Engineered surface Bloch waves in graphenebased hyperbolic metamaterials Yuanjiang Xiang,1,2,3 Jun Guo,1,2 Xiaoyu Dai,1,2 Shuangchun Wen,2 and Dingyuan Tang1,* 2
1 School of Electrical and Electronic Engineering, Nanyang Technological University, 639798 Singapore Key Laboratory for Micro-/Nano-Optoelectronic Devices of Ministry of Education, College of Physics and Microelectronic Science, Hunan University, Changsha 410082, China 3 [email protected] * [email protected]
Abstract: A kind of tunable hyperbolic metamaterial (HMM) based on the graphene-dielectric layered structure at near-infrared frequencies is presented, and the engineered surface Bloch waves between graphene-based HMM and isotropic medium are investigated. Our calculations demonstrate that the frequency and frequency range of surface Bloch waves existence can be tuned by varying the Fermi energy of graphene sheets via electrostatic biasing. Moreover, we show that the frequency range of surface Bloch waves existence can be broadened by decreasing the thickness of the dielectric in the graphene-dielectric layered structure or by increasing the layer number of graphene sheets. ©2014 Optical Society of America OCIS codes: (240.0240) Optics at surfaces; (160.3918) Metamaterials.
References and links 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.
B. E. Sernelius, Surface Modes in Physics (John Wiley, 2001). J. A. Polo, Jr. and A. Lakhtakia, “Surface electromagnetic waves: a review,” Laser Photonics Rev. 5(2), 234–246 (2011). H. Raether, Surface Plasmon on Smooth and Rough Surfaces and on Gratings (Springer, 1988). A. V. Zayats, I. I. Smolyaninov, and A. A. Maradudin, “Nano-optics of surface plasmon polaritons,” Phys. Rep. 408(3–4), 131–314 (2005). W. L. Barnes, A. Dereux, and T. W. Ebbesen, “Surface plasmon subwavelength optics,” Nature 424(6950), 824– 830 (2003). J. M. Pitarke, V. M. Silkin, E. V. Chulkov, and P. M. Echenique, “Theory of surface plasmons and surfaceplasmon polaritons,” Rep. Prog. Phys. 70(1), 1–87 (2007). P. Yeh, A. Yariv, and C. S. Hong, “Electromagnetic propagation in periodic stratified media. I. General theory,” J. Opt. Soc. Am. 67(4), 423–438 (1977). P. Yeh, A. Yariv, and A. Y. Cho, “Optical surface-waves in periodic layered media,” Appl. Phys. Lett. 32(2), 104–105 (1978). T. Sfez, E. Descrovi, L. Yu, M. Quaglio, L. Dominici, W. Nakagawa, F. Michelotti, F. Giorgis, and H. P. Herzig, “Two dimensional optics on silicon nitride multilayer: refraction of Bloch surface waves,” Appl. Phys. Lett. 96(15), 151101 (2010). E. Guillermain, V. Lysenko, R. Orobtchouk, T. Benyattou, S. Roux, A. Pillonnet, and P. Perriat, “Bragg surface wave device based on porous silicon and its application for sensing,” Appl. Phys. Lett. 90(24), 241116 (2007). F. Giorgis, E. Descrovi, C. Summonte, L. Dominici, and F. Michelotti, “Experimental determination of the sensitivity of Bloch Surface Waves based sensors,” Opt. Express 18(8), 8087–8093 (2010). M. Liscidini and J. E. Sipe, “Enhancement of diffraction for biosensing applications via Bloch surface waves,” Appl. Phys. Lett. 91(25), 253125 (2007). Y. H. Wan, Z. Zheng, W. J. Kong, X. Zhao, Y. Liu, Y. S. Bian, and J. S. Liu, “Nearly three orders of magnitude enhancement of Goos-Hanchen shift by exciting Bloch surface wave,” Opt. Express 20(8), 8998–9003 (2012). S. Pirotta, X. G. Xu, A. Delfan, S. Mysore, S. Maiti, G. Dacarro, M. Patrini, M. Galli, G. Guizzetti, D. Bajoni, J. E. Sipe, G. C. Walker, and M. Liscidini, “Surface-enhanced Raman scattering in purely dielectric structures via Bloch surface waves,” J. Phys. Chem. C 117(13), 6821–6825 (2013). S. M. Vukovic, I. V. Shadrivov, and Y. S. Kivshar, “Surface Bloch waves in metamaterial and metal-dielectric supperlattices,” Appl. Phys. Lett. 95(4), 041902 (2009). D. R. Smith and D. Schurig, “Electromagnetic wave propagation in media with indefinite permittivity and permeability tensors,” Phys. Rev. Lett. 90(7), 077405 (2003). Z. Jacob, J.-Y. Kim, G. V. Naik, A. Boltasseva, E. E. Narimanov, and V. M. Shalaev, “Engineering photonic density of states using metamaterials,” Appl. Phys. B 100(1), 215–218 (2010).
