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Experimental study of air-core dielectric tube at terahertz frequencies
G Model IJLEO-54275; No. of Pages 4
ARTICLE IN PRESS Optik xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Experimental study of air-core dielectric tube at terahertz frequencies Guo-Zhu Jia a , Zhihui Wang b,∗ a b
College of Physics and Electronics Engineering, Sichuan Normal University, Chengdu 610066, China Southwest China Institute of Electronic Technology, Chengdu 610036, China
a r t i c l e
i n f o
Article history: Received 30 June 2013 Accepted 17 December 2013 Available online xxx Keywords: Surface wave Guided waves Terahertz Energy focusing
a b s t r a c t In this paper, an experimental study of air-core dielectric tube waveguide is proposed at terahertz frequencies. By using the THz time domain measure system, the terahertz dispersion characteristics, loss characteristic and energy focusing characteristic of air-core single-layer and dual-layer dielectric tube are obtained. The results show that this type of air-core dielectric tube can realize low dispersion characteristics. Due to the difference of refractive index between two dielectric materials, stronger energy focusing can be achieved in air-core dual-layer dielectric tube. After the coupling of the THz pulse using the dual-layer dielectric tube waveguide, the THz pulse increased 2.4 times compared with the single-layer dielectric tube waveguide at 1.5 THz. © 2014 Elsevier GmbH. All rights reserved.
1. Introduction Terahertz (THz), locating between the infrared and microwave wave bands in the electromagnetic spectrum, is one of the hot research issues because of its great potential applicability in many scientific and technological fields. The interest in THz technology has strongly increased in the last years with diverse applications in the fields of biotechnology [1,2], spectroscopy [3], imaging [4,5], and so on. Efficient guided THz transmission solutions are still under investigation. Many kinds of THz waveguides have been presented [6–14]. Among them, low-loss and high energy coupling THz waveguide which are of great importance for the practical THz applications. However, THz power is strongly absorbed in most kinds of materials, which gives a challenge to achieve low-loss and high energy coupling THz waveguide. Dry air is the most transparent broadly available transmission medium for THz waves, and then a technically useful waveguide has of course to be materialized in some way. Several polymer fibers have been proposed to reduce the loss and enhance the energy coupling for THz guiding [15–19]. Those research results indicate that the polymer fiber has risen up to be one of the most important candidates of THz waveguides. But it is difficult to fabricate those fibers due to its complex cross sections. Then, a novel polymer tube THz waveguide with low loss is proposed by Chen et al. [20]. The polymer tube has some merits, such as low loss, better confinement, and the ease of fabrication, compared with solid polymer fiber. In [20], the refractive
∗ Corresponding author. E-mail address: wzh [email protected] (Z. Wang).
index of the polymer material is assumed to be a low value 1.5. When THz wave propagation along polymer tube, electromagnetic energy distributes in polymer material and the surrounding air region. To enhance the energy focusing characteristic in air-core dielectric tube waveguide and reduce the radiated interference further, a dual-layer dielectric tube waveguide is proposed to be used at terahertz frequencies. In this paper, the terahertz propagation characteristics of air-core single-layer and dual-layer dielectric tube are demonstrated by using experimental method.
2. Structure Fig. 1 shows the geometry and refractive index profile of the dual-layer dielectric tube waveguide. 1 is the radius of air core and n0 is the refractive index of air. 2 is the outer radius of high refractive index dielectric layer and n2 is the refractive index. 3 is the outer radius of low refractive index dielectric layer and the refractive index is n1 . d = 2 − 1 is the thickness of high refractive index dielectric layer and d = 3 − 2 is the thickness of low refractive index dielectric layer. Fig. 2 shows the pictures of the air-core single-layer and dual-layer dielectric tube. For the single-layer dielectric tube, the dielectric material is Teflon. The length is 10 mm, and = 3 = 1.5 mm, 1 = 2 = 1 mm, n = n1 = 1.43, the thickness is d = 0.5 mm. And for the dual-layer dielectric tube, the outer dielectric material is Teflon and the inner dielectric material is HDPE. The length is 10 mm, 1 = 0.5 mm, 2 = 1 mm, 3 = 1.5 mm, n1 = 1.43, n2 = 1.52, the thickness is d = 0.5 mm and d = 0.5 mm, respectively.
