Nanofocusing of electromagnetic radiation

Journal name:
Nature Photonics
Volume:
8,
Pages:
13–22
Year published:
DOI:
doi:10.1038/nphoton.2013.232
Received
Accepted
Published online

Abstract

Nanofocusing of electromagnetic radiation, that is, reducing the cross sections of propagating optical modes far beyond the diffraction limit in dielectric media, can be achieved in tapered metal–dielectric waveguides that support surface plasmon–polariton modes. Although the main principles of nanofocusing were formulated over a decade ago, a deep theoretical understanding and conclusive experimental verification were achieved only a few years ago. These advances have spawned a variety of new important technological possibilities for the efficient delivery, control and manipulation of optical radiation on the nanoscale. Here, we present the underlying physical principles of radiation nanofocusing in metallic nanostructures, overview recent progress and major developments, and consider future directions and potential applications of this subfield of nano-optics.

At a glance

Figures

  1. Insulator-metal-insulator and metal-insulator-insulator nanofocusing configurations.
    Figure 1: Insulator–metal–insulator and metal–insulator–insulator nanofocusing configurations.

    Insulator–metal–insulator (IMI) structures: a, conical tapered metal rod with a rounded tip16, 17, 19, 20; b, metal wedge surrounded by dielectric media15, 28, 29, 30; c, tapered metal strip with varying width and constant thickness31, 32; d, cylindrical crescent with an electromagnetic singularity41; e, optical fibre with hemispherical termination coated with a tapered metal film whose smallest thickness is at the top of the hemisphere33. Metal–insulator–insulator (MII) structure: f, tapered high-permittivity dielectric wedge on a metal substrate with SPP focusing in the opposite direction to the taper39, 40. Figure d reproduced with permission from ref. 41, © 2010 ACS.

  2. Metal-insulator-metal and hybrid nanofocusing configurations.
    Figure 2: Metal–insulator–metal and hybrid nanofocusing configurations.

    Metal–insulator–metal (MIM) structures: a, one-dimensionally tapered gap between two metal media15, 18, 21, 22, 23, 24, 27; b, two-dimensionally tapered gap between two metal films26; c, tapered V-shaped groove with gradually reducing taper angle and depth34; d, two 'kissing' cylinders or touching spherical particles with an electromagnetic singularity at the contact point (which is also the focal point of the structure)41, 42, 43. Hybrid IMI/MIM structure: e, tapered chain of coupled nanoparticles (combines the features of nanoantennas and nanofocusing structures with IMI and MIM configurations)47. Figure reproduced with permission from: b, ref. 26, © 2012 NPG; c, ref. 1, © 2010 NPG; d, ref. 39, © 2010 ACS.

  3. Typical field distributions in nanofocusing structures.
    Figure 3: Typical field distributions in nanofocusing structures.

    a, A typical distribution of |E|2 along a tapered section of a metal film31, 32 or a tapered metal ridge55. The top inset shows a typical cross-sectional distribution of the field near the tip of a metal film on a dielectric substrate31, 32. The bottom inset shows an expanded view of the area near the structural tip. b, Distribution of the z-component of the electric field near the tip of a glass sphere of 500-nm radius coated with a tapered gold film of minimum thickness of 5 nm at the tip at λvac = 632.8 nm (the z-axis corresponds to the axis of the structure)33. c, Distribution of |E| in a tapered cylindrical gold rod in air with γ = 30°, tip radius R = 5 nm and λvac = 632.8 nm (ref. 11). d, Field distribution in a tapered air gap in gold with the incident bulk radiation coupled to the gap SPP72. e, Distribution of the electric field intensity in a nanofocusing silicon wedge with γ = 1.43° between a silver surface and air for λvac = 577 nm (ref. 39). Figure reproduced with permission from: a, ref. 31, © 2008 OSA; b, ref. 33, © 2012 OSA; d, ref. 72, © 2010 ACS; e, ref. 39, © 2010 ACS.

