Fiber Endoscopes Utilizing Liquid Tunable-Focus Microlenses Actuated Through Infrared Light

We report on prototype fiber endoscopes with tunable-focus liquid microlenses integrated at their distal ends and actuated through infrared (IR) light. Tunable-focus microlenses allow minimal back-and-forth movements of the scopes themselves and different depths of focus (DOFs), thus having spatial depth perception in the obtained images. The liquid microlens was formed by a water-oil meniscus pinned at a hydrophobic-hydrophilic boundary at an aperture. IR light-responsive hydrogel microstructures were formed by photopatterning thermo-responsive N-isopropylacrylamide hydrogel with entrapped IR light absorbing gold nanoparticles. The volumetric change in the hydrogel microstructures regulated the pressure difference across the water-oil interface and thus varied its focal length. The operations of the microlenses were realized through light transmitted via optical fibers. The images obtained from the microlenses were transferred via image fiber bundles. For two alignments between the hydrogel structures and the fibers, the response times of the microlenses are 65 and 20 s, respectively. Images of the simulated polyps in simulated colons were obtained. The range of focal length of a typical microlens was from 52 to 8 mm. The angle of view of an endoscope was from 77° to 128°. A microlens array could potentially be utilized to simultaneously obtain different DOFs and to increase the field of view.