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Focal length measurement of a varifocal liquid lens with capacitance detection

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Abstract

This paper reports on a detailed deformation model of varifocal liquid lenses fabricated by Parylene-on-liquid-deposition (POLD), which can be applied to measure and adjust the focal length of such lenses without using extra sensors or sensing mechanisms. The lens was fabricated by encapsulating a liquid between a transparent electrode and a polymer film that was covered with a metal electrode. When voltage is applied to the two electrodes, the lens deforms due to the electrostatic force, and its focal length and the capacitance between the two electrodes change simultaneously. This characteristic enables the focal length of the lens to be adjusted and detected by measuring the capacitance change. The focal length of the fabricated varifocal liquid lens changed from 153.6 to 82.6 mm by applying 150-V. The focal length change of the liquid lens was calculated from the change in its capacitance. Finally, to confirm the efficiency of this varifocal liquid lens, we fabricated a confocal distance sensor using the lens for laser scanning and demonstrated that this system can be used to measure distances of 94–140 mm with an average error of 0.83 mm and a standard deviation of 0.77 mm.

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Acknowledgments

This work was supported by the Japan Science and Technology Agency (JST). The photomasks were made by using the University of Tokyo VLSI Design and Education Center’s (VDEC) 8-inch EB write F5112 + VD01 donated by ADVANTEST Corporation.

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Authors and Affiliations

  1. Department of Mechano-Informatics, Graduate School of Information Science and Technology, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan

    Kentaro Noda, Yusuke Takei, Tomoyuki Takahata & Isao Shimoyama

  2. Information and Robot Technology Research Initiative, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan

    Nguyen Binh-Khiem & Kiyoshi Matsumoto

  3. Room No. 81B, Eng. Bld. 2, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan

    Kentaro Noda, Nguyen Binh-Khiem & Yusuke Takei

  4. Room No. 81D3, Eng. Bld. 2, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan

    Tomoyuki Takahata, Kiyoshi Matsumoto & Isao Shimoyama

  5. Room No. 81D4, Eng. Bld. 2, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan

    Isao Shimoyama

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  1. Kentaro Noda
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  2. Nguyen Binh-Khiem
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  3. Yusuke Takei
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  4. Tomoyuki Takahata
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  5. Kiyoshi Matsumoto
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  6. Isao Shimoyama
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Correspondence to Kentaro Noda.

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Noda, K., Binh-Khiem, N., Takei, Y. et al. Focal length measurement of a varifocal liquid lens with capacitance detection. Appl. Phys. B 115, 69–76 (2014). https://doi.org/10.1007/s00340-013-5574-3

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  • DOI: https://doi.org/10.1007/s00340-013-5574-3

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