skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Design of Photonic Crystal Pixels using Guided Semi-Natural Genetic Optimization.

Abstract

Abstract not provided.

Authors:
; ; ; ;
Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1141513
Report Number(s):
SAND2007-2120C
506887
DOE Contract Number:
AC04-94AL85000
Resource Type:
Conference
Resource Relation:
Conference: Proposed for presentation at the Photonic and Electromagnetic Crystal Structures (PECS) VII held April 8-11, 2007 in Monterey, CA.
Country of Publication:
United States
Language:
English

Citation Formats

El-Kady, Ihab F, Rammohan, R. R., Farfan, G. B., Su, Mehmet F., and Taha, M. R. Design of Photonic Crystal Pixels using Guided Semi-Natural Genetic Optimization.. United States: N. p., 2007. Web.
El-Kady, Ihab F, Rammohan, R. R., Farfan, G. B., Su, Mehmet F., & Taha, M. R. Design of Photonic Crystal Pixels using Guided Semi-Natural Genetic Optimization.. United States.
El-Kady, Ihab F, Rammohan, R. R., Farfan, G. B., Su, Mehmet F., and Taha, M. R. Sun . "Design of Photonic Crystal Pixels using Guided Semi-Natural Genetic Optimization.". United States. doi:. https://www.osti.gov/servlets/purl/1141513.
@article{osti_1141513,
title = {Design of Photonic Crystal Pixels using Guided Semi-Natural Genetic Optimization.},
author = {El-Kady, Ihab F and Rammohan, R. R. and Farfan, G. B. and Su, Mehmet F. and Taha, M. R.},
abstractNote = {Abstract not provided.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Apr 01 00:00:00 EDT 2007},
month = {Sun Apr 01 00:00:00 EDT 2007}
}

Conference:
Other availability
Please see Document Availability for additional information on obtaining the full-text document. Library patrons may search WorldCat to identify libraries that hold this conference proceeding.

Save / Share:
  • Abstract not provided.
  • An algorithm to correct for constant attenuation in SPECT is derived from the singular value decomposition (SVD) of a discrete representation of the exponential Radon transform using natural pixels. The algorithm is based on the assumption that a continuous image can be obtained by backprojecting the discrete array q, which is the least squares solution to Mq = p, where p is the array of discrete measurements, and the matrix M represents the composite operator of the backprojection operator A*[sub [mu]] followed by the projection operator A[sub [mu]]. A singular value decomposition of M is used to solve the equationmore » Mq = p, and the final image is obtained by sampling the backprojection of the solution q at a discrete array of points. Analytical expressions are given to calculate the matrix elements of M that are integrals of exponential factors over the overlapped area of two projection strip functions (natural pixels). A spectral analysis of the exponential Radon transform is compared with that of the Radon transform. The condition number of the spectrum increases with increased attenuation coefficient, which correlates with the increase in statistical error propagation seen in clinical images obtained with low-energy radionuclides. Computer simulations using 32 projections sampled over 360 degrees show an improvement in the SVD reconstruction over the convolution backprojection reconstruction, especially when the projection data is corrupted with noise.« less
  • A new two-dimensional photonic crystal (2D PC) slab structure was created with a full three-dimensional light confinement. Guided modes with broad bandwidth and high transmission within the band gap are also observed. As an optical analog to electronic crystals, PC promises a revolution in the photonic world similar to the electronic revolution created by the electronic band gap engineering in semiconductor. 2D PC has an advantage of being easier to fabricate at optical wavelength ({lambda}) comparing with 3D PC. However, the light leakage in the vertical direction has been the main problem for using 2D PC in opto-electronic application. Inmore » this study, the authors solve this problem by combining traditional 2D PC with strong vertical index guiding between the waveguide layer (GaAs) and the cladding layer (Al{sub x}O{sub y}). A set of triangular lattice holes 2D PC's were fabricated with lattice constant a=460nm, hole diameter (d=0.6a) and waveguide layer thickness (t = 0.5a). Those parameters were chosen to maximize the TE photonic band gap (PBG) around {lambda} = 1.55{micro}m. The depth of etched holes is {approximately}0.6{micro}m and the 2{micro}m thick Al{sub x}O{sub y} cladding layer is obtained by thermal oxidation of Al{sub 0.9}Ga{sub 0.1}As. PC waveguides were also created by introducing line defects along {Gamma}K direction. The authors perform transmission measurement by coupling light to PC with 3{micro}m wide waveguides which extends {approximately}0.6mm on both sides of PC. An aspheric lens with NA = 0.4 is used to focus the collimated light from tunable diode laser into the input waveguide. Another identical lens is used to collect the transmitted light and focus to an infrared (IR) camera and a calibrated photo-detector with a beamsplitter. The Gaussian waveguide mode indicates that the signal detected by the photodetector comes only from the light interacting with PC and propagating along the waveguide. The absolute transmittance is obtained by normalizing the transmission with a reference measured with a nominally identical waveguide without PC.« less
  • A major limitation in tomographic inverse problems is inadequate computation speed, which frequently impedes the application of engineering ideas and principles in medical science more than in the physical and engineering sciences. Medical problems are computationally taxing because a minimum description of the system often involves 5 dimensions (3 space, 1 energy, 1 time), with the range of each space coordinate requiring up to 512 samples. The computational tasks for this problem can be simply expressed by posing the problem as one in which the tomograph system response function is spatially invariant, and the noise is additive and Gaussian. Undermore » these assumptions, a number of reconstruction methods have been implemented with generally satisfactory results for general medical imaging purposes. However, if the system response function of the tomograph is assumed more realistically to be spatially variant and the noise to be Poisson, the computational problem becomes much more difficult. Some of the algorithms being studied to compensate for position dependent resolution and statistical fluctuations in the data acquisition process, when expressed in canonical form, are not practical for clinical applications because the number of computations necessary exceeds the capabilities of high performance computer systems currently available. Reconstruction methods based on natural pixels, specifically orthonormal natural pixels, preserve symmetries in the data acquisition process. Fast implementations of orthonormal natural pixel algorithms can achieve orders of magnitude speedup relative to general implementations. Thus, specialized thought in algorithm development can lead to more significant increases in performance than can be achieved through hardware improvements alone.« less
  • The spatially varying geometric response of the collimator-detector system in SPECT produces loss in resolution in addition to shape distortions, reconstructed density non-uniformity, and quantitative inaccuracies. A projection space image reconstruction with projectors that use strip functions to calculate pixels more {open_quotes}natural{close_quotes} for modeling the geometric response of the SPECT collimator is used to correct these reconstruction artifacts. Two projection models were evaluated for modeling the system geometric response function. For one projector each strip is of equal weight, whereas for the other a Gaussian weighting is used. Fan beam projection of a physical Hoffman brain phantom was used tomore » evaluate the geometric response correction. Reconstructions produced by the two proposed projectors showed improved resolution when compared against a unit-strip {open_quotes}natural{close_quotes} pixel model and the filtered backprojection algorithm.« less