Breakthroughs in Photonics 2013: Advances in Nanoantennas
Breakthroughs in Photonics 2013: Advances in Nanoantennas Volume 6, Number 2, April 2014 Gilliard N. Malheiros-Silveira Lucas H. Gabrielli Connie J. Chang-Hasnain, Fellow, IEEE Hugo E. Hernandez-Figueroa, Senior Member, IEEE
DOI: 10.1109/JPHOT.2014.2311438 1943-0655 Ó 2014 IEEE
Invited Paper
IEEE Photonics Journal
Breakthroughs in Photonics 2013
Breakthroughs in Photonics 2013: Advances in Nanoantennas Gilliard N. Malheiros-Silveira, 1;2 Lucas H. Gabrielli, 1 Connie J. Chang-Hasnain,2 Fellow, IEEE, and Hugo E. Hernandez-Figueroa,1 Senior Member, IEEE (Invited Paper) 1
2
Department of Communications, School of Electrical and Computer Engineering, University of Campinas, Campinas, SP 13083-852, Brazil Department of Electrical Engineering and Computer Sciences, University of California at Berkeley, Berkeley, CA 94720 USA
DOI: 10.1109/JPHOT.2014.2311438 1943-0655 Ó 2014 IEEE. Translations and content mining are permitted for academic research only. Personal use is also permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
Manuscript received February 11, 2014; revised March 3, 2014; accepted March 4, 2014. Date of publication March 12, 2014; date of current version April 30, 2014. This work was supported in part by Sa˜o Paulo Research Foundation (FAPESP) under Grants #2010/18857-7, #2013/03947-9, and #2012/22517-2 and in part by the INCT FOTONICOM/CNPq/FAPESP. Corresponding author: G. N. Malheiros-Silveira (e-mail: [email protected]).
Abstract: The field of nanoantennas overlaps several areas of scientific interest, from fundamental physics to commercial technologies. Advances in the understanding of such complex devices hold the promises to novel applications in sensing, telecommunications, optical processing, and security, among others. Here, we review the main advances in the field of nanoantennas in 2013, from single metallic and dielectric devices to nanostructured metasurfaces and phased arrays. Index Terms: Antenna arrays, dielectric resonator antenna, nanophotonics, optical beams, beam steering, nanostructures.
1. Introduction The continued advances in fabrication technologies at the nanoscale enable the creation of ever more complex devices and systems for optical manipulation. In special the field of nanoantennas saw in 2013 amazing results in a wide range of applications, from telecommunications and optical signal processing to molecular sensing and nonlinear enhancement. In this review of the 2013 nanoantenna breakthroughs we group the main achievements in the following 5 sections: phased arrays, metasurfaces, tunable design capability, all-dielectric design, and metal nanoantennas.
2. Phased Arrays Phased arrays are one of the most interesting aspects of antenna design. By controlling the feeds of each radiating element, the radiation pattern of an array can be modified. This feature is commonly used in microwave systems to enable beam steering and shaping. Depending on the number of antennas and their positioning in an array more or less freedom of control over the radiation pattern is obtained. Taking advantage of the high complexity and integration levels provided by CMOS fabrication, Sun et al. [1] demonstrated the largest dynamically and statically controlled optical phased array to
Vol. 6, No. 2, April 2014
0700706
IEEE Photonics Journal
Breakthroughs in Photonics 2013
Fig. 1. (a) Scheme of the 8 8 array dynamic controlled (adapted by permission from Macmillan Publishers Ltd: Nature [1], copyright 2013). (b) Scheme of the electrical tuning of graphene-loaded plasmonic antennas (adapted with permission from [2], copyright 2013, American Chemical Society). (c) Scheme of buried nanoantenna arrays (reprinted with permission from [3], copyright 2013, American Chemical Society). (d) Scheme of nonuniform nano-DRA reflectarray (adapted from [4], copyright 2013, OSA). (e) Scheme of high directional nanoantenna design with embedded quantum dots (adapted by permission from Macmillan Publishers Ltd: Scientific Reports [5], copyright 2013).
date at 1.55 m. They used a 4096-element array to statically generate a highly complex beam with the MIT (Massachusetts Institute of Technology) logo. The power balance and excitation phase for each element in the 64 64 array were calculated beforehand and designed to generate the desired pattern. In the same paper they also show a smaller 8 8 array with dynamic beam steering and shaping capabilities, where the thermo-optic effect in silicon was used to externally control the phases of each column or row of elements [see Fig. 1(a)]. A pitch size of 9 m was used in both arrays. Another work that demonstrated the flexibility of CMOS-compatible optical phased arrays, employed metallic apertures in an 8 1 linear array. In their paper, DeRose et al. [6] achieved 8 of continuous steering angle at a fixed wavelength in the telecommunications band. Due to their reduced size, the metallic nanoantennas enabled an array pitch size of only 6 m (the authors also show results for a 9 m-pitch array). Reflective elements can also be used to compose a beam shaping array, as demonstrated by Yoo et al. [7] in the near infrared range. They used high contrast gratings (HCG) and micro-electromechanical structure (MEMS) technology to build a dynamic phased array capable of fast response times due to the low mass of HCG in comparison to other types of reflectors. Additionally, by avoiding the use of reflective coatings, the proposed HCG phased array is capable of handling high optical power density while maintaining response times in the order of microseconds.