  4. Plasmon nanofocusing configurations with tapered nanowires.
    Figure 4: Plasmon nanofocusing configurations with tapered nanowires.

    a, Scanning electron microscope (SEM) image of an electrochemically etched gold tip with a grating coupler. Superimposed on this SEM image is an optical image of grating excitation of SPPs, which shows their subsequent propagation, nanofocusing and re-radiation at the tip apex for a wavelength of ~800 nm (ref. 63). b, A tapered section of a gold film on a sapphire substrate; the fundamental mode in the strip is nanofocused near the taper tip31. c,d, Experimental realization of nanofocusing in gold-film tapers similar to that shown in b and connected by a 2-m-long nanowire32, showing an SEM image of the connected taper structure (c) and a near-field amplitude of forward-propagating waves at a wavelength of 1,550 nm (d). e,f, Near-field Raman imaging with a tapered nanowire61. An SEM image (e) of a photonic-crystal cavity fabricated on a silicon nitride membrane with a tapered silver nanowire having a conical shape and a radius of curvature at the apex of 5 nm. A Raman intensity map (f) (in kilocounts per second, kcps) with a scanning step size of 7 nm across a submicrometre silicon nanocrystal/SiOx trench. Variations of the Raman signal along the dashed red line in f indicate the spatial resolution of ~7 nm. Figure reproduced with permission from: a, ref. 63 © 2010 ACS; b, ref. 1 © 2010 NPG; c,d, ref. 32 © 2009 APS; e,f, ref. 61 © 2010 NPG.

  5. Plasmonic nanofocusing configurations with tapered gaps.
    Figure 5: Plasmonic nanofocusing configurations with tapered gaps.

    a, A gold V-shaped groove structure supported by a silicon wafer for nanofocusing at 1.5 μm (ref. 71). b, A cross section of a 350-nm-period array of ultrasharp, 450-nm-deep convex grooves milled in gold (scale bar, 300 nm) that absorbs on average >90% of light polarized perpendicular to the groove direction in the range 450–800 nm (ref. 52). The inset shows the 2D groove array discussed in the text. c,d, Experimental realization of 3D nanofocusing with the two-dimensionally tapered-gap nanofocusing configuration26 shown in Fig. 2b, showing a tapered silica-filled gap sandwiched between two 50-nm-thick gold layers (c), and a map of the two-photon-induced photoluminescence signal obtained by illuminating the back aperture of the structure using a focused laser beam (wavelength, 830 nm) polarized perpendicular to the propagation direction in the tapered gap waveguide (d). Figure reproduced with permission from: a, ref. 1 © 2010 NPG; b, ref. 52 © 2012 NPG; c,d ref. 26 © NPG.

