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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 17, Iss. 19 — Sep. 14, 2009
  • pp: 16527–16534
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Broadband resonant terahertz transmission in a composite metal-dielectric structure

Jiaguang Han, Jianqiang Gu, Xinchao Lu, Mingxie He, Qirong Xing, and Weili Zhang  »View Author Affiliations


Optics Express, Vol. 17, Issue 19, pp. 16527-16534 (2009)
http://dx.doi.org/10.1364/OE.17.016527


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Abstract

We present a systematic numerical study of a metal-dielectric-metal sandwich plasmonic structure for broadband resonant transmission at terahertz frequencies. The proposed structure consists of periodic slotted metallic arrays on both sides of a thin dielectric substrate and is demonstrated to exhibit a broad passband transmission response. Various design considerations have been investigated to exploit their influence on the transmission passband width and the center resonance frequency. The structure ensures a broadband transmission over a wide range of incident angles.

© 2009 OSA

1. Introduction

The recent studies on metamaterial and plasmonic structures have been gaining enormous interest experimentally and theoretically in a broad range of disciplines [1

1. S. A. Ramakrishna, “Physics of negative refractive index materials,” Rep. Prog. Phys. 68(2), 449–521 (2005). [CrossRef]

3

3. T. W. Ebbesen, H. J. Lezec, H. F. Ghaemi, T. Thio, and P. A. Wolff, “Extraordinary optical transmission through sub-wavelength hole arrays,” Nature 391(6668), 667–669 (1998). [CrossRef]

]. The initial research has paved a way for a series of fundamental understandings of the rich phenomena and thus has raised the possibility of delivering unique structures unavailable in natural for controlling electromagnetic waves. Continued interest in the subject is fueled by various promising applications in nanofabrication, biochemical sensing, integrated devices, and so on [4

4. T. J. Yen, W. J. Padilla, N. Fang, D. C. Vier, D. R. Smith, J. B. Pendry, D. N. Basov, and X. Zhang, “Terahertz magnetic response from artificial materials,” Science 303(5663), 1494–1496 (2004). [CrossRef] [PubMed]

6

6. J. B. Pendry, “Negative refraction makes a perfect lens,” Phys. Rev. Lett. 85(18), 3966–3969 (2000). [CrossRef] [PubMed]

].

Among these, the research into optical devices at terahertz (THz) frequencies gathered a great attention due to the unique and important applications of THz technology, which has a large impact on various research fields such as material characterizing, security detection, molecule sensing, imaging, and etc [7

7. B. Ferguson and X.-C. Zhang, “Materials for terahertz science and technology,” Nat. Mater. 1(1), 26–33 (2002). [CrossRef]

9

9. J. Han, W. Zhang, W. Chen, S. Ray, J. Zhang, M. He, A. Azad, and Z. Zhu, “Terahertz dielectric properties and low-frequency phonon resonances of Zno nanostructures,” J. Phys. Chem. C 111(35), 13000–13006 (2007). [CrossRef]

]. A THz device is desired to control the pulsed or continuous-wave freely propagating THz radiation. Depending on the application, the frequency, bandwidth, transmission power and modulation scheme of THz radiation may vary widely. Typical THz devices usually include resonant filters, polarizers, compensators and modulators [10

10. A. M. Melo, M. A. Kornberg, P. Kaufmann, M. H. Piazzetta, E. C. Bortolucci, M. B. Zakia, O. H. Bauer, A. Poglitsch, and A. M. P. Alves da Silva, “Metal mesh resonant filters for terahertz frequencies,” Appl. Opt. 47(32), 6064–6069 (2008). [CrossRef] [PubMed]

]. There is an increasing demand for a THz bandpass resonant filter to be designed for ensuring high tolerances to manufacturing parameters and multi-frequency operations. In this study, we report on a strategy to create a novel structure that combines a metal-dielectric-metal (MDM) sandwich with a periodic slot structure to perform an ultrabroadband THz resonant filter with flatter transmission top. Such a device may provide a desirable filtering method and operation to select frequency band in the THz regime and thus lead to most practical applications.