#202058 - $15.00 USD Received 26 Nov 2013; revised 15 Jan 2014; accepted 17 Jan 2014; published 3 Feb 2014 (C) 2014 OSA 10 February 2014 | Vol. 22, No. 3 | DOI:10.1364/OE.22.003054 | OPTICS EXPRESS 3054
18. T. U. Tumkur, L. Gu, J. K. Kitur, E. E. Narimanov, and M. A. Noginov, “Control of absorption with hyperbolic metamaterials,” Appl. Phys. Lett. 100(16), 161103 (2012). 19. M. A. Noginov, A. Barnakov, G. Zhu, T. Tumkur, H. Li, and E. E. Narimanov, “Bulk photonic metamaterial with hyperbolic dispersion,” Appl. Phys. Lett. 94(15), 151105 (2009). 20. M. A. Noginov, H. Li, Y. A. Barnakov, D. Dryden, G. Nataraj, G. Zhu, C. E. Bonner, M. Mayy, Z. Jacob, and E. E. Narimanov, “Controlling spontaneous emission with metamaterials,” Opt. Lett. 35(11), 1863–1865 (2010). 21. C. Rizza, A. Ciattoni, E. Spinozzi, and L. Columbo, “Terahertz active spatial filtering through optically tunable hyperbolic metamaterials,” Opt. Lett. 37(16), 3345–3347 (2012). 22. G. Naik and A. Boltasseva, “Semiconductors for plasmonics and metamaterials,” Phys. Status Solidi 4, 295–297 (2010). 23. A. J. Hoffman, L. Alekseyev, S. S. Howard, K. J. Franz, D. Wasserman, V. A. Podolskiy, E. E. Narimanov, D. L. Sivco, and C. Gmachl, “Negative refraction in semiconductor metamaterials,” Nat. Mater. 6(12), 946–950 (2007). 24. J. Yao, Z. W. Liu, Y. M. Liu, Y. Wang, C. Sun, G. Bartal, A. M. Stacy, and X. Zhang, “Optical negative refraction in bulk metamaterials of nanowires,” Science 321(5891), 930 (2008). 25. Z. Jacob, I. Smolyaninov, and E. E. Narimanov, “Broadband purcell effect: Radiative decay engineering with metamaterials,” Appl. Phys. Lett. 100(18), 181105 (2012). 26. Z. Jacob, L. V. Alekseyev, and E. Narimanov, “Optical Hyperlens: Far-field imaging beyond the diffraction limit,” Opt. Express 14(18), 8247–8256 (2006). 27. Z. W. Liu, H. Lee, Y. Xiong, C. Sun, and X. Zhang, “Far-field optical hyperlens magnifying sub-diffractionlimited objects,” Science 315(5819), 1686 (2007). 28. A. V. Kabashin, P. Evans, S. Pastkovsky, W. Hendren, G. A. Wurtz, R. Atkinson, R. Pollard, V. A. Podolskiy, and A. V. Zayats, “Plasmonic nanorod metamaterials for biosensing,” Nat. Mater. 8(11), 867–871 (2009). 29. Y. He, S. He, and X. Yang, “Optical field enhancement in nanoscale slot waveguides of hyperbolic metamaterials,” Opt. Lett. 37(14), 2907–2909 (2012). 30. S. A. Biehs, M. Tschikin, and P. Ben-Abdallah, “Hyperbolic metamaterials as an analog of a blackbody in the near field,” Phys. Rev. Lett. 109(10), 104301 (2012). 31. A. H. Castro Neto, F. Guinea, N. M. R. Peres, K. S. Novoselov, and A. K. Geim, “The electronic properties of graphene,” Rev. Mod. Phys. 81(1), 109–162 (2009). 32. A. N. Grigorenko, M. Polini, and K. S. Novoselov, “Graphene plasmonics,” Nat. Photonics 6(11), 749–758 (2012). 33. M. Liu, X. Yin, E. Ulin-Avila, B. Geng, T. Zentgraf, L. Ju, F. Wang, and X. Zhang, “A graphene-based broadband optical modulator,” Nature 474(7349), 64–67 (2011). 34. I. V. Iorsh, I. S. Mukhin, I. V. Shadrivov, P. A. Belov, and Y. S. Kivshar, “Hyperbolic metamaterials based on multilayer graphene structures,” Phys. Rev. B 87(7), 075416 (2013). 35. M. A. K. Othman, C. Guclu, and F. Capolino, “Graphene-based tunable hyperbolic metamaterials and enhanced near-field absorption,” Opt. Express 21(6), 7614–7632 (2013). 36. K. V. Sreekanth, A. De Luca, and G. Strangi, “Negative refraction in graphene-based metamaterials,” Appl. Phys. Lett. 103(2), 023107 (2013). 37. I. S. Nefedov, C. A. Valaginnopoulos, and L. A. Melnikov, “Perfect absorption in graphene multilayers,” J. Opt. 15(11), 114003 (2013). 38. T. Zhang, L. Chen, and X. Li, “Graphene-based tunable broadband hyperlens for far-field subdiffraction imaging at mid-infrared frequencies,” Opt. Express 21(18), 20888–20899 (2013). 39. B. Zhu, G. Ren, S. Zheng, Z. Lin, and S. Jian, “Nanoscale dielectric-graphene-dielectric tunable infrared waveguide with ultrahigh refractive indices,” Opt. Express 21(14), 17089–17096 (2013). 40. C. J. Zapata-Rodríguez, J. J. Miret, S. Vuković, and M. R. Belić, “Engineered surface waves in hyperbolic metamaterials,” Opt. Express 21(16), 19113–19127 (2013).
