Photonic Crystal Templates Obtained by Two-Photon Laser Lithography in Photoresist SU-8
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Photonic Crystal Templates Obtained by Two-Photon Laser Lithography in Photoresist SU-8 Vygantas Mizeikis, Kock Khuen Seet, Saulius Juodkazis, Vygandas Jarutis, and Hiroaki Misawa Core Research for Evolutionary Science and Technology - Japan Science and Technology Corporation, Research Institute for Electronic Science, Hokkaido University, CRIS building, N21 W10 Kita-ku Sapporo 001-0021, Japan
ABSTRACT High quality templates of three-dimensional photonic crystals were fabricated in photoresist SU-8 using femtosecond laser lithography. The templates have woodpile and spiral architectures, which are widely expected to yield spectrally wide and robust photonic band gaps. Their optical characterization reveals fundamental and higher-order photonic stop-gaps in the infrared wavelength range of 2.0-8.0 µm. These templates are mechanically stable, nearly free of shrinkage-related deformations, and can be used for subsequent infiltration by optically active or high refractive index materials. INTRODUCTION Photonic crystals are periodic dielectric structures which are expected to play important role in optics and optoelectronics due to their unique capabilities of controlling the emission and propagation of light via photonic band gap (PBG) effects [1,2]. These capabilities can be best exploited in three-dimensional (3D) photonic crystals. Since the direct, large scale 3D microfabrication of photonic crystals from semiconductors has proven to be tedious [3], cheaper and simpler fabrication strategies are highly demanded. Some of these strategies involve microfabrication of so-called photonic crystal templates using more feasible techniques and materials [4,5]. The templates can be subsequently infiltrated by other materials having higher refractive index [6,7]. Two-photon laser lithography by direct laser writing (DLW) is a promising method for the realization of large-scale 3D photonic crystals and their templates with submicrometric resolution. Here we demonstrate fabrication by DLW of photonic crystals belonging to two distinct classes. The first of them, well-known woodpile structure [8], which is widely popular due to the possibility of a simple layer-by-layer buildup, and due to its diamond-like architecture known for its tendency to open spectrally wide PBGs. The second class of structures whose spiral architecture [9], though not amenable to layer-by-layer fabrication, is easy to obtain by DLW, and has PBG properties even more pronounced than those of the woodpile structures. Self-supporting 3D samples of both architectures were recorded in negative photoresist SU-8 by a focused beam of a femtosecond laser. The samples are demonstrated to be negligibly affected by deformations due to the polymer shrinkage and to show the signatures of photonic stop-gaps at infrared wavelengths.
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EXPERIMENTAL DETAILS The setup for 3D laser lithography is shown in Fig. 1 (a). The light source used was a femtosecond amplified Ti:Sapphire laser system Hurricane X (Spectra-Physics) with pulse length ∆τpulse=130 fs, cen
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