Due to their advances in achieving large focal-length tuning ranges with compact structures, solid tunable lenses based on the Alvarez-Lohmann principle show a promising potential in various applications, especially modern miniature imaging systems. In this paper, we report miniature endoscopic systems integrated with solid tunable lenses for optical adjustable focusing or zooming. The solid tunable lenses are designed according to the improved Alvarez-Lohmann principle, where two independent extended polynomials are employed to govern the two freeform surfaces, respectively. Slim piezo benders aligned along the optical axis are utilized to drive the solid tunable lenses to move laterally. An image fiber bundle is used to transmit the images captured by the optical system to the external cameras. Results show that the endoscopic system is equipped with a capability of optical power tuning from about 135 diopters to about 205 diopters when there is a single solid tunable lens integrated in the system, which enables it to achieve adjustable focus for objects located at different positions. The integration of two solid tunable lenses and two fixed lenses further enables the endoscopic system to have the optical-zooming capability. A zoom ratio of 3x and a maximum full field of view as high as about 80 degrees are realized experimentally. The cross sectional diameter of the endoscopic probe is controlled below 4 mm. The captured images are clear and sharp. Such adjustable-focus or zoom endoscopic systems would be useful in future medical or industrial applications.
Yongchao Zou, Fook Siong Chau, and Guangya Zhou, "Application of solid tunable lenses in endoscopic systems (Conference Presentation)," Proc. SPIE 10116, MOEMS and Miniaturized Systems XVI, 1011602 (Presented at SPIE OPTO: January 30, 2017; Published: 2 June 2017); https://doi.org/10.1117/12.2251762.5397361458001.
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