1. Introduction Surface electromagnetic waves (SEWs) are a special type of waves that are confined at the interface between two media with different properties [1, 2]. One of the best known examples of SEWs is surface plasmon polariton (SPP), which is formed at the interfaces between metals and dielectrics [3, 4]. SPPs only exist for TM polarization and there is no surface modes exist for TE polarization. SPP has attracted a wide spread attention in the last decade mainly due to their applications in sensing, microscopy, or integrated optics [5, 6]. However, when one of the two media at the interface is periodic structures (photonic crystals or superlattices), the Bloch surface waves (BSWs) may appear at the boundary within the photonic bandgaps [7, 8]. It has also been shown the lateral conðnement of the BSWs in the waveguide is well described by the 2D Snell’s [9]. BSWs have potential applications in optical sensing [10–12], enhancement of Goos-Hanchen shift [13], and surface-enhanced Raman spectroscopy [14]. For BSWs, the Bloch wavevector is perpendicular to the interface of the periodic structure and the dielectric layer, and hence the Bloch wavevector is not propagating along the interface. Moreover, most recently, Vukovic et al. proposed another
#202058 - $15.00 USD Received 26 Nov 2013; revised 15 Jan 2014; accepted 17 Jan 2014; published 3 Feb 2014 (C) 2014 OSA 10 February 2014 | Vol. 22, No. 3 | DOI:10.1364/OE.22.003054 | OPTICS EXPRESS 3055
surface wave propagating in metal-dielectric superlattices and isotropic dielectric medium where the Bloch wavevector is parallel to the interface of the two media [15]. This surface wave has been named as surface Bloch waves owing to the Bloch wave propagating along the interface [15]. Hyperbolic metamaterial (HMM) is a uniaxial anisotropic medium having the hyperbolic form of the dispersion relation [16]. HMMs can be realized at optical frequencies using metal-dielectric multilayers [17, 18] or metallic nanorods/nanowires in a dielectric host [19, 20], and at terahertz and infrared frequencies using semiconductor-dielectric multilayers [21, 22]. HMM promises a variety of potential applications including negative refraction [23, 24], broadband Purcell effect [20, 25], imaging hyperlens [26, 27], optical waveguide [28, 29], and perfect thermal emitters [30]. Recently, graphene has attracted intensive scientific interest owing to its incredible physical properties showing great potential applications in nano-electronic devices and optoelectric devices with ultrahigh electron mobility, ultrafast relaxation time for photoexcited carriers, and gate variable optical conductivity [31]. Graphene plasmonics have generated great interest among scientific community because of the ability of graphene to tune the plasmon dispersion by varying the chemical potential [32]. It seems to be a good candidate for designing tunable optical device that operates in both THz and optical frequency ranges [33]. Most recently, graphene-based HMMs composed of stacked graphene sheets separated by thin dielectric layers have been proposed and investigated [34, 35], it has been demonstrated that such graphene-based HMMs can be used for the negative refraction at THz frequencies [36], the spontaneous emission enhancement [34, 35], the perfect absorption [37], tunable broadband hyperlens [38], tunable infrared waveguide [39], and so on. However, these HMMs have be realized and investigated mainly at THz frequencies, and mid- or far-infrared frequencies. Graphene-based HMMs at the near-infrared frequencies and visible light are still not demonstrated. In the present paper, we suggest a new class of tunable HMMs for near-infrared frequencies based on the graphene-dielectric layered structure, and reveal that such graphene structures can support a controllable surface Bloch wave between graphene-based HMM and isotropic medium.