References

  1. Gramotnev, D. K. & Bozhevolnyi, S. I. Plasmonics beyond the diffraction limit. Nature Photon. 4, 8391 (2010).
  2. Schuller, J. A. et al. Plasmonics for extreme light concentration and manipulation. Nature Mater. 9, 193204 (2010).
  3. Han, Z. & Bozhevolnyi, S. I. Radiation guiding with surface plasmon polaritons. Rep. Prog. Phys. 76, 016402 (2013).
  4. Sorger, V. J., Oulton, R. F., Ma, R.-M. & Zhang, X. Toward integrated plasmonic circuits. MRS Bulletin 37, 728738 (2012).
  5. Feng, J. et al. Nanoscale plasmonic interferometers for multispectral, high-throughput biochemical sensing. Nano Lett. 12, 602609 (2012).
  6. Dmitriev, A. (ed.) Nanoplasmonic Sensors (Springer, 2012).
  7. Chung, T., Lee, S.-Y., Song, E. Y., Chun, H. & Lee, B. Plasmonic nanostructures for nano-scale bio-sensing. Sensors 11, 1090710929 (2011).
  8. Juan, M. L., Righini, M. & Quidant, R. Plasmon nano-optical tweezers. Nature Photon. 5, 349356 (2011).
  9. Roxworthy, B. J. & Toussaint, K. C. Jr. Femtosecond-pulsed plasmonic nanotweezers. Sci. Rep. 2, 660 (2012).
  10. Novotny, L., Bian, R. X. & Xie, X. S. Theory of nanometric optical tweezers. Phys. Rev. Lett. 79, 645648 (1997).
  11. Gramotnev, D. K. & Vogel, M. W. Ultimate capabilities of sharp metal tips for plasmon nanofocusing, near-field trapping and sensing. Phys. Lett. A 375, 34643468 (2011).
  12. Novotny, L. & van Hulst, N. Antennas for light. Nature Photon. 5, 8390 (2011).
  13. Zayats, A. V., Smolyaninov, I. I. & Maradudin, A. A. Nano-optics of surface plasmon polaritons. Phys. Rep. 408, 131314 (2005).
  14. Verma, P., Ichimura, T., Yano, T., Saito, Y. & Kawata, S. Nano-imaging through tip-enhanced Raman spectroscopy: stepping beyond the classical limits. Las. Photon. Rev. 4, 548561 (2010).
  15. Nerkararyan, K. V. Superfocusing of a surface polariton in a wedge-like structure. Phys. Lett. A 237, 103105 (1997).
  16. Babadjanyan, A. J., Margaryan, N. L. & Nerkararyan, K. V. Superfocusing of surface polaritons in the conical structure. J. Appl. Phys. 87, 37853788 (2000).
  17. Stockman, M. I. Nanofocusing of optical energy in tapered plasmonic waveguides. Phys. Rev. Lett. 93, 137404 (2004).
  18. Gramotnev, D. K. Adiabatic nanofocusing of plasmons by sharp metallic grooves: geometrical optics approach. J. Appl. Phys. 98, 104302 (2005).
  19. Issa, N. A. & Guckenberger, R. Optical nanofocusing on tapered metallic waveguides. Plasmonics 2, 3137 (2007).
  20. Gramotnev, D. K., Vogel, M. W. & Stockman, M. I. Optimized nonadiabatic nanofocusing of plasmons by tapered metal rods. J. Appl. Phys. 104, 034311 (2008).
  21. Pile, D. F. P. & Gramotnev, D. K. Adiabatic and nonadiabatic nanofocusing of plasmons by tapered gap plasmon waveguides. Appl. Phys. Lett. 89, 041111 (2006).
  22. Ginzburg, P., Arbel, D. & Orenstein, M. Gap plasmon polariton structure for very efficient microscale-to-nanoscale interfacing. Opt. Lett. 31, 32883290 (2006).
  23. Conway, J. Efficient optical coupling to the nanoscale. 32102 PhD thesis, Univ. California (2006).
  24. Gramotnev, D. K., Pile, D. F. P., Vogel, M. W. & Zhang, X. Local electric field enhancement during nanofocusing of plasmons by a tapered gap. Phys. Rev. B 75, 035431 (2007).
  25. Vedantam, S. et al. A plasmonic dimple lens for nanoscale focusing of light. Nano Lett. 9, 34473452 (2009).
  26. Choo, H. et al. Nanofocusing in a metal–insulator–metal gap plasmon waveguide with a three-dimensional linear taper. Nature Photon. 6, 838844 (2012).