0030-4026/$ – see front matter © 2014 Elsevier GmbH. All rights reserved. http://dx.doi.org/10.1016/j.ijleo.2013.12.050
Please cite this article in press as: G.-Z. Jia, Z. Wang, Experimental study of air-core dielectric tube at terahertz frequencies, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2013.12.050
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Fig. 1. (a) Geometry of dual-layer dielectric tube waveguide. (b) Refractive index profile of dual-layer dielectric tube waveguide.
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Fig. 2. (a) Air-core single-layer HDPE tube (left) and Teflon tube (right) and (b) air-core dual-layer dielectric tube.
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Time ( ps ) Fig. 4. The experimental results of air-core dielectric tube. (a) The air-core duallayer dielectric tube; (b) the air-core single-layer Teflon tube and (c) air.
Single-layer Teflon tube (Experimental result) Single-layer Teflon tube (Simluated result) Dual-layer dielectric tube (Experimental result) Dual-layer dielectric tube (Simulated result)
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Effective refractive index
Fig. 3 shows the terahertz time domain system. By using the measure system, the experimental results can be obtained, as shown in Fig. 4. Using Fourier transform, the frequency-dependent propagation characteristics of air-core dielectric tube can be obtained, as shown in Fig. 5. Fig. 5 shows the frequency-dependent effective refractive index neff of air-core dielectric tube. It is clearly seen that at low THz frequency range, especially at 0.1–0.4 THz, the dispersion of the air-core dual-layer dielectric tube waveguide and the single-layer dielectric tube waveguide increases. But with the increase of frequency, the dispersion decreases. The dispersion effect in terms of dheff /df is more and more flat for this type of waveguide. And the measured data exhibit very good agreement with the simulated results that obtained by using HFSS. The results mean that the air-core dielectric tube can realize low dispersion characteristics. Fig. 6 shows the normalized Hr magnitude at the end surface of the cylindrical tube with single polymer layer and the cylindrical tube with double polymer layers by using HFSS, which is based on the finite element method. The outer radius of the cylindrical tube with single low refractive index polymer layer (Teflon: n = 1.43) is 1 mm, and the thickness of polymer layer is 0.5 mm. The configuration parameters of the cylindrical tube with double polymer layers (n0 = 1, Teflon: n1 = 1.43 and HDPE: n2 = 1.52) are 1 = 0.5 mm, 2 = 1 mm, 3 = 1.5 mm. The radiation frequency is 0.5 THz. As shown in Fig. 6, it can be seen that THz wave is well confined in the high refractive index polymer layer. In terahertz system, low radiated interference is necessary. By using the
1.4 1.3 1.2 1.1 1.0 0.0
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Frequency ( THz ) Fig. 3. (a) Schematic of the terahertz time-domain system and (b) picture of the terahertz time-domain system.
Fig. 5. Frequency-dependent effective index refractive of air-core dielectric tube versus frequency.
Please cite this article in press as: G.-Z. Jia, Z. Wang, Experimental study of air-core dielectric tube at terahertz frequencies, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2013.12.050
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Fig. 6. Normalized H field component at 0.5 THz. (a) The air-core single-layer Teflon tube. (b) The air-core dual-layer dielectric tube.
Single-layer Teflon tube (Theoretical result)
3
characteristic than the single-layer Teflon tube. And with the increasing of frequency, the ratio of power also increases. After the coupling of the THz pulse using the dual-layer dielectric tube waveguide, the THz pulse increased 2.4 times compared with the single-layer dielectric tube waveguide at 1.5 THz. The experimental results demonstrate that with the adding of high refractive index dielectric layer, the terahertz power can be focused in the inner of air-core dual-layer dielectric tube effectively. The terahertz power focusing characteristic is enhanced, resulting in the power that distributed in the outer air region is reduced effectively. It means that this type of waveguide can be used for terahertz imaging and sensing applications. 4. Conclusions
Single-layer Teflon tube (Experimental result) Dual-layer dielectric tube (Theoretical result)
1.8
Dual-layer dielectric tube (Experimental result)
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Loss ( 1/m )
1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0.0
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In this paper, the frequency-dependent characteristic of aircore dielectric tube is studied by using experimental method at terahertz frequencies. Due to the difference of refractive index between two dielectric materials, stronger energy focusing can be achieved. After the coupling of the THz pulse using the air-core dual-layer dielectric tube, the THz pulse increased 2.4 times compared with the single-layer Teflon tube waveguide at 1.5 THz. The experimental results show that this type of terahertz waveguide has lower dispersion and the air-core dual-layer dielectric tube waveguide can realize stronger energy focusing characteristic than normal single-layer dielectric tube at terahertz frequencies. The loss characteristic of the air-core dielectric tube is also demonstrated, and the simulation results exhibit very good agreement with the experimental results. The analysis results are very useful for the development of terahertz wave applications, such as spectroscopy, and sensing applications.
