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Proceedings Paper

Micro diffraction lenses with subwavelength structures designed by the genetic algorithm
Author(s): Tatsuya Shirakawa; Kenichi L. Ishikawa; Shuichi Suzuki; Yasufumi Yamada; Hiroyuki Takahashi
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Paper Abstract

We design subwavelength structure (SWS) micro diffraction lenses by a method based on the finite-difference timedomain (FDTD) method and the genetic algorithm (GA). By using this GA-FDTD method, we designed lenses with binary subwavelength structures whose grating width is 100 nm at least and grating aspect ratio is 5 at most. The material refractive index, and lens radius are 2.1466 at 660 nm and 4.0 ìm, respectively. The focusing efficiency (59.3 %) of the obtained structure at 660 nm at a focal distance of 8.3 ìm is close to that of the Fresnel lens (70.4 %) and is more than twice as high as that (28.0 %) previously reported based on direct binarization of the Fresnel lens. The optimized grating height (400 nm) is different from that of the usual Fresnel lens (576 nm), and the relation between the widths of neighboring gratings cannot be expressed in a simple way. Also, the designed lens turns out to be robust against fabrication error. Furthermore, we have designed a lens with equal focal length of 8.3 ìm at three different wavelengths (660, 532, and 445 nm). The structures, which are not intuitive, are hard to deduce from experiences. These results indicate the effectiveness of the GA-FDTD method in the design of SWS diffractive optical elements.

Paper Details

Date Published: 25 February 2010
PDF: 10 pages
Proc. SPIE 7597, Physics and Simulation of Optoelectronic Devices XVIII, 75970S (25 February 2010); doi: 10.1117/12.837449
Show Author Affiliations
Tatsuya Shirakawa, Univ. of Tokyo (Japan)
Kenichi L. Ishikawa, Univ. of Tokyo (Japan)
Shuichi Suzuki, Ricoh Co., Ltd. (Japan)
Yasufumi Yamada, Ricoh Co., Ltd. (Japan)
Hiroyuki Takahashi, Univ. of Tokyo (Japan)

Published in SPIE Proceedings Vol. 7597:
Physics and Simulation of Optoelectronic Devices XVIII
Bernd Witzigmann; Fritz Henneberger; Yasuhiko Arakawa; Marek Osinski, Editor(s)

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