  27. Desiatov, B., Goykhman, I. & Levy, U. Plasmonic nanofocusing of light in an integrated silicon photonics platform. Opt. Express 14, 1315013157 (2011).
  28. Gramotnev, D. K. & Vernon, K. C. Adiabatic nano-focusing of plasmons by sharp metallic wedges. Appl. Phys. B 86, 717 (2007).
  29. Durach, M., Rusina, A., Stockman, M. I. & Nelson, K. Toward full spatiotemporal control on the nanoscale. Nano Lett. 7, 31453149 (2007).
  30. Vernon, K. C., Gramotnev, D. K. & Pile, D. F. P. Adiabatic nanofocusing of plasmons by a sharp metal wedge on a dielectric substrate. J. Appl. Phys. 101, 104312 (2007).
  31. Verhagen, E., Polman, A. & Kuipers, L. K. Nanofocusing in laterally tapered plasmonic waveguides. Opt. Express 16, 4557 (2008).
  32. Verhagen, E., Spasenović, M., Polman, A. & Kuipers, L. K. Nanowire plasmon excitation by adiabatic mode transformation. Phys. Rev. Lett. 102, 203904 (2009).
  33. Mason, D. R., Gramotnev, D. K. & Kim, K. S. Plasmon nanofocusing in a dielectric hemisphere covered in tapered metal film, Opt. Express 20, 1286612876 (2012).
  34. Volkov, V. S. et al. Nanofocusing with channel plasmon polaritons. Nano Lett. 9, 12781262 (2009).
  35. Liu, Z., Steele, J. M., Lee, H. & Zhang, X. Tuning the focus of a plasmonic lens by the incident angle. Appl. Phys. Lett. 88, 171108 (2006).
  36. Lerman, G. M., Yanai, A. & Levy, U. Demonstration of nanofocusing by the use of plasmonic lens illuminated with radially polarized light. Nano Lett. 9, 21392143 (2009).
  37. Davoyan, A. R., Shadrivov, I. V., Kivshar, Y. S. & Gramotnev, D. K. Optimal tapers for compensating losses in plasmonic waveguides. Physica Status Solidi RRL 4, 277279 (2010).
  38. Khurgin, J. B. & Sun, G. Practicality of compensating the loss in the plasmonic waveguides using semiconductor gain medium. Appl. Phys. Lett. 100, 011105 (2012).
  39. Verhagen, E., Kuipers, L. K. & Polman, A. Plasmonic nanofocusing in a dielectric wedge. Nano Lett. 10, 36653669 (2010).
  40. Gramotnev, D. K., Tan, S. J. & Kurth, M. L. Plasmon nanofocusing with negative refraction in a high-refractive index dielectric wedge. http://dx.doi.org/10.1007/s11468-013-9610-2 Plasmonics (2013).
  41. Aubry, A. et al. Plasmonic light-harvesting devices over the whole visible spectrum. Nano Lett. 10, 25742579 (2010).
  42. Fernández-Domínguez, A. I., Maier, S. A. & Pendry, J. B. Collection and concentration of light by touching spheres: a transformation optics approach. Phys. Rev. Lett. 105, 266807 (2010).
  43. Nerkararyan, K. V., Nerkararyan, S. K. & Bozhevolnyi, S. I. Plasmonic black-hole: broadband omnidirectional absorber of gap surface plasmons. Opt. Lett. 36, 43114313 (2011).
  44. Nordlander, P., Oubre, C., Prodan, E., Li, K. & Stockman, M. I. Plasmon hybridization in nanoparticle dimers. Nano Lett. 4, 899903 (2004).
  45. Fernández-Domínguez, A. I., Wiener, A., García-Vidal, F. J., Maier, S. A. & Pendry, J. B. Transformation-optics description of nonlocal effects in plasmonic nanostructures. Phys. Rev. Lett. 108, 106802 (2012).
  46. Wang, F. & Shen, Y. R. General properties of local plasmons in metal nanostructures. Phys. Rev. Lett. 97, 206806 (2006).
  47. Li, K., Stockman, M. I. & Bergman, D. J. Self-similar chain of metal nanospheres as an efficient nanolens. Phys. Rev. Lett. 91, 227402 (2003).
