Browsing by Subject "Superlens"
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Item Open Access Characterization and applications of negative-index metamaterials(2008) Aydın, KorayMetamaterials offer novel electromagnetic properties and promising applications including negative refraction, flat-lenses, superlenses, cloaking devices. In this thesis, we characterized the negative-index metamaterials that is composed of periodic arrangements of split-ring resonators (providing negative permeability) and thin wire (providing negative permittivity) arrays. The resonances of split-ring resonators (SRR) are investigated experimentally and theoretically. By combining SRR and wire arrays together, we observed a transmission band where both permittivity and permeability are simultaneously negative, indicating a left-handed behavior. Reflection measurements reveal that the impedance is matched to the free space at a certain frequency range. The lefthanded metamaterial is also shown to exhibit negative refractive index by using three different experimental methods namely, refraction from a wedge-shaped negative-index metamaterial (NIM), beam-shift from a slab-shaped NIM and phase shift from NIMs with different lengths. Flat-lens behavior is observed from a slabshaped negative-index metamaterial based microwave lenses. Furthermore, we demonstrated subwavelength imaging and subwavelength resolution by using thin superlenses constructed from SRR-wire arrays with an effective negative index. We have been able to image a point source with a record-level, λ/8 resolution. SRRand wire arrays exhibit negative index provided that the wave propagates parallel to the plane of SRR structure which makes it hard to fabricate at higher frequencies. An alternative structure called fishnet metamaterial however could yield negative index with wave propagation normal to the structure. We observed left-handed transmission and negative phase velocity in fishnet type metamaterials. Finally, we studied enhanced transmission from a single subwavelength aperture by coupling incident electromagnetic wave to a single SRR placed at the near-field of the aperture.Item Open Access Experimental study of subwavelength focusing by lefthanded metamaterials with a negative refractive index(2007) Özbay, Ekmel; Aydin, K.Two dimensional (2D) left-handed metamaterials (LHM) exhibiting negative refraction and subwavelength imaging are studied experimentally. A left-handed transmission band is observed at the frequencies where both dielectric permittivity and magnetic permeability are simultaneously negative. 2D LHM structure is verified to have a negative refractive index by measuring the refraction through a prism-shaped sample. Subwavelength focusing is observed by using a flat LHM superlens.Item Open Access Focusing of electromagnetic waves by a left-handed metamaterial flat lens(Optical Society of America, 2005-10-31) Aydin, K.; Bulu, I.; Özbay, EkmelWe present here the experimental results from research conducted on negative refraction and focusing by a two-dimensional (2D) left-handed metamaterial (LHM) slab. By measuring the refracted electromagnetic (EM) waves from a LHM slab, we find an effective refractive index of -1.86. A 2D scanning transmission measurement technique is used to measure the intensity distribution of the EM waves that radiate from the point source. The flat lens behavior of a 2D LHM slab is demonstrated for two different point source distances of ds = 0.5λ and λ. The full widths at half maximum of the focused beams are 0.36λ and 0.4λ, respectively, which are both below the diffraction limit. © 2005 Optical Society of AmericaItem Open Access The magical world of metamaterials(SPIE, 2009) Çağlayan, Hümeyra; Özbay, EkmelWe review experimental and theoretical studies performed on left-handed metamaterials (LHM). The metamaterials exhibit quiet unusual electromagnetic properties such as negative refraction, negative phase velocity, subwavelength focusing, subwavelength cavities and enhanced transmission.Item Open Access Negative refraction and imaging beyond the diffraction limit by a two-dimensional left-handed metamaterial(Elsevier BV, 2008) Özbay, Ekmel; Aydin, K.We report our experimental results on two-dimensional left-handed metamaterials (LHM) exhibiting negative refraction and subwavelength imaging. Transmission and reflection spectra of LHM are studied and a left-handed transmission band is observed at the frequencies where both dielectric permittivity and magnetic permeability are negative. Impedance matching is verified both with the experiments and simulations. The two-dimensional LHM structure is verified to have a negative refractive index. We employed three different methods to observe negative refraction; refraction through prism-shaped LHM, beam shifting method, and phase shift experiments. We further demonstrated subwavelength imaging and resolution using LHM superlenses. The effect of thickness on the resolving power is investigated experimentally.Item Open Access Negative refraction and subwavelength focusing using