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Adibi, Ali

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Now showing 1 - 7 of 7
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    Simple and efficient software-based stabilized holographic recording system
    (Georgia Institute of Technology, 2006-12) Cadena, George H. ; Momtahan, Omid ; Adibi, Ali
    A simple, inexpensive, and efficient stabilized holographic recording setup is described which precludes the destructive fringe movement encountered in long-lasting holographic exposures. Utilizing a straightforward methodology, stability greater than ƛ/25 (recording wavelength ƛ=532 nm) for holographic recording sessions longer than 6 h can be achieved. Due to the software basis of this design, in the LabVIEW platform, the functionality of expensive hardware components is provided in software. Moreover, this setup is modularly designed and can be easily replicated for multiple labs, with the need only of the following hardware components: a piezo-shifting mirror, a computer, a data-acquisition card, and a photodetector.
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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.
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    Core-shell diamond-like silicon photonic crystals from 3D polymer templates created by holographic lithography
    (Georgia Institute of Technology, 2006-06) Moon, Jun Hyuk ; Yang, Shu ; Dong, Wenting ; Perry, Joseph W. ; Adibi, Ali ; Yang, Seung-Man
    We have fabricated diamond-like silicon photonic crystals through a sequential silica/silicon chemical vapor deposition (CVD) process from the corresponding polymer templates photopatterned by holographic lithography. Core-shell morphology is revealed due to the partial backfilling of the interstitial pores. To model the shell formation and investigate its effect to the bandgap properties, we developed a two-parameter level-set approach that closely approximated the core-shell morphology, and compare the bandgap simulation with the measured optical properties of the 3D crystals at each processing step. Both experimental and calculation results suggest that a complete filling is necessary to maximize the photonic bandgap in the diamond-like structures.
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    Analysis of slitless holographic spectrometers implemented by spherical beam volume holograms
    (Georgia Institute of Technology, 2006-05) Momtahan, Omid ; Hsieh, Chaoray ; Adibi, Ali ; Brady, David J.
    The analysis of a slitless volume holographic spectrometer is presented in detail. The spectrometer is based on a spherical beam volume hologram followed by a Fourier-transforming lens and a CCD. It is shown that the spectrometer is not sensitive to the incident angle of the input beam for the practical range of applications. A holographic spectrometer based on the conventional implementation is also analyzed, and the results are used to compare the performance of the proposed method with the conventional one. The experimental results are consistent with the theoretical study. It is also shown that the slitless volume holographic spectrometer lumps three elements (the entrance slit, the collimator, and the diffractive element) of the conventional spectrometer into one spherical beam volume hologram. Based on the unique features of the slitless volume holographic spectrometer, we believe it is a good candidate for portable spectroscopy for environmental and biological applications.
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    Compact wavelength demultiplexing using focusing negative index photonic crystal superprisms
    (Georgia Institute of Technology, 2006-03) Momeni, Babak ; Huang, Jiandong ; Soltani, Mohammad ; Askari, Murtaza ; Mohammadi, Saeed ; Rakhshandehroo, Mohammad ; Adibi, Ali
    Here, we demonstrate a compact photonic crystal wavelength demultiplexing device based on a diffraction compensation scheme with two orders of magnitude performance improvement over the conventional superprism structures reported to date. We show that the main problems of the conventional superprism-based wavelength demultiplexing devices can be overcome by combining the superprism effect with two other main properties of photonic crystals, i.e., negative diffraction and negative refraction. Here, a 4-channel optical demultiplexer with a channel spacing of 8 nm and cross-talk level of better than -6.5 dB is experimentally demonstrated using a 4500 μm² photonic crystal region.
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    Observation of large parity-change-induced dispersion in triangular-lattice photonic crystal waveguides using phase sensitive techniques
    (Georgia Institute of Technology, 2006-02) Huang, Jiandong ; Reinke, Charles M. ; Jafarpour, Aliakbar ; Momeni, Babak ; Soltani, Mohammad ; Adibi, Ali
    We experimentally studied W1 triangular-lattice photonic crystal waveguides (PCWs) fabricated on semiconductor-on-insulator substrates using phase-sensitive lock-in techniques. In addition to the improved signal-to-noise ratio for power transmission measurements, we observed two large group delay peaks at frequencies corresponding to the photonic mode gap and parity changes of Bloch modes inside the PCWs.
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    Nonlinear finite-difference time-domain method for the simulation of anisotropic, chi((2)), and chi((3)) optical effects
    (Georgia Institute of Technology, 2006-01) Reinke, Charles M. ; Jafarpour, Aliakbar ; Momeni, Babak ; Soltani, Mohammad ; Khorasani, Sina ; Adibi, Ali ; Xu, Yong ; Lee, Reginald K.
    A two-dimensional (2-D) finite-difference timedomain (FDTD) code for the study of nonlinear optical phenomena, in which both the slowly varying and the rapidly varying components of the electromagnetic fields are considered, has been developed. The algorithm solves vectorial Maxwell’s equations for all field components and uses the nonlinear constitutive relation in matrix form as the equations required to describe the nonlinear system. The stability of the code is discussed and its effectiveness is demonstrated through the simulations of self-phase modulation (SPM) and second-harmonic generation (SHG). The authors also show that the combination of nonlinear effects with PCs can result in a significant improvement in device size and integrability, using the example of a Mach–Zehnder interferometer (MZI).