Frequency ( THz ) Acknowledgment Fig. 7. Loss of the air-core dielectric tube versus frequency.
cylindrical tube with double polymer layers, enhanced field confinement can be achieved at terahertz frequencies. Fig. 7 shows the loss of air-core dielectric tube. As shown in Fig. 6, the dual-layer dielectric tube shows greater energy coupling characteristic than the single-layer dielectric tube, while greater electromagnetic energy is absorbed by the high refractive index dielectric layer, resulting in the increasing of loss, as show in Fig. 7. Fig. 8 shows P/P (P is the total power of air-core dual-layer dielectric tube and P is the total power of air-core single-layer Teflon tube) versus frequency. As shown in Fig. 8, both the measured results and the simulated results demonstrate that the air-core dual-layer dielectric tube has greater energy focusing Simulation result
2.6
Experimental result
Ratio of P / P
/
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Frequency ( THz ) Fig. 8. The ratio of P/P versus frequency. (P is the total power of dual-layer dielectric tube and P is the total power of single-layer Teflon tube.)
Thanks for the supporting of the National Natural Science Foundation of China (61102044). References [1] P.H. Siegel, Terahertz technology in biology and medicine, IEEE Trans. Microw. Theory Technol. 52 (2004) 2438–2447. [2] M. Nagel, P. Haring Bolivar, M. Brucherseifer, H. Kurz, Integrated THz technology for label-free genetic diagnostics, Appl. Phys. Lett. 80 (2002) 154–156. [3] C.A. Schmuttenmaer, Exploring dynamics in the far-Infrared with terahertz spectroscopy, Chem. Rev. 104 (2004) 1759–1779. [4] X.C. Zhang, Terahertz wave imaging: horizons and hurdles, Phys. Med. Biol. 47 (2002) 3667–3677. [5] M.M. Awad, R.A. Cheville, Transmission terahertz waveguide-based imaging below the diffraction limit, Appl. Phys. Lett. 86 (2005) 1–3. [6] R. Mendis, D. Grischkowsky, Plastic ribbon THz waveguides, J. Appl. Phys. 88 (2000) 4449–4451. [7] S.P. Jamison, R.W. McGown, D. Grischkowsky, Single-mode waveguide propagation and reshaping of sub-ps terahertz pulses in sapphire fiber, Appl. Phys. Lett. 76 (2000) 1987–1989. [8] C.S. Ponseca Jr., R. Pobre, E. Estacio, N. Sarukura, et al., Transmission of terahertz radiation using a microstructured polymer optical fiber, Opt. Lett. 33 (2008) 902–904. [9] H. Han, H. Park, M. Cho, J. Kim, Terahertz pulse propagation in a plastic photonic crystal fiber, Appl. Phys. Lett. 80 (2002) 2634–2636. [10] J.A. Harrington, R. George, P. Pedersen, E. Mueller, Hollow polycarbonate waveguides with inner Cu coatings for delivery of terahertz radiation, Opt. Express 12 (2004) 5263–5268. [11] K.L. Wang, D.M. Mittleman, Dispersion of surface plasmon polaritons on metal wires in the terahertz frequency range, Phys. Rev. Lett. 96 (2006) 157401. [12] T.-I. Jeon, J. Zhang, D. Grischkowsky, THz Sommerfeld wave propagation on a single metal wire, Appl. Phys. Lett. 86 (2005) 161904. [13] Y.B. Ji, E.S. Lee, J.S. Jang, T.-I. Jeon, Enhancement of the detection of THz Sommerfeld wave using a conical wire waveguide, Opt. Express 16 (2008) 271–278. [14] M.I. Stockman, Nanofocusing of optical energy in tapered plasmonic waveguides, Phys. Rev. Lett. 93 (2004) 137404. [15] A. Hassani, A. Dupuis, M. Skorobogatiy, Porous polymer fibers for low-loss terahertz guiding, Opt. Express 16 (9) (2008) 6340–6351.
