Biomedical subjects

Hwi Kim

Publications and source records attributed to Hwi Kim.

5 recordsLinked to original sources

PubMed2006

Real-time digital holographic beam-shaping system with a genetic feedback tuning loop.

A novel implementation of a real-time digital holographic system with a genetic feedback tuning loop is proposed. The proposed genetic feedback tuning loop is effective in encoding optimal phase holograms on a liquid-crystal spatial light modulator in the system. Optimal calibration of the liquid-crystal spatial light modulator can be achieved via the genetic feedback tuning loop, and the optimal phase hologram can then overcome the aberration of the internal optics of the system.

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PubMed2006

Pseudo-Fourier modal analysis on dielectric slabs with arbitrary longitudinal permittivity and permeability profiles.

A pseudo-Fourier modal analysis method for analyzing finite-sized dielectric slabs with arbitrary longitudinal permittivity and permeability profiles is proposed. In the proposed method, the permittivity and permeability profiles are represented by the Fourier expansion without using the conventional staircase approximation. The total electromagnetic field distribution inside a dielectric slab is a linear superposition of extracted pseudo-Fourier eigenmodes with specific coupling coefficients selected to satisfy given boundary conditions. The proposed pseudo-Fourier modal analysis method shows excellent agreement with the conventional rigorous coupled-wave analysis with the S-matrix method.

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PubMed2005

Optimal nonmonotonic convergence of the iterative Fourier-transform algorithm.

The increase of the monotonic convergence rate is an important issue for iterative Fourier-transform algorithms. However, the steepest monotonic convergence of the iterative Fourier-transform algorithm does not always promise an optimal solution in the design of a diffractive optical element. The optimal nonmonotonic convergence of the iterative Fourier-transform algorithm is investigated by employing a microgenetic algorithm. The proposed hybrid scheme of the iterative Fourier-transform algorithm and the microgenetic algorithm show nonmonotonic convergence, and this results in a superior design.

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PubMed2004

Filter characteristics of a chirped volume holographic grating.

We compare and analyze the filter properties of transmission-type volume holographic gratings, especially the dispersion characteristics for uniform and chirped gratings. It is theoretically and experimentally shown that the dispersion characteristics can be controlled by introducing one-dimensional chirping to the volume grating in a photorefractive crystal. The filter response including output power and dispersion comes from a combined effect of the spatial spectra of the grating structure, input beam, and output-coupling fiber mode. Filter responses can be designed by controlling these parameters for optical communication applications.

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PubMed2004

Iterative Fourier transform algorithm with regularization for the optimal design of diffractive optical elements.

There is a trade-off between uniformity and diffraction efficiency in the design of diffractive optical elements. It is caused by the inherent ill-posedness of the design problem itself. For the optimal design, the optimum trade-off needs to be obtained. The trade-off between uniformity and diffraction efficiency in the design of diffractive optical elements is theoretically investigated based on the Tikhonov regularization theory. A novel scheme of an iterative Fourier transform algorithm with regularization to obtain the optimum trade-off is proposed.

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