Abstract
Crossed 1D patterning allows to generate regular 2D optical microstructures like refractive microlens arrays with high fill factors which are of interest for photonics and laser applications (image sensing / processing, coupling, beam shaping, mode selection [1]). In general, a surface can be treated sequentially or simultaneously by (a) subtractive, (b) additive or (c) modifying processes thus forming a deepened or elevated relief or a periodically changed refractive index. Type (a) has been published for excimer laser ablation by means of crossed linear scans with laser spots or contour masks [2] and by direct writing laser lithography with two subsequent (crossed) exposures by linear intensity arrays followed by a tranfer into the substrate by ion etching [3]. Problems emerge from the unwanted deposition of debris, nonlinearities and the necessary control of the laser beam quality during a sufficiently long time. A well-known approach is the holographic method of Cowan [4,5] with three beam interference in a recording photoresist medium. By this method, high-definition, replicable hexagonal hole arrays with extremely small element diameters have been found. On the other hand, the set-up is not flexible enough for a fast change of the geometry and requires a proper adjustment, a homogeneous beam and the knowledge of the nonlinearities. Direct changes of the refractive index (e.g. in photorefractive media) can be used for a process of type (b). We report on an alternative, relatively simple technology of type (c) for the fabrication of close-packed arrays (orthogonal, hexagonal) based on the crossed vapour deposition which is preferentially suitable for moderate microlens parameters (pitches, focal lengths).
© 1996 Optical Society of America
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