2. Analysis and numerical results

Figure 2(a)
Fig. 2 (a) Comparison of the transmission spectra of the chosen MDM with the MD structure of only one single metallic layer, as well as the sandwich patch array. The parameters are: L = 100 μm, P = 120 μm, W = 20 μm, d = 21 μm and ε d = 2.89. The metal is Aluminum of thickness 200 nm. (b) and (c) are electric field distributions at lower resonance frequency for the MD and MDM structures, respectively.
shows the simulated transmission of a typical MDM structure with dimensional parameters: P = 120 μm, L = 100 μm, W = 20 μm and d = 21 μm, where the simulated model assumes that the metal is chosen as Aluminum and the middle dielectric is Mylar of relative permittivity ε d = 2.89. For comparison, a MD structure with only one single metallic layer of the same square-loop hole array as that in MDM is also presented by the blue curve. Inspection of the transmission clearly shows that the MDM structure of double metallic layers has a much flatter transmission top as compared to that in MD. Clearly, the additional second array has the significant effect of flattering the transmission top and thus leads to an ultrawide passband. The resonance top in the MDM structure is pulled broadly by the two resonance frequency f i = 0.95 THz and f a = 1.28 THz away from each other, and the simulated passband response centers at f 0 = 1.12 THz.

The effect of linewidth W of the square loop can be seen in Figs. 3(c) and 3(d). With increase of W from 5 to 25 μm, we can see that the center resonance frequency f 0 blueshifts from 0.84 to 1.44 THz, approximately twice variations. Meanwhile, Δf is significantly broadened from 0.16 to 0.47 THz, corresponding 294% variations. Although both f 0 and Δf are enhanced with increasing W, the variations are not linear. We now consider the influence of the length L in the square loop. Similar as the case of changing W, L also affects the transmission profile of the MDM structure remarkably. The pronounced feature can be seen from Figs. 3(e) and 3(f) that f 0 is reduced from 1.82 to 1.24 THz if L becomes longer from 70 to 100 μm. However, it is of interest to notice that a maximum value of Δf is achieved when L equals to 85 μm, and further increased L leads to a decrease of Δf. This may suggest an optimum length for device design for performance at various center resonance frequencies with different passbands.

In practice, except for the aforementioned dimensional parameters that influence the transmission profile naturally, we can deduce that variation of permittivity ε d of the dielectric spacer has a similar effect on the response of the MDM structure. Actually, the permittivity of substrate dielectric is flexible depending on the material selection and at THz frequencies we also have various dielectric substrates with good transparent features such as Mylar, Quartz, Teflon, Zitex (a kind of porous Teflon) and so on. The transmission of the MDM structure with different dielectrics is plotted in Fig. 4
Fig. 4 (a) Computed transmission spectra for various permittivity ε d of the middle dielectric substrate. (b) Dependence of the simulated values of the center resonance frequency f 0 with corresponding Δf on ε d. The solid line shows the fitting result.
. The primary effect of varying the dielectric is to tune the center frequency f 0 and Δf. Decreasing the permittivity ε d, f 0 is blueshifted and Δf is broadened. The decrease of ε d also makes the transmission top flatter.

The preceding discussion concerning the effect of various dimensional parameters and permittivity of middle dielectric on the response of the presented MDM structure demonstrated that these parameters are essentially that of making the resonant transmission curve broader, or flatter, or making the center resonance frequency shift. All may be taken as optima in the practical device designs owing to their simplicity in fabrications. The appropriate choice of these parameters of the MDM structure thus provides to obtain desired center frequency and bandwidth, but if an analytical model can be given, it is of more help. An analytical model for the center resonance frequency can be developed approximately in a similar way as that proposed in Ref [20

20. L. Shafai, “Wideband Microstrip Antennas,” in Antenna Engineering Handbook, J. Volakis, ed. (McGraw-Hill, New York, 2007).

]. based on a circuit theory approach of microstrip patch antennas, given as:
f0=cξ(P,L,W)εeff.
(1)
The approximation by Eq. (1) to f 0 primarily takes both substrate and geometry parameters of slots into account and can be used to give the supplement to the numerical method for determining desirable design. Here c is the velocity of light in free space. ξ(P,L,W) depicts the contribution of dimensional parameters to the resonant transmission and is calculated from:
ξ(P,L,W)=iβiζi+Δζ,
(2)
where we define i = 1, 2, 3 and thusζicorresponds to P, L and W. βi is the coefficient of each dimensional parameters denoting the contribution to the resonant transmission and Δζis the

correction index. εeffis the effective permittivity considering an effective contribution of the middle dielectric and air, and can be calculated from [14

14. J. Han, X. Lu, and W. Zhang, “Terahertz transmission in subwavelength holes of asymmetric metal-dielectric interfaces: the effect of a dielectric layer,” J. Appl. Phys. 103(3), 033108 (2008). [CrossRef]

]:
εeff=εddλd+εair(1dλd),
(3)
where εair = 1.0 is the permittivity of air and λdis the critical thickness. The best fits to the center resonance frequency by the model for various cases are presented by the solid lines in Figs. 3(b), 3(d) and 3(f) and 4(b) with β1=1.36, β2=   6.32, β3=1.88and λd=90μm.

