Shashanka Ashili

Publications (22) View all

• Conference Proceeding: Optical Transport Phenomena in Coupled Spherical Cavities

  V.N. Astratov, S.P. Ashili, Seungmoo Yang
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  ABSTRACT: The efficiency of optical transport is studied in one-dimensional (ID) chains and in 3D lattices of coupled microspheres with ~1-3% size disorder. To couple light into such structures we used sources of light formed by dye-doped fluorescent microspheres. Using techniques of spatially resolved scattering spectroscopy we observed large propagation losses (~ 3 dB per sphere) along the chain at the frequencies of whispering gallery modes (WGMs) in the source sphere. Away from the resonance with WGMs we observed much smaller losses (< 1 dB per sphere) due to formation of nanojet-induced modes. The propagation of light in 3D lattices of disordered coupled cavities with WGM resonances is interpreted in terms of percolation theory. In transmission spectra of such 3D structures we observed spectral signatures of strong coupling between multiple spheres with nearly resonant WGMs. The results indicate that the transmission properties can be significantly improved in 3D structures formed by more uniform spheres due to achieving an optical percolation threshold for WGM transport.
  Transparent Optical Networks, 2007. ICTON '07. 9th International Conference on; 08/2007
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  Available from: Shashanka Ashili

  Conference Proceeding: Optical Properties of Mesoscopic Systems of Coupled Microspheres

  V. N. Astratov, S. P. Ashili, A. M. Kapitonov
  01/2007
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  Available from: Shashanka Ashili

  Article: The effects of inter-cavity separation on optical coupling in dielectric bispheres.

  Shashanka P Ashili, Vasily N Astratov, E Charles H Sykes
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  ABSTRACT: The optical coupling between two size-mismatched spheres was studied by using one sphere as a local source of light with whispering gallery modes (WGMs) and detecting the intensity of the light scattered by a second sphere playing the part of a receiver of electromagnetic energy. We developed techniques to control inter-cavity gap sizes between microspheres with ~30nm accuracy. We demonstrate high efficiencies (up to 0.2-0.3) of coupling between two separated cavities with strongly detuned eigenstates. At small separations (<1 microm) between the spheres, the mechanism of coupling is interpreted in terms of the Fano resonance between discrete level (true WGMs excited in a source sphere) and a continuum of "quasi"-WGMs with distorted shape which can be induced in the receiving sphere. At larger separations the spectra detected from the receiving sphere originate from scattering of the radiative modes.
  Optics Express 11/2006; 14(20):9460-6. · 3.59 Impact Factor
• Conference Proceeding: Integrated Circuits of Coupled Mircospheres for Optoelectronics Applications

  V.N. Astratov, S.P. Ashili, A.M. Kapitonov, A.V. Kanaev
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  ABSTRACT: The paper is devoted to theoretical modeling, fabrication, and advanced spectroscopic characterization of circuits of microspheres with high quality whispering gallery modes (WGMs). The discussion of results is based on three mechanisms of optical coupling between spherical cavities: (i) resonant coupling between WGMs in identical cavities, (ii) Fano resonance between a discrete energy state (true WGM excited in the source sphere) and a continuum of quasi-WGM states with distorted noncircular shape which can be induced in the receiving cavity, and (iii) photonic nanojet mechanism. For the case of identical cavities we present numerical modeling results demonstrating a good impedance matching, and a tunable nanosecond delay for propagating pulses. We experimentally studied optical coupling in size-mismatched bispheres with controllable inter-cavity separations, and showed the validity of mechanism based on Fano resonance. Finally, we observed photonic nanojets in extremely long chains of fluorescent microspheres with propagation losses less than 1 dB per sphere
  Transparent Optical Networks, 2006 International Conference on; 07/2006
• Conference Proceeding: Integrated Circuits of Coupled Mircospheres for Optoelectronics Applications

  V. N. Astratov, S. P. Ashili, A. M. Kapitonov, A. V. Kanaev
  01/2006