Design and Fabrication of Ball Type Microlens Array

• Main Authors: Ying-Ruei Huang, 黃英叡
• Other Authors: Hwai-Pwu Chou
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/71990280838168427031

碩士 === 國立清華大學 === 工程與系統科學系 === 91 === This paper presents a ball type microlens array for optcal fiber coupling. In contrast to conventional microlenses made in a half-spherical geometry, the ball type microlens is a sphere which allows light focusing in all directions on the substrate surface and thus provides the flexibility for fiber coupling in applications of optical communication, optical storage system, and biomedical instruments. The present microlens is made of photoresist SU-8. We have developed a low temperature batch process by spin-coating SU-8 on a silicon wafer. The thick SU-8 film is patterned by UV lithography to form an array of holes for holding micro-balls. Bulk machining is then applied to formulate an array of nozzles on the wafer. Molten SU-8 is poured onto the wafer and pressed through the nozzle. Micro-balls are formed by a balance between surface tension and cohesion. The diameter of balls is controlled by varying the amount of SU-8 pressed through the nozzle. In the experimental stage, we have formulated a pattern for a 24 x 24 lens array and can produce micro-balls with numerical aperture about 0.63. Diameters range from 80 to 500μm and focal lengths range from 50 to 300μm. Measurements indicated that the fluctuation of the diameter was within 3%; variations among batches are within 10%. The major contribution to the uncertainty is due to the variation of the pressing force.