| 1. |
- Karlholm, J
(författare)
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Generalizations of the maximum average correlation height filter
- 2000
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Ingår i: Journal of the Optical Society of America A. - 0740-3232. ; 17:8, s. 1399-1406
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Tidskriftsartikel (refereegranskat)abstract
- Recently several approaches have been presented in which the shape of the correlation peak is used to distinguish between target and clutter. The well-known maximum average correlation height (MACH) filter was specifically designed to produce similar correlation planes for target variations present in the training set. Results are presented of a study of certain generalizations of the MACH filter intended to enhance the performance in clutter. It is shown that by taking into account the nonoverlapping character of the background noise and focusing the MACH correlation plane similarity requirement to the peak neighborhood, it is possible to simultaneously achieve a small variation in correlation peak shape and high peak-to-sidelobe ratios for cluttered images. (C) 2000 Optical Society of America [S0740-3232(00)01508-8].
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| 2. |
- Burvall, Anna, 1976-, et al.
(författare)
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Elementary functions : Propagation of partially coherent light
- 2009
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Ingår i: Journal of the Optical Society of America A. - : Optical Society of America. - 0740-3232. ; 26:7, s. 1721-1729
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Tidskriftsartikel (refereegranskat)abstract
- The theory of propagation of partially coherent light is well known, but performing numerical calculations still presents a difficulty because of the dimensionality of the problem. We propose using a recently introduced method based on the use of elementary functions [Wald et al. Proc. SPIE6040, 59621G (2005)] to reduce the integrals to two dimensions. We formalize the method, describe its inherent assumptions and approximations, and introduce a sampling criterion for adequate interpolation. We present an analysis of some special cases, such as the Gaussian Schell-model beam, and briefly discuss generalized numerical propagation of two-dimensional field distributions.
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| 3. |
- Börjeson, Charlie, et al.
(författare)
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Implementing a non-4f relay system for Hartmann–Shack wavefront sensing
- 2022
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Ingår i: Journal of the Optical Society of America A. - : Optica Publishing Group. - 0740-3232 .- 1084-7529 .- 1520-8532. ; 40:6
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Tidskriftsartikel (refereegranskat)abstract
- Hartmann–Shack wavefront sensors (HSWSs) are used in many disciplines to measure optical aberrations. Conventionally, the wavefront of interest is transferred onto the lenslet array of the HSWS with a telescopic 4f relay system. However, the 4f relay design restricts the choice of focal lengths and distances used for the relay system. In this paper, we describe a non-4f variant and demonstrate both theoretically and experimentally that its wavefront relaying properties equal that of a 4f system. We also present an alignment method for conjugating the wavefront with the lenslet array of the HSWS for both 4f and non-4f systems.
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| 4. |
- Dai, Daoxin, et al.
(författare)
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Analysis of characteristics of bent rib waveguides
- 2004
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Ingår i: Journal of the Optical Society of America A. - 0740-3232. ; 21:1, s. 113-121
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Tidskriftsartikel (refereegranskat)abstract
- With a perfectly matched layer boundary treatment, a semivectorial finite-difference method is used to calculate the eigenmodes of a single-mode (SM) or multimode (MM) bent rib waveguide. A detailed analysis is given for the dependence of the bending losses (including the pure bending loss and the transition loss) on geometrical parameters of the bent rib waveguide such as the rib width, the rib height, and the bending radius. The characteristics of the higher-order modes are analyzed. It is shown that the bending loss of the fundamental mode can be reduced effectively by increasing the width and height of the rib. For an integrated device, undesired effects due to the higher-order modes of a MM bent waveguide can be removed by appropriate choice of the geometrical parameters. An appropriately designed MM bent waveguide is used to reduce effectively the bending loss of the fundamental mode, and a low-loss SM propagation in a MM bent waveguide is realized when the bending losses of the higher-order modes are large enough.