left-handed composite metamaterials(SPIE, 2008-01) Özbay, Ekmel; Aydın, KorayWe review experimental studies performed on left-handed metamaterials (LHM) at microwave frequencies. The metamaterial structure is composed of periodic arrays of split-ring resonators and wire meshes and exhibits a left-handed propagation band at frequencies of negative permittivity and negative permeability. Negative refraction is verified using prism shaped LHM and also by beam-shifting method. Subwavelength focusing of a point source is achieved with a resolution of 0.13λ, through a flat LHM superlens.Item Open Access Optimization and tunability of deep subwavelength resonators for metamaterial applications: complete enhanced transmission through a subwavelength aperture(Optical Society of American (OSA), 2009) Alici, K.B.; Bilotti F.; Vegni L.; Özbay, EkmelIn the present work, we studied particle candidates for metamaterial applications, especially in terms of their electrical size and resonance strength. The analyzed particles can be easily produced via planar fabrication techniques. The electrical size of multi-split ring resonators, spiral resonators, and multi-spiral resonators are reported as a function of the particle side length and substrate permittivity. The study is continued by demonstrating the scalability of the particles to higher frequencies and the proposition of the optimized particle for antenna, absorber, and superlens applications: a multi-spiral resonator with ë/30 electrical size operating at 0.810 GHz. We explain a method for tuning the resonance frequency of the multi-split structures. Finally, we demonstrate that by inserting deep subwavelength resonators into periodically arranged subwavelength apertures, complete transmission enhancement can be obtained at the magnetic resonance frequency. © 2009 Optical Society of America.Item Open Access Science meets magic: photonic metamaterials(Society of Photo-Optical Instrumentation Engineers, 2012-05) Özbay, EkmelThe word "magic" is usually associated with movies, fiction, children stories, etc. but seldom with the natural sciences. Recent advances in metamaterials have changed this notion, in which we can now speak of "almost magical" properties that scientists could only dream about only a decade ago. In this article, we review some of the recent "almost magical" progress in the field of meta-materials. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).Item Open Access Sub-wavelength resolution in a photonic crystal superlens(2003) Çubukçu, ErtuğrulMaterials that can bend light in the opposite direction to normal (’left-handed’ materials) reverse the way in which refraction usually works-this negative refractive index is due to simultaneously negative permeability and permittivity. Here we demonstrate negative refraction of electromagnetic waves in a two-dimensional dielectric photonic crystal that has a periodically modulated positive permeability and a permeability of unity. This experimental verification of negative refraction is a step towards the realization of a ’superlens’ that will be able to focus features smaller than the wavelength of light. Our structure consists of a square array of alumina rods in air. To obtain the frequency range within which the negative refraction and the other peculiar properties incorporated with it, we have calculated the the equal frequency contours of our photonic crystal with the photonic plane wave expansion method. We found out that 13.7 GHz is the optimum frequency for negative refraction. We took transmission measurements to confirm our structure’s predicted negative refraction: we used the the interfaces of the photonic crystal in the Γ − M direction. Our experiments were simulated with the finite-difference time-domain method (FDTD). The negative index of refraction was determined to be −1.94, which is close to the theoretical value of −2.06 calculated by the FDTD method. Since we know that we have a negative refractive material , we used our crystal to test the superlensing effect that was predicted for negative refractive materials. We have demonstrated that the image of two coherent point sources separated by a distance of λ/3 can be resolved. We have extended our approach to the case with two incoherent point sources, and we have achieved subwavelength resolution for this configuration as well. To our knowledge, this is the first demonstration of subwavelength resolution of electromagnetic waves in a negative index material.Item Open Access Subwavelength resolution in a two-dimensional photonic-crystal-based superlens(American Physical Society, 2003) Cubukcu, E.; Aydin, K.; Özbay, Ekmel; Foteinopolou, S.; Soukoulis, C. M.The experimental and theoretical demonstration of a single-beam negative refraction and a superlensing effect in 2D photonic crystals was reported. As such, negative refraction was observed for the incidence angles of >20°. This broad angle range was used to demonstrate the superlensing effect, where the electromagnetic waves emitted from a point source were focused on the other side of the PC.