Adibi, Ali

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Now showing 1 - 10 of 18
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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.
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    Planar photonic crystals infiltrated with nanoparticle/polymer composites
    (Georgia Institute of Technology, 2007-11) Tay, Savaş ; Thomas, Jayan ; Momeni, Babak ; Askari, Murtaza ; Adibi, Ali ; Hotchkiss, Peter J. ; Jones, Simon C. ; Marder, Seth R. ; Norwood, Robert A. ; Peyghambarian, Nasser
    Infiltration of planar two-dimensional silicon photonic crystals with nanocomposites using a simple yet effective melt processing technique is presented. The nanocomposites that were developed by evenly dispersing functionalized TiO₂ nanoparticles into a photoconducting polymer were completely filled into photonic crystals with hole sizes ranging from 90 to 500 nm. The infiltrated devices show tuning of the photonic band gap that is controllable by the adjustment of the nanoparticle loading level. These results may be useful in the development of tunable photonic crystal based devices and hybrid light emitting diodes and solar cells.
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    Effective impedance model for analysis of reflection at the interfaces of photonic crystals
    (Georgia Institute of Technology, 2007-04) Momeni, Babak ; Eftekhar, Ali Asghar ; Adibi, Ali
    We present an alternative definition of impedance to describe the reflection at the interfaces of photonic crystals. We show that this effective impedance can be defined only by the properties of the photonic crystal modes and is independent of the properties of the incident region. This approximate model successfully explains the main features in the reflection spectrum and of various interface terminations of photonic crystals. In particular, we show an impedance matching condition at which reflectionless transmission of power to a low-group-velocity photonic crystal mode is possible, a property that is attractive for various dispersion-based applications of photonic crystals.
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    Preconditioned superprism-based photonic crystal demultiplexers: analysis and design
    (Georgia Institute of Technology, 2006-11) Momeni, Babak ; Adibi, Ali
    We present the analysis and design of a new type of photonic crystal (PC) demultiplexers (i.e., preconditioned demultiplexer), in which the simultaneous existence of the superprism effect and the negative effective index for diffraction results in a compact structure by canceling the second-order spectral phase to avoid beam broadening inside the PC. This approach considerably relaxes the requirements for the large area of the structure and the small divergence of the input beam. As a result, the size of the preconditioned demultiplexers varies as N².⁵ (N being the number of wavelength channels) compared to the N⁴ variation in the conventional superprism-based PC demultiplexers. We use a generalized effective index model to analyze, design, and optimize these demultiplexing structures. This approximate model can be used to extract all the basic properties of the PC device simply from the band structure and eliminates the need to go through tedious simulations especially for three-dimensional structures. Our results show that the preconditioned superprism-based PC demultiplexers have 2 orders of magnitude smaller size compared to the conventional ones.