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| 5. |
- Edström, Per
(författare)
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Examination of the Revised Kubelka-Munk Theory : Considerations of Modeling Strategies
- 2007
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Ingår i: Journal of the Optical Society of America A. - 0740-3232. ; 24:2, s. 548-556
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Tidskriftsartikel (refereegranskat)abstract
- The revised Kubelka-Munk theory is examined theoretically and experimentally. Systems of dyed paper sheets are simulated, and the results are compared with other models. The results show that the revised Kubelka-Munk model yields significant errors in predicted dye-paper mixture reflectances, and is not self-consistent. The absorption is noticeably overestimated. Theoretical arguments show that properties in the revised Kubelka-Munk theory are inadequately derived. The main conclusion is that the revised Kubelka-Munk theory is wrong in the inclusion of the so-called scattering-induced-path-variation factor. Consequently, the theory should not be used for light scattering calculations. Instead, the original Kubelka-Munk theory should be used where its accuracy is sufficient, and a radiative transfer tool of higher resolution should be used where higher accuracy is needed.
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| 6. |
- Karlsson, Stefan, et al.
(författare)
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Multiscale complex moments of the local power spectrum
- 2007
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Ingår i: Journal of the Optical Society of America A. - Washington : Optical Society of America. - 0740-3232. ; 24:3, s. 618-625
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Tidskriftsartikel (refereegranskat)abstract
- Complex moments of the local power spectrum (CMP) are investigated in a multiscale context. The multiscale CMPs are shown to approximate well the 1D angular Fourier transform of the band in question. This observation is used to derive further properties of the power spectrum in terms of texture orientations or n-folded symmetry patterns. A method is presented to approximate the power spectrum using only separable filtering in the spatial domain. Interesting implications to the Gabor decomposition are shown. The number of orientations in the filter bank is related to the order of n-folded symmetry detectable. Furthermore, the multiscale CMPs can be estimated incrementally in the spatial domain, which is both fast and reliable. Experiments on power spectrum estimation, orientation estimation, and texture segmentation are presented.
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| 7. |
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| 8. |
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| 9. |
- Lundström, Linda, et al.
(författare)
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Population distribution of wavefront aberrations in the peripheral human eye
- 2009
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Ingår i: Optical Society of America. Journal A. - 1084-7529 .- 1520-8532. ; 26:10, s. 2192-2198
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Tidskriftsartikel (refereegranskat)abstract
- We present a population study of peripheral wavefront aberrations in large off-axis angles in terms of Zernike coefficients. A laboratory Hartmann-Shack sensor was used to assess the aberrations in 0 degrees, 20 degrees, and 30 degrees in the nasal visual field of 43 normal eyes. The elliptical pupil meant that the quantification could be done in different ways. The three approaches used were (1) over a circular aperture encircling the pupil, (2) over a stretched version of the elliptical pupil, and (3) over a circular aperture within the pupil (MATLAB conversion code given). Astigmatism (c(2)(2)) increased quadratically and coma (c(3)(1)) linearly with the horizontal viewing angle, whereas spherical aberration (c(4)(0)) decreased slightly toward the periphery. There was no correlation between defocus and angle, although some trends were found when the subjects were divided into groups depending on refractive error. When comparing results of different studies it has to be kept in mind that the coefficients differ depending on how the elliptical pupil is taken into consideration.
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| 10. |
- Lundström, Linda, et al.
(författare)
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Transformation of Zernike coefficients : scaled, translated, and rotated wavefronts with circular and elliptical pupils
- 2007
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Ingår i: Journal of the Optical Society of America A. - 0740-3232. ; 24:3, s. 569-577
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Tidskriftsartikel (refereegranskat)abstract
- Zernike polynomials and their associated coefficients are commonly used to quantify the wavefront aberrations of the eye. When the aberrations of different eyes, pupil sizes, or corrections are compared or averaged, it is important that the Zernike coefficients have been calculated for the correct size, position, orientation, and shape of the pupil. We present the first complete theory to transform Zernike coefficients analytically with regard to concentric scaling, translation of pupil center, and rotation. The transformations are described both for circular and elliptical pupils. The algorithm has been implemented in MATLAB, for which the code is given in an appendix.
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