Adibi, Ali

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Now showing 1 - 9 of 9
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    Quantitative modeling of coupling-induced resonance frequency shift in microring resonators
    (Georgia Institute of Technology, 2009-12) Li, Qing ; Soltani, Mohammad ; Atabaki, Amir Hossein ; Yegnanarayanan, Siva ; Adibi, Ali
    We present a detailed study on the behavior of coupling-induced resonance frequency shift (CIFS) in dielectric microring resonators. CIFS is related to the phase responses of the coupling region of the resonator coupling structure, which are examined for various geometries through rigorous numerical simulations. Based on the simulation results, a model for the phase responses of the coupling structure is presented and verified to agree with the simulation results well, in which the first-order coupled mode theory (CMT) is extended to second order, and the important contributions from the inevitable bent part of practical resonators are included. This model helps increase the understanding of the CIFS behavior and makes the calculation of CIFS for practical applications without full numerical simulations possible.
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    Multiplex coherent anti-Stokes Raman scattering (MCARS) for chemically sensitive, label-free flow cytometry
    (Georgia Institute of Technology, 2009-12) Camp, Charles Henry, Jr. ; Yegnanarayanan, Siva ; Eftekhar, Ali Asghar ; Sridhar, Hamsa ; Adibi, Ali
    Flow cytometry is an ever-advancing high-throughput multivariate analysis tool that natively provides size and morphological information. To obtain molecular information, however, typically requires the addition of fluorophores, which are limited by spectral overlap, nonspecific binding, available conjugation chemistries, and cellular toxicity. A complementary or alternative, label-free approach to molecular information is through multiplex coherent anti-Stokes Raman scattering (MCARS), which is a coherent, nonlinear optical method that provides a wealth of molecular information by probing the Raman energies within a molecule. In this work, we demonstrate the unique capability of our MCARS flow cytometer to distinguish flowing particles and discuss system performance capabilities and possibilities.
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    Large-scale array of small high-Q microdisk resonators for on-chip spectral analysis
    (Georgia Institute of Technology, 2009-10) Soltani, Mohammad ; Li, Qing ; Yegnanarayanan, Siva ; Momeni, Babak ; Eftekhar, Ali Asghar ; Adibi, Ali
    We demonstrate on-chip, large-scale arrays of small high-Q microdisk resonators, suitable for both in-plane coupling and out-of-plane (imaging) spectral analysis devices with high resolution (linewidth < 50pm to 0.5nm), and large FSR (> 50nm).
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    Sub-microsecond thermal reconfiguration of silicon photonic devices
    (Georgia Institute of Technology, 2009-10) Atabaki, Amir H. ; Eftekhar, Ali A. ; Yegnanarayanan, Siva ; Adibi, Ali
    Using the experimental data we show the possibility of sub-microsecond reconfiguration of silicon photonics microresonators through pulse shaping of micro-heater excitation. Also, a novel heater structure based on small microdisk resonators with sub-hundred-nanosecond reconfiguration speed is proposed and investigated theoretically.
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    High quality planar silicon nitride microdisk resonators for integrated photonics in the visible wavelength range
    (Georgia Institute of Technology, 2009-08) Hosseini, Ehsan Shah ; Yegnanarayanan, Siva ; Atabaki, Amir Hossein ; Soltani, Mohammad ; Adibi, Ali
    High quality factor (Q≈3.4×10⁶) microdisk resonators are demonstrated in a Si3N4 on SiO₂ platform at 652–660 nm with integrated in-plane coupling waveguides. Critical coupling to several radial modes is demonstrated using a rib-like structure with a thin Si3N4 layer at the air-substrate interface to improve the coupling.
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    Design and demonstration of compact, wide bandwidth coupled-resonator filters on a silicon-on-insulator platform
    (Georgia Institute of Technology, 2009-02) Li, Qing ; Soltani, Mohammad ; Yegnanarayanan, Siva ; Adibi, Ali
    We design and fabricate a compact third-order coupled-resonator filter on the silicon-on-insulator platform with focused application for on-chip optical interconnects. The filter shows a large flat bandwidth (3dB 3.3nm), large FSR (~18nm), more than 18dB out-of-band rejection at the drop port and more than 12 dB extinction at the through port, as well as a negligible drop loss (<0.5dB) within a footprint of 0.0004 mm².
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    Sustained GHz oscillations in ultra-high Q silicon microresonators
    (Georgia Institute of Technology, 2009) Soltani, Mohammad ; Yegnanarayanan, Siva ; Li, Qing ; Atabaki, Amir ; Eftekhar, Ali A. ; Adibi, Ali
    We report the experimental observation of long-sustained GHz electronic oscillations resulting from coupled electron-photon dynamics in ultra-high-Q Si microdisk resonators with CW pumping. Theoretical analysis identifies conditions for steady-state GHz oscillations while suppressing thermal oscillations.
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    Improvement of thermal properties of ultra-high Q silicon microdisk resonators
    (Georgia Institute of Technology, 2007-12) Soltani, Mohammad ; Li, Qing ; Yegnanarayanan, Siva ; Adibi, Ali
    We present a detailed study of the thermal properties of ultra-high quality factor (Q) microdisk resonators on silicon-on-insulator (SOI) platforms. We show that by preserving the buried oxide layer underneath the Si resonator and by adding a thin Si pedestal layer at the interface between the resonator and the oxide layer we can increase the overall thermal conductivity of the structure while the ultra-high Q property is preserved. This allows higher field intensities inside the resonator which are crucial for nonlinear optics applications.
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    Ultra-high Q planar silicon microdisk resonators for chip-scale silicon photonics
    (Georgia Institute of Technology, 2007-04) Soltani, Mohammad ; Yegnanarayanan, Siva ; Adibi, Ali
    We report the fabrication and experimental characterization of an ultra-high Q microdisk resonator in a silicon-on-insulator (SOI) platform. We examine the role of the substrate in the performance of such microdisk resonators. While substrate leakage loss has warranted the necessity of substrate undercut structures in the past, we show here that the substrate has a very useful role to play for both passive chip-scale device integration as well as active electronic device integration. Two device architectures for the disk-on-substrate are studied in order to assess the possibility of such an integration of high Q resonators and active components. Using an optimized process for fabrication of such a resonator device, we experimentally demonstrate a Q~3×10 ⁶, corresponding to a propagation loss ~0.16 dB/cm. This, to our knowledge, is the maximum Q observed for silicon microdisk cavities of this size for disk-on-substrate structures. Critical coupling for a resonance mode with an unloaded Q~0.7×10 ⁶ is observed. We also report a detailed comparison of the obtained experimental resonance spectrum with the theoretical and simulation analysis. The issue of waveguide-cavity coupling is investigated in detail and the conditions necessary for the existence or lack of critical coupling is elaborated.