Adibi, Ali

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Now showing 1 - 10 of 21
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    Absorbing boundary conditions for low group velocity electromagnetic waves in photonic crystals
    (Georgia Institute of Technology, 2011-03) Askari, Murtaza ; Momeni, Babak ; Reinke, Charles M. ; Adibi, Ali
    We present an efficient method for the absorption of slow group velocity electromagnetic waves in photonic crystal waveguides (PCWs). We show that adiabatically matching the low group velocity waves to high group velocity waves of the PCW and extending the PCW structure into the perfectly matched layer (PML) region results in a 15 dB reduction of spurious reflections from the PML. We also discuss the applicability of this method to structures other than PCWs.
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    Systematic Design of Wide-Bandwidth Photonic Crystal Waveguide Bends With High Transmission and Low Dispersion
    (Georgia Institute of Technology, 2010-06) Askari, Murtaza ; Momeni, Babak ; Soltani, Mohammad ; Adibi, Ali
    We identify factors affecting transmission and dispersive properties of photonic crystal waveguide (PCW) bends, using 2-D simulations and present a method for systematic design of PCW bends to achieve high transmission and low dispersion over large bandwidths. The bends presented here have higher bandwidth and lower dispersion than bends already reported.
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    Tuning of resonance-spacing in a traveling-wave resonator device
    (Georgia Institute of Technology, 2010-04) Atabaki, Amir Hossein ; Momeni, Babak ; Eftekhar, Ali Asghar ; Hosseini, Ehsan Shah ; Yegnanarayanan, Siva ; Adibi, Ali
    In this work a traveling-wave resonator device is proposed and experimentally demonstrated in silicon-on-insulator platform in which the spacing between its adjacent resonance modes can be tuned. This is achieved through the tuning of mutual coupling of two strongly coupled resonators. By incorporating metallic microheaters, tuning of the resonance-spacing in a range of 20% of the free-spectral-range (0.4nm) is experimentally demonstrated with 27mW power dissipation in the microheater. To the best of our knowledge this is the first demonstration of the tuning of resonance-spacing in an integrated traveling-wave-resonator. It is also numerically shown that these modes exhibit high field-enhancements which makes this device extremely useful for nonlinear optics and sensing applications.
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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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    Athermal operation in polymer-clad silicon microdisk resonators
    (Georgia Institute of Technology, 2009-10) Alipour, Payam ; Hosseini, Ehsan Shah ; Eftekhar, Ali Asghar ; Momeni, Babak ; Adibi, Ali
    We have used a urethane polymer as cladding to reduce the temperature sensitivity of resonance in high-Q silicon microdisk resonators. A two-order-of-magnitude improvement in resonance stability is demonstrated, and effects on the Q-factor are discussed.
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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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    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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    Modeling the propagation of optical beams in three-dimensional photonic crystals
    (Georgia Institute of Technology, 2008-05) Momeni, Babak ; Badieirostami, Majid ; Adibi, Ali
    We show that the propagation effects of optical beams in three-dimensional photonic crystal structures can be modeled using a direction-dependent effective diffractive index model. The parameters of the model (i.e., the effective diffractive indices) can be calculated using the curvatures of the band structure of the photonic crystal at the operation point. After finding these indices, the wave propagation inside the photonic crystal can be analyzed using simple geometrical optics formulas. We show that the model has good accuracy for most practical applications of photonic crystals. As an example, the application of the model for diffraction compensation in a tetragonal woodpile photonic crystal is demonstrated
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    Accurate and efficient techniques for the analysis of reflection at the interfaces of three-dimensional photonic crystals
    (Georgia Institute of Technology, 2007-12) Momeni, Babak ; Badieirostami, Majid ; Adibi, Ali
    We present two efficient and accurate models for the analysis and optimization of reflection at the interface of three-dimensional (3D) photonic crystal structures. For the most general photonic crystal interfaces, we develop a rigorous technique based on mode matching at the interface. We also explain a more efficient (yet accurate) model based on effective impedance definition for the analysis of 3D photonic crystals (PC) structures that are highly desired for practical applications. The two techniques are used to model practical 3D PC structures, and the issue of reflection minimization at the interface of such structures is addressed.