Design and Fabrication of Compact Optical Devices:Organic Deformable Mirror and Microlens Arrays

• Main Authors: Hsin-Ta Hsieh, 謝欣達
• Other Authors: Guo-Dung Su
• Format: Others
• Language: en_US
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/79292171663560714349

博士 === 國立臺灣大學 === 光電工程學研究所 === 98 === We demonstrated the potential of wafer level optical components for compact optical systems by developing two micro optical components: organic deformable mirror (DM) and microlens arrays (MLA) which was fabricated by MEMS technology. In the development of organic deformable mirror, we fabricated a highly flexible polyimide membrane which has low Young’s modulus (<10 GPa) and low residual stress (<5 MPa, by choosing the CTE of membrane material, which matches to a silicon substrate). The incident light is reflected or focused by the Aluminum coating layer on the membrane. The optical power (diopter, m-1) of DM is curved and controlled by the gap-closing force results from the applied voltage between membrane (Aluminum coating) and bottom electrode pad. This polymer DM has advantages on large stroke and low applied voltage (~150 V achieved 20-diopters, lower voltage is possible). The fabricated DM could be integrated with other optical components for imaging applications. We show a thin 2M-pixels camera module with autofocus (AF) facility provided by DM rather than voice coil motor (VCM). The object position of clear image varies from 4 cm to infinity. In addition, we derived an analytic model, which predicts the optical power with required applied voltage according the material properties of membrane. Besides, an automatic system for measurement on Young’s modulus and residual stress was developed and implemented by a motorized stage, optical microscope, and image processing algorithm (Tenengrad). In microlens process, we developed two fabrication techniques. One is “boundary-confined method” which achieves high fill factor and small radius of curvature or high numerical aperture (NA) simultaneously. The height of microlens is 22 μm and the diameter is 48 μm, and the gap is 2 μm. In addition, the various curvature distribution (VCD) over microlenses in a MLA could be made based on this method. The other technique in microlens process extends the focal length of microlens by a covering Polydimethylsiloxane (PDMS) layer. The focal length of microlens with 240 μm diameter is extended to around 2.1 mm or 3 times larger than origin. It is longer than the maximum focal length of microlens, which is limited by the contact angle of photoresist and substrate in thermal reflow process. Therefore, designer could have more flexibility on the MLA design for specific applications. Finally, we believe this integration on MEMS technology and optical systems could inspire the researchers to develop compact and convenient optical systems which might benefit to the human.