Optically variable micro-mirror arrays fabricated by graytone lithography

The fabrication of micro-mirror based portrait and non-portrait images has been demonstrated by graytone lithography. The depiction of a portrait image was achieved by a novel modulation of the width of micro-apertures in the variable transparency mask. The non-portrait image was encoded as micro-mirrors of an opposing slope and orientation. An optical switch effect between the portrait and a non-portrait image was encoded into the mask by the arrangement of the micro-mirrors as a separate interleaved channel for each image. The lithographic exposure of the pattern into a layer of thick resist has produced an array of micro-mirrors with a depth of 10–30 μm. Various configurations of the micro-mirror arrays have been examined in relation to the type of micro-apertures and their orientation. Optically variable effects achieved in the micro-mirror devices have included a portrait to non-portrait switch, a positive to negative image switch and a non-portrait to non-portrait image switch. The micro-mirror structures have been hot embossed into polypropylene sheet using a Ni shim to create high quality optically variable images.