3. Metasurfaces A very promising concept in the field of nanoantenna arrays is that of metasurfaces, where the array is composed by carefully designed anisotropic metallic nanoantennas. Each element is responsible for abrupt polarization and phase changes that add up to perform any number of beam manipulations. This versatile platform has been used to realize vortex beams with orbital angular momentum and nondiffracting beams, as well as to provide beam steering and polarization control in the mid infrared range [8]. Designing such complex structures is not a simple task, and the conventional numerical computational methods become inefficient when analyzing large non-uniform arrays. Aiming at
Vol. 6, No. 2, April 2014
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IEEE Photonics Journal
Breakthroughs in Photonics 2013
increasing this computational efficiency, Dong et al. [9] introduced the Characteristic Basis Function Method, which reduces both time and memory requirements for the simulation of large problems in comparison to conventional methods. The authors show an amazing 100 fold decrease in memory requirement for large metasurfaces composed of nanorods in comparison to the Method of Moments, and similar results are expected for the computational time. Along the lines of optical signal processing, Farmahini-Farahani et al. [10] proposed a method for controlling not only the phase but also the amplitude of beams transmitted through metasurfaces at 5 m. They designed an L-shaped antenna that is able to control the amplitude of the transmitted beam in one polarization. By cascading this layer with one that controls the transmitted phaseVvia concentric loop elementsVthey were able to tune both parameters independently, enabling the design of unique spatial filters. Numerical simulations are presented to demonstrate a spatial differentiator and triangular beam shaper. The freedom of design provided by metasurfaces can be used not only to tailor the transmission profiles of incident beams, but also to modify or, as in the case of Kabiri and co-authors’ work [3], to suppress their reflections. They achieved a minimum of 0.002% reflectance in the mid-infrared range using a nanoantenna array buried in a silicon layer [see Fig. 1(c)]. Their versatile design allows for reflection suppression over a narrow-, wide-, or multifrequency band. The design can be made polarization dependent or independent and wide-angle reflection mitigation can also be attained.
4. Tunable Design Capability An experimental realization related to the nanocircuit paradigm has been presented in [11] by Liu et al., where three-dimensional lumped elements were applied to control the optical response of individual nanoantennas in visible wavelengths. For that, individual gold dimmer nanoantennas were used as a test platform in order to demonstrate series and parallel 3-dimensional nanocircuit elements. By loading the nanoantenna gap with specific arrangements of dielectric, semiconducting, and metallic nanoparticules, the tunability of the nanoantenna impedance, resonance wavelength, and filtering, and scattering characteristics were experimentally confirmed. Dynamic control over nanoantennas properties was demonstrated by Yao et al. [2]. The authors loaded the plasmonic nanoantenna gap with graphene [see Fig. 1(b)], which provides dynamic electrical tuning of the antenna resonance peak over a wavelength range of 650 nm (approximately 10% of the central wavelength). In the same work, a doubly resonant nanoantenna array was used to achieve mid-infrared optical intensity modulation with maximum depth of more than 30% and bandwidth of 600 nm. The presented concept, can be extended to the electrical tuning of optical and optoelectronic devices by combining metallic nanostructures with graphene. The tuning of the resonance frequency in aluminum nanoantenna array assuming different positions on top of, inside, and below a dielectric layer of phase-change materials (PCM) was investigated by Michel et al. [12] in the mid infrared domain. They used either Ge3 Sb2 Te6 or InSb as low-loss PCM to compose the layer and achieved maximum frequency shift of 19.3% by changing the refractive index of those materials. Authors suggested that reversibly and ultrafast response of the resonance tuning can be achieved by means of electrical or optical switching of the PCM. In the visible range, dynamic tuning of silver nanoantennas is shown by Earl et al. [13] by controlling the optical properties of the antenna substrate itself. The substrate is composed of silicon under a thin layer of VO2 , which presents a phase transition around 68 C. By heating the subtrate the resonance peak of the antennas changed by 110 nm (about 13% of the central wavelength), in good agreement with the simulated model.
5. All-Dielectric Design Although not a new concept, dielectric optical antennas received a lot of attention in 2013, inspired by designs derived from their microwave counterparts, in special that of dielectric resonator antennas (DRA). In [14] Coenen et al. numerically and experimentally determined the spectral and spatial characteristics of the eigenmodes of isolated silicon nanocylinders with dimensions raging from 60 nm to 350 nm via angle-resolved cathodoluminescence imaging spectroscopy.
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IEEE Photonics Journal
Breakthroughs in Photonics 2013
A nonuniform nano-DRA array [see Fig. 1(d)] was used by Zou et al. [4] to demonstrate optical beam deflection at 633 nm. The near reasonances of the TiO2 nano-DRA on a silver film imposed progressive phase delays onto an incoming beam, resulting in a deflection of 19.9 . Deflection angles up to 27 were also measured by the authors. The use of dielectric antennas instead of plasmonic ones has the potential to reduce the power dissipation to a minimum, while maintaining the nanoantenna array versatility. A nano-DRA was also proposed as an efficient way of coupling free-space light into and out of plasmonic circuits. Malheiros-Silveira et al. [15] designed a nano-DRA fed by a nanostrip plasmonic waveguide operating at 1.55 m with broadband impedance matching and consistent radiation pattern covering the entire S, C, and L telecommunication bands. The design represent a promising result for optical wireless applications in inter- and intrachip communications. Staude et al. [16] demonstrated that the suppression of the backward scattering and the enhancement of the forward one for the particular case of overlapping electric and magnetic resonances can be obtained by varying the nanodisk aspect ratio of high-index all-dielectric nanoparticles. They shown that such technique can produce optical nanoantennas based on silicon nanodisks with strong unidirectional emission once fed from a dipole source. Finally, a current and interesting approach by using dielectric resonator comes from the nanopillars/nanoneedles grown on top of crystalline or polycrystalline platforms. High-quality grown of InP nanoneedles on silicon was demonstrated by Ren et al. [17]. Even a single dielectric pillar can exhibit a reasonable quality factor on the order of a few hundred. Such resonators provide simple and high efficiency optical coupling with external optics and are promising as low-cost sensors, optical filters and multiplexers.
