Browsing by Subject "Cavity"

Now showing 1 - 9 of 9

Open Access
Cavity formation in split ring resonators
(Elsevier BV, 2008-12) Caglayan, H.; Bulu, I.; Loncar, M.; Özbay, Ekmel
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 SRR-based 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 SRR-based 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.
Open Access
Defect structures in metallic photonic crystals
(A I P Publishing LLC, 1996-12-16) Özbay, Ekmel; Temelkuran, B.; Sigalas, M.; Tuttle, G.; Soukoulis, C. M.; Ho, K. M.
We have investigated metallic photonic crystals built around a layer‐by‐layer geometry. Two different crystal structures (face‐centered‐tetragonal and tetragonal) were built and their properties were compared. We obtained rejection rates of 7–8 dB per layer from both metallic crystals. Defect modes created by removing rods resulted in high peak transmission (80%), and high quality factors (1740). Our measurements were in good agreement with theoretical simulations.
Open Access
Enhancement and inhibition of photoluminescence in hydrogenated amorphous silicon nitride microcavities
(Optical Society of America, 1997-09-01) Serpenguzel, A.; Aydınlı, Atilla; Bek, A.
A Fabry-Perot microcavity is used for the enhancement and inhibition of photoluminescence in hydrogenated amorphous silicon nitride. The amplitude of the photoluminescence is enhanced 4 times, while its linewidth is reduced 8 times with respect to the bulk hydrogenated amorphous silicon nitride. The transmittance, reflectance, and absorptance spectra of the microcavity were also measured and calculated. The calculated spectra agree well with the experimental ones. (C) 1997 Optical Society of America
Open Access
Fabrication, characterization and simulation of plasmonic cavities
(2010) Karabıyık, Mustafa
Surface plasmon polaritons (SPPs) originate from the collective oscillations of conduction electrons coupled with photons propagating at metal-dielectric interfaces. A uniform metallic gratings change the dispersion (energy-momentum relation) of a flat metal surfaces due to the interaction of SPPs with the periodic structure. By breaking the symmetry of the periodic plasmonic structure, SPP cavities can be achieved and SPPs can be localized inside the cavity regions. The aim of this thesis is to understand the physics of phase shifted grating based plasmonic cavities. To this end, we fabricated uniform gratings and phase shifted gratings using electron beam lithography, and optically characterized these SPP structures with polarization dependent reflection spectroscopy. We verified experimental results with numerical simulations SPP propagation and localization on the grating structures. Dispersion curves of SPPs have been calculated by solving Maxwell’s wave equations using finite difference time domain method (FDTD) with appropriate boundary conditions in agreement with experimentally obtained data. We studied the dispersion curve as a function of grating profile modulation where we vary the ridge height and width of the ridges. We find that the plasmonic band gap width increases as the ridge height of the ridges in the grating increases. Optimum duty cycle of grating to observe plasmonic band gap is determined to be half of the grating period. Amount of the phase shift added to the periodicity of the uniform grating defines the energy of the cavity state, which is periodically related to the phase shift. A plasmonic cavity with a quality factor 80 has been achieved. The propagation mechanism of SPPs on coupled cavities is plasmon hopping from a given cavity to the next one.
Open Access
Grating based plasmonic cavities
(2009) Şenlik, Servet Seçkin
Surface plasmon polaritons are dipole carrying electromagnetic excitations occur- ing at metal-dielectric interfaces. Metallic periodic structures exhibit modi¯ed transmission and re°ection spectra owing to the interaction of propagating SPPs with the periodicity. These periodic surfaces are used to demonstrate localiza- tion of propagating SPPs. Thin metallic ¯lms surrounded by Bragg re°ectors, selective loading of biharmonic metallic surfaces and Moire patterns are used to demonstrate plasmonic cavity formation. The quality factor, Q, a characteristic value that indicates rate of energy loss relative to the stored energy in the cavity is a crucial parameter for classifying these cavities. It was proposed that the Q factor should strongly depend on the surface geometry. However, there was not a sytematic study on the Q factor of these cavity structures. In this work, we report on a comparative study of grating based plasmonic band gap cavities. Numerically, we calculate the quality factors of the cavities based on three types of grating surfaces; uniform, biharmonic and Moirµe surfaces. Experimentally, we demonstrate the existence of plasmonic cavities based on uniform gratings. E®ective index perturbation and cavity geometries are obtained by additional dielectric loading. Furthermore, we fabricate 2D plasmonic structures, observe plasmonic band gaps in the symetry axis and propose cavity geometries for this structure.
Open Access
Low-threshold Lasing eigenmodes of infinite periodic chain of quantum wires
(Optical Society of America, 2010-10-26) Byelobrov, V.; Ctyroky, J.; Benson, T. M.; Sauleau, R.; Altintas, A.; Nosich, A. I.
