Demonstration and modeling of a tapered-lensed optical fiber trap

Abstract

Optical trapping is a novel technique that utilizes radiation pressure for the non-contact manipulation and control of micron sized particles including living cells and micro-organisms. Typically, optical trapping is performed using a high power microscope and a complicated optical setup to form a single beam optical gradient trap or `optical tweezers.' Recent work has demonstrated three dimensional optical trapping using the counterpropagating beams from two optical fiber cleaves. This results in a simple and low cost implementation of an optical trap. Our paper discuses a refinement of this technique using pigtailed 1.3 micrometers semiconductor lasers and tapered lensed optical fibers with hemispherically machined microlens ends. Our optical trap consists of two tapered fiber lenses separated by distances of between 100 and 400 microns, with optical power ranges between 2 and 40 mW. Adjusting the relative powers of the optical fibers allowed us to trap and position 3, 5 and 10 micron beads over axial distances of several hundred microns. Our refinements improve trap accessibility while simultaneously increasing the trap stability. We have also used a ray optics model to simulate the performance of the optical fiber trap and predict the forces generated throughout the trapping volume. Axial and transverse trapping efficiencies up to 0.1 are predicted. The model can be used to predict trap strength and stability for various combinations of fiber spacings and particle sizes. Experimental observations of trapping and manipulation of 3 micrometers , 5 micrometers , and 10 micrometers beads are also presented and compared to the model.