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Variable-Focus Lens with 1-kHz Bandwidth


High-speed focusing is required in many application fields as a result of the recent development and widespread use of optical devices. For example, rapid axial scanning of the focal plane is important for confocal scanning microscopes to acquire three-dimensional information of objects at high speed. In these application fields, since millisecond-order scanning is required, we assume that 1-kHz bandwidth is adequate for our proposed high-speed focusing device.

However, no previous focusing mechanisms have yet attained a 1-kHz bandwidth. For example, the axial tracking mechanism of optical disks, which is one known fast-focusing system, has a first resonant frequency of around 100 Hz.

To solve this problem, we proposed a variable-focus lens with 1-kHz bandwidth. The lens transforms its shape rapidly using the liquid pressure generated by a piezo stack actuator. This mechanism also includes a built-in motion amplifier with high bandwidth to compensate for the short working range of the piezo stack actuator. Prototypes have been developed to validate the proposed design. A 1-kHz bandwidth of the lenses was confirmed by measuring the frequency responses. Refractive power ranging from -1/167 to 1/129 mm-1 and a maximum resolution of 12.3 cycles/mm were attained.

Photograph of the prototype of the 1-kHz high-speed focusing lens

Schematic figure of focusing mechanism


  1. Hiromasa Oku, Koichi Hashimoto, and Masatoshi Ishikawa: Variable-focus lens with 1-kHz bandwidth, Optics Express, vol. 12, No. 10, pp. 2138-2149, 2004.
  2. Hiromasa OKU, and Masatoshi ISHIKAWA: A Variable-Focus Lens with 1kHz Bandwidth Applied to Axial-Scan of A Confocal Scanning Microscope, Proc. of the 16th Annual Meeting of the IEEE Lasers & Electro-Optics Society (LEOS) 2003 (Tucson, U.S.A., Oct. 26-30, 2003) (IEEE Catalog Number: 03CH37460, ISSN: 1092-8081), vol. 1, pp. 309-310. [PDF (459K)] *IEEE

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