Adibi, Ali

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Now showing 1 - 10 of 53
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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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    Planar photonic crystal microspectrometers in silicon-nitride for the visible range
    (Georgia Institute of Technology, 2009-09) Momeni, Babak ; Hosseini, Ehsan Shah ; Adibi, Ali
    We demonstrate the feasibility of forming a compact integrated photonic spectrometer for operation in the visible wavelength range using the dispersive properties of a planar photonic crystal structure fabricated in silicon nitride. High wavelength resolution and compact device sizes in these spectrometers are enabled by combining superprism effect, negative diffraction effect, and negative refraction effect in a 45° rotated square lattice photonic crystal. Our experimental demonstration shows 1.2 nm wavelength resolution in a 70 µm by 130 µm photonic crystal structure with better performance than alternative structures for on-chip spectroscopy, confirming the unique capability of the proposed approach to realize compact integrated spectrometers.
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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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    45 Degree Polymer Micromirror Integration for Board-Level Three-Dimensional Optical Interconnects
    (Georgia Institute of Technology, 2009-06) Wang, Fengtao ; Liu, Fuhan ; Adibi, Ali
    We introduce here a simple method of integrating 45° total internal reflection micro-mirrors with polymer optical waveguides by an improved tilted beam photolithography on printed circuit boards to provide surface normal light coupling between waveguides and optoelectronic devices for optical interconnects. De-ionized water is used to couple ultraviolet beam through the waveguide core polymer layer at 45° angle during the photo exposure process. This technique is compatible with PCB manufacturing facility and suitable to large panel board-level manufacturing. The mirror slope is controlled accurately (within ±1°) with high repeatability. The insertion loss of an uncoated micro-mirror is measured to be 1.6 dB.
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    High-Q micromechanical resonators in a two-dimensional phononic crystal slab
    (Georgia Institute of Technology, 2009-02) Mohammadi, Saeed ; Eftekhar, Ali Asghar ; Hunt, William D. ; Adibi, Ali
    By creating line defects in the structure of a phononic crystal (PC) made by etching a hexagonal array of holes in a 15 μm thick slab of silicon, high-Q PC resonators are fabricated using a complimentary-metal-oxide-semiconductor-compatible process. The complete phononic band gap of the PC structure supports resonant modes with quality factors of more than 6000 at frequencies as high as 126 MHz. The confinement of acoustic energy is achieved by using only a few PC layers confining the cavity region. The calculated frequencies of resonance of the structure using finite element method are in a very good agreement with the experimental data. The performance of these PC resonator structures makes them excellent candidates for wireless communication and sensing applications.
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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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    Compact on-chip interferometers with high spectral sensitivity
    (Georgia Institute of Technology, 2009-01) Chamanzar, Maysamreza ; Momeni, Babak ; Adibi, Ali
    We introduce on-chip interferometers in which the spatial output interference pattern is observed along a detection plane. We show that by using photonic crystals with strong dispersive properties in these devices, highly sensitive interferometers can be realized. We discuss potentials of these interferometers in spectroscopy and sensing applications using their strong wavelength sensitivity and their ability to spatially map the spectral information of an input signal.
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    Strong angular dispersion using higher bands of planar silicon photonic crystals
    (Georgia Institute of Technology, 2008-09) Momeni, Babak ; Chamanzar, Maysamreza ; Hosseini, Ehsan Shah ; Askari, Murtaza ; Soltani, Mohammad ; Adibi, Ali
    We present experimental evidence for strong angular dispersion in a planar photonic crystal (PC) structure by properly engineering the modes in the second PC band. We show that by using the second photonic band of a square lattice PC, angular dispersion of 4°/nm can be achieved. We also show that major challenges in designing practical PC devices using second band modes can be addressed by engineering the lattice and adding input/output buffer stages designed to eliminate unwanted effects.
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    Evidence of large high frequency complete phononic band gaps in silicon phononic crystal plates
    (Georgia Institute of Technology, 2008-06-02) Mohammadi, Saeed ; Eftekhar, Ali Asghar ; Khelif, Abdelkrim ; Hunt, William D. ; Adibi, Ali
    We show the evidence of the existence of large complete phononic band gaps (CPBGs) in two-dimensional phononic crystals (PCs) formed by embedding cylindrical air holes in a solid plate (slab). The PC structure is made by etching a hexagonal array of air holes through a freestanding plate of silicon. A fabrication process compatible with metal-oxide-semiconductor technology is used on silicon-on-insulator substrate to realize the PC devices. Measuring the transmission of elastic waves through eight layers of the hexagonal lattice PC in the ΓK direction, more than 30 dB attenuation is observed at a high frequency; i.e., 134 MHz, with a band gap to midgap ratio of 23%. We show that this frequency region matches very well with the expected CPBG found through theoretical calculations.