Please cite this article in press as: G.-Z. Jia, Z. Wang, Experimental study of air-core dielectric tube at terahertz frequencies, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2013.12.050
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[16] S. Atakaramians, S.V. Afshar, B.M. Fischer, D. Abbott, T.M. Monro, Porous fibers: a novel approach to low loss THz waveguides, Opt. Express 16 (12) (2008) 8845–8854. [17] J.Y. Lu, C.P. Yu, H.C. Chang, H.W. Chen, Y.T. Li, C.L. Pan, C.K. Sun, Terahertz air-core microstructure fiber, Appl. Phys. Lett. 92 (6) (2008) 064105. [18] A. Dupuis, J.F. Allard, D. Morris, K. Stoeffler, C. Dubois, M. Skorobogatiy, Fabrication and THz loss measurements of porous subwavelength
fibers using a directional coupler method, Opt. Express 17 (10) (2009) 8012–8028. [19] K. Nielsen, H.K. Rasmussen, A.J.L. Adam, P.C.M. Planken, O. Bang, P.U. Jepsen, Bendable, low-loss Topas fibers for the terahertz frequency range, Opt. Express 17 (10) (2009) 8592–8601. [20] D. Chen, H. Chen, A novel low-loss terahertz waveguide: polymer tube, Opt. Express 18 (4) (2010) 3762–3767.
Please cite this article in press as: G.-Z. Jia, Z. Wang, Experimental study of air-core dielectric tube at terahertz frequencies, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2013.12.050
ARTICLE IN PRESS Optik xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Experimental study of air-core dielectric tube at terahertz frequencies Guo-Zhu Jia a , Zhihui Wang b,∗ a b
College of Physics and Electronics Engineering, Sichuan Normal University, Chengdu 610066, China Southwest China Institute of Electronic Technology, Chengdu 610036, China
a r t i c l e
i n f o
Article history: Received 30 June 2013 Accepted 17 December 2013 Available online xxx Keywords: Surface wave Guided waves Terahertz Energy focusing
a b s t r a c t In this paper, an experimental study of air-core dielectric tube waveguide is proposed at terahertz frequencies. By using the THz time domain measure system, the terahertz dispersion characteristics, loss characteristic and energy focusing characteristic of air-core single-layer and dual-layer dielectric tube are obtained. The results show that this type of air-core dielectric tube can realize low dispersion characteristics. Due to the difference of refractive index between two dielectric materials, stronger energy focusing can be achieved in air-core dual-layer dielectric tube. After the coupling of the THz pulse using the dual-layer dielectric tube waveguide, the THz pulse increased 2.4 times compared with the single-layer dielectric tube waveguide at 1.5 THz. © 2014 Elsevier GmbH. All rights reserved.
1. Introduction Terahertz (THz), locating between the infrared and microwave wave bands in the electromagnetic spectrum, is one of the hot research issues because of its great potential applicability in many scientific and technological fields. The interest in THz technology has strongly increased in the last years with diverse applications in the fields of biotechnology [1,2], spectroscopy [3], imaging [4,5], and so on. Efficient guided THz transmission solutions are still under investigation. Many kinds of THz waveguides have been presented [6–14]. Among them, low-loss and high energy coupling THz waveguide which are of great importance for the practical THz applications. However, THz power is strongly absorbed in most kinds of materials, which gives a challenge to achieve low-loss and high energy coupling THz waveguide. Dry air is the most transparent broadly available transmission medium for THz waves, and then a technically useful waveguide has of course to be materialized in some way. Several polymer fibers have been proposed to reduce the loss and enhance the energy coupling for THz guiding [15–19]. Those research results indicate that the polymer fiber has risen up to be one of the most important candidates of THz waveguides. But it is difficult to fabricate those fibers due to its complex cross sections. Then, a novel polymer tube THz waveguide with low loss is proposed by Chen et al. [20]. The polymer tube has some merits, such as low loss, better confinement, and the ease of fabrication, compared with solid polymer fiber. In [20], the refractive
∗ Corresponding author. E-mail address: wzh [email protected] (Z. Wang).
