An endoscopic microscope with liquid-tunable aspheric lenses for continuous zoom capability

Continuous optical zoom is an enabling feature for an endoscopic microscope system combining high resolution and large field-of-view (FOV) imaging. Conventional zoom systems utilize translating lenses to achieve optical zoom, but this further reduces the already narrow optical aperture available in the endoscopic probe. Liquid-tunable membrane lenses combine the actuator and optical aperture, and thus allow an efficient use of the available aperture. However, currently, such lenses suffer from significant spherical and other optical aberrations. In this paper, we present a miniaturized continuous zoom microscope design with an optical aperture of 1mm featuring two liquid-tunable aspheric lenses for optical zoom and two fixed lenses for aberration and color dispersion correction. The liquid-tunable aspherical lenses are formed by liquid reservoir sealed with a PDMS membrane of non-uniform thickness. A systematic approach to identify the membrane thickness profile yielding a desired deflection shapes also discussed. The continuous magnification range of the zoom system is from 1.5 to 3.5 using a 1×1mm CCD as the imaging element. With an object distance smaller than 3mm, the total length of the system is less than 9mm. We demonstrate that with the introduction of the aspherical tunable lenses, the optical performance of the zoom system is considerably improved. Keywords: Zoom optics, endomicroscopy, liquid-tunable lenses, aspherical microlenses.