We study the lasing eigenvalue problems for a periodic open optical resonator made of an infinite grating of circular dielectric cylinders standing in free space, in the E- and H-polarization modes. If possessing a “negative-absorption” refractive index, such cylinders model a chain of quantum wires made of the gain material under pumping. The initial-guess values for the lasing frequencies are provided by the plane-wave scattering problems. We demonstrate a new effect: the existence of specific grating eigenmodes that have a low threshold of lasing even if the wires are optically very thin.
Open Access
Observation of cavity structures in composite metamaterials
(S P I E - International Society for Optical Engineering, 2010-07-29) Caglayan, H.; Özbay, Ekmel
We investigated the cavity structure by the deformation of a unit cell of a Composite Metamaterial (CMM) structure. We considered different cavity structures with different resonance frequencies and Q-factors. We observed the Q-factor of the cavity resonance as 108 for a CMM based single cavity wherein the cavity structure is a closed ring structure. We investigated the reduced photon lifetime and observed that at the cavity resonance, the effective group velocity was reduced by a factor of 20 for a CMM based single cavity compared to the electromagnetic waves propagating in free space. Since the unit cells of metamaterials are much smaller than the operation wavelength, subwavelength localization is possible within these metamaterial cavity structures. We found that the electromagnetic field is localized into a region of/8, where is the cavity resonance wavelength. Subsequently, we brought two cavities together with an intercavity distance of two metamaterial unit cells and then investigated the transmission spectrum of CMM based interacting 2-cavity system. Finally, using the tight-binding picture we observed the normalized group velocity corresponding to the coupled cavity structure.
Open Access
Plasmonic band gap cavities
(2008) Kocabaş, Aşkın
Surface plasmon polaritons (SPP’s) are trapped electromagnetic waves coupled to free electrons in metals that propagate at the metal-dielectric interfaces. Due to their surface confinement and potential in sub-wavelength optics, SPP’s have been extensively studied for sensing and nanophotonic applications. Dielectric structures and metallic surfaces, both periodically modulated, can form photonic band gaps. Creating a defect cavity region in the periodicity of dielectrics allows specific optical modes to localize inside a cavity region. However, despite the demonstration of numerous plasmonic surfaces and unlike its dielectric counterparts, low index modulation in metallic surfaces limits the formation of plasmonic defect cavity structures. This thesis describes new approaches for plasmonic confinement in a cavity through the use of selective loading of grating structures as well as through the use of Moiré surfaces. In our first approach, we demonstrate that a high dielectric superstructure can perturb the optical properties of propagating SPPs dramatically and enable the formation of a plasmonic band gap cavity. Formation of the cavity is confirmed by the observation of a cavity mode in the band gap both in the infrared and the visible wavelengths. In addition to the confinement of SPP’s in the vertical direction, such a cavity localizes the SPP’s in their propagation direction. Additionally, we have demonstrated that such biharmonic grating structures can be used to enhance Raman scattering and photoluminescence (PL). Using biharmonic grating structure 105 times enhancement in Raman signal and 30 times enhancement in PL were measured. Furthermore, we show that metallic Moiré surfaces can also serve as a basis for plasmonic cavities with relatively high quality factors. We have demonstrated localization and slow propagation of surface plasmons on metallic Moiré surfaces. Phase shift at the node of the Moiré surface localizes the propagating surface plasmons in a cavity and adjacent nodes form weakly coupled plasmonic cavities. We demonstrate group velocities around v = 0.44c at the center of the coupled cavity band and almost zero group velocity at the band edges can be achieved. Furthermore, sinusoidally modified amplitude about the node suppresses the radiation losses and reveals a relatively high quality factor for plasmonic cavities.
Open Access
Visible photoluminescence from planar amorphous silicon nitride microcavities
(Optical Society of America, 1998) Serpengüzel, A.; Aydınlı, Atilla; Bek, A.; Güre, M.
Fabry-Perot microcavities were used for the enhancement and inhibition of photoluminescence (PL) in a hydrogenated amorphous silicon nitride (a-SiNx:H) microcavity fabricated with and without ammonia. A planar microcavity was realized that included a metallic back mirror and an a-SiNx:H-air or a metallic front mirror. The PL extends from the red part of the spectrum to the near infrared for the samples grown without ammonia. The PL is in the blue-green part of the spectrum for the samples grown with ammonia. The PL amplitude is enhanced and the PL linewidth is reduced with respect to those in bulk a-SiNx:H. The numerically calculated transmittance, reflectance, and absorbance spectra agree well with the experimentally measured spectra. (C) 1998 Optical Society of America [S0740-3224(98)00211-2] OCIS codes: 230.5750, 250.5230, 310.0310.