Browsing by Subject "Subwavelength aperture"

Now showing 1 - 5 of 5

Open Access
Applications of electromagnetic phenomena in periodic structures
(2012) Çakmak, Atilla Özgür
The field of Electromagnetics encompasses several research areas and finds itself applications in all frequency ranges starting from very low frequencies up to optical wavelengths. Periodic structures offer a vast research area in Electromagnetics. Amongst these periodic configurations metamaterials and photonic crystals have been investigated in this study. Metamaterials (MTMs) are artificial materials which are carefully engineered to give outstanding electromagnetic responses, e.g. negative phase velocity, negative refraction. On the other hand, Photonic Crystals (PhCs) offer band stopping and full reflection at certain wavelengths and they are highly favored due their particular properties. PhCs are even commercially available nowadays in optical communication. In the first part of the study, we have been concentrated on the enhanced transmission through subwavelength apertures with the incorporation of the MTMs. Resonators that are inspired from the MTM research field are placed in the vicinity of the subwavelength apertures such that a near-field electromagnetic wave localization at the output side can be observed. The considered subwavelength apertures have poor transmission figures on the order of 1/10,000 (in terms of intensity) on the average throughout the investigated frequency band, which dramatically limits the propagation. We show that once the subwavelength resonators are allowed to interact with such subwavelength pertures, astonishingly high transmission enhancement figures (typically ranging from 30 dB up to 50 dB) can be attained, which in turn results in electromagnetic wave localization in the near-field. On top of these single aperture related studies, we investigated the propagation of the electromagnetic waves in aperture arrays. We explicitly distinguish the working mechanisms of the presently studied aperture arrays which also cause a transmission enhancement below the cutoff frequency of the regarding apertures. The transmission enhancement has been shown to be accompanied by the left handed propagation, which is a characteristic of the MTMs. We show that both right and left handed transmission channels can be opened simultaneously in these periodically stacked aperture arrays. Alternatively, we have worked on the graded-index PhCs (GRIN PhCs) in order to tailor the course of the propagating electromagnetic waves. It has been demonstrated that modified Gauss-Hermite modes are available in GRIN PhCs similar to the those in conventional homogenous GRIN structures that are already in use in the field of optics. The underlying physics of the propagation has been discussed and a focusing lens has been proposed, which is based on the GRIN PhCs. The proposed lens has been shown to provide improved input and output coupling figures for the waveguide configurations. The input coupling efficiency has been boosted by a factor of 8 dB, while the GRIN PhC at the output side of the waveguide achieved a collimated beam with 7 degrees of half power beam width according to the results of the far-field measurements. Lastly, PhC based gratings have been utilized to search for an optical diode. It has been shown that such a PhC grating can offer an extremely good contrast (on the order of 1000) between the intensities of the electromagnetic waves that are approaching from different sides of the proposed design. The working mechanism of the optical diode has been shown to rely on the gratings that opened higher order diffraction channels as the zeroth order diffractions are suppressed.
Open Access
Enhanced confined microwave transmission by single subwavelength apertures
(2005) Çağlayan, Hümeyra
Grating-coupling phenomena between surface plasmons and electromagnetic waves are studied in the microwave spectrum using metallic circular apertures surrounded by an array of grooves. The measurements are performed in the microwave spectrum of 10-18 GHz, corresponding to a wavelength region of 16.7-30 mm. The metallic samples have a subwavelength hole with a diameter of 8 mm and have concentric grooves with a periodicity of 16 mm. We first present the experimental and theoretical results of enhanced microwave transmission though a subwavelength circular aperture with concentric periodic grooves around the surface plasmon resonance frequency. This is followed by transmission studies through circular annular apertures with and without concentric periodic grooves around the aperture. We demonstrate a 145-fold enhancement factor could be obtained with a subwavelength circular annular aperture surrounded by concentric periodic grooves. Moreover, we study the diffraction of electromagnetic waves from subwavelength metallic circular annular apertures in the microwave spectrum. The theoretical and experimental demonstration of the near- and far-field EM distributions for subwavelength circular apertures and circular annular apertures surrounded by concentric periodic grooves is reported. We present the angular transmission distributions from circular apertures and circular annular apertures surrounded by concentric periodic grooves. At the surface mode resonance frequency the transmitted electromagnetic waves from the subwavelength circular annular aperture surrounded by concentric periodic grooves have a strong angular confinement with an angular divergence of ±3°. This represents a fourfold reduction when compared to the angular divergence of the beam transmitted from a subwavelength aperture. These results show, that not only high transmission but also a confined beam is achieved at the surface plasmon resonance frequency using a circular annular aperture with grooves .