Fig. 1. (a) Scheme of the interface of the semi-infinite graphene-based hyperbolic metamaterial and the semi-infinite isotropic dielectric; (b) effective permittivity of the graphene-based layered metamaterial; (c) dispersion curve of the graphene-based hyperbolic metamaterial.
2. Graphene-based HMMs at the near-infrared frequencies 2.1 The optical properties of graphene sheets Consider the geometry shown in Fig. 1(a), where the semi-infinite periodic structure created by alternating layers of graphene and conventional dielectric is placed on the left of the homogeneous dielectric. The unit cell of the layered structure is formed by a transparent material of dielectric constant ε d and slab thickness td and graphene sheets of surface
#202058 - $15.00 USD Received 26 Nov 2013; revised 15 Jan 2014; accepted 17 Jan 2014; published 3 Feb 2014 (C) 2014 OSA 10 February 2014 | Vol. 22, No. 3 | DOI:10.1364/OE.22.003054 | OPTICS EXPRESS 3056
conductivity σ and slab thickness t g . The period of the layered structure is t = td + t g . Experimentally, the multilayer composed of dielectric and graphene can be prepared by the following procedures: the dielectric layer is first coated on a SiO2 substrate through thermal evaporation, and then the high quality graphene sheets prepared using CVD method are coated on the top of the dielectric layer after a chemical vapor deposition, finally the multilayer is realized by stacking of many graphene/dielectric layers on the SiO2 substrate. The surface conductivity of graphene is highly dependent on the working wavelength and Fermi energy. Within the random-phase approximation and without external magnetic field, the graphene is isotropic and the surface conductivity σ can be written as a sum of the intraband σ intra and the interband term σ inter [39], where
σ intra
E − F EF 2 EF − (ω + iτ −1 ) ie2 k BT ie 2 kBT = + 2 ln(e + 1) , σ inter = ln , (1) π 2 (ω + i τ ) k BT 4π 2 EF + (ω + iτ −1 )
where ω is the frequency of the incident light, e and are universal constants related to the electron charge and reduced Planck’s constants, respectively. EF and τ are the Fermi energy (or chemical potential) and electron-phonon relaxation time, respectively. k B is the Boltzmann constant, and T is a temperature in K. The Fermi energy EF can be straightforwardly obtained from the carrier density ( n2 D ) in a graphene sheet, EF = ν F (π n2 D ) , ν F = 106 m/s is the Fermi velocity of electrons. Here, the carrier density 12
n2D can be electrically controlled by an applied gate voltage, thereby leading to a voltagecontrolled Fermi energy EF and hence the voltage-controlled surface conductivity σ , this could provide an effective route to achieve electrically controlled surface Bloch wave. We assume that the electronic band structure of a graphene sheet is not affected by the neighboring graphene sheets, hence the graphene’s effective permittivity ε g be written as
ε g = 1 + iσ ( ε 0ωt g ) , where ε 0 is the permittivity in the vacuum.
2.2 Bulk Bloch waves of the graphene-dielectric layered structure Assuming that the electric (magnetic) field is in the form A exp ( ik z z + ik x x + ik y y − iωt ) , the dispersion relation of Bloch modes in the infinite layered media is described by the twocomponents bulk Bloch waves, 1 F F cos ( k z t ) = cos ( k g t g ) cos ( kd td ) − 1 + 2 sin ( k g t g ) sin ( kd td ) , 2 F2 F1
where k g = ( ε g k02 − k⊥2 )
12
, kd = ( ε d k02 − k⊥2 )
12
(2)
, k0 = ω c , k⊥2 = k x2 + k y2 , F1 = ε g k g ,
F2 = ε d kd for p-polarized mode, and F1 = 1 k g , F2 = 1 kd for s-polarized mode.