6. Metal Nanoantennas Plasmonic nanoantennas found applications in myriad fields in the past decade, and continues to do so following the advances in design and fabrication. Among design innovations, directionality control and multifrequency structures were proposed using different antenna structures [18]–[21]. The coupling mechanism between waveguides and gold nanowires working as nanoantennas was studied by Arnaud et al. [22]. A theoretical study relating the coupling of dipole radiation into integrated strip waveguide by means of metallic nanoantenna was performed by Peyskens et al. [23]. Authors outlined that device enables efficient coupling of enhanced Raman signals into dielectric waveguides. Waveguide-coupled nanoLED with enhanced spontaneous emission was demonstrated by Eggleston and Wu [24]. They achieved directional emission down the waveguide with 70% of efficiency by adding passive reflector and director elements. A linear effect related to nonreciprocal light emission based on timed Dicke states was predicted by Slepyan and Boag [25]. They have theoretically investigated such characteristic asymmetry from the radiation pattern in nanoantenna arrays. By applying near-field optical microscopy combined with far-field excitation spectroscopy on plasmonic nanoantennas, Alonso-Gonza´lez et al. [26] have experimentally demonstrated the spectral shift between near- and far-field peak intensities in infrared domain. Moreover, authors analyzed via numerical simulations the implications of that shift in surface-enhanced infrared spectroscopy (SEIRS) and suggested that such shift should be considered in order to optimize the molecular spectral absorption contrast in plasmonic (bio)sensing devices. Deterministic multipolar radiation of quantum dots was demonstrated by Curto et al. [27] through selective coupling to multipolar resonances of nanowire antennas of increasing length, with alternating symmetry, and with multipole parity. Those findings can provide opportunities on the development of new concepts of quantum nano-optics components. On the other hand, an interesting high directional nanoantenna design, which has quantum dots tightly embedded in its structure was proposed by Tong et al. [5] [see Fig. 1(e)]. The concept of antenna-in-box platform, in which a gap-nanoantenna (that provides fluorescent signal enhancement) is located inside a nanoaperture (that provides background screening) was proposed by Punj et al. [28]. By using that platform authors got isolated detection volumes of 58 zl
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Breakthroughs in Photonics 2013
and 1100-fold fluorescence enhancement. According to the authors, this concept preludes a new class of nanoscale biomolecular studies in enzymatic reactions and nanoscale composition of live cell membranes. In comparison with nonlinear bulk media, cascaded four-wave mixing (FWM) presenting 300-fold enhancement of frequency conversion was theoretically evaluated by Maksymov et al. [29]. They engineered the number and length of plasmonic nanoantennas disposed in a tapered configuration and embedded in nonlinear mediumVindium-tin-oxide (ITO)Vin order to obtain resonances at the frequencies involved in the FWM. Finally, a novel optical antenna design assuming an arch-dipole shape, with a gap spacing of 5 nm, was proposed by Seok et al. [30] and fabricated by current CMOS technology. Authors demonstrated strong surface-enhanced Raman spectroscopy (SERS) signal with an enhancement factor exceeding 108 from an arch-dipole 2D array, which is two order of magnitude stronger than that from an equivalent 2D array composed of standard dipole nanoantennas fabricated by e-beam lithography. This work also points out to new perspectives in mass-producible optical antennas.
7. Conclusion and Future Challenges Great breakthroughs in nanoantennas were established in 2013. From single elements to large arrays the versatility of such devices in manipulating optical fields represented a key aspect in their widespread use in a myriad applications. Continued efforts are necessary, though, to tackle issues still presents in each application, be it the reduction in pitch size of phased arrays for larger angular steering range, the increase in metasurfaces conversion efficiency, or improvements in fabrication techniques for higher precision nanostructures in general, these questions are sure to be present in future research around this exciting and promising field.