  48. Vogel, M. W. & Gramotnev, D. K. Optimization of plasmon nano-focusing in tapered metal rods. J. Nanophoton. 2, 021852 (2008).
  49. Kurihara, K. et al. Superfocusing modes of surface plasmon polaritons in conical geometry based on the quasi-separation of variables approach. J. Phys. A 40, 12479 (2007).
  50. Kurihara, K., Yamamoto, K., Takahara, J. & Otomo, A. Superfocusing modes of surface plasmon polaritons in a wedge-shaped geometry obtained by quasi-separation of variables. J. Phys. A 41, 295401 (2008).
  51. Vogel, M. W. & Gramotnev, D. K. Shape effects in tapered metal rods during adiabatic nanofocusing of plasmons. J. Appl. Phys. 107, 044303 (2010).
  52. Søndergaard, T. et al. Plasmonic black gold by adiabatic nanofocusing and absorption of light in ultra-sharp convex grooves. Nature Commun. 3, 969 (2012).
  53. Søndergaard, T. & Bozhevolnyi, S. I. Theoretical analysis of plasmonic black gold: periodic arrays of ultra-sharp grooves. New J. Phys. 15, 013034 (2013).
  54. Rui, G. et al. Plasmonic near-field probe using the combination of concentric rings and conical tip under radial polarization illumination. J. Opt. 12, 035004 (2010).
  55. Ongarello, T. et al. Focusing dynamics on circular distributed tapered metallic waveguides by means of plasmonic vortex lenses. Opt. Lett. 37, 45164518 (2012).
  56. He, X., Yang, L. & Yang, T. Optical nanofocusing by tapering coupled photonic-plasmonic waveguides. Opt. Express 19, 1286512872 (2011).
  57. Ropers, C. et al. Grating-coupling of surface plasmons onto metallic tips: a nanoconfined light source. Nano Lett. 7, 27842788 (2007).
  58. Tan, S. J. & Gramotnev, D. K. Analysis of efficiency and optimization of plasmon energy coupling into nanofocusing metal wedges. J. Appl. Phys. 107, 094301 (2010).
  59. Neacsu, C. C. et al. Near-field localization in plasmonic superfocusing: a nanoemitter on a tip. Nano Lett. 10, 592596 (2010).
  60. De Angelis, F. et al. A hybrid plasmonic–photonic nanodevice for label-free detection of a few molecules. Nano Lett. 8, 23212327 (2008).
  61. De Angelis, F. et al. Nanoscale chemical mapping using three-dimensional adiabatic compression of surface plasmon polaritons. Nature Nanotech. 5, 6772 (2010).
  62. Lindquist, N. C., Nagpal, P., Lesuffleur, A., Norris, D. J. & Oh, S.-H. Three-dimensional plasmonic nanofocusing. Nano Lett. 10, 13691373 (2010).
  63. Berweger, S., Atkin, J. M., Olmon, R. L. & Raschke, M. B. Adiabatic tip-plasmon focusing for nano-Raman spectroscopy. J. Phys. Chem. Lett. 1, 34273432 (2010).
  64. Sadiq, D. et al. Adiabatic nanofocusing scattering-type optical nanoscopy of individual gold nanoparticles. Nano Lett. 11, 16091613 (2011).
  65. Hillenbrand, R. & Keilmann, F. Complex optical constants on a subwavelength scale. Phys. Rev. Lett. 85, 30293032 (2000).
  66. De Angelis, F. et al. Breaking the diffusion limit with super-hydrophobic delivery of molecules to plasmonic nanofocusing SERS structures. Nature Photon. 5, 682687 (2011).
  67. Berweger, S., Atkin, J. M., Xu, X. G., Olmon, R. L. & Raschke, M. B. Femtosecond nanofocusing with full optical waveform control. Nano Lett. 11, 43094313 (2011).
  68. Berweger, S., Atkin, J. M., Olmon, R. L. & Raschke, M. B. Light on the tip of a needle: plasmonic nanofocusing for spectroscopy on the nanoscale. J. Phys. Chem. Lett. 3, 945952 (2012).
  69. Schmidt, S. et al. Adiabatic nanofocusing on ultrasmooth single-crystalline gold tapers creates a 10-nm-sized light source with few-cycle time resolution. ACS Nano 6, 60406048 (2012).
