Miniaturized all-fibre probe for three-dimensional optical trapping and manipulation

Optical tweezers represent a powerful tool for a variety of applications both in biology and in physics. Standard optical tweezers make use of a freely propagating laser beam that is tightly focused near the sample by means of a high-numerical-aperture microscope objective. Most of the limitations associated with the microscope's bulky structure could be overcome by exploiting optical fibres for the delivery of the trapping radiation, provided that proper beam-shaping is performed. Here we present the design and the realization of a miniaturized single-fibre optical tweezer that is able to create a purely optical three-dimensional trap. The tweezer uses engineered fibre structures with microstructured end surfaces, and its effectiveness is demonstrated by trapping 10-νm-diameter polystyrene beads. The optical tweezer is able to provide optical manipulation and analysis of microscale specimens and could be the fundamental building block in future integrated fibre-based devices.