References [1] J. Sun, E. Timurdogan, A. Yaacobi, E. S. Hosseini, and M. R. Watts, BLarge-scale nanophotonic phased array,[ Nature, vol. 493, no. 7431, pp. 195–199, Jan. 2013. [2] Y. Yao, M. A. Kats, P. Genevet, N. Yu, Y. Song, J. Kong, and F. Capasso, BBroad electrical tuning of graphene-loaded plasmonic antennas,[ Nano Lett., vol. 13, no. 3, pp. 1257–1264, Mar. 2013. [3] A. Kabiri, E. Girgis, and F. Capasso, BBuried nanoantenna arrays: Versatile antireflection coating,[ Nano Lett., vol. 13, no. 12, pp. 6040–6047, Dec. 2013. [4] L. Zou, W. Withayachumnankul, C. M. Shah, A. Mitchell, M. Bhaskaran, S. Sriram, and C. Fumeaux, BDielectric resonator nanoantennas at visible frequencies,[ Opt. Exp., vol. 21, no. 1, pp. 1344–1352, Jan. 2013. [5] L. Tong, T. Pakizeh, L. Feuz, and A. Dmitriev, BHighly directional bottom-up 3d nanoantenna for visible light,[ Sci. Rep., vol. 3, p. 2311, Jul. 2013. [6] C. T. DeRose, R. D. Kekatpure, D. C. Trotter, A. Starbuck, J. R. Wendt, A. Yaacobi, M. R. Watts, U. Chettiar, N. Engheta, and P. S. Davids, BElectronically controlled optical beam-steering by an active phased array of metallic nanoantennas,[ Opt. Exp., vol. 21, no. 4, pp. 5198–5208, Feb. 2013. [7] B.-W. Yoo, M. Megens, T. Chan, T. Sun, W. Yang, C. J. Chang-hasnain, D. A. Horsley, and M. C. Wu, BOptical phased array using high contrast gratings for two dimensional beamforming and beamsteering,[ Opt. Exp., vol. 21, no. 10, pp. 2807–2815, May 2013. [8] P. Genevet, F. Aieta, M. A. Kats, R. Blanchard, G. Aoust, J.-P. Tetienne, Z. Gaburro, and F. Capasso, BFlat optics: Controlling wavefronts with optical antenna metasurfaces,[ IEEE J. Sel. Topics Quantum Electron., vol. 19, no. 3, p. 4 700 423, May/Jun. 2013. [9] T. Dong, X. Ma, and R. Mittra, BModeling large nonuniform optical antenna arrays for metasurface application,[ J. Appl. Phys., vol. 114, no. 4, pp. 043103-1–043103-10, Jul. 2013. [10] M. Farmahini-Farahani, J. Cheng, and H. Mosallaei, BMetasurfaces nanoantennas for light processing,[ J. Opt. Soc. Amer. B, vol. 30, no. 9, pp. 2365–2370, Sep. 2013. [11] N. Liu, F. Wen, Y. Zhao, Y. Wang, P. Nordlander, N. J. Halas, and A. Alu`, BIndividual nanoantennas loaded with threedimensional optical nanocircuits,[ Nano Lett., vol. 13, no. 1, pp. 142–147, Jan. 2013. [12] A.-K. U. Michel, D. N. Chigrin, T. W. W. Ma, K. Schnauer, M. Salinga, M. Wuttig, and T. Taubner, BUsing low-loss phase-change materials for mid-infrared antenna resonance tuning,[ Nano Lett., vol. 13, no. 8, pp. 3470–3475, Aug. 2013. [13] S. K. Earl, T. D. James, T. J. Davis, J. C. McCallum, R. E. Marvel, R. F. Haglund, and A. Roberts, BTunable optical antennas enabled by the phase transition in vanadium dioxide,[ Opt. Exp., vol. 21, no. 22, pp. 27 503–27 508, Nov. 2013. [14] T. Coenen, J. van de Groep, and A. Polman, BResonant modes of single silicon nanocavities excited by electron irradiation,[ ACS Nano, vol. 7, no. 2, pp. 1689–1698, Jan. 2013. [15] G. N. Malheiros-Silveira, G. S. Wiederhecker, and H. E. Herna´ndez-Figueroa, BDielectric resonator antenna for applications in nanophotonics,[ Opt. Exp., vol. 21, no. 1, pp. 1234–1239, Jan. 2013.
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[16] I. Staude, A. E. Miroshnichenko, M. Decker, N. T. Fofang, S. Liu, E. Gonzales, J. Dominguez, T. S. Luk, D. N. Neshev, I. Brener, and Y. Kivshar, BTailoring directional scattering through magnetic and electric resonances in subwavelength silicon nanodisks,[ ACS Nano, vol. 7, no. 9, pp. 7824–7832, 2013. [17] F. Ren, K. W. Ng, K. Li, H. Sun, and C. J. Chang-Hasnain, BHigh-quality InP nanoneedles grown on silicon,[ Appl. Phys. Lett., vol. 102, no. 1, pp. 012115-1–012115-4, Jan. 2013. [18] Z. Xi, Y. Lu, W. Yu, P. Yao, P. Wang, and H. Ming, BTailoring the directivity of both excitation and emission of dipole simultaneously with two-colored plasmonic antenna,[ Opt. Exp., vol. 21, no. 24, pp. 29 365–29 373, Dec. 2013. [19] D. Vercruysse, Y. Sonnefraud, N. Verellen, F. B. Fuchs, G. Di Martino, L. Lagae, V. V. Moshchalkov, S. A. Maier, and P. Van Dorpe, BUnidirectional side scattering of light by a single-element nanoantenna,[ Nano Lett., vol. 13, no. 8, pp. 3843–3849, Aug. 2013. [20] T. D. James, Z. Q. Teo, D. E. Gomez, T. J. Davis, and A. Roberts, BThe plasmonic J-pole antenna,[ Appl. Phys. Lett., vol. 102, no. 3, pp. 033106-1–033106-4, Jan. 2013. ˇ ´ıpova´, M. Rahmani, M. Navarro-Cia, K. Hegnerova´, J. Homola, M. Hong, and S. A. Maier, BUltrasensitive [21] H. Aouani, H. S broadband probing of molecular vibrational modes with multifrequency optical antennas,[ ACS Nano, vol. 