2.3 Dispersion relation of graphene-dielectric layered structure in the subwavelength limit In the subwavelength limit, i.e., k g t g
1 School of Electrical and Electronic Engineering, Nanyang Technological University, 639798 Singapore Key Laboratory for Micro-/Nano-Optoelectronic Devices of Ministry of Education, College of Physics and Microelectronic Science, Hunan University, Changsha 410082, China 3 [email protected] * [email protected]
Abstract: A kind of tunable hyperbolic metamaterial (HMM) based on the graphene-dielectric layered structure at near-infrared frequencies is presented, and the engineered surface Bloch waves between graphene-based HMM and isotropic medium are investigated. Our calculations demonstrate that the frequency and frequency range of surface Bloch waves existence can be tuned by varying the Fermi energy of graphene sheets via electrostatic biasing. Moreover, we show that the frequency range of surface Bloch waves existence can be broadened by decreasing the thickness of the dielectric in the graphene-dielectric layered structure or by increasing the layer number of graphene sheets. ©2014 Optical Society of America OCIS codes: (240.0240) Optics at surfaces; (160.3918) Metamaterials.
References and links 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.
B. E. Sernelius, Surface Modes in Physics (John Wiley, 2001). J. A. Polo, Jr. and A. Lakhtakia, “Surface electromagnetic waves: a review,” Laser Photonics Rev. 5(2), 234–246 (2011). H. Raether, Surface Plasmon on Smooth and Rough Surfaces and on Gratings (Springer, 1988). A. V. Zayats, I. I. Smolyaninov, and A. A. Maradudin, “Nano-optics of surface plasmon polaritons,” Phys. Rep. 408(3–4), 131–314 (2005). W. L. Barnes, A. Dereux, and T. W. Ebbesen, “Surface plasmon subwavelength optics,” Nature 424(6950), 824– 830 (2003). J. M. Pitarke, V. M. Silkin, E. V. Chulkov, and P. M. Echenique, “Theory of surface plasmons and surfaceplasmon polaritons,” Rep. Prog. Phys. 70(1), 1–87 (2007). P. Yeh, A. Yariv, and C. S. Hong, “Electromagnetic propagation in periodic stratified media. I. General theory,” J. Opt. Soc. Am. 67(4), 423–438 (1977). P. Yeh, A. Yariv, and A. Y. Cho, “Optical surface-waves in periodic layered media,” Appl. Phys. Lett. 32(2), 104–105 (1978). T. Sfez, E. Descrovi, L. Yu, M. Quaglio, L. Dominici, W. Nakagawa, F. Michelotti, F. Giorgis, and H. P. Herzig, “Two dimensional optics on silicon nitride multilayer: refraction of Bloch surface waves,” Appl. Phys. Lett. 96(15), 151101 (2010). E. Guillermain, V. Lysenko, R. Orobtchouk, T. Benyattou, S. Roux, A. Pillonnet, and P. Perriat, “Bragg surface wave device based on porous silicon and its application for sensing,” Appl. Phys. Lett. 90(24), 241116 (2007). F. Giorgis, E. Descrovi, C. Summonte, L. Dominici, and F. Michelotti, “Experimental determination of the sensitivity of Bloch Surface Waves based sensors,” Opt. Express 18(8), 8087–8093 (2010). M. Liscidini and J. E. Sipe, “Enhancement of diffraction for biosensing applications via Bloch surface waves,” Appl. Phys. Lett. 91(25), 253125 (2007). Y. H. Wan, Z. Zheng, W. J. Kong, X. Zhao, Y. Liu, Y. S. Bian, and J. S. Liu, “Nearly three orders of magnitude enhancement of Goos-Hanchen shift by exciting Bloch surface wave,” Opt. Express 20(8), 8998–9003 (2012). S. Pirotta, X. G. Xu, A. Delfan, S. Mysore, S. Maiti, G. Dacarro, M. Patrini, M. Galli, G. Guizzetti, D. Bajoni, J. E. Sipe, G. C. Walker, and M. Liscidini, “Surface-enhanced Raman scattering in purely dielectric structures via Bloch surface waves,” J. Phys. Chem. C 117(13), 6821–6825 (2013). S. M. Vukovic, I. V. Shadrivov, and Y. S. Kivshar, “Surface Bloch waves in metamaterial and metal-dielectric supperlattices,” Appl. Phys. Lett. 95(4), 041902 (2009). D. R. Smith and D. Schurig, “Electromagnetic wave propagation in media with indefinite permittivity and permeability tensors,” Phys. Rev. Lett. 90(7), 077405 (2003). Z. Jacob, J.-Y. Kim, G. V. Naik, A. Boltasseva, E. E. Narimanov, and V. M. Shalaev, “Engineering photonic density of states using metamaterials,” Appl. Phys. B 100(1), 215–218 (2010).