Figures 5(a)
Fig. 5 The 3D profile of simulated transmission response for various incident angles θ in (a) TE polarization and (b) TM polarization, respectively. The parameters are: P = 120 μm, L = 100 μm, W = 20 μm, d = 50 μm, and ε d = 1.50.
and 5(b) show the computed transmission curves of the MDM structure in the H- and E-planes, respectively, for various angles of incidence θ. For TE-incidence, the passband stays almost the same over wide angles of wave incidence. For TM-incidence, the higher resonance frequency f a is shifted towards lower frequency slightly with increasing incident angles. The simulated Δf is 0.36 THz for normal incidence and 0.17 THz for TM 45°, respectively. Hence, the presented MDM structure normally provides a stable resonant passband with incident angles.

We now consider the effect of placing multiple layers. In Fig. 6(a)
Fig. 6 (a) Effect on the transmission response using various MDM layers. (b) Comparison of the MDM structure with its complementary structure. The used dimensional parameters are as same as those in Fig. 5.
, we compare the simulated transmission of the design of different MDM layers, where up to four layers are cascaded. It was not found significant effect when stack more layers, and the passband keeps approximately the same as that of the two-array configuration, although more arrays causes increased ripple and slightly broaden Δf. The ripple may be due to the scattering of different layers. Finally, as an extension, we present the simulated transmission of a complementary structure of the chosen MDM structure in Fig. 6(b), namely, a metallic square-ring array printed on both sides of the middle dielectric substrate, where a broad stopband can be found. This provides a good choice for stopband THz devices and our recent research also demonstrate such a structure exhibit a negative index in the THz regime [21

21. J. Gu, et al., “A close-ring pair metamaterial resonating at terahertz frequencies,” unpublished.

].

3. Conclusion

In conclusion, a unique plasmonic sandwich configuration has been considered to produce a structure having a broad passband at THz frequencies. We found that the geometry parameters, as well as the permittivity of the dielectric substrate, have visible influence on the transmission width and the center resonance frequency, which are capable of giving us the versatility required in the practical device design. The stability in the passband transmission response of the proposed structure is also obtained over wide angles of wave incidences, as well as in placing a multiple-layers case. The structure could lead to potential applications in THz optical devices, such as filters, etc.

Acknowledgments

The author acknowledges financial support from the MOE Academic Research Fund of Singapore and the Lee Kuan Yew Fund.

References and links

1.

S. A. Ramakrishna, “Physics of negative refractive index materials,” Rep. Prog. Phys. 68(2), 449–521 (2005). [CrossRef]

2.

D. Schurig, J. J. Mock, B. J. Justice, S. A. Cummer, J. B. Pendry, A. F. Starr, and D. R. Smith, “Metamaterial electromagnetic cloak at microwave frequencies,” Science 314(5801), 977–980 (2006). [CrossRef] [PubMed]

3.

T. W. Ebbesen, H. J. Lezec, H. F. Ghaemi, T. Thio, and P. A. Wolff, “Extraordinary optical transmission through sub-wavelength hole arrays,” Nature 391(6668), 667–669 (1998). [CrossRef]

4.

T. J. Yen, W. J. Padilla, N. Fang, D. C. Vier, D. R. Smith, J. B. Pendry, D. N. Basov, and X. Zhang, “Terahertz magnetic response from artificial materials,” Science 303(5663), 1494–1496 (2004). [CrossRef] [PubMed]

5.

M. W. Klein, C. Enkrich, M. Wegener, and S. Linden, “Second-harmonic generation from magnetic metamaterials,” Science 313(5786), 502–504 (2006). [CrossRef] [PubMed]

6.

J. B. Pendry, “Negative refraction makes a perfect lens,” Phys. Rev. Lett. 85(18), 3966–3969 (2000). [CrossRef] [PubMed]

7.

B. Ferguson and X.-C. Zhang, “Materials for terahertz science and technology,” Nat. Mater. 1(1), 26–33 (2002). [CrossRef]

8.

D. Grischkowsky, S. Keiding, M. V. Exter, and Ch. Fattinger, “Far-infrared time-domain spectroscopy with terahertz beams of dielectric and semiconductors,” J. Opt. Soc. Am. B 7(10), 2006–2015 (1990). [CrossRef]

9.