7, no. 1, pp. 669–675, Jan. 2013. [22] L. Arnaud, A. Bruyant, M. Renault, Y. Hadjar, R. Salas-Montiel, A. Apuzzo, G. Le´rondel, A. Morand, P. Benech, E. Le Coarer, and S. Blaize, BWaveguide-coupled nanowire as an optical antenna,[ J. Opt. Soc. Amer. A, Opt., Image Sci., Vis., vol. 30, no. 11, pp. 2347–2355, Nov. 2013. [23] F. Peyskens, A. Subramanian, A. Dhakal, N. L. Thomas, and R. Baets, BEnhancement of raman scattering efficiency by a metallic nano-antenna on top of a high index contrast waveguide,[ presented at the Conf. Lasers Electro-Optics, San Jose, CA, USA, 2013, CM2F.5. [24] M. Eggleston and M. C. Wu, BEfficient coupling of optical-antenna based nanoLED to a photonic waveguide,[ in Proc. IEEE IPC, Sep. 2013, pp. 331–332. [25] G. Y. Slepyan and A. Boag, BQuantum nonreciprocity of nanoscale antenna arrays in timed dicke states,[ Phys. Rev. Lett., vol. 111, no. 2, p. 023602, Jul. 2013. [26] P. Alonso-Gonza´lez, P. Albella, F. Neubrech, C. Huck, J. Chen, F. Golmar, F. Casanova, L. E. Hueso, A. Pucci, J. Aizpurua, and R. Hillenbrand, BExperimental verification of the spectral shift between near- and far-field peak intensities of plasmonic infrared nanoantennas,[ Phys. Rev. Lett., vol. 110, no. 20, p. 203 902, May 2013. [27] A. G. Curto, T. H. Taminiau, G. Volpe, M. P. Kreuzer, R. Quidant, and N. F. van Hulst, BMultipolar radiation of quantum emitters with nanowire optical antennas,[ Nature Commun., vol. 4, p. 1750, Apr. 2013. [28] D. Punj, M. Mivelle, S. B. Moparthi, T. S. van Zanten, H. Rigneault, N. F. van Hulst, M. F. Garcı´a-Parajo´, and J. Wenger, BA plasmonic Fantenna-in-box_ platform for enhanced single-molecule analysis at micromolar concentrations,[ Nature Nanotechnol., vol. 8, no. 7, pp. 512–516, Jul. 2013. [29] I. S. Maksymov, A. E. Miroshnichenko, and Y. S. Kivshar, BCascaded four-wave mixing in tapered plasmonic nanoantenna,[ Opt. Lett., vol. 38, no. 1, pp. 79–81, Jan. 2013. [30] T. J. Seok, A. Jamshidi, M. Eggleston, and M. C. Wu, BMass-producible and efficient optical antennas with cmosfabricated nanometer-scale gap,[ Opt. Exp., vol. 21, no. 14, pp. 16 561–16 569, Jul. 2013.
Vol. 6, No. 2, April 2014
0700706
DOI: 10.1109/JPHOT.2014.2311438 1943-0655 Ó 2014 IEEE
Invited Paper
IEEE Photonics Journal
Breakthroughs in Photonics 2013
Breakthroughs in Photonics 2013: Advances in Nanoantennas Gilliard N. Malheiros-Silveira, 1;2 Lucas H. Gabrielli, 1 Connie J. Chang-Hasnain,2 Fellow, IEEE, and Hugo E. Hernandez-Figueroa,1 Senior Member, IEEE (Invited Paper) 1
2
Department of Communications, School of Electrical and Computer Engineering, University of Campinas, Campinas, SP 13083-852, Brazil Department of Electrical Engineering and Computer Sciences, University of California at Berkeley, Berkeley, CA 94720 USA
DOI: 10.1109/JPHOT.2014.2311438 1943-0655 Ó 2014 IEEE. Translations and content mining are permitted for academic research only. Personal use is also permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
Manuscript received February 11, 2014; revised March 3, 2014; accepted March 4, 2014. Date of publication March 12, 2014; date of current version April 30, 2014. This work was supported in part by Sa˜o Paulo Research Foundation (FAPESP) under Grants #2010/18857-7, #2013/03947-9, and #2012/22517-2 and in part by the INCT FOTONICOM/CNPq/FAPESP. Corresponding author: G. N. Malheiros-Silveira (e-mail: [email protected]).
Abstract: The field of nanoantennas overlaps several areas of scientific interest, from fundamental physics to commercial technologies. Advances in the understanding of such complex devices hold the promises to novel applications in sensing, telecommunications, optical processing, and security, among others. Here, we review the main advances in the field of nanoantennas in 2013, from single metallic and dielectric devices to nanostructured metasurfaces and phased arrays. Index Terms: Antenna arrays, dielectric resonator antenna, nanophotonics, optical beams, beam steering, nanostructures.
1. Introduction The continued advances in fabrication technologies at the nanoscale enable the creation of ever more complex devices and systems for optical manipulation. In special the field of nanoantennas saw in 2013 amazing results in a wide range of applications, from telecommunications and optical signal processing to molecular sensing and nonlinear enhancement. In this review of the 2013 nanoantenna breakthroughs we group the main achievements in the following 5 sections: phased arrays, metasurfaces, tunable design capability, all-dielectric design, and metal nanoantennas.