index of the polymer material is assumed to be a low value 1.5. When THz wave propagation along polymer tube, electromagnetic energy distributes in polymer material and the surrounding air region. To enhance the energy focusing characteristic in air-core dielectric tube waveguide and reduce the radiated interference further, a dual-layer dielectric tube waveguide is proposed to be used at terahertz frequencies. In this paper, the terahertz propagation characteristics of air-core single-layer and dual-layer dielectric tube are demonstrated by using experimental method.
2. Structure Fig. 1 shows the geometry and refractive index profile of the dual-layer dielectric tube waveguide. 1 is the radius of air core and n0 is the refractive index of air. 2 is the outer radius of high refractive index dielectric layer and n2 is the refractive index. 3 is the outer radius of low refractive index dielectric layer and the refractive index is n1 . d = 2 − 1 is the thickness of high refractive index dielectric layer and d = 3 − 2 is the thickness of low refractive index dielectric layer. Fig. 2 shows the pictures of the air-core single-layer and dual-layer dielectric tube. For the single-layer dielectric tube, the dielectric material is Teflon. The length is 10 mm, and = 3 = 1.5 mm, 1 = 2 = 1 mm, n = n1 = 1.43, the thickness is d = 0.5 mm. And for the dual-layer dielectric tube, the outer dielectric material is Teflon and the inner dielectric material is HDPE. The length is 10 mm, 1 = 0.5 mm, 2 = 1 mm, 3 = 1.5 mm, n1 = 1.43, n2 = 1.52, the thickness is d = 0.5 mm and d = 0.5 mm, respectively.
0030-4026/$ – see front matter © 2014 Elsevier GmbH. All rights reserved. http://dx.doi.org/10.1016/j.ijleo.2013.12.050
Please cite this article in press as: G.-Z. Jia, Z. Wang, Experimental study of air-core dielectric tube at terahertz frequencies, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2013.12.050
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Air-core dual-layer dielectric tube
Amplitude ( A.U. )
0.00004 0.00002 0.00000 -0.00002 -0.00004 -0.00006 -0.00008
Fig. 1. (a) Geometry of dual-layer dielectric tube waveguide. (b) Refractive index profile of dual-layer dielectric tube waveguide.
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Fig. 2. (a) Air-core single-layer HDPE tube (left) and Teflon tube (right) and (b) air-core dual-layer dielectric tube.
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Time ( ps ) Fig. 4. The experimental results of air-core dielectric tube. (a) The air-core duallayer dielectric tube; (b) the air-core single-layer Teflon tube and (c) air.
Single-layer Teflon tube (Experimental result) Single-layer Teflon tube (Simluated result) Dual-layer dielectric tube (Experimental result) Dual-layer dielectric tube (Simulated result)
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Effective refractive index
Fig. 3 shows the terahertz time domain system. By using the measure system, the experimental results can be obtained, as shown in Fig. 4. Using Fourier transform, the frequency-dependent propagation characteristics of air-core dielectric tube can be obtained, as shown in Fig. 5. Fig. 5 shows the frequency-dependent effective refractive index neff of air-core dielectric tube. It is clearly seen that at low THz frequency range, especially at 0.1–0.4 THz, the dispersion of the air-core dual-layer dielectric tube waveguide and the single-layer dielectric tube waveguide increases. But with the increase of frequency, the dispersion decreases. The dispersion effect in terms of dheff /df is more and more flat for this type of waveguide. And the measured data exhibit very good agreement with the simulated results that obtained by using HFSS. The results mean that the air-core dielectric tube can realize low dispersion characteristics. Fig. 6 shows the normalized Hr magnitude at the end surface of the cylindrical tube with single polymer layer and the cylindrical tube with double polymer layers by using HFSS, which is based on the finite element method. The outer radius of the cylindrical tube with single low refractive index polymer layer (Teflon: n = 1.43) is 1 mm, and the thickness of polymer layer is 0.5 mm. The configuration parameters of the cylindrical tube with double polymer layers (n0 = 1, Teflon: n1 = 1.43 and HDPE: n2 = 1.52) are 1 = 0.5 mm, 2 = 1 mm, 3 = 1.5 mm. The radiation frequency is 0.5 THz. As shown in Fig. 6, it can be seen that THz wave is well confined in the high refractive index polymer layer. In terahertz system, low radiated interference is necessary. By using the
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Frequency ( THz ) Fig. 3. (a) Schematic of the terahertz time-domain system and (b) picture of the terahertz time-domain system.