#202058 - $15.00 USD Received 26 Nov 2013; revised 15 Jan 2014; accepted 17 Jan 2014; published 3 Feb 2014 (C) 2014 OSA 10 February 2014 | Vol. 22, No. 3 | DOI:10.1364/OE.22.003054 | OPTICS EXPRESS 3054
18. T. U. Tumkur, L. Gu, J. K. Kitur, E. E. Narimanov, and M. A. Noginov, “Control of absorption with hyperbolic metamaterials,” Appl. Phys. Lett. 100(16), 161103 (2012). 19. M. A. Noginov, A. Barnakov, G. Zhu, T. Tumkur, H. Li, and E. E. Narimanov, “Bulk photonic metamaterial with hyperbolic dispersion,” Appl. Phys. Lett. 94(15), 151105 (2009). 20. M. A. Noginov, H. Li, Y. A. Barnakov, D. Dryden, G. Nataraj, G. Zhu, C. E. Bonner, M. Mayy, Z. Jacob, and E. E. Narimanov, “Controlling spontaneous emission with metamaterials,” Opt. Lett. 35(11), 1863–1865 (2010). 21. C. Rizza, A. Ciattoni, E. Spinozzi, and L. Columbo, “Terahertz active spatial filtering through optically tunable hyperbolic metamaterials,” Opt. Lett. 37(16), 3345–3347 (2012). 22. G. Naik and A. Boltasseva, “Semiconductors for plasmonics and metamaterials,” Phys. Status Solidi 4, 295–297 (2010). 23. A. J. Hoffman, L. Alekseyev, S. S. Howard, K. J. Franz, D. Wasserman, V. A. Podolskiy, E. E. Narimanov, D. L. Sivco, and C. Gmachl, “Negative refraction in semiconductor metamaterials,” Nat. Mater. 6(12), 946–950 (2007). 24. J. Yao, Z. W. Liu, Y. M. Liu, Y. Wang, C. Sun, G. Bartal, A. M. Stacy, and X. Zhang, “Optical negative refraction in bulk metamaterials of nanowires,” Science 321(5891), 930 (2008). 25. Z. Jacob, I. Smolyaninov, and E. E. Narimanov, “Broadband purcell effect: Radiative decay engineering with metamaterials,” Appl. Phys. Lett. 100(18), 181105 (2012). 26. Z. Jacob, L. V. Alekseyev, and E. Narimanov, “Optical Hyperlens: Far-field imaging beyond the diffraction limit,” Opt. Express 14(18), 8247–8256 (2006). 27. Z. W. Liu, H. Lee, Y. Xiong, C. Sun, and X. Zhang, “Far-field optical hyperlens magnifying sub-diffractionlimited objects,” Science 315(5819), 1686 (2007). 28. A. V. Kabashin, P. Evans, S. Pastkovsky, W. Hendren, G. A. Wurtz, R. Atkinson, R. Pollard, V. A. Podolskiy, and A. V. Zayats, “Plasmonic nanorod metamaterials for biosensing,” Nat. Mater. 8(11), 867–871 (2009). 29. Y. He, S. He, and X. Yang, “Optical field enhancement in nanoscale slot waveguides of hyperbolic metamaterials,” Opt. Lett. 37(14), 2907–2909 (2012). 30. S. A. Biehs, M. Tschikin, and P. Ben-Abdallah, “Hyperbolic metamaterials as an analog of a blackbody in the near field,” Phys. Rev. Lett. 109(10), 104301 (2012). 31. A. H. Castro Neto, F. Guinea, N. M. R. Peres, K. S. Novoselov, and A. K. Geim, “The electronic properties of graphene,” Rev. Mod. Phys. 81(1), 109–162 (2009). 32. A. N. Grigorenko, M. Polini, and K. S. Novoselov, “Graphene plasmonics,” Nat. Photonics 6(11), 749–758 (2012). 33. M. Liu, X. Yin, E. Ulin-Avila, B. Geng, T. Zentgraf, L. Ju, F. Wang, and X. Zhang, “A graphene-based broadband optical modulator,” Nature 474(7349), 64–67 (2011). 34. I. V. Iorsh, I. S. Mukhin, I. V. Shadrivov, P. A. Belov, and Y. S. Kivshar, “Hyperbolic metamaterials based on multilayer graphene structures,” Phys. Rev. B 87(7), 075416 (2013). 35. M. A. K. Othman, C. Guclu, and F. Capolino, “Graphene-based tunable hyperbolic metamaterials and enhanced near-field absorption,” Opt. Express 21(6), 7614–7632 (2013). 36. K. V. Sreekanth, A. De Luca, and G. Strangi, “Negative refraction in graphene-based metamaterials,” Appl. Phys. Lett. 103(2), 023107 (2013). 37. I. S. Nefedov, C. A. Valaginnopoulos, and L. A. Melnikov, “Perfect absorption in graphene multilayers,” J. Opt. 15(11), 114003 (2013). 38. T. Zhang, L. Chen, and X. Li, “Graphene-based tunable broadband hyperlens for far-field subdiffraction imaging at mid-infrared frequencies,” Opt. Express 21(18), 20888–20899 (2013). 39. B. Zhu, G. Ren, S. Zheng, Z. Lin, and S. Jian, “Nanoscale dielectric-graphene-dielectric tunable infrared waveguide with ultrahigh refractive indices,” Opt. Express 21(14), 17089–17096 (2013). 40. C. J. Zapata-Rodríguez, J. J. Miret, S. Vuković, and M. R. Belić, “Engineered surface waves in hyperbolic metamaterials,” Opt. Express 21(16), 19113–19127 (2013).