J. Han, W. Zhang, W. Chen, S. Ray, J. Zhang, M. He, A. Azad, and Z. Zhu, “Terahertz dielectric properties and low-frequency phonon resonances of Zno nanostructures,” J. Phys. Chem. C 111(35), 13000–13006 (2007). [CrossRef]

10.

A. M. Melo, M. A. Kornberg, P. Kaufmann, M. H. Piazzetta, E. C. Bortolucci, M. B. Zakia, O. H. Bauer, A. Poglitsch, and A. M. P. Alves da Silva, “Metal mesh resonant filters for terahertz frequencies,” Appl. Opt. 47(32), 6064–6069 (2008). [CrossRef] [PubMed]

11.

A. K. Azad, Y. Zhao, W. Zhang, and M. He, “Effect of dielectric properties of metals on terahertz transmission subwavelength hole arrays,” Opt. Lett. 31(17), 2637–2639 (2006). [CrossRef] [PubMed]

12.

X. Lu, J. Han, and W. Zhang, “Resonant terahertz reflection of periodic arrays of subwavelength metallic rectangles,” Appl. Phys. Lett. 92(12), 121103 (2008). [CrossRef]

13.

F. Miyamaru and M. Hangyo, “Finite size effect of transmission property for metal hole arrays in subterahertz region,” Appl. Phys. Lett. 84(15), 2742–2744 (2004). [CrossRef]

14.

J. Han, X. Lu, and W. Zhang, “Terahertz transmission in subwavelength holes of asymmetric metal-dielectric interfaces: the effect of a dielectric layer,” J. Appl. Phys. 103(3), 033108 (2008). [CrossRef]

15.

J. Han, A. Lakhtakia, Z. Tian, X. Lu, and W. Zhang, “Magnetic and magnetothermal tunabilities of subwavelength-hole arrays in a semiconductor sheet,” Opt. Lett. 34(9), 1465–1467 (2009). [CrossRef] [PubMed]

16.

W. Fan, S. Zhang, B. Minhas, K. J. Malloy, and S. R. J. Brueck, “Enhanced infrared transmission through subwavelength coaxial metallic arrays,” Phys. Rev. Lett. 94(3), 033902 (2005). [CrossRef] [PubMed]

17.

A. I. Fernández-Domínguez, L. Martín-Moreno, F. J. García-Vidal, S. R. Andrews, and S. A. Maier, “Spoof surface plasmon polariton modes propagating along periodically corrugated wires,” IEEE J. Sel. Top. Quantum Electron. 14(6), 1515–1521 (2008). [CrossRef]

18.

B. A. Munk, R. J. Luebbers, and R. D. Fulton, “Transmission through a two-layer array of loaded slots,” IEEE Trans. Antenn. Propag. 22(6), 804–809 (1974). [CrossRef]

19.

B. A. Munk, Frequency selected surfaces: theory and design (John-Wily and Sons, New York, 2000).

20.

L. Shafai, “Wideband Microstrip Antennas,” in Antenna Engineering Handbook, J. Volakis, ed. (McGraw-Hill, New York, 2007).

21.

J. Gu, et al., “A close-ring pair metamaterial resonating at terahertz frequencies,” unpublished.

OCIS Codes
(240.6680) Optics at surfaces : Surface plasmons
(300.6270) Spectroscopy : Spectroscopy, far infrared
(310.4165) Thin films : Multilayer design

ToC Category:
Optics at Surfaces

History
Original Manuscript: July 1, 2009
Revised Manuscript: August 24, 2009
Manuscript Accepted: August 31, 2009
Published: September 1, 2009

Citation
Jiaguang Han, Jianqiang Gu, Xinchao Lu, Mingxie He, Qirong Xing, and Weili Zhang, "Broadband resonant terahertz transmission in a composite metal-dielectric structure," Opt. Express 17, 16527-16534 (2009)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-19-16527


