys. Lett. 90(11), 113514 (2007). [CrossRef]

13.

R.-J. Yu, B. Zhang, Y.-Q. Zhang, C.-Q. Wu, Z.-G. Tian, and X.-Z. Bai, “Proposal for ultralow loss hollow-core plastic Bragg fiber with cobweb-structured cladding for terahertz waveguiding,” IEEE Photon. Technol. Lett. 19(12), 910–912 (2007). [CrossRef]

14.

J.-Y. Lu, C.-P. Yu, H.-C. Chang, H.-W. Chen, Y.-T. Li, C.-L. Pan, and C.-K. Sun, “Terahertz air-core microstructure fiber,” Appl. Phys. Lett. 92(6), 064105 (2008). [CrossRef]

15.

A. Hassani, A. Dupuis, and M. Skorobogatiy, “Porous polymer fibers for low-loss Terahertz guiding,” Opt. Express 16(9), 6340–6351 (2008), http://www.opticsinfobase.org/oe/abstract.cfm?uri=OE-16-9-6340. [CrossRef] [PubMed]

16.

S. Atakaramians, S. Afshar V, B. M. Fischer, D. Abbott, and T. M. Monro, “Porous fibers: a novel approach to low loss THz waveguides,” Opt. Express 16(12), 8845–8854 (2008), http://www.opticsinfobase.org/abstract.cfm?uri=oe-16-12-8845. [CrossRef] [PubMed]

17.

J.-Y. Lu, C.-M. Chiu, C.-C. Kuo, Y.-J. Hwang, C.-L. Pan, and C.-K. Sun, “Terahertz scanning imaging with a subwavelength plastic fiber,” Appl. Phys. Lett. 92(8), 084102 (2008). [CrossRef]

18.

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), http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-17-10-8592. [CrossRef] [PubMed]

19.

H.-W. Chen, C.-M. Chiu, J.-L. Kuo, P.-J. Chiang, H.-C. Chang, and C.-K. Sun, “Subwavelength dielectric-fiber-based terahertz coupler,” J. Lightwave Technol. 27(11), 1489–1495 (2009). [CrossRef]

20.

C.-H. Lai, Y.-C. Hsueh, H.-W. Chen, Y.-J. Huang, H.-C. Chang, and C.-K. Sun, “Low-index terahertz pipe waveguides,” Opt. Lett. 34(21), 3457–3459 (2009). [CrossRef] [PubMed]

21.

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), http://www.opticsinfobase.org/abstract.cfm?uri=oe-18-1-309. [CrossRef] [PubMed]

22.

N. M. Litchinitser, A. K. Abeeluck, C. Headley, and B. J. Eggleton, “Antiresonant reflecting photonic crystal optical waveguides,” Opt. Lett. 27(18), 1592–1594 (2002). [CrossRef]

23.

S. Février, B. Beaudou, and P. Viale, “Understanding origin of loss in large pitch hollow-core photonic crystal fibers and their design simplification,” Opt. Express 18(5), 5142–5150 (2010), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-5-5142. [CrossRef] [PubMed]

24.

F. Gérôme, R. Jamier, J.-L. Auguste, G. Humbert, and J.-M. Blondy, “Simplified hollow-core photonic crystal fiber,” Opt. Lett. 35(8), 1157–1159 (2010). [CrossRef] [PubMed]

25.

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]

26.

V. Astley, J. Scheiman, R. Mendis, and D. M. Mittleman, “Bending and coupling losses in terahertz wire waveguides,” Opt. Lett. 35(4), 553–555 (2010). [CrossRef] [PubMed]

27.

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), http://www.opticsinfobase.org/oe/abstract.cfm?URI = OPEX-12–21–5263.

28.

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]

29.

http://www.ptfe-plastic.com.tw

30.

J.-Y. Lu, C.-C. Kuo, C.-M. Chiu, H.-W. Chen, Y.-J. Hwang, C.-L. Pan, and C.-K. Sun, “THz interferometric imaging using subwavelength plastic fiber based THz endoscopes,” Opt. Express 16(4), 2494–2501 (2008), http://www.opticsinfobase.org/abstract.cfm?uri=oe-16-4-2494. [CrossRef] [PubMed]

31.

C.-M. Chiu, H.-W. Chen, Y.-R. Huang, Y.-J. Hwang, W.-J. Lee, H.-Y. Huang, and C.-K. Sun, “All-THz fiber-scanning near-field microscopy,” Opt. Lett. 34(7), 1084–1086 (2009). [CrossRef] [PubMed]

32.

Y.-W. Huang, T.-F. Tseng, C.-C. Kuo, Y.-J. Hwang, and C.-K. Sun, “Fiber-based swept-source terahertz radar,” Opt. Lett. 35(9), 1344–1346 (2010). [CrossRef] [PubMed]

OCIS Codes
(130.2790) Integrated optics : Guided waves
(230.7370) Optical devices : Waveguides

ToC Category:
Integrated Optics

History
Original Manuscript: October 4, 2010
Revised Manuscript: November 6, 2010
Manuscript Accepted: November 7, 2010
Published: December 1, 2010

Citation
Jen-Tang Lu, Yu-Chun Hsueh, Yu-Ru Huang, Yuh-Jing Hwang, and Chi-Kuang Sun, "Bending loss of terahertz pipe waveguides," Opt. Express 18, 26332-26338 (2010)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-25-26332


