An optical drill for the fabrication of photonic crystals

An optical drill is proposed for the nanofabrication of three-dimensional (3D) (diamond-like) lattices in positive photoresists, thereby opening a way towards 3D photonic crystals at optical wavelengths. Basically, an ensemble of coherent light beams is used to produce a holographic pattern in a photoresist of strongly nonlinear response. Multiple exposures are then performed for different phase shifts of one (several) of the beams. By doing this, not only are atomic bonds simulated with the spatial shift of the holographic pattern, but also the interconnections allow the resist development after exposure. An experimental demonstration is shown in a 2D case where three diffracted beams originating from the same UV Ar+ laser are combined to create a triangular lattice of circular holes. Results are given for various phase shifts of one of the diffracted beams and for different exposure times of the photoresist. The extension to the four laser beam case necessary for the fabrication of 3D structures is discussed.