METAMATERIALS

PLASMONIC STRUCTURES WITH HIGHLY DIRECTIONAL BEAMING PROPERTIES

  The transmission of electromagnetic (EM) waves through a single subwavelength aperture has been studied for many years. As defined in the standard   diffraction theory by Bethe [1] in 1944, a circular aperture with a subwavelength diameter transmits EM waves rather poorly and exiting EM waves are   fully diffracted in all directions. These two disadvantages of low transmission and diffraction are the main problems of manipulating light, especially at the   subwavelength scales. However, it has been shown that the confinement of the transmitted beam is possible by surrounding the metal surface of the   subwavelength apertures with periodic corrugations. This effect is attributed to the coupling of incident light to surface plasmons (SPs) [2].

Fig.1 EM waves are fully diffracted.

  SPs are the collective excitation of electrons at the surface of a conductor in the longitu- dinal direction. As SP modes have longer wave vectors than   light waves of the same energy, electromagnetic radiation does not interact with the SP modes of a smooth metal surface [3]. When the metal surface   surrounding the subwavelength hole is corrugated, the incident light can couple to SPs. A resonant interaction leads to an enhanced transmission at   wavelengths determined by the corrugation period [4, 5].

   In our work, we used metallic (aluminum) structures with a subwavelength hole in the center with a diameter of (a) 8 mm. The gratingless sample with _a   thickness of (t) 8 mm was used as a reference sample. We dressed this structure with grooves in order to invoke SPs. We also combined the annular   aperture and grooved structure in order to obtain higher transmission. The combination of the annular aperture and grooved structure showed   extraordinary high transmission at 12.9 GHz (23.25 mm) via the coupling to the surface waves and the guided mode of annular aperture. Including the   reduction in the area of the aperture, a 450-fold enhancement was achieved through the subwavelength annular aperture.

Fig.2 Schematics of the annular aperture with circular grooves and transmission spectrum of the reference and annular aperture with circular grooves.

Fig.3 Electric field distribution on the surface of the grooved structure at resonance frequency (12.9 GHz). Red indicates the maximum and blue indicates the minimum.

The light emerging from the groove structure is emitted through a subwavelength aperture. It is expected that the emitted EM waves would quickly diffract in all directions due to the subwavelength dimensions of the   aperture [1]. On the contrary; we observed that the emitted EM waves are confined to a narrow spatial region when the subwavelength aperture was   surrounded by periodic circular grooves. The surface wave momentum and the momentum of the corrugation around the subwavelength aperture limit the   allowed range of momentum of the re-radiated EM waves. The circular symmetry of the structure suggests that the off-axis beams are suppressed due to   the destructive interference. In addition, the beams normal to the surface of the aperture constructively interfere since the beams emitted from the hole   and grooves are in phase.

  Angular divergence of the transmitted beam from reference sample is 12 degrees, whereas the transmitted beam that emerges from grooved sample is 3   degrees. The angular divergence of the beam reduced four times compared to the transmitted beam from reference sample.

Fig.4 Normalized angular transmission distribution for reference sample (left) and grooved sample (right) at resonance frequency (13 GHz).

  The electric field distribution of the transmitted beam calculated and measured for the grooved sample shows clearly the beaming effect. The electric     f ield intensity transmitted through the grooved sample is confined to a narrow spatial region and propagates without diffracting into a wide angular region   at the resonance frequency.

Fig.5 Calculated(top) and measured(bottom) electric field distribution from Sample 4 at the resonance frequency. Red indicates the maximum and blue indicates the minimum.

     References

  1. H. A. Bethe, “Theory of Diffraction by Small Holes,” Phys. Rev. 66, 163182 (1944).

  2. H. J. Lezec, A. Degiron, E. Devaux, R. A. Linke, L. Martin-Moreno, F. J. Garcia-Vidal and T. W. Ebbesen, “Beaming Light from a Subwavelength   Aperture,” Science 297,      820-22 (2002).

   3.H. Raether, Surface Plasmons on Smooth and Rough Surfaces and on Gratings (Springer-Verlag, Berlin 1988).

  4. Y. Teng, E. A. Stern, “Plasma Radiation from Metal Grating Surfaces,” Phys. Rev. Lett. 19, 511-514 (1967).

  5. T. Thio, H.J. Lezec, T.W. Ebessen, K. M. Pellerin, G. D. Lewen, A. Nahata, and R.A. Linke, “Giant optical transmission of sub-wavelength   apertures: physics and       applications,” Nanotechnology 13, 429-432 (2002).

     Related Publications

  1. Humeyra Caglayan, Irfan Bulu, and Ekmel Ozbay, “Extraordinary grating-coupled microwave transmission through a subwavelength annular aperture,    Optics Express 13,      1666 (2005).

  2. Humeyra Caglayan, Irfan Bulu, and Ekmel Ozbay, “Beaming of electromagnetic waves emitted through a subwavelength annular aperture” Journal of   Optical Society of      America B. 22, xxxx (2005).

  Negative refraction and subwavelength focusing using photonic crystals

  Metallodielectric photonic crystals with negative refraction and focusing

  Highly directional radiation using sources embedded in photonic crystals

  Coupling and phase analysis of cavity structures in photonic structures

  Enhanced transmission and beaming via photonic crystal surface modes

  Plasmonic Structures With Highly Directional Beaming Properties

Metamaterials   -   Photonic Crystals  -  GaN/AlGaN Devices  -  Other Semiconductor Devices and Fabrication Techniques

© Copyright - com.web.tr. This page is best viewed with IE v.5.0 or higher, at minimum 1024x768 resolution.