UV-curable liquid-core fiber lenses with controllable focal length.

Lensed fiber optics is of great importance to many applications such as optical sensing, optical coupling, laser trapping etc. In this paper we have demonstrated a unique method to fabricate liquid-core lensed fibers by filling UV curable adhesive into hollow fibers, and to control the focal length and spot size by pumping liquid into or out of the fiber end. In experiment, tuning of focal length from 2.414 to 0.810 mm has been obtained, and solidification of the adhesive core has also been carried out successfully. Further simulation suggests that the focused spot size can be reduced to <10 micron by adjusting the refractive index and fiber geometry. Such technique has the potential to manufacture custom-made solid lensed fibers and liquid-core solid-tip lensed fibers in volume at low cost. The same technique may be used for input and output coupling of optofluidic waveguides with external optical components like optical fibers and lasers.