2. Phased Arrays Phased arrays are one of the most interesting aspects of antenna design. By controlling the feeds of each radiating element, the radiation pattern of an array can be modified. This feature is commonly used in microwave systems to enable beam steering and shaping. Depending on the number of antennas and their positioning in an array more or less freedom of control over the radiation pattern is obtained. Taking advantage of the high complexity and integration levels provided by CMOS fabrication, Sun et al. [1] demonstrated the largest dynamically and statically controlled optical phased array to
Vol. 6, No. 2, April 2014
0700706
IEEE Photonics Journal
Breakthroughs in Photonics 2013
Fig. 1. (a) Scheme of the 8 8 array dynamic controlled (adapted by permission from Macmillan Publishers Ltd: Nature [1], copyright 2013). (b) Scheme of the electrical tuning of graphene-loaded plasmonic antennas (adapted with permission from [2], copyright 2013, American Chemical Society). (c) Scheme of buried nanoantenna arrays (reprinted with permission from [3], copyright 2013, American Chemical Society). (d) Scheme of nonuniform nano-DRA reflectarray (adapted from [4], copyright 2013, OSA). (e) Scheme of high directional nanoantenna design with embedded quantum dots (adapted by permission from Macmillan Publishers Ltd: Scientific Reports [5], copyright 2013).
date at 1.55 m. They used a 4096-element array to statically generate a highly complex beam with the MIT (Massachusetts Institute of Technology) logo. The power balance and excitation phase for each element in the 64 64 array were calculated beforehand and designed to generate the desired pattern. In the same paper they also show a smaller 8 8 array with dynamic beam steering and shaping capabilities, where the thermo-optic effect in silicon was used to externally control the phases of each column or row of elements [see Fig. 1(a)]. A pitch size of 9 m was used in both arrays. Another work that demonstrated the flexibility of CMOS-compatible optical phased arrays, employed metallic apertures in an 8 1 linear array. In their paper, DeRose et al. [6] achieved 8 of continuous steering angle at a fixed wavelength in the telecommunications band. Due to their reduced size, the metallic nanoantennas enabled an array pitch size of only 6 m (the authors also show results for a 9 m-pitch array). Reflective elements can also be used to compose a beam shaping array, as demonstrated by Yoo et al. [7] in the near infrared range. They used high contrast gratings (HCG) and micro-electromechanical structure (MEMS) technology to build a dynamic phased array capable of fast response times due to the low mass of HCG in comparison to other types of reflectors. Additionally, by avoiding the use of reflective coatings, the proposed HCG phased array is capable of handling high optical power density while maintaining response times in the order of microseconds.
3. Metasurfaces A very promising concept in the field of nanoantenna arrays is that of metasurfaces, where the array is composed by carefully designed anisotropic metallic nanoantennas. Each element is responsible for abrupt polarization and phase changes that add up to perform any number of beam manipulations. This versatile platform has been used to realize vortex beams with orbital angular momentum and nondiffracting beams, as well as to provide beam steering and polarization control in the mid infrared range [8]. Designing such complex structures is not a simple task, and the conventional numerical computational methods become inefficient when analyzing large non-uniform arrays. Aiming at
Vol. 6, No. 2, April 2014
0700706
IEEE Photonics Journal
Breakthroughs in Photonics 2013
increasing this computational efficiency, Dong et al. [9] introduced the Characteristic Basis Function Method, which reduces both time and memory requirements for the simulation of large problems in comparison to conventional methods. The authors show an amazing 100 fold decrease in memory requirement for large metasurfaces composed of nanorods in comparison to the Method of Moments, and similar results are expected for the computational time. Along the lines of optical signal processing, Farmahini-Farahani et al. [10] proposed a method for controlling not only the phase but also the amplitude of beams transmitted through metasurfaces at 5 m. They designed an L-shaped antenna that is able to control the amplitude of the transmitted beam in one polarization. By cascading this layer with one that controls the transmitted phaseVvia concentric loop elementsVthey were able to tune both parameters independently, enabling the design of unique spatial filters. Numerical simulations are presented to demonstrate a spatial differentiator and triangular beam shaper. The freedom of design provided by metasurfaces can be used not only to tailor the transmission profiles of incident beams, but also to modify or, as in the case of Kabiri and co-authors’ work [3], to suppress their reflections. They achieved a minimum of 0.002% reflectance in the mid-infrared range using a nanoantenna array buried in a silicon layer [see Fig. 1(c)]. Their versatile design allows for reflection suppression over a narrow-, wide-, or multifrequency band. The design can be made polarization dependent or independent and wide-angle reflection mitigation can also be attained.
4. Tunable Design Capability An experimental realization related to the nanocircuit paradigm has been presented in [11] by Liu et al., where three-dimensional lumped elements were applied to control the optical response of individual nanoantennas in visible wavelengths. For that, individual gold dimmer nanoantennas were used as a test platform in order to demonstrate series and parallel 3-dimensional nanocircuit elements. By loading the nanoantenna gap with specific arrangements of dielectric, semiconducting, and metallic nanoparticules, the tunability of the nanoantenna impedance, resonance wavelength, and filtering, and scattering characteristics were experimentally confirmed. Dynamic control over nanoantennas properties was demonstrated by Yao et al. [2]. The authors loaded the plasmonic nanoantenna gap with graphene [see Fig. 1(b)], which provides dynamic electrical tuning of the antenna resonance peak over a wavelength range of 650 nm (approximately 10% of the central wavelength). In the same work, a doubly resonant nanoantenna array was used to achieve mid-infrared optical intensity modulation with maximum depth of more than 30% and bandwidth of 600 nm. The presented concept, can be extended to the electrical tuning of optical and optoelectronic devices by combining metallic nanostructures with graphene. The tuning of the resonance frequency in aluminum nanoantenna array assuming different positions on top of, inside, and below a dielectric layer of phase-change materials (PCM) was investigated by Michel et al. [12] in the mid infrared domain. They used either Ge3 Sb2 Te6 or InSb as low-loss PCM to compose the layer and achieved maximum frequency shift of 19.3% by changing the refractive index of those materials. Authors suggested that reversibly and ultrafast response of the resonance tuning can be achieved by means of electrical or optical switching of the PCM. In the visible range, dynamic tuning of silver nanoantennas is shown by Earl et al. [13] by controlling the optical properties of the antenna substrate itself. The substrate is composed of silicon under a thin layer of VO2 , which presents a phase transition around 68 C. By heating the subtrate the resonance peak of the antennas changed by 110 nm (about 13% of the central wavelength), in good agreement with the simulated model.
