Showing papers by "Irfan Bulu published in 2008"

Off-axis directional beaming via photonic crystal surface modes

Abstract: We investigated off-axis directional beaming from a photonic crystal (PC) waveguide. We theoretically and experimentally demonstrated that it is possible to control beaming from a PC waveguide via PC surface modes using a gratinglike layer with different periods on different sides of the waveguide. We observed off-axis directional beaming with full width at half maximum of 10° with a beaming angle of 14° from a PC waveguide. Since the beaming angle only depends on the periods of the gratinglike layer on the output side, this beaming angle can be easily changed by arranging the grating periods asymmetrically.

Off-axis beaming from subwavelength apertures

Abstract: Photonic crystal waveguides and metallic subwavelength apertures are promising tools for light manipulation. It is possible to obtain enhanced directional beams by using these structures via coupling to surface waves. In addition, these apertures can be designed to steer such directional beams by introducing asymmetrical gratings on the output surface. In the present paper, we report directional yet off-axis beaming from subwavelength apertures at microwave frequencies. The full width at half maximum of the beam is 10° while the beaming angle is 15°. Our results show that it is possible to steer the beam by the appropriate modification of the output surface.

Experimental observation of cavity formation in composite metamaterials.

Abstract: In this paper, we investigated one of the promising applications of left-handed metamaterials: composite metamaterial based cavities. Four different cavity structures operating in the microwave regime were constructed, and we observed cavity modes on the transmission spectrum with different quality factors. The effective permittivity and permeability of the CMM structure and cavity structure were calculated by use of a retrieval procedure. Subsequently, in taking full advantage of the effective medium theory, we modeled CMM based cavities as one dimensional Fabry-Perot resonators with a subwavelength cavity at the center. We calculated the transmission from the Fabry-Perot resonator model using the one-dimensional transfer matrix method, which is in good agreement with the measured result. Finally, we investigated the Fabry-Perot resonance phase condition for a CMM based cavity, in which the condition was satisfied at the cavity frequency. Therefore, our results show that it is possible to treat metamaterial based cavities as one-dimensional Fabry-Perot resonators with a subwavelength cavity.

Focusing surface plasmons via changing the incident angle

Abstract: We report a circular metallic aperture with a subwavelength circular slit in the microwave regime, in which we experimentally demonstrate that this aperture can excite and focus surface plasmons. Under normal illumination, there is no focusing of the surface plasmons. However, by changing the incident angle, it is possible to focus surface plasmons. We showed that under a 20° illumination angle surface plasmons focus at 4cm away from the center on the surface of the aperture.

Cavity formation in split ring resonators

Abstract: We report that it is possible to obtain a cavity structure by the deformation of a unit cell of an split ring resonator (SRR) structure. We presented the Q-factor of the cavity resonance as 192 for an SRR-based single cavity. Subsequently, we brought two and three cavities together with an intercavity distance of two metamaterial unit cells and investigated the transmission spectrum of SRRbased interacting 2-cavity and 3-cavity systems. The splitting of eigenmodes due to the interaction between the localized electromagnetic cavity modes was observed. Eventually, in taking full advantage of the effective medium theory, we modeled SRRbased cavities as 1D Fabry–Perot reflectors (FPRs) with a subwavelength cavity at the center. Finally, we observed that at the cavity resonance, the effective group velocity was reduced by a factor of 67 for an SRR-based single cavity compared to the electromagnetic waves propagating in free space. # 2008 Elsevier B.V. All rights reserved.

Observation of coupled-cavity structures in metamaterials

Abstract: In this letter, we investigated the transmission properties of metamaterial based coupled-cavity structures. We first calculated the effective parameters of a split-ring resonator SRR and composite metamaterial CMM structures. Subsequently, we introduced coupled-cavity structures and presented the transmission spectrum of SRR and CMM based coupled-cavity structures. The splitting of eigenmodes was observed due to the interaction between the localized electromagnetic cavity modes. Finally, the dispersion relation and normalized group velocity of the coupled-cavity structures were calculated. The maximum group velocity was found to be 100 times smaller than the speed of light in vacuum. © 2008 American Institute of Physics. DOI: 10.1063/1.2988286 Left-handed materials have recently attracted much attention in the scientific community. This new type of artificial materials can provide simultaneous negative permittivity and permeability over a certain frequency range. Therefore, these materials possess promising physical prop