Person:
Adibi, Ali

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Publication Search Results

Now showing 1 - 10 of 11
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    Self-sustained gigahertz electronic oscillations in ultrahigh-Q photonic microresonators
    (Georgia Institute of Technology, 2012-05) Soltani, Mohammad ; Yegnanarayanan, Siva ; Li, Qing ; Eftekhar, Ali Asghar ; Adibi, Ali
    We report on theoretical and experimental observations of self-sustained fast [gigahertz (GHz)] electronic oscillations resulting from coupled electron-photon dynamics in ultrahigh-Q Si microdisk resonators with cw pumping. Our theoretical analysis identifies conditions for generating steady-state GHz oscillations while suppressing thermal oscillations [megahertz (MHz)] with submilliwatt input laser power. Such fast oscillations are tunable via changing the free-carrier (FC) lifetime of the resonator. Integrating a p-i-n diode with these high-Q resonators for controlling the FC lifetime promises the realization of an integrated voltage-controlled oscillator (VCO) in a silicon photonics chip.
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    A Temperature-Insensitive Third-Order Coupled-Resonator Filter for On-Chip Terabit/s Optical Interconnects
    (Georgia Institute of Technology, 2010-12) Li, Qing ; Yegnanarayanan, Siva ; Soltani, Mohammad ; Alipour, Payam ; Adibi, Ali
    We design and demonstrate a temperature-insensitive third-order coupled-resonator filter in the silicon-on-insulator platform for on-chip terabit/s optical interconnects. Optimum filter design enables up to 21 flat-band filter channels with more than 10 dB through-port extinction, more than 0.75-nm 3-dB bandwidth, and less than 1-dB insertion loss. By overlaying a negative thermo-optic coefficient polymer cladding on top of the silicon device, the sensitivity of the filter performance to the ambient temperature variations is significantly reduced. Moreover, through careful balancing between the dispersion of the bandwidth and the thermal property of the filter, the redundant bandwidth of filter channels due to dispersion is employed as thermal guard bands. As a result, the filter can accommodate 21 wavelength-division-multiplexing channels with data rates up to 100 Gb/s per wavelength channel while providing sufficient thermal guard bands to tolerate more than 15 C temperature fluctuations in the on-chip environment.
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    Toward ultimate miniaturization of high Q silicon traveling-wave microresonators
    (Georgia Institute of Technology, 2010-09) Soltani, Mohammad ; Li, Qing ; Yegnanarayanan, Siva ; Adibi, Ali
    High Q traveling-wave resonators (TWR)s are one of the key building block components for VLSI Photonics and photonic integrated circuits (PIC). However, dense VLSI integration requires small footprint resonators. While photonic crystal resonators have shown the record in simultaneous high Q (~10⁵-10⁶) and very small mode volumes; the structural simplicity of TWRs has motivated many ongoing researches on miniaturization of these resonators with maintaining Q in the same range. In this paper, we investigate the scaling issues of silicon traveling-wave microresonators down to ultimate miniaturization levels in SOI platforms. Two main constraints that are considered during this down scaling are: 1) Preservation of the intrinsic Q of the resonator at high values, and 2) Compatibility of resonator with passive (active) integration by preserving the SiO₂ BOX layer (plus a thin Si slab layer for P-N junction fabrication). Microdisk and microdonut (an intermediate design between disk and ring shape) are considered for high Q, miniaturization, and single-mode operation over a wide wavelength range (as high as the free-spectral range). Theoretical and experimental results for miniaturized resonators are demonstrated and Q's as high as ~10⁵ for resonators as small as 1.5 μm radius are achieved.
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    Systematic design and fabrication of high-Q single-mode pulley-coupled planar silicon nitride microdisk resonators at visible wavelengths
    (Georgia Institute of Technology, 2010-02) Hosseini, Ehsan Shah ; Yegnanarayanan, Siva ; Atabaki, Amir Hossein ; Soltani, Mohammad ; Adibi, Ali
    High quality (Q ≈ 6 × 10⁵) microdisk resonators are demonstrated in a Si₃N₄ on SiO₂platform at 652–660 nm with integrated in-plane wrap-around coupling waveguides to enable critical coupling to specific microdisk radial modes. Selective coupling to the first three radial modes with >20dB suppression of the other radial modes is achieved by controlling the wrap-around waveguide width. Advantages of such pulley-coupled microdisk resonators include single mode operation, ease of fabrication due to larger waveguide-resonator gaps, the possibility of resist reflow during the lithography phase to improve microdisk etched surface quality, and the ability to realize highly over-coupled microdisks suitable for low-loss delay lines and add-drop filters.
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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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    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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    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.