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Optical system with off-axis holographic lens group for fabricating large-size photonic crystals

In this paper, we propose an improved hologrpahic technique for fabricating 2D hexagonal and 3D hexagonal packed photonic crystals (PhCs). The key element in the fabrication system is an off-axis holographic lens group (OHLG) consisting of three off-axis holographic lenses. Under the illumination of an expanded laser beam, three collimated beams can be generated by the OHLG to form a uniform hexagonal lattice pattern without using a collimating lens. The utilization of OHLG in the system eliminates the noise in the interference pattern resulted from the collimating lens so that lattice quality is enhanced. The system is simple and stable and can be used to fabricate large-size PhCs.