5. All-Dielectric Design Although not a new concept, dielectric optical antennas received a lot of attention in 2013, inspired by designs derived from their microwave counterparts, in special that of dielectric resonator antennas (DRA). In [14] Coenen et al. numerically and experimentally determined the spectral and spatial characteristics of the eigenmodes of isolated silicon nanocylinders with dimensions raging from 60 nm to 350 nm via angle-resolved cathodoluminescence imaging spectroscopy.
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A nonuniform nano-DRA array [see Fig. 1(d)] was used by Zou et al. [4] to demonstrate optical beam deflection at 633 nm. The near reasonances of the TiO2 nano-DRA on a silver film imposed progressive phase delays onto an incoming beam, resulting in a deflection of 19.9 . Deflection angles up to 27 were also measured by the authors. The use of dielectric antennas instead of plasmonic ones has the potential to reduce the power dissipation to a minimum, while maintaining the nanoantenna array versatility. A nano-DRA was also proposed as an efficient way of coupling free-space light into and out of plasmonic circuits. Malheiros-Silveira et al. [15] designed a nano-DRA fed by a nanostrip plasmonic waveguide operating at 1.55 m with broadband impedance matching and consistent radiation pattern covering the entire S, C, and L telecommunication bands. The design represent a promising result for optical wireless applications in inter- and intrachip communications. Staude et al. [16] demonstrated that the suppression of the backward scattering and the enhancement of the forward one for the particular case of overlapping electric and magnetic resonances can be obtained by varying the nanodisk aspect ratio of high-index all-dielectric nanoparticles. They shown that such technique can produce optical nanoantennas based on silicon nanodisks with strong unidirectional emission once fed from a dipole source. Finally, a current and interesting approach by using dielectric resonator comes from the nanopillars/nanoneedles grown on top of crystalline or polycrystalline platforms. High-quality grown of InP nanoneedles on silicon was demonstrated by Ren et al. [17]. Even a single dielectric pillar can exhibit a reasonable quality factor on the order of a few hundred. Such resonators provide simple and high efficiency optical coupling with external optics and are promising as low-cost sensors, optical filters and multiplexers.
6. Metal Nanoantennas Plasmonic nanoantennas found applications in myriad fields in the past decade, and continues to do so following the advances in design and fabrication. Among design innovations, directionality control and multifrequency structures were proposed using different antenna structures [18]–[21]. The coupling mechanism between waveguides and gold nanowires working as nanoantennas was studied by Arnaud et al. [22]. A theoretical study relating the coupling of dipole radiation into integrated strip waveguide by means of metallic nanoantenna was performed by Peyskens et al. [23]. Authors outlined that device enables efficient coupling of enhanced Raman signals into dielectric waveguides. Waveguide-coupled nanoLED with enhanced spontaneous emission was demonstrated by Eggleston and Wu [24]. They achieved directional emission down the waveguide with 70% of efficiency by adding passive reflector and director elements. A linear effect related to nonreciprocal light emission based on timed Dicke states was predicted by Slepyan and Boag [25]. They have theoretically investigated such characteristic asymmetry from the radiation pattern in nanoantenna arrays. By applying near-field optical microscopy combined with far-field excitation spectroscopy on plasmonic nanoantennas, Alonso-Gonza´lez et al. [26] have experimentally demonstrated the spectral shift between near- and far-field peak intensities in infrared domain. Moreover, authors analyzed via numerical simulations the implications of that shift in surface-enhanced infrared spectroscopy (SEIRS) and suggested that such shift should be considered in order to optimize the molecular spectral absorption contrast in plasmonic (bio)sensing devices. Deterministic multipolar radiation of quantum dots was demonstrated by Curto et al. [27] through selective coupling to multipolar resonances of nanowire antennas of increasing length, with alternating symmetry, and with multipole parity. Those findings can provide opportunities on the development of new concepts of quantum nano-optics components. On the other hand, an interesting high directional nanoantenna design, which has quantum dots tightly embedded in its structure was proposed by Tong et al. [5] [see Fig. 1(e)]. The concept of antenna-in-box platform, in which a gap-nanoantenna (that provides fluorescent signal enhancement) is located inside a nanoaperture (that provides background screening) was proposed by Punj et al. [28]. By using that platform authors got isolated detection volumes of 58 zl
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and 1100-fold fluorescence enhancement. According to the authors, this concept preludes a new class of nanoscale biomolecular studies in enzymatic reactions and nanoscale composition of live cell membranes. In comparison with nonlinear bulk media, cascaded four-wave mixing (FWM) presenting 300-fold enhancement of frequency conversion was theoretically evaluated by Maksymov et al. [29]. They engineered the number and length of plasmonic nanoantennas disposed in a tapered configuration and embedded in nonlinear mediumVindium-tin-oxide (ITO)Vin order to obtain resonances at the frequencies involved in the FWM. Finally, a novel optical antenna design assuming an arch-dipole shape, with a gap spacing of 5 nm, was proposed by Seok et al. [30] and fabricated by current CMOS technology. Authors demonstrated strong surface-enhanced Raman spectroscopy (SERS) signal with an enhancement factor exceeding 108 from an arch-dipole 2D array, which is two order of magnitude stronger than that from an equivalent 2D array composed of standard dipole nanoantennas fabricated by e-beam lithography. This work also points out to new perspectives in mass-producible optical antennas.