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References

  1. S. A. Ramakrishna, “Physics of negative refractive index materials,” Rep. Prog. Phys. 68(2), 449–521 (2005). [CrossRef]
  2. D. Schurig, J. J. Mock, B. J. Justice, S. A. Cummer, J. B. Pendry, A. F. Starr, and D. R. Smith, “Metamaterial electromagnetic cloak at microwave frequencies,” Science 314(5801), 977–980 (2006). [CrossRef] [PubMed]
  3. T. W. Ebbesen, H. J. Lezec, H. F. Ghaemi, T. Thio, and P. A. Wolff, “Extraordinary optical transmission through sub-wavelength hole arrays,” Nature 391(6668), 667–669 (1998). [CrossRef]
  4. T. J. Yen, W. J. Padilla, N. Fang, D. C. Vier, D. R. Smith, J. B. Pendry, D. N. Basov, and X. Zhang, “Terahertz magnetic response from artificial materials,” Science 303(5663), 1494–1496 (2004). [CrossRef] [PubMed]
  5. M. W. Klein, C. Enkrich, M. Wegener, and S. Linden, “Second-harmonic generation from magnetic metamaterials,” Science 313(5786), 502–504 (2006). [CrossRef] [PubMed]
  6. J. B. Pendry, “Negative refraction makes a perfect lens,” Phys. Rev. Lett. 85(18), 3966–3969 (2000). [CrossRef] [PubMed]
  7. B. Ferguson and X.-C. Zhang, “Materials for terahertz science and technology,” Nat. Mater. 1(1), 26–33 (2002). [CrossRef]
  8. D. Grischkowsky, S. Keiding, M. V. Exter, and Ch. Fattinger, “Far-infrared time-domain spectroscopy with terahertz beams of dielectric and semiconductors,” J. Opt. Soc. Am. B 7(10), 2006–2015 (1990). [CrossRef]
  9. J. Han, W. Zhang, W. Chen, S. Ray, J. Zhang, M. He, A. Azad, and Z. Zhu, “Terahertz dielectric properties and low-frequency phonon resonances of Zno nanostructures,” J. Phys. Chem. C 111(35), 13000–13006 (2007). [CrossRef]
  10. A. M. Melo, M. A. Kornberg, P. Kaufmann, M. H. Piazzetta, E. C. Bortolucci, M. B. Zakia, O. H. Bauer, A. Poglitsch, and A. M. P. Alves da Silva, “Metal mesh resonant filters for terahertz frequencies,” Appl. Opt. 47(32), 6064–6069 (2008). [CrossRef] [PubMed]
  11. A. K. Azad, Y. Zhao, W. Zhang, and M. He, “Effect of dielectric properties of metals on terahertz transmission subwavelength hole arrays,” Opt. Lett. 31(17), 2637–2639 (2006). [CrossRef] [PubMed]
  12. X. Lu, J. Han, and W. Zhang, “Resonant terahertz reflection of periodic arrays of subwavelength metallic rectangles,” Appl. Phys. Lett. 92(12), 121103 (2008). [CrossRef]
  13. F. Miyamaru and M. Hangyo, “Finite size effect of transmission property for metal hole arrays in subterahertz region,” Appl. Phys. Lett. 84(15), 2742–2744 (2004). [CrossRef]
  14. J. Han, X. Lu, and W. Zhang, “Terahertz transmission in subwavelength holes of asymmetric metal-dielectric interfaces: the effect of a dielectric layer,” J. Appl. Phys. 103(3), 033108 (2008). [CrossRef]
  15. J. Han, A. Lakhtakia, Z. Tian, X. Lu, and W. Zhang, “Magnetic and magnetothermal tunabilities of subwavelength-hole arrays in a semiconductor sheet,” Opt. Lett. 34(9), 1465–1467 (2009). [CrossRef] [PubMed]
  16. W. Fan, S. Zhang, B. Minhas, K. J. Malloy, and S. R. J. Brueck, “Enhanced infrared transmission through subwavelength coaxial metallic arrays,” Phys. Rev. Lett. 94(3), 033902 (2005). [CrossRef] [PubMed]
  17. A. I. Fernández-Domínguez, L. Martín-Moreno, F. J. García-Vidal, S. R. Andrews, and S. A. Maier, “Spoof surface plasmon polariton modes propagating along periodically corrugated wires,” IEEE J. Sel. Top. Quantum Electron. 14(6), 1515–1521 (2008). [CrossRef]
  18. B. A. Munk, R. J. Luebbers, and R. D. Fulton, “Transmission through a two-layer array of loaded slots,” IEEE Trans. Antenn. Propag. 22(6), 804–809 (1974). [CrossRef]
  19. B. A. Munk, Frequency selected surfaces: theory and design (John-Wily and Sons, New York, 2000).
  20. L. Shafai, “Wideband Microstrip Antennas,” in Antenna Engineering Handbook, J. Volakis, ed. (McGraw-Hill, New York, 2007).
  21. J. Gu, et al., “A close-ring pair metamaterial resonating at terahertz frequencies,” unpublished.

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