Rapid fabrication of two- and three-dimensional photonic crystals using multiple-exposure of two-beam interference pattern technique

摘要

A simple optical interference method for fabricating two- and three-dimensional (2D and 3D) periodical structures is theoretically and experimentally demonstrated. Multiple-exposure of two-beam interference pattern into a photopolymerizable resist creates high quality 2D or 3D microstructures. The type of periodic structure depends on the orientation of the photoresist with respect to the laser beams and the number of exposure. Square or hexagonal structures are obtained by choosing an angle of 90° or 60°, respectively, between two different exposures. 2D structures are obtained with two or three equal exposures. 3D structures with different types (bcc, fcc, Woodpile, etc.) are obtained with three or four exposures and appropriate rotation angles. This method presents many advantages over others using multi-beam (three-, four-, or five-beam) interference: ⅰ) easy to fabricate different structures (hexagonal or square) by simply rotating the sample, ⅱ) best contrast between the minimal and maximal intensities of interference pattern due to the identical polarization of two laser beams in the interference area, ⅲ) in particular, 3D periodical structures have the same period in three dimensions, which can't be obtained by one exposure of multi-beam interference. The experimental results obtained with SU-8 negative photoresist are well in agreement with the theoretical predictions. Such fabrication technique can be useful for applications in photonic crystals research.