Patent ID: 6835535
Filing Date: 2004-12-28
Classification: G02B,H01L,Y10S

Abstract:
A method for producing a microlens array, said microlens array having a surface configuration having peaks and valleys and comprising a plurality of unit cells and a plurality of microlenses, one microlens per unit cell, said method comprising:(a) providing a positive photoresist; (b) exposing the positive photoresist with a laser beam having a finite beam width at the photoresist of less than the transverse size of any of the microlenses being formed, said exposing being performed using a direct laser writing process which employs relative movement between the finite beam width of the laser beam and the positive photoresist to form a latent image in the photoresist; (c) developing the latent image to form a photoresist master, said photoresist master having a surface configuration which is substantially the negative of the surface configuration of the microlens array; and (d) using the photoresist master to: (i) produce the microlens array, and/or (ii) produce a further master used to form the microlens array, said further master having a surface configuration which is substantially the negative of the surface configuration of the microlens array; wherein:(A) said microlens array comprises only convex microlenses at adjacent unit cells so that the photoresist master and the further master if produced comprises only concavities at adjacent unit cells; (B) the microlens array has a focusing efficiency greater than 50 percent; and (C) the microlens array would have a focusing efficiency of 50 percent or less if prepared by the same direct laser writing process using the same laser beam with the same finite beam width at the photoresist but with the photoresist master being written so as to comprise convexities at adjacent unit cells rather than concavities.