3D Photonic Crystals Fabricated by Micromanipulation Technique
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3D Photonic Crystals Fabricated by Micromanipulation Technique Kanna Aoki1, Hideki T. Miyazaki2, Hideki Hirayama1, Kyoji Inoshita3, Toshihiko Baba3, Norio Shinya2, and Yoshinobu Aoyagi1 1 Semiconductors Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan 2 National Institute for Material Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan 3 Yokohama Natl. Univ., 79-5 Tokiwadai, Hodogaya-ku, Yokohama, Kanagawa 240-8501, Japan ABSTRACT Three-dimensional (3D) photonic crystals with one to four layers of woodpile structures have been fabricated by stacking two-dimensional (2D) photonic plates by micromanipulation. First, air-bridge photonic plates were fabricated as unit structures using conventional IC processing techniques. Then, the 2D photonic plates were stacked using a micromanipulation system. To obtain lattices with precise periodicity, microspheres were inserted into the round openings which were prepared in the frame of the plates. Since neighboring plates have pore openings at the same position, plates were laminated at the proper position automatically. Consequently, positioning error was kept within 50 nm. Optical characteristics of the crystals were evaluated by their reflectance and transmittance at wavenumber between 700 and 7000 cm-1. The formed photonic crystals were expected to have a photonic band gap at around 3030 cm-1. As the number of layers was increased, the reflectance at around 3030 cm-1 increased to 60 %, and the transmittance at the same wavelength region decreased to 30 %. INTRODUCTION As a material for photonic crystal devices, three-dimensional (3D) structures are desirable since such materials can control the flow of light tridimensionally. However, most efforts are aimed at two-dimensional (2D) photonic devices since the realization of intricate 3D structures is far beyond the current fine structure processing technologies. Thus, there are yet no decisive 3D crystal fabrication techniques for optical communication wavelengths. Currently, 3D photonic crystals are fabricated by tridimensional dry etching [1], colloidal precipitation [2, 3], or layer-by-layer techniques [4-7]. All of these techniques are effective for fabricating defect-free crystals rather than designing flexible crystals, which is a prerequisite for the realization practical photonic devices. In our method, 2D photonic plates, which serve as unit components for 3D crystals, are prepared by conventional IC processing techniques. Then, those plates are assembled by micromanipulation. To achieve the correct lamination of each layer, fiducial holes with a diameter corresponding to twice the thickness of the plate, are prepared in the frame of plates, and spheres with a diameter equal to that of the holes are inserted into the holes as stoppers. Since neighboring plates have fiducial holes in the same position, layers are automatically fixed at the proper position by inserting spheres into the holes. Compared to the aforementioned techniques, our technique possesses the following advantages. 1. A sufficient nu
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