1. Introduction Surface electromagnetic waves (SEWs) are a special type of waves that are confined at the interface between two media with different properties [1, 2]. One of the best known examples of SEWs is surface plasmon polariton (SPP), which is formed at the interfaces between metals and dielectrics [3, 4]. SPPs only exist for TM polarization and there is no surface modes exist for TE polarization. SPP has attracted a wide spread attention in the last decade mainly due to their applications in sensing, microscopy, or integrated optics [5, 6]. However, when one of the two media at the interface is periodic structures (photonic crystals or superlattices), the Bloch surface waves (BSWs) may appear at the boundary within the photonic bandgaps [7, 8]. It has also been shown the lateral conðnement of the BSWs in the waveguide is well described by the 2D Snell’s [9]. BSWs have potential applications in optical sensing [10–12], enhancement of Goos-Hanchen shift [13], and surface-enhanced Raman spectroscopy [14]. For BSWs, the Bloch wavevector is perpendicular to the interface of the periodic structure and the dielectric layer, and hence the Bloch wavevector is not propagating along the interface. Moreover, most recently, Vukovic et al. proposed another
#202058 - $15.00 USD Received 26 Nov 2013; revised 15 Jan 2014; accepted 17 Jan 2014; published 3 Feb 2014 (C) 2014 OSA 10 February 2014 | Vol. 22, No. 3 | DOI:10.1364/OE.22.003054 | OPTICS EXPRESS 3055
surface wave propagating in metal-dielectric superlattices and isotropic dielectric medium where the Bloch wavevector is parallel to the interface of the two media [15]. This surface wave has been named as surface Bloch waves owing to the Bloch wave propagating along the interface [15]. Hyperbolic metamaterial (HMM) is a uniaxial anisotropic medium having the hyperbolic form of the dispersion relation [16]. HMMs can be realized at optical frequencies using metal-dielectric multilayers [17, 18] or metallic nanorods/nanowires in a dielectric host [19, 20], and at terahertz and infrared frequencies using semiconductor-dielectric multilayers [21, 22]. HMM promises a variety of potential applications including negative refraction [23, 24], broadband Purcell effect [20, 25], imaging hyperlens [26, 27], optical waveguide [28, 29], and perfect thermal emitters [30]. Recently, graphene has attracted intensive scientific interest owing to its incredible physical properties showing great potential applications in nano-electronic devices and optoelectric devices with ultrahigh electron mobility, ultrafast relaxation time for photoexcited carriers, and gate variable optical conductivity [31]. Graphene plasmonics have generated great interest among scientific community because of the ability of graphene to tune the plasmon dispersion by varying the chemical potential [32]. It seems to be a good candidate for designing tunable optical device that operates in both THz and optical frequency ranges [33]. Most recently, graphene-based HMMs composed of stacked graphene sheets separated by thin dielectric layers have been proposed and investigated [34, 35], it has been demonstrated that such graphene-based HMMs can be used for the negative refraction at THz frequencies [36], the spontaneous emission enhancement [34, 35], the perfect absorption [37], tunable broadband hyperlens [38], tunable infrared waveguide [39], and so on. However, these HMMs have be realized and investigated mainly at THz frequencies, and mid- or far-infrared frequencies. Graphene-based HMMs at the near-infrared frequencies and visible light are still not demonstrated. In the present paper, we suggest a new class of tunable HMMs for near-infrared frequencies based on the graphene-dielectric layered structure, and reveal that such graphene structures can support a controllable surface Bloch wave between graphene-based HMM and isotropic medium.
