Fast fabrication of polymer out-of-plane optical coupler by gray-scale lithography

A lithographic method for making an out-of-plane optical coupler, comprising:

• forming a photoresist layer of positive photoresist material over a substrate;
• flood exposing the positive photoresist layer to light through a binary mask to pattern a latent image of a mirror blank in the photoresist layer, the positive photoresist layer having a nonlinear response to laser power over a range of dosages of laser power such that within that range a nonlinear removal rate arises in which a removal rate of the positive photoresist material increases as an applied dosage of laser power decreases;
• applying controlled dosages to the mirror blank by scanning a laser beam over the latent image of the mirror blank only a plurality of times only along a single scanning line at a single fixed distance from an edge of the mirror blank, the laser beam having an intensity profile within a region that is nonlinear such that within that region the controlled dosage has a controlled nonlinear dosage profile, the scanning balancing the controlled nonlinear dosage profile and the nonlinear removal rate of the positive photoresist material to thereby form a latent image of a planar mirror surface that is oriented at a prescribed non-zero angle to a plane in which the substrate extends;
• and
• developing the positive photoresist material so that a remaining portion of the developed positive photoresist material forms an out-of-plane optical coupler having a planar mirror surface that is oriented at the prescribed angle.