Browsing by Subject "Coupled cavity"
Now showing 1 - 7 of 7
Results Per Page
Sort Options
Item Open Access Coupled plasmonic cavities on moire surfaces(Springer, 2010-08) Balcı, Sinan; Karabıyık, Mustafa; Kocabaş, Aşkın; Kocabaş, Coşkun; Aydınlı, AtillaSurface plasmon polariton (SPP) waveguides formed by coupled plasmonic cavities on metallic Moire surfaces have been investigated both experimentally and numerically. The Moire surface, fabricated by interference lithography, contains periodic arrays of one-dimensional cavities. The coupling strength between the cavities has been controlled by changing the periodicities of the Moire surface. The ability to control the coupling strength allows us to tune the dispersion and the group velocity of the plasmonic coupled cavity mode. Reflection measurements and numerical simulation of the array of SPP cavities have shown a coupled resonator type plasmonic waveguide band formation within the band gap. Coupling coefficients of cavities and group velocities of SPPs are calculated for a range of cavity sizes from weakly coupled regime to strongly coupled regime.Item Open Access Direct imaging of localized surface plasmon polaritons(Optical Society of America, 2011-08) Balcı, Sinan; Karademir, Ertuğrul; Kocabaş, Coşkun; Aydınlı, AtillaIn this Letter, we report on dark field imaging of localized surface plasmon polaritons (SPPs) in plasmonic waveguiding bands formed by plasmonic coupled cavities. We image the light scattered from SPPs in the plasmonic cavities excited by a tunable light source. Tuning the excitation wavelength, we measure the localization and dispersion of the plasmonic cavity mode. Dark field imaging has been achieved in the Kretschmann configuration using a supercontinuum white-light laser equipped with an acoustooptic tunable filter. Polarization dependent spectroscopic reflection and dark field imaging measurements are correlated and found to be in agreement with finite-difference time-domain calculations.Item Open Access Observation of cavity structures in composite metamaterials(S P I E - International Society for Optical Engineering, 2010-07-29) Caglayan, H.; Özbay, EkmelWe 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.Item Open Access Physics and applications of defect structures in photonic crystals(SPIE, 2003) Özbay, Ekmel; Güven, Kaan; Bayındır, MehmetPhotonic crystals are three dimensional periodic structures having the property of reflecting the electromagnetic (EM) waves in all dimensions, for a certain range of frequencies. Defects or cavities around the same geometry can also be built by means of adding or removing material. The electrical fields in such cavities are usually enhanced, and by placing active devices in such cavities, one can make the device benefit from the wavelength selectivity and the large enhancement of the resonant EM field within the cavity. By using coupled periodic defects, we have experimentally observed a new type of waveguiding in a photonic crystal. A complete transmission was achieved throughout the entire waveguiding band. The transmission, phase, and delay time characteristics of the various coupled-cavity structures were measured and calculated. We observed the eigenmode splitting, waveguiding through the coupled cavities, splitting and switching of electromagnetic waves in waveguide ports, and Mach-Xender interferometer effect in such structures. The corresponding field patterns and the transmission spectra were obtained from the finite-difference-time-domain (FDTD) simulations. We developed a theory based on the classical wave analog of the tight-binding (TB) approximation in solid state physics. Experimental results are in good agreement with the FDTD simulations and predictions of the TB approximation.Item Open Access Single-mode engineering in semiconductor lasers using parity-time-symmetry and coupled-cavity structures(Bilkent University, 2021-07) Şeker, EnesHigh power single spatial mode semiconductor lasers are of interest for various applications, including optical communication, material processing, and pumping single-mode optical fibers. The output power of a typical index guided ridge waveguide single-mode laser is limited by its narrow waveguide width required to cut off higher-order optical modes. To overcome the output power limitation, conventional techniques rely on structures increasing the mode size without introducing new modes. These methods are based on lateral mode discrimination in a single waveguide to enforce single-mode operation. In contrast to the conventional methods, our work utilizes the concept of parity-time-symmetry (PTS) and coupled-cavity (CC) structures. By exploiting these two approaches, we employ multi-mode waveguides to achieve single-mode lasing in edge-emitting laser diodes. The PTS laser is based on coupling two identical waveguides. By electrically tuning the gain and loss in each waveguide, the optical modes are manipulated to realize a single-mode operation. On the other hand, the CC approach is based on the resonant coupling of waveguides with different widths to realize single-mode operation. In contrast to the PTS method, CC lasers have an unpumped waveguide to introduce loss instead of tuning the loss with an electrical pump. Towards this goal, the design parameters are numerically explored by detailed optical simulations, and their sensitivities are investigated for PTS and CC methods. I fabricated and experimentally demonstrated the control of the optical mode profiles promising single-mode operation for PTS and CC structures. The results are encouraging for future research and industrial applications.Item Open Access Slowing surface plasmon polaritons on plasmonic coupled cavities by tuning grating grooves(American Institute of Physics, 2010-09) Balcı, Sinan; Kocabaş, Aşkın; Kocabaş, Coşkun; Aydınlı, AtillaWe investigate slow surface plasmon polaritons (SPPs) in plasmonic waveguiding bands formed by coupled plasmonic cavities on Moiŕ surfaces. We demonstrate controlling the group velocity and dispersion of the SPPs by varying the depth of the plasmonic Bragg grating groove. Changing the grating depth results in modification of coupling coefficients between the cavities and hence the SPPs group velocity is altered. Variation in the group velocity and dispersion of SPPs can be measured with polarization dependent spectroscopic reflection measurements. Dispersion of SPPs has been calculated by finite-difference time-domain method in agreement with the experimental data.Item Open Access Tight-binding mechanism in slow light regime(IEEE, 2011) Akosman, Ahmet Emin; Mutlu, Mehmet; Kurt, Hamza; Özbay, EkmelIn this study, tight-binding formalism is applied to a photonic crystal coupled cavity structure in order to investigate the characteristics of ultra slow light modes. Eigen-mode splitting is observed and resulting group indices obtained from the tight-binding formalism and numerical results are compared. © 2011 IEEE.