Open Access
One-way reciprocal spoof surface plasmons and relevant reversible diodelike beaming
(American Physical Society, 2013-05-15) Mutlu, M.; Cakmakyapan, S.; Serebryannikov, A. E.; Özbay, Ekmel
One - way excitation of spoof surface plasmons (SPs) and strongly pronounced diodelike extraordinary transmission of linearly polarized waves in the beaming regime can be obtained by combining spoof SPs and cross-polarization conversion resonances. The reciprocal composite structure that is suggested to realize this mechanism consists of a symmetric metallic grating with a subwavelength slit and a metamaterial based ultrathin 90 degrees polarization rotator and, therefore, shows the broken spatial inversion symmetry. In contrast to the earlier studies of SP inspired transmission through subwavelength slits, asymmetric (one-way) beaming is demonstrated at normal incidence and for both s- and p-polarized incident waves. Furthermore, as an implication of Lorentz reciprocity, the studied diodelike mechanism is reversible, which manifests itself in that transmission is significant for one of the two opposite illumination directions at s polarization and for the other direction at p polarization. The obtained numerical and experimental results verify the general idea and enable us to select the optimal operation regimes.
Open Access
Plasmonic structures with extraordinary transmission and highly directional beaming properties
(Wiley Periodicals, 2006) Cağlayan, H.; Bulu, I.; Özbay, Ekmel
We studied the grating-coupling phenomena between surface plasmons and electromagnetic waves in the microwave spectrum. We first present the experimental and theoretical results of an enhanced microwave transmission though a subwavelength circular annular aperture with and without metallic gratings. We demonstrate that a 145-fold enhancement factor could be obtained with a subwavelength circular annular aperture that was surrounded by periodic metallic gratings. This was assisted by the guided mode of the coaxial waveguide and by coupling to the surface plasmons. We present the angular transmission distributions from circular annular apertures, and circular annular apertures surrounded by concentric periodic grooves. At the surface mode resonance frequency, the transmitted electromagnetic waves from the subwavelength circular annular aperture surrounded by concentric periodic grooves have a strong angular confinement with an angular divergence of ±3°. We demonstrate that only the output surface is responsible for the beaming effect. Furthermore, we present the field distributions and showed that there is no beaming effect at the off-resonance frequency. © 2006 Wiley Periodicals, Inc.
Open Access
Resonant excitation of surface plasmons in one-dimensional metallic grating structures at microwave frequencies
(Institute of Physics Publishing, 2005) Akarca-Biyikli, S. S.; Bulu, I.; Özbay, Ekmel
Grating-coupling phenomena between surface plasmons and electromagnetic waves were studied in the microwave spectrum using metallic gratings. Transmission measurements were carried out to observe the transmitted radiation around the surface plasmon resonance frequencies. Grating structures with subwavelength apertures were designed for transmission experiments. Measurements were made in the microwave spectrum of 10-37.5 GHz, corresponding to a wavelength region of 8-30 mm. The A1 samples had a grating periodicity of 16 mm. A 2 mm wide subwavelength slit was opened for transmission samples. Samples with one/double-sided gratings displayed remarkably enhanced transmission and directivity with respect to the reference sample without gratings. The experimental results agreed well with theoretical simulations. ∼50% transmission at 20.7 mm, ∼25-fold enhancement, and ±4° angular divergence were achieved with a ∼λ/10 aperture.