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Fabrication of 3D polymer photonic crystals for near-IR applications
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Paper Abstract

Photonic crystals[1, 2] have stirred enormous research interest and became a growing enterprise in the last 15 years. Generally, PhCs consist of periodic structures that possess periodicity comparable with the wavelength that the PhCs are designed to modulate. If material and periodic pattern are properly selected, PhCs can be applied to many applications based on their unique properties, including photonic band gaps (PBG)[3], self-collimation[4], super prism[5], etc. Strictly speaking, PhCs need to possess periodicity in three dimensions to maximize their advantageous capabilities. However, many current research is based on scaled two-dimensional PhCs, mainly due to the difficulty of fabrication such three-dimensional PhCs. Many approaches have been explored for the fabrication of 3D photonic crystals, including layer-by-layer surface micromachining[6], glancing angle deposition[7], 3D micro-sculpture method[8], self-assembly[9] and lithographical methods[10-12]. Among them, lithographic methods became increasingly accepted due to low costs and precise control over the photonic crystal structure. There are three mostly developed lithographical methods, namely X-ray lithography[10], holographic lithography[11] and two-photon polymerization[12]. Although significant progress has been made in developing these lithography-based technologies, these approaches still suffer from significant disadvantages. X-ray lithography relies on an expensive radiation source. Holographic lithography lacks the flexibility to create engineered defects, and multi-photon polymerization is not suitable for parallel fabrication. In our previous work, we developed a multi-layer photolithography processes[13, 14] that is based on multiple resist application and enhanced absorption upon exposure. Using a negative lift-off resist (LOR) and 254nm DUV source, we have demonstrated fabrication of 3D arbitrary structures with feature size of several microns. However, severe intermixing problem occurred as we reduced the lattice constant for near-IR applications. In this work, we address this problem by employing SU8. The exposure is vertically confined by using a mismatched 220nm DUV source. Intermixing problem is eliminated due to more densely crosslinked resist molecules. Using this method, we have demonstrated 3D "woodpile" structure with 1.55μm lattice constant and a 2mm-by-2mm pattern area.

Paper Details

Date Published: 6 February 2008
PDF: 9 pages
Proc. SPIE 6883, Advanced Fabrication Technologies for Micro/Nano Optics and Photonics, 688313 (6 February 2008); doi: 10.1117/12.768698
Show Author Affiliations
Peng Yao, Univ. of Delaware (United States)
Liang Qiu, Univ. of Delaware (United States)
Shouyuan Shi, Univ. of Delaware (United States)
Garrett J. Schneider, Univ. of Delaware (United States)
Dennis W. Prather, Univ. of Delaware (United States)
Ahmed Sharkawy, EM Photonics, Inc. (United States)
Eric Kelmelis, EM Photonics, Inc. (United States)

Published in SPIE Proceedings Vol. 6883:
Advanced Fabrication Technologies for Micro/Nano Optics and Photonics
Thomas J. Suleski; Winston V. Schoenfeld; Jian Jim Wang, Editor(s)

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