  70. Kravtsov, V., Atkin, J. M. & Raschke, M. B. Group delay and dispersion in adiabatic plasmonic nanofocusing. Opt. Lett. 38, 13221324 (2013).
  71. Choi, H., Pile, D. F. P., Nam, S., Bartal, G. & Zhang, X. Compressing surface plasmons for nano-scale optical focusing. Opt. Express 17, 75197524 (2009).
  72. Søndergaard, T. et al. Resonant plasmon nanofocusing by closed tapered gaps. Nano Lett. 10, 291295 (2010).
  73. Søndergaard, T. et al. Extraordinary optical transmission enhanced by nanofocusing. Nano Lett. 10, 31233128 (2010).
  74. Beermann, J. et al. Localized field enhancements in two-dimensional V-groove metal arrays. J. Opt. Soc. Am. B 28, 372378 (2011).
  75. Beermann, J. et al. Field enhancement and extraordinary optical transmission by tapered periodic slits in gold films. New J. Phys. 13, 063029 (2011).
  76. Søndergaard, T. & Bozhevolnyi, S. I. Surface-plasmon polariton resonances in triangular-groove metal gratings. Phys. Rev. B 80, 195407 (2009).
  77. Genet, C. & Ebbesen, T. W. Light in tiny holes. Nature 445, 3946 (2007).
  78. Schnell, M. et al. Nanofocusing of mid-infrared energy with tapered transmission lines. Nature Photon. 5, 283287 (2011).
  79. Volkov, V. S. et al. Plasmonic candle: towards efficient nanofocusing with channel plasmon polaritons. New J. Phys. 11, 113043 (2009).
  80. Liu, L., Han, Z. & He, S. Novel surface plasmon waveguide for high integration. Opt. Express 13, 66456650 (2005).
  81. Veronis, G. & Fan, S. Guided subwavelength plasmonic mode support by a slot in a thin metal film. Opt. Lett. 30, 33593361 (2005).
  82. Pile, D. F. P. et al. Two-dimensionally localized modes of a nanoscale gap plasmon waveguide. Appl. Phys. Lett. 87, 261114 (2005).
  83. Pile, D. F. P., Gramotnev, D. K., Oulton, R. F. & Zhang, X. On long-range plasmonic modes in metallic gaps. Opt. Express 15, 1366913674 (2007).
  84. Park, I.-Y. et al. Plasmonic generation of ultrashort extreme-ultraviolet light pulses. Nature Photon. 5, 677681 (2011).
  85. Tan, S. J. & Gramotnev, D. K. Heating effects in nanofocusing metal wedges. J. Appl. Phys. 110, 034310 (2011).
  86. Kauranen, M. & Zayats, A. V. Nonlinear plasmonics. Nature Photon. 6, 737748 (2012).
  87. Verhagen, E., Kuipers, L. & Polman, A. Enhanced nonlinear optical effects with a tapered plasmonic waveguide. Nano Lett. 7, 334337 (2007).
  88. Davoyan, A. R., Shadrivov, I. V., Zharov, A. A., Gramotnev, D. K. & Kivshar, Y. S. Nonlinear nanofocusing in tapered plasmonic waveguides. Phys. Rev. Lett. 105, 116804 (2010).
  89. MacDonald, K. F., Sámson, Z. L., Stockman, M. I. & Zheludev, N. I. Ultrafast active plasmonics. Nature Photon. 3, 5558 (2009).
  90. Akimov, A. V. et al. Generation of single optical plasmons in metallic nanowires coupled to quantum dots. Nature 450, 402406 (2007).
  91. Scholl, J. A., Koh, A. L. & Dionne, J. A. Quantum plasmon resonances of individual metallic nanoparticles. Nature 483, 421427 (2012).

Download references

Author information

Affiliations

  1. Nanophotonics Pty. Ltd., GPO Box 786, Albany Creek, Queensland 4035, Australia

    • Dmitri K. Gramotnev
  2. Institute of Technology and Innovation, University of Southern Denmark, Niels Bohrs Allé 1, DK-5230 Odense M, Denmark

    • Sergey I. Bozhevolnyi

Competing financial interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to:

Author details

Additional data