7. Conclusion and Future Challenges Great breakthroughs in nanoantennas were established in 2013. From single elements to large arrays the versatility of such devices in manipulating optical fields represented a key aspect in their widespread use in a myriad applications. Continued efforts are necessary, though, to tackle issues still presents in each application, be it the reduction in pitch size of phased arrays for larger angular steering range, the increase in metasurfaces conversion efficiency, or improvements in fabrication techniques for higher precision nanostructures in general, these questions are sure to be present in future research around this exciting and promising field.
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[16] I. Staude, A. E. Miroshnichenko, M. Decker, N. T. Fofang, S. Liu, E. Gonzales, J. Dominguez, T. S. Luk, D. N. Neshev, I. Brener, and Y. Kivshar, BTailoring directional scattering through magnetic and electric resonances in subwavelength silicon nanodisks,[ ACS Nano, vol. 7, no. 9, pp. 7824–7832, 2013. [17] F. Ren, K. W. Ng, K. Li, H. Sun, and C. J. Chang-Hasnain, BHigh-quality InP nanoneedles grown on silicon,[ Appl. Phys. Lett., vol. 102, no. 1, pp. 012115-1–012115-4, Jan. 2013. [18] Z. Xi, Y. Lu, W. Yu, P. Yao, P. Wang, and H. Ming, BTailoring the directivity of both excitation and emission of dipole simultaneously with two-colored plasmonic antenna,[ Opt. Exp., vol. 21, no. 24, pp. 29 365–29 373, Dec. 2013. [19] D. Vercruysse, Y. Sonnefraud, N. Verellen, F. B. Fuchs, G. Di Martino, L. Lagae, V. V. Moshchalkov, S. A. Maier, and P. Van Dorpe, BUnidirectional side scattering of light by a single-element nanoantenna,[ Nano Lett., vol. 13, no. 8, pp. 3843–3849, Aug. 2013. [20] T. D. James, Z. Q. Teo, D. E. Gomez, T. J. Davis, and A. Roberts, BThe plasmonic J-pole antenna,[ Appl. Phys. Lett., vol. 102, no. 3, pp. 033106-1–033106-4, Jan. 2013. ˇ ´ıpova´, M. Rahmani, M. Navarro-Cia, K. Hegnerova´, J. Homola, M. Hong, and S. A. Maier, BUltrasensitive [21] H. Aouani, H. S broadband probing of molecular vibrational modes with multifrequency optical antennas,[ ACS Nano, vol. 7, no. 1, pp. 669–675, Jan. 2013. [22] L. Arnaud, A. Bruyant, M. Renault, Y. Hadjar, R. Salas-Montiel, A. Apuzzo, G. Le´rondel, A. Morand, P. Benech, E. Le Coarer, and S. Blaize, BWaveguide-coupled nanowire as an optical antenna,[ J. Opt. Soc. Amer. A, Opt., Image Sci., Vis., vol. 30, no. 11, pp. 2347–2355, Nov. 2013. [23] F. Peyskens, A. Subramanian, A. Dhakal, N. L. Thomas, and R. Baets, BEnhancement of raman scattering efficiency by a metallic nano-antenna on top of a high index contrast waveguide,[ presented at the Conf. Lasers Electro-Optics, San Jose, CA, USA, 2013, CM2F.5. [24] M. Eggleston and M. C. Wu, BEfficient coupling of optical-antenna based nanoLED to a photonic waveguide,[ in Proc. IEEE IPC, Sep. 2013, pp. 331–332. [25] G. Y. Slepyan and A. Boag, BQuantum nonreciprocity of nanoscale antenna arrays in timed dicke states,[ Phys. Rev. Lett., vol. 111, no. 2, p. 023602, Jul. 2013. [26] P. Alonso-Gonza´lez, P. Albella, F. Neubrech, C. Huck, J. Chen, F. Golmar, F. Casanova, L. E. Hueso, A. Pucci, J. Aizpurua, and R. Hillenbrand, BExperimental verification of the spectral shift between near- and far-field peak intensities of plasmonic infrared nanoantennas,[ Phys. Rev. Lett., vol. 110, no. 20, p. 203 902, May 2013. [27] A. G. Curto, T. H. Taminiau, G. Volpe, M. P. Kreuzer, R. Quidant, and N. F. van Hulst, BMultipolar radiation of quantum emitters with nanowire optical antennas,[ Nature Commun., vol. 4, p. 1750, Apr. 2013. [28] D. Punj, M. Mivelle, S. B. Moparthi, T. S. van Zanten, H. Rigneault, N. F. van Hulst, M. F. Garcı´a-Parajo´, and J. Wenger, BA plasmonic Fantenna-in-box_ platform for enhanced single-molecule analysis at micromolar concentrations,[ Nature Nanotechnol., vol. 8, no. 7, pp. 512–516, Jul. 2013. [29] I. S. Maksymov, A. E. Miroshnichenko, and Y. S. Kivshar, BCascaded four-wave mixing in tapered plasmonic nanoantenna,[ Opt. Lett., vol. 38, no. 1, pp. 79–81, Jan. 2013. [30] T. J. Seok, A. Jamshidi, M. Eggleston, and M. C. Wu, BMass-producible and efficient optical antennas with cmosfabricated nanometer-scale gap,[ Opt. Exp., vol. 21, no. 14, pp. 16 561–16 569, Jul. 2013.
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