Fig. 1. (a) Scheme of the interface of the semi-infinite graphene-based hyperbolic metamaterial and the semi-infinite isotropic dielectric; (b) effective permittivity of the graphene-based layered metamaterial; (c) dispersion curve of the graphene-based hyperbolic metamaterial.
2. Graphene-based HMMs at the near-infrared frequencies 2.1 The optical properties of graphene sheets Consider the geometry shown in Fig. 1(a), where the semi-infinite periodic structure created by alternating layers of graphene and conventional dielectric is placed on the left of the homogeneous dielectric. The unit cell of the layered structure is formed by a transparent material of dielectric constant ε d and slab thickness td and graphene sheets of surface
#202058 - $15.00 USD Received 26 Nov 2013; revised 15 Jan 2014; accepted 17 Jan 2014; published 3 Feb 2014 (C) 2014 OSA 10 February 2014 | Vol. 22, No. 3 | DOI:10.1364/OE.22.003054 | OPTICS EXPRESS 3056
conductivity σ and slab thickness t g . The period of the layered structure is t = td + t g . Experimentally, the multilayer composed of dielectric and graphene can be prepared by the following procedures: the dielectric layer is first coated on a SiO2 substrate through thermal evaporation, and then the high quality graphene sheets prepared using CVD method are coated on the top of the dielectric layer after a chemical vapor deposition, finally the multilayer is realized by stacking of many graphene/dielectric layers on the SiO2 substrate. The surface conductivity of graphene is highly dependent on the working wavelength and Fermi energy. Within the random-phase approximation and without external magnetic field, the graphene is isotropic and the surface conductivity σ can be written as a sum of the intraband σ intra and the interband term σ inter [39], where
σ intra
E − F EF 2 EF − (ω + iτ −1 ) ie2 k BT ie 2 kBT = + 2 ln(e + 1) , σ inter = ln , (1) π 2 (ω + i τ ) k BT 4π 2 EF + (ω + iτ −1 )
where ω is the frequency of the incident light, e and are universal constants related to the electron charge and reduced Planck’s constants, respectively. EF and τ are the Fermi energy (or chemical potential) and electron-phonon relaxation time, respectively. k B is the Boltzmann constant, and T is a temperature in K. The Fermi energy EF can be straightforwardly obtained from the carrier density ( n2 D ) in a graphene sheet, EF = ν F (π n2 D ) , ν F = 106 m/s is the Fermi velocity of electrons. Here, the carrier density 12
n2D can be electrically controlled by an applied gate voltage, thereby leading to a voltagecontrolled Fermi energy EF and hence the voltage-controlled surface conductivity σ , this could provide an effective route to achieve electrically controlled surface Bloch wave. We assume that the electronic band structure of a graphene sheet is not affected by the neighboring graphene sheets, hence the graphene’s effective permittivity ε g be written as
ε g = 1 + iσ ( ε 0ωt g ) , where ε 0 is the permittivity in the vacuum.
2.2 Bulk Bloch waves of the graphene-dielectric layered structure Assuming that the electric (magnetic) field is in the form A exp ( ik z z + ik x x + ik y y − iωt ) , the dispersion relation of Bloch modes in the infinite layered media is described by the twocomponents bulk Bloch waves, 1 F F cos ( k z t ) = cos ( k g t g ) cos ( kd td ) − 1 + 2 sin ( k g t g ) sin ( kd td ) , 2 F2 F1
where k g = ( ε g k02 − k⊥2 )
12
, kd = ( ε d k02 − k⊥2 )
12
(2)
, k0 = ω c , k⊥2 = k x2 + k y2 , F1 = ε g k g ,
F2 = ε d kd for p-polarized mode, and F1 = 1 k g , F2 = 1 kd for s-polarized mode.
2.3 Dispersion relation of graphene-dielectric layered structure in the subwavelength limit In the subwavelength limit, i.e., k g t g
