Semiellipsoid microlens fabrication method using the lift-off and alignment exposure processes

We present a new semiellipsoid microlens fabrication method using the lift-off and alignment exposure processes. The lift-off method is used to create an elliptical base before the thermal reflow process. During the photoresist thermal reflow process, the elliptical base can precisely define the bottom shape of the liquid photoresist, and fabricate the semiellipsoid microlens array with a large height and small radius of curvature. The prolate spheroid approximation method is developed to estimate the thickness of the elliptic photoresist column required by the semiellipsoid microlens of a certain height, with the error being controlled within ±3%. Electroforming technology is then used to convert the photoresist patterns into a metallic mold for a PDMS ellipsoidal microlens. The experiment results show that the geometries of a semiellipsoid microlens can be accurately defined by three parameters: the length of the major axis of the elliptical base, the length of the minor axis of the elliptical base and the thickness of the elliptical photoresist column. The proposed fabrication method facilitates mass production to achieve a high-yield and high-coupling semiellipsoid microlens that is suitable for use in commercial fiber transmission systems (paper)