Fabrication of Three-Dimensional Photonic Crystal by Wafer Fusion Approach
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Fabrication of Three-Dimensional Photonic Crystal by Wafer Fusion Approach Noritsugu Yamamoto2, 3, Katsuhiro Tomoda1, and Susumu Noda1, 3 1
Dept. of Electronic Science and Engineering, Kyoto University, Yoshidahonmachi, Sakyo-ku, Kyoto 606-8501, Japan 2 Research Institute of Photonics, National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 2, 1-1-1, Umezono, Tsukuba 303-8568, Japan 3 Core Research for Evolution Science and Technology (CREST), Japan Science and Technology Corporation (JST) ABSTRACT Based on a set of requirements identified for photonic crystals intended for use in optoelectronic devices, we have developed a method of fabricating three-dimensional photonic crystals that involves stacking air/semiconductor gratings by wafer fusion approach. Precise alignment of the stacked layers is achieved through the use of a laser beam assisted very precise alignment system, and three-dimensional photonic crystal has been successfully fabricated for the infrared and optical communication wavelength regions. We have also developed a photonic crystal waveguide providing sharp 90° bend. INTRODUCTION Photonic crystals, new optical materials with a periodic dielectric structure, have attracted great interest. The periodic structure of these crystals creates a periodic variation in refractive index, forming a band structure in terms of photon energy and wavevector [1-4]. The dispersion relation in the crystal has strong nonlinearity, unlike ordinary optical materials; photonic crystals are characterized by a photonic bandgap in which all electromagnetic wave propagation for all wave vectors is blocked. Various scientific and engineering applications, such as control of spontaneous emission, zero-threshold lasing, and sharp bending of light are expected to be developed using photonic bandgaps and artificially introduced defects. To make the best use of the potential of photonic crystals, the crystals should satisfy the following conditions: (i) crystals should be three-dimensional photonic crystals with a complete photonic bandgap, (ii) there should be the possibility of introducing defects at an arbitrary position or (iii) introducing light-emitting elements, and (iv) crystals should have high electrical conductivity, which is important for actual device applications. Specific functional devices, such as two-dimensional surface-emitting photonic crystal lasers and add-drop filter waveguides can be realized using two-dimensional photonic crystal membranes [4, 5], which satisfy not all of the above conditions. However, for the most advanced applications such as spontaneous emission control and ultrasmall optical integrated circuits, the crystal must satisfy the above conditions. A number of approaches to fabricate three-dimensional photonic crystals have been proposed, including the use of self-assembled colloidal crystal (artificial opal), GaAs-based three-axis dry-etched crystal, and silicon-based layer-by-layer crystal with a woodpile structure [6-8]. However, all these techniques have d
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