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References

  1. G. Gallot, S. P. Jamison, R. W. McGowan, and D. Grischkowsky, “Terahertz waveguides,” J. Opt. Soc. Am. B 17(5), 851–863 (2000). [CrossRef]
  2. R. Mendis and D. Grischkowsky, “Plastic ribbon THz waveguides,” J. Appl. Phys. 88(7), 4449–4451 (2000). [CrossRef]
  3. R. Mendis and D. Grischkowsky, “Undistorted guided-wave propagation of subpicosecond terahertz pulses,” Opt. Lett. 26(11), 846–848 (2001). [CrossRef]
  4. H. Han, H. Park, M. Cho, and J. Kim, “THz pulse propagation in plastic photonic crystal fiber,” Appl. Phys. Lett. 80(15), 2634–2636 (2002). [CrossRef]
  5. K. Wang and D. M. Mittleman, “Metal wires for terahertz wave guiding,” Nature 432(7015), 376–379 (2004). [CrossRef] [PubMed]
  6. M. Goto, A. Quema, H. Takahashi, S. Ono, and N. Sarukura, “Teflon photonic crystal fiber as terahertz waveguide,” Jpn. J. Appl. Lett. 43(No. 2B), L317–L319 (2004). [CrossRef]
  7. T. Hidaka, H. Minamide, H. Ito, J.-I. Nishizawa, K. Tamura, and S. Ichikawa, “Ferroelectric PVDF cladding terahertz waveguide,” J. Lightwave Technol. 23(8), 2469–2473 (2005). [CrossRef]
  8. 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]
  9. M. Nagel, A. Marchewka, and H. Kurz, “Low-index discontinuity terahertz waveguides,” Opt. Express 14(21), 9944–9954 (2006), http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-14-21-9944 . [CrossRef] [PubMed]
  10. 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]
  11. H.-W. Chen, Y.-T. Li, C. L. Pan, J. L. Kuo, J. Y. Lu, L. J. Chen, and C.-K. Sun, “Investigation on spectral loss characteristics of subwavelength terahertz fibers,” Opt. Lett. 32(9), 1017–1019 (2007). [CrossRef] [PubMed]
  12. M. Skorobogatiy and A. Dupuis, “Ferroelectric all-polymer hollow Bragg fibers for terahertz guidance,” Appl. Phys. Lett. 90(11), 113514 (2007). [CrossRef]
  13. R.-J. Yu, B. Zhang, Y.-Q. Zhang, C.-Q. Wu, Z.-G. Tian, and X.-Z. Bai, “Proposal for ultralow loss hollow-core plastic Bragg fiber with cobweb-structured cladding for terahertz waveguiding,” IEEE Photon. Technol. Lett. 19(12), 910–912 (2007). [CrossRef]
  14. J.-Y. Lu, C.-P. Yu, H.-C. Chang, H.-W. Chen, Y.-T. Li, C.-L. Pan, and C.-K. Sun, “Terahertz air-core microstructure fiber,” Appl. Phys. Lett. 92(6), 064105 (2008). [CrossRef]
  15. A. Hassani, A. Dupuis, and M. Skorobogatiy, “Porous polymer fibers for low-loss Terahertz guiding,” Opt. Express 16(9), 6340–6351 (2008), http://www.opticsinfobase.org/oe/abstract.cfm?uri=OE-16-9-6340 . [CrossRef] [PubMed]
  16. S. Atakaramians, S. Afshar V, B. M. Fischer, D. Abbott, and T. M. Monro, “Porous fibers: a novel approach to low loss THz waveguides,” Opt. Express 16(12), 8845–8854 (2008), http://www.opticsinfobase.org/abstract.cfm?uri=oe-16-12-8845 . [CrossRef] [PubMed]
  17. J.-Y. Lu, C.-M. Chiu, C.-C. Kuo, Y.-J. Hwang, C.-L. Pan, and C.-K. Sun, “Terahertz scanning imaging with a subwavelength plastic fiber,” Appl. Phys. Lett. 92(8), 084102 (2008). [CrossRef]
  18. 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), http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-17-10-8592 . [CrossRef] [PubMed]
  19. H.-W. Chen, C.-M. Chiu, J.-L. Kuo, P.-J. Chiang, H.-C. Chang, and C.-K. Sun, “Subwavelength dielectric-fiber-based terahertz coupler,” J. Lightwave Technol. 27(11), 1489–1495 (2009). [CrossRef]
  20. C.-H. Lai, Y.-C. Hsueh, H.-W. Chen, Y.-J. Huang, H.-C. Chang, and C.-K. Sun, “Low-index terahertz pipe waveguides,” Opt. Lett. 34(21), 3457–3459 (2009). [CrossRef] [PubMed]
  21. 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), http://www.opticsinfobase.org/abstract.cfm?uri=oe-18-1-309 . [CrossRef] [PubMed]
  22. N. M. Litchinitser, A. K. Abeeluck, C. Headley, and B. J. Eggleton, “Antiresonant reflecting photonic crystal optical waveguides,” Opt. Lett. 27(18), 1592–1594 (2002). [CrossRef]
  23. S. Février, B. Beaudou, and P. Viale, “Understanding origin of loss in large pitch hollow-core photonic crystal fibers and their design simplification,” Opt. Express 18(5), 5142–5150 (2010), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-5-5142 . [CrossRef] [PubMed]
  24. F. Gérôme, R. Jamier, J.-L. Auguste, G. Humbert, and J.-M. Blondy, “Simplified hollow-core photonic crystal fiber,” Opt. Lett. 35(8), 1157–1159 (2010). [CrossRef] [PubMed]
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