Fig. 5. Frequency-dependent effective index refractive of air-core dielectric tube versus frequency.
Please cite this article in press as: G.-Z. Jia, Z. Wang, Experimental study of air-core dielectric tube at terahertz frequencies, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2013.12.050
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Fig. 6. Normalized H field component at 0.5 THz. (a) The air-core single-layer Teflon tube. (b) The air-core dual-layer dielectric tube.
Single-layer Teflon tube (Theoretical result)
3
characteristic than the single-layer Teflon tube. And with the increasing of frequency, the ratio of power also increases. After the coupling of the THz pulse using the dual-layer dielectric tube waveguide, the THz pulse increased 2.4 times compared with the single-layer dielectric tube waveguide at 1.5 THz. The experimental results demonstrate that with the adding of high refractive index dielectric layer, the terahertz power can be focused in the inner of air-core dual-layer dielectric tube effectively. The terahertz power focusing characteristic is enhanced, resulting in the power that distributed in the outer air region is reduced effectively. It means that this type of waveguide can be used for terahertz imaging and sensing applications. 4. Conclusions
Single-layer Teflon tube (Experimental result) Dual-layer dielectric tube (Theoretical result)
1.8
Dual-layer dielectric tube (Experimental result)
1.6
Loss ( 1/m )
1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0.0
0.2
0.4
0.6
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1.0
In this paper, the frequency-dependent characteristic of aircore dielectric tube is studied by using experimental method at terahertz frequencies. Due to the difference of refractive index between two dielectric materials, stronger energy focusing can be achieved. After the coupling of the THz pulse using the air-core dual-layer dielectric tube, the THz pulse increased 2.4 times compared with the single-layer Teflon tube waveguide at 1.5 THz. The experimental results show that this type of terahertz waveguide has lower dispersion and the air-core dual-layer dielectric tube waveguide can realize stronger energy focusing characteristic than normal single-layer dielectric tube at terahertz frequencies. The loss characteristic of the air-core dielectric tube is also demonstrated, and the simulation results exhibit very good agreement with the experimental results. The analysis results are very useful for the development of terahertz wave applications, such as spectroscopy, and sensing applications.
Frequency ( THz ) Acknowledgment Fig. 7. Loss of the air-core dielectric tube versus frequency.
cylindrical tube with double polymer layers, enhanced field confinement can be achieved at terahertz frequencies. Fig. 7 shows the loss of air-core dielectric tube. As shown in Fig. 6, the dual-layer dielectric tube shows greater energy coupling characteristic than the single-layer dielectric tube, while greater electromagnetic energy is absorbed by the high refractive index dielectric layer, resulting in the increasing of loss, as show in Fig. 7. Fig. 8 shows P/P (P is the total power of air-core dual-layer dielectric tube and P is the total power of air-core single-layer Teflon tube) versus frequency. As shown in Fig. 8, both the measured results and the simulated results demonstrate that the air-core dual-layer dielectric tube has greater energy focusing Simulation result
2.6
Experimental result
Ratio of P / P
/
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1.6
Frequency ( THz ) Fig. 8. The ratio of P/P versus frequency. (P is the total power of dual-layer dielectric tube and P is the total power of single-layer Teflon tube.)
Thanks for the supporting of the National Natural Science Foundation of China (61102044). References [1] P.H. Siegel, Terahertz technology in biology and medicine, IEEE Trans. Microw. Theory Technol. 52 (2004) 2438–2447. [2] M. Nagel, P. Haring Bolivar, M. Brucherseifer, H. Kurz, Integrated THz technology for label-free genetic diagnostics, Appl. Phys. Lett. 80 (2002) 154–156. [3] C.A. Schmuttenmaer, Exploring dynamics in the far-Infrared with terahertz spectroscopy, Chem. Rev. 104 (2004) 1759–1779. [4] X.C. Zhang, Terahertz wave imaging: horizons and hurdles, Phys. Med. Biol. 47 (2002) 3667–3677. [5] M.M. Awad, R.A. Cheville, Transmission terahertz waveguide-based imaging below the diffraction limit, Appl. Phys. Lett. 86 (2005) 1–3. [6] R. Mendis, D. Grischkowsky, Plastic ribbon THz waveguides, J. Appl. Phys. 88 (2000) 4449–4451. [7] S.P. Jamison, R.W. McGown, D. Grischkowsky, Single-mode waveguide propagation and reshaping of sub-ps terahertz pulses in sapphire fiber, Appl. Phys. Lett. 76 (2000) 1987–1989. [8] C.S. Ponseca Jr., R. Pobre, E. Estacio, N. Sarukura, et al., Transmission of terahertz radiation using a microstructured polymer optical fiber, Opt. Lett. 33 (2008) 902–904. [9] H. Han, H. Park, M. Cho, J. Kim, Terahertz pulse propagation in a plastic photonic crystal fiber, Appl. Phys. Lett. 80 (2002) 2634–2636. [10] J.A. Harrington, R. George, P. Pedersen, E. Mueller, Hollow polycarbonate waveguides with inner Cu coatings for delivery of terahertz radiation, Opt. Express 12 (2004) 5263–5268. [11] K.L. Wang, D.M. Mittleman, Dispersion of surface plasmon polaritons on metal wires in the terahertz frequency range, Phys. Rev. Lett. 96 (2006) 157401. [12] T.-I. Jeon, J. Zhang, D. Grischkowsky, THz Sommerfeld wave propagation on a single metal wire, Appl. Phys. Lett. 86 (2005) 161904. [13] Y.B. Ji, E.S. Lee, J.S. Jang, T.-I. Jeon, Enhancement of the detection of THz Sommerfeld wave using a conical wire waveguide, Opt. Express 16 (2008) 271–278. [14] M.I. Stockman, Nanofocusing of optical energy in tapered plasmonic waveguides, Phys. Rev. Lett. 93 (2004) 137404. [15] A. Hassani, A. Dupuis, M. Skorobogatiy, Porous polymer fibers for low-loss terahertz guiding, Opt. Express 16 (9) (2008) 6340–6351.
Please cite this article in press as: G.-Z. Jia, Z. Wang, Experimental study of air-core dielectric tube at terahertz frequencies, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2013.12.050
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ARTICLE IN PRESS G.-Z. Jia, Z. Wang / Optik xxx (2014) xxx–xxx
[16] S. Atakaramians, S.V. Afshar, B.M. Fischer, D. Abbott, T.M. Monro, Porous fibers: a novel approach to low loss THz waveguides, Opt. Express 16 (12) (2008) 8845–8854. [17] J.Y. Lu, C.P. Yu, H.C. Chang, H.W. Chen, Y.T. Li, C.L. Pan, C.K. Sun, Terahertz air-core microstructure fiber, Appl. Phys. Lett. 92 (6) (2008) 064105. [18] A. Dupuis, J.F. Allard, D. Morris, K. Stoeffler, C. Dubois, M. Skorobogatiy, Fabrication and THz loss measurements of porous subwavelength
fibers using a directional coupler method, Opt. Express 17 (10) (2009) 8012–8028. [19] K. Nielsen, H.K. Rasmussen, A.J.L. Adam, P.C.M. Planken, O. Bang, P.U. Jepsen, Bendable, low-loss Topas fibers for the terahertz frequency range, Opt. Express 17 (10) (2009) 8592–8601. [20] D. Chen, H. Chen, A novel low-loss terahertz waveguide: polymer tube, Opt. Express 18 (4) (2010) 3762–3767.
Please cite this article in press as: G.-Z. Jia, Z. Wang, Experimental study of air-core dielectric tube at terahertz frequencies, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2013.12.050