Liquid crystal lens array for a 3D endoscope

Liquid crystals (LCs) have unique electro-optical characteristics that make them useful for studying and fabricating practical optical devices. Recently, the properties of LC lenses have received much research attention. They are thin, tunable in focus, and electrically switchable to 2D/3D modes. Rather than controlling light by varying the thickness and shape of a polished material, in an LC lens system the refractive index of the LC is tuned by applying a voltage. LC lenses are thus suitable for enhancing endoscope imaging systems, which usually have a solid lens a few millimeters in diameter, but for which it is an advantage to have a smaller lens with a short focal length with 3D image capabilities. It is also an advantage for the device to work at low voltage (i.e., less than 20V) so that it can be used in an integrated circuit, which cannot tolerate high voltages. The advantages of 3D endoscopy are to improve the speed and accuracy of surgery. 3D imaging also helps surgeons learn to control the instrument more quickly.1 Numerous types of LC lenses have been proposed, such as a 3D sensing system,2 a 3D imaging system,3 and an optical tunable LC lens.4–6 These systems have been built for research and are not in clinical use. There are several challenges tomaking a better LC lens. For instance, photopolymerized LC lenses have short focal lengths but require high applied voltage7 and have a complicated structure that is costly to manufacture.8 An optical system for a 200 m aperture size based on an LC lens array has been developed, but suffers from distortion. Although this can be reduced, it is impossible to extract a 3D image as a result.9 Other LC lens systems use low applied voltage,10, 11 a patterned lenticular LC lens,12–14 and a liquid lens actuated by LC pistons,15 but none combines low-voltage operation with a small aperture and 3D imaging capability. Figure 1. Fabrication of the curved circular electrode. AZ 40XT: Photoresist. ITO: Indium tin oxide. NOA81: UV-curable Norland Optical Adhesive that acts as an insulating layer.