METHOD OF MANUFACTURING A MOULD FOR USE IN THE MANUFACTURE OF AN OPTICAL ELEMENT COMPRISING OPTICAL SUB-ELEMENTS MUTUALLY ARRANGED IN A PATTERN AND DEVICE FOR IMPLEMENTING SUCH A METHOD

A method of manufacturing an optical element ( 69, 149, 171, 203, 225 ) provided with mutually adjoining optical sub-elements ( 71, 155, 193, 219, 241 ) which are mutually arranged in a pattern such as, for example, a microlens array ( 69, 171, 203 ) with a two-dimensional orthogonal or hexagonal matrix of spherical lenses ( 71, 193, 219 ) or a faceted lens ( 149, 225 ) with a two-dimensional orthogonal matrix of facets ( 155, 241 ). According to the method, the optical element ( 69, 149, 171, 203, 225 ) is manufactured by means of a mould ( 7, 147 ) by a replication technique. The mould ( 7, 147 ) is manufactured from a ductile metal and is given a mould shape ( 83, 161 ) which corresponds to the pattern of sub-elements ( 71, 155, 193, 219, 241 ) by means of a die ( 65, 129 ) having a die surface ( 67, 131 ) which corresponds to the optical sub-element ( 71, 155, 193, 219, 241 ) and which is imprinted in the mould ( 7, 147 ) with a predetermined force in consecutive positions in accordance with the pattern. Preferably, the mould ( 7, 147 ) is provided with a surface smoothness desired for the optical element ( 69, 149, 171, 203, 225 ) before the mould shape ( 83, 161 ) is provided. The optical elements ( 69, 149, 171, 203, 225 ) manufactured by the method have a particularly high dimensional accuracy and a particularly large optically useful surface area. A device ( 1, 95 ) for implementing a method according to the invention comprises a workpiece holder ( 3 ) for fastening the mould ( 7, 147 ) to be manufactured, a tool holder ( 45, 91 ) for fastening the die ( 65, 129 ), and a positioning device ( 11 ). The tool holder ( 45, 91 ) comprises a straight guide ( 53 ) which is displaceable relative to the workpiece holder ( 3 ) by means of the positioning device ( 11 ), and a die holder ( 57, 93 ) which is guided with sliding possibility relative to the straight guide ( 53 ) and which bears on a stop ( 63 ) of the straight guide ( 53 ) under the influence of a predetermined elastic pretensioning force. A microlens array ( 171 ) manufactured by the method is used in a picture display device ( 169 ) which is provided with a liquid crystal display panel ( 181 ). Another microlens array ( 203 ) manufactured by the method is used in a solid state image sensor device ( 207 ) provided with a semiconductor body ( 209 ) with a charge coupled device ( 215, 217 ) and a pattern of image sensor elements ( 213 ). A faceted